558 research outputs found
Deep Galaxy survey at 6.75 micron with the ISO satellite
Deep 6.75um mid-IR ISOCAM observations were obtained of the Canada-France
Redshift Survey (CFRS) 1415+52 field with the Infrared Space Observatory. The
identification of the sources with optical counterparts is described in detail,
and a classification scheme is devised which depends on the S/N of the
detection and the inverse probability of chance coincidence. 83% of the 54
ISOCAM sources are identified with Iab<23.5 counterparts. The (I-K)ab colors,
radio properties, spectrophotometric properties and frequency of nuclear
activity of these counterparts differ on average from those of typical CFRS
galaxies. CFRS spectra are available for 21 of the sources which have Iab <=
22.5 (including 7 stars). Most of the strongest sources are stars or AGN. Among
the non--stellar counterparts with spectra, 40% are AGNs, and 53% are galaxies
that display star formation activity and/or significant contributions of A
stars. The ISOCAM sources also display an IR excess, even when compared with
heavily-reddened local starburst galaxies. An upper limit of 30% of
extragalactic ISO sources could be at z>1 of the 44 S6.75um > 150uJy sources
which are non-stellar (7 "spectroscopic" and 3 "photometric" stars excluded)Comment: 13 pages, 12 figures. Accepted for publication in A
Achieving safe management: A case for strengthening the attention to liquid streams in on-site and local sanitation
The Evolution of the Stellar Hosts of Radio Galaxies
We present new near-infrared images of z>0.8 radio galaxies from the
flux-limited 7C-III sample of radio sources for which we have recently obtained
almost complete spectroscopic redshifts. The 7C objects have radio luminosities
about 20 times fainter than 3C radio galaxies at a given redshift. The absolute
magnitudes of the underlying host galaxies and their scale sizes are only
weakly dependent on radio luminosity. Radio galaxy hosts at z~2 are
significantly brighter than the hosts of radio-quiet quasars at similar
redshifts and the model AGN hosts of Kauffmann & Haehnelt (2000). There is no
evidence for strong evolution in scale size, which shows a large scatter at all
redshifts. The hosts brighten significantly with redshift, consistent with the
passive evolution of a stellar population that formed at z>~3. This scenario is
consistent with studies of host galaxy morphology and submillimeter continuum
emission, both of which show strong evolution at z>~2.5. The lack of a strong
``redshift cutoff'' in the radio luminosity function to z>4 suggests that the
formation epoch of the radio galaxy host population lasts >~1Gyr from z>~5 to
z~3. We suggest these facts are best explained by models in which the most
massive galaxies and their associated AGN form early due to high baryon
densities in the centres of their dark matter haloes.Comment: To appear in A
The Infestation of Fungus Cultures by Mites.(Its Nature and Control, together with some Remarks on the toxic Properties of Pyridine.)
RESP-33
Submillimeter Observations of the Ultraluminous BAL Quasar APM 08279+5255
With an inferred bolometric luminosity of 5\times10^{15}{\rm \lsun}, the
recently identified z=3.87, broad absorption line quasar APM 08279+5255 is
apparently the most luminous object currently known. As half of its prodigious
emission occurs in the infrared, APM 08279+5255 also represents the most
extreme example of an Ultraluminous Infrared Galaxy. Here, we present new
submillimeter observations of this phenomenal object; while indicating that a
vast quantity of dust is present, these data prove to be incompatible with
current models of emission mechanisms and reprocessing in ultraluminous
systems. The influence of gravitational lensing upon these models is considered
and we find that while the emission from the central continuum emitting region
may be significantly enhanced, lensing induced magnification cannot easily
reconcile the models with observations. We conclude that further modeling,
including the effects of any differential magnification is required to explain
the observed emission from APM 08279+5255.Comment: 12 Pages with Two figures. Accepted for publication in the
Astrophysical Journal Letter
15um ISO observations of a CFRS field: the cosmic SFR as derived from UV, optical, mid-IR and radio photometry
The CFRS 1452+52 field has been deeply imaged with the Infrared Space
Observatory (ISO) using ISOCAM through the LW3 filter (12-18um). Careful data
analysis and comparison to deep optical and radio data have allowed us to
generate a catalog of 78 15um sources with both radio and optical
identifications. They are redder and lie at higher redshift than I-band
selected galaxies, with most of them being star-forming galaxies. We have
considered the galaxies detected at radio and 15m wavelengths which
potentially include all strong and heavily extincted starbursts, up to z=1.
