231 research outputs found
Relativistic Iron lines at high redshifts
The shape and the intensity of the 6.4 keV iron line bring unique information
on the geometrical and physical properties of the supermassive black hole and
the surrounding accreting gas at the very center of Active Galactic Nuclei.
While there are convincing evidences of a relativistically broadened iron line
in a few nearby bright objects, their properties at larger distances are
basically unknown. We have searched for the presence of iron line by fully
exploiting Chandra observations in the deep fields. The line is clearly
detected in the average spectra of about 250 sources stacked in several
redshift bins over the range z=0.5-4.0. We discuss their average properties
with particular enphasys on the presence and intensity of a broad component.Comment: 6 pages, 4 figures. To appear in the proceedings of "Relativistic
Astrophysics and Cosmology - Einstein's Legacy" (Eds.: B. Aschenbach, V.
Burwitz, G. Hasinger, and B. Leibundgut), 7 - 11 November 2005, Munich,
German
Massive Black Holes: formation and evolution
Supermassive black holes are nowadays believed to reside in most local
galaxies. Observations have revealed us vast information on the population of
local and distant black holes, but the detailed physical properties of these
dark massive objects are still to be proven. Accretion of gas and black hole
mergers play a fundamental role in determining the two parameters defining a
black hole: mass and spin. We briefly review here the basic properties of the
population of supermassive black holes, focusing on the still mysterious
formation of the first massive black holes, and their evolution from early
times to now.Comment: review to appear in Proc. IAU Symp. 238, "Black Holes: from stars to
galaxies - across the range of masses
Spectral properties of X-ray background sources
In this thesis we analysed the deepest XMM-Newton observations of the Chandra Deep Field South and the Lockman Hole. These two reference fields for studies of different X-ray background source classes, provide a unique opportunity to study physical and evolutionary properties of distant normal and active galaxies, clusters of galaxies and even faint Galactic stars using statistically significant
samples. The main goal of the work was a further improvement of the knowledge about X-ray properties of AGN and galaxies in the distant Universe using the statistical treatment of these large samples of detected sources
Strong gravity effects: X-ray spectra, variability and polarimetry
Accreting black holes often show iron line emission in their X-ray spectra.
When this line emission is very broad or variable then it is likely to
originate from close to the black hole. The theory and observations of such
broad and variable iron lines are briefly reviewed here. In order for a clear
broad line to be found, one or more of the following have to occur: high iron
abundance, dense disk surface and minimal complex absorption. Several excellent
examples are found from observations of Seyfert galaxies and Galactic Black
Holes. In some cases there is strong evidence that the black hole is rapidly
spinning. Further examples are expected as more long observations are made with
XMM-Newton, Chandra and Suzaku. The X-ray spectra show evidence for the strong
gravitational redshifts and light bending expected around black holes.Comment: 8 pages, 16 figures, For proceedings of IAU Symposium No. 238 "Black
Holes - From Stars to Galaxies" edited by Vladimir Karas & Giorgio Mat
Discovery of a massive supercluster system at
Superclusters are the largest relatively isolated systems in the cosmic web.
Using the SDSS BOSS survey we search for the largest superclusters in the
redshift range .
We generate a luminosity-density field smoothed over
to detect the large-scale over-density regions. Each individual over-density
region is defined as single supercluster in the survey. We define the
superclusters in the way that they are comparable with the superclusters found
in the SDSS main survey.
We found a system we call the BOSS Great Wall (BGW), which consists of two
walls with diameters 186 and 173 Mpc, and two other major superclusters
with diameters of 64 and 91 Mpc. As a whole, this system consists of
830 galaxies with the mean redshift 0.47. We estimate the total mass to be
approximately . The morphology of the
superclusters in the BGW system is similar to the morphology of the
superclusters in the Sloan Great Wall region.
