APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Francesco Belfiore (Cambridge)
Title: The spatially resolved transition between star formation and quiescence with SDSS IV MaNGA
Date (JST): Thu, Jul 14, 2016, 13:30 - 14:30
Place: Seminar Room A
Abstract: I will present recent results from the SDSS-IV MaNGA survey, an integral field spectroscopy (IFS) survey aiming to observe 10.000 local galaxies. We make use of the first year of spatially resolved spectroscopic data to study the properties of the ionized interstellar medium in a sample of more than 600 galaxies.

By making use of several emission line diagnostics, combined with tracers of the age of the underlying stellar population, we demonstrate that low ionization emission-line regions (LIERs) on extended (kpc) scales are inconsistent with ionization from a central point source (active galactic nucleus). Instead, LIERs are consistent with photoionization by hot evolved (post-asymptotic giant branch) stars, which become the main source of ionizing photons once star formation has ceased. Importantly, LIERs are ubiquitous both in early type galaxies (with no signs of current star formation) and in the central regions of late type galaxies, thus providing key insights into the physical properties of regions which have stopped forming stars (i.e. are effectively `quenched').

To demonstrate the importance of correctly associating LIER emission with quiescent regions, I will discuss the properties of a sample of late type galaxies showing LIER-like emission in the central regions. These galaxies are located around the green valley in UV-optical colours and lie below the star formation main sequence defined by star forming galaxies by 0.8 dex. Both morphological indices (Sersic and concentration indices) and stellar kinematics data from MaNGA demonstrate that these galaxies have larger bulges than star forming counterparts. These galaxies are therefore consistent with being star forming galaxies in the process of being slowly quenched `inside-out'.