Figure 2 - uploaded by Ian Smail
Content may be subject to copyright.
Redshift distribution for cluster members. The two lowest redshift galaxies in the distribution have been eliminated as members of the surrounding supercluster.
Source publication
![Figure 8. Distribution of the equivalent widths of the Hδ and [O ii]...](profile/Ian-Smail/publication/231049347/figure/fig2/AS:669980618153989@1536747235383/Distribution-of-the-equivalent-widths-of-the-Hd-and-O-ii-lines-in-Abell-851-a-and-a_Q320.jpg)
We use extensive new observations of the very rich z ~ 0.4 cluster of galaxies A851 to examine the nature and origin of starburst galaxies in intermediate-redshift clusters. New HST observations, 24 μm Spitzer photometry and ground-based spectroscopy cover most of a region of the cluster about 10' across, corresponding to a cluster-centric radial d...
Contexts in source publication
Context 1
... on the redshift histogram we show in Figure 2, we define cluster members to be all galaxies with redshifts 0.385 < z < 0.420, and identify 44 new cluster members. This excludes, in particular, two outliers at z = 0.373 that are probable members of the A851 supercluster but not the cluster itself. ...
Context 2
... redshift histogram of Figure 2 is highly suggestive of substructure in A851, but a sample of 101 cluster member velocities is too small for a decisive test of substructure. However, by combining spatial and velocity information for the galaxies, using the Dressler & Shectman (1988b) method, evidence for substructure is clear. ...
Context 3
... promised in the previous section, the clear-cut morphological differences between a+k/k+a galaxies with and without 24 μm flux seen in Figure 11 is consistent with our previous conclusion that the former are buried starbursts, but the latter are true post- starburst galaxies, rather than merely weaker buried starbursts. Figure 12 presents images of all e(a) and e(b) galaxies in A851 which lie within the post-refurbishment HST frames, and which have redshift qualities Q 3. These visible starbursts form a more heterogeneous collection of objects than the buried starbursts in the top group of Figure 11. ...
Similar publications
We present new results of a program to study the detailed morphologies of galaxies in intermediate-redshift clusters and hence understand the physical origin of the enhanced star formation seen in these environments at earlier epochs. Deep, high-resolution imagery has been obtained of three rich clusters, AC 103, AC 118, and AC 114 at z = 0.31, thr...
This project explores the relative role of “nature versus nurture” (intrinsically versus environmentally driven influences) in shaping the morphology and evolution of galaxies by performing a detailed photometric analysis of early-type spiral galaxies found in galaxy pairs. We use Fourier analysis to model the properties of the spiral arms and bulg...
We present a catalogue of isolated field elliptical (IfE) galaxies drawn from the W1 field of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). 228 IfEs were identified from a flux-limited $(r<21.8)$ galaxy catalogue which corresponds to a density of 3 IfE/sq.deg. For comparison we consider a sample of elliptical galaxies living in dense e...
We present a novel approach for measuring the two-point correlation function of galaxies in narrow pencil beam surveys with varying depths. Our methodology is utilized to expand high-redshift galaxy clustering investigations up to z ∼ 8 by analyzing a comprehensive sample consisting of Ng = 160 Lyman break galaxy candidates obtained through optical...
We describe Hubble Space Telescope (HST) imaging of 10 of the 20 ESO Distant Cluster Survey (EDisCS) fields. Each ~40 arcmin2 field was imaged in the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based on these data, we present visual morphological classifications for the ~920 sources per field that are brighter than Iauto =...
Citations
... [32]). This evolution was later observed in IR-selected populations as well, including a rise in the (U)LIRG fraction [138,170,378,419,421,[455][456][457][458][459][460][461][462][463][464][465][466], mirroring the steep rise in SF in the field to z ∼ 1 − 3 (e.g., [142], Zavala & Casey, in prep.), though with a lower normalization. The nature of this evolution provides a vital complement to the studies focused on quenched populations discussed in Section 4. ...
Environment is one of the primary drivers of galaxy evolution; via multiple mechanisms, it can control the critical process of transforming galaxies from star forming to quiescent, commonly termed “quenching”. Despite its importance, however, we still do not have a clear view of how environmentally-driven quenching proceeds even in the most extreme environments: galaxy clusters and their progenitor proto-clusters. Recent advances in infrared capabilities have enabled transformative progress not only in the identification of these structures but in detailed analyses of quiescence, obscured star formation, and molecular gas in (proto-)cluster galaxies across cosmic time. In this review, we will discuss the current state of the literature regarding the quenching of galaxies in (proto-)clusters from the observational, infrared perspective. Our improved understanding of environmental galaxy evolution comes from unique observables across the distinct regimes of the near-, mid-, and far-infrared, crucial in the push to high redshift where massive galaxy growth is dominated by highly extinct, infrared-bright galaxies.
