Poor Clusters Of Galaxies Research Articles

The Missing Metal Problem in Galaxy Clusters: Characterizing the Early Enrichment Population

Abstract Rich and poor galaxy clusters have the same measured halo metallicity, 0.35–0.4 Z ⊙, even though they are an order of magnitude apart in stellar fraction, M */M gas. The measured intracluster medium (ICM) metallicity in high-mass clusters cannot be explained by the visible stellar population as stars typically make up 3%–20% of the total baryon mass. The independence of metallicity of M */M gas suggests an external and universal source of metals such as an early enrichment population (EEP). Galaxy cluster RX J1416.4+2315, classified as a fossil system, has a stellar fraction of M */M gas = 0.054 ± 0.018, and here we improve the halo metallicity determination using archival Chandra and XMM-Newton observations. We determine the ICM metallicity of RXJ1416 to be 0.303 ± 0.053 Z ⊙ within 0.3 < R/R 500 < 1, excluding the central galaxy. We combine this measurement with other clusters with a wider range of M */M gas, resulting in the fit of Z tot = (0.36 ± 0.01) + (0.10 ± 0.17)(M */M gas). This fit is largely independent of M */M gas and shows that for a low M */M gas system, the observed stellar population can make only 10%–20% of the total metals. We quantify the Fe contribution of the EEP further by adopting a standard Fe yield for visible stellar populations, and find that Z EEP = (0.36 ± 0.01) − − (0.96 ± 0.17)(M */M gas). To account for the observed Fe mass, a supernova (SN) rate of 10 ± 5 SNe yr−1 (Type Ia) and 40 ± 19 SNe yr−1 (core collapse) is required over the redshift range 3 < z < 10 for a single galaxy cluster with mass ∼3 × 1014 M ⊙ at z = 0. These SNe might be visible in observations of high-redshift clusters and protoclusters with the James Webb Space Telescope.

Low X-Ray Luminosity Galaxy Clusters. IV. SDSS galaxy clusters at z < 0.2

This is the fourth of a series of papers on low X-ray luminosity galaxy clusters. The sample comprises 45 galaxy clusters with X-ray luminosities fainter than 0.7 10$^{44}$ erg s$^{-1}$ at redshifts lower than 0.2 in the regions of the Sloan Digital Sky Survey. The sample of spectroscopic members of the galaxy clusters was obtained with the criteria: r$_p$ $\le$ 1 Mpc and $\Delta V \leq \sigma$ using our $\sigma$ estimates containing 21 galaxy clusters with more than 6 spectroscopic members. We have also defined a sample of photometric members with galaxies that satisfy r$_p \le $ 1 Mpc, and $\Delta V \leq $ 6000 \kms including 45 galaxy clusters with more than 6 cluster members. We have divided the redshift range in three bins: $z \leq 0.065$; 0.065 $<$ z $<$ 0.10; and z $\ge$ 0.10. We have stacked the galaxy clusters using the spectroscopic sub-sample and we have computed the best RS linear fit within 1$\sigma$ dispersion. With the photometric sub-sample, we have added more data to the RS obtaining the photometric 1$\sigma$ dispersion relative to the spectroscopic RS fit. We have computed the luminosity function using the $1/V_{max}$ method fitting it with a Schechter function. The obtained parameters for these galaxy clusters with low X-ray luminosities are remarkably similar to those for groups and poor galaxy clusters at these lower redshifts.

