https://phys.org/news/2020-08-hubble-giant-halo-andromeda-galaxy.html Hubble maps giant halo around Andromeda Galaxy: Please Register or Log in to view the hidden image! This illustration shows the location of the 43 quasars scientists used to probe Andromeda's gaseous halo. These quasars--the very distant, brilliant cores of active galaxies powered by black holes--are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars' light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo's material. Credit: NASA, ESA, and E. Wheatley (STScI) In a landmark study, scientists using NASA's Hubble Space Telescope have mapped the immense envelope of gas, called a halo, surrounding the Andromeda galaxy, our nearest large galactic neighbor. Scientists were surprised to find that this tenuous, nearly invisible halo of diffuse plasma extends 1.3 million light-years from the galaxy—about halfway to our Milky Way—and as far as 2 million light-years in some directions. This means that Andromeda's halo is already bumping into the halo of our own galaxy. They also found that the halo has a layered structure, with two main nested and distinct shells of gas. This is the most comprehensive study of a halo surrounding a galaxy. "Understanding the huge halos of gas surrounding galaxies is immensely important," explained co-investigator Samantha Berek of Yale University in New Haven, Connecticut. "This reservoir of gas contains fuel for future star formation within the galaxy, as well as outflows from events such as supernovae. It's full of clues regarding the past and future evolution of the galaxy, and we're finally able to study it in great detail in our closest galactic neighbor." more at link...... the paper: https://iopscience.iop.org/article/10.3847/1538-4357/aba49c Project AMIGA: The Circumgalactic Medium of Andromeda* Abstract: Project AMIGA (Absorption Maps In the Gas of Andromeda) is a survey of the circumgalactic medium (CGM) of Andromeda (M31, Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image! 300 kpc) along 43 QSO sightlines at impact parameters 25 ≤ R ≤ 569 kpc (25 at R Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image!). We use ultraviolet absorption measurements of Si ii, Si iii, Si iv, C ii, and C iv from the Hubble Space Telescope/Cosmic Origins Spectrograph and O vi from the Far Ultraviolet Spectroscopic Explorer to provide an unparalleled look at how the physical conditions and metals are distributed in the CGM of M31. We find that Si iii and O vi have a covering factor near unity for R Please Register or Log in to view the hidden image! 1.2 Please Register or Log in to view the hidden image! and Please Register or Log in to view the hidden image!1.9 Please Register or Log in to view the hidden image!, respectively, demonstrating that M31 has a very extended ~104–105.5 K ionized CGM. The metal and baryon masses of the 104–105.5 K CGM gas within Please Register or Log in to view the hidden image! are Please Register or Log in to view the hidden image!108 and Please Register or Log in to view the hidden image!4 × 1010 (Z/0.3 Z ⊙)−1 M ⊙, respectively. There is not much azimuthal variation in the column densities or kinematics, but there is with R. The CGM gas at R Please Register or Log in to view the hidden image! 0.5 Please Register or Log in to view the hidden image! is more dynamic and has more complicated, multiphase structures than at larger radii, perhaps a result of more direct impact of galactic feedback in the inner regions of the CGM. Several absorbers are projected spatially and kinematically close to M31 dwarf satellites, but we show that those are unlikely to give rise to the observed absorption. Cosmological zoom simulations of ~L* galaxies have O vi extending well beyond Please Register or Log in to view the hidden image! as observed for M31 but do not reproduce well the radial column density profiles of the lower ions. However, some similar trends are also observed, such as the lower ions showing a larger dispersion in column density and stronger dependence on R than higher ions. Based on our findings, it is likely that the Milky Way has a ~104–105.5 K CGM as extended as for M31 and their CGM (especially the warm–hot gas probed by O vi) are overlapping.
