Astrophys. J., 849, 128-128 (2017/November-2)
The fraction of stars that form in clusters in different galaxies.
CHANDAR R., FALL S.M., WHITMORE B.C. and MULIA A.J.
Abstract (from CDS):
We estimate the fraction of stars that form in compact clusters (bound and unbound), ΓF, in a diverse sample of eight star-forming galaxies, including two irregulars, two dwarf starbursts, two spirals, and two mergers. The average value for our sample is ΓF~24 % ±9 % . We also calculate the fraction of stars in clusters that survive to ages between τ1 and τ2, denoted by ΓS(τ1,τ2), and find ΓS(10,100)=4.6 % ±2.5 % and ΓS(100,400)=2.4 % ±1.1 % , significantly lower than ΓF for the same galaxies. We do not find any systematic trends in ΓF or ΓS with the star formation rate (SFR), the SFR per unit area (ΣSFR), or the surface density of molecular gas (ΣH2_) within the host galaxy. Our results are consistent with those found previously from the CMF/SFR statistic (where CMF is the cluster mass function), and with the quasi-universal model in which clusters in different galaxies form and disrupt in similar ways. Our results, however, contradict many previous claims that the fraction of stars in bound clusters increases strongly with ΣSFR and ΣH2_. We find that the previously reported trends are largely driven by comparisons that mixed ΓF~ΓS(0,10) and ΓS(10,100), where ΓS(0,10) was systematically used for galaxies with higher ΣSFR and ΣH2_, and ΓS(10,100) for galaxies with lower ΣSFR and ΣH2_.
© 2017. The American Astronomical Society. All rights reserved.
galaxies: star clusters: general - stars: formation - stars: formation
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