A CO survey of the southern Milky Way - The mean radial distribution of molecular clouds within the solar circle

the CS J=2 →1 molecular line at 98 GHz, a normally optically thin line requiring high densities to be excited, has been detected with SEST (Swedish ESO Submillimeter Telescope) toward 294 IRAS pointlike sources having the characteristic FIR colors of embedded stellar objects and apparently associated with the largest molecular cloud complexes in the southern Milky Way. We present here their Galactocentric radial distribution and a correlation between their FIR and CS luminosities.

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Molecular Clouds Within 100 pc

International Astronomical Union Colloquium ◽

10.1017/s0252921100098250 ◽

1984 ◽

Vol 81 ◽

pp. 229-234

Author(s):

Leo Blitz ◽

Loris Magnani ◽

Lee Mundy

Keyword(s):

Interstellar Medium ◽

Molecular Hydrogen ◽

Molecular Clouds ◽

Milky Way ◽

Velocity Dispersion ◽

Scale Height ◽

Galactic Latitude ◽

Local Interstellar Medium ◽

High Galactic Latitude ◽

The Mean

AbstractObservations at the 2.6 mm line of CO reveal the presence of a large number of molecular clouds at high galactic latitude. If the velocity dispersion of the clouds is a measure of their scale height, the mean distance of the ensemble we have detected is 100 pc. The clouds are unusual in that either they are not gravitationally bound or they are very deficient in CO relative to molecular hydrogen. These clouds represent a heretofore unrecognized component of the local interstellar medium. If they are pervasive in the Milky Way, they probably represent the small molecular cloud component of the interstellar medium.

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A CS survey of massive stars embedded in molecular clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900198730 ◽

1991 ◽

Vol 147 ◽

pp. 25-28

Author(s):

L. Bronfman ◽

J. May ◽

L. A. Nyman ◽

P. Thaddeus

Keyword(s):

Radial Distribution ◽

Molecular Cloud ◽

Molecular Clouds ◽

Milky Way ◽

Massive Stars ◽

Molecular Line ◽

Stellar Objects ◽

Thin Line

the CS J=2 →1 molecular line at 98 GHz, a normally optically thin line requiring high densities to be excited, has been detected with SEST (Swedish ESO Submillimeter Telescope) toward 294 IRAS pointlike sources having the characteristic FIR colors of embedded stellar objects and apparently associated with the largest molecular cloud complexes in the southern Milky Way. We present here their Galactocentric radial distribution and a correlation between their FIR and CS luminosities.

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The Ballistic Particle Model

Symposium - International Astronomical Union ◽

10.1017/s0074180900032629 ◽

1983 ◽

Vol 100 ◽

pp. 133-134

Author(s):

Frank N. Bash

Keyword(s):

Radial Velocity ◽

Gravitational Potential ◽

Molecular Clouds ◽

Milky Way ◽

Terminal Velocity ◽

Particle Model ◽

The Sun ◽

Giant Molecular Clouds ◽

Spiral Pattern ◽

Armed Spiral

Bash and Peters (1976) suggested that giant molecular clouds (GMC's) can be viewed as ballistic particles launched from the two-armed spiral-shock (TASS) wave with orbits influenced only by the overall galactic gravitational potential perturbed by the spiral gravitational potential in the arms. For GMC's in the Milky Way, the model predicts that the radial velocity observed from the Sun increases with age (time since launch). We showed that the terminal velocity of CO observed from l ≃ 30° to l ≃ 60° can be understood if all GMC's are born in the spiral pattern given by Yuan (1969) and live 30 × 106 yrs. Older GMC's were predicted to have radial velocities which exceed observed terminal velocities.

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Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732568 ◽

2018 ◽

Vol 615 ◽

pp. A100 ◽

Cited By ~ 5

Author(s):

A. Gómez ◽

P. Di Matteo ◽

M. Schultheis ◽

F. Fragkoudi ◽

M. Haywood ◽

...

Keyword(s):

Milky Way ◽

Thin Disk ◽

Secular Evolution ◽

Thick Disc ◽

Thin Disc ◽

The Mean ◽

The Difference ◽

Different Origins ◽

Argos Data ◽

Internal Evolution

Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity (ΔVGC) between metal-rich stars ([Fe/H] ≥ 0) and moderately metal-poor stars (–1.0 ≤ [Fe/H] < 0) in two models, one containing a thin disc and a small classical bulge (B/D = 0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate ΔVGC at different latitudes (b = 0°, − 2°, − 4°, − 6°, − 8° and − 10°) and longitudes (l = 0°, ± 5°, ± 10° and ± 15°) and show that the ΔVGC trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] < –1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.

