4,164 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
The Iron Line Background
We investigate the presence of iron line emission among faint X-ray sources
identified in the 1Ms Chandra Deep Field South and in the 2Ms Chandra Deep
Field North. Individual source spectra are stacked in seven redshift bins over
the range z=0.5-4. We find that iron line emission is an ubiquitous property of
X-ray sources up to z~3. The measured line strengths are in good agreement with
those expected by simple pre-Chandra estimates based on X-ray background
synthesis models. The average rest frame equivalent width of the iron line does
not show significant changes with redshift.Comment: 5 pages, 2 figures, ApJ Letters in press (include emulateapj.sty
AGN and QSOs in the eROSITA All-Sky Survey -- Part I: Statistical properties
Context. The main element of the observing program of the
Spectrum-Roentgen-Gamma orbital observatory is a four-year all-sky survey, in
the course of which the entire sky will be scanned eight times.
Aims. We analyze the statistical properties of AGN and QSOs that are expected
to be detected in the course of the eROSITA all-sky survey (eRASS).
Methods. According to the currently planned survey strategy and based on the
parameters of the Galactic and extragalactic X-ray background as well as on the
results of the recent calculations of the eROSITA instrumental background, we
computed a sensitivity map of the eRASS. Using the best available
redshift-dependent AGN X-ray luminosity function (XLF), we computed various
characteristics of the eRASS AGN sample, such as their luminosity- and redshift
distributions, and the brightness distributions of their optical counterparts.
Results. After four years of the survey, a sky-average sensitivity of
~1x10^(-14) erg/s/cm^2 will be achieved in the 0.5-2.0keV band. With this
sensitivity, eROSITA is expected to detect ~3 million AGN on the extragalactic
sky (|b|>10deg). The median redshift of the eRASS AGN will be z~1 with ~40% of
the objects in the z=1-2 redshift range. About 10^4 - 10^5 AGN are predicted
beyond redshift z=3 and about 2 000 - 30 000 AGN beyond redshift z=4, the exact
numbers depend on the poorly known behavior of the AGN XLF in the high-redshift
and luminosity regimes. Of the detected AGN, the brightest 10% will be detected
with more than ~38 counts per PSF HEW, while the faintest 10% will have fewer
than ~9 counts. The optical counterparts of ~95% of the AGN will be brighter
than I_(AB)=22.5mag. The planned scanning strategy will allow one to search for
transient events on a timescale of half a year and a few hours with a
0.5-2.0keV sensitivity of ~2x10^(-14) to ~2x10^(-13) erg/s/cm^2, respectively.Comment: minor additions, accepted for publication in A&
Calibration of force actuators on an adaptive secondary prototype
In the context of the Large Binocular Telescope project, we present the
results of force actuator calibrations performed on an adaptive secondary
prototype called P45, a thin deformable glass with magnets glued onto its back.
Electromagnetic actuators, controlled in a closed loop with a system of
internal metrology based on capacitive sensors, continuously deform its shape
to correct the distortions of the wavefront. Calibrations of the force
actuators are needed because of the differences between driven forces and
measured forces. We describe the calibration procedures and the results,
obtained with errors of less than 1.5%.Comment: 7 page
Two-Face(s): ionized and neutral gas winds in the local Universe
We present a comprehensive study of the Na I 5890, 5895 (Na I D)
resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample
to look for neutral gas outflows in the local galaxies. Individual galaxy
spectra are stacked in bins of M and SFR to investigate the dependence
of galactic wind occurrence and velocity as a function of the galaxy position
in the SFR- plane. In massive galaxies at the high SFR tail we find
evidence of a significant blue-shifted Na I D absorption, which we interpret as
evidence of neutral outflowing gas. The occurrence of the blue-shifted
absorption is observed at the same significance for purely SF galaxies, AGN and
composite systems at fixed SFR. In all classes of objects the blue-shift is the
largest and the Na I D equivalent width the smallest for face-on galaxies while
the absorption feature is at the systemic velocity for edge-on systems. This
indicates that the neutral outflow is mostly perpendicular or biconical with
respect to the galactic disk. We also compare the kinematics of the neutral gas
with the ionized gas phase as traced by the [OIII]5007, H,
[NII] and [NII] emission lines. Differently for the
neutral gas phase, all the emission lines show evidence of perturbed kinematics
only in galaxies with a significant level of nuclear activity and, they are
independent from the disk inclination. In conclusion, we find that, in the
local Universe, galactic winds show two faces which are related to two
different ejection mechanisms, namely the neutral outflowing gas phase related
to the SF activity along the galaxy disk and the ionized phase related to the
AGN feedback. In both the neutral and ionized gas phases, the observed wind
velocities suggest that the outflowing gas remains bound to the galaxy with no
definitive effect on the gas reservoir.Comment: Accepted to A&A, 13 pages, 9 figure
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