Grain Alignment in Starless Cores

Abstract

We present near infrared polarimetry data of background stars shining through a selection of starless cores taken in the $K$ band, probing visual extinctions up to $A_V\sim 48$. We find that $P_K/{\tau }_K$ continues to decline with increasing $A_V$ with a power law slope of roughly -0.5. Examination of published submillimeter (submm) polarimetry of starless cores suggests that by $A_V\gtrsim 20$ the slope for $P$ vs. $\tau$ becomes $\sim -1$, indicating no grain alignment at greater optical depths. Combining these two data sets, we find good evidence that, in the absence of a central illuminating source, the dust grains in dense molecular cloud cores with no internal radiation source cease to become aligned with the local magnetic field at optical depths greater than $A_V\sim 20$. A simple model relating the alignment efficiency to the optical depth into the cloud reproduces the observations well.

33 pages, 5 figures

References in corpus (7)

• Radiative torques: Analytical Model and Basic Properties
• Radiative torque alignment: Essential Physical Processes
• The Efficiency of Grain Alignment in Dense Interstellar Clouds: A Reassessment of Constraints from Near Infrared Polarization
• On the radiation driven alignment of dust grains: Detection of the polarization hole in a starless core
• Radiative torques alignment in the presence of pinwheel torques
• SCUBA polarisation observations of the magnetic fields in the prestellar cores L1498 and L1517B
• Simulations of polarized dust emission

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• The Magnetic Field of L1544: I. Near-Infrared Polarimetry and the Non-Uniform Envelope
• Study of magnetic field geometry and extinction in Bok globule CB130