56 research outputs found
The Dwarf Galaxy Population at z ∼ 0.7: A Catalog of Emission Lines and Redshifts from Deep Keck Observations
We present a catalog of spectroscopically measured redshifts over
and emission line fluxes for 1440 galaxies. The majority (65\%) of the
galaxies come from the HALO7D survey, with the remainder from the DEEPwinds
program. This catalog includes redshifts for 646 dwarf galaxies with
. 810 catalog galaxies did not have previously
published spectroscopic redshifts, including 454 dwarf galaxies. HALO7D used
the DEIMOS spectrograph on the Keck II telescope to take very deep (up to 32
hours exposure, with a median of 7 hours) optical spectroscopy in the
COSMOS, EGS, GOODS-North, and GOODS-South CANDELS fields, and in some areas
outside CANDELS. We compare our redshift results to existing spectroscopic and
photometric redshifts in these fields, finding only a 1\% rate of discrepancy
with other spectroscopic redshifts. We measure a small increase in median
photometric redshift error (from 1.0\% to 1.3\%) and catastrophic outlier rate
(from 3.5\% to 8\%) with decreasing stellar mass. We obtained successful
redshift fits for 75\% of massive galaxies, and demonstrate a similar 70-75\%
successful redshift measurement rate in
galaxies, suggesting similar survey sensitivity in this low-mass range. We
describe the redshift, mass, and color-magnitude distributions of the catalog
galaxies, finding HALO7D galaxies representative of CANDELS galaxies up to
\textit{i}-band magnitudes of 25. The catalogs presented will enable studies of
star formation (SF), the mass-metallicity relation, SF-morphology relations,
and other properties of the dwarf galaxy population.Comment: 23 pages, 19 Figures, updated to version accepted by ApJ
PEARLS: A Potentially Isolated Quiescent Dwarf Galaxy with a TRGB Distance of 31 Mpc
A wealth of observations have long suggested that the vast majority of
isolated classical dwarf galaxies (- M) are currently
star-forming. However, recent observations of the large abundance of
"Ultra-Diffuse Galaxies" beyond the reach of previous large spectroscopic
surveys suggest that our understanding of the dwarf galaxy population may be
incomplete. Here we report the serendipitous discovery of an isolated quiescent
dwarf galaxy in the nearby Universe, which was imaged as part of the PEARLS GTO
program. Remarkably, individual red-giant branch stars are visible in this
near-IR imaging, suggesting a distance of Mpc, and a wealth of archival
photometry point to an sSFR of yr. Spectra obtained
with the Lowell Discovery Telescope find a recessional velocity consistent with
the Hubble Flow and km/s separated from the nearest massive galaxy in
SDSS, suggesting that this galaxy was either quenched from internal mechanisms
or had a very high-velocity interaction with a nearby massive galaxy in the
past. This analysis highlights the possibility that many nearby quiescent dwarf
galaxies are waiting to be discovered and that JWST has the potential to
identify them.Comment: Submitted to ApJ Letters. Comments welcome
JWST NIRCam Photometry: A Study of Globular Clusters Surrounding Bright Elliptical Galaxy VV 191a at z=0.0513
James Webb Space Telescope NIRCam images have revealed 443 globular cluster
(GC) candidates around the elliptical galaxy VV 191a. NIRCam
broadband observations are made at 0.9-4.5 m using filters F090W, F150W,
F356W, and F444W. Using photometry, the data is analyzed to present
color-magnitude diagrams (CMDs) that suggest a fairly uniform population of
GCs. Color histograms show a unimodal color distribution that is well fit by a
single Gaussian, using color to primarily trace the metallicity. The findings
show the sample's globular cluster luminosity function (GCLF) does not reach
the turnover value and is, therefore, more luminous than what is typically
expected, with an absolute AB magnitude, mag, reaching
within nearly one magnitude of the classical turnover value. We attribute this
to the completeness in the sample. Models show that the mass estimate of the
GCs detected tends to be more massive, reaching upward of . However, the results show that current GC models do not quite align
with the data. We find that the models appear to be bluer than the JWST data in
the reddest (F356W-F444W) filters and redder than the data in the bluest
(F090W-F150W) filters and may need to be revised to improve the modeling of
near-IR colors of old, metal-poor stellar populations.Comment: 11 pages, 7 figure
SKYSURF-4: Panchromatic HST All-Sky Surface-Brightness Measurement Methods and Results
The diffuse, unresolved sky provides most of the photons that the Hubble
Space Telescope (HST) receives, yet remains poorly understood. HST Archival
Legacy program SKYSURF aims to measure the 0.2-1.6 m sky surface
brightness (sky-SB) from over 140,000 HST images. We describe a sky-SB
measurement algorithm designed for SKYSURF that is able to recover the input
sky-SB from simulated images to within 1% uncertainty. We present our sky-SB
measurements estimated using this algorithm on the entire SKYSURF database.
Comparing our sky-SB spectral energy distribution (SED) to measurements from
the literature shows general agreements. Our SKYSURF SED also reveals a
possible dependence on Sun angle, indicating either non-isotropic scattering of
solar photons off interplanetary dust or an additional component to Zodiacal
Light. Finally, we update Diffuse Light limits in the near-IR based on the
methods from Carleton et al. (2022), with values of 0.009 MJy sr (22 nW
m sr) at 1.25 m, 0.015 MJy sr (32 nW m
sr) at 1.4 m, and 0.013 MJy sr (25 nW m sr) at
1.6 m. These estimates provide the most stringent all-sky constraints to
date in this wavelength range. SKYSURF sky-SB measurements are made public on
the official SKYSURF website and will be used to constrain Diffuse Light in
future papers.Comment: Revised based on helpful comments from the reviewer, and accepted to
AJ on April 12th, 2023. Main paper: 18 pages, 9 figures, 4 tables.
Appendices: 16 pages, 10 figures, 1 table. Main results shown in Figure 7 and
Table
PEARLS: Low Stellar Density Galaxies in the El Gordo Cluster Observed with JWST
A full understanding of how unusually large "Ultra Diffuse Galaxies" (UDGs)
fit into our conventional understanding of dwarf galaxies remains elusive,
despite the large number of objects identified locally. A natural extension of
UDG research is the study of similar galaxies at higher redshift to establish
how their properties may evolve over time. However, this has been a challenging
task given how severely systematic effects and cosmological surface brightness
dimming inhibit our ability to study low-surface brightness galaxies at
high-. Here, we present an identification of low stellar surface density
galaxies (LDGs), likely the progenitors of local UDGs, at moderate redshift
with deep near-IR observations of the El Gordo cluster at with JWST.
By stacking 8 NIRCAM filters, we are able to achieve an apparent surface
brightness sensitivity of mag arcsec, faint enough to be
complete to the bright end of the LDG population. Our analysis identifies
significant differences between this population and local UDGs, such as their
color and size distributions, which suggest that UDG progenitors are bluer and
more extended at high- than at . This suggests that multiple
mechanisms are responsible for UDG formation and that prolonged transformation
of cluster dwarfs is not a primary UDG formation mechanism at high-.
Furthermore, we find a slight overabundance of LDGs in El Gordo, and, in
contrast to findings in local clusters, our analysis does not show a deficit of
LDGs in the center of El Gordo, implying that tidal destruction of LDGs is
significant between and .Comment: Resubmitted to ApJ after minor revision
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
Searching for Intragroup Light in Deep U-band Imaging of the COSMOS Field
We present the results of deep, ground based U-band imaging with the Large
Binocular Telescope of the Cosmic Evolution Survey (COSMOS) field as part of
the near-UV imaging program, UVCANDELS. We utilize a seeing sorted stacking
method along with night-to-night relative transparency corrections to create
optimal depth and optimal resolution mosaics in the U-band, which are capable
of reaching point source magnitudes of AB 26.5 mag at 3 sigma. These ground
based mosaics bridge the wavelength gap between the HST WFC3 F27W and ACS F435W
images and are necessary to understand galaxy assembly in the last 9-10 Gyr. We
use the depth of these mosaics to search for the presence of U-band intragroup
light (IGrL) beyond the local Universe. Regardless of how groups are scaled and
stacked, we do not detect any U-band IGrL to unprecedented U-band depths of
29.1-29.6 mag/arcsec2, which corresponds to an IGrL fraction of less than 1% of
the total group light. This stringent upper limit suggests that IGrL does not
contribute significantly to the Extragalactic Background Light at short
wavelengths. Furthermore, the lack of UV IGrL observed in these stacks suggests
that the atomic gas observed in the intragroup medium (IGrM) is likely not
dense enough to trigger star formation on large scales. Future studies may
detect IGrL by creating similar stacks at longer wavelengths or by
pre-selecting groups which are older and/or more dynamically evolved similar to
past IGrL observations of compact groups and loose groups with signs of
gravitational interactions.Comment: Accepted to PAS
Are JWST/NIRCam color gradients in the lensed z=2.3 dusty star-forming galaxy El Anzuelo due to central dust attenuation or inside-out galaxy growth?
Gradients in the mass-to-light ratio of distant galaxies impede our ability
to characterize their size and compactness. The long-wavelength filters of
's NIRCam offer a significant step forward. For galaxies at Cosmic Noon
(), this regime corresponds to the rest-frame near-infrared, which is
less biased towards young stars and captures emission from the bulk of a
galaxy's stellar population. We present an initial analysis of an extraordinary
lensed dusty star-forming galaxy (DSFG) at behind the
cluster (), named ("The Fishhook") after its partial
Einstein-ring morphology. The FUV-NIR SED suggests an intrinsic star formation
rate of and dust attenuation , in line with other DSFGs on the star-forming main sequence. We develop a
parametric lens model to reconstruct the source-plane structure of dust imaged
by the Atacama Large Millimeter/submillimeter Array, far-UV to optical light
from , and near-IR imaging with 8 filters of /NIRCam, as part of
the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS)
program. The source-plane half-light radius is remarkably consistent from m, despite a clear color gradient where the inferred galaxy center is
redder than the outskirts. We interpret this to be the result of both a
radially-decreasing gradient in attenuation and substantial spatial offsets
between UV- and IR-emitting components. A spatial decomposition of the SED
reveals modestly suppressed star formation in the inner kiloparsec, which
suggests that we are witnessing the early stages of inside-out quenching.Comment: 29 pages, 11 figures, 5 tables. Accepted for publication in Ap
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