The Rotation of the Hot Gas Around the Milky Way

Abstract

The hot gaseous halos of galaxies likely contain a large amount of mass and are an integral part of galaxy formation and evolution. The Milky Way has a2 10 6 K halo that is detected in emission and by absorption in the O VII resonance line against bright background active galactic nuclei (AGNs), and for which the best current model is an extended spherical distribution. Using XMM-Newton Reflection Grating Spectrometer data, we measure the Doppler shifts of the O VII absorption-line centroids toward an ensemble of AGNs. These Doppler shifts constrain the dynamics of the hot halo, ruling out a stationary halo at about s 3 and a co-rotating halo at s 2 , and leading to a best-fit rotational velocity of =  f v 183 41 km s −1 for an extended halo model. These results suggest that the hot gas rotates and that it contains an amount of angular momentum comparable to that in the stellar disk. We examined the possibility of a model with a kinematically distinct disk and spherical halo. To be consistent with the emission-line X-ray data, the disk must contribute less than 10% of the column density, implying that the Doppler shifts probe motion in the extended hot halo.

Probing Galactic Halos with Fast Radio Bursts

“…These large uncertainties aside, Figure 5 indicates that the dominant ionization state of oxygen along sightlines through the Galactic halo is O vii. While the location of this O vii is debated (Wang et al 2005;Hodges-Kluck et al 2016;Faerman et al 2017), the gas must contribute a large column density of electrons for any FRB event. There is no apparent correlation (Pearson correlation coefficient of 0.04 and p-value of 0.82) and we conclude that the O vii gas lies beyond the Galactic ISM.…”

A guided map to the spiral arms in the galactic disk of the Milky Way

“…It is noted that the ω value for the hot halo gas is close to but slightly smaller than the ω value for the spiral pattern, although there is no obvious direct explanation. Hodges-Kluck et al [88] suggested that outflows from the disk into the halo may follow galactic rotation but eventually lag behind the gas in the disk. Expectations for the bulge bar vary.…”

“…For the hot gaseous halo around the Milky Way (within 50 kpc) at a temperature near 2 × 10 6 K, one can use at a radius of 8.0 kpc the observed rotation velocity 183 ± 41 km/s around the Galactic Center [88].…”

Neutral Gas Accretion onto Nearby Galaxies

“…Both the Milky Way (MW) and M31 have a hot 10 6−7 K circumgalactic medium (CGM) of enormous mass and extent, possibly dwarfing the baryon content of the disks themselves (Anderson & Bregman, 2011;Hodges-Kluck et al, 2016;Lehner et al, 2015). This gas may cool and condense, feeding the disk.…”