The distance to the high-velocity clouds - Mass infall and galactic disk formation

Songaila, A.; Cowie, L. L.; Weaver, Harold F.

doi:10.1086/166405

Cited by 27 publications

(15 citation statements)

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“…7: Is SAO 6253 in Lilienthal et al (1990). 8: Is SAO 14733 in Songaila et al (1988). 9: Definitively shown to be stellar by Lilienthal et al (1990).…”

Section: Column 18mentioning

confidence: 96%

Distances and Metallicities of High‐ and Intermediate‐Velocity Clouds

Wakker

2001

ASTROPHYS J SUPPL S

335

573

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A table is presented that summarizes published absorption line measurements for the high-and intermediate velocity clouds (HVCs and IVCs). New values are derived for N(H I) in the direction of observed probes, in order to arrive at reliable abundances and abundance limits (the H I data are described in Paper II). Distances to stellar probes are revisited and calculated consistently, in order to derive distance brackets or limits for many of the clouds, taking care to properly interpret non-detections. The main conclusions are the following. 1) Absolute abundances have been measured using lines of S II, N I and O I, with the following resulting values: ∼0.1 solar for one HVC (complex C), ∼0.3 solar for the Magellanic Stream, ∼0.5 solar for a southern IVC, and ∼ solar for two northern IVCs (the IV Arch and LLIV Arch). Finally, approximate values in the range 0.5−2 solar are found for three more IVCs. 2) Depletion patterns in IVCs are like those in warm disk or halo gas. 3) Most distance limits are based on strong UV lines of C II, Si II and Mg II, a few on Ca II. Distance limits for major HVCs are >5 kpc, while distance brackets for several IVCs are in the range 0.5−2 kpc. 4) Mass limits for major IVCs are 0.5−8×10 5 M ⊙ , but for major HVCs they are >10 6 M ⊙ . 5) The Ca II/ H I ratio varies by up to a factor 2−5 within a single cloud, somewhat more between clouds. 6) The NaI/ H I ratio varies by a factor >10 within a cloud, and even more between clouds. Thus, Ca II can be useful for determining both lower and upper distance limits, but Na I only yields upper limits.

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“…7: Is SAO 6253 in Lilienthal et al (1990). 8: Is SAO 14733 in Songaila et al (1988). 9: Definitively shown to be stellar by Lilienthal et al (1990).…”

Section: Column 18mentioning

confidence: 96%

Distances and Metallicities of High‐ and Intermediate‐Velocity Clouds

Wakker

2001

ASTROPHYS J SUPPL S

335

573

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“…Allowing for uncertainties in the stellar distances (typically 25%), the model successfully predicts the distances for eight of ten clouds, including the HVC Complex M, assuming the warm ionized medium is principally responsible for their deceleration. For clouds at sufficiently high z, these distances predictions probably tend to be overestimates since the ambient pressure is lower, and the expected neutral fraction of clouds is expected to be f c < 1 (Songaila, Cowie, & Weaver 1988;Ferrara & Field 1994). Accounting for this will have the effect of reducing the predicted distance by ∆z ∼ = H ln(f −1 c ), where H = 910 pc for the warm ionized density distribution.…”

Section: Testsmentioning

confidence: 99%

High‐Velocity Rain: The Terminal Velocity Model of Galactic Infall

Benjamin

Danly

1997

ApJ

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A model is proposed for determining the distances to falling interstellar clouds in the galactic halo by measuring the cloud velocity and column density and assuming a model for the vertical density distribution of the Galactic interstellar medium. It is shown that falling clouds with N (H I) < ∼ 10 19 cm −2 may be decelerated to a terminal velocity which increases with increasing height above the Galactic plane. This terminal velocity model correctly predicts the distance to high velocity cloud Complex M and several other interstellar structures of previously determined distance. It is demonstrated how interstellar absorption spectra alone may be used to predict the distances of the clouds producing the absorption.If the distance, velocities, and column densities of enough interstellar clouds are known independently, the procedure can be reversed, and the terminal velocity model can be used to estimate the vertical density structure (both the mean density and the porosity) of the interstellar medium. Using the data of Danly and assuming a drag coefficient of C D ∼ = 1, the derived density distribution is consistent with the expected density distribution of the warm ionized medium, characterized by Reynolds. There is also evidence that for z > ∼ 0.4 kpc one or more of the following occurs: (1) the neutral fraction of the cloud decreases to ∼ 31 ± 14%, (2) the density drops off faster than characterized by Reynolds, or (3) there is a systematic decrease in C D with increasing z. Current data do not place strong constraints on the porosity of the interstellar medium.

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“…Oort (1966) suggested that the HVCs are infalling primordial gas and associated the HVCs Send offprint requests to: E. Casuso, e-mail: eca@ll.iac.es detected near the Galaxy with the Local Group (Verschuur 1969;Oort 1970). Although the case for the primordiality of the gas is no longer convincing (Lehner et al 2001;Weiner et al 1999;Wakker et al 1999c;Gibson et al 1999;Lubowich et al 2000;Wakker 2001;Wakker et al 2003;Savage et al 2003;Sembach et al 2003;Tripp et al 2003), the fact that at least some HVCs are Local Group members rather than gravitationally bound to the Galaxy has received considerable observational and theoretical support (Mirabel 1982;Songaila et al 1988;Lepine & Duvert 1994;Blitz et al 1999;Lopez-Corredoira et al 1999;Sembach et al 1999;Gibson et al 2001;Casuso & Beckman 2001;Putman et al 2002).…”

Section: Introductionmentioning

confidence: 99%

The K-dwarf problem and the time-dependence of gaseous accretion to the Galactic disc

Casuso

Beckman

2004

A&A

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Abstract. In this article we compare and contrast the predictions of models we have published previously, with the most recent observational data on the G-dwarf/K-dwarf metallicity distribution in the local Galaxy, as well as with up to date plots showing the relation between the Be and B abundances of local stars and their Fe abundances. We show how the data clearly support models in which infall to the plane has not declined secularly during the disc lifetime, and that the best fits are to models in which the accretion rate has tended to a slow increase. These models, devised to give the best possible account of the G-dwarf metallicity distribution, turn out to give an even better account of the K-dwarf distribution. They also do surprisingly well at predicting the observed plots of Be and B vs. Fe in the disc.

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The distance to the high-velocity clouds - Mass infall and galactic disk formation

Cited by 27 publications

References 0 publications

Distances and Metallicities of High‐ and Intermediate‐Velocity Clouds

Distances and Metallicities of High‐ and Intermediate‐Velocity Clouds

High‐Velocity Rain: The Terminal Velocity Model of Galactic Infall

The K-dwarf problem and the time-dependence of gaseous accretion to the Galactic disc

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