Butcher-Oemler Effect Research Articles

Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution

ABSTRACTThe determination of the dynamical causes of the morphological Butcher-Oemler (BO) effect, or the rapid transformation of a large population of late-type galaxies to earlier Hubble types in the rich cluster environment between intermediate redshifts and the local universe, has been an important unsolved problem that is central to our understanding of the general problems of galaxy formation and evolution. In this article, we survey the existing proposed mechanisms for cluster galaxy transformation, and discuss their relevance and limitations to the explanation of the morphological BO effect. A new infrared diagnostic approach is devised to disentangle the relative importance of several major physical mechanisms to account for the BO effect, and an example of the first application of this procedure to a single rich intermediate redshift galaxy cluster is given to demonstrate the viability of this approach. The preliminary result of this analysis favors the interaction-enhanced secular evolution process as the major cause of the cluster galaxy morphological transformation. This conclusion is also supported by a wide range of other published results that are assembled here to highlight their implications on a coherent physical origin for the morphological BO effect.

First Measurement of a Rapid Increase in the AGN Fraction in High-Redshift Clusters of Galaxies

We present the first measurement of the AGN fraction in high-redshift clusters of galaxies (z~0.6) with spectroscopy of one cluster and archival data for three additional clusters. We identify 8 AGN in all four of these clusters from the Chandra data, which are sensitive to AGN with hard X-ray (2-10keV) luminosity L_{X,H} > 10^43 erg/s in host galaxies more luminous than a rest frame M_R 10^43 erg/s we discovered in our earlier study of eight low-redshift clusters with z=0.06-0.31 (average z~0.2). Three of the four high-redshift cluster datasets are sensitive to nearly L_{X,H} > 10^42 erg/s and we identify seven AGN above this luminosity limit, compared to two in eight, low-redshift clusters. Based on membership estimates for each cluster, we determine that the AGN fraction at z~0.6 is f_A(L_X>10^42;M_R 10^43;M_R<-20) = 0.020 (+0.012/-0.008). These values are approximately a factor of 20 greater than the AGN fractions in lower-redshift (average z~0.2) clusters of galaxies and represent a substantial increase over the factors of 1.5 and 3.3 increase, respectively, in the measured space density evolution of the hard X-ray luminosity function over this redshift range. Potential systematic errors would only increase the significance of our result. The cluster AGN fraction increases more rapidly with redshift than the field and the increase in cluster AGN indicates the presence of an AGN Butcher-Oemler Effect.

The Butcher-Oemler effect at z 0.35: a change in perspective

In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven groups/clusters at z ∼ 0.35, we have measured the blue fraction from the cluster core to the cluster outskirts and the field mainly using wide-field Cerro Tololo Inter- American Observatory images. This sample represents a random selection of a volume complete X-ray selected cluster sample, selected so that there is no physical connection with the studied quantity (blue fraction), to minimize observational biases. In order to statistically assess the significance of the Butcher-Oemler effect, we introduce the tools of Bayesian inference. Furthermore, we have modified the blue fraction definition in order to take into account the reduced age of the Universe at higher redshifts, because we should no longer attempt to reject an unphysical universe in which the age of the Universe does depend on redshift, whereas the age of its content does not. We have measured the blue fraction from the cluster centre to the field and we find that the cluster affects the properties of the galaxies up to two virial radii at z ∼ 0.35. Data suggest that during the last 3 Gyr no evolution of the blue fraction, from the cluster core to the field value, is seen beyond that needed to account for the varying age with the redshift of the Universe and of its content. The agreement of the radial profiles of the blue fraction at z = 0 and z ∼ 0.35 implies that the pattern infall did not change over the last 3 Gyr, or, at least, its variation has no observational effect on the studied quantity.

Cluster Populations in Abell 2125 and 2218

We combine new narrowband photometry with archival Wide Field Planetary Camera 2 (WFPC2) data for A2218 (z = 0.18) and A2125 (z = 0.25), two clusters with intermediate redshifts but very different cluster properties, in order to examine the evolution of galaxy populations. A2218 is a dense, elliptical-rich cluster (Bautz-Morgan type II) similar to the Coma Cluster in its evolutionary appearance, whereas A2125 is a less dense, more open cluster (Bautz-Morgan type II–III), although similar in richness to A2218. The color-magnitude relation indicates that A2125 has a more developed blue population than A2218 (the Butcher-Oemler effect), although both clusters have significant numbers of blue galaxies (ranging in star formation rate from normal, star-forming disks to starburst systems) as compared to a present-day cluster. The colors of the red populations are identical in A2125 and A2218 and are well fitted by passive evolution models. We are able, for the first time, to combine archived WFPC2 images with our narrowband photometry for a color, morphological, and structural analysis of the blue Butcher-Oemler population. We find the blue population to be composed of two subpopulations, a bright, spiral population and a fainter, dwarf starburst population. A2125 is richer in bright starburst systems, a phenomenon apparently induced by the cluster's younger dynamical state. In addition, a majority of the S0 population in A2125 and A2218 is composed of bulge + disk systems, whereas nearby clusters such as Coma are composed primarily of lenticulars (pure disk S0s). The structural parameters of the S0 bulges in A2125 and A2218 are identical to the structure parameters of cluster ellipticals, suggesting that the disks of some S0s in intermediate-redshift clusters are stripped away, with the leftover bulges evolving into present-day ellipticals.

The Canada-France-Hawaii Telescope Legacy Survey: The Morphology-Density Relation of Galaxies out to z ~ 1

We study the relationships between galaxy total luminosity (M_g), morphology, color and environment as a function of redshift. We use a magnitude-limited sample of 65,624 galaxies in the redshift range 0<z<1.3 taken from one of the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. We parametrize galaxy morphology according to the Sersic index n. Our n>2 number fractions at z=0.1 agree well with those based on SDSS galaxies. We find that the n>2 galaxy number fraction is constant with redshift in the field. However, for overdense environments this fraction is larger and increases towards lower redshifts, higher densities and higher luminosities. Rest-frame color-magnitude diagrams show that the color distribution is bimodal out to our redshift limit of z~1 with a prominent red-sequence of galaxies at 0.2<z<0.4 and a large blue-peak dominance at 0.8<z<1. We use this bimodality to define a red galaxy fraction (rest-frame u-g>1). For all environments, this fraction increases towards lower redshifts and higher luminosities. The red fraction within cluster-like regions changes 60% faster with redshift as compared to the field for M_g<-19.5. Using, for the first time, observations across many cluster-field interfaces distributed over a single, large volume, we trace the large-scale morphology-density relation and the Butcher-Oemler effect over a period of almost 8 Gyr.

Velocity dispersion of 335 galaxy clusters selected from the Sloan Digital Sky Survey: statistical evidence for dynamical interaction and against ram-pressure stripping

There has been plenty of observational evidence of cluster galaxy evolution, such as the Butcher-Oemler effect and the morphology-density relation. However, it is hard to identify the origin of cluster galaxy evolution, simply because it is difficult to trace the complicated process of galaxy evolution over a time-scale of several gigayears using observations that only give information about a single epoch. Here we show that gravitational interaction/friction between galaxies is the statistically dominant physical mechanism responsible for cluster galaxy evolution, and that the well-favoured ram-pressure stripping by the cluster gas is not statistically driving cluster galaxy evolution. We have constructed the largest composite cluster with 14 548 member galaxies out of 335 clusters with σ > 300 km s -1 carefully selected from the Sloan Digital Sky Survey. By measuring the velocity dispersions of various subsamples of galaxies in this composite cluster, we found that bright cluster galaxies (M z < -23) have significantly smaller velocity dispersion than faint galaxies (M z ≥ -23), with much greater precision than previous results (e.g. those of Adami et al.). We interpret this as direct evidence of the dynamical interaction/friction between cluster galaxies, where massive galaxies lose their velocity through energy equipartition during the dynamical interaction/friction with less massive galaxies. We also found that star-forming late-type galaxies have a larger velocity dispersion than passive late-type galaxies. This is inconsistent with the ram-pressure stripping model; since ram pressure is proportional to a v 2 (i.e. stronger for galaxies with high velocity), ram-pressure stripping cannot explain the observed trends of passive (evolved) galaxies having low velocity rather than high velocity. On the other hand, the result is again consistent with the dynamical galaxy-galaxy interaction/friction, where more evolved (passive) galaxies lose their velocity through dynamical interaction/friction.

An ISOCAM survey through gravitationally lensing galaxy clusters

Observations of the core of the massive cluster Cl 0024+1654, at a redshift z=0.39, were obtained with the Infrared Space Observatory using ISOCAM at 6.7 mum and 14.3 mum (hereafter 15 mum). Thirty five sources were detected at 15 mum and thirteen of them are spectroscopically identified with cluster galaxies. The remaining sources consist of four stars, one quasar, one foreground galaxy, three background galaxies and thirteen sources with unknown redshift. The ISOCAM sources have best-fit SEDs typical of spiral or starburst models observed 1 Gyr after the main starburst event. The median infrared luminosity of the twelve cluster galaxies is 1.0x10^11 Lsun, with 10 having infrared luminosity above 9x10^10 Lsun, and so lying near or above the 1x10^11 Lsun threshold for identification as a luminous infrared galaxy (LIRG). The [OII] star formation rates obtained for 3 cluster galaxies are one to two orders of magnitude lower than the infrared values, implying that most of the star formation is missed in the optical because it is enshrouded by dust in the starburst galaxy. The counterparts of about half of the 15 mum cluster sources are blue, luminous, star-forming systems and the type of galaxy that is usually associated with the Butcher-Oemler effect. Dust obscuration may be a major cause of the 15 mum sources appearing on the cluster main sequence. The majority of the ISOCAM sources in the Butcher-Oemler region of the colour-magnitude diagram are best fit by spiral-type SEDs whereas post-starburst models are preferred on the main sequence, with the starburst event probably triggered by interaction with one or more galaxies. Finally, the mid-infrared results on Cl 0024+1654 are compared with four other clusters observed with ISOCAM.

Infall, the Butcher‐Oemler Effect, and the Descendants of Blue Cluster Galaxies atz ∼ 0.6

Using wide-field Hubble Space Telescope WFPC2 imaging and extensive Keck LRIS spectroscopy, we present a detailed study of the galaxy populations in MS 2053-04, a massive, X-ray-luminous cluster at z = 0.5866 ± 0.0011. Analysis of 149 confirmed cluster members shows that MS 2053 is composed of two structures that are gravitationally bound to each other; their respective velocity dispersions are 865 ± 71 km s-1 (113 members) and 282 ± 51 km s-1 (36 members). MS 2053's total dynamical mass is 1.2 × 1015 M☉. MS 2053 is a classic Butcher-Oemler cluster with a high fraction of blue members (24% ± 5%) and an even higher fraction of star-forming members (44% ± 7%), as determined from their [O II] λ3727 emission. The number fraction of blue/star-forming galaxies is much higher in the infalling structure than in the main cluster. This result is the most direct evidence to date that the Butcher-Oemler effect is linked to galaxy infall. In terms of their colors, luminosities, estimated internal velocity dispersions, and [O II] λ3727 equivalent widths, the infalling galaxies are indistinguishable from the field population. MS 2053's deficit of S0 galaxies combined with its overabundance of blue spirals implies that many of these late-type galaxies will evolve into S0 members. The properties of the blue cluster members in both the main cluster and infalling structure indicate that they will evolve into low-mass, L 3.

Do star formation rates of galaxy clusters depend on mass? Blue/late-type fractions and total star formation rates of 115 galaxy clusters as a function of cluster virial mass

Abstract There has been plenty of observational evidence of cluster galaxy evolution such as the Butcher–Oemler effect and the decrease in S0 fraction with increasing redshift. As a modern version, the redshift evolution of total star formation rate (SFR) in clusters has been actively debated recently. However, these studies of redshift trend have been always hampered by the possible mass dependence; due to the observational selection effects, clusters found at higher redshift inevitably tend to be more massive and luminous than local counterparts. Consequently, one has to correct for the mass trend before interpreting the redshift trend. As an attempt to break this degeneracy, we investigate the mass dependence of blue/late-type fractions and total SFR of 115 clusters at z≤ 0.09 selected from the Sloan Digital Sky Survey. We find that none of the blue/late-type fractions, total SFR and total SFR normalized by cluster mass show significant dependence on cluster virial mass. The scatter is much larger at each cluster mass than a possible trend. Our results indicates that physical mechanisms that depend on cluster mass (such as the ram-pressure stripping) are not likely to be solely responsible for cluster galaxy evolution. Our results also provide an excellent low-redshift comparison sample for future high-redshift cluster SFR studies.

Stellar Populations, Butcher-Oemler Effect, Star Formation in Clusters

AbstractIn this brief overview of the stellar populations of galaxies in clusters I highlight some of the most recent results, including the downsizing of the k+a population and the star formation-local density relation. I conclude discussing some open questions regarding the interpretation of the observational results, and speculating on the current meaning of the words “primordial” and “environmental”.

Are passive spiral galaxies truly ‘passive’ and ‘spiral’? A near-infrared perspective

Passive spiral galaxies – unusual galaxies with spiral morphology without any sign of on-going star formation – have recently been found to exist preferentially in cluster infalling regions (at about the virial radius, or at a local galaxy density of ∼1 Mpc−2). The discovery directly connects passive spiral galaxies to cluster galaxy evolution studies such as the Butcher–Oemler effect or the morphology–density relation, i.e. passive spiral galaxies are likely to be transition objects between high-z blue, spiral galaxies and low-z red, cluster early-type galaxies. Thus, detailed study of passive spiral galaxies could potentially bring new insight into the underlying physical mechanisms governing cluster galaxy evolution. However, in previous work, passive spiral galaxies were selected from low-resolution optical images with ∼1.5 arcsec of seeing. Therefore, passive spirals could be a misidentification of S0 galaxies; or dusty starburst galaxies which are not passive at all. To answer these questions, we performed deep, high-resolution, near-infrared imaging of 32 passive spiral galaxies. Our high-resolution K-band images show clear spiral-arm structures. Thus, passive spirals are not S0s. Optical–infrared colour does not show any signs of dusty starburst at all. Therefore, it is likely that they are truly ‘passive’ and ‘spiral’ galaxies in the midst of cluster galaxy evolution.

Optical/infrared observations of high-redshift galaxy clusters

Galaxy clusters at are particularly important in the study of cluster evolution and the application of clusters to cosmological studies. We briefly discuss the difficulties in creating well-defined, large, high-redshift cluster samples, and some of the techniques used in optical/IR imaging to overcome them. We give a summary of the current state of optical/IR observations of the relatively small number of high-redshift clusters identified so far, including discussions of the galaxy luminosity function, the Fundamental Plane, the color-magnitude relation, and the Butcher-Oemler effect. The application of photometric redshift techniques is also highlighted.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Galaxy evolution in dense environments: a concise HI perspective

Observing the neutral hydrogen in galaxy clusters provides crucial insights in the physical processes that influence the evolution of gas-rich galaxies as they migrate from the lower-density filaments through the cluster outskirts into to the higher-density central regions. The morphology-density relation, the Butcher-Oemler effect, and the observed HI deficiencies in the central regions of galaxy clusters suggest that infalling galaxies experience a strong transformation of their morphologies, star formation rates, and gas content. The physical mechanisms that trigger and govern these transformations may depend strongly on environment. This contribution aims to illustrate that the morphological and kinematic characteristics of the cold gas provide a sensitive tool to determine which mechanisms dominate in which environments.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The 2dF Galaxy Redshift Survey: the blue galaxy fraction and implications for the Butcher-Oemler effect

We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.

Evolution of the colour-radius and morphology-radius relations in SDSS galaxy clusters

We have investigated the redshift evolution of the colour--cluster-centric-radius relation and the morphology--cluster-centric-radius relation in three redshift bins, $0.02\leq z\leq 0.14$, $0.14< z\leq 0.20$, and $0.20< z\leq 0.30$ using a homogeneous sample of 736 galaxy clusters selected from the Sloan Digital Sky Survey. Both the relations are well-defined in all the redshift bins; the fraction of blue/late-type galaxies increases toward outside of clusters.Blue/late-type galaxy fractions are found to decrease with decreasing redshift at any cluster-centric radius. The trend is consistent with the Butcher-Oemler effect and the morphological Butcher-Oemlereffect. In addition, we find that colour (spectral) evolution is almost completed by $z\sim0.2$, whereas morphological evolution continues to the present day. The colour-radius relation is smooth inall the redshift bins, while the morphology--radius relation has a break only in the highest redshift bin. It is also found thatfractions of blue-late type galaxies decreases mostly between the highest and the intermediate redshift bins, while fractions of red-late type galaxies continuously decreases with decreasing redshift through all the redshift bins. These results are consistent with the interpretation that the timescale of the colour (spectral) evolution is shorter than that of the morphological evolution. It is suggested that red-late type galaxies in the middle of the transformation are observed as passive spiral galaxies.

XMM-Newton witness of M 86 X-ray metamorphosis

The environmental influence of cluster media on its member galaxies, known as Butcher-Oemler effect, has recently been subject to revision due to numerous observations of strong morphological transformations occurring outside the cluster virial radii, caused by some unidentified gas removal processes. In this context we present new XMM-Newton observations of M 86 group. The unique combination of high spatial and spectral resolution and large field of view of XMM-Newton allows an in-depth investigation of the processes involved in the spectacular disruption of this object. We identify a possible shock with Mach number of ∼1.4 in the process of crushing the galaxy in the North-East direction. The latter is ascribed to the presence of a dense X-ray emitting filament, previously revealed in the RASS data. The shock is not associated with other previously identified features of M 86 X-ray emission, such as the plume, the north-eastern arm and the southern extension, which are found to have low entropy, similar to the inner 2 kpc of M 86. Finally, mere existence of the large scale gas halo around the M 86 group, suggests that the disruptions of M 86's X-ray halo may be caused by small-scale types of interactions such as galaxy-galaxy collisions.

