239 research outputs found
The Atacama Cosmology Telescope: CO(J = 3 - 2) mapping and lens modeling of an ACT-selected dusty star-forming galaxy
We report Northern Extended Millimeter Array (NOEMA) CO()
observations of the dusty star-forming galaxy ACT-S\,J020941+001557 at , which was detected as an unresolved source in the Atacama Cosmology
Telescope (ACT) equatorial survey. Our spatially resolved spectral line data
support the derivation of a gravitational lens model from 37 independent
velocity channel maps using a pixel-based algorithm, from which we infer a
velocity-dependent magnification factor with a
luminosity-weighted mean \left\approx 13. The resulting
source-plane reconstruction is consistent with a rotating disk, although other
scenarios cannot be ruled out by our data. After correction for lensing, we
derive a line luminosity , a cold gas mass , a dynamical mass , and a gas mass
fraction . The line brightness
temperature ratio of relative to a Green Bank Telescope
CO() detection may be elevated by a combination of external heating of
molecular clouds, differential lensing, and/or pointing errors.Comment: 8 pages, 5 figures, accepted to Ap
Multiwavelength characterisation of an ACT-selected, lensed dusty star-forming galaxy at z=2.64
We present \ci\,(2--1) and multi-transition CO observations of a dusty
star-forming galaxy, ACT\,J2029+0120, which we spectroscopically confirm to lie
at \,=\,2.64. We detect CO(3--2), CO(5--4), CO(7--6), CO(8--7), and
\ci\,(2--1) at high significance, tentatively detect HCO(4--3), and place
strong upper limits on the integrated strength of dense gas tracers (HCN(4--3)
and CS(7--6)). Multi-transition CO observations and dense gas tracers can
provide valuable constraints on the molecular gas content and excitation
conditions in high-redshift galaxies. We therefore use this unique data set to
construct a CO spectral line energy distribution (SLED) of the source, which is
most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy
of the \textit{Herschel} Comprehensive ULIRG Emission Survey. We employ RADEX
models to fit the peak of the CO SLED, inferring a temperature of T117 K
and cm, most consistent with a ULIRG/QSO object
and the presence of high density tracers. We also find that the velocity width
of the \ci\ line is potentially larger than seen in all CO transitions for this
object, and that the ratio is also larger
than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if
confirmed, this anomaly could be an effect of differential lensing of a shocked
molecular outflow.Comment: Accepted for publication in Ap
The Atacama Cosmology Telescope: Physical Properties of Sunyaev-Zel'dovich Effect Clusters on the Celestial Equator
We present the optical and X-ray properties of 68 galaxy clusters selected
via the Sunyaev-Zel'dovich Effect at 148 GHz by the Atacama Cosmology Telescope
(ACT). Our sample, from an area of 504 square degrees centered on the celestial
equator, is divided into two regions. The main region uses 270 square degrees
of the ACT survey that overlaps with the co-added ugriz imaging from the Sloan
Digital Sky Survey (SDSS) over Stripe 82 plus additional near-infrared pointed
observations with the Apache Point Observatory 3.5-meter telescope. We confirm
a total of 49 clusters to z~1.3, of which 22 (all at z>0.55) are new
discoveries. For the second region the regular-depth SDSS imaging allows us to
confirm 19 more clusters up to z~0.7, of which 10 systems are new. We present
the optical richness, photometric redshifts, and separation between the SZ
position and the brightest cluster galaxy (BCG). We find no significant offset
between the cluster SZ centroid and BCG location and a weak correlation between
optical richness and SZ-derived mass. We also present X-ray fluxes and
luminosities from the ROSAT All Sky Survey which confirm that this is a massive
sample. One of the newly discovered clusters, ACT-CL J0044.4+0113 at z=1.1
(photometric), has an integrated XMM-Newton X-ray temperature of kT_x=7.9+/-1.0
keV and combined mass of M_200a=8.2(-2.5,+3.3)x10^14 M_sun/h70 placing it among
the most massive and X-ray-hot clusters known at redshifts beyond z=1. We also
highlight the optically-rich cluster ACT-CL J2327.4-0204 (RCS2 2327) at z=0.705
(spectroscopic) as the most significant detection of the whole equatorial
sample with a Chandra-derived mass of M_200a=1.9(-0.4,+0.6)x10^15 M_sun/h70,
comparable to some of the most massive known clusters like "El Gordo" and the
Bullet Cluster.Comment: 18 pages, 12 figures. Accepted to the Astrophysical Journal. New
version includes minor changes in the accepted pape
The Cosmology Large Angular Scale Surveyor
The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array
designed to characterize relic primordial gravitational waves from inflation
and the optical depth to reionization through a measurement of the polarized
cosmic microwave background (CMB) on the largest angular scales. The
frequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one
dichroic system at 145/217 GHz, are chosen to avoid spectral regions of high
atmospheric emission and span the minimum of the polarized Galactic
foregrounds: synchrotron emission at lower frequencies and dust emission at
higher frequencies. Low-noise transition edge sensor detectors and a rapid
front-end polarization modulator provide a unique combination of high
sensitivity, stability, and control of systematics. The CLASS site, at 5200 m
in the Chilean Atacama desert, allows for daily mapping of up to 70\% of the
sky and enables the characterization of CMB polarization at the largest angular
scales. Using this combination of a broad frequency range, large sky coverage,
control over systematics, and high sensitivity, CLASS will observe the
reionization and recombination peaks of the CMB E- and B-mode power spectra.
CLASS will make a cosmic variance limited measurement of the optical depth to
reionization and will measure or place upper limits on the tensor-to-scalar
ratio, , down to a level of 0.01 (95\% C.L.)
The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectra
We present cosmological parameters derived from the angular power spectrum of
the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz
over 296 deg^2 with the Atacama Cosmology Telescope (ACT) during its 2008
season. ACT measures fluctuations at scales 500<l<10000. We fit a model for the
lensed CMB, Sunyaev-Zel'dovich (SZ), and foreground contribution to the 148 GHz
and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from
radio and infrared point sources, and clustered power from infrared point
sources. The power from thermal and kinetic SZ at 148 GHz is estimated to be
B_3000 = 6.8+-2.9 uK^2, where B_l=l(l+1)C_l/2pi. We estimate primary
cosmological parameters from the 148 GHz spectrum, marginalizing over SZ and
source power. The LCDM cosmological model is a good fit to the data, and LCDM
parameters estimated from ACT+WMAP are consistent with the 7-year WMAP limits,
with scale invariant n_s = 1 excluded at 99.7% CL (3sigma). A model with no CMB
lensing is disfavored at 2.8sigma. By measuring the third to seventh acoustic
peaks, and probing the Silk damping regime, the ACT data improve limits on
cosmological parameters that affect the small-scale CMB power. The ACT data
combined with WMAP give a 6sigma detection of primordial helium, with Y_P =
0.313+-0.044, and a 4sigma detection of relativistic species, assumed to be
neutrinos, with Neff = 5.3+-1.3 (4.6+-0.8 with BAO+H0 data). From the CMB alone
the running of the spectral index is constrained to be dn/dlnk = -0.034 +-
0.018, the limit on the tensor-to-scalar ratio is r<0.25 (95% CL), and the
possible contribution of Nambu cosmic strings to the power spectrum is
constrained to string tension Gmu<1.6 \times 10^-7 (95% CL).Comment: 20 pages, 13 figures. Submitted to ApJ. This paper is a companion to
Hajian et al. (2010) and Das et al. (2010
The Atacama Cosmology Telescope (ACT): Beam Profiles and First SZ Cluster Maps
The Atacama Cosmology Telescope (ACT) is currently observing the cosmic
microwave background with arcminute resolution at 148 GHz, 218 GHz, and 277
GHz. In this paper, we present ACT's first results. Data have been analyzed
using a maximum-likelihood map-making method which uses B-splines to model and
remove the atmospheric signal. It has been used to make high-precision beam
maps from which we determine the experiment's window functions. This beam
information directly impacts all subsequent analyses of the data. We also used
the method to map a sample of galaxy clusters via the Sunyaev-Zel'dovich (SZ)
effect, and show five clusters previously detected with X-ray or SZ
observations. We provide integrated Compton-y measurements for each cluster. Of
particular interest is our detection of the z = 0.44 component of A3128 and our
current non-detection of the low-redshift part, providing strong evidence that
the further cluster is more massive as suggested by X-ray measurements. This is
a compelling example of the redshift-independent mass selection of the SZ
effect.Comment: 16 pages, 10 figures. Accepted for publication in ApJS. See Marriage
et al. (arXiv:1010.1065) and Menanteau et al. (arXiv:1006.5126) for
additional cluster result
Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope
We report the first detection of the gravitational lensing of the cosmic
microwave background through a measurement of the four-point correlation
function in the temperature maps made by the Atacama Cosmology Telescope. We
verify our detection by calculating the levels of potential contaminants and
performing a number of null tests. The resulting convergence power spectrum at
2-degree angular scales measures the amplitude of matter density fluctuations
on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The
measured amplitude of the signal agrees with Lambda Cold Dark Matter cosmology
predictions. Since the amplitude of the convergence power spectrum scales as
the square of the amplitude of the density fluctuations, the 4-sigma detection
of the lensing signal measures the amplitude of density fluctuations to 12%.Comment: 4 pages, 4 figures, replaced title and author list with version
accepted by Physical Review Letters. Likelihood code can be downloaded from
http://bccp.lbl.gov/~sudeep/ACTLensLike.htm
- …