59 research outputs found
Recommended from our members
The LSST DESC data challenge 1: Generation and analysis of synthetic images for next-generation surveys
Data Challenge 1 (DC1) is the first synthetic data set produced by the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC). DC1 is designed to develop and validate data reduction and analysis and to study the impact of systematic effects that will affect the LSST data set. DC1 is comprised of r-band observations of 40 deg2 to 10 yr LSST depth. We present each stage of the simulation and analysis process: (a) generation, by synthesizing sources from cosmological N-body simulations in individual sensor-visit images with different observing conditions; (b) reduction using a development version of the LSST Science Pipelines; and (c) matching to the input cosmological catalogue for validation and testing. We verify that testable LSST requirements pass within the fidelity of DC1. We establish a selection procedure that produces a sufficiently clean extragalactic sample for clustering analyses and we discuss residual sample contamination, including contributions from inefficiency in star-galaxy separation and imperfect deblending. We compute the galaxy power spectrum on the simulated field and conclude that: (i) survey properties have an impact of 50 per cent of the statistical uncertainty for the scales and models used in DC1; (ii) a selection to eliminate artefacts in the catalogues is necessary to avoid biases in the measured clustering; and (iii) the presence of bright objects has a significant impact (2-6) in the estimated power spectra at small scales (> 1200), highlighting the impact of blending in studies at small angular scales in LSST
The Nearby Type Ibn Supernova 2015G: Signatures of Asymmetry and Progenitor Constraints
SN 2015G is the nearest known SN Ibn to date at 23.2 Mpc and it has proven itself a truly remarkable example of this rare subclass. We present the results of an extensive observational campaign including data from radio through ultraviolet wavelengths. SN 2015G was asymmetric, showing late-time nebular lines redshifted by 1000 km/s. It shared many features with the prototypical SN Ibn 2006jc, including extremely strong He I emission lines and a late-time blue pseudocontinuum. The young SN 2015G showed narrow P-Cygni profiles of He I, but never in its evolution did it show any signature of hydrogen - arguing for a dense, ionized, and hydrogen-free circumstellar medium moving outward with a velocity of 1000 km/s and created by relatively recent mass loss from the progenitor star. Ultraviolet through infrared observations show that the fading SN 2015G (which was probably discovered some 20 days post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. Archival HST images provide upper limits on the luminosity of SN 2015G's progenitor, while nondetections of any luminous radio afterglow and optical nondetections of outbursts over the past two decades provide constraints upon its mass-loss history
Type Ia Supernovae as Stellar Endpoints and Cosmological Tools
Empirically, Type Ia supernovae are the most useful, precise, and mature
tools for determining astronomical distances. Acting as calibrated candles they
revealed the presence of dark energy and are being used to measure its
properties. However, the nature of the SN Ia explosion, and the progenitors
involved, have remained elusive, even after seven decades of research. But now
new large surveys are bringing about a paradigm shift --- we can finally
compare samples of hundreds of supernovae to isolate critical variables. As a
result of this, and advances in modeling, breakthroughs in understanding all
aspects of SNe Ia are finally starting to happen.Comment: Invited review for Nature Communications. Final published version.
Shortened, update
X-Ray Emitting Blast Wave from the Recurrent Nova RS Ophiuchi
Stellar explosions such as novae and supernovae produce most of the heavy
elements in the Universe. Although the onset of novae from runaway
thermonuclear fusion reactions on the surface of a white dwarf in a binary star
system is understood[1], the structure, dynamics, and mass of the ejecta are
not well known. In rare cases, the white dwarf is embedded in the wind nebula
of a red-giant companion; the explosion products plow through the nebula and
produce X-ray emission. Early this year, an eruption of the recurrent nova RS
Ophiuchi[2,3] provided the first opportunity to perform comprehensive X-ray
observations of such an event and diagnose conditions within the ejecta. Here
we show that the hard X-ray emission from RS Ophiuchi early in the eruption
emanates from behind a blast wave, or outward-moving shock wave, that expanded
freely for less than 2 days and then decelerated due to interaction with the
nebula. The X-rays faded rapidly, suggesting that the blast wave deviates from
the standard spherical shell structure[4-6]. The early onset of deceleration
indicates that the ejected shell had a low mass, the white dwarf has a high
mass[7], and that RS Ophiuchi is a progenitor of the type of supernova integral
to studies of the expansion of the universe.Comment: To appear in Nature; 7 pages, including 2 color figures; removed
incorrect statement of embargo polic
Alternative High-z Cosmic Tracers and the Dark Energy Equation of State
We propose to use alternative cosmic tracers to measure the dark energy
equation of state and the matter content of the Universe [w(z) & \Omega_m]. Our
proposed method consists of two components: (a) tracing the Hubble relation
using HII-like starburst galaxies, as an alternative to SNIa, which can be
detected up to very large redshifts, z~4, and (b) measuring the clustering
pattern of X-ray selected AGN at a median redshift of ~1. Each component of the
method can in itself provide interesting constraints on the cosmological
parameters, especially under our anticipation that we will reduce the
corresponding random and systematic errors significantly. However, by joining
their likelihood functions we will be able to put stringent cosmological
constraints and break the known degeneracies between the dark energy equation
of state (whether it is constant or variable) and the matter content of the
universe and provide a powerful and alternative rute to measure the
contribution to the global dynamics, and the equation of state, of dark energy.
