Observing the millimeter Universe with the NIKA2 camera

Frederic Mayet (LPSC)

  • Aina Andrianasolo
  • Alain Omont
  • Alessandro Fasano
  • Alessandro Monfardini
  • Alessia Ritacco
  • Alexandre Beelen
  • Andrea Catalano
  • Anna Silvia Baldi
  • Annie Hughes
  • Antonio Ferragamo
  • Aurore Bacmann
  • Bilal Ladjelate
  • Blanchard Clara
  • Boris Bolliet
  • Carsten Kramer
  • Cecile Renault
  • Cecilia Ceccarelli
  • Charlène Lefevre
  • Christophe Hoarau
  • Clément Mibord
  • Céline Combet
  • Daisuke Nagai
  • Denis Barkats
  • Dominique Eckert
  • Eduard Driessen
  • Etienne Pointecouteau
  • Florian Keruzore
  • Florian Ruppin
  • François-Xavier Désert
  • Frederic Gueth
  • Frederick Poidevin
  • Frédéric Mayet
  • Frédérique Motte
  • Guilaine Lagache
  • Gustavo Yepes
  • Hamza Ajeddig
  • Herve Bourdin
  • Herve Dole
  • Hélène Roussel
  • Iacopo Bartalucci
  • Isabelle Ristorcelli
  • Ivan Delvecchio
  • J. Ricardo Rizzo
  • Jean-Francois Lestrade
  • Jean-François Robitaille
  • Johannes Goupy
  • Jonathan Aumont
  • Juan Francisco Macias Perez
  • Karl Schuster
  • Laurence Perotto
  • Lea Bonnefoy
  • Marco De Petris
  • Mariachiara Rossetti
  • Marina Ricci
  • Marine Kuna
  • Martino Calvo
  • Maximilien Franco
  • Miguel Sánchez-Portal
  • Monique Arnaud
  • Nicolas Andres
  • Nicolas Peretto
  • Nicolas Ponthieu
  • PABLO Torne
  • Patrick Stassi
  • Philippe André
  • Pranshu Mandal
  • Rashid Sunyaev
  • Roberto Neri
  • Samuel Leclercq
  • Shibo Shu
  • Stefano Berta
  • Stefano Ettori
  • Vincent Guillet
  • Yixian Cao
  • Yohan Pouteau
    • Registration / welcome
    • 12:00 PM
    • Introduction
      • 1
        Introducing mm Universe @ NIKA2
        Introducing mm Universe @ NIKA2
        Speaker: Prof. Frédéric Mayet (LPSC)
    • NIKA2: instrument and observations
      • 2
        NIKA2: description, status and possible upgrades
        I will describe in general the NIKA2 instrument. I will then focus on some possible points for improvements. For example: new dichroic, new 1mm arrays (developed at Néel), 1GHz electronics (LPSC), potential telescope upgrade (IRAM).
        Speaker: Alessandro Monfardini (Néel)
      • 3
        Calibration and performance of NIKA2
        The performance of the NIKA2 camera at the IRAM 30-m telescope have been assessed using a reference data set including observations acquired between January 2017 and February 2018. This data set consists of a large amount of observations of primary and secondary calibrators and faint sources, which span the whole range of observing elevations and atmospheric conditions encountered at the IRAM 30-m telescope. Using the reference data set, the stability of the performance parameters have been extensively tested against time evolution and observing conditions. The performance assessment relies on a standard calibration method, referred to as the 'baseline' method, that goes from raw data to flux density measurements. This method includes the determination of the KID positions in the sky, the KID selection, the characterisation of the beam pattern, the atmospheric opacity estimation, the calibration of the absolute scale of the flux density, the flat fielding and the point source photometry. Alternative calibration methods have also been used to check the robustness of the 'baseline' results against systematic effects. I will present the calibration method, which is currently used for the science data calibration, and will review the performance assessment.
        Speaker: Dr Laurence Perotto (LPSC)
      • 4
        Observing faint sources with NIKA2
        With its large FOV and high sensitivity, NIKA2 is a high mapping speed instrument, uniquely suited for deep surveys. During commissioning, we had the opportunity to observe faint and moderately faint sources with NIKA2. This talk will summarize the latest developments on the NIKA2 data reduction pipeline and show its first application to small deep fields and source counting.
        Speaker: Dr Nicolas Ponthieu (IPAG)
      • 3:20 PM
      • 5
        Observing with NIKA2 in total power: the AoD perspective
        Most of the people attending the conference have already an experience with NIKA2 observations and some of its subtleties. The NIKA2 observing sessions are organized in pools, a shared risk way of scheduling projects according to their priorities, and weather and stability requests, in order to ensure that everyone gets the best of their data. As NIKA2 reaches its second year of science operation, I will review the evolution of the observing pools and their overall performances over time, as well as the milestones achieved during these observing adventures.
        Speaker: Dr Bilal Ladjelate (IRAM Granada)
      • 6
        NIKA2 observing pools: the work behind.
        NIKA2 has been permanently installed at the IRAM Pico Veleta 30m telescope since October 2015. After the first commissioning campaigns, NIKA2 is now open to the international community and has been used in many scientific observing pools. Although invisible to the final user, the complexity of the instrument requires a lot of careful work to get everything ready before each pool, starting from the cryostat cooldown to all the sanity checks and performance verifications that are paramount to assure the smooth running of the campaign and the quality of the recorded data. In my talk, I will describe this hidden work, and the way it is being handed over to the local personnel, with the aim of making NIKA2 an IRAM facility instrument.
        Speaker: Martino Calvo (Institut Néel)
      • 7
        The first pulsar detection with a KID camera (NIKA2)
        Pulsars are fascinating astrophysical objects that enable a variety of experiments usually with unrivalled precision. For example, pulsars have been used to test the equation-of-state of ultra-dense matter, or General Relativity up to the highest precision to date. However, although we have been very successful using pulsars as astronomical tools, we still do not fully understand their radio emission mechanism. In addition, the type of experiments that can be carried out depend on the pulsar systems available, so finding new pulsars is always a way to expand our capabilities to do new science. In this talk, I will present the first pulsar detection with a Kinetic Inductance Detector (KID) camera, achieved recently with NIKA2 at the IRAM 30-m Telescope. I will also discuss the potential of KIDs to help us understand the emission mechanism of pulsars, and also to potentially discover new pulsars, in particular in regions where the scattering is very strong and we may need to use high radio frequencies for the searches. Finally, the technical adjustments desired to make NIKA2 a complete and versatile pulsar instrument will be summarised.
        Speaker: Dr PABLO TORNE (Instituto de Radioastronomia Milimetrica, IRAM)
    • SZ observations
      • 8
        The Sunyaev-Zeldovich effect from clusters of galaxies
        I will review the evolution of observations of the Sunyaev-Zeldovich (SZ) signal from groups and clusters of galaxies within the course of the past two decades. The SZ effect has become an efficient way to investigate the astrophysics of the hot intra-cluster gas, very competitive and complementary to X-ray observations, and thereby renew the use of massive halos as a cosmological probe. I will discuss the SZ observational and theoretical progress in the perspective of the NIKA2 observations of galaxy clusters.
        Speaker: Dr Etienne Pointecouteau (IRAP Toulouse)
      • 9
        Planck satellite cluster cosmology via the Sunyaev-Zeldovich effect
        Clusters of galaxies are unique cosmological probes sensitive to the primordial density fluctuations, and the expansion history and energy content of the Universe. The thermal Sunyaev-Zeldovich (tSZ) effect is an observable of choice for cluster cosmology due to the low scatter in the relationship between SZ flux and cluster mass, and the construction of large tSZ selected cluster catalogs. The Planck satellite because of its spectral coverage (30-857 GHz) and its 9 channels is well adapted to the detection of the Sunyaev-Zeldovich effect in clusters of galaxies. The Planck data have been used to produce both a catalogue of 1653 clusters of galaxies and a full sky map of the Compton parameter. We present here Planck cluster cosmological results obtained from: 1) the number counts of tSZ Planck cluster catalogue, and 2) the angular power spectrum and high order statistics of the Planck Compton parameter map.The constraints obtained on the universe matter density and matter fluctuations are consistent between the two analyses and with other LSS probes. However, there exists a weak tension between Planckcluster and CMB cosmological constraints. This discrepancy, which may due to bias in the observable-mass relation or unkonwn systematics, will be discussed in details.
