The Scaling Relations and Star Formation Laws of Mini-Starburst Complexes

Abstract

The scaling relations and the star formation laws for molecular cloud complexes in the Milky Way is investigated using data from the 12 CO 1-0 CfA survey and from the literatures. We compare their masses M gas , mass surface densities Σ Mgas , radii R, velocity dispersions σ, star formation rates SF R, and SFR densities Σ SFR with those of structures ranging from cores, clumps, Giant Molecular Clouds (GMCs), to Molecular Cloud Complexes (MCCs), and to Galaxies, spanning 8 orders of magnitudes in size and 13 orders of magnitudes in mass. MCC are mostly large (R > 50 pc), massive (∼ 10 6 M ⊙ ) gravitationally unbound cloud structures. This results in the following universal relations:Mgas , SF R ∼ M gas 0.9 , and SF R ∼ σ 2.7 .Variations in the slopes and the coefficients of these relations are found at individual scales signifying different physics acting at different scales. Additionally, there are breaks at the MCC scale in the σ − R relation and between the starburst and the normal star-forming objects in the SF R − M gas and Σ SFR -Σ Mgas relations. Therefore, we propose to use the Schmidt-Kennicutt diagram to distinguish the starburst from the normal star-forming structures by applying a Σ Mgas threshold of ∼ 100 M ⊙ pc −2 and a Σ SFR threshold of 1 M ⊙ yr −1 kpc −2 . Mini-starburst complexes are gravitationally unbound MCCs that have enhanced Σ SFR (>1 M ⊙ yr −1 kpc −2 ), probably caused by dynamic events such as radiation pressure, colliding flows, or spiral arm gravitational instability. Because of the dynamical evolution, gravitational boundedness does not play a significant role in characterizing the star formation activity of MCCs, especially the mini-starburst complexes, which leads to the conclusion that the formation of massive stars and clusters is dynamic. We emphasize the importance of understanding mini-starburst in investigating the physics of starburst galaxies.

Extreme star formation in the Milky Way: luminosity distributions of young stellar objects in W49A and W51

“…Examples are RCW 106, Cygnus X, W43, W49, and W51 (Rodgers, Campbell & Whiteoak 1960;Schneider et al 2006;Nguyen-Luong et al 2011;Galván-Madrid et al 2013;Ginsburg et al 2015) with their inferred star-formation efficiency, the amount of star-forming material and current, ongoing star formation cited as reasons for this classification. However, the star-formation rate densities of W43, W49, and W51 are an order of magnitude greater than the other regions on this list, with W49 and W51 having an order of magnitude greater SFR than all other regions (Nguyen-Luong et al 2016). This, together with other results implying that the presence of W49 and W51 significantly affects the mean starformation efficiency on kiloparsec scales (Moore et al 2012), makes it clear that these two regions are exceptional within the Galaxy.…”

The MALATANG Survey: The LGAS–LIR Correlation on Sub-kiloparsec Scale in Six Nearby Star-forming Galaxies as Traced by HCN J = 4 → 3 and HCO+ J = 4 → 3

“…However, the slope steepens for the SFR H 2 S S -relation if we expand the sample to include galaxies with extreme starbursts, such as luminous infrared galaxies (LIRGs, L L L 10 10 11 IR 12  <   ) and ultraluminous infrared galaxies (ULIRGs, L L 10 IR 12   ), which is evident from both observations (e.g., Gao & Solomon 2004b;Daddi et al 2010;Liu et al 2015b) and theoretical predictions (e.g., Krumholz & McKee 2005;Elmegreen 2015Elmegreen , 2018. In addition, a breakdown of the KS law is found at giant molecular cloud (GMC) scales of a few tens of parsecs (e.g., Onodera et al 2010;Nguyen-Luong et al 2016), which is attributed to the dynamical evolution of GMCs and the drift of young clusters from their GMCs.…”

Testing star formation laws in a starburst galaxy at redshift 3 resolved with ALMA

“…Numerous star formation relations have been proposed in a quest to universalize the theory of star formation, by linking the star formation rate (SFR) with the mass of gas, its freefall time, virial parameter, magnetic field strength and turbulence (Silk 1997;Kennicutt 1998a;Elmegreen 2002;Shi et al 2011;Krumholz et al 2012 (hereafter, KDM12); Renaud et al 2012;Escala 2015;Elmegreen & Hunter 2015;Salim et al 2015 (hereafter, SFK15) ;Elmegreen 2015;Nguyen-Luong et al 2016;Miettinen et al 2017). While E-mail: f2013440@pilani.bits-pilani.ac.in (PS) these relations have been shown to be valid for star-forming regions in the Milky Way and local galaxies (Bigiel et al 2008), the lack of spatial resolution has limited us in testing them on high-redshift sources with z > 1.…”