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Molecular gas and a new young stellar cluster in the far outer Galaxy

J. L. Yun, D. Elia, P. M. Palmeirim, M. Werner, A. M. Martins

Abstract
Aims: We investigate the star-formation ocurring in the region towards IRAS 07527-3446 in the molecular cloud [MAB97]250.63-3.63, in the far outer Galaxy. We report the discovery of a new young stellar cluster, and describe its properties and those of its parent molecular cloud. Methods: Near-infrared JHKS images were obtained with VLT/ISAAC, and millimetre line CO spectra were obtained with the SEST telescope. VLA archive date were also used. Results: The cloud and cluster are located at a distance of 10.3 kpc and a Galactocentric distance of 15.4 kpc, in the far outer Galaxy. Morphologically, IRAS 07527-3446 appears as a young embedded cluster of a few hundred stars seen towards the position of the IRAS source, extending for about 2-4 pc and exhibiting sub-clustering. The cluster contains low and intermediate-mass young reddened stars, a large fraction having cleared the inner regions of their circumstellar discs responsible for(H-K_S) colour excess. The observations are compatible with a <=5 Myr cluster with variable spatial extinction of between A_V=5 and A_V=11. Decomposition of CO emission in clumps, reveals a clump clearly associated with the cluster position, of mass 3.3 ◊ 103 M_&sun;. Estimates of the slopes of the K_S-band luminosity function and of the star-formation efficiency yield values similar to those seen in nearby star-formation sites. These findings reinforce previous results that the distant outer Galaxy continues to be active in the production of new and rich stellar clusters, with the physical conditions required for the formation of rich clusters continuing to be met in the very distant environment of the outer Galactic disc. Based on observations collected at the ESO 8.2-m VLT-UT1 Antu telescope(program 66.C-0015A). Table 2 is only available in electonic form at http://www.aanda.org

Keywords
stars: formation - ISM: clouds - ISM: individual: objects: IRAS 07527-3446 - infrared: stars - ISM: dust - extinction - stars: pre-main: sequence

Astronomy and Astrophysics
Volume 500, Number 2, Page 833
2009 June

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia