141 research outputs found
Optimal Mass Configurations for Lensing High-Redshift Galaxies
We investigate the gravitational lensing properties of lines of sight
containing multiple cluster-scale halos, motivated by their ability to lens
very high-redshift (z ~ 10) sources into detectability. We control for the
total mass along the line of sight, isolating the effects of distributing the
mass among multiple halos and of varying the physical properties of the halos.
Our results show that multiple-halo lines of sight can increase the magnified
source-plane region compared to the single cluster lenses typically targeted
for lensing studies, and thus are generally better fields for detecting very
high-redshift sources. The configurations that result in optimal lensing cross
sections benefit from interactions between the lens potentials of the halos
when they overlap somewhat on the sky, creating regions of high magnification
in the source plane not present when the halos are considered individually. The
effect of these interactions on the lensing cross section can even be
comparable to changing the total mass of the lens from 10^15 M_sun to 3x10^15
M_sun. The gain in lensing cross section increases as the mass is split into
more halos, provided that the lens potentials are projected close enough to
interact with each other. A nonzero projected halo angular separation, equal
halo mass ratio, and high projected halo concentration are the best mass
configurations, whereas projected halo ellipticity, halo triaxiality, and the
relative orientations of the halos are less important. Such high mass,
multiple-halo lines of sight exist in the SDSS.Comment: Accepted for publication in ApJ; emulateapj format; 24 pages, 13
figures, 1 table; plots updated to reflect erratu
Spatially Resolved Stellar Populations of Eight GOODS-South Active Galactic Nuclei at z ~ 1
We present a pilot study of the stellar populations of eight active galactic nucleus (AGN) hosts at z ~ 1 and compare with (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the Great Observatories Origins Deep Survey South field obtained with the laser guide star adaptive optics system at Keck Observatory. We combine these K' data with B, V, i, and z imaging from the Advanced Camera for Surveys on Hubble Space Telescope to give multicolor photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGNs as inferred from their high X-ray luminosities (LX > 10^42 erg s^–1) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [O III] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there are only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR spectral energy distributions of the strong Type II AGNs indicate that they are excited to Luminous InfraRed Galaxy (LIRG) status via galactic starbursting, while the strong Type I AGNs are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGNs at z ~ 1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are by-products of this starbursting
Astrometric performance of the Gemini multi-conjugate adaptive optics system in crowded fields
The Gemini Multi-conjugate adaptive optics System (GeMS) is a facility
instrument for the Gemini-South telescope. It delivers uniform,
near-diffraction-limited image quality at near-infrared wavelengths over a 2
arcminute field of view. Together with the Gemini South Adaptive Optics Imager
(GSAOI), a near-infrared wide field camera, GeMS/GSAOI's combination of high
spatial resolution and a large field of view will make it a premier facility
for precision astrometry. Potential astrometric science cases cover a broad
range of topics including exo-planets, star formation, stellar evolution, star
clusters, nearby galaxies, black holes and neutron stars, and the Galactic
center. In this paper, we assess the astrometric performance and limitations of
GeMS/GSAOI. In particular, we analyze deep, mono-epoch images, multi-epoch data
and distortion calibration. We find that for single-epoch, un-dithered data, an
astrometric error below 0.2 mas can be achieved for exposure times exceeding
one minute, provided enough stars are available to remove high-order
distortions. We show however that such performance is not reproducible for
multi-epoch observations, and an additional systematic error of ~0.4 mas is
evidenced. This systematic multi-epoch error is the dominant error term in the
GeMS/GSAOI astrometric error budget, and it is thought to be due to
time-variable distortion induced by gravity flexure.Comment: 16 pages, 22 figures, accepted for publication in MNRA
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
Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10-Meter Telescope at Visible Wavelengths
One important frontier for astronomical adaptive optics (AO) involves methods
such as Multi-Object AO and Multi-Conjugate AO that have the potential to give
a significantly larger field of view than conventional AO techniques. A second
key emphasis over the next decade will be to push astronomical AO to visible
wavelengths. We have conducted the first laboratory simulations of wide-field,
laser guide star adaptive optics at visible wavelengths on a 10-meter-class
telescope. These experiments, utilizing the UCO/Lick Observatory's Multi-Object
/ Laser Tomography Adaptive Optics (MOAO/LTAO) testbed, demonstrate new
techniques in wavefront sensing and control that are crucial to future on-sky
MOAO systems. We (1) test and confirm the feasibility of highly accurate
atmospheric tomography with laser guide stars, (2) demonstrate key innovations
allowing open-loop operation of Shack-Hartmann wavefront sensors (with errors
of ~30 nm) as will be needed for MOAO, and (3) build a complete error budget
model describing system performance. The AO system maintains a performance of
32.4% Strehl on-axis, with 24.5% and 22.6% at 10" and 15", respectively, at a
science wavelength of 710 nm (R-band) over the equivalent of 0.8 seconds of
simulation. The MOAO-corrected field of view is ~25 times larger in area than
that limited by anisoplanatism at R-band. Our error budget is composed of terms
