Publication Date:
2016-12-10
Description:
We present physical properties of spectroscopically confirmed Lyα emitters (LAEs) with very large rest-frame Lyα equivalent widths EW 0 (Lyα). Although the definition of large EW 0 (Lyα) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from ~3000 LAEs at z ~ 2 with reliable measurements of EW 0 (Lyα) ~= 200–400 Å given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW 0 (Lyα) LAEs do not have signatures of AGN, but notably small stellar masses of M * = 10 7–8 M and high specific star formation rates (star formation rate per unit galaxy stellar mass) of ~100 Gyr –1 . These LAEs are characterized by the median values of L (Lyα) = 3.7 x 10 42 erg s –1 and M UV = –18.0 as well as the blue UV continuum slope of β = –2.5 ± 0.2 and the low dust extinction $E(B-V)_{\rm *} = 0.02^{+0.04}_{-0.02}$ , which indicate a high median Lyα escape fraction of $f_{\rm esc}^{\rm Ly\alpha }=0.68\pm 0.30$ . This large $f_{\rm esc}^{\rm Ly\alpha }$ value is explained by the low H i column density in the interstellar medium which is consistent with full width at half-maximum (FWHM) of the Lyα line, FWHM(Lyα) = 212 ± 32 km s –1 , significantly narrower than those of small EW 0 (Lyα) LAEs. Based on the stellar evolution models, our observational constraints of the large EW 0 (Lyα), the small β, and the rest-frame He ii EW imply that at least a half of our large EW 0 (Lyα) LAEs would have young stellar ages of 20 Myr and very low metallicities of Z 〈 0.02 Z regardless of the star formation history.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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