6,259 research outputs found
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 detection and photometric redshift determination of distant galaxies using SIRTF's Infrared Array Camera
We investigate the ability of the Space Infrared Telescope Facility's
Infrared Array Camera to detect distant (z ~ 3)galaxies and measure their
photometric redshifts. Our analysis shows that changing the original long
wavelength filter specifications provides significant improvements in
performance in this and other areas.Comment: 28 pages incl 12 figures; to appear in June 1999 PASP. Fig.12
replaced with corrected versio
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
Morphologies and Spectral Energy Distributions of Extremely Red Galaxies in the GOODS-South Field
Using U'- through Ks-band imaging data in the GOODS-South field, we construct
a large, complete sample of 275 ``extremely red objects'' (EROs; K_s<22.0,
R-K_s>3.35; AB), all with deep HST/ACS imaging in B_435, V_606, i_775, and
z_850, and well-calibrated photometric redshifts. Quantitative concentration
and asymmetry measurements fail to separate EROs into distinct morphological
classes. We therefore visually classify the morphologies of all EROs into four
broad types: ``Early'' (elliptical-like), ``Late'' (disk galaxies),
``Irregular'' and ``Other'' (chain galaxies and low surface brightness
galaxies), and calculate their relative fractions and comoving space densities.
For a broad range of limiting magnitudes and color thresholds, the relative
number of early-type EROs is approximately constant at 33-44%, and the comoving
space densities of Early- and Late-type EROs are comparable. Mean rest-frame
spectral energy distributions (SEDs) at wavelengths between 0.1 and 1.2 um are
constructed for all EROs. The SEDs are extremely similar in their range of
shapes, independent of morphological type. The implication is that any
differences between the broad-band SEDs of Early-type EROs and the other types
are relatively subtle, and there is no robust way of photometrically
distinguishing between different morphological types with usual
optical/near-infrared photometry.Comment: Submitted to the ApJL. A version with full-resolution figures, all
GOODS data and all GOODS collaboration papers may be found at
http://www.stsci.edu/science/goods
Characterizing the Mid-IR Extragalactic Sky with WISE and SDSS
The Wide-field Infrared Survey Explorer (WISE) has completed its all-sky
survey at 3.4-22 micron. We merge the WISE data with optical SDSS data and
provide a phenomenological characterization of mid-IR, extragalactic sources.
WISE is most sensitive at 3.4micron(W1) and least at 22micron(W4). The W1 band
probes massive early-type galaxies out to z\gtrsim1. This is more distant than
SDSS identified early-type galaxies, consistent with the fact that 28% of
3.4micron sources have faint or no r-band counterparts (r>22.2). In contrast,
92-95% of 12 and 22micron sources have SDSS optical counterparts with r<22.2.
WISE 3.4micron detects 89.8% of the entire SDSS QSO catalog at SNR(W1)>7, but
only 18.9% at 22micron with SNR(W4)>5. We show that WISE colors alone are
effective in isolating stars (or local early-type galaxies), star-forming
galaxies and strong AGN/QSOs at z<3. We highlight three major applications of
WISE colors: (1) Selection of strong AGN/QSOs at z0.8 and
W2<15.2 criteria, producing a census of this population. The surface density of
these strong AGN/QSO candidates is 67.5+-0.14/deg^2. (2) Selection of
dust-obscured, type-2 AGN/QSO candidates. We show that WISE W1-W2>0.8, W2<15.2
combined with r-W2>6 (Vega) colors can be used to identify type-2 AGN
candidates. The fraction of these type-2 AGN candidates is 1/3rd of all WISE
color-selected AGNs. (3) Selection of ULIRGs at z\sim2 with extremely red
colors, r-W4>14 or well-detected 22micron sources lacking detections in the 3.4
and 4.6micron bands. The surface density of z~2 r-W4>14 ULIRGs is
0.9+-0.07/deg^2 at SNR(W4)>5 (flux(W4)>=2.5mJy), which is consistent with that
inferred from smaller area Spitzer surveys. Optical spectroscopy of a small
number of these high-redshift ULIRGs confirms our selection, and reveals a
possible trend that optically fainter or r-W4 redder candidates are at higher
redshifts.Comment: 41 pages, 20 figures, Accepted for publication by the Astronomical
Journa
Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Luminous Infrared Galaxy Candidates
We present Spitzer 3.6 and 4.5 m photometry and positions for a sample
of 1510 brown dwarf candidates identified by the WISE all-sky survey. Of these,
166 have been spectroscopically classified as objects with spectral types M(1),
L(7), T(146), and Y(12); Sixteen other objects are non-(sub)stellar in nature.
The remainder are most likely distant L and T dwarfs lacking spectroscopic
verification, other Y dwarf candidates still awaiting follow-up, and assorted
other objects whose Spitzer photometry reveals them to be background sources.
We present a catalog of Spitzer photometry for all astrophysical sources
identified in these fields and use this catalog to identify 7 fainter (4.5
m 17.0 mag) brown dwarf candidates, which are possibly wide-field
companions to the original WISE sources. To test this hypothesis, we use a
sample of 919 Spitzer observations around WISE-selected high-redshift
hyper-luminous infrared galaxy (HyLIRG) candidates. For this control sample we
find another 6 brown dwarf candidates, suggesting that the 7 companion
candidates are not physically associated. In fact, only one of these 7 Spitzer
brown dwarf candidates has a photometric distance estimate consistent with
being a companion to the WISE brown dwarf candidate. Other than this there is
no evidence for any widely separated ( 20 AU) ultra-cool binaries. As an
adjunct to this paper, we make available a source catalog of 7.33
objects detected in all of these Spitzer follow-up fields for use
by the astronomical community. The complete catalog includes the Spitzer 3.6
and 4.5 m photometry, along with positionally matched and
photometry from USNO-B; , , and photometry from 2MASS; and ,
, , and photometry from the WISE all-sky catalog
The Exemplar T8 Subdwarf Companion of Wolf 1130
We have discovered a wide separation (188.5") T8 subdwarf companion to the
sdM1.5+WD binary Wolf 1130. Companionship of WISE J200520.38+542433.9 is
verified through common proper motion over a ~3 year baseline. Wolf 1130 is
located 15.83 +/- 0.96 parsecs from the Sun, placing the brown dwarf at a
projected separation of ~3000 AU. Near-infrared colors and medium resolution
(R~2000-4000) spectroscopy establish the uniqueness of this system as a
high-gravity, low-metallicity benchmark. Although there are a number of
low-metallicity T dwarfs in the literature, WISE J200520.38+542433.9 has the
most extreme inferred metallicity to date with [Fe/H] = -0.64 +/- 0.17 based on
Wolf 1130. Model comparisons to this exemplar late-type subdwarf support it
having an old age, a low metallicity, and a small radius. However, the
spectroscopic peculiarities of WISE J200520.38+542433.9 underscore the
importance of developing the low-metallicity parameter space of the most
current atmospheric models.Comment: Accepted to ApJ on 05 September 2013; 33 pages in preprint format, 8
figures, 3 table
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