The BGW is one of the most extended and massive system of superclusters yet
found in the Universe.Comment: 4 pages, accepted as a letter in A&
Dust in the reionization era: ALMA observations of a =8.38 Galaxy
We report on the detailed analysis of a gravitationally-lensed Y-band
dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the
Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large
Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm
continuum flux suggesting the presence of dust for a star-forming galaxy with a
photometric redshift of . Deep X-SHOOTER spectra confirms the high
redshift identity of A2744_YD4 via the detection of Lyman emission at
a redshift =8.38. The association with the ALMA detection is confirmed by
the presence of [OIII] 88m emission at the same redshift. Although both
emission features are only significant at the 4 level, we argue their
joint detection and the positional coincidence with a high redshift dropout in
the HST images confirms the physical association. Analysis of the available
photometric data and the modest gravitational magnification ()
indicates A2744_YD4 has a stellar mass of 210 M, a
star formation rate of M/yr and a dust mass of
610 M. We discuss the implications of the
formation of such a dust mass only 200 Myr after the onset of cosmic
reionisation.Comment: Accepted for publication in ApJ
Quasars with PV broad absorption in BOSS data release 9
Broad absorption lines (BALs) found in a significant fraction of quasar
spectra identify high-velocity outflows that might be present in all quasars
and could be a major factor in feedback to galaxy evolution. Understanding the
nature of these flows requires further constraints on their physical
properties, including their column densities, for which well-studied BALs, such
as CIV 1548,1551, typically provide only a lower limit because of saturation
effects. Low-abundance lines, such as PV 1118,1128, indicate large column
densities, implying outflows more powerful than measurements of CIV alone would
indicate. We search through a sample of 2694 BAL quasars from the SDSS-III/BOSS
DR9 quasar catalog for such absorption, and we identify 81 `definite' and 86
`probable' detections of PV broad absorption, yielding a firm lower limit of
3.0-6.2% for the incidence of such absorption among BAL quasars. The
PV-detected quasars tend to have stronger CIV and SiIV absorption, as well as a
higher incidence of LoBAL absorption, than the overall BAL quasar population.
Many of the PV-detected quasars have CIV troughs that do not reach zero
intensity (at velocities where PV is detected), confirming that the outflow gas
only partially covers the UV continuum source. PV appears significantly in a
composite spectrum of non-PV-detected BAL quasars, indicating that PV
absorption (and large column densities) are much more common than indicated by
our search results. Our sample of PV detections significantly increases the
number of known PV detections, providing opportunities for follow-up studies to
better understand BAL outflow energetics.Comment: 18 pages, 12 figures. All spectral plots available at
http://www.dancapellupo.com/boss-pv-bal-spectral-plots.htm
BOSS Great Wall: morphology, luminosity, and mass
We study the morphology, luminosity and mass of the superclusters from the
BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at
the redshift . We have employed the Minkowski functionals to quantify
supercluster morphology. We calculate supercluster luminosities and masses
using two methods. Firstly, we used data about the luminosities and stellar
masses of high stellar mass galaxies with .
Secondly, we applied a scaling relation that combines morphological and
physical parameters of superclusters to obtain supercluster luminosities, and
obtained supercluster masses using the mass-to-light ratios found for local
rich superclusters. We find that the BGW superclusters are very elongated
systems, with shape parameter values of less than . This value is lower
than that found for the most elongated local superclusters. The values of the
fourth Minkowski functional for the richer BGW superclusters (
and ) show that they have a complicated and rich inner structure. We
identify two Planck SZ clusters in the BGW superclusters, one in the richest
BGW supercluster, and another in one of the poor BGW superclusters. The
luminosities of the BGW superclusters are in the range of , and masses in the range of . Supercluster luminosities and masses obtained
with two methods agree well. We conclude that the BGW is a complex of massive,
luminous and large superclusters with very elongated shape. The search and
detailed study, including the morphology analysis of the richest superclusters
and their complexes from observations and simulations can help us to understand
formation and evolution of the cosmic web.Comment: Comments: 10 pages, 2 figures, A&A, in pres
A revision of the X-ray absorption nature of BALQSOs
Aims. Broad absorption-line quasars (BALQSOs) are key objects for studying the structure and emission/absorption properties of AGN. However, despite their fundamental importance, the properties of BALQSOs remain poorly understood. To investigate the X-ray nature of these sources, as well as the correlations between X-ray and rest-frame UV properties, we compile a large sample of BALQSOs observed by XMM-Newton.
