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Open Access Publications from the University of California

A Multi-Wavelength Spectroscopic and Photometric Study of Star Formation and Dust in Galaxies in the Early Universe

  • Author(s): Shivaei, Irene
  • Advisor(s): Reddy, Naveen A
  • et al.
Creative Commons Attribution 4.0 International Public License

Redshift of z ~ 2 is an important era in the history of the universe, as it contains the peak of star formation rate (SFR) and quasar activity. In this work, I investigate the properties of galaxies during this era from two different, yet complementary, aspects: star formation and stellar mass (M*) assembly, and galactic dust enrichment. I use a wealth of spectroscopic data obtained by the MOSFIRE Deep Evolution Field (MOSDEF) survey, which is a multi-institutional project that uses the near-IR MOSFIRE spectrograph on the Keck I telescope to characterize the gaseous and stellar contents of ~ 1500 rest-frame optically selected galaxies at z=1.37-3.80. Furthermore, I incorporate the mid- and far-IR data from the Spitzer and Herschel telescopes to obtain a complete census of obscured and unobscured star formation in galaxies. By comparing H-alpha derived SFRs with those inferred from panchromatic SED modeling, I show that the Balmer decrement accurately predicts the obscuration of the nebular lines and can be used to robustly calculate SFRs of galaxies at z~2 with SFRs up to ~200 Msun/yr. I dissect the scatter and slope of the SFR-M* relation at z~2, using multi-wavelength SFR tracers (UV, H-alpha, 24 micron, and far-IR). I find a large intrinsic scatter of 0.36 dex and a shallower slope of ~0.7 than found previously. Moreover, I investigate, for the first time, the variation of PAH emission at 7.7 micron, traced by Spitzer/MIPS 24 micron, in galaxies spanning a wide range in metallicity at z~2. Our results have indicate a higher IR luminosity density at z~2 than previously measured, corresponding to a ~30% increase in the SFR density. Lastly, I utilize H-alpha and H-beta spectroscopic measurements to constrain the ionizing photon production efficiency of galaxies at z~2. Our results pave the way for future observations with the James Webb Space Telescope to improve our knowledge about dust enrichment during the epoch of peak of star formation activity and to investigate the role of galaxies in maintaining the cosmic reionization.

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