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Molecular and atomic gas in the Local Group galaxy M 33

P. Gratier ; J. Braine ; N. J. Rodriguez-Fernandez ; K. F. Schuster ; C. Kramer ; E. M. Xilouris ; F. S. Tabatabaei ; C. Henkel ; E. Corbelli ; F. Israel ; P. P. van der Werf ; D. Calzetti ; S. Garcia-Burillo ; A. Sievers ; F. Combes ; T. Wiklind ; N. Brouillet ; F. Herpin ; S. Bontemps ; Susanne Aalto (Institutionen för radio- och rymdvetenskap, Radioastronomi och astrofysik) ; B. Koribalski ; F. van der Tak ; M. C. Wiedner ; M. Rollig ; B. Mookerjea
Astronomy & Astrophysics (0004-6361). Vol. 522 (2010),
[Artikel, refereegranskad vetenskaplig]

We present high-resolution large-scale observations of the molecular and atomic gas in the Local Group galaxy M 33. The observations were carried out using the HEterodyne Receiver Array (HERA) at the 30 m IRAM telescope in the CO(2-1) line, achieving a resolution of 12 '' x 2.6 km s(-1), enabling individual giant molecular clouds (GMCs) to be resolved. The observed region is 650 square arcminutes mainly along the major axis and out to a radius of 8.5 kpc, and covers entirely the 2' x 40' radial strip observed with the HIFI and PACS Spectrometers as part of the HERM33ES Herschel key program. The achieved sensitivity in main-beam temperature is 20-50 mK at 2.6 km s(-1) velocity resolution. The CO(2-1) luminosity of the observed region is 1.7 +/- 0.1 x 10(7) K km s(-1) pc(2) and is estimated to be 2.8 +/- 0.3 x 10(7) K km s(-1) pc(2) for the entire galaxy, corresponding to H-2 masses of 1.9 x 10(8) M-circle dot and 3.3 x 10(8) M-circle dot respectively (including He), calculated with N(H-2)/ICO(1-0) twice the Galactic value due to the half-solar metallicity of M 33. The HI 21 cm VLA archive observations were reduced, and the mosaic was imaged and cleaned using the multi-scale task in the CASA software package, yielding a series of datacubes with resolutions ranging from 5 '' to 25 ''. The HI mass within a radius of 8.5 kpc is estimated to be 1.4 x 10(9) M-circle dot. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9 +/- 0.1 kpc whereas the atomic gas surface density is constant at Sigma(HI) = 6 +/- 2 M-circle dot pc(-2) deprojected to face-on. For an N(H-2)/ICO(1-0) conversion factor twice that of the Milky Way, the central kiloparsec H-2 surface density is Sigma(H2) = 8.5 +/- 0.2 M-circle dot pc(-2). The star formation rate per unit molecular gas (SF efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to H-alpha and FIR brightness, is constant with radius. The SFE, with a N(H-2)/ICO(1-0) factor twice galactic, appears 2-4 times greater than for large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8 kpc from the galaxy center, are presented.

Nyckelord: galaxies: individual: M 33, Local Group, galaxies: evolution, galaxies:, ISM, ISM: clouds, stars: formation, star-formation efficiency, radio-continuum survey, stellar population, formation history, far-ultraviolet, spiral galaxies, co emission, m33, clouds, metallicity



Denna post skapades 2010-12-27. Senast ändrad 2014-09-02.
CPL Pubid: 131835

 

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Institutioner (Chalmers)

Institutionen för radio- och rymdvetenskap, Radioastronomi och astrofysik (2005-2010)

Ämnesområden

Astronomi, astrofysik och kosmologi

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