56 research outputs found
Stellar Populations of Highly Magnified Lensed Galaxies: Young Starbursts at z~2
We present a comprehensive analysis of the rest-frame UV to near-IR spectral
energy distributions and rest-frame optical spectra of four of the brightest
gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at
z=1.70, MS1512-cB58 at z=2.73, SGAS J152745.1+065219 at z=2.76 and SGAS
J122651.3+215220 at z=2.92. This includes new Spitzer imaging for RCSGA0327 as
well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and
SGAS1226. Lensing magnifications of 3-4 magnitudes allow a detailed study of
the stellar populations and physical conditions. We compare star formation
rates as measured from the SED fit, the H-alpha and [OII] emission lines, and
the UV+IR bolometric luminosity where 24 micron photometry is available. The
SFR estimate from the SED fit is consistently higher than the other indicators,
which suggests that the Calzetti dust extinction law used in the SED fitting is
too flat for young star-forming galaxies at z~2. Our analysis finds similar
stellar population parameters for all four lensed galaxies: stellar masses
3-7*10^9 M_sun, young ages ~ 100 Myr, little dust content E(B-V)=0.10-0.25, and
star formation rates around 20-100 M_sun/yr. Compared to typical values for the
galaxy population at z~2, this suggests we are looking at newly formed,
starbursting systems that have only recently started the build-up of stellar
mass. These results constitute the first detailed, uniform analysis of a sample
of the growing number of strongly lensed galaxies known at z~2.Comment: 13 pages, 8 figures, Accepted to Ap
Properties of galaxy dark matter halos from weak lensing
We present the results of a study of weak lensing by galaxies based on 45.5
deg of band imaging data from the Red-Sequence Cluster Survey (RCS).
We present the first weak lensing detection of the flattening of galaxy dark
matter halos. We use a simple model in which the ellipticity of the halo is
times the observed ellipticity of the lens. We find a best fit value of
, suggesting that the dark matter halos are somewhat
rounder than the light distribution. The fact that we detect a significant
flattening implies that the halos are well aligned with the light distribution.
Given the average ellipticity of the lenses, this implies a halo ellipticity of
, in fair agreement with results from
numerical simulations of CDM. This result provides strong support for the
existence of dark matter, as an isotropic lensing signal is excluded with 99.5%
confidence. We also study the average mass profile around the lenses, using a
maximum likelihood analysis. We consider two models for the halo mass profile:
a truncated isothermal sphere (TIS) and an NFW profile. We adopt
observationally motivated scaling relations between the lens luminosity and the
velocity dispersion and the extent of the halo. The best fit NFW model yields a
mass and a scale
radius kpc. This value for the scale radius is
in excellent agreement with predictions from numerical simulations for a halo
of this mass.Comment: Significantly revised version, accepted for publication in ApJ 11
pages, 6 figure
The X-ray Properties of Optically Selected Clusters of Galaxies
We present the results of Chandra and Suzaku X-ray observations of nine
moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence
Cluster Survey (RCS). Surface brightness profiles are fitted to beta models,
gas masses are determined, integrated spectra are extracted within R2500, and
X-ray temperatures and luminosities are inferred. The Lx-Tx relationship
expected from self-similar evolution is tested by comparing this sample to our
previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically
selected clusters. We find that optically selected clusters are systematically
less luminous than X-ray selected clusters of similar X-ray temperature at both
moderate and high-z. We are unable to constrain evolution in the Lx-Tx relation
with these data, but find it consistent with no evolution, within relatively
large uncertainties. To investigate selection effects, we compare the X-ray
properties of our sample to those of clusters in the representative X-ray
selected REXCESS sample, also determined within R2500. We find that while RCS
cluster X-ray properties span the entire range of those of massive clusters
selected by other methods, their average X-ray properties are most similar to
those of dynamically disturbed X-ray selected clusters. This similarity
suggests that the true cluster distribution might contain a higher fraction of
