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The changes in colors across a galaxy are intimately connected to the galaxy's formation, growth, quenching history, and dust content. A particularly important epoch in the growth of galaxies is near $z \sim 2$ often referred to as 'cosmic noon', where galaxies on average reach the peak of their star formation. We study a population of 125 cluster galaxies at $z \sim 1.6$ in three Hubble Space Telescope (HST) filters, F475W, F625W, and F160W, roughly corresponding to the rest-frame FUV, NUV, and r band, respectively. By comparing to a control sample of 200 field galaxies at similar redshift, we reveal clear, statistically significant differences in the overall spatially resolved colors and color gradients in galaxies across these two different environments. On average, cluster galaxies have redder UV colors in both the inner and outer regions bounded by $r_{\mathrm{50}}$, as well as an overall wider dispersion of outside-in color gradients. The presence of these observed differences, along with evidence from ancillary data from previous studies, strongly suggests that the environment drives these population-level color differences, by affecting the stellar populations and/or dust content., Comment: Submitted to ApJ

Intracluster light is thought to originate from stars that were ripped away from their parent galaxies by gravitational tides and galaxy interactions during the build up of the cluster. The stars from such interactions will accumulate over time, so semi-analytic models suggest that the abundance of intracluster stars is negligible in young proto-clusters at z~2 and grows to around a quarter of the stellar mass in the oldest, most mature clusters. In contrast to these theoretical expectations, we report on the detection of intracluster light within two proto-clusters at z=2 using deep HST images. We use the colour of the intracluster light to estimate its mass-to-light ratio in annuli around the brightest cluster galaxies (BCG), up to a radius of 100 kpc. We find that $54\pm5$% and $71\pm3$% of the stellar mass in these regions is located more than 10 kpc away from the BCGs in the two proto-clusters. This low concentration is similar to BCGs in lower redshift clusters, and distinct from other massive proto-cluster galaxies. This suggests that intracluster stars are already present within the core 100 kpc of proto-clusters. We compare these observations to the Hydrangea hydrodynamical galaxy cluster simulations and find that intracluster stars are predicted to be a generic feature of group-sized halos at z=2. These intracluster stars will gradually move further away from the BCG as the proto-cluster assembles into a cluster., Comment: 14 pages, 9 figures, accepted for publication in MNRAS

We present the JWST Cycle 1 53.8hr medium program FRESCO, short for "First Reionization Epoch Spectroscopically Complete Observations". FRESCO covers 62 arcmin$^2$ in each of the two GOODS/CANDELS fields for a total area of 124 arcmin$^2$ exploiting JWST's powerful new grism spectroscopic capabilities at near-infrared wavelengths. By obtaining ~2 hr deep NIRCam/grism observations with the F444W filter, FRESCO yields unprecedented spectra at R~1600 covering 3.8 to 5.0 $\mu$m for most galaxies in the NIRCam field-of-view. This setup enables emission line measurements over most of cosmic history, from strong PAH lines at z~0.2-0.5, to Pa$\alpha$ and Pa$\beta$ at z~1-3, HeI and [SIII] at z~2.5-4.5, H$\alpha$ and [NII] at z~5-6.5, up to [OIII] and H$\beta$ for z~7-9 galaxies, and possibly even [OII] at z~10-12. FRESCO's grism observations provide total line fluxes for accurately estimating galaxy stellar masses and calibrating slit-loss corrections of NIRSpec/MSA spectra in the same field. Additionally, FRESCO results in a mosaic of F182M, F210M, and F444W imaging in the same fields to a depth of ~28.2 mag (5 $\sigma$ in 0.32" diameter apertures). Together with this publication, the v1 imaging mosaics are released as high-level science products via MAST. Here, we describe the overall survey design and the key science goals that can be addressed with FRESCO. We also highlight several, early science results, including: spectroscopic redshifts of Lyman break galaxies that were identified almost 20 years ago, the discovery of broad-line active galactic nuclei at z>4, and resolved Pa$\alpha$ maps of galaxies at z~1.4. These results demonstrate the enormous power for serendipitous discovery of NIRCam/grism observations., Comment: 12 pages, 11 figures; MNRAS in press; for more information on the survey and data releases, see http://jwst-fresco.astro.unige.ch/ and https://archive.stsci.edu/hlsp/fresco

We investigate the resolved kinematics of the molecular gas, as traced by the Atacama Large Millimeter/submillimeter Array in CO (2-1), of 25 cluster member galaxies across three different clusters at a redshift of z similar to 1.6. This is the first large-scale analysis of the molecular gas kinematics of cluster galaxies at this redshift. By separately estimating the rotation curve of the approaching and receding sides of each galaxy via kinematic modeling, we quantify the difference in total circular velocity to characterize the overall kinematic asymmetry of each galaxy. 3/14 of the galaxies in our sample that we are able to model have similar degrees of asymmetry as that observed in galaxies in the field at similar redshift based on observations of mainly ionized gas. However, this leaves 11/14 galaxies in our sample with significantly higher asymmetry, and some of these galaxies have degrees of asymmetry of up to similar to 50 times higher than field galaxies observed at similar redshift. Some of these extreme cases also have one-sided tail-like morphology seen in the molecular gas, supporting a scenario of tidal and/or ram pressure interaction. Such stark differences in the kinematic asymmetry in clusters versus the field suggest the evolutionary influence of dense environments, established as being a major driver of galaxy evolution at low redshift, is also active in the high-redshift universe.