... Hα emission line cannot escape from the star-forming regions. Such highly attenuated starbursts are reported in other clusters and fields (e.g., Smail et al. 1999;Poggianti et al. 2001;Dressler et al. 2009;Oemler et al. 2009). ...
Galaxies change their properties as they assemble into clusters. In order to understand the physics behind that, we need to go back in time and observe directly what is occurring in galaxies as they fall into a cluster. We have conducted a narrowband and J -band imaging survey on a cluster CL1604-D at z = 0.923 using a new infrared instrument SWIMS installed at the Subaru Telescope. The narrowband filter, NB1261, matches to H α emission from the cluster at z = 0.923. Combined with a wide range of existing data from various surveys, we have investigated galaxy properties in and around this cluster in great detail. We have identified 27 H α emitters associated with the cluster. They have significant overlap with MIPS sources and are located exclusively in the star-forming regime on the rest-frame UVJ diagram. We have identified two groups of galaxies near the cluster in the 2D spatial distribution and the phase-space diagram, which are likely to be in-falling to the cluster main body. We have compared various physical properties of star-forming galaxies, such as specific star formation rates (burstiness) and morphologies (merger) as a function of environment, cluster center, older group, younger group, and the field. As a result, a global picture has emerged on how the galaxy properties are altered as they assemble into a denser region. This includes the occurrence of mergers, enhancement of star formation activity, excursion to the dusty starburst phase, and eventual quenching to a passive phase.
... In these galaxies, dust extinction may be so strong that even Hα emission line cannot escape from the star forming regions. Such highly attenuated starbursts are reported in other clusters and fields (e.g., Smail et al. 1999;Poggianti et al. 2001;Dressler et al. 2009;Oemler et al. 2009). ...
Galaxies change their properties as they assemble into clusters. In order to understand the physics behind that, we need to go back in time and observe directly what is occurring in galaxies as they fall into a cluster. We have conducted a narrow-band and $J$-band imaging survey on a cluster CL1604-D at $z=0.923$ using a new infrared instrument SWIMS installed at the Subaru Telescope. The narrow-band filter, NB1261, matches to H$\alpha$ emission from the cluster at $z=0.923$. Combined with a wide range of existing data from various surveys, we have investigated galaxy properties in and around this cluster in great detail. We have identified 27 H$\alpha$ emitters associated with the cluster. They have significant overlap with MIPS 24$\mu$m sources and are located exclusively in the star forming regime on the rest-frame $UVJ$ diagram. We have identified two groups of galaxies near the cluster in the 2D spatial distribution and the phase-space diagram, which are likely to be in-falling to the cluster main body. We have compared various physical properties of star forming galaxies, such as specific star formation rates (burstiness) and morphologies (merger) as a function of environment; cluster center, older group, younger group, and the field. As a result, a global picture has emerged on how the galaxy properties are altered as they assemble into a denser region. This includes the occurrence of mergers, enhancement of star formation activity, excursion to the dusty starburst phase, and eventual quenching to a passive phase.
... It is believed that in observed PSBs the star formation decreased roughly a few Myr (bluer PSBs) to a few Gyr (redder PSBs) prior to the time of emission of the light we observe, based on the lifetime of the observed stars with strong Balmer lines (Poggianti & Barbaro, 1996, 1997Poggianti et al., 1999;Mercurio et al., 2004). By identifying the spatial and dynamical location of these PSBs, it is believed that we can determine which of the mechanisms discussed above is responsible for the differences in star formation rate between galaxies in recently merged clusters and dynamically relaxed systems (Bekki et al., 2010;Muzzin et al., 2014;Dressler et al., 2013;Lewis et al., 2002;Owen et al., 2005;Mercurio et al., 2004;Oemler et al., 2009). ...
... With enough member galaxies, studies are able to investigate the substructure and dynamics as a function of star formation rate of the individual galaxies, providing critical astrophysical insights that allow us to better understand galaxy cluster formation. Such insights are important in properly understanding the systematics of these complex objects for use as cosmological probes (Czoske et al., 2002;Mercurio et al., 2004Mercurio et al., , 2008Oemler et al., 2009;Ma et al., 2010;Girardi et al., 2015). ...