disturbed objects than are typically detected in X-ray selected surveys.Comment: 13 pages, 5 figures; accepted for publication in MNRAS. Figure
quality reduced to comply with arXiv file size requirement
The EXPLORE Project I: A Deep Search for Transiting Extrasolar Planets
(Abridged) We discuss the design considerations of the EXPLORE (EXtra-solar
PLanet Occultation REsearch) project, a series of transiting planet searches
using 4-m-class telescopes to continuously monitor a single field of stars in
the Galactic Plane in each ~2 week observing campaign. We discuss the general
factors which determine the efficiency and the number of planets found by a
transit search, including time sampling strategy and field selection. The
primary goal is to select the most promising planet candidates for radial
velocity follow-up observations. We show that with very high photometric
precision light curves that have frequent time sampling and at least two
detected transits, it is possible to uniquely solve for the main parameters of
the eclipsing system (including planet radius) based on several important
assumptions about the central star. Together with a measured spectral type for
the star, this unique solution for orbital parameters provides a powerful
method for ruling out most contaminants to transiting planet candidates. For
the EXPLORE project, radial velocity follow-up observations for companion mass
determination of the best candidates are done on 8-m-class telescopes within
two or three months of the photometric campaigns. This same-season follow-up is
made possible by the use of efficient pipelines to produce high quality light
curves within weeks of the observations. We conclude by presenting early
results from our first search, EXPLORE I, in which we reached <1% rms
photometric precision (measured over a full night) on ~37,000 stars to I <=
18.2.Comment: accepted by ApJ. Main points unchanged but more thorough discussion
of some issues. 36 pages, including 14 figure
Dissecting a 30 kpc galactic outflow at 1.7
We present the spatially resolved measurements of a cool galactic outflow in
the gravitationally lensed galaxy RCS0327 at using VLT/MUSE
IFU observations. We probe the cool outflowing gas, traced by blueshifted Mg II
and Fe II absorption lines, in 15 distinct regions of the same galaxy in its
image-plane. Different physical regions, 5 to 7 kpc apart within the galaxy,
drive the outflows at different velocities ( to km
s), and mass outflow rates ( 183 to 527 $M_{\odot}\
yr^{-1}^{-1}^2^2
\sim -120-242^{-1}\simM_{\odot}\ yr^{-1}\geq\approx$ 10% of the total energy flux
provided by star-formation. These estimates suggest that the outflow in RCS0327
is energy driven. This work shows the importance of small scale variations of
outflow properties due to the variations of local stellar properties of the
host galaxy in the context of galaxy evolution.Comment: 24 pages, 15 figures, 6 tables, submitted to MNRA
A 30 kpc Spatially Extended Clumpy and Asymmetric Galactic Outflow at z 1.7
We image the spatial extent of a cool galactic outflow with fine structure Fe
II emission and resonant Mg II emission in a gravitationally lensed
star-forming galaxy at . The Fe II and Mg II
(continuum-subtracted) emissions span out to radial distances of 14.33
kpc and 26.5 kpc, respectively, with maximum spatial extents of 21 kpc
for Fe II emission and 30 kpc for Mg II emission. Mg II residual
emission is patchy and covers a total area of 184 kpc, constraining
the minimum area covered by the outflowing gas to be 13% of the total
area. Mg II emission is asymmetric and shows 21% more extended emission
along the declination direction. We constrain the covering fractions of the Fe
II and Mg II emission as a function of radial distance and characterize
them with a power law model. The Mg II 2803 emission line shows two
kinematically distinct emission components, and may correspond to two distinct
shells of outflowing gas with a velocity separation of 400
km/s. By using multiple images with different magnifications of the galaxy in
the image plane, we trace the Fe II, Mg II emissions around three
individual star-forming regions. In all cases, both the Fe II and Mg II
emissions are more spatially extended compared to the star forming regions
traced by the [O II] emission. These findings provide robust constraints on the
spatial extent of the outflowing gas, and combined with outflow velocity and
column density measurements will give stringent constraints on mass outflow
rates of the galaxy.Comment: 22 pages, 14 figures, 4 tables, accepted to ApJ, the referee comments
are incorporated in this versio
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