Local Volume Late-Type Galaxies with an Extreme Ratio of $H\alpha$-to-$FUV$ Star-Formation Rates

Abstract

Using a currently most representative sample of 477 late-type galaxies within 11 Mpc of the Milky Way with measured star-formation rates ($SFR$s) from the far ultraviolet ($FUV$) and H$\alpha$ emission line fluxes, we select galaxies with the extreme ratios: $SFR(H\alpha )/SFR(FUV)>2$ and $SFR(H\alpha )/SFR(FUV)<1/20$. Each subsample amounts to $\sim 5$\% of the total number and consists of dwarf galaxies with the stellar masses $M^{\ast }/M_{\odot }=(5.5-9.5)$~dex. In spite of a huge difference in their $SFR(H\alpha )$ activity on a scale of $\sim 10$~ Myr, the temporarily "excited" and temporarily "quiescent" galaxies follow one and the same relation between $SFR(FUV)$ and $M^{\ast }$ on a scale of $\sim 100$~Myr. Their average specific star-formation rate $\log [SFR(FUV)/M^{\ast }]=-10.1\pm 0.1$ (yr${}^{-1}$) coinsides with the Hubble parameter $\log (H_0)=-10.14$ (yr${}^{-1}$). On a scale of $t\sim 10$~Myr, variations of $SFR$ have a moderate flash amplitude of less than 1 order above the main-sequence and a fading amplitude to 2 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 neighbor exhibits only a low average excess of $SFR$ caused by tidal interactions.

Will be published in MNRAS, 11 pages, 6 figures, 3 tables

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Cited by in corpus (4)

• What Causes The Formation of Disks and End of Bursty Star Formation?
• ELVES III: Environmental Quenching by Milky Way-Mass Hosts
• Ultra-Diffuse Galaxies as Extreme Star-forming Environments I: Mapping Star Formation in HI-Rich UDGs
• The recent star formation history of NGC 628 on resolved scales