The fidelity of the core mass functions derived from dust column density data
TKK/Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland e-mail: email@example.com
2 Observatory, PO Box 14, 00014 University of Helsinki, Finland
3 Harvard-Smithsonian Center for Astrophysics, Mail Stop 72, 60 Garden Street, Cambridge, MA 02138, USA
4 Calar Alto Observatory, Centro Astronomico Hispano, Alemán, C/q Jesús Durbán Remón 2-2, 04004 Almeria, Spain
Accepted: 29 January 2009
Aims. We examine the recoverability and completeness limits of the dense core mass functions (CMFs) derived for a molecular cloud using extinction data and a core identification scheme based on two-dimensional thresholding. We study how the selection of core extraction parameters affects the accuracy and completeness limit of the derived CMF and the core masses, and also how accurately the CMF can be derived in varying core crowding conditions.
Methods. We performed simulations where a population of artificial cores was embedded in the variable background extinction field of the Pipe nebula. We extracted the cores from the simulated extinction maps, constructed the CMFs, and compared them to the input CMFs. The simulations were repeated using a variety of extraction parameters and several core populations with differing input mass functions and differing degrees of crowding.
Results. The fidelity of the observed CMF depends on the parameters selected for the core extraction algorithm for our background. More importantly, it depends on how crowded the core population is. We find that the observed CMF recovers the true CMF reliably when the mean separation of cores is larger than the mean diameter of the cores (). If this condition holds, the derived CMF for the Pipe nebula background is accurate and complete above , depending on the parameters used for the core extraction. In the simulations, the best fidelity was achieved with the detection threshold of 1 or 2 times the rms-noise of the extinction data, and with the contour level spacings of 3 times the rms-noise. Choosing a higher threshold and wider level spacings increases the limiting mass. The simulations also show that, when , the masses of individual cores are recovered with a typical uncertainty of %. When , the uncertainty is ~60%. In very crowded cases where the core identification algorithm is unable to recover the masses of the cores adequately, and the derived CMF is unlikely to represent the underlying CMF. For the cores of the Pipe nebula thereby justifying the use of the method in that region.
Key words: dust, extinction / ISM: clouds / ISM: structure / stars: formation / stars: luminosity function, mass function
© ESO, 2009