Spectral energy distributions (SED) for each of the sources have been derived
using deep radio, mid-IR, near-IR, optical and UV photometry. The sources were
then spectrally classified by comparing to SEDs of well known nearby galaxies.
By deriving their FIR luminosities by interpolation, we can estimate their Star
Formation Rate (SFR) in a way which does not depend sensitively on the
extinction. 75% (-40%, +10%) of the star formation at is related to
IR emission and the global extinction is in the range Av=0.5 -- 0.85. While
heavily extincted starbursts, with SFR in excess of 100 Mo/yr constitute less
than a percent of all galaxies, they contribute about 18% of the SFR density
out to z=1. Their morphologies range from S0 to Sab, and more than a third are
interacting systems. The SFR derived by FIR fluxes is likely to be ~2.9 times
higher than those previously estimated from UV fluxes. The derived stellar mass
formed since the redshift of 1 could be too high when compared to the present
day stellar mass density. This might be due to an IMF in distant star-forming
galaxies different from the solar neighborhood one, or to an underestimate of
the local stellar mass density.Comment: 15 figures and 5 tables (with lower res. fig. 1, 5 & 6). Accepted for
publication in Ap
Massive Ellipticals at High Redshift: NICMOS Imaging of Z~1 Radio Galaxies
We present deep, continuum images of eleven high-redshift (0.811 < z < 1.875)
3CR radio galaxies observed with NICMOS. Our images probe the rest-frame
optical light where stars are expected to dominate the galaxy luminosity. The
rest-frame UV light of eight of these galaxies demonstrates the well-known
``alignment effect''. Most of the radio galaxies have rounder, more symmetric
morphologies at rest-frame optical wavelengths. Here we show the most direct
evidence that in most cases the stellar hosts are normal elliptical galaxies
with de Vaucouleurs law light profiles. For a few galaxies very faint traces of
the UV-bright aligned component are also visible in the infrared images. We
derive both the effective radius and surface-brightness for nine of eleven
sample galaxies by fitting surface-brightness models to them. We find their
sizes are similar to those of local FRII radio source hosts and are in general
larger than other local galaxies. The derived host galaxy luminosities are very
high and lie at the bright end of luminosity functions constructed at similar
redshifts. The galaxies in our sample are also brighter than the rest-frame
size--surface-brightness locus defined by the low-redshift sources. Passive
evolution roughly aligns the z ~ 1 galaxies with the low-redshift samples. The
optical host is sometimes centered on a local minimum in the rest-frame UV
emission, suggesting the presence of substantial dust obscuration. We also see
good evidence of nuclear point sources in three galaxies. Overall, our results
are consistent with the hypothesis that these galaxies have already formed the
bulk of their stars at redshifts greater than z >~ 2, and that the AGN
phenomenon takes place within otherwise normal, perhaps passively evolving,
galaxies. (abridged)Comment: 28 pages, 14 figures, accepted to ApJ. Uses AASTEX and emulateapj
Precise Identifications of Submillimeter Galaxies: Measuring the History of Massive Star-Forming Galaxies to z>5
We carried out extremely sensitive Submillimeter Array (SMA) 340 GHz (860
micron) continuum imaging of a complete sample of SCUBA 850 micron sources (>4
sigma) with fluxes >3 mJy in the GOODS-N. Using these data and new SCUBA-2
data, we do not detect 4 of the 16 SCUBA sources, and we rule out the original
SCUBA fluxes at the 4 sigma level. Three more resolve into multiple fainter SMA
galaxies, suggesting that our understanding of the most luminous high-redshift
dusty galaxies may not be as reliable as we thought. 10 of the 16 independent
SMA sources have spectroscopic redshifts (optical/infrared or CO) to z=5.18.
Using a new, ultradeep 20 cm image obtained with the Karl G. Jansky Very Large
Array (rms of 2.5 microJy), we find that all 16 of the SMA sources are detected
at >5 sigma. Using Herschel far-infrared (FIR) data, we show that the five
isolated SMA sources with Herschel detections are well described by an Arp 220
spectral energy distribution template in the FIR. They also closely obey the
local FIR-radio correlation, a result that does not suffer from a radio bias.
We compute the contribution from the 16 SMA sources to the universal star
formation rate (SFR) per comoving volume. With individual SFRs in the range
700-5000 solar masses per year, they contribute ~30% of the
extinction-corrected ultraviolet-selected SFR density from z=1 to at least z=5.
Star formation histories determined from extinction-corrected ultraviolet
populations and from submillimeter galaxy populations only partially overlap,
due to the extreme ultraviolet faintness of some submillimeter galaxies.Comment: 26 pages, minor changes to match published versio
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