6,429 research outputs found
EVOLUTION OF IR-SELECTED GALAXIES IN Z~0.4 CLUSTERS
Wide-field optical and near--IR () imaging is presented for two rich
galaxy clusters: Abell~370 at and Abell~851 (Cl0939+47) at .
Galaxy catalogs selected from the near--IR images are 90\% complete to
approximately 1.5 mag below resulting in samples with 100
probable member galaxies per cluster in the central 2 Mpc. Comparison
with WFPC images yields subsamples of 70 galaxies in each cluster
with morphological types. Analysis of the complete samples and the
subsamples shows that the E/S0s are bluer than those in the Bower
et al.\ (1992) Coma sample in the optical color by ~mag for Abell~370
and by ~mag for Abell~851. If real, the bluing of the E/S0 populations at
moderate redshift is consistent with that calculated from the Bruzual and
Charlot (1993) models of passive elliptical galaxy evolution. In both clusters
the intrinsic scatter of the known E/S0s about their optical color--mag
relation is small ( mag) and not significantly different from that
of Coma E/S0s as given by Bower et al.\ (1992), indicating that the galaxies
within each cluster formed at the same time at an early epoch.Comment: uuencoded gzipped tar file containing latex files of manuscript (42
pages) plus tables (9 pages); figures available by anonymous ftp at
ftp://ipac.caltech.edu//pub/pickup/sed ; accepted for publication in the Ap
Distant radio galaxies in the near IR
We are carrying out a program of near IR imaging and spectroscopy of radio galaxies with redshifts of 1.5 and greater. One of its principal goals is to constrain the ages and star formation histories of massive galaxies at early epochs. The radio galaxies are drawn from the survey of 1Jy class sources by McCarthy et al (1989) and McCarthy (1990). The sample contains 18 radio galaxies with redshifts greater than 2 and an additional 10 objects with 1.5 less than z less than 2.0. The redshifts were obtained from long slit spectra with the CTIO 4 m. While the galaxies are quite faint (r approximately = 21-24.5) all have Lyman alpha emission with rest frame equivalent widths of 100 - 1000 A. Multicolor photometry in the g,r,i and J,H,K bands has been obtained with the 2.5-m Du Pont Telescope on Las Campanas and with the Hale 5 m telescope at Palomar. We have recently obtained near IR spectra, using the 4 m telescopes at KPNO and CTIO, of a few objects with the goal of determining the Lyman alpha/H-alpha ratio and hence the reddening
Near-IR imaging of moderate redshift galaxy clusters
We have obtained near-IR imaging of 3 moderate-z clusters on the 1.3 m at KPNO with SQIID, a new camera offering wide-field (5.5 arcmin) simultaneous JHK band imaging. Our photometry on a sample of approximately 100 likely member galaxies in one of the clusters, Abell 370 at z = 0.37, shows that we can obtain magnitudes good to 20 percent down to K = 18, considerably below the estimated K* = 16.5 at this redshift. These data indicate that there are no systematic problems in obtaining photometry at faint levels with SQIID. With the development of larger arrays, the field is open to progress. The resulting J, H, and K data for three clusters are combined with previously obtained multiband optical photometry. We present an investigation of the spectral properties and evolution of the dominant cold stellar populations by comparing optical-to-IR colors and color-magnitude diagrams to predictions from population synthesis models and galaxy spectral evolution codes
The WISE AGN Catalog
We present two large catalogs of AGN candidates identified across ~75% of the
sky from the Wide-field Infrared Survey Explorer's AllWISE Data Release. Both
catalogs, some of the largest such catalogs published to date, are selected
purely on the basis of mid-IR photometry in the WISE W1 and W2 bands. The
catalogs are designed to be appropriate for a broad range of scientific
investigations, with one catalog emphasizing reliability while the other
emphasizes completeness. Specifically, the R90 catalog consists of 4,543,530
AGN candidates with 90% reliability, while the C75 catalog consists of
20,907,127 AGN candidates with 75% completeness. We provide a detailed
discussion of potential artifacts, and excise portions of the sky close to the
Galactic Center, Galactic Plane, nearby galaxies, and other expected
contaminating sources. Our final catalogs cover 30,093 deg^2 of extragalactic
sky. These catalogs are expected to enable a broad range of science, and we
present a few simple illustrative cases. From the R90 sample we identify 45
highly variable AGN lacking radio counterparts in the FIRST survey, implying
they are unlikely to be blazars. One of these sources, WISEA
J142846.71+172353.1, is a mid-IR-identified changing-look quasar at z=0.104. We
characterize our catalogs by comparing them to large, wide-area AGN catalogs in
the literature, specifically UV-to-near-IR quasar selections from SDSS and
XDQSOz, mid-IR selection from Secrest et al. (2015) and X-ray selection from
ROSAT. From the latter work, we identify four ROSAT X-ray sources that each are
matched to three WISE-selected AGN in the R90 sample within 30". Palomar
spectroscopy reveals one of these systems, 2RXS J150158.6+691029, to consist of
a triplet of quasars at z=1.133 +/- 0.004, suggestive of a rich group or
forming galaxy cluster.(Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplements.
