AAS 204th Meeting, June 2004
Session 48 Galaxy Evolution and Galaxy Clustering in the NDWFS' Bootes Field
Topical Session, Wednesday, June 2, 2004, 8:30-10:00am, 10:45am-12:30pm, 603/605/607

## [48.04] Spectroscopic Properties of the z = 4.5 Ly\alpha--emitters

S. Dawson (UC Berkeley), S. Malhotra, J. E. Rhoads (STScI), D. Stern (JPL), A. Dey (NOAO), H. Spinrad (UC Berkeley), B. T. Jannuzi (NOAO)

We present Keck/LRIS and Keck/DEIMOS optical spectra of ~50 star--forming galaxies at z \approx 4.5 discovered in the Large Area Lyman Alpha (LALA) survey. The survey has identified a sample of ~350 candidate Ly\alpha--emitting galaxies at z \approx 4.5 in a search volume of 1.5 \times 106 comoving Mpc3; the spectroscopic confirmations presented herein suggest a selection reliability of ~80%. The large equivalent widths (median W\lambda\mbox{\tiny rest} \approx 80 Å) but narrow physical widths (\Delta v < 500 km s-1) of the Ly\alpha emission lines, along with the lack of accompanying high--ionization state emission lines, suggests that these galaxies are young systems powered by star formation rather than by AGN activity. Theoretical models of galaxy formation in the primordial Universe suggest that a small fraction of Ly\alpha--emitting galaxies at z \approx 4.5 may still be nascent, metal--free objects. Indeed, we find with 96% confidence that at least ~20% of the confirmed sources show W\lambda\mbox{\tiny rest} > 240 Å, exceeding the maximum Ly\alpha equivalent width predicted for normal stellar populations. Nonetheless, we find no evidence for \ion{He}{2} \lambda1640 emission in either individual or composite spectra, indicating that though these galaxies are young, they are not truly primitive, Population III objects.