Morphology and Enhanced Star Formation in a Cartwheel-Like Ring Galaxy F

Morphology and enhanced star formation in a Cartwheel-like ring galaxy F. Renaud, E. Athanassoula, P. Amram, A. Bosma, F. Bournaud, P. -A. Duc, B. Epinat, J. Fensch, K. Kraljic, V. Perret, et al. To cite this version: F. Renaud, E. Athanassoula, P. Amram, A. Bosma, F. Bournaud, et al.. Morphology and enhanced star formation in a Cartwheel-like ring galaxy. Monthly Notices of the Royal Astronomical Soci- ety, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2018, 473 (1), pp.585-602. 10.1093/mnras/stx2360. hal-02015393 HAL Id: hal-02015393 https://hal.archives-ouvertes.fr/hal-02015393 Submitted on 12 Feb 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. MNRAS 000, 000–000 (0000) Preprint 9 October 2018 Compiled using MNRAS LATEX style file v3.0 Morphology and enhanced star formation in a Cartwheel-like ring galaxy F. Renaud1?, E. Athanassoula2, P. Amram2, A. Bosma2, F. Bournaud3, P.-A. Duc3;4, B. Epinat2, J. Fensch3, K. Kraljic2, V. Perret5, C. Struck6 1 Department of Physics, University of Surrey, Guildford, GU2 7XH, UK 2 Aix Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, 13388 Marseille, France 3 Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp, Universite´ Paris Diderot, F-91191 Gif-sur-Yvette Cedex, France 4 Observatoire Astronomique de Strasbourg, Universite´ de Strasbourg, CNRS UMR 7550, 11 rue de l’Universite,´ F-67000 Strasbourg, France 5 Institute for Theoretical Physics, University of Zurich,¨ CH-8057 Zurich,¨ Switzerland 6 Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA Accepted 2017 September 7. Received 2017 September 1; in original form 2017 June 26 ABSTRACT We use hydrodynamical simulations of a Cartwheel-like ring galaxy, modelled as a nearly head-on collision of a small companion with a larger disc galaxy, to probe the evolution of the gaseous structures and flows, and to explore the physical conditions setting the star formation activity. Star formation is first quenched by tides as the companion approaches, before being enhanced shortly after the collision. The ring ploughs the disc material as it radially extends, and almost simultaneously depletes its stellar and gaseous reservoir into the central region, through the spokes, and finally dissolve 200 Myr after the collision. Most of star formation first occurs in the ring before this activity is transferred to the spokes and then the nucleus. We thus propose that the location of star formation traces the dynamical stage of ring galaxies, and could help constrain their star formation histories. The ring hosts tidal compression associated with strong turbulence. This compression yields an azimuthal asymmetry, with maxima reached in the side furthest away from the nucleus, which matches the star formation activity distribution in our models and in observed ring systems. The interaction triggers the formation of star clusters significantly more massive than before the collision, but less numerous than in more classical galaxy interactions. The peculiar geometry of Cartwheel-like objects thus yields a star (cluster) formation activity comparable to other interacting objects, but with notable second order differences in the nature of turbulence, the enhancement of the star formation rate, and the number of massive clusters formed. Key words: galaxies: interactions – galaxies: starburst – galaxies: star clusters – stars:formation – ISM: structure – methods: numerical 1 INTRODUCTION Marcell 1996, for reviews). Gas flows onto the nuclear region and inner ring and fuels star formation there (Struck-Marcell & Ap- In the spectacular zoo of interacting galaxies, collisional rings are pleton 1987; Struck et al. 1996). Collisions with a more off-centred arXiv:1709.02826v1 [astro-ph.GA] 8 Sep 2017 one of the most peculiar species. Lynds & Toomre(1976), Theys impact lead to less symmetric configurations and could explain why & Spiegel(1977) and Toomre(1978) showed that rings result from some ring systems do not show a nuclear component, which could the head-on high-speed collision of a companion galaxy on a target also result from the destruction of a loosely bound nucleus during disc galaxy. The gravitational acceleration induced by the compan- the interaction (Madore et al. 2009). The densest structures like the ion first drags the matter of the target toward the (almost) central main ring and the inner ring often host a strong star formation activ- impact point. As the intruder flies away, the disc material rebounds, ity. Such activity is rapidly evolving in