Conference Programme

Wednesday, June 16 (11:30 - 16:30 UTC)




Poster session and science discussions


11:30 - 12:00

Session 4: The formation, evolution, star-formation and quenching of galaxies in merging clusters

Chairs: David Sobral, Sophie Maurogordato

12:00 - 13:45 

Review talk: The interaction between the ICM and galaxies in merging clusters DOI:10.5281/zenodo.4977980

Matt Owers

12:00 - 12:20

The 3D large scale structures of star forming galaxies and the projection corrected environmental effects back to z=1.5 revealed by the novel double narrow-band filter technique DOI:10.5281/zenodo.4993463

Ronaldo Laishram

12:20 - 12:35

Galaxies are distributed inhomogeneously on small scales in the Universe and thus define large-scale structures. Understanding the evolution of cluster galaxies is to determine precisely how galaxies change their properties as a result of the hierarchical growth of large-scale structures. The difficulty is the need for accurate determination of the redshift to determine the precise environment of the galaxies. We present a very unique and novel method to estimate accurate redshifts of star-forming galaxies by measuring the flux ratio of the same emission line observed through two adjacent narrow-band filters. We apply this method to our NB921 and new NB926 data taken with Hyper Suprime-Cam on the Subaru Telescope. We obtain redshifts for [OII] emission line galaxies at z ∼ 1.5, [OIII] emission line galaxies at z~ 0.84 and [Ha] emission-line galaxies at z~0.41. This allows us to reveal 3D structures and can correct the projection effect. We also find that the projected celestial distribution does not precisely trace the real distribution of galaxies, indicating the importance of the three-dimensional view of structures to properly identify and quantify galaxy environments. We then investigate the projection corrected environmental dependence of galaxy properties.

Shocking tales of structure formation: Evolving galaxies and black holes in evolving environments DOI:10.5281/zenodo.4976622

Andra Stroe

12:35 - 12:50

Understanding the interplay between galaxy evolution, star formation, and black hole activity from the perspective of structure formation remains one of the most fascinating challenges in modern astrophysics. On the largest scales, pairs of galaxy clusters colliding drive the growth of structure. Cluster mergers are the most energetic events since the Big Bang, which release 10^64 ergs over 1-2 billion years and produce dramatic, long-lasting effects. I will introduce the ENISALA survey, a collection of panchromatic observations aimed at understanding how large-scale structure drives galaxy and black hole evolution. I will show new results which demonstrate that the merger of galaxy clusters can trigger star formation and black hole activity in cluster galaxies, shape the evolution of cluster galaxies, and reverse typical environmental trends observed in relaxed clusters at low redshift. I will draw parallels between the fundamental drivers of galaxy and black hole evolution in low-redshift clusters and the processes relevant in the context of proto-clusters and high-redshift clusters, where mergers and associated non-thermal phenomena were far more common than in the nearby Universe.

1-min poster presentations


12:50 - 13:05

Passive spirals and shock-influenced star formation in merging cluster A3376

Kshitija Kelkar


Galaxy cluster environments are known to leave distinct imprints on structural and star formation evolution of member galaxies. However, the instantaneous effects of hierarchical growth of large-scale structure, through accretion and merging of galaxy clusters, on the inherent galaxy populations is still poorly understood. This talk focuses on constraining such effects through a multi-wavelength study of a merging cluster A3376, employing data products from one of the widest spectroscopic surveys OmegaWINGS and widefield optical imaging. This talk will also showcase the results of this analysis through a detailed discussion on cluster spirals and post-starburst galaxies in A3376, and put forth plausible pathways through which cluster merging activity can affect the star formation history of cluster galaxies and thus explain the environmental trends observed today.

Exploring the mass assembly of the Fornax Galaxy Cluster DOI:10.5281/zenodo.4991405

Avinash Chaturvedi


Nearby galaxy clusters are in an evolved state of their evolution, but many of them are still growing via the accretion of sub-groups along filaments. Thus, they provide ideal testbeds to study assembly processes, which might be similar to those in proto-galaxy clusters, like pre-processing in galaxy groups and sub-group merging. The Fornax cluster is dynamically quite active and is still accreting various sub-groups. Recent photometric studies of the cluster core revealed an excess of globular clusters (GCs) around the central massive galaxy NGC 1399, suggesting accretion of GCs from nearby, interacting major galaxies like NGC 1404. Comprehending the assembly history of Fornax via the kinematics of its GC systems thus could provide insight into the accretion processes of early proto-galaxy clusters. To understand the mass assembly of the Fornax cluster, we have analyzed a VLT/VIMOS spectroscopic survey of GCs in the cluster core covering half of the cluster's virial radius (~300 kpc). Combined with previous spectroscopic measurements, this leads to the most extensive catalog of radial velocity measurements with a total of 2341 confirmed GCs in Fornax. Our first analysis of this dataset provides the kinematical characterization of the cluster's intra-cluster component. In this talk, I will present the kinematics of GCs in the core of the cluster, discussing possible kinematical interaction signatures between NGC 1399 and the major galaxies of the Fornax cluster.

