Star Formation Thresholds in Galactic Disks

By Crystal L. Martin, Robert C. Kennicutt Jr.. 2001

390 citations recorded by the source corpus.

We report the first results of a detailed study of the star formation law in a sample of 32 nearby spiral galaxies with well-measured rotation curves, H I and H2 (as traced by CO) surface density profiles, and new Hα CCD photometry. In this paper we present an atlas of Hα images and radial surface brightness profiles and describe a surface density threshold in the star formation law. Prominent breaks in the Hα surface brightness profiles are identified in nearly all of the actively star-forming disks, confirming previous claims of star formation thresholds based on lower quality data. We measure the ratio of the gas density to the critical density for local gravitational stability at the threshold radii. The outer threshold radii observed in Sab-Sdm galaxies are in general agreement with those expected from the Toomre Q stability criterion, confirming earlier work, but with a significant variation that appears to be weakly correlated with galaxy type. Such a trend could plausibly reflect variations in the relative contribution of the stellar disk to the instability of the gas disk across this range of galaxy types. Among disks with subcritical gas surface densities, and outside the threshold radius in star-forming disks, the number of isolated H II regions increases as the gas surface density approaches the critical density. At the thresholds, the gas surface densities span a wide range, and the atomic/molecular gas fraction is highest in the disks having the lowest total gas surface density. The simple Toomre condition fails to account for the active star formation in the inner disks of low-mass spirals such as NGC 2403 and M33. An alternative stability criterion based on the shear in the disk provides a better description of these disks but is a less accurate indicator of the outer edges of star-forming disks than the Toomre criterion. These results strongly support the view that the formation of gravitationally bound interstellar clouds regulates the onset of widespread star formation, at least in the outer regions of galactic disks.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/b3b6a61cf17feb4eca4ecaa846509bc84efd6c0a

