151 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&
An X-ray/SDSS sample (II): outflowing gas plasma properties
Galaxy-scale outflows are nowadays observed in many active galactic nuclei
(AGNs); however, their characterisation in terms of (multi-) phase nature,
amount of flowing material, effects on the host galaxy, is still unsettled. In
particular, ionized gas mass outflow rate and related energetics are still
affected by many sources of uncertainties. In this respect, outflowing gas
plasma conditions, being largely unknown, play a crucial role.
Taking advantage of the spectroscopic analysis results we obtained studying
the X-ray/SDSS sample of 563 AGNs at z presented in our companion paper,
we analyse stacked spectra and sub-samples of sources with high signal-to-noise
temperature- and density-sensitive emission lines to derive the plasma
properties of the outflowing ionized gas component. For these sources, we also
study in detail various diagnostic diagrams to infer information about
outflowing gas ionization mechanisms. We derive, for the first time, median
values for electron temperature and density of outflowing gas from medium-size
samples ( targets) and stacked spectra of AGNs. Evidences of shock
excitation are found for outflowing gas.
We measure electron temperatures of the order of K and
densities of cm for faint and moderately luminous AGNs
(intrinsic X-ray luminosity in the 2-10 keV band). We
caution that the usually assumed electron density ( cm) in
ejected material might result in relevant overestimates of flow mass rates and
energetics and, as a consequence, of the effects of AGN-driven outflows on the
host galaxy.Comment: 16 pages, 10 figures. Accepted for publication in A&
The MUSE view of He 2-10: no AGN ionization but a sparkling starburst
We study the physical and dynamical properties of the ionized gas in the
prototypical HII galaxy Henize 2-10 using MUSE integral field spectroscopy. The
large scale dynamics is dominated by extended outflowing bubbles, probably the
results of massive gas ejection from the central star forming regions. We
derive a mass outflow rate dMout/dt~0.30 Msun/yr, corresponding to mass loading
factor eta~0.4, in range with similar measurements in local LIRGs. Such a
massive outflow has a total kinetic energy that is sustainable by the stellar
winds and Supernova Remnants expected in the galaxy. We use classical emission
line diagnostic to study the dust extinction, electron density and ionization
conditions all across the galaxy, confirming the extreme nature of the highly
star forming knots in the core of the galaxy, which show high density and high
ionization parameter. We measure the gas phase metallicity in the galaxy taking
into account the strong variation of the ionization parameter, finding that the
external parts of the galaxy have abundances as low as 12 + log(O/H)~8.3, while
the central star forming knots are highly enriched with super solar
metallicity. We find no sign of AGN ionization in the galaxy, despite the
recent claim of the presence of a super massive active Black Hole in the core
of He~2-10. We therefore reanalyze the X-ray data that were used to propose the
presence of the AGN, but we conclude that the observed X-ray emission can be
better explained with sources of a different nature, such as a Supernova
Remnant.Comment: 11 pages, 8 Figures, Accepted for publication in A&
Multi-phase outflows in Mkn 848 observed with SDSS-MaNGA Integral Field Spectroscopy
The characterisation of galaxy-scale outflows in terms of their multi-phase
nature, amount, and effects of flowing material is crucial to place constraints
on models of galaxy evolution. This study can proceed only with the detailed
investigation of individual targets.
We present a spatially resolved spectroscopic optical data analysis of Mkn
848, a complex system consisting of two merging galaxies at z~0.04 that are
separated 7.5 kpc (projected distance). Motivated by the presence of a
multi-phase outflow in the north-west system revealed by the SDSS integrated
spectrum, we analysed the publicly available MaNGA data, which cover almost the
entire merging system, to study the physical properties of cool and warm gas in
detail.
Galaxy-wide outflowing gas in multiple phases is revealed for the first time
in the two merging galaxies. We also detect spatially resolved resonant NaID
emission associated with the outflows. The derived outflow energetics may be
consistent with a scenario in which both winds are accelerated by stellar
processes and AGN activity, although we favour an AGN origin given the high
outflow velocities and the ionisation conditions observed in the outflow
regions. Deeper observations are required, however, to better constrain the
nature of these multi-phase outflows. Outflow energetics in the north-west
system are strongly different between the ionised and atomic gas components,
the latter of which is associated with mass outflow rate and kinetic and
momentum powers that are 1-2 dex higher; those associated with the south-east
galaxy are instead similar.
Strong kp-scale outflows are revealed in an ongoing merger system, suggesting
that feedback can potentially impact the host galaxy even in the early merger
phases. The characterisation of the neutral and ionised gas phases has proved
to be crucial for a comprehensive study of the outflow phenomena.Comment: 19 pages, 14 figures, accepted for publication in A&
- …