SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs

Abstract

We study the spatially resolved excitation properties of the ionised gas in a sample of 646 galaxies using integral field spectroscopy data from SDSS-IV MaNGA. Making use of Baldwin-Philips-Terlevich diagnostic diagrams we demonstrate the ubiquitous presence of extended (kpc scale) low ionisation emission-line regions (LIERs) in both star forming and quiescent galaxies. In star forming galaxies LIER emission can be associated with diffuse ionised gas, most evident as extra-planar emission in edge-on systems. In addition, we identify two main classes of galaxies displaying LIER emission: 'central LIER' (cLIER) galaxies, where central LIER emission is spatially extended, but accompanied by star formation at larger galactocentric distances, and 'extended LIER' (eLIER) galaxies, where LIER emission is extended throughout the whole galaxy.In eLIER and cLIER galaxies, LIER emission is associated with radially flat, low Hα equivalent width of line emission (< 3 Å) and stellar population indices demonstrating the lack of young stellar populations, implying that line emission follows tightly the continuum due to the underlying old stellar population. The Hα surface brightness radial profiles are always shallower than 1/r 2 and the line ratio [OIII]λ 5007/[OII]λ 3727,29 (a tracer of the ionisation parameter of the gas) shows a flat gradient. This combined evidence strongly supports the scenario in which LIER emission is not due to a central point source but to diffuse stellar sources, the most likely candidates being hot, evolved (post-asymptotic giant branch) stars. Shocks are observed to play a significant role in the ionisation of the gas only in rare merging and interacting systems.

The MASSIVE Survey. VI. The Spatial Distribution and Kinematics of Warm Ionized Gas in the Most Massive Local Early-type Galaxies

“…In several of our galaxies, non-central fibers tend to also exhibit these so-called "extended LINER-like" excitation ratios (i.e., low-ionization emission regions or LIERs; Belfiore et al 2016;Johansson et al 2016). In principle, the [N I]/Hβ ratio can help us distinguish between excitation grids for fast shocks and H II regions (see thedetailed discussion by Sarzi et al 2010), but the [N I] line is detected in the centers of only three galaxies.…”

SDSS-IV MaNGA IFS GALAXY SURVEY—SURVEY DESIGN, EXECUTION, AND INITIAL DATA QUALITY

“…For all galaxies observed in the first year, we subtracted the stellar continuum from the spectrum in each spaxel, performedVoronoi binning based on the Hα S/N, and then measured the emission fluxes in each bin, as done by Belfiore et al (2016). We then classified the bins according to their positions on line ratio diagnostic diagrams.…”

SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA

“…The stellar mass surface density ( * S ) is then obtained using the stellar mass derived for each spaxel and then normalized to the physical area of one spaxel. We derive the emission line fluxes following the same procedure described in Belfiore et al (2016). Briefly speaking, the fittings are performed on continuum subtracted spectra using sets of Gaussians (one per line) with a common velocity.…”