        Speaker: Dr Juan Francisco Macias-Perez (LPSC)
      • 10
        Cluster cosmology with the NIKA2 SZ Large program
        The main limiting factor of cosmological analyses based on thermal Sunyaev-Zel’dovich (SZ) cluster statistics comes from the bias and systematic uncertainties that affect the estimates of the mass of galaxy clusters. High-angular resolution SZ observations at high redshift are needed to study a potential redshift or morphology dependence of both the mean pressure profile and the mass-observable scaling relation used in SZ cosmological analyses.
The NIKA2 camera is a new generation continuum instrument installed at the IRAM 30-m telescope. The combination of a large field of view (6.5 arcmin), a high angular resolution (17.7 arcsec), and a high-sensitivity of 8 mJy.s1/2 at 150 GHz provides the NIKA2 camera with unique SZ mapping capabilities. The NIKA2 SZ observation program will allow us to observe a large sample of clusters (50) at redshifts between 0.5 and 0.9. I will present the NIKA2 SZ Large program and the characterization of the first NIKA2 SZ observations of galaxy clusters at the IRAM 30-m telescope. I will then emphasize the synergy between the high quality NIKA2 SZ and XMM-Newton X-ray data for the calibration of the mass-observable scaling relation and the evaluation of the mean pressure profile.
        Speaker: Prof. Frédéric Mayet (LPSC)
      • 10:30 AM
      • 11
        Cartography of the ICM properties of the on-going merger MOO J1142+1527 at z = 1.2 from a joint analysis of NIKA2 and Chandra data
        Upcoming optical/IR surveys will have both the sensitivity and the area to push cluster detection to $z > 2$. The SZ and X-ray follow-ups of richness-selected clusters enable investigating the ICM properties at high redshift and improve our understanding of cluster formation. With both a wide field of view and a high angular resolution, NIKA2 is a very well suited instrument to map the SZ signal of high redshift clusters up to $R_{500}$. The observations of MOO J1142+1527, an IR-detected galaxy cluster at $z = 1.2$, using both the Chandra satellite and NIKA2 have led to very promising results. The Chandra data obtained with a $48~\mathrm{ks}$ ACIS-I exposure are combined with the high quality SZ data measured by NIKA2 in order to estimate the radial profiles of all the ICM thermodynamic properties. We confirm the high mass of the cluster found by CARMA using low angular resolution SZ data. The high angular resolution of both Chandra and NIKA2 allows us to study the cluster morphological properties. The identification of a ~200 kpc offset between the X-ray and the SZ peaks as well as a clear elongation of the ICM along the R.A. axis are hints that this cluster is an on-going merger. This conclusion is confirmed by combining the SZ and X-ray data at the map level in order to obtain maps of the ICM temperature and entropy. These maps show that the ICM regions on the west side of the X-ray peak, coincident with a radio loud AGN, present a high temperature and entropy. I will present the on-going SZ/X-ray follow-up program of 6 high redshift clusters ($z > 1$) selected from the MaDCoWS and IDCS surveys and its main goals. I will then describe the characterization of the first cluster of this sample: the very massive, high redshift, and morphological disturbed cluster MOO J1142+1527 from the first joint analysis of Chandra and NIKA2 data.
        Speaker: Dr Florian Ruppin (MIT)
      • 12
        CT-CL J0215.4+0030: a test case for faint galaxy clusters within the NIKA2 SZ Large Program
        The NIKA2 SZ large program (LPSZ) was designed to take advantage of the NIKA2 high angular resolution and large eld of view to help us improve our knowledge of galaxy clusters. It consists in observing ∼50 clusters from intermediate to high red- shift (z ∈ [0.5, 0.9]) to re-compute the relations needed for cluster-based cosmological analysis, i.e. the mean pressure pro le of the intra-cluster medium, and the SZ observ- able – mass scaling relation. The rst analysis of a galaxy cluster within the NIKA2 LPSZ was published in Ruppin et al. 2018, as a science veri cation of the abilities of the NIKA2 camera on a high quality galaxy cluster (with low-z, high mass, and a large observing time). The most natural next step for the LPSZ is then to move on to the analysis of a trickier source, to evaluate how much can be expected from the individual analysis of standard LPSZ clusters. In this presentation, I will show the analysis of the ACT-CL J0215.4+0030 galaxy cluster, which is the one with the highest redshift and the lowest mass in the sample for which the observations have been completed. I will show how challenging data reduction can be for low SNR clusters, in which case the contamination by point sources becomes crucial and may worsen the quality of our analysis.
        Speaker: Mr Florian Kéruzoré (LPSC Grenoble)
      • 13
        Extracting the thermal SZ signal from heterogeneous millimeter data sets
        Complementarily to X-ray observations, the thermal SZ effect is a powerful tool to probe the baryonic content of galaxy clusters from their core to their peripheries. While contaminations by astrophysical (Galactic and extragalactic thermal dust) and insrumental backgrounds require us to scan the thermal SZ signal across various frequencies, the multi-scale nature of cluster morphologies require us to observe such objects at various angular resolutions. We developed component separation algorithms that take advantage of sparse representations to combine these heterogeneous pieces of information, separate the thermal SZ signal from its contaminants, detect and map the thermal SZ signal of galaxy clusters from nearby to more distant clusters of the Planck catalogue. Spatially weighted likelihoods allow us in particular to combine parametric fitings of the component Spectral Energy Distribution with wavelet and curvelet imaging, but also to deconvolve and combine signals registered with heterogeneous beams. I will show how such techniques allow us to detect substructures in the peripheries of nearby clusters with Planck, and discuss our prospects to extend them to observations performed at lower (Planck all-sky maps) and/or higher angular resolutions (e.g. Planck + SPT).
        Speaker: Mr Herve Bourdin (University of Rome "Tor vergata")
    • 12:25 PM
    • SZ and X-rays
      • 14
        X-ray, SZ and dark matter in galaxy clusters
        Galaxy clusters are dark-matter dominated systems enclosed in a volume that is a high-density microcosm of the rest of the universe. What is their true mass scale? What are the statistical properties of the representative population? How does their detectability depend on baryon physics? We have learned a lot on these fundamental questions with our current projects, like XMM-Newton Cluster Outskirts Project (X-COP) and CLASH. More has to be understood and will be the focus of our next XMM-Newton Heritage Cluster Project that will pave the way in using the next generation of observatories, like XRISM SKA Athena, to construct a consistent picture of the formation and composition of galaxy clusters.
        Speaker: Dr Stefano Ettori (INAF-Osservatorio di Astrofisica e Scienza dello Spazio in Bologna)
      • 15
        The X-COP project: Galaxy cluster reconstruction with joint X-ray and SZ data
        X-ray and Sunyaev-Zeldovich observations provide independent and complementary ways of determining the properties of the intracluster medium (ICM). Joint reconstructions of galaxy cluster properties combining X-ray and SZ data are clearly superior to similar analyzes based on one observable only, since the two methods have a different radial dependency and probe different thermodynamic quantities. The XMM Cluster Outskirts Project (X-COP) is a very large programme on XMM-Newton which follows up the strongest SZ detections in the Planck survey. The primary goal of the project is to perform a joint X-ray/SZ reconstruction of cluster properties in a SZ-selected sample of 12 nearby clusters. X-COP provides the most accurate view of thermodynamic properties, hydrostatic mass profiles and gas fraction ever reached. I will present the main results of the survey and the tools developed for joint X-ray/SZ cluster reconstruction. I will then emphasize how NIKA2 can be combined in a similar way with X-ray instruments (XMM, Chandra, eROSITA) to bring high-quality constraints on cluster properties at higher redshifts.
