Substructure and Gas Clumping in the Outskirts of Abell 133

Galaxy clusters are powerful tools for studying various astrophysical principles. Gas accreting onto the cluster is heated to 10^7-10^8 K through adiabatic compression and shocks, making clusters highly luminous in X-ray imaging. Measurements of the gas density and temperature profiles can be used to calculate the gas mass fraction f_gas, which is expected to closely match the cosmic baryon fraction Ω_b/Ω_m. Recent observations have found entropy profiles in cluster outskirts that are shallower than predicted and values of f_gas that are higher than the Universal baryon fraction inferred from the Cosmic Microwave Background (CMB). Abell 133 was an ideal candidate for studying this phenomenon, since it had recently been observed in a wide (R≈30') Chandra mosaic with an exposure time of ∼2 Ms. The X-ray imaging was combined with existing optical imaging from the Canada-France-Hawaii Telescope (CFHT) and spectroscopy obtained from the Magellan telescope, to search for any possible gas clumps and to study their properties. The photometric analysis yielded over 3200 red sequence galaxies to a depth of r'=22.5, which were used to create a Gaussian smoothed intensity map and a significance map of the cluster (compared to CFHT Legacy Survey data). About 6 significant overdensities were detected in the significance map, although these did not fully correspond to contours obtained from the X-ray image. Spectroscopy obtained on the cluster yielded ∼700 secure redshifts, of which about 180 were cluster members. This included data from the NOAO Fundamental Plane Survey (NFPS) and the 6 Degree Field Galaxy Survey (6dFGS). We found a cluster redshift of z=0.0561±0.0002 and a velocity dispersion of σ=743±43 km/s. The dynamical analysis gave a virial radius of r_v=1.44±0.03 Mpc and a virial mass of M_v=(5.9±0.8)×10^14 M_sun. We also found values of R_500=1.21±0.07 Mpc and M_500=(5.3±0.9)×10^14 M_sun for γ=1/3 and R_500=0.99±0.05 Mpc and M_500=(2.9±0.5)×10^14 M_sun for γ=1/2, where γ is a parameter related to the assumed density profile and the velocity anisotropy. About 30 overdensities with a radius R_c≥30" were detected as gas clumps on the X-ray image. The galaxy distribution in these clumps was analyzed, both for the stacked signal as well as the individual clumps, in ten parallel colour-magnitude bands to find any significant red sequences associated with them. Most of these clumps appeared to be background systems, some consisting of 1-2 galaxies, others being small groups or clusters. Only 2-3 clumps appeared to be associated with the cluster itself. This suggests that the cluster density profile is actually quite smooth, which may not agree with recent numerical simulations. Further studies are required to determine if the cluster density distribution is consistent with what is predicted and the nature of the background systems

Mass segregation trends in SDSS galaxy groups

It has been shown that galaxy properties depend strongly on their host environment. In order to understand the relevant physical processes driving galaxy evolution it is important to study the observed properties of galaxies in different environments. Mass segregation in bound galaxy structures is an important indicator of evolutionary history and dynamical friction timescales. Using group catalogues derived from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) we investigate mass segregation trends in galaxy groups at low redshift. We investigate average galaxy stellar mass as a function of group-centric radius and find evidence for weak mass segregation in SDSS groups. The magnitude of the mass segregation depends on both galaxy stellar mass limits and group halo mass. We show that the inclusion of low mass galaxies tends to strengthen mass segregation trends, and that the strength of mass segregation tends to decrease with increasing group halo mass. We find the same trends if we use the fraction of massive galaxies as a function of group-centric radius as an alternative probe of mass segregation. The magnitude of mass segregation that we measure, particularly in high-mass haloes, indicates that dynamical friction is not acting efficiently.Comment: 6 pages, 2 figures, accepted for publication in MNRAS Letter

Jellyfish galaxies with the IllustrisTNG simulations -- Citizen-science results towards large distances, low-mass hosts, and high redshifts

