400 research outputs found
Galaxy Clusters in the Line of Sight to Background Quasars: II. Environmental effects on the sizes of baryonic halo sizes
Based on recent results on the frequency of MgII absorption line systems in
the "QSO behind RCS clusters" survey (QbC), we analyse the effects of the
cluster environment on the sizes of baryonic haloes around galaxies. We use two
independent models, i) an empirical halo occupation model which fits current
measurements of the clustering and luminosity function of galaxies at low and
high redshifts, and ii) the GALFORM semi-analytic model of galaxy formation,
which follows the evolution of the galaxy population from first principles,
adjusted to match the statistics of low and high redshift galaxies. In both
models we constrain the MgII halo sizes of field and cluster galaxies using
observational results on the observed MgII statistics. Our results for the
field are in good agreement with previous works, indicating a typical \mgii\
halo size of $r_MgII ~ 50h_71^-1kpc in the semi-analytic model, and slightly
lower in the halo occupation number approach. For the cluster environment, we
find that both models require a median MgII halo size of r_MgII< 10h_71^-1kpc
in order to reproduce the observed statistics on absorption line systems in
clusters of galaxies. Based on the Chen & Tinker (2008) result that stronger
systems occur closer to the MgII halo centre, we find that strong absorption
systems in clusters of galaxies occur at roughly a fixed fraction of the
cold-warm halo size out to 1h_71^-1Mpc from the cluster centres. In contrast,
weaker absorption systems appear to occur at progressively shorter relative
fractions of this halo as the distance to the cluster centre decreases.Comment: 12 pages, 8 figures, accepted for publication in MNRA
Evidence for Spatial Separation of Galactic Dust Components
We present an implementation of a Bayesian mixture model using Hamiltonian
Monte Carlo (HMC) techniques to search for spatial separation of Galactic dust
components. Utilizing intensity measurements from \Planck High Frequency
Instrument (HFI), we apply this model to high-latitude Galactic dust emission.
Our analysis reveals a strong preference for a spatially-varying two-population
dust model in intensity, with each population being well characterized by a
single-component dust spectral-energy distribution (SED). While no spatial
information is built into the likelihood, our investigation unveils spatially
coherent structures with high significance, pointing to a physical origin for
the observed spatial separation. These results are robust to our choice of
likelihood and of input data. Furthermore, they are favored over a
single-component dust model by Bayesian evidence calculations.
Incorporating \IRAS 100\, to constrain the Wein-side of the blackbody
function, we find the dust populations differ at the level on the
spectral index () vs. temperature plane. The presence of a
multi-population dust has implications for component separation techniques
frequently employed in the recovery of the Cosmic Microwave Background.Comment: 16 pages, 8 figures. Submitted to Ap
An ALMA survey of submillimetre galaxies in the COSMOS field: The extent of the radio-emitting region revealed by 3 GHz imaging with the Very Large Array
We determine the radio size distribution of a large sample of 152 SMGs in
COSMOS that were detected with ALMA at 1.3 mm. For this purpose, we used the
observations taken by the VLA-COSMOS 3 GHz Large Project. One hundred and
fifteen of the 152 target SMGs were found to have a 3 GHz counterpart. The
median value of the major axis FWHM at 3 GHz is derived to be kpc.
The radio sizes show no evolutionary trend with redshift, or difference between
different galaxy morphologies. We also derived the spectral indices between 1.4
and 3 GHz, and 3 GHz brightness temperatures for the sources, and the median
values were found to be and K. Three of the
target SMGs, which are also detected with the VLBA, show clearly higher
brightness temperatures than the typical values. Although the observed radio
emission appears to be predominantly powered by star formation and supernova
activity, our results provide a strong indication of the presence of an AGN in
the VLBA and X-ray-detected SMG AzTEC/C61. The median radio-emitting size we
have derived is 1.5-3 times larger than the typical FIR dust-emitting sizes of
SMGs, but similar to that of the SMGs' molecular gas component traced through
mid- line emission of CO. The physical conditions of SMGs probably render
the diffusion of cosmic-ray electrons inefficient, and hence an unlikely
process to lead to the observed extended radio sizes. Instead, our results
point towards a scenario where SMGs are driven by galaxy interactions and
mergers. Besides triggering vigorous starbursts, galaxy collisions can also
pull out the magnetised fluids from the interacting disks, and give rise to a
taffy-like synchrotron-emitting bridge. This provides an explanation for the
spatially extended radio emission of SMGs, and can also cause a deviation from
the well-known IR-radio correlation.Comment: 32 pages (incl. 5 appendices), 17 figures, 7 tables; accepted for
publication in A&A; abstract abridged for arXi
Testing CMB Anomalies in E-mode Polarization with Current and Future Data
In this paper, we explore the power of the cosmic microwave background (CMB)
polarization (E-mode) data to corroborate four potential anomalies in CMB
temperature data: the lack of large angular-scale correlations, the alignment
of the quadrupole and octupole (Q-O), the point-parity asymmetry, and the
hemispherical power asymmetry. We use CMB simulations with noise representative
of three experiments -- the Planck satellite, the Cosmology Large Angular Scale
Surveyor (CLASS), and the LiteBIRD satellite -- to test how current and future
data constrain the anomalies. We find the correlation coefficients
between temperature and E-mode estimators to be less than , except for the
point-parity asymmetry ( for cosmic-variance-limited simulations),
confirming that E-modes provide a check on the anomalies that is largely
independent of temperature data. Compared to Planck component-separated CMB
data (SMICA), the putative LiteBIRD survey would reduce errors on E-mode
anomaly estimators by factors of for hemispherical power asymmetry and
point-parity asymmetry, and by for lack of large-scale correlation.