verified through independent, empirical experiments. Error terms arising from
calibration inaccuracies and optical drift are comparable in magnitude to
traditional terms like fitting error and tomographic error. This makes a strong
case for implementing additional calibration facilities in future AO systems,
including accelerometers on powered optics, 3D turbulators, telescope and LGS
simulators, and external calibration ports for deformable mirrors.Comment: 29 pages, 11 figures, submitted to PAS
Joint Strong and Weak Lensing Analysis of the Massive Cluster Field J0850+3604
We present a combined strong and weak lensing analysis of the
J085007.6+360428 (J0850) field, which was selected by its high projected
concentration of luminous red galaxies and contains the massive cluster Zwicky
1953. Using Subaru/Suprime-Cam imaging and
MMT/Hectospec spectroscopy, we first perform a weak lensing shear analysis to
constrain the mass distribution in this field, including the cluster at and a smaller foreground halo at . We then add a strong
lensing constraint from a multiply-imaged galaxy in the imaging data with a
photometric redshift of . Unlike previous cluster-scale lens
analyses, our technique accounts for the full three-dimensional mass structure
in the beam, including galaxies along the line of sight. In contrast with past
cluster analyses that use only lensed image positions as constraints, we use
the full surface brightness distribution of the images. This method predicts
that the source galaxy crosses a lensing caustic such that one image is a
highly-magnified "fold arc", which could be used to probe the source galaxy's
structure at ultra-high spatial resolution ( pc). We calculate the mass
of the primary cluster to be with a concentration of , consistent with the mass-concentration relation of
massive clusters at a similar redshift. The large mass of this cluster makes
J0850 an excellent field for leveraging lensing magnification to search for
high-redshift galaxies, competitive with and complementary to that of
well-studied clusters such as the HST Frontier Fields.Comment: Accepted for publication in The Astrophysical Journal; 14 pages, 13
figures, 3 table
Identifying Very Metal-Rich Stars with Low-Resolution Spectra: Finding Planet-Search Targets
We present empirical calibrations that estimate stellar metallicity,
effective temperature and surface gravity as a function of Lick/IDS indices.
These calibrations have been derived from a training set of 261 stars for which
(1) high-precision measurements of [Fe/H], T_eff and log g have been made using
spectral-synthesis analysis of HIRES spectra, and (2) Lick indices have also
been measured. Our [Fe/H] calibration, which has precision 0.07 dex, has
identified a number of bright (V < 9) metal-rich stars which are now being
screened for hot Jupiter-type planets. Using the Yonsei-Yale stellar models, we
show that the calibrations provide distance estimates accurate to 20% for
nearby stars.
This paper outlines the second tier of the screening of planet-search targets
by the N2K Consortium, a project designed to identify the stars most likely to
harbor extrasolar planets. Discoveries by the N2K Consortium include the
transiting hot Saturn HD 149026 b (Sato et al. 2005, astro-ph/0507009) and HD
88133 b (Fischer et al. 2005). See Ammons et al. (2005, In Press) for a
description of the first tier of N2K metallicity screening, calibrations using
broadband photometry.Comment: Accepted for publication in the Astrophysical Journa
Spatially Resolved Stellar Populations of Eight GOODS-South AGN at z~1
We present a pilot study of the stellar populations of 8 AGN hosts at z~1 and
compare to (1) lower redshift samples and (2) a sample of nonactive galaxies of
similar redshift. We utilize K' images in the GOODS South field obtained with
the laser guide star adaptive optics (LGSAO) system at Keck Observatory. We
combine this K' data with B, V, i, and z imaging from the ACS on HST to give
multi-color photometry at a matched spatial resolution better than 100 mas in
all bands. The hosts harbor AGN as inferred from their high X-ray luminosities
(L_X > 10^42 ergs/s) or mid-IR colors. We find a correlation between the
presence of younger stellar populations and the strength of the AGN, as
measured with [OIII] line luminosity or X-ray (2-10 keV) luminosity. This
finding is consistent with similar studies at lower redshift. Of the three Type
II galaxies, two are disk galaxies and one is of irregular type, while in the
Type I sample there only one disk-like source and four sources with smooth,
elliptical/spheroidal morphologies. In addition, the mid-IR SEDs of the strong
Type II AGN indicate that they are excited to LIRG (Luminous InfraRed Galaxy)
status via galactic starbursting, while the strong Type I AGN are excited to
LIRG status via hot dust surrounding the central AGN. This supports the notion
that the obscured nature of Type II AGN at z~1 is connected with global
starbursting and that they may be extincted by kpc-scale dusty features that
are byproducts of this starbursting.Comment: 56 pages, 39 figures, accepted to A
Point Source Polarimetry with the Gemini Planet Imager: Sensitivity Characterization with T5.5 Dwarf Companion HD 19467 B
Detecting polarized light from self-luminous exoplanets has the potential to provide key information about rotation, surface gravity, cloud grain size, and cloud coverage. While field brown dwarfs with detected polarized emission are common, no exoplanet or substellar companion has yet been detected in polarized light. With the advent of high contrast imaging spectro-polarimeters such as GPI and SPHERE, such a detection may now be possible with careful treatment of instrumental polarization. In this paper, we present 28 minutes of H-band GPI polarimetric observations of the benchmark T5.5 companion HD 19467 B. We detect no polarization signal from the target, and place an upper limit on the degree of linear polarization of p_(CL99.73%) ⩽ 2.4%. We discuss our results in the context of T dwarf cloud models and photometric variability
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