Café-club

 

October 18th, we will have the pleasure to listen to Paola POPESSO (ESO Garching), who will talk about “The X-ray invisible Universe. A look into the halos undetected by eROSITA”.

The cafe-club will take place at 2:00 pm [CET] on the AMU virtual room (link below). The broadcast in the Library at LAM will be confirmed on Wednesday reminder.

   https://univ-amu-fr.zoom.us/j/81779670775?pwd=dDNDdTBhcDB6THk5TTg3NkQ5M2hqdz09
(Meeting ID : 817 7967 0775 — Passcode : 749629)

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub .

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ABSTRACT

I will show the results of the analsyis of the X-ray properties of z<0.2 optically selected GAMA groups and clusters (log M = 13-14.7) in the eFEDS (eROSITA Final Equatorial Depth Survey) area at the final nominal depth of the eROSITA All Sky Survey (eRASS). I will show how the optical selection is necessary to sample the bulk of the group population to mitigate the biases of the X-ray selection. Indeed, the stacked surface brightness profile of eROSITA-undetected groups is less concentrated than the mean surface brightness profile of the detected ones, and this is also true of the total mass and galaxy distributions. Undetected groups tend to be younger (as inferred by the 1st to 2nd ranked galaxies magnitude difference), and to host a younger galaxy population. The difference between detected and undetected systems does not seem to be related to the current AGN activity which is similar for the two classes. Instead, we argue that this might be linked to the group location in the cosmic web, which affects the halo formation epoch and concentration. Our conclusion is supported by the analysis of the Lx-M relation for the groups of the two classes, as a function of the group location in the cosmic web. I will also show how the derived gas mass fraction – halo mass relation of detected and undetected stacked groups can robustly constrain the predictions of the current state-of-the-art hydrodynamical simulations.

Joseph D. ROMANO (Texas Tech University): “Results from recent pulsar timing array observations“.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub .

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

I will briefly describe the reports of “strong evidence of a correlated GW signal” recently reported by several pulsar timing array collaborations. As a member of the NANOGrav Collaboration, I will focus on the NANOGrav results, and a potential astrophysical source of the observed signal.

Kamlesh RAJPUROHIT (CfA, Harvard; Università di Bologna; INAF, Institute of Radio Astronomy), who will talk about “Abell 746: A highly disturbed cluster undergoing multiple mergers“.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub .

Take care,
Carlo, Meriam, Paolo

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ABSTRACT

Merging galaxy clusters host Mpc-scale diffuse radio sources known as radio relics and radio halos. With their enormous extent, these sources trace the largest particle accelerators in the Universe. Relics are illuminated by relativistic electrons accelerated at shock fronts while radio halos are believed to be formed by merger-induced turbulence. However, the currently proposed particle acceleration mechanisms are not efficient enough to accelerate particles from the thermal pool of the intracluster medium (ICM). In this talk, I will present deep XMM-Newton and radio observations of the merging galaxy Abell 746 which hosts a plethora of diffuse emission sources that provide evidence for the acceleration of relativistic particles. Our new images reveal a complex morphology of the ICM with multiple substructures and an asymmetric temperature distribution. We found evidence of four X-ray edges, of which three are merger-driven shock fronts. Our findings suggest that Abell 746 is a complex system that involves multiple mergers.

Antonio DE UGARTE POSTIGO (Observatoire de la Côte d’Azur): “Stellar and galactic evolution studied with gamma-ray bursts“.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Gamma-ray bursts (GRBs) are some of the most violent and luminous astronomical phenomena that we can witnessed in the Universe. They are produced either by the collapse of very massive stars or by the merger of compact objects. Their observation teaches us about the extreme physics involved in the final stages of stellar evolution. These explosions require the prior existence of intense star formation and the correct environment to build up their progenitors. When exploding, they are important contributors to the interstellar environment enrichment. Due to their extreme luminosity, they can be also used as probes to study their host galaxies in absorption through spectroscopy, up to very large redshifts. Once they fade out, they pinpoint the location of distant galaxies that can be then observed also in emission.