We present the ``Cosmological Jellyfish'' project - a citizen-science classification program to identify jellyfish galaxies within the IllustrisTNG cosmological simulations. Jellyfish (JF) are satellite galaxies that exhibit long trailing gas features -- `tails' -- extending from their stellar body. Their distinctive morphology arises due to ram-pressure stripping (RPS) as they move through the background gaseous medium. Using the TNG50 and TNG100 simulations, we construct a sample of $\sim 80,000$ satellite galaxies spanning an unprecedented range of stellar masses, $10^{8.3-12.3}\,\mathrm{M_\odot}$, and host masses of $M_\mathrm{200,c}=10^{10.4-14.6}\,\mathrm{M_\odot}$ back to $z=2$ \citep[extending the work of][]{yun_jellyfish_2019}. Based on this sample, $\sim 90,000$ galaxy images were presented to volunteers in a citizen-science project on the Zooniverse platform who were asked to determine if each galaxy image resembles a jellyfish. Based on volunteer votes, each galaxy was assigned a score determining if it is a JF or not. This paper describes the project, the inspected satellite sample, the methodology, and the classification process that resulted in a dataset of $5,307$ visually-identified jellyfish galaxies. We find that JF galaxies are common in nearly all group- and cluster-sized systems, with the JF fraction increasing with host mass and decreasing with satellite stellar mass. We highlight JF galaxies in three relatively unexplored regimes: low-mass hosts of $M_\mathrm{200,c}\sim10^{11.5-13}\,\mathrm{M_\odot}$, radial positions within hosts exceeding the virial radius $R_\mathrm{200,c}$, and at high redshift up to $z=2$. The full dataset of our jellyfish scores is publicly available and can be used to select and study JF galaxies in the IllustrisTNG simulations.Comment: submitted to MNRAS ; See additional jellyfish companion papers today on astro-ph: Rohr et al. and Goeller et al.; Jellyfish image gallery: https://www.tng-project.org/explore/gallery/zinger23

Jellyfish galaxies with the IllustrisTNG simulations -- No enhanced population-wide star formation according to TNG50

Due to ram-pressure stripping, jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity+magnetohydrodynamical simulation, with an average spatial resolution of 50-200 pc in the star-forming regions of galaxies, to quantify the star formation activity and rates (SFRs) of more than 700 jellyfish galaxies at $z=0-1$ with stellar masses $10^{8.3-11}\,\mathrm{M}_\odot$ in hosts with mass $10^{11.5-14.3}\,\mathrm{M}_\odot$. We extract their global SFRs, the SFRs within their main stellar body vs. within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely-constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction and host halo mass. According to TNG50, star formation and ram-pressure stripping can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analog satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch.Comment: 20 pages, 10 figures, 1 table, submitted to MNRAS. See additional jellyfish companion papers today on astro-ph: Zinger et al. and Rohr et a

Jellyfish galaxies with the IllustrisTNG simulations – No enhanced population-wide star formation according to TNG50

Due to ram-pressure stripping, jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity+magnetohydrodynamical simulation, with an average spatial resolution of 50-200 pc in the star-forming regions of galaxies, to quantify the star formation activity and rates (SFRs) of more than 700 jellyfish galaxies at z = 0 − 1 with stellar masses 108.3 − 10.8 M⊙ in hosts with mass 1010.5 − 14.3 M⊙. We extract their global SFRs, the SFRs within their main stellar body vs. within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely-constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction and host halo mass. According to TNG50, star formation and ram-pressure stripping can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analogue satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch

Jellyfish galaxies with the IllustrisTNG simulations -- When, where, and for how long does ram pressure stripping of cold gas occur?

Jellyfish galaxies are the prototypical examples of satellite galaxies undergoing strong ram pressure stripping (RPS). We analyze the evolution of 535 unique, first-infalling jellyfish galaxies from the TNG50 cosmological hydrodynamical galaxy simulation. These have been visually inspected to be undergoing RPS sometime in the past 5 billion years (since $z=0.5$), have satellite stellar masses $M_{\star}^{\rm sat}\sim10^{8-10.5}{\rm M}_\odot$, and live in hosts with $M_{\rm 200c}\sim10^{12-14.3}{\rm M}_\odot$ at $z=0$. We quantify the cold gas $(\leq10^{4.5}$K) removal using the tracer particles, confirming that for these jellyfish, RPS is the dominant driver of cold gas loss after infall. Half of these jellyfish are completely devoid of cold gas by $z=0$, and these galaxies have earlier infall times and smaller satellite-to-host mass ratios than those that still have some gas today. RPS can act on jellyfish galaxies over long timescales of $\approx1.5-8$Gyr. Jellyfish in more massive hosts are impacted by RPS for a shorter time span and, at a fixed host halo mass, jellyfish with lower stellar masses at $z=0$ have shorter RPS time spans. While RPS may act for long periods of time, the peak RPS period -- where at least 50% of the total RPS occurs -- begins within $\approx1$Gyr of infall and lasts $\lesssim2$Gyr. During this period, the jellyfish are at host-centric distances between $\sim0.2-2R_{\rm 200c}$, illustrating that much of RPS occurs at large distances from the host galaxy. Jellyfish continue forming stars until they have lost $\approx98$% of their cold gas. For groups and clusters in TNG50 $(M_{\rm 200c}\sim10^{13-14.3}{\rm M}_\odot)$, jellyfish galaxies deposit more cold gas ($\sim10^{11-12}{\rm M}_\odot$) into halos than exist in them at $z=0$, demonstrating that jellyfish, and in general satellite galaxies, are a significant source of cold gas accretion.Comment: 20 pages, 11 figures + 3 appendices with 4 figures. Submitted to MNRAS. Key figures are 2, 8, 9, 11. See additional jellyfish companion papers today on astro-ph: Zinger+ and Goeller+. All data used in this publication, including the Cosmological Jellyfish Project results, are publicaly availabl

