2,216 research outputs found
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This sample is composed of 13 pairs of previously unpublished spectra and four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
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
Exploring the gravitationally lensed system HE 1104-1805: Near-IR Spectroscopy
(Abridged) A new technique for the spatial deconvolution of spectra is
applied to near-IR (0.95 - 2.50 micron) NTT/SOFI spectra of the lensed,
radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is
revealed between 1.5 and 2.5 micron. It is used in combination with previous
optical and IR photometry to infer a plausible redshift in the range 0.8 < z <
1.2. Modeling of the system shows that the lens is probably composed of the red
galaxy seen between the quasar images and a more extended component associated
with a galaxy cluster with fairly low velocity dispersion (~ 575 km/s). The
spectra of the two lensed images of the source show no trace of reddening at
the redshift of the lens nor at the redshift of the source. Additionally, the
difference between the spectrum of the brightest component a nd that of a
scaled version of the faintest component is a featureless continuum. Broad and
narrow emission lines, including the FeII features, are perfectly subtracted.
The very good quality of our spectrum makes it possible to fit precisely the
optical Fe II feature, taking into account the underlying continuum over a wide
wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter.
Finally, the slope of the continuum in the brightest image is steeper than the
continuum in the faintest image and supports the finding by Wisotzki et al.
(1993) that the brightest image is microlensed. This is particularly
interesting in view of the new source reconstruction methods from
multiwavelength photometric monitoring.Comment: to be published in A&A, 8 pages, 9 postscript figure
The Mass Function of Main Sequence Stars in NGC6397 from Near IR and Optical High Resolution HST Observations
We have investigated the properties of the stellar mass function in the
globular cluster NGC6397 using a large set of HST observations that include
WFPC2 images in V and I, obtained at ~4' and 10' radial distances, and a series
of deep images in the J and H bands obtained with the NIC2 and NIC3 cameras of
NICMOS pointed to regions located ~4.5' and ~3.2' from the center. These
observations span the region from ~1 to ~3 times the cluster's half-light
radius. All luminosity functions, derived from color magniutde diagrams,
increase with decreasing luminosity up to a peak at M_I~8.5 or M_H~7 and then
precipitously drop well before photometric incompleteness becomes significant.
Within the observational uncertainties, at M_I~12 or M_H~10.5 (~0.09 Msun) the
luminosity functions are compatible with zero. By applying the best available
mass- luminosity relation appropriate to the metallicity of NGC6397 to both the
optical and IR data, we obtain a mass function that shows a break in slope at
\~0.3 Msun. No single exponent power-law distribution is compatible with these
data, regardless of the value of the exponent. We find that a dynamical model
of the cluster can simultaneously reproduce all the luminosity functions
observed throughout the cluster only if the IMF rises as m**-1.6 in the range
0.8-0.3 Msun and then drops as m**0.2 below ~0.3 Msun. Adopting a more physical
log-normal distribution for the IMF, all these data taken together imply a best
fit distribution with characteristic mass m_c~0.3 and sigma~1.8.Comment: 18 pages, 6 figures (ps). Accepted for publication in Ap
Resolved Stellar Populations of Super-Metal-Rich Star Clusters in the Bulge of M31
We have applied the MCS image deconvolution algorithm (Magain, Courbin & Sohy
1998) to HST/WFPC2 V, I data of three M31 bulge globular clusters (G170, G177,
and G198) and control fields near each cluster. All three clusters are clearly
detected, with an increase in stellar density with decreasing radius from the
cluster centers; this is the first time that stars have been resolved in bulge
clusters in the inner regions of another galaxy. From the RGB slopes of the
clusters and the difference in I magnitude between the HB and the top of the
RGB, we conclude that these three clusters all have roughly solar metallicity,
in agreement with earlier integrated-light spectroscopic measurements. Our data
support a picture whereby the M31 bulge clusters and field stars were born from
the same metal-rich gas, early in the galaxy formation.Comment: 7 pages, 4 Postscript figures, accepted for publication in A&
Palomar 13: An Unusual Stellar System in the Galactic Halo
We have measured Keck/HIRES radial velocities for 30 candidate red giants in
the direction of Palomar 13: an object traditionally cataloged as a compact,
low-luminosity globular cluster. From a sample of 21 confirmed members, we find
a systemic velocity of 24.1 km/s and a projected, intrinsic velocity dispersion
of 2.2 km/s. Although small, this dispersion is several times larger than that
expected for a globular cluster of this luminosity and central concentration.
