Real and counterfeit cores: how feedback expands halos and disrupts tracers of inner gravitational potential in dwarf galaxies

• Published in: arXiv.org
• Main Authors: Jahn, Ethan D, Sales, Laura V, Marinacci, Federico, Vogelsberger, Mark, Torrey, Paul, Jia Qi, Smith, Aaron, Li, Hui, Kannan, Rahul, Burger, Jan D, Zavala, Jesús
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 01.10.2021
• Subjects: Astronomical models; Cold dark matter; Counterfeit; Dark matter; Density; Dwarf galaxies; Feedback; Finite element method; Galactic evolution; Galactic halos; Initial conditions; Interstellar matter; Physics - Astrophysics of Galaxies; Rotation; Star & galaxy formation; Star formation; Stars & galaxies; Velocity distribution
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2110.00142

The tension between the diverging density profiles in Lambda Cold Dark Matter (\(\Lambda\)CDM) simulations and the constant-density inner regions of observed galaxies is a long-standing challenge known as the `core-cusp' problem. We demonstrate that the \texttt{SMUGGLE} galaxy formation model implemented in the \textsc{Arepo} moving mesh code forms constant-density cores in idealized dwarf galaxies of \(M_\star \approx 8 \times 10^7\) M\(_{\odot}\) with initially cuspy dark matter halos of \(M_{200} \approx 10^{10}\) M\(_{\odot}\). Identical initial conditions run with the Springel and Hernquist (2003; SH03) feedback model preserve cuspiness. Literature on the subject has pointed to the low density threshold for star formation, \(\rho_\text{th}\), in SH03-like models as an obstacle to baryon-induced core formation. Using a \texttt{SMUGGLE} run with equal \(\rho_\text{th}\) to SH03, we demonstrate that core formation can proceed at low density thresholds, indicating that \(\rho_\text{th}\) is insufficient on its own to determine whether a galaxy develops a core. We suggest that the ability to resolve a multiphase interstellar medium at sufficiently high densities is a more reliable indicator of core formation than any individual model parameter. In \texttt{SMUGGLE}, core formation is accompanied by large degrees of non-circular motion, with gas rotational velocity profiles that consistently fall below the circular velocity \(v_\text{circ} = \sqrt{GM/R}\) out to \(\sim 2\) kpc. This may artificially mimic larger core sizes when derived from observable quantities compared to the size measured from the dark matter distribution (\(\sim 0.5\) kpc), highlighting the need for careful modeling in the inner regions of dwarfs to infer the true distribution of dark matter.