The Magellanic Stream: Circumnavigating the Galaxy

D’Onghia, Elena; Fox, Andrew

doi:10.1146/annurev-astro-081915-023251

Cited by 157 publications

(101 citation statements)

References 254 publications

(202 reference statements)

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“…Although we can see that the Stream and the Leading Arm are anchored in the stellar systems of the Magellanic Clouds, there are no stars associated with the gas of either object (D'Onghia & Fox, 2016). The absence of stars in the gas mirrors the fact that none of the stellar streams around the Milky Way or M31 have been found to have a convincing association with any neutral gas (Lewis et al, 2013).…”

Section: H I Outside Local Group Galaxiesmentioning

confidence: 92%

Neutral Gas Accretion onto Nearby Galaxies

Lockman¹

2017

Gas Accretion Onto Galaxies

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While there is no lack of evidence for the accretion of stellar systems onto nearby galaxies, direct evidence for the accretion of gas without stars is scarce. Here we consider an inventory of starless gas "clouds" in and around galaxies of the Local Group to discern their general properties and see how they might appear in distant systems. The conclusion is that accreting gas without stars is detected almost entirely within the circumgalactic medium of large galaxies and is rare otherwise. If our Local Group is any example, the best place to detect starless gas clouds is relatively close to galaxies.

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Section: H I Outside Local Group Galaxiesmentioning

confidence: 92%

Neutral Gas Accretion onto Nearby Galaxies

Lockman¹

2017

Gas Accretion Onto Galaxies

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“…Next, we produce a cleaned sample by removing HVCs that are associated with the Magellanic Stream and its Leading Arm, since these structures are much more distant than the general HVC population (Brüns et al 2005;Nidever et al 2008;D'Onghia & Fox 2016). This is achieved by cross-matching the R17 sample with the Fox et al (2014) catalog of Stream absorbers, which covers sightlines within 30 • of the 21 cm emission from the Stream, and then removing matched sightlines from the sample.…”

Section: Derivation Of Hvc Mass and Mass Flow Ratementioning

confidence: 99%

The Mass Inflow and Outflow Rates of the Milky Way

Richter

Ashley

Heckman

et al. 2019

ApJ

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We present new calculations of the mass inflow and outflow rates around the Milky Way (MW), derived from a catalog of ultraviolet metal-line high velocity clouds (HVCs). These calculations are conducted by transforming the HVC velocities into the Galactic Standard of Rest (GSR) reference frame, identifying inflowing (v GSR < 0 km s −1 ) and outflowing (v GSR > 0 km s −1 ) populations, and using observational constraints on the distance, metallicity, dust content, covering fractions, and total silicon column density of each population. After removing HVCs associated with the Magellanic Stream and the Fermi Bubbles, we find inflow and outflow rates in cool (T ∼ 10 4 K) ionized gas of dM in /dt (0.53± 0.23) (d/12 kpc)(Z/0.2Z ) −1 M yr −1 and dM out /dt (0.16 ± 0.07) (d/12 kpc)(Z/0.5Z ) −1 M yr −1 . The apparent excess of inflowing over outflowing gas suggests that the MW is currently in an inflowdominated phase, but the presence of substantial mass flux in both directions supports a Galactic fountain model, in which gas is constantly recycled between the disk and the halo. We also find that the metal flux in both directions (in and out) is indistinguishable. By comparing the outflow rate to the Galactic star formation rate, we present the first estimate of the mass loading factor (η HVC ) of the disk-wide MW wind, finding η HVC (0.10±0.06) (d/12 kpc)(Z/0.5Z ) −1 . Including the contributions from low-and intermediate-velocity clouds and from hot gas would increase these inflow and outflow estimates.

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“…The only neutral high-velocity structure in the Galactic CGM that clearly reaches beyond 30 kpc distance is the MS, a massive stream (10 8 − 10 9 M ⊙ ) of neutral and ionized gas that originates from the interaction of the two Magellanic Clouds as they approach the Milky Way (Dieter 1971;Wannier & Wrixon 1972;Mathewson et al 1974;D'Onghia & Fox 2016). Our recent studies of the MS based on UV data from FUSE, HST/STIS and HST/COS (Fox et al 2010Richter et al 2013) indicate that the MS contains more gas than the Small and Large Magellanic Clouds, feeding the Milky Way over the next 0.5 − 1.0 Gyr with large amounts of mostly metal-poor gas.…”

Section: Introductionmentioning

confidence: 99%

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

Richter

Nuza

Fox

et al. 2017

A&A

113

131

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Context. The Milky Way is surrounded by large amounts of diffuse gaseous matter that connects the stellar body of our Galaxy with its large-scale Local Group (LG) environment. Aims. To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Methods. Along 270 sightlines we measure metal absorption in the lines of Si ii, Si iii, C ii, and C iv and associated H i 21 cm emission in HVCs in the velocity range |vLSR| = 100 − 500 km s −1 . With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the HVC absorption characteristics with that of Damped Lyman α absorbers (DLAs) and constrained cosmological simulations of the LG (CLUES project). Results. The overall sky-covering fraction of high-velocity absorption is 77 ± 6 percent for the most sensitive ion in our survey, Si iii, and for column densities log N (Si iii) ≥ 12.1. This value is ∼ 4 − 5 times higher than the covering fraction of 21 cm neutral hydrogen emission at log N (H i) ≥ 18.7 along the same lines of sight, demonstrating that the Milky Way's CGM is multi-phase and predominantly ionized. The measured equivalent-width ratios of Si ii, Si iii, C ii, and C iv are inhomogeneously distributed on large and small angular scales, suggesting a complex spatial distribution of multi-phase gas that surrounds the neutral 21 cm HVCs. We estimate that the total mass and accretion rate of the neutral and ionized CGM traced by HVCs is MHVC ≥ 3.0×10 9 M⊙ and dMHVC/dt ≥ 6.1M⊙ yr −1 , where the Magellanic Stream (MS) contributes with more than 90 percent to this mass/mass-flow. If seen from an external vantage point, the Milky Way disk plus CGM would appear as a DLA that would exhibit for most viewing angles an extraordinary large velocity spread of ∆v ≈ 400 − 800 km s −1 , a result of the complex kinematics of the Milky Way CGM that is dominated by the presence of the MS. We detect a velocity dipole of high-velocity absorption at low/high galactic latitudes that we associate with LG gas that streams to the LG barycenter. This scenario is supported by the gas kinematics predicted from the LG simulations. Conclusions. Our study confirms previous results, indicating that the Milky Way CGM contains sufficient gaseous material to feed the Milky Way disk over the next Gyr at a rate of a few solar masses per year, if the CGM gas can actually reach the MW disk. We dem...

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The Magellanic Stream: Circumnavigating the Galaxy

Cited by 157 publications

References 254 publications

Neutral Gas Accretion onto Nearby Galaxies

Neutral Gas Accretion onto Nearby Galaxies

The Mass Inflow and Outflow Rates of the Milky Way

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

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