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Probing Population III Initial Mass Functions with He ii/Hα Intensity Mapping

Parsons, Jasmine and Mas-Ribas, Lluís and Sun, Guochao and Chang, Tzu-Ching and Gonzalez, Michael O. and Mebane, Richard H. (2022) Probing Population III Initial Mass Functions with He ii/Hα Intensity Mapping. Astrophysical Journal, 933 (2). Art. No. 141. ISSN 0004-637X. doi:10.3847/1538-4357/ac746b.

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We demonstrate the potential of line-intensity mapping to place constraints on the initial mass function (IMF) of Population III stars via measurements of the mean He ii 1640 Å/Hα line-intensity ratio. We extend the 21cmFAST code with modern high-redshift galaxy-formation and photoionization models, and estimate the line emission from Population II and Population III galaxies at redshifts 5 ≤ z ≤ 20. In our models, mean ratio values of He ii/H α ≳ 0.1 indicate top-heavy Population III IMFs with stars of several hundred solar masses, reached at z ≳ 10 when Population III stars dominate star formation. A next-generation space mission with capabilities moderately superior to those of CDIM will be able to probe this scenario by measuring the He ii and Hα fluctuation power spectrum signals and their cross-correlation at high significance up to z ∼ 20. Moreover, regardless of the IMF, a ratio value of He ii/Hα ≲ 0.01 indicates low Population III star formation and, therefore, it signals the end of the period dominated by this stellar population. However, a detection of the corresponding He ii power spectrum may be only possible for top-heavy Population III IMFs or through cross-correlation with the stronger Hα signal. Finally, ratio values of 0.01 ≲ He ii/Hα ≲ 0.1 are complex to interpret because they can be driven by several competing effects. We discuss how various measurements at different redshifts and the combination of the line-intensity ratio with other probes can assist in constraining the Population III IMF in this case.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Parsons, Jasmine0000-0002-6013-4655
Mas-Ribas, Lluís0000-0003-4584-8841
Sun, Guochao0000-0003-4070-497X
Chang, Tzu-Ching0000-0001-5929-4187
Mebane, Richard H.0000-0003-2739-8779
Alternate Title:Probing Population III IMFs with He II/Hα Intensity Mapping
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 December 17; revised 2022 May 24; accepted 2022 May 27; published 2022 July 11. We thank the anonymous referee for comments that helped improve this paper. We also thank Steven Furlanetto, Adrian Liu, Adam Trapp, and Taj Dyson for useful discussions and comments on the manuscript. We acknowledge support from the JPL R&TD grant. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Software: 21cmFAST (Mesinger & Furlanetto 2007; Mesinger et al. 2011), ARES (Mirocha et al. 2017), Cloudy (version 17.02, Ferland et al. 2017), LIMFAST (L. Mas-Ribas et al. 2022, in preparation; G. Sun et al. 2022, in preparation), CloudyFSPS (Byler et al. 2017, 2018).
Funding AgencyGrant Number
JPL Research and Technology Development FundUNSPECIFIED
Subject Keywords:Initial mass function; Population III stars; Stellar populations; Line intensities; Cosmology
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Initial mass function (796); Population III stars (1285); Stellar populations (1622); Line intensities (2084); Cosmology (343)
Record Number:CaltechAUTHORS:20220411-225141510
Persistent URL:
Official Citation:Jasmine Parsons et al 2022 ApJ 933 141
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114220
Deposited By: George Porter
Deposited On:12 Apr 2022 19:26
Last Modified:22 Jul 2022 17:15

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