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SUMMARY:Nebular emission line ratios in z~2-3 star-forming galaxies: explo
 ring the impact of ionization\, excitation\, and abundance patterns - Alli
 son Strom (Caltech)
DTSTART:20160617T103000Z
DTEND:20160617T113000Z
UID:TALK65732@talks.cam.ac.uk
CONTACT:Martin Haehnelt
DESCRIPTION:I will present new results from the MOSFIRE component of the K
 eck Baryonic Structure Survey (KBSS-MOSFIRE)\, focusing on the rest-optica
 l spectra of around 350 star-forming galaxies at z=2-3\, for which we have
  robust measurements of many of the strong diagnostic emission lines (incl
 uding H-alpha\, H-beta\, [OIII]\, [OII]\, [NII]\, [SII]\, and [NeIII]). Th
 e observations strongly suggest that the primary difference between HII re
 gions in z=2 galaxies and those in local galaxies is a strong enhancement 
 in the degree of excitation\, driven by the hard ionizing radiation from p
 opulations of metal-poor stars. At the same time\, z=2 KBSS-MOSFIRE galaxi
 es have significantly higher gas-phase oxygen abundances than local star-f
 orming galaxies with similar ionization and excitation properties\, along 
 with values of N/O at fixed O/H that are consistent with galaxies in the l
 ocal Universe. I will show that the combination of these two effects natur
 ally explains the combined nebular properties of high-z galaxies---includi
 ng the controversial 'BPT offset'---and highlights a population of young\,
  massive galaxies at high-redshift that must have accumulated their stella
 r mass significantly more rapidly than the majority of galaxies today.
LOCATION:Kavli LMR\, IoA
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