6,772 research outputs found
Spitzer Constraints on the z=6.56 Galaxy Lensed by Abell 370
We report on Spitzer IRAC observations of the spectroscopically confirmed
z=6.56 lensed Ly-alpha emitting source HCM 6A which was found behind the
cluster Abell 370. Detection of the source at 3.6 and 4.5 microns,
corresponding to rest-frame optical emission, allows us to study the stellar
population of this primeval galaxy. The broadband flux density at 4.5 microns
is enhanced compared to the continuum at other wavelengths, likely due to the
presence of strong H-alpha in emission. The derived H-alpha line flux
corresponds to a star-formation rate of around 140 M_{sun}/yr, more than an
order of magnitude larger than estimates from the ultraviolet continuum and
Ly-alpha emission line. The dust extinction required to explain the discrepancy
is A_V of about 1 mag. The inference of dust at such high redshifts is
surprising and implies that the first epoch of star-formation in this galaxy
occurred at z~20.Comment: 11 pages, 3 figures, ApJ Letters in pres
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
The Formation of Massive Cluster Galaxies
We present composite 3.6 and 4.5 micron luminosity functions for cluster
galaxies measured from the Spitzer Deep, Wide-Field Survey (SDWFS) for 0.3<z<2.
We compare the evolution of m* for these luminosity functions to models for
passively evolving stellar populations to constrain the primary epoch of star
formation in massive cluster galaxies. At low redshifts (z < 1.3) our results
agree well with models with no mass assembly and passively evolving stellar
populations with a luminosity-weighted mean formation redshift zf=2.4 assuming
a Kroupa initial mass function (IMF). We conduct a thorough investigation of
systematic biases that might influence our results, and estimate systematic
uncertainites of Delta zf=(+0.16-0.18) (model normalization), Delta
zf=(+0.40-0.05) (alpha), and Delta zf=(+0.30-0.45) (choice of stellar
population model). For a Salpeter type IMF, the typical formation epoch is thus
strongly constrained to be z ~2-3. Higher formation redshifts can only be made
consistent with the data if one permits an evolving IMF that is bottom-light at
high redshift, as suggested by van Dokkum et al 2008. At high redshift (z >
1.3) we also witness a statistically significant (>5sigma) disagreement between
the measured luminosity function and the continuation of the passive evolution
model from lower redshifts. After considering potential systematic biases that
might influence our highest redshift data points, we interpret the observed
deviation as potential evidence for ongoing mass assembly at this epoch.Comment: 17 pages, 14 figures, accepted for publication in Ap
WISE Brown Dwarf Binaries: The Discovery of a T5+T5 and a T8.5+T9 System
The multiplicity properties of brown dwarfs are critical empirical constraints for formation theories, while multiples themselves provide unique opportunities to test evolutionary and atmospheric models and examine empirical trends. Studies using high-resolution imaging cannot only uncover faint companions, but they can also be used to determine dynamical masses through long-term monitoring of binary systems. We have begun a search for the coolest brown dwarfs using preliminary processing of data from the Wide-field Infrared Survey Explorer and have confirmed many of the candidates as late-type T dwarfs. In order to search for companions to these objects, we are conducting observations using the Laser Guide Star Adaptive Optics system on Keck II. Here we present the first results of that search, including a T5 binary with nearly equal mass components and a faint companion to a T8.5 dwarf with an estimated spectral type of T9
The Porcupine Survey: A Distributed Survey and WISE Followup
Spitzer post-cryogen observations to perform a moderate depth survey distributed around the sky are proposed. Field centers are chosen to be WISE brown dwarf candidates, which will typically be 160 µJy at 4.7 µm and randomly distributed around the sky. The Spitzer observations will give much higher sensitivity, higher angular resolution, and a time baseline to measure both proper motions and possibly parallaxes. The distance and velocity data obtained on the WISE brown dwarf candidates will greatly improve our knowledge of the mass and age distribution of brown dwarfs. The outer parts of the Spitzer fields surrounding the WISE positions will provide a deep survey in many narrow fields of view distributed around the sky, and the volume of this survey will contain many more distant brown dwarfs, and many extragalactic objects
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
Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
We present a sample of brown dwarfs identified with the {\it Wide-field
Infrared Survey Explorer} (WISE) for which we have obtained {\it Hubble Space
Telescope} ({\it HST}) Wide Field Camera 3 (WFC3) near-infrared grism
spectroscopy. The sample (twenty-two in total) was observed with the G141 grism
covering 1.101.70 m, while fifteen were also observed with the G102
grism, which covers 0.901.10 m. The additional wavelength coverage
provided by the G102 grism allows us to 1) search for spectroscopic features
predicted to emerge at low effective temperatures (e.g.\ ammonia bands) and 2)
construct a smooth spectral sequence across the T/Y boundary. We find no
evidence of absorption due to ammonia in the G102 spectra. Six of these brown
dwarfs are new discoveries, three of which are found to have spectral types of
T8 or T9. The remaining three, WISE J082507.35280548.5 (Y0.5), WISE
J120604.38840110.6 (Y0), and WISE J235402.77024015.0 (Y1) are the
nineteenth, twentieth, and twenty-first spectroscopically confirmed Y dwarfs to
date. We also present {\it HST} grism spectroscopy and reevaluate the spectral
types of five brown dwarfs for which spectral types have been determined
previously using other instruments.Comment: Accepted for publication in the Astrophysical Journal. 20 pages, 18
figures, 7 table
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