In this talk I will review the observational techniques that we use for studying GRBs and present some of the highlights in which I have participated lately. These include observations of the brightest GRB of all time, recent Kilonova detections, and host galaxy studies. I will also go over the instrumentation that we are using for these observations and what is being planned and built for future observations.

Boris KALITA (Kavli IPMU, The University of Tokyo): “Clumpy galaxies at z > 1 in the era of JWST: moving beyond the UV wavelengths”.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub .

Take care,
Carlo, Meriam, Paolo

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ABSTRACT

A key question in galaxy evolution has been the importance of the apparent ‘clumpiness’ of high redshift galaxies. Until now, this property has been primarily investigated in rest-frame UV, limiting our understanding of their relevance. Are they short-lived or are associated with more long-lived massive structures that are part of the underlying stellar disks? We use JWST/NIRCam imaging from CEERS to explore the connection between the presence of these ‘clumps’ in a galaxy and its overall stellar morphology at 1.0 < z < 2.0. Exploiting the uninterrupted access to rest-frame UV, optical and near-IR light, we simultaneously map the clumps in galactic disks across our wavelength coverage, along with measuring the distribution of stars among their bulges and disks. In this talk I will be discussing the confirmation of these clumps as massive structures containing at least a few percent of the total stellar mass of the parent galaxies. A secondary consequence is that these will hence be expected to increase the dynamical friction within galactic disks leading to gas inflow. I will also be bridging the regime of clumps observed previously in UV to that of clumps now detected in near-IR. Finally, I will be presenting the strong negative correlation we find between how clumpy a galaxy is and the strength of its central bulge. This firmly suggests an evolutionary connection, either through clumps driving bulge growth, or the bulge stabilising the galaxy against clump formation, or a combination of the two.

James PEARSON (The Open University, Milton Keynes, UK), who will talk about “A large population of strongly lensed faint submillimetre galaxies in future dark energy surveys”.

The cafe-club will take place at 2:00 pm [CET] on the AMU virtual room (link below). The broadcast in the Library at LAM will be confirmed on Wednesday reminder.

https://univ-amu-fr.zoom.us/j/81779670775?pwd=dDNDdTBhcDB6THk5TTg3NkQ5M2hqdz09
(Meeting ID : 817 7967 0775 — Passcode : 749629)

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub .

Take care,
Carlo, Meriam, Paolo

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ABSTRACT

Bright galaxies at sub-millimetre wavelengths are now well known to be predominantly strongly gravitationally lensed. The same models that successfully predicted this strongly lensed population also predict about one percent of faint 450 micron-selected galaxies from deep JCMT surveys will also be strongly lensed, tending to appear in near-infrared channels only. I will discuss my discovery of a compelling gravitational lens system confirming the lensing population predictions, identified through public JWST imaging of a 450 micron source in the SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES) catalogue. Extrapolating to the Euclid-Wide survey, we predict tens of thousands of strongly lensed near-infrared galaxies that will be transformative for the study of dusty star-forming galaxies at cosmic noon, but will be a contaminant population in searches for strongly lensed ultra-high-redshift galaxies in Euclid and Roman.

Carla CORNIL BAÏOTTO (Instituto de Física y Astronomía, Universidad de Valparaíso): “Strong lens modeling of rich galaxy clusters”.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub

Take care,
Carlo, Meriam, Mathilde

 

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ABSTRACT

In the inner core of rich galaxy clusters, gravity can create remarkable visual mirages through the significant bending of light by high concentrations of mass. This phenomenon, known as strong gravitational lensing, magnifies distant galaxies located behind these dense structures, providing an excellent opportunity to study distant sources with enhanced resolution and flux. Strong lens modeling plays a key role in mapping the mass distribution of galaxy clusters and helps us better understand the distribution of dark matter and its role in cluster evolution. In this presentation, I will introduce the concept of strong lensing and detail the approach to model the mass distribution of a galaxy cluster core that hosts a giant arc and multiple images of distant galaxies in the optical, using the software Lenstool. Additionally, we will discuss the impact of the high-disturbance environment observed in radio and X-rays on our results. Strong lensing has applications in various wavelengths, and ALMA, with its high sensitivity and subarcsec resolution, is particularly well-suited for studying dust and molecular gas in lensed galaxies. I will present the two ALMA proposals I submitted in Cycle 10: one focused on studying star formation in a highly magnified, clumpy lensed galaxy at z~1.5, while the other investigates a hypothetical Einstein ring. Finally, I will outline my upcoming research projects in the field of extragalactic radio astronomy, including ALMA data reduction and analysis for my PhD thesis project in Chile.