Galaxy Clusters are the largest gravitationally bound objects in the Universe, residing at the boundary between the expansive push of dark energy in the vacuum and the attractive pull of dark matter the fills the halo in which a cluster resides. By leveraging the power of spectroscopy, I used the three-dimensional information it provides about galaxies within these clusters to infer dynamical properties about the galaxy cluster and the underlying dark matter halo. The dynamical state and dynamic mass inferences are valuable to future cosmological studies that aim to use the unique nature of galaxy clusters and the role they play in constraining the properties of dark energy and dark matter. In this work I focus on transforming galaxy spectra into line-of-sight velocities which, when paired with projected sky locations, allow me to probe the gravitational potential of the total cluster system. I designed, targeted, acquired, reduced, and analyzed 4427 galaxy spectra from 22 galaxy clusters, of which 3054 passed my strict quality cuts. Of those that passed the cuts, 1679 were identified as cluster members based on radial-velocity phase-space cuts. The data was acquired using the Michigan-Magellan Fiber System (M2FS) multi-fiber spectrograph on the 6.5m Magellan Clay telescope. The reductions were performed using a fully-featured pipeline that I created and that I describe in this work. I also summarize the resulting dataset using spatial, redshift, magnitude, and signal-to-noise information for individual galaxies, and show that there is good agreement when comparing my re-observed redshifts with those in the literature. To convey the amount of information contained in this dataset, I perform an analysis on one specifically selected massive cluster, Abell S1063, which was observed twice. I use two approaches for estimating cluster masses, the first is a velocity dispersion technique that takes the distribution of velocities, reduces it to a statistical measure of the width of the distribution, and maps that spread to a mass based on a model motivated in part by theory and calibrated with simulations. The second uses the velocity-radial distance information from the cluster center to identify the escape velocity edge of the cluster, which is observed as the velocity extrema in a given radial bin. This edge is directly related to the gravitational potential and can be used to infer the total mass of the system. I compare these techniques to one another and against other mass proxies and find that the velocity dispersion measurement differs from other estimates for the system, favoring a higher mass, while the escape velocity edge technique is in good agreement with other estimates. This is expected for a galaxy cluster with substructure, which previous studies have hypothesized for this system but could not verify. I am able to visually confirm the existence of clumps using galaxies as tracers, and quantify the substructure using the Dressler-Shectman statistic, where I found a significant result with p< 0.0001.
... Of the 20 traditional K+As targeted with MOSFIRE for which we could make meaningful measurements, five exhibited significant (> 3σ) Hα emission in tandem with [NII]/Hα ratios (or upper limits) consistent with originating from regions of ongoing star formation. Such galaxies are likely the product of heavy dust obscuration in which the [OII] (and potentially Hβ when it was possible to observe) is heavily differentially attenuated within H ii regions strong enough to suppress even the EW ([OII]) measurement, but from which appreciable numbers of Hα photons can escape (see, e.g., Oemler et al. 2009). As post-starburst galaxies cannot, by definition, house ongoing star formation, traditional classification of z ∼ 1 K+A galaxies based solely on observed-frame optical spectroscopy results in sample 25% contaminated by galaxies with active star formation. ...
In this study we present the exploration of $\sim$500 spectroscopically confirmed galaxies in and around two large scale structures at $z\sim1$ drawn from the ORELSE survey. A sub-sample of these galaxies ($\sim$150) were targeted for the initial phases of a near-infrared MOSFIRE spectroscopic campaign investigating the differences in selections of galaxies which had recently ended a burst of star formation or had rapidly quenched (i.e., post-starburst or K+A galaxies). Selection with MOSFIRE resulted in a post-starburst sample more than double that selected by traditional $z\sim1$ (observed-frame optical) methods even after the removal of the relatively large fraction of dusty starburst galaxies selected through traditional methods. While the traditional post-starburst fraction increased with increased global density, the MOSFIRE-selected post-starburst fraction was found to be constant in field, group, and cluster environments. However, this fraction relative to the number of galaxies with ongoing star formation was observed to elevate in the cluster environment. Post-starbursts selected with MOSFIRE were predominantly found to exhibit moderately strong [OII] emission originating from activity other than star formation. Such galaxies, termed K+A with ImposteR [OII]-derived Star formation (KAIROS) galaxies, were found to be considerably younger than traditionally-selected post-starbursts and likely undergoing some form of feedback absent or diminished in traditional post-starbursts. A comparison between the environments of the two types of post-starbursts suggests a picture in which the evolution of a post-starburst galaxy is considerably different in cluster environments than in the more rarefied environments of a group or the field.
