NOAO >   Observing Info >   Approved Programs >   2005A-0490

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Proposal Information for 2005A-0490


PI: James Rhoads, STScI, rhoads@stsci.edu
Address: 3700 San Martin Drive, Baltimore, MD 21210, USA

CoI: Sangeeta Malhotra, STScI

Title: The Nature of High Equivalent Width Lyman Alpha Galaxies

Abstract: We have identified a population of high redshift galaxies that show large equivalent width \lya emission, beyond the maximum expected for normal stellar populations. Our followup X-ray imaging and optical spectroscopy demonstrates that this emission is not powered by active galactic nuclei. Star formation activity could produce such large equivalent widths if the stellar photospheres are hotter than ``normal,'' which might be expected for star formation in low metallicity galaxies. Alternatively, differences in the radiative transfer of \lya and continuum photons could allow \lya photons to escape a galaxy whose continuum light is suppressed by dust, thus enhancing the equivalent width. We propose to distinguish among these scenarios through deep optical broad band imaging of our \lya galaxies. This will yield better equivalent width measurements and continuum colors. We will compare the colors with expectations for hot stars (blue) vs. extinguished continuum flux (red). We will also compare the improved equivalent width distribution with the detailed predictions of different stellar population models, which may respond differently to modified initial mass functions and stellar metallicity. We will identify the parent population of our \lya sample using a Lyman break selection from our deep, cospatial images. Finally, we will leverage our refined photometric data to select subsets of our 63 spectroscopically confirmed \lya galaxies in this field according to their color and equivalent width, allowing us to search for trends in composite spectra.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



NOAO >   Observing Info >   Approved Programs >   2005A-0490

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