The impact of star formation histories on the inner dark matter density slopes of galaxies

¹ Instituto de Astrofísica de Canarias (IAC), Calle Via Láctea s/n, E-38205 La Laguna, Tenerife, Spain
² Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez s/n, E-38206 La Laguna, Tenerife, Spain
³ Department of Physics & Astronomy, University of Southern California, Los Angeles, CA 90089, USA
⁴ New York University Abu Dhabi, PO Box 129188 Abu Dhabi, United Arab Emirates
⁵ Center for Astrophysics and Space Science, New York University Abu Dhabi, Abu Dhabi, PO Box 129188 Abu Dhabi, UAE

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 22 December 2025
Accepted: 26 April 2026

Abstract

Aims. We aim to investigate the connection between star formation histories (SFHs) and the inner dark matter density profiles of simulated galaxies. In particular, we tested whether the burstiness and temporal distribution of star formation influence the formation of cored versus cuspy dark matter profiles.

Methods. We homogeneously analysed simulated galaxies from the NIHAO and FIRE-2 projects. For each galaxy, we derived dark matter density profiles and measured the logarithmic slope in the inner region of the dark matter halo (1–2% of R_vir). To characterise the star formation burstiness, we introduced a criterion based on comparing the star formation rate (SFR) averaged over two distinct timescales. We further quantified the temporal concentration of SFHs by computing the ratio of stellar mass formed after versus before the epoch of re-ionisation at redshift z ∼ 6.5, expressed as M_★, post/M_★, pre.

Results. A homogeneous analysis reveals that inner slope versus stellar-to-halo mass ratio trends for NIHAO and FIRE-2 galaxies are in much better agreement than what has been reported in previous works. The burstiness and post-to-pre re-ionisation stellar mass ratio explain the scatter in the inner slope versus stellar-to-halo mass ratio relation, revealing that galaxies with a burstiness above average and a more extended SFH are more efficient at developing cored dark matter profiles. In contrast, galaxies with smoother SFHs and an earlier stellar mass assembly time tend to maintain cuspier dark matter profiles. We present an analytic expression that improves predictions for the inner slope using M_★, post/M_★, pre, which reduces the mean square error in both simulation suites relative to previous formulations based solely on the stellar-to-halo mass ratio.