... Indeed, deep mid-infrared observations of intermediate redshift clusters with Spitzer and Herschel have revealed an abundance of such dusty star-forming galaxies which are missing from optical studies (e.g. Coia et al. 2005; Geach et al. 2006 Geach et al. , 2009 Elbaz et al. 2007; Marcillac et al. 2007; Koyama et al. 2008; Oemler et al. 2009; Kocevski et al. 2011; Alberts et al. 2014). In an era in which clusters were still accreting much of their mass, there not only appears to be a significant population of star-forming galaxies, but also many with their star formation temporarily enhanced in this dense environment. ...
To investigate what drives the reversal of the morphology–density relation at intermediate/high redshift, we present a multiwavelength
analysis of 27 dusty starburst galaxies in the massive cluster Cl 0024+17 at z = 0.4. We combine Hα dynamical maps from the VLT/FLAMES multi-IFU system with far-infrared imaging using Herschel/SPIRE
and millimetre spectroscopy from IRAM/NOEMA, in order to measure the dynamics, star formation rates and gas masses of this
sample. Most galaxies appear to be rotationally supported, with a median ratio of rotational-support to line-of-sight velocity
dispersion v/σ ∼ 5 ± 2, and specific angular momentum λR = 0.83 ± 0.06 – comparable to field spirals of a similar mass at this redshift. The star formation rates of 3–26 M⊙ yr−1 and average 12CO-derived gas mass of ∼ 1 × 1010 M⊙ suggest gas depletion time-scales of ∼1 Gyr (∼0.25 of the cluster crossing time). We derive characteristic dust temperatures
(mean Td = 26 ± 1 K) consistent with local galaxies of similar far-infrared luminosity, suggesting that the low-density gas is yet
to be stripped. Taken together, these results suggest that these starbursts have only recently accreted from the field, with
star formation rates likely enhanced due to the effects of ram pressure. In order to make the transition to cluster S0s these
galaxies must lose ∼40 per cent of their specific angular momentum. We suggest this must occur ≥1 Gyr later, after the molecular
gas has been depleted and/or stripped, via multiple tidal interactions with other cluster members.
... The Cl 0939+4713 cluster at z = 0.41 (Abell 851) is one of the best-studied clusters at intermediate redshifts, and several studies have focused on the cluster central region(s) (e.g. Dressler & Gunn 1992; Dressler et al. 1994; Stanford et al. 1995; Smail et al. 1999; Sato & Martin 2006; Dressler et al. 2009; Oemler et al. 2009 ). Furthermore, widefield (∼30 ×30 ) optical broad-band and narrow-band imaging surveys of this cluster have also been conducted (e.g. ...
Cluster star-forming galaxies are found to have an excess of Far-Infrared emission relative to Hα, when compared to those
in the field, which could be caused by intense AGN activity, dust and/or declining star formation histories. Here we present
spectroscopic observations of Hα emitters in the Cl 0939+4713 (Abell 851) super-cluster at $z$ = 0.41, using AF2+ WYFFOS on the WHT. We measure [Oii], Hβ, [Oiii], Hα and [Nii] for a sample of 119 Hα emitters in and around the cluster. We find that 17 ± 5% of the Hα emitters are AGN, irrespective
of environment. For star-forming galaxies, we obtain Balmer decrements, metallicities and ionisation parameters with different
methods, individually and by stacking. We find a strong mass-metallicity relation at all environments, with no significant
dependence on environment. The ionisation parameter declines with increasing stellar mass for low-mass galaxies. Hα emitters
residing in intermediate environments show the highest ionisation parameters (along with high [Oiii]/Hα and high [Oiii]/[Oii] line ratios, typically twice as large as in the highest and lowest densities), which decline with increasing environmental
density. Dust extinction (AHα) correlates strongly with stellar mass, but also with environmental density. Star-forming galaxies in the densest environments
are found to be significantly dustier (AHα ≈ 1.5 − 1.6) than those residing in the lowest density environments (AHα ≈ 0.6), deviating significantly from what would be predicted given their stellar masses.