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

The Relationship between Molecular Gas Tracers and Kennicutt-Schmidt Laws (2007, background): “Moreover, in a galactic disk, h ∝ Σg/n and n ∝ Ω2/Q (e.g. Thompson et al. 2005); since in star-forming disks the Toomre-Q is about unity (Martin & Kennicutt 2001), substituting for h immediately gives Σ̇∗ ∝ ΣΩ, the alternate form of the Kennicutt (1998a,b) law.”
THE STATE OF THE GAS AND THE RELATION BETWEEN GAS AND STAR FORMATION AT LOW METALLICITY: THE SMALL MAGELLANIC CLOUD (2011, background): “Several subsequent studies focused on the star formation law within galaxies, employing high resolution molecular and H I observations (Martin & Kennicutt 2001; Wong & Blitz 2002; Boissier et al. 2003).”
The Role of Pressure in GMC Formation II: The H2-Pressure Relation (2006, methodology): “In general, the interstellar medium in dwarf galaxies is dominated by H I rather than molecular gas, and it is in M33 and in dwarf galaxies that Martin & Kennicutt (2001) find that their star formation prescription breaks down.”
A General Theory of Turbulence-regulated Star Formation, from Spirals to Ultraluminous Infrared Galaxies (2005, background): “While this is well justified observationally (Quirk 1972; Kennicutt 1989; Martin & Kennicutt 2001), previous work has also provided a theoretical explanation, which is part of any complete theory of star formation.”
Cold gas properties of the Herschel Reference Survey - II. Molecular and total gas scaling relations (2014, result): “…the existence of a tight relation between the gas and the star-formation-ratesurface density, generally called Schmidt law (Schmidt 1959; Kennicutt 1998), thereby extending earlier results from Kennicutt (1989), Martin & Kennicutt (2001), and Wong & Blitz (2002) on a local cale of a few 100 pc.”
Disk Galaxy Formation in a Λ Cold Dark Matter Universe (2004, background): “The stiffer equation of state helps to regulate star formation so that it occurs at a rate consistent with observations of isolated disk galaxies (Kennicutt 1989, 1998; Martin & Kennicutt 2001) once the free parameter t 0 of the model is properly adjusted (see Springel & Hernquist 2003a, 2003b).”
An uncertainty principle for star formation - I. Why galactic star formation relations break down below a certain spatial scale (2014, background): “This is why discsdo not show the same truncation in the UV (Thilker et al. 2007) as when observed in Hα (Martin & Kennicutt 2001; also see Bigiel et al. 2010).”
On the fraction of star formation occurring in bound stellar clusters (2012, background): “As a fiducial value Q = 1.5 is assumed, but it is known to vary between 0.5 and 6 (e.g. Kennicutt 1989; Martin & Kennicutt 2001).”
Toward First-Principle Simulations of Galaxy Formation: I. How Should We Choose Star-Formation Criteria in High-Resolution Simulations of Disk Galaxies? (2008, methodology): “The value of this parameter is usually calibrated by the global star formation properties, the SchmidtKennicutt relation (Kennicutt 1998; Martin & Kennicutt 2001).”
Theory of Star Formation (2007, background): “Kennicutt (1989) and Martin & Kennicutt (2001) argue that disk thresholds are set by gravitational stability considerations in shearing, rotating disks, and find a mean value of Q ≈ 1.4 when they adopt a constant value ceff = 6 km s −1 for their sample.”
The correlation of star formation quenching with internal galaxy properties and environment (2008, background): “Cold gas is turned into stars in the galactic disc following the Schmidt–Kennicutt law (Kennicutt 1989, 1998), and gas with surface density lower than a critical threshold density (e.g. Martin & Kennicutt 2001) does not form stars.”
The Mass-Metallicity Relation at z≳2 (2006, background): “In a typical disk galaxy today, ∼ 40% of the gas mass is not included by the Schmidt law (Martin & Kennicutt 2001); this fraction could plausibly be higher in the young starbursts in our sample.”
ENVIRONMENTAL DEPENDENCE OF THE KENNICUTT–SCHMIDT RELATION IN GALAXIES (2010, background): “For example, instead of a well-defined surface density threshold at low ΣH below which ΣSFR drops to zero (Martin & Kennicutt 2001), observations indicate continuous relation between star formation rate and gas surface densities (Boissier et al. 2007) down to small ΣH, albeit with a steeper slope…”
The Relation between Quasar and Merging Galaxy Luminosity Functions and the Merger-driven Star Formation History of the Universe (2006, background): “This gives an e-folding time for fgas of tH/ ln (10) 6 Gyr, similar to that expected for quiescent spiral galaxies following a Schmidt-type star formation law (Kennicutt 1998; Rownd & Young 1999; Martin & Kennicutt 2001; Springel & Hernquist 2003a; Li et al. 2005, 2006).”
Star formation and feedback in smoothed particle hydrodynamic simulations – I. Isolated galaxies (2006, methodology): “The density criterion limits star formation to the dense regions of galaxies, which corresponds well to the density limits observed by Martin & Kennicutt (2001).”
Cosmological smoothed particle hydrodynamics simulations: a hybrid multiphase model for star formation (2002, background): “In addition, there is a clear threshold behaviour for star formation, with ΣSFR very rapidly falling at densities below ∼ 10M⊙pc −2 (Kennicutt, 1989, 1998; Martin & Kennicutt, 2001).”
STAR FORMATION IN DISK GALAXIES. I. FORMATION AND EVOLUTION OF GIANT MOLECULAR CLOUDS VIA GRAVITATIONAL INSTABILITY AND CLOUD COLLISIONS (2008, background): “Martin & Kennicutt (2001) argued that the outer edge of the star-forming disk is set by the boundary between the gravitationally unstable Q .”
What controls star formation in the central 500 pc of the Galaxy (2013, methodology): “The existence of such a threshold is suggested by the sharply truncated HII discs in galaxies, which indicate that beyond a certain galactocentric radiusΣSFR falls off more rapidly than suggested by equations (1–2) (Kennicutt 1989; Martin & Kennicutt 2001; Bigiel et al. 2010).”
The evolution of the Milky Way from its earliest phases: Constraints on stellar nucleosynthesis (2004, background): “…differs from other models in the literature in two aspects: it considers an almost independent evolution between the halo and thin disk components (see also Pagel and Tautvaisiene 1995), and it assumes a threshold in the star formation process (see Kennicutt 1989, 1998; Martin & Kennicutt 2001).”