Inaugural Address

Caswell, Hollis L.

doi:10.1080/00131725609338181

Cited by 13 publications

(24 citation statements)

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“…This distance is derived from a line center velocity of -23 km s −1 , and circular motion within the galaxy. This kinematic distance agrees well with the findings from Caswell & Haynes (1987). Our new observations, using a revised R 0 = 8.5 kpc, and a line velocity of -20.0 ± 0.1 km s −1 suggest a distance of 3.0±0.3 kpc for NGC 3576.…”

Section: Distances To Ngc 3576 and Ngc 3603supporting

confidence: 91%

NGC 3576 and NGC 3603: Two Luminous Southern H [CSC]ii[/CSC] Regions Observed at High Resolution with the Australia Telescope Compact Array

Pree

Nysewander

Goss

1999

The Astronomical Journal

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NGC 3576 (G291.28-0.71; l = 291.3 o , b = -0.7 o ) and NGC 3603 (G291.58-0.43; l = 291.6 o , b = -0.5 o ) are optically visible, luminous HII regions located at distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australian Telescope Compact Array (ATCA) observations of these two sources in the continuum and the H90α, He90α, C90α and H113β recombination lines with an angular resolution of 7 ′′ and a velocity resolution of 2.6 km s −1 . All four recombination lines are detected in the integrated profiles of the two sources. Broad radio recombination lines are detected in both NGC 3576 (∆V F W HM ≥ 50 km s −1 ) and NGC 3603 (∆V F W HM ≥ 70 km s −1 ). In NGC 3576 a prominent N-S velocity gradient (∼30 km s −1 pc −1 ) is observed, and a clear temperature gradient (6000 K to 8000 K) is found from east to west, consistent with a known IR color gradient in the source. In NGC 3603, the H90α, He90α and the H113β lines are detected from 13 individual sources. The Y + (He/H) ratios in the two sources range from 0.08±0.04 to 0.26±0.10. The H113β/H90α ratio in NGC 3576 is close to the theoretical value, suggesting that local thermodynamic equilibrium (LTE) exists. This ratio is enhanced for most regions in NGC 3603; enhanced β/α ratios in other sources have been attributed to high optical depth or stimulated emission. We compare the morphology and kinematics of the ionized gas at 3.4 cm with the distribution of stars, 10µm emission and H 2 O, OH, and CH 3 OH maser emission. These comparisons suggest that both NGC 3576 and NGC 3603 have undergone sequential star formation.

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Section: Distances To Ngc 3576 and Ngc 3603supporting

confidence: 91%

NGC 3576 and NGC 3603: Two Luminous Southern H [CSC]ii[/CSC] Regions Observed at High Resolution with the Australia Telescope Compact Array

Pree

Nysewander

Goss

1999

The Astronomical Journal

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“…In the model (l, v) diagrams we also show molecular cloud observations of Dame et al (1986) and Bronfman, Nyman & Thaddeus (1989) (symbol '×' in the plots) and H II region observations of Georgelin & Georgelin (1976), Downes et al (1980) and Caswell & Haynes (1987) (symbol '+'). Most of our models do not contain a halo potential and therefore underestimate the velocities for |l| 40 • -50 • .…”

Section: Comparison With Observational Datamentioning

confidence: 81%

“…For comparison with observations, the spiral arm ridge lines from Fig. 4 are overplotted, as are the data for giant molecular clouds from Dame et al (1986) and Bronfman et al (1989) ('×' symbols) and for H II regions from Georgelin & Georgelin (1976), Downes et al (1980) and Caswell & Haynes (1987) ('+' symbols); see Section 2-4. The short vertical lines mark the observed spiral arm tangent directions from Englmaier & Gerhard (1999).…”

