11 research outputs found
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
The census of nuclear activity of late-type galaxies in the Virgo cluster
The first spectroscopic census of AGNs associated to late-type galaxies in
the Virgo cluster is carried on by observing 213 out of a complete set of 237
galaxies more massive than M_dyn>10^{8.5} solar masses. Among them, 77 are
classified as AGNs (including 21 transition objects, 47 LINERs and 9 Seyferts),
and comprize 32% of the late-type galaxies in Virgo. Due to spectroscopic
incompleteness at most 21 AGNs are missed in the survey, so that the fraction
would increase up to 41%. Using corollary Near-IR observations, that enable us
to estimate galaxies dynamical masses, it is found that AGNs are hosted
exclusively in massive galaxies, i.e. M_dyn\gsim 10^{10} solar masses. Their
frequency increases steeply with the dynamical mass from zero at
M_dyn\approx10^{9.5} solar masses to virtually 1 at M_dyn>10^{11.5} solar
masses. These frequencies are consistent with the ones of low luminosity AGNs
found in the general field by the SDSS. Massive galaxies that harbor AGNs
commonly show conspicuous r-band star-like nuclear enhancements. Conversely
they often, but not necessarily contain massive bulges. Few well known AGNs
(e.g. M61, M100, NGC4535) are found in massive Sc galaxies with little or no
bulge. The AGN fraction seems to be only marginally sensitive to galaxy
environment. We infer the black hole masses using the known scaling relations
of quiescent black holes. No black holes lighter than \msol are
found active in our sample.Comment: The paper contains 13 figures and 5 tables; accepted for publication
in MNRA
Panchromatic Properties of 99,000 Galaxies Detected by SDSS, and (some by) ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS Surveys
We discuss the panchromatic properties of 99,088 galaxies selected from the
SDSS Data Release 1 spectroscopic sample (a flux-limited sample for 1360
deg^2). These galaxies are positionally matched to sources detected by ROSAT,
GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS. We find strong correlations
between the detection fraction at other wavelengths and optical properties such
as flux, colors, and emission-line strengths. Using GALEX, SDSS, and 2MASS
data, we construct the UV-IR broad-band spectral energy distributions for
various types of galaxies, and find that they form a nearly one-parameter
family. For example, based on SDSS u- and r-band data, supplemented with
redshift, the K-band 2MASS magnitudes can be "predicted" with an rms scatter of
only 0.2 mag. When a dust content estimate determined from SDSS data by
Kauffmann et al. (2003) is also utilized, this scatter decreases to 0.1 mag. We
demonstrate that this dust content is indeed higher for galaxies detected by
IRAS and that it can be used to "predict" measured IRAS 60 micron flux density
within a factor of two using only SDSS data. We also show that the position of
a galaxy in the emission-line-based Baldwin-Phillips-Terlevich diagram is
correlated with the optical light concentration index and u-r color determined
from the SDSS broad-band imaging data, and discuss changes in the morphology of
this diagram induced by requiring detections at other wavelengths. We study the
IR-radio correlation and find evidence that its slope may be different for AGN
and star-forming galaxies and related to the H_alpha/H_beta line strength
ratio.Comment: Accepted for publication in MNRAS; 25 pages, 32 color figure
The star-formation history of K-selected galaxies
We have studied the uJy radio properties of K-selected galaxies detected in
the Ultra-Deep Survey portion of UKIDSS using 610- and 1,400-MHz images from
the VLA and GMRT. These deep radio mosaics, combined with the largest and
deepest K image currently available, allow high-S/N detections of many
K-selected sub-populations, including sBzK and pBzK star-forming and passive
galaxies. We find a strong correlation between the radio and K fluxes and a
linear relationship between SFR and K luminosity. We find no evidence, from
either radio spectral indices or a comparison with submm-derived SFRs, that the
full sample is strongly contaminated by AGN. The sBzK and pBzK galaxies have
similar levels of radio flux, SFR and specific SFR (SSFR) at z < 1.4,
suggesting there is strong contamination of the pBzK sample by star-forming
galaxies. At z > 1.4, pBzK galaxies become difficult to detect in the radio