        Speaker: Dr Dominique Eckert (University of Geneva)
      • 16
        Spectral imaging and pressure profiles of the X-COP galaxy clusters with the Sunyaev-Zel'dovich effect
        The imaging of galaxy clusters through the Sunyaev-Zel'dovich effect is a valuable tool to probe the thermal pressure of the intra-cluster gas especially in the outermost regions, where X-ray observations suffer from photon statistics. For the first time, we produce maps of the Comptonization parameter by applying a locally parametric algorithm for sparse component separation to the latest *Planck* data. Our sample consists of twelve low-redshift galaxy clusters detected by *Planck* with the highest signal-to-noise ratio, considered for the XMM-Cluster Oustkirts Project (X-COP). Our images of the thermal Sunyaev-Zel'dovich effect show the presence of anisotropic features, such as small-scale blobs and filamentary substructures, located in the outskirts of a number of objects in the sample. In particular, we present a qualitative comparison with X-ray data for two interesting systems, namely A2029 and RXC1825. We use our maps to isolate and mask significant signal features in the virial region, in order to get unbiased pressure profiles of the intra-cluster gas.
        Speaker: Anna Silvia Baldi (Sapienza University of Rome)
      • 17
        Review of SZ science with NIKA
        Speaker: Mr Juan Francisco Macias-Perez (LPSC)
      • 3:30 PM
      • 18
        Evolution of cluster profiles with XMM and Chandra at z>0.5 and status of the NIKA2 LP X-ray follow-up
        We present the dynamical properties and the individual spatially resolved radial mass profiles of a sample of 77 massive clusters in the [0.05-1] redshift range detected via the Sunyaev-Zel'dovich effect. For the 5 clusters at z>0.9, we present a method to study such objects that optimally exploits information from XMM-Newton and Chandra observations. The combination of Chandra’s excellent spatial resolution and XMM-Newton’s photon collecting power allows us to investigate the properties for the first time in such objects. For the lowest mass clusters which are in common with the NIKA2 LP, we present the results of the XMM-Newton follow-up and the future prospects for high-resolution X-ray/SZ combination. We discuss simultaneously the dispersion and evolution of the thermodynamical, mass and dark matter profiles shape and show the link with the underlying dynamical state. We contrast the optical and X-ray mass estimates by comparing our results with lensing values. Finally, we verify theoretical predictions by contrasting our results with RAMSES cosmological simulations covering our same mass and redshift range.
        Speaker: Dr Iacopo Bartalucci (CEA Saclay)
      • 19
        Exploiting the Plank legacy: properties of SZ-selected galaxy clusters at high-z and high-mass
        The Sunyaev-Zeldovich effect provides an observational window to the intracluster medium complementary to X-ray observations, and over the last few years has proved to be a mature technique to efficiently detect and characterize galaxy clusters. For instance, the Planck survey has mapped the whole microwave sky, detecting almost 2000 candidate massive clusters up to z~1, performing the first all-sky survey of galaxy clusters 20 years after the RASS. I will present preliminary results on the population of massive and high-redshift clusters in the PSZ2 catalogue that we followed-up with Chandra. These observations have allowed us to identify interesting extreme merging systems, candidate cool cores and to study the evolution of the density profiles with respect to Planck-selected samples at lower z and mass. These objects are ideal targets for observations with NIKA2.
        Speaker: Dr Mariachiara Rossetti (IASF-Milano/INAF)
      • 20
        Biases in the estimation of galaxy clusters dynamical mass
        The abundance of galaxy clusters, per unit of mass and redshift, is a very powerful tool in order to constrain cosmological parameters as the matter density Ωm, and the amplitude of the primordial fluctuation σ8. However, the cluster mass is not an observable. The multicomponent nature of galaxy clusters helps to bypass this problem. In fact, from the observation of each different cluster component, it is possible to measure quantities that are directly correlated with the total mass of the cluster. These quantities are known as mass proxies. Spectroscopic observations in optical and infrared wavelengths allow to measure the redshift of cluster members and so obtain their velocity dispersion, which is an estimate of how galaxies are moving into the cluster potential well. Therefore, under the assumption of dynamical equilibrium, the virial theorem correlates the velocity dispersion with the total cluster mass. However, as all mass proxies, the velocity dispersion suffers from biases that have to be corrected in order to obtain an unbiased cluster mass. By using hydrodynamical simulations, we have studied statistical and physical effects induced by the choice of a particular dispersion estimator and other effects such as the reduced number of cluster members considered the interlopers contamination and the projected radius in which the clusters members are sampled. The result of this study is a series of corrections in order to obtain a bias-corrected velocity dispersion and therefore, a bias-corrected cluster mass. As a test example, I will discuss the application of this methodology to our follow-up effort for characterizing the Planck PSZ1 sample in the northern sky.
        Speaker: Mr Antonio Ferragamo (Intistuto de Astrofísica de Canarias)
      • 21
        Physics of Galaxy Cluster Outskirts
        High-resolution spectral imaging observations of the SZ effects promise to provide a vastly broaden view of structure and evolution of galaxy clusters, by enabling unique measurements of thermodynamic and kinematic properties of the cluster gas via thermal and kinematic SZ effects. One of the new frontiers includes the exploration of the extremely low-density regions in the outskirts of galaxy clusters and its connection to the Cosmic Web, where X-ray observations would require exceptionally long integration times. Modern hydrodynamical simulations make robust testable predictions about their properties. However, recent X-ray and microwave observations revealed tensions with the theoretical predictions. Resolving these puzzles will likely require improved understanding of the cluster gas physics. In this talk, I will discuss recent advances in our understanding of the physics of galaxy cluster outskirts, with highlights on emerging problems and challenges and implications for cluster cosmology in the era of multi-wavelength cluster surveys.
        Speaker: Prof. Daisuke Nagai (Yale University)
    • Instrumental session
      • 22
        NIKA2 arrays for the 1mm and 2mm spectral bands
        The NIKA2 instrument, operating at the IRAM 30-meters telescope, is based on the LEKID array technology dedicated to millimeter wave astronomy. This instrument is composed of one low frequency array for the 120-180GHz range, and two high frequency polarization sensitive arrays for the 220-280GHz range. Since 2013 different versions of the arrays have been developed for NIKA2. We will describe the fabrication process developed for these arrays and review the results of their in-lab measurements and characterization.
        Speaker: Dr Johannes GOUPY (CNRS - Institut Neel)
      • 23
        Progress on NIKA2 future development
        The NIKA2 team are continuously working on improving the performance of the NIKA2 arrays. In this talk, we present our recent developments on the 1mm array from three aspects. Firstly, a small pixel design has been studied to achieve higher angular resolution. Secondly, a thorough simulation and FTS measurements have been performed to understand the frequency response. Thirdly, a capacitor trimming technique has been performed on a 112-pixel test array and 96.4% optical yield is achieved. These developments could be applied for future arrays.
        Speaker: Mr Shibo Shu (Institut de Radioastronomie Millimétrique)
      • 24
        Beam characteristics of Nobeyama 45m 100GHz band MKID camera
        We are developing a 100GHz band camera designed for survey of distant galaxies. Field-of-view of this camera is around 3-arcmin, and 100GHz band observation helps peer through the characteristics of very distant galaxies. This is also a prototype for the future 10m Antarctic telescope to survey southern distant galaxies. The focal plane array of this camera is 109 pixel antenna-coupled Microwave Kinetic Inductance Detectors(MKIDs). The camera at its current state of development has been commissioned at Nobeyama 45m telescope twice, and the results from the commissioning are presented. Observations of Mars and Venus were made to study the beam characteristics. Beammaps of Mars observations were synthesized by combining each pixel beammaps according to their proper offset from the central beam. The image synthesis pipeline is written in Python using HEALPix gridding system and Cygrid. The methods used make it a versatile tool for individual source imaging as well as enables it to be expanded into a galactic survey mapping.
        Speaker: Mr Pranshu Mandal (University of Tsukuba)
      • 10:30 AM
    • Wednesday Morning-2
      • 25
        I will introduce NOEMA interferometer, its latest upgrades and capabilities. In particular, I will detail the increase of sensitivity with more antennas, increase of spatial resolution with track extension, and increase of bandwidth with new receiver generation as well as future dual band upgrade. Finally, I will discuss the complementarity between NOEMA and NIKA2 and possible synergies from galactic to high-z sources.
        Speaker: Dr Charlène LEFEVRE (Institut de RadioAstronomie Millimétrique)
      • 26
        Constraining dust physics with NIKA2 polarization : new road maps after Planck
        The Planck mission has brought considerable constraints on the properties of dust, and their evolution from the most diffuse, high-latitude, Galactic ISM to the densest regions of the Gould Belt (Planck 2013 results. XI, Planck Int. Results 2015, XXIX). The combined analysis of ancillary and Planck HFI data has imposed a revision of dust models for the diffuse/translucent ISM, both in total and polarized emission (Planck Int. Results 2015, XXI, XXII). Planck maps have also revealed peaks of very high polarization fractions in the diffuse ISM (up to 20-22%, Planck Int. Results 2015 XIX, Planck 2018 results. XII), much higher than expected from models based on polarization observations in the optical (p/EBV = 9%), This high dust polarization efficiency has been recently confirmed by a direct follow-up in the optical by the RobolPol instrument, yielding p/EBV > 13% (Panopoulou+2019). The full-sky statistics of Planck polarization maps at 353GHz has allowed to demonstrate that the variations of the dust polarization fraction observed at 353GHz through the diffuse and translucent ISM were primarily driven by the magnetic field structure on the line of sight (Planck Int. Results 2015, XX), and not by a variation in the grain alignment efficiency, which was proved to remain high everywhere below a column density NH = 2.10^22 cm-2 (Planck 2018 results. XII). At higher, subarcmin, resolution and higher optical depths, polarization measurements from starlight in the NIR, from dust emission in the FIR (SOFIA/HAWC+ at 89 and 154 µm) and submm (BLASTPol from 250 to 500 µm, POL-2 instrument on the JCMT/SCUBA-2 at 450 and 850 µm) allow to measure dust polarization at much higher extinctions (Av from a few tens to a few hundreds), with diverse conclusions. NIKA2 will probe Galactic dust polarization on scales of 0.01 to 0.1 pc, at resolutions comparable to those probed by SOFIA/HAWC+ and SCUBA-2/POL-2, but at longer wavelengths (1.3 mm/260GHz). Provided that we are able to disentangle in polarization observables between what is due to dust and what is due to the structure of the magnetic field on the line of sight, all these instruments allow to study how the grain polarization efficiency evolves with the density. In that perspective, I will present the recent methodology proposed by Planck results XII (2018). These studies are of particular importance to reassess the reliability of dust polarization as a tracer of the magnetic field in dense regions, but also for our understanding of dust evolution. Combining observations of the same regions at wavelengths ranging from 100 µm to 1 mm in total and polarized emission, we will also be able to study the correlation of the variation of the dust optical properties (variations in the dust emissivity and spectral index) with the observed variations in the dust polarization properties (alignment efficiency, shape). Eventually, we should not exclude a priori the possibility of observing grain growth in high-density regions through the polarization expected from the self-scattering of dust emission by very large grains (Kataoka+2015). If such polarization signatures is detected, the joint analysis of FIR (SOFIA/HAWC), submm (SCUBA-2/POL-2) and mm (NIKA2) polarized observations may provide onstraints on grain size, as is now done for protoplanetary discs from multiple-bands ALMA observations (e.g. Yang+2019).
        Speaker: Dr Vincent Guillet (IAS)
      • 27
        Unveiling the AGN-galaxy connection at high-z with NIKA2 and radio facilities
        The relationship between supermassive black hole (SMBH) accretion and star formation has lead to controversial studies claiming that Active Galactic Nuclei (AGN) activity might both quench and enhance galaxies' star-forming content. Especially at high redshift (z>2), their interplay is still poorly understood, also due to the lack of accurate estimates of star formation rate (SFR) and AGN power in active galaxies. The unique synergy between NIKA2 and current/upcoming (VLA, VLBA, SKA) radio facilities will enable us (i) to calibrate IR and radio emission as SFR tracers at z>2 via the infrared-radio correlation; (2) to better isolate the AGN contribution via panchromatic SED-fitting; (3) to ultimately explore the relationship between AGN and star formation with unprecedented accuracy. I will present the latest results obtained from deep radio surveys in this context, and discuss the exciting prospects with NIKA2.
        Speaker: Ivan Delvecchio (CEA Saclay)
    • 12:25 PM
    • NIKA2-polarization
      • 28
        Magnetic fields in star-forming filaments: NIKA2-POL as a pathfinder for SPICA-B-BOP
        Herschel imaging surveys of Galactic molecular clouds have emphasized the quasi-universality of the filamentary structure of the cold ISM and the key role of filaments in the star formation process. Planck polarization data moreover suggest that the formation and evolution of star-forming filaments is at least partly controlled by magnetic fields. I will summarize the main objectives and prospects of the B-FUN large program with NIKA2-POL, which will probe the morphology of magnetic field lines in a selected sample of nearby molecular filaments on the critical < 0.1 pc scales where fragmentation into prestellar cores occurs. I will also discuss how 1.2mm polarimetric observations with NIKA2-POL can be used to prepare for more extensive high-resolution polarimetric imaging studies of Galactic ISM structures with SPICA-POL (B-BOP), the far-IR polarimetric imager of the proposed SPICA cryogenic space telescope.
        Speaker: Dr Philippe André (CEA Saclay)
      • 29
        Observing with NIKA2Pol from the 30m telescope. Early results on the commissioning phase.
        NIKA2 is equipped with a polarization system composed by a multi-mesh half wave plate (HWP) and a polarizer placed at the cryostat stage of 100 mK which transmits and re ects the two orientation of the linear polarization on two 1mm KID-arrays. The polarizer is needed because the NIKA2 detectors KIDs are unsensitive to the polarization, the warm HWP placed in front of the cryostat window modulates the incoming polarization shifting the polarized signal at higher frequency (4 times the HWP rotation frequency). This technique allows us to have a quasi-simultaneous measurement of the three Stokes parameters I, Q, and U and places the polarization far from low frequency noise. This contribution aims at giving an overview on the status of the commissioning of NIKA2Pol. On one hand it will be shown how do perform observations with NIKA2Pol from a technical point of view, which constraints should be considered, which mapping speed should be used etc. On the other hand preliminary results obtained on the calibration and the study of the performances of the polarimeter will be given.
        Speaker: Dr Alessia Ritacco (IRAM - Granada)
      • 30
        Preliminary results from the NIKA2-Pol commissioning : Analyzing and correcting for instrumental polarization
        Highlighting the role of magnetic fields in the star formation process is crucial. Observations have already shown that magnetic fields play an important role in the early stages of star formation. The high spatial resolution (~0.01 to 0.05 pc) provided by NIKA2-Pol 1.2 mm polarimetric imaging of nearby clouds will help us to start clarifying the geometry of the B field within dense cores and molecular filament(as part of the IRAM 30m large program B-FUN). There are numerous challenging issues in the validation of NIKA-Pol such as the calibration of instrumental polarization and performance. The commissioning data analysis of NIKA2-Pol is helping us to characterize the beam or “leakage” pattern of the instrument in polarization mode. We will present a synthetic analysis of the intensity to polarization leakage pattern, and its dependence with elevation. We will also present the current leakage correction made possible by NIKA2 pipeline in polarization mode based on the NIKA2-Pol commissioning data from Dec. 2018. We will show reduced Stokes I, Q, U maps before and after leakage correction for a number of calibrators.
        Speaker: Mr Hamza AJEDDIG (Département d’Astrophysique (AIM), CEA Saclay, 91191 Gif-sur-Yvette, France)
      • 31
        In-depth multiscale analysis of polarisation maps
        Observations of the polarised dust emission with Planck and the future SPICA at large scale and with ALMA, SCUBA2 and NIKA2 at smaller scales trace the interaction between the magnetic field and the denser part of the ISM as molecular clouds and star formation regions. However, a clear interpretation of the Stokes parameters Q and U, and of the associated polarisation vector P, is difficult. The confusion along the line-of-sight, the mixture between the ordered and turbulent component in the Galaxy and the fluctuations of the polarised signal on a broad range of spatial scales are properties of the magnetic field that makes it hard to interpret. In this talk, I will present different approaches to analyse and visualise ISM polarisation maps based on multiscale analyses. The first technique called the Multiscale non-Gaussian segmentation (MnGSeg; Robitaille et al. 2014, 2019 to be submitted), was first applied on dust emission and column density maps to locate and extract dense molecular structures and turbulence intermittency. I will show how one can apply this technique on polarisation data to separate the diffuse/“regular” magnetic field fluctuations from singular structures associated with sharp changes of the polarisation angle or intensity. I will also show how this new approach is closely related to the multiscale polarisation gradient technique (Robitaille et al. 2015, 2017) and how both can be used to characterise the Galactic magnetic field and its relation with ISM structures. Both techniques can be applied on the polarised infrared dust emission and the radio synchrotron emission.
