211 research outputs found
Accounting for selection effects in the BH-bulge relations: No evidence for cosmological evolution
The redshift evolution of the black hole - bulge relations is an essential
observational constraint for models of black hole - galaxy coevolution. In
addition to the observational challenges for these studies, conclusions are
complicated by the influence of selection effects. We demonstrate that there is
presently no statistical significant evidence for cosmological evolution in the
black hole-bulge relations, once these selection effects are taken into account
and corrected for. We present a fitting method, based on the bivariate
distribution of black hole mass and galaxy property, that accounts for the
selection function in the fitting and is therefore able to recover the
intrinsic black hole - bulge relation unbiased. While prior knowledge is
restricted to a minimum, we at least require knowledge of either the sample
selection function and the mass dependence of the active fraction, or the
spheroid distribution function and the intrinsic scatter in the black hole -
bulge relation. We employed our fitting routine to existing studies of the
black hole-bulge relation at z~1.5 and z~6, using our current best knowledge of
the distribution functions. There is no statistical significant evidence for
positive evolution in the MBH-M* ratio out to z~2. At z~6 the current
constraints are less strong, but we demonstrate that the large observed
apparent offset from the local black hole-bulge relation at z~6 is fully
consistent with no intrinsic offset. The method outlined here provides a tool
to obtain more reliable constraints on black hole - galaxy co-evolution in the
future.Comment: 13 pages, 8 figures, published in MNRA
Low redshift AGN in the Hamburg/ESO Survey: II. The active black hole mass function and the distribution function of Eddington ratios
We estimated black hole masses and Eddington ratios for a well defined sample
of local (z<0.3) broad line AGN from the Hamburg/ESO Survey (HES), based on the
Hbeta line and standard recipes assuming virial equilibrium for the broad line
region. The sample represents the low-redshift AGN population over a wide range
of luminosities, from Seyfert 1 galaxies to luminous quasars. From the
distribution of black hole masses we derived the active black hole mass
function (BHMF) and the Eddington ratio distribution function (ERDF) in the
local universe, exploiting the fact that the HES has a well-defined selection
function. While the directly determined ERDF turns over around L/L_Edd ~ 0.1,
similar to what has been seen in previous analyses, we argue that this is an
artefact of the sample selection. We employed a maximum likelihood approach to
estimate the intrinsic distribution functions of black hole masses and
Eddington ratios simultaneously in an unbiased way, taking the sample selection
function fully into account. The resulting ERDF is well described by a
Schechter function, with evidence for a steady increase towards lower Eddington
ratios, qualitatively similar to what has been found for type~2 AGN from the
SDSS. Comparing our best-fit active BHMF with the mass function of inactive
black holes we obtained an estimate of the fraction of active black holes, i.e.
an estimate of the AGN duty cycle. The active fraction decreases strongly with
increasing black hole mass. A comparison with the BHMF at higher redshifts also
indicates that, at the high mass end, black holes are now in a less active
stage than at earlier cosmic epochs. Our results support the notion of
anti-hierarchical growth of black holes, and are consistent with a picture
where the most massive black holes grew at early cosmic times, whereas at
present mainly smaller mass black holes accrete at a significant rate.Comment: 19 pages, 15 figures, accepted for publication in A&
LSDCat: Detection and cataloguing of emission-line sources in integral-field spectroscopy datacubes
We present a robust, efficient, and user-friendly algorithm for detecting
faint emission-line sources in large integral-field spectroscopic datacubes
together with the public release of the software package LSDCat (Line Source
Detection and Cataloguing). LSDCat uses a 3-dimensional matched filter
approach, combined with thresholding in signal-to-noise, to build a catalogue
of individual line detections. In a second pass, the detected lines are grouped
into distinct objects, and positions, spatial extents, and fluxes of the
detected lines are determined. LSDCat requires only a small number of input
parameters, and we provide guidelines for choosing appropriate values. The
software is coded in Python and capable to process very large datacubes in a
short time. We verify the implementation with a source insertion and recovery
experiment utilising a real datacube taken with the MUSE instrument at the ESO
Very Large Telescope.Comment: 14 pages. Accepted for publication in Astronomy & Astrophysics. The
LSDCat software is available at https://bitbucket.org/Knusper2000/lsdcat, v2
corrected typos and language editin
Resolving stellar populations with crowded field 3D spectroscopy
(Abridged) We describe a new method to extract spectra of stars from
observations of crowded stellar fields with integral field spectroscopy (IFS).
Our approach extends the well-established concept of crowded field photometry
in images into the domain of 3-dimensional spectroscopic datacubes. The main
features of our algorithm are: (1) We assume that a high-fidelity input source
catalogue already exists and that it is not needed to perform sophisticated
source detection in the IFS data. (2) Source positions and properties of the
point spread function (PSF) vary smoothly between spectral layers of the
datacube, and these variations can be described by simple fitting functions.
(3) The shape of the PSF can be adequately described by an analytical function.
Even without isolated PSF calibrator stars we can therefore estimate the PSF by
a model fit to the full ensemble of stars visible within the field of view. (4)
By using sparse matrices to describe the sources, the problem of extracting the
spectra of many stars simultaneously becomes computationally tractable. We
present extensive performance and validation tests of our algorithm using
realistic simulated datacubes that closely reproduce actual IFS observations of
the central regions of Galactic globular clusters. We investigate the quality
of the extracted spectra under the effects of crowding. The main effect of
blending between two nearby stars is a decrease in the S/N in their spectra.
The effect increases with the crowding in the field in a way that the maximum
number of stars with useful spectra is always ~0.2 per spatial resolution
element. This balance breaks down when exceeding a total source density of ~1
significantly detected star per resolution element. We close with an outlook by
applying our method to a simulated globular cluster observation with the
upcoming MUSE instrument at the ESO-VLT.Comment: accepted for publication in A&A, 19 pages, 19 figure
Spatial decomposition of on-nucleus spectra of quasar host galaxies
In order to study the host galaxies of type 1 (broad-line) quasars, we
present a semi-analytic modelling method to decompose the on-nucleus spectra of
quasars into nuclear and host galaxy channels. The method uses the spatial
information contained in long-slit or slitlet spectra. A routine determines the
best fitting combination of the spatial distribution of the point like nucleus
and extended host galaxy. Inputs are a simultaneously observed PSF, and
external constraints on galaxy morphology from imaging. We demonstrate the
capabilities of the method to two samples of a total of 18 quasars observed
with EFOSC at the ESO 3.6m telescope and FORS1 at the ESO VLT.
~50% of the host galaxies with sucessful decomposition show distortions in
their rotation curves or peculiar gas velocities above normal maximum
velocities for disks. This is consistent with the fraction from optical
imaging. All host galaxies have quite young stellar populations, typically 1-2
Gyr. For the disk dominated hosts these are consistent with their inactive
counterparts, the luminosity weighted stellar ages are much younger for the
bulge dominated hosts, compared to inactive early type galaxies. While this
presents further evidence for a connection of galaxy interaction and AGN
activity for half of the sample, this is not clear for the other half: These
are often undistorted disk dominated host galaxies, and interaction on a
smaller level might be detected in deeper high-resolution images or deeper
spectroscopic data. The velocity information does not show obvious signs for
large scale outflows triggered by AGN feedback - the data is consistent with
velocity fields created by galaxy interaction.Comment: Accepted for publication in MNRAS; 19 pages, 12 figure
First estimate of the time delay in HE 1104-1805
We present first results from five years of spectrophotometric monitoring of
the bright double QSO and gravitational lens HE 1104-1805. The quasar has
varied considerably over this time, while the emission line fluxes appear to
have remained constant. We have constructed monochromatic continuum light
curves for components A and B, finding that B leads the variability. A
quantitative analysis with the Pelt method gives a best estimate for the light
travel time delay of about 0.73 years, although a value as low as 0.3 cannot
yet be excluded. We discuss possible models for the QSO-lens configuration and
use our measured time delay to predict the redshift of the lens, z_d. Finding
that most likely z_d < 1, we can rule out the hitherto favoured values of z_d =
1.32 or 1.66. A new candidate is an absorption system at z=0.73, but the lens
could also be an elliptical not detected in absorption.Comment: 4 pages, 4 figures, accepted for A&A, Letters to the edito
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