We investigate the resolved kinematics of the molecular gas, as traced by ALMA in CO (2-1), of 25 cluster member galaxies across three different clusters at a redshift of $z\sim1.6$. This is the first large-scale analysis of the molecular gas kinematics of cluster galaxies at this redshift. By separately estimating the rotation curve of the approaching and receding side of each galaxy via kinematic modeling, we quantify the difference in total circular velocity to characterize the overall kinematic asymmetry of each galaxy. 3/14 of the galaxies in our sample that we are able to model have similar degrees of asymmetry as that observed in galaxies in the field at similar redshift. However, this leaved 11/14 galaxies in our sample with significantly higher asymmetry, and some of these galaxies have degrees of asymmetry of up to $\sim$50 times higher than field galaxies observed at similar redshift. Some of these extreme cases also have one-sided tail-like morphology seen in the molecular gas, supporting a scenario of tidal and/or ram pressure interaction. Such stark differences in the kinematic asymmetry in clusters versus the field suggest the evolutionary influence of dense environments, established as being a major driver of galaxy evolution at low-redshift, is also active in the high-redshift universe., Comment: Submission pre-referee report

© 2019. The American Astronomical Society. All rights reserved. We present the first spatially resolved observations of molecular gas in a sample of cluster galaxies beyond z > 0.1. Using ALMA, we detect CO (2-1) in eight z ∼ 1.6 cluster galaxies, all within a single 70″ primary beam. The cluster, SpARCS-J0225, was discovered by the Spitzer Adaptation of the Red-sequence Cluster Survey, and is replete with gas-rich galaxies in close proximity, thus affording an efficient multiplexing strategy to amass the first sample of resolved CO in distant clusters. Mapping out the kinematic structure and morphology of molecular gas on ∼3.5 kpc scales reveals rotating gas disks in the majority of the galaxies, and some kinematic peculiarities, including a central gas void, a merger, and one-sided gas tails. We find that the extent of the molecular gas is slightly smaller than that of the optical HST stellar component; this is even more pronounced in low-redshift Virgo cluster galaxies. However, limited by small sample sizes of spatially resolved CO, we are unable to differentiate the distribution of stellar-to-gas radii between cluster and field environments at high redshift. Thus, at first glance, while the cluster galaxies generally look like galaxies infalling from the field, with typical main-sequence star formation rates and massive molecular gas reservoirs situated in rotating disks, they have potentially remarkable attributes, including elevated gas fractions, slightly smaller CO disks, and asymmetric gas tails. Taken in tandem, these signatures are tentative evidence for gas stripping in the z ∼ 1.6 cluster, though verification of these trends will require larger samples.

© 2019. The American Astronomical Society. All rights reserved. We present the first spatially resolved observations of molecular gas in a sample of cluster galaxies beyond z > 0.1. Using ALMA, we detect CO (2-1) in eight z ∼ 1.6 cluster galaxies, all within a single 70″ primary beam. The cluster, SpARCS-J0225, was discovered by the Spitzer Adaptation of the Red-sequence Cluster Survey, and is replete with gas-rich galaxies in close proximity, thus affording an efficient multiplexing strategy to amass the first sample of resolved CO in distant clusters. Mapping out the kinematic structure and morphology of molecular gas on ∼3.5 kpc scales reveals rotating gas disks in the majority of the galaxies, and some kinematic peculiarities, including a central gas void, a merger, and one-sided gas tails. We find that the extent of the molecular gas is slightly smaller than that of the optical HST stellar component; this is even more pronounced in low-redshift Virgo cluster galaxies. However, limited by small sample sizes of spatially resolved CO, we are unable to differentiate the distribution of stellar-to-gas radii between cluster and field environments at high redshift. Thus, at first glance, while the cluster galaxies generally look like galaxies infalling from the field, with typical main-sequence star formation rates and massive molecular gas reservoirs situated in rotating disks, they have potentially remarkable attributes, including elevated gas fractions, slightly smaller CO disks, and asymmetric gas tails. Taken in tandem, these signatures are tentative evidence for gas stripping in the z ∼ 1.6 cluster, though verification of these trends will require larger samples.

