55 research outputs found
A Submillimetre Survey of the Hubble Deep Field: Unveiling Dust-Enshrouded Star Formation in the Early Universe
The advent of sensitive sub-mm array cameras now allows a proper census of
dust-enshrouded massive star-formation in very distant galaxies, previously
hidden activity to which even the deepest optical images are insensitive. We
present the deepest sub-mm survey, taken with the SCUBA camera on the James
Clerk Maxwell Telescope (JCMT) and centred on the Hubble Deep Field (HDF). The
high source density on this image implies that the survey is confusion-limited
below a flux density of 2 mJy. However within the central 80 arcsec radius
independent analyses yield 5 reproducible sources with S(850um) > 2 mJy which
simulations indicate can be ascribed to individual galaxies. These data lead to
integral source counts which are completely inconsistent with a no evolution
model, whilst the combined brightness of the 5 most secure sources in our map
is sufficient to account for 30-50% of the previously unresolved sub-mm
background, and statistically the entire background is resolved at about the
0.3 mJy level. Four of the five brightest sources appear to be associated with
galaxies which lie in the redshift range 2 < z < 4. With the caveat that this
is a small sample of sources detected in a small survey area, these submm data
imply a star-formation density over this redshift range that is at least five
times higher than that inferred from the rest-frame ultraviolet output of HDF
galaxies.Comment: to appear in the proceedings of `The Birth of Galaxies', Xth
Rencontres de Blois, 4 pages, 1 postscript figure, uses blois.sty (included
Unveiling Dust-enshrouded Star Formation in the Early Universe: a Sub-mm Survey of the Hubble Deep Field
The advent of sensitive sub-mm array cameras now allows a proper census of
dust-enshrouded massive star-formation in very distant galaxies, previously
hidden activity to which even the faintest optical images are insensitive. We
present the deepest sub-mm survey of the sky to date, taken with the SCUBA
camera on the James Clerk Maxwell Telescope and centred on the Hubble Deep
Field. The high source density found in this image implies that the survey is
confusion-limited below a flux density of 2 mJy. However, within the central 80
arcsec radius independent analyses yield 5 reproducible sources with S(850um) >
2 mJy which simulations indicate can be ascribed to individual galaxies. We
give positions and flux densities for these, and furthermore show using
multi-frequency photometric data that the brightest sources in our map lie at
redshifts z~3. These results lead to integral source counts which are
completely inconsistent with a no-evolution model, and imply that massive
star-formation activity continues at redshifts > 2. The combined brightness of
the 5 most secure sources in our map is sufficient to account for 30 - 50% of
the previously unresolved sub-mm background, and we estimate statistically that
the entire background is resolved at about the 0.3 mJy level. Finally we
discuss possible optical identifications and redshift estimates for the
brightest sources. One source appears to be associated with an extreme
starburst galaxy at z~1, whilst the remaining four appear to lie in the
redshift range 2 < z < 4. This implies a star-formation density over this
redshift range that is at least five times higher than that inferred from the
ultraviolet output of HDF galaxies.Comment: 19 pages, 6 figures (to appear as a Nature Article
THE ALMA SPECTROSCOPIC SURVEY IN THE HUBBLE ULTRA DEEP FIELD: CONTINUUM NUMBER COUNTS, RESOLVED 1.2 mm EXTRAGALACTIC BACKGROUND, AND PROPERTIES OF THE FAINTEST DUSTY STAR-FORMING GALAXIES
We present an analysis of a deep (1σ = 13 μJy) cosmological 1.2 mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin2 covered by ASPECS we detect nine sources at significance at 1.2 mm. Our ALMA-selected sample has a median redshift of , with only one galaxy detected at z > 2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cutoff and similar frequencies. Most galaxies have specific star formation rates (SFRs) similar to that of main-sequence galaxies at the same epoch, and we find median values of stellar mass and SFRs of and yr−1, respectively. Using the dust emission as a tracer for the interstellar medium (ISM) mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from ~0.1 to 1.0. As noted by previous studies, these values are lower than those using CO-based ISM estimates by a factor of ~2. The 1 mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover 55% ± 4% of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover 80% ± 7% of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at z\sim 1\mbox{--}2, with stellar masses of (1–3) × 1010 M . For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm
The SCUBA Bright Quasar Survey (SBQS): 850micron observations of the z>4 sample
We present initial results of a new, systematic search for massive
star-formation in the host galaxies of the most luminous and probably most
massive z>=4 radio-quiet quasars (M(B) 10^13Lsun).
