A Wide-Field Hubble Space Telescope Study of the Cluster Cl 0024+ 1654 at z= 0.4. II. The Cluster Mass Distribution (original) (raw)
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The Astrophysical …, 2008
We describe a new wide field Hubble Space Telescope survey of the galaxy cluster Cl0024+16 (z ≈ 0.4) consisting of a sparse-sampled mosaic of 39 Wide Field and Planetary Camera 2 images which extends to a cluster radius of ∼ 5 Mpc. Together with extensive ground-based spectroscopy taken from the literature, augmented with over a hundred newly-determined redshifts, this unique dataset enables us to examine environmental influences on the properties of cluster members from the inner core to well beyond the virial radius (∼ 1.7 Mpc). We catalog photometric measures for 22,000 objects to I 25 and assign morphological types for 2181 to I = 22.5, of which 195 are spectroscopically-confirmed cluster members. We examine both the morphology-radius (T-R) and morphology-density (T-Σ) relations and demonstrate sensitivities adequate for measures from the core to a radius of ∼ 5 Mpc, spanning over 3 decades in local projected density. The fraction of early-type galaxies declines steeply from the cluster center to 1 Mpc radius and more gradually thereafter, asymptoting towards the field value at the periphery. We discuss our results in the context of three distinct cluster zones, defined according to different physical processes that may be effective in transforming galaxy morphology in each. By treating infalling galaxies as isolated test particles, we deduce that the most likely processes responsible for the mild gradient in the morphological mix outside the virial radius are harassment and starvation. Although more data are needed to pin down the exact mechanisms, starvation seems more promising in that it would naturally explain the stellar and dynamical homogeneity of cluster E/S0s. However, we find significant scatter in the local density at any given radius outside ∼0.5 Mpc, and that the same T-Σ relation holds in subregions of the cluster, independent of location. In this hitherto unprobed region, where the potential of the cluster is weak, galaxies apparently retain their identities as members of infalling sub-groups whose characteristic morphological properties remain intact. Only upon arrival in the central regions is the substructure erased, as indicated by the tight correlation between cluster radius and Σ.
The Astrophysical Journal, 2005
We report results from a panoramic spectroscopic survey of 955 objects in the field of the rich cluster Cl 0024+1654 (z ≃ 0.4), complementing the HST imaging presented in the first paper in this series. Combining with previous work, we compile a catalog of 1394 unique redshifts in the field of this cluster, including 486 cluster members spread across an area 10 Mpc in diameter. Our new spectroscopic sample includes over 200 high quality spectra of cluster members. We examine the properties of a large sample of 104 cluster early-types as a function of cluster radius and local density, using them as sensitive tracers of the various physical processes that may be responsible for galaxy evolution. By constructing the Fundamental Plane of Cl 0024, we infer an evolution in the mean mass to light ratio of early-types with respect to z = 0 of ∆ < Log(M/L V ) >= −0.14 ± 0.02. In the cluster center, we detect a significantly increased scatter in the relationship compared to that seen in local clusters. Moreover, we observe a clear radial trend in the mass to light ratios of individual early types, with the oldest galaxies located in the cluster core. Galaxies are apparently younger at larger radius, with E+S0s in the periphery having M/L V ratios that nearly match values seen in the field at a similar redshift. The strong radial trend is seen even when the sample is restricted to a narrow range in galaxy mass. Independent spectral indicators used in combination reveal an abrupt interaction with the cluster environment which occurs near the virial radius of Cl 0024, revealed by small bursts of star formation in a population of dim early-types, as well as by enhanced Balmer absorption for a set of larger E+S0s closer to the cluster core. We construct a simple infall model used to compare the timescales and strengths of the observed interactions in this cluster. We examine the possibility that bursts of star formation are triggered when galaxies suffer shocks as they encounter the intra-cluster medium, or by the onset of galaxy harassment.
The Evolution of the Galactic Morphological Types in Clusters
Astrophysical Journal, 2000
The morphological types of galaxies in nine clusters in the redshift range 0.1<z<0.25 are derived from very good seeing images taken at the NOT and the La Silla Danish telescopes. With the purpose of investigating the evolution of the fraction of different morphological types with redshift, we compare our results with the morphological content of nine distant clusters studied by the MORPHS group, five clusters observed with HST-WFPC2 at redshift z = 0.2-0.3, and Dressler's (1980) large sample of nearby clusters. After having checked the reliability of our morphological classification both in an absolute sense and relative to the MORPHS scheme, we analyze the relative occurrence of elliptical, S0 and spiral galaxies as a function of the cluster properties and redshift. We find a large intrinsic scatter in the S0/E ratio, mostly related to the cluster morphology. In particular, in our cluster sample, clusters with a high concentration of ellipticals display a low S0/E ratio and, vice-versa, low concentration clusters have a high S0/E. At the same time, the trend of the morphological fractions and ratios with redshift clearly points to a morphological evolution: as the redshift decreases, the S0 population tends to grow at the expense of the spiral population, whereas the frequency of Es remains almost constant. We also analyze the morphology-density (MD) relation in our clusters and find that -similarly to higher redshift clusters- a good MD relation exists in the high-concentration clusters, while it is absent in the less concentrated clusters. Finally, the comparison of the MD relation in our clusters with that of the D97 sample suggests that the transformation of spirals into S0 galaxies becomes more efficient with decreasing local density.
