Testing core creation in hydrodynamical simulations using the HI kinematics of field dwarfs

¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
e-mail: papastergis@astro.rug.nl; ponomareva@astro.rug.nl
² Research School of Astronomy & Astrophysics, Australian National University, Canberra, ACT 2611, Australia

Received: 18 August 2016
Accepted: 17 February 2017

Abstract

The majority of recent hydrodynamical simulations indicate the creation of central cores in the mass profiles of low-mass halos, a process that is attributed to star formation-related baryonic feedback. Core creation is regarded as one of the most promising solutions to potential issues faced by lambda cold dark matter (ΛCDM) cosmology on small scales. For example, the reduced dynamical mass enclosed by cores can explain the low rotational velocities measured for nearby dwarf galaxies, thus possibly lifting the seeming contradiction with the ΛCDM expectations (the so-called “too big to fail” problem). Here we test core creation as a solution of cosmological issues by using a sample of dwarfs with measurements of their atomic hydrogen (HI) kinematics extending to large radii. Using the NIHAO hydrodynamical simulation as an example, we show that core creation can successfully reproduce the kinematics of dwarfs with small kinematic radii, R ≲ 1.5 kpc. However, the agreement with observations becomes poor once galaxies with kinematic measurements extending beyond the core region, R ≈ 1.5−4 kpc, are considered. This result illustrates the importance of testing the predictions of hydrodynamical simulations that are relevant for cosmology against a broad range of observational samples. We would like to stress that our result is valid only under the following set of assumptions: i) that our sample of dwarfs with HI kinematics is representative of the overall population of field dwarfs; ii) that there are no severe measurement biases in the observational parameters of our HI dwarfs (e.g., related to inclination estimates); and iii) that the HI velocity fields of dwarfs are regular enough to allow the recovery of the true enclosed dynamical mass.