 

Shawn KNABEL (University of California-Los Angeles): “Breaking MAD: joint constraints on the mass profiles and orbital anisotropies of elliptical galaxies with spatially resolved kinematics”.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub

Take care,
Carlo, Meriam, Mathilde
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ABSTRACT Shawn KNABEL)

We measure spatially-resolved kinematics and show preliminary models of the dynamics of 14 SLACS lenses. Using observations from Keck KCWI integral field spectroscopy and Jeans Anisotropic Modeling, we constrain the mass profile and anisotropy of large elliptical galaxies. The constraints from these non-time-delay lenses will also be used in the inference of cosmological parameters through time-delays of lensed quasars. Each galaxy is classified as a fast (regular) or slow (nonregular) rotator in comparison with the kinematics of nearby galaxies. These classifications, as well as interesting features like kinematically decoupled cores, trace distinct evolutionary paths (i.e. quenching vs dry mergers) and are important for properly handling the dynamical modeling. We begin to model the dynamics in spherical and axisymmetric coordinates and constrain radial profiles of orbital anisotropy, mass profiles, and dark matter content of the 14 galaxies. This work, within the broader strategy of the TDCOSMO collaboration, is able to overcome degeneracies in the orbital anisotropies and mass profiles that dominate the uncertainties on the inference of the Hubble constant through time-delays of lensed quasars.

Michal BILEK (LERMA, Observatoire de Paris; Collège de France; Université de Strasbourg), who will talk about “What is the origin of the different kinematic morphologies of early-type galaxies?”.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub

Take care,
Carlo, Meriam, Mathilde

 

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ABSTRACT

Early-type galaxies (i.e. elliptical and lenticular) are divided into slow and fast rotators according to the appearance of their maps of
line-of-sight velocity. Fast rotators show clear ordered rotation, while slow are supported mostly by velocity dispersion. I will speak about our work on investigation of the origin of this diversity. Inspired by cosmological simulations, we assumed that galaxies first form as fast rotators and then mergers transform some of them to slow rotators. We investigated the correlations of a measure of rotational support with various properties of galaxies that are sensitive to mergers. These include stellar ages, the presence of tidal features, and kinematically distinct cores. Each of these parameters is sensitive to a different type of merger and has a different lifetime. The found correlations, or their lack, together with observations of high-redshift universe, are explained the easiest, if the rotation support of early-type galaxies was decreased by multiple minor wet mergers more than 10 Gyr ago. Moreover, galaxies with a low rotational support continue accreting more satellites until today.

Andrea SACCARDI and Susanna VERGANI (Observatoire de Paris, Université PSL), who will talk about “Dissecting the interstellar medium of an extremely distant galaxy with GRB spectroscopy“.

The cafe-club will take place at 2:00 pm on usual AMU virtual room (link below). The broadcast in the Library at LAM will be confirmed on Wednesday reminder.

https://univ-amu-fr.zoom.us/j/96876832544?pwd=NnBaZEdXd3dFUFBRSkRFY05WS1d4dz09
(Meeting ID : 968 7683 2544 — Passcode : 173347)

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub .

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Gamma-ray bursts (GRBs) are an amazing class of transient phenomena in the Universe. GRBs are detected from space by satellites thanks to the flash of gamma-ray photons released within an ultra-relativistic jet. The gamma-ray prompt emission is followed by an afterglow, detectable at all wavelengths. Long GRBs, the class of GRBs produced by a new-born accreting black hole formed after the collapse of a massive star, are unique tools to probe distant galaxies. Their bright afterglows can be used as powerful background sources capable of unveiling the gas along their line-of-sight that absorbs their light. This includes also the gas of the host galaxy of the GRB. Afterglow spectroscopy allows detailed studies of the properties of the interstellar medium of star-forming galaxies up to the highest redshift, independently of the galaxy luminosity.

