In Search of Cool Flow Accretion onto Galaxies: Where Does the Disk Gas End?

Joss Bland-Hawthorn, Philip R. Maloney, Alex Stephens, Anna Zovaro, Attila Popping

Research output: Contribution to journalArticle

Abstract

The processes taking place in the outermost reaches of spiral disks (the "protodisk") are intimately connected to the build-up of mass and angular momentum in galaxies. The thinness of spiral disks suggests that the activity is mostly quiescent, and presumably this region is fed by cool flows coming into the halo from the intergalactic medium. While there is abundant evidence for the presence of a circumgalactic medium around disk galaxies as traced by quasar absorption lines, it has been very difficult to connect this material to the outer gas disk. This has been a very difficult transition region to explore because baryon tracers are hard to observe. In particular, H i disks have been argued to truncate at a critical column density (cm-2 at 30 kpc for an galaxy) where the gas is vulnerable to the external ionizing background. But new, deep observations of nearby spirals (e.g., Milky Way, NGC 2997) suggest that H i disks may extend much farther than recognized to date, up to 60 kpc at cm-2. Motivated by these observations, here we show that a clumpy outer disk of dense clouds or cloudlets is potentially detectable to much larger radii and lower H i column densities than previously discussed. This extended protodisk component is likely to explain some of the Mg ii forest seen in quasar spectra as judged from absorption-line column densities and kinematics. We fully anticipate that the armada of new radio facilities and planned H i surveys coming on line will detect this extreme outer disk (scree) material. We also propose a variant on the successful "Dragonfly" technique to go after the very weak Hα signals expected in the protodisk region.

LanguageEnglish
Article number51
JournalAstrophysical Journal
Volume849
Issue number1
DOIs
StatePublished - 1 Nov 2017

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accretion
galaxies
gases
gas
dragonfly
angular momentum
quasars
kinematics
tracer
radio
intergalactic media
disk galaxies
tracers
baryons
halos
material
momentum
radii

Cite this

Bland-Hawthorn, J., Maloney, P. R., Stephens, A., Zovaro, A., & Popping, A. (2017). In Search of Cool Flow Accretion onto Galaxies: Where Does the Disk Gas End? Astrophysical Journal, 849(1), [51]. DOI: 10.3847/1538-4357/aa8f45
Bland-Hawthorn, Joss ; Maloney, Philip R. ; Stephens, Alex ; Zovaro, Anna ; Popping, Attila. / In Search of Cool Flow Accretion onto Galaxies : Where Does the Disk Gas End?. In: Astrophysical Journal. 2017 ; Vol. 849, No. 1.
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Bland-Hawthorn, J, Maloney, PR, Stephens, A, Zovaro, A & Popping, A 2017, 'In Search of Cool Flow Accretion onto Galaxies: Where Does the Disk Gas End?' Astrophysical Journal, vol 849, no. 1, 51. DOI: 10.3847/1538-4357/aa8f45

In Search of Cool Flow Accretion onto Galaxies : Where Does the Disk Gas End? / Bland-Hawthorn, Joss; Maloney, Philip R.; Stephens, Alex; Zovaro, Anna; Popping, Attila.

In: Astrophysical Journal, Vol. 849, No. 1, 51, 01.11.2017.

Research output: Contribution to journalArticle

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T2 - The Astrophysical Journal

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AU - Popping,Attila

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Bland-Hawthorn J, Maloney PR, Stephens A, Zovaro A, Popping A. In Search of Cool Flow Accretion onto Galaxies: Where Does the Disk Gas End? Astrophysical Journal. 2017 Nov 1;849(1). 51. Available from, DOI: 10.3847/1538-4357/aa8f45