arXiv subjects

Cameron Yozin

Publications and source records attributed to Cameron Yozin.

5 recordsLinked to original sources

arXiv2018

The innate origin of radial and vertical gradients in a simulated galaxy disc

We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrody- namical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital reso- nances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration timescales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age-velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes.

astro-ph.GA↗

arXiv2017

Formation of the Young Massive Cluster R136 triggered by Tidally-driven Colliding HI Flows

Understanding of massive cluster formation is one of the important issues of astronomy. By analyzing the HI data, we have identified that the two HI velocity components (L- and D-components) are colliding toward the HI Ridge, in the southeastern end of the LMC, which hosts the young massive cluster R136 and $\sim$400 O/WR stars (Doran et al. 2013) including the progenitor of SN1987A. The collision is possibly evidenced by bridge features connecting the two HI components and complementary distributions between them. We frame a hypothesis that the collision triggered the formation of R136 and the surrounding high-mass stars as well as the HI & Molecular Ridge. Fujimoto & Noguchi (1990) advocated that the last tidal interaction between the LMC and the SMC about 0.2 Gyr ago induced collision of the L- and D-components. This model is consistent with numerical simulations (Bekki & Chiba 2007b). We suggest that a dense HI partly CO cloud of 10$^{6}$ $M_{\odot}$, a precursor of R136, was formed at the shock-compressed interface between the colliding L- and D-components. We suggest that part of the low-metalicity gas from the SMC was mixed in the tidal interaction based on the $Planck/IRAS$ data of dust optical depth (Planck Collaboration et al. 2014).

astro-ph.GA↗

arXiv2015

The transformation and quenching of simulated gas-rich dwarf satellites within a group environment

The underlying mechanisms driving the quenching of dwarf-mass satellite galaxies remain poorly constrained, but recent studies suggest they are particularly inefficient for those satellites with stellar mass 10$^{\rm 9}$ M$_{\odot}$. We investigate the characteristic evolution of these systems with chemodynamical simulations and idealised models of their tidal/hydrodynamic interactions within the 10$^{\rm 13-13.5}$ M$_{\odot}$ group-mass hosts in which they are preferentially quenched. Our fiducial simulations highlight the role played by secular star formation and stellar bars, and demonstrate a transition from a gas-rich to passive, HI-deficient state (i.e. $Δ$SFR$\le$-1, def$_{\rm HI}$$\ge$0.5) within 6 Gyr of first infall. Furthermore, in the 8-10 Gyr in which these systems have typically been resident within group hosts, the bulge-to-total ratio of an initially bulgeless disc can increase to 0.3$<$B/T$<$0.4, its specific angular momentum $λ_{\rm R}$ reduce to $\sim$0.5, and strong bisymmetries formed. Ultimately, this scenario yields satellites resembling dwarf S0s, a result that holds for a variety of infall inclinations/harassments albeit with broad scatter. The key assumptions here lie in the rapid removal of the satellite's gaseous halo upon virial infall, and the satellite's local intra-group medium density being defined by the host's spherically-averaged profile. We demonstrate how quenching can be greatly enhanced if the satellite lies in an overdensity, consistent with recent cosmological-scale simulations but contrasting with observationally-inferred quenching mechanisms/timescales; an appraisal of these results with respect to the apparent preferential formation of dS0s/S0s in groups is also given.

astro-ph.GA↗

arXiv2014

Evolution of dust and molecular hydrogen in the Magellanic System

We investigate the evolution of the interstellar medium (ISM) in self-consistent, chemodynamical simulations of the Magellanic Clouds (MCs) during their recent (z<0.3) past. An explicit modelling of dust and molecular hydrogen lifecycles enables the comparison of our models against the observed properties of the ISM, including elemental depletion from the gas-phase. Combining this model with a tidal-dominated paradigm for the formation for the Magellanic Stream and Bridge, we reproduce the age-metallicity relations, long gas depletion timescales, and presently observed dust and molecular hydrogen masses of the MCs to within their respective uncertainties. We find that these models' enrichment depends sensitively on the processing of dust within the ISM and the dynamical influence of external tides/stellar bars. The ratio of characteristic dust destruction timescales in our SMC and LMC models, a governing parameter of our models' evolution, is consistent with estimates based on observed supernova (SN) rates. Our reference MC models tend to exhibit the disputed universal dust-to-metal ratio, which we argue stems from the adoption of high SNe II condensation efficiencies. Our models are the first to reproduce the one-tenth solar metallicity of the Stream/Leading Arm following tidal stripping of the SMC; the hypothesis that the LMC contributes a metal-rich filament to the Stream, as implied by recent kinematic and abundance analyses, is also appraised in this study.

astro-ph.GA↗

arXiv2014

Tidal-induced lopsidedness in Magellanic-type galaxies

We investigate the tidally-induced conversion of barred late-type spirals to Magellanic-type discs with numerical simulations, to establish how the lifetime of lopsidedness (asymmetry) varies with numerical parametrizations. Using a reference model based on observed properties of the Large Magellanic Cloud (LMC), we show that its off-centre bar, one-arm spiral and one-sided star formation can be induced by a brief tidal interaction. We thereafter perform a detailed parameter study, and find that at the dynamical mass of LMC-type discs ($\sim$10$^{\rm 10}$ \md{}), stellar lopsidedness (as quantified by the m$=$1 Fourier mode) and bar off-centredness can vary widely in amplitude, but are generally short-lived ($\sim$Gyr). Tidal interactions induce more persistent lopsidedness in lower mass galaxies (several Gyr), in particular those with large halo-to-disc mass ratios as implied by recent halo occupation models. We suggest that the tidal interactions play a larger role in the observed ubiquity of lopsidedness than the presently favoured gas accretion mechanism for lower mass galaxies. Other characteristics of Magellanic-type galaxies, such as one-sided star formation, are quantified and tend to arise more prominently in discs with later-type spiral structure (more halo dominated inner disc, weaker bars) following retrograde orbital encounters.

astro-ph.GA↗