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STUDY OF AN INTERMEDIATE AGE OPEN CLUSTER IC 1434 USING GROUND-BASED IMAGING AND GAIA DR2 ASTROMETRY

Revista Mexicana de Astronomía y Astrofísica ◽

10.22201/ia.01851101p.2021.57.02.10 ◽

2021 ◽

Vol 57 (2) ◽

pp. 381-389

Author(s):

Y. H. M. Hendy ◽

D. Bisht

Keyword(s):

Radial Distribution ◽

Proper Motion ◽

Open Cluster ◽

Membership Probability ◽

Kinematical Analysis ◽

The Mean ◽

First Time ◽

Right Ascension ◽

Cluster Age ◽

Gaia Dr2

We present a detailed photometric and kinematical analysis of the poorly studied open cluster IC 1434 using CCD VRI, APASS, and Gaia DR2 database for the first time. By determining the membership probability of stars we identify the 238 most probable members with a probability higher than 60%; by using proper motion and parallax data as taken from the Gaia DR2 catalog. The mean proper motion of the cluster is obtained as μx=−3.89±0.19 and μy=−3.34±0.19 mas yr−1 in both the directions of right ascension and declination. The radial distribution of member stars provides the cluster extent as 7.6 arcmin. We estimate the interstellar reddening E(B−V) as 0.34 mag using the transformation equations from the literature. We obtain the values of cluster age and distance as 631±73 Myr and 3.2±0.1 kpc.

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Molecular Clouds and Star Formation at Large R

Symposium - International Astronomical Union ◽

10.1017/s0074180900088987 ◽

1991 ◽

Vol 144 ◽

pp. 121-130

Author(s):

J. Brand ◽

J.G.A. Wouterloot

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Density Wave ◽

Cosmic Ray ◽

Volume Density ◽

Kinetic Temperature ◽

Galactocentric Distance ◽

The Galaxy ◽

The Mean ◽

Cosmic Ray Flux

In the outer Galaxy (defined here as those parts of our system with galactocentric radii R>R0) the HI gas density (Wouterloot et al., 1990), the cosmic ray flux (Bloemen et al, 1984) and the metallicity (Shaver et al., 1983) are lower than in the inner parts. Also, the effect of a spiral density wave is much reduced in the outer parts of the Galaxy due to corotation. This changing environment might be expected to have its influence on the formation of molecular clouds and on star formation within them. In fact, some differences with respect to the inner Galaxy have been found: the ratio of HI to H2 surface density is increasing from about 5 near the Sun to about 100 at R≈20kpc (Wouterloot et al., 1990). Because of the “flaring” of the gaseous disk, the scale height of both the atomic and the molecular gas increases by about a factor of 3 between R0 and 2R0 (Wouterloot et al., 1990), so the mean volume density of both constituents decreases even more rapidly than their surface densities. The size of HII regions decreases significantly with increasing galactocentric distance (Fich and Blitz, 1984), probably due to the fact that outer Galaxy clouds are less massive (see section 3.3), and therefore form fewer O-type stars than their inner Galaxy counter parts. There are indications that the cloud kinetic temperature is lower by a few degrees (Mead and Kutner, 1988), although it is not clear to what extent this is caused by beam dilution.

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The last breath of the Sagittarius dSph

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2114 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4162-4182 ◽

Cited By ~ 3

Author(s):

Eugene Vasiliev ◽

Vasily Belokurov

Keyword(s):

Milky Way ◽

Dwarf Galaxy ◽

3D Structure ◽

Major Axis ◽

Final State ◽

Tidal Forces ◽

The Galaxy ◽

The Mean ◽

Red Clump ◽

Astrometric Data

ABSTRACT We use the astrometric and photometric data from Gaia Data Release 2 and line-of-sight velocities from various other surveys to study the 3D structure and kinematics of the Sagittarius dwarf galaxy. The combination of photometric and astrometric data makes it possible to obtain a very clean separation of Sgr member stars from the Milky Way foreground; our final catalogue contains 2.6 × 105 candidate members with magnitudes G < 18, more than half of them being red clump stars. We construct and analyse maps of the mean proper motion and its dispersion over the region ∼30 × 12 deg, which show a number of interesting features. The intrinsic 3D density distribution (orientation, thickness) is strongly constrained by kinematics; we find that the remnant is a prolate structure with the major axis pointing at ∼45° from the orbital velocity and extending up to ∼5 kpc, where it transitions into the stream. We perform a large suite of N-body simulations of a disrupting Sgr galaxy as it orbits the Milky Way over the past 2.5 Gyr, which are tailored to reproduce the observed properties of the remnant (not the stream). The richness of available constraints means that only a narrow range of parameters produce a final state consistent with observations. The total mass of the remnant is $\sim \!4\times 10^8\, \mathrm{M}_\odot$, of which roughly a quarter resides in stars. The galaxy is significantly out of equilibrium, and even its central density is below the limit required to withstand tidal forces. We conclude that the Sgr galaxy will likely be disrupted over the next Gyr.

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