GS100-02-41: a new large H i  shell in the outer part of the Galaxy

¹ Instituto Argentino de Radioastronomía (IAR) (CCT - La PLata), CC 5, 1894 Villa Elisa, Argentina
e-mail: lasuad@iar.unlp.edu.ar
² Instituto de Astronomía y Física del Espacio (IAFE), CC 67, Suc. 28, 1428 Buenos Aires, Argentina
³ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina

Received: 13 September 2011
Accepted: 26 November 2011

Abstract

Context. Massive stars have a profound effect on the surrounding interstellar medium. They ionize and heat the neutral gas, and with their strong winds they sweep up the gas, forming large H i shells. In this way, they generate a dense shell that provides the physical conditions for the formation of new stars.

Aims. The aim of this study is to analyze the origin and evolution of the large H i shell GS 100–02–41  and its role in triggering star-forming processes.

Methods. To characterize the shell and its environs, we carried out a multi-wavelength study. We analyzed the H i 21 cm line, the radio continuum, and infrared emission distributions.

Results. The analysis of the H i data shows an expanding shell structure centered at (l,b) = (100°.6, –2°.04) in the velocity range from –29 to –51.7  km   s^-1. Taking into account noncircular motions, we infer for GS 100–02–41  a kinematical distance of 2.8  ±  0.6 kpc. Several massive stars belonging to Cep OB1 are located in projection within the large H i  shell boundaries. The analysis of the radio continuum and infrared data reveals that there is no continuum counterpart of the H i shell. On the other hand, three slightly extended radio continuum sources are observed in projection onto the dense H i shell. From their flux density determinations we infer that they are thermal in nature. An analysis of the H i emission distribution in the environs of these sources shows a region of low emissivity for each of them, which correlates well morphologically with the ionized gas in a velocity range similar to the one where GS 100–02–41  is detected.

Conclusions. Based on an energy analysis, we conclude that the origin of GS 100–02–41  could have been mainly caused by the action of the Cep OB1 massive stars located inside the H i shell. The obtained age difference between the H i shell and the H ii regions, together with their relative location, lead us to conclude that the ionizing stars could have been created as a consequence of the shell evolution.