Schönau-Berzdorf, Germany
Schönau-Berzdorf, Germany

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Wang J.,CSIRO | Serra P.,CSIRO | Jozsa G.I.G.,SKA South Africa Radio Astronomy Research Group | Jozsa G.I.G.,Rhodes University | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

Using data taken as part of the Bluedisk project, we study the connection between neutral hydrogen (HI) in the environment of spiral galaxies and that in the galaxies themselves. We measure the total HI mass present in the environment in a statistical way by studying the distribution of noise peaks in the HI data cubes obtained for 40 galaxies observed with Westerbork Synthesis Radio Telescope. We find that galaxies whose HI mass fraction is high relative to standard scaling relations have an excess HI mass in the surrounding environment as well. Gas in the environment consists of gas clumps which are individually below the detection limit of our HI data. These clumps may be hosted by small satellite galaxies and/or be the high-density peaks of a more diffuse gas distribution in the intergalactic medium. We interpret this result as an indication for a picture in which the HI-rich central galaxies accrete gas from an extended gas reservoir present in their environment. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Xilouris E.M.,National institute for astrophysics | Tabatabaei F.S.,Max Planck Institute for Astronomy | Boquien M.,French National Center for Scientific Research | Kramer C.,Instituto Radioastronomia Milimetrica IRAM | And 26 more authors.
Astronomy and Astrophysics | Year: 2012

In the framework of the open-time key program "Herschel M 33 extended survey (HerM33es)", we study the far-infrared emission from the nearby spiral galaxy M 33 in order to investigate the physical properties of the dust such as its temperature and luminosity density across the galaxy. Taking advantage of the unique wavelength coverage (100, 160, 250, 350, and 500 μm) of the Herschel Space Observatory and complementing our dataset with Spitzer-IRAC 5.8 and 8 μm and Spitzer-MIPS 24 and 70 μm data, we construct temperature and luminosity density maps by fitting two modified blackbodies of a fixed emissivity index of 1.5. We find that the "cool" dust grains are heated to temperatures of between 11 K and 28 K, with the lowest temperatures being found in the outskirts of the galaxy and the highest ones both at the center and in the bright HII regions. The infrared/submillimeter total luminosity (5-1000 μm) is estimated to be 1.9 × 10 9 +4.0×108 -4.4×10 8 L ·. Fifty-nine percent of the total infrared/submillimeter luminosity of the galaxy is produced by the "cool" dust grains (∼15 K), while the remaining 41% is produced by "warm" dust grains (~55 K). The ratio of the cool-to-warm dust luminosity is close to unity (within the computed uncertainties), throughout the galaxy, with the luminosity of the cool dust being slightly higher at the center than the outer parts of the galaxy. Decomposing the emission of the dust into two components (one emitted by the diffuse disk of the galaxy and one emitted by the spiral arms), we find that the fraction of the emission from the disk in the mid-infrared (24 μm) is 21%, while it gradually rises up to 57% in the submillimeter (500 μm). We find that the bulk of the luminosity comes from the spiral arm network that produces 70% of the total luminosity of the galaxy with the rest coming from the diffuse dust disk. The "cool" dust inside the disk is heated to temperatures in a narrow range between 18 K and 15 K (going from the center to the outer parts of the galaxy). © 2012 ESO.

Serra P.,Netherlands Institute for Radio Astronomy | Jurek R.,CSIRO | Fler L.,Argelander Institute Fr Astronomie
Publications of the Astronomical Society of Australia | Year: 2012

We describe a simple method to determine the reliability of source finders based on the detection of sources with both positive and negative total flux. Under the assumption that the noise is symmetric and that real sources have positive total flux, negative detections can be used to assign to each positive detection a probability of being real. We discuss this method in the context of upcoming, interferometric Hi surveys. Journal compilation © Australian Mammal Society 2012.

Fler L.,Argelander Institute Fr Astronomie | Winkel B.,Max Planck Institute for Radio Astronomy
Publications of the Astronomical Society of Australia | Year: 2012

Today, image denoising by thresholding of wavelet coefficients is a commonly used tool for 2D image enhancement. Since the data product of spectroscopic imaging surveys has two spatial dimensions and one spectral dimension, the techniques for denoising have to be adapted to this change in dimensionality. In this paper we will review the basic method of denoising data by thresholding wavelet coefficients and implement a 2D1D wavelet decomposition to obtain an efficient way of denoising spectroscopic data cubes. We conduct different simulations to evaluate the usefulness of the algorithm as part of a source finding pipeline. Journal compilation © Australian Mammal Society 2012.

Braine J.,University of Bordeaux 1 | Gratier P.,University of Bordeaux 1 | Kramer C.,Instituto Radioastronomia Milimetrica IRAM | Xilouris E.M.,National institute for astrophysics | And 22 more authors.
Astronomy and Astrophysics | Year: 2010

We present an analysis of the first space-based far-IR-submm observations of M 33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M 33 is a first step towards young low-metallicity galaxies where the submm may be able to provide an alternative to CO mapping to measure their H2 content. In this Letter, we measure the dust emission cross-section σ using SPIRE and recent CO and H i observations; a variation in σ is present from a near-solar neighborhood cross-section to about half-solar with the maximum being south of the nucleus. Calculating the total H column density from the measured dust temperature and cross-section, and then subtracting the H i column, yields a morphology similar to that observed in CO. The H2/H i mass ratio decreases from about unity to well below 10% and is about 15% averaged over the optical disk. The single most important observation to reduce the potentially large systematic errors is to complete the CO mapping of M 33. © ESO 2010.

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