The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus

Abstract

We present an unbiased census of starless cores in Perseus, Serpens, and Ophiuchus, assembled by comparing large-scale Bolocam 1.1 mm continuum emission maps with Spitzer c2d surveys. We use the c2d catalogs to separate 108 starless from 92 protostellar cores in the 1.1 mm core samples from Enoch et al. (2006), and Enoch et al. (2007. A comparison of these populations reveals the initial conditions of the starless cores. Starless cores in Perseus have similar masses but larger sizes and lower densities on average than protostellar cores, with sizes that suggest density profiles substantially flatter than ρ ∝ r −2 . By contrast, starless cores in Serpens are compact and have lower masses than protostellar cores; future star formation will likely result in lower mass objects than the currently forming protostars. Comparison to dynamical masses estimated from the NH 3 survey of Perseus cores by Rosolowsky et al. (2008) suggests that most of the starless cores are likely to be gravitationally bound, and thus prestellar. The combined prestellar core mass distribution includes 108 cores and has a slope of α = −2.3 ± 0.4 for M > 0.8 M ⊙ . This slope is consistent with recent measurements of the stellar initial mass function, providing further evidence that stellar masses are directly linked to the core formation process. We place a lower limit on the core-to-star efficiency of 25%. There are approximately equal numbers of prestellar and protostellar cores in each cloud, thus the dense prestellar core lifetime must be similar to the lifetime of embedded protostars, or 4.5 × 10 5 years, with a total uncertainty of a factor of two. Such a short lifetime suggests a dynamic, rather than quasi-static, core evolution scenario, at least at the relatively high mean densities (n > 2 × 10 4 cm −3 ) to which we are sensitive.

APEX/SABOCA observations of small-scale structure of infrared-dark clouds

“…While most of the cold cores are below the ensemble median column density, 24 of the 40 PACS cores are above the median value. The column density values and the tendency for the higher column density structures to have star formation (appearing as a PACS core) are consistent with what is observed in local clouds (Enoch et al 2008).For more accurate mass estimates, we evaluate Eq.(1) at the best-fit or upper-limit temperature, for recovered cores and leaves, respectively. The best-fit temperature is given in Table 3, and the upper-limit temperature for leaves with no Herschel counterpart is calculated by fitting an SED to the 3σ detection limit of PACS fluxes in all bands plus the corrected 350 µm flux and is used to determine the leaf mass, giving a lower limit.…”

“…In the simplest case, if we assume that all the candidate starless objects will ultimately form protostars, and the rate of this progession is independent of the core mass, then the ratio of the number of starless to protostellar cores is the same as the ratio of the lifetimes (see Enoch et al 2008). If we assume that our protostars are predominantly in the "Class 0"-like phase as our evolutionary diagnostics indicate (see Figs.…”

“…Because we lack spectral information at shorter wavelengths (in part due to high extinction and poor sensitivity in distant clouds such as IRDCs) which in nearby clouds provide empirical divisions between Class 0/I/II protostellar stages in nearby clouds, we do not further refine the protostellar classification scheme here. However, based on our evolutionary diagnostics, we assume that the PACS cores are in the high-mass protostellar object (HMPO) stage (Sridharan et al 2002;Beuther et al 2002;Motte et al 2007), previous to the formation of an HII region.In the simplest case, if we assume that all the candidate starless objects will ultimately form protostars, and the rate of this progession is independent of the core mass, then the ratio of the number of starless to protostellar cores is the same as the ratio of the lifetimes (see Enoch et al 2008). If we assume that our protostars are predominantly in the "Class 0"-like phase as our evolutionary diagnostics indicate (see Figs.…”

Origin of the prestellar core mass function and link to the IMF – Herschel first results

“…2006; Nutter & Ward-Thompson 2007;Enoch et al 2008). There is thus good evidence in nearby star-forming regions such as Ophiuchus, Serpens, Orion A & B, and Perseus that the shape of the prestellar CMF (e.g.…”

Submillimetre Studies of Prestellar and Starless Cores in the Ophiuchus, Taurus and Cepheus Molecular Clouds

“…There have been many previous wide-field millimetre and submillimetre studies of the starless core population in the L1688 cloud (e.g. Motte et al 1998, hereafter MAN98;Johnstone et al 2000;Enoch et al 2008;Simpson et al 2008, hereafter S08;Simpson et al 2011). 3.1 Observations…”