The evolution of rest-frame UV properties, Ly α EWs, and the SFR–stellar mass relation at z ∼ 2–6 for SC4K LAEs. Issue 1 (14th January 2020)

• Record Type: Journal Article
• Authors: Santos, S; Sobral, D; Matthee, J; Calhau, J; da Cunha, E; Ribeiro, B; Paulino-Afonso, A; Arrabal Haro, P; Butterworth, J
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 493:Issue 1(2020)
• Page Start: 141
• Page End: 160
• Publication Date: 2020-01-14
• Subjects: galaxies: evolution -- galaxies: formation -- galaxies: high-redshift -- galaxies: star formation; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa093
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We explore deep rest-frame UV to FIR data in the COSMOS field to measure the individual spectral energy distributions (SED) of the ∼4000 SC4K (Sobral et al.) Lyman α (Ly α) emitters (LAEs) at z ∼ 2–6. We find typical stellar masses of 10 9.3 ± 0.6 M⊙ and star formation rates (SFR) of SFR$_{\rm SED}=4.4^{+10.5}_{-2.4}$ M⊙ yr −1 and SFR$_{\rm Ly\, \alpha }=5.9^{+6.3}_{-2.6}$ M⊙ yr −1, combined with very blue UV slopes of $\beta =-2.1^{+0.5}_{-0.4}$, but with significant variations within the population. M UV and β are correlated in a similar way to UV-selected sources, but LAEs are consistently bluer. This suggests that LAEs are the youngest and/or most dust-poor subset of the UV-selected population. We also study the Ly α rest-frame equivalent width (EW0 ) and find 45 'extreme' LAEs with EW0 > 240 Å (3σ), implying a low number density of (7 ± 1) × 10 −7 Mpc −3 . Overall, we measure little to no evolution of the Ly α EW0 and scale length parameter ( w 0 ), which are consistently high (EW$_0=140^{+280}_{-70}$ Å, $w_0=129^{+11}_{-11}$ Å) from z ∼ 6 to z ∼ 2 and below. However, w 0 is anticorrelated with M UV and stellar mass. Our results imply that sources selected as LAEs have a high Ly α escape fraction ( f esc, Ly α ) irrespective of cosmic time, but f esc, Ly α is still higher for UV-fainter and lower mass LAEs. The least massive LAEs (<10 9.5 M⊙ ) are typically located above the star formation 'main sequence' (MS), but the offset from the MS decreases towards z ∼ 6 and towards 10 10 M⊙ . Our results imply a lack of evolution in the properties of LAEs across time and reveals the increasing overlap in properties of LAEs and UV-continuum selected galaxies as typical star-forming galaxies at high redshift effectively become LAEs.