The Astrophysical Journal, 2002
We present a morphological analysis of 17 X-ray selected clusters at z ∼ 0.25, imaged uniformly with Hubble Space Telescope WFPC2. Eight of these clusters comprise a subsample selected for their low X-ray luminosities ( < ∼ 10 44 erg s −1 ), called the Low-L X sample. The remaining nine clusters comprise a High-L X subsample with L X > 10 45 ergs s −1 . The two subsamples differ in their mean X-ray luminosity by a factor of 30, and span a range of more than 300. The clusters cover a relatively small range in redshift (z =0.17-0.3, σ z /z ∼ 0.15) and the data are homogeneous in terms of depth, resolution (0. ′′ 17= 1h −1 50 kpc at z = 0.25) and rest wavelength observed, minimizing differential corrections from cluster to cluster. We fit the two dimensional surface brightness profiles of galaxies down to very faint absolute magnitudes: M 702 ≤ −18.2 + 5 log h 50 (roughly 0.01L * R ) with parametric models, and quantify their morphologies using the fractional bulge luminosity (B/T). Within a single WFPC2 image, covering a field of ∼ 3 ′ (1h −1 50 Mpc at z = 0.25) in the cluster centre, we find that the Low-L X clusters are dominated by galaxies with low B/T (∼ 0), while the High-L X clusters are dominated by galaxies with intermediate B/T (∼ 0.4). We test whether this difference could arise from a universal morphology-density relation due to differences in the typical galaxy densities in the two samples. We find that small differences in the B/T distributions of the two samples persist with marginal statistical significance (98% confidence based on a binned χ 2 test) even when we restrict the comparison to galaxies in environments with similar projected local galaxy densities. A related difference (also of low statistical significance) is seen between the bulge luminosity functions of the two cluster samples, while no difference is seen between the disk luminosity functions. From the correlations between these quantities, we argue that the global environment affects the population of bulges, over and above trends seen with local density. On the basis of this result we conclude that the destruction of disks through ram pressure stripping or harassment is not solely responsible for the morphology-density relation, and that bulge formation is less efficient in low mass clusters, perhaps reflecting a less rich merger history.
Astronomy and Astrophysics, 2009
Aims. We investigate the dependence of several galaxy properties on the environment and cluster identification techniques. Methods. We select clusters of galaxies from two catalogues based on the SDSS: the ROSAT-SDSS Galaxy Cluster Survey, which is an X-ray selected cluster sample and the MaxBCG Catalogue, in which clusters are optically selected. Based on a volume limited sample of galaxies drawn from the spectroscopic DR5 SDSS, we constructed sub-samples of clusters of galaxies with more than ten members. Scaling relations as well as segregation of galaxy properties as a function of the normalized clustocentric radii are analyzed. The properties of galaxies in clusters are compared with those of field galaxies. Results. Galaxies in X-ray and MaxBCG selected clusters show similar size-luminosity relations. At equal luminosity, late type galaxies in the field have sizes smaller than cluster galaxies of the same morphological type. The Faber-Jackson relation for early-type galaxies in clusters is also the same for X-ray selected and MaxBCG clusters. We found clear differences between the dynamical properties of galaxies in clusters, the brightest cluster galaxies (BCG s) and field galaxies. Using several criteria to classify galaxies into morphological types, we reproduce the well know morphological segregation. The correlation is up to r/r 200 ∼ 1. For the whole range of clustocentric distances, X-ray selected clusters present a higher fraction of early type galaxies than MaxBCG clusters. We also found that bright galaxies preferentially inhabit the cluster centers. Median sizes of galaxies, such as the radius that enclose 50% of Petrosian flux r 50 , present a behaviour that also depends on the cluster selection criteria. For galaxies in X-ray selected clusters, median values of r 50 decrease as r/r 200 goes to zero, whereas the opposite is observed for galaxies in the MaxBCG clusters. These different behaviours are mainly due to early type galaxies. The results are discussed in terms of the different processes that affect the evolution of galaxies in different environments.
Quantifying galactic morphological transformations in the cluster environment
Monthly Notices of the Royal Astronomical Society, 2011
We study the effects of the cluster environment on galactic morphology by defining a dimensionless angular momentum parameter λ d , to obtain a quantitative and objective measure of galaxy type. The use of this physical parameter allows us to take the study of morphological transformations in clusters beyond the measurements of merely qualitative parameters, e.g. S/E ratios, to a more physical footing. To this end, we employ an extensive Sloan Digital Sky Survey sample (Data Release 7), with galaxies associated with Abell galaxy clusters. The sample contains 121 relaxed Abell clusters and over 51,000 individual galaxies, which guarantees a thorough statistical coverage over a wide range of physical parameters. We find that the median λ d value tends to decrease as we approach the cluster center, with different dependences according to the mass of the galaxies and the hosting cluster; low and intermediate mass galaxies showing a strong dependence, while massive galaxies seems to show, at all radii, low λ d values. By analysing trends in λ d as functions of the nearest neighbour environment, clustercentric radius and velocity dispersion of clusters, we can identify clearly the leading physical processes at work. We find that in massive clusters (σ > 700 km/s), the interaction with the cluster central region dominates, whilst in smaller clusters galaxy-galaxy interactions are chiefly responsible for driving galactic morphological transformations.
