The morphology of the Milky Way – II. Reconstructing CO maps from disc galaxies with live stellar distributions

Pettitt, Alex R.; Dobbs, Clare; Acreman, David M.; Bate, Matthew R.

doi:10.1093/mnras/stv600

Cited by 51 publications

(77 citation statements)

References 75 publications

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“…All non-axisymmetric components are assumed to rotate as rigid features. While there is increasing evidence that a more dynamic and transient spiral structure exists in disc galaxies from both simulations (Pettitt et al 2015;Grand et al 2015) and observations (Meidt et al 2009;Foyle et al 2011;Choi et al 2015), we use fixed potentials for their simplicity and more canonical acceptance in the literature. We note that the nature of spiral arms is still a topic of uncertainty (see Dobbs & Baba 2014 for a review), and different theories have repercussions for disc kinematics (Grand et al 2015;Sellwood et al 2019), radial migration (Sellwood & Binney 2002) and giant molecular cloud properties (Dobbs et al 2012;Baba et al 2017).…”

Section: Numerical Simulationsmentioning

confidence: 99%

Young stars as tracers of a barred-spiral Milky Way

Pettitt

Ragan

Smith

2019

Monthly Notices of the Royal Astronomical Society

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Identifying the structure of our Galaxy has always been fraught with difficulties, and while modern surveys continue to make progress building a map of the Milky Way, there is still much to understand. The arm and bar features are important drivers in shaping the interstellar medium, but their exact nature and influence still require attention. We present results of smoothed particle hydrodynamic simulations of gas in the Milky Way including star formation, stellar feedback, and ISM cooling, when exposed to different arm and bar features, with the aim of better understanding how well newly formed stars trace out the underlying structure of the Galaxy. The bar is given a faster pattern speed than the arms, resulting in a complex, time-dependent morphology and star formation. Inter-arm branches and spurs are easily influenced by the bar, especially in the two-armed spiral models where there is a wide region of resonance overlap in the disc. As the bar over-takes the spiral arms it induces small boosts in star formation and enhances spiral features, which occur at regularly spaced beat-like intervals. The locations of star formation events are similar to those seen in observational data, and do not show a perfect 1:1 correspondence with the underlying spiral potential, though arm tangencies are generally well traced by young stars. Stellar velocity fields from the newly formed stars are compared to data from Gaia DR2, showing that the spiral and bar features can reproduce many of the nonaxisymmetric features seen in the data. A simple analytical model is used to show many of these feature are a natural response of gas to rigidly rotating spiral and bar potentials.

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Section: Numerical Simulationsmentioning

confidence: 99%

Young stars as tracers of a barred-spiral Milky Way

Pettitt

Ragan

Smith

2019

Monthly Notices of the Royal Astronomical Society

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“…In order to quantify the structures of each model, we compute a Fourier decomposition of the material in each disc, as in Pettitt et al 2015. The Fourier am and bm coefficients as a function of galactocentric radius, R, and time, t, for each order symmetry, m, are given by:…”

Section: Mode Analysismentioning

confidence: 99%

“…The first is to directly trace the peaks in density as a function of azimuth and then simply track their motion over time at any given radius (e.g. Grand et al 2012;Pettitt et al 2015 equations 5 and 6). The change in θ of each peak for a given m then gives the pattern speed of that specific mode.…”

Section: Pattern Speedsmentioning

confidence: 99%

“…In Figure 19 we show the wind-up rate for the tidal spirals in all S05 calculations (blue started points). These spiral arms are fit using a simple direct tracing method (Grand et al 2012;Pettitt et al 2015), as the temporal resolution of the spectrogram analysis in the pervious section is far too coarse to resolve such a wind-up rate. We plot cot(α) to give a linearly increasing plot, against t − tperi, the time since perigalacticon passage of the companion.…”

Section: Nature Of the Spiralsmentioning

confidence: 99%

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Bars and spirals in tidal interactions with an ensemble of galaxy mass models

Pettitt

Wadsley

2017

Monthly Notices of the Royal Astronomical Society

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We present simulations of the gaseous and stellar material in several different galaxy mass models under the influence of different tidal fly-bys to assess the changes in their bar and spiral morphology. Five different mass models are chosen to represent the variety of rotation curves seen in nature. We find a multitude of different spiral and bar structures can be created, with their properties dependent on the strength of the interaction. We calculate pattern speeds, spiral wind-up rates, bar lengths, and angular momentum exchange to quantify the changes in disc morphology in each scenario. The wind-up rates of the tidal spirals follow the 2:1 resonance very closely for the flat and dark matter dominated rotation curves, whereas the more baryon dominated curves tend to wind-up faster, influenced by their inner bars. Clear spurs are seen in most of the tidal spirals, most noticeable in the flat rotation curve models. Bars formed both in isolation and interactions agree well with those seen in real galaxies, with a mixture of "fast" and "slow" rotators. We find no strong correlation between bar length or pattern speed and the interaction strength. Bar formation is, however, accelerated/induced in four out of five of our models. We close by briefly comparing the morphology of our models to real galaxies, easily finding analogues for nearly all simulations presenter here, showing passages of small companions can easily reproduce an ensemble of observed morphologies.

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“…The ISM in galaxies often shows coherent filamentary structures, even in interarm regions (seen as dust lanes in optical images; e.g., Hubble Heritage images-http:// heritage.stsci.edu), which explains the minor, apparent gas/ dust spiral arms. In addition, gas filaments in the interarm regions of stellar spiral arms develop naturally in numerical simulations (e.g., Kim & Ostriker 2002;Chakrabarti et al 2003;Martos et al 2004;Wada & Koda 2004;Pettitt et al 2015).…”

Section: Structures Of the Mwmentioning

confidence: 99%

Evolution of Molecular and Atomic Gas Phases in the Milky Way

Koda

Scoville

Heyer

2016

ApJ

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We analyze radial and azimuthal variations of the phase balance between the molecular and atomic interstellar medium (ISM) in the Milky Way (MW) using archival CO( J=1-0) and HI 21 cm data. In particular, the azimuthal variations-between the spiral arm and interarm regions-are analyzed without any explicit definition of the spiral arm locations. We show that the molecular gas mass fraction, i.e.,, varies predominantly in the radial direction: starting from~100% at the center, remaining 50% toR 6 kpc and decreasing to ∼10%-20% at = R 8.5 kpc when averaged over the whole disk thickness (from ∼100% to ≳60%, then to ∼50% in the midplane). Azimuthal, arm-interarm variations are secondary: only~20% in the globally molecule-dominated inner MW, but becoming larger, ∼40%-50%, in the atom-dominated outskirts. This suggests that in the inner MW the gas remains highly molecular ( > f 50% mol ) as it moves from an interarm region into a spiral arm and back into the next interarm region. Stellar feedback does not dissociate molecules much, and the coagulation and fragmentation of molecular clouds dominate the evolution of the ISM at these radii. The trend differs in the outskirts where the gas phase is globally atomic ( < f 50% mol ). The HI and H 2 phases cycle through spiral arm passage there. These different regimes of ISM evolution are also seen in external galaxies (e.g., the LMC, M33, and M51). We explain the radial gradient of f mol using a simple flow continuity model. The effects of spiral arms on this analysis are illustrated in the Appendix.

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The morphology of the Milky Way – II. Reconstructing CO maps from disc galaxies with live stellar distributions

Cited by 51 publications

References 75 publications

Young stars as tracers of a barred-spiral Milky Way

Young stars as tracers of a barred-spiral Milky Way

Bars and spirals in tidal interactions with an ensemble of galaxy mass models

Evolution of Molecular and Atomic Gas Phases in the Milky Way

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