Spectroscopic Properties of thez≈ 4.5 Lyα Emitters

Abstract

We present Keck Low Resolution Imaging Spectrometer optical spectra of 17 Ly-emitting galaxies and one Lyman break galaxy at z % 4:5 discovered in the Large Area Lyman Alpha survey. The survey has identified a sample of $350 candidate Ly-emitting galaxies at z % 4:5 in a search volume of 1:5 ; 10 6 comoving Mpc 3 . We targeted 25 candidates for spectroscopy; hence, the 18 confirmations presented herein suggest a selection reliability of 72%. The large equivalent widths (median W rest k % 80 8) but narrow physical widths (Áv < 500 km s À1 ) of the Ly emission lines, along with the lack of accompanying high-ionization state emission lines, suggest that these galaxies are young systems powered by star formation rather than by active galactic nucleus activity. Theoretical models of galaxy formation in the primordial universe suggest that a small fraction of Ly-emitting galaxies at z % 4:5 may still be nascent, metal-free objects. Indeed, we find with 90% confidence that three to five of the confirmed sources show W rest k > 240 8, exceeding the maximum Ly equivalent width predicted for normal stellar populations. Nonetheless, we find no evidence for He ii k1640 emission in either individual or composite spectra, indicating that although these galaxies are young, they are not truly primitive, Population III objects.

Lymanαline and continuum radiative transfer in a clumpy interstellar medium

“…Several physical possibilities have already been investigated to explain these high EW(Lyα), such as the presence of either population III stars or active galactic nuclei (AGNs) in the host galaxies. But none of them have proven to be consistent with the observations (Dawson et al 2004;Wang et al 2004;Gawiser et al 2006). Another possibility is that the high EW(Lyα) values found are due to the combined effect of IGM absorption (lowering the continuum on the blue side of Lyα at high z) and observational errors biasing the average EW(Lyα) to higher values (Hayes & Östlin 2006).…”

The environments of Ly α blobs – I. Wide-field Ly α imaging of TN J1338−1942, a powerful radio galaxy at z ≃ 4.1 associated with a giant Ly α nebula★

“…The existing LAE survey data cover a small field (two 7 arcmin × 7 arcmin) making it hard to map any overdensity, and there is no matched blank-field observations which means that even the magnitude of the overdensity is uncertain. [Venemans et al (2007) used the Large-Area Lyman α survey results (Rhoads et al 2000;Dawson et al 2004) for the reference, which are taken with the different telescope and instrument, targeting a slightly different redshift]. Accordingly, the relationship between the structure hosting the radio galaxy (and the protocluster) and the wider surrounding environment cannot be probed with the existing data.…”

Gemini GMOS spectroscopy of HeII nebulae in M 33

“…The metal-poor sensitivity is a primary motivation to develop diagnostics for relatively unevolved starbursts, and strong nebular HeIIλ1640, 4686 emission is expected to be one of the best signatures of massive Population III stars (e.g., Schaerer 2002;Schaerer 2003 and references therein). Several searches for this spectral signature in high-redshift galaxies have been carried out (e.g., Dawson et al 2004;Nagao et al 2008;Ouchi et al 2008, andreview in Schaerer 2008).…”