The precise evolution of metallicity radial gradients at cosmic noon and its constraints on galaxy evolution

Xin Wang (UCLA)
Friday, January 19, 2018 - 9:15am
The chemo-structural evolution of galaxies at the peak epoch of cosmic star formation is a key issue in galaxy evolution physics that we do not yet fully understand. To address this, we investigate the spatial distribution of gas-phase metallicity in emission-line galaxies in the redshift range of z~1-3, i.e., at the cosmicĀ noon. In a series of papers, we bring forward a novel method of obtaining sub-kpc resolution metallicity maps using space-based grism spectroscopy of strongly lensed galaxies. The sufficient spatial sampling, achievable only through the synergy of diffraction-limited data and lensing magnification, is crucial to avoid spuriously flat gradient measurements. Combining the deep HST/WFC3 near infrared grism data acquired by the GLASS project and a novel Bayesian method inferring metallicity from line fluxes directly, we obtained over 80 unbiased metallicity maps. This improves the number of such measurements at high redshift by one order of magnitude. Our maps reveal diverse galaxy morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, and other physical processes which can affect the gas and metallicity distributions in individual galaxies. We also observe an intriguing correlation between stellar mass and metallicity gradient, consistent with the ``downsizing'' galaxy formation picture that more massive galaxies are more evolved into a later phase of disk growth, where they experience more coherent mass assembly at all radii and thus show shallower metallicity gradients. Our techniques can also be applied to data from future space missions employing grism instruments, i.e., JWST, WFIRST, Euclid, etc.
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