MOS spectroscopy of protocluster candidate galaxies at z = 6.5

Abstract

The epoch corresponding to a redshift of z ∼ 6.5 is close to full re-ionisation of the Universe, and early enough to provide an intriguing environment to observe the early stage of large-scale structure formation. It is also en epoch that can be used to verify the abundance of a large population of low luminosity star-forming galaxies, that are deemed responsible for cosmic re-ionisation. Here, we present the results of follow-up multi-object spectroscopy using OSIRIS at Gran Telescopio Canarias (GTC) of 16 Lyα emitter (LAE) candidates discovered in the Subaru/XMM Newton Deep Survey. We have securely confirmed 10 LAEs with sufficient signal-to-noise ratio of the Lyα emission line. The inferred star formation rates of the confirmed LAEs are on the low side, within the range 0.9-4.7 M yr −1 . However, they show relatively high Lyα rest frame equivalent widths. Finally we have shown that the mechanical energy released by the star formation episodes in these galaxies is enough to create holes in the neutral hydrogen medium such that Lyman continuum photons can escape to the intergalactic medium, thus contributing to the re-ionisation of the Universe.

An ionized superbubble powered by a protocluster at z = 6.5

“…In particular, in Calvi et al (2019) we show the spectroscopic confirmation of a sample of the proto-cluster sources. Moreover, we claim that the mechanical energy thrown out by supernovae and stellar winds in the proto-cluster is huge (Calvi et al 2019). Thus we expect that this mechanical energy will pierce holes c 2020 The Authors arXiv:2003.05859v1 [astro-ph.GA] 12 Mar 2020 in the circumgalactic medium (CGM) throughout which Lyman continuum photons would be able to escape to the intergalactic medium (IGM), hence ionising it.…”

“…We have confirmed spectroscopically a proto-cluster of LAEs in the SXDS/XMM-Newton deep Survey field. For the 10 sources we have spectroscopically confirmed (Calvi et al 2019), we have determined their intrinsic Lyα photon luminosities as well as their ionising photon fluxes. We have also derived the corresponding intrinsic "stellar" ionising continuum photon fluxes.…”

Is the Bremer Deep Field reionized, at z ∼ 7?

“…Most of the detections have been done through broad band searches (Stark et al 2010;Bouwens et al 2010Bouwens et al , 2006Steidel et al 2005), but also with narrow band filters tuned to the Lyman α line (Chanchaiworawit et al 2017;Ouchi et al 2008Ouchi et al , 2010. However the number of spectroscopic confirmations of the sources detected in the various surveys is rather scarce (Calvi et al 2019;Castellano et al 2018;Harikane et al 2018). In particular, Vanzella et al (2011) discovered spectroscopically two sources in the Bremer Deep Field (BDF) at redshift 7.…”

A Lyman-α protocluster at redshift 6.9

“…Protoclusters, the progenitors of the most massive structures in the Universe, have been identified at redshifts up to 6.6 [refs [1][2][3][4][5][6] ]. Besides exploring early structure formation, searching for protoclusters at even higher redshifts is particularly useful to probe the reionization.…”

“…As narrowband imaging can constrain the redshift of LAEs to a very narrow range ∆z < 0.1, corresponding to a line-of-sight (LOS) distance of 30 -45 cMpc at z = 6 -8, it is also a promising approach to search for overdense structures, for example, protoclusters, in the early Universe [1][2][3][4][5][6] . Fig.…”