We report on the results of a Chandra search for evidence of triggered nuclear activity within the Cl0023+0423 four-way group merger at z {approx} 0.84. The system consists of four interacting galaxy ...groups in the early stages of hierarchical cluster formation and, as such, provides a unique look at the level of processing and evolution already under way in the group environment prior to cluster assembly. We present the number counts of X-ray point sources detected in a field covering the entire Cl0023 structure, as well as a cross-correlation of these sources with our extensive spectroscopic database. Both the redshift distribution and cumulative number counts of X-ray sources reveal little evidence to suggest that the system contains X-ray luminous active galactic nuclei (AGNs) in excess to what is observed in the field population. If preprocessing is under way in the Cl0023 system, our observations suggest that powerful nuclear activity is not the predominant mechanism quenching star formation and driving the evolution of Cl0023 galaxies. We speculate that this is due to a lack of sufficiently massive nuclear black holes required to power such activity, as previous observations have found a high late-type fraction among the Cl0023 population. It may be that disruptive AGN-driven outflows become an important factor in the preprocessing of galaxy populations only during a later stage in the evolution of such groups and structures when sufficiently massive galaxies (and central black holes) have built up, but prior to hydrodynamical processes stripping them of their gas reservoirs.
We study the stellar population properties of the IRAC-detected 6 < ~ z < ~ 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman Break selection technique, we find a ...total of 17 galaxy candidates at 6 < ~ z < ~ 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios > or = 3 in at least one of the IRAC 3.6 and 4.5 mum channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of ~1.2-5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M sub(1600) are between -21.2 and -18.9 mag, while their intrinsic stellar masses are between 2 x 10 super(8)M sub(middot in circle) and 2.9 x 10 super(9)M sub(middot in circle). We identify two Lyalpha emitters in our sample from the Keck DEIMOS spectra, one at z sub(Lyalpha) = 6.76 (in RXJ 1347) and one at z sub(Lyalpha) = 6.32 (in MACS 0454). We find that 4 out of 17 z > ~ 6 galaxy candidates are favored by z 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC 3.6-4.5 color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.
Faint star-forming galaxies at z ∼ 2-3 can be used as alternative background sources to probe the Ly forest in addition to quasars, yielding high sightline densities that enable 3D tomographic ...reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Ly Mapping And Tomography Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck I telescope. Over an observational footprint of 0.157 deg2 within the COSMOS field, we used 240 galaxies and quasars at 2.17 < z < 3.00, with a mean comoving transverse separation of , as background sources probing the foreground Ly forest absorption at 2.05 < z < 2.55. The Ly forest data was then used to create a Wiener-filtered tomographic reconstruction over a comoving volume of with an effective smoothing scale of . In addition to traditional figures, this map is also presented as a virtual-reality visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently discovered galaxy protoclusters in the volume. Quantitatively, the map signal-to-noise is over a 3 h−1Mpc top-hat kernel based on the variances estimated from the Wiener filter. This data release includes the redshift catalog, reduced spectra, extracted Ly forest pixel data, and reconstructed tomographic map of the absorption. These can be downloaded from Zenodo (10.5281/zenodo.1292459).
We present the results of ALMA spectroscopic follow-up of a z= 6.766 Lyalpha emitting galaxy behind the cluster RX J1347.1?1145. We report the detection of Cii 158 mu m line fully consistent with the ...Lyalpha redshift and with the peak of the optical emission. Given the magnification of mu= 5.0 + or - 0.3, the intrinsic (corrected for lensing) luminosity of the CII line is L sub(CII)= (ProQuest: Formulae and/or non-USASCII text omitted), roughlt ~5 times fainter than other detections of z~ 7 galaxies. The result indicates that low L sub(CII) in z~ 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset (Delta sub(nu)= (ProQuest: Formulae and/or non-USASCII text omitted)) between the Lyalpha and CII line is unusual, and may be indicative of ionizing photons escaping.
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 H delta and OII 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.
We present the results of ALMA spectroscopic follow-up of a z = 6.766 Ly emitting galaxy behind the cluster RX J1347.1−1145. We report the detection of C ii 158 m line fully consistent with the Ly ...redshift and with the peak of the optical emission. Given the magnification of = 5.0 0.3, the intrinsic (corrected for lensing) luminosity of the C ii line is LC ii , roughly ∼5 times fainter than other detections of z ∼ 7 galaxies. The result indicates that low LC ii in z ∼ 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset ( ) between the Ly and C ii line is unusual, and may be indicative of ionizing photons escaping.
We have employed emission-line diagnostics derived from DEIMOS and NIRSPEC spectroscopy to determine the origin of the O II emission line observed in six active galactic nucleus (AGN) hosts at z ~ ...0.9. These galaxies are a subsample of AGN hosts detected in the Cl1604 supercluster that exhibit strong Balmer absorption lines in their spectra and appear to be in a post-starburst or post-quenched phase, if not for their O II emission. Examining the flux ratio of the N II to H Delta *a lines, we find that in five of the six hosts the dominant source of ionizing flux is AGN continuum emission. Furthermore, we find that four of the six galaxies have over twice the O II line luminosity that could be generated by star formation alone given their H Delta *a line luminosities. This strongly suggests that AGN-excited narrow-line emission is contaminating the O II line flux. A comparison of star formation rates calculated from extinction-corrected O II and H Delta *a line luminosities indicates that the former yields a five-fold overestimate of the current activity in these galaxies. Our findings reveal the O II line to be a poor indicator of star formation activity in a majority of these moderate-luminosity Seyferts. This result bolsters our previous findings that an increased fraction of AGN at high redshifts is hosted by galaxies in a post-starburst phase. The relatively high fraction of AGN hosts in the Cl1604 supercluster that show signs of recently truncated star formation activity may suggest that AGN feedback plays an increasingly important role in suppressing ongoing activity in large-scale structures at high redshift.
The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence ...remain under debate. Several recent works support a relation in the local universe steeper than previously thought. Based on comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z similar to 1 for stellar masses M-star greater than or similar to 2 x 10(11) M-circle dot. Specifically, we find significant evidence for a high-mass end slope of beta greater than or similar to 0.35-0.70 instead of the usual beta less than or similar to 0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent Baryon Oscillation Spectroscopic Survey clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (less than or similar to 0.15 dex) in stellar mass at fixed halo mass, in the redshift range z \textless 0.8 and for M-star \textgreater 3 x 10(11) M-circle dot, suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z similar to 1.
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![ALMA [CII] 158 [mu]m Detect...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2041-8205/small "ALMA [CII] 158 [mu]m Detection of a Redshift 7 Lensed Galaxy behind RX J1347.1?1145")