Jellyfish galaxies with the IllustrisTNG simulations – When, where, and for how long does ram pressure stripping of cold gas occur?

Jellyfish galaxies are prototypical examples of satellite galaxies undergoing strong ram pressure stripping (RPS). We analyze the evolution of 512 unique, first-infalling jellyfish galaxies from the TNG50 cosmological simulation. These have been visually inspected to be undergoing RPS sometime in the past 5 billion years (since z = 0.5), have satellite stellar masses $M_\star ^{\rm sat}\sim 10^{8-10.5}\, {\rm M}_\odot$, and live in hosts with M200c ∼ 1012 − 14.3 M⊙ at z = 0. We quantify the cold gas (T ≤ 104.5 K) removal using the tracer particles, confirming that for these jellyfish, RPS is the dominant driver of cold gas loss after infall. Half of these jellyfish are completely gas-less by z = 0, and these galaxies have earlier infall times and smaller satellite-to-host mass ratios than their gaseous counterparts. RPS can act on jellyfish galaxies over long time scales of ≈1.5 − 8 Gyr. Jellyfish in more massive hosts are impacted by RPS for a shorter time span and, at a fixed host mass, jellyfish with less cold gas at infall and lower stellar masses at z = 0 have shorter RPS time spans. While RPS may act for long periods of time, the peak RPS period – where at least 50 per cent of the total RPS occurs – begins within ≈1 Gyr of infall and lasts ≲ 2 Gyr. During this period, the jellyfish are at host-centric distances ∼0.2 − 2R200c, illustrating that much of RPS occurs at large distances from the host galaxy. Interestingly, jellyfish continue forming stars until they have lost ≈98 per cent of their cold gas. For groups and clusters in TNG50 $(M_{\rm 200c}^{\rm host}\sim 10^{13-14.3}\, {\rm M}_\odot )$, jellyfish galaxies deposit more cold gas (∼1011 − 12 M⊙) into halos than exist in them at z = 0, demonstrating that jellyfish, and in general satellite galaxies, are a significant source of cold gas accretion

Jellyfish galaxies with the IllustrisTNG simulations: I. Gas-stripping phenomena in the full cosmological context

We use IllustrisTNG, a suite of gravity and MHD simulations, to study the demographics and properties of jellyfish galaxies in the full cosmological context. By jellyfish galaxies, we mean satellites orbiting in massive groups and clusters that exhibit highly asymmetric distributions of gas and gas tails. We use the TNG100 run and select galaxies at redshifts $z\le0.6$ with stellar mass exceeding $10^{9.5}{\rm M_\odot}$ and with host halo masses of $10^{13}-10^{14.6}\,{\rm M_\odot}$. Among more than about 6000 (2600) galaxies with stars (and some gas), we identify 800 jellyfish galaxies by visually inspecting their gas and stellar mass maps in random projections. About $31\%$ of cluster satellites are found with signatures of ram-pressure stripping and gaseous tails stemming from the main luminous bodies. This is a lower limit, since the random orientation entails a loss of about $30\%$ of galaxies that in an optimal projection would otherwise be identified as jellyfish. The connection with ram-pressure stripping is further confirmed by a series of findings: jellyfish galaxies are more frequent at intermediate and large cluster-centric distances ($r/R_{\rm 200c}\gtrsim 0.25$); they move through the ICM with larger bulk velocities and Mach numbers than the general cluster population, typically orbiting supersonically and experiencing larger ram pressures. Furthermore, the gaseous tails usually extend in opposite directions to the galaxy trajectory, with no relation between tail orientation and the host's center. The frequency of jellyfish galaxies shows a very weak dependence on redshift $(0\le z\le0.6)$ but larger fractions of disturbed gaseous morphologies occur in more massive hosts and at smaller satellite masses. Finally, jellyfish galaxies are late infallers ($< 2.5-3$ Gyrs ago, at $z=0$) and the emergence of gaseous tails correlates well with the presence of bow shocks in the ICM.Comment: 25 pages, 15 figures, Accepted for publication on MNRAS after minor revision