PI Total time #CoIs, team Bob Fosbury 10n (ELT 42m) ~5. Skills: lens modelling, photoionization modelling, massive star SED modelling, practical nebular spectroscopy Early epoch star formation: nebular spectroscopy Restframe UV-optical emission line spectroscopy reveals properties of the exciting stars as well as the nebular abundances. Pockets of primordial gas may persist to z ~ 3-4 (Jimenez & Haiman 2006) - offering the possibility of observing ‘first light’ physics at accessible epochs. Propose wide wavelength range, moderate R spectroscopy of colour- and morphologically-selected (including lensed) sources up to z ~ 10.

Scientific rationale Use restframe UV-optical spectroscopy to investigate the astrophysics of ultra- low metallicity star formation (pop III) Wide wavelength coverage emission line spectroscopy gives nebular abundances, ionizing stellar properties (eg. T eff ) and virial and wind kinematics Measurements of - or upper limits on - the stellar continuum constrains the IMF Sources expected to cover a range of metallicity from Z ~ 0 to Immediate objectives Preparatory work: candidates are found from multicolour imaging (HST and JWST). The emission lines from these objects dominate the UV-optical spectrum and produce colours quite unlike continuum sources. Cluster lenses can be exploited to go to low intrinsic star formation rates - by searching ‘critical lines’ at specific redshifts. Proposed observations: Long-slit (~1 arcsec) spectroscopy with excellent sky subtraction/absorption correction. Marginally resolved sources (on a scale ~ 200 mas). Wavelength coverage: I (or R) through K. Sources rare - so probably no advantage from multiplexing. Need to select and measure sources from z~3 to the reionization epoch: Ly  to z ~ 14 and C IV to z ~ The pilot programme will study 5 sources to a limit of m AB ~ 30 (10 hr with JWST in one band). The limiting line flux corresponds to a nebula excited by ~10 5 O-stars at z = 10. The observation of lensed sources will improve this sensitivity.

C IV Ly  [Ne III] [O III] HH He II Observations near critical lines in clusters => gains in sensitivity by factors of 10 or so H II region models predict strong diagnostic lines over a wide wavelength range. He II 1640 is critical for stellar T eff

ELT Justification: Need to access faint lines - especially HeII: photon- limited regime. Discovery imaging done from space - including colour- selected gravitationally lensed sources. R chosen to allow the determination of  gas ~ 20 km/s Legacy Value: HII region atlas Data Reduction: Computation of ‘critical lines’ for selected redshifts in clusters. Extraction of emission line measurements in non-optimum parts of atmospheric windows Target list: 5 sources brighter than m AB = 30. Total on-target time = 100h RunMPModeAOT.FOVPixel Notes A1R=5000GLAO5h/ band 1”100I,J,H,KLong slit