The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure

By C. Lada, August Muench, Jill M. Rathborne, Joao F. Alves, M. Lombardi. 2007

189 citations recorded by the source corpus.

In this paper we present the results of a systematic investigation of an entire population of predominately starless dust cores within a single molecular cloud, the Pipe Nebula. Analysis of extinction data shows the cores to be dense objects characterized by a narrow range of density with a median value of n(H2) = 7 × 103. The nonthermal velocity dispersions measured in molecular emission lines are found to be subsonic for the large majority of the cores and show no correlation with core mass (or size). Thermal pressure is found to be the dominate source of internal gas pressure and support for most of the core population. The total internal pressures of the cores are found to be roughly independent of core mass over the entire (0.2-20 M☉) range of the core mass function (CMF) indicating that the cores are in pressure equilibrium with an external source of pressure. This external pressure is most likely provided by the weight of the surrounding molecular cloud. Most of the cores appear to be pressure confined, gravitationally unbound entities whose fundamental physical properties are determined by only a few factors, which include self-gravity, gas temperature, and the simple requirement of pressure equilibrium with the surrounding environment. The entire core population is found to be characterized by a single critical Bonnor-Ebert mass of approximately 2 M☉. This mass coincides with the characteristic mass of the Pipe CMF suggesting that the CMF (and ultimately the stellar IMF) has its origin in the physical process of thermal fragmentation in a pressurized medium.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/33603b8fb7bef6999815a1aef244ce6f9f1e0fa5

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Citations in the corpus

LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, methodology): “Monolithic Collapse Models The monolithic collapse model rests on the similarity between the shape of the observed core mass distribution (Motte et al. 1998; Johnstone et al. 2000, 2006; Lada et al. 2008) and the stellar initial mass function, IMF (Kroupa 2002; Chabrier 2003).”
Can Supermassive Black Holes Form in Metal-enriched High-Redshift Protogalaxies? (2008, background): “…spectrum that resembles the stellar initial mass function (IMF), indicating that cloud fragmentation must be responsible for setting some fundamental properties of the star formation process (e.g., Motte et al. 1998; Lada et al. 2008; for recent reviews see Bonnell et al. 2007; Elmegreen 2008).”
MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, background): “Taurus hosts solar-type binary systems with separations of up to ∼ 104 AU, which is similar to the characteristic size of prestellar cores in regions like the Pipe Nebula that could resemble the Taurus progenitor (Lada et al. 2008).”
Physical Processes in the Interstellar Medium (2014, background): “1 appear to be stable entities (Johnstone et al., 2000, 2001, 2006; Lada et al., 2008), and thus are unlikely to be in a state of active star formation.”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, methodology): “Moreover, low-mass cores often appear to be gravitationally unbound, thus requiring an external confning pressure to keep them from dispersing (e.g., Lada et al. 2008).”
The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, background): “Previous explanations for the unusually high peak mass in Taurus have generally involved a higher average Jeans mass compared to other regions (Briceño et al. 2002; Goodwin, Whitworth & Ward-Thompson 2004; Lada et al. 2008; Luhman 2004c; Luhman et al. 2003b).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Extinction mapping with sufficiently high spatial resolution can identify cores (e.g., Alves et al. 2007), but many are not gravitationally bound (Lada et al. 2008), and they are likely to dissipate.”
Hierarchical fragmentation and differential star formation in the Galactic ‘Snake’: infrared dark cloud G11.11−0.12 (2014, background): “34-P1 (Wang et al. 2011), and in contrast to low-mass star formation regions (Lada et al. 2008).”
DIRECT OBSERVATION OF A SHARP TRANSITION TO COHERENCE IN DENSE CORES (2010, background): “Lada et al. (2008) argued that most of the cores in the Pipe can be pressure confined by the MC’s own weight, see also Bertoldi & McKee (1992) and Johnstone et al. (2004).”
Magnetically Regulated Star Formation in Three Dimensions: The Case of the Taurus Molecular Cloud Complex (2008, background): “The Taurus cloud complex is discussed further in § 6.2.1, along with the Pipe Nebula (§ 6.2.2), which may represent an earlier phase of star formation in a magnetically dominated cloud (Lada et al. 2008; F. Alves et al., in preparation).”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, methodology): “Specifically, the HMSF samples from Pillai et al. (2011), Li et al. (2013), Tan et al. (2013), and Wienen et al. (2012) contain virial parameters much smaller than those in the non–HMSF samples by Lada et al. (2008) and Enoch et al. (2006).”
Stellar Multiplicity (2013, background): “The observed correlation between primary mass and “maximum” binary separation is plausibly linked to the typical prestellar core size (both on the order of∼ 0.1 pc Bahcall & Soneira 1981, Lada et al. 2008).”
AN INFRARED/X-RAY SURVEY FOR NEW MEMBERS OF THE TAURUS STAR-FORMING REGION (2009, background): “Possible explanations for the distinctive shape of the IMF in Tau- rus have been discussed in previous studies and generally involve a higher average Jeans mass in this region (Briceño et al. 2002; Luhman et al. 2003b; Luhman 2004c; Goodwin et al. 2004; Lada et al. 2008).”
The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus (2008, background): “In fact, recent C18O and NH3 observations suggest that the dust extinction sources in the Pipe Nebula are pressure confined, gravitationally unbound starless cores (Lada et al. 2008; Muench et al. 2007).”
THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, background): “Lifetimes of cores with lower mean densities are clearly longer (Ward-Thompson et al. 2007), and may vary from cloud to cloud [cf. the Pipe nebula (Lada et al. 2008)].”