The volumetric star formation law in the Milky Way

Fraternali, Filippo; Pezzulli, Gabriele; Marasco, Antonino; Iorio, Giuliano; Nipoti, Carlo

doi:10.1051/0004-6361/201936559

Cited by 39 publications

(20 citation statements)

References 126 publications

(183 reference statements)

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“…Taken at face value, the results presented in this work can be interpreted in a broader context, in which SN feedback and starformation are key elements of the same self-regulating cycle (see for example Dopita 1985;Ostriker & Shetty 2011). In B19a and Bacchini et al (2019b), we showed that the SFR volume density correlates with the total gas volume density, following a tight power-law with index ≈2, the volumetric star formation (VSF) law, which is valid for nearby galaxies (both dwarfs and spirals) and the Milky Way. The observed surface densities of the gas and the SFR were converted into volume densities by dividing by the scale height derived under the assumption of hydrostatic equilibrium (same as here).…”

Section: Empirical Evidence For the Self-regulating Cycle Of Star Formation?mentioning

confidence: 69%

Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies

Fraternali

Iorio

Pezzulli

et al. 2020

A&A

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It is widely known that the gas in galaxy discs is highly turbulent, but there is much debate on which mechanism can energetically maintain this turbulence. Among the possible candidates, supernova (SN) explosions are likely the primary drivers but doubts remain on whether they can be sufficient in regions of moderate star formation activity, in particular in the outer parts of discs. Thus, a number of alternative mechanisms have been proposed. In this paper, we measure the SN efficiency η, namely the fraction of the total SN energy needed to sustain turbulence in galaxies, and verify that SNe can indeed be the sole driving mechanism. The key novelty of our approach is that we take into account the increased turbulence dissipation timescale associated with the flaring in outer regions of gaseous discs. We analyse the distribution and kinematics of HI and CO in ten nearby star-forming galaxies to obtain the radial profiles of the kinetic energy per unit area for both the atomic gas and the molecular gas. We use a theoretical model to reproduce the observed energy with the sum of turbulent energy from SNe, as inferred from the observed star formation rate (SFR) surface density, and the gas thermal energy. For the atomic gas, we explore two extreme cases in which the atomic gas is made either of cold neutral medium or warm neutral medium, and the more realistic scenario with a mixture of the two phases. We find that the observed kinetic energy is remarkably well reproduced by our model across the whole extent of the galactic discs, assuming η constant with the galactocentric radius. Taking into account the uncertainties on the SFR surface density and on the atomic gas phase, we obtain that the median SN efficiencies for our sample of galaxies are ⟨ηatom⟩ = 0.015−0.008+0.018 for the atomic gas and ⟨ηmol⟩ = 0.003−0.002+0.006 for the molecular gas. We conclude that SNe alone can sustain gas turbulence in nearby galaxies with only few percent of their energy and that there is essentially no need for any further source of energy.

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Section: Empirical Evidence For the Self-regulating Cycle Of Star Formation?mentioning

confidence: 69%

Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies

Fraternali

Iorio

Pezzulli

et al. 2020

A&A

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“…Next, we must also account for the fast-moving atomic phase of the ISM. Based on the findings of Marasco et al (2017), Bacchini et al (2019) model the velocity dispersion of HI as being directly proportional to the velocity dispersion of H2 with σHI /σH 2 = 2; here, we adopt this approach.…”

Section: Diffusion Coefficient (κ)mentioning

confidence: 99%

“…This is known to be a simplifying assumption. Studies of gas discs have shown that there is significant flaring of scale height with radius; see e.g Bacchini et al (2019). for a discussion.…”

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confidence: 99%

A geostatistical analysis of multiscale metallicity variations in galaxies [I]: Introduction and comparison of high-resolution metallicity maps to an analytic metal transport model

Metha,

Trenti,

Chu

2021

Preprint

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Thanks to recent advances in integral field spectroscopy (IFS), modern surveys of nearby galaxies are capable of resolving metallicity maps of Hii regions down to scales of ∼ 50pc. However, statistical analysis of these metallicity maps has seldom gone beyond fitting basic linear regressions and comparing parameters to global galaxy properties. In this paper (the first of a series), we introduce techniques from spatial statistics that are well suited for detailed analysis of both small-and large-scale metallicity variations within the interstellar media (ISMs) of local galaxies. As a first application, we compare the observed structure of small-scale metallicity fluctuations within 7 local galaxies observed by the PHANGS collaboration to predictions from a stochastic, physically motivated, analytical model developed by Krumholz & Ting. We show that while the theoretical model underestimates the amount of correlated scatter in the galactic metallicity distributions by 3 − 4 orders of magnitude, it provides good estimates of the physical scale of metallicity correlations. We conclude that the ISM of local spiral galaxies is far from homogeneous, with regions of size ∼ 1 kpc showing significant departures from the mean metallicity at each galactocentric radius.

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“…Several authors found that even this "local" SK relation breaks down in lowdensity (Σ gas 10 M pc −2 ) and HI-dominated environments, such as the outskirts of nearby spiral galaxies and of the MW (e.g. Wong & Blitz 2002;Boissier et al 2003;Misiriotis et al 2006;Kennicutt et al 2007;Bigiel et al 2008;Bacchini et al 2019a, hereafter B19a;Bacchini et al 2019b, hereafter B19b), low surface brightness galaxies (e.g. Boissier et al 2008;Wyder et al 2009), and dwarf galaxies (e.g.…”

Section: Introductionmentioning

confidence: 99%

The volumetric star formation law for nearby galaxies

Fraternali

Pezzulli

Marasco

2020

A&A

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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.

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The volumetric star formation law in the Milky Way

Cited by 39 publications

References 126 publications

Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies

Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies

A geostatistical analysis of multiscale metallicity variations in galaxies [I]: Introduction and comparison of high-resolution metallicity maps to an analytic metal transport model

The volumetric star formation law for nearby galaxies

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