Disc galaxies formed from major mergers in Illustris

Peschken, Nicolas; Łokas, Ewa L.; Athanassoula, E.

doi:10.1093/mnras/staa299

Cited by 33 publications

(26 citation statements)

References 41 publications

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“…In 2 other hosts (m12c and Juliet), 1 of the 3 mergers caused the orientation of the disk to settle, but other subsequent mergers caused the disk to then change orientation again. Our results qualitatively agree with Peschken et al (2020) and suggest that mergers were a dominant mode of promoting the transition to thin-disk morphology, with much of the gas mass mentioned above likely contributing to subsequent star formation in the disk region.…”

Section: Discussionsupporting

confidence: 87%

The origin of metal-poor stars on prograde disc orbits in FIRE simulations of Milky Way-mass galaxies

Santistevan

Wetzel

Sanderson

et al. 2021

Monthly Notices of the Royal Astronomical Society

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In hierarchical structure formation, metal-poor stars in and around the Milky Way (MW) originate primarily from mergers of lower-mass galaxies. A common expectation is therefore that metal-poor stars should have isotropic, dispersion-dominated orbits that do not correlate strongly with the MW disk. However, recent observations of stars in the MW show that metal-poor ([Fe/H]≲ −2) stars are preferentially on prograde orbits with respect to the disk. Using the FIRE-2 suite of cosmological zoom-in simulations of MW/M31-mass galaxies, we investigate the prevalence and origin of prograde metal-poor stars. Almost all (11 of 12) of our simulations have metal-poor stars on preferentially prograde orbits today and throughout most of their history: we thus predict that this is a generic feature of MW/M31-mass galaxies. The typical prograde-to-retrograde ratio is ∼2 : 1, which depends weakly on stellar metallicity at [Fe/H]≲ −1. These trends predicted by our simulations agree well with MW observations. Prograde metal-poor stars originate largely from a single LMC/SMC-mass gas-rich merger 7 − 12.5Gyr ago, which deposited existing metal-poor stars and significant gas on an orbital vector that sparked the formation of and/or shaped the orientation of a long-lived stellar disk, giving rise to a prograde bias for all low-metallicity stars. We find sub-dominant contributions from in-situ stars formed in the host galaxy before this merger, and in some cases, additional massive mergers. We find few clear correlations between any properties of our MW/M31-mass galaxies at z = 0 and the degree of this prograde bias as a result of diverse merger scenarios.

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Section: Discussionsupporting

confidence: 87%

The origin of metal-poor stars on prograde disc orbits in FIRE simulations of Milky Way-mass galaxies

Santistevan

Wetzel

Sanderson

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…Our work focuses exclusively on major galaxy interactions, meant to represent typical galaxy pairs in the local Universe. In future work, we plan to explore the effect of varying the mass ratio (Cox et al 2008;Lotz et al 2010), and will extend our analysis into the post-coalescence period (Thorp et al 2019;Hani et al 2020b;Peschken, Łokas & Athanassoula 2020). We also intend to explore the region outside our two 10-kpc spheres, and evaluate the role of tidal compression in driving extended star formation (Renaud et al 2014(Renaud et al , 2015.…”

Section: S U M M a Rymentioning

confidence: 99%

Spatially resolved star formation and fuelling in galaxy interactions

Moreno

Torrey

Ellison

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We investigate the spatial structure and evolution of star formation and the interstellar medium (ISM) in interacting galaxies. We use an extensive suite of parsec-scale galaxy merger simulations (stellar mass ratio = 2.5:1), which employs the ’Feedback In Realistic Environments-2’ model (fire-2). This framework resolves star formation, feedback processes, and the multi-phase structure of the ISM. We focus on the galaxy-pair stages of interaction. We find that close encounters substantially augment cool (HI) and cold-dense (H2) gas budgets, elevating the formation of new stars as a result. This enhancement is centrally-concentrated for the secondary galaxy, and more radially extended for the primary. This behaviour is weakly dependent on orbital geometry. We also find that galaxies with elevated global star formation rate (SFR) experience intense nuclear SFR enhancement, driven by high levels of either star formation efficiency (SFE) or available cold-dense gas fuel. Galaxies with suppressed global SFR also contain a nuclear cold-dense gas reservoir, but low SFE levels diminish SFR in the central region. Concretely, in the majority of cases, SFR-enhancement in the central kiloparsec is fuel-driven (55% for the secondary, 71% for the primary) - whilst central SFR-suppression is efficiency-driven (91% for the secondary, 97% for the primary). Our numerical predictions underscore the need of substantially larger, and/or merger-dedicated, spatially-resolved galaxy surveys - capable of examining vast and diverse samples of interacting systems - coupled with multi-wavelength campaigns aimed to capture their internal ISM structure.

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“…Galaxies which have evolved via mergers are easily recognisable, as mergers are able to redistribute angular momentum in galaxy systems, transferring stars from rotation-supported orbits to pressuresupported orbits in a central bulge, similar to an elliptical galaxy. While there is also an increasing number of simulations finding that a disk can reform post-gas rich merger (Hopkins et al 2009;Sparre & Springel 2017;Pontzen et al 2017;Peschken et al 2020;Jackson et al 2020), a significant bulge component still forms even in a minor merger (i.e. when the mass ratio in the merger exceeds 10 : 1; Walker et al 1996;Hopkins et al 2012;Tonini et al 2016;Stevens et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Kiloparsec-scale AGN outflows and feedback in merger-free galaxies

Smethurst

Simmons

Coil

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Recent observations and simulations have challenged the long-held paradigm that mergers are the dominant mechanism driving the growth of both galaxies and supermassive black holes (SMBH), in favour of non-merger (secular) processes. In this pilot study of merger-free SMBH and galaxy growth, we use Keck Cosmic Web Imager spectral observations to examine four low-redshift (0.043 < z < 0.073) disk-dominated ‘bulgeless’ galaxies hosting luminous AGN, assumed to be merger-free. We detect blueshifted broadened [O iii] emission from outflows in all four sources, which the $\rm{[O\, \small {III}]}$/$\rm {H}\beta$ ratios reveal are ionised by the AGN. We calculate outflow rates in the range $0.12-0.7~\rm {M}_{\odot }~\rm {yr}^{-1}$, with velocities of $675-1710~\rm {km}~\rm {s}^{-1}$, large radial extents of $0.6-2.4~\rm {kpc}$, and SMBH accretion rates of $0.02-0.07~\rm {M}_{\odot }~\rm {yr}^{-1}$. We find that the outflow rates, kinematics, and energy injection rates are typical of the wider population of low-redshift AGN, and have velocities exceeding the galaxy escape velocity by a factor of ∼30, suggesting that these outflows will have a substantial impact through AGN feedback. Therefore, if both merger-driven and non-merger-driven SMBH growth lead to co-evolution, this suggests that co-evolution is regulated by feedback in both scenarios. Simulations find that bars and spiral arms can drive inflows to galactic centres at rates an order of magnitude larger than the combined SMBH accretion and outflow rates of our four targets. This work therefore provides further evidence that non-merger processes are sufficient to fuel SMBH growth and AGN outflows in disk galaxies.

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Disc galaxies formed from major mergers in Illustris

Cited by 33 publications

References 41 publications

The origin of metal-poor stars on prograde disc orbits in FIRE simulations of Milky Way-mass galaxies

The origin of metal-poor stars on prograde disc orbits in FIRE simulations of Milky Way-mass galaxies

Spatially resolved star formation and fuelling in galaxy interactions

Kiloparsec-scale AGN outflows and feedback in merger-free galaxies

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