31 research outputs found
Effects of Strong Gravitational Lensing on Millimeter-Wave Galaxy Number Counts
We study the effects of strong lensing on the observed number counts of mm
sources using a ray tracing simulation and two number count models of unlensed
sources. We employ a quantitative treatment of maximum attainable magnification
factor depending on the physical size of the sources, also accounting for
effects of lens halo ellipticity. We calculate predicted number counts and
redshift distributions of mm galaxies including the effects of strong lensing
and compare with the recent source count measurements of the South Pole
Telescope (SPT). The predictions have large uncertainties, especially the
details of the mass distribution in lens galaxies and the finite extent of
sources, but the SPT observations are in good agreement with predictions. The
sources detected by SPT are predicted to largely consist of strongly lensed
galaxies at z>2. The typical magnifications of these sources strongly depends
on both the assumed unlensed source counts and the flux of the observed
sources
Spectroscopy of CASSOWARY gravitationally-lensed galaxies in SDSS: characterisation of an extremely bright reionization-era analog at
We present new observations of sixteen bright () gravitationally
lensed galaxies at selected from the CASSOWARY survey. Included
in our sample is the galaxy CSWA-141, one of the brightest known
reionization-era analogs at high redshift (g=20.5), with a large sSFR (31.2
Gyr) and an [OIII]+H equivalent width
(EW=730~\r{A}) that is nearly identical to the average
value expected at . In this paper, we investigate the rest-frame
UV nebular line emission in our sample with the goal of understanding the
factors that regulate strong CIII] emission. Whereas most of the sources in our
sample show weak UV line emission, we find elevated CIII] in the spectrum of
CSWA-141 (EW=4.6~\r{A}) together with detections of
other prominent emission lines (OIII], Si III], Fe II, Mg II). We
compare the rest-optical line properties of high redshift galaxies with strong
and weak CIII] emission, and find that systems with the strongest UV line
emission tend to have young stellar populations and nebular gas that is
moderately metal-poor and highly ionized, consistent with trends seen at low
and high redshift. The brightness of CSWA-141 enables detailed investigation of
the extreme emission line galaxies which become common at . We find that
gas traced by the CIII] doublet likely probes higher densities than that traced
by [OII] and [SII]. Characterisation of the spectrally resolved Mg II emission
line and several low ionization absorption lines suggests neutral gas around
the young stars is likely optically thin, potentially facilitating the escape
of ionizing radiation.Comment: 20 pages, 9 figures, Accepted for publication in MNRA
Detection of lensing substructure using ALMA observations of the dusty galaxy SDP.81
We study the abundance of substructure in the matter density near galaxies
using ALMA Science Verification observations of the strong lensing system
SDP.81. We present a method to measure the abundance of subhalos around
galaxies using interferometric observations of gravitational lenses. Using
simulated ALMA observations, we explore the effects of various systematics,
including antenna phase errors and source priors, and show how such errors may
be measured or marginalized. We apply our formalism to ALMA observations of
SDP.81. We find evidence for the presence of a
subhalo near one of the images, with a significance of in a joint
fit to data from bands 6 and 7; the effect of the subhalo is also detected in
both bands individually. We also derive constraints on the abundance of dark
matter subhalos down to , pushing down to the
mass regime of the smallest detected satellites in the Local Group, where there
are significant discrepancies between the observed population of luminous
galaxies and predicted dark matter subhalos. We find hints of additional
substructure, warranting further study using the full SDP.81 dataset
(including, for example, the spectroscopic imaging of the lensed carbon
monoxide emission). We compare the results of this search to the predictions of
CDM halos, and find that given current uncertainties in the host halo
properties of SDP.81, our measurements of substructure are consistent with
theoretical expectations. Observations of larger samples of gravitational
lenses with ALMA should be able to improve the constraints on the abundance of
galactic substructure.Comment: 18 pages, 13 figures, Comments are welcom