226 research outputs found
Engagement & Activities in Virtual & Hybrid Classrooms
Empowering Student Cocreators of Knowledge, Cas Laskowski Increasing engagement through Storytelling, Kimball Fontein Using Peer Assessment to Build Community in a remote or Hybrid Learning Environment, Amy Emerson
Attached presentation slides correspond with Amy Emerson\u27s portion of the program
Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
We present a sample of 1317 Infrared-Faint Radio Sources (IFRSs) that, for
the first time, are reliably detected in the infrared, generated by
cross-correlating the Wide-Field Infrared Survey Explorer (WISE) all-sky survey
with major radio surveys. Our IFRSs are brighter in both radio and infrared
than the first generation IFRSs that were undetected in the infrared by the
Spitzer Space Telescope. We present the first spectroscopic redshifts of IFRSs,
and find that all but one of the IFRSs with spectroscopy has z > 2. We also
report the first X-ray counterparts of IFRSs, and present an analysis of radio
spectra and polarization, and show that they include Gigahertz-Peaked Spectrum,
Compact Steep Spectrum, and Ultra-Steep Spectrum sources. These results,
together with their WISE infrared colours and radio morphologies, imply that
our sample of IFRSs represents a population of radio-loud Active Galactic
Nuclei at z > 2. We conclude that our sample consists of lower-redshift
counterparts of the extreme first generation IFRSs, suggesting that the fainter
IFRSs are at even higher redshift.Comment: 23 pages, 17 figures. Submitted to MNRA
Probing Obscured Massive Black Hole Accretion and Growth since Cosmic Dawn
Most of the stars today reside in galactic spheroids, whose properties are tightly tied to the supermassive black holes (MBHs) at their centers, implying that the accretion activity onto MBHs leaves a lasting imprint on the evolution of their host galaxies. Despite the importance of this so-called MBH-galaxy co-evolution, the physical mechanisms responsible for driving this relationship - such as the dominant mode of energetic feedback from active galactic nuclei (AGN) - remain a poorly understand aspect of galaxy assembly. A key challenge for identifying and characterizing AGN during the peak epoch of galaxy assembly and beyond is the presence of large columns of gas and dust, which fuels the growth of their MBHs but effectively obscures them from view in optical and X-ray studies. The high sensitivity of the ngVLA will capture emission from AGN in an extinction-free manner out to z ∼ 6 and beyond. At lower-redshifts (z ∼ 2), the high angular resolution of the ngVLA will enable spatially-resolved studies capable of localizing the sites of actively growing MBHs within their host galaxies during the peak epoch of cosmic assembly
Spitzer observations of a gravitationally lensed quasar, QSO 2237+0305
The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by
stars in the lens galaxy. The amplitude of microlensing variability can be used
to infer the relative size of the quasar as a function of wavelength; this
provides a test of quasar models. Toward this end, we present Spitzer Space
Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations
of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy
distribution (SED) is similar to that of other bright radio-quiet quasars,
contrary to an earlier claim. (2) A dusty torus model with a small opening
angle fits the overall shape of the IR SED well, but the quantitative agreement
is poor due to an offset in wavelength of the silicate feature. (3) The flux
ratios of the four lensed images can be derived from the IRAC data despite
being unresolved. We find that the near-IR fluxes are increasingly affected by
microlensing toward shorter wavelengths. (4) The wavelength dependence of the
IRAC flux ratios is consistent with the standard quasar model in which an
accretion disk and a dusty torus both contribute near 1 micron in the rest
frame. This is also consistent with recent IR spectropolarimetry of nearby
quasars
Principal Component Analysis of SDSS Stellar Spectra
We apply Principal Component Analysis (PCA) to ~100,000 stellar spectra
obtained by the Sloan Digital Sky Survey (SDSS). In order to avoid strong
non-linear variation of spectra with effective temperature, the sample is
binned into 0.02 mag wide intervals of the g-r color (-0.20<g-r<0.90, roughly
corresponding to MK spectral types A3 to K3), and PCA is applied independently
for each bin. In each color bin, the first four eigenspectra are sufficient to
describe the observed spectra within the measurement noise. We discuss
correlations of eigencoefficients with metallicity and gravity estimated by the
Sloan Extension for Galactic Understanding and Exploration (SEGUE) Stellar
Parameters Pipeline. The resulting high signal-to-noise mean spectra and the
other three eigenspectra are made publicly available. These data can be used to
generate high quality spectra for an arbitrary combination of effective
temperature, metallicity, and gravity within the parameter space probed by the
SDSS. The SDSS stellar spectroscopic database and the PCA results presented
here offer a convenient method to classify new spectra, to search for unusual
spectra, to train various spectral classification methods, and to synthesize
accurate colors in arbitrary optical bandpasses.Comment: 25 pages, 15 figures, accepted by the Astronomical Journa
- …