1,153 research outputs found
Resource Letter: Gravitational Lensing
This Resource Letter provides a guide to a selection of the literature on
gravitational lensing and its applications. Journal articles, books, popular
articles, and websites are cited for the following topics: foundations of
gravitational lensing, foundations of cosmology, history of gravitational
lensing, strong lensing, weak lensing, and microlensing.Comment: Resource Letter, 2012, in press
(http://ajp.dickinson.edu/Readers/resLetters.html); 21 pages, no figures;
diigo version available at
http://groups.diigo.com/group/gravitational-lensin
"Refsdal" meets Popper: comparing predictions of the re-appearance of the multiply imaged supernova behind MACSJ1149.5+2223
Supernova "Refsdal," multiply imaged by cluster MACS1149.5+2223, represents a rare opportunity to make a true blind test of model predictions in extragalactic astronomy, on a timescale that is short compared to a human lifetime. In order to take advantage of this event, we produced seven gravitational lens models with five independent methods, based on Hubble Space Telescope (HST) Hubble Frontier Field images, along with extensive spectroscopic follow-up observations by HST, the Very Large and the Keck Telescopes. We compare the model predictions and show that they agree reasonably well with the measured time delays and magnification ratios between the known images, even though these quantities were not used as input. This agreement is encouraging, considering that the models only provide statistical uncertainties, and do not include additional sources of uncertainties such as structure along the line of sight, cosmology, and the mass sheet degeneracy. We then present the model predictions for the other appearances of supernova "Refsdal." A future image will reach its peak in the first half of 2016, while another image appeared between 1994 and 2004. The past image would have been too faint to be detected in existing archival images. The future image should be approximately one-third as bright as the brightest known image (i.e., H_(AB) ≈ 25.7 mag at peak and H_(AB) ≈ 26.7 mag six months before peak), and thus detectable in single-orbit HST images. We will find out soon whether our predictions are correct
Measuring the mass of high-z galaxies with NGST
We discuss dynamical mass measurements of high-z galaxies with the Next
Generation Space Telescope (NGST). In particular, we review some of the
observational limits with the current instrument/telescope generation, we
discuss the redshift limits and caveats for absorption and emission lines
studies with NGST, and the existence of suitable targets at high redshift. We
also briefly summarize strengths and weaknesses of proposed NGST instruments
for dynamical studies.Comment: to appear in "The Mass of Galaxies at Low and High Redshift" R.
Bender and A. Renzini ed
The Cosmic Evolution of Faint Satellite Galaxies as a Test of Galaxy Formation and the Nature of Dark Matter
The standard cosmological model based on cold dark matter (CDM) predicts a
large number of subhalos for each galaxy-size halo. It is well known that
matching the subhalos to the observed properties of luminous satellites of
galaxies in the local universe poses a significant challenge to our
understanding of the astrophysics of galaxy formation. We show that the cosmic
evolution and host mass dependence of the luminosity function of satellites
provides a powerful new diagnostic to disentangle astrophysical effects from
variations in the underlying dark matter mass function. We illustrate this by
comparing the results of recent observations of satellites out to based
on Hubble Space Telescope images with the predictions of three different sets
of state-of-the art semi-analytic models with underlying CDM power spectra and
one semi-analytic model with an underlying Warm Dark Matter (WDM) power
spectrum. We find that even though CDM models provide a reasonable fit to the
local luminosity function of satellites around galaxies comparable or slightly
larger than the Milky Way, they do not reproduce the data as well for different
redshift and host galaxy stellar mass. This tension indicates that further
improvements are likely to be needed in the description of star formation if
the models are to be reconciled with the data. The WDM model matches the
observed mass dependence and redshift evolution of satellite galaxies more
closely than any of the CDM models, indicating that a modification of the
underlying power spectrum may offer an alternative solution to this tension. We
conclude by presenting predictions for the color magnitude relation of
satellite galaxies to demonstrate how future observations will be able to
further distinguish between these models and help constrain baryonic and
non-baryonic physics.Comment: Accepted for publication in ApJ, revised to incorporate referee
comment
The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
Based on 58 SLACS strong-lens early-type galaxies with direct total-mass and
stellar-velocity dispersion measurements, we find that inside one effective
radius massive elliptical galaxies with M_eff >= 3x10^10 M_sun are
well-approximated by a power-law ellipsoid with an average logaritmic density
slope of = -dlog(rho_tot)/dlog(r)=2.085^{+0.025}_{-0.018} (random
error on mean) for isotropic orbits with beta_r=0, +-0.1 (syst.) and
sigma_gamma' <= 0.20^{+0.04}_{-0.02} intrinsic scatter (all errors indicate the
68 percent CL). We find no correlation of gamma'_LD with galaxy mass (M_eff),
rescaled radius (i.e. R_einst/R_eff) or redshift, despite intrinsic differences
in density-slope between galaxies. Based on scaling relations, the average
logarithmic density slope can be derived in an alternative manner, fully
independent from dynamics, yielding =1.959 +- 0.077. Agreement
between the two values is reached for =0.45 +- 0.25, consistent with
mild radial anisotropy. This agreement supports the robustness of our results,
despite the increase in mass-to-light ratio with total galaxy mass: M_eff ~
L_{V,eff}^(1.363+-0.056). We conclude that massive early-type galaxies are
structurally close-to homologous with close-to isothermal total density
profiles (<=10 percent intrinsic scatter) and have at most some mild radial
anisotropy. Our results provide new observational limits on galaxy formation
and evolution scenarios, covering four Gyr look-back time.Comment: Accepted for publication by ApJL; 4 pages, 2 figure
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