12,091 research outputs found
The Rest-frame Optical Colors of 99,000 SDSS Galaxies
We synthesize the rest-frame Stroemgren colors using SDSS spectra for 99,088
galaxies selected from Data Release 1. This narrow-band ~200 AA photometric
system (uz, vz, bz, yz), first designed for the determination of effective
temperature, metallicity and gravity of stars, measures the continuum spectral
slope of galaxies in the rest-frame 3200-5800 AA wavelength range. Galaxies
form a remarkably narrow locus (~0.03 mag) in the resulting color-color
diagram. The Bruzual & Charlot population synthesis models suggest that the
position of a galaxy along this locus is controlled by a degenerate combination
of metallicity and age of the dominant stellar population. Galaxy distribution
along the locus is bimodal, with the local minimum corresponding to an ~1 Gyr
old single stellar population. The position perpendicular to the locus is
independent of metallicity and age, and reflects the galaxy's dust content, as
implied by both the models and the statistics of IRAS detections. A comparison
of this locus with the galaxy locus in the H_delta-D_n(4000) diagram, utilized
by Kauffmann et al. (2003) to estimate stellar masses, reveals a tight
correlation, although the two analyzed spectral ranges barely overlap. Overall,
the galaxy spectral energy distribution in the entire UV to near-IR range can
be described as a single-parameter family with an accuracy of 0.1 mag, or
better. This nearly one-dimensional distribution of galaxies in the
multi-dimensional space of measured parameters strongly supports the conclusion
of Yip et al. (2004), based on a principal component analysis, that SDSS galaxy
spectra can be described by a small number of eigenspectra. Apparently, the
contributions of stellar populations that dominate the optical emission from
galaxies are combined in a simple and well-defined way.Comment: Accepted for publication in MNRAS; 19 pages, 28 color figure
Four New Stellar Debris Streams in the Galactic Halo
We report on the detection of four new stellar debris streams and a new dwarf
galaxy candidate in the Sloan Digital Sky Survey. Three of the streams, ranging
between 3 and 15 kpc in distance and spanning between 37 and 84 degrees on the
sky, are very narrow and are most probably tidal streams originating in extant
or disrupted globular clusters. The fourth stream is much broader, roughly 45
kpc distant, at least 53 degrees in length, and is most likely the tidal debris
from a dwarf galaxy. As the streams each span multiple constellations, we
extend tradition and designate them the Acheron, Cocytos, Lethe, and Styx
streams. At the same distance and apparently embedded in the Styx stream is a
~1 kpc-wide concentration of stars with a similar color-magnitude distribution
which we designate Bootes III. Given its very low surface density, its location
within the stream, and its apparently disturbed morphology, we argue that
Bootes III may be the progenitor of Styx and in possibly the final throes of
tidal dissolution. While the current data do not permit strong constraints,
preliminary orbit estimates for the streams do not point to any likely
progenitors among the known globular clusters and dwarf galaxies.Comment: 10 pages, accepted for publication in the Astrophysical Journa
The UV, Optical, and IR Properties of SDSS Sources Detected by GALEX
We discuss the UV, optical, and IR properties of the SDSS sources detected by
GALEX as part of its All-sky Imaging Survey Early Release Observations.
Virtually all of the GALEX sources in the overlap region are detected by SDSS.
GALEX sources represent ~2.5% of all SDSS sources within these fields and about
half are optically unresolved. Most unresolved GALEX/SDSS sources are bright
blue turn-off thick disk stars and are typically detected only in the GALEX
near-UV band. The remaining unresolved sources include low-redshift quasars,
white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically
unresolved sources detected in both GALEX bands.
Almost all the resolved SDSS sources detected by GALEX are fainter than the
SDSS 'main' spectroscopic limit. These sources have colors consistent with
those of blue (spiral) galaxies (u-r<2.2), and most are detected in both GALEX
bands. Measurements of their UV colors allow much more accurate and robust
estimates of star-formation history than are possible using only SDSS data.
