87 research outputs found
High-resolution VLA Imaging of SDSS Stripe 82 at 1.4 GHz
We present a high-resolution radio survey of the Sloan Digital Sky Survey
(SDSS) Southern Equatorial Stripe, a.k.a. Stripe 82. This 1.4 GHz survey was
conducted with the Very Large Array (VLA) primarily in the A-configuration,
with supplemental B-configuration data to increase sensitivity to extended
structure. The survey has an angular resolution of 1.8" and achieves a median
rms noise of 52 microJy/bm over 92 deg^2. This is the deepest 1.4 GHz survey to
achieve this large of an area, filling a gap in the phase space between small,
deep and large, shallow surveys. It also serves as a pilot project for a larger
high-resolution survey with the Expanded Very Large Array (EVLA). We discuss
the technical design of the survey and details of the observations, and we
outline our method for data reduction. We present a catalog of 17,969 isolated
radio components, for an overall source density of ~195 sources/deg^2. The
astrometric accuracy of the data is excellent, with an internal check utilizing
multiply-observed sources yielding an rms scatter of 0.19" in both right
ascension and declination. A comparison to the SDSS DR7 Quasar Catalog further
confirms that the astrometry is well tied to the optical reference frame, with
mean offsets of 0.02" +/- 0.01" in right ascension, and 0.01" +/- 0.02" in
declination. A check of our photometry reveals a small, negative CLEAN-like
bias on the level of 35 microJy. We report on the catalog completeness, finding
that 97% of FIRST-detected quasars are recovered in the new Stripe 82 radio
catalog, while faint, extended sources are more likely to be resolved out by
the resolution bias. We conclude with a discussion of the optical counterparts
to the catalog sources, including 76 newly-detected radio quasars. The full
catalog as well as a search page and cutout server are available online at
http://third.ucllnl.org/cgi-bin/stripe82cutout.Comment: 18 pages, 22, figures. Submitted to AJ, revised to address referee's
comment
Plausible association of distant late M dwarfs with low-frequency radio emission
We present the serendipitous discovery of 8 distant ( 50 pc) late M dwarfs
with plausible associated radio emission at 144 MHz. The M dwarf nature of our
sources has been confirmed with optical spectroscopy performed using HET/LRS2
and Subaru/FOCAS, and their radio flux densities are within the range of
0.5-1.0 mJy at 144 MHz. Considering the radio-optical source separation and
source densities of the parent catalogues, we suggest that it is statistically
probable the M dwarfs are associated with the radio emission. However, it
remains plausible that for some of the sources the radio emission originates
from an optically faint and red galaxy hiding behind the M dwarf. The isotropic
radio luminosities ( erg s Hz) of the M dwarfs
suggest that if the association is real, the radio emission is likely driven by
a coherent emission process produced via plasma or electron-cyclotron maser
instability processes, which is potentially caused by binary interaction. Long
term monitoring in the radio and high-resolution radio follow-up observations
are necessary to search for any variability and pinpoint the radio emission to
determine whether our tentative conclusion that these ultracool dwarfs are
radio emitting is correct. If the low-frequency radio emission is conclusively
associated with the M dwarfs, this would reveal a new population of optically
faint and distant ( 50 pc) radio emitting M dwarfs.Comment: 10 pages, 5 figures, accepted for publication in A&
The Era of Star Formation in Galaxy Clusters
We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at 1 1.35. Using infrared luminosities measured with deep Spitzer/Multiband Imaging Photometer for Spitzer observations at 24 μm, along with robust optical + IRAC photometric redshifts and spectral-energy-distribution-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates, and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that z ~ 1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift, the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at z > 1.4 environment-dependent quenching had not yet been established in ISCS clusters. By combining these observations with complementary studies showing a rapid increase in the active galactic nucleus (AGN) fraction, a stochastic star formation history, and a major merging episode at the same epoch in this cluster sample, we suggest that the starburst activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGNs. The totality of the evidence suggests we are witnessing the final quenching period that brings an end to the era of star formation in galaxy clusters and initiates the era of passive evolution
The HETDEX Survey: Emission Line Exploration and Source Classification
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted
spectroscopic survey that aims to measure the expansion rate of the Universe at
to 1% precision for both and . HETDEX is in the
process of mapping in excess of one million Lyman Alpha emitting (LAE) galaxies