The improvement in Q-O alignment is not obvious due to large cosmic variance,
but we found the ability to pin down the estimator value will be improved by a
factor . Improvements with CLASS are intermediate to these.Comment: 23 pages, 15 figures, 6 table
On-sky performance of new 90 GHz detectors for the Cosmology Large Angular Scale Surveyor (CLASS)
The Cosmology Large Angular Scale Surveyor (CLASS) is a
polarization-sensitive telescope array located at an altitude of 5,200 m in the
Chilean Atacama Desert and designed to measure the polarized Cosmic Microwave
Background (CMB) over large angular scales. The CLASS array is currently
observing with three telescopes covering four frequency bands: one at 40 GHz
(Q); one at 90 GHz (W1); and one dichroic system at 150/220 GHz (HF). During
the austral winter of 2022, we upgraded the first 90 GHz telescope (W1) by
replacing four of the seven focal plane modules. These new modules contain
detector wafers with an updated design, aimed at improving the optical
efficiency and detector stability. We present a description of the design
changes and measurements of on-sky optical efficiencies derived from
observations of Jupiter.Comment: 5 pages, 3 figures, to appear in the IEEE Transactions on Applied
Superconductivity. arXiv admin note: text overlap with arXiv:2208.0500
Design of 280 GHz feedhorn-coupled TES arrays for the balloon-borne polarimeter SPIDER
We describe 280 GHz bolometric detector arrays that instrument the
balloon-borne polarimeter SPIDER. A primary science goal of SPIDER is to
measure the large-scale B-mode polarization of the cosmic microwave background
in search of the cosmic-inflation, gravitational-wave signature. 280 GHz
channels aid this science goal by constraining the level of B-mode
contamination from galactic dust emission. We present the focal plane unit
design, which consists of a 1616 array of conical, corrugated feedhorns
coupled to a monolithic detector array fabricated on a 150 mm diameter silicon
wafer. Detector arrays are capable of polarimetric sensing via waveguide
probe-coupling to a multiplexed array of transition-edge-sensor (TES)
bolometers. The SPIDER receiver has three focal plane units at 280 GHz, which
in total contains 765 spatial pixels and 1,530 polarization sensitive
bolometers. By fabrication and measurement of single feedhorns, we demonstrate
14.7 FHWM Gaussian-shaped beams with 1% ellipticity in a 30%
fractional bandwidth centered at 280 GHz. We present electromagnetic
simulations of the detection circuit, which show 94% band-averaged,
single-polarization coupling efficiency, 3% reflection and 3% radiative loss.
Lastly, we demonstrate a low thermal conductance bolometer, which is
well-described by a simple TES model and exhibits an electrical noise
equivalent power (NEP) = 2.6 10 W/,
consistent with the phonon noise prediction.Comment: Proceedings of SPIE Astronomical Telescopes + Instrumentation 201
Venus Observations at 40 and 90 GHz with CLASS
Using the Cosmology Large Angular Scale Surveyor, we measure the
disk-averaged absolute Venus brightness temperature to be 432.3 2.8 K and
355.6 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz,
respectively. At both frequency bands, these are the most precise measurements
to date. Furthermore, we observe no phase dependence of the measured
temperature in either band. Our measurements are consistent with a
CO-dominant atmospheric model that includes trace amounts of additional
absorbers like SO and HSO.Comment: 7 pages, 3 figures, published in PS
Two Year Cosmology Large Angular Scale Surveyor (CLASS) Observations: Long Timescale Stability Achieved with a Front-End Variable-delay Polarization Modulator at 40 GHz
The Cosmology Large Angular Scale Surveyor (CLASS) is a four-telescope array
observing the largest angular scales () of the
cosmic microwave background (CMB) polarization. These scales encode information
about reionization and inflation during the early universe. The instrument
stability necessary to observe these angular scales from the ground is achieved
through the use of a variable-delay polarization modulator (VPM) as the first
optical element in each of the CLASS telescopes. Here we develop a demodulation
scheme used to extract the polarization timestreams from the CLASS data and
apply this method to selected data from the first two years of observations by
the 40 GHz CLASS telescope. These timestreams are used to measure the
noise and temperature-to-polarization () leakage present in the
CLASS data. We find a median knee frequency for the pair-differenced
demodulated linear polarization of 15.12 mHz and a leakage of
(95\% confidence) across the focal plane. We examine the
sources of noise present in the data and find the component of due
to atmospheric precipitable water vapor (PWV) has an amplitude of for 1 mm of PWV when evaluated at 10 mHz;
accounting for of the noise in the central pixels of the focal
plane. The low level of leakage and noise achieved
through the use of a front-end polarization modulator enables the observation
of the largest scales of the CMB polarization from the ground by the CLASS
telescopes.Comment: Submitted to Ap
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