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The Dark Matter Distributions in Low-mass Disk Galaxies. II. The Inner Density Profiles

Relatores, Nicole C. and Newman, Andrew B. and Simon, Joshua D. and Ellis, Richard S. and Truong, Phuongmai and Blitz, Leo and Bolatto, Alberto and Martin, Christopher and Matuszewski, Matt and Morrissey, Patrick and Neill, James D. (2019) The Dark Matter Distributions in Low-mass Disk Galaxies. II. The Inner Density Profiles. Astrophysical Journal, 887 (1). Art. No. 94. ISSN 1538-4357. doi:10.3847/1538-4357/ab5305.

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Dark-matter-only simulations predict that dark matter halos have steep, cuspy inner density profiles, while observations of dwarf galaxies find a range of inner slopes that are often much shallower. There is debate whether this discrepancy can be explained by baryonic feedback or if it may require modified dark matter models. In Paper I of this series, we obtained high-resolution integral field Hα observations for 26 dwarf galaxies with M* = 10^(8.1)−10^(9.7) M_⊙. We derived rotation curves from our observations, which we use here to construct mass models. We model the total mass distribution as the sum of a generalized Navarro–Frenk–White (NFW) dark matter halo and the stellar and gaseous components. Our analysis of the slope of the dark matter density profile focuses on the inner 300–800 pc, chosen based on the resolution of our data and the region resolved by modern hydrodynamical simulations. The inner slope measured using ionized and molecular gas tracers is consistent, and it is additionally robust to the choice of stellar mass-to-light ratio. We find a range of dark matter profiles, including both cored and cuspy slopes, with an average of ρ}_(DM ~ r^(-0.74 ± 0.07), shallower than the NFW profile, but steeper than those typically observed for lower-mass galaxies with M* ~ 10^(7.5) M_⊙. Simulations that reproduce the observed slopes in those lower-mass galaxies also produce slopes that are too shallow for galaxies in our mass range. We therefore conclude that supernova feedback models do not yet provide a fully satisfactory explanation for the observed trend in dark matter slopes.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Relatores, Nicole C.0000-0002-6041-6388
Newman, Andrew B.0000-0001-7769-8660
Ellis, Richard S.0000-0001-7782-7071
Truong, Phuongmai0000-0001-9248-6631
Blitz, Leo0000-0002-4272-4432
Bolatto, Alberto0000-0002-5480-5686
Martin, Christopher0000-0002-8650-1644
Morrissey, Patrick0000-0001-8177-1023
Neill, James D.0000-0002-0466-1119
Additional Information:© 2019. The American Astronomical Society. Received 2019 June 19; revised 2019 October 28; accepted 2019 October 29; published 2019 December 13. We would like to thank Alex Lazar and James Bullock for providing data used in Figure 11 in advance of publication, T. K. Chan for providing data used in Figure 11 and for helpful discussions, and Andrew Pontzen and J.A. Sellwood for their insightful comments. We acknowledge the usage of the HyperLeda database ( This research has made use of NASA's Astrophysics Data System.
Group:Space Radiation Laboratory
Subject Keywords:Galaxy structure ; Galaxy kinematics ; Dwarf galaxies ; Dark matter
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Galaxy structure (622); Galaxy kinematics (602); Dwarf galaxies (416); Dark matter (353)
Record Number:CaltechAUTHORS:20191213-105055057
Persistent URL:
Official Citation:Nicole C. Relatores et al 2019 ApJ 887 94
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100292
Deposited By: George Porter
Deposited On:16 Dec 2019 15:34
Last Modified:16 Nov 2021 17:53

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