Astronomy & Astrophysics, 2014
Context. Cluster galaxies are the ideal sites to look at when studying the influence of the environment on the various aspects of galaxies' evolution, such as the changes in their stellar content and morphological transformations. In the framework of wings, the WIde-field Nearby Galaxy-cluster Survey, we have obtained optical spectra for ∼ 6000 galaxies selected in fields centered on 48 local (0.04 < z < 0.07) X-ray selected clusters to tackle these issues. Aims. By classifying the spectra based on given spectral lines, we investigate the frequency of the various spectral types as a function both of the clusters' properties and of the galaxies' characteristics. In this way, using the same classification criteria adopted for studies at higher redshift, we can consistently compare the properties of the local cluster population to those of their more distant counterparts. Methods. We describe a method we have developed to automatically measure the equivalent width of spectral lines in a robust way even in spectra with a non optimal signal to noise. Like this, we can derive a spectral classification reflecting the stellar content, based on the presence and strength of the [Oii] and Hδ lines. Results. After a quality check, we are able to measure 4381 of the ∼ 6000 originally observed spectra, in the fields of 48 clusters, 2744 of which are spectroscopically confirmed cluster members. The spectral classification is then analyzed as a function of galaxies' luminosity, stellar mass, morphology, local density and host cluster's global properties, and compared to higher redshift samples (MORPHS and EDisCS). The vast majority of galaxies in the local clusters population are passive objects, being also the most luminous and massive. At a magnitude limit of MV < −18, galaxies in a post-starburst phase represent only ∼ 11% of the cluster population and this fraction is reduced to ∼ 5% at MV < −19.5, which compares to the 18% at the same magnitude limit for high-z clusters. "Normal" star forming galaxies (e(c)) are proportionally more common in local clusters. Conclusions. The relative occurrence of post-starbursts suggests a very similar quenching efficiency in clusters at redshifts in the 0 to ∼ 1 range. Furthermore, more important than the global environment, the local density seems to be the main driver of galaxy evolution in local clusters, at least with respect to their stellar populations content.
The Astrophysical Journal, 2013
We present an analysis of the levels and evolution of star formation activity in a representative sample of 30 massive galaxy clusters at 0.15<z<0.30 from the Local Cluster Substructure Survey (LoCuSS), combining wide-field Spitzer/MIPS 24µm data with extensive spectroscopy of cluster members. The specific-SFRs of massive (M 10 10 M ⊙ ) star-forming cluster galaxies within r 200 are found to be systematically ∼28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7σ level. This is the unambiguous signature of star formation in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their star formation rates (SFRs) declining exponentially on quenching time-scales in the range 0.7-2.0 Gyr. We measure the mid-infrared Butcher-Oemler effect over the redshift range 0.0-0.4, finding rapid evolution in the fraction (f SF ) of massive (M K <−23.1) cluster galaxies within r 200 with SFRs>3 M ⊙ yr −1 , of the form f SF ∝(1 + z) 7.6±1.1 . We dissect the origins of the Butcher-Oemler effect, revealing it to be due to the combination of a ∼3× decline in the mean specific-SFRs of star-forming cluster galaxies since z∼0.3 with a ∼1.5× decrease in number density. Two-thirds of this reduction in the specific-SFRs of star-forming cluster galaxies is due to the steady cosmic decline in the specific-SFRs among those field galaxies accreted into the clusters. The remaining one-third reflects an accelerated decline in the star formation activity of galaxies within clusters. The slow quenching of star-formation in cluster galaxies is consistent with a gradual shut down of star formation in infalling spiral galaxies as they interact with the intra-cluster medium via ram-pressure stripping or starvation mechanisms. The observed sharp decline in star formation activity among cluster galaxies since z∼0.4 likely reflects the increased susceptability of low-redshift spiral galaxies to gas removal mechanisms as their gas surface densities decrease with time. We find no evidence for the build-up of cluster S0 bulges via major nuclear star-burst episodes. . separate panel. The maximal redshift range of the cluster is shown as the red shaded range, while the adjacent redshift ranges used to identify field galaxies in the same dataset are shown by green (foreground field) and blue (background field) shaded regions. The vertical dotted lines indicate the overall 0.15<z<0.30 redshift limits used to define our LoCuSS cluster and field galaxy sample. The horizontal dot-dashed lines indicate the overall M * K +2 limit for selecting cluster members for spectroscopy, with M * K (z cl )+2.0 used to define our faint K-band apparent magnitude limit for targeting galaxies for almost all of the clusters. The sloping solid curve shows how this K-band apparent magnitude limit produces an effective M K (z) limit which becomes increasingly bright with redshift. The horizontal dashed lines indicate the M * K +1.5 absolute magnitude limit used throughout this work.