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Lyman Alpha Emitting Galaxies in the Nearby Universe
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Number of Authors: 1
2015 (English)In: Publications Astronomical Society of Australia, ISSN 1323-3580, E-ISSN 1448-6083, Vol. 32, e027Article in journal (Refereed) Published
Abstract [en]

The Lyman alpha emission line (Ly alpha) of neutral hydrogen (Hi) is intrinsically the brightest emission feature in the spectrum of astrophysical nebulae, making it a very attractive observational feature with which to survey galaxies. Moreover as an ultraviolet resonance line, Ly alpha possesses several unique characteristics that make it useful to study the properties of the interstellar medium and ionising stellar population at all cosmic epochs. In this review, I present a summary of Ly alpha observations of galaxies in the nearby universe. By ultraviolet continuum selection, at the magnitudes reachable with current facilities, only approximate to 5% of the local galaxy population shows a Ly alpha equivalent width (W-Ly alpha) that exceeds 20 angstrom. This fraction increases dramatically at higher redshifts, but only in the local universe can we study galaxies in detail and assemble unprecedented multi-wavelength datasets. I discuss many local Ly alpha observations, showing that when galaxies show net Ly alpha emission, they ubiquitously also produce large-scale halos of scattered Ly alpha, that dominate the integrated luminosity. Concerning global measurements, we discuss how W-Ly alpha and the Ly alpha escape fraction (f(esc)(Ly alpha)) are higher (W-Ly alpha greater than or similar to 20 angstrom and f(esc)(Ly alpha) greater than or similar to 10%) in galaxies that represent the less massive and younger end of the distribution for local objects. This is connected with various properties, such that Ly alpha-emitting galaxies have lower metal abundances (median value of 12 + log(O/H) similar to 8.1) and dust reddening. However, the presence of galactic outflows/winds is also vital to Doppler shift the Ly alpha line out of resonance with the atomic gas, and high W-Ly alpha is found only among galaxies with winds faster than similar to 50 km s(-1). The empirical evidence is then assembled into a coherent picture, and the requirement for star-formation-driven feedback is discussed in the context of an evolutionary sequence where the interstellar medium is accelerated and/or subject to hydrodynamical instabilities, which reduce the scattering of Ly alpha. Concluding remarks take the form of perspectives upon future developments, and the most pressing questions that can be answered by observation.

Place, publisher, year, edition, pages
2015. Vol. 32, e027
Keyword [en]
Galaxies: evolution, Galaxies: individual: Haro 11, iZw 18, SBS 0335-052, Haro 2, Mrk 701, IRAS 08208+2816, Galaxies: starburst, Physical data and processes: radiative transfer, Ultraviolet: galaxies
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-119296DOI: 10.1017/pasa.2015.25ISI: 000357861000001OAI: diva2:844198
Available from: 2015-08-04 Created: 2015-08-03 Last updated: 2015-08-04Bibliographically approved

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Hayes, Matthew
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Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
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