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Issue A&A
Volume 435, Number 1, May III 2005
Page(s) 29 - 41
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041585



A&A 435, 29-41 (2005)
DOI: 10.1051/0004-6361:20041585

The stellar populations of the bluest low surface brightness galaxies

E. Zackrisson1, N. Bergvall1 and G. Östlin2

1  Department of Astronomy and Space Physics, Box 515, 751 20 Uppsala Sweden
    e-mail: [ez;nils.bergvall]@astro.uu.se
2  Stockholm Observatory, SCFAB, 106 91 Stockholm, Sweden
    e-mail: ostlin@astro.su.se

(Received 2 July 2004 / Accepted 27 January 2005 )

Abstract
Using optical/near-IR broadband photometry together with H$\alpha$ emission line data, we attempt to constrain the star formation histories, ages, total stellar masses and stellar mass-to-light ratios for a sample of extremely blue low surface brightness galaxies. We find that, under standard assumptions about the stellar initial mass function, the H$\alpha$ equivalent widths of these objects appear inconsistent with recently suggested scenarios including constant or increasing star formation rates over cosmological time scales. In a critical assessment of the prospects of obtaining ages from integrated broadband photometry, we conclude that even with near-IR data, the ages are poorly constrained and that current observations cannot rule out the possibility that these objects formed as recently as 1-2 Gyr ago. Methods which could potentially improve the age estimates are discussed. The stellar masses of these galaxies are inferred to lie below $10^{10}~M_\odot$. This, in combination with low ages, could constitute a problem for current hierarchical models of galaxy formation, which predict objects of this mass to form predominantly early in the history of the universe. The possibility to use the ages of the bluest low surface brightness galaxies as a test of such models is demonstrated.


Key words: galaxies: formation -- galaxies: evolution -- galaxies: fundamental parameters

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© ESO 2005


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