... Therefore super-solar [α/Fe] abundances imply that almost all star formation was completed in 1 Gyr (Worthey et al. 1992;Terndrup 1993;Matteucci 1994;Bender & Paquet 1995;Thomas et al. 1999Thomas et al. , 2002Thomas et al. , 2005. Small amounts of star formation seen in some BCGs and cDs (Oemler et al. 2009;Voit et al. 2015) cannot add up to a significant luminosity-weighed dilution of the [α/Fe]-enhanced starlight. ...
Hobby–Eberly Telescope (HET) spectroscopy is used to measure the velocity dispersion profile of the nearest prototypical cD galaxy, NGC 6166 in the cluster Abell 2199. We also present composite surface photometry from many telescopes. We confirm the defining feature of a cD galaxy; i.e., (we suggest), a halo of stars that fills the cluster center and that is controlled dynamically by cluster gravity, not by the central galaxy. Our HET spectroscopy shows that the velocity dispersion of NGC 6166 rises from σ ≃ 300 km s[superscript −1] in the inner r ~ 10" to σ = 865 ± 58 km s[superscript −1] at r ~ 100'' in the cD halo. This extends published observations of an outward σ increase and shows for the first time that σ rises all the way to the cluster velocity dispersion of 819 ± 32 km s[superscript −1]. We also observe that the main body of NGC 6166 moves at +206 ± 39 km s[superscript −1] with respect to the cluster mean velocity, but the velocity of the inner cD halo is ~70 km s[superscript −1] closer to the cluster velocity. These results support our picture that cD halos consist of stars that were stripped from individual cluster galaxies by fast tidal encounters.
However, our photometry does not confirm the widespread view that cD halos are identifiable as an extra, low-surface-brightness component that is photometrically distinct from the inner, steep-Sérsic-function main body of an otherwise-normal giant elliptical galaxy. Instead, all of the brightness profile of NGC 6166 outside its core is described to ±0.037 V mag arcsec[superscript −2] by a single Sérsic function with index n ≃ 8.3. The cD halo is not recognizable from photometry alone. This blurs the distinction between cluster-dominated cD halos and the similarly-large-Sérsic-index halos of giant, core-boxy-nonrotating ellipticals. These halos are believed to be accreted onto compact, high-redshift progenitors ("red nuggets") by large numbers of minor mergers. They belong dynamically to their central galaxies. Still, cDs and core-boxy-nonrotating Es may be more similar than we think: both may have outer halos made largely via minor mergers and the accumulation of tidal debris.
We construct a main-body+cD-halo decomposition that fits both the brightness and dispersion profiles. To fit σ(r), we need to force the component Sérsic indices to be smaller than a minimum-x[superscript 2] photometric decomposition would suggest. The main body has M[subscript V] ≃ -22.8 ≃ 30% of the total galaxy light. The cD halo has M[subscript V] ≃ -23.7, ~1/2 mag brighter than the brightest galaxy in the Virgo cluster. A mass model based on published cluster dynamics and X-ray observations fits our observations if the tangential dispersion is larger than the radial dispersion at r ≃ 20"–60". The cD halo is as enhanced in α element abundances as the main body of NGC 6166. Quenching of star formation in [< over ~]1 Gyr suggests that the center of Abell 2199 has been special for a long time during which dynamical evolution has liberated a large mass of now-intracluster stars.
... Two clusters were observed both in the broadband (W-S-Z+; z-band) and in the narrowband corresponding to Hα: A851 at z = 0.405 in N- B-L921(NB921) and CL0024+17 at z = 0.390 in N-B-L912 (NB912). The redshifts of these clusters are taken from Oemler et al. (2009) and Moran et al. (2007). The distance modulus is m-M = 41.74(A851) and m-M = 41.64(CL0024+17). ...
... Five out of the nine parent galaxies (C1–C5) are known spectroscopic members of A851, confirmed by Oemler et al. (2009) and/or F. Nakata et al. (2015, in preparation), while the others (C6–C9) did not have spectroscopic redshifts. We therefore performed a spectroscopic observation on 2013 October 31 UT with the Faint Object Camera and Spectrograph (FOCAS; Kashikawa et al. 2002) at the Subaru Telescope. ...
... The value is comparable to those in previous studies—z = 0.4064 (F. Nakata et al. 2015, in preparation) and z = 0.4060 (Oemler et al. 2009). The redshift of the C2 bright spot showed [O II], Hβ, [O III], Hα, and [N II]. ...
