29,040 research outputs found
Stellar mass functions of galaxies at 4<z<7 from an IRAC-selected sample in COSMOS/UltraVISTA: limits on the abundance of very massive galaxies
We build a Spitzer IRAC complete catalog of objects, obtained by
complementing the -band selected UltraVISTA catalog with objects
detected in IRAC only. With the aim of identifying massive (i.e.,
) galaxies at , we consider the systematic effects
on the measured photometric redshifts from the introduction of an old and dusty
SED template and from the introduction of a bayesian prior taking into account
the brightness of the objects, as well as the systematic effects from different
star formation histories (SFHs) and from nebular emission lines in the recovery
of stellar population parameters. We show that our results are most affected by
the bayesian luminosity prior, while nebular emission lines and SFHs only
introduce a small dispersion in the measurements. Specifically, the number of
galaxies ranges from 52 to 382 depending on the adopted configuration.
Using these results we investigate, for the first time, the evolution of the
massive end of the stellar mass functions (SMFs) at . Given the rarity
of very massive galaxies in the early universe, major contributions to the
total error budget come from cosmic variance and poisson noise. The SMF
obtained without the introduction of the bayesian luminosity prior does not
show any evolution from to , implying that massive
galaxies could already be present when the Universe was ~Gyr old.
However, the introduction of the bayesian luminosity prior reduces the number
of galaxies with best fit masses by 83%, implying
a rapid growth of very massive galaxies in the first 1.5 Gyr of cosmic history.
From the stellar-mass complete sample, we identify one candidate of a very
massive (), quiescent galaxy at , with
MIPS m detection suggesting the presence of a powerful obscured AGN.Comment: 23 pages, 18 figures. ApJ accepte
A fast Bayesian approach to discrete object detection in astronomical datasets - PowellSnakes I
A new fast Bayesian approach is introduced for the detection of discrete
objects immersed in a diffuse background. This new method, called PowellSnakes,
speeds up traditional Bayesian techniques by: i) replacing the standard form of
the likelihood for the parameters characterizing the discrete objects by an
alternative exact form that is much quicker to evaluate; ii) using a
simultaneous multiple minimization code based on Powell's direction set
algorithm to locate rapidly the local maxima in the posterior; and iii)
deciding whether each located posterior peak corresponds to a real object by
performing a Bayesian model selection using an approximate evidence value based
on a local Gaussian approximation to the peak. The construction of this
Gaussian approximation also provides the covariance matrix of the uncertainties
in the derived parameter values for the object in question. This new approach
provides a speed up in performance by a factor of `hundreds' as compared to
existing Bayesian source extraction methods that use MCMC to explore the
parameter space, such as that presented by Hobson & McLachlan. We illustrate
the capabilities of the method by applying to some simplified toy models.
Furthermore PowellSnakes has the advantage of consistently defining the
threshold for acceptance/rejection based on priors which cannot be said of the
frequentist methods. We present here the first implementation of this technique
(Version-I). Further improvements to this implementation are currently under
investigation and will be published shortly. The application of the method to
realistic simulated Planck observations will be presented in a forthcoming
publication.Comment: 30 pages, 15 figures, revised version with minor changes, accepted
for publication in MNRA
Fast, Robust, and Versatile Event Detection through HMM Belief State Gradient Measures
Event detection is a critical feature in data-driven systems as it assists
with the identification of nominal and anomalous behavior. Event detection is
increasingly relevant in robotics as robots operate with greater autonomy in
increasingly unstructured environments. In this work, we present an accurate,
robust, fast, and versatile measure for skill and anomaly identification. A
theoretical proof establishes the link between the derivative of the
log-likelihood of the HMM filtered belief state and the latest emission
probabilities. The key insight is the inverse relationship in which gradient
analysis is used for skill and anomaly identification. Our measure showed
better performance across all metrics than related state-of-the art works. The
result is broadly applicable to domains that use HMMs for event detection.Comment: 8 pages, 7 figures, double col, ieee conference forma
The Hunt for Exomoons with Kepler (HEK): I. Description of a New Observational Project
Two decades ago, empirical evidence concerning the existence and frequency of
planets around stars, other than our own, was absent. Since this time, the
detection of extrasolar planets from Jupiter-sized to most recently Earth-sized
worlds has blossomed and we are finally able to shed light on the plurality of
Earth-like, habitable planets in the cosmos. Extrasolar moons may also be
frequent habitable worlds but their detection or even systematic pursuit
remains lacking in the current literature. Here, we present a description of
the first systematic search for extrasolar moons as part of a new observational
project called "The Hunt for Exomoons with Kepler" (HEK). The HEK project
distills the entire list of known transiting planet candidates found by Kepler
(2326 at the time of writing) down to the most promising candidates for hosting
a moon. Selected targets are fitted using a multimodal nested sampling
algorithm coupled with a planet-with-moon light curve modelling routine. By
comparing the Bayesian evidence of a planet-only model to that of a
planet-with-moon, the detection process is handled in a Bayesian framework. In
the case of null detections, upper limits derived from posteriors marginalised
over the entire prior volume will be provided to inform the frequency of large
moons around viable planetary hosts, eta-moon. After discussing our
methodologies for target selection, modelling, fitting and vetting, we provide
two example analyses.Comment: 21 pages, 8 figures, 4 tables, accepted in Ap
Building an Optimal Census of the Solar Neighborhood with Pan-STARRS Data
We estimate the fidelity of solar neighborhood (D < 100 pc) catalogs soon to
be derived from Pan-STARRS astrometric data. We explore two quantities used to
measure catalog quality: completeness, the fraction of desired sources included
in a catalog; and reliability, the fraction of entries corresponding to desired
sources. We show that the main challenge in identifying nearby objects with
Pan-STARRS will be reliably distinguishing these objects from distant stars,
which are vastly more numerous. We explore how joint cuts on proper motion and
parallax will impact catalog reliability and completeness. Using synthesized
astrometry catalogs, we derive optimum parallax and proper motion cuts to build
a census of the solar neighborhood with the Pan-STARRS 3 Pi Survey. Depending
on the Galactic latitude, a parallax cut pi / sigma pi > 5 combined with a
proper motion cut ranging from mu / sigma mu > 1-8 achieves 99% reliability and
60% completeness.Comment: 7 Pages, 4 Figures, 3 Tables. PASP in pres
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