Mon. Not. R. Astron. Soc., 506, 1346-1354 (2021/September-1)
Local Volume late-type galaxies with an extreme ratio of H α-to-FUV SFRs.
KARACHENTSEV I.D., KAISINA E.I. and KAISIN S.S.
Abstract (from CDS):
Using a currently most representative sample of 477 late-type galaxies within 11 Mpc of the Milky Way with measured star formation rates (SFRs) from the far-ultraviolet (FUV) and H α emission line fluxes, we select galaxies with the extreme ratios: SFR(H α)/SFR(FUV) > 2 and SFR(H α)/SFR(FUV) < 1/20. Each subsample amounts to ∼5 per cent of the total number and consists of dwarf galaxies with the stellar masses M*/M☉ = (5.5 - 9.5) dex. In spite of a huge difference in their SFR(H α) activity on a scale of ∼10 Myr, the temporarily 'excited' and temporarily 'quiescent' galaxies follow one and the same relation between SFR(FUV) and M* on a scale of ∼100 Myr. Their average specific SFR log [SFR(FUV)/M*] = -10.1 ± 0.1 (yr–1) coinsides with the Hubble parameter log (H0) = -10.14 (yr–1). On a scale of t ∼ 10 Myr, variations of SFR have a moderate flash amplitude of less than one order above the main sequence and a fading amplitude to two orders below the average level. In general, both temporarily excited and temporarily quiescent galaxies have almost similar gas fractions as normal main-sequence galaxies, being able to maintain the current rate of star formation on another Hubble time-scale. Ranging the galaxies according to the density contrast produced by the nearest massive neighbour exhibits only a low average excess of SFR caused by tidal interactions.