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

By M. Enoch, N. Evans II, A. Sargent, J. Glenn, Erik Rosolowsky, P. Myers. 2008

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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 and Young and their coworkers. 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 NH3 survey of Perseus cores by Rosolowsky and coworkers 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 × 105 yr, with a total uncertainty of a factor of 2. Such a short lifetime suggests a dynamic, rather than quasi-static, core evolution scenario, at least at the relatively high mean densities (n > 2 × 104 cm−3) to which we are sensitive.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f9ffd80a2e4b3dab3fd43d1cea0ef19606037dd4

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A CORRELATION BETWEEN SURFACE DENSITIES OF YOUNG STELLAR OBJECTS AND GAS IN EIGHT NEARBY MOLECULAR CLOUDS (2011, background): “…axis quantitites, following the analysis of Press et al. (1992). well-studied dark clouds in Perseus, such as B5 and L1448, where the YSOs in these objects are predominantly confirmed Class 0 and Class I objects (Jørgensen et al. 2008; Enoch et al. 2008) with very few more evolved Class II sources.”
HOW MANY INFRARED DARK CLOUDS CAN FORM MASSIVE STARS AND CLUSTERS? (2010, background): “Typical freefall timescales of their natal cores ∼ 105 yr (Enoch et al. 2008) then imply εff ≈ 1/7.”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, result): “…et al. 1998; Pineda et al. 2010), but if one treats the dense cores as point particles like stars and analyzes their positions relative to one another, the result is again 12 a powerlaw very similar to that observed for stars (e.g., Johnstone et al. 2000; Stanke et al. 2006; Enoch et al. 2008).”
The Stellar IMF, Core Mass Function, & The Last-Crossing Distribution (2012, background): “The same behaviors are observed and agree well with our prediction without the need to invoke an uncertain rescaling factor (see e.g. Stanke et al. 2006; Enoch et al. 2008; Rathborne et al. 2009; Sadavoy et al. 2010; Belloche et al. 2011).”
RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION (2011, background): “For Mcore, the observations presented by Enoch et al. (2009a) are generally complete above 0.8 M⊙, but the exact completeness limit depends on core size due to observing and data reduction limitations (see Enoch et al. 2008 for details).”
STAR FORMATION RELATIONS IN NEARBY MOLECULAR CLOUDS (2014, background): “To be specific, Enoch et al. (2008) found that 75% of prestellar cores were found above AV = 6.5, 8, and 19.5 mag in Perseus, Serpens, and Ophiuchus, respectively.”
STAR FORMATION ACTIVITY OF CORES WITHIN INFRARED DARK CLOUDS (2009, background): “If we assume that each quiescent core will form only one star with a 30% star formation efficiency (e.g., Alves et al. 2007; Enoch et al. 2008), then the lower mass limit for a core which can produce a high-mass (M 8 M ) star is ∼25 M .”
THE FORMATION OF LOW-MASS BINARY STAR SYSTEMS VIA TURBULENT FRAGMENTATION (2010, background): “Observations of starless cores indicate that the core mass function shape is similar to the stellar IMF but is shifted to higher masses by a factor of three (Alves et al. 2007; Enoch et al. 2008).”
THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, methodology): “However, the resulting values of α from the c2d catalog scatter widely and do not correlate with other discriminants such as Tbol for the early classes (Enoch et al. 2008a).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “A turnover in the mass function appears at a mass about 3-4 times that seen in the stellar IMF (Alves et al. 2007; Enoch et al. 2008).”
PROPERTIES OF THE YOUNGEST PROTOSTARS IN PERSEUS, SERPENS, AND OPHIUCHUS (2008, methodology): “In a companion paper (Enoch et al. 2008) we use a similar argument to derive the lifetime of the prestellar phase from the ratio of the number of starless cores to the total number of embedded protostars (Class 0 + Class I).”
ANALYTICAL THEORY FOR THE INITIAL MASS FUNCTION. II. PROPERTIES OF THE FLOW (2009, background): “…core mass function (CMF) has been found to have a shape very similar to the IMF (Motte et al. 1998, Testi & Sargent 1998, Johnstone et al. 2000, Alvés et al. 2007, Nutter & Ward-Thompson 2007, Simpson et al. 2008, Enoch et al. 2008), although shifted towards larger masses by a factor of about 2-3.”
THE EFFECTS OF RADIATIVE TRANSFER ON LOW-MASS STAR FORMATION (2009, result): “Adopting an efficiency factor of ǫcore = 1 3 to account for mass loss due to outflows (Matzner & McKee 2000; Alves et al. 2007; Enoch et al. 2008), we find that the mean protostellar mass of these protostars is m̄ = 0.4 M⊙, which is comparable to the expected mean mass of the system initial mass…”
The chemical history of molecules in circumstellar disks - I. Ices (2009, result): “This is theame value as used by Rodgers & Charnley (2003) and BWH08, and it is consistent with recent observations by Enoch et al. (2008).”
THE BOLOCAM GALACTIC PLANE SURVEY: SURVEY DESCRIPTION AND DATA REDUCTION (2010, background): “We suspect that higher resolution observations will resolve BGPS clumps into clusters of protostellar objects, as has been seen in Serpens (Enoch et al. 2008; Testi & Sargent 1998), OMC 1 (Beuther et al. 2004; Johnstone & Bally 1999), and S255N (Cyganowski et al. 2007) where bolometer observations…”
A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, methodology): “…versions of this CMF) is based on a core sample ∼2– 9 times larger than the CMFs derived from earlier ground-based studies (e.g., Motte et al. 1998; Johnstone et al. 2000; Stanke et al. 2006; Alves et al. 2007; Enoch et al. 2008) and that its shape is therefore much more robustly defined.”