Is ram pressure enhanced by cluster mergers? DOI:10.5281/zenodo.5022208

Ana Carolina Lourenco


In a hierarchical Universe, galaxy clusters continue to grow with cosmic time, and thus a large number of them are disturbed by the accretion of groups or major collisions. Hydrodynamical simulations show that ram pressure stripping can be enhanced during cluster interactions providing an alternative way of forming jellyfish galaxies. In this work, we use X-ray, optical, and radio data to robustly investigate this hypothesis, supplying a statistical analysis of the incidence of the jellyfish galaxies from the WINGS, OmegaWINGS, and GASP surveys with respect to the dynamical state of their host clusters. We found that disturbed clusters tend to be more massive and host less ram pressure stripping candidates than the relaxed clusters. Our conclusions hold even when the counting is done in different fractions of R200 and correcting by the infalling population. These results are twice counter-intuitive since in massive clusters the higher gas density leads to stronger ram-pressure and that in messy environments the higher relative velocity between the gas and the galaxies should also provide a ram-pressure enhancement.

Nucleation zones in superclusters and the future largest galaxy clusters DOI:10.5281/zenodo.5009397

César Caretta


The assembling of galaxy clusters by mergers and accretions happens concurrently with the quest of these systems to reach virialization. Depending on the environment where the cluster resides, each of these processes may predominate, and the time the system will take to reach its final dynamical state may extend longer. In a relatively isolated environment, the cluster will only pass a single virialization process, while in the core of a supercluster it will go through different unrelaxed/relaxed states, till reaching a maximum size, the same way as fossil D galaxies clean completely their surroundings at some time. In this work we study the case of these probable largest clusters that someday will reach equilibrium, that is, we are searching for what we call ``nucleation zones'', which are these supercluster cores that are expected to still collapse despite of the accelerated expansion of the Universe. We have studied a sample of 50 rich superclusters of galaxies (m ≥5), with z ≤ 0.15, for identifying their nucleation zones and characterizing their structure. We use mainly the entropy of these structures, calculated based on the properties and distribution of galaxies and galaxy groups and clusters inside these cores, to delimit the collapse regions. Here we present the preliminary results of this study. We have found that some superclusters possess more than one nucleation zone. Our results agree with the very few cases previously studied according to the literature.

Resolved spectroscopy of cluster galaxies at z>1 DOI:10.5281/zenodo.4974137

Nicholas Amos


The star formation rate density of the universe peaks at z=1-3 and has subsequently declined to the present day. We are focusing our attention on the decline of star formation in the densest environments at z~1.5. I will present results that spatially resolve the gas properties of star-forming galaxies in the clusters XMMXCS2215 (z~1.47) and XMMUJ2235 (z~1.39), taken from the KMOS Cluster Survey (KCS). We have used this state-of-the-art IFU data to obtain the star formation rate and dynamical properties of the galaxies, and have combined this with morphology from HST imaging. From this we obtain a median ratio of stellar mass to dynamical mass of 0.38. On average, for the galaxies in XMMXCX2215 54% of the total galaxy mass is stellar mass and for XMMUJ2235 this is much lower at approximately 35%. The majority of our sample is rotation dominated with a median v/sigma of 2.55, this being higher in the z~1.39 cluster. We find a rotation- to dispersion-dominated galaxy ratio of 5 across both clusters. Quantifying these parameters are crucial in determining the impact of environmental quenching mechanisms in z=1.4 clusters.

Kinematics of proto-cluster disk galaxies at z=1.5

Asmus Boehm


I will present results from our VLT/KMOS spectroscopy of 46 star-forming galaxies in two proto-clusters at redshift z=1.47. The galaxies were selected from narrow-band imaging (matching [OII]3727 at the proto-clusters' redshift) of the HyperSuprimeCam Survey. Only approx. 50% of the galaxies with spatially extended Hα emission are regular rotators for which the maximum rotation velocity Vmax can be derived. Many of these galaxies show large offsets from the rotation velocity-luminosity (Tully-Fisher) relation. These offsets are driven by relatively low ratios between Vmax and gas velocity dispersion σ (nevertheless, all galaxies have ratios Vmax/σ>2). This could be due to galaxy-galaxy interactions - the low proto-cluster velocity dispersions allow more efficient tidal interactions than is typical for more evolved, massive clusters at later epochs - and/or the generally (i.e. environment-independent) lower fraction of fully settled disks at high redshifts than in the present-day Universe.

