Yashar D. Hezaveh, Neal Dalal, Daniel P. Marrone, Yao Yuan Mao, Warren Morningstar, Di Wen, Roger D. Blandford, John E. Carlstrom, Christopher D. Fassnacht, Gilbert P. Holder, Athol Kemball, Philip J. Marshall, Norman Murray, Laurence Perreault Levasseur, Joaquin D. Vieira, Risa H. Wechsler

Research output: Contribution to journalArticlepeer-review

219 Scopus citations


We study the abundance of substructure in the matter density near galaxies using ALMA Science Verification observations of the strong lensing system SDP.81. We present a method to measure the abundance of subhalos around galaxies using interferometric observations of gravitational lenses. Using simulated ALMA observations we explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. We apply our formalism to ALMA observations of SDP.81. We find evidence for the presence of a M = 108.96±0.12 M o subhalo near one of the images, with a significance of 6.9σ in a joint fit to data from bands 6 and 7; the effect of the subhalo is also detected in both bands individually. We also derive constraints on the abundance of dark matter (DM) subhalos down to M ∼ 2 ×107 M o, pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted DM subhalos. We find hints of additional substructure, warranting further study using the full SDP.81 data set (including, for example, the spectroscopic imaging of the lensed carbon monoxide emission). We compare the results of this search to the predictions of ΛCDM halos, and find that given current uncertainties in the host halo properties of SDP.81, our measurements of substructure are consistent with theoretical expectations. Observations of larger samples of gravitational lenses with ALMA should be able to improve the constraints on the abundance of galactic substructure.

Original languageEnglish (US)
Article number37
JournalAstrophysical Journal
Issue number1
StatePublished - May 20 2016


  • dark matter
  • gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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