In this seminar, I will show the results obtained with the X-shooter spectrograph, installed at the VLT, to dissect the host galaxy of GRB210905A at z=6.3. Metallicity, kinematics, chemical abundance pattern, dust depletion, and dust-to-metal mass ratio could be determined. Such studies provide unique information to understand the first galaxies and their chemical enrichment and could be performed more often at higher redshift with future facilities.

 

Patrice THEULÉ (LAM): “Warm temperature formation of interstellar molecular hydrogen on a carbonaceous surface”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Molecular hydrogen is a key ingredient and the physics and chemistry of the interstellar medium. The micro-physics of its formation has huge implications on the galactic-scale star formation rate over cosmic times and  the interstellar medium phases large-scale organisation. Molecular hydrogen cooling lines are an important component of the interstellar medium cooling function, which regulates the star formation efficiency and molecular hydrogen shielding of the interstellar radiation field defines the extent of the molecular component in the ISM, where new stars are formed. We report the possibility to form molecular hydrogen  at warm temperature (up to 250 K) on surfaces exhibiting defects in laboratory. A gas of atomic hydrogen at few hundreds kelvins can overcome barriers of chemisorption sites of surface with defects at temperature up to 250 K, to recombine following a diffusion-reaction mechanism. Molecular hydrogen is detected by mass spectroscopy and the formation yield is given as a function of the surface temperature. Pushing the molecular hydrogen efficiency to warmer temperatures has a huge influence on the star formation efficiency in the Milky Way and in high-redshift galaxies.

Matthew LEHNERT (CRAL, Lyon), who will talk about “A possible stream of accreting cold atomic and molecular gas in the halo of a high redshift radio galaxy”.

The cafe-club will take place at 2:00 pm on usual AMU virtual room (link below). The broadcast in the Library at LAM will be confirmed on Wednesday reminder.

https://univ-amu-fr.zoom.us/j/96876832544?pwd=NnBaZEdXd3dFUFBRSkRFY05WS1d4dz09
(Meeting ID : 968 7683 2544 — Passcode : 173347)

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

I discuss our recent article, https://arxiv.org/abs/2303.17484, on the detection of the fine structure 3P1-3P0 transition of atomic carbon in and around a massive radio galaxy at z=3.8. This transition of neutral carbon is generally emitted in cold dense regions of atomic and molecular gas.  One of the interesting features we observe is a filamentary structure that is ~100 kpc in projected length, is narrow, has a velocity gradient of ~600 km/s over its length, and appears to terminate in both projection and velocity at the extended emission in the immediate environment of the radio galaxy. Furthermore, I put this result in context of our previous and on-going work on detecting low surface brightness molecular gas in galaxy halos and proto-intracluster media at high redshifts and in understanding the physics underlying how such gas might arise in halos and streams.

 

Richard FEDER-STAEHLE (Caltech): “PCAT-DE: Reconstructing point-like and diffuse emission using spatial and spectral information”

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

I will present recent progress on probabilistic cataloging (PCAT), a transdimensional, Bayesian hierarchical modelling framework initially designed for crowded field photometry. I will discuss the extension to simultaneously model point-like and diffuse signals (PCAT-DE), enabling robust photometry in images with spatially varying foregrounds and, conversely, measurement of diffuse signals in the presence of point source contamination. While this machinery has been used successfully on real data (Butler & Feder 2022), I will present two applications characterizing its performance on synthetic multi-band Herschel-SPIRE maps. The first uses PCAT-DE to perform detection and photometry of CIB galaxies in the presence of galactic cirrus emission, while in the second we show that the spatially extended thermal Sunyaev-Zel’dovich effect signal can be measured in galaxy clusters even when it is subdominant to the point-like emission of CIB galaxies.

