Why do stars form in clusters? An analytic model for stellar correlation functions
- Creators
- Hopkins, Philip F.
Abstract
Recently, we have shown that if the interstellar medium is governed by supersonic turbulent flows, the excursion-set formalism can be used to calculate the statistics of self-gravitating objects over a wide range of scales. On the largest self-gravitating scales ('first crossing'), these correspond to giant molecular clouds (GMCs), and on the smallest non-fragmenting self-gravitating scales ('last crossing'), to protostellar cores. Here, we extend this formalism to rigorously calculate the autocorrelation and cross-correlation functions of cores (and by extension, young stars) as a function of spatial separation and mass, in analogy to the cosmological calculation of halo clustering. We show that this generically predicts that star formation is very strongly clustered on small scales: stars form in clustered regions, themselves inside GMCs. Outside the binary-star regime, the projected correlation function declines as a weak power law, until a characteristic scale which corresponds to the characteristic mass scale of GMCs. On much larger scales the clustering declines such that star formation is not strongly biased on galactic scales, relative to the actual dense gas distribution. The precise correlation function shape depends on properties of the turbulent spectrum, but its qualitative behaviour is quite general. The predictions agree well with observations of young star and core autocorrelation functions over ∼4 dex in radius. Clustered star formation is a generic consequence of supersonic turbulence if most of the power in the velocity field, hence the contribution to density fluctuations, comes from large scales ∼h. The distribution of self-gravitating masses near the sonic length is then imprinted by fluctuations on larger scales. We similarly show that the fraction of stars formed in 'isolated' modes should be small, ≲10 per cent.
Additional Information
© 2012 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2012 October 4. Received 2012 October 4; in original form 2012 February 9. We thank Chris McKee and Eliot Quataert for helpful discussions in the development of this work, as well as Eli Bressert, Stella Offner and our referee, Federico Pelupessy, for a number of suggestions and comments. Support for PFH was provided by NASA through Einstein Postdoctoral Fellowship Award Number PF1-120083 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060.Attached Files
Published - sts147.pdf
Accepted Version - 1202.2122.pdf
Files
Name | Size | Download all |
---|---|---|
md5:308961067b487795cfc8eb4bbabb08c3
|
353.1 kB | Preview Download |
md5:653ab185275cb5eaa26be6a6d0fc8dbd
|
333.5 kB | Preview Download |
Additional details
- Eprint ID
- 103413
- Resolver ID
- CaltechAUTHORS:20200522-113949381
- NASA Einstein Fellowship
- PF1-120083
- NASA
- NAS8-03060
- Created
-
2020-05-22Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field