Distances and Metallicities of High- and Intermediate-Velocity Clouds

By B. Wakker. 2001

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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 nondetections. 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 greater than 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 × 105 M☉, but for major HVCs they are more than 106 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 Na I/H I ratio varies by a factor of more than 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.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Hα Emission from High-Velocity Clouds and Their Distances (2003, methodology): “We include the T98 detections of Complexes A and C with a model distance because they have direct distance limits of 4-10 kpc (van Woerden et al. 1999) and > 6 kpc (Wakker 2001), respec- tively.”
Highly Ionized High-Velocity Gas in the Vicinity of the Galaxy (2002, background): “…A Sight lines to two extragalactic objects in our sample (Mrk 106, Mrk 116) pass through high-velocity cloud Complex A. Complex A is located at a distance of 4–10 kpc (z ¼ 2:6 6:8 kpc), has a mass of 2:0 106 M , and has H i velocities of 210dvLSRd 140 km s 1 (van Woerden et al. 1999b; Wakker 2001).”
HI4PI: a full-sky H i survey based on EBHIS and GASS (2016, background): “In addition, there are intermediate-velocity clouds (Wakker 2001) and high-velocity clouds (Wakker & van Woerden 1997) in the halo of the Milky Way (which account for the non-galaxy objects in the HyperLEDA catalog).”
The Parkes HI survey of the Magellanic System (2004, methodology): “The Magellanic coordinate system was defined by Wakker (2001) as follows: the line of zero latitude is defined as the line from Galactic longitude l = 90◦ across the southern Galactic pole to l = 270◦.”
The gravitational and hydrodynamical interaction between the Large Magellanic Cloud and the Galaxy (2004, methodology): “The Magellanic coordinate system adopted is the same as used by (Putman et al. 2003a) and previously described by Wakker (2001).”
The Origin of the Magellanic Stream and Its Leading Arm (2007, methodology): “A Magellanic coordinate system was defined by Wakker (2001), in terms of the great circle along the l = 90◦ and l = 270◦ Galactic meridian.”
Distribution and Kinematics of O VI in the Galactic Halo (2002, methodology): “Furthermore, the IVCs have abundances and z-distances consistent with the idea that they represent gas participating in a Galactic fountain flow (Wakker 2001; Richter et al 2001a, 2001b).”
Distances to Galactic High-Velocity Clouds. I. Cohen Stream, Complex GCP, Cloud g1 (2007, methodology): “In contrast, the IVCs are usually found to have near-solar metallicity (Wakker 2001; Richter et al. 2001a).”
The Magellanic Stream, High-Velocity Clouds, and the Sculptor Group (2002, methodology): “Wakker (2001), by comparison, estimates a somewhat lower Stream mass at 55 kpc of 1.2× 108 M⊙ (based on the data of Hulsbosch & Wakker (1988) and Morras et al (2000)), however he has also quoted 6× 108 M⊙ (Wakker & van Woerden 1991), representing the ambiguity in defining the Stream.”
A UNIFIED REPRESENTATION OF GAS-PHASE ELEMENT DEPLETIONS IN THE INTERSTELLAR MEDIUM (2009, background): “Infalling gas at high velocities (Wakker 2001) is not included in this study, since the kinematics of this material point to an origin outside the Galactic disk, and the intrinsic abundances of the heavy elements are low (Wakker et al. 1999; Murphy et al. 2000; Gibson et al. 2001; Richter et al.…”
Turbulent Structure of a Stratified Supernova-driven Interstellar Medium (2005, background): “1 kpc with intermediate velocity clouds (Wakker 2001).”
The Wisconsin Hα Mapper Northern Sky Survey (2001, background): “Many of the intermediate-velocity complexes cataloged by Wakker (2001) also have associated H emission revealed in the WHAM-NSS.”
The Cold Gaseous Halo of NGC 891 (2007, background): “The cloud complexes with anomalous velocities found in galaxies like NGC 2403 (Fraternali et al. 2002) have similar masses and velocity deviations with respect to the disk as the largest galactic HVCs for which the distances are known (e.g., complex A; Wakker 2001).”
CHARACTERIZING THE CIRCUMGALACTIC MEDIUM OF NEARBY GALAXIES WITH HST/COS AND HST/STIS ABSORPTION-LINE SPECTROSCOPY (2012, methodology): “For our own Galaxy, the detection of some small amount of CGM gas has been made possible by observing the so-called high velocity clouds (HVCs) using H I 21-cm emission (Wakker & van Woerden 1997; Wakker 2001; Putman, Peek & Joung 2012), but the number of baryons in HVCs is not substantial.”
The Progenitors of Dwarf Spheroidal Galaxies (2002, background): “Horizontal lines separate spatially defined galaxy subgroups: The first set of galaxies are possible or likely companions of the Milky Way, the second companions of M31, the third more distant possible Local Group members, the fourth possible members of the Sextans-Antlia group, and the fifth are se”