359 research outputs found
Improved Templates for Photometric Redshifts of Submm Sources
There is growing evidence that some star-forming galaxies at z>1 are
characterized by high efficiencies and specific star formation rates. In the
local universe, these traits are shared by ``active'' Blue Compact Dwarf
galaxies (BCDs) with compact and dense star-forming regions. The Spectral
Energy Distributions (SEDs) of these BCDs are dominated by young massive star
clusters, embedded in a cocoon of dust. In this Letter, we incorporate these
BCD SEDs as templates for two samples of high-redshift galaxy populations
selected at submm wavelengths. Because of the severe absorption of the optical
light, the featureless mid-infrared spectrum, and the relatively flat radio
continuum, the dusty star-cluster SEDs are good approximations to most of the
submm sources in our samples. In most cases, the active BCD SEDs fit the
observed photometric points better than the ``standard'' templates, M 82 and
Arp 220, and predict photometric redshifts significantly closer to the
spectroscopic ones. Our results strongly suggest that the embedded dusty star
clusters in BCD galaxies are superior to other local templates such as M 82 and
Arp 220 in fitting distant submm starburst galaxies.Comment: Accepted by ApJL: 4 pages, 2 figures, 2 table
Asteroids Observed by The Sloan Digital Sky Survey
We announce the first public release of the SDSS Moving Object Catalog, with
SDSS observations for 58,117 asteroids. The catalog lists astrometric and
photometric data for moving objects observed prior to Dec 15, 2001, and also
includes orbital elements for 10,592 previously known objects. We analyze the
correlation between the orbital parameters and optical colors for the known
objects, and confirm that asteroid dynamical families, defined as clusters in
orbital parameter space, also strongly segregate in color space. Their
distinctive optical colors indicate that the variations in chemical composition
within a family are much smaller than the compositional differences between
families, and strongly support earlier suggestions that asteroids belonging to
a particular family have a common origin.Comment: 6 pages, 1 color figure, to be presented at "Astronomical Telescopes
& Instrumentation", SPIE 200
Far-Infrared Spectral Energy Distributions and Photometric Redshifts of Dusty Galaxies
We infer the large-scale source parameters of dusty galaxies from their
observed spectral energy distributions (SEDs) using the analytic radiative
transfer methodology presented in Chakrabarti & McKee (2005). For local
ultra-luminous infrared galaxies (ULIRGs), we show that the millimeter to
far-infrared (FIR) SEDs can be well fit using the standard dust opacity index
of 2 when self-consistent radiative transfer solutions are employed, indicating
that the cold dust in local ULIRGs can be described by a single grain model. We
develop a method for determining photometric redshifts of ULIRGs and sub-mm
galaxies from the millimeter-FIR SED; the resulting value of is typically
accurate to about 10%. As such, it is comparable to the accuracy of near-IR
photometric redshifts and provides a complementary means of deriving redshifts
from far-IR data, such as that from the upcoming . Since our analytic radiative transfer solution is developed for
homogeneous, spherically symmetric, centrally heated, dusty sources, it is
relevant for infrared bright galaxies that are primarily powered by compact
sources of luminosity that are embedded in a dusty envelope. We discuss how
deviations from spherical symmetry may affect the applicability of our
solution, and we contrast our self-consistent analytic solution with standard
approximations to demonstrate the main differences.Comment: 37 pages, 14 Figures, 3 Tables, submitted to ApJ. submitted to Ap
Object-X: The Brightest Mid-IR Point Source in M33
We discuss the nature of the brightest mid-IR point source (which we dub
Object X) in the nearby galaxy M33. Although multi-wavelength data on this
object have existed in the literature for some time, it has not previously been
recognized as the most luminous mid-IR object in M33 because it is entirely
unremarkable in both optical and near-IR light. In the Local Group Galaxies
Survey, Object X is a faint red source visible in VRI and H-alpha but not U or
B. It was easily seen at JHK_s in the 2MASS survey. It is the brightest point
source in all four Spitzer IRAC bands and is also visible in the MIPS 24-micron
band. Its bolometric luminosity is 5x10^5 L_sun. The source is optically
variable on short time scales (tens of days) and is also slightly variable in
the mid-IR, indicating that it is a star. Archival photographic plates (from
1949 and 1991) show no optical source, so the star has been obscured for at
least half a century. Its properties are similar to those of the Galactic OH/IR
star IRC+10420 which has a complex dusty circumstellar structure resulting from
episodic low velocity mass ejections. We propose that Object X is a M>30 M_sun
evolved star obscured in its own dust ejected during episodic mass loss events
over at least half a century. It may emerge from its current ultra-short
evolutionary phase as a hotter post-RSG star analogous to M33 Var A. The
existence and rarity of such objects can be an important probe of a very brief
yet eventful stellar evolutionary phase.Comment: 20 pages, 10 figures. Accepted for publication by Ap
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