Methods. We collect information for 88 sources from the literature and existing catalogues, creating the largest BALQSO sample analysed optically and in X-ray to date. We performed a full X-ray spectral analysis (using unabsorbed and both neutral and ionized absorption models) on a sample of 39 sources with higher X-ray spectral quality, and an approximate hardness-ratio analysis on the remaining sources. Using available optical spectra, we calculate the BALnicity index and investigate the dependence of this optical parameter on different X-ray properties.
Results. Using the neutral absorption model, we find that 36% of our BALQSOs have NnH
< 5 Ă 1021 cmâ2, lower than the expected X-ray absorption for these objects. However, when we used a physically-motivated model for the X-ray absorption in BALQSOs, i.e.,
ionized absorption, âŒ90% of the objects are absorbed. The observed difference in ionized properties of sources with the BALnicity index (BI) =0 and BI > 0 might be explained by different physical conditions of the outflow and/or inclination effects. The absorption properties also suggest that LoBALs may be physically different objects from HiBALs. In addition, we report on a correlation between the ionized absorption column density and BAL parameters. There is evidence (at the 98% level) that the amount of X-ray absorption is
correlated with the strength of high-ionization UV absorption. Not previously reported, this correlation can be naturally understood in virtually all BALQSO models, as being driven by the total amount of gas mass flowing towards the observer. We also find a hint of a correlation between the BI and the ionization level detected in X-rays.We thank the anonymous referee for helpful comments. The first author would like to thank the Spanish Ministerio de Ciencia e InnovaciĂłn for a Juan de la Cierva contract. XB, FJC and RGM acknowledge financial support by the Spanish MICINN under project ESP2006-13608-C02-01.We also acknowledge the Sloan Digital Sky Survey (http://www.sdss.org/). Funding for the SDSS has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England
Statistics of relativistically broadened Fe K-alpha lines in AGN
We present preliminary results on the properties of relativistically
broadened Fe K-alpha lines in a collection of more then 100 Active Galactic
Nuclei (AGN) observed by the XMM-Newton EPIC-pn camera. Our main conclusions
can be summarized as follows: a) we detect broad lines in about 25% of the
sample objects. This fraction increases to 42+/-13% if we consider only objects
with more than 10000 counts in the hard (2-10 keV) band, and to 50+/-32% for
the small sub-sample (6 objects) of type~1 Piccinotti AGN with optimal
XMM-Newton exposure (at least 200000 counts in the hard band); b) we find no
significant difference in the detection rate of broad lines between obscured
and unobscured AGN; c) the strongest relativistic profiles are measured in
low-luminosity (< 10^43 erg/s) AGN; d) Equivalent Widths (EWs) associated with
relativistic profiles in stacked spectra are ~150 eV for all luminosity
classes; e) models of relativistically broadened iron line profiles ("kyrline",
Dovciak et al. 2005), which include full relativistic treatment of the
accretion disk emission around a Kerr black hole in the strong gravity regime,
yield an average disk inclination angle ~30 degrees, and a radial dependence of
the disk emissivity profile ~-3. The distribution of EW is very broad, with
=2.4. We estimate that an investment of about 1 Ms of XMM-Newton time
would be required to put these results on a sound statistical basis.Comment: 4 pages, 9 figures, to appear in Astronomische Nachrichten,
Proceedings of the ESAC Workshop "Variable and broad lines around black
holes
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