Examinando por Autor "Webb, T.M.A."

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    ALMA Observations of Gas-rich Galaxies in z ~ 1.6 Galaxy Clusters: Evidence for Higher Gas Fractions in High-density Environments
    (Institute of Physics Publishing, 2017-06) Noble, A.G.; McDonald, M.; Muzzin, A.; Nantais, J.; Rudnick, G.; Van Kampen, E.; Webb, T.M.A.; Wilson, G.; Yee, H.K.C.; Boone, K.; Cooper, M.C.; DeGroot, A.; Delahaye, A.; Demarco, R.; Foltz, R.; Hayden, B.; Lidman, C.; Manilla-Robles, A.; Perlmutter, S.
    We present ALMA CO (2-1) detections in 11 gas-rich cluster galaxies at z ∼ 1.6, constituting the largest sample of molecular gas measurements in z > 1.5 clusters to date. The observations span three galaxy clusters, derived from the Spitzer Adaptation of the Red-sequence Cluster Survey. We augment the >5σ detections of the CO (2-1) fluxes with multi-band photometry, yielding stellar masses and infrared-derived star formation rates, to place some of the first constraints on molecular gas properties in z ∼ 1.6 cluster environments. We measure sizable gas reservoirs of 0.5-2 × 1011 M in these objects, with high gas fractions (f gas) and long depletion timescales (τ), averaging 62% and 1.4 Gyr, respectively. We compare our cluster galaxies to the scaling relations of the coeval field, in the context of how gas fractions and depletion timescales vary with respect to the star-forming main sequence. We find that our cluster galaxies lie systematically off the field scaling relations at z = 1.6 toward enhanced gas fractions, at a level of ∼4σ, but have consistent depletion timescales. Exploiting CO detections in lower-redshift clusters from the literature, we investigate the evolution of the gas fraction in cluster galaxies, finding it to mimic the strong rise with redshift in the field. We emphasize the utility of detecting abundant gas-rich galaxies in high-redshift clusters, deeming them as crucial laboratories for future statistical studies.
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    Galaxy Merger Candidates in High-redshift Cluster Environments
    (Institute of Physics Publishing, 2017-07) Delahaye, A.G.; Webb, T.M.A.; Nantais, J.; Degroot, A.; Wilson, G.; Muzzin, A.; Yee, H.K.C.; Foltz, R.; Noble, A.G.; Demarco, R.; Tudorica, A.; Cooper, M.C.; Lidman, C.; Perlmutter, S.; Hayden, B.; Boone, K.; Surace, J.
    We compile a sample of spectroscopically and photometrically selected cluster galaxies from four high-redshift galaxy clusters (1.59 < z < 1.71) from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), and a comparison field sample selected from the UKIDSS Deep Survey. Using near-infrared imaging from the Hubble Space Telescope, we classify potential mergers involving massive (M∗ ≥ 3 × 1010M⊙) cluster members by eye, based on morphological properties such as tidal distortions, double nuclei, and projected near neighbors within 20 kpc. With a catalog of 23 spectroscopic and 32 photometric massive cluster members across the four clusters and 65 spectroscopic and 26 photometric comparable field galaxies, we find that after taking into account contamination from interlopers, 11+7.0-5.6% of the cluster members are involved in potential mergers, compared to 24.7+5.3-4.6% of the field galaxies. We see no evidence of merger enhancement in the central cluster environment with respect to the field, suggesting that galaxy-galaxy merging is not a stronger source of galaxy evolution in cluster environments compared to the field at these redshifts.
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    Ítem
    Resolving CO (2-1) in z ∼ 1.6 Gas-rich Cluster Galaxies with ALMA: Rotating Molecular Gas Disks with Possible Signatures of Gas Stripping
    (Astrophysical Journal, 2019-01-10) Noble, A.G.; Muzzin, A.; McDonald, M.; Rudnick, G.; Matharu, J.; Cooper, M.C.; Demarco, R.; Lidman, C.; Nantais, J.; Van Kampen, E.; Webb, T.M.A.; Wilson, G.; Yee, H.K.C.
    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.