 

Malgorzata SIUDEK (Institut de Física d’Altes Energies, The Barcelona Institute of Science and Technology & Institute of Space Sciences (ICE, CSIC), Barcelona): “Supermassive black holes found in distant dwarf galaxies”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

The statistical power of the VIPERS survey, which observed ~90,000 galaxies at intermediate redshifts (0.5 < z < 1), and the application of an unsupervised clustering algorithm, allowed us to distinguish between passive galaxies, star-forming galaxies and galaxies hosting active galactic nuclei (AGN), among other types. A follow-up study of their environmental dependence indicates that this classification may actually reflect different galaxy evolutionary paths revealing for instance a rare population of small and passive red galaxies or a population of AGN in dwarf galaxies. Among them, we found a sample of seven broad-line AGN in dwarf galaxies powered by supermassive black holes, more massive than expected from the scaling relations, contradicting standardly accepted models of synchronized growth. These black holes may originate from dwarf galaxies with intermediate-mass black holes in the early universe and over time will grow until their mass matches the one of the black hole they host. In my talk, I will discuss the implications of these findings for our understating of the growth of supermassive black holes.

Catherine CERNY (Centre for Extragalactic Astronomy, Durham University): “Probing the inner density profile of galaxy clusters with strong lensing and MUSE spectroscopy”.

The cafe-club will take place at 2:00 pm in the Library at LAM and on usual AMU virtual room.
(Meeting ID : 968 7683 2544 — Passcode : 173347)

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Galaxy clusters are the most massive gravitationally-bound objects in the universe, and analysis of their structure can yield many fascinating answers and equally fascinating questions about the nature of the physics that holds them together. The presence of dark matter in galaxy clusters is a particularly interesting question, and there are many techniques that are currently being used to study everything from the ‘core-cusp’ tension in cluster cores to the exact distribution of DM throughout the clusters. One of these techniques is called strong gravitational lensing, which effectively allows us to use massive objects -like galaxy clusters- as natural ‘cosmic telescopes’ to study highly magnified background sources. Lensing can also be used to study cluster substructure and model dark matter distribution in clusters. In this talk, I will discuss the use of lensing as a way to probe the mass distribution of several galaxy clusters. I will also demonstrate how the combination of lensing and 2-D galaxy kinematics of the BCG can be used to effectively- and cheaply- study the shape of the dark matter distribution near the center of the cluster. I will use these models to discuss how we can effectively constrain the shape of the density profiles in galaxy clusters with strong lensing, as well as what impact this can  have on our current physical understanding of the universe.

Pierre BOLDRINI (Institut d’Astrophysique de Paris): “ΛCDM cosmological simulation of Monge-Ampère gravity via
optimal transport theory”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Monge-Ampère gravitation is a modification of the classical Newtonian gravity where the linear Poisson equation is replaced by the nonlinear Monge-Ampère equation. First, I will show how Monge-Ampère gravity emerges from a system of non-interacting Brownian particles, through the application of the large deviation principle. Then, I will present the results of the first cosmological N-body simulation of Monge-Ampère gravity, which is solved by a performant semi-discrete algorithm based on optimal transport theory. Analysis of evolution of power spectra shows that the Monge-Ampère equation produces less power on small scales and more on large scales than the Poisson equation. Besides, a tentative first study of density profile of haloes, indicate that MA gravity might primarily result in dark matter core central profiles.

Franciele KRUCZKIEWICZ (LAM): “Water’s journey to Earth: A Virtual Reality outreach project +++ with demo with VR headset“.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Astrochemistry, a relatively new field within astronomy, uses molecules in space as a tool to better understand various processes, such as the formation of stars and planets, as well as the potential contribution of molecules formed in space to the development of life on Earth. However, communicating these concepts to a general audience can be a challenge. Fortunately, science outreach can help bridge this gap by explaining complex concepts in a way that is accessible to everyone.

One of the most exciting outreach tools today is Virtual Reality (VR), which has been gaining interest around the world. With this in mind, we developed a VR project specifically designed to introduce the public to the field of astrochemistry. Our VR game takes the player on a journey through the different phases of star and planet formation, highlighting the role of water in each phase, from its formation in molecular clouds to its potential delivery to early Earth via comets.

During this talk, I will provide an overview of virtual reality tools and our goal in developing the astrochemistry VR game. I will also discuss the challenges we faced in developing this project during a PhD, as well as its limitations. Finally, I will explore the future perspectives for creating similar educational games and outreach projects to increase public understanding of science.

