35 research outputs found
Luminosity-dependent unification of Active Galactic Nuclei and the X-ray Baldwin effect
The existence of an anti-correlation between the equivalent width (EW) of the
narrow core of the iron Kalpha line and the luminosity of the continuum (i.e.
the X-ray Baldwin effect) in type-I active galactic nuclei has been confirmed
over the last years by several studies carried out with XMM-Newton, Chandra and
Suzaku. However, so far no general consensus on the origin of this trend has
been reached. Several works have proposed the decrease of the covering factor
of the molecular torus with the luminosity (in the framework of the
luminosity-dependent unification models) as a possible explanation for the
X-ray Baldwin effect. Using the fraction of obscured sources measured by recent
X-ray and IR surveys as a proxy of the half-opening angle of the torus, and the
recent Monte-Carlo simulations of the X-ray radiation reprocessed by a
structure with a spherical-toroidal geometry by Ikeda et al. (2009) and
Brightman & Nandra (2011), we test the hypothesis that the X-ray Baldwin effect
is related to the decrease of the half-opening angle of the torus with the
luminosity. Simulating the spectra of an unabsorbed population with a
luminosity-dependent covering factor of the torus as predicted by recent X-ray
surveys, we find that this mechanism is able to explain the observed X-ray
Baldwin effect. Fitting the simulated data with a log-linear L_{2-10keV}-EW
relation, we found that in the Seyfert regime (L_{2-10keV}< 10^44.2 erg s^-1)
luminosity-dependent unification produces a slope consistent with the
observations for average values of the equatorial column densities of the torus
of log N_H^T > 23.1. In the quasar regime (L_{2-10 keV}> 10^44.2 erg s^-1) a
decrease of the covering factor of the torus with the luminosity slower than
that observed in the Seyfert regime (as found by recent hard X-ray surveys) is
able to reproduce the observations for 23.2 < log N_H^T < 24.2.Comment: 9 pages, 9 figures, 1 table. Accepted for pubblication in A&
The Complete Calibration of the Color-Redshift Relation (C3R2) Survey: Survey Overview and Data Release 1
A key goal of the Stage IV dark energy experiments Euclid, LSST and WFIRST is
to measure the growth of structure with cosmic time from weak lensing analysis
over large regions of the sky. Weak lensing cosmology will be challenging: in
addition to highly accurate galaxy shape measurements, statistically robust and
accurate photometric redshift (photo-z) estimates for billions of faint
galaxies will be needed in order to reconstruct the three-dimensional matter
distribution. Here we present an overview of and initial results from the
Complete Calibration of the Color-Redshift Relation (C3R2) survey, designed
specifically to calibrate the empirical galaxy color-redshift relation to the
Euclid depth. These redshifts will also be important for the calibrations of
LSST and WFIRST. The C3R2 survey is obtaining multiplexed observations with
Keck (DEIMOS, LRIS, and MOSFIRE), the Gran Telescopio Canarias (GTC; OSIRIS),
and the Very Large Telescope (VLT; FORS2 and KMOS) of a targeted sample of
galaxies most important for the redshift calibration. We focus spectroscopic
efforts on under-sampled regions of galaxy color space identified in previous
work in order to minimize the number of spectroscopic redshifts needed to map
the color-redshift relation to the required accuracy. Here we present the C3R2
survey strategy and initial results, including the 1283 high confidence
redshifts obtained in the 2016A semester and released as Data Release 1.Comment: Accepted to ApJ. 11 pages, 5 figures. Redshifts can be found at
http://c3r2.ipac.caltech.edu/c3r2_DR1_mrt.tx
The narrow Fe K line and the molecular torus in active galactic nuclei - an IR/X-ray view
The narrow component of the iron K is an almost ubiquitous feature in
the X-ray spectra of active galactic nuclei (AGN) and is believed to originate
in neutral material, possibly located in the molecular torus. This would imply
a tight connection between the Fe K equivalent width (EW) and the
physical properties of the torus. In a recent work we have shown that the
decrease of the covering factor of the torus with the luminosity, as expected
by luminosity-dependent unification models, would be able to explain the
decrease of Fe K EW with the luminosity (i.e., the X-ray Baldwin
effect). Recent developments in the study of the mid-IR (MIR) spectrum of AGN
allow important parameters of the torus to be deduced, such as its covering
factor () and equatorial column density (),
by applying clumpy torus models. Using XMM-Newton/EPIC observations of a sample
of 24 type-I AGN, we investigate the relation between the physical parameters
of the torus obtained by recent MIR works and the properties of the Fe
K line. We correct the values of the Fe K EW by taking the
inclination angle, the photon index, the equatorial column density, and
half-opening angle of the torus into account using a physical torus model of
X-ray reprocessed radiation. We find that the relation between Fe K EW
and shows a slope that is consistent with the expected value,
albeit with a low statistical significance. A trend that is consistent with the
theoretical prediction is also found when comparing the Fe K EW to
. Our work seems to confirm that the bulk of the narrow Fe
K line is produced by the same material responsible for the MIR
emission.Comment: A&A in press, 15 pages, 5 Figures, 3 tables - Few references update
Dynamics of the Lyman alpha and C IV emitting gas in 3C 273
In this paper we study the variability properties of the Lyman alpha and C IV
emission lines in 3C273 using archival IUE observations. Our data show for the
first time the existence of variability on time scales of several years. We
study the spatial distribution and the velocity field of the emitting gas by
performing detailed analyses on the line variability using correlations, 1D and
2D response functions, and principal component analysis. In both lines we find
evidence for two components, one which has the dynamic properties of gas in
Keplerian motion around a black hole with a mass of the order of 10^9 Mo, and
one which is characterized by high, blue-shifted velocities at large lag. There
is no indication of the presence of optically thick emission medium neither in
the Lya, nor in the Civ response functions. The component characterized by
blue-shifted velocities, which is comparatively much stronger in Civ than in
Lya, is more or less compatible with being the result of gas falling towards
the central black hole with free-fall acceleration. We propose however that the
line emission at high, blue-shifted velocities is better explained in terms of
entrainment of gas clouds by the jet. This gas is therefore probably
collisionally excited as a result of heating due to the intense infrared
radiation from the jet, which would explain the strength of this component in
Civ relative to Lya. This phenomenon might be a signature of disk-jet
interaction.Comment: 16 pages, 10 figures. Accepted for publication in ApJ. Uses aaste
Accretion and outflow of gas in Markarian 509
A major uncertainty in models for photoionised outflows in AGN is the
distance of the gas to the central black hole. We present the results of a
massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk
509 to constrain the location of the outflow components dominating the soft
X-ray band.
Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in
2009. We have studied the response of the photoionised gas to the changes in
the ionising flux produced by the central regions. We were able to put tight
constraints on the variability of the absorbers from day to year time scales.
This allowed us to develop a model for the time-dependent photoionisation in
this source.
We find that the more highly ionised gas producing most X-ray line opacity is
at least 5 pc away from the core; upper limits to the distance of various
absorbing components range between 20 pc up to a few kpc. The more lowly
ionised gas producing most UV line opacity is at least 100 pc away from the
nucleus.
These results point to an origin of the dominant, slow (v<1000 km/s) outflow
components in the NLR or torus-region of Mrk 509. We find that while the
kinetic luminosity of the outflow is small, the mass carried away is likely
larger than the 0.5 Solar mass per year accreting onto the black hole.
We also determined the chemical composition of the outflow as well as
valuable constraints on the different emission regions. We find for instance
that the resolved component of the Fe-K line originates from a region 40-1000
gravitational radii from the black hole, and that the soft excess is produced
by Comptonisation in a warm (0.2-1 keV), optically thick (tau~10-20) corona
near the inner part of the disk.Comment: 4 pages, 1 figure, Proceedings of IAUS 290 "Feeding Compact Objects:
Accretion on All Scales", C. M. Zhang, T. Belloni, M. Mendez & S. N. Zhang
(eds.
Mapping the Galaxy Color-Redshift Relation: Optimal Photometric Redshift Calibration Strategies for Cosmology Surveys
Calibrating the photometric redshifts of >10^9 galaxies for upcoming weak
lensing cosmology experiments is a major challenge for the astrophysics
community. The path to obtaining the required spectroscopic redshifts for
training and calibration is daunting, given the anticipated depths of the
surveys and the difficulty in obtaining secure redshifts for some faint galaxy
populations. Here we present an analysis of the problem based on the
self-organizing map, a method of mapping the distribution of data in a
high-dimensional space and projecting it onto a lower-dimensional
representation. We apply this method to existing photometric data from the
COSMOS survey selected to approximate the anticipated Euclid weak lensing
sample, enabling us to robustly map the empirical distribution of galaxies in
the multidimensional color space defined by the expected Euclid filters.
Mapping this multicolor distribution lets us determine where - in galaxy color
space - redshifts from current spectroscopic surveys exist and where they are
systematically missing. Crucially, the method lets us determine whether a
spectroscopic training sample is representative of the full photometric space
occupied by the galaxies in a survey. We explore optimal sampling techniques
and estimate the additional spectroscopy needed to map out the color-redshift
relation, finding that sampling the galaxy distribution in color space in a
systematic way can efficiently meet the calibration requirements. While the
analysis presented here focuses on the Euclid survey, similar analysis can be
applied to other surveys facing the same calibration challenge, such as DES,
LSST, and WFIRST.Comment: ApJ accepted, 17 pages, 10 figure
Accretion and outflow of gas in Markarian 509
A major uncertainty in models for photoionised outflows in AGN is the distance of the gas to the central black hole. We present the results of a massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk 509 to constrain the location of the outflow components dominating the soft X-ray band. Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in 2009. We have studied the response of the photoionised gas to the changes in the ionising flux produced by the central regions. We were able to put tight constraints on the variability of the absorbers from day to year time scales. This allowed us to develop a model for the time-dependent photoionisation in this source. We find that the more highly ionised gas producing most X-ray line opacity is at least 5 pc away from the core; upper limits to the distance of various absorbing components range between 20 pc up to a few kpc. The more lowly ionised gas producing most UV line opacity is at least 100 pc away from the nucleus. These results point to an origin of the dominant, slow (v<1000 km sâ1) outflow components in the NLR or torus-region of Mrk 509. We find that while the kinetic luminosity of the outflow is small, the mass carried away is likely larger than the 0.5 Solar mass per year accreting onto the black hole. We also determined the chemical composition of the outflow as well as valuable constraints on the different emission regions. We find for instance that the resolved component of the Fe-K line originates from a region 40-1000 gravitational radii from the black hole, and that the soft excess is produced by Comptonisation in a warm (0.2-1 keV), optically thick (Ï~ 10-20) corona near the inner part of the dis