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Register a new userK-CLASH: spatially-resolving star-forming galaxies in field and cluster environments at $z approx 0.2$-$0.6$
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Alfred L. Tiley
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We present the KMOS-CLASH (K-CLASH) survey, a K-band Multi-Object Spectrograph (KMOS) survey of the spatially-resolved gas properties and kinematics of 191 (predominantly blue) H$alpha$-detected galaxies at $0.2 lesssim z lesssim 0.6$ in field and cluster environments. K-CLASH targets galaxies in four Cluster Lensing And Supernova survey with Hubble (CLASH) fields in the KMOS $IZ$-band, over $7$ radius ($approx2$-$3$ Mpc) fields-of-view. K-CLASH aims to study the transition of star-forming galaxies from turbulent, highly star-forming disc-like and peculiar systems at $zapprox1$-$3$, to the comparatively quiescent, ordered late-type galaxies at $zapprox0$, and to examine the role of clusters in the build-up of the red sequence since $zapprox1$. In this paper, we describe the K-CLASH survey, present the sample, and provide an overview of the K-CLASH galaxy properties. We demonstrate that our sample comprises star-forming galaxies typical of their stellar masses and epochs, residing both in field and cluster environments. We conclude K-CLASH provides an ideal sample to bridge the gap between existing large integral-field spectroscopy surveys at higher and lower redshifts. We find that star-forming K-CLASH cluster galaxies at intermediate redshifts have systematically lower stellar masses than their star-forming counterparts in the field, hinting at possible downsizing scenarios of galaxy growth in clusters at these epochs. We measure no difference between the star-formation rates of H$alpha$-detected, star-forming galaxies in either environment after accounting for stellar mass, suggesting that cluster quenching occurs very rapidly during the epochs probed by K-CLASH, or that star-forming K-CLASH galaxies in clusters have only recently arrived there, with insufficient time elapsed for quenching to have occured.
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Galaxy clusters have long been theorised to quench the star-formation of their members. This study uses integral-field unit observations from the $K$-band Multi-Object Spectrograph (KMOS) - Cluster Lensing And Supernova survey with Hubble (CLASH) survey (K-CLASH) to search for evidence of quenching in massive galaxy clusters at redshifts $0.3<z<0.6$. We first construct mass-matched samples of exclusively star-forming cluster and field galaxies, then investigate the spatial extent of their H$alpha$ emission and study their interstellar medium conditions using emission line ratios. The average ratio of H$alpha$ half-light radius to optical half-light radius ($r_{rm{e},rm{H}alpha}/r_{rm{e},R_c}$) for all galaxies is $1.14pm0.06$, showing that star formation is taking place throughout stellar discs at these redshifts. However, on average, cluster galaxies have a smaller $r_{rm{e},rm{H}alpha}/r_{rm{e},R_c}$ ratio than field galaxies: $langle r_{rm{e},rm{H}alpha}/r_{rm{e},R_c}rangle = 0.96pm0.09$ compared to $1.22pm0.08$ (smaller at a 98% credibility level). These values are uncorrected for the wavelength difference between H$alpha$ emission and $R_c$-band stellar light, but implementing such a correction only reinforces our results. We also show that whilst the cluster and field samples follow indistinguishable mass-metallicity (MZ) relations, the residuals around the MZ relation of cluster members correlate with cluster-centric distance; galaxies residing closer to the cluster centre tend to have enhanced metallicities (significant at the 2.6$sigma$ level). Finally, in contrast to previous studies, we find no significant differences in electron number density between the cluster and field galaxies. We use simple chemical evolution models to conclude that the effects of disc strangulation and ram-pressure stripping can quantitatively explain our observations.
