A rumble in the dark: signatures of self-interacting dark matter in supermassive black hole dynamics and galaxy density profiles

MNRAS 469, 2845–2854 (2017) doi:10.1093/mnras/stx1043 Advance Access publication 2017 May 3 A rumble in the dark: signatures of self-interacting dark matter in supermassive black hole dynamics and galaxy density profiles Arianna Di Cintio,1,2‹ † Michael Tremmel,3 Fabio Governato,3 Andrew Pontzen,4 Jesús Zavala,5 Alexander Bastidas Fry,3 Alyson Brooks6 and Mark Vogelsberger7 ‡ 1 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany 3 Astronomy Department, University of Washington, PO Box 351580, Seattle, WA 98195-1580, USA 4 Department of Physics and Astronomy, University College London, London WC1E 6BT, UK 5 Center for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavik, Iceland 6 Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Rd, Piscataway, NJ 08854, USA 7 Department of Physics, Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA 02139, USA 2 Leibniz ABSTRACT We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of supermassive black hole (SMBH) formation and evolution is used, as in Tremmel et al., allowing us to explicitly follow the SMBH dynamics at the centre of galaxies. A high SIDM constant cross-section is chosen, σ = 10 cm2 gr−1 , to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in cold dark matter (CDM), with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals, the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80 per cent of the SMBH population is offcentred in the SIDM case, as opposed to the CDM case in which ∼90 per cent of SMBHs have reached their host’s centre. SMBHs are found as far as ∼9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction time-scale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in core stalling. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to the SMBH physics to study their influence on galaxy formation. Key words: galaxies: evolution – cosmology: theory – dark matter. 1 I N T RO D U C T I O N Self-interacting dark matter (SIDM), originally introduced over a decade ago by Spergel & Steinhardt (2000) as a heuristic model to solve the problem of observed shallow dark matter (DM) profiles in galaxies, is also the simplest case of non-standard DM structure formation models with ‘dark sector’ interactions. SIDM has recently captured an increasing interest within the community. The collisional, self-scattering particles can create cores of DM within  E-mail: † DARK-Carlsberg, Karl Schwarzschild fellow. ‡ Alfred P. Sloan Fellow. galaxies by transferring mass from the dense central regions of the DM haloes, where the probability of collisions is higher towards the halo outskirts (Balberg, Shapiro & Inagaki 2002; Colı́n et al. 2002; Koda & Shapiro 2011). This process represents a viable solution to the so-called core-cusp problem (Moore 1994; Oh et al. 2008; Walker & Peñarrubia 2011; Adams et al. 2014). The rate of collisions, determined by the cross-section per unit mass σ /m (from now on simply σ ) is constrained from several astrophysical observations, such as the necessity of forming cores in very faint galaxies without evaporating the satellites of Milky Way (MW)-sized haloes or the galaxies in clusters, maintaining the ellipsoidal shape of haloes and clusters and avoiding the gravothermal catastrophe (Firmani et al. 2001; Gnedin & Ostriker 2001; Peter et al. 2013; Robertson, Massey & Eke 2017). Several authors have  C 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Accepted 2017 April 27. Received 2017 April 26; in original form 2017 January 13 2846 A. Di Cintio et al. MNRAS 469, 2845–2854 (2017) this is a unique capability of our runs and represents a step forwards compared to previous work in the field. We run a box of 8 Mpc in side up to z = 0.5, with the most massive galaxy being a Milky Way analogue. Both runs include a novel parametrization of the SMBH physics following Tremmel et al. (2015, 2016), in which SMBHs are allowed to form in dense pristine gas regions and their orbits can be followed as they sink towards the galaxy centre due to dynamical friction forces (Chandrasekhar 1943; Binney & Tremaine 2008). This approach is a significant improvement over previous ‘advection’ schemes that force SMBHs at the galaxy centre during merger events or satellite accretion (Di Matteo, Springel & Hernquist 2005; Sijacki et al. 2007), resulting in unrealistic time-scales for SMBH orbital decays. In order to highlight differences between CDM and SIDM, we used a cross-section of σ = 10 cm2 gr−1 , which is allowed at the scale of the Milky Way, and it is in agreement with the upper limits derived by Kaplinghat et al. (2016) using rotation curves of low surface brightness galaxies. This manuscript is organized as follows: in Section 2, we show the characteristics of the simulated galaxies, including a full description of self-interactions, SMBH and stellar physics implementations; in Section 3, we discuss the main results, focusing on the DM density profiles, SFHs and the SMBH properties in massive (Section 3.1) and intermediate mass galaxies (Section 3.2) and on the global properties of the SMBH population in the SIDM and CDM cosmologies (Sections 3.3 and 3.4); we conclude in Section 4. 2 S I M U L AT I O N S We run hydrodynamical simulations of the formation of galaxies in a full cosmological context, within a box of 8 Mpc in side, employing cosmological parameters from the latest Planck results in a  dominated universe (0 = 0.3,  = 0.7, h = 0.67, σ 8 = 0.83, Planck Collaboration XVI 2014) and following the evolution of structure formation until z = 0.5. We used two underlying models for DM, a CDM and an SIDM one, with the same set of initial conditions. We employ a constant cross-section of σ = 10 cm2 gr−1 for the SIDM model. The simulations are run using the new N-body + SPH code ChaNGa1 (Menon et al. 2015), which is an improved version of the code Gasoline and includes several standard modules such as a cosmic UV background, SF and blastwave feedback from SN (Wadsley, Stadel & (...truncated)