A total of 38 z>=4 radio-quiet quasars have been observed at the JCMT using
SCUBA at 850microns: 8 were detected (>3sigma) with S(850microns)>~ 10mJy
(submillimetre-loud). The new detections almost triple the number of optically
selected, submillimetre-loud z>~4 radio-quiet quasars known to date. We include
a detailed description of how our quasar sample is defined in terms of radio
and optical properties.
There is no strong evidence for trends in either detectability or 850microns
flux with absolute magnitude, M(B). We find that the weighted mean flux of the
undetected sources is 2.0 +/- 0.6mJy, consistent with an earlier estimate of
\~3mJy based on more sensitive observations of a sample z>~4 radio-quiet
quasars (McMahon et al., 1999). This corresponds to an inferred starformation
rate of \~1000Msun/yr, similar to Arp220. The typical starformation timescale
for the submillimetre-bright sources is ~1Gyr, 10 times longer than the typical
accretion-driven e-folding timescale of ~5x10^7 years. Our 850micron detection
of the z=4.4 quasar PSS J1048+4407 when analysed in conjunction with 1.2mm
single-dish and interferometric observations suggests that this source is
resolved on angular scales of 1-2" (6-12 kpc). In addition, we present a new
optical spectrum of this source, identifying it as a broad absorption line
(BAL) quasar. The new redshift is outside that covered in a recent CO line
search by Guilloteau et al., (1999), highlighting the need for accurate
redshifts for the obervation and interpretation of high-redshift line studies.Comment: 16 pages, 11 figures. Accepted by Monthly Notices of the Royal
Astronomical Societ
A Deep 1.2 mm Map of the Lockman Hole North Field
We present deep 1.2 mm continuum mapping of a 566 arcmin^2 area within the
Lockman Hole North field, previously a target of the Spitzer Wide-area Infrared
Extragalactic (SWIRE) survey and extremely deep 20 cm mapping with the Very
Large Array, which we have obtained using the Max-Planck millimeter bolometer
(MAMBO) array on the IRAM 30 m telescope. After filtering, our full map has an
RMS sensitivity ranging from 0.45 to 1.5 mJy/beam, with an average of 0.75
mJy/beam. Using the pixel flux distribution in a map made from our best data,
we determine the shape, normalization, and approximate flux density cutoff for
1.2 mm number counts well below our nominal sensitivity and confusion limits.
After validating our full dataset through comparison with this map, we
successfully detect 41 1.2 mm sources with S/N > 4.0 and S(1.2 mm)\simeq 2-5
mJy. We use the most significant of these detections to directly determine the
integral number counts down to 1.8 mJy, which are consistent with the results
of the pixel flux distribution analysis. 93% of our 41 individual detections
have 20 cm counterparts, 49% have Spitzer/MIPS 24 micron counterparts, and one
may have a significant Chandra X-ray counterpart. We resolve \simeq 3% of the
cosmic infrared background (CIB) at 1.2 mm into significant detections, and
directly estimate a 0.05 mJy faint-end cutoff for the counts that is consistent
with the full intensity of the 1.2 mm CIB. The median redshift of our 17
detections with spectroscopic or robust photometric redshifts is z(median)=2.3,
and rises to z(median)=2.9 when we include redshifts estimated from the
radio/far-infrared spectral index. By using a nearest neighbor and angular
correlation function analysis, we find evidence that our S/N>4.0 detections are
clustered at the 95% confidence level.Comment: 40 pages, 25 figures, accepted for publication in Ap
MAMBO 1.2mm observations of luminous starbursts at z~2 in the SWIRE fields
We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected
star-forming galaxies from the SWIRE survey. The sources are selected on the
basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated
near-infrared spectral energy distributions in order to favor z~2 starburst
galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our
analysis focuses on 29 sources in the Lockman Hole field where the average
1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The
analysis of the sources multi-wavelength spectral energy distributions
indicates that they are starburst galaxies with far-infrared luminosities
~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to
sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among
those with the largest 24um/millimeter flux ratios. The origin of such large
ratios is investigated by comparing the average mid-infrared spectra and the
stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources
and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm
dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared
emission, and is likely associated with an AGN component. This constribution is
consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are
thus not due to AGN emission, but rather to enhanced PAH emission compared to
SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust
temperatures than typically observed in SMGs. Our selection favors warm
ultra-luminous infrared sources at high-z, a class of objects that is rarely
found in SMG samples. Our sample is the largest Spitzer-selected sample
detected at millimeter wavelengths currently available.Comment: Accepted for publication in ApJ (51 pages; 16 figures). The quality
of some figures has been degraded for arXiv purposes. Full resolution version
available at this
http://www.iasf-milano.inaf.it/~polletta/mambo_swire/lonsdale08_ApJ_accepted.pd
Scattered Radiation from Obscured Quasars in Distant Radio Galaxies
We present optical spectropolarimetric and imaging polarimetric observations
of four high-redshift radio galaxies (HzRGs) obtained with the 10-m Keck I
telescope. A broad Mg II emission line is detected in the total and polarized
