Constraint on the quadrupole moment of super-massive black hole candidates from the estimate of the mean radiative efficiency of AGN

The super-massive objects at the center of many galaxies are commonly thought to be black holes. In 4-dimensional general relativity, a black hole is completely specified by its mass $M$ and by its spin angular momentum $J$. All the higher multipole moments of the gravitational field depend in a very specific way on these two parameters. For instance, the mass quadrupole moment is $Q = - J^2/M$. If we can estimate $M$, $J$, and $Q$ for the super-massive objects in galactic nuclei, we over-constrain the theory and we can test the black hole hypothesis. While there are many works studying how this can be done with future observations, in this paper a constraint on the quadrupole moment of these objects is obtained by using the current estimate of the mean radiative efficiency of AGN. In terms of the anomalous quadrupole moment $q$, the bound is $-2.01 < q < 0.14$.Comment: 4 pages, 2 figures. v2: refereed versio

What X-ray source counts can tell about large-scale matter distribution

Sources generating most of the X-ray background (XRB) are dispersed over a wide range of redshifts. Thus, statistical characteristics of the source distribution carry information on matter distribution on very large scales. We test the possibility of detecting the variation in the X-ray source number counts over the celestial sphere. A large number of Chandra pointings spread over both galactic hemispheres are investigated. We searched for all the point-like sources in the soft band of 0.5 - 2 keV and statistically assessed the population of sources below the detection threshold. A homogeneous sample of the number counts at fluxes above ~10^{-15} erg s^{-1} cm^{-2} was constructed for more than 300 ACIS fields. The sources were counted within a circular area of 15 arcmin diameter. The count correlations between overlapping fields were used to assess the accuracy of the computational methods used in the analysis. The average number of sources in the investigated sample amounts to 46 per field. It is shown that the source number counts vary between fields at a level exceeding the fluctuation amplitude expected for the random (Poissonian) distribution. The excess fluctuations are attributed to the cosmic variance generated by the large-scale structures. The rms variations of the source counts due to the cosmic variance within the 15$ arcmin circle reach 8% of the average number counts. An amplitude of the potential correlations of the source counts on angular scales larger than the size of a single pointing remains below the noise level.Comment: 8 pages, 4 figures; expansion of observational material resulted in substantial changes; accepted for publication in A&

Hydrodynamic Simulation of the Cosmological X-ray Background

(Abridged) We use a hydrodynamic simulation of a LambdaCDM model to predict the extragalactic X-ray background (XRB), focussing on emission from the intergalactic medium (IGM). We also include X-rays from point sources associated with galaxies in the simulation, and make maps of the angular distribution of the emission. We find that filaments in the maps are not evident, being diluted by projection. In the soft (0.5-2 keV) band, the mean intensity of radiation from intergalactic and cluster gas is 2.3*10^-12 ergdeg^-2cm^-2s^-1, 35% of the total soft band emission. This is compatible at the ~1 sigma level with estimates of the unresolved soft background from ROSAT and {\it Chandra}. Only 4% of the hard (2-10 keV) emission is associated with the IGM. Relative to AGN flux, the IGM component peaks at a lower redshift (median z~0.45) so its clustering makes an important contribution to that of the total XRB. The angular correlations on 0.1-10 arcmin scales are significant, with an amplitude roughly consistent with an extrapolation of recent ROSAT results to small scales. A cross-correlation of the XRB against nearby galaxies taken from a simulated redshift survey also yields a strong signal from the IGM. Although some recent papers have argued that the expected soft band intensity from gas in galaxy, group, and cluster halos would exceed XRB limits unless much of the gas is expelled by supernova feedback, we obtain reasonable compatibility with current observations in a simulation that incorporates cooling, star formation, and only modest feedback. A prediction of our model is that the unresolved portion of the soft XRB will remain mostly unresolved.Comment: Improved referencing of related papers. Submitted to ApJ, 19 pages, 17 postscript figures, most reduced in resolution, emulateapj.sty, for full resolution version, see http://cfa-www.harvard.edu/~rcroft/xray.ps.g

The Relation between Black Hole Mass, Bulge Mass, and Near-Infrared Luminosity

We present new accurate near-infrared (NIR) spheroid (bulge) structural parameters obtained by two-dimensional image analysis for all galaxies with a direct black hole (BH) mass determination. As expected, NIR bulge luminosities Lbul and BH masses are tightly correlated, and if we consider only those galaxies with secure BH mass measurement and accurate Lbul (27 objects), the spread of MBH-Lbul is similar to MBH-sigma, where sigma is the effective stellar velocity dispersion. We find an intrinsic rms scatter of ~0.3 dex in log MBH. By combining the bulge effective radii R_e measured in our analysis with sigma, we find a tight linear correlation (rms ~ 0.25 dex) between MBH and the virial bulge mass (propto R_e sigma^2), with ~ 0.002. A partial correlation analysis shows that MBH depends on both sigma and R_e, and that both variables are necessary to drive the correlations between MBH and other bulge properties.Comment: Astrophysical Journal Letters, in pres

