Distances and Metallicities of High‐ and Intermediate‐Velocity Clouds

Wakker, Bart P.

doi:10.1086/321783

Cited by 335 publications

(602 citation statements)

References 169 publications

(394 reference statements)

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“…This event caused a new episode of star formation in both the field and cluster population as well as the formation of the LMC bar and Magellanic Stream. The average metallicity of the Stream is [Fe/H] = −0.6 ± 0.2 dex (Wakker 2001), suggesting a similar age to that of disc RGB and cluster stars (Fig. 2).…”

Section: Chemical Enrichment and Dynamicsmentioning

confidence: 65%

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

Cioni¹

2009

A&A

133

154

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Context. The stellar metallicity and its gradient place constraints on the formation and evolution of galaxies. Aims. This is a study of the metallicity gradient of the LMC, SMC and M33 galaxies derived from their asymptotic giant branch (AGB) stars. Methods. The [Fe/H] abundance was derived from the ratio between C-and M-type AGB stars and its variation analysed as a function of galactocentric distance. Galaxy structure parameters were adopted from the literature.Results. The metallicity of the LMC decreases linearly as −0.047± 0.003 dex kpc −1 out to ∼8 kpc from the centre. In the SMC, [Fe/H] has a constant value of ∼−1.25 ± 0.01 dex up to ∼12 kpc. The gradient of the M33 disc, until ∼9 kpc, is −0.078 ± 0.003 dex kpc −1 while the outer disc/halo, out to ∼25 kpc, has [Fe/H] ∼ −1.7 dex. Conclusions. The metallicity of the LMC, as traced by different populations, bears the signature of two major star forming episodes: the first one constituting a thick disc/halo population and the second one a thin disc and bar due to a close encounter with the Milky Way and SMC. The [Fe/H] of the recent episode supports an LMC origin for the Stream. The metallicity of the SMC supports star formation, ∼3 Gyr ago, as triggered by LMC interaction and sustained by the bar in the outer region of the galaxy. The SMC [Fe/H] agrees with the present-day abundance in the Bridge and shows no significant gradient. The metallicity of M33 supports an "insideout" disc formation via accretion of metal poor gas from the interstellar medium.

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Section: Chemical Enrichment and Dynamicsmentioning

confidence: 65%

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

Cioni¹

2009

A&A

133

154

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“…Figure 5 is also overlaid with a set of markers which show the approximate Magellanic longitude for different parts of the system. The Magellanic coordinate system has been previously described by Wakker (2001) and was chosen as a simple way to have the Magellanic Stream lie at approximately the equator. The north pole of the Magellanic coordinate system is defined to lie at Galactic coordinates l ¼ 180 , b ¼ 0 .…”

Section: The Magellanic Streammentioning

confidence: 99%

The Magellanic Stream, High‐Velocity Clouds, and the Sculptor Group

Putman

Staveley‐Smith

Freeman

et al. 2003

ApJ

286

401

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The Magellanic Stream is a 100 Â 10 filament of gas that lies within the Galactic halo and contains $2 Â 10 8 M of neutral hydrogen. In this paper we present data from the H i Parkes All Sky Survey (HIPASS) in the first complete survey of the entire Magellanic Stream and its surroundings. We also present a summary of the reprocessing techniques used to recover large-scale structure in the Stream. The substantial improvement in spatial resolution and angular coverage compared to previous surveys reveals a variety of prominent features, including bifurcation along the main Stream filament; dense, isolated clouds that follow the entire length of the Stream; head-tail structures; and a complex filamentary web at the head of the Stream where gas is being freshly stripped away from the Small Magellanic Cloud and the Bridge. Debris that appears to be of Magellanic origin extends out to 20 from the main Stream filaments. The Magellanic Stream has a velocity gradient of 700 km s À1 from the Clouds to the tail of the Stream, $390 km s À1 greater than that due to Galactic rotation alone, therefore implying a noncircular orbit. The dual filaments comprising the Stream are likely to be relics from gas stripped separately from the Magellanic Bridge and the SMC. This implies that (1) the Bridge is somewhat older than conventionally assumed; and (2) the Clouds have been bound together for at least one or two orbits. The transverse velocity gradient of the Stream also appears to support long-term binary motion of the Clouds. A significant number of the most elongated cataloged Stream clouds (containing $1% of the Stream mass) have position angles aligned along the Stream. This suggests the presence of shearing motions within the Stream, arising from tidal forces or interaction with the tenuous Galactic halo. As previously noted, clouds within one region of the Stream, along the sight line to the less distant half (southern half on the sky) of the Sculptor Group, show anomalous properties. There are more clouds along this sight line than any other part of the Stream, and their velocity distribution significantly deviates from the gradient along the Stream. We argue that this deviation could be due to a combination of halo material, and not to distant Sculptor clouds, based on a spatial and kinematic comparison between the Sculptor Group galaxies and the anomalous clouds and the lack of cloud detection in the northern half of the group. This result has significant implications for the hypothesis that there might exist distant, massive high-velocity clouds within the Local Group. Cataloged clouds within the Magellanic Stream do not have a preferred scale size. Their mass spectrum f ðM H i Þ / M À2:0 H i and column density spectrum f ðN H i Þ / N À2:8 H i are steep compared with Ly absorbers and galaxies, and similar to the anomalous clouds along the Sculptor Group sight line.

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“…In contrast, the IVCs (H i clouds with a lower anomalous velocities) seem to constitute a different population, since their distances are shorter (∼1 kpc), their metallicity is higher (∼1 Z ), and their kinematics more closely follow the Galactic rotation. Therefore these clouds have been regarded as possible Galactic fountain objects (Wakker 2001).…”

Section: Introductionmentioning

confidence: 99%

Modelling the H i halo of the Milky Way

Marasco

Fraternali

2010

A&A

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Aims. We studied the global distribution and kinematics of the extra-planar neutral gas in the Milky Way.Methods. We built 3D models for a series of Galactic H i layers, projected them for an inside view, and compared them with the Leiden-Argentina-Bonn 21-cm observations. Results. We show that the Milky Way disk is surrounded by an extended halo of neutral gas with a vertical scale-height of 1.6 +0.6 −0.4 kpc and an H i mass of 3.2 +1.0 −0.9 × 10 8 M , which is ∼5−10% of the total Galactic H i. This H i halo rotates more slowly than the disk with a vertical velocity gradient of −15 ± 4 km s −1 kpc −1 . We found evidence for a global infall motion in the halo, both vertical (20 +5 −7 km s −1 ) and radial (30 +7 −5 km s −1 ). Conclusions.The Milky Way H i extra-planar layer shows properties similar to the halos of external galaxies, which is compatible with it being predominantly produced by supernova explosions in the disk. It is most likely composed of distinct gas complexes with masses of ∼10 4−5 M , of which the intermediate velocity clouds are the local manifestations. The classical high-velocity clouds appear to be a separate population.

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Distances and Metallicities of High‐ and Intermediate‐Velocity Clouds

Cited by 335 publications

References 169 publications

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

The Magellanic Stream, High‐Velocity Clouds, and the Sculptor Group

Modelling the H i halo of the Milky Way

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