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Issue A&A
Volume 408, Number 2, September III 2003
Page(s) 493 - 498
Section Galactic structure and dynamics
DOI 10.1051/0004-6361:20031009



A&A 408, 493-498 (2003)
DOI: 10.1051/0004-6361:20031009

Cold dust and its relation to molecular gas in the dwarf irregular galaxy NGC 4449

C. Böttner, U. Klein and A. Heithausen

Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
(Received 5 November 2002 / Accepted 24 June 2003)

Abstract
We present observations of the dwarf irregular galaxy NGC 4449 at 850 $\mu$m and 450  $\mu$m obtained with SCUBA at the JCMT. The distribution of the cold dust agrees well with that of the CO and H $\alpha$ emission. To explain the integrated mm- through far-infrared continuum spectrum three dust components are required, with temperatures of 16 K, 39 K and 168 K, respectively. The dust mass is dominated by the cold dust component; we derive a total dust mass of ~ $3.8\times10^6~{M_\odot}$, and with the local gas-to-dust ratio of ~130 a total gas mass of $M_{\rm HI+H_2}\sim4.9\times10^8~{M_\odot}$. Comparison with the HI mass leads to a total molecular gas mass of ~ $3.4\times10^8~{M_\odot}$. We derive a conversion factor of the CO line intensity to molecular hydrogen column density $X_{\rm CO}=N_{\rm H_2}/I_{\rm CO}$ which is at least 11 times larger than the Galactic value. These values are in accord with the lower metallicity of NGC 4449 .


Key words: galaxies: individual: NGC 4449 -- galaxies: ISM -- galaxies: irregular -- ISM: dust, extinction

Offprint request: C. Böttner, cboettne@astro.uni-bonn.de

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