10 research outputs found
ACS Observations of a Strongly Lensed Arc in a Field Elliptical
We report the discovery of a strongly lensed arc system around a field
elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys
(ACS) images of a parallel field observed during NICMOS observations of the HST
Ultra-Deep Field. The ACS parallel data comprise deep imaging in the F435W,
F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1.6 arcsec
from the galaxy center and subtends about 120 deg. Spectroscopic follow-up at
Magellan Observatory yields a redshift z=0.6174 for the lensing galaxy, and we
photometrically estimate z_phot = 2.4\pm0.3 for the arc. We also identify a
likely counter-arc at a radius of 0.6 arcsec, which shows structure similar to
that seen in the main arc. We model this system and find a good fit to an
elliptical isothermal potential of velocity dispersion
\kms, the value expected from the fundamental plane, and some external shear.
Several other galaxies in the field have colors similar to the lensing galaxy
and likely make up a small group.Comment: Accepted for publication in ApJ Letters. 10 pages, 3 figures. Figures
have been degraded to meet size limit; a higher resolution version and
addtional pictures available at http://acs.pha.jhu.edu/~jpb/UDFparc
Error analysis of the photometric redshift tecnique
We present a calculation of the systematic component of the error budget in
the photometric redshift technique. We make use of it to describe a simple
technique that allows for the assignation of confidence limits to redshift
measurements obtained through photometric methods. We show that our technique,
through the calculation of a redshift probability function, gives complete
information on the probable redshift of an object and its associated confidence
intervals. This information can and must be used in the calculation of any
observable quantity which makes use of the redshift.Comment: 6 pages, 5 figures, MNRAS style. Accepted for publication in MNRA
Discovery of Globular Clusters in the Proto-Spiral NGC2915: Implications for Hierarchical Galaxy Evolution
We have discovered three globular clusters beyond the Holmberg radius in
Hubble Space Telescope Advanced Camera for Surveys images of the gas-rich dark
matter dominated blue compact dwarf galaxy NGC2915. The clusters, all of which
start to resolve into stars, have M_{V606} = -8.9 to -9.8 mag, significantly
brighter than the peak of the luminosity function of Milky Way globular
clusters. Their colors suggest a metallicity [Fe/H] ~ -1.9 dex, typical of
metal-poor Galactic globular clusters. The specific frequency of clusters is at
a minimum normal, compared to spiral galaxies. However, since only a small
portion of the system has been surveyed it is more likely that the luminosity
and mass normalized cluster content is higher, like that seen in elliptical
galaxies and galaxy clusters. This suggests that NGC2915 resembles a key phase
in the early hierarchical assembly of galaxies - the epoch when much of the old
stellar population has formed, but little of the stellar disk. Depending on the
subsequent interaction history, such systems could go on to build-up larger
elliptical galaxies, evolve into normal spirals, or in rare circumstances
remain suspended in their development to become systems like NGC2915.Comment: ApJ Letters accepted; 6 pages, 2 figures, 3 table
HST/ACS Coronagraphic Imaging of the Circumstellar Disk around HD1415659A
Multicolor coronagraphic images of the circumstellar disk around HD141569A
have been obtained with the Hubble Space Telescope (HST) Advanced Camera for
Surveys. B, V, and I images show that the disk's previously-described
multiple-ring structure is actually a continuous distribution of dust with a
tightly-wound spiral structure. Two, more open spiral arms extend from the
disk, one of which appears to reach the nearby binary star HD141569BC. Diffuse
dust is seen up to 1200AU from HD141569A. Although planets may exist in the
inner region of the disk, tidal interaction with HD141569BC seems more likely
to be the cause of these phenomena. The disk appears redder than the star (B-V
= 0.21 and V-I = 0.25), and its color is spatially uniform. A scattering
asymmetry factor of g = 0.25-0.35 is derived. The azimuthal density
distribution is asymmetric, varying by a factor of ~3 at some radii.Comment: 13 pages, 9 figures, accepted in the Astronomical Journa
Classical Simulation of Relativistic Quantum Mechanics in Periodic Optical Structures
Spatial and/or temporal propagation of light waves in periodic optical
structures offers a rather unique possibility to realize in a purely classical
setting the optical analogues of a wide variety of quantum phenomena rooted in
relativistic wave equations. In this work a brief overview of a few optical
analogues of relativistic quantum phenomena, based on either spatial light
transport in engineered photonic lattices or on temporal pulse propagation in
Bragg grating structures, is presented. Examples include spatial and temporal
photonic analogues of the Zitterbewegung of a relativistic electron, Klein
tunneling, vacuum decay and pair-production, the Dirac oscillator, the
relativistic Kronig-Penney model, and optical realizations of non-Hermitian
extensions of relativistic wave equations.Comment: review article (invited), 14 pages, 7 figures, 105 reference
Advanced Camera for Surveys Photometry of the Cluster RDCS 1252.9-2927: The Color-Magnitude Relation at z
Genome-Wide Meta-Analyses of Breast, Ovarian, and Prostate Cancer Association Studies Identify Multiple New Susceptibility Loci Shared by at Least Two Cancer Types
Breast, ovarian, and prostate cancers are hormone-related and may have a shared genetic basis but this has not been investigated systematically by genome-wide association (GWA) studies. Meta-analyses combining the largest GWA meta-analysis data sets for these cancers totaling 112,349 cases and 116,421 controls of European ancestry, all together and in pairs, identified at P < 10-8 seven new cross-cancer loci: three associated with susceptibility to all three cancers (rs17041869/2q13/BCL2L11; rs7937840/11q12/INCENP; rs1469713/19p13/GATAD2A), two breast and ovarian cancer risk loci (rs200182588/9q31/SMC2; rs8037137/15q26/RCCD1), and two breast and prostate cancer risk loci (rs5013329/1p34/NSUN4; rs9375701/6q23/L3MBTL3). Index variants in five additional regions previously associated with only one cancer also showed clear association with a second cancer type. Cell-type specific expression quantitative trait locus and enhancer-gene interaction annotations suggested target genes with potential cross-cancer roles at the new loci. Pathway analysis revealed significant enrichment of death receptor signaling genes near loci with P < 10-5 in the three-cancer meta-analysis