M.-A. Miville-Deschênes

MIPSGAL: A Survey of the Inner Galactic Plane at 24 and 70 μm

MIPSGAL is a 278 deg^2 survey of the inner Galactic plane using the Multiband Infrared Photometer for Spitzer aboard the Spitzer Space Telescope. The survey field was imaged in two passbands, 24 and 70 μm with resolutions of 6″ and 18″, respectively. The survey was designed to provide a uniform, well-calibrated and well-characterized data set for general inquiry of the inner Galactic plane and as a longer-wavelength complement to the shorter-wavelength Spitzer survey of the Galactic plane: Galactic Plane Infrared Mapping Survey Extraordinaire. The primary science drivers of the current survey are to identify all high-mass (M > 5 M⊙) protostars in the inner Galactic disk and to probe the distribution, energetics, and properties of interstellar dust in the Galactic disk. The observations were planned to minimize data artifacts due to image latents at 24 μm and to provide full coverage at 70 μm. Observations at ecliptic latitudes within 15° of the ecliptic plane were taken at multiple epochs to help reject asteroids. The data for the survey were collected in three epochs, 2005 September–October, 2006 April, and 2006 October with all of the data available to the public. The estimated point-source sensitivities of the survey are 2 and 75 mJy (3 σ) at 24 and 70 μm, respectively. Additional data processing was needed to mitigate image artifacts due to bright sources at 24 μm and detector responsivity variations at 70 μm due to the large dynamic range of the Galactic plane. Enhanced data products including artifact-mitigated mosaics and point-source catalogs are being produced with the 24 μm mosaics already publicly available from the NASA/IPAC Infrared Science Archive. Some preliminary results using the enhanced data products are described.

IRIS: A New Generation of IRAS Maps

The Infrared Astronomical Satellite (IRAS) had a tremendous impact on many areas of modern astrophysics. In particular, it revealed the ubiquity of infrared cirrus that are a spectacular manifestation of the interstellar medium complexity but also an important foreground for observational cosmology. With the forthcoming Planck satellite there is a need for all-sky complementary data sets with arcminute resolution that can bring informations on specific foreground emissions that contaminate the cosmic microwave background radiation. With its ~4 resolution matching perfectly the high-frequency bands of Planck, IRAS is a natural data set to study the variations of dust properties at all scales. But the latest version of the images delivered by the IRAS team (the ISSA plates) suffer from calibration, zero level, and striping problems that can preclude its use, especially at 12 and 25 μm. In this paper we present how we proceeded to solve each of these problems and enhance significantly the general quality of the ISSA plates in the four bands (12, 25, 60, and 100 μm). This new generation of IRAS images, called IRIS, benefits from a better zodiacal light subtraction, from a calibration and zero level compatible with DIRBE, and from a better destriping. At 100 μm the IRIS product is also a significant improvement from the Schlegel et al. maps. IRIS keeps the full ISSA resolution, it includes well-calibrated point sources, and the diffuse emission calibration at scales smaller than 1° was corrected for the variation of the IRAS detector responsivity with scale and brightness. The uncertainty on the IRIS calibration and zero level is dominated by the uncertainty on the DIRBE calibration and on the accuracy of the zodiacal light model.

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 σe(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 > 1022 cm–2) and small enough to ensure a uniform dust temperature. We find σe(1200) is typically (2-4) × 10–25 cm2 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 σe(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.

Correlated anisotropies in the cosmic far-infrared background detected by the multiband imaging photometer for spitzer : Constraint on the bias

We report the detection of correlated anisotropies in the cosmic far-infrared background at 160 μm. We measure the power spectrum in the SWIRE Lockman Hole field. It reveals unambiguously a strong excess above cirrus and Poisson contributions, at spatial scales between 5 and 30, interpreted as the signature of infrared galaxy clustering. Using our model of infrared galaxy evolution, we derive a linear bias b = 1.74 ± 0.16. It is a factor 2 higher than the bias measured for the local IRAS galaxies. Our model indicates that galaxies dominating the 160 μm correlated anisotropies are at z ~ 1. This implies that infrared galaxies at high redshifts are biased tracers of mass, unlike in the local universe.

Probing the origin of the microwave anomalous foreground

The galactic anomalous microwave emission detected between 10 and 90 GHz is a major foreground to CMB fluctuations. Well correlated to dust emission at 100

SPIRE spectroscopy of the prototypical Orion Bar photodissociation region

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The physical properties of the dust in the RCW 120 HII region as seen by Herschel

m, the anomalous emission is interstellar but its origin is still debated. Some possible explanations relate it to dust: emission of spinning, small (nanometric) grains carrying a permanent electric dipole or magnetic fluctuations in larger (submicronic) grains. To probe the origin of the anomalous emission, we compare microwave data to dust IR emission and search for specific signatures predicted by models of spinning dust. For the anomalous emission, we use the 23 GHz all-sky map deduced from WMAP data by Miville-Deschenes et al. (2008). The dust emission is traced by IRAS data. Models show that spinning dust emission is little sensitive to the intensity of the radiation field (Go) for 10<nu<30 GHz while the corresponding mid-IR emission is proportional to Go. To test this behaviour in our comparison, we derive Go from the dust temperature maps of Schlegel et al. (1998). From all-sky maps, we show that the anomalous emission is better correlated to the emission of small grains (at 12

High resolution 21 cm mapping of the Ursa Major Galactic cirrus: Power spectra of the high-latitude HI gas

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EVIDENCE FOR DUST EVOLUTION WITHIN THE TAURUS COMPLEX FROM SPITZER IMAGES

m) than to that of big grains (at 100

On the Use of Fractional Brownian Motion Simulations to Determine the Three-dimensional Statistical Properties of Interstellar Gas

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