725 research outputs found
A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: The Group Catalog
With a large, unique spectroscopic survey in the fields of 28 galaxy-scale
strong gravitational lenses, we identify groups of galaxies in the 26
adequately-sampled fields. Using a group finding algorithm, we find 210 groups
with at least five member galaxies; the median number of members is eight. Our
sample spans redshifts of 0.04 0.76 with a median of 0.31,
including 174 groups with . Groups have radial velocity
dispersions of 60 1200 km s with a median of 350
km s. We also discover a supergroup in field B0712+472 at 0.29
consisting of three main groups. We recover groups similar to 85% of
those previously reported in these fields within our redshift range of
sensitivity and find 187 new groups with at least five members. The properties
of our group catalog, specifically 1) the distribution of , 2)
the fraction of all sample galaxies that are group members, and 3) the fraction
of groups with significant substructure, are consistent with those for other
catalogs. The distribution of group virial masses agrees well with theoretical
expectations. Of the lens galaxies, 12 of 26 (46%) (B1422+231, B1600+434,
B2114+022, FBQS J0951+2635, HE0435-1223, HST J14113+5211, MG0751+2716,
MGJ1654+1346, PG 1115+080, Q ER 0047-2808, RXJ1131-1231, and WFI J2033-4723)
are members of groups with at least five galaxies, and one more (B0712+472)
belongs to an additional, visually identified group candidate. There are groups
not associated with the lens that still are likely to affect the lens model; in
six of 25 (24%) fields (excluding the supergroup), there is at least one
massive ( 500 km s) group or group candidate projected
within 2 of the lens.Comment: 87 pages, 8 figures, a version of this was published in Ap
A Spectroscopic Study of the Environments of Gravitational Lens Galaxies
(Abridged) We present the first results from our spectroscopic survey of the
environments of strong gravitational lenses. The lens galaxy belongs to a poor
group of galaxies in six of the eight systems in our sample. We discover three
new groups associated with the lens galaxies of BRI 0952-0115 (five members),
MG 1654+1346 (seven members), and B2114+022 (five members). We more than double
the number of members for another three previously known groups around the
lenses MG 0751+2716 (13 total members), PG 1115+080 (13 total members), and
B1422+231 (16 total members). We determine the kinematics of the six groups,
including their mean velocities, velocity dispersions, and projected spatial
centroids. The velocity dispersions of the groups range from 110 +170, -80 to
470 +100, -90 km/s. In at least three of the lenses -- MG0751, PG1115, and
B1422 -- the group environment significantly affects the lens potential. These
lenses happen to be the quadruply-imaged ones in our sample, which suggests a
connection between image configuration and environment. The lens galaxy is the
brightest member in fewer than half of the groups. Our survey also allows us to
assess for the first time whether mass structures along the line of sight are
important for lensing. We first show that, in principle, the lens potential may
be affected by line-of-sight structures over a wide range of spatial and
redshift offsets from the lens. We then quantify real line-of-sight effects
using our survey and find that at least four of the eight lens fields have
substantial interloping structures close in projection to the lens, and at
least one of those structures (in the field of MG0751) significantly affects
the lens potential.Comment: Accepted for publication in the Astrophysical Journal. Figure 6
posted as a JPEG image. Requires emulateapj.st
The Velocity Function of Galaxies
We present a galaxy circular velocity function, Psi(log v), derived from
existing luminosity functions and luminosity-velocity relations. Such a
velocity function is desirable for several reasons. First, it enables an
objective comparison of luminosity functions obtained in different bands and
for different galaxy morphologies, with a statistical correction for dust
extinction. In addition, the velocity function simplifies comparison of
observations with predictions from high-resolution cosmological N-body
simulations.