Indeed, galaxies with the most recent (<20 Myr) star formation can be robustly
selected from the GALEX data by requiring that they be brighter in the far-UV
than in the near-UV band. However, older starburst galaxies have UV colors
similar to AGN, and thus cannot be selected unambiguously on the basis of GALEX
fluxes alone.
With the aid of 2MASS data, we construct and discuss median 10 band
UV-optical-IR spectral energy distributions for turn-off stars, hot white
dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out
the high degree of correlation between the UV color and the contribution of the
UV flux to the UV-optical-IR flux of galaxies detected by GALEX.Comment: 35 pages, 11 figures, 3 tables; to appear in the AJ. PS with better
figures available from http://www.astro.washington.edu/agueros/pub
A Statistical Survey of Peculiar L and T Dwarfs in SDSS, 2MASS, and WISE
We present the final results from a targeted search for brown dwarfs with
unusual near-infrared colors. From a positional cross-match of SDSS, 2MASS and
WISE, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy
confirms that 20 of the objects are peculiar or are candidate binaries. Nine of
the 420 objects in our sample are young (200 Myr; 2.1%) and another 8
(1.9%) are unusually red with no signatures of youth. With a spectroscopic
color of 2.58 0.11 mag, one of the new objects, the L6 dwarf
2MASS J03530419+0418193, is among the reddest field dwarfs currently known and
is one of the reddest objects with no signatures of youth known to date. We
have also discovered another potentially very low gravity object, the L1 dwarf
2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS
J00440332+0228112, first reported by Schneider and collaborators. Our results
confirm that signatures of low gravity are no longer discernible in low to
moderate resolution spectra of objects older than 200 Myr. The 1.9% of
unusually red L dwarfs that do not show other signatures of youth could be
slightly older, up to 400 Myr. In this case a red color may be
more diagnostic of moderate youth than individual spectral features. However,
its is also possible that these objects are relatively metal-rich, and so have
an enhanced atmospheric dust content.Comment: 27 pages, 7 figures, 5 tables, accepted to A
A Photometric System for Detection of Water and Methane Ices on Kuiper Belt Objects
We present a new near-infrared photometric system for detection of water ice
and methane ice in the solar system. The system consists of two medium-band
filters in the K-band region of the near-infrared, which are sensitive to water
ice and methane ice, plus continuum observations in the J-band and Y-band. The
primary purpose of this system is to distinguish between three basic types of
Kuiper Belt Objects (KBOs) --- those rich in water ice, those rich in methane
ice, and those with little absorbance. In this work, we present
proof-of-concept observations of 51 KBOs using our filter system, 21 of which
have never been observed in the near-IR spectroscopically. We show that our
custom photometric system is consistent with previous spectroscopic
observations while reducing telescope observing time by a factor of 3. We use
our filters to identify Haumea collisional family members, which are thought to
be collisional remnants of a much larger body and are characterized by large
fractions of water ice on their surfaces. We add 2009 YE7 to the Haumea
collisional family based on our water ice band observations(J-H2O = -1.03 +/-
0.27) which indicate a high amount of water ice absorption, our calculated
proper orbital elements, and the neutral optical colors we measured, V-R = 0.38
+/- 0.04, which are all consistent with the rest of the Haumea family. We
identify several objects dynamically similar to Haumea as being distinct from
the Haumea family as they do not have water ice on their surfaces. In addition,
we find that only the largest KBOs have methane ice, and we find that Haumea
itself has significantly less water ice absorption than the smaller Haumea
family members. We find no evidence for other families in the Kuiper Belt.Comment: 38 pages, 7 figure
The globular cluster system of NGC1316. I. Wide-field photometry in the Washington system
NGC 1316 (Fornax A) is a prominent merger remnant in the outskirts of the
Fornax cluster. The cluster system has not yet been studied in its entirety. We
therefore present a wide-field study of the globular cluster system of NGC
1316, investigating its properties in relation to the global morphology of NGC
1316. We used the MOSAIC II camera at the 4-m Blanco telescope at CTIO in the
filters Washington C and Harris R. We identify globular cluster candidates and
study their color distribution and the structural properties of the system. In
an appendix, we also make morphological remarks, present color maps, and
present new models for the brightness and color profiles of the galaxy. The
cluster system is well confined to the optically visible outer contours of NGC
1316. The color distribution of the entire sample is unimodal, but the color
distribution of bright subsamples in the bulge shows two peaks that, by
comparison with theoretical Washington colors with solar metallicity,
correspond to ages of about 2 Gyr and 0.8 Gyr, respectively. We also find a
significant population of clusters in the color range 0.8 < C-R < 1.1 which
must be populated by clusters younger than 0.8 Gyr, unless they are very
metal-poor. The color interval 1.3 < C-R < 1.6 hosts the bulk of
intermediate-age clusters which show a surface density profile with a sharp
decline at about 4 arcmin. The outer cluster population shows an unimodal color
distribution with a peak at C-R=1.1, indicating a larger contribution of old,
metal-poor clusters. Their luminosity function does not show the expected
turn-over, so the fraction of younger clusters is still significant. Cluster
formation in NGC 1316 has continued after an initial burst, presumably related
to the main merger. A toy model with two bursts of ages 2 Gyr and 0.8 Gyr is
consistent with photometric properties and dynamical M/L-values.Comment: 19 pages, to appear in Astronomy and Astrophysics, abstract abridged,
format slightly different from the printed versio
A Search for Wolf-Rayet Stars in the Small Magellanic Cloud
We conducted an extensive search for Wolf-Rayet stars (W-Rs) in the SMC,
using the same interference filter imaging techniques that have proved
successful in finding W-Rs in more distant members of the Local Group.
Photometry of some 1.6 million stellar images resulted in some 20 good
candidates, which we then examined spectroscopically. Two of these indeed
proved to be newly found W-Rs, bringing the total known in the SMC from 9 to
11. Other finds included previously unknown Of-type stars (one as early as
O5f?p)),the recovery of the Luminous Blue Variable S18, and the discovery of a
previously unknown SMC symbiotic star. More important, however, is the fact
that there does not exist a significant number of W-Rs waiting to be discovered
in the SMC. The number of W-Rs in the SMC is a factor of 3 lower than in the
LMC (per unit luminosity), and we argue this is the result of the SMC's low
metallicity on the evolution of the most massive stars.Comment: Accepted by Astrophysical Journal. Postscript version available via
ftp.lowell.edu/pub/massey/smcwr.ps.gz Revised version contains slightly
revised spectral types for the Of stars but is otherwise unchange
Time-Resolved Near-Infrared Photometry of Extreme Kuiper Belt Object Haumea
We present time-resolved near-infrared (J and H) photometry of the extreme
Kuiper belt object (136108) Haumea (formerly 2003 EL61) taken to further
investigate rotational variability of this object. The new data show that the
near-infrared peak-to-peak photometric range is similar to the value at visible
wavelengths, \Delta m_R = 0.30+/-0.02 mag. Detailed analysis of the new and
previous data reveals subtle visible/near-infrared color variations across the
surface of Haumea. The color variations are spatially correlated with a
previously identified surface region, redder in B-R and darker than the mean
surface. Our photometry indicates that the J-H colors of Haumea
(J-H=-0.057+/-0.016 mag) and its brightest satellite Hi'iaka
(J-H=-0.399+/-0.034 mag) are significantly (>9 sigma) different. The satellite
Hi'iaka is unusually blue in J-H, consistent with strong 1.5 micron water-ice
absorption. The phase coefficient of Haumea in the J-band is found to increase
monotonically with wavelength in the range 0.4<lambda<1.3. We compare our
findings with other Solar system objects and discuss implications regarding the
surface of Haumea.Comment: 10 pages, 10 figures, 6 tables. Accepted for publication in The
Astronomical Journal (2008 November 28
- …