Denis BURGARELLA (LAM): “Spectroscopic verification of very luminous galaxy candidates in the early universe”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

During the first 500 million years of cosmic history, the first stars and galaxies formed and seeded the cosmos with heavy elements. These early galaxies illuminated the transition from the cosmic “dark ages” to the reionization of the intergalactic medium. This transitional period has been largely inaccessible to direct observation until the recent commissioning of JWST, which has extended our observational reach into that epoch. Excitingly, the first JWST science observations uncovered a surprisingly high abundance of early star-forming galaxies. However, the distances (redshifts) of these galaxies were, by necessity, estimated from multi-band photometry. Photometric redshifts, while generally robust, can suffer from uncertainties and/or degeneracies. Spectroscopic measurements of the precise redshifts are required to validate these sources and to reliably quantify their space densities, stellar masses, and star formation rates, which provide powerful constraints on galaxy formation models and cosmology. Here we present the results of JWST follow-up spectroscopy of a small sample of galaxies suspected to be amongst the most distant yet observed. We confirm redshifts z > 10 for two galaxies, including one of the first bright JWST-discovered candidates with z = 11.4, and show that another galaxy with suggested z ~ 16 instead has z = 4.9, with strong emission lines that mimic the expected colors of more distant objects. These results reinforce the evidence for the rapid production of luminous galaxies in the very young Universe, while also highlighting the necessity of spectroscopic verification for remarkable candidates.

Mohammad Taher SAFARZADEH (NASA Goddard Space Flight Center): “How to use LISA to constrain Hubble expansion rate at high redshifts”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Our understanding of the formation channels of stellar mass compact objects have been challenged by the discovery of massive binary black holes in the third observing run of LIGO/Virgo Collaboration. It is imaginable that our theories of supermassive black hole formation should be revisited by the launch of LISA that targets gravitational wave observations of supermassive black holes at high redshifts. I will talk about how we can leverage LISA observations to constrain models of supermassive black hole formation together with the expansion rate of the universe at high redshift. The proposed approach is simple and yet powerful and will help us to also gain a better understanding of seed formation in the early universe.

Massimo GUIDI (Università Roma Tre): “Constraining Large-Scale-Structure with new modelling approaches of the three-point correlation function“.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Three-point statistics play a key role in the investigation of the properties of the universe. This talk addresses the modelling of three-point correlation functions (3PCF) in Galaxy Clustering analysis, in the context of current and upcoming generations of cosmic surveys such as Euclid, DESI, LSST and the Roman Telescope. Particular attention will be given to second-order modelling within a perturbative expansion framework, bridging the gap with theory developed in Fourier space, thus enabling the use of the 3PCF to extract cosmological information in non-linear regimes and providing a direction for combining the 3PCF and bispectrum to mitigate potential systematics in cosmological data analysis.

Hiroya UMEDA (Institute for Cosmic Ray Research, University of Tokyo): “Cosmic reionization sources and history probed with large galaxy surveys and photoionization modeling”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Cosmic reionization scenarios are explored by investigating cosmic reionization history and sources from galaxy observations with Subaru telescope. We first consider the possibility of contributions from high energy photons from young galaxies suggested by the detection of strong high-ionization line (e.g., HeII), which are notoriously hard to reproduce with normal stellar populations. We investigated the general ionizing spectrum shapes for the young galaxies using photoionization modeling to explain high ionization lines with other major emission lines. We confirmed that hard power-law like emission explains HeII/Hb flux consistently with other emission line ratios. We also investigated the origin of the hard sources and the contributions to cosmic reionization. We will also present our on-going work on high-z Lya emitters with Subaru/Hyper Suprime Cam to constrain neutral hydrogen fraction evolution at z>6. I also present some on-going efforts on the massive spectroscopy of LAEs with Subaru/Prime Focus Spectrograph (PFS) and future prospects on the synergy with 21cm observations. At last, I would like to discuss the possible science with upcoming instruments such as ROMAN and Subaru/ULTIMATE.

Jorge VILLA-VÉLEZ (École Normale Supérieure, Paris): “Molecular hydrogen (H2) emission as a tracer of dissipation in the extragalactic ISM“.

