278 research outputs found
The Evolution of Dusty Star Formation and Stellar Mass Assembly in Clusters: Results from the IRAC 3.6, 4.5, 5.8, and 8.0 ÎŒm Cluster Luminosity Functions
We present a catalog of 99 candidate clusters and groups of galaxies in the redshift range 0.1 1.5). Using the 3.6 ÎŒm LF as a proxy for stellar luminosity, we remove this component from the MIR (5.8 and 8.0 ÎŒm ) cluster LFs and measure the LF of dusty star formation/AGNs in clusters. We find that at z 0.4, an additional population of dusty starburst galaxies is required to properly model the 8.0 ÎŒm LFs. Comparison to field studies at similar redshifts shows a strong differential evolution in the field and cluster 8.0 ÎŒm LFs with redshift. At z ~ 0.65 8.0 ÎŒm -detected galaxies are more abundant in clusters compared to the field, but thereafter the number of 8.0 ÎŒm sources in clusters declines with decreasing redshift, and by z ~ 0.15, clusters are underdense relative to the field by a factor of ~5. The rapid differential evolution between the cluster and field LFs is qualitatively consistent with recent field galaxy studies that show that the star formation rates of galaxies in high-density environments are larger than those in low-density environments at higher redshift
BAFFLES: Bayesian Ages for Field Lower-mass Stars
Funding: R.D. acknowledges support from the Fonds de Recherche du QuĂ©bec. Supported by NSF grants AST-1411868 (E.L.N., B.M.), and AST-1518332 (R.J.D.R.). Supported by NASA grants NNX14AJ80G (E.L.N., B.M.), NNX15AC89G and NNX15AD95G (B.M., R.J.D.R.), 80NSSC17K0535 (B.M., E.L.N., R.J.D.R), and NASA Hubble Fellowship grant HST-HF2-51405.001-A (I.C.).Age is a fundamental parameter of stars, yet in many cases, ages of individual stars are presented without robust estimates of the uncertainty. We have developed a Bayesian framework, BAFFLES, to produce the age posterior for a star from its calcium emission strength (log(RâČHK)) or lithium abundance (Li EW) and B â V color. We empirically determine the likelihood functions for calcium and lithium as functions of age from literature measurements of stars in benchmark clusters with well-determined ages. We use a uniform prior on age, which reflects a uniform star formation rate. The age posteriors we derive for several test cases are consistent with literature ages found from other methods. BAFFLES represents a robust method to determine the age posterior probability distribution for any field star with 0.45 †B â V †0.9 and a measurement of RâČHK and/or 0.35 †B â V †1.9 and measured Li EW. We compile colors, RâČHK, and Li EW from over 2630 nearby field stars from the literature, and present the derived BAFFLES age posterior for each star.PostprintPeer reviewe
Cosmic Chronometers: Constraining the Equation of State of Dark Energy. II. A Spectroscopic Catalog of Red Galaxies in Galaxy Clusters
We present a spectroscopic catalog of (mostly) red galaxies in 24 galaxy
clusters in the redshift range 0.17 < z < 0.92 obtained with the LRIS
instrument on the Keck I telescope. Here we describe the observations and the
galaxy spectra, including the discovery of three cD galaxies with LINER
emission spectra, and the spectroscopic discovery of four new galaxy-galaxy
lenses in cluster environments.Comment: Submitted to ApJ
Star Formation and AGN Activity in Galaxy Clusters from : a Multi-wavelength Analysis Featuring /PACS
We present a detailed, multi-wavelength study of star formation (SF) and AGN
activity in 11 near-infrared (IR) selected, spectroscopically confirmed,
massive () galaxy clusters at . Using
new, deep /PACS imaging, we characterize the optical to far-IR
spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding
that they can, on average, be well described by field galaxy templates.
