AKARI Near-Infrared Spectroscopy of SDSS-Selected Blue Early-Type Galaxies

TL;DR

This study uses AKARI near-infrared spectroscopy to analyze SDSS-selected blue early-type galaxies, revealing their stellar populations, dust attenuation, and star formation activity, and proposing an evolutionary sequence involving SF, Seyfert, and LINER phases.

Contribution

First near-infrared spectroscopic survey of SDSS-selected blue early-type galaxies, providing insights into their stellar populations and evolutionary stages.

Findings

BEGs are old, metal-rich, with moderate dust and active star formation.

Seyfert BEGs exhibit more active star formation than LINER BEGs.

Evidence suggests an evolutionary sequence: star-forming, Seyfert, then LINER BEGs.

Abstract

A near-infrared (NIR; 2.5 - 4.5 micron) spectroscopic survey of SDSS(Sloan Digital Sky Survey)-selected blue early-type galaxies (BEGs) has been conducted using the AKARI. The NIR spectra of 36 BEGs are secured, which are well balanced in their star-formation(SF)/Seyfert/LINER type composition. For high signal-to-noise ratio, we stack the BEG spectra all and in bins of several properties: color, specific star formation rate and optically-determined spectral type. We estimate the NIR continuum slope and the equivalent width of 3.29 micron PAH emission. In the comparison between the estimated NIR spectral features of the BEGs and those of model galaxies, the BEGs seem to be old-SSP(Simple Stellar Population)-dominated metal-rich galaxies with moderate dust attenuation. The dust attenuation in the BEGs may originate from recent star formation or AGN activity and the BEGs have a clear feature of PAH emission, the evidence of current SF. BEGs show NIR features different from those of ULIRGs, from which we do not find any clear relationship between BEGs and ULIRGs. We find that Seyfert BEGs have more active SF than LINER BEGs, in spite of the fact that Seyferts show stronger AGN activity than LINERs. One possible scenario satisfying both our results and the AGN feedback is that SF, Seyfert and LINER BEGs form an evolutionary sequence: SF - Seyfert - LINER.