We report a Giant Metrewave Radio Telescope (GMRT) search for HI 21cm emission from a large sample of star-forming galaxies at $z approx 1.18 - 1.34$, lying in sub-fields of the DEEP2 Redshift Survey. The search was carried out by co-adding (stacking) the HI 21cm emission spectra of 857 galaxies, after shifting each galaxys HI 21cm spectrum to its rest frame. We obtain the $3sigma$ upper limit S$_{rm{HI}} < 2.5 mu$Jy on the average HI 21cm flux density of the 857 galaxies, at a velocity resolution of $approx 315$ km s$^{-1}$. This yields the $3sigma$ constraint M$_{rm{HI}} < 2.1 times 10^{10} times left[Delta {rm V}/315 rm{km/s} right]^{1/2} textrm{M}_odot$ on the average HI mass of the 857 stacked galaxies, the first direct constraint on the atomic gas mass of galaxies at $z > 1$. The implied limit on the average atomic gas mass fraction (relative to stars) is ${rm M}_{rm GAS}/{rm M}_* < 0.5$, comparable to the cold molecular gas mass fraction in similar star-forming galaxies at these redshifts. We find that the cosmological mass density of neutral atomic gas in massive star-forming galaxies at $z approx 1.3$ is $Omega_{rm GAS} < 3.7 times 10^{-4}$, significantly lower than $Omega_{rm GAS}$ estimates in both galaxies in the local Universe and damped Lyman-$alpha$ absorbers at $z geq 2.2$. Massive blue star-forming galaxies thus do not appear to dominate the neutral atomic gas content of the Universe at $z approx 1.3$.
We present near-infrared and optical spectroscopic observations of a sample of 450$mu$m and 850$mu$m-selected dusty star-forming galaxies (DSFGs) identified in a 400 arcmin$^2$ area in the COSMOS field. Thirty-one sources of the 102 targets were spectroscopically confirmed at $0.2<z<4$, identified primarily in the near-infrared with Keck MOSFIRE and some in the optical with Keck LRIS and DEIMOS. The low rate of confirmation is attributable both to high rest-frame optical obscuration in our targets and limited sensitivity to certain redshift ranges. The high-quality photometric redshifts available in the COSMOS field allow us to test the robustness of photometric redshifts for DSFGs. We find a subset (11/31$approx35$%) of DSFGs with inaccurate ($Delta z/(1+z)>0.2$) or non-existent photometric redshifts; these have very distinct spectral energy distributions from the remaining DSFGs, suggesting a decoupling of highly obscured and unobscured components. We present a composite rest-frame 4300--7300AA spectrum for DSFGs, and find evidence of 200$pm$30 km s$^{-1}$ gas outflows. Nebular line emission for a sub-sample of our detections indicate that hard ionizing radiation fields are ubiquitous in high-z DSFGs, even more so than typical mass or UV-selected high-z galaxies. We also confirm the extreme level of dust obscuration in DSFGs, measuring very high Balmer decrements, and very high ratios of IR to UV and IR to H$alpha$ luminosities. This work demonstrates the need to broaden the use of wide bandwidth technology in the millimeter to the spectroscopic confirmations of large samples of high-z DSFGs, as the difficulty in confirming such sources at optical/near-infrared wavelengths is exceedingly challenging given their obscuration.
We report on the gas-phase metallicity gradients of a sample of 264 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12-orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lya Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies (84%) in this sample are consistent with a zero or slightly positive metallicity gradient across the full mass range probed (8.5 < log M_*/M_sun < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass---consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider---including star-formation rates, sizes, star-formation rate surface densities, and star-formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.
We utilize 16 band Hubble Space Telescope (HST) observations of 18 lensing clusters obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program to search for $zsim6-8$ galaxies. We report the discovery of 204, 45, and 13 Lyman-break galaxy candidates at $zsim6$, $zsim7$, and $zsim8$, respectively, identified from purely photometric redshift selections. This large sample, representing nearly an order of magnitude increase in the number of magnified star-forming galaxies at $zsim 6-8$ presented to date, is unique in that we have observations in four WFC3/UVIS UV, seven ACS/WFC optical, and all five WFC3/IR broadband filters, which enable very accurate photometric redshift selections. We construct detailed lensing models for 17 of the 18 clusters to estimate object magnifications and to identify two new multiply lensed $z gtrsim 6$ candidates. The median magnifications over the 17 clusters are 4, 4, and 5 for the $zsim6$, $zsim7$, and $zsim8$ samples, respectively, over an average area of 4.5 arcmin$^2$ per cluster. We compare our observed number counts with expectations based on convolving blank field UV luminosity functions through our cluster lens models and find rough agreement down to $sim27$ mag, where we begin to suffer significant incompleteness. In all three redshift bins, we find a higher number density at brighter observed magnitudes than the field predictions, empirically demonstrating for the first time the enhanced efficiency of lensing clusters over field surveys. Our number counts also are in general agreement with the lensed expectations from the cluster models, especially at $zsim6$, where we have the best statistics.
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