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A Data-driven Technique Using Millisecond Transients to Measure the Milky Way Halo

Platts, E. and Prochaska, J. Xavier and Law, Casey J. (2020) A Data-driven Technique Using Millisecond Transients to Measure the Milky Way Halo. Astrophysical Journal Letters, 895 (2). Art. No. L49. ISSN 2041-8213. doi:10.3847/2041-8213/ab930a.

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We introduce a new technique to constrain the line-of-sight integrated electron density of our Galactic halo DM_(MW,halo) through analysis of the observed dispersion measure distributions of pulsars DM_(pulsar) and fast radio bursts (FRBs) DM_(FRB). We model these distributions, correcting for the Galactic interstellar medium, with kernel density estimation—well-suited to the small data regime—to find lower/upper bounds to the corrected DM_(pulsar)/DM_(FRB) distributions: max[DM_(pulsar)] ≈ 7±2 (stat)±9 (sys) pc cm⁻³ and min[DM_(FRB)] ≈ 63⁺²⁷₋₂₁ (stat)±9 (sys) pc cm⁻³. Using bootstrap resampling to estimate uncertainties, we set conservative limits on the Galactic halo dispersion measure −2 < DM_(MW,halo) < 123 pc cm⁻³ (95% c.l.). The upper limit is especially conservative because it may include a nonnegligible contribution from the FRB host galaxies and a nonzero contribution from the cosmic web. It strongly disfavors models where the Galaxy has retained the majority of its baryons with a density profile tracking the presumed dark matter density profile. Last, we perform Monte Carlo simulations of larger FRB samples to validate our technique and assess the sensitivity of ongoing and future surveys. We recover bounds of several tens of pc cm⁻³ that may be sufficient to test whether the Galaxy has retained a majority of its baryonic mass. We estimate that a sample of several thousand FRBs will significantly tighten constraints on DM_(MW,halo) and offer a valuable complement to other analyses.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Platts, E.0000-0002-9931-5672
Prochaska, J. Xavier0000-0002-7738-6875
Law, Casey J.0000-0002-4119-9963
Additional Information:© 2020 The American Astronomical Society. Received 2020 April 8; revised 2020 May 12; accepted 2020 May 14; published 2020 June 4. We would like to thank the anonymous referee for insightful, thorough, and valuable input. E.P. and J.X.P., as members of the Fast and Fortunate for FRB Follow-up team F4 (, acknowledge support from NSF grant AST-1911140. C.J.L. acknowledges support under NSF grant 2022546. This work was initiated as a project for the Kavli Summer Program in Astrophysics held at the University of California, Santa Cruz in 2019. The program was funded by the Kavli Foundation, The National Science Foundation, UC Santa Cruz, and the Simons Foundation. We thank them for their generous support. E.P. is supported by a L'Oréal-UNESCO For Women in Science Young Talents Fellowship, by a PhD fellowship from the South African National Institute for Theoretical Physics (NITheP), and by a top-up bursary from the South African Research Chairs Initiative of the Department of Science and Technology (SARChI) and the National Research Foundation (NRF) of South Africa. Any opinion, finding and conclusion or recommendation expressed in this material is that of the authors and the NRF does not accept any liability in this regard.
Funding AgencyGrant Number
Kavli FoundationUNSPECIFIED
University of California, Santa CruzUNSPECIFIED
Simons FoundationUNSPECIFIED
L'Oréal-UNESCO For Women In ScienceUNSPECIFIED
National Institute for Theoretical Physics (NITheP)UNSPECIFIED
Department of Science and Technology (South Africa)UNSPECIFIED
National Research Foundation (South Africa)UNSPECIFIED
Subject Keywords:Radio transient sources ; Circumgalactic medium ; Astrostatistics techniques
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Radio transient sources (2008); Circumgalactic medium (1879); Astrostatistics techniques (1886)
Record Number:CaltechAUTHORS:20200608-093108523
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Official Citation:E. Platts et al 2020 ApJL 895 L49
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103740
Deposited By: Tony Diaz
Deposited On:08 Jun 2020 17:12
Last Modified:16 Nov 2021 18:24

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