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Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

Hopkins, Philip F. and Conroy, Charlie (2017) Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics? Astrophysical Journal, 835 (2). Art. No. 154. ISSN 0004-637X. doi:10.3847/1538-4357/835/2/154.

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Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutral turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars can form in dust-enhanced regions almost immediately after some dust forms even if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of these "promoted" stars may contain interesting signatures as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced and/or fluctuate almost independently. Remarkably, the otherwise puzzling abundance patterns of some metal-poor stars can be well fit by standard IMF-averaged core-collapse SNe yields if we allow for fluctuating local dust-to-gas ratios. We also show that the observed log-normal distribution of enhancements in these species agrees with our simulations. Moreover, we confirm that Mg and Si are correlated in these stars; the abundance ratios are similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows very large enhancements and variations up to factors of ≳100 as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. Together, this suggests that (1) dust exists in second-generation star formation, (2) local dust-to-gas ratio fluctuations occur in protogalaxies and can be important for star formation, and (3) the light element abundances of these stars may be affected by the local chemistry of dust where they formed, rather than directly tracing nucleosynthesis from earlier populations.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Conroy, Charlie0000-0002-1590-8551
Additional Information:© 2017 The American Astronomical Society. Received 2015 December 11; revised 2016 October 8; accepted 2016 October 10; published 2017 January 24. We thank Jessie Christiansen, Evan Kirby, and Selma de Mink for many helpful discussions during the development of this work. Support for P.F.H. was provided by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER grant #1455342. Numerical calculations were run on the Caltech compute cluster "Zwicky" (NSF MRI award #PHY-0960291) and allocation TG-AST130039 granted by the Extreme Science and Engineering Discovery Environment (XSEDE) supported by the NSF. C.C. is supported by the Packard Foundation, NASA grant NNX13AI46G, and NSF grant AST-1313280.
Group:TAPIR, Astronomy Department
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:dark ages, reionization, first stars – galaxies: formation – galaxies: star formation – stars: abundances – stars: formation – turbulence
Issue or Number:2
Record Number:CaltechAUTHORS:20170126-160443858
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Official Citation:Philip F. Hopkins and Charlie Conroy 2017 ApJ 835 154
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73763
Deposited By: Tony Diaz
Deposited On:27 Jan 2017 00:31
Last Modified:11 Nov 2021 05:21

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