Understanding the shape and diversity of dwarf galaxy rotation curves in ΛCDM

By Justin I. Read, G. Iorio, O. Agertz, Filippo Fraternali. 2016

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The shape and wide diversity of dwarf galaxy rotation curves is at apparent odds with dark matter halos in LCDM. We generate mock rotation curve data from dwarf galaxy simulations to show that this owes to bursty star formation driven by stellar feedback. There are three main effects. Firstly, stellar feedback transforms dark matter cusps into cores. Ignoring such transformations leads to a poor fit of the rotation curve shape and a large systematic bias on the halo concentration parameter c. Secondly, if close to a recent starburst, large HI bubbles push the rotation curve out of equilibrium. This makes the gas rotational velocity a poor probe of the underlying potential, leading to a systematic error on the halo virial mass M200 of up to half a dex. Thirdly, when galaxies are viewed near face-on (i<40deg), it is challenging to properly correct for their inclination i. This leads to a very shallow rotation curve, with a systematic underestimate of M200 of over a dex. All three problems can be easily avoided, however. Using a new coreNFW profile that accounts for cusp-core transformations, we show that we are able to successfully recover the rotation curve shape; dark matter halo mass M200; and concentration parameter c within our quoted uncertainties, provided that the galaxy is close to equilibrium. We fit our coreNFW model to four dwarf irregulars chosen to span a range of rotation curve shapes. We obtain an excellent fit for NGC 6822 and WLM. However, IC 1613 and DDO 101 give a poor fit. For IC 1613, this owes to disequilibria and its uncertain inclination; for DDO 101, the problem is its uncertain distance. Assuming i_IC1613 ~ 15deg and D_DDO101 ~ 12Mpc, we are able to fit both galaxies very well. We conclude that, once we avoid disequilibrium galaxies, or those with poorly measured inclination and/or distance, LCDM gives a remarkable match to dwarf galaxy rotation curves.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/712131348cc8dbab60e8bbe90d655e3acfd05ed3

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Citations in the corpus

Dark matter heats up in dwarf galaxies (2018, methodology): “As discussed in Read et al. (2016a), early infalling dwarfs have their star formation shut down before they can fully transform their cusp to a core.”
The stellar mass-halo mass relation of isolated field dwarfs : a critical test of ΛCDM at the edge of galaxy formation (2016, background): “…that resolve the effect of individual supernovae explosions are substantially more predictive (e.g. Oñorbe et al. 2015; Chan et al. 2015; Read et al. 2016a, hereafter R16a); these demonstrate that dark matter cores are an unavoidable prediction of ΛCDM (with baryons) for all low mass…”