The volumetric star formation law for nearby galaxies

Abstract

In the last decades, much effort has been put into finding the star formation law, which could unequivocally link the gas and the star formation rate (SFR) densities measured on a sub-kiloparsec scale in star-forming galaxies. The conventional approach of using the observed surface densities to infer star formation laws has however revealed a major and well-known issue, as such relations are valid for the high-density regions of galaxies but break down in low-density and HI-dominated environments. Recently, an empirical correlation between the total gas (HI+H2) and the SFR volume densities was obtained for a sample of nearby disc galaxies and for the Milky Way. This volumetric star formation (VSF) law is a single power-law with no break and a smaller intrinsic scatter with respect to the star formation laws based on the surface density. In this work, we explore the VSF law in the regime of dwarf galaxies in order to test its validity in HI-dominated, low-density, and low-metallicity environments. In addition, we assess this relation in the outskirts of spiral galaxies, which are low-density and HI-dominated regions similar to dwarf galaxies. Remarkably, we find that the VSF law, namely ρSFR ∝ ρgasα with α ≈ 2, is valid for both these regimes. This result indicates that the VSF law, which holds unbroken for a wide range of gas (≈3 dex) and SFR (≈6 dex) volume densities, is the empirical relation with the smallest intrinsic scatter and is likely more fundamental than surface-based star formation laws.

Star formation scaling relations at ∼100 pc from PHANGS: Impact of completeness and spatial scale

“…Moreover, the scatter of the rKS has been interpreted as individual star-forming regions undergoing independent evolutionary life cycles (Schruba et al 2010;Feldmann et al 2011), and its dependence on spatial scale provides insight into the timescales of the star formation cycle (Kruijssen & Longmore 2014;Kruijssen et al 2018). Additionally, Bacchini et al (2019aBacchini et al ( , 2020 found a tight correlation between the gas and the SFR volume densities in nearby disk galaxies, suggesting that the scatter of the rKS could be in part related to projection effects caused by the flaring scale height of gas disks. In addition to the rSFMS and the rKS, recently Lin et al (2019), Ellison et al (2021), and Morselli et al (2020) reported the existence of a resolved molecular gas main sequence (rMGMS) as the correlation between the local Σ mol.…”

Star formation in the nearby dwarf galaxy DDO 53: interplay between gas accretion and stellar feedback

“…These values translated into a gas mass densities are typical for other nearby dwarfs and the outskirts of massive galaxies (e.g. Abramova & Zasov 2011;Bacchini et al 2019Bacchini et al , 2020, however the derived values depend on two very uncertain parameters -disc scale height and inclination. In particular, the inclination angle estimates for DDO 53 vary significantly in the literature -from i = 27 • Oh et al (2011) to i = 56 • Boisvert & Rhee (2016).…”

Determining the Timescale over Which Stellar Feedback Drives Turbulence in the ISM: A Study of four Nearby Dwarf Irregular Galaxies

“…As individual and clustered SNe (superbubbles) are likely the most important mechanism for driving turbulence in the ISM (Norman & Ferrara 1996;Ostriker & Shetty 2011;Kim et al 2011;El-Badry et al 2019), the maximum physical scale was limited to the scale of these events. From simulations and theory, the predicted range over which superbubbles input momentum into the ISM is about one to a few times the scale height of the galaxy (Kim et al 2017;Gentry et al 2017), or roughly 200 to 600 pc for dwarf galaxy disk thicknesses (Bacchini et al 2020b). Thus, region sizes larger than 400 pc would not be able to identify the impacts of the local star formation activity from the global star formation activity on the ISM.…”