        Speaker: Dr Jean-François Robitaille (IPAG - Univ. Grenoble Alpes)
      • 3:25 PM
      • 32
        The NIKA polarimeter on science targets: Crab nebula observations at 150 GHz and dual-band images of Orion Molecular Cloud OMC-1
        NIKA, the NIKA2 pathnder, was equipped of a room temperature polarization system (a half wave plate and a grid polarizer facing the cryostat window). This polarization system was the test bench for the NIKA2 polarimeter and was used during few observational/technical campaigns between 2014 and 2015. In particular during the last observing week of NIKA at the IRAM 30m telescope, in February 2015, we could demonstrate the ability of such a technology in detecting the polarization of the sky. Among the different targets used to constrain the instrumental polarization and to verify the calibration of the polarization degree and angle, we observed the Crab nebula and Orion Molecular Cloud region OMC-1. The molecular cloud OMC-1 represents a typical astrophysical target for future NIKA2Pol observations, aiming at tracing magnetic elds structures in star forming regions. The comparison with sub-millimetre and mm instruments showed a good reconstruction of the polarization. Furthermore thanks to the dual-band capability of NIKA we could trace the spatial distribution of the spectral index which showed interesting results along the bar, in the southern part of the source. In polarization the main filament is detected and it shows a well ordered magnetic field following the total intensity structure of the source. The Crab nebula is a supernova remnant exhibiting a highly polarized synchrotron radiation at radio and millimeter wavelengths. It is the brightest source in the microwave sky with an extension of 7 by 5 arcminutes and commonly used as a standard candle for any experiment which aims at measuring the polarization of the sky. Though its spectral energy distribution has been well characterized in total intensity, polarization data are still lacking at millimetre wavelengths. Using the high resolution observation at 150 GHz and the observations of CMB satellites, WMAP and Planck, we could trace for the first time the Spectral Energy Distribution in polarization in the frequency range: 30-353 GHz. The analysis highlights a single population of electrons responsible for both the total power and polarization radiation. Moreover averaging across the source by using aperture photometry techniques we find that the Crab nebula polarization angle is consistent with being constant over a wide range of frequencies with a value of -87.3+-0.3 in Galactic coordinates. This analysis provides a very good calibration for the next generation of ground-based instruments and space missions that aim at measuring the polarization radiation at these wavelengths. This contribution aims at giving an overview on the most interesting results obtained with the NIKA Polarimeter. The measurements performed with NIKA, together with the developed techniques to deal with systematics, opened the way to the current observations with NIKA2 that will provide important advances in the field of galactic and extra-galactic emission and interactions with the magnetic field.
        Speaker: Dr Alessia Ritacco (IRAM - Granada)
      • 33
        Absolute calibration of the polarisation angle for future CMB B-mode experiments from current and future measurements of the Crab nebula
        A tremendous international effort is currently dedicated to observing the so-called primordial $B$ modes of the Cosmic Microwave Background (CMB) polarisation. If measured, this faint signal imprinted by the primordial gravitational wave background, would be an evidence of the inflation epoch and quantify its energy scale, providing a rigorous test of fundamental physics far beyond the reach of accelerators. At the unprecedented sensitivity level that the new generation of CMB experiments aims to reach, every uncontrolled instrumental systematic effect will potentially result in an analysis bias that is larger than the much sought-after CMB $B$-mode signal. The absolute calibration of the polarisation angle is particularly important in this sense, as any associated error will end up in a leakage from the much larger $E$ modes into $B$ modes. The Crab nebula (Tau A), with its bright microwave synchrotron emission, is one of the few objects in the sky that can be used as absolute polarisation calibrators. In this talk, we review the best current constraints on its polarisation angle from 23 to 353\,GHz, at typical angular scales for CMB observations, from WMAP, XPOL, Planck and NIKA data. We will show that these polarisation angle measurements are compatible with a constant angle and we will present a study of the uncertainty on this mean angle, making different considerations on how to combine the individual measurement errors. For each of the cases, the potential impact on the CMB $B$-mode spectrum and on the recovered $r$ parameter will be explored.
        Speaker: Mr Jonathan Aumont (LPSC)
      • 34
        Analysis of Galactic molecular clouds polarization maps: a review of the methods
        Galactic molecular clouds are made of subparsec scale filamentary structures in which star formation occurs. The role of the magnetic fields in the formation and evolution of such structures leading to the formation of prestellar cores is still poorly understood, one reason being the lack of resolution provided by current and previous experiments. By measuring the linear polarized emission of the magnetically aligned dust grain material such experiments (e.g. Planck, BLASTPol, JCMT) have provided crucial information about the structure of the magnetic fields on large scales. The new data provided by NIKA2 will help to make similar measurements and fill this gap by resolving the structures of the magnetic fields at subparsec scales. In this talk I will give a review of the methods used to analyse linear polarimetry maps in order to retrieve information about the magnetic fields components. Some aspects regarding dust grains polarization properties will also be adressed.
        Speaker: Frédérick Poidevin (IAC)
      • 35
        Impact of B field in building clouds filaments and their hosted high-mass stars
        Star formation is a key process in astrophysics. At large scale, it regulates the energy budget of galaxies (especially massive stars) while at a small scale it sets the initial conditions for planet formation. It has been shown that the formation of stars, and the nature of the stars that will be formed, is very sensitive to the physical conditions at the cloud scale. Hence, star formation is a multi-scale process, whose comprehension requires a global view from the molecular cloud scale (tens of parsec) down to the accretion onto the proto-stellar embryo (a few au). The theoretical and numerical models that best reproduce the observational constraints (mass segregation and gas dynamics) all stand on the play of the magnetic field. Indeed magnetic fields were put forward to explain for the formation of filamentary structures, for the fragmentation of these structures into cores, for the collapse of these cores (magnetic braking), or for the accretion processes in the disks. To put observational constraints on these processes the community needs performant instruments to measure the magnetic fields: SPICA/B-BOP to study the largest scales, IRAM/NIKA2-POL to study the intermediate scales - from the molecular clouds down to the cores - and ALMA/NOEMA-POL to study the smallest scales (cf the Figure hereinafter). Getting the intermediate-scale magnetic field with NIKA2-POL is crucial to determine if small-scale magnetic fields are inherited from the larger scales, and build a coherent view of the effect of the magnetic fields for all processes of star formation. I will present new ALMA data and projects with NIKA2-POL in the framework of high-mass star formation.
        Speaker: Frédérique Motte (IPAG)
    • Cluster cosmology
      • 36
        The MUSIC of Galaxy Clusters: A database of synthetic clusters from cosmological hydrodynamical simulations
        Galaxy clusters are the most massive gravitationally collapsed objects in the Universe. They are also the most rare objects and, therefore, large computational volumes have to be simulated if one wants to obtain a statistical significant sample of such objects that can be used to calibrate the global scaling relations, or to understand the possible mass biases due to inaccuracies of the classical assumption of hydrostatic equilibrium of the Intra Cluster medium. But, due to computational limitations, it is still not possible to simulate Gigaparsec size volumes with enough numerical resolution to accurately describe the internal structures of massive clusters. Therefore, an alternative is to identify the most massive clusters formed in pure N-body simulations of Gigaparsec size boxes, and then re-simulate regions around these objects with high resolution, including baryons (gas and stars) and their complex interactions (hydrodynamics and radiative, short scale processes). Using this technique we have developed the Marenostrum MUltidark SImulations of galaxy Clusters (MUSIC) database of numerical massive galaxy clusters, composed by several thousands of these objects in different cosmologies and with different physic modelling of the baryonic effects. This database has proved to be extremely useful for a number of cosmological and astrophysical studies on clusters. From the raw numerical data we have computed synthetic observations in different wavelengths ranging from radio, through the Sunyaev-Zeldovich effect, optical from star light formed in simulations, to the X-rays of the intra cluster gas. These synthetic observations can then be used for comparison and forecasting with the present and upcoming observational experiments on galaxy clusters.
