Implications for the formation of star clusters from extragalactic star formation rates

By C. Weidner, Pavel Kroupa, S. Larsen. 2004

150 citations recorded by the source corpus.

Observations indicate that young massive star clusters in spiral and dwarf galaxies follow a relation between luminosity of the brightest young cluster and the star formation rate (SFR) of the host galaxy, in the sense that higher SFRs lead to the formation of brighter clusters. Assuming that the empirical relation between maximum cluster luminosity and SFR reflects an underlying similar relation between maximum cluster mass (M ecl,max ) and SFR, we compare the resulting SFR(M ecl,max ) relation with different theoretical models. The empirical correlation is found to suggest that individual star clusters form on a free-fall time-scale with their pre-cluster molecular-cloud-core radii typically being a few parsecs independent of mass. The cloud cores contract by factors of 5-10 while building up the embedded cluster. A theoretical SFR(M ecl,max ) relation in very good agreement with the empirical correlation is obtained if the CMF of a young population has a Salpeter exponent of β 2.35 and if this cluster population forms within a characteristic time-scale of a 1-10 Myr. This short time-scale can be understood if the interstellar medium is pressurized, thus precipitating rapid local fragmentation and collapse on a galactic scale. Such triggered star formation on a galactic scale is observed to occur in interacting galaxies. With a global SFR of 3-5 M ○. yr -1 , the Milky Way appears to lie on the empirical SFR(M ecl,max ) relation, given the recent detections of very young clusters with masses near 10 5 M ○. in the Galactic disc. The observed properties of the stellar population of very massive young clusters suggests that there may exist a fundamental maximum cluster mass, 10 6 < M ecl,max */M ○. < 10 7 .

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/2f75793743e1959a4bfe2c6483dbdcb8ce07a404

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Citations in the corpus

Star Cluster Demographics. I. A General Framework and Application to the Antennae Galaxies (2006, background): “Several other studies have also begun to address the important role this size-of-sample effect can play in the observed properties of star cluster systems (e.g., Billet et al. 2002; Hunter et al. 2003; Weidner et al. 2004).”
Probing the role of the galactic environment in the formation of stellar clusters, using M83 as a test bench (2015, methodology): “The dashed black line is a fit to the sample by Larsen (2002) and presented in Weidner et al. (2004).”
On the star formation rate – brightest cluster relation: estimating the peak star formation rate in post-merger galaxies (2008, methodology): “Weidner et al. (2004), on the other hand, attribute this offset to star formation proceeding in short bursts in small galaxies (e.g. Searle & Sargent 1972).”
The maximum stellar mass, star-cluster formation and composite stellar populations (2005, methodology): “M ecl,min (=5 M , Taurus–Auriga type ‘clusters’) is the minimal cluster mass, while the maximal cluster mass, M ecl,max, depends on the galaxy-wide SFR (Weidner et al. 2004).”
The stellar and sub-stellar IMF of simple and composite populations (2011, methodology): “1 in Weidner & Kroupa 2005, as derived by Weidner et al. 2004 using observed maximum star cluster masses).”
Constraints on star formation driven galaxy winds from the mass–metallicity relation at z= 0 (2010, background): “Like Köppen et al. (2007), we follow Weidner et al. (2004) and take the minimum mass a star cluster can have to be 5M⊙ and the maximum mass to be governed by the galaxy-wide star formation rate such that log(Mecl,max/M⊙) = 4.93 + 0.75 log(ṀSFR/[M⊙ yr −1]).”
Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, methodology): “The mmax − Mecl relation, mmax = K1(Mecl), has been established from observed ECs [287] and Mecl,max = K2(SFR) is constrained by extragalactic star-forming galaxies [288].”
The mass function of young star clusters in spiral galaxies (2008, background): “…linear relation between the luminosity of the brightest cluster in a galaxy and the total number of clusters, as expected if luminosities are drawn at random from a power-law distribution with slope≈−2 (Billett et al. 2002; Larsen 2002; Weidner et al. 2004; Whitmore 2003; Whitmore et al. 2007).”
Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity (2012, background): “Under conditions when the galaxy-wide star formation rate SFR> 27M⊙ yr −1 star burst clusters with masses Mecl > 10 6M⊙ form (Weidner et al. 2004).”
Local-Group tests of dark-matter concordance cosmology - Towards a new paradigm for structure formation (2010, background): “TDGs may also form with globular clusters as long as the star-formation rate surpasses a fewM⊙/yr for 10 Myr (Weidner et al. 2004).”
The spatial distribution of star formation in the solar neighbourhood: do all stars form in dense clusters? (2010, background): “We also review what surface densities are required to identify “clusters” according to definitions provided by Carpenter (2000); Lada & Lada (2003); Allen et al. (2007); Jørgensen et al. (2008); Gutermuth et al. (2009) in § 5.”
The Variation of Integrated Star Initial Mass Functions among Galaxies (2005, methodology): “The Star Formation Rate–Maximal Cluster Mass Relation In Weidner et al. (2004) we derived a relation between the maximal cluster mass in a galaxy and the current SFR of the galaxy, logMecl;max ¼ logkMLþ (0:75 0:03)logSFRþ (6:77 0:02); ð1Þ where kML is the mass-to-light ratio, typically 0.0144 for…”
Stellar Populations in the Nuclei of Late-Type Spiral Galaxies (2006, background): “Weidner et al. (2004) argue that the typical formation timescale Ton of massive star clusters is between 10 6 and 107 years.”