EDP Sciences
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Volume 377, Number 2, October II 2001
Page(s) 425 - 427
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20011128

A&A 377, 425-427 (2001)
DOI: 10.1051/0004-6361:20011128

The enigma in the heart of Ursa Minor

S. Demers1 and P. Battinelli2

1  Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
2  Osservatorio Astronomico di Roma Viale del Parco Mellini 84, 00136 Roma, Italy
    e-mail: battinel@oarhp1.rm.astro.it

(Received 18 June 2001 / Accepted 9 August 2001)

To investigate the physical nature of the observed deficiency of stars in the very center of the Ursa Minor Dwarf Spheroidal galaxy, we recently obtained JCMT-SCUBA 850 $\mu$m photometry of this region. The observed void could be explained by $\approx$0.5 mag of extinction. While the amount of dust needed to produce such absorption (under certain assumptions for the dust temperature and the $\beta$ exponent in the dust emissivity term) would yield a 5 mJy signal -easily detectable by SCUBA -we found no signal at 850 $\mu$m, after 256 min of integration. This finding rules out the presence of a few solar masses of cold dust cloud as the explanation for the central lack of stars observed in Ursa Minor. We discuss possible explanations.

Key words: galaxies: individual: Ursa Minor -- galaxies: ISM -- ISM: dust, extinction

Offprint request: S. Demers, demers@astro.umontreal.ca

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