A preliminary joint analysis of X-ray selected AGN (based on a small XMM
survey) and the currently largest SNIa sample (Kowalski et al 2008), provides:
Omega_m=0.28^{+0.02}_{-0.04} and w=-1.0 +-0.1.Comment: 19 pages, 11 figures, to appear in JOP, proceedings of the "Recent
Developments in Gravity, NEB XIII" conference, held in Thessaloniki,
Macedonia, Greece, 4-6 June 200
Recommended from our members
The Sloan Digital Sky Survey quasar catalog: Tenth data release â&dagger
We present the Data Release 10 Quasar (DR10Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky
Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the first 2.5 years of the survey and that are
confirmed as quasars via visual inspection of the spectra, have luminosities Mi[z = 2] < −20.5 (in a ΛCDMcosmology with H0 = 70 km s−1 Mpc−1,
ΩM = 0.3, and ΩΛ = 0.7), and either display at least one emission line with a full width at half maximum (FWHM) larger than 500 km s−1 or,
if not, have interesting/complex absorption features. The catalog also includes known quasars (mostly from SDSS-I and II) that were reobserved
by BOSS. The catalog contains 166 583 quasars (74 454 are new discoveries since SDSS-DR9) detected over 6373 deg2 with robust identification
and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (117 668) is ∼5 times greater
than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii,
Mg ii). The catalog identifies 16 461 broad absorption line quasars and gives their characteristics. For each object, the catalog presents five-band
(u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag and information on the optical morphology and selection method. The
catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys.
The calibrated digital spectra cover the wavelength region 3600−10 500 Å at a spectral resolution in the range 1300 < R < 2500; the spectra can
be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 2376 quasars that have been identified
among the galaxy targets of the SDSS-III/BOSS.I.P. received partial support from Center of Excellence in
Astrophysics and Associated Technologies (PFB 06). The French Participation
Group to SDSS-III was supported by the Agence Nationale de la Recherche
under contracts ANR-08-BLAN-0222 and ANR-12-BS05-0015. A.D.M. is
a research fellow of the Alexander von Humboldt Foundation of Germany
and was partially supported through NSF Grant 1211112 and NASA ADAP
award NNX12AE38G. Funding for SDSS-III has been provided by the
Alfred P. Sloan Foundation, the Participating Institutions, the National Science
Foundation, and the US Department of Energy Office of Science.This is the published version. It originally appeared in Astronomy and Astrophysics and is available online at http://www.aanda.org/articles/aa/abs/2014/03/aa22691-13/aa22691-13.html
Recommended from our members
The Sloan Digital Sky Survey quasar catalog: Tenth data release â&dagger
We present the Data Release 10 Quasar (DR10Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky
Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the first 2.5 years of the survey and that are
confirmed as quasars via visual inspection of the spectra, have luminosities Mi[z = 2] < −20.5 (in a ΛCDMcosmology with H0 = 70 km s−1 Mpc−1,
ΩM = 0.3, and ΩΛ = 0.7), and either display at least one emission line with a full width at half maximum (FWHM) larger than 500 km s−1 or,
if not, have interesting/complex absorption features. The catalog also includes known quasars (mostly from SDSS-I and II) that were reobserved
by BOSS. The catalog contains 166 583 quasars (74 454 are new discoveries since SDSS-DR9) detected over 6373 deg2 with robust identification
and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (117 668) is ∼5 times greater
than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii,
Mg ii). The catalog identifies 16 461 broad absorption line quasars and gives their characteristics. For each object, the catalog presents five-band
(u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag and information on the optical morphology and selection method. The
catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys.
The calibrated digital spectra cover the wavelength region 3600−10 500 Å at a spectral resolution in the range 1300 < R < 2500; the spectra can
be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 2376 quasars that have been identified
among the galaxy targets of the SDSS-III/BOSS.I.P. received partial support from Center of Excellence in
Astrophysics and Associated Technologies (PFB 06). The French Participation
Group to SDSS-III was supported by the Agence Nationale de la Recherche
under contracts ANR-08-BLAN-0222 and ANR-12-BS05-0015. A.D.M. is
a research fellow of the Alexander von Humboldt Foundation of Germany
and was partially supported through NSF Grant 1211112 and NASA ADAP
award NNX12AE38G. Funding for SDSS-III has been provided by the
Alfred P. Sloan Foundation, the Participating Institutions, the National Science
Foundation, and the US Department of Energy Office of Science.This is the published version. It originally appeared in Astronomy and Astrophysics and is available online at http://www.aanda.org/articles/aa/abs/2014/03/aa22691-13/aa22691-13.html
The Sloan Digital Sky Survey quasar catalog: tenth data release
We present the Data Release 10 Quasar (DR10Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the first 2.5 years of the survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities M-i[z = 2] 2.15 (117 668) is similar to 5 times greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C IV, C III, Mg II). The catalog identifies 16 461 broad absorption line quasars and gives their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag and information on the optical morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3600-10 500 angstrom at a spectral resolution in the range 1300 < R < 2500; the spectra can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 2376 quasars that have been identified among the galaxy targets of the SDSS-III/BOSS
Spectroscopic Observations and Analysis of the Peculiar SN 1999aa
We present an extensive new time-series of spectroscopic data of the peculiar
SN 1999aa in NGC 2595. Our data set includes 25 optical spectra between -11 and
+58 days with respect to B-band maximum light, providing an unusually complete
time history. The early spectra resemble those of a SN 1991T-like object but
with a relatively strong Ca H&K absorption feature. The first clear sign of Si
II 6355, characteristic of Type Ia supernovae, is found at day -7 and its
velocity remains constant up to at least the first month after B-band maximum
light. The transition to normal-looking spectra is found to occur earlier than
in SN 1991T suggesting SN 1999aa as a possible link between SN 1991T-like and
Branch-normal supernovae. Comparing the observations with synthetic spectra,
doubly ionized Fe, Si and Ni are identified at early epochs. These are
characteristic of SN 1991T-like objects. Furthermore, in the day -11 spectrum,
evidence is found for an absorption feature which could be identified as high
velocity C II 6580 or H-alpha. At the same epoch C III 4648.8 at photospheric
velocity is probably responsible for the absorption feature at 4500 A. High
velocity Ca is found around maximum light together with Si II and Fe II
confined in a narrow velocity window. Implied constraints on supernovae
progenitor systems and explosion hydrodynamical models are briefly discussed.Comment: 46 pages including 23 figures. Accepted for publication by AJ. For
full-resolution figures see http://www.physto.se/~gabri/sn99aa
The establishment of the Standard Cosmological Model through observations
Over the last decades, observations with increasing quality have
revolutionized our understanding of the general properties of the Universe.
Questions posed for millenia by mankind about the origin, evolution and
structure of the cosmos have found an answer. This has been possible mainly
thanks to observations of the Cosmic Microwave Background, of the large-scale
distribution of matter structure in the local Universe, and of type Ia
supernovae that have revealed the accelerated expansion of the Universe. All
these observations have successfully converged into the so-called "concordance
model". In spite of all these observational successes, there are still some
important open problems, the most obvious of which are what generated the
initial matter inhomogeneities that led to the structure observable in today's
Universe, and what is the nature of dark matter, and of the dark energy that
drives the accelerated expansion. In this chapter I will expand on the previous
aspects. I will present a general description of the Standard Cosmological
Model of the Universe, with special emphasis on the most recent observations
that have us allowed to consolidate this model. I will also discuss the
shortfalls of this model, its most pressing open questions, and will briefly
describe the observational programmes that are being planned to tackle these
issues.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern
Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka;
publisher Springer Nature) funded by the European Union Erasmus+ Strategic
Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556
- …