A Keck/DEIMOS Spectroscopy of Lyα Blobs at Redshift z = 3.1

Abstract

We present the results of intermediate-resolution (~2 ?) spectroscopy of a sample of 37 candidate Ly? blobs and emitters at redshift z = 3.1 using the DEIMOS spectrograph on the 10 m Keck telescope. The emission lines are detected for all 37 objects and show variety in their line profiles. The Ly? velocity widths (FWHM) of the 28 objects with higher quality spectra, measured by fitting a single Gaussian profile, are in the range of 150-1700 km s-1 and correlate with the Ly? spatial extents. All 12 Ly? blobs (?16 arcsec2) have large velocity widths of 500 km s-1. While there are several possible physical interpretations of the Ly? velocity widths (the motion of gravitationally bound gas clouds, inflows, the merging of clumps, or outflows from superwinds), the large velocity widths of the Ly? blobs suggest that they are the sites of massive galaxy formation. If we assume gravitationally bound gas clouds, the dynamical masses of the Ly? blobs are estimated to be ~1012-1013 M?. Even for the case of outflows, the outflow velocities are likely to be comparable to the rotation velocities as inferred from the observational evidence for local starburst galaxies.