224 research outputs found
AGN evolution from large and deep X-ray surveys
Over the last few years, the existence of mutual feedback effects between
accreting supermassive black holes powering AGN and star formation in their
host galaxies has become evident. This means that the formation and the
evolution of AGN and galaxies should be considered as one and the same problem.
As a consequence, the search for, and the characterization of the evolutive and
physical properties of AGN over a large redshift interval is a key topic of
present research in the field of observational cosmology. Significant advances
have been obtained in the last ten years thanks to the sizable number of
XMM-Newton and Chandra surveys, complemented by multiwavelength follow-up
programs. We will present some of the recent results and the ongoing efforts
(mostly from the COSMOS and CDFS surveys) aimed at obtaining a complete census
of accreting Black Holes in the Universe, and a characterization of the host
galaxies properties.Comment: 8 pages, 5 figures. Invited talk, to be published in the proceedings
of the IAU Symposium 267 "Co-evolution of central Black Holes and galaxies",
B.M. Peterson, R.S. Somerville, & T. Storchi-Bergmann, eds
On the arcmin structure of the X-ray Universe
We present the angular correlation function of the X-ray population of 1063
XMM-Newton observations at high Galactic latitudes, comprising up to ~30000
sources over a sky area of ~125 sq. degrees in the energy bands: soft (0.5-2
keV) and hard (2-10 keV). This is the largest sample of serendipitous X-ray
sources ever used for clustering analysis purposes to date and the results have
been determined with unprecedented accuracy. We detect significant clustering
signals in the soft and hard bands (~10 sigma and ~5 sigma, respectively). We
deproject the angular correlation function via Limber's equation and calculate
the typical spatial lengths. We infer that AGN at redshifts ~1 are embedded in
dark matter halos with typical masses of log M ~ 12.6/h Msol and lifetimes in
the range ~3-5 x 10^8 years, which indicates that AGN activity is a transient
phase in the life of galaxies.Comment: 4 pages, 1 figure. Proc. of the conference "X-ray Astronomy 2009:
Present status, multiwavelength approach and future perspectives", September
2009, Bologna. To appear in AIP Conf. Proc. (editors: A. Comastri, M. Cappi,
L. Angelini)
X-ray absorbed QSOs and the QSO evolutionary sequence
Unexpected in the AGN unified scheme, there exists a population of broad-line
z~2 QSOs which have heavily absorbed X-ray spectra. These objects constitute
10% of the population at luminosities and redshifts characteristic of the main
producers of QSO luminosity in the Universe. Our follow up observations in the
submm show that these QSOs are often embedded in ultraluminous starburst
galaxies, unlike most QSOs at the same redshifts and luminosities. The
radically different star formation properties between the absorbed and
unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus
invoked in AGN unification schemes. Instead, these results suggest that the
objects represent a transitional phase in an evolutionary sequence relating the
growth of massive black holes to the formation of galaxies. The most puzzling
question about these objects has always been the nature of the X-ray absorber.
We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton
spectroscopy. We show that the absorption is most likely due to a dense ionised
wind driven by the QSO. This wind could be the mechanism by which the QSO
terminates the star formation in the host galaxy, and ends the supply of
accretion material, to produce the present day black hole/spheroid mass ratio.Comment: 4 pages, to appear in conference proceedings "Studying Galaxy
Evolution with Spitzer and Herschel
Precision Cosmology from X-ray AGN clustering
We place tight constraints on the main cosmological parameters of spatially
flat cosmological models by using the recent angular clustering results of
XMM-{\it Newton} soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009a), which
have a redshift distribution with a median of . Performing a standard
likelihood procedure, assuming a constant in comoving coordinates AGN
clustering evolution, the AGN bias evolution model of Basilakos et al. (2008)
and the WMAP5 value of , we find stringent simultaneous constraints
in the (w) plane, with ,
w.Comment: Accepted for publication, MNRAS Lett. in press, 5 pages, 2 figure
The nature of X-ray-absorbed quasi-stellar objects
There exists a significant population of broad line, z∼ 2 quasi-stellar objects (QSOs) which have heavily absorbed X-ray spectra. Follow-up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. Here we present X-ray spectra from XMM–Newton for a sample of five such X-ray-absorbed QSOs that have been detected at submillimetre wavelengths. We also present spectra in the rest-frame ultraviolet from ground-based telescopes. All the five QSOs are found to exhibit strong C iv absorption lines in their ultraviolet spectra with equivalent width >5 Å. The X-ray spectra are inconsistent with the hypothesis that these objects show normal QSO continua absorbed by low-ionization gas. Instead, the spectra can be modelled successfully with ionized absorbers, or with cold absorbers if they possess unusually flat X-ray continuum shapes and unusual optical to X-ray spectral energy distributions. We show that the ionized absorber model provides the simplest, most self-consistent explanation for their observed properties. We estimate that the fraction of radiated power that is converted into kinetic luminosity of the outflowing winds is typically ∼4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M–σ relation, and consistent with the hypothesis that the X-ray-absorbed QSOs represent the transition phase between obscured accretion and the luminous QSO phase in the evolution of massive galaxies
High-precision multi-band measurements of the angular clustering of X-ray sources
In this paper we present the two-point angular correlation function of the
X-ray source population of 1063 XMM-Newton observations at high Galactic
latitudes, comprising up to ~30000 sources over a sky area of 125.5 sq. deg, in
three energy bands: 0.5-2 (soft), 2-10 (hard), and 4.5-10 (ultrahard) keV. We
have measured the angular clustering of our survey and find significant
positive clustering signals in the soft and hard bands, and a marginal
clustering detection in the ultrahard band. We find dependency of the
clustering strength on the flux limit and no significant differences in the
clustering properties between sources with high hardness ratios and those with
low hardness ratios. Our results show that obscured and unobscured objects
share similar clustering properties and therefore they both reside in similar
environments, in agreement with the unified model of AGN. We deprojected the
angular clustering parameters via Limber's equation to compute their typical
spatial lengths. From that we have inferred the typical mass of the dark matter
haloes in which AGN at redshifts of ~1 are embedded. The short AGN lifetimes
derived suggest that AGN activity might be a transient phase that can be
experienced several times by a large fraction of galaxies throughout their
lives.Comment: 14 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
The use of geographic information systems for the optimal location of biomass power plants in the Madrid Community (Spain)
This article has been extracted from the results of a thesis entitled “Potential bioelectricity production of the
Madrid Community Agricultural Regions based on rye and triticale biomass.” The aim was, first, to quantify the potential of rye (Secale Cereale L.) and triticale (
Triticosecale Aestivum L.) biomass in each of the Madrid Community agricultural regions, and second, to locate the
most suitable areas for the installation of power plants using biomass. At least 17,339.9 t d.m. of rye and triticale would be required to satisfy the biomass needs of a 2.2 MW power plant, (considering an efficiency of 21.5%, 8,000 expected operating hours/year and a biomass LCP of 4,060 kcal/kg for both crops), and 2,577 ha would be used (which represent 2.79% of the Madrid Community fallow dry land surface). Biomass yields that could be achieved in Madrid Community using 50% of the fallow dry land surface (46,150 ha representing 5.75% of the Community area), based on rye and triticale crops, are estimated at 84,855, 74,906, 70,109, 50,791, 13,481, and 943 t annually for the Campiña, Vegas, Sur Occidental, Área Metropolitana, Lozoya-Somosierra, and Guadarrama regions. The latter represents a bioelectricity potential of 10.77, 9.5, 8.9, 6.44, 1.71, and 0.12 MW, respectively
Computing Efficient Financial Strategies: An Extended Compromise Programming Approach
This paper proposes a mathematical model to plan the financial strategy of a large company. The model links the philosophy of new behavioural economics with the multiple criteria decision making paradigm. Within this theoretical approach, the proposed model is supported by more realistic behavioral hypotheses. After formulating the initial multi-objective programming model, it has, due to its underlying computational difficulties, to be transformed into an easily computable extended compromise programming model. The functional and empirical potential of the model is illustrated with the help of a case study concerning a “stock market quoted” Spanish company operating in the energy sector. This paper shows how such an approach can open up new prospects for research linking economic problems with applied mathematic
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