Reports on the Progress of Astronomy the Galactic System as a Spiral Nebula

Oort, J. H.; Kerr, F. J.; Westerhout, G.

doi:10.1093/mnras/118.4.379

Cited by 161 publications

(18 citation statements)

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“…Under the assumption of constant circular rotation of the MW, a simple geometric consideration provides the equation for conversion from (l, v) to R (e.g., Oort et al 1958;Kellermann & Verschuur 1988;Nakanishi & Sofue 2003): . This equation is applicable in a particular velocity range at each l (explained later): in summary,…”

Section: The Constant Circular Rotation Modelmentioning

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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Section: The Constant Circular Rotation Modelmentioning

confidence: 99%

Evolution of Molecular and Atomic Gas Phases in the Milky Way

Koda

Scoville

Heyer

2016

ApJ

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“…Despite our embedded location, the main structural parameters of the Milky Way have been determined with some confidence (see Bland-Hawthorn & Gerhard 2016, for a thorough review). The spiral arm structure of the Milky Way's disk was first revealed by ionised Hydrogen distributions and observations of the 21cm line in the 1950s (See Oort et al 1958, for a review of early work). The Galactic bar took longer to elucidate due to the high extinction in the central regions of the Galaxy.…”

Section: Introductionmentioning

confidence: 99%

From the outside looking in: what can Milky Way analogues tell us about the star formation rate of our own galaxy?

Fraser-McKelvie

Merrifield

Aragón-Salamanca

2019

Monthly Notices of the Royal Astronomical Society

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The Milky Way has been described as an anaemic spiral, but is its star formation rate (SFR) unusually low when compared to its peers? To answer this question, we define a sample of Milky Way Analogues (MWAs) based on stringent cuts on the best literature estimates of non-transient structural features for the Milky Way. This selection yields only 176 galaxies from the whole of the SDSS DR7 spectroscopic sample which have morphological classifications in GZ2, from which we infer SFRs from two separate indicators. The mean SFRs found are log(SFR SED /M yr −1 ) = 0.53 with a standard deviation of 0.23 dex from SED fits, and log(SFR W4 /M yr −1 ) = 0.68 with a standard deviation of 0.41 dex from a mid-infrared calibration. The most recent estimate for the Milky Way's star formation rate of log(SFR MW /M yr −1 ) = 0.22 fits well within 2σ of these values, where σ is the standard deviation of each of the SFR indicator distributions. We infer that the Milky Way, while being a galaxy with a somewhat low SFR, is not unusual when compared to similar galaxies.

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“…Knowledge of warps in the gas discs of the MW and M31 date back to the mid-20 th century (e.g. Oort et al 1958;Roberts & Whitehurst 1975;Newton & Emerson 1977). Both warps reach heights up to several kiloparsecs above the disc plane.…”

Section: Introductionmentioning

confidence: 99%

Orbits of massive satellite galaxies – I. A close look at the Large Magellanic Cloud and a new orbital history for M33

Patel

Besla

Sohn

2016

Mon. Not. R. Astron. Soc.

108

134

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The Milky Way (MW) and M31 both harbor massive satellite galaxies, the Large Magellanic Cloud (LMC) and M33, which may comprise up to 10 per cent of their host's total mass. Massive satellites can change the orbital barycentre of the host-satellite system by tens of kiloparsecs and are cosmologically expected to harbor dwarf satellite galaxies of their own. Assessing the impact of these effects depends crucially on the orbital histories of the LMC and M33. Here, we revisit the dynamics of the MW-LMC system and present the first detailed analysis of the M31-M33 system utilizing high precision proper motions and statistics from the dark matter-only Illustris cosmological simulation. With the latest Hubble Space Telescope proper motion measurements of M31, we reliably constrain M33's interaction history with its host. In particular, like the LMC, M33 is either on its first passage (t inf < 2 Gyr ago) or if M31 is massive (≥ 2 × 10 12 M ), it is on a long period orbit of about 6 Gyr. Cosmological analogs of the LMC and M33 identified in Illustris support this picture and provide further insight about their host masses. We conclude that, cosmologically, massive satellites like the LMC and M33 are likely completing their first orbits about their hosts. We also find that the orbital energies of such analogs prefer a MW halo mass ∼1.5 × 10 12 M and an M31 halo mass ≥ 1.5 × 10 12 M . Despite conventional wisdom, we conclude it is highly improbable that M33 made a close (< 100 kpc) approach to M31 recently (t peri < 3 Gyr ago). Such orbits are rare (< 1 per cent) within the 4σ error space allowed by observations. This conclusion cannot be explained by perturbative effects through four body encounters between the MW, M31, M33, and the LMC. This surprising result implies that we must search for a new explanation for M33's strongly warped gas and stellar discs.

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Reports on the Progress of Astronomy the Galactic System as a Spiral Nebula

Cited by 161 publications

References 0 publications

Evolution of Molecular and Atomic Gas Phases in the Milky Way

Evolution of Molecular and Atomic Gas Phases in the Milky Way

From the outside looking in: what can Milky Way analogues tell us about the star formation rate of our own galaxy?

Orbits of massive satellite galaxies – I. A close look at the Large Magellanic Cloud and a new orbital history for M33

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