Lorenzo Moncelsi

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 μm in the rest frame. At 1 ≤ z ≤ 4, the peak is redshifted to wavelengths between 200 and 500 μm. 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 μm. Combining our results at 500 μm with those at 24 μm, we determine that all of the FIRB comes from individual galaxies, with galaxies at z ≥ 1.2 accounting for 70% of it. As expected, at the longest wavelengths the signal is dominated by ultraluminous galaxies at z > 1.

BLAST: RESOLVING THE COSMIC SUBMILLIMETER BACKGROUND

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has made 1 deg2, 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 μm sources from the Far-Infrared Deep Extragalactic Legacy Survey, 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 μm, respectively. These numbers are more precise than previous estimates of the cosmic infrared background (CIB) and are consistent with 24 μm-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 μm. At all BLAST wavelengths, the relative intensity of high-z sources is higher for 24 μm-faint sources than that for 24 μm-bright sources. Galaxies identified as active galactic nuclei (AGNs) by their Infrared Array Camera colors are 1.6-2.6 times brighter than the average population at 250-500 μm, consistent with what is found for X-ray-selected AGNs. BzK-selected galaxies are found to be moderately brighter than typical 24 μm-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.

BLAST: the far‐infrared/radio correlation in distant galaxies

We investigate the correlation between far-infrared (FIR) and radio luminosities in distant galaxies, a lynchpin of modern astronomy. We use data from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), Spitzer, the Large Apex BOlometer CamerA (LABOCA), the Very Large Array and the Giant Metre-wave Radio Telescope (GMRT) in the Extended Chandra Deep Field South (ECDFS). For a catalogue of BLAST 250-μm-selected galaxies, we remeasure the 70–870-μm flux densities at the positions of their most likely 24-μm counterparts, which have a median [interquartile] redshift of 0.74 [0.25, 1.57]. From these, we determine the monochromatic flux density ratio, q_(250)(= log_(10) [ S_(250 μm)/S_(1400 MHz)]), and the bolometric equivalent, q_(IR). At z ≈ 0.6 , where our 250-μm filter probes rest-frame 160-μm emission, we find no evolution relative to q_(160) for local galaxies. We also stack the FIR and submm images at the positions of 24-μm- and radio-selected galaxies. The difference between q_(IR) seen for 250-μm- and radio-selected galaxies suggests that star formation provides most of the IR luminosity in ≲100-μJy radio galaxies, but rather less for those in the mJy regime. For the 24-μm sample, the radio spectral index is constant across 0 < z < 3 , but q_(IR) exhibits tentative evidence of a steady decline such that q_(IR) ∝ (1 +z)^(−0.15±0.03) – significant evolution, spanning the epoch of galaxy formation, with major implications for techniques that rely on the FIR/radio correlation. We compare with model predictions and speculate that we may be seeing the increase in radio activity that gives rise to the radio background.

A joint analysis of BLAST 250–500 μm and LABOCA 870 μm observations in the Extended Chandra Deep Field-South

We present a joint analysis of the overlapping Balloon-borne Large Aperture Submillimetre Telescope (BLAST) 250, 350, 500 μm, and LABOCA 870 μm observations [from the LABOCA ECDFS Submm Survey (LESS) survey] of the Extended Chandra Deep Field-South. Out to z∼ 3, the BLAST filters sample near the peak wavelength of thermal far-infrared (FIR) emission from galaxies (rest-frame wavelengths ∼60–200 μm), primarily produced by dust heated through absorption in star-forming clouds. However, identifying counterparts to individual BLAST peaks is very challenging, given the large beams [full-width at half-maximum (FWHM) 36–60 arcsec]. In contrast, the ground-based 870 μm observations have a significantly smaller 19 arcsec FWHM beam, and are sensitive to higher redshifts (z∼ 1–5, and potentially beyond) due to the more favourable negative K-correction. We use the LESS data, as well as deep Spitzer and VLA imaging, to identify 118 individual sources that produce significant emission in the BLAST bands. We characterize the temperatures and FIR luminosities for a subset of 69 sources which have well-measured submillimetre (submm) spectral energy distributions (SEDs) and redshift measurements out to z∼ 3. For flux-limited sub-samples in each BLAST band, and a dust emissivity index β= 2.0, we find a median temperature T= 30 K (all bands) as well as median redshifts: z= 1.1 (interquartile range 0.2–1.9) for S250 > 40 mJy; z= 1.3 (interquartile range 0.6–2.1) for S350 > 30 mJy; and z= 1.6 (interquartile range 1.3–2.3) for S500 > 20 mJy. Taking into account the selection effects for our survey (a bias towards detecting lower-temperature galaxies), we find no evidence for evolution in the local FIR–temperature correlation out to z∼ 2.5. Comparing with star-forming galaxy SED templates, about 8 per cent of our sample appears to exhibit significant excesses in the radio and/or mid-IR, consistent with those sources harbouring active galactic nuclei (AGN). Since our statistical approach differs from most previous studies of submm galaxies, we describe the following techniques in two appendices: our ‘matched filter’ for identifying sources in the presence of point-source confusion; and our approach for identifying counterparts using likelihood ratios. This study is a direct precursor to future joint FIR/submm surveys, for which we outline a potential identification and SED measurement strategy.

BLAST: A Far-Infrared Measurement of the History of Star Formation

We directly measure redshift evolution in the mean physical properties (far-infrared luminosity, temperature, and mass) of the galaxies that produce the cosmic infrared background (CIB), using measurements from the Balloon-borne Large Aperture Submillimeter Telescope (BLAST), and Spitzer which constrain the CIB emission peak. This sample is known to produce a surface brightness in the BLAST bands consistent with the full CIB, and photometric redshifts are identified for all of the objects. We find that most of the 70 μm background is generated at z lsim 1 and the 500 μm background generated at z gsim 1. A significant growth is observed in the mean luminosity from ~109-1012 L sun, and in the mean temperature by 10 K, from redshifts 0 < z < 3. However, there is only weak positive evolution in the comoving dust mass in these galaxies across the same redshift range. We also measure the evolution of the far-infrared luminosity density, and the star formation rate history for these objects, finding good agreement with other infrared studies up to z ~ 1, exceeding the contribution attributed to optically selected galaxies.

THE HERSCHEL STRIPE 82 SURVEY (HERS): MAPS AND EARLY CATALOG †

We present the first set of maps and band-merged catalog from the Herschel Stripe 82 Survey (HerS). Observations at 250, 350, and 500 μm were taken with the Spectral and Photometric Imaging Receiver instrument aboard the Herschel Space Observatory. HerS covers 79 deg^2 along the SDSS Stripe 82 to an average depth of 13.0, 12.9, and 14.8 mJy beam–1 (including confusion) at 250, 350, and 500 μm, respectively. HerS was designed to measure correlations with external tracers of the dark matter density field—either point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing)—in order to measure the bias and redshift distribution of intensities of infrared-emitting dusty star-forming galaxies and active galactic nuclei. By locating HerS in Stripe 82, we maximize the overlap with available and upcoming cosmological surveys. The band-merged catalog contains 3.3 × 10^4 sources detected at a significance of ≳ 3σ (including confusion noise). The maps and catalog are available at http://www.astro.caltech.edu/hers/.

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 ≥5σ over ~9 deg2 centered on the Chandra Deep Field South by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) at 250, 350, and 500 μm. We have matched 114 of these counterparts to optical sources with previously derived photometric redshifts and fitted spectral energy distributions to the BLAST fluxes and fluxes at 70 and 160 μm acquired with the Spitzer Space Telescope. In this way, we have constrained dust temperatures, total far-infrared/submillimeter 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 submillimeter sources detected in surveys conducted at 850 μm. 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 multiwavelength catalog of ≥5σ BLAST sources contained within the complete ~9 deg2 survey area.

BLAST: THE REDSHIFT SURVEY

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has recently surveyed sime8.7 deg2 centered on Great Observatories Origins Deep Survey-South at 250, 350, and 500 μm. In Dye et al., we presented the catalog of sources detected at 5σ in at least one band in this field and the probable counterparts to these sources in other wavebands. In this paper, we present the results of a redshift survey in which we succeeded in measuring redshifts for 82 of these counterparts. The spectra show that the BLAST counterparts are mostly star-forming galaxies but not extreme ones when compared to those found in the Sloan Digital Sky Survey. Roughly one quarter of the BLAST counterparts contain an active nucleus. We have used the spectroscopic redshifts to carry out a test of the ability of photometric redshift methods to estimate the redshifts of dusty galaxies, showing that the standard methods work well even when a galaxy contains a large amount of dust. We have also investigated the cases where there are two possible counterparts to the BLAST source, finding that in at least half of these there is evidence that the two galaxies are physically associated, either because they are interacting or because they are in the same large-scale structure. Finally, we have made the first direct measurements of the luminosity function in the three BLAST bands. We find strong evolution out to z = 1, in the sense that there is a large increase in the space density of the most luminous galaxies. We have also investigated the evolution of the dust-mass function, finding similar strong evolution in the space density of the galaxies with the largest dust masses, showing that the luminosity evolution seen in many wavebands is associated with an increase in the reservoir of interstellar matter in galaxies.

New artificial dielectric metamaterial and its application as a terahertz antireflection coating

We describe a novel artificial dielectric material that has applications at millimeter and submillimeter wavelengths. The material is manufactured from layers of metal mesh patterned onto thin polypropylene sheets, which are then bonded together using a hot pressing process to provide planar rugged discs that can be reliably cycled to cryogenic temperatures. The refractive index of this material can be tuned by adjusting the geometry and spacing of the metal mesh layers. We demonstrate its usage by designing and characterizing a broadband antireflection coating for a Z-cut crystalline quartz plate. The coating was fabricated and applied to the quartz using the hot press technique and characterized using a Fourier transform spectrometer. The performance is shown to be in good agreement with a high frequency structure simulator and transmission line modeling results.

Lupus I Observations from the 2010 Flight of the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was created by adding polarimetric capability to the BLAST experiment that was flown in 2003, 2005, and 2006. BLASTPol inherited BLASTs 1.8 m primary and its Herschel/SPIRE heritage focal plane that allows simultaneous observation at 250, 350, and 500 μm. We flew BLASTPol in 2010 and again in 2012. Both were long duration Antarctic flights. Here we present polarimetry of the nearby filamentary dark cloud Lupus I obtained during the 2010 flight. Despite limitations imposed by the effects of a damaged optical component, we were able to clearly detect submillimeter polarization on degree scales. We compare the resulting BLASTPol magnetic field map with a similar map made via optical polarimetry. (The optical data were published in 1998 by J. Rizzo and collaborators.) The two maps partially overlap and are reasonably consistent with one another. We compare these magnetic field maps to the orientations of filaments in Lupus I, and we find that the dominant filament in the cloud is approximately perpendicular to the large-scale field, while secondary filaments appear to run parallel to the magnetic fields in their vicinities. This is similar to what is observed in Serpens South via near-IR polarimetry, and consistent with what is seen in MHD simulations by F. Nakamura and Z. Li.