arXiv subjects

Mark Halpern

Publications and source records attributed to Mark Halpern.

At least 145 records · Page 8Linked to original sources

arXiv2009

BLAST: Resolving the Cosmic Submillimeter Background

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has made one square degree, deep, confusion limited maps at three different bands, centered on the Great Observatories Origins Deep Survey South field. By calculating the covariance of these maps with catalogs of 24 micron sources from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL), we have determined that the total submillimeter intensities are 8.60 +/- 0.59, 4.93 +/- 0.34, and 2.27 +/- 0.20 nW m^2 sr^(-1) at 250, 350, and 500 micron, respectively. These numbers are more precise than previous estimates of the cosmic infrared background (CIB) and are consistent with 24 micron-selected galaxies generating the full intensity of the CIB. We find that the fraction of the CIB that originates from sources at z >= 1.2 increases with wavelength, with 60% from high redshift sources at 500 micron. At all BLAST wavelengths, the relative intensity of high-z sources is higher for 24 micron-faint sources than it is for 24 micron-bright sources. Galaxies identified as active galactic nuclei (AGN) by their Infrared Array Camera (IRAC) colors are 1.6-2.6 times brighter than the average population at 250-500 micron, consistent with what is found for X-ray-selected AGN. BzK-selected galaxies are found to be moderately brighter than typical 24 micron-selected galaxies in the BLAST bands. These data provide high precision constraints for models of the evolution of the number density and intensity of star forming galaxies at high redshift.

astro-ph.CO↗

arXiv2009

BLAST: The Mass Function, Lifetimes, and Properties of Intermediate Mass Cores from a 50 Square Degree Submillimeter Galactic Survey in Vela (l = ~265)

We present first results from an unbiased 50 deg^2 submillimeter Galactic survey at 250, 350, and 500 micron from the 2006 flight of the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). The map has resolution ranging from 36 arcsec to 60 arcsec in the three submillimeter bands spanning the thermal emission peak of cold starless cores. We determine the temperature, luminosity, and mass of more than one thousand compact sources in a range of evolutionary stages and an unbiased statistical characterization of the population. From comparison with C^(18)O data, we find the dust opacity per gas mass, kappa r = 0.16 cm^2 g^(-1) at 250 micron, for cold clumps. We find that 2% of the mass of the molecular gas over this diverse region is in cores colder than 14 K, and that the mass function for these cold cores is consistent with a power law with index alpha = -3.22 +/- 0.14 over the mass range 14 M_sun < M < 80 M_sun. Additionally, we infer a mass-dependent cold core lifetime of t_c(M) = 4E6 (M/20 M_sun)^(-0.9) years - longer than what has been found in previous surveys of either low or high mass cores, and significantly longer than free fall or likely turbulent decay times. This implies some form of non-thermal support for cold cores during this early stage of star formation.

astro-ph.GA↗

arXiv2009

Radio and mid-infrared identification of BLAST source counterparts in the Chandra Deep Field South

We have identified radio and/or mid-infrared counterparts to 198 out of 350 sources detected at >=5 sigma over ~ 9 square degrees centered on the Chandra Deep Field South (CDFS) by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) at 250, 350 and 500 um. We have matched 114 of these counterparts to optical sources with previously derived photometric redshifts and fitted SEDs to the BLAST fluxes and fluxes at 70 and 160 um acquired with the Spitzer Space Telescope. In this way, we have constrained dust temperatures, total far-infrared/sub-millimeter luminosities and star formation rates for each source. Our findings show that on average, the BLAST sources lie at significantly lower redshifts and have significantly lower rest-frame dust temperatures compared to submm sources detected in surveys conducted at 850 um. We demonstrate that an apparent increase in dust temperature with redshift in our sample arises as a result of selection effects. Finally, we provide the full multi-wavelength catalog of >= 5 sigma BLAST sources contained within the complete ~ 9 square degree survey area.

astro-ph.CO↗

arXiv2009

Over half of the far-infrared background light comes from galaxies at z >= 1.2

Submillimetre surveys during the past decade have discovered a population of luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z <= 4, these massive submillimetre galaxies go through a phase characterized by optically obscured star formation at rates several hundred times that in the local Universe. Half of the starlight from this highly energetic process is absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K with spectral energy distributions peaking at 100 microns in the rest frame. At 1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns. The cumulative effect of these galaxies is to yield extragalactic optical and far-infrared backgrounds with approximately equal energy densities. Since the initial detection of the far-infrared background (FIRB), higher-resolution experiments have sought to decompose this integrated radiation into the contributions from individual galaxies. Here we report the results of an extragalactic survey at 250, 350 and 500 microns. Combining our results at 500 microns with those at 24 microns, we determine that all of the FIRB comes from individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of it. As expected, at the longest wavelengths the signal is dominated by ultraluminous galaxies at z > 1.

astro-ph.CO↗

arXiv2009

Observing the Evolution of the Universe

How did the universe evolve? The fine angular scale (l>1000) temperature and polarization anisotropies in the CMB are a Rosetta stone for understanding the evolution of the universe. Through detailed measurements one may address everything from the physics of the birth of the universe to the history of star formation and the process by which galaxies formed. One may in addition track the evolution of the dark energy and discover the net neutrino mass. We are at the dawn of a new era in which hundreds of square degrees of sky can be mapped with arcminute resolution and sensitivities measured in microKelvin. Acquiring these data requires the use of special purpose telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and the South Pole Telescope (SPT). These new telescopes are outfitted with a new generation of custom mm-wave kilo-pixel arrays. Additional instruments are in the planning stages.

astro-ph.CO↗

arXiv2009

21 cm Intensity Mapping

Using the 21 cm line, observed all-sky and across the redshift range from 0 to 5, the large scale structure of the Universe can be mapped in three dimensions. This can be accomplished by studying specific intensity with resolution ~ 10 Mpc, rather than via the usual galaxy redshift survey. The data set can be analyzed to determine Baryon Acoustic Oscillation wavelengths, in order to address the question: 'What is the nature of Dark Energy?' In addition, the study of Large Scale Structure across this range addresses the questions: 'How does Gravity effect very large objects?' and 'What is the composition our Universe?' The same data set can be used to search for and catalog time variable and transient radio sources.

astro-ph.IM↗

arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) -- VI. 350 micron mapping of submillimetre galaxies

A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 microns has been carried out to map the regions around several 850 micron-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared luminosities and hence star-formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350 micron flux densities for 24 850 micron sources, seven of which are detected at >2.5-sigma within a 10 arcsec search radius of the 850 micron positions. When results from the literature are included the total number of 350 micron flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-infrared (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich (Mdust~9x10^8 Msun), luminous (Lfir~2x10^12 Lsun), star-forming galaxies with intrinsic dust temperatures of ~35 K and star-formation rates of ~400 Msun/yr. We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350 micron source counts, N350(>25mJy)~200-500 deg^-2.

astro-ph↗

arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - IV: Radio-mm-FIR photometric redshifts

We present the redshift distribution of the SHADES galaxy population based on the rest-frame radio-mm-FIR colours of 120 robustly detected 850um sources in the Lockman Hole East (LH) and Subaru XMM-Newton Deep Field (SXDF). The redshift distribution derived from the full SED information is shown to be narrower than that determined from the radio-submm spectral index, as more photometric bands contribute to a higher redshift accuracy. The redshift distribution of sources derived from at least two photometric bands peaks at z ~ 2.4 and has a near-Gaussian distribution, with 50 per cent (interquartile range) of sources at z=1.8-3.1. We find a statistically-significant difference between the measured redshift distributions in the two fields; the SXDF peaking at a slightly lower redshift (median z ~ 2.2) than the LH (median z ~ 2.7), which we attribute to the noise-properties of the radio observations. We demonstrate however that there could also be field-to-field variations that are consistent with the measured differences in the redshift distributions, and hence, that the incomplete area observed by SHADES with SCUBA, despite being the largest sub-mm survey to date, may still be too small to fully characterize the bright sub-mm galaxy population. Finally we present a brief comparison with the predicted, or assumed, redshift distributions of sub-mm galaxy formation and evolution models, and we derive the contribution of these SHADES sources and the general sub-mm galaxy population to the star formation-rate density at different epochs.

astro-ph↗

arXiv2006

An upper limit to polarized submillimetre emission in Arp 220

We report the results of pointed observations of the prototypical ultra-luminous infrared galaxy (ULIRG) Arp 220 at 850 microns using the polarimeter on the SCUBA instrument on the James Clerk Maxwell Telescope. We find a Bayesian 99 per cent confidence upper limit on the polarized emission for Arp 220 of 1.54 per cent, averaged over the 15 arcsec beam-size. Arp 220 can serve as a proxy for other, more distant such galaxies. This upper limit constrains the magnetic field geometry in Arp 220 and also provides evidence that polarized ULIRGs will not be a major contaminant for next-generation cosmic microwave background polarization measurements.

astro-ph↗

arXiv2006

Prototype finline-coupled TES bolometers for CLOVER

CLOVER is an experiment which aims to detect the signature of gravitational waves from inflation by measuring the B-mode polarization of the cosmic microwave background. CLOVER consists of three telescopes operating at 97, 150, and 220 GHz. The 97-GHz telescope has 160 feedhorns in its focal plane while the 150 and 220-GHz telescopes have 256 horns each. The horns are arranged in a hexagonal array and feed a polarimeter which uses finline-coupled TES bolometers as detectors. To detect the two polarizations the 97-GHz telescope has 320 detectors while the 150 and 220-GHz telescopes have 512 detectors each. To achieve the target NEPs (1.5, 2.5, and 4.5x10^-17 W/rtHz) the detectors are cooled to 100 mK for the 97 and 150-GHz polarimeters and 230 mK for the 220-GHz polarimeter. Each detector is fabricated as a single chip to ensure a 100% operational focal plane. The detectors are contained in linear modules made of copper which form split-block waveguides. The detector modules contain 16 or 20 detectors each for compatibility with the hexagonal arrays of horns in the telescopes' focal planes. Each detector module contains a time-division SQUID multiplexer to read out the detectors. Further amplification of the multiplexed signals is provided by SQUID series arrays. The first prototype detectors for CLOVER operate with a bath temperature of 230 mK and are used to validate the detector design as well as the polarimeter technology. We describe the design of the CLOVER detectors, detector blocks, and readout, and present preliminary measurements of the prototype detectors performance.

astro-ph↗

arXiv2006

TES imaging array technology for CLOVER

CLOVER is an experiment which aims to detect the signature of gravitational waves from inflation by measuring the B-mode polarization of the cosmic microwave background. CLOVER consists of three telescopes operating at 97, 150, and 220 GHz. The 97-GHz telescope has 160 horns in its focal plane while the 150 and 220-GHz telescopes have 256 horns each. The horns are arranged in a hexagonal array and feed a polarimeter which uses finline-coupled TES bolometers as detectors. To detect the two polarizations the 97-GHz telescope has 320 detectors while the 150 and 220-GHz telescopes have 512 detectors each. To achieve the required NEPs the detectors are cooled to 100 mK for the 97 and 150-GHz polarimeters and 230 mK for the 220-GHz polarimeter. Each detector is fabricated as a single chip to guarantee fully functioning focal planes. The detectors are contained in linear modules made of copper which form split-block waveguides. The detector modules contain 16 or 20 detectors each for compatibility with the hexagonal arrays of horns in the telescopes' focal planes. Each detector module contains a time-division SQUID multiplexer to read out the detectors. Further amplification of the multiplexed signals is provided by SQUID series arrays. The first prototype detectors for CLOVER operate with a bath temperature of 230 mK and are used to validate the detector design as well as the polarimeter technology. We describe the design of the CLOVER detectors, detector blocks, and readout, and give an update on the detector development.

astro-ph↗

arXiv2006

SCUBA-2: a 10,000 pixel submillimeter camera for the James Clerk Maxwell Telescope

SCUBA-2 is an innovative 10,000 pixel submillimeter camera due to be delivered to the James Clerk Maxwell Telescope in late 2006. The camera is expected to revolutionize submillimeter astronomy in terms of the ability to carry out wide-field surveys to unprecedented depths addressing key questions relating to the origins of galaxies, stars and planets. This paper presents an update on the project with particular emphasis on the laboratory commissioning of the instrument. The assembly and integration will be described as well as the measured thermal performance of the instrument. A summary of the performance results will be presented from the TES bolometer arrays, which come complete with in-focal plane SQUID amplifiers and multiplexed readouts, and are cooled to 100mK by a liquid cryogen-free dilution refrigerator. Considerable emphasis has also been placed on the operating modes of the instrument and the common-user aspect of the user interface and data reduction pipeline. These areas will also be described in the paper.

astro-ph↗

arXiv2005

An upper limit to [C II] emission in a z ~= 5 galaxy

Low-ionization-state far-infrared (FIR) emission lines may be useful diagnostics of star-formation activity in young galaxies, and at high redshift may be detectable from the ground. In practice, however, very little is known concerning how strong such line emission might be in the early Universe. We attempted to detect the 158 micron [C II] line from a lensed galaxy at z = 4.926 using the Caltech Submillimeter Observatory. This source is an ordinary galaxy, in the sense that it shows high but not extreme star formation, but lensing makes it visible. Our analysis includes a careful consideration of the calibrations and weighting of the individual scans. We find only modest improvement over the simpler reduction methods, however, and the final spectrum remains dominated by systematic baseline ripple effects. We obtain a 95 per cent confidence upper limit of 33 mJy for a 200 km/s full width at half maximum line, corresponding to an unlensed luminosity of 1x10^9 L_sun for a standard cosmology. Combining this with a marginal detection of the continuum emission using the James Clerk Maxwell Telescope, we derive an upper limit of 0.4 per cent for the ratio of L_CII/L_FIR in this object.

astro-ph↗

arXiv2004

An 850-micron SCUBA map of the Groth Strip and reliable source extraction

We present an 850-micron map and list of candidate sources in a 70 arcmin^2 sub-area of the Groth Strip observed using SCUBA. We initially detect 7 candidate sources with signal-to-noise ratios (SNRs) between 3.0 and 3.5 and 4 candidate sources with SNR > 3.5. Simulations suggest that on average in a map this size one expects 1.6 false positive sources for SNR > 3.5 and 4.5 for 3 < SNR < 3.5. Flux boosting in maps is a well known effect and we have developed a simple Bayesian prescription for estimating the unboosted flux distribution and used this method to determine the best flux estimates of our sources. This method is easily adapted for any other modest signal-to-noise survey in which there is prior knowledge of the source counts. We performed follow-up photometry in an attempt to confirm or reject 5 of our source candidates. We confirm the reality of 2 of the SCUBA sources, although at lower levels than suggested in the map and we find that the photometry results are consistent with and confirm the de-boosted map fluxes. Our final candidate source list contains 3 sources, including the 2 confirmed detections and 1 further candidate source with SNR > 3.5 which has a reasonable chance of being real.

astro-ph↗

arXiv2004

An update on the SCUBA-2 project

SCUBA-2, which replaces SCUBA (the Submillimeter Common User Bolometer Array) on the James Clerk Maxwell Telescope (JCMT) in 2006, is a large-format bolometer array for submillimeter astronomy. Unlike previous detectors which have used discrete bolometers, SCUBA-2 has two dc-coupled, monolithic, filled arrays with a total of ~10,000 bolometers. It will offer simultaneous imaging of a 50 sq-arcmin field of view at wavelengths of 850 and 450 microns. SCUBA-2 is expected to have a huge impact on the study of galaxy formation and evolution in the early Universe as well as star and planet formation in our own Galaxy. Mapping the sky to the same S/N up to 1000 times faster than SCUBA, it will also act as a pathfinder for the new submillimeter interferometers such as ALMA. SCUBA-2's absorber-coupled pixels use superconducting transition edge sensors operating at 120 mK for performance limited by the sky background photon noise. The monolithic silicon detector arrays are deep-etched by the Bosch process to isolate the pixels on silicon nitride membranes. Electrical connections are made through indium bump bonds to a SQUID time-domain multiplexer (MUX). We give an overview of the SCUBA-2 system and an update on its status, and describe some of the technological innovations that make this unique instrument possible.

astro-ph↗

arXiv2004

Submillimetre Constraints on Hyper-Extremely Red Objects in the Subaru Deep Field

We have mapped the submillimetre wavelength continuum emission from the Subaru Deep Field (SDF) at 450 and 850 microns with the Submillimetre Common-User Bolometer Array (SCUBA) detector on the James Clerk Maxwell Telescope (JCMT). The near-IR image of the SDF is one of the deepest near-IR images available and contains four `hyper extremely red objects' (HEROs). These data allow us to test the connection between `extremely red objects' (EROs) found in IR surveys and the population of bright submillimetre sources found with SCUBA. We present a weak measurement of the average flux of the four K-band selected HEROs of 1.15 (+/-0.46) mJy, which fails to support the hypothesis that HEROs should be bright SCUBA sources. Our data are consistent with the HEROs being objects with SEDs like that of Arp220 out to z~1.7, however, the extinction in the HEROs must be about 1 magnitude greater in the J-band than is the case for Arp220 and they would need to be 1.7 times as luminous as Arp220. On the other hand, an evolutionary model of elliptical galaxies at z~2-3 in a dusty starburst phase is also in agreement with the submillimetre data, as was originally proposed for the HEROs.

astro-ph↗

arXiv2003

Measurement of the Sunyaev-Zel'dovich Increment in Massive Galaxy Clusters

We have detected the Sunyaev-Zel'dovich (SZ) increment at 850 microns in two galaxy clusters (Cl 0016+16 and MS 1054.4-0321) using SCUBA (Sub-millimetre Common User Bolometer Array) on the James Clerk Maxwell Telescope. Fits to the isothermal βmodel yield a central Compton y parameter of (2.2 \pm 0.7) x 10^{-4} and a central 850 micron flux of ΔI_{0} = 2.2 \pm 0.7 mJy/beam in Cl 0016. This can be combined with decrement measurements to infer y = (2.38 \pm_{0.34}^{0.36}) x 10^{-4} and v_{pec} = 400 \pm_{1400}^{1900} km/s. In MS 1054 we find a peak 850 micron flux of ΔI_{0} = 2.0 \pm 1.0 mJy/beam and y = (2.0 \pm 1.0) x 10^{-4}. To be successful such measurements require large chop throws and non-standard data analysis techniques. In particular, the 450 micron data are used to remove atmospheric variations in the 850 micron data. An explicit annular model is fit to the SCUBA difference data in order to extract the radial profile, and separately fit to the model differences to minimize the effect of correlations induced by our scanning strategy. We have demonstrated that with sufficient care, SCUBA can be used to measure the SZ increment in massive, compact galaxy clusters.

astro-ph↗

arXiv2003

Estimates of Confusion and Gravitational Lensing Limits in Sunyaev-Zel'dovich Increment Measurements

We present estimates of the confusion limit of measurements of the Sunyaev-Zel'dovich effect (SZ) increment near its peak intensity based on Monte Carlo simulations of sub-millimetre observations of galaxy clusters. Specifically, we evaluate the contribution of gravitational lensing of high redshift background sources by a target cluster to its inferred SZ signal. We find that the background confusion limit is 0.6 mJy per beam without any lensing. With gravitational lensing, the confusion limit increases to 0.9 mJy per beam. Removing bright sources in the gravitationally lensed fields decreases the confusion limit to 0.7 mJy per beam, essentially background levels. These limits are found by removing exceptionally poor fits to the expected SZ profile, which are due to the different structure of the SZ and lensing angular profiles. We conclude that experiments designed to measure the SZ increment must have high enough angular resolution to identify background point sources while surveying enough of the sky to determine the SZ profile. Observations of the SZ increment with SCUBA, which has sufficient sensitivity and resolution for the task, should be straight forward.

astro-ph↗