12 research outputs found
Observing Supermassive Black Holes across cosmic time: from phenomenology to physics
In the last decade, a combination of high sensitivity, high spatial
resolution observations and of coordinated multi-wavelength surveys has
revolutionized our view of extra-galactic black hole (BH) astrophysics. We now
know that supermassive black holes reside in the nuclei of almost every galaxy,
grow over cosmological times by accreting matter, interact and merge with each
other, and in the process liberate enormous amounts of energy that influence
dramatically the evolution of the surrounding gas and stars, providing a
powerful self-regulatory mechanism for galaxy formation. The different
energetic phenomena associated to growing black holes and Active Galactic
Nuclei (AGN), their cosmological evolution and the observational techniques
used to unveil them, are the subject of this chapter. In particular, I will
focus my attention on the connection between the theory of high-energy
astrophysical processes giving rise to the observed emission in AGN, the
observable imprints they leave at different wavelengths, and the methods used
to uncover them in a statistically robust way. I will show how such a combined
effort of theorists and observers have led us to unveil most of the SMBH growth
over a large fraction of the age of the Universe, but that nagging
uncertainties remain, preventing us from fully understating the exact role of
black holes in the complex process of galaxy and large-scale structure
formation, assembly and evolution.Comment: 46 pages, 21 figures. This review article appears as a chapter in the
book: "Astrophysical Black Holes", Haardt, F., Gorini, V., Moschella, U and
Treves A. (Eds), 2015, Springer International Publishing AG, Cha
Dynamics of back‐arc extension controlled by subducting slab retreat: Insights from 2D thermo‐mechanical modelling
Longitudinal Study of Growth of Children with Unilateral Cleft Lip and Palate: 2 to 10 Years of Age
GOODS-Herschel: ultra-deep XMM-Newton observations reveal AGN/star-formation connection.
Models of galaxy evolution assume some connection between the AGN and star
formation activity in galaxies. We use the multi-wavelength information of the
CDFS to assess this issue. We select the AGNs from the 3Ms XMM-Newton survey
and measure the star-formation rates of their hosts using data that probe
rest-frame wavelengths longward of 20 um. Star-formation rates are obtained
from spectral energy distribution fits, identifying and subtracting an AGN
component. We divide the star-formation rates by the stellar masses of the
hosts to derive specific star-formation rates (sSFR) and find evidence for a
positive correlation between the AGN activity (proxied by the X-ray luminosity)
and the sSFR for the most active systems with X-ray luminosities exceeding
Lx=10^43 erg/s and redshifts z~1. We do not find evidence for such a
correlation for lower luminosity systems or those at lower redshifts. We do not
find any correlation between the SFR (or the sSFR) and the X-ray absorption
derived from high-quality XMM-Newton spectra either, showing that the
absorption is likely to be linked to the nuclear region rather than the host,
while the star-formation is not nuclear. Comparing the sSFR of the hosts to the
characteristic sSFR of star-forming galaxies at the same redshift we find that
the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN
- sSFR connection. Limiting our analysis to the highest X-ray luminosity AGNs
(X-ray QSOs with Lx>10^44 erg/s), we find that the highest-redshift QSOs (with
z>2) reside predominantly in starburst hosts, with an average sSFR more than
double that of the "main sequence", and we find a few cases of QSOs at z~1.5
with specific star-formation rates compatible with the main-sequence, or even
in the "quiescent" region. (abridged)Comment: Accepted for publication in A&
Numerical modeling of flow patterns around subducting slabs in a viscoelastic medium and its implications in the lithospheric stress analysis
A new thermal and rheological model of the European lithosphere
We present a new thermal and rheological model of the European lithosphere (10°W-35°E; 35°N-60°N), which is based on a combination of recently obtained geophysical models. To determine temperature distribution we use a new tomography model, which is principally improved by an a-priori correction of the crustal effect, by using EuCRUST-07, a new digital model of the European crust. The inversion approach is similar to those used in previous studies, but the employment of a more robust tomography model essentially improves the result. The uppermost mantle under western and central Europe is mostly characterized by temperatures in a range of 900°-1100 °C, with the hottest areas corresponding to the basins, which have experienced recent extension (e.g. Tyrrhenian Sea and Pannonian Basin). By contrast, the mantle temperatures under eastern Europe are about 550°-750 °C at the same depth and the minimum values are found in the northeastern part of the study area. The new temperature estimates are used to trace the lithosphere-asthenosphere thermal boundary, as a depth of the isotherm of 1200 °C. The lithospheric thickness is less than 100 km beneath the hottest part of western and central Europe, while the maximum values are observed beneath the East European Platform (200-230 km), the Alps and the Dinarides-Hellenic Arc (150-180 km). EuCRUST-07 and the new thermal model are used to calculate the strength distribution within the European lithosphere. Differently from previous estimates, the new model adopts lateral variations of lithology and density, which are derived from the crustal model. According to these estimates, in western and central Europe the lithosphere is more heterogeneous than in eastern Europe, the latter being generally characterized by higher strength values. These strength variations are also in a good agreement with other geophysical characteristics of the lithosphere such as residual mantle gravity anomalies. © 2009 Elsevier B.V. All rights reserved