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Astron. Astrophys. 326, 929-935 (1997)

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Evidences for an expanding shell
in the blue compact dwarf galaxy Haro 2

F. Legrand 1, D. Kunth 1, J.M. Mas-Hesse 2 and J. Lequeux 3

1 Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, F-75014 Paris, France
2 LAEFF-INTA, Apdo 50727, E-28080 Madrid, Spain
3 Observatoire de Paris, DEMIRM, 77, Av. Denfert Rochereau, F-75014 Paris, France

Received 13 January 1997 / Accepted 5 June 1997


Long-slit observations of the blue compact galaxy Haro 2 have been performed around H [FORMULA] and H [FORMULA]. The main aim of these observations was to detect the H [FORMULA] emission originating in the partially ionized wind outflowing at 200 km/s, that had been previously detected with the Hubble Space Telescope (HST). A shallow broadening of the H [FORMULA] line wings has been observed, consistent with the existence of an expanding shell. The rotation curve shows two dips at the same systemic velocity as the nucleus. We interpret this feature as an evidence that the expanding shell is decoupled from the disk rotation. At the positions of the dips the H [FORMULA] line is clearly broadened with respect to the central core. This broadening is produced by the outer layers of the expanding shell. From the position of these dips we estimate the size of the shell to be around 20" in diameter, with a corresponding kinematical age between 5 and 6 Myr. This shell has most certainly been powered by the massive star formation process that takes place in the central region of this galaxy. A comparison of the H [FORMULA] and Ly [FORMULA] profiles shows that Ly [FORMULA] is significantly broader than H [FORMULA], with an additional emission in the red wing. We interpret this redshifted source of Ly [FORMULA] emission as line photons backscattered by the receding part of the expanding shell. These observations outline the extremely high sensitivity of the Ly [FORMULA] line to the structure and kinematics of the interstellar medium (ISM). Finally the analysis of stellar Balmer lines in the H [FORMULA] region indicates that stars less massive than 10 M [FORMULA] have probably been formed.

Key words: galaxies: ISM - galaxies: starburst - galaxies: kinematics and dynamics - galaxies: individual: Haro 2

Send offprint requests to: F. Legrand

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998