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

Benjamin, Robert A.; Danly, L.

doi:10.1086/304078

Cited by 76 publications

(84 citation statements)

References 51 publications

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“…He found that if the cold clouds fall ballistically, their vertical highest velocities could reach -80 km s −1 and up to -150 km s −1 . Similar results are found if we use the terminal velocity equation from Benjamin & Danly (1997) to calculate the terminal velocities of free-falling clouds at the diskhalo interface. This is consistent with the high velocity v acc = 110 km s −1 found in our Accreting Layer model.…”

Section: The Origin Of the Ionized Gas Inflowsupporting

confidence: 81%

HST/Cos Observations of Ionized Gas Accretion at the Disk–halo Interface of M33

Zheng

Peek

Werk

et al. 2017

ApJ

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We report the detection of accreting ionized gas at the disk-halo interface of the nearby galaxy M33. We analyze HST/COS absorption-line spectra of seven ultraviolet-bright stars evenly distributed across the disk of M33. We find Si IV absorption components consistently redshifted relative to the bulk M33's ISM absorption along all the sightlines. The Si IV detection indicates an enriched, diskwide, ionized gas inflow toward the disk. This inflow is most likely multi-phase as the redshifted components can also be observed in ions with lower ionization states (e.g., S II, P II, Fe II, Si II). Kinematic modeling of the inflow is consistent with an accreting layer at the disk-halo interface of M33, which has an accretion velocity of 110 +15 −20 km s −1 at a distance of 1.5+1.0 −1.0 kiloparsec above the disk. The modeling indicates a total mass of ∼ 3.9 × 10 7 M for the accreting material at the diskhalo interface on the near side of the M33 disk , with an accretion rate of ∼ 2.9 M yr −1 . The high accretion rate and the level of metal-enrichment suggest the inflow is likely to be the fall back of M33 gas from a galactic fountain and/or the gas pulled loosed during a close interaction between M31 and M33. Our study of M33 is the first to unambiguously reveal the existence of a disk-wide, ionized gas inflow beyond the Milky Way, providing a better understanding of gas accretion in the vicinity of a galaxy disk.

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Section: The Origin Of the Ionized Gas Inflowsupporting

confidence: 81%

HST/Cos Observations of Ionized Gas Accretion at the Disk–halo Interface of M33

Zheng

Peek

Werk

et al. 2017

ApJ

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“…The WHIM was formed by shock heating in the early stages of cosmological structure formation and should pervade the connected large-scale structure predicted to form (Melott et al 1983) in the cold dark matter scenario. Our Galaxy moves at the speed of $150-200 km s À1 toward the Virgo Cluster ( Williams et al 2006b;Benjamin & Danly 1997), which is close to the Galactic north pole.…”

Section: Galactic Shock Modelmentioning

confidence: 97%

Do Extragalactic Cosmic Rays Induce Cycles in Fossil Diversity?

Medvedev

Melott

2007

ApJ

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Recent work has revealed a 62 AE 3 Myr cycle in fossil diversity in the past 542 Myr; however, no plausible mechanism has been found. We propose that the cycle may be caused by modulation of cosmic-ray (CR) flux by the solar system vertical oscillation (64 Myr period ) in the Galaxy, the Galactic north-south anisotropy of CR production in the Galactic halo/wind /termination shock (due to the Galactic motion toward the Virgo Cluster), and the shielding by Galactic magnetic fields. We revisit the mechanism of CR propagation and show that CR flux can vary by a factor of about 4.6 and reach a maximum at northernmost displacement of the Sun. The very high statistical significance of (1) the phase agreement between solar northward excursions and the diversity minima and (2) the correlation of the magnitude of diversity drops with CR amplitudes through all cycles provide solid support for our model. Various observational predictions which can be used to confirm or falsify our hypothesis are presented.

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“…These short lifetimes are a problem unless the clouds are continually regenerated on short timescales. In addition, some HVCs that are not clearly linked to satellite accretion have velocities that cannot be reached through gravitational acceleration within several hundred Myr (Benjamin & Danly, 1997;Peek et al, 2007). The exact lifetime of a cloud depends on several factors such as cloud density, halo density, and velocity, but the total mass of the cloud seems to be one of the largest factors increasing their lifetimes (Heitsch & Putman, 2009;Kwak et al, 2011).…”

Section: Halo Cloud Survivalmentioning

confidence: 99%

Gaseous Galaxy Halos

Putman

Peek

Joung

2012

Annu. Rev. Astron. Astrophys.

461

479

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Galactic halo gas traces inflowing star formation fuel and feedback from a galaxy's disk and is therefore crucial to our understanding of galaxy evolution. In this review, we summarize the multi-wavelength observational properties and origin models of Galactic and low redshift spiral galaxy halo gas. Galactic halos contain multiphase gas flows that are dominated in mass by the ionized component and extend to large radii. The densest, coldest halo gas observed in neutral hydrogen (HI) is generally closest to the disk (< 20 kpc), and absorption line results indicate warm and warm-hot diffuse halo gas is present throughout a galaxy's halo. The hot halo gas detected is not a significant fraction of a galaxy's baryons. The disk-halo interface is where the multiphase flows are integrated into the star forming disk, and there is evidence for both feedback and fueling at this interface from the temperature and kinematic gradient of the gas and HI structures. The origin and fate of halo gas is considered in the context of cosmological and idealized local simulations. Accretion along cosmic filaments occurs in both a hot (> 10 5.5 K) and cold mode in simulations, with the compressed material close to the disk the coldest and densest, in agreement with observations. There is evidence in halo gas observations for radiative and mechanical feedback mechanisms, including escaping photons from the disk, supernova-driven winds, and a galactic fountain. Satellite accretion also leaves behind abundant halo gas. This satellite gas interacts with the existing halo medium, and much of this gas will become part of the diffuse halo before it can reach the disk. The accretion rate from cold and warm halo gas is generally below a galaxy disk's star formation rate, but gas at the disk-halo interface and stellar feedback may be important additional fuel sources.

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

Cited by 76 publications

References 51 publications

HST/Cos Observations of Ionized Gas Accretion at the Disk–halo Interface of M33

HST/Cos Observations of Ionized Gas Accretion at the Disk–halo Interface of M33

Do Extragalactic Cosmic Rays Induce Cycles in Fossil Diversity?

Gaseous Galaxy Halos

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