65 research outputs found
Spectral energy distributions, dust, and black hole properties: a statistical, multi-wavelength quasar analysis
Ph.D., Physics -- Drexel University, 201
Cosmology from Large Populations of Galaxy-Galaxy Strong Gravitational Lenses
We present a forecast analysis on the feasibility of measuring the
cosmological parameters with a large number of galaxy-galaxy scale strong
gravitational lensing systems. Future wide area surveys are expected to
discover and measure the properties of more than 10 000 strong lensing systems.
We develop a hierarchical model that can simultaneously constrain the lens
population and cosmological parameters by combining Einstein radius
measurements with stellar dynamical mass estimates for every lens.
Marginalizing over the lens density profiles and stellar orbital anisotropies,
we find that can be constrained to a precision of with 10 000
galaxy-galaxy lens systems, which would be better than any existing
single-probe constraint. We test our method on 161 existing lenses, finding
. We also show how to mitigate against the potential systematic
of redshift evolution in the mean lens density profile of the population
Re-examining Larson's Scaling Relationships in Galactic Molecular Clouds
The properties of Galactic molecular clouds tabulated by Solomon etal (1987)
(SRBY) are re-examined using the Boston University-FCRAO Galactic Ring Survey
of 13CO J=1-0 emission. These new data provide a lower opacity tracer of
molecular clouds and improved angular and spectral resolution than previous
surveys of molecular line emission along the Galactic Plane. We calculate GMC
masses within the SRBY cloud boundaries assuming LTE conditions throughout the
cloud and a constant H2 to 13CO abundance, while accounting for the variation
of the 12C/13C with Galacto-centric radius. The LTE derived masses are
typically five times smaller than the SRBY virial masses. The corresponding
median mass surface density of molecular hydrogen for this sample is 42
Msun/pc^2, which is significantly lower than the value derived by SRBY (median
206 Msun/pc^2) that has been widely adopted by most models of cloud evolution
and star formation. This discrepancy arises from both the extrapolation by SRBY
of velocity dispersion, size, and CO luminosity to the 1K antenna temperature
isophote that likely overestimates the GMC masses and our assumption of
constant 13CO abundance over the projected area of each cloud. Owing to the
uncertainty of molecular abundances in the envelopes of clouds, the mass
surface density of giant molecular clouds could be larger than the values
derived from our 13CO measurements. From velocity dispersions derived from the
13CO data, we find that the coefficient of the cloud structure functions,
vo=sigma_v/R^{1/2}, is not constant, as required to satisfy Larson's scaling
relationships, but rather systematically varies with the surface density of the
cloud as Sigma^{0.5} as expected for clouds in self-gravitational equlibrium.Comment: Accepted by ApJ. Newest version includes modifications from the
refere
Bayesian High-Redshift Quasar Classification from Optical and Mid-IR Photometry
We identify 885,503 type 1 quasar candidates to i<22 using the combination of
optical and mid-IR photometry. Optical photometry is taken from the Sloan
Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey
(SDSS-III/BOSS), while mid-IR photometry comes from a combination of data from
the Wide-Field Infrared Survey Explorer (WISE) "ALLWISE" data release and
several large-area Spitzer Space Telescope fields. Selection is based on a
Bayesian kernel density algorithm with a training sample of 157,701
spectroscopically-confirmed type-1 quasars with both optical and mid-IR data.
Of the quasar candidates, 733,713 lack spectroscopic confirmation (and 305,623
are objects that we have not previously classified as photometric quasar
candidates). These candidates include 7874 objects targeted as high probability
potential quasars with 3.5<z<5 (of which 6779 are new photometric candidates).
Our algorithm is more complete to z>3.5 than the traditional mid-IR selection
"wedges" and to 2.2<z<3.5 quasars than the SDSS-III/BOSS project. Number counts
and luminosity function analysis suggests that the resulting catalog is
relatively complete to known quasars and is identifying new high-z quasars at
z>3. This catalog paves the way for luminosity-dependent clustering
investigations of large numbers of faint, high-redshift quasars and for further
machine learning quasar selection using Spitzer and WISE data combined with
other large-area optical imaging surveys.Comment: 54 pages, 17 figures; accepted by ApJS Data for tables 1 and 2
available at
http://www.physics.drexel.edu/~gtr/outgoing/optirqsos/data/master_quasar_catalogs.011414.fits.bz2
and
http://www.physics.drexel.edu/~gtr/outgoing/optirqsos/data/optical_ir_quasar_candidates.052015.fits.bz
Lensed type Ia supernovae in light of SN Zwicky and iPTF16geu
Strong gravitationally lensed supernovae (glSNe) are a powerful probe to
obtain a measure of the expansion rate of the Universe, but they are also
extremely rare. To date, only two glSNe with multiple images strongly lensed by
galaxies have been found, but their short time delays make them unsuitable for
cosmography. We simulate a realistic catalogue of lensed supernovae and study
the characteristics of the population of detectable systems for different
surveys. Our simulations show that the properties of glSNe in shallow surveys
(such as the Zwicky Transient Facility; ZTF) are determined by the need for
large magnifications, which favours systems of four images with short time
delays and low image separations. This picture is consistent with the
properties of iPTF16geu and SN~Zwicky, but is not representative of the
population found in deeper surveys, which are limited by the volume of the
Universe that is strongly lensed. In our simulations of the Legacy Survey of
Space and Time (LSST), glSNe show longer time delays and greater angular
separations. Of these systems in LSST, 35\% will allow for time-delay
measurements with a precision of 10\% or better. In the 10 years of the survey
LSST should be able to find 180 systems, of which 60 will be suited
for cosmography enabling a precision measurement with
LSST glSNe.Comment: 11 pages, 9 figures. Submitte
Mean Spectral Energy Distributions and Bolometric Corrections for Luminous Quasars
We explore the mid-infrared (mid-IR) through ultraviolet (UV) spectral energy
distributions (SEDs) of 119,652 luminous broad-lined quasars with 0.064<z<5.46
using mid-IR data from Spitzer and WISE, near-infrared data from Two Micron All
Sky Survey and UKIDSS, optical data from Sloan Digital Sky Survey, and UV data
from Galaxy Evolution Explorer. The mean SED requires a bolometric correction
(relative to 2500A) of BC=2.75+-0.40 using the integrated light from 1um-2keV,
and we further explore the range of bolometric corrections exhibited by
individual objects. In addition, we investigate the dependence of the mean SED
on various parameters, particularly the UV luminosity for quasars with 0.5<z<3
and the properties of the UV emission lines for quasars with z>1.6; the latter
is a possible indicator of the strength of the accretion disk wind, which is
expected to be SED dependent. Luminosity-dependent mean SEDs show that,
relative to the high-luminosity SED, low-luminosity SEDs exhibit a harder
(bluer) far-UV spectral slope, a redder optical continuum, and less hot dust.
Mean SEDs constructed instead as a function of UV emission line properties
reveal changes that are consistent with known Principal Component Analysis
(PCA) trends. A potentially important contribution to the bolometric correction
is the unseen extream-UV (EUV) continuum. Our work suggests that
lower-luminosity quasars and/or quasars with disk-dominated broad emission
lines may require an extra continuum component in the EUV that is not present
(or much weaker) in high-luminosity quasars with strong accretion disk winds.
As such, we consider four possible models and explore the resulting bolometric
corrections. Understanding these various SED-dependent effects will be
important for accurate determination of quasar accretion rates.Comment: 19 pages, 18 figure
SDSS-IV MaNGA: spatially resolved dust attenuation in spiral galaxies
Dust attenuation in star-forming spiral galaxies affects stars and gas in
different ways due to local variations in dust geometry. We present spatially
resolved measurements of dust attenuation for a sample of 232 such star-forming
spiral galaxies, derived from spectra acquired by the SDSS-IV MaNGA survey. The
dust attenuation affecting the stellar populations of these galaxies (obtained
using full spectrum stellar population fitting methods) is compared with the
dust attenuation in the gas (derived from the Balmer decrement). Both of these
attenuation measures increase for local regions of galaxies with higher star
formation rates; the dust attenuation affecting the stellar populations
increases more so than the dust attenuation in the gas, causing the ratio of
the dust attenuation affecting the stellar populations to the dust attenuation
in the gas to decrease for local regions of galaxies with higher star formation
rate densities. No systematic difference is discernible in any of these dust
attenuation quantities between the spiral arm and inter-arm regions of the
galaxies. While both the dust attenuation in the gas and the dust attenuation
affecting the stellar populations decrease with galactocentric radius, the
ratio of the two quantities does not vary with radius. This ratio does,
however, decrease systematically as the stellar mass of the galaxy increases.
Analysis of the radial profiles of the two dust attenuation measures suggests
that there is a disproportionately high concentration of birth clouds
(incorporating gas, young stars and clumpy dust) nearer to the centres of
star-forming spiral galaxies.Comment: 17 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
CIV Emission and the Ultraviolet through X-ray Spectral Energy Distribution of Radio-Quiet Quasars
In the restframe UV, two of the parameters that best characterize the range
of emission-line properties in quasar broad emission-line regions are the
equivalent width and the blueshift of the CIV line relative to the quasar rest
frame. We explore the connection between these emission-line properties and the
UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ)
quasars. Our sample consists of a heterogeneous compilation of 406 quasars from
the Sloan Digital Sky Survey and Palomar-Green survey that have well-measured
CIV emission-line and X-ray properties (including 164 objects with measured
Gamma). We find that RQ quasars with both strong CIV emission and small CIV
blueshifts can be classified as "hard-spectrum" sources that are (relatively)
strong in the X-ray as compared to the UV. On the other hand, RQ quasars with
both weak CIV emission and large CIV blueshifts are instead "soft-spectrum"
sources that are (relatively) weak in the X-ray as compared to the UV. This
work helps to further bridge optical/soft X-ray "Eigenvector 1" relationships
to the UV and hard X-ray. Based on these findings, we argue that future work
should consider systematic errors in bolometric corrections (and thus accretion
rates) that are derived from a single mean SED. Detailed analysis of the CIV
emission line may allow for SED-dependent corrections to these quantities.Comment: AJ, in press; 39 pages, 11 figures, 3 table
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