From deep H alpha imaging data of Suprime-Cam/Subaru, we discovered nine extended ionized gas clouds (EIG) around galaxies in the Abell 851 cluster (A851) at z = 0.4. We surveyed a 30 x 25 arcmin region, and the EIGs were found only near the cluster center (<2.3 arcmin similar to 750 kpc). The parent galaxies of the EIGs are star-forming or post-starburst galaxies, all of which are spectroscopically confirmed members of the cluster. Four out of the nine parent galaxies show distortion of stellar distribution in the disk, which can be a sign of recent interaction, and the interaction may have made the EIGs. On the other hand, six parent galaxies (one overlaps those exhibiting distortion) show Ha emission without stars, which implies ram pressure stripping. The spectrum of the brightest parent galaxy shows a post-starburst signature and resembles the Ha stripped galaxies found in the Coma cluster. Meanwhile, two brightest parent galaxies in A851 are more massive than the EIG parent galaxies in the Coma cluster. This is consistent with a "downsizing" of star-forming galaxies, though it is still within the statistical variance. We also analyzed Suprime-Cam data of another z = 0.39 cluster, CL0024+17, but found no EIGs. The key difference between A851 and CL0024+17 would be the existence of a subcluster colliding with the main body of A851, in which six or seven out of the nine parent galaxies in A851 exist, and the fraction of EIGs in the subcluster is significantly higher than the main subcluster of A851 and CL0024+17.
... Although the prevalence of post-starburst galaxies in high-density regions shows that environmental effects play an important role, it is still unclear what environmentally dependent mechanisms are responsible. Several investigations have been undertaken, but a consensus on which are dominant has not yet been achieved (Poggianti et al. 1999; Tran et al. 2004; Pracy et al. 2005; Ma et al. 2008; Oemler et al. 2009; Snyder et al. 2011; Dressler et al. 2013, to name a few). In this work, we examine high-redshift large-scale structures, where quenching is actively under way. ...
... Regardless of the physical trigger(s) that result(s) in a post-starburst galaxy, there are two basic components: (1) a significant star formation period in the recent past, followed by (2) no ongoing star formation. Practically, the [O ii] λ3727 doublet emission line is often used as an indicator of ongoing star formation, and the Hδ absorption feature as a proxy for the presence of A-type stars (e.g., Poggianti et al. 1999; Dressler et al. 1999; Oemler et al. 2009; Vergani et al. 2010). If one uses these spectroscopic diagnostics, a galaxy in its post-starburst phase should have no or little [O ii] emission due to the lack of H ii regions that are forming O-and B-type stars, but have strong Hδ absorption from the dominant A-type star population born in the recent past. ...
... In the Cl 1604 groups, 11% of members are K+A galaxies, comparable to the fraction in Cluster B but much lower than the 19% seen in Cluster A. If mergers and interactions are the only routes producing K+A galaxies, the higher K+A fraction in Cluster A implies a higher frequency of merger-induced starbursts in Cluster A than in the Cl 1604 groups. The enhanced merger rate in cluster cores had been proposed by Struck (2006) and observed by Oemler et al. (2009) in a cluster at z ∼ 0.4. For this enhancement to happen, galaxies fall into the cluster as bound pairs or small groups rather than individually. ...
The Cl 1604 supercluster at z ~ 0.9 is one of the most extensively studied high-redshift large-scale structures, with more than 500 spectroscopically confirmed members. It consists of eight clusters and groups, with members numbering from a dozen to nearly a hundred, providing a broad range of environments for investigating the large-scale environmental effects on galaxy evolution. Here we examine the properties of 48 post-starburst galaxies in Cl 1604, comparing them to other galaxy populations in the same supercluster. Incorporating photometry from ground-based optical and near-infrared imaging, along with Spitzer mid-infrared observations, we derive stellar masses for all Cl 1604 members. The colors and stellar masses of the K+A galaxies support the idea that they are progenitors of red sequence galaxies. Their morphologies, residual star formation rates, and spatial distributions suggest that galaxy mergers may be the principal mechanism producing post-starburst galaxies. Interaction between galaxies and the dense intracluster medium (ICM) is also effective, but only in the cores of dynamically evolved clusters. The prevalence of post-starburst galaxies in clusters correlates with the dynamical state of the host cluster, as both galaxy mergers and the dense ICM produce post-starburst galaxies. We also investigate the incompleteness and contamination of K+A samples selected by means of Hδ and [O II] equivalent widths. K+A samples may be up to ~50% incomplete due to the presence of LINERs/Seyferts, and up to ~30% of K+A galaxies could have substantial star formation activity.
