SDSS IV MaNGA - The smooth transition between star formation and quiescence and the role of LI(N)ER emission in the z =0 Universe with
We study the spatially resolved excitation properties of the ionised gas in local galaxies by exploiting the first year of data collected by the SDSS-IV MaNGA survey. Based on the spatial distribution of the line ratios we identify 5 classes of galaxies. 1) star forming galaxies; 2) galaxies in which the central few/several kpc are characterised by LINER-like (or LIER) emission, but star formation is occurring in the outer disc (`central LIER', or cLIER); 3) galaxies in which line emission is LINER-like throughout the whole galaxy extent, without evidence for star formation (`extended LIER', or eLIER); 4) passive (line-less) galaxies; 5) a small fraction of merging/interacting galaxies with peculiar line emission.In cLIER and eLIER galaxies LIER emission is associated with old stellar populations and low equivalent width of line emission. This strongly supports the scenario where LIER emission in these galaxies is associated with ionisation by hot, evolved stars, disfavoring models associating LIER emission with shocks. Some contribution to the nuclear LIER emission by a weak AGN cannot be excluded by our data.Except for the common excitation mechanism, cLIERs and eLIERs do not appear to be part of a continuous population. cLIERs are morphologically late types, are mostly located in the green valley, tend to have younger stellar populations (though older than SF galaxies) and have regular gaseous and stellar rotation patterns. These results are in line with a scenario in which SF galaxies are quenched `inside-out', with the central regions producing stars more efficiently and thus exhausting their molecular gas supply sooner.eLIERs are morphological early types, have older stellar populations (indistinguishable from passive) and for most of them the ionised gas either does not show a rotation pattern or the rotation axis is strongly misaligned (or even counter-rotating) relative to the stellar component. These features indicate that eLIERs are likely to be passive galaxies that have re-acquired some gas (either by accretion or stellar mass loss), but this gas is prevented from forming stars, possibly as a consequence of the hard radiation field produced by evolved stars.
American Astronomical Society Meeting Abstracts #227
- Pub Date:
- January 2016