Deep Imaging of the HCG 95 Field. I. Ultra-diffuse Galaxies

Abstract We present a detection of 89 candidates of ultra-diffuse galaxies (UDGs) in a 4.9 degree2 field centered on the Hickson Compact Group 95 (HCG 95) using deep g- and r-band images taken with the Chinese Near Object Survey Telescope. This field contains one rich galaxy cluster (Abell 2588 at z = 0.199) and two poor clusters (Pegasus I at z = 0.013 and Pegasus II at z = 0.040). The 89 candidates are likely associated with the two poor clusters, giving about 50–60 true UDGs with a half-light radius and a central surface brightness mag arcsec−2. Deep -band images are available for 84 of the 89 galaxies from the Dark Energy Camera Legacy Survey (DECaLS), confirming that these galaxies have an extremely low central surface brightness. Moreover, our UDG candidates are spread over a wide range in g − r color, and ∼26% are as blue as normal star-forming galaxies, which is suggestive of young UDGs that are still in formation. Interestingly, we find that one UDG linked with HCG 95 is a gas-rich galaxy with H i mass M ⊙ detected by the Very Large Array, and has a stellar mass of M ⊙. This indicates that UDGs at least partially overlap with the population of nearly dark galaxies found in deep H i surveys. Our results show that the high abundance of blue UDGs in the HCG 95 field is favored by the environment of poor galaxy clusters residing in H i-rich large-scale structures.

Sardinia Radio Telescope observations of Abell 194

Aims. We study the intra-cluster magnetic field in the poor galaxy cluster Abell 194 by complementing radio data, at different frequencies, with data in the optical and X-ray bands.

Radio Galaxy Zoo: discovery of a poor cluster through a giant wide-angle tail radio galaxy

We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project. We obtained a spectroscopic redshift of $z=0.0897$ for the E0-type host galaxy, 2MASX J08231289+0333016, leading to M$_r = -22.6$ and a $1.4\,$GHz radio luminosity density of $L_{\rm 1.4} = 5.5\times10^{24}$ W Hz$^{-1}$. These radio and optical luminosities are typical for wide-angle tailed radio galaxies near the borderline between Fanaroff-Riley (FR) classes I and II. The projected largest angular size of $\approx8\,$arcmin corresponds to $800\,$kpc and the full length of the source along the curved jets/trails is $1.1\,$Mpc in projection. X-ray data from the XMM-Newton archive yield an upper limit on the X-ray luminosity of the thermal emission surrounding RGZ J082312.9+033301,at $1.2-2.6\times10^{43}$ erg s$^{-1}$ for assumed intra-cluster medium temperatures of $1.0-5.0\,$keV. Our analysis of the environment surrounding RGZ J082312.9+033301 indicates that RGZ J082312.9+033301 lies within a poor cluster. The observed radio morphology suggests that (a) the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster, and that (b) the source may have had two ignition events of the active galactic nucleus with $10^7\,$yrs in between. This reinforces the idea that an association between RGZ J082312.9+033301, and the newly discovered poor cluster exists.

ACTIVE GALACTIC NUCLEUS INTERACTION WITH THE HOT GAS ENVIRONMENT: UNDERSTANDING FROM THE RADIO AND X-RAY DATA

Recognition of the role of radio galaxies in the universe has been increasing in recent years. Their colossal energy output over huge volumes is now widely believed to play a key role not only in the formation of galaxies and their supermassive black holes, but also in the evolution of clusters of galaxies and, possibly, the cosmic web itself. In this regard, we need to understand the ination of radio bubbles in the hot gas atmospheres of clusters and the importance of the role that radio galaxies play in the overall energy budget of the intracluster medium. Here, we present results from X-ray and radio band observations of the hot gas atmospheres of powerful, nearby radio galaxies in poor clusters.

The baryon budget on the galaxy group/cluster boundary

We present a study of the hot gas and stellar content of 5 optically-selected poor galaxy clusters, including a full accounting of the contribution from intracluster light (ICL) and a combined hot gas and hydrostatic X-ray mass analysis with XMM observations. We find weighted mean stellar (including ICL), gas and total baryon mass fractions within r500 of 0.026+/-0.003, 0.070+/-0.005 and 0.096+/-0.006, respectively, at a corresponding weighted mean M500 of (1.08_{-0.18}^{+0.21}) x 10^14 Msun. Even when accounting for the intracluster stars, 4 out of 5 clusters show evidence for a substantial baryon deficit within r500, with baryon fractions (f_bary) between 50+/-6 to 59+/-8 per cent of the Universal mean level (i.e. Omega_b / Omega_m); the remaining cluster having f_bary = 75+/-11 per cent. For the 3 clusters where we can trace the hot halo to r500 we find no evidence for a steepening of the gas density profile in the outskirts with respect to a power law, as seen in more massive clusters. We find that in all cases, the X-ray mass measurements are larger than those originally published on the basis of the galaxy velocity dispersion (sigma) and an assumed sigma-M500 relation, by a factor of 1.7-5.7. Despite these increased masses, the stellar fractions (in the range 0.016-0.034, within r500) remain consistent with the trend with mass published by Gonzalez, Zaritsky & Zabludoff (2007), from which our sample is drawn.

