71 research outputs found
Quasars in the 2MASS Second Incremental Data Release
Using the 2MASS Second Incremental Data Release, we have searched for near
infrared counterparts to 13214 quasars from the Veron-Cetty & Veron(2000)
catalog. We have detected counterparts within 4 arcsec for 2277 of the
approximately 6320 quasars within the area covered by the 2MASS Second
Incremental Data Release. Only 1.6% of these are expected to be chance
coincidences. Though this sample is heterogeneous, we find that known
radio-loud quasars are more likely to have large near-infrared-to-optical
luminosity ratios than radio-quiet quasars are, at a statistically significant
level. This is consistent with dust-reddened quasars being more common in
radio-selected samples than in optically-selected samples, due to stronger
selection effects against dust-reddened quasars in the latter. We also find a
statistically significant dearth of optically luminous quasars with large
near-infrared-to-optical luminosity ratios. This can be explained in a dust
obscuration model but not in a model where synchrotron emission extends from
the radio into the near-infrared and creates such large ratios. We also find
that selection of quasar candidates from the B-J/J-K color-color diagram,
modelled on the V-J/J-K selection method of Warren, Hewett & Foltz (2000), is
likely to be more sensitive to dust-obscured quasars than selection using only
infrared-infrared colors.Comment: To be published in May issue of Astronomical Journal (26 pages, 8
figures, 2 tables) Replaced Figure 6 and
The Galaxy Population of Low-Redshift Abell Clusters
We present a study of the luminosity and color properties of galaxies
selected from a sample of 57 low-redshift Abell clusters. We utilize the
non-parametric dwarf-to-giant ratio (DGR) and the blue galaxy fraction (fb) to
investigate the clustercentric radial-dependent changes in the cluster galaxy
population. Composite cluster samples are combined by scaling the counting
radius by r200 to minimize radius selection bias. The separation of galaxies
into a red and blue population was achieved by selecting galaxies relative to
the cluster color-magnitude relation. The DGR of the red and blue galaxies is
found to be independent of cluster richness (Bgc), although the DGR is larger
for the blue population at all measured radii. A decrease in the DGR for the
red and red+blue galaxies is detected in the cluster core region, while the
blue galaxy DGR is nearly independent of radius. The fb is found not to
correlate with Bgc; however, a steady decline toward the inner-cluster region
is observed for the giant galaxies. The dwarf galaxy fb is approximately
constant with clustercentric radius except for the inner cluster core region
where fb decreases. The clustercentric radial dependence of the DGR and the
galaxy blue fraction, indicates that it is unlikely that a simple scenario
based on either pure disruption or pure fading/reddening can describe the
evolution of infalling dwarf galaxies; both outcomes are produced by the
cluster environment.Comment: 28 pages, 6 figures, accepted for publication in Ap
Globular cluster population of the HST frontier fields galaxy J07173724+3744224
We present the first measurement of the globular cluster population
surrounding the elliptical galaxy J07173724+3744224 (z=0.1546). This galaxy is
located in the foreground in the field-of-view of the Hubble Space Telescope
(HST) Frontier Fields observations of galaxy cluster MACS J0717.5+3745
(z=0.5458). Based on deep HST ACS F435W, F606W, and F814W images, we find a
total globular cluster population of N_tot = 3441 +/- 1416. Applying the
appropriate extinction correction and filter transformation from ACS F814W to
the Johnson V-band, we determine that the host galaxy has an absolute magnitude
of M_V = -22.2. The specific frequency was found to be S_N = 4.5 +/- 1.8. The
radial profile of the globular cluster system was best fit using a powerlaw of
the form , with the globular cluster population found to
be more extended than the halo light of the host galaxy (). The F435W-F814W colour distribution suggests a bimodal population,
with red globular clusters 1-3x more abundant than blue clusters. These results
are consistent with the host elliptical galaxy J07173724+3744224 having formed
its red metal-rich GCs in situ, with the blue metal-poor globular clusters
accreted from low-mass galaxies.Comment: 21 pages, 14 figures, 2 tables, revised following peer-review,
accepted for publication in MNRA
Multi-Band Optical and Near-Infrared Properties of Faint Submillimeter Galaxies with Serendipitous ALMA Detections
We present a catalog of 26 faint submillimeter galaxies (SMGs) in the XMM Large Scale Structure (XMM-LSS) field identified by cross-matching serendipitously detected sources in archival pre–Atacama Large Millimeter Array (ALMA) band 6 and 7 data with multiband near-infrared (NIR) and optical data from the Spitzer Extragalactic Representative Volume Survey, the VISTA Deep Extragalactic Survey, the Canada–France–Hawaii Telescope Legacy Large Survey, and the Hyper Suprime-Cam Subaru Strategic Program. Of the 26 SMGs in our sample, 15 are identified here for the first time. The majority of the sources in our sample (16/26) have faint submillimeter fluxes (0.1 mJy \u3c S 1mm \u3c 1 mJy). In addition to the 26 SMGs with multiband optical and NIR detections, there are 60 highly reliable (\u3e5σ) ALMA sources with no counterpart in any other band down to an Infrared Array Camera (IRAC) [4.5] AB magnitude of ≈23.7. To further characterize the 26 galaxies with both ALMA and optical/NIR counterparts, we provide 13-band forced photometry for the entire catalog using the Tractor and calculate photometric redshifts and rest-frame colors. The median redshift of our sample is . We find that our sample galaxies have bluer colors compared to bright SMGs, and the UVJ color plot indicates that their colors are consistent with main-sequence star-forming galaxies. Our results provide new insights into the nature of the faint population of SMGs and also highlight opportunities for galaxy evolution studies based on archival ALMA data
A Parameterized Galaxy Catalog Simulator for Testing Cluster Finding, Mass Estimation, and Photometric Redshift Estimation in Optical and Near-infrared Surveys
