Direct Lyman continuum and Ly α escape observed at redshift 4

Abstract

We report on the serendipitous discovery of a z = 4.0, M 1500 = −22.20 star-forming galaxy (Ion3) showing copious Lyman continuum (LyC) leakage (∼ 60% escaping), a remarkable multiple peaked Lyα emission, and significant Lyα radiation directly emerging at the resonance frequency. This is the highest redshift confirmed LyC emitter in which the ionising and Lyα radiation possibly share a common ionised channel (with N HI < 10 17.2 cm −2 ). Ion3 is spatially resolved, it shows clear stellar winds signatures like the P-Cygni Nvλ1240 profile, and has blue ultraviolet continuum (β = −2.5 ± 0.25, F λ ∼ λ β ) with weak low-ionisation interstellar metal lines. Deep VLT/HAWKI Ks and Spitzer/IRAC 3.6µm and 4.5µm imaging show a clear photometric signature of the Hα line with equivalent width of 1000Å rest-frame emerging over a flat continuum (Ks−4.5µm 0). From the SED fitting we derive a stellar mass of 1.5 × 10 9 M , SFR of 140 M yr −1 and age of ∼ 10 Myr, with a low dust extinction, E(B-V) 0.1, placing the source in the starburst region of the SFR−M * plane. Ion3 shows similar properties of another LyC emitter previously discovered (z = 3.21, Ion2, Vanzella et al. 2016). Ion3 (and Ion2) represents ideal high-redshift reference cases to guide the search for reionising sources at z > 6.5 with JWST.

Lyman continuum escape fraction in Ly α emitters at z ≃ 3.1

“…Studies have suggested that galaxies with high LyC escape fractions commonly shows strong Lyα emission (EW 0 (Lyα) > 70Å) and high Lyα emission line escape fraction > 20% (e.g., Verhamme et al 2017;Kimm et al 2019). To our knowledge, the Lyα EW 0 in the composite spectrum of these LAEs is higher than all of the known LyC-leaking galaxies with f esc > 30% (e.g., Verhamme et al 2017;Vanzella et al 2016Vanzella et al , 2018 (Figure 4). The other properties of the LAEs in this work are also in favour to having high LyC escape fraction, including lower stellar mass and UV luminosity, compared to those individual galaxies with high LyC escape fraction ( f esc > 30%) at the similar redshift range, such as Ion2, Ion3, and A2218-Flank (Figure 4).…”

“…However, LyC escape fraction can not be directly measured in galaxies beyond z = 4.5 due to the high opacity of the IGM to LyC ionising photons (e.g., Vanzella et al 2018). Thus we have to infer the LyC escape in the galaxies at the epoch of the reioisation based on either directly measuring LyC escape fraction in galaxies at lower redshift or correlating galaxy spatial positions with the Lyman alpha forest at z > 6 (e.g., Kakiichi et al 2018).…”

Finding forming globular clusters at high redshifts

“…So, as far as we know, all GCs might have formed inside dwarfs. However, objects similar to the lensed ones found by Vanzella et al (2017a), which have halflight radii of ∼ 60 pc, would be barely resolved with NIRCam.…”

“…Thus, for metalpoor GCPs dust extinction is likely to have only a minor effect. It is worth noting in this context that the candidate GCPs detected by Vanzella et al (2017a) have indeed a very blue UV continuum, hence low extinction.…”

“…On the other hand, a few candidate GCPs at z > 3 have already been identified, thanks to strong gravitational lensing (Vanzella et al 2016(Vanzella et al , 2017a, with a stellar mass ∼ 10 7 M and half-light radius ∼ 60 pc. Hence, times are ripe to start thinking at GCP searches on a more industrial scale.…”