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SUMMARY:An emission line study of a unique\, strongly lensed galaxy at z ~
  5: connecting Lyman-α and MgII λ 2796 Å emission at high redshift - Jo
 ris Witstok
DTSTART:20201021T123000Z
DTEND:20201021T130000Z
UID:TALK150376@talks.cam.ac.uk
CONTACT:Emma Curtis Lake
DESCRIPTION:We present a detailed analysis of a highly magnified galaxy at
  z = 4.88\, behind the strong lensing cluster RCS 0224–0002. Only 2 sour
 ces at z > 5 are known with this lensing magnification\, and this particul
 ar source has been shown to exhibit widespread\, high equivalent width CIV
  λ 1549 Å emission\, suggesting it is a unique example of a metal-poor g
 alaxy\, with a hard radiation field and high χ_ion\, likely representing 
 the galaxy population that is responsible for Cosmic Reionization. X-shoot
 er observations rule out the presence of an AGN in this source from the UV
  nebular line ratio diagnostics\, suggesting a stellar origin of the hard 
 radiation field in this source. Furthermore\, we present a new detection o
 f [NeIII] λ 3870 Å and use the [NeIII]/[OII] line ratio (the highest red
 shift measurement of this rest-frame optical line diagnostic to date) to p
 ut this galaxy in context of the z ~ 0-2 galaxy population and put constra
 ints on the ionisation parameter and gas-phase metallicity. Closely relate
 d to the widely used [OIII]/[OII] ratio\, our [NeIII]/[OII] measurement su
 ggests this source is similar to extreme emission line galaxies such as "G
 reen Pea" galaxies in the local Universe. Finally\, we present the highest
  redshift detection to date of the MgII line at 2796 Å\, observed at high
  equivalent width in emission\, in contrast to more evolved systems where 
 MgII is mostly seen in absorption. Strong MgII emission has been observed 
 in most of the z ~ 0 Lyman-continuum leakers known and has recently been p
 roposed as an indirect tracer of escaping ionising radiation in the Epoch 
 of Reionization\, where the widely used Lyman-α line is longer be observa
 ble due to the neutral IGM. Our detection of bright MgII at z ~ 5 – just
  300 Myr after Reionization ends – demonstrates the feasibility of obser
 ving this line in the near future with JWST and ELTs at z > 6. In conclusi
 on\, this galaxy illustrates how gravitational lensing can present us inva
 luable insights regarding our understanding of the early Universe and offe
 r a glimpse into the discovery space of next-generation observatories like
  JWST.
LOCATION: Webinar  (via Zoom online)
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