26,366 research outputs found
Bulge plus disc and S\'ersic decomposition catalogues for 16,908 galaxies in the SDSS Stripe 82 co-adds: A detailed study of the structural measurements
Quantitative characterization of galaxy morphology is vital in enabling
comparison of observations to predictions from galaxy formation theory.
However, without significant overlap between the observational footprints of
deep and shallow galaxy surveys, the extent to which structural measurements
for large galaxy samples are robust to image quality (e.g., depth, spatial
resolution) cannot be established. Deep images from the Sloan Digital Sky
Survey (SDSS) Stripe 82 co-adds provide a unique solution to this problem -
offering magnitudes improvement in depth with respect to SDSS Legacy
images. Having similar spatial resolution to Legacy, the co-adds make it
possible to examine the sensitivity of parametric morphologies to depth alone.
Using the Gim2D surface-brightness decomposition software, we provide public
morphology catalogs for 16,908 galaxies in the Stripe 82 co-adds. Our
methods and selection are completely consistent with the Simard et al. (2011)
and Mendel et al. (2014) photometric decompositions. We rigorously compare
measurements in the deep and shallow images. We find no systematics in total
magnitudes and sizes except for faint galaxies in the -band and the
brightest galaxies in each band. However, characterization of bulge-to-total
fractions is significantly improved in the deep images. Furthermore, statistics
used to determine whether single-S\'ersic or two-component (e.g., bulge+disc)
models are required become more bimodal in the deep images. Lastly, we show
that asymmetries are enhanced in the deep images and that the enhancement is
positively correlated with the asymmetries measured in Legacy images.Comment: 27 pages, 14 figures. MNRAS accepted. Our catalogs are available in
TXT and SQL formats at
http://orca.phys.uvic.ca/~cbottrel/share/Stripe82/Catalogs
The Massive Star Forming Region Cygnus OB2. I. Chandra catalogue of association members
We present a catalogue of 1696 X-ray sources detected in the massive star
forming region (SFR) Cygnus OB2 and extracted from two archival Chandra
observations of the center of the region. A deep source extraction routine,
exploiting the low background rates of Chandra observations was employed to
maximize the number of sources extracted. Observations at other wavelengths
were used to identify low count-rate sources and remove likely spurious
sources. Monte Carlo simulations were also used to assess the authenticity of
these sources. We used a Bayesian technique to identify optical or near-IR
counterparts for 1501 (89%) of our sources, using deep observations from the
INT Photometric H-alpha Survey, the Two Micron All Sky Survey, and the UKIRT
Infrared Deep Sky Survey-Galactic plane Survey. 755 (45%) of these objects have
six-band r', H-alpha, i', J, H, and K optical and near-IR photometry. From an
analysis of the Poisson false-source probabilities for each source we estimate
that our X-ray catalogue includes < 1% of false sources, and an even lower
fraction when only sources with optical or near-IR associations are considered.
A Monte Carlo simulation of the Bayesian matching scheme allows this method to
be compared to more simplified matching techniques and enables the various
sources of error to be quantified. The catalogue of 1696 objects presented here
includes X-ray broad band fluxes, model fits, and optical and near-IR
photometry in what is one of the largest X-ray catalogue of a single SFR to
date. The high number of stellar X-ray sources detected from relatively shallow
observations confirms the status and importance of Cygnus OB2 as one of our
Galaxy's most massive SFRs.Comment: Accepted for publication in ApJS. 39 pages, 5 figures, 5 tables (full
tables available in the published version or on request to the author
Informative Features for Model Comparison
Given two candidate models, and a set of target observations, we address the
problem of measuring the relative goodness of fit of the two models. We propose
two new statistical tests which are nonparametric, computationally efficient
(runtime complexity is linear in the sample size), and interpretable. As a
unique advantage, our tests can produce a set of examples (informative
features) indicating the regions in the data domain where one model fits
significantly better than the other. In a real-world problem of comparing GAN
models, the test power of our new test matches that of the state-of-the-art
test of relative goodness of fit, while being one order of magnitude faster.Comment: Accepted to NIPS 201
Outflow-Dominated Emission from the Quiescent Massive Black Holes in NGC 4621 and NGC 4697
The nearby elliptical galaxies NGC 4621 and NGC 4697 each host a supermassive
black hole with a mass more than 1e8 Solar masses. Analysis of archival Chandra
data and new NRAO Very Large Array data shows that each galaxy contains a
low-luminosity active galactic nucleus (LLAGN), identified as a faint, hard
X-ray source that is astrometrically coincident with a faint 8.5-GHz source.
The latter has a diameter less than 0.3 arcsec (26 pc for NGC 4621, 17 pc for
NGC 4697). The black holes energizing these LLAGNs have Eddington ratios L(2-10
keV) / L(Edd) ~ 1e-9, placing them in the so-called quiescent regime. The
emission from these quiescent black holes is radio-loud, with log Rx = log
nuLnu(8.5 GHz) / L(2-10 keV) ~ -2, suggesting the presence of a radio outflow.
Also, application of the radio-X-ray-mass relation from Yuan & Cui for
quiescent black holes predicts the observed radio luminosities nuLnu(8.5 GHz)
to within a factor of a few. Significantly, that relation invokes X-ray
emission from the outflow rather than from an accretion flow. The faint, but
detectable, emission from these two massive black holes is therefore consistent
with being outflow-dominated. Observational tests of this finding are
suggested.Comment: 11 pages; 4 figures: emulateapj; to appear in Ap
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