WHAT IS DRIVING THE H i VELOCITY DISPERSION?

By D. Tamburro, H. Rix, A. Leroy, M.-M. Mac Low, F. Walter, Robert C. Kennicutt Jr., Elias Brinks, W. D. de Blok. 2009

254 citations recorded by the source corpus.

We explore what dominant physical mechanism sets the kinetic energy contained in neutral, atomic (H i) gas. Both supernova (SN) explosions and magnetorotational instability (MRI) have been proposed to drive turbulence in gas disks and we compare the H i line widths predicted from turbulence driven by these mechanisms to direct observations in 11 disk galaxies. We use high-quality maps of the H i mass surface density and line width, obtained by The H i Nearby Galaxy Survey. We show that all sample galaxies exhibit a systematic radial decline in the H i line width, which appears to be a generic property of H i disks and also implies a radial decline in kinetic energy density of H i. At a galactocentric radius of r25—often comparable to the extent of significant star formation—there is a characteristic value of the H i velocity dispersion of 10 ± 2 km s−1. Inside this radius, galaxies show H i line widths well above the thermal value (corresponding to ∼8 km s−1) expected from a warm H i component, implying that turbulence drivers must be responsible for maintaining this line width. Therefore, we compare maps of H i kinetic energy to maps of the star formation rate (SFR)—a proxy for the SN rate—and to predictions for energy generated by MRI. We find a positive correlation between kinetic energy of H i and SFR; this correlation also holds at fixed , as expected if SNe were driving turbulence. For a given turbulence dissipation timescale, we can estimate the energy input required to maintain the observed kinetic energy. The SN rate implied by the observed recent SFR is sufficient to maintain the observed velocity dispersion, if the SN feedback efficiency is at least ϵSN ≃ 0.1 × (107 yr/τD), assuming τD ≃ 107 yr for the turbulence dissipation timescale. Beyond r25, this efficiency would have to increase to unrealistic values, ϵ ≳ 1, suggesting that mechanical energy input from young stellar populations does not supply most kinetic energy in outer disks. On the other hand, both thermal broadening and turbulence driven by MRI can plausibly produce the velocity dispersions and kinetic energies that we observe in this regime (≳r25).

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/92111999c98313d9d700f70a9b225fa5cd5007bd

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Citations in the corpus

ON THE INTERPLAY BETWEEN STAR FORMATION AND FEEDBACK IN GALAXY FORMATION SIMULATIONS (2014, background): “A cold gaseous disk is present with velocity dispersions of ∼ 10kms−1 outside of the bulge (r & 1.5kpc), typical of local spiral galaxies (Tamburro et al. 2009; Agertz et al. 2009a).”
TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS (2012, methodology): “…(Mac Low & Klessen 2004; McKee & Ostriker 2007, and references therein), driving turbulence (Kim et al. 2001; de Avillez & Breitschwerdt 2004; Joung & Mac Low 2006; Agertz et al. 2009a; Tamburro et al. 2009) and generating galactic scale outflows (Martin 1999, 2005; Oppenheimer & Davé 2006).”
EXTREMELY INEFFICIENT STAR FORMATION IN THE OUTER DISKS OF NEARBY GALAXIES (2010, methodology): “We take σgas ≈ 11 km/s everywhere, which is a reasonable approximation for the H I velocity dispersion (to within a few km/s) over outer galaxy disks (see Tamburro et al. 2009).”
THE STAR FORMATION RATE OF SUPERSONIC MAGNETOHYDRODYNAMIC TURBULENCE (2009, background): “…for example by the expansion of supernova remnants (Korpi et al. 1999; Kim et al. 2001; de Avillez & Breitschwerdt 2005; Joung & Mac Low 2006; de Avillez & Breitschwerdt 2007; Tamburro et al. 2009), the turbulence integral scale could be much larger than the size of individual star-forming regions.”
The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae (2016, background): “…show that warm, cold, and molecular gas are shaped by supersonic turbulent motions with a typical velocity dispersion from few to ≈10 km s−1 (Larson 1981; Goodman et al. 1998; Heiles & Troland 2003; Petric & Rupen 2007; Tamburro et al. 2009; Caldú-Primo et al. 2013; Ianjamasimanana et al. 2015).”
A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, methodology): “This is true regardless of whether these motions are traced using the 21 cm line of H I (van Zee & Bryant 1999; Petric & Rupen 2007; Tamburro et al. 2009; Burkhart et al. 2010; Ianjamasimanana et al. 2012, 2015; Stilp et al. 2013; Chepurnov et al. 2015), the low-J lines of CO (Caldú-Primo et al.…”
On the universality of supersonic turbulence (2013, background): “…VázquezSemadeni et al. 2010; Federrath et al. 2011b; Robertson & Goldreich 2012; Choi, Shlosman & Begelman 2013), and galactic spiralarm compression of HI clouds (Dobbs & Bonnell 2008; Dobbs et al. 2008), as well as magneto-rotational instability (Piontek & Ostriker 2007; Tamburro et al. 2009).”
MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED (2009, background): “For star-forming galaxies, Tamburro et al. (2009) indi- cate a characteristic HI linewidth value of 8-12 km s−1 in 11 spiral galaxies.”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “…2010; Elmegreen & Burkert 2010; VázquezSemadeni et al. 2010; Federrath et al. 2011c; Robertson & Goldreich 2012), and galactic spiral-arm compression of HI clouds (Dobbs & Bonnell 2008; Dobbs et al. 2008) and magnetorotational instability (MRI) (Piontek & Ostriker 2007; Tamburro et al. 2009).”
Comparing the statistics of interstellar turbulence in simulations and observations - Solenoidal versus compressive turbulence forcing (2009, background): “The dispersion of the probability distribution function (PDF) of the gas density is roughly three times larger for com- 6 See also Tamburro et al. (2009) for an observational study. pressive forcing than for solenoidal forcing.”
Physical Processes in the Interstellar Medium (2014, methodology): “One of the remarkable features of spiral galaxies is the nearly constant velocity dispersion σ, e.g. as measured using the Hi 21 cm emission line, seemingly independent of galaxy mass and type (Dickey & Lockman, 1990; van Zee & Bryant, 1999; Tamburro et al., 2009).”
REGULATION OF STAR FORMATION RATES IN MULTIPHASE GALACTIC DISKS: A THERMAL/DYNAMICAL EQUILIBRIUM MODEL (2010, background): “Total vertical velocity dispersions in HI gas in external galaxies are also observed to be in the range 5− 15 km s−1, decreasing outward from the center (Tamburro et al. 2009).”
Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, methodology): “Here accretion from the extended gaseous halo, maybe in concert with the magneto-rotational instability (Tamburro et al. 2009), is the only astrophysical driving source available.”