        Speaker: Prof. Gustavo Yepes (Universidad autónoma de Madrid)
      • 37
        Confirmation of NIKA2 investigation of the Sunyaev-Zel'dovich effect by using synthetic clusters of galaxies
        The NIKA2 Sunyaev-Zel'dovich Large Program (LPSZ) is focused on mapping the thermal SZ signal of a representative sample of selected Planck and ACT clusters spanning the redshift range 0.5 < z < 0.9. Clusters science implementation to Cosmology can be biased due to inaccurate knowledge of IntraCluster Medium (ICM) pressure profiles in shape, scatter and redshift evolution. Hydrodynamical N-body simulations prove to be a powerful tool to endorse NIKA2 capabilities for estimating the impact of ICM disturbances when recovering the pressure radial profiles. For this goal we employ a subsample of objects, extracted from Marenostrum MUltidark SImulations of galaxy Clusters (MUSIC), spanning equivalent redshift and mass ranges of LPSZ. Realistic NIKA2 and Planck tSZ observations, jointly analyzed, enable to validate the NIKA2 pipeline and to estimate the ICM pressure profile of each cluster. Moreover, the possibility to identify a priori the dynamical state of all the synthetic clusters allows us to verify its impact on the recovered ICM profile shapes and their scatters. Morphological analysis of maps of the Comptonization parameter of each synthetic cluster seems to be a way to observationally segregate the sample between relaxed and disturbed objects. The clusters morphology is also correlated with the mass bias and its impact on the scatter of the integrated Comptonization parameter, Y500, and total mass, M500, scaling relation is discussed. Other observational dinamical state indicators, besides morphology, are also explored.
        Speaker: Prof. Marco De Petris (Dept. of Physics - University La Sapienza)
      • 38
        Implication of an evolution of the mean pressure profile of galaxy clusters on the cosmological parameters estimated from the Planck tSZ power spectrum
        Most recent studies show that the tension observed between the cosmological constraints based on cluster abundance from SZ catalogs and from CMB primary anisotropies can be cancelled by a variation of the hydrostatic bias parameter. However, the value of the hydrostatic bias needed in order to alleviate this tension is in strong disagreement with the current estimates of this parameter based on lensing, X-ray, and SZ observations. The mean pressure profile of the galaxy cluster population plays an essential role in cosmological analyses. It is used in cluster counts analyses in order to estimate the value of the integrated Compton parameter of each cluster in tSZ catalogs and in analyses based on the tSZ power spectrum in order to model the latter. While the modification of the shape of the mean pressure profile only has an effect at high multipole, a variation of its amplitude plays a role that is similar to the one of the hydrostatic bias in cosmological analyses. If the self-similar hypothesis is not verified in the whole mass-redshift plane, the amplitude of the mean pressure profile of the cluster population could be different from the one observed at high mass and low redshift. I will present an analysis of the Planck tSZ power spectrum based on threes different mean pressure profiles. This study shows that a variation of the amplitude of the mean pressure profile of the cluster population, compatible with the current constraints on the cluster gas mass fraction, leads to significant differences in the final cosmological parameter estimates. I will conclude on the necessity to accurately characterize the shape, the intrinsic scatter and the redshift evolution of the mean pressure profile in order to estimate part of the biases and systematic effects that currently prevent cosmological analyses based on tSZ surveys to obtain precise and unbiased cosmological constraints. This is one of the goals of the on-going NIKA2 SZ large program.
        Speaker: Dr Florian Ruppin (MIT)
      • 39
        Cosmological constraints from the thermal Sunyaev Zeldovich power spectrum and cluster counts
        In this talk we review the formalism for the modelling of the Sunyaev Zeldovich (SZ) power spectrum and cluster counts and how to compare them with observations. We outline their dependencies on cosmological parameters, as well as the mass bias associated with the X-ray calibration of the cluster masses. We outline the role played by the pressure profile of the intra cluster medium, for which NIKA2 is collecting new and precise data. Then, we discuss the consistency between Planck SZ data, Planck Primary CMB, and other LSS probes. Finally, we study constraints on extensions of the LCDM cosmology by including massive neutrinos and the equation of state of dark energy in the analysis.
        Speaker: Dr Boris Bolliet (The University of Manchester)
      • 11:00 AM
      • 40
        X-Ray and Microwave Cosmology: synergy and competition - What we expect from SRG/eRosita spacecraft and ground based microwave telescopes?
        Our Universe is filled by cosmic microwave background radiation (CMB) which is extremely isotropic and has excellent black body spectrum with temperature 2.7 Kelvin and no spectral deviations from black body are detected in the CMB monopole till now. But 50 years ago it was recognised that "shadows" in the angular distribution of CMB in the directions where clouds of very hot T_e~10^6-10^8 K and rarefied plasma exist. Today we know that such objects exist and they are clusters of galaxies containing thousands of galaxies each, a lot of dark matter, and a hot gas filling the huge potential well. And "shadows" with very peculiar frequency spectrum arise due to Thomson interaction of CMB photons with hot electrons. Today this method permitted to discover several thousands of before unknown clusters of galaxies at relatively high redshifts 0.25 < z < 2. Behind practically every new discovered rich cluster of galaxies we see the extremely distant galaxies with shape distorted and brightness increased due to gravitational lensing by huge gravitational potential of a cluster connected mainly with invisible "dark matter". Good to mention that amplitude of the CMB brightness "shadow" corresponds only to a few tens or hundreds of microKelvin. There is also a usual way to observe the same hot gas, and Russia plans to launch this June SRG spacecraft with German eRosita X-Ray telescope having grazing incidence optics. This telescope is planning to discover more than 100,000 clusters of galaxies (i.e. all rich clusters of galaxies in the observable Universe) during 4 years of the all sky survey. At the same time, ground-based millimeter wavelenghts telescopes on the South Pole of the Earth and Atacama desert at 5 km altitude, equipped by tens of thousands cryogenic bolometers in their focal planes, promise to detect all these clusters due to their "shadows" on CMB. The data will be very complimentary because the X-ray emission due to free-free emission of the hot gas is proportional to the square of the electron density and amplitude of shadows depends linearly on the plasma pressure NeTe. There will be a lot of synergy in these data. At the same time there is a competition: who will be first to discover the most interesting clusters of galaxies? Ensemble of 10^5 clusters, their distribution in space, mass and redshift will provide a unique sample of data for testing cosmological models. Detailed spectroscopic study of the shadow with high angular resolution will permit to understand the internal structure of the hot plasma (including merging shocks, turbulent motions) and to measure the temperature of the plasma using the relativistic corrections to the thermal effect. Interaction of CMB photons with free electrons opens a unique way to measure a peculiar velocity of a cluster of galaxies relative to the unique system of coordinates in which CMB is isotropic. Observers can now measure peculiar velocities and even bulk and turbulent velocities inside clusters of galaxies at any distance from us because both effects (thermal and kinematic) do not depend on the redshift of the object.
        Speaker: Prof. Rashid Sunyaev (Max Planck Garching)
    • 12:30 PM
    • From dust to planets and stars
      • 41
        Debris disks around stars in the NIKA2 era
        Planets and planetesimals are formed in the gas- and dust-rich protoplanetary disks surrounding nascent stars in the first 10 Myr of their life. Planetesimals belts, or debris disks, that remain afterward are unique objets to study planetary systems that have evolved from these primordial structures. On one hand, optical/IR observations reveal small sized grains that are partly blown out the system, on the other hand millimetre-wave observations are sensitive to large grains that are tidly bound to the planetesimal belt itself and so can be used to probe it. We shall discuss complementarity between millimeter-wave interferometer and single dish observations in the NIKA2 era in using recent observations of the iconic debris disks around Vega, HR8799, HD107146 and of the field around the star GJ526.
