Keck Spectroscopy of Lyman-break Galaxies and its Implications for the UV-continuum and Lyₐlpha Luminosity Functions at z>6

الأصل · EN

We present Keck spectroscopic observations of z>6 Lyman-break galaxy (LBG) candidates in the Subaru Deep Field (SDF). The candidates were selected as i'-dropout objects down to z'=27 AB magnitudes from an ultra-deep SDF z'-band image. With the Keck spectroscopy we identified 19 LBGs with prominent Lyₐlpha emission lines at 6< z < 6.4. The median value of the Lyₐlpha rest-frame equivalent widths (EWs) is 50 A, with four EWs >100 A. This well-defined spectroscopic sample spans a UV-continuum luminosity range of -21.8< MUV<-19.5 (0.6 5 L*UV) and a Lyₐlpha luminosity range of (0.3 3) x 10⁴³ erg s⁻¹ (0.3 3 L*Lyₐlpha). We derive the UV and Lyₐlpha luminosity functions (LFs) from our sample at <z> 6.2 after we correct for sample incompleteness. We find that our measurement of the UV LF is consistent with the results of previous studies based on photometric LBG samples at 5<z<7. Our Lyₐlpha LF is also generally in agreement with the results of Lyₐlpha-emitter surveys at z 5.7 and 6.6. This study shows that deep spectroscopic observations of LBGs can provide unique constraints on both the UV and Lyₐlpha LFs at z>6.