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High-resolution absorption spectroscopy toward bright background sources has had a paramount role in understanding early galaxy formation, the evolution of the intergalactic medium and the reionisation of the Universe. However, these studies are now approaching the boundaries of what can be achieved at ground-based 8-10m class telescopes. The identification of primeval systems at the highest redshifts, within the reionisation epoch and even into the dark ages, and of the products of the first generation of stars and the chemical enrichment of the early Universe, requires observing very faint targets with a signal-to-noise ratio high enough to detect very weak spectral signatures. In this paper, we describe the giant leap forward that will be enabled by ANDES