Taken at face value, this dispersion implies a mass-to-light ratio of ~ 40 (in
solar units) based on the best-fit King-Michie model. The surface density
profile of Palomar 13 also appears to be anomalous among Galactic globular
clusters -- depending upon the details of background subtraction and
model-fitting, Palomar 13 either contains a substantial population of
"extra-tidal" stars, or it is far more spatially extended than previously
suspected. The full surface density profile is equally well-fit by a
King-Michie model having a high concentration and large tidal radius, or by a
NFW model. We examine -- and tentatively reject -- a number of possible
explanations for the observed characteristics of Palomar 13 (e.g., velocity
"jitter" among the red giants, spectroscopic binary stars, non-standard mass
functions, modified Newtonian dynamics), and conclude that the two most
plausible scenarios are either catastrophic heating during a recent
perigalacticon passage, or the presence of a massive dark halo. Thus, the
available evidence suggests that Palomar 13 is either a globular cluster which
is now in the process of dissolving into the Galactic halo, or a faint,
dark-matter-dominated stellar system (ABRIDGED).Comment: 31 pages, 13 postscript figures and 1 color gif image. Also available
at http://www.physics.rutgers.edu/ast/ast-rap.html. Accepted for publication
in the Astrophysical Journa
The Initial Mass Functions in the Super-Star-Clusters NGC 1569A and NGC 1705-1
I use recent photometric and stellar velocity dispersion measurements of the
super-star-clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their
present-day luminosity/mass (L_V/M) ratios. I then use the inferred L_V/M
ratios, together with population synthesis models of evolving star-clusters, to
constrain the initial-mass-functions (IMFs) in these objects.
I find that (L_V/M)_solar=28.9 in 1569A, and (L_V/M)_solar=126 in 1705-1. It
follows that in 1569A the IMF is steep with alpha~2.5 for m**(-alpha)dm IMFs
which extend to 0.1 M_sun. This implies that most of the stellar mass in 1569A
is contained in low-mass (< 1 M_sun) stars. However, in 1705-1 the IMF is
either flat, with alpha<2$, or it is truncated at a lower mass-limit between 1
and 3 M_sun.
I compare the inferred IMFs with the mass functions (MFs) of Galactic
globular clusters. It appears that 1569A has a sufficient reservoir of low-mass
stars for it to plausibly evolve into an object similar to Galactic globular
clusters. However, the apparent deficiency of low-mass stars in 1705-1 may make
it difficult for this SSC to become a globular cluster. If low-mass stars do
dominate the cluster mass in 1705-1, the large L_V/M ratio in this SSC may be
evidence that the most massive stars have formed close to the cluster cores.Comment: ApJ, in press. 19 Pages, Latex; [email protected]
Recommended from our members
Rejuvenation through plastic deformation of a La-based metallic glass measured by fast-scanning calorimetry
We explore the glassy states achievable after a metallic glass is formed on liquid quenching. Samples of La55Al25Ni20 (at.%) metallic glass (rod and ribbon) are studied. The extent of structural relaxation at room temperature is characterized for this low-glass-transition temperature glass. Plastic deformation (uniaxial compression) rejuvenates the glass to states of higher enthalpy characteristic of glass formation at high cooling rate. Deformation increases the heterogeneity of the glass, widening the spectrum of relaxation times. The extent of rejuvenation in samples of low aspect ratio is compared with that under conditions of high constraint in notched samples. The deformation-induced rejuvenation is particularly susceptible to reduction on subsequent ageing. Fast-scanning calorimetry is useful in characterizing the dynamics of structural relaxation. The shadow glass transition is more evident on fast heating, and is observed in this glass for the first time. A new excess exothermic effect is observed before the glass transition
Experimental enhancement of corticosterone levels positively affects subsequent male survival.
Corticosterone is an important hormone of the stress response that regulates physiological processes and modifies animal behavior. While it positively acts on locomotor activity, it may negatively affect reproduction and social activity. This suggests that corticosterone may promote behaviors that increase survival at the cost of reproduction. In this study, we experimentally investigate the link between corticosterone levels and survival in adult common lizards (Lacerta vivipara) by comparing corticosterone-treated with placebo-treated lizards. We experimentally show that corticosterone enhances energy expenditure, daily activity, food intake, and it modifies the behavioral time budget. Enhanced appetite of corticosterone-treated individuals compensated for increased energy expenditure and corticosterone-treated males showed increased survival. This suggests that corticosterone may promote behaviors that reduce stress and it shows that corticosterone per se does not reduce but directly or indirectly increases longer-term survival. This suggests that the production of corticosterone as a response to a stressor may be an adaptive mechanism that even controls survival
Discovery of a Probable Physical Triple Quasar
We report the discovery of the first known probable case of a physical triple
quasar (not a gravitational lens). A previously known double system, QQ
1429-008 at z = 2.076, is shown to contain a third, fainter QSO component at
the same redshift within the measurement errors. Deep optical and IR imaging at
the Keck and VLT telescopes has failed to reveal a plausible lensing galaxy
group or a cluster, and moreover, we are unable to construct any viable lensing
model which could lead to the observed distribution of source positions and
relative intensities of the three QSO image components. Furthermore, there are
hints of differences in broad-band spectral energy distributions of different
components, which are more naturally understood if they are physically distinct
AGN. Therefore, we conclude that this system is most likely a physical triple
quasar, the first such close QSO grouping known at any redshift. The projected
component separations in the restframe are ~ 30 - 50 kpc for the standard
concordance cosmology, typical of interacting galaxy systems. The existence of
this highly unusual system supports the standard picture in which galaxy
interactions lead to the onset of QSO activity.Comment: Submitted to ApJL, LaTeX, 13 pages, 4 eps figures, all include
- …