        Speaker: Dr Jean-François Lestrade (Observatoire de Paris)
      • 42
        Probing the subsurface of the two faces of Iapetus
        Saturn’s icy satellites, which are in synchronous rotation around Saturn, often present a different albedo on their leading and trailing sides, which interact differently with Saturn’s dusty rings. Because longer wavelengths probe deeper into the subsurface, observing both sides at a variety of wavelengths indicates possible changes in thermal and physical properties with depth. The Cassini mission has observed the near-surface thermal emission from Saturn’s moons in the far-infrared (with Cassini’s Composite Infrared Spectrometer CIRS) [1] and at 2.2 cm wavelength (with the Cassini Radar/Radiometer) [2,3]. Ongoing analysis of the radiometry data by comparison with a thermal model of the surface suggests several of these satellites also show a leading/trailing dichotomy at 2.2 cm. The contrast in brightness temperature is especially strong for Iapetus; this dichotomy should also be visible at millimeter wavelengths i.e. at IRAM NIKA2 operating wavelengths. We are currently conducting an observing campaign to bridge the gap between the CIRS and radar datasets by observing different longitudes of Iapetus at mm and cm wavelengths with, respectively, IRAM NIKA2 and the JVLA (Jansky Very Large Array, New Mexico, USA). In May 2018, we acquired 1- and 2-mm observations of Iapetus’ anti-Saturn side from IRAM NIKA2, and in February-March 2019 we collected data on Iapetus’s leading and trailing sides. These observations will allow us to detect and quantify the brightness temperature variation with longitude. Combined with data from CIRS, the Cassini Radar/radiometer and JVLA, NIKA2 will provide insights into the thermal, physical, and compositional properties of Iapetus’s near-surface as well as into their variations with both depth and longitude. We will report on the analysis of the NIKA2 data to produce an image of the satellites Titan and Iapetus in the proximity of Saturn, which is 1,000 to 10,000 times brighter, respectively. References: [1] Howett et al., 2010, Icarus 206, 573–593. [2] Ostro et al., 2006, Icarus 183 (2), 479–490. [3] Le Gall et al., 2014, Icarus 241, 221–238.
        Speaker: Ms Lea Bonnefoy (LESIA/LATMOS)
      • 43
        Galactic LBV stars and their circumstellar material surveyed by NIKA2
        Luminous Blue Variable (LBV) stars are evolved massive objects, previous to core-collapse supernova. LBVs are characterized by photometric and spectroscopic variability, produced by strong and dense winds, mass-loss events and very intense UV radiation. LBVs strongly disturb their surroundings by heating and shocking, and produce important amounts of dust. The study of the circumstellar material is therefore crucial to understand how these massive stars evolve, and also to characterize their effects onto the interstellar medium. The versatility of NIKA2 is a key in providing simultaneous observations of both the stellar continuum and the extended, circumstellar contribution. The frequencies surveyed (150 and 260 GHz) are in the range where thermal dust and free-free emission compete, and hence NIKA2 has the capacity to provide key information about the spatial distribution of both mechanisms. We show the results of the first NIKA2 survey in four fields towards five LBVs. Spectral indexes has a complex distribution without a clear dominance of an emission mechanism. At the stellar sources, there is a correlation of the spectral indexes with respect to the 1mm flux densities. In one of the sources, G79.29+0.46, we also found a strong correlation of the 1 and 2mm continuum emission with respect to nested molecular shells at 0.1 pc from the LBV.
        Speaker: Ricardo Rizzo (CAB)
      • 3:30 PM
    • Forthcoming instruments
      • 44
        BICEP Array: a Next-Generation CMB Polarimeter to probe the primordial universe from the South Pole
        The inflationary scenario generically predicts the existence of primordial gravitational waves (GW) over a wide range of amplitudes from slow-roll to multi-field models. Currently the most promising method for constraining, and potentially detecting an inflationary GW background is to search for the imprint of these tensor perturbations in the cosmic microwave background (CMB) B-mode polarization. With ever-increasing sensitivity at degree angular scales, the BICEP/Keck program targets these B-modes, producing the most stringent constraints on primordial inflation to date. BICEP Array, a “Stage 3” generation instrument, will begin observing at the South Pole in 2020. BICEP Array expands the frequency coverage of its predecessors with four receivers operating in six bands. The first receiver is currently being commissioned and will operate at 30-40GHz to constrain synchrotron foreground emission. In later years, 95 GHz and 150 GHz receivers will continue to deepen our maps of the CMB, while higher-frequency channels at 220/270GHz will provide unprecedented constraints on the galactic dust foreground. This talk will present an overview of the design and expected performance of the BICEP Array instruments. I will show predicted constraints on the synchrotron foreground provided by the first low-frequency receiver. I will also outline how BICEP Array will inform CMB ‘Stage 4’ experiments, in particular future Small Aperture Telescopes targeting signatures of inflation.
        Speaker: Dr Denis Barkats (Harvard)
      • 45
        KISS: a spectro-imager dedicated to the secondary anisotropies of the CMB
        Mapping millimetre continuum emission of the astronomical sky has become a key issue in modern multi-wavelength astrophysics as such mapping is required to tackle a series of very important questions related to cosmology, galaxy evolution, formation of individual and clustered starts and finally the nature of circumstellar envelops and disks. In particular the spectro-imaging at low resolution frequency is necessary today for the characterisation of the cluster of galaxies. They are studied through the Sunyaev-Zel’dovich (SZ) effect and used as probes of the large-scale structures and evolution of the universe. In this context, we built and installed a ground-based spectro-imager: KISS the KIDs-Interfero-Spectrometer-Survey.
        Speaker: Mr Alessandro Fasano (Institut Néel)
      • 46
        Low-resolution spectroscopic surveys with CONCERTO at APEX
        CONCERTO is a new instrument planned to be installed in the APEX Cassegrain Cabin in early 2021. It is a spectrometer with an instantaneous field of view exceeding 300 Sq. arcmin. and a spectral resolution of 1.5 GHz. It covers the frequency band 120-360 GHz. The main scientific aim of CONCERTO is to map in three dimensions the fluctuations of the CII line intensity in the reionisation and post-reionisation epoch (z=4.5-8.5). This technique, known as "intensity mapping", will allow to answer the questions of whether dusty star-formation contributes to early galaxy evolution, and whether dusty galaxies play an important role in shaping cosmic reionization. CONCERTO will be one of two instruments in the world to perform intensity mapping of the CII line. In addition to the main CII survey, we expect CONCERTO to bring a significant contribution in a number of areas, including the study of galaxy clusters (via the thermal and kinetic SZ effect), the follow-up of Herschel and SCUBA-2 deep surveys (with the longer wavelength of CONCERTO probing to higher redshifts, and simultaneous redshift identification available through lines), the observation of local and intermediate-redshift galaxies, and the study of Galactic star-forming clouds. CONCERTO will also observe the CO intensity fluctuations arising from galaxies at z=0.3-2, giving the spatial distribution and abundance of molecular gas over a broad range of cosmic time. In this talk, I will present the CONCERTO experiment and review its major scientific goals.
        Speaker: Prof. Guilaine Lagache (LAM)
    • SZ Observations (cont'd)
      • 47
        Unveiling the inner structure of distant XXL clusters with NIKA2: a multi-wavelength approach
        Galaxy cluster analyses at different wavelengths allows a better understanding of their formation and evolution, leading to a more realistic modeling of their physics. Comparing optical, X-ray and SZ cluster samples also enables us to check the selection functions of the surveys, and to test the cosmological representativeness of the detections. As a consequence, the multi-wavelength approach is a key to reduce uncertainties and systematics in both astrophysics and cosmological studies of galaxy clusters. The XXL survey, conducted by XMM-Newton, allows us to select relatively low mass clusters up to high redshift. I will present an ongoing observational project, aiming at mapping the inner structure of three distants XXL clusters with NIKA2. The main motivation is to conduct a multi- wavelength (X-ray + millimetre + optical) characterization of clusters in a mass and redshift regime that is barely explored to date, but which will be extensively probed by future large X-ray and optical/NIR missions, and that is becoming accessible to ground based SZ surveys. I will expose the characterization of XLSSC102, a ~ XXL cluster at z=0.97, in terms of morphology, dynamical state and thermodynamic profiles. I will show that XLSSC102 appears to be a highly perturbed, post-merger cluster and I will discuss how this impacts the shape of its thermodynamic profiles. Finally, I will conclude on what can be learned for future surveys.
        Speaker: Dr Marina Ricci (LAPP)
    • Conference Picture
    • 6:10 PM
      Cocktail Dinner
    • Friday session
      • 48
        NIKA2 mapping and cross-instrument SED extraction of extended sources with Scanamorphos
        The steps taken to tailor to NIKA2 observations the Scanamorphos algorithm (initially developed to subtract low-frequency noise from Herschel on-the-fly observations) will be described, focussing on the consequences of the different instrument architecture and observation strategy. The method, making the most extensive use of the redundancy built in the multi-scan coverage with large arrays of a given region of the sky, is applicable to extended sources, while the pipeline is optimized for compact sources. A few examples of application will be given. A related tool to build consistent broadband SEDs from 60 microns to 2 mm, combining Herschel and NIKA2 data, will also be presented. Its main task is to process the data least affected by low-frequency noise and coverage limitations (i.e. the Herschel data) through the same transfer function as the NIKA2 data, after simulating the same scan geometry and applying the same noise and atmospheric signal as extracted from the 1mm data.
        Speaker: Helene Roussel (IAP)
      • 49
        Status of the NIKA2 Cosmology Legacy Survey (N2CLS)
        More than half of the photons emitted by stars across cosmic times have been absorbed by cosmic dust and re-emitted in the far-infrared and millimeter wavelength domain. Herschel and ALMA revealed that very massive and very dusty galaxies already exist in the early Universe (up to z~7). These objects are one of the keys to understand the formation of the most massive galaxies. However, these objects are rare and significant volumes need to be probed to perform a census of the obscured star formation at z>3. ALMA is inefficient to map large area, while the previous generation of single-dish instruments were not enough sensitive. The NIKA2 camera is perfectly suited to fill the gap between these two types of instruments. Thanks to a new technology of detectors (the KIDs for Kinetic Inductance Detectors), we reach mapping speeds competitive with ALMA at 1.2 and 2 millimeter for a much smaller operational cost. The N2CLS is performing a confusion-limited survey in GOODS-N and a 0.4 deg2 deep mapping in the COSMOS field. We expect to obtain a volume- and SFR-complete sample of tens of star-forming sources above z=4. I will present the updated goal and status of the large program and the expected outcome of N2CLS.
        Speaker: Alexandre Beelen (Institut d'Astrophysique Spatiale / Laboratoire d'Astrophysique de Marseille)
      • 50
        GOODS-ALMA: 1.1 mm extragalactic survey : Physical properties of massive star-forming galaxies at z > 2
        We will present the latest results of a 69 arcmin2 ALMA survey at 1.1mm, GOODS-ALMA, matching the deepest HST-WFC3 H-band observed region of the GOODS-South field. We have extracted two catalogs, one of galaxies purely selected by ALMA, from which we have identified sources both with and without HST counterparts, and another catalog based on priors. Our wide contiguous survey allows us to push the ALMA blind detection of massive galaxies further in redshift, with a median redshift of z = 2.92 and a median stellar mass of M=1.1 x 10^11 solar masses. Our sample includes 20% HST-dark galaxies (4/20), all of which are detected in the mid-infrared with Spitzer-IRAC. We will also present the main characteristics of the ALMA-detected galaxies (star formation rate, gas fraction, star formation efficiency, temperature etc.) and discuss whether these galaxies present global properties and could be the progenitors of the compact passive galaxies observed at z~2.
        Speaker: Mr Maximilien FRANCO (DAp CEA-Saclay)
      • 10:30 AM
      • 51
        Galactic star formation with NIKA2: the GASTON large programme
        Over the last decade, Herschel observations of the Galactic interstellar medium have transformed our understanding of the early stages of star formation. At the low-mass end of the stellar initial mass function (IMF), a paradigm has emerged in which low-mass cores – the progenitors of stars with masses from ~0.1 to a couple of solar masses – are thought to form as the result of gravitational instabilities developing along gravitationally bound filaments, providing a compact and fixed mass reservoir for the protostars forming inside them. However, on either side of that mass range, processes that lead to the formation of massive stars on the one hand, and to the formation of brown-dwarfs on the other, remain elusive. Indeed, it is well known that thermal Jeans-type fragmentation cannot explain the formation of cores more massive than a few solar masses, and there are strong indications that the dynamical evolution of the larger-scale mass reservoirs in star-forming regions play a key role in the formation of high-mass stars. Furthermore, the formation mechanism of brown dwarfs is also controversial, and in particular it is unknown whether a continuation of the filamentary paradigm at even lower masses could be an important formation pathway. The GASTON large programme at the IRAM 30m telescope is exploiting the high angular resolution of the 30m telescope at 1.2 mm, and the high mapping speed of the NIKA2 camera to scrutinise the formation mechanisms of stars across all mass ranges in unprecedented detail. Specifically, GASTON is aimed at bridging the divides between the brown dwarf, the low-mass, and the high-mass star-formation regimes. An additional goal to the project is to constrain the evolution of dust properties – upon which so much of our understanding of ISM physics is based – as a function of environment. In the context of this talk, we will present the current status of the GASTON project, mostly focussing on our deep NIKA2 survey of the Galactic plane, and the first statistical results on the link between intermediate-mass and high-mass core populations.
        Speaker: Dr Nicolas Peretto (Cardiff University)
      • 52
        Searching for candidate pre-brown dwarf with NIKA2
        From molecular clouds to young stellar objects, every step in the evolution of young stars can be observed in the millimetric range. As part of the NIKA2 (Adam et al. 2018) Large Program GASTON (PI: Nicolas Peretto), we observed at 1.2mm and 2mm the Ophiuchus Molecular Cloud. The dual band capabilities of NIKA2 allow us to understand the properties of dust in star-forming regions, and their relationship with the objects they form, in this case, low-mass stars, under ten solar masses. In L1688, the main region of this cloud, Oph B-11, detected with interferometric observations, is a pre-brown dwarf i.e a prestellar core in the brown dwarf mass regime. Its final mass will not be important enough for the final star to burn hydrogen. The rationale for this part of the GASTON large program is to try to detect more of these kind of brown dwarf precursors to understand their environment and mechanisms of formation, with the unrivaled sensitivity of NIKA2. In this talk, I will explain the goals of the brown dwarf part of the GASTON Large Program and the scientific results already achieved with 10h on L1688 and L1689 each.
        Speaker: Dr Bilal Ladjelate (IRAM Granada)
      • 53
        Dust evolution from pre-stellar cores
        Dust is the only tracer that is present from the edge of the interstellar cloud to the densest part, inside which stars and planets will form, named pre-stellar cores. It allows to trace the density structure of the cloud, of the core(s), and of the subsequent protoplanetary disk where it becomes a major actor of the planet formation. Dust grains evolve from bare simple elongated shape in the diffuse medium to large icy aggregates with irregular shapes inside dense cores. While dust properties in the diffuse medium are well-constrained, dust models able to explain multi-wavelength observations for dense environment including large grains are still lacking. Grain growth is expected from mid and far infrared (FIR) observations but to fulfil all observational constraints, a dust model must at least be consistent in terms of dust composition but also dust shape and size distribution. The way dust grains absorb and scatter light does not depend on temperature but relies mainly on dust geometry (size and shape). On the contrary, the emission process implies a degeneracy between dust properties and temperatures. Hence, the retrieval of dust properties (size, composition, shape) from observations is a degenerate problem that requests multi-wavelength observations and multiple tracers among which absorption, scattering, polarization of the incoming radiation field, and thermal emission at long wavelengths. I will present how NIKA2 observations are crucial to better constrain dust properties. In this framework, I will introduce SIGMA: a new flexible dust model in open access (Lefèvre et al. 2019). We rely on effective medium theory to compute refractive indexes from laboratory measurements and Mie theory applied to a distribution of hollow spheres to mimic non–spherical dust shapes. In particular I will illustrate how I reproduce the expected impact when balancing the iron fraction between silicates and other iron components making iron rich silicates less emissive at NIKA2 wavelengths compared to iron–poor silicates (Demyk et al. 2017a, 2017b). I will also discuss the impact of ice mantle thickness.
        Speaker: Dr Charlène LEFEVRE (Institut de RadioAstronomie Millimétrique)
    • 12:30 PM