34 research outputs found
Constituents of the soft X-ray background
The X-ray background is generated by various classes of objects and variety
of emission mechanisms. Relative contribution of individual components depends
on energy. The goal is to assess the integral emission of the major components
of the soft X-ray background (extragalactic discrete sources dominated by AGNs,
galactic plasma, and the Warm/Hot Intergalactic Medium), investigating the
angular structure of the background. Fluctuations of the background are
measured using the auto-correlation function of the XRB determined in 5 energy
bands between 0.3 and 4.5 keV. The investigation is based on the extensive
observational data set selected from the XMM-Newton archives. Amplitudes of the
auto-correlation functions calculated in three energy bands above ~1 keV are
consistent with the conjecture that the background fluctuations result solely
from clustering of sources which produce the background. At energies below 1
keV the relative fluctuation amplitude decreases indicating that a fraction of
the soft XRB is associated with a smooth plasma emission in the Galaxy. It is
shown, however, that the mean spectrum of extragalactic discrete sources
steepens in the soft X-rays and is not well represented by a single power law
in the energy range 0.3-4.5 keV. The WHIM contribution to the total background
fluctuations is small and consistent with the WHIM properties derived from the
cross-correlation of the XRB with galaxies.Comment: 7 pages, 2 figure
Missing baryons and the soft X-ray background
The X-ray background intensity around Lick count galaxies and rich clusters
of galaxies is investigated in three ROSAT energy bands. It is found that the
X-ray enhancements surrounding concentrations of galaxies exhibit significantly
softer spectrum than the standard cluster emission and the average
extragalactic background. The diffuse soft emission accompanying the galaxies
is consistent with the thermal emission of the hot gas postulated first by the
Cen & Ostriker hydrodynamic simulations. Our estimates of the gas temperature -
although subject to large uncertainties - averaged over several Mpc scales are
below 1 keV, which is substantially below the temperature of the intra-cluster
gas, but consistent with temperatures predicted for the local intergalactic
medium. It is pointed out that the planned ROSITA mission would be essential
for our understanding of the diffuse thermal component of the background.Comment: AA accepted, 6 pages, incl. 4 figure
The diffuse X-ray background
The deepest observations of the X-ray background approach the surface
brightness of the truly diffuse component generated by Thomson scattering of
cosmic X-ray photons. Available estimates of the electron density and the X-ray
luminosity density of AGNs as a function of cosmological epoch are used to
calculate the integral scattered X-ray background component. It is shown that
the scattered component constitutes 1.0 - 1.7 % of the total background,
depending on the AGN cosmic evolution. Albeit this is a minute fragment of the
total flux, it becomes a perceptible fraction of the still unresolved part of
the background and should be taken into account in the future rigorous
assessments of the X-ray background structure. This diffuse component at
energies < 1 keV sums up with the emission by WHIM to 3 - 4 %. Consequently,
one should expect that integrated counts of discrete sources account for just
96 - 97 % for soft background and ~99 % at higher energies.Comment: 5 pages, 2 figures, AA in prin
The harmonic power spectrum of the soft X-ray background I. The data analysis
Fluctuations of the soft X-ray background are investigated using harmonic
analysis. A section of the ROSAT All-Sky Survey around the north galactic pole
is used. The flux distribution is expanded into a set of harmonic functions and
the power spectrum is determined. Several subsamples of the RASS have been used
and the spectra for different regions and energies are presented. The effects
of the data binning in pixels are assessed and taken into account. The spectra
of the analyzed samples reflect both small scale effects generated by strong
discrete sources and the large scale gradients of the XRB distribution. Our
results show that the power spectrum technique can be effectively used to
investigate anisotropy of the XRB at various scales. This statistics will
become a useful tool in the investigation of various XRB components.Comment: 12 pages, A&A accepte
Infinite-dimensional Compact Quantum Semigroup
In this paper we construct a compact quantum semigroup structure on the
Toeplitz algebra . The existence of a subalgebra, isomorphic to
the algebra of regular Borel's measures on a circle with convolution product,
in the dual algebra is shown. The existence of Haar functionals
in the dual algebra and in the above-mentioned subalgebra is proved. Also we
show the connection between and the structure of weak Hopf
algebra.Comment: 17 page
A Characterization of right coideals of quotient type and its application to classification of Poisson boundaries
Let be a co-amenable compact quantum group. We show that a right coideal
of is of quotient type if and only if it is the range of a conditional
expectation preserving the Haar state and is globally invariant under the left
action of the dual discrete quantum group. We apply this result to theory of
Poisson boundaries introduced by Izumi for discrete quantum groups and
generalize a work of Izumi-Neshveyev-Tuset on for co-amenable compact
quantum groups with the commutative fusion rules. More precisely, we prove that
the Poisson integral is an isomorphism between the Poisson boundary and the
right coideal of quotient type by maximal quantum subgroup of Kac type. In
particular, the Poisson boundary and the quantum flag manifold are isomorphic
for any q-deformed classical compact Lie group.Comment: 28 pages, Remark 4.9 adde
The nature of the unresolved extragalactic soft CXB
In this paper we investigate the power spectrum of the unresolved 0.5-2 keV
CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal
which, on scales >30", is significantly higher than the Shot-Noise and is
increasing with the angular scale. We interpreted this signal as the joint
contribution of clustered undetected sources like AGN, Galaxies and
Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources
fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall,
our modeling predicts that \sim 20% of the unresolved CXB flux is made by low
luminosity AGN, \sim 25% by galaxies and \sim 55% by the IGM (Inter Galactic
Medium). We do not find any direct evidence of the so called Warm Hot
Intergalactic Medium (i.e. matter with 10^5K<T<10^7K and density contrast
{\delta} <1000), but we estimated that it could produce about 1/7 of the
unresolved CXB. We placed an upper limit to the space density of postulated
X-ray-emitting early black hole at z>7.5 and compared it with SMBH evolution
models.Comment: 15 pages, 9 figures, accepted by MNRA
On the cosmic evolution of the scaling relations between black holes and their host galaxies: Broad Line AGN in the zCOSMOS survey
(Abriged) We report on the measurement of the rest frame K-band luminosity
and total stellar mass of the hosts of 89 broad line Active Galactic Nuclei
detected in the zCOSMOS survey in the redshift range 1<z<2.2. The unprecedented
multiwavelength coverage of the survey field allows us to disentangle the
emission of the host galaxy from that of the nuclear black hole in their
Spectral Energy Distributions. We derive an estimate of black hole masses
through the analysis of the broad Mg II emission lines observed in the
medium-resolution spectra taken with VIMOS/VLT as part of the zCOSMOS project.
We found that, as compared to the local value, the average black hole to host
galaxy mass ratio appears to evolve positively with redshift, with a best fit
evolution of the form (1+z)^{0.68 \pm0.12 +0.6 -0.3}, where the large
asymmetric systematic errors stem from the uncertainties in the choice of IMF,
in the calibration of the virial relation used to estimate BH masses and in the
mean QSO SED adopted. A thorough analysis of observational biases induced by
intrinsic scatter in the scaling relations reinforces the conclusion that an
evolution of the MBH-M* relation must ensue for actively growing black holes at
early times: either its overall normalization, or its intrinsic scatter (or
both) appear to increase with redshift. This can be interpreted as signature of
either a more rapid growth of supermassive black holes at high redshift, a
change of structural properties of AGN hosts at earlier times, or a significant
mismatch between the typical growth times of nuclear black holes and host
galaxies.Comment: 47 pages, 8 figures. Accepted for publication in Ap
Local Supermassive Black Holes, Relics of Active Galactic Nuclei and the X-ray Background
We quantify the importance of mass accretion during AGN phases in the growth
of supermassive black holes (BH) by comparing the mass function of black holes
in the local universe with that expected from AGN relics, which are black holes
grown entirely with mass accretion during AGN phases. The local BH mass
function (BHMF) is estimated by applying the well-known correlations between BH
mass, bulge luminosity and stellar velocity dispersion to galaxy luminosity and
velocity functions. The density of BH's in the local universe is 4.6 (-1.4;
+1.9) (h/0.7)^2 10^5 Msun Mpc^-3. The relic BHMF is derived from the continuity
equation with the only assumption that AGN activity is due to accretion onto
massive BH's and that merging is not important. We find that the relic BHMF at
z=0 is generated mainly at z<3. Moreover, the BH growth is anti-hierarchical in
the sense that smaller BH's (MBH< 10^7 Msun) grow at lower redshifts (z<1) with
respect to more massive one's (z~1-3). Unlike previous work, we find that the
BHMF of AGN relics is perfectly consistent with the local BHMF indicating the
local BH's were mainly grown during AGN activity. This agreement is obtained
while satisfying, at the same time, the constraints imposed from the X-ray
background. The comparison with the local BHMF also suggests that the merging
process is not important in shaping the relic BHMF, at least at low redshifts
(z<3). Our analysis thus suggests the following scenario: local black holes
grew during AGN phases in which accreting matter was converted into radiation
with efficiencies epsilon = 0.04-0.16 and emitted at a fraction lambda =
0.1-1.7 of the Eddington luminosity. The average total lifetime of these active
phases ranges from ~4.5 10^8 yr for MBH
10^9 Msun. (abridged)Comment: 19 pages, 18 figures, MNRAS in press, minor changes following
referee's comment