Rest-frame UV spectroscopy of extreme [O iii] emitters at 1.3 < z < 3.7: toward a high-redshift UV reference sample for JWST. Issue 3 (7th November 2020)

• Record Type: Journal Article
• Authors: Tang, Mengtao; Stark, Daniel P; Chevallard, Jacopo; Charlot, Stéphane; Endsley, Ryan; Congiu, Enrico
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 501:Issue 3(2021)
• Page Start: 3238
• Page End: 3257
• Publication Date: 2020-11-07
• Subjects: galaxies: evolution -- galaxies: formation -- cosmology: observations; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3454
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Deep spectroscopy of galaxies in the reionization era has revealed intense C iii ] and C iv line emission (equivalent width, EW &gt;15–20 Å). In order to interpret the nebular emission emerging at z &gt; 6, we have begun targeting rest-frame ultraviolet (UV) emission lines in galaxies with large specific star formation rates (sSFRs) at 1.3 &lt; z &lt; 3.7. We find that C iii ] reaches the EWs seen at z &gt; 6 only in large sSFR galaxies with [O iii ]+Hβ EW &gt;1500 Å. In contrast to previous studies, we find that many galaxies with intense [O iii ] have weak C iii ] emission (EW = 5–8 Å), suggesting that the radiation field associated with young stellar populations is not sufficient to power strong C iii ]. Photoionization models demonstrate that the spread in C iii ] among systems with large sSFRs ([O iii ]+Hβ EW &gt;1500 Å) is driven by variations in metallicity, a result of the extreme sensitivity of C iii ] to electron temperature. We find that the strong C iii ] emission seen at z &gt; 6 (EW &gt;15 Å) requires metal-poor gas (≃ 0.1 Z ⊙ ), whereas the weaker C iii ] emission in our sample tends to be found at moderate metallicities (≃ 0.3 Z ⊙ ). The luminosity distribution of the C iii ] emitters in our z ≃ 1–3 sample presents a consistent picture, with stronger emission generally linked to low-luminosity systems ( M UV &gt; −19.5) where low metallicities are more likely. We quantify the fraction of strong C iii ] and C iv emitters at z ≃ 1–3, providing a baseline for comparison against z &gt; 6 samples. We suggest that the first UV line detections at z &gt; 6 can be explained if a significant fraction of the early galaxy population is found at large sSFR (&gt;200 Gyr −1 ) and low metallicity (&lt; 0.1 Z ⊙ ).