Project AMIGA (Absorption Maps In the Gas of Andromeda) is a survey of the circumgalactic medium (CGM) of Andromeda (M31, R vir ;300 kpc) along 43 QSO sightlines at impact parameters 25 R569 kpc (25 at RR vir). 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1.2 R vir and 1.9 R vir , respectively, demonstrating that M31 has a very extended ∼10 4-10 5.5 K ionized CGM. The metal and baryon masses of the 10 4-10 5.5 K CGM gas within R vir are 10 8 and 4×10 10 (Z/0.3 Z e) −1 M e , respectively. There is not much azimuthal variation in the column densities or kinematics, but there is with R. The CGM gas at R0.5 R vir 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 R vir 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 ∼10 4-10 5.5 K CGM as extended as for M31 and their CGM (especially the warm-hot gas probed by O VI) are overlapping.

Observing the circumgalactic medium (CGM) in emission provides 3D maps of the spatial and kinematic extent of the gas that fuels galaxies and receives their feedback. We present mock emission-line maps of highly resolved CGM gas from the Figuring Out Gas & Galaxies in Enzo (FOGGIE) project and link these maps back to physical and spatial properties of the gas. In particular, we examine the ionization source leading to most O vi emission and how resolution affects the physical properties of the gas generating the emission. Finally, when increasing the spatial resolution alone, the total luminosity of the line emission increases by an order of magnitude for some lines considered. Current integral field unit instruments like Keck Cosmic Web Imager and Multi Unit Spectroscopic Explorer should be able to detect the brightest knots and filaments of such emission, and use this to infer the bulk kinematics of the CGM gas with respect to the galaxy. We conclude that the spatial resolution of simulated CGM gas can significantly influence the distribution of gas temperatures, densities, and metallicities that contribute to a given observable region. Greater spatial resolution than has been typically included in cosmological simulations to date is needed to properly interpret observations in terms of the underlying gas structure driving emission.

We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM ≡ CGM2) survey. The CGM2 survey consists of 1689 galaxies, all with high-quality Gemini-GMOS spectra, within 1 Mpc of 22 z ≲ 1 quasars, all with a signal-to-noise ratio of ∼10 Hubble Space Telescope/COS G130M+G160M spectra. For 572 of these galaxies with stellar masses 107 M ⊙ < M ⋆ < 1011 M ⊙ and z ≲ 0.5, we show that the H i covering fraction above a threshold of N HI > 1014cm−2 is ≳0.5 within 1.5 virial radii (R vir ∼ R 200m). We examine the H i kinematics and find that the majority of absorption lies within ±250 km s−1 of the galaxy systemic velocity. We examine H i covering fractions over a range of impact parameters to infer a characteristic size of the CGM, , as a function of galaxy mass. is the impact parameter at which the probability of observing an absorber with N HI >1014 cm−2 is >50%. In this framework, the radial extent of the CGM of M ⋆ > 109.9 M ⊙ galaxies is kpc or . Intermediate-mass galaxies with 109.2 < M ⋆/M ⊙ < 109.9 have an extent of kpc or . Low-mass galaxies, M ⋆ < 109.2 M ⊙, show a smaller physical scale of kpc and extend to . Our analysis suggests that using R vir as a proxy for the characteristic radius of the CGM likely underestimates its extent.

The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are the closest massive satellite galaxies of the Milky Way. They are probably on their first passage on an infalling orbit towards our Galaxy1 and trace the continuing dynamics of the Local Group2. Recent measurements of a high mass for the LMC (Mhalo ≈ 1011.1–11.4 M⊙)3–6 imply that the LMC should host a Magellanic Corona: a collisionally ionized, warm-hot gaseous halo at the virial temperature (105.3–5.5 K) initially extending out to the virial radius (100–130 kiloparsecs (kpc)). Such a corona would have shaped the formation of the Magellanic Stream7, a tidal gas structure extending over 200° across the sky2,8,9 that is bringing in metal-poor gas to the Milky Way10. Here we show evidence for this Magellanic Corona with a potential direct detection in highly ionized oxygen (O+5) and indirectly by means of triply ionized carbon and silicon, seen in ultraviolet (UV) absorption towards background quasars. We find that the Magellanic Corona is part of a pervasive multiphase Magellanic circumgalactic medium (CGM) seen in many ionization states with a declining projected radial profile out to at least 35 kpc from the LMC and a total ionized CGM mass of log10(MH II,CGM/M⊙) ≈ 9.1 ± 0.2. The evidence for the Magellanic Corona is a crucial step forward in characterizing the Magellanic group and its nested evolution with the Local Group.

We present a census of neutral gas in the Milky Way disk and halo down to limiting column densities of N(H i) ∼ 1014 cm−2 using measurements of H i Lyman series absorption from the Far Ultraviolet Spectroscopic Explorer. Our results are drawn from an analysis of 25 AGN sight lines spread evenly across the sky with Galactic latitude ∣b∣ ≳ 20°. By simultaneously fitting multi-component Voigt profiles to 11 Lyman series absorption transitions covered by FUSE (Lyβ–Lyμ) plus HST measurements of Lyα, we derive the kinematics and column densities of a sample of 152 H i absorption components. While saturation prevents accurate measurements of many components with column densities 17 ≲ log N(H i) ≲ 19, we derive robust measurements at log N(H i) ≲ 17 and log N(H i) ≳ 19. We derive the first ultraviolet H i column density distribution function (CDDF) of the Milky Way, both globally and for low-velocity (ISM), intermediate-velocity clouds (IVCs), and high-velocity clouds (HVCs). We find that IVCs and HVCs show statistically indistinguishable CDDF slopes, with β IVC = − 1.01 − 0.14 + 0.15 and β HVC = − 1.05 − 0.06 + 0.07 . Overall, the CDDF of the Galactic disk and halo appears shallower than that found by comparable extragalactic surveys, suggesting a relative abundance of high column density gas in the Galactic halo. We derive the sky-covering fractions as a function of H i column density, finding an enhancement of IVC gas in the northern hemisphere compared to the south. We also find evidence for an excess of inflowing H i over outflowing H i, with −0.88 ± 0.40 M ⊙ yr−1 of HVC inflow versus ≈0.20 ± 0.10 M ⊙ yr−1 of HVC outflow, confirming an excess of inflowing HVCs seen in UV metal lines.