3,677 research outputs found
High Sensitivity Array Observations of the z=1.87 Sub-Millimeter Galaxy GOODS 850-3
We present sensitive phase-referenced VLBI results on the radio continuum
emission from the z=1.87 luminous submillimeter galaxy (SMG) GOODS 850-3. The
observations were carried out at 1.4 GHz using the High Sensitivity Array
(HSA). Our sensitive tapered VLBI image of GOODS 850-3 at 0.47 x 0.34 arcsec
(3.9 x 2.9 kpc) resolution shows a marginally resolved continuum structure with
a peak flux density of 148 \pm 38 uJy/beam, and a total flux density of 168 \pm
73 uJy, consistent with previous VLA and MERLIN measurements. The derived
intrinsic brightness temperature is > 5 \pm 2 x 10^3 K. The radio continuum
position of this galaxy coincides with a bright and extended near-infrared
source that nearly disappears in the deep HST optical image, indicating a dusty
source of nearly 9 kpc in diameter. No continuum emission is detected at the
full VLBI resolution (13.2 x 7.2 mas, 111 x 61 pc), with a 4-sigma point source
upper limit of 26 uJy/beam, or an upper limit to the intrinsic brightness
temperature of 4.7 x 10^5 K. The extent of the observed continuum source at 1.4
GHz and the derived brightness temperature limits are consistent with the radio
emission (and thus presumably the far-infrared emission) being powered by a
major starburst in GOODS 850-3, with a star formation rate of ~2500 M_sun/yr.
Moreover, the absence of any continuum emission at the full resolution of the
VLBI observations indicates the lack of a compact radio AGN source in this
z=1.87 SMG.Comment: 19 pages, 4 figures, accepted for publication in A
An Extremely Deep Wide-Field Near-Infrared Survey: Bright Galaxy Counts and Local Large Scale Structure
We present a deep, wide-field near-infrared (NIR) survey over five widely
separated fields at high Galactic latitude covering a total of ~ 3 deg^2 in J,
H, and Ks. The deepest areas of the data (~ 0.25 deg^2) extend to a 5 sigma
limiting magnitude of JHKs > 24 in the AB magnitude system. Although depth and
area vary from field to field, the overall depth and large area of this dataset
make it one of the deepest wide-field NIR imaging surveys to date. This paper
discusses the observations, data reduction, and bright galaxy counts in these
fields. We compare the slope of the bright galaxy counts with the Two Micron
All Sky Survey (2MASS) and other counts from the literature and explore the
relationship between slope and supergalactic latitude. The slope near the
supergalactic equator is sub- Euclidean on average pointing to the possibility
of a decreasing average space density of galaxies by ~ 10-15% over scales of ~
250-350 Mpc. On the contrary, the slope at high supergalactic latitudes is
strongly super-Euclidean on average suggesting an increase in the space density
of galaxies as one moves from the voids just above and below the supergalactic
plane out to distances of ~ 250-350 Mpc. These results suggest that local large
scale structure could be responsible for large discrepancies in the measured
slope between different studies in the past. In addition, the local universe
away from the supergalactic plane appears to be underdense by ~ 25-100%
relative to the space densities of a few hundred megaparsecs distant. Subject
headings: cosmology: observations and large scale structure of
universe-galaxies: fundamental parameters (counts)-infrared: galaxiesComment: Accepted to ApJS, 18 Pages, 14 Figures, 8 Table
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
Radio and X-ray properties of submillimeter galaxies in the A2125 field
We present the radio and X-ray properties of 1.2 mm MAMBO source candidates
in a 1600 sq. arcmin field centered on the Abell 2125 galaxy cluster at
z=0.247. The brightest, non-synchrotron mm source candidate in the field has a
photometric redshift, z = 3.93^+1.11_-0.80, and is not detected in a 31 ks
Chandra X-ray exposure. These findings are consistent with this object being an
extremely dusty and luminous starburst galaxy at high-redshift, possibly the
most luminous yet identified in any blank-field mm survey. The deep 1.4 GHz VLA
imaging identifies counterparts for 83% of the 29 mm source candidates
identified at >=4-sigma S(1.2mm) = 2.7 - 52.1 mJy, implying that the majority
of these objects are likely to lie at z <~ 3.5. The median mm-to-radio
wavelength photometric redshift of this radio-detected sample is z~2.2 (first
and third quartiles of 1.7 and 3.0), consistent with the median redshift
derived from optical spectroscopic surveys of the radio-detected subsample of
bright submm galaxies (S(850um) > 5 mJy). Three mm-selected quasars are
confirmed to be X-ray luminous in the high resolution Chandra imaging, while
another mm source candidate with potential multiple radio counterparts is also
detected in the X-ray regime. Both of these radio counterparts are positionally
consistent with the mm source candidate. One counterpart is associated with an
elliptical galaxy at z = 0.2425, but we believe that a second counterpart
associated with a fainter optical source likely gives rise to the mm emission
at z~1.Comment: Accepted for publication in Ap
Apparatus for Converting Direct Current to Alternating Current using Multiple Converters
