256 research outputs found
Imprints of the quasar structure in time-delay light curves: Microlensing-aided reverberation mapping
Owing to the advent of large area photometric surveys, the possibility to use
broad band photometric data, instead of spectra, to measure the size of the
broad line region of active galactic nuclei, has raised a large interest. We
describe here a new method using time-delay lensed quasars where one or several
images are affected by microlensing due to stars in the lensing galaxy. Because
microlensing decreases (or increases) the flux of the continuum compared to the
broad line region, it changes the contrast between these two emission
components. We show that this effect can be used to effectively disentangle the
intrinsic variability of those two regions, offering the opportunity to perform
reverberation mapping based on single band photometric data. Based on simulated
light curves generated using a damped random walk model of quasar variability,
we show that measurement of the size of the broad line region can be achieved
using this method, provided one spectrum has been obtained independently during
the monitoring. This method is complementary to photometric reverberation
mapping and could also be extended to multi-band data. Because the effect
described above produces a variability pattern in difference light curves
between pairs of lensed images which is correlated with the time-lagged
continuum variability, it can potentially produce systematic errors in
measurement of time delays between pairs of lensed images. Simple simulations
indicate that time-delay measurement techniques which use a sufficiently
flexible model for the extrinsic variability are not affected by this effect
and produce accurate time delays.Comment: Accepted for publication in Astronomy and Astrophysic
Optical linear polarization measurements of quasars obtained with the 3.6m telescope at the La Silla Observatory
We report 192 previously unpublished optical linear polarization measurements
of quasars obtained in April 2003, April 2007, and October 2007 with the
European Southern Observatory Faint Object Spectrograph and Camera (EFOSC2)
instrument attached to the 3.6m telescope at the La Silla Observatory. Each
quasar was observed once. Among the 192 quasars, 89 have a polarization degree
, 18 have , and two have .Comment: Accepted for publication in A&
Probing the inner structure of distant AGNs with gravitational lensing
Microlensing is a powerful technique which can be used to study the continuum
and the broad line emitting regions in distant AGNs. After a brief description
of the methods and required data, we present recent applications of this
technique. We show that microlensing allows one to measure the temperature
profile of the accretion disc, estimate the size and study the geometry of the
region emitting the broad emission lines.Comment: 6 pages, Proceedings of the Seyfert 2012 conferenc
Evidence for two spatially separated UV continuum emitting regions in the Cloverleaf broad absorption line quasar
Testing the standard Shakura-Sunyaev model of accretion is a challenging task
because the central region of quasars where accretion takes place is unresolved
with telescopes. The analysis of microlensing in gravitationally lensed quasars
is one of the few techniques that can test this model, yielding to the
measurement of the size and of temperature profile of the accretion disc. We
present spectroscopic observations of the gravitationally lensed broad
absorption line quasar H1413+117, which reveal partial microlensing of the
continuum emission that appears to originate from two separated regions: a
microlensed region, corresponding to the compact accretion disc; and a
non-microlensed region, more extended and contributing to at least 30\% of the
total UV-continuum flux. Because this extended continuum is occulted by the
broad absorption line clouds, it is not associated with the host galaxy, but
rather with light scattered in the neighbourhood of the central engine. We
measure the amplitude of microlensing of the compact continuum over the
rest-frame wavelength range 1000-7000 \AA. Following a Bayesian scheme, we
confront our measurements to microlensing simulations of an accretion disc with
a temperature varying as . We find a most likely source
half-light radius of cm (i.e., 0.002\,pc) at
0.18\,m, and a most-likely index of . The standard disc
() model is not ruled out by our data, and is found within the 95\%
confidence interval associated with our measurements. We demonstrate that, for
H1413+117, the existence of an extended continuum in addition to the disc
emission only has a small impact on the inferred disc parameters, and is
unlikely to solve the tension between the microlensing source size and standard
disc sizes, as previously reported in the literature.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages.
Minor changes w.r.t. v1 (language editing, Fig. 5-6
Microlensing of the broad line region in 17 lensed quasars
When an image of a strongly lensed quasar is microlensed, the different
components of its spectrum are expected to be differentially magnified owing to
the different sizes of the corresponding emitting region. Chromatic changes are
expected to be observed in the continuum while the emission lines should be
deformed as a function of the size, geometry and kinematics of the regions from
which they originate. Microlensing of the emission lines has been reported only
in a handful of systems so far. In this paper we search for microlensing
deformations of the optical spectra of pairs of images in 17 lensed quasars.
This sample is composed of 13 pairs of previously unpublished spectra and four
pairs of spectra from literature. Our analysis is based on a spectral
decomposition technique which allows us to isolate the microlensed fraction of
the flux independently of a detailed modeling of the quasar emission lines.
