Journal Article

Star formation in blue compact dwarf galaxies: Mkn 104 and I Zw 97

S. Ramya, D. K. Sahu and T. P. Prabhu

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 1, pages 97-108
Published in print June 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14731.x
Star formation in blue compact dwarf galaxies: Mkn 104 and I Zw 97

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Two blue compact dwarf galaxies, Mkn 104 and I Zw 97, are studied photometrically and spectroscopically. Mkn 104 is found to contain three distinct bright star-forming regions, whereas I Zw 97 is found to contain three bright and two faint star-forming regions. Medium-resolution spectra of three bright H ii regions in the two galaxies were obtained. Estimation of oxygen abundance in these regions yields a value equal to log(O/H) + 12 = 8.5 (Z= Z/2.7). Star-formation rates in these star-forming regions are estimated. The highest star-formation rate for I Zw 97 is found to be 0.04 M yr−1, and for Mkn 104 it is 0.02 M yr−1. I Zw 97 is realized to be a cometary blue compact dwarf galaxy undergoing a strong burst of star formation. A UB versus VI colour–colour mixed population model is created using the Starburst99 evolutionary model curves. The spectrum of the bright star-forming knot of I Zw 97 does not show any strong signature of an underlying relatively older stellar population, but the UB versus VI two-colour diagram indicates the strong contribution of a ∼500 Myr population. A spectrum of the central region of Mkn 104 gives a hint about the underlying old stellar population. The age of this underlying population using the UB versus VI two-colour diagram is estimated to be ∼ 500 Myr. Surface-brightness profiles and colour profiles for these galaxies are presented. The surface-brightness profile of both the galaxies can be represented well by a two-component Sérsic profile consisting of a near-exponential distribution and a Gaussian nuclear starburst. To conclude, neither of these galaxies is a young system; instead they are undergoing episodic star formation superposed on a faint older component. I Zw 97 is a cometary blue compact dwarf galaxy where the underlying low-surface-brightness (LSB) galaxy is a dwarf irregular observed during a major stochastic enhancement of its otherwise moderate star-formation activity, a phenomenon widely accepted as self-propagating stochastic star formation. Both of these galaxies are very similar in their stellar content, showing an older 4-Gyr population, an intermediate 500-Myr population and the current burst of star formation of age 5–13 Myr.

Keywords: techniques: photometric; galaxies: individual: I Zw 97; galaxies: individual: Mkn 104; galaxies: starburst

Journal Article.  8061 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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