772 research outputs found
Serendipitously Detected Galaxies in the Hubble Deep Field
We present a catalog of 74 galaxies detected serendipitously during a
campaign of spectroscopic observations of the Hubble Deep Field North (HDF) and
its environs. Among the identified objects are five candidate Ly-alpha emitters
at z > 5, a galaxy cluster at z = 0.85, and a Chandra source with a heretofore
undetermined redshift of z = 2.011. We report redshifts for 25 galaxies in the
central HDF, 13 of which had no prior published spectroscopic redshift. Of the
remaining 49 galaxies, 30 are located in the single-orbit HDF Flanking Fields.
We discuss the redshift distribution of the serendipitous sample, which
contains galaxies in the range 0.10 < z < 5.77 with a median redshift of z =
0.85, and we present strong evidence for redshift clustering. By comparing our
spectroscopic redshifts to optical/IR photometric studies of the HDF, we find
that photometric redshifts are in most cases capable of producing reasonable
predictions of galaxy redshifts. Finally, we estimate the line-of-sight
velocity dispersion and the corresponding mass and expected X-ray luminosity of
the galaxy cluster, we present strong arguments for interpreting the Chandra
source as an obscured AGN, and we discuss in detail the spectrum of one of the
candidate z > 5 Ly-alpha emitters.Comment: 18 pages, 9 figures, accepted for publication in the Astronomical
Journa
A Submillimeter and Radio Survey of Gamma-Ray Burst Host Galaxies: A Glimpse into the Future of Star Formation Studies
We present the first comprehensive search for submillimeter and radio
emission from the host galaxies of twenty well-localized gamma-ray bursts
(GRBs). With the exception of a single source, all observations were undertaken
months to years after the GRB explosions to ensure negligible contamination
from the afterglows. We detect the host galaxy of GRB 000418 in both the sub-mm
and radio, and the host galaxy of GRB 000210 only in the sub-mm. These
observations, in conjunction with the previous detections of the host galaxies
of GRB 980703 and GRB 010222, indicate that about 20% of GRB host galaxies are
ultra-luminous and have star formation rates of about 500 M_sun/yr. As an
ensemble, the non-detected hosts have a star formation rate of about 100
M_sun/yr (5-sigma) based on their radio emission. The detected and ensemble
star formation rates exceed the optical values by an order of magnitude,
indicating significant dust obscuration. In the same vein, the ratio of
bolometric dust luminosity to UV luminosity for the hosts detected in the
sub-mm and radio ranges from 20-800, and follows the known trend of increasing
obscuration with increasing bolometric luminosity. We also show that, both as a
sample and individually, the GRB host galaxies have bluer R-K colors as
compared with galaxies selected in the sub-mm in the same redshift range. This
possibly indicates that the stellar populations in the GRB hosts are on average
younger, supporting the massive stellar progenitor scenario for GRBs, but it is
also possible that GRB hosts are on average less dusty.Comment: Submitted to ApJ; 36 pages, 3 tables, 7 figures; updated reference
VLT-ISAAC near-IR Spectroscopy of ISO selected Hubble Deep Field South Galaxies
We report the results of near-infrared VLT-ISAAC spectroscopy of a sample of
12 galaxies at z = 0.4-1.4, drawn from the ISOCAM survey of the Hubble Deep
Field South. We find that the rest frame R-band spectra of the ISOCAM galaxies
resemble those of powerful dust-enshrouded starbursts. Halpha emission is
detected in 11 out of 12 objects down to a flux limit of 7x10^(-17) erg/cm^2/s,
corresponding to a luminosity limit of 10^41 erg/s at z = 0.6, (for an Ho = 50
and Omega = 0.3 cosmology). From the Halpha luminosities in these galaxies we
derive estimates of the star formation rate in the range 2--50 Mo/yr for
stellar masses 1--100 Mo. The raw Halpha-based star formation rates are an
order of magnitude or more lower than SFR(FIR) estimates based on ISOCAM LW3
fluxes. If the Halpha emission is corrected for extinction the median offset is
reduced to a factor of 3. The sample galaxies are part of a new population of
optically faint but infrared--luminous active starburst galaxies, which are
characterized by an extremely high rate of evolution with redshift up to z~1.5
and expected to contribute significantly to the cosmic far-IR extragalactic
background.Comment: Accepted for publication in the Astrophysical Journal Letters, 16
pages, 2 figure
Formation of the compact jets in the black hole GX 339-4
Galactic black hole binaries produce powerful outflows with emit over almost
the entire electromagnetic spectrum. Here, we report the first detection with
the Herschel observatory of a variable far-infrared source associated with the
compact jets of the black hole transient GX 339-4 during the decay of its
recent 2010-2011 outburst, after the transition to the hard state. We also
outline the results of very sensitive radio observations conducted with the
Australia Telescope Compact Array, along with a series of near-infrared,
optical (OIR) and X-ray observations, allowing for the first time the
re-ignition of the compact jets to be observed over a wide range of
wavelengths. The compact jets first turn on at radio frequencies with an
optically thin spectrum that later evolves to optically thick synchrotron
emission. An OIR reflare is observed about ten days after the onset of radio
and hard X-ray emission, likely reflecting the necessary time to build up
enough density, as well as to have acceleration (e.g. through shocks) along an
extended region in the jets. The Herschel measurements are consistent with an
extrapolation of the radio inverted power-law spectrum, but they highlight a
more complex radio to OIR spectral energy distribution for the jets.Comment: Accepted for publication in MNRAS Letter, 6 pages, 3 Figures + 1
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