We derive velocity functions from five different data sets and find rough
agreement among them, but about a factor of 2 variation in amplitude. These
velocity functions are then compared with N-body simulations of a LCDM model
(corrected for baryonic infall) in order to demonstrate both the utility and
current limitations of this approach. The number density of dark matter halos
and the slope of the velocity function near v_*, the circular velocity
corresponding to an ~L_* spiral galaxy, are found to be comparable to that of
observed galaxies. The primary sources of uncertainty in construction of
Psi(log v) from observations and N-body simulations are discussed and
explanations are suggected to account for these discrepancies.Comment: Latex. 28 pages, 4 figures. Accepted by Ap
Directional Reflectance Studies in Support of the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley
The Radiometric Calibration Test Site (RadCaTS) is a suite of commercial and custom instruments used to make measurements of the surface reflectance and atmosphere throughout the day at Railroad Valley, Nevada. It was developed in response to the need for daily radiometric calibration data for the vast array of Earth-observing sensors on orbit, which is continuously increasing as more nations and private companies launch individual environmental satellites as well as large constellations. The current suite of instruments at RadCaTS includes five ground-viewing radiometers (GVRs), four of which view the surface in a nadir-viewing configuration. Many sensors such as those on Landsat-7 and Landsat-8 view Railroad Valley within 3 of nadir, while others such as those on Sentinel-2A and -2B, RapidEye, Aqua, Suomi NPP, and Terra can view Railroad Valley at off-nadir angles. Past efforts have shown that the surface bidirectional reflectance distribution function (BRDF) has minimal impact on vicarious calibration uncertainties for views <10, but the desire to use larger view angles has prompted the effort to develop a BRDF correction for data from RadCaTS. The current work investigates the application of Railroad Valley BRDF data derived from a BRF camera developed at the University of Arizona in the 1990s (but is no longer in use) to the current RadCaTS surface reflectance measurements. Also investigated are early results from directional reflectance studies using a mobile spectro-goniometer system during a round-robin field campaign in 2018. This work describes the preliminary results, the effects on current measurements, and the approach for future measurements
Discovery of a Nova-Like Cataclysmic Variable in the Kepler Mission Field
We announce the identification of a new cataclysmic variable star in the
field of the Kepler Mission, KIC J192410.81+445934.9. This system was
identified during a search for compact pulsators in the Kepler field.
High-speed photometry reveals coherent large-amplitude variability with a
period of 2.94 h. Rapid, large-amplitude quasi-periodic variations are also
detected on time scales of ~1200 s and ~650 s. Time-resolved spectroscopy
covering one half photometric period shows shallow, broad Balmer and He I
absorption lines with bright emission cores as well as strong He II and Bowen
blend emission. Radial velocity variations are also observed in the Balmer and
He I emission lines that are consistent with the photometric period. We
therefore conclude that KIC J192410.81+445934.9 is a nova-like variable of the
UX UMa class in or near the period gap, and it may belong to the rapidly
growing subclass of SW Sex systems. Based on 2MASS photometry and companion
star models, we place a lower limit on the distance to the system of ~500 pc.
Due to limitations of our discovery data, additional observations including
spectroscopy and polarimetry are needed to confirm the nature of this object.
Such data will help to further understanding of the behavior of nova-like
variables in the critical period range of 3-4 h, where standard cataclysmic
variable evolutionary theory finds major problems. The presence of this system
in the Kepler mission field-of-view also presents a unique opportunity to
obtain a continuous photometric data stream of unparalleled length and
precision on a cataclysmic variable system.Comment: Accepted for publication in the Astronomical Journal. 8 pages, 7
figures, uses emulateapj
Toward Models for the Full Oxygen-Evolving Complex of Photosystem II by Ligand Coordination To Lower the Symmetry of the Mn_3CaO_4 Cubane: Demonstration That Electronic Effects Facilitate Binding of a Fifth Metal
Synthetic model compounds have been targeted to benchmark and better understand the electronic structure, geometry, spectroscopy, and reactivity of the oxygen-evolving complex (OEC) of photosystem II, a low-symmetry Mn_4CaO_n cluster. Herein, low-symmetry Mn^(IV)_3GdO_4 and Mn^(IV_)3CaO_4 cubanes are synthesized in a rational, stepwise fashion through desymmetrization by ligand substitution, causing significant cubane distortions. As a result of increased electron richness and desymmetrization, a specific μ_3-oxo moiety of the Mn_3CaO_4 unit becomes more basic allowing for selective protonation. Coordination of a fifth metal ion, Ag+, to the same site gives a Mn_3CaAgO_4 cluster that models the topology of the OEC by displaying both a cubane motif and a “dangler” transition metal. The present synthetic strategy provides a rational roadmap for accessing more accurate models of the biological catalyst
Cool White Dwarfs in the Sloan Digital Sky Survey
A reduced proper motion diagram utilizing Sloan Digital Sky Survey (SDSS)
photometry and astrometry and USNO-B plate astrometry is used to separate cool
white dwarf candidates from metal-weak, high-velocity main sequence Population
II stars (subdwarfs) in the SDSS Data Release 2 imaging area. Follow-up
spectroscopy using the Hobby-Eberly Telescope, the MMT, and the McDonald 2.7m
Telescope is used to demonstrate that the white dwarf and subdwarf loci
separate cleanly in the reduced proper motion diagram, and that the
contamination by subdwarfs is small near the cool white dwarf locus. This
enables large statistically complete samples of white dwarfs, particularly the
poorly understood cool white dwarfs, to be created from the SDSS imaging
survey, with important implications for white dwarf luminosity function
studies. SDSS photometry for our sample of cool white dwarfs is compared to
current white dwarf models.Comment: AJ accepted, 36 pages, 11 figures (Figure 1 low-rez version
Development of a Low-Resource Combined Gamma-Ray and Neutron Spectrometer for Planetary Science
Planetary neutron and gamma-ray spectroscopy (NGRS) has become a standard technique to measure distinctive geochemical composition and volatile abundance signatures for key elements relevant to planetary structure and evolution. Previous NGRS measurements have led to the discovery of the concentration of many elements including hydrogen on the Moon, Mars, Mercury, and the asteroids Eros, Vesta, and Ceres, but by utilizing separate NGRS. We have developed the Elpasolite Planetary Ice and Composition Spectrometer (EPICS) instrument, an innovative and combined NGRS with low resource requirements. EPICS incorporates elpasolite scintillator read out by silicon photomultipliers (SiPMs) to provide significant reduction in size, weight, and power, while achieving excellent neutron detection sensitivity and gamma-ray energy resolution as good as 2.9% full-width half-maximum at 662 keV. EPICS is ideally suited to resource constrained missions and is applicable to numerous targets such as the Moon, Mars, and small planetary bodies. An overview of the EPICS instrument and its simulated performance on a few notional missions is presented. We have integrated and done performance testing of a prototype of the EPICS instrument, including optimization of an amplification and summing circuit for a 64-element SiPM array that preserves pulse shape discrimination capability, which will be summarized
A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey
We present optical spectroscopy and near-infrared photometry of 126 cool
white dwarfs in the Sloan Digital Sky Survey (SDSS). Our sample includes high
proper motion targets selected using the SDSS and USNO-B astrometry and a dozen
previously known ultracool white dwarf candidates. Our optical spectroscopic
observations demonstrate that a clean selection of large samples of cool white
dwarfs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic
Survey Telescope datasets) is possible using a reduced proper motion diagram
and a tangential velocity cut-off (depending on the proper motion accuracy) of
30 km/s. Our near-infrared observations reveal eight new stars with significant
absorption. We use the optical and near-infrared photometry to perform a
detailed model atmosphere analysis. More than 80% of the stars in our sample
are consistent with either pure hydrogen or pure helium atmospheres. However,
the eight stars with significant infrared absorption and the majority of the
previously known ultracool white dwarf candidates are best explained with mixed
hydrogen and helium atmosphere models. The age distribution of our sample is
consistent with a Galactic disk age of 8 Gyr. A few ultracool white dwarfs may
be as old as 12-13 Gyr, but our models have problems matching the spectral
energy distributions of these objects. There are only two halo white dwarf
candidates in our sample. However, trigonometric parallax observations are
required for accurate mass and age determinations and to confirm their
membership in the halo.Comment: ApJ Supplements, in pres
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