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When the Jeans do not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

El-Badry, Kareem and Wetzel, Andrew R. and Geha, Marla and Quataert, Eliot and Hopkins, Philip F. and Kereš, Dušan and Chan, T. K. and Faucher-Giguère, Claude-André (2017) When the Jeans do not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies. Astrophysical Journal, 835 (2). Art. No. 193. ISSN 1538-4357.

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In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies' starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy's dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ~20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
El-Badry, Kareem0000-0002-6871-1752
Wetzel, Andrew R.0000-0003-0603-8942
Geha, Marla0000-0002-7007-9725
Quataert, Eliot0000-0001-9185-5044
Hopkins, Philip F.0000-0003-3729-1684
Kereš, Dušan0000-0002-1666-7067
Additional Information:© 2017 The American Astronomical Society. Received 2016 October 12; revised 2016 December 9; accepted 2016 December 27; published 2017 January 31. We thank the referee for helpful comments, Justin Read for advice on Jeans modeling, and Andrew Hearin for suggesting comparisons with observations. We also thank Dan Weisz, Ryan Trainor, Chung-Pei Ma, Susan Kassin, and Jenny Greene for productive discussions. K.E. gratefully acknowledges support from the Caltech SURF program, a Berkeley graduate fellowship, and a Hellman award for graduate study. A.R.W. was supported by the Moore Center for Theoretical Cosmology and Physics at Caltech via a Moore Prize Fellowship, and by Carnegie Observatories via a Carnegie Fellowship in Theoretical Astrophysics. M.G. was supported by a fellowship from the John S. Guggenheim Memorial Foundation. E.Q. was supported by NASA ATP grant 12-ATP-120183, a Simons Investigator award from the Simons Foundation, and the David and Lucile Packard Foundation. P.F.H. was supported by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER grant #1455342. D.K. and T.K.C. were supported by NSF grant AST-1412153 and funds from the University of California San Diego. D.K. was additionally supported by the Cottrell Scholar Award. C.-A.F.-G. was supported by the NSF through grants AST-1412836 and AST-1517491, and by NASA through grant NNX15AB22G. We ran numerical calculations on the Caltech compute cluster "Zwicky" (NSF MRI award #PHY-0960291) and allocation TG-AST120025 granted by the Extreme Science and Engineering Discovery Environment (XSEDE) supported by NSF.
Group:TAPIR, Moore Center for Theoretical Cosmology and Physics
Funding AgencyGrant Number
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
University of California BerkeleyUNSPECIFIED
Caltech Moore Center for Theoretical Cosmology and PhysicsUNSPECIFIED
John S. Guggenheim Memorial FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
University of California San DiegoUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:galaxies: dwarf – galaxies: kinematics and dynamics – galaxies: starburst – Local Group – methods: numerical
Record Number:CaltechAUTHORS:20170616-094907367
Persistent URL:
Official Citation:Kareem El-Badry et al 2017 ApJ 835 193
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78266
Deposited By: Tony Diaz
Deposited On:16 Jun 2017 19:02
Last Modified:17 Aug 2017 20:25

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