Two Speakers: Sandro Tacchella (Harvard CfA) And Jorge K. Barrera-Ballesteros (John Hopkins)

Monday October 2, 2017 12:05 pm

The Formation and Evolution of Bulges and Disks in High-Redshift Galaxies
Speaker: Sandro Tacchella (Harvard CfA)

I will present observations of z~2 star-forming galaxies combining rest-frame far-UV-to-optical HST imaging and VLT SINFONI Adaptive-Optics spectra of the H-alpha line emission. I demonstrate not only that these massive galaxies at the peak of cosmic star-formation activity have already achieved the stellar density distributions that we see in massive spheroids at z=0, but also that they have outward-increasing specific SFR radial profiles, i.e., suppressed star-formation activity in their central bulge regions. I will then use cosmological hydrodynamical zoom-in simulations to explore the physical processes that are responsible for the formation and evolution of bulges in galaxies at these early cosmic times. In addition of comparing these models with my observations, I will present evidence from the simulations that gas-driven compaction is a key phase in the life of galaxies while they evolve along the so-called star-forming Main Sequence.


Chemical Evolution in the Era of IFU surveys
Speaker: Jorge K. Barrera-Ballesteros (John Hopkins)

Abstract:  We have determined the local metallicity of the ionized gas for more than 5×10^5 star forming regions (spaxels) located in 1023 nearby galaxies included in the SDSS-IV MaNGA IFU survey. We use the dust extinction and stellar template fitting in each spaxel to estimate the local gas and stellar mass densities, respectively. We also use the measured rotation curves from H-alpha velocity fields to determine the local escape velocity. We have then analyzed the relationships between the local metallicity and both the local gas fraction (μ) and Vesc. We find that metallicity decreases with both increasing μ and decreasing Vesc. By examining the residuals in these relations we show that the μ-Z relation is more important. We show that the gas-regulator model of chemical evolution seems to provide a reasonable explanation of the metallicity on local scales. The best-fit model parameters of this model are consistent with metal loss been caused by momentum-driven galactic outflows. We also argue that both the gas fraction and local escape velocity are connected to the local stellar surface density, which in turn is a tracer of the epoch at which the local dominant stellar population formed.