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 $\bar{R}$ and dispersion $\sigma_{\ln R}$. For late-type galaxies, there is a characteristic luminosity at $M_{r,0}\sim -20.5$ (assuming $h=0.7$) corresponding to a stellar mass M_0\sim 10^{10.6}\Msun. Galaxies more massive than $M_0$ have $\bar{R}\propto M^{0.4}$ and $\sigma_{\ln R}\sim 0.3$, while less massive galaxies have $\bar{R}\propto M^{0.15}$ and $\sigma_{\ln R}\sim 0.5$. For early-type galaxies, the $\bar{R}$ - $M$ relation is significantly steeper, $\bar{R}\propto M^{0.55}$, but the $\sigma_{\ln R}$ - $M$ 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 ($L_{2500}$) and in [OIII] ($L_{[\rm{OIII}]}$) span more than three orders of magnitude, while redshifts range over $0.1<z<5.4$. 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 $\sim 0.40$, 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 $\sim 0.53$ for $L_{2500}$ and $\sim 0.30$ for $L_{[\rm{OIII}]}$. 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 $L_{[\rm{OIII}]}$. At low redshift and at given $L_{[\rm{OIII}]}$ 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.