time and space, as suggested and forms an annular over-density that travels radially. Therefore, by colour gradients across the structures (Marcum et al. 1992; Ap- an empty region appears behind the ring but in some cases, a nu- pleton & Marston 1997) and as modelled by e.g. Struck-Marcell & cleus near the impact point can survive. Secondary, inner rings, Appleton(1987). in the outskirts of nuclear region can then form from second rebounds (see Athanassoula & Bosma 1985; Appleton & Struck- Their peculiar morphology make ring galaxies more easily identifiable in observations than other interacting systems. There- fore, rings are often used as probes to reconstruct the galaxy in- ? [email protected] teraction and merger rates and their dependence with redshift to c 0000 The Authors 2 Renaud et al. better constraint the assembly history of galaxies (Lavery et al. et al. 1999; Higdon et al. 2015) and ultra-luminous X-ray sources 2004; D’Onghia et al. 2008). However, these galaxies are fast (Gao et al. 2003; Wolter & Trinchieri 2004). These points indicate evolving systems, as the ring dissolves or fragments within a few an enhanced star formation activity in the form of massive stars and ∼ 100 Myr (Theys & Spiegel 1977), and therefore their detectabil- star clusters in this region. However, Amram et al.(1998) reported ity is a strong function of time. Dynamical models are thus neces- little Hα emission in the spokes and the nucleus, indicating a lower sary to pin down the conditions required to form a ring and the level of star formation there. Furthermore, the nucleus contains hot possible other structures (inner ring, nucleus) and to time the evo- dust (traced by mid-infrared, Charmandaris et al. 1999) and cold, lution of such systems as well as that of the observable components diffuse gas (Horellou et al. 1998), consistent with a weak star for- (neutral gas, excited gas, dust, star forming regions etc.). mation activity. Understanding why most star formation occurs in Numerous analytical and numerical models have addressed the ring despite large quantities of gas found in the spokes and the the questions of the formation of ring galaxies, mostly focussing nuclear region requires detailed hydrodynamics models capturing on the large-scale dynamics of the galaxies, either to constrain the the physical processes coupling the galactic-scale dynamics with formation scenario of a specific system (e.g. Struck-Marcell & Ap- the star formation activity. pleton 1987; Gerber et al. 1992; Struck-Marcell & Higdon 1993; We use the simulations presented here (i) to better understand Hernquist & Weil 1993; Bosma 2000; Horellou & Combes 2001; the (hydro-)dynamics of Cartwheel-like systems and the evolution Vorobyov 2003; Bournaud et al. 2007; Ghosh & Mapelli 2008; of their main components, and (ii) as a laboratory to explore the Mapelli et al. 2008; Michel-Dansac et al. 2010; Smith et al. 2012), physics of enhanced star formation and the formation of massive or to explore the parameter space leading to the formation of ring- star clusters in a (relatively) simple geometry. The goal of this work like systems (e.g. Huang & Stewart 1988; Appleton & James 1990; is not to improve the match between models and observations, but Struck-Marcell & Lotan 1990; Gerber & Lamb 1994; Gerber et al. rather to study the formation and evolution of Cartwheel-like ob- 1996; Athanassoula et al. 1997; Romano et al. 2008; D’Onghia jects, i.e. disc galaxies with two rings linked by what is commonly et al. 2008; Mapelli & Mayer 2012; Fiacconi et al. 2012). Such ap- referred to as spokes. More generally, we treat these simulations proach calls for a large number of simulations either in surveys or as numerical experiments in which we probe a series of physical with a trial-and-error method, at a high numerical cost. Therefore, processes over a range of physical conditions in the multi-scale and resolution and/or the range of physical processes captured are most multi-physics problem of triggered star formation. often sacrificed. However, modelling the physics of star formation and the associated feedback, both key in the evolution of galaxies and their structures, requires to capture the organisation of the 2 METHOD dense phase of the interstellar medium (ISM), which goes through resolving the turbulent cascade from its injection scale(s) down to, We use the adaptive mesh refinement (AMR) code RAMSES at least, its supersonic regime. Renaud et al.(2014a) showed that, (Teyssier 2002) and the same methods

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