Stephen Muchovej

Application of a Self-Similar Pressure Profile to Sunyaev-Zel'Dovich Effect Data from Galaxy Clusters

We investigate the utility of a new, self-similar pressure profile for fitting Sunyaev–Zel’dovich (SZ) effect observations of galaxy clusters. Current SZ imaging instruments–such as the Sunyaev–Zel’dovich Array (SZA)– are capable of probing clusters over a large range in a physical scale. A model is therefore required that can accurately describe a cluster’s pressure profile over a broad range of radii from the core of the cluster out to a significant fraction of the virial radius. In the analysis presented here, we fit a radial pressure profile derived from simulations and detailed X-ray analysis of relaxed clusters to SZA observations of three clusters with exceptionally high-quality X-ray data: A1835, A1914, and CL J1226.9+3332. From the joint analysis of the SZ and X-ray data, we derive physical properties such as gas mass, total mass, gas fraction and the intrinsic, integrated Compton y-parameter. We find that parameters derived from the joint fit to the SZ and X-ray data agree well with a detailed, independent X-ray-only analysis of the same clusters. In particular, we find that, when combined with X-ray imaging data, this new pressure profile yields an independent electron radial temperature profile that is in good agreement with spectroscopic X-ray measurements.

Disk and Envelope Structure in Class 0 Protostars. II. High Resolution Millimeter Mapping of the Serpens Sample

We present high-resolution CARMA 230 GHz continuum imaging of nine deeply embedded protostars in the Serpens Molecular Cloud, including six of the nine known Class 0 protostars in Serpens. This work is part of a program to characterize disk and envelope properties for a complete sample of Class 0 protostars in nearby low-mass star-forming regions. Here, we present CARMA maps and visibility amplitudes as a function of uv-distance for the Serpens sample. Observations are made in the B, C, D, and E antenna configurations, with B configuration observations utilizing the CARMA Paired Antenna Calibration System. Combining data from multiple configurations provides excellent uv-coverage (4-500 kλ), allowing us to trace spatial scales from 10^2 to 10^4 AU. We find evidence for compact disk components in all of the observed Class 0 protostars, suggesting that disks form at very early times (t < 0.2 Myr) in Serpens. We make a first estimate of disk masses using the flux at 50 kλ, where the contribution from the envelope should be negligible, assuming an unresolved disk. The resulting disk masses range from 0.04 M_☉ to 1.7 M_☉, with a mean of approximately 0.2 M_☉. Our high-resolution maps are also sensitive to binary or multiple sources with separations ≳ 250 AU, but significant evidence of multiplicity on scales <2000 AU is seen in only one source.

C-Band All-Sky Survey: a first look at the Galaxy

We present an analysis of the diffuse emission at 5 GHz in the first quadrant of the Galactic plane using two months of preliminary intensity data taken with the C-Band All-Sky Survey (C-BASS) northern instrument at the Owens Valley Radio Observatory, California. Combining C-BASS maps with ancillary data to make temperature–temperature plots, we find synchrotron spectral indices of β = −2.65 ± 0.05 between 0.408 and 5 GHz and β = −2.72 ± 0.09 between 1.420 and 5 GHz for −10° < |b| < −4°, 20° < l < 40°. Through the subtraction of a radio recombination line free–free template, we determine the synchrotron spectral index in the Galactic plane (|b| < 4°) to be β = −2.56 ± 0.07 between 0.408 and 5 GHz, with a contribution of 53 ± 8 per cent from free–free emission at 5 GHz. These results are consistent with previous low-frequency measurements in the Galactic plane. By including C-BASS data in spectral fits, we demonstrate the presence of anomalous microwave emission (AME) associated with the H ii complexes W43, W44 and W47 near 30 GHz, at 4.4σ, 3.1σ and 2.5σ, respectively. The CORNISH (Co-Ordinated Radio ‘N’ Infrared Survey for High mass star formation) VLA 5-GHz source catalogue rules out the possibility that the excess emission detected around 30 GHz may be due to ultracompact H ii regions. Diffuse AME was also identified at a 4σ level within 30° < l < 40°, −2° < b < 2° between 5 and 22.8 GHz.

RADIO SOURCES FROM A 31 GHz SKY SURVEY WITH THE SUNYAEV-ZEL'DOVICH ARRAY

We present the rst sample of 31-GHz selected sources to ux levels of 1 mJy. From late 2005 to mid 2007, the Sunyaev-Zel’dovich Array (SZA) observed 7.7 square degrees of the sky at 31 GHz to a median rms of 0:18 mJy=beam. We identify 209 sources at greater than 5 signicance in the 31 GHz maps, ranging in ux from 0.7 mJy to 200 mJy. Archival NVSS data at 1.4 GHz and observations at 5 GHz with the Very Large Array are used to characterize the sources. We determine the maximumlikelihood integrated source count to be N (>S ) = (27:2 2:5 ) deg 2 (SmJy) 1:18 0:12 over the ux range 0 :7 15 mJy. This result is signicantly higher than predictions based on 1.4-GHz selected samples, a discrepancy which can be explained by a small shift in the spectral index distribution for faint 1.4 GHz sources. From comparison with previous measurements of sources within the central arcminute of massive clusters, we derive an overdensity of 6:8 4:4, relative to eld sources. Subject headings: techniques: interferometric, catalogs, surveys, cosmology: cosmic microwave background, cosmology: observations, radio continuum: general

The C-Band All-Sky Survey: instrument design, status, and first-look data

The C-Band All-Sky Survey (C-BASS) aims to produce sensitive, all-sky maps of diffuse Galactic emission at 5 GHz in total intensity and linear polarization. These maps will be used (with other surveys) to separate the several astrophysical components contributing to microwave emission, and in particular will allow an accurate map of synchrotron emission to be produced for the subtraction of foregrounds from measurements of the polarized Cosmic Microwave Background. We describe the design of the analog instrument, the optics of our 6.1 m dish at the Owens Valley Radio Observatory, the status of observations, and first-look data.

The C-Band All-Sky Survey (C-BASS): design and implementation of the northern receiver

The C-Band All-Sky Survey is a project to map the full sky in total intensity and linear polarization at 5 GHz. The northern component of the survey uses a broad-band single-frequency analogue receiver fitted to a 6.1-m telescope at the Owens Valley Radio Observatory in California, USA. The receiver architecture combines a continuous-comparison radiometer and a correlation polarimeter in a single receiver for stable simultaneous measurement of both total intensity and linear polarization, using custom-designed analogue receiver components. The continuous-comparison radiometer measures the temperature difference between the sky and temperature-stabilized cold electrical reference loads. A cryogenic front-end is used to minimize receiver noise, with a system temperature of ≈30 K in both linear polarization and total intensity. Custom cryogenic notch filters are used to counteract man-made radio frequency interference. The radiometer 1/f noise is dominated by atmospheric fluctuations, while the polarimeter achieves a 1/f noise knee frequency of 10 mHz, similar to the telescope azimuthal scan frequency.

Using cm observations to constrain the abundance of very small dust grains in Galactic cold cores

In this analysis, we illustrate how the relatively new emission mechanism, known as spinning dust, can be used to characterize dust grains in the interstellar medium. We demonstrate this by using spinning dust emission observations to constrain the abundance of very small dust grains (a ≲ 10 nm) in a sample of Galactic cold cores. Using the physical properties of the cores in our sample as inputs to a spinning dust model, we predict the expected level of emission at a wavelength of 1 cm for four different very small dust grain abundances, which we constrain by comparing to 1 cm CARMA observations. For all of our cores, we find a depletion of very small grains, which we suggest is due to the process of grain growth. This work represents the first time that spinning dust emission has been used to constrain the physical properties of interstellar dust grains.

A Circularly Symmetric Antenna Design With High Polarization Purity and Low Spillover

We describe the development of two circularly symmetric antennas with high polarization purity and low spill-over. Both were designed to be used in an all-sky polarization and intensity survey at 5 GHz (the C-Band All-Sky Survey, C-BASS). The survey requirements call for very low cross-polar signal levels and far-out sidelobes. Two different existing antennas, with 6.1-m and 7.6-m diameter primaries, were adapted by replacing the feed and secondary optics, resulting in identical beam performances of 0.73° FWHM, cross-polarization better than - 50 dB, and far-out sidelobes below -70 dB. The polarization purity was realized by using a symmetric low-loss dielectric foam support structure for the secondary mirror, avoiding the need for secondary support struts. Ground spill-over was largely reduced by using absorbing baffles around the primary and secondary mirrors, and by the use of a low-sidelobe profiled corrugated feedhorn. The 6.1-m antenna and receiver have been completed and tested. Results show that the co-polar beam matches the design simulations very closely in the main beam and down to levels of - 80 dB in the backlobes. With the absorbing baffles in place the far-out ( >; 100°) sidelobe response is reduced below -90 dB. Cross-polar response could only be measured down to a noise floor of - 20 dB but is also consistent with the design simulations. Temperature loading and groundspill due to the secondary support were measured at less than 1 K.

CARMA observations of Galactic cold cores: searching for spinning dust emission

We present the first search for spinning dust emission from a sample of 34 Galactic cold cores, performed using the CARMA interferometer. For each of our cores, we use photometric data from the Herschel Space Observatory to constrain N¯_H, T¯_d, n¯_H, and G¯_0. By computing the mass of the cores and comparing it to the Bonnor–Ebert mass, we determined that 29 of the 34 cores are gravitationally unstable and undergoing collapse. In fact, we found that six cores are associated with at least one young stellar object, suggestive of their protostellar nature. By investigating the physical conditions within each core, we can shed light on the cm emission revealed (or not) by our CARMA observations. Indeed, we find that only three of our cores have any significant detectable cm emission. Using a spinning dust model, we predict the expected level of spinning dust emission in each core and find that for all 34 cores, the predicted level of emission is larger than the observed cm emission constrained by the CARMA observations. Moreover, even in the cores for which we do detect cm emission, we cannot, at this stage, discriminate between free–free emission from young stellar objects and spinning dust emission. We emphasize that although the CARMA observations described in this analysis place important constraints on the presence of spinning dust in cold, dense environments, the source sample targeted by these observations is not statistically representative of the entire population of Galactic cores.

CARMA observations of massive Planck-discovered cluster candidates at z ≳ 0.5 associated with WISE overdensities: strategy, observations and validation

We present 1–2 arcmin spatial resolution Combined Array for Research in Millimetre-wave Astronomy (CARMA)-8 31 GHz observations towards 19 unconfirmed Planck cluster candidates, selected to have significant galaxy overdensities from the WISE early data release and thought to be at z ≳ 1 from the WISE colours of the putative brightest cluster galaxy. We find a Sunyaev–Zeldovich (SZ) detection in the CARMA-8 data towards nine candidate clusters, where one detection is considered tentative. For each cluster candidate we present CARMA-8 maps, a study of their radio-source environment and we assess the reliability of the SZ detection. The CARMA SZ detections appear to be SZ bright, with the mean, primary-beam-corrected peak flux density of the decrement being −2.9 mJy beam^(−1) with a standard deviation of 0.8, and are typically offset from the Planck position by ≈80 arcsec. Using archival imaging data in the vicinity of the CARMA SZ centroids, we present evidence that one cluster matches Abell 586 – a known z ≈ 0.2 cluster; four candidate clusters are likely to have 0.3 ≲ z ≲ 0.7; and, for the remaining four, the redshift information is inconclusive. We also argue that the sensitivity limits resulting from the cross-correlation between Planck and WISE makes it challenging to use our selection criterion to identify clusters at z > 1.