The environmental processing of late-type dwarf satellite galaxies

Cameron James Robert Yozin-Smith

    Research output: ThesisDoctoral Thesis

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    The environmental mechanisms that drive late-type dwarf satellite galaxy evolution represent one of the key puzzles in astrophysics. In this thesis, we adopted numerical modelling of their dominant tidal and hydrodynamical interactions to reproduce observational constraints in the context of a CDM cosmology. Commencing with a holistic study of satellite galaxies with stellar mass M*≃109 M⊙, we addressed the proposition that they are preferentially quenched in group-mass hosts (dynamical mass ≃1013-13:5 M⊙), albeit inefficiently, with a quenching timescale of as much as 8 Gyr. Using cosmologically-motivated orbits and accounting for the stochastic influence of satellite harassment, our parameter study revealed their characteristic evolution tends towards a passive dS0 morphology, driven by strangulation (if assuming an efficiently stripped hot gas halo) and tidal torques acting on a gas-rich disc. Ram pressure stripping played an insignificant role for a spherically-symmetric model of the intragroup medium; however, we also demonstrated that satellites can be quenched within a single orbit if they encounter overdense substructure in the medium.

    In a second study, we examined a subset of these mechanisms in more detail with a suite of simulations that broadly replicate the wealth of multi-wavelength data for the Magellanic Clouds, a pair of M*≃108:5-9:5 M⊙ satellites of the Galaxy. The results support the tidal- dominated paradigm for the Clouds’ morphology and recent enrichment, reproducing for the first time the metallicity and dust mass of the Stream (as a tidal arm of the small Cloud) and a young stellar population in the Bridge. This study also constitutes a valuable test of a novel subgrid dust lifecycle model; after modifying this model to accommodate a low-metallicity galaxy, we confirm the governing role of destructive stellar feedback in the dwarf-mass regime.

    There remain key features that were not reproduced, including the Stream’s mass, gas- phase depletion and filamentary structure. A promising approach towards refining our model involves the adoption of larger pre-infall halo masses and a high energy orbit more consistent with recent proper motion measurements and Magellanic-analogues in the CDM model. In a third, related study, motivated by recent detections of ultra-faint dwarf galaxies (UFDs; M*≃103-5 M⊙) in the Magellanic System, we test this scenario together with a further predic- tion of the CDM model which states that Magellanic-type galaxies should be accompanied by their own satellites. Accordingly, we showed how the locations of these UFDs are consistent with the recent (<4-5 Gyr ago) infall of a dwarf association centred on the Large Magellanic Cloud. Our models also permitted a demonstration of how these gas-poor UFDs may have been stripped by the Galactic hot halo (if their gas was not previously lost to cosmic reionisa- tion), indicating the possibility of an evolutionary link between these UFDs and the emerging population of extra-Galactic gas-rich galaxy candidates.

    A similar mechanism has been proposed to explain the surprising discovery of many ultra- diffuse galaxies (UDGs) in the Coma cluster. With numerical simulations of their assumed progenitors, we reproduced in our fourth study the spectral and morphological properties of the UDGs as a product of rapid quenching and successive tidal interactions following infall to the cluster up to 7-10 Gyr ago. Our models thus conveyed these extremely dark-matter dominated galaxies as specific products of the cluster environment. In the fifth and final study, we challenged the assumption underlying these aforementioned studies in which dwarf satellite mergers are sufficiently insignificant to be excluded, with simulations that reproduced the morphology of the Fornax dSph as a remnant of a recent minor merger. In the general discussion that concludes this thesis, we comment on the successes of our numerical approach, while also highlighting where viable refinements can be applied with respect to more recent research in this field.

    Original languageEnglish
    QualificationDoctor of Philosophy
    • Bekki, Kenji, Supervisor
    • Power, Chris, Supervisor
    Publication statusUnpublished - Jan 2016


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