We present a galaxy catalog simulator that converts N -body simulations with halo and subhalo catalogs into mock, multiband photometric catalogs. The simulator assigns galaxy properties to each subhalo in a way that reproduces the observed cluster galaxy halo occupation distribution, the radial and mass-dependent variation in fractions of blue galaxies, the luminosity functions in the cluster and the field, and the color-magnitude relation in clusters. Moreover, the evolution of these parameters is tuned to match existing observational constraints. Parameterizing an ensemble of cluster galaxy properties enables us to create mock catalogs with variations in those properties, which in turn allows us to quantify the sensitivity of cluster finding to current observational uncertainties in these properties. Field galaxies are sampled from existing multiband photometric surveys of similar depth. We present an application of the catalog simulator to characterize the selection function and contamination of a galaxy cluster finder that utilizes the cluster red sequence together with galaxy clustering on the sky. We estimate systematic uncertainties in the selection to be at the ≤15% level with current observational constraints on cluster galaxy populations and their evolution. We find the contamination in this cluster finder to be ~35% to redshift z ~ 0.6. In addition, we use the mock galaxy catalogs to test the optical mass indicator B gc and a red-sequence redshift estimator. We measure the intrinsic scatter of the B gc -mass relation to be approximately log normal with ##IMG## [http://ej.iop.org/images/0004-637X/747/1/58/apj417488ieqn1.gif] {\sigma _{\log _{10M\sim 0.25 and we demonstrate photometric redshift accuracies for massive clusters at the ~3% level out to z ~ 0.7.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98548/1/0004-637X_747_1_58.pd
Globular Cluster Population of Hickson Compact Group 22a and 90c
We present the first measurement of the globular cluster populations of
galaxies in Hickson compact groups, in order to investigate the effect of these
high density environments on the formation and evolution of globular cluster
systems. Based on V and R band images that we obtained of HCG 22a and HCG 90c
with the ESO New Technology Telescope (NTT), we find a total globular cluster
population of for HCG 22a and for 90c. The specific
frequency for HCG 22a was found to be and for HCG 90c. A power-law fit to the globular cluster radial profile of HCG
22a yields and for HCG 90c we found . A comparison of the globular cluster radial profiles with
the surface brightness of the parent galaxy shows that the globular cluster
systems are at least as extended as the halo light. The measured values for the
specific frequency are consistent with a scenario in which the host galaxies
were in a low density ``field-like'' environment when they formed their
globular cluster systems.Comment: 28 pages, 13 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Star formation in low-redshift cluster dwarf galaxies
Evolution of galaxies in dense environments can be affected by close encounters with neighbouring galaxies and interactions with the intracluster medium. Dwarf galaxies (dGs) are important as their low mass makes them more susceptible to these effects than giant systems. Combined luminosity functions (LFs) in the r and u band of 15 galaxy clusters were constructed using archival data from the Canada–France–Hawaii Telescope. LFs were measured as a function of clustercentric radius from stacked cluster data. Marginal evidence was found for an increase in the faint-end slope of the u-band LF relative to the r-band with increasing clustercentric radius. The dwarf-to-giant ratio (DGR) was found to increase toward the cluster outskirts, with the u-band DGR increasing faster with clustercentric radius compared to the r-band. The dG blue fraction was found to be ∼2 times larger than the giant galaxy blue fraction over all clustercentric distance (∼5σ level). The central concentration (C) was used as a proxy to distinguish nucleated versus non-nucleated dGs. The ratio of high-C to low-C dGs was found to be ∼2 times greater in the inner cluster region compared to the outskirts (2.8σ level). The faint-end slope of the r-band LF for the cluster outskirts (0.6 ≤ r/r200 \u3c 1.0) is steeper than the Sloan Digital Sky Survey field LF, while the u-band LF is marginally steeper at the 2.5σ level. Decrease in the faint-end slope of the r- and u-band cluster LFs towards the cluster centre is consistent with quenching of star formation via ram pressure stripping and galaxy–galaxy interactions
The Luminosity Function of Low-Redshift Abell Galaxy Clusters
We present the results from a survey of 57 low-redshift Abell galaxy clusters
to study the radial dependence of the luminosity function (LF). The dynamical
radius of each cluster, r200, was estimated from the photometric measurement of
cluster richness, Bgc. The shape of the LFs are found to correlate with radius
such that the faint-end slope, alpha, is generally steeper on the cluster
outskirts. The sum of two Schechter functions provides a more adequate fit to
the composite LFs than a single Schechter function. LFs based on the selection
of red and blue galaxies are bimodal in appearance. The red LFs are generally
flat for -22 < M_Rc < -18, with a radius-dependent steepening of alpha for M_Rc
> -18. The blue LFs contain a larger contribution from faint galaxies than the
red LFs. The blue LFs have a rising faint-end component (alpha ~ -1.7) for M_Rc
> -21, with a weaker dependence on radius than the red LFs. The dispersion of
M* was determined to be 0.31 mag, which is comparable to the median measurement
uncertainty of 0.38 mag. This suggests that the bright-end of the LF is
universal in shape at the 0.3 mag level. We find that M* is not correlated with
cluster richness when using a common dynamical radius. Also, we find that M* is
weakly correlated with BM-type such that later BM-type clusters have a brighter
M*. A correlation between M* and radius was found for the red and blue galaxies
such that M* fades towards the cluster center.Comment: Accepted for publication in ApJ, 16 pages, 4 tables, 24 figure
- …