Deconvolution of Images from BLAST 2005: Insight into the K3-50 and IC 5146 Star-forming Regions

We present an implementation of the iterative flux-conserving Lucy-Richardson (L-R) deconvolution method of image restoration for maps produced by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). Compared to the direct Fourier transform method of deconvolution, the L-R operation restores images with better-controlled background noise and increases source detectability. Intermediate iterated images are useful for studying extended diffuse structures, while the later iterations truly enhance point sources to near the designed diffraction limit of the telescope. The L-R method of deconvolution is efficient in resolving compact sources in crowded regions while simultaneously conserving their respective flux densities. We have analyzed its performance and convergence extensively through simulations and cross-correlations of the deconvolved images with available high-resolution maps. We present new science results from two BLAST surveys, in the Galactic regions K3-50 and IC 5146, further demonstrating the benefits of performing this deconvolution. We have resolved three clumps within a radius of 4'.5 inside the star-forming molecular cloud containing K3-50. Combining the well-resolved dust emission map with available multi-wavelength data, we have constrained the spectral energy distributions (SEDs) of five clumps to obtain masses (M), bolometric luminosities (L), and dust temperatures (T). The L-M diagram has been used as a diagnostic tool to estimate the evolutionary stages of the clumps. There are close relationships between dust continuum emission and both 21 cm radio continuum and ^(12)CO molecular line emission. The restored extended large-scale structures in the Northern Streamer of IC 5146 have a strong spatial correlation with both SCUBA and high-resolution extinction images. A dust temperature of 12 K has been obtained for the central filament. We report physical properties of ten compact sources, including six associated protostars, by fitting SEDs to multi-wavelength data. All of these compact sources are still quite cold (typical temperature below ~ 16 K) and are above the critical Bonner-Ebert mass. They have associated low-power young stellar objects. Further evidence for starless clumps has also been found in the IC 5146 region

Correlations in the (Sub)millimeter Background from ACT × BLAST

We present measurements of the auto- and cross-frequency correlation power spectra of the cosmic (sub)millimeter background at 250, 350, and 500 μm (1200, 860, and 600 GHz) from observations made with the Balloon-borne Large Aperture Submillimeter Telescope (BLAST); and at 1380 and 2030 μm (218 and 148 GHz) from observations made with the Atacama Cosmology Telescope (ACT). The overlapping observations cover 8.6 deg^2 in an area relatively free of Galactic dust near the south ecliptic pole. The ACT bands are sensitive to radiation from the cosmic microwave background, to the Sunyaev-Zel'dovich effect from galaxy clusters, and to emission by radio and dusty star-forming galaxies (DSFGs), while the dominant contribution to the BLAST bands is from DSFGs. We confirm and extend the BLAST analysis of clustering with an independent pipeline and also detect correlations between the ACT and BLAST maps at over 25σ significance, which we interpret as a detection of the DSFGs in the ACT maps. In addition to a Poisson component in the cross-frequency power spectra, we detect a clustered signal at 4σ, and using a model for the DSFG evolution and number counts, we successfully fit all of our spectra with a linear clustering model and a bias that depends only on redshift and not on scale. Finally, the data are compared to, and generally agree with, phenomenological models for the DSFG population. This study demonstrates the constraining power of the cross-frequency correlation technique to constrain models for the DSFGs. Similar analyses with more data will impose tight constraints on future models

Evidence for Environmental Changes in the Submillimeter Dust Opacity

The submillimeter opacity of dust in the diffuse interstellar medium (ISM) in the Galactic plane has been quantified using a pixel-by-pixel correlation of images of continuum emission with a proxy for column density. We used multi-wavelength continuum data: three Balloon-borne Large Aperture Submillimeter Telescope bands at 250, 350, and 500 μm and one IRAS band at 100 μm. The proxy is the near-infrared color excess, E(J – K_s), obtained from the Two Micron All Sky Survey. Based on observations of stars, we show how well this color excess is correlated with the total hydrogen column density for regions of moderate extinction. The ratio of emission to column density, the emissivity, is then known from the correlations, as a function of frequency. The spectral distribution of this emissivity can be fit by a modified blackbody, whence the characteristic dust temperature T and the desired opacity σ_e(1200) at 1200 GHz or 250 μm can be obtained. We have analyzed 14 regions near the Galactic plane toward the Vela molecular cloud, mostly selected to avoid regions of high column density (N_H > 10^(22) cm^(–2)) and small enough to ensure a uniform dust temperature. We find σ_e(1200) is typically (2-4) × 10^(–25) cm^2 H^(–1) and thus about 2-4 times larger than the average value in the local high Galactic latitude diffuse atomic ISM. This is strong evidence for grain evolution. There is a range in total power per H nucleon absorbed (and re-radiated) by the dust, reflecting changes in the strength of the interstellar radiation field and/or the dust absorption opacity. These changes in emission opacity and power affect the equilibrium T, which is typically 15 K, colder than at high latitudes. Our analysis extends, to higher opacity and lower temperature, the trend of increasing σ_e(1200) with decreasing T that was found at high latitudes. The recognition of changes in the emission opacity raises a cautionary flag because all column densities deduced from dust emission maps, and the masses of compact structures within them, depend inversely on the value adopted

Submillimetre observations of galaxy clusters with the BLAST: the star formation activity in Abell 3112

We present observations at 250, 350 and 500 μm of the nearby galaxy cluster Abell 3112 (z = 0.075) carried out with the Balloon-borne Large Aperture Submillimeter Telescope. Five cluster members are individually detected as bright submillimetre (submm) sources. Their far-infrared spectral energy distributions and optical colours identify them as normal star-forming galaxies of high mass, with globally evolved stellar populations. They all have (B−R) colours of 1.38 ± 0.08, transitional between the blue, active population and the red, evolved galaxies that dominate the cluster core. We stack to estimate the mean submm emission from all cluster members, which is determined to be 16.6 ± 2.5, 6.1 ± 1.9 and 1.5 ± 1.3 mJy at 250, 350 and 500 μm, respectively. Stacking analyses of the submm emission of cluster members reveal trends in the mean far-infrared luminosity with respect to clustercentric radius and K_(S-)band magnitude. We find that a large fraction of submm emission comes from the boundary of the inner, virialized region of the cluster, at clustercentric distances around R_(500). Stacking also shows that the bulk of the submm emission arises in intermediate-mass galaxies with K_S magnitude ~1 mag fainter than the characteristic magnitude K^*_s. The results and constraints obtained in this work will provide a useful reference for the forthcoming surveys to be conducted on galaxy clusters by Herschel

The Balloon-Borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 10 deg^2 Survey of Star Formation in Cygnus X

We present Cygnus X in a new multi-wavelength perspective based on an unbiased BLAST survey at 250, 350, and 500 μm, combined with rich data sets for this well-studied region. Our primary goal is to investigate the early stages of high-mass star formation. We have detected 184 compact sources in various stages of evolution across all three BLAST bands. From their well-constrained spectral energy distributions, we obtain the physical properties mass, surface density, bolometric luminosity, and dust temperature. Some of the bright sources reaching 40 K contain well-known compact H_(II) regions. We relate these to other sources at earlier stages of evolution via the energetics as deduced from their position in the luminosity-mass (L-M) diagram. The BLAST spectral coverage, near the peak of the spectral energy distribution of the dust, reveals fainter sources too cool (~10 K) to be seen by earlier shorter-wavelength surveys like IRAS. We detect thermal emission from infrared dark clouds and investigate the phenomenon of cold "starless cores" more generally. Spitzer images of these cold sources often show stellar nurseries, but these potential sites for massive star formation are "starless" in the sense that to date there is no massive protostar in a vigorous accretion phase. We discuss evolution in the context of the L-M diagram. Theory raises some interesting possibilities: some cold massive compact sources might never form a cluster containing massive stars, and clusters with massive stars might not have an identifiable compact cold massive precursor

The Early Universe was Dust-Rich and Extremely Hot

We investigate the dust properties and star-formation signature of galaxies in the early universe by stacking 111,227 objects in the recently released COSMOS catalogue on maps at wavelengths bracketing the peak of warmed dust emission. We find an elevated far-infrared luminosity density to redshift 10, indicating abundant dust in the early universe. We further find an increase of dust temperature with redshift, reaching ~ 119 +- 7 K at z ~ 9, suggesting either the presence of silicate rich dust originating from Population II stars, or sources of heating beyond simply young hot stars. Lastly, we try to understand how these objects have been missed in previous surveys, and how to design observations to target them. All code, links to the data, and instructions to reproduce this research in full is located at https://github.com/marcoviero/simstack3/

A measurement of the millimetre emission and the Sunyaev–Zel'dovich effect associated with low-frequency radio sources

We present a statistical analysis of the millimetre-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev–Zel'dovich (SZ) effect associated with the haloes that host them. We stack data at 148, 218 and 277 GHz from the Atacama Cosmology Telescope at the positions of a large sample of radio AGN selected at 1.4 GHz. The thermal SZ effect associated with the haloes that host the AGN is detected at the 5σ level through its spectral signature, representing a statistical detection of the SZ effect in some of the lowest mass haloes (average M_(200) ≈ 10^(13) M⊙ h^(−1)_(70) studied to date. The relation between the SZ effect and mass (based on weak lensing measurements of radio galaxies) is consistent with that measured by Planck for local bright galaxies. In the context of galaxy evolution models, this study confirms that galaxies with radio AGN also typically support hot gaseous haloes. Adding Herschel observations allows us to show that the SZ signal is not significantly contaminated by dust emission. Finally, we analyse the contribution of radio sources to the angular power spectrum of the cosmic microwave background

A Foreground Masking Strategy for [CII] Intensity Mapping Experiments Using Galaxies Selected by Stellar Mass and Redshift

Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by the energetic photons emitted from the first galaxies. The [CII] 158$\mu$m fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star-formation activity. However, [CII] intensity maps at $6 \lesssim z \lesssim 8$ are contaminated by interloping CO rotational line emission ($3 \leq J_{\rm upp} \leq 6$) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming [CII] intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at $z 10^{8}\,\rm M_{\rm \odot}$ selected in $K$-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment (TIME), we find that masking out the "voxels" (spectral-spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a $z$-dependent criterion $m^{\rm AB}_{\rm K} \lesssim 22$ (or $M_{*} \gtrsim 10^{9} \,\rm M_{\rm \odot}$) at $z < 1$ and makes a [CII]/CO$_{\rm tot}$ power ratio of $\gtrsim 10$ at $k=0.1$ $h$/Mpc achievable, at the cost of a moderate $\lesssim 8\%$ loss of total survey volume.Comment: 14 figures, 4 tables, re-submitted to ApJ after addressing reviewer's comments. Comments welcom