Abstracts Astronomy & Space Science

Using strong gravitationally lensed galaxies to probe the metallicity history of star-forming galaxies between redshift 1 and 3

by Tiantian Yuan

Ph.D. University of Hawaii at Manoa 2012. This thesis conducts the investigation into the metallicity history of galaxies between redshift 1 and 3, using gravitationally lensed galaxies. We use metallicity as a tool to understand the formation and evolution history of galaxies. We direct our research in two areas. 1. We combine our new sample of gravitationally lensed galaxies with existing lensed and nonlensed samples to conduct the largest investigation so far into the mass-metallicity (MZ) relation at z > 1. We apply a self-consistent metallicity calibration scheme to investigate the metallicity evolution of star-forming galaxies as a function of redshift. We find that at the median redshift of z = 2.07, the median metallicity of the lensed sample is 0.35 dex lower than the local SDSS starforming galaxies and 0.18 dex lower than the z ∼ 0.8 DEEP2 galaxies. Our lensed sample shows a much larger metallicity range and scatter (> 0.2 dex) than the z ∼ 2 UV selected galaxies at similar masses. These offsets translate into a metallicity evolution of-0.23±0.01 dex per unit redshift from z ∼ 0 → 1, and-0.14 ± 0.08 dex per unit redshift from z ∼ 1 → 3. A more rapid evolution is seen between z ∼ 1 → 3 (with a mean fall in metallicity of-0.05 ± 0.01 dex Gyr−1) than z ∼ 0 → 1 (-0.020 ±0.001 dex Gyr−1). This evolution agrees with the most recent cosmological hydrodynamic simulations with momentum driven winds within the errors. 2. Combining the magnification power of gravitational lensing and AO-aided Integral Field Unit spectrographs (IFUs) is the only way to achieve sufficient signal-to-noise and angular resolution for spatially resolved metallicity studies. Using this technique, we present the first metallicity gradient measurement for a grand-design face-on spiral galaxy at z ∼ 1.5. The gradients of our spiral and another 2 lensed galaxies at z ∼ 2 are much steeper than local disk galaxies, supporting an 'inside-out' galaxy formation scenario. We also report spatially resolved emission lines of a z ∼ 1 lensed galaxy. We find significant shock excitation due to galactic outflows. Our analysis suggests that shocked regions may mimic flat or inverted metallicity gradients at high redshift. We find that high angular resolution observations provide the most accurate metallicity gradient measurement,whereas seeing-limited studies under estimate the slope of the gradients