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Cloud Structure and the Origins of the Stellar Initial
Mass Function in ρ-Ophiuchus
Dylan R. NelsonDepartment of Astronomy, University of California, Berkeley
Jonathan J. SwiftInstitute for Astronomy, University of Hawaii, Manoa
Jonathan P. WilliamsInstitute for Astronomy, University of Hawaii, Manoa
- 7 August, 2007 -
Introduction• Stars: fundamental objects in
astronomy– Stellar IMF determines the
evolution of the chemical composition of the universe
• How do we probe the initial conditions of star formation?– Deep, multi-wavelength coverage of
regions of active SF
Motivation• Isolated grav. collapse
ok, but active SF sites more complicated:– environment &
interactions• Nearby dense
molecular clouds:– active low-mass SF– objects in a wide range
of evolutionary stagesM16: Eagle Nebula
“Pillars of Creation”
• Cold & dense cores stars
• DCMF tail has a Salpeter slope!
• Two distributions have the same shape?– “Direct progenitors”
& 1-to-1 mapping
Motte et al., 1998.
Motivation
Alves et al., 2007.
~30%
Motivation• Cold & dense cores
stars• DCMF tail has a
Salpeter slope!• Two distributions
have the same shape?– “Direct progenitors”
& 1-to-1 mapping
• Giant molecular cloud (GMC)– Nearby (D ~ 130pc), Cold (Td ~ 15K)
• Large number of young stars• Large amount of mass in cold molecular gas• Goals:
– Examine relation between clump/stellar populations– Comment on the origins of the stellar IMF– Examine previous claims of similarity between the
DCMF and IMF
ρ-Ophiuchus
AV Dust Extinction
1.2mm Dust Emission
Spitzer IR (IRAC/MIPS)
Molecular Line Tracers (13CO, N2H+)
Stellar Surveys (NIR/MIR)
• Dust emission: high resolution, good tracer• Algorithms and techniques:
– Clumpfind: Contour following & shape independence• Wavelet decomposition & background subtraction
– Gaussclumps: Iterative Gaussian fitting & subtraction– Bayesian: Source likelihood & MCMC photometry
Finding Clumps
• What do we know?– size, mass, location, velocity dispersion
Core Mass Function
“Starless” Cores
Stars Masquerading as Cores
Column Density vs Clump Size
AV ~ 1
AV ~ 2
Substructure
• Virial mass approach:– Balance grav. potential energy U with internal
kinetic support K
Gravitational Stability
• Fit 13CO line for velocity dispersion of clumps:
☺
Gravitational Stability
• Fit seven hyperfine components of the N2H+ (Andre et al., preprint) line for velocity dispersion of clumps:
Gravitational Stability
Conclusions• 1-to-1 mapping of cores stars questionable• Clearly some relationship exists between clump and star
distributions– But, “direct progenitors” idea in doubt– Multiple star systems?
• Big unknowns:– turbulence & fractal nature of the ISM– magnetic/other internal support– outflows, feedback, self-regulation– how do we, really, define a clump?
• What we need: next generation, multi-wavelength, observations w/ higher sensitivity and resolution
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