Identification and decomposition of AGN through SED fittings allows us to
include the contribution to cluster SF from AGN host galaxies. We quantify the
star-forming fraction, dust-obscured SF rates (SFRs), and specific-SFRs for
cluster galaxies as a function of cluster-centric radius and redshift. In good
agreement with previous studies, we find that SF in cluster galaxies at
is largely consistent with field galaxies at similar epochs,
indicating an era before significant quenching in the cluster cores
(Mpc). This is followed by a transition to lower SF activity as
environmental quenching dominates by . Enhanced SFRs are found in lower
mass () cluster galaxies. We
find significant variation in SF from cluster-to-cluster within our uniformly
selected sample, indicating that caution should be taken when evaluating
individual clusters. We examine AGN in clusters from , finding an
excess AGN fraction at , suggesting environmental triggering of AGN
during this epoch. We argue that our results a transition from field-like
to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and
excess AGN are consistent with a co-evolution between SF and AGN in
clusters and an increased merger rate in massive haloes at high redshift.Comment: 26 pages, 14 figures, 6 tables with appendix, accepted for
publication in the Astrophysical Journa
The XMM Cluster Survey: The Dynamical State of XMMXCS J2215.9-1738 at z=1.457
We present new spectroscopic observations of the most distant X-ray selected
galaxy cluster currently known, XMMXCS J2215.9-1738 at z=1.457, obtained with
the DEIMOS instrument at the W. M. Keck Observatory, and the FORS2 instrument
on the ESO Very Large Telescope. Within the cluster virial radius, as estimated
from the cluster X-ray properties, we increase the number of known
spectroscopic cluster members to 17 objects, and calculate the line of sight
velocity dispersion of the cluster to be 580+/-140 km/s. We find mild evidence
that the velocity distribution of galaxies within the virial radius deviates
from a single Gaussian. We show that the properties of J2215.9-1738 are
inconsistent with self-similar evolution of local X-ray scaling relations,
finding that the cluster is underluminous given its X-ray temperature, and that
the intracluster medium contains ~2-3 times the kinetic energy per unit mass of
the cluster galaxies. These results can perhaps be explained if the cluster is
observed in the aftermath of an off-axis merger. Alternatively, heating of the
intracluster medium through supernovae and/or Active Galactic Nuclei activity,
as is required to explain the observed slope of the local X-ray
luminosity-temperature relation, may be responsible.Comment: 13 pages, 6 figures, accepted for publication in Ap
Adaptive Optics Imaging Survey of Luminous Infrared Galaxies
We present high resolution imaging observations of a sample of previously
unidentified far-infrared galaxies at z < 0.3. The objects were selected by
cross-correlating the IRAS Faint Source Catalog with the VLA FIRST catalog and
the HST Guide Star Catalog to allow for adaptive optics observations. We found
two new ULIGs (with L_FIR equal to or greater than 10^{12} L_sun) and 19 new
LIGs (with L_FIR equal to or greater than 10^{11} L_sun). Twenty of the
galaxies in the sample were imaged with either the Lick or Keck adaptive optics
systems in H or K'. Galaxy morphologies were determined using the two
dimensional fitting program GALFIT and the residuals examined to look for
interesting structure. The morphologies reveal that at least 30% are involved
in tidal interactions, with 20% being clear mergers. An additional 50% show
signs of possible interaction. Line ratios were used to determine powering
mechanism; of the 17 objects in the sample showing clear emission lines - four
are active galactic nuclei and seven are starburst galaxies. The rest exhibit a
combination of both phenomena.Comment: 29 pages, 8 figures, accepted for publication in A
Giant Lya nebulae associated with high redshift radio galaxies
We report deep Keck narrow-band Lya images of the luminous z > 3 radio
galaxies 4C 41.17, 4C 60.07, and B2 0902+34. The images show giant, 100-200 kpc
scale emission line nebulae, centered on these galaxies, which exhibit a wealth
of morphological structure, including extended low surface brightness emission
in the outer regions, radially directed filaments, cone-shaped structures and
(indirect) evidence for extended Lya absorption. We discuss these features
within a general scenario where the nebular gas cools gravitationally in large
Cold Dark Matter (CDM) halos, forming stars and multiple stellar systems.
Merging of these ``building'' blocks triggers large scale starbursts, forming
the stellar bulges of massive radio galaxy hosts, and feeds super-massive black
holes which produce the powerful radio jets and lobes. The radio sources,
starburst superwinds and AGN radiation then disrupt the accretion process
limiting galaxy and black hole growth, and imprint the observed filamentary and
cone-shaped structures of the Lya nebulae.Comment: 36 Pages, including 8 Postscript figures. Accepted for publication in
the Astrophysical Journa
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