GCAV: Galaxy Clusters At Vircam

Mario Nonino


GCAV is a second generation ESO VIRCAM-VISTA Public Survey observing 20 massive clusters of galaxies aimed to explore galaxy evolution over a large, and mostly unexplored, diversity of high-density environments, also thanks to the rich wealth of ancillary data for the cluster targets.

Searching for Massive Galaxy Clusters at z~1 with WISE+VISTA+SDSS Catalogues DOI:10.5281/zenodo.4982827

Anastasio Díaz-Sánchez


We have applied an algorithm to search the most massive Galaxy Clusters (GCs) at z~1 in the ALLWISE, VISTA and SDSS Stripe 82 photometric catalogs. The algorithm CARTAGO (Convolution Algorithm Remarking Totally Asymmetrical Galaxy Overdensities) performs asymmetrical convolutions to enhance detectability. Then overdensity regions are selected and a Friends-of-Friends algorithm is applied to the galaxies in these regions. We have found some hundreds of GC candidates and selected the richest ones. One of them has been observed with multiobject spectroscopy using GTC/OSIRIS. From the 46 slits in the mask we have only 20 good spectra, due to the short integration time, with a peak of 5 galaxies in the redshift distribution at z~1.10 within 1.5 arcmin from the cluster center. Other 8 rich GC candidates have been observed with GTC/EMIR in the broad band imaging mode in order to improve the photometric redshift accuracy. So, we have reached deeper in the J and Ks bands for these candidates. With these data we have obtained their photometric confirmation and chosen the galaxies to follow up spectroscopically. One of these GCs has been observed with GTC/EMIR/MOS Science Verification. From the 13 slits on science targets we have only 9 with enough signal to noise to measure their redshift and from them we have found 5 galaxies with z ~ 0.76. Another galaxy is a QSO which is behind the cluster, and perhaps lensed by the GC, with z=2.8485.

The photoionization by galaxy cluster photons and its impact on the plasma in the cluster vicinity DOI:10.5281/zenodo.5497702

Lýdia Štofanová


The physical properties of the faint and extremely tenuous plasma in the far outskirts of galaxy clusters, the circumgalactic media of normal galaxies, and filaments of the cosmic web, remain one of the biggest unknowns in our story of large-scale structure evolution. Modeling the spectral features due to emission and absorption from this very diffuse plasma poses unique challenges, as both collisional and photo-ionization processes must be accounted for. In this project, we study the photo-ionization by galaxy cluster photons in addition to the photo-ionization by the cosmic UV/X-ray background and its impact on the ionization balance. We model more realistic spectra by taking into account the cosmic UV/X-ray background together with the emission from representative cool-core galaxy clusters, and illuminate the photo-ionized gas in the galaxy cluster vicinity. We find that depending on the distance from the galaxy cluster, and assuming plasma temperatures and densities typical for the intergalactic medium, the total photo-ionization rate can reach 10% or even 100% of the total ionization rate. We show how this affects the ionization fractions of O VI, O VII, O VIII, Ne IX, Fe XVII, N VII, C V and C VI ions and compare it with the emission by cosmic background only as well as with plasma that is in the collisional ionization equilibrium. We assume a simplified model of a cosmic web filament and predict the column densities for different lines of sight.

Mass Ratio Evolution in Clusters Between Halos and Sub-halos

Guillaume Mahler


Structure in our universe grows hierarchically, where small structures (stars and galaxies) assemble first and later on galaxies group/proto-clusters together in large potential wells to form clusters. Clusters of galaxies are the largest structure observable in our Universe and can contain more than hundreds of galaxies. We believe that every galaxy carries its own small halo of dark matter, and when they fall in a cluster part of that halo is stripped and diffused in the larger halo of the cluster. I will present here how I am using the strong gravitational lensing effect in combination with IFU of cluster fields to answer questions on the evolution of the halos and sub-halos dark matter components. Indeed galaxies and their dark matter falling in the cluster and losing their dark matter to the profit of the cluster also called the sub-halos mass loss. Using a large number of models spanning a wide range of redshifts (0.3 < z < 1.0) I will show how clusters transfer their mass from their cluster members to their host halos.

