[22.09] The Nature of High Equivalent Width Lyman-$\alpha$ Galaxies

AAS 207th Meeting, 8-12 January 2006
Session 22 Evolution of Galaxies, Galaxies Surveys I
Poster, Monday, 9:20am-7:00pm, January 9, 2006, Exhibit Hall

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[22.09] The Nature of High Equivalent Width Lyman-\alpha Galaxies

S. L. Finkelstein, J. E. Rhoads, S. Malhotra (Arizona State University), N. Pirzkal (Space Telescope Science Institute), J. Wang (University of Science and Technology of China)

We present new results on the nature of the high equivalent width Ly\alpha lines seen in high-redshift galaxies. These galaxies were identified on the basis of their large equivalent width Ly\alpha emission, beyond the maximum expected for normal stellar populations. To be produced, this strong Ly\alpha emission requires a strong ionizing continuum. Previous X-ray images and optical spectra show that this emission is not powered by active galactic nuclei. The optical colors of these galaxies provide a diagnostic of the stellar populations. The large equivalent widths seen in the Ly\alpha line in these galaxies could be produced via star formation if the stellar photospheres are hotter than normal, which might be expected for star formation in low metallicity galaxies. They could also result from a top-heavy initial mass function. Both of these scenarios might be expected in primitive galaxies.

To investigate these galaxies, we have computed stellar population models using the stellar population synthesis code created by Bruzual and Charlot (2003). We will use these models to predict the equivalent width distribution of the Ly\alpha line in these high-redshift galaxies. We will also be able to derive estimates of stellar masses and stellar population ages, and be able to determine if these systems are indeed young and relatively primitive. Furthermore, we are obtaining new deep broadband imaging data on high-redshift galaxies taken from the Large Area Lyman Alpha (LALA) survey. These observations will yield better equivalent width measurements and continuum colors than previous data has allowed. We will compare these colors with the expectations for hot stars. We will also be able to constrain the star-formation rate using the UV continuum light from these galaxies, which will provide a valuable comparison with star-formation rates derived from the Ly\alpha luminosity alone.

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