flux spectra of 3C 265 and 3C 277.2. The fractional polarization is high, and
both it and the position angle are constant with wavelength after accounting
for dilution by unpolarized starlight of the host galaxy, which can contribute
substantially. An extended unpolarized continuum similar to that observed in
other AGNs is also detected. Imaging polarimetry reveals a rough double-fan
morphology of the polarized light coincident with the extended aligned emission
regions, with the position angle essentially perpendicular to the radial
structure of the extended UV/optical emission, and with the degree of
polarization increasing with radius away from the nucleus. The radio jets lie
inside the extended emission regions and, like every radius, are roughly
perpendicular to the polarization PA. These results strengthen the view that
powerful radio galaxies would be called quasars if viewed from a proper
direction. Based on the polarimetric data presented in this paper and in
previous studies, scattering of radiation from an obscured quasar source
appears to be the preferred interpretation over jet-induced star formation for
explaining the alignment effect in HzRGs. Both electrons and dust can play a
major role in the scattering process. However, the lack of strong direct
evidence for either case, and our ignorance of the properties and distribution
of the scatterers in these galaxies make it very difficult to discriminate
between the two. Our data reveal a chance alignment of 3C 343.1 with a
foreground galaxy, which dominates the observed optical flux from the system.Comment: 36 pages, 12 figures, 2 tables, Astrophysical Journal, accepted Dec.
21, 199
Last Men Standing: Chlamydatus Portraits and Public Life in Late Antique Corinth
Notable among the marble sculptures excavated at Corinth are seven portraits of men wearing the long chlamys of Late Antique imperial office. This unusual costume, contemporary portrait heads, and inscribed statue bases all help confirm that new public statuary was created and erected at Corinth during the 4th and 5th centuries. These chlamydatus portraits, published together here for the first time, are likely to represent the Governor of Achaia in his capital city, in the company of local benefactors. Among the last works of the ancient sculptural tradition, they form a valuable source of information on public life in Late Antique Corinth
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics
This paper describes the Hubble Space Telescope imaging data products and
data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). This survey is designed to document the evolution of
galaxies and black holes at , and to study Type Ia SNe beyond
. Five premier multi-wavelength sky regions are selected, each with
extensive multiwavelength observations. The primary CANDELS data consist of
imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and
UVIS channel, along with the Advanced Camera for Surveys (ACS). The
CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and
GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a
total of \sim800 square arcminutes across GOODS and three additional fields
(EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as
motivated by the scientific goals and present a detailed description of the
data reduction procedures and products from the survey. Our data reduction
methods utilize the most up to date calibration files and image combination
procedures. We have paid special attention to correcting a range of
instrumental effects, including CTE degradation for ACS, removal of electronic
bias-striping present in ACS data after SM4, and persistence effects and other
artifacts in WFC3/IR. For each field, we release mosaics for individual epochs
and eventual mosaics containing data from all epochs combined, to facilitate
photometric variability studies and the deepest possible photometry. A more
detailed overview of the science goals and observational design of the survey
are presented in a companion paper.Comment: 39 pages, 25 figure
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
is designed to document the first third of galactic evolution, over the
approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies
using three separate cameras on the Hubble Space Telescope, from the
mid-ultraviolet to the near-infrared, and will find and measure Type Ia
supernovae at z>1.5 to test their accuracy as standardizable candles for
cosmology. Five premier multi-wavelength sky regions are selected, each with
extensive ancillary data. The use of five widely separated fields mitigates
cosmic variance and yields statistically robust and complete samples of
galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the
knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8.
The survey covers approximately 800 arcmin^2 and is divided into two parts. The
CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125
arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and
three additional fields (EGS, COSMOS, and UDS) and covers the full area to a
5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble
Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach
that has proven efficient for extragalactic surveys. Data from the survey are
nonproprietary and are useful for a wide variety of science investigations. In
this paper, we describe the basic motivations for the survey, the CANDELS team
science goals and the resulting observational requirements, the field selection
and geometry, and the observing design. The Hubble data processing and products
are described in a companion paper.Comment: Submitted to Astrophysical Journal Supplement Series; Revised
version, subsequent to referee repor
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