Astronomy and Astrophysics Letters dedicated to ISO

ISOCAM Mapping of the Whirlpool Galaxy (M 51)

M. Sauvage J. Blommaert F. Boulanger C.J. Cesarsky D.A. Cesarsky F.X. D\'esert D. Elbaz P. Gallais G. Joncas L. Metcalfe K. Okumura S. Ott R. Siebenmorgen J.L. Starck D. Tran L. Vigroux


We have obtained the first images of the 6.75 and 15 microns continuum emission in the Whirlpool galaxy with ISOCAM, the infrared camera of the ISO. These data reveal the well-developed, spiral arms of the galaxy, in addition to diffuse emission between arms and in the outer regions of the disk. There is a striking correspondence with the 15 microns emission and the Halpha emission over the galaxy. We tighten this link by looking at the properties of the individual HII regions and show that the 15 microns emission traces massive star formation and is not affected by extinction as is Halpha. The data show systematic mid-infrared color variations perpendicular to the arms, which we interpret as two distinct dust components contributing to the mid-infrared emission. We examine the implication of these color variations in light of our current understanding of dust at these wavelength.

Galaxies: individual: M~51 -- Galaxies: ISM -- Galaxies: spiral -- Infrared: interstellar: continuum -- Stars: formation

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