108 research outputs found
Young and Intermediate-age Distance Indicators
Distance measurements beyond geometrical and semi-geometrical methods, rely
mainly on standard candles. As the name suggests, these objects have known
luminosities by virtue of their intrinsic proprieties and play a major role in
our understanding of modern cosmology. The main caveats associated with
standard candles are their absolute calibration, contamination of the sample
from other sources and systematic uncertainties. The absolute calibration
mainly depends on their chemical composition and age. To understand the impact
of these effects on the distance scale, it is essential to develop methods
based on different sample of standard candles. Here we review the fundamental
properties of young and intermediate-age distance indicators such as Cepheids,
Mira variables and Red Clump stars and the recent developments in their
application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in
Space Science Reviews (Chapter 3 of a special collection resulting from the
May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space
Age
A Multiband Study of the Galaxy Populations of the First Four Sunyaev--Zeldovich Effect selected Galaxy Clusters
We present first results of an examination of the optical properties of the
galaxy populations in SZE selected galaxy clusters. Using clusters selected by
the South Pole Telescope survey and deep multiband optical data from the Blanco
Cosmology Survey, we measure the radial profile, the luminosity function, the
blue fraction and the halo occupation number of the galaxy populations of these
four clusters with redshifts ranging from 0.3 to 1. Our goal is to understand
whether there are differences among the galaxy populations of these SZE
selected clusters and previously studied clusters selected in the optical and
the X-ray. The radial distributions of galaxies in the four systems are
consistent with NFW profiles with a galaxy concentration of 3 to 6. We show
that the characteristic luminosities in bands are consistent with
passively evolving populations emerging from a single burst at redshift .
The faint end power law slope of the luminosity function is found to be on
average in griz. Halo occupation numbers (to ) for
these systems appear to be consistent with those based on X-ray selected
clusters. The blue fraction estimated to , for the three lower
redshift systems, suggests an increase with redshift, although with the current
sample the uncertainties are still large. Overall, this pilot study of the
first four clusters provides no evidence that the galaxy populations in these
systems differ significantly from those in previously studied cluster
populations selected in the X-ray or the optical.Comment: 12 pages, 12 figures and 3 tables. Accepted for publication in Ap
The Blanco Cosmology Survey: Data Acquisition, Processing, Calibration, Quality Diagnostics and Data Release
The Blanco Cosmology Survey (BCS) is a 60 night imaging survey of 80
deg of the southern sky located in two fields: (,)= (5 hr,
) and (23 hr, ). The survey was carried out between
2005 and 2008 in bands with the Mosaic2 imager on the Blanco 4m
telescope. The primary aim of the BCS survey is to provide the data required to
optically confirm and measure photometric redshifts for Sunyaev-Zel'dovich
effect selected galaxy clusters from the South Pole Telescope and the Atacama
Cosmology Telescope. We process and calibrate the BCS data, carrying out PSF
corrected model fitting photometry for all detected objects. The median
10 galaxy (point source) depths over the survey in are
approximately 23.3 (23.9), 23.4 (24.0), 23.0 (23.6) and 21.3 (22.1),
respectively. The astrometric accuracy relative to the USNO-B survey is
milli-arcsec. We calibrate our absolute photometry using the stellar
locus in bands, and thus our absolute photometric scale derives from
2MASS which has % accuracy. The scatter of stars about the stellar locus
indicates a systematics floor in the relative stellar photometric scatter in
that is 1.9%, 2.2%, 2.7% and2.7%, respectively.
A simple cut in the AstrOmatic star-galaxy classifier {\tt spread\_model}
produces a star sample with good spatial uniformity. We use the resulting
photometric catalogs to calibrate photometric redshifts for the survey and
demonstrate scatter with an outlier fraction %
to . We highlight some selected science results to date and provide a
full description of the released data products.Comment: 23 pages, 23 figures . Response to referee comments. Paper accepted
for publication. BCS catalogs and images available for download from
http://www.usm.uni-muenchen.de/BC
Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008 South Pole Telescope Observations
We present a detection-significance-limited catalog of 21 Sunyaev-Zel'dovich
selected galaxy clusters. These clusters, along with 1 unconfirmed candidate,
were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole
Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the
Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and
in some cases spectroscopic) redshift estimates, with catalog redshifts ranging
from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy
clusters, three were previously identified as Abell clusters, three were
presented as SPT discoveries in Staniszewski et al, 2009, and three were first
identified in a recent analysis of BCS data by Menanteau et al, 2010; the
remaining 12 clusters are presented for the first time in this work. Simulated
observations of the SPT fields predict the sample to be nearly 100% complete
above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness
threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14
M_sun/h at z=1. The size and redshift distribution of this catalog are in good
agreement with expectations based on our current understanding of galaxy
clusters and cosmology. In combination with other cosmological probes, we use
the cluster catalog to improve estimates of cosmological parameters. Assuming a
standard spatially flat wCDM cosmological model, the addition of our catalog to
the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a
~50% improvement in precision on both parameters over WMAP7 alone.Comment: 19 pages, 9 figures, 4 appendice
SPT-CL J0546-5345: A Massive z > 1 Galaxy Cluster Selected Via the Sunyaev-Zel'dovich Effect with the South Pole Telescope
We report the spectroscopic confirmation of SPT-CL J0546-5345 at = 1.067.
To date this is the most distant cluster to be spectroscopically confirmed from
the 2008 South Pole Telescope (SPT) catalog, and indeed the first z > 1 cluster
discovered by the Sunyaev-Zel'dovich Effect (SZE). We identify 21 secure
spectroscopic members within 0.9 Mpc of the SPT cluster position, 18 of which
are quiescent, early-type galaxies. From these quiescent galaxies we obtain a
velocity dispersion of 1179^{+232}_{-167} km/s, ranking SPT-CL J0546-5345 as
the most dynamically massive cluster yet discovered at z > 1. Assuming that
SPT-CL J0546-5345 is virialized, this implies a dynamical mass of M_200 =
1.0^{+0.6}_{-0.4} x 10^{15} Msun, in agreement with the X-ray and SZE mass
measurements. Combining masses from several independent measures leads to a
best-estimate mass of M_200 = (7.95 +/- 0.92) x 10^{14} Msun. The spectroscopic
confirmation of SPT-CL J0546-5345, discovered in the wide-angle, mass-selected
SPT cluster survey, marks the onset of the high redshift SZE-selected galaxy
cluster era.Comment: ApJ, in pres
X-ray Properties of the First SZE-selected Galaxy Cluster Sample from the South Pole Telescope
We present results of X-ray observations of a sample of 15 clusters selected
via their imprint on the cosmic microwave background (CMB) from the thermal
Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first
SZ-selected cluster catalog, obtained from observations of 178 deg^2 of sky
surveyed by the South Pole Telescope. Using X-ray observations with Chandra and
XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the
intracluster medium (ICM) within r_500 for each cluster. From these, we
calculate Y_X=M_g T_X and estimate the total cluster mass using a M_500-Y_X
scaling relation measured from previous X-ray studies. The integrated
Comptonization, Y_SZ, is derived from the SZ measurements, using additional
information from the X-ray measured gas density profiles and a universal
temperature profile. We calculate scaling relations between the X-ray and SZ
observables, and find results generally consistent with other measurements and
the expectations from simple self-similar behavior. Specifically, we fit a
Y_SZ-Y_X relation and find a normalization of 0.82 +- 0.07, marginally
consistent with the predicted ratio of Y_SZ/Y_X=0.91+-0.01 that would be
expected from the density and temperature models used in this work. Using the
Y_X derived mass estimates, we fit a Y_SZ-M_500 relation and find a slope
consistent with the self-similar expectation of Y_SZ ~ M^5/3 with a
normalization consistent with predictions from other X-ray studies. We compare
the X-ray mass estimates to previously published SZ mass estimates derived from
cosmological simulations of the SPT survey. We find that the SZ mass estimates
are lower by a factor of 0.89+-0.06, which is within the ~15% systematic
uncertainty quoted for the simulation-based SZ masses.Comment: 28 pages, 19 figures, submitted to Ap
Evidence for Late-stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient
We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr-1) and luminous (Mg,peak = -20 mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity (Lbol ≳ 3 × 1044 erg s-1), the short rise time (trise = 3 days in g band), and the blue colors at peak (g-r ∼ -0.4) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature (Teff ≳ 40,000 K) spectra of a stripped-envelope SN. A retrospective search revealed luminous (Mg ∼ Mr ≈ mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release E γ,iso 10 days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56
A kilometer-scale asteroid inside Venus's orbit
Near-Earth asteroid population models predict the existence of asteroids located inside the orbit of Venus. However, despite searches up to the end of 2019, none have been found. Here we report the discovery by the Zwicky Transient Facility of the first known asteroid located inside of Venus' orbit, 2020 AV₂, possessing an aphelion distance of 0.65 au and ∼2 km in size. While it is possible that 2020 AV₂ is the largest of its kind, we find that its discovery is surprising in the context of population models where the expected count is close to zero. If this discovery is not a statistical fluke, then 2020 AV₂ may come from a yet undiscovered source population of asteroids interior to Venus, and currently favored asteroid population models may need to be adjusted
A kilometer-scale asteroid inside Venus's orbit
Near-Earth asteroid population models predict the existence of asteroids located inside the orbit of Venus. However, despite searches up to the end of 2019, none have been found. Here we report the discovery by the Zwicky Transient Facility of the first known asteroid located inside of Venus' orbit, 2020 AV₂, possessing an aphelion distance of 0.65 au and ∼2 km in size. While it is possible that 2020 AV₂ is the largest of its kind, we find that its discovery is surprising in the context of population models where the expected count is close to zero. If this discovery is not a statistical fluke, then 2020 AV₂ may come from a yet undiscovered source population of asteroids interior to Venus, and currently favored asteroid population models may need to be adjusted
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