69 research outputs found
Soft X--Ray Properties of Seyfert Galaxies in the Rosat All--Sky Survey
We present the results of ROSAT All-Sky Survey observations of Seyfert and
IR-luminous galaxies from the Extended 12 Micron Galaxy Sample and the
optically-selected CfA Sample. Roughly half of the Seyferts (mostly Seyfert 1s)
have been fitted to an absorbed power-law model, yielding an average gamma of
2.26+-0.11 for 43 Seyfert 1s and 2.45+-0.18 for 10 Seyfert 2s, with both types
having a median value of 2.3.
The soft X-ray (SXR) luminosity correlates with the 12um luminosity, with
Seyfert 1s having relatively more SXR emission than Seyfert 2s of similar
mid-infrared luminosities, by a factor of 1.6+-0.3. Several physical
interpretations of these results are discussed, including the standard unified
model for Seyfert galaxies. Infrared-luminous non-Seyferts are shown to have
similar distributions of SXR luminosity and X-ray-to-IR slope as Seyfert 2s,
suggesting that some of them may harbor obscured active nuclei (as has already
been shown to be true for several objects) and/or that the soft X-rays from
some Seyferts 2s may be non-nuclear.
A SXR luminosity function (XLF) is calculated for the 12um sample, which is
well described by a single power-law with a slope of -1.75. The normalization
of this XLF agrees well with that of a HXR selected sample. Several of our
results, related to the XLF and the X-ray-to-IR relation are shown to be
consistent with the HXR observations of the 12um sample by Barcons et al.Comment: AASTeX, 40 pages. Text and Table 2 only. PostScript versions of this
file, figures, and Table 1, and a latex version of Table 1 are available by
ftp://ftp.astro.ucla.edu/pub/rush/papers, get rmfv*. Accepted by ApJ ~1996
May 10. Should be published in late 199
Search for GRB X-ray Afterglows in the ROSAT All-sky Survey
We report on the status of our search for X-ray afterglows of gamma-ray burts (GRBs) using ROSAT all-sky survey (RASS) date. The number of potential X-ray afterglow candidates with respect to the expected number of bearmed GRBs allows to constrain the relative beaming angles of GRB emission and afterglow emission at about 1-5 hrs after the GRB
The size distribution of galaxies in the Sloan Digital Sky Survey
abridged: We use a complete sample of about 140,000 galaxies from the Sloan
Digital Sky Survey (SDSS) to study the size distribution of galaxies and its
dependence on their luminosity, stellar mass, and morphological type. The large
SDSS database provides statistics of unprecedented accuracy. For each type of
galaxy, the size distribution at given luminosity (or stellar mass) is well
described by a log-normal function, characterized by its median and
dispersion . For late-type galaxies, there is a characteristic
luminosity at (assuming ) corresponding to a stellar
mass M_0\sim 10^{10.6}\Msun. Galaxies more massive than have
and , while less massive
galaxies have and . For
early-type galaxies, the - relation is significantly steeper,
, but the - relation is similar
to that of late-type galaxies. Faint red galaxies have sizes quite independent
of their luminosities.Comment: 42 pages, 18 figures, 2 tables; replaced with the version accepted by
MNRA
The X-ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies: A Cosmological Probe
In this letter, we present a new determination of the local (z<0.09) X-ray
luminosity function (XLF) using a large, statistical sample of 294 Abell
clusters and the ROSAT All-Sky-Survey. Given our large sample size, we have
reduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine
our data with previous work in order to explore possible constraints imposed by
the shape of the XLF on cosmological models. A set of currently viable
cosmologies is used to construct theoretical XLFs assuming Lx is proportional
to M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the
local X-ray temperature function. We fit these models to our observed XLF and
verify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser
1986) disagrees strongly with observations. If we assume that clusters can be
described by the pre-heated, constant core-entropy models of Evrard & Henry
(1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the
energy per unit mass in galaxies is roughly equal to the gas energy (ie if
beta=1). (abridged)Comment: 4 pages, 2 figures, accepted for publication in ApJ Letters. uses
emulateapj.st
Double-Peaked Low-Ionization Emission Lines in Active Galactic Nuclei
We present a new sample of 116 double-peaked Balmer line Active Galactic
Nuclei (AGN) selected from the Sloan Digital Sky Survey. Double-peaked emission
lines are believed to originate in the accretion disks of AGN, a few hundred
gravitational radii (Rg) from the supermassive black hole. We investigate the
properties of the candidate disk emitters with respect to the full sample of
AGN over the same redshifts, focusing on optical, radio and X-ray flux, broad
line shapes and narrow line equivalent widths and line flux-ratios. We find
that the disk-emitters have medium luminosities (~10^44erg/s) and FWHM on
average six times broader than the AGN in the parent sample. The double-peaked
AGN are 1.6 times more likely to be radio-sources and are predominantly (76%)
radio quiet, with about 12% of the objects classified as LINERs. Statistical
comparison of the observed double-peaked line profiles with those produced by
axisymmetric and non-axisymmetric accretion disk models allows us to impose
constraints on accretion disk parameters. The observed Halpha line profiles are
consistent with accretion disks with inclinations smaller than 50 deg, surface
emissivity slopes of 1.0-2.5, outer radii larger than ~2000 Rg, inner radii
between 200-800Rg, and local turbulent broadening of 780-1800 km/s. The
comparison suggests that 60% of accretion disks require some form of asymmetry
(e.g., elliptical disks, warps, spiral shocks or hot spots).Comment: 60 pages, 19 figures, accepted for publication in AJ. For high
quality figures and full tables, please see
http://astro.princeton.edu/~iskra/disks.htm
The soft X-ray properties of quasars in the Sloan Digital Sky Survey
We use the ROSAT All Sky Survey (RASS) to study the soft X-ray properties of
a homogeneous sample of 46,420 quasars selected from the third data release of
the Sloan Digital Sky Survey (SDSS). Optical luminosities, both at rest-frame
2500\AA () and in [OIII] () span more than three
orders of magnitude, while redshifts range over . We detect 3366
quasars directly in the observed 0.1--2.4 keV band. Sub-samples of radio-loud
and radio-quiet objects (RLQs and RQQs) are obtained by cross-matching with the
FIRST catalogue. We study the distribution of X-ray luminosity as a function of
optical luminosity, redshift and radio power using both individual detections
and stacks of complete sets of similar quasars. At every optical luminosity and
redshift \log L_{2\kev} is, to a good approximation, normally distributed
with dispersion , at least brightwards of the median X-ray
luminosity. This median X-ray luminosity of quasars is a power law of optical
luminosity with index for and for
. RLQs are systematically brighter than RQQs by about a factor
of 2 at given optical luminosity. The zero-points of these relations increase
systematically with redshift, possibly in different ways for RLQs and RQQs.
Evolution is particularly strong at low redshift and if the optical luminosity
is characterised by . At low redshift and at given
the soft X-ray emission from type II AGN is more than 100
times weaker than that from type I AGN.Comment: 16 pages, 15 figures, 3 tables, replaced with final version accepted
by MNRA
Cataclysmic Variables from SDSS II. The Second Year
The first full year of operation following the commissioning year of the
Sloan Digital Sky Survey has revealed a wide variety of newly discovered
cataclysmic variables. We show the SDSS spectra of forty-two cataclysmic
variables observed in 2002, of which thirty-five are new classifications, four
are known dwarf novae (CT Hya, RZ Leo, T Leo and BZ UMa), one is a known CV
identified from a previous quasar survey (Aqr1) and two are known ROSAT or
FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS
positions, colors and spectra of all forty-two systems are presented. In
addition, the results of follow-up studies of several of these objects identify
the orbital periods, velocity curves and polarization that provide the system
geometry and accretion properties. While most of the SDSS discovered systems
are faint (>18th mag) with low accretion rates (as implied from their spectral
characteristics), there are also a few bright objects which may have escaped
previous surveys due to changes in the mass transfer rate.Comment: Accepted for publication in The Astronomical Journal, Vol. 126, Sep.
2003, 44 pages, 25 figures (now with adjacent captions), AASTeX v5.
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