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.

We model the kinematics of the high- and intermediate- velocity clouds (HVCs and IVCs) observed in absorption towards a sample of 55 Galactic halo stars with accurate distance measurements. We employ a simple model of a thick disc whose main free parameters are the gas azimuthal, radial and vertical velocities (vφ, vR and vz), and apply it to the data by fully accounting for the distribution of the observed features in the distance-velocity space. We find that at least two separate components are required to reproduce the data. A scenario where the HVCs and the IVCs are treated as distinct populations provides only a partial description of the data, which suggests that a pure velocity-based separation may give a biased vision of the gas physics at the Milky Way’s disc–halo interface. Instead, the data are better described by a combination of an inflow and an outflow components, both characterised by rotation with vφ comparable to that of the disc and vz of 50–100 km s−1. Features associated with the inflow appear to be diffused across the sky, while those associated with the outflow are mostly confined within a bi-cone pointing towards (l = 220○, b = +40○) and (l = 40○, b = −40○). Our findings indicate that the lower (|z| ≲ 10 kpc) Galactic halo is populated by a mixture of diffuse inflowing gas and collimated outflowing material, which are likely manifestations of a galaxy-wide gas cycle triggered by stellar feedback, that is, the galactic fountain.

We present the first spectroscopically resolved Hα emission map of the Large Magellanic Cloud’s (LMC) galactic wind. By combining new Wisconsin H-alpha Mapper observations (I Hα ≳ 10 mR) with existing H i 21 cm emission observations, we (1) mapped the LMC’s nearside galactic wind over a local standard of rest (LSR) velocity range of +50 ≤ v LSR ≤ +250 km s−1, (2) determined its morphology and extent, and (3) estimated its mass, outflow rate, and mass-loading factor. We observe Hα emission from this wind to typically 1° off the LMC’s H i disk. Kinematically, we find that the diffuse gas in the warm-ionized phase of this wind persists at both low (≲100 km s−1) and high (≳100 km s−1) velocities, relative to the LMC’s H i disk. Furthermore, we find that the high-velocity component spatially aligns with the most intense star-forming region, 30 Doradus. We, therefore, conclude that this high-velocity material traces an active outflow. We estimate the mass of the warm (T e ≈ 104 K) ionized phase of the nearside LMC outflow to be for the combined low and high-velocity components. Assuming an ionization fraction of 75% and that the wind is symmetrical about the LMC disk, we estimate that its total (neutral and ionized) mass is , its mass-flow rate is , and its mass-loading factor is η ≈ 4.54. Our average mass-loading factor results are roughly a factor of 2.5 larger than previous Hα imaging and UV absorption line studies, suggesting that those studies are missing nearly half the gas in the outflows.

Complex A is a high-velocity cloud (HVC) that is traversing through the Galactic halo toward the Milky Way’s disk. We combine both new and archival Green Bank Telescope observations to construct a spectroscopically resolved H i 21 cm map of this entire complex at a 17.1 ≲ log ( N H I , 1 σ / cm − 2 ) ≲ 17.9 sensitivity for a FWHM = 20 km s − 1 line and Δθ = 9.′1 or 17 ≲ Δd θ  ≲ 30 pc spatial resolution. We find that Complex A has a Galactic standard of rest frame velocity gradient of Δ v GSR / Δ L = 25 km s − 1 kpc − 1 along its length, that it is decelerating at a rate of 〈 a 〉 GSR = 55 km yr − 2 , and that it will reach the Galactic plane in Δt ≲ 70 Myr if it can survive the journey. We have identified numerous signatures of gas disruption. The elongated and multi-core structure of Complex A indicates that either thermodynamic instabilities or shock-cascade processes have fragmented this stream. We find Rayleigh–Taylor fingers on the low-latitude edge of this HVC; many have been pushed backward by ram pressure stripping. On the high-latitude side of the complex, Kelvin–Helmholtz instabilities have generated two large wings that extend tangentially off Complex A. The tips of these wings curve slightly forward in the direction of motion and have an elevated H i column density, indicating that these wings are forming Rayleigh–Taylor globules at their tips and that this gas is becoming entangled with unseen vortices in the surrounding coronal gas. These observations provide new insights on the survivability of low-metallicity gas streams that are accreting onto L ⋆ galaxies.