2,466 research outputs found
All-purpose, all-sky photometric redshifts for the Legacy Imaging Surveys Data Release 8
In this paper we present photometric redshift (photo-) estimates for the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, currently
the most sensitive optical survey covering the majority of the extra-galactic
sky. Our photo- methodology is based on a machine-learning approach, using
sparse Gaussian processes augmented with Gaussian mixture models (GMMs) that
allow regions of parameter space to be identified and trained separately in a
purely data-driven way. The same GMMs are also used to calculate cost-sensitive
learning weights that mitigate biases in the spectroscopic training sample. By
design, this approach aims to produce reliable and unbiased predictions for all
parts of the parameter space present in wide area surveys. Compared to previous
literature estimates using the same underlying photometry, our photo-s are
significantly less biased and more accurate at , with negligible loss in
precision or reliability for resolved galaxies at . Our photo-
estimates offer accurate predictions for rare high-value populations within the
parent sample, including optically selected quasars at the highest redshifts
(), as well as X-ray or radio continuum selected populations across a
broad range of flux (densities) and redshift. Deriving photo- estimates for
the full Legacy Imaging Surveys Data Release 8, the catalogues provided in this
work offer photo- estimates predicted to be high quality for
galaxies over and
spanning , offering one of the most extensive samples of
redshift estimates ever produced.Comment: 22 pages, 19 figures - Accepted for publication in MNRAS. Catalogues
produced will be made available through queryable public databases - users
interested in the full catalogues or early access to subsets are also
encouraged to contact the author directl
A Spitzer survey of Deep Drilling Fields to be targeted by the Vera C. Rubin Observatory Legacy Survey of Space and Time
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. In this paper, we describe the âDeepDrillâ survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centred on 3.6 and 4.5 ÎŒm. These observations expand the area that was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep FieldâSouth (ECDFS) field, the ELAIS-S1 field (ES1), and the XMM-Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate 5Ï point-source depth of 2 ÎŒJy (corresponding to an AB magnitude of 23.1; sufficient to detect a 10ÂčÂčMâ galaxy out to z â 5) in each of the two bands over a total area of â29 degÂČ. The dual-band catalogues contain a total of 2.35 million sources. In this paper, we describe the observations and data products from the survey, and an overview of the properties of galaxies in the survey. We compare the source counts to predictions from the SHARK semi-analytic model of galaxy formation. We also identify a population of sources with extremely red ([3.6]â[4.5] >1.2) colours which we show mostly consists of highly obscured active galactic nuclei
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
A 3D extinction map of the northern Galactic plane based on IPHAS photometry
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a 3D map of extinction in the northern Galactic plane derived using photometry from the INT/WFC Photometric Hα Survey of the northern Galactic plane. The map has fine angular (~10 arcmin) and distance (100 pc) sampling allied to a significant depth (âł5 kpc). We construct the map using a method based on a hierarchical Bayesian model described in a previous article by Sale. In addition to mean extinction, we also measure differential extinction, which arises from the fractal nature of the interstellar medium, and show that it will be the dominant source of uncertainty in estimates of extinction to some arbitrary position. The method applied also furnishes us with photometric estimates of the distance, extinction, effective temperature, surface gravity, and mass for ~38 million stars. Both the extinction map and the catalogue of stellar parameters are made publicly available via http://www.iphas.org/extinction.Peer reviewe
ExELS: an exoplanet legacy science proposal for the ESA Euclid mission I. Cold exoplanets
Euclid is the second M-class mission of the ESA Cosmic Vision programme, with
the principal science goal of studying dark energy. Euclid is also expected to
undertake additional Legacy Science programmes. One proposal is the Exoplanet
Euclid Legacy Survey (ExELS) which will be the first survey able to measure the
abundance of exoplanets down to Earth mass for host separations from ~1AU out
to the free-floating (unbound) regime. The cold and free-floating exoplanet
regimes represent a crucial discovery space for testing planet formation
theories. ExELS will use the gravitational microlensing technique and will
detect 1000 microlensing events per month over 1.6 deg^2 of the Galactic bulge.
We assess how many of these events will have detectable planetary signatures
using a detailed multi-wavelength microlensing simulator (MABuLS) which
incorporates the Besancon Galactic model with 3D extinction. MABuLS is the
first theoretical simulation of microlensing to treat the effects of point
spread function (PSF) blending self-consistently with the underlying Galactic
model. We use MABuLS, together with current numerical models for the Euclid
PSFs, to explore a number of designs and de-scope options for ExELS, including
the exoplanet yield as a function of filter choice and slewing time, and the
effect of systematic photometry errors. Using conservative extrapolations of
current empirical exoplanet mass functions determined from ground-based
microlensing and radial velocity surveys, ExELS can expect to detect a few
hundred cold exoplanets around mainly G, K and M-type stellar hosts, including
~45 Earth-mass planets and ~6 Mars-mass planets for an observing programme
totalling 10 months. ExELS will be capable of measuring the cold exoplanet mass
function down to Earth mass or below, with orbital separations from ~1AU to the
free-floating regime. (Abridged)Comment: 22 pages. Submitted to MNRAS. New version re-normalises the Besancon
model predictions using current luminosity function and microlensing data
towards the bulge. Exoplanet predictions are revised (upwards) accordingly.
The Euclid exoplanet sensitivity contours shown in Fig 10 are available to
download as an ancillary data fil
Data Mining by Grid Computing in the Search for Extrasolar Planets
A system is presented here to provide improved precision in ensemble differential photometry. This is achieved by using the power of grid computing to analyse astronomical catalogues. This produces new catalogues of optimised pointings for each star, which maximise the number and quality of reference stars available. Astronomical phenomena such as exoplanet transits and small-scale structure within quasars may be observed by means of millimagnitude photometric variability on the timescale of minutes to hours. Because of atmospheric distortion, ground-based observations of these phenomena require the use of differential photometry whereby the target is compared with one or more reference stars. CCD cameras enable the use of many reference stars in an ensemble. The more closely the reference stars in this ensemble resemble the target, the greater the precision of the photometry that can be achieved. The Locus Algorithm has been developed to identify the optimum pointing for a target and provide that pointing with a score relating to the degree of similarity between target and the reference stars. It does so by identifying potential points of aim for a particular telescope such that a given target and a varying set of references were included in a field of view centred on those pointings. A score is calculated for each such pointing. For each target, the pointing with the highest score is designated the optimum pointing. The application of this system to the Sloan Digital Sky Survey (SDSS) catalogue demanded the use of a High Performance Computing (HPC) solution through Grid Ireland. Pointings have thus been generated for 61,662,376 stars and 23,697 quasars
The HerMES submillimetre local and low-redshift luminosity functions
We used wide-area surveys over 39 deg2 by the HerMES (Herschel Multi-tiered Extragalactic Survey) collaboration, performed with the Herschel Observatory SPIRE multiwavelength camera, to estimate the low-redshift, 0.02 < z < 0.5, monochromatic luminosity functions (LFs) of galaxies at 250, 350 and 500âÎŒm. Within this redshift interval, we detected 7087 sources in five independent sky areas, âŒ40 per cent of which have spectroscopic redshifts, while for the remaining objects photometric redshifts were used. The SPIRE LFs in different fields did not show any field-to-field variations beyond the small differences to be expected from cosmic variance. SPIRE flux densities were also combined with Spitzer photometry and multiwavelength archival data to perform a complete spectral energy distribution fitting analysis of SPIRE detected sources to calculate precise k-corrections, as well as the bolometric infrared (IR; 8â1000âÎŒm) LFs and their low-z evolution from a combination of statistical estimators. Integration of the latter prompted us to also compute the local luminosity density and the comoving star formation rate density (SFRD) for our sources, and to compare them with theoretical predictions of galaxy formation models. The LFs show significant and rapid luminosity evolution already at low redshifts, 0.02 < z < 0.2, with L^â_(IR)â(1+z)^(6.0±0.4) and Ί^â_(IR) â(1+z)^(â2.1±0.4), L^â_(250)â(1+z)5.3±0.2 and Ί^â_(250)â(1+z)^(â0.6±0.4) estimated using the IR bolometric and the 250âÎŒm LFs, respectively. Converting our IR LD estimate into an SFRD assuming a standard Salpeter initial mass function and including the unobscured contribution based on the UV dust-uncorrected emission from local galaxies, we estimate an SFRD scaling of SFRD_0 + 0.08z, where SFRD_0 â (1.9 ± 0.03) Ă 10^(â2)â[M_ââMpc^(â3)] is our total SFRD estimate at z ⌠0.02
Radio Continuum Surveys with Square Kilometre Array Pathfinders
In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return
Report from the Tri-Agency Cosmological Simulation Task Force
The Tri-Agency Cosmological Simulations (TACS) Task Force was formed when
Program Managers from the Department of Energy (DOE), the National Aeronautics
and Space Administration (NASA), and the National Science Foundation (NSF)
expressed an interest in receiving input into the cosmological simulations
landscape related to the upcoming DOE/NSF Vera Rubin Observatory (Rubin),
NASA/ESA's Euclid, and NASA's Wide Field Infrared Survey Telescope (WFIRST).
The Co-Chairs of TACS, Katrin Heitmann and Alina Kiessling, invited community
scientists from the USA and Europe who are each subject matter experts and are
also members of one or more of the surveys to contribute. The following report
represents the input from TACS that was delivered to the Agencies in December
2018.Comment: 36 pages, 3 figures. Delivered to NASA, NSF, and DOE in Dec 201
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