Section: B E S T-f I T T I N G M O D E L F O R T H E M I L K Y Waymentioning

confidence: 99%

“…What is the morphology of the MW spiral arms? Most authors infer four spiral arms from tracers, which directly or indirectly measure the gas density, such as molecular clouds, H II regions, pulsars and the galactic magnetic field Georgelin & Georgelin (1976), Sanders, Scoville & Solomon (1985), Caswell & Haynes (1987), Grabelsky et al (1988), Taylor & Cordes (1993), Vallée (1995); however, Bash (1981) infers a two-armed pattern from the same H II data as used by Georgelin & Georgelin). The problem is that all spiral arm parameters other than the tangent point directions (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Gas dynamics in the Milky Way: second pattern speed and large-scale morphology

Bissantz

Englmaier

Gerhard

2003

Monthly Notices of the Royal Astronomical Society

202

286

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We present new gas flow models for the Milky Way inside the solar circle. We use smoothed particles hydrodynamics (SPH) simulations in gravitational potentials determined from the near‐infrared (NIR) luminosity distribution of the bulge and disc, assuming a constant NIR mass‐to‐light ratio, with an outer halo added in some cases. The luminosity models are based on the COBE/DIRBE maps and on clump giant star counts in several bulge fields and include a spiral arm model for the disc. Gas flows in models that include massive spiral arms clearly match the observed 12CO (l, v) diagram better than if the potential does not include spiral structure. Furthermore, models in which the luminous mass distribution and the gravitational potential of the Milky Way have four spiral arms are better fits to the observed (l, v) diagram than two‐armed models. Besides single‐pattern speed models we investigate models with separate pattern speeds for the bar and spiral arms. The most important difference is that in the latter case the gas spiral arms go through the bar corotation region, keeping the gas aligned with the arms there. In the (l, v) plot this results in characteristic regions that appear to be nearly devoid of gas. In single‐pattern speed models these regions are filled with gas because the spiral arms dissolve in the bar corotation region. Comparing with the 12CO data we find evidence for separate pattern speeds in the Milky Way. From a series of models the preferred range for the bar pattern speed is Ωp= 60 ± 5 Gyr−1, corresponding to corotation at 3.4 ± 0.3 kpc. The spiral pattern speed is less well constrained, but our preferred value is Ωsp≈ 20 Gyr−1. A further series of gas models is computed for different bar angles, using separately determined luminosity models and gravitational potentials in each case. We find acceptable gas models for 20°≲ϕbar≲ 25°. The model with (ϕbar= 20°, Ωp= 60 Gyr−1, Ωsp= 20 Gyr−1) gives an excellent fit to the spiral arm ridges in the observed (l, v) plot.

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“…Some small angular size nebulae are from Wray (1966). The radio nebula G designations are from various studies, namely Wilson et al (1970), Caswell (1987 and Kuchar & Clark (1997). MSH is from Mills et al (1961) and references therein, and MHR from Mathewson et al (1962).…”

Section: Newly Found Objectsmentioning

confidence: 99%

New infrared star clusters in the southern Milky Way with 2MASS

Dutra

Bica

Soares

et al. 2003

A&A

187

243

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Abstract. We carried out a 2MASS J, H and K s survey of infrared star clusters in the Milky Way sector 230• < < 350• . This zone was the least studied in the literature, previously including only 12 infrared clusters or stellar groups with |b| < 10• , according to the recent catalogue by Bica et al. (2003). We concentrated efforts on embedded clusters, which are those expected in the areas of known radio and optical nebulae. The present study provides 179 new infrared clusters and stellar groups, which are interesting targets for detailed future infrared studies. The sample of catalogued infrared clusters and stellar groups in the Galaxy is now increased by 63%.

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Inaugural Address

Cited by 13 publications

References 0 publications

NGC 3576 and NGC 3603: Two Luminous Southern H [CSC]ii[/CSC] Regions Observed at High Resolution with the Australia Telescope Compact Array

NGC 3576 and NGC 3603: Two Luminous Southern H [CSC]ii[/CSC] Regions Observed at High Resolution with the Australia Telescope Compact Array

Gas dynamics in the Milky Way: second pattern speed and large-scale morphology

New infrared star clusters in the southern Milky Way with 2MASS

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