Tools for computing the AGN feedback: radio-loudness distribution and the kinetic luminosity function

We studied the Active Galactic Nuclei (AGN) radio emission from a compilation of hard X-ray selected samples, all observed in the 1.4 GHz band. A total of more than 1600 AGN with 2-10 keV de-absorbed luminosities higher than 10^42 erg/s were used. For a sub-sample of about 50 z\lsim 0.1 AGN it was possible to reach a ~80% fraction of radio detections and therefore, for the first time, it was possible to almost completely measure the probability distribution function of the ratio between the radio and the X-ray luminosity Rx=log[L(1.4)/Lx]. The probability distribution function of Rx was functionally fitted as dependent on the X-ray luminosity and redshift, P(Rx|Lx,z). It roughly spans over 6 decades (-7<Rx<-1), and does not show any sign of bi-modality. It resulted that the probability of finding large values of the Rx ratio increases with decreasing X-ray luminosities and (possibly) with increasing redshift. No statistical significant difference was found between the radio properties of the X-ray absorbed and unabsorbed AGN. The measure of the probability distribution function of Rx allowed us to compute the kinetic luminosity function and the kinetic energy density which, at variance with what assumed in many galaxy evolution models, is observed to decrease of about a factor of five at redshift below 0.5. About half of the kinetic energy density results to be produced by the more radio quiet (Rx<-4) AGN. In agreement with previous estimates, the AGN efficiency in converting the accreted mass energy into kinetic power is, on average, ~5x10-3.Comment: 13 pages, ApJsty; ApJ in pres

Optimal Strategies in Infinite-state Stochastic Reachability Games

We consider perfect-information reachability stochastic games for 2 players on infinite graphs. We identify a subclass of such games, and prove two interesting properties of it: first, Player Max always has optimal strategies in games from this subclass, and second, these games are strongly determined. The subclass is defined by the property that the set of all values can only have one accumulation point -- 0. Our results nicely mirror recent results for finitely-branching games, where, on the contrary, Player Min always has optimal strategies. However, our proof methods are substantially different, because the roles of the players are not symmetric. We also do not restrict the branching of the games. Finally, we apply our results in the context of recently studied One-Counter stochastic games

Fresh Activity in Old Systems: Radio AGN in Fossil Groups of Galaxies

We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from SDSS Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L_1.4GHz > 10^23 W Hz^-1) active galactic nucleus (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.Comment: Accepted for publication in A

The crystal structure of Trz1, the long form RNase Z from yeast.

tRNAs are synthesized as precursor RNAs that have to undergo processing steps to become functional. Yeast Trz1 is a key endoribonuclease involved in the 3΄ maturation of tRNAs in all domains of life. It is a member of the β-lactamase family of RNases, characterized by an HxHxDH sequence motif involved in coordination of catalytic Zn-ions. The RNase Z family consists of two subfamilies: the short (250-400 residues) and the long forms (about double in size). Short form RNase Z enzymes act as homodimers: one subunit embraces tRNA with a protruding arm, while the other provides the catalytic site. The long form is thought to contain two fused β-lactamase domains within a single polypeptide. Only structures of short form RNase Z enzymes are known. Here we present the 3.1 Å crystal structure of the long-form Trz1 from Saccharomyces cerevisiae. Trz1 is organized into two β-lactamase domains connected by a long linker. The N-terminal domain has lost its catalytic residues, but retains the long flexible arm that is important for tRNA binding, while it is the other way around in the C-terminal domain. Trz1 likely evolved from a duplication and fusion of the gene encoding the monomeric short form RNase Z

Optically bright Active Galactic Nuclei in the ROSAT-Faint Source Catalogue

To build a large, optically bright, X-ray selected AGN sample we have correlated the ROSAT-FSC catalogue of X-ray sources with the USNO catalogue limited to objects brighter than O=16.5 and then with the APS database. Each of the 3,212 coincidences was classified using the slitless Hamburg spectra. 493 objects were found to be extended and 2,719 starlike. Using both the extended objects and the galaxies known from published catalogues we built up a sample of 185 galaxies with O_APS < 17.0 mag, which are high-probability counterparts of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and for another 34 we obtained new spectra. The fraction of Seyfert galaxies in this sample is 20 %. To select a corresponding sample of 144 high-probability counterparts among the starlike sources we searched for very blue objects in an APS-based color-magnitude diagram. Forty-one were already known AGN and for another 91 objects we obtained new spectra, yielding 42 new AGN, increasing their number in the sample to 83. This confirms that surveys of bright QSOs are still significantly incomplete. On the other hand we find that, at a flux limit of 0.02 count /-1 and at this magnitude, only 40 % of all QSOs are detected by ROSAT.Comment: 17 pages, 16 figures, accepted by A&

Balmer Emission Line Profiles and the Complex Properties of Broad Line Regions in Active Galactic Nuclei

In this work we analyze a sample of AGN spectra, selected from the 6th Data Release of the Sloan Digital Sky Survey, exploiting a generalized technique of line profile analysis, designed to take into account the whole profiles of their broad emission lines. We find that the line profile broadening functions result from a complex structure, but we may be able to infer some constraints about the role of the geometrical factor, thus improving our ability to estimate AGN properties and their relation with the host galaxy. Our results suggest that flattening and inclination within the structure of the Broad Line Region (BLR) must be taken into account. We detect low inclinations of the BLR motion plane with respect to our line of sight, typically i < 20 degrees, with a geometrical effect which generally decreases as the line profile becomes broader.Comment: 13 pages, 11 figures, updated reference list. ApJ accepte

Linking radio to infrared: a radio source count model

We investigate the populations and evolution of normal and active galaxies by extending the infrared source count model of Rowan-Robinson (2001) into the radio. The FIR-radio correlation is used to extend the SEDs to the radio region and it is assumed that there are two distinct populations of quasar: radio loud and radio quiet. It is found that the radio luminosity function and source count data are best fit when the fraction of quasars that are radio loud is allowed to increase with optical luminosity. This implications for this are discussed, as are the possible causes for the variation in radio loud fraction.Comment: 9 pages (TeX file), 9 figures (eps format), submitted to MNRAS and corrected for referee's comment

A Warp in Progress : H I and Radio Continuum Observations of the Spiral NGC 3145

Date of Acceptance: 16/06/2015We present VLA H I and 6 cm radio continuum observations of the spiral NGC 3145 and H I observations of its two companions, NGC 3143 and PGC 029578. In optical images NGC 3145 has stellar arms that appear to cross, forming "X"-features. Our radio continuum observations rule out shock fronts at 3 of the 4 "X"-features. In the middle-to-outer disk, the H I line-profiles of NGC 3145 are skewed. Relative to the disk, the gas in the skewed wing of the line-profiles has z-motions away from us on the approaching side of the galaxy and z-motions of about the same magnitude (about 40 km/s) towards us on the receding side. These warping motions imply that there has been a perturbation with a sizeable component perpendicular to the disk over large spatial scales. Two features in NGC 3145 have velocities indicating that they are out-of-plane tidal arms. One is an apparent branch of a main spiral arm; the velocity of the branch is 150 km/s greater than the spiral arm where they appear to intersect in projection. The other is an arm that forms 3 of the "X"-features. It differs in velocity by 56 km/s from the disk at the same projected location. Based on its SFR and H I properties, NGC 3143 is the more likely of the two companions to have interacted with NGC 3145 recently. A simple analytic model demonstrates that an encounter between NGC 3143 and NGC 3145 is a plausible explanation for the observed warping motions in NGC 3145.Peer reviewe

XMM-Newton survey of the Local Group galaxy M 33

In an XMM-Newton raster observation of the bright Local Group spiral galaxy M 33 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 408 sources in an area of 0.80 square degree. We correlate these newly detected sources with earlier M 33 X-ray catalogues and information from optical, infra-red and radio wavelengths. As M 33 sources we detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources, and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44 confirmed and candidate SNRs more than double the number of X-ray detected SNRs in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the first time. On the other hand, there are several sources not connected to M 33: five foreground stars, 30 foreground star candidates, 12 active galactic nucleus candidates, one background galaxy and one background galaxy candidate. Extrapolating from deep field observations we would expect 175 to 210 background sources in this field. This indicates that about half of the sources detected are sources within M 33.Comment: 14 pages, 6 figures, accepted for publication in A&A, the images of Figs. 1,2,3,4,6 are available in jpg format, a full version of the paper is available at ftp://ftp.xray.mpe.mpg.de/people/fwh/docs/M33_AA0068.p

Is there a Dichotomy in the Radio Loudness Distribution of Quasars?

We present a new approach to tackle the issue of radio loudness in quasars. We constrain a (simple) prescription for the intrinsic distribution of radio-to-optical ratios by comparing properties of Monte Carlo simulated samples with those of observed optically selected quasars. We find strong evidence for a dependence of the radio luminosity on the optical one, even though with a large scatter. The dependence of the fraction of radio loud quasars on apparent and absolute optical magnitudes results in a selection effect related to the radio and optical limits of current surveys. The intrinsic distribution of the radio-to-optical ratios shows a peak at $R^*_{1.4} \sim 0.3$, with only \simlt 5 per cent of objects being included in a high $R^*_{1.4}$ tail which identifies the radio loud regime. No lack or deficit of sources -- but only a steep transition region -- is present between the radio loud and radio quiet populations at any $R^*_{1.4}$. We briefly discuss possible origins for this behaviour (e.g. absence of jets in radio quiet sources, large range of radiative radio efficiency, different life-times for the accretion and jet ejection phenomena, ...).Comment: 10 pages, 7 figures, accepted for publication in MNRA