SHAO Astrophysics Colloquium
Title: Galaxy assembly across cosmic time
Speaker: Yingjie Peng (KIAA)
Time: 3:00 pm, December 26th (Thursday)
Location: Lecture Hall, 3rd floor
Abstract:
I will discuss galaxy assembly across cosmic time in four key aspects: star formation, quenching, stellar mass function evolution and galaxy-halo connection, in both observation and theory. I will show new evidences from multi-wavelength observations from optical to radio that demonstrate the detailed quenching process of galaxies, which provides stringent constraint on the physical mechanism of quenching. These new observational evidences are then compared to theoretic predictions and hydrodynamical simulations. I will discuss the great success and failure of simulations in reproducing observations, which put new constraints on the AGN feedback physics. If time allows, I will also discuss plans to explore galaxy assembly with forthcoming major observing facilities.
Seminar talk
Title: Dissecting the Baryon Cycle and Star Formation with Space-based Slitless Spectroscopy
Speaker: Xin Wang (Caltech/UCLA)
Time: 3:00 pm, December 24th (Tuesday).
Location: Middle conference room, 3rd floor
Abstract:
To explore the chemo-structural properties of galaxies and understand quantitatively the cycling of baryons at the peak epoch of cosmic star formation, I developed a highly effective method for sub-kiloparsec scale spatially resolved spectroscopy of strongly lensed galaxies using space-based wide-field slitless grism data. Applying this method to the deep Hubble Space Telescope (HST) near-infrared grism observations, I obtained precise gas-phase metallicity maps for a sample of 79 star-forming galaxies in the redshift range of 1.2 ? z ? 2.3. Over half of the galaxies in my sample reside in the dwarf mass regime (Mstar ? 10^9 Msun), making my sample the first statistically representative sample of high-redshift dwarf galaxies with their metallicity spatial distribution measured with sufficient resolution. The metallicity maps obtained in my work 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 star-forming galaxies. For the first time, I discovered two dwarf 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. I also measure a negative correlation between stellar mass and metallicity gradient, which strongly suggests that strong feedback, not secular processes, is the primary governor of the chemo-structural evolution of star-forming galaxies at high redshifts. Furthermore, I find that the intrinsic scatter of metallicity gradients increases with decreasing stellar mass and increasing specific star-formation rate. This increase in the intrinsic scatter is likely caused by the combined effect of cold-mode gas accretion and merger-induced starbursts, with the latter more predominant in the dwarf mass regime. My method can be readily applied to data from future space missions employing grism instruments, e.g., JWST, Euclid, WFIRST, and the Chinese Space Station Telescope. Combined with the continuous input of HST resources, these data will revolutionize our understanding of the chemo-structural evolution of galaxies throughout vast cosmic time.