stack, though the implied SFRs are still much higher than expected for
passively evolving galaxies. Their radio emission may come from low-luminosity
AGN. EROs straddle the passive and star-forming regions of the BzK diagram and
also straddle the two groups in terms of their radio properties. K-bright ERO
samples are dominated by passive galaxies and faint ERO samples contain more
star-forming galaxies. The star-formation history (SFH) from stacking all K
sources in the UDS agrees well with that derived for other wavebands and other
radio surveys, at least out to z ~ 2. The radio-derived SFH then appears to
fall more steeply than that measured at other wavelengths. The SSFR for
K-selected sources rises strongly with redshift at all stellar masses, and
shows a weak dependence on stellar mass. High- and low-mass galaxies show a
similar decline in SSFR since z ~ 2 (abridged).Comment: Published in MNRAS, 20 pages, colou
The ASTRODEEP Frontier Fields catalogues. I. Multiwavelength photometry of Abell-2744 and MACS-J0416
Context. The Frontier Fields survey is a pioneering observational program aimed at collecting photometric data, both from space (Hubble Space Telescope and Spitzer Space Telescope) and from ground-based facilities (VLT Hawk-I), for six deep fields pointing at clusters of galaxies and six nearby deep parallel fields, in a wide range of passbands. The analysis of these data is a natural outcome of the Astrodee
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Panchromatic properties of 99ā000 galaxies detected by SDSS, and (some by) ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS surveys
We discuss the panchromatic properties of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 āmainā spectroscopic sample (a flux-limited sample for 1360 deg2). These galaxies are positionally matched to sources detected by ROSAT, Galaxy Evolution Explorer (GALEX), two-Micron All-Sky Survey (2MASS), Infrared Astronomical Satellite (IRAS), Green Bank GB6 survey (GB6), Faint Images of the Radio Sky at Twenty-centimetres (FIRST), NRAO VLA Sky Survey (NVSS) and Westerbork Northern Sky Survey (WENSS). The matching fraction varies from <1 per cent for ROSAT and GB6 to ā¼40 per cent for GALEX and 2MASS. In addition to its size, the advantages of this sample are well-controlled selection effects, faint flux limits and the wealth of measured parameters, including accurate X-ray to radio photometry, angular sizes and optical spectra. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colours and emission-line strengths. For example, ā¼2/3 of SDSS āmainā galaxies classified as active galactic nucleus (AGN) using emission-line strengths are detected by 2MASS, while the corresponding fraction for star-forming galaxies (SFs) is only ā¼1/10. Similarly, over 90 per cent of galaxies detected by IRAS display strong emission lines in their optical spectra, compared to ā¼50 per cent for the whole SDSS sample. Using GALEX, SDSS and 2MASS data, we construct the ultravioletāinfrared (UVāIR) broad-band spectral energy distributions for various types of galaxies, and find that they form a nearly one-parameter family. For example, the SDSS u- and r-band data, supplemented with redshift, can be used to āpredictāK-band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag. When a dust content estimate determined from SDSS spectra with the aid of models is also utilized, this scatter decreases to 0.1 mag and can be fully accounted for by measurement uncertainties. We demonstrate that this interstellar dust content, inferred from optical SDSS spectra by Kauffmann et al., is indeed higher for galaxies detected by IRAS and that it can be used to āpredictā measured IRAS 60 Ī¼m flux density within a factor of 2 using only SDSS data. We also show that the position of a galaxy in the emission-line-based BaldwināPhillipsāTerlevich diagram is correlated with the optical light concentration index and uār colour determined from the SDSS broad-band imaging data, and discuss changes in the morphology of this diagram induced by requiring detections at other wavelengths. Notably, we find that SDSS āmainā galaxies detected by GALEX include a non-negligible fraction (10ā30 per cent) of AGNs, and hence do not represent a clean sample of starburst galaxies. We study the IRāradio correlation and find evidence that its slope may be different for AGN and SFs and related to the HĪ±/HĪ² line-strength ratio.Astronom