Cloud Structure and the Origins of the Stellar Initial ...dnelson/doc/dnelson.hawaii… · Origins...

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Cloud Structure and the Origins of the Stellar Initial Mass Function in ρ-Ophiuchus Dylan R. Nelson Department of Astronomy, University of California, Berkeley Jonathan J. Swift Institute for Astronomy, University of Hawaii, Manoa Jonathan P. Williams Institute for Astronomy, University of Hawaii, Manoa - 7 August, 2007 -

Transcript of Cloud Structure and the Origins of the Stellar Initial ...dnelson/doc/dnelson.hawaii… · Origins...

Page 1: Cloud Structure and the Origins of the Stellar Initial ...dnelson/doc/dnelson.hawaii… · Origins of the Stellar Initial Mass Function in ρ-Ophiuchus Dylan R. Nelson Department

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 -

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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

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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”

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• 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

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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

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• 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

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AV Dust Extinction

1.2mm Dust Emission

Spitzer IR (IRAC/MIPS)

Molecular Line Tracers (13CO, N2H+)

Stellar Surveys (NIR/MIR)

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• 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

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Core Mass Function

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“Starless” Cores

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Stars Masquerading as Cores

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Column Density vs Clump Size

AV ~ 1

AV ~ 2

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Substructure

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• Virial mass approach:– Balance grav. potential energy U with internal

kinetic support K

Gravitational Stability

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• Fit 13CO line for velocity dispersion of clumps:

Gravitational Stability

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• Fit seven hyperfine components of the N2H+ (Andre et al., preprint) line for velocity dispersion of clumps:

Gravitational Stability

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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