The Hα Luminosity Function of the Galaxy Cluster A521 atz= 0.25

We present an optical multicolor-imaging study of the galaxy cluster A521 at z = 0.25, using Suprime-Cam on the Subaru Telescope, covering an area of 32' × 20' (9.4 × 5.8 h Mpc2 at z = 0.25). Our imaging data taken with both a narrowband filter, NB816 (λ0 = 8150 A and Δλ = 120 A), and broadband filters, B,V,RC,i', and z', allow us to find 165 Hα emitters. We obtain the Hα luminosity function (LF) for the cluster galaxies within 2 Mpc; the Schechter parameters are α = -0.75 ± 0.23, * = 10-0.45 to 10-0.05 Mpc-3, and L* = 1041.86 to 1042.2 ergs s-1. Although the faint-end slope α is consistent with that of the local cluster Hα LFs, the characteristic luminosity L* is about 6 times (or ≈2 mag) brighter. This strong evolution implies that A521 contains more active star-forming galaxies than the local clusters, being consistent with the observed Butcher-Oemler effect. However, the bright L* of A521 may be, at least in part, due to the dynamical condition of this cluster.

TheK‐selected Butcher‐Oemler Effect

We derive the blue fraction for a sample of K -selected galaxies in 25 clusters at 0.15 < z < 0.92. We find a much smaller blue fraction and weaker trend with redshift than measured in optically selected samples. We suggest that the Butcher-Oemler effect is primarily due to star fonning low luminosity galaxies.

Morphological Butcher–Oemler Effect in the SDSS “Cut and Enhance” Galaxy Cluster Catalog

Abstract We investigated the evolution of the fractions of late-type cluster galaxies as a function of redshift using one of the largest, most uniform cluster samples available. The sample consisted of 514 clusters of galaxies in the range of $0.02 \leq z\leq 0.3$ from the Sloan Digital Sky Survey “Cut and Enhance” galaxy cluster catalog. This catalog was created using a single automated cluster-finding algorithm applied to uniform data from a single telescope, with accurate CCD photometry, thus minimizing the selection biases. We used four independent methods to analyze the evolution of the late-type galaxy fraction. Specifically, we selected late-type galaxies based on each of the rest-frame $g-r$ color, the $u-r$ color, galaxy profile fitting, and the concentration index. The first criterion corresponds to that used in classical Butcher–Oemler analyses. The last two criteria are more sensitive to the morphological type of galaxies. In all four cases, we find an increase in the fraction of late-type galaxies with increasing redshift, significant at the 99.9% level. The results confirm that cluster galaxies do change colors with redshift (the Butcher–Oemler effect) and, in addition, they change their morphology to later-type toward a higher redshift — indicating a morphological equivalence of the Butcher–Oemler effect. We also found a tendency of richer clusters to have lower fractions of late-type galaxies. This trend is consistent with a ram-pressure stripping model, where galaxies in richer clusters are affected by stronger ram pressure due to the higher temperature of clusters.

The Environment of Passive Spiral Galaxies in the SDSS

Abstract In previous work on galaxy clusters, several authors reported the discovery of an unusual population of galaxies, which have spiral morphologies, but do not show any star-formation activity. These galaxies are called “passive spirals”, and have been interesting since it has been difficult to understand the existence of such galaxies. Using a volume-limited sample ($0.05 &amp;lt; z &amp;lt; 0.1$ and $M_{r^{*}} &amp;lt;-20.5$; 25813 galaxies) of the Sloan Digital Sky Survey data, we found 73 ($0.28 \pm 0.03\%$) passive spiral galaxies and studied their environments. It is found that passive spiral galaxies exist in a local galaxy density of $1 \hbox{--} 2 \,\textrm{Mpc}^{-2}$ and have a 1–10 cluster-centric virial radius. Thus, the origins of passive spiral galaxies are likely to be cluster-related. These characteristic environments coincide with a previously reported environment where the galaxy star-formation rate suddenly declines and the so-called morphology-density relation turns. It is likely that the same physical mechanism is responsible for all of these observational results. The existence of passive spiral galaxies suggests that a physical mechanism that works calmly is preferred to dynamical origins such as major merger/interaction since such a mechanism would destroy the spiral-arm structures. Compared with the observed cluster galaxy evolution such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect, passive spiral galaxies are likely to be a key galaxy population in transition between red, elliptical/S0 galaxies in low-redshift clusters and blue, spiral galaxies more numerous in higher-redshift clusters.