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Astron. Astrophys. 329, 409-430 (1998)


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Bidimensional spectroscopy of NGC 4214: evolutionary state
and interstellar extinction

J. Maz-Apellániz 1, 2, J.M. Mas-Hesse 1, C. Muñoz-Tuñón 3, J.M. Vlchez 3 and H.O. Castañeda 3

1 Laboratorio de Astrofsica Espacial y Fsica Fundamental - INTA, POB 50727, E-28080 Madrid, Spain
2 Departamento de Matemáticas y Fsica Aplicada, Universidad Alfonso X el Sabio, E-28691 Villanueva de la Cañada, Madrid, Spain
3 Instituto de Astrofsica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 6 August 1997 / Accepted 22 August 1997

Abstract

We have mapped spectrophotometrically the star-forming regions in the center of the nearby SBm galaxy NGC 4214 with the aim of analyzing the spatial distribution of some of its physical properties (density, excitation, emission line intensity, extinction) and their relationship with the distribution and evolutionary state of the stellar population. Star formation takes place mainly in two big complexes, although several smaller star-forming regions spread over the central bar of the galaxy have also been identified. The comparison of different observable parameters ([FORMULA] H [FORMULA], Wolf-Rayet population, effective temperature, UV absorption lines) with the predictions of synthesis models provides a consistent picture in which the different star formation episodes took all place around 3 Myr ago, with a very narrow spread in time (in any case within 1 Myr). The brightest star forming complex, located at the visible nucleus of the galaxy, is apparently the most evolved one. The surrounding interstellar medium is being disrupted, with a clear spatial decoupling between stars, gas and dust clouds. The dust appears concentrated at the boundaries of the ionized region, affecting mainly the nebular emission lines, while the stellar continuum itself is located in a region relatively free of dust and gas. This decoupling may explain the differences in extinction found previously between the stellar continuum and the emission lines. On the other hand, the ionized gas is essentially co-spatial with the massive stellar clusters in the SE complex, which apparently is less evolved. Nevertheless, the dust tends to be concentrated in isolated clouds located generally at the boundaries of the line emitting nebulae. We postulate that stellar winds have contributed to concentrate these dust particles in the inter-cluster medium.

Key words: galaxies: individual NGC 4214 – galaxies: ISM – galaxies: irregular – galaxies: starburst

Send offprint requests to: Jesús Maz-Apellániz (jma@laeff.esa.es)

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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