The central spectra of massive star-forming galaxies

We have examined the nuclear spectra of very massive star-forming galaxies at z ∼ 0 to understand how they differ from other galaxies with comparable masses, which are typically passive. We selected a sample of 126 nearby massive star-forming galaxies (< 100 Mpc, 10^11.3 M ≤ M_stellar ≤ 10^11.7 M, 1 M yr⁻¹ < SFR < 13 M yr⁻¹) from the 2MRS-Bright WXSC catalogue. LEDA morphologies indicate at least 63% of our galaxies are spirals, while visual inspection of Dark Energy Survey images reveals 75% of our galaxies to be spirals with the remainder being lenticular. Of our sample 59 have archival nuclear spectra, which we have modelled and subsequently measured emission lines ([NII]λ6583, Hαλ6563, [OIII]λ5008, and Hβλ4863), classifying galaxies as star-forming, LINERS or AGNs. Using a BPT diagram we find 83 ± 6 % of our galaxies, with sufficient signal-to-noise to measure all 4 emission lines, to be LINERs. Using the [NII]λ6583/Hαλ6563 emission line ratio alone we find that 79 ± 6 % of the galaxies (46 galaxies) with archival spectra are LINERs, whereas just ∼ 30% of the overall massive galaxy population are LINERs (Belfiore et al., 2016). Our sample can be considered a local analogue of the Ogle et al. (2016, 2019) sample of z ∼ 0.22 massive star-forming galaxies in terms of selection criteria, and we find 64% of their galaxies are LINERs using SDSS spectra. The high frequency of LINER emission in these massive star-forming galaxies indicates that LINER emission in massive galaxies may be linked to the presence of gas that fuels star formation.