Using this technique, we detect microlensing of the continuum in 85% of the
systems. Among them, 80% show microlensing of the broad emission lines.
Focusing on the most common lines in our spectra (CIII] and MgII) we detect
microlensing of either the blue or the red wing, or of both wings with the same
amplitude. This observation implies that the broad line region is not in
general spherically symmetric. In addition, the frequent detection of
microlensing of the blue and red wings independently but not simultaneously
with a different amplitude, does not support existing microlensing simulations
of a biconical outflow. Our analysis also provides the intrinsic flux ratio
between the lensed images and the magnitude of the microlensing affecting the
continuum. These two quantities are particularly relevant for the determination
of the fraction of matter in clumpy form in galaxies and for the detection of
dark matter substructures via the identification of flux ratio anomalies.Comment: Accepted for publication in Astronomy and Astrophysics. Main data set
available via the German virtual observatory
http://dc.g-vo.org/mlqso/q/web/form and soon via CDS. Additional material
available on reques
Mid-infrared microlensing of accretion disc and dusty torus in quasars: effects on flux ratio anomalies
Multiply-imaged quasars and AGNs observed in the mid-infrared (MIR) range are
commonly assumed to be unaffected by the microlensing produced by the stars in
their lensing galaxy. In this paper, we investigate the validity domain of this
assumption. Indeed, that premise disregards microlensing of the accretion disc
in the MIR range, and does not account for recent progress in our knowledge of
the dusty torus. To simulate microlensing, we first built a simplified image of
the quasar composed of an accretion disc, and of a larger ring-like torus. The
mock quasars are then microlensed using an inverse ray-shooting code. We
simulated the wavelength and size dependence of microlensing for different
lensed image types and fraction of compact objects projected in the lens. This
allows us to derive magnification probabilities as a function of wavelength, as
well as to calculate the microlensing-induced deformation of the spectral
energy distribution of the lensed images. We find that microlensing variations
as large as 0.1 mag are very common at 11 microns (observer-frame). The main
signal comes from microlensing of the accretion disc, which may be significant
even when the fraction of flux from the disc is as small as 5 % of the total
flux. We also show that the torus of sources with Lbol <~ 10^45 erg/s is
expected to be noticeably microlensed. Microlensing may thus be used to get
insight into the rest near-infrared inner structure of AGNs. Finally, we
investigate whether microlensing in the mid-infrared can alter the so-called
Rcusp relation that links the fluxes of the lensed images triplet produced when
the source lies close to a cusp macro-caustic. This relation is commonly used
to identify massive (dark-matter) substructures in lensing galaxies. We find
that significant deviations from Rcusp may be expected, which means that
microlensing can explain part of the flux ratio problem.Comment: Updated to match the version published in Astronomy and Astrophysics.
12 pages. Abridged version of the abstract. Microlensing maps and source
profiles used in the simulations are available via CDS -
http://vizier.cfa.harvard.edu/viz-bin/VizieR?-source=J/A+A/553/A5
H0LiCOW – X. Spectroscopic/imaging survey and galaxy-group identification around the strong gravitational lens system WFI 2033−4723
Galaxies and galaxy groups located along the line of sight towards gravitationally lensed quasars produce high-order perturbations of the gravitational potential at the lens position. When these perturbation are too large, they can induce a systematic error on H0 of a few per cent if the lens system is used for cosmological inference and the perturbers are not explicitly accounted for in the lens model. In this work, we present a detailed characterization of the environment of the lens system WFI 2033−4723 (z_(src) = 1.662, z_(lens) = 0.6575), one of the core targets of the H0LiCOW project for which we present cosmological inferences in a companion paper. We use the Gemini and ESO-Very Large telescopes to measure the spectroscopic redshifts of the brightest galaxies towards the lens, and use the ESO-MUSE integral field spectrograph to measure the velocity-dispersion of the lens (σ_(los) = 250^(+15)_(−21) km s⁻¹) and of several nearby galaxies. In addition, we measure photometric redshifts and stellar masses of all galaxies down to i < 23 mag, mainly based on Dark Energy Survey imaging (DR1). Our new catalogue, complemented with literature data, more than doubles the number of known galaxy spectroscopic redshifts in the direct vicinity of the lens, expanding to 116 (64) the number of spectroscopic redshifts for galaxies separated by less than 3 arcmin (2 arcmin ) from the lens. Using the flexion-shift as a measure of the amplitude of the gravitational perturbation, we identify two galaxy groups and three galaxies that require specific attention in the lens models. The ESO MUSE data enable us to measure the velocity-dispersions of three of these galaxies. These results are essential for the cosmological inference analysis presented in Rusu et al
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