and a similar number of lower-z galaxies as a tracer of the large-scale
structure. The success of the measurement is predicated on the post-observation
separation of galaxies with Ly emission from the lower- interloping
galaxies, primarily [OII], with low contamination and high recovery rates. The
Emission Line eXplorer (ELiXer) is the principal classification tool for
HETDEX, providing a tunable balance between contamination and completeness as
dictated by science needs. By combining multiple selection criteria, ELiXer
improves upon the 20 Angstrom rest-frame equivalent width cut commonly used to
distinguish LAEs from lower- [OII] emitting galaxies. Despite a spectral
resolving power, R , that cannot resolve the [OII] doublet, we
demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1%
accuracy. We estimate a contamination rate of Ly by [OII] of 1.2% and a
Ly recovery rate of 99.1% using the default ELiXer configuration. These
rates meet the HETDEX science requirements.Comment: 38 pages, 11 figure
A Giant Planet Candidate Transiting a White Dwarf
Astronomers have discovered thousands of planets outside the solar system,
most of which orbit stars that will eventually evolve into red giants and then
into white dwarfs. During the red giant phase, any close-orbiting planets will
be engulfed by the star, but more distant planets can survive this phase and
remain in orbit around the white dwarf. Some white dwarfs show evidence for
rocky material floating in their atmospheres, in warm debris disks, or orbiting
very closely, which has been interpreted as the debris of rocky planets that
were scattered inward and tidally disrupted. Recently, the discovery of a
gaseous debris disk with a composition similar to ice giant planets
demonstrated that massive planets might also find their way into tight orbits
around white dwarfs, but it is unclear whether the planets can survive the
journey. So far, the detection of intact planets in close orbits around white
dwarfs has remained elusive. Here, we report the discovery of a giant planet
candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4
days. The planet candidate is roughly the same size as Jupiter and is no more
than 14 times as massive (with 95% confidence). Other cases of white dwarfs
with close brown dwarf or stellar companions are explained as the consequence
of common-envelope evolution, wherein the original orbit is enveloped during
the red-giant phase and shrinks due to friction. In this case, though, the low
mass and relatively long orbital period of the planet candidate make
common-envelope evolution less likely. Instead, the WD 1856+534 system seems to
demonstrate that giant planets can be scattered into tight orbits without being
tidally disrupted, and motivates searches for smaller transiting planets around
white dwarfs.Comment: 50 pages, 12 figures, 2 tables. Published in Nature on Sept. 17,
2020. The final authenticated version is available online at:
https://www.nature.com/articles/s41586-020-2713-
The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections
We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyα emitting galaxies between 1.88 < z < 3.52, in a 540 deg2 area encompassing a comoving volume of 10.9 Gpc3. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra
ZFIRE: Similar Stellar Growth in Hα-emitting Cluster and Field Galaxies at z ~ 2
We compare galaxy scaling relations as a function of environment at
with our ZFIRE survey where we have measured H fluxes for 90
star-forming galaxies selected from a mass-limited
[] sample based on ZFOURGE. The cluster galaxies
(37) are part of a confirmed system at z=2.095 and the field galaxies (53) are
at ; all are in the COSMOS legacy field. There is no statistical
difference between H-emitting cluster and field populations when
comparing their star formation rate (SFR), stellar mass (), galaxy
size (), SFR surface density [(H)], and stellar
age distributions. The only difference is that at fixed stellar mass, the
H-emitting cluster galaxies are larger than in
the field. Approximately 19% of the H-emitters in the cluster and 26%
in the field are IR-luminous (). Because the
LIRGs in our combined sample are times more massive than the low-IR
galaxies, their radii are % larger. To track stellar growth, we
separate galaxies into those that lie above, on, and below the H
star-forming main sequence (SFMS) using SFR dex.
Galaxies above the SFMS (starbursts) tend to have higher H SFR surface
densities and younger light-weighted stellar ages compared to galaxies below
the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field
at are growing their stellar cores. Lastly, we compare to the
(SFR-) relation from RHAPSODY cluster simulations and find the
predicted slope is nominally consistent with the observations. However, the
predicted cluster SFRs tend to be too low by a factor of which seems to
be a common problem for simulations across environment.Comment: ApJ in press; full version of Table 1 available from ApJ and upon
request. Survey websites are http://zfire.swinburne.edu.au and
http://zfourge.tamu.ed
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