X-Ray and Radio Emissions of AWM and MKW Clusters

A grasp of the life-cycles of large-scale structures is critical to understanding the Universe. This can be accomplished through the study of poor clusters-- that is, younger clusters that are likely evolving to another state. The selected clusters are significant in that they are poor but also possess a type-cD galaxy. This brighter central galaxy suggests that these clusters may be dynamically evolved and are potential candidates for fossil groups. In order to more fully understand the structure and behavior of poor galaxy clusters, 12 clusters were selected and analyzed. Using data from the Sloan Digital Sky Survey, Chandra X-Ray Archive, and the VLA FIRST Survey, we present x-ray profiles and radio observations of these 12 galaxy clusters.Â

FINDING FOSSIL GROUPS: OPTICAL IDENTIFICATION AND X-RAY CONFIRMATION

We report the discovery of 12 new fossil groups of galaxies, systems dominated by a single giant elliptical galaxy and cluster-scale gravitational potential, but lacking the population of bright galaxies typically seen in galaxy clusters. These fossil groups (FGs), selected from the maxBCG optical cluster catalog, were detected in snapshot observations with the Chandra X-ray Observatory. We detail the highly successful selection method, with an 80% success rate in identifying 12 FGs from our target sample of 15 candidates. For 11 of the systems, we determine the X-ray luminosity, temperature, and hydrostatic mass, which do not deviate significantly from expectations for normal systems, spanning a range typical of rich groups and poor clusters of galaxies. A small number of detected FGs are morphologically irregular, possibly due to past mergers, interaction of the intra-group medium (IGM) with a central AGN, or superposition of multiple massive halos. Two-thirds of the X-ray-detected FGs exhibit X-ray emission associated with the central BCG, although we are unable to distinguish between AGN and extended thermal galaxy emission using the current data. This sample, a large increase in the number of known FGs, will be invaluable for future planned observations to determine FG temperature, gas density, metal abundance, and mass distributions, and to compare to normal (non-fossil) systems. Finally, the presence of a population of galaxy-poor systems may bias mass function determinations that measure richness from galaxy counts. When used to constrain power spectrum normalization and {\Omega}_m, these biased mass functions may in turn bias these results.

EXTENDED REGIONS OF RADIO EMISSION NOT ASSOCIATED WITH THE AGN PHENOMENON AS SOURCES OF ACCELERATION OF COSMIC RAYS: THE CASE OF cD GALAXIES

Diffuse, non-thermal extended emission not associated with the AGN phenomenon, found in many clusters of galaxies hosted by an AGN, are related to the acceleration of cosmic rays. In the current work we present preliminary evidence of absence of such formations in clusters of galaxies hosted by optically identified cD galaxies. Our subsample consists of three powerful low redshift radiogalaxies, centered in poor clusters of galaxies. We have searched for radio relics and (mini) halos which could be forming as a result of the confinement of cosmic rays by bubbles creayed by the AGN. We report on the work in progress.