Updated with comments from the referee. 20 pages, 15 figures, 8 tables. The
WISE AGN Catalogs can be made available upon request by writing to
[email protected]
High sensitivity operation of discrete solid state detectors at 4 K
Techniques are described to allow operation of discrete, solid state detectors at 4 K with optimized JFET amplifiers. Three detector types cover the 0.6 to 4 mm spectral range with NEP approximately equal to 10 to the 16th power Hz (-1/2) for two of the types and potential improvement to this performance for the third. Lower NEP's are anticipated at longer infrared wavelengths
Thermal Model Calibration for Minor Planets Observed with Wide-Field Infrared Survey Explorer/Neowise
With the Wide-field Infrared Survey Explorer (WISE), we have observed over 157,000 minor planets. Included in these are a number of near-Earth objects, main-belt asteroids, and irregular satellites which have well measured physical properties (via radar studies and in situ imaging) such as diameters. We have used these objects to validate models of thermal emission and reflected sunlight using the WISE measurements, as well as the color corrections derived in Wright et al. for the four WISE bandpasses as a function of effective temperature. We have used 50 objects with diameters measured by radar or in situ imaging to characterize the systematic errors implicit in using the WISE data with a faceted spherical near-Earth asteroid thermal model (NEATM) to compute diameters and albedos. By using the previously measured diameters and H magnitudes with a spherical NEATM model, we compute the predicted fluxes (after applying the color corrections given in Wright et al.) in each of the four WISE bands and compare them to the measured magnitudes. We find minimum systematic flux errors of 5%-10%, and hence minimum relative diameter and albedo errors of ~10% and ~20%, respectively. Additionally, visible albedos for the objects are computed and compared to the albedos at 3.4 μm and 4.6 μm, which contain a combination of reflected sunlight and thermal emission for most minor planets observed by WISE. Finally, we derive a linear relationship between subsolar temperature and effective temperature, which allows the color corrections given in Wright et al. to be used for minor planets by computing only subsolar temperature instead of a faceted thermophysical model. The thermal models derived in this paper are not intended to supplant previous measurements made using radar or spacecraft imaging; rather, we have used them to characterize the errors that should be expected when computing diameters and albedos of minor planets observed by WISE using a spherical NEATM model
The Galaxy Population of Cluster RXJ0848+4453 at z=1.27
We present a study of the galaxy population in the cluster RXJ0848+4453 at
z=1.27, using deep HST NICMOS and WFPC2 images. We morphologically classify all
galaxies to K_s=20.6 that are covered by the HST imaging, and determine
photometric redshifts using deep ground based BRIzJK_s photometry. Of 22 likely
cluster members with morphological classifications, eleven (50%) are classified
as early-type galaxies, nine (41%) as spiral galaxies, and two (9%) as
``merger/peculiar''. At HST resolution the second brightest cluster galaxy is
resolved into a spectacular merger between three red galaxies of similar
luminosity, separated from each other by ~6 kpc, with an integrated magnitude
K=17.6 (~3 L* at z=1.27). The two most luminous early-type galaxies also show
evidence for recent or ongoing interactions. Mergers and interactions between
galaxies are possible because RXJ0848+4453 is not yet relaxed. The fraction of
early-type galaxies in our sample is similar to that in clusters at 0.5<z<1,
and consistent with a gradual decrease of the number of early-type galaxies in
clusters from z=0 to z=1.3. We find evidence that the color-magnitude relation
of the early-type galaxies is less steep than in the nearby Coma cluster. This
may indicate that the brightest early-type galaxies have young stellar
populations at z=1.27, but is also consistent with predictions of single age
``monolithic'' models with a galactic wind. The scatter in the color-magnitude
relation is ~0.04 in rest frame U-V, similar to that in clusters at 0<z<1.
Taken together, these results show that luminous early-type galaxies exist in
clusters at z~1.3, but that their number density may be smaller than in the
local Universe. Additional observations are needed to determine whether the
brightest early-type galaxies harbor young stellar populations.Comment: Accepted for publication in The Astrophysical Journal Letter
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