Recent studies show that a universal relation between black-hole (BH) growth and stellar mass ($M_\bigstar$) or star formation rate (SFR) is an oversimplification of BH-galaxy co-evolution, and that morphological and structural properties of host galaxies must also be considered. Particularly, a possible connection between BH growth and host-galaxy compactness was identified among star-forming (SF) galaxies. Utilizing $\approx 6300$ massive galaxies with $I_{\rm 814W}~<~24$ at $z$ $<$ 1.2 in the COSMOS field, we perform systematic partial-correlation analyses to investigate how sample-averaged BH accretion rate ($\rm \overline{BHAR}$) depends on host-galaxy compactness among SF galaxies, when controlling for morphology and $M_\bigstar$ (or SFR). The projected central surface-mass density within 1 kpc, $\Sigma_{1}$, is utilized to represent host-galaxy compactness in our study. We find that the $\rm \overline{BHAR}$-$\Sigma_{1}$ relation is stronger than either the $\rm \overline{BHAR}$-$M_\bigstar$ or $\rm \overline{BHAR}$-SFR relation among SF galaxies, and this $\rm \overline{BHAR}$-$\Sigma_{1}$ relation applies to both bulge-dominated galaxies and galaxies that are not dominated by bulges. This $\rm \overline{BHAR}$-$\Sigma_{1}$ relation among SF galaxies suggests a link between BH growth and the central gas density of host galaxies on the kpc scale, which may further imply a common origin of the gas in the vicinity of the BH and in the central $\sim$ kpc of the galaxy. This $\rm \overline{BHAR}$-$\Sigma_{1}$ relation can also be interpreted as the relation between BH growth and the central velocity dispersion of host galaxies at a given gas content, indicating the role of the host-galaxy potential well in regulating accretion onto the BH., Comment: 21 pages, 21 figures. Accepted for publication in MNRAS

We present the first spatially resolved observations of molecular gas in a sample of cluster galaxies beyond z > 0.1. Using ALMA, we detect CO (2-1) in eight z ∼ 1.6 cluster galaxies, all within a single 70″ primary beam. The cluster, SpARCS-J0225, was discovered by the Spitzer Adaptation of the Red-sequence Cluster Survey, and is replete with gas-rich galaxies in close proximity, thus affording an efficient multiplexing strategy to amass the first sample of resolved CO in distant clusters. Mapping out the kinematic structure and morphology of molecular gas on ∼3.5 kpc scales reveals rotating gas disks in the majority of the galaxies, and some kinematic peculiarities, including a central gas void, a merger, and one-sided gas tails. We find that the extent of the molecular gas is slightly smaller than that of the optical HST stellar component; this is even more pronounced in low-redshift Virgo cluster galaxies. However, limited by small sample sizes of spatially resolved CO, we are unable to differentiate the distribution of stellar-to-gas radii between cluster and field environments at high redshift. Thus, at first glance, while the cluster galaxies generally look like galaxies infalling from the field, with typical main-sequence star formation rates and massive molecular gas reservoirs situated in rotating disks, they have potentially remarkable attributes, including elevated gas fractions, slightly smaller CO disks, and asymmetric gas tails. Taken in tandem, these signatures are tentative evidence for gas stripping in the z ∼ 1.6 cluster, though verification of these trends will require larger samples.

We present the first spatially-resolved observations of molecular gas in a sample of cluster galaxies beyond z>0.1. Using ALMA, we detect CO (2-1) in 8 z~1.6 cluster galaxies, all within a single 70" primary beam, in under 3 hours of integration time. The cluster, SpARCS-J0225, is replete with gas-rich galaxies in close proximity. It thus affords an efficient multiplexing strategy to build up the first sample of resolved CO in distant galaxy clusters. Mapping out the kinematic structure and morphology of the molecular gas on 3.5 kpc scales reveals rotating gas disks in the majority of the galaxies, as evidenced by smooth velocity gradients. Detailed velocity maps also uncover kinematic peculiarities, including a central gas void, a merger, and a few one-sided gas tails. We compare the extent of the molecular gas component to that of the optical stellar component, measured with rest-frame optical HST imaging. We find that the cluster galaxies, while broadly consistent with a ratio of unity for stellar-to-gas effective radii, have a moderately larger ratio compared to the coeval field; this is consistent with the more pronounced trend in the low-redshift Universe. Thus, at first glance, the z~1.6 cluster galaxies generally look like galaxies infalling from the field, with typical main-sequence star formation rates and massive molecular gas reservoirs situated in rotating disks. However, there are potentially important differences from their field counterparts, including elevated gas fractions, slightly smaller CO disks, and possible asymmetric gas tails. Taken in tandem, these signatures are tentative evidence for gas-stripping in the z~1.6 cluster. However, the current sample size of spatially-resolved molecular gas in galaxies at high redshift is small, and verification of these trends will require much larger samples of both cluster and field galaxies., Comment: 11 pages, 5 figures, 1 table; submitted to ApJ