Revealing galaxy quenching's dependence on stellar mass and environment in galaxy clusters DOI:10.5281/zenodo.4980169

Zhiying Mao


Quenching is a vital phase in galaxy evolution. A key population, recently-quenched galaxy(RQG) can convey information directly from the quenching process. In this work, we investigate RQGs in clusters. They span from cluster centers to outskirts. From galaxy overdensities in the COSMOS field, we pick out 14 galaxy clusters and determine their center coordinates from 5 redshift bins at z~0.5-1.0. Our galaxy sample consists of galaxies within a 1.25 Mpc radius from these cluster centers. Using photometric data from the COSMOS2015 catalog and rest-frame UVJ selection method, we classify all galaxies into star-forming, quiescent, and recently-quenched populations. We use number ratios of different populations to quantify properties of quenching processes. In particular, we use model evolutionary tracks on the UVJ diagram to distinguish fast and slow quenching paths hence understand the quenching timescale's dependence on mass and environment. Our results support the downsizing scenario and the existence of both mass quenching and environmental quenching. The efficiency of mass quenching increases with stellar mass, while environmental quenching is only efficient for low-mass systems. Quenching timescale shows dependence on stellar mass but no clear relation with the environment alone. In the future, we wish to take advantage of Subaru/PFS' large FOV and high efficiency to obtain spectra of our RQG sample and further study the physical mechanisms driving quenching processes.

Environmental Quenching seen in CO Emitting Galaxies in a Massive Cluster SPT-CL J0615-5746 DOI:10.5281/zenodo.4984218

Satoya Nakano


The cosmic star formation rate (SFR) density continues to decrease after it peaks at z ~ 2. Previous studies suggested that the environmental quenching of star formation is one of the plausible causes for this decrease. Though several scenarios have been proposed for the environmental quenching process, it is not clear what the dominant mechanism is for individual clusters and galaxies. In order to understand the mechanism of environmental quenching, we used ALMA to investigate the physical properties of 4 member galaxies located at the center (~ 0.2 R_200) of SPT-CL J0615-5746 (SPT0615) at z = 0.972. Since SPT0615 is considered to be filled with high temperature ICM, it is expected that environmental quenching will be observed in the center of the cluster. Four member galaxies are detected in dust continuum, and three of these are also detected in CO(J = 5 – 4) with the significance over 5σ. The inferred SFR and molecular mass are high (SFR ~ 10 – 10^2 M_Sun/yr and M_mol ~ 10^10 M_Sun), implying the existence of active star formation. In addition, a CO(J = 5 – 4) tail feature is detected in one of those galaxies with the significance 5.7σ, which is likely to be molecular gas stripped from this galaxy by interaction with the ICM. In this galaxy, HST rest–frame UV to NIR images show that star formation takes place even in the stripped gas. Here we show, for the first time, gas stripping in a cluster at z ~ 1.

Molecular gas scaling relations in galaxy clusters: a statistical comparison to the field since z=2

Giulia Rodighiero

13:05 - 13:20

We study the average gas scaling relations of star-forming galaxies residing in clusters at various cosmic epochs. We combine literature data including sources from the local Universe up to z=2. We report CO based gas mass measurements and our compilation of CLASH/Herschel galaxies for which the gas mass is derived from the dust continuum. Up to z=1.5, we find that cluster members follow basically the standard Schmidt-Kennicutt law, as the one of normal field star-forming galaxies. The relation in clusters is, however, slightly narrower with a systematic offset of about 0.2 dex toward larger gas masses at fixed SFR (i.e. smaller star formation efficiencies). At higher redshifts the scatter of the relation gets broader, indicating that the elusive nature of protoclusters is more affected by different in situ evolutionary stages

Strangulation in a high redshift cluster revealed by enhanced metallicities and ALMA molecular gas DOI:10.5281/zenodo.4984663

Christian Maier

13:20 - 13:35

One of the most striking examples of a high-z cluster with an active core is XMMXCSJ2215.9-1738 at z~1.5. Using spectroscopic redshifts of about 100 galaxies in and around the cluster I computed the location of galaxies in the projected velocity-versus-position phase-space to separate the cluster sample into a virialized region of objects accreted longer ago and a region of infalling galaxies. I used KMOS spectroscopy of Halpha and [NII] covering a region that corresponds to about one virial radius, and found the computed metallicities of z~1.5 cluster galaxies inside half R200 to be enhanced compared to infalling galaxies and field galaxies at z~1.5 of similar masses. This indicates that the density of the intracluster medium in this massive cluster becomes high enough toward the cluster center such that the ram pressure exceeds the restoring pressure of the hot gas reservoir of cluster galaxies. This can remove the gas reservoir stopping the inflow of diluting gas thereby enhancing gas metallicities and initiating quenching. Although the galaxies continue to form stars, albeit at slightly lower rates, using the available cold gas in the disk which is not stripped: Molecular gas masses derived from ALMA CO(2-1) for several cluster galaxies suggest that the main component of the stripped gas is the neutral gas reservoir, while the molecular gas is relatively much less affected by the ram pressure, such that the galaxies continue to form stars from the molecular gas.

