MPIfR MPG

Bonn, Germany

MPIfR MPG

Bonn, Germany
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Molinari S.,National institute for astrophysics | Swinyard B.,Rutherford Appleton Laboratory | Bally J.,University of Colorado at Boulder | Barlow M.,University College London | And 96 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2010

Hi-GAL, the Herschel infrared Galactic Plane Survey, is an Open Time Key Project of the Herschel Space Observatory. It will make an unbiased photometric survey of the inner Galactic plane by mapping a 2° wide strip in the longitude range |ℓ| < 60° in five wavebands between 70 μm and 500 μm. The aim of Hi-GAL is to detect the earliest phases of the formation of molecular clouds and high-mass stars and to use the optimum combination of Herschel wavelength coverage, sensitivity, mapping strategy, and speed to deliver a homogeneous census of starforming regions and cold structures in the interstellar medium. The resulting representative samples will yield the variation of source temperature, luminosity, mass and age in a wide range of Galactic environments at all scales from massive YSOs in protoclusters to entire spiral arms, providing an evolutionary sequence for the formation of intermediate and high-mass stars. This information is essential to the formulation of a predictive global model of the role of environment and feedback in regulating the star-formation process. Such a model is vital to understanding star formation on galactic scales and in the early universe. Hi-GAL will also provide a science legacy for decades to come with incalculable potential for systematic and serendipitous science in a wide range of astronomical fields, enabling the optimum use of future major facilities such as JWST and ALMA. © 2010. The Astronomical Society of the Pacific.


Molinari S.,National institute for astrophysics | Swinyard B.,Rutherford Appleton Laboratory | Bally J.,University of Colorado at Boulder | Barlow M.,University College London | And 125 more authors.
Astronomy and Astrophysics | Year: 2010

We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key program that will map the inner Galactic plane of the Milky Way in 5 bands. We outline our data reduction strategy and present some science highlights on the two observed 2° × 2° tiles approximately centered at l = 30° and l = 59°. The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around AV ∼ 1 is exceeded for the regions in the l = 59° field; a AV value between 5 and 10 is found for the l = 30° field, likely due to the relatively higher distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm -2. Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows. © 2010 ESO.


Russeil D.,French National Center for Scientific Research | Pestalozzi M.,National institute for astrophysics | Mottram J.C.,University of Exeter | Bontemps S.,French National Center for Scientific Research | And 19 more authors.
Astronomy and Astrophysics | Year: 2011

Context. Hi-GAL, an open time key-project of the Herschel satellite, was awarded 343 hours observing time to carry out a 5-band photometric imaging survey at 70, 160, 250, 350, and 500 μmof a |b| ≥ 1° wide strip of the Milky Way Galactic plane in the longitude range -70° ≥ l ≥ 70°. Two 2° × 2° fields centred at l ≥ 30° and l ≥ 59° have been observed with the SPIRE and PACS photometric cameras in parallel mode during the Herschel science demonstration phase (SDP). From the images, compact sources are extracted for which the distance must be established in order to determine their physical properties. Aims. The aim of this paper is to present the distance determination strategy for the Hi-GAL compact sources. We illustrate this strategy for the two fields at l ≥ 30° and l ≥ 59°. Methods.The first step to determine the distance is to establish the LSR (local standard of rest) velocity of each compact source. The kinematic distance is then determined assuming a rotation curve for our Galaxy. To resolve the distance ambiguity for sources within the solar circle, we adopt a multiwavelength approach combining extinction maps, optical, and near infrared images, and velocity information from NH3, CO and HI data. When sources can be kinematically linked to optical Hii regions, the stellar distance of the exciting stars, when known, can be attributed to all linked sources. Results. In the two 2° × 2° SDP fields, 2678 compact sources have been identified and listed in the band-merged catalogue. About 93% of these sources have been assigned a radial velocity and distance. Conclusions. A multiwavelength approach is necessary to assign the correct velocity to sources (especially when CO spectra have a lot of features) and to determine the distance by solving the distance ambiguity. Also, several Hi-GAL sources seem to be in the interarm region. These sources have to be investigated with dedicated programme to be compared with sources located in the spiral arms. © 2011 ESO.


Molinari S.,National institute for astrophysics | Bally J.,University of Colorado at Boulder | Noriega-Crespo A.,California Institute of Technology | Compiegne M.,California Institute of Technology | And 42 more authors.
Astrophysical Journal Letters | Year: 2011

Thermal images of cold dust in the Central Molecular Zone of the Milky Way, obtained with the far-infrared cameras on board the Herschel satellite, reveal a ∼3 × 107 M⊙ ring of dense and cold clouds orbiting the Galactic center. Using a simple toy model, an elliptical shape having semi-major axes of 100 and 60pc is deduced. The major axis of this 100pc ring is inclined by about 40° with respect to the plane of the sky and is oriented perpendicular to the major axes of the Galactic Bar. The 100pc ring appears to trace the system of stable x 2 orbits predicted for the barred Galactic potential. Sgr A is displaced with respect to the geometrical center of symmetry of the ring. The ring is twisted and its morphology suggests a flattening ratio of 2 for the Galactic potential, which is in good agreement with the bulge flattening ratio derived from the 2MASS data. © 2011. The American Astronomical Society. All rights reserved.

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