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Published July 2010 | Published
Journal Article Open

PACS and SPIRE photometer maps of M 33: First results of the HERschel M 33 Extended Survey (HERM33ES)

Abstract

Context. Within the framework of the HERM33ES key program, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M 33, exploiting the high resolution and sensitivity of Herschel. Aims. We use PACS and SPIRE maps at 100, 160, 250, 350, and 500 μm wavelength, to study the variation of the spectral energy distributions (SEDs) with galacto-centric distance. Methods. Detailed SED modeling is performed using azimuthally averaged fluxes in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance. Simple isothermal and two-component grey body models, with fixed dust emissivity index, are fitted to the SEDs between 24 μm and 500 μm using also MIPS/Spitzer  data, to derive first estimates of the dust physical conditions. Results. The far-infrared and submillimeter maps reveal the branched, knotted spiral structure of M 33. An underlying diffuse disk is seen in all SPIRE maps (250–500 μm). Two component fits to the SEDs agree better than isothermal models with the observed, total and radially averaged flux densities. The two component model, with β fixed at 1.5, best fits the global and the radial SEDs. The cold dust component clearly dominates; the relative mass of the warm component is less than 0.3% for all the fits. The temperature of the warm component is not well constrained and is found to be about 60 K ± 10 K. The temperature of the cold component drops significantly from ~24 K in the inner 2 kpc radius to 13 K beyond 6 kpc radial distance, for the best fitting model. The gas-to-dust ratio for β = 1.5, averaged over the galaxy, is higher than the solar value by a factor of 1.5 and is roughly in agreement with the subsolar metallicity of M 33.

Additional Information

© 2010 ESO. Received 31 March 2010; Accepted 3 May 2010; Published online 16 July 2010. Herschel  is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. We would like to thank all those who helped us processing the PACS and SPIRE data. In particular we would like to acknowledge support from Pierre Royer, Bruno Altieri, Pat Morris, Bidushi Bhattacharya, Marc Sauvage, Michael Pohlen, Pierre Chanial, George Bendo. MR acknowledges the MC-IEF within the 7th European Community Framework Programme.

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August 22, 2023
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