J0454-0309: evidence of a strong lensing fossil group falling into a poor galaxy cluster

We have discovered a strong lensing fossil group (J0454) at z=0.26, projected near the well-studied cluster MS0451-0305. Using multicolour Subaru/Suprime-Cam and CFHT/Megaprime imaging together with Keck spectroscopy we identify member galaxies. A VLT/FORS2 spectrum was taken to determine the redshifts of the brightest elliptical and the lensed arc. Using HST/ACS images we determine the group's weak lensing signal and model the strong lens system. This is the first time that a fossil group is analysed with lensing methods. The X-ray luminosity and temperature are derived from XMM-Newton data. We find two filaments extending over 4 Mpc, and within the virial radius we identify 31 members spectroscopically and 33 via the red sequence with i<22 mag. They segregate into spirals and a dynamically cooler central concentration of ellipticals with a velocity dispersion of 480 km/s. Weak lensing and cluster richness relations yield r200 = 830 kpc and M200 = 0.85 x 10^14 Msun. The brightest group galaxy (BGG) is inconsistent with the dynamic centre of J0454. It strongly lenses a galaxy at z~2.1, and we model the lens with a pseudo-isothermal elliptical mass distribution. A large external shear requires that the BGG must be offset from J0454's dark halo centre by at least 90-130 kpc. The X-ray halo is offset by 24 kpc from the BGG, shows no signs of a cooling flow and is well described by a beta-model. With L = 1.4 x 10^43 erg/s J0454 falls well onto standard X-ray cluster scaling relations, but appears cooler (1.1 keV) than expected (2 keV). We conclude that J0454 consists of two systems, a sparse cluster and an infalling fossil group, the latter seeding the BCG. An alternative explanation is that galaxies in a filament, projected along the line of sight, stream towards the denser fossil group.

Revisiting the low-luminosity galaxy population of the NGC 5846 group with SDSS

Low-luminosity galaxies are known to outnumber the bright galaxy population in poor groups and clusters of galaxies. Yet, the investigation of low-luminosity galaxy populations outside the Local Group remains rare and the dependence on different group environments is still poorly understood. Previous investigations revealed photometric scaling relations for early-type dwarfs and a strong dependence of morphology with environment. The present study aims to analyse the photometric and spectroscopic properties of the low-luminosity galaxy population in the nearby, well-evolved and early-type dominated NGC 5846 group of galaxies. It is the third most massive aggregate of early-type galaxies after the Virgo and Fornax clusters in the local universe. Photometric scaling relations and the distribution of morphological types as well as the characteristics of emission-line galaxies are investigated. Spectroscopically selected low-luminosity group members from the Sloan Digital Sky Survey with cz<3000 km/s within a radius of 2 deg=0.91 Mpc around NGC 5846 are analysed. Surface brightness profiles of early-type galaxies are fit by a Sersic model r^(1/n). Star formation rates, oxygen abundances and emission characteristics are determined for emission-line galaxies. [abridged]

Luminosity function of galaxies in rich and poor galaxy clusters

AbstractUsing photometric data from SDSS survey we study the galaxy luminosity function in the 75 rich and poor Abell clusters. The integrated Schechter functions were fitted to unbinned data in the four g, r, i, and z photometric passbands. We find that the luminosity function differs with Abell richness class (R). In all bands the faint‐end slope α is steeper in poor clusters than in rich clusters. Moreover, the value of characteristic magnitude M * decreasing with richness class R (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A Giant Metrewave Radio Telescope Multifrequency Radio Study of the Isothermal Core of the Poor Galaxy Cluster AWM 4

We present a detailed radio morphological study and spectral analysis of the wide-angle tail radio source 4C +24.36 associated with the dominant galaxy in the relaxed galaxy cluster AWM 4. Our study is based on new high-sensitivity GMRT observations at 235, 327, and 610 MHz and on literature and archival data at other frequencies. We find that the source major axis is likely oriented at a small angle with respect to the plane of the sky. The wide-angle tail morphology can be reasonably explained by adopting a simple hydrodynamical model in which both ram pressure (driven by the motion of the host galaxy) and buoyancy forces contribute to bend the radio structure. The spectral index progressively steepens along the source major axis from α ~ 0.3 in the region close to the radio nucleus to beyond 1.5 in the lobes. The results of the analysis of the spectral index image allow us to derive an estimate of the radiative age of the source of ~160 Myr. The cluster X-ray-emitting gas has a relaxed morphology and short cooling time, but its temperature profile is isothermal out to at least 160 kpc from the center. Therefore, we seek evidence of energy ejection from the central AGN to prevent catastrophic cooling. We find that the energy injected by 4C +24.36 in the form of synchrotron luminosity during its lifetime is far less than the energy required to maintain the high gas temperature in the core. We also find that it is not possible for the central source to eject the requisite energy in the intracluster gas in terms of the enthalpy of buoyant bubbles of relativistic fluid, without creating discernible large cavities in the existing X-ray XMM-Newton observations.

Radio morphology and spectral analysis of cD galaxies in rich and poor galaxy clusters

Aims. We present a radio morphological study and spectral analysis of a sample of 13 cD galaxies in rich and poor clusters of galaxies. Methods. Our study is based on new high sensitivity Giant Metrewave Radio Telescope (GMRT) observations at 1.28 GHz, 610 MHz and 235 MHz, and on archival data. From a statistical sample of cluster cD galaxies we selected those sources with little information available in the literature and promising for the detection of aged radio emission. As well as the high sensitivity images for all 13 radio galaxies, we present also a detailed spectral analysis for 7 of them. Results. We found a variety of morphologies and linear sizes, as typical for radio galaxies in the radio power range sampled here (low to intermediate power radio galaxies). The spectral analysis shows that 10/13 radio galaxies have a steep radio spectrum, with spectral index α ≥ 1. In general, the radiative ages and growth velocities are consistent with previous findings that the evolution of radio galaxies at cluster centres is affected by the dense external medium (i.e. low growth velocities and old ages). We suggest that the dominant galaxies in A 2622 and MKW 03s are dying radio sources, which at present are not fed by nuclear activity. On the other hand, the spectacular source at the centre of A 2372 might be a very interesting example of a restarted radio galaxy. For this source we estimated a life cycle of the order of 10 6 yr.

Shredded Galaxies as the Source of Diffuse Intrahalo Light on Varying Scales

We make predictions for diffuse stellar mass fractions in dark matter halos from the scales of small spiral galaxies to those of large galaxy clusters. We use an extensively-tested analytic model for subhalo infall and evolution and empirical constraints from galaxy survey data to set the stellar mass in each accreted subhalo to model diffuse light. We add stellar mass to the diffuse light as subhalos become disrupted due to interactions within their host halos. We predict that the stellar mass fraction in diffuse, intrahalo light should rise on average from ~0.5% to approximately 20% from small galaxy halos to poor groups. The trend with mass flattens considerably beyond the group scale, increasing weakly from a fraction of ~20% in poor galaxy clusters (~10^14 M_sun) to roughly ~30% in massive clusters (~10^15 M_sun). The mass-dependent diffuse light fraction is governed primarily by the empirical fact that the mass-to-light ratio in galaxy halos must vary as a function of halo mass. Galaxy halos have little diffuse light because they accrete most of their mass in small subhalos that themselves have high mass-to-light ratios; stellar halos around galaxies are built primarily from disrupted dwarf-irregular-type galaxies with M*~10^8.5 M_sun. The diffuse light in group and cluster halos is built from satellite galaxies that form stars efficiently and have correspondingly low mass-to-light ratios; intracluster light is dominated by material liberated from massive galaxies with M*~10^11 M_sun. Our results are consistent with existing observations spanning the galaxy, group, and cluster scale; however, they can be tested more rigorously in future deep surveys for faint diffuse light.

The Dependence of the Evolution of Early‐Type Galaxies on Their Environment

This thesis describes the analysis of a data set of 121 elliptical and lenticular (S0) galaxies, located in different environments and at distances corresponding to look-back times between 2 and 5 Gyrs. Such a sample allows to study the environmental dependence of the internal properties of these early-type galaxies to draw conclusions on the formation epoch and evolutionary history of their sub-classes of elliptical and S0 galaxies.As a discrimination factor for the environment, the X-ray luminosity flux is utilised, which is proportional to the square of the mass of a galaxy. The highest galaxy density is found in rich galaxy clusters, (low-mass) poor galaxy clusters exhibit a factor of 10 lower number density whereas the lowest density is defined by individual, isolated field galaxies. Theoretical predictions based on a hierarchical structure growth suggest for various environments different evolutionary tracks which yield to a diversity of galaxy ages.All objects analysed in this work were selected based upon deep ground-based multi-band imaging data. In addition, for the central regions of the galaxy clusters and the two extended sky areas which comprise the field galaxies, the FORS Deep Field and the William Herschel Deep Field, the high resolution images of the Hubble Space Telescope (HST) provide a detailed morphological classification and structural parameter analysis. Multi-Object-Spectroscopy was conducted for all galaxies at the 8.2-m Very Large Telescope (VLT, Chile) and the Calar Alto 3.5-m telescope (Spain). Using high signal-to-noise spectroscopy the internal velocity dispersions (i.e., the random motion of the individual stars) of the galaxies are measured, which are an indicator for the total galaxy masses. Based on different scaling relations, in particular the Faber-Jackson relation between velocity dispersion and luminosity, the absolute brightnesses of the distant galaxies are compared to galaxies in the local universe. While high-mass elliptical and S0 galaxies show only a mild evolution, the distant low-mass galaxies are more luminous by up to a factor of 2 with respect to their local counterparts as seen today.The observed mass-dependence of the luminosity evolution is found in all environments. By contrast, numerical simulations based on the hierarchical scenario expect only for the isolated field galaxy population a significant increase of the luminosity towards higher redshifts that is independent on the galaxy type. Elliptical and S0 galaxies are not a homogeneous galaxy group but follow different evolutionary tracks. Lenticular galaxies indicate in all environments a stronger evolution and more recent formation epochs (1<zform≤2), whereas elliptical galaxies evolve passively on longer timescales yielding to older stellar population ages (zform≈3). Possible explanations for the deviations could be different stellar populations or more complex, extended star formation histories in the case of S0 galaxies. The discrepancies between the predicted and observed luminosity evolution are most likely due to a lack of sufficiently realistic modelling of the involved processes of the stellar content in the simulations.

Does a Galaxy Fly?

Abstract Disk galaxies in a cluster of galaxies move in hot gas that fills the cluster. Generally, they move at transonic or supersonic velocities. If ram-pressure stripping is insufficient to destroy the gas disk, the galaxies should be affected by the wind of the surrounding hot gas, similar to an airfoil. In this paper, it is considered whether the aerodynamic interaction can be strong enough to force a disk galaxy to deviate from the orbit that it would have been in. It is shown that while the lift force is not effective, the drag force could affect face-on disk galaxies in poor clusters on a long time scale.

X‐Ray Properties of Intermediate‐Redshift Groups of Galaxies

We have undertaken a multiwavelength project to study the relatively unknown properties of groups and poor clusters of galaxies at intermediate redshifts. In this paper, we describe the XMM-Newton observations of six X-ray-selected groups with 0.2 < z < 0.6. The X-ray properties of these systems are generally in good agreement with the properties of low-redshift groups. They appear to follow the scaling relations between luminosity, temperature, and velocity dispersion defined by low-redshift groups and clusters. The X-ray emission in four of the six groups is also centered on a dominant early-type galaxy. The lack of a bright elliptical galaxy at the peak of the group X-ray emission is rare at low redshifts, and the other two groups may be less dynamically evolved. We find indications of excess entropy in these systems over self-similar predictions out to large radii. We also confirm the presence of at least one X-ray-luminous AGN associated with a group member galaxy and find several other potential group AGNs.

Nature of X-ray Sources From the Field of Nearby, Poor Cluster of Galaxies

AbstractA194 and A1060 are studied for the nature of point source properties. X-ray to optical luminosity ratios (Lx/Lb) are evaluated for selected galaxies. Cumulative log(N)-log(S) and intrinsic luminosity functions are applied for a comparative evaluation with Lockman Hole. 46 and 32 X-ray point sources are detected by EPIC-PN, for A194 and A1060 respectively. The XLF space density shows significant excess compared to field and local group space density. The result is interpreted as the fueling of AGNs as they enter the ICM from outskirts of the clusters and dimming of the very bright AGNs as they further proceed into cluster core.