The AGN-starburst connection, Galactic superwinds, and M_BH - sigma

Recent observations of young galaxies at redshifts z ~ 3 have revealed simultaneous AGN and starburst activity, as well as galaxy-wide superwinds. I show that there is probably a close connection between these phenomena by extending an earlier treatment of the M_BH - sigma relation (King, 2003). As the black hole grows, an outflow drives a shell into the surrounding gas. This stalls after a dynamical time at a size determined by the hole's current mass and thereafter grows on the Salpeter timescale. The gas trapped inside this bubble cools and forms stars and is recycled as accretion and outflow. The consequent high metallicity agrees with that commonly observed in AGN accretion. Once the hole reaches a critical mass this region attains a size such that the gas can no longer cool efficiently. The resulting energy-driven flow expels the remaining gas as a superwind, fixing both the M_BH - sigma relation and the total stellar bulge mass at values in good agreement with observation. Black hole growth thus produces starbursts and ultimately a superwind.Comment: ApJ, in press, 4 page

Efficiency improvements to the Groupe Special Mobile (GSM) digital mobile radio system

Groupe Spécial Mobile (GSM) has been developed as the pan-European second generation of digital mobile systems. GSM operates in the 900 MHz frequency band and employs digital technology instead of the analogue technology of its predecessors. Digital technology enables the GSM system to operate in much smaller zones in comparison with the analogue systems. The GSM system will offer greater roaming facilities to its subscribers, extended throughout the countries that have installed the system. The GSM system could be seen as a further enhancement to European integration. GSM has adopted a contention-based protocol for multipoint-to-point transmission. In particular, the slotted-ALOHA medium access protocol is used to coordinate the transmission of the channel request messages between the scattered mobile stations. Collision still happens when more than one mobile station having the same random reference number attempts to transmit on the same time-slot. In this research, a modified version of this protocol has been developed in order to reduce the number of collisions and hence increase the random access channel throughput compared to the existing protocol. The performance evaluation of the protocol has been carried out using simulation methods. Due to the growing demand for mobile radio telephony as well as for data services, optimal usage of the scarce availability radio spectrum is becoming increasingly important. In this research, a protocol has been developed whereby the number of transmitted information packets over the GSM system is increased without any additional increase of the allocated radio spectrum. Simulation results are presented to show the improvements achieved by the proposed protocol. Cellular mobile radio networks commonly respond to an increase in the service demand by using smaller coverage areas. As a result, the volume of the signalling exchanges increases. In this research, a proposal for interconnecting the various entitles of the mobile radio network over the future broadband networks based on the IEEE 802.6 Metropolitan Area Network (MAN) is outlined. Simulation results are presented to show the benefits achieved by interconnecting these entities over the broadband Networks

The black hole mass versus velocity dispersion relation in QSOs/Active Galactic Nuclei: observational appearance and black hole growth

Studies of massive black holes (BHs) in nearby galactic centers have revealed a tight correlation between BH mass and galactic velocity dispersion. In this paper we investigate how the BH mass versus velocity dispersion relation and the nuclear luminosity versus velocity dispersion relation in QSOs/active galactic nuclei (AGNs) are connected with the BH mass versus velocity dispersion relation in local galaxies, through the nuclear luminosity evolution of individual QSOs/AGNs and the mass growth of individual BHs. In the study we ignore the effects of BH mergers and assume that the velocity dispersion does not change significantly during and after the nuclear activity phase. Using the observed correlation in local galaxies and an assumed form of the QSO/AGN luminosity evolution and BH growth, we obtain the simulated observational appearance of the BH mass versus velocity dispersion relation in QSOs/AGNs. The simulation results illustrate how the BH accretion history (e.g., the lifetime of nuclear activity and the possibility that QSOs/AGNs accrete at a super-Eddington accretion rate at the early evolutionary stage) can be inferred from the difference between the relation in QSOs/AGNs and that in local galaxies. We also show how the difference may be weakened by the flux limit of telescopes. We expect that a large complete sample of QSOs/AGNs with accurate BH mass and velocity dispersion measurements will help to quantitatively constrain QSO/AGN luminosity evolution and BH growth models.Comment: 20 pages, including 4 figures; revised to match the published versio