Discussion and summary of session

Matt Owers, David Sobral, Sophie Maurogordato

13:35 - 13:45



13:45 - 14:15

Session 5: Lessons learned from multiwavelength studies of local/nearby clusters

Chairs: Andra Stroe, Yusei Koyama, Remco van der  Burg

14:15 - 16:00

Review talk: Lessons learned from multiwavelength studies of the local/nearby clusters DOI:10.5281/zenodo.4973487

Julie Hlavacek-Larrondo

14:15 - 14:35

Galaxy clusters are fantastic laboratories for understanding the physics of the cosmos. They not only play a pivotal role in our understanding of black hole feedback and plasma physics, but they also provide some of the most compelling cases for dark matter and dark energy. The goal of this talk is to highlight these discoveries – with an emphasis on lessons learned from multiwavelength studies of local/nearby clusters. This includes our current understanding of AGN feedback processes in local/nearby clusters, to the details of ICM cooling and heating. I will also present new results on how machine learning can (and will) play a vital role in our understanding of nearby/local clusters, proto-clusters, and merging clusters for the next decades.

Hunting for jellyfish galaxies in clusters DOI:10.5281/zenodo.4975081

Florence Durret

14:35 - 14:50

Galaxies in clusters undergo several phenomena such as ram pressure and tidal interactions, that can trigger or quench their star formation and, in some cases, lead to galaxies showing unusual shapes and long tails, such as jellyfish galaxies. We have searched for such galaxies in 39 clusters covering the redshift range between 0.2 and 0.9, and in more detail in the cluster MACS J0717.5+3745 (z=0.5458) for which we had a large spatial coverage and abundant spectroscopic redshift sampling. Altogether, we detected almost 200 jellyfish candidates in 22 clusters. For a subsample of these galaxies, we performed a stellar population synthesis and derived several quantities such as the star formation rate and the stellar mass. As expected, the great majority of our jellyfish candidates show quite strong star formation and therefore differs from « normal » star forming cluster galaxies. For MACSJ0717, a merging, dynamically young cluster, our results indicate that jellyfish candidates tend to avoid the densest regions of this complex cluster, a striking result that will be discussed.

The role of environment in the TNG simulation: the fate of group and cluster satellites

Martina Donnari

14:50 - 15:05

I will discuss two important aspects of the evolution of galaxies and the formation of present-day groups and clusters, using the outcome of the IllustrisTNG cosmological-magnetohydrodynamical simulations, which provide us with a unique set of thousands of galaxies in massive hosts. Firstly I will focus on the role of the groups and clusters of M200>10^13 Msun in quenching the star formation of their satellite (Mstars> 10^9 Msun). Importantly, I will demonstrate how important pre-processing is in determining the fate of satellite galaxies. More than 50% of galaxies with Mstars> 10^(9-11.5) Msun that are found today in massive clusters have been pre-processed in smaller groups before infalling in their current host. Once the pre-processing is taken into account we found that satellites having Mstars=10^(9-10.5) Msun might have spent more than 6-7 Gyr in groups before infalling in the z=0 clusters. About 30% of group and cluster massive satellites that are quenched at z = 0 were already quenched before falling into their current host, and the bulk of them quenched as early as 4 to 10 Gyr ago, suggesting that both environmental and internal star-formation quenching can occur at early cosmic epochs (Donnari+ 2021). Then, I'll show how the metallicity enhancement of cluster galaxies appears prior to their infall into the central cluster potential, indicating for the first time a systematic ""chemical pre-processing"" signature for infalling cluster galaxies (Gupta+ 2018).

1-min poster presentations


15:05 - 15:20

Unveiling the origin of the cold gas in Brightest Group Galaxies with MUSE

Valeria Olivares


The origin of the cold gas in brightest group galaxies (BGGs) is still a matter of debate. In this talk, I will present a study of the warm ionized gas for a sample of 18 nearby BGGs optically selected using Multi-Unit Spectroscopic Explorer (MUSE) observations. Our MUSE observations reveal a distribution of morphologies from complex networks of filaments to extended (>10~kpc) and compact (<3 kpc) disk-dominated structures. Based on the thermodynamical properties of the hot atmospheres, we find that the cold gas lying in filamentary structures and compact disks is likely precipitating from the hot gas. It is not clear whether the extended gas disks have formed after hot gas cooling accretion, or whether they trace the residual gas of previous merger events.

