The First Census of Precise Metallicity Gradients in Dwarf Galaxies at Cosmic Noon

Xin Wang (UCLA)
Friday, November 9, 2018 - 3:00pm

Dwarf galaxies (Mstar < 10^9 Msun) provide unique probes of 

cosmic structure formation on the smallest scales, and represent the most

compelling testbeds for galactic feedback since they are more susceptible 

to feedback processes than their high-mass counterparts. However, their

chemo-structural properties at cosmic noon (i.e. z~2) have remained

unexplored, due to their intrinsically small size and insufficient spatial sampling.

To address this, we develop a highly effective method to obtain sub-kiloparsec

resolution (i.e. precise) gas-phase metallicity maps of strongly lensed galaxies

using space-based slitless spectroscopy. Applying our method to the deep

Hubble Space Telescope near-infrared grism data, we obtain precise metallicity

maps of 81 star-forming galaxies at z~1.2-2.3, over half of which reside in the

dwarf mass regime. Our work presents the first statistically representative

sample of high-z dwarf galaxies with their metallicity spatial distribution 

measured with sufficient resolution. These metallicity maps reveal a variety

of baryonic physics, such as efficient radial mixing from tidal torques, rapid

accretion of low-metallicity gas, and various feedback processes which can

significantly influence the chemo-structural properties of dwarf galaxies. In

particular, we find two galaxies at z~2 displaying strongly inverted metallicity

radial gradients, suggesting that powerful galactic winds triggered by central

starbursts carry the bulk of stellar nucleosynthesis yields to the outskirts.

Furthermore, 10% of the metallicity gradients measured in our sample are

inverted, which are hard to explain by current cosmological zoom-in hydro-

simulations and analytical chemical evolution models. Our method can also 

be readily applied to data from future space missions employing grism

instruments, e.g. JWST, WFIRST, Euclid.

Talk Type: