244 research outputs found
Hundreds of Milky Way satellites? Luminosity bias in the satellite luminosity function
We correct the observed Milky Way satellite luminosity function for
luminosity bias using published completeness limits for the Sloan Digital Sky
Survey DR5. Assuming that the spatial distribution of Milky Way satellites
tracks the subhalos found in the Via Lactea LCDM N-body simulation, we show
that there should be between ~300 and ~600 satellites within 400 kpc of the Sun
that are brighter than the faintest known dwarf galaxies, and that there may be
as many as ~ 1000, depending on assumptions. By taking into account
completeness limits, we show that the radial distribution of known Milky Way
dwarfs is consistent with our assumption that the full satellite population
tracks that of subhalos. These results alleviate the primary worries associated
with the so-called missing satellites problem in CDM. We show that future, deep
wide-field surveys such as SkyMapper, the Dark Energy Survey (DES), PanSTARRS,
and the Large Synoptic Survey Telescope (LSST) will deliver a complete census
of ultra-faint dwarf satellites out to the Milky Way virial radius, offer new
limits on the free-streaming scale of dark matter, and provide unprecedented
constraints on the low-luminosity threshold of galaxy formation.Comment: 13 pages, 10 figures, ApJ In Pres
Occupational Exposure to Trichloroethylene and Cancer Risk for Workers at the Paducah Gaseous Diffusion Plant
Objective: The Paducah Gaseous Diffusion Plant (PGDP) became operational in 1952; it is located in the western part of Kentucky. We conducted a mortality study for adverse health effects that workers may have suffered while working at the plant, including exposures to chemicals. Materials and Methods: We studied a cohort of 6820 workers at the PGDP for the period 1953 to 2003; there were a total of 1672 deaths to cohort members. Trichloroethylene (TCE) is a specific concern for this workforce; exposure to TCE occurred primarily in departments that clean the process equipment. The Life Table Analysis System (LTAS) program developed by NIOSH was used to calculate the standardized mortality ratios for the worker cohort and standardized rate ratio relative to exposure to TCE (the U.S. population is the referent for age-adjustment). LTAS calculated a significantly low overall SMR for these workers of 0.76 (95% CI: 0.72-0.79). A further review of three major cancers of interest to Kentucky produced significantly low SMR for trachea, bronchus, lung cancer (0.75, 95% CI: 0.72-0.79) and high SMR for Non-Hodgkin\u27s lymphoma (NHL) (1.49, 95% CI: 1.02-2.10). Results: No significant SMR was observed for leukemia and no significant SRRs were observed for any disease. Both the leukemia and lung cancer results were examined and determined to refect regional mortality patterns. However, the Non-Hodgkin\u27s Lymphoma finding suggests a curious amplification when living cases are included with the mortality experience. Conclusions: Further examination is recommended of this recurrent finding from all three U.S. Gaseous Diffusion plants
Galaxies behind the Galactic plane: First results and perspectives from the VVV Survey
Vista Variables in The Via Lactea (VVV) is an ESO variability survey that is
performing observations in near infrared bands (ZYJHKs) towards the Galactic
bulge and part of the disk with the completeness limits at least 3 mag deeper
than 2MASS. In the present work, we searched in the VVV survey data for
background galaxies near the Galactic plane using ZYJHKs photometry that covers
1.636 square degrees. We identified 204 new galaxy candidates by analyzing
colors, sizes, and visual inspection of multi-band (ZYJHKs) images. The galaxy
candidates colors were also compared with the predicted ones by star counts
models considering a more realistic extinction model at the same completeness
limits observed by VVV. A comparison of the galaxy candidates with the expected
one by Milennium simulations is also presented. Our results increase the number
density of known galaxies behind the Milky Way by more than one order of
magnitude. A catalog with galaxy properties including ellipticity, Petrosian
radii and ZYJHKs magnitudes is provided, as well as comparisons of the results
with other surveys of galaxies towards Galactic plane.Comment: 27 pages, 10 figures, 2 tables; in press at The Astronomical Journa
A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
We report five Local Volume dwarf galaxies (two of which are presented here
for the first time) uncovered during a comprehensive archival search for
optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC
population of HI clouds are thought to be candidate gas-rich, low mass halos at
the edge of the Local Group and beyond, but no comprehensive search for stellar
counterparts to these systems has been presented. Careful visual inspection of
all publicly available optical and ultraviolet imaging at the position of the
UCHVCs revealed six blue, diffuse counterparts with a morphology consistent
with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all
six candidate dwarf counterparts show that five have an H-derived
velocity consistent with the coincident HI cloud, confirming their association,
the sixth diffuse counterpart is likely a background object. The size and
luminosity of the UCHVC dwarfs is consistent with other known Local Volume
dwarf irregular galaxies. The gas fraction () of the five
dwarfs are generally consistent with that of dwarf irregular galaxies in the
Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC
HVC274.68+74.70123) has a very high 40. Despite the
heterogenous nature of our search, we demonstrate that the current dwarf
companions to UCHVCs are at the edge of detectability due to their low surface
brightness, and that deeper searches are likely to find more stellar systems.
If more sensitive searches do not reveal further stellar counterparts to
UCHVCs, then the dearth of such systems around the Local Group may be in
conflict with CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte
Pegasus V -- a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda
We report the discovery of an ultra-faint dwarf in the constellation of
Pegasus. Pegasus~V (Peg~V) was initially identified in the public imaging data
release of the DESI Legacy Imaging Surveys and confirmed with deep imaging from
Gemini/GMOS-N. The colour-magnitude diagram shows a sparse red giant branch
(RGB) population and a strong over-density of blue horizontal branch stars. We
measure a distance to Peg~V of ~kpc, making it a distant
satellite of Andromeda with and a half-light radius of ~pc. It is located ~kpc from Andromeda in the outskirts
of its halo. The RGB is well-fit by a metal-poor isochrone with [Fe/H],
suggesting it is very metal poor. This, combined with its blue horizontal
branch could imply that it is a reionisation fossil. This is the first
detection of an ultra-faint dwarf outside the deep Pan-Andromeda Archaeological
Survey area, and points to a rich, faint satellite population in the outskirts
of our nearest neighbour.Comment: Submitted to MNRAS Letters. 6 pages, 4 figures. Comments welcom
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