Title：Precise gas-phase metallicity maps of star-forming galaxies at cosmic noon with HST grism spectroscopy

　　Speaker：王鑫(PhD candidate, Department of Physics and Astronomy, UCLA)

　　Personal Info：Xin Wang is currently a 4th year graduate student at Department of Physics and Astronomy, University of California Los Angeles. Xin studies how gas flows, star formation and galactic feedback influence the cycle of baryons and metals as a key ingredient to high-redshift galaxy evolution using diffraction-limited spatially-resolved spectroscopy. In particular, Xin has gained great expertise in slitless grism data reduction associated with the Wide-Field Camera 3 near-infrared channels on the HST, and has been responsible for producing simulations for data that will be acquired by future space-based large missions, e.g., NIRISS on JWST and HLS of WFIRST. Xin has also been working on modeling the mass distribution of galaxy clusters using strong and weak gravitational lensing signals, and improve the source plane morphology reconstruction of multiply imaged galaxies at high redshifts. Previously, Xin was working in the fields of cosmology and gamma-ray bursts.

　　Abstract：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 cosmic noon. For the first time, we bring forward a novel method of obtaining sub-kpc resolution metallicity maps using HST grism spectroscopy of strongly lensed galaxies. The sufficient spatial sampling, achievable only through the synergy of diffraction-limited data and lensing magnification at high redshift, is crucial to avoid spuriously flat gradient measurements. In our most recent paper (Wang et al. 2017), we publish 10 unbiased metallicity maps, using the deep WFC3 near infrared grism data acquired by the Grism Lens-Amplified Survey from Space (GLASS). 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. Tying theories to data, we find that predictions given by analytical chemical evolution models assuming a relatively extended star-formation profile in the early disk formation phase can explain the majority of observed metallicity gradients, without involving galactic feedback or radial outflows. 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 published 10 gradients constitute one third of the entire sample of currently existing sub-kpc resolution metallicity gradient measurements at high redshift. The analysis of the entire GLASS dataset will bring about over 100 more. Our results will revolutionize our understanding of the cycling of metals and how that regulates galaxy growth.

　　Time：Sep. 13 (Wednesday), 10:00 am

　　Place：Room 402, Astronomy Building

欢迎各位老师、同学参加！

　 　南京大学天文与空间科学学院