You can find the schedule of upcoming café-clubs and the video of old ones at http://wiki.lam.fr/geco/CafeClub 



Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

Shocks are ubiquitous in the interstellar medium (ISM) as a result of a variety of astrophysical phenomena such as outflows, supernovae, jets, accretion among others. The perturbations created by these phenomena traverse the ISM, disturbing and changing the thermal, chemical, and physical characteristics of the environment. Therefore, understanding the underlying physics of shocks provides us with a powerful tool to study how energy is dissipated in extragalactic sources by shocks. In this talk, I will present an ongoing research project focused on the interpretation of H2 molecular emission (e.g., pure rotational and rovibrational transitions) in radiogalaxies observed with the Spitzer IR Spectrograph and VLT/SINFONI imaging spectroscopy assuming the emission is produced by ensembles of shocks inside the observation beam. I will show the current status of the Paris-Durham shock code, a brief introduction on how users can make use of this powerful tool to interpret emission in galactic and extragalactic environments, and some future James Webb Space Telescope (JWST) applications. The impact of this study opens a door to understanding energy dissipation in extragalactic sources produced by ensembles of shocks.

Happy New Year!

Michelle COLLINS (University of Surrey): “The hunt for new ultra-faint dwarf galaxies”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

If the Lambda cold dark matter model is correct, we expect hundreds of faint, low mass galaxies to be lurking around the Local Group awaiting detection. These objects are interesting not only because they can allow us to constrain the nature of the dark matter particle, but also as they are extremely sensitive probes of galaxy formation physics. With the start of the Vera Rubin Observatory’s Large Survey of Space and Time in 2024, we should finally find these ‘missing’ low mass galaxies if they are there. In this talk, I will discuss the hunt for the lowest mass galaxies, the challenges in the era of LSST, and present findings from our recent search of archival DESI-Legacy Imaging. In particular, I will focus on two new detections: Pisces VII
and Pegasus V.

Clément STAHL (Observatoire astronomique de Strasbourg): “Exploring the effects of primordial non-Gaussianity at galactic scales”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

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ABSTRACT

In this talk, I will show you my investigation of the effect of significant small-scale primordial non-Gaussianity on structure formation and the galaxy formation process. Specifically, we explored four different types of non-Gaussianities: positive and negative skeweness and kurtosis. Generically, we find a distinct and potentially detectable feature in the matter power spectrum around the non-linear scale. The feature might have interesting consequences for the S8 tension. We then show in particular that a positively skewed distribution with fNL of the order of 1000 at these scales, implies
that typical galaxy-sized halos reach half of their present-day mass at an earlier stage. Building up galaxies earlier is highly relevant in the light the young massive galaxies observed by JWST. These galaxies have a quieter merging history at z < 3 than in the Gaussian case and their environment between 0.5 and 4 virial radii at z = 0 is less dense than in the Gaussian case. This quieter history and less dense environment has potentially interesting consequences in terms of the formation of bulges and bars. Moreover, we show that the two most massive subhalos around their host tend to display an interesting anti-correlation of velocities, indicative of kinematic coherence. Finally, all feedback prescriptions being otherwise identical,
simulations with a negative (positive) fNL on small scales, display a slightly more (less) disky kinematics than in the Gaussian case. All these hints will need to be statistically confirmed in larger-box simulations with scale-dependent non-Gaussian initial conditions, followed by hydrodynamical zoom-in simulations to explore the detailed consequences of small-scale non-Gaussianities on galaxy formation.

 

Georg HERZOG (Università di Milano “Bicocca”): “The present-day gas content of simulated field dwarf galaxies”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

—————-
ABSTRACT

It is known from theory and observations that galaxy evolution can be
influenced by environmental effects. Processes like ram pressure
stripping in groups, clusters or the cosmic web as well as tidal
stripping can affect the final properties of galaxies. However, until
now no estimate exists on the relative importance of different
processes for the final properties of field galaxies. Based on a
high-resolution cosmological simulation I will show that there are two
distinct processes that affect the present-day gas content of field
dwarf galaxies. 1) Past interactions with massive hosts, in which a
dwarf loses gas and dark matter via tidal and ram-pressure forces; and
2) hydrodynamic interactions with the gaseous filaments and sheets of
the cosmic web, in which a dwarf loses gas via ram-pressure. I will
refer to these galaxies as “flybys” and “COSWEBs”,
respectively. While flybys are located in high-density regions,
tracing the location of the most massive galaxies in the simulation,
COSWEBs are dispersed throughout the volume and trace the cosmic web.
For dwarf galaxies with M_200 < 5*10^9 Msun the fraction of COSWEBs
can be as high as 35%, while flybys make up 100% of galaxies with
M_200 < 3*10^8 Msun. The deficit of gas of flyby and COSWEB galaxies
can preclude the detection of a large fraction of field dwarfs in
future HI surveys.

Silvia MARTOCCHIA (Astronomisches Rechen-Institut, Universität Heidelberg): “The origin of globular clusters and their anomalous stellar populations”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

ABSTRACT

Globular clusters (GCs),agglomerates of hundreds of thousands stars, are among the oldest (age > 10 Gyr) luminous sources  in the Universe, bearing witness to the earliest stages of galaxy formation as well as their evolution to the present day. While GCs have played a critical role in our understanding of the assembly of galaxies, their full potential remains unfulfilled due to our lack of understanding of how they form. Indeed, GCs were traditionally thought to be simple stellar systems, assuming that all the stars within a given cluster were born at the same time and have the same chemical composition. However, already in the ’70s, light-element abundance variations (e.g. He, C, N, Na, O) within GCs stars were discovered thanks to spectroscopy and photometry. A typical GC optical and near-UV colour-magnitude diagram shows discrete multiple sequences at almost any evolutionary stage, which indicate the presence of multiple stellar populations (MPs). The origin of such MPs is still far from being understood.

The discovery of young GCs forming in nearby galaxies has opened a new window on the problem, allowing us to directly search for the origin of MPs. I will report on the recent discoveries of MPs in young and intermediate age GCs and how their properties change as a function of cosmic time. It is crucial to understand whether the young star clusters are the same stellar systems as the ancient GCs, just observed at a different stage of their lifetimes. If confirmed, this will provide crucial constraints on star cluster formation studies, which fundamentally impact our understanding of how GCs relate to galaxy formation and evolution in general.

 

Devon POWELL (Max Planck Institute for Astrophysics, Garching): “Fuzzy dark matter constraints using a single VLBI observation of a gravitationally lensed radio jet”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Meriam, Mathilde

—————-
ABSTRACT

Strong gravitational lensing by galaxies provides us with a powerful laboratory for testing dark matter models. Various particle models for dark matter give rise to different small-scale distributions of mass in the lens galaxy, which can be differentiated if the observation is sensitive enough. The sensitivity of a gravitational lens observation to the presence (or absence) of low-mass dark structures in the lens galaxy is determined mainly by the angular resolution of the instrument and the spatial structure of the source.

I will present results from the analysis of a global VLBI observation of a gravitationally lensed radio jet. With an angular resolution better than 5 milli-arcseconds and a highly extended, spatially resolved source, we are able to place competitive constraints on the particle mass in fuzzy dark matter models using this single observation. Our results illustrate the key role that VLBI observations will play in revealing the nature of dark matter, especially in light of the ~10^5 gravitational lens systems with radio-bright sources which will be discovered by the Square Kilometre Array.

Yun-Ting Cheng (Caltech): “Cosmology and Astrophysics from Intensity Mapping”.

You can find the schedule of upcoming café-clubs and the video of old ones here.

Take care,
Carlo, Mathilde, Meriam

—————-
ABSTRACT

Intensity mapping has emerged as a promising tool to study the high redshift universe and the faint, diffuse extragalactic populations. Without resolving individual galaxies, IM uses the integrated light from all sources to statistically probe the emission properties of the sources and the underlying large-scale structure. In this talk, I will first give an overview on intensity mapping, followed by a few example science cases with intensity mapping including studying the extragalactic background light and the intra-halo light from the diffuse intensity maps. Next, I will introduce the upcoming NASA satellite mission — SPHEREx, which will conduct an all-sky near-infrared spectral survey. Finally, I will discuss the prospect of measuring the extragalactic background light with SPHEREx using cross correlation, and a novel data-driven technique to constrain the 3D large-scale structures from multi-frequency intensity maps.