An inverter for converting an input direct current (DC) waveform from a DC source to an output alternating current (AC) waveform for delivery to an AC grid includes an input converter, an output converter, and an active filter, each of which is electrically coupled to a bus. The bus may be a DC bus or an AC bus. The input converter is configured to convert the input DC waveform to a DC or AC bus waveform. The output converter is configured to convert the bus waveform to the output AC waveform at a grid frequency. The active filter is configured to reduce a double-frequency ripple power of the bus waveform by supplying power to and absorbing power from the power bus
Apparatus for Converting Direct Current to Alternating Current using Multiple Converters
An inverter for converting an input direct current (DC) waveform from a DC source to an output alternating current (AC) waveform for delivery to an AC grid includes an input converter, an output converter, and an active filter, each of which is electrically coupled to a bus. The bus may be a DC bus or an AC bus. The input converter is configured to convert the input DC waveform to a DC or AC bus waveform. The output converter is configured to convert the bus waveform to the output AC waveform at a grid frequency. The active filter is configured to reduce a double-frequency ripple power of the bus waveform by supplying power to and absorbing power from the power bus
Apparatus and Method for Controlling DC-AC Power Conversion
An apparatus and method for controlling the delivery of power from a DC source to an AC grid includes an inverter configured to deliver power from the unipolar input source to the AC grid and an inverter controller. The inverter includes an input converter, an active filter, and an output converter. The inverter controller includes an input converter controller, an active filter controller and an output converter controller. The input converter controller is configured to control a current delivered by the input converter to a galvanically isolated unipolar bus of the inverter. The output converter is configured to control the output converter to deliver power to the AC grid. Additionally, the active filter controller is configured to control the active filter to supply substantially all the power that is deliver by the output controller to the AC grid at a grid frequency
A population of z> 2 far-infrared Herschel-spire-selected starbursts
We present spectroscopic observations for a sample of 36 Herschel-SPIRE
250-500um selected galaxies (HSGs) at 2<z<5 from the Herschel Multi-tiered
Extragalactic Survey (HerMES). Redshifts are confirmed as part of a large
redshift survey of Herschel-SPIRE-selected sources covering ~0.93deg^2 in six
extragalactic legacy fields. Observations were taken with the Keck I Low
Resolution Imaging Spectrometer (LRIS) and the Keck II DEep Imaging
Multi-Object Spectrograph (DEIMOS). Precise astrometry, needed for
spectroscopic follow-up, is determined by identification of counterparts at
24um or 1.4GHz using a cross-identification likelihood matching method.
Individual source luminosities range from log(L_IR/Lsun)=12.5-13.6
(corresponding to star formation rates 500-9000Msun/yr, assuming a Salpeter
IMF), constituting some of the most intrinsically luminous, distant infrared
galaxies yet discovered. We present both individual and composite rest-frame
ultraviolet spectra and infrared spectral energy distributions (SEDs). The
selection of these HSGs is reproducible and well characterized across large
areas of sky in contrast to most z>2 HyLIRGs in the literature which are
detected serendipitously or via tailored surveys searching only for high-z
HyLIRGs; therefore, we can place lower limits on the contribution of HSGs to
the cosmic star formation rate density at (7+-2)x10^(-3)Msun/yr h^3Mpc^(-3) at
z~2.5, which is >10% of the estimated total star formation rate density (SFRD)
of the Universe from optical surveys. The contribution at z~4 has a lower limit
of 3x10^(-3)Msun/yr h^3 Mpc^(-3), ~>20% of the estimated total SFRD. This
highlights the importance of extremely infrared-luminous galaxies with high
star formation rates to the build-up of stellar mass, even at the earliest
epochs.Comment: 25 pages, 10 figures; ApJ accepte
The HELLAS2XMM Survey. XII. The infrared/sub-millimeter view of an X-ray selected Type 2 quasar at z=2
We present multi-wavelength observations (from optical to sub-millimeter,
including Spitzer and SCUBA) of H2XMMJ 003357.2-120038 (also GD158_19), an
X-ray selected, luminous narrow-line (Type 2) quasar at z=1.957 selected from
the HELLAS2XMM survey. Its broad-band properties can be reasonably well modeled
assuming three components: a stellar component to account for the optical and
near-IR emission, an AGN component (i.e., dust heated by an accreting active
nucleus), dominant in the mid-IR, with an optical depth at 9.7 micron along the
line of sight (close to the equatorial plane of the obscuring matter) of
tau(9.7)=1 and a full covering angle of the reprocessing matter (torus) of 140
degrees, and a far-IR starburst component (i.e., dust heated by star formation)
to reproduce the wide bump observed longward of 70 micron. The derived
star-formation rate is about 1500 solar masses per year. The overall modeling
indicates that GD158_19 is a high-redshift X-ray luminous, obscured quasar with
coeval powerful AGN activity and intense star formation. It is probably caught
before the process of expelling the obscuring gas has started, thus quenching
the star formation.Comment: 7 pages, 3 figures, 1 table, accepted for publication by MNRA
- …