109 research outputs found
The inner mass power spectrum of galaxies using strong gravitational lensing: beyond linear approximation
In the last decade the detection of individual massive dark matter sub-halos
has been possible using potential correction formalism in strong gravitational
lens imaging. Here we propose a statistical formalism to relate strong
gravitational lens surface brightness anomalies to the lens potential
fluctuations arising from dark matter distribution in the lens galaxy. We
consider these fluctuations as a Gaussian random field in addition to the
unperturbed smooth lens model. This is very similar to weak lensing formalism
and we show that in this way we can measure the power spectrum of these
perturbations to the potential. We test the method by applying it to simulated
mock lenses of different geometries and by performing an MCMC analysis of the
theoretical power spectra. This method can measure density fluctuations in
early type galaxies on scales of 1-10 kpc at typical rms-levels of a percent,
using a single lens system observed with the Hubble Space Telescope with
typical signal-to-noise ratios obtained in a single orbit
Dissecting the 3D structure of elliptical galaxies with gravitational lensing and stellar kinematics
The combination of strong gravitational lensing and stellar kinematics
provides a powerful and robust method to investigate the mass and dynamical
structure of early-type galaxies. We demonstrate this approach by analysing two
massive ellipticals from the XLENS Survey for which both high-resolution HST
imaging and X-Shooter spectroscopic observations are available. We adopt a
flexible axisymmetric two-component mass model for the lens galaxies,
consisting of a generalised NFW dark halo and a realistic self-gravitating
stellar mass distribution. For both systems, we put constraints on the dark
halo inner structure and flattening, and we find that they are dominated by the
luminous component within one effective radius. By comparing the tight
inferences on the stellar mass from the combined lensing and dynamics analysis
with the values obtained from stellar population studies, we conclude that both
galaxies are characterised by a Salpeter-like stellar initial mass function.Comment: Proceedings of the IAU Symposium 309, Contributed Talk, Vienna, July
2014; 4 pages, 2 figure
The non-universality of the low-mass end of the IMF is robust against the choice of SSP model
We perform a direct comparison of two state-of-the art single stellar
population (SSP) models that have been used to demonstrate the non-universality
of the low-mass end of the Initial Mass Function (IMF) slope. The two public
versions of the SSP models are restricted to either solar abundance patterns or
solar metallicity, too restrictive if one aims to disentangle elemental
enhancements, metallicity changes and IMF variations in massive early-type
galaxies (ETGs) with star formation histories different from the solar
neighborhood. We define response functions (to metallicity and
\alpha-abundance) to extend the parameter space of each set of models. We
compare these extended models with a sample of Sloan Digital Sky Survey (SDSS)
ETGs spectra with varying velocity dispersions. We measure equivalent widths of
optical IMF-sensitive stellar features to examine the effect of the underlying
model assumptions and ingredients, such as stellar libraries or isochrones, on
the inference of the IMF slope down to ~0.1 solar masses. We demonstrate that
the steepening of the low-mass end of the Initial Mass Function (IMF) based on
a non-degenerate set of spectroscopic optical indicators is robust against the
choice of the stellar population model. Although the models agree in a relative
sense (i.e. both imply more bottom-heavy IMFs for more massive systems), we
find non-negligible differences on the absolute values of the IMF slope
inferred at each velocity dispersion by using the two different models. In
particular, we find large inconsistency in the quantitative predictions of IMF
slope variations and abundance patterns when sodium lines are used. We
investigate the possible reasons for these inconsistencies.Comment: 16 pages, 9 figures, 2 tables, accepted for publication on Ap
Inferring the properties of the sources of reionization using the morphological spectra of the ionized regions
High-redshift 21-cm observations will provide crucial insights into the
physical processes of the Epoch of Reionization. Next-generation
interferometers such as the Square Kilometer Array will have enough sensitivity
to directly image the 21-cm fluctuations and trace the evolution of the
ionizing fronts. In this work, we develop an inferential approach to recover
the sources and IGM properties of the process of reionization using the number
and, in particular, the morphological pattern spectra of the ionized regions
extracted from realistic mock observations. To do so, we extend the Markov
Chain Monte Carlo analysis tool 21CMMC by including these 21-cm tomographic
statistics and compare this method to only using the power spectrum. We
demonstrate that the evolution of the number-count and morphology of the
ionized regions as a function of redshift provides independent information to
disentangle multiple reionization scenarios because it probes the average
ionizing budget per baryon. Although less precise, we find that constraints
inferred using 21-cm tomographic statistics are more robust to the presence of
contaminants such as foreground residuals. This work highlights that combining
power spectrum and tomographic analyses more accurately recovers the
astrophysics of reionization.Comment: 28 pages, 16 figures. Accepted to MNRA
Quantifying dwarf satellites through gravitational imaging: the case of SDSS J120602.09+514229.5
SDSS J120602.09+514229.5 is a gravitational lens system formed by a group of
galaxies at redshift z=0.422 lensing a bright background galaxy at redshift
z=2.001. The main peculiarity of this system is the presence of a luminous
satellite near the Einstein radius, that slightly deforms the giant arc. This
makes SDSS J120602.09+514229.5 the ideal system to test our grid-based Bayesian
lens modelling method, designed to detect galactic satellites independently
from their mass-to-light ratio, and to measure the mass of this dwarf galaxy
despite its high redshift. Thanks to the pixelized source and potential
reconstruction technique of Vegetti and Koopmans 2009a we are able to detect
the luminous satellite as a local positive surface density correction to the
overall smooth potential. Assuming a truncated Pseudo-Jaffe density profile,
the satellite has a mass M=(2.75+-0.04)10^10 M_sun inside its tidal radius of
r_t=0.68". We determine for the satellite a luminosity of L_B=(1.6+-0.8)10^9
L_sun, leading to a total mass-to-light ratio within the tidal radius of
(M/L)_B=(17.2+-8.5) M_sun/L_sun. The central galaxy has a sub-isothermal
density profile as in general is expected for group members. From the SDSS
spectrum we derive for the central galaxy a velocity dispersion of
sigma_kinem=380+-60 km/s within the SDSS aperture of diameter 3". The
logarithmic density slope of gamma=1.7+0.25-0.30 (68% CL), derived from this
measurement, is consistent within 1-sigma with the density slope of the
dominant lens galaxy gamma~1.6, determined from the lens model. This paper
shows how powerful pixelized lensing techniques are in detecting and
constraining the properties of dwarf satellites at high redshift.Comment: Submitted to MNRAS; Abstract abridge
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