AGN feedback in the Planck selected Clusters: a detailed study of X-ray cavities DOI:10.5281/zenodo.5026069

Valeria Olivares


I will present the statistical study of X-ray cavities in 77 CC and 112 NCC Planck selected clusters using Chandra observations, with the aim of providing further insight into how AGN feedback operates on clusters. The Planck cluster sample is an all-sky mass-selected nearly unbiased sample of galaxy clusters at moderate redshift (z<0.5), which could reflect the entire AGN feedback cycle at the centers of galaxy clusters. We find that the AGN heating traced by the power of the X-ray cavities alone is able to balance the radiative losses of the ICM in our sample. Our observations show a hint on how the dynamical state of the clusters could affect the asymmetries of the cavities. We also found that clusters that have cavities also display Halpha emission, indicating the important role that plays the AGN feedback on the condensation of gas in CC clusters. However, a few Halpha emitting systems lack X-ray cavities, suggesting either different heating mechanisms or different timescales for the dissipation of the X-ray cavities and the cold gas.

Linking Ram Pressure and AGN in the RomulusC Simulation DOI:10.5281/zenodo.5007246

Angelo Ricarte


Surveys of "jellyfish galaxies", galaxies morphologically transformed by ram pressure stripping, have found an overabundance of active galactic nuclei (AGN) in this population. RomulusC, a high-resolution cosmological zoom-in simulation of a 10^14 solar mass galaxy cluster, offers an opportunity to test this hypothesis. We find that peaks of black hole activity punctuate the end of the ram pressure stripping process. As long as a galaxy is able to retain its gas, elevated Eddington ratios are expected for those experiencing larger amounts of ram pressure. In these simulations, the heating and outflows due to subsequent AGN feedback may serve to aid galaxy quenching in tandem with ram pressure.

Analysis of Newly Obtained High Spectral Resolution Data of NGC 1275

Benjamin Vigneron


The Perseus Cluster hosts a massive brightest cluster galaxy, NGC 1275, which displays an extended protruding filamentary nebula. Previous low-resolution observations of these gaseous filaments revealed a chaotic velocity structure. However, the observations did not have the requisite resolving power to disentangle multiple velocity components. Therefore, we have obtained new, high-resolution observations of NGC 1275 with the SITELLE instrument. Nevertheless, the resolution is unprecedented for SITELLE, and thus, requires a careful analysis to properly disentangle the spectral features belonging to different emission lines. Using a novel analysis technique combining both Bayesian Inference and Machine Learning we will obtain new velocity maps of the filamentary nebula which will allow us to gain more insight on the dynamics and evolution of the gas.

AGN Feedback: Keeping Clusters Cores in Check for Gigayears

Yu Qiu


Outflows driven by active galactic nuclei (AGN) are an important channel for accreting supermassive black holes (SMBHs) to interact with their host galaxies and clusters. Properties of the outflows are however poorly constrained due to the lack of kinetically resolved data of the hot plasma that permeates the circumgalactic and intracluster space. We define a single parameter, outflow-to-accretion mass-loading factor m=\dot{M}_out/\dot{M}_BH, to characterize the outflows that mediate the interaction between SMBHs and their hosts. By modeling both M87 and Perseus, and comparing the simulated thermal profiles with the X-ray observations of these two systems, we demonstrate that m can be constrained between 200-500. This parameter corresponds to a bulk flow speed between 4,000-7,000 km/s at around 1 kpc, and a thermalized outflow temperature between 10^8.7-10^9 K. Our results indicate that the dominant outflow speeds in giant elliptical galaxies and clusters are much lower than in the close vicinity of the SMBH, signaling an efficient coupling with and deceleration by the surrounding medium on length scales below 1 kpc. Consequently, AGNs may be efficient at launching outflows ~10 times more massive than previously uncovered by measurements of cold obscuring material, and are thus able to regulate the core plasma properties for billions of years.

Evolution in Clusters and Groups Behind the Magellanic Clouds DOI:10.5281/zenodo.5032036

Jessica Craig


Environment plays a key role in influencing the evolution of galaxies, and clusters provide ‘laboratories’ in which to study galaxy interactions and the effect of environment on these. Meanwhile, the VISTA Magellanic Clouds Survey (VMC) provides a high-resolution near-infrared view covering the Magellanic Clouds and Magellanic Bridge. Due to its high resolution and sensitivity, the VMC also contains information about many background galaxies, most of which have not been captured by past surveys. Modern surveys such as the VMC now make it possible to investigate galaxy clusters and groups that would previously have been obscured by foreground stars, and hence provide us with new ‘laboratories’ in which to study galaxy evolution. We make use of VMC data in combination with our own follow-up spectroscopy and data from optical and infrared surveys and new radio continuum images from the Australian SKA Pathfinder to study the evolution of galaxies in clusters and groups. To this end, we map galaxy clusters in the VMC survey using photometric colours and redshift estimates in order to quantify the environments in which background galaxies reside. We can also study the properties of clusters and groups by using near-infrared as a tracer of stellar mass and of AGN dust and using radio lobes as a probe of the intracluster medium. In the future, we aim to use these data to investigate evolutionary phenomena such as quenching in clusters behind the Magellanic Clouds.

The cycle of metals in the elliptical galaxy NGC1404 DOI:10.5281/zenodo.4986352

Francois Mernier


As the building blocks of complex life, metals are an essential component of our Universe. Quite spectacularly, these chemical elements essentially synthesised in (Type Ia and core-core-collapse) supernovae are found not only in stars and their local interstellar medium, but also at Mpc scales, in the hot, X-ray emitting intracluster medium pervading clusters, groups, and elliptical galaxies. Studying the abundance of these metals and their spatial distribution using X-ray spectroscopy is essential to understand the entire chemodynamics of clusters and groups, from their formation till their age of maturity. Here, we focus on very deep XMM-Newton and Chandra observations of NGC1404, an elliptical galaxy plunging toward the center of the Fornax cluster. The intense ram-pressure processes at play on the hot gas of this galaxy makes it an unique target to capture the entire journey of metals at beyond kpc-scales, from its total (gas and stellar) metal budget within the galaxy to the diffusion mechanisms of these elements into the surrounding ICM. We will discuss the unprecedented accurate abundance measurements (overall metallicity and alpha/Fe ratios) of NGC1404 we obtained, both globally and spatially resolved, and interpret them in the context of the chemical history of the galaxy and of the Fornax cluster.

Dependence of IR-Bright AGN Activity on Halo Mass and Redshift in the SPT Cluster Surveys DOI:10.5281/zenodo.5009054

Benjamin Floyd


The number of active galactic nuclei (AGN) in galaxy clusters has been observed to grow by nearly two orders of magnitude from the local universe to z ~ 1.5. Star formation rates in clusters have also been observed to rise rapidly over this redshift interval. These trends, along with several other recent observations of high-redshift clusters, have led to the idea that this enhanced star formation and AGN activity may be driven by galaxy mergers within the clusters. Since mergers are more efficient in lower mass clusters with smaller galaxy velocity dispersions, the expectation is that AGN incidence should scale inversely with cluster mass. A recent study using X-ray selected AGN has offered some support for this model in low-redshift clusters, though with large uncertainties. We select infrared-bright AGN from a large, uniform, essentially mass-selected galaxy cluster sample from the South Pole Telescope spanning a redshift range of 0.15 < z < 1.7 for which we have acquired follow-up Spitzer Space Telescope observations. With these data we explore the incidence of IR-bright AGN in clusters as a function of cluster mass and redshift.

Testing Web Feeding Model for Star Formation in Galaxy Clusters in the COSMOS Field DOI:10.5281/zenodo.4951159

Eunhee Ko


It is yet to be understood what controls the star formation activity in high-redshift galaxy clusters. One recently proposed mechanism is that the star formation activity in galaxy clusters is fed by gas and galaxies in large-scale structures surrounding them, which we call a “web feeding model”. Using galaxies in the COSMOS2015 catalog, with mass completeness at log(M/M)≥9.54 and reliable photometric redshift dataσδz/(1+z)≈0.01, we study the star formation activities of galaxy clusters and their surrounding environment to test the web feeding model. We first identify the overdense regions with number density exceeding the 4σ-level from photometric redshift data as galaxy clusters, and we find that they are well matched with clusters identified in the X-ray extended source catalog. Furthermore, we identify galaxy large-scale structures, and will present the correlation between quiescent galaxy fraction, an indicator of star-forming activity, and the prevalence of galaxy large scale structures.

Stellar populations and ionised gas in central spheroidal galaxies DOI:10.5281/zenodo.4987927

Vanessa Lorenzoni


We investigate the stellar populations and ionised gas properties of a sample of central spheroidal galaxies in order to better constrain their history of star formation and gas excitation mechanism. We select galaxies from Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER) catalogue and separate these galaxies in different regimes of halo and galaxy mass. To characterise the stellar population properties of these galaxies we use the stellar population synthesis method with the Starlight code, and the presence of ionised gas is identified by measurements of the Hα equivalent width. We analyse how these properties behave as a function of the galaxy stellar mass and the parent halo mass. A trend is observed in the sense of increased ionised gas emission for low-mass centrals in high-mass halos. We interpret this trend in a scenario of intracluster medium (ICM) cooling versus active galactic nuclei (AGN) feedback in a Bondi accretion context.

The relation between the central galaxy properties and the dynamical state of the cluster DOI:10.5281/zenodo.4979340

Gilvan Souza


In X-ray analysis, a variety of cooling criteria have been proposed to separate cool-core clusters and non-cool core clusters, in which classification attempts are generally based on core properties because cluster centres are more easily accessible. These indicators are typically based on a central temperature drop (e.g., Burns et al. 2008), a central cooling time shorter than the Hubble time (e.g., Bauer et al. 2005), or a significant mass deposition (Chen et al. 2007). Through 2D spectral maps, we provide the most detailed and extended view of the spatial distribution of temperature (kT), pressure (P), and entropy (S) of galaxy clusters with the aim of analyze their relation to the cluster galaxies, specifically the central one. In this work we present a preliminary study of a sample of 42 clusters from Lovisari & Reiprich (2019) with spectroscopic data available in the Sloan Digital Sky Survey (SDSS). The optical analysis of the central galaxy was performed using the Starlight spectral synthesis code (Cid Fernandes et al., 2005). For the X-ray analysis, we use data from the XMM-Newton and Chandra satellites. As preliminary results, we verified a first indication of the relation between the global dynamical state of the cluster and the position of the central galaxy of the cluster in two diagnostic diagrams, namely the BPT (Baldwin et al., 1981) and WHAN (Cid Fernandes 2011).

Markers of Evolution in Rich Galaxy clusters

Elena Panko


We detected statistically significant regular substructures in 2D distribution of galaxies in rich clusters with redshifts till to 0.15. Input data were extracted from “The Catalogue of Galaxy Clusters and Groups” (Panko & Flin). Main type of substructures are linear elongated overdense regions in the cluster field. The direction of the linear substructure points usually to the nearest neighbor. In addition we found X- or Y- type regular substructures as well as short and/or compact chains. Bright galaxies in clusters are located in the regular substructures mainly and galaxies in the chains also show significant alignment along the chain. Found peculiarities can be considered as a result of the formation of galaxy clusters at the intersection of DM filaments or filament-wall interaction.

Time-Averaged Analysis of Environmental Effects on Star Formation in Cluster Galaxies Since z~1

Keunho Kim

15:20 - 15:35

The environments where galaxies reside play a key role in shaping their star formation histories over cosmic time. There is no clear consensus yet concerning statistical trends of such environmental effects at higher redshift, compared to the well-established trends in the local Universe. Notably, at higher redshift, we use a kinematic analysis and investigate the time-averaged environmental effects on star formation in cluster galaxies. Uniquely, we span a wider range of redshift 0.26 < z < 1.13 with a larger number of sample galaxies (i.e., a uniform set of ~100 galaxy clusters and ~2000 galaxies from the South Pole Telescope survey). From the survey, we obtained cluster mass, accurate cluster membership, and galaxy luminosity and the spectral 4000 A break index. We find a gradual increase in the constituent stellar age of galaxies with their time spent in the cluster environment. This finding suggests that galaxies have suppressed star formation since their infall into clusters. This environmental trend is observed regardless of galaxies’ luminosity whether faint or bright. Remarkably, we show a significant redshift dependence on this environmental quenching trend. That is, at a fixed time since infall, low-redshift galaxies show more suppressed star formation compared to high-redshift counterparts. Our results provide new insights into environmental effects on star formation in galaxy clusters based on a wider redshift range since z ~1 and a large sample size.

The importance of low-mass clusters for satellite quenching in C-EAGLE simulations

Diego Pallero

15:35 - 15:50

One of the fundamental problems in modern astrophysics is the understanding of the role that the environment plays on the evolution of galaxies. Many works, both theoretical and observational, have focused on this topic. Nevertheless, it is not clear yet which are the main physical mechanisms that lead to the cessation of star formation, or quenching, in galaxies that reside in dense environments. State-of-the-art hydrodynamical simulations are perfect tools to study the evolution of galaxies in extremely dense environments such as galaxy clusters. Following the quenching history of cluster satellites in the C-EAGLE simulation, we found that most galaxies reach their quenching state in dense environments, with an M200 similar to low mass clusters. After galaxies cross the R200 of these structures, quickly get quenched in a timescale of 1Gyr. This event can be related with a ram pressure stripping event, and is produced when the gas density of the ICM reaches a minimum threshold of ρ(ICM) > 10^-28 gr cm^-3. This threshold takes place typically near the cluster R200, regardless of their M200.

Discussion and summary of session

Julie Hlavacek-Larrondo, Andra Stroe, Yusei Koyama, Remco van der Burg

15:50 - 16:00

Poster session and science discussions


16:00 - 16:30

End of day



GCF 2021 channels on

This workshop is supported by ESO and the Smithsonian Astrophysical Observatory.

Keywords: merging clusters | high-z clusters | proto-clusters | detection, classification & comparison | ICM physics | AGN feedback | star formation | galaxy evolution | future facilities

Workshop email: