EDP Sciences
Free Access
Volume 404, Number 2, June III 2003
Page(s) 495 - 504
Section Galactic structure and dynamics
DOI https://doi.org/10.1051/0004-6361:20030479
Published online 02 June 2003

A&A 404, 495-504 (2003)
DOI: 10.1051/0004-6361:20030479

CI and CO in the nearby spiral galaxies IC 342 and Maffei 2

F. P. Israel1 and F. Baas1, 2

1  Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
2  Joint Astronomy Centre, 660 N. A'ohoku Pl., Hilo, Hawaii, 96720, USA

(Received 19 February 2003 / Accepted 27 March 2003)

We present J=2-1, J=3-2, J=4-3 ${\rm ^{12}CO}$ and 492 GHz [CI] maps as well as J=2-1 and J=3-2 ${\rm ^{13}CO}$ measurements of the central regions in the nearby Sc galaxies IC 342 and Maffei 2. In both galaxies, the distribution of CO and [CI] is strongly concentrated towards the center. These centers harbour modest starbursts. Both galaxies have nearly identical ${\rm ^{12}CO}$ transitional ratios but the relative intensities of their ${\rm ^{13}CO}$ and [CI] emission lines differ significantly. The observed sets of line intensities require modelling with a multi-component molecular gas. In both galaxies, a dense component must be present ( $n({\rm H_{2}}) \approx 10^{4} {-} 10^{5}~{\rm cm^{-3}}$) with kinetic temperatures $T_{\rm kin} = 10{-}20$ K (IC 342) or 20-60 K (Maffei 2), as well as a less dense (IC 342: a few hundred $~{\rm cm^{-3}}$ at most; Maffei 2: $\approx 3 \times 10^{3}~{\rm cm^{-3}}$) and hotter ( $T_{\rm kin}
= 100{-}150$  K) component. In both galaxies, neutral and ionized atomic carbon amounts are between 1.5 and 2.5 times those of CO. In both starburst centers about half to two thirds of the molecular gas mass is associated with the hot PDR phase. The center of IC 342 contains within R = 0.25 kpc an (atomic and molecular) gas mass of 1 $\times 10^{7} ~M_{\odot}$ and a peak face-on gas mass density of about 70 $~M_{\odot}$ pc -2. For Maffei 2 these numbers are less clearly defined, mainly because of uncertainties in its distance and carbon abundance. We find a gass mass $M_{\rm gas}
\geq 0.5 \times 10^{7} ~M_{\odot}$ , and a peak face-on gas mass density of about 35 $~M_{\odot}$ pc -2.

Key words: galaxies: individual: IC 342; Maffei 2 -- galaxies: ISM -- radio lines: galaxies -- ISM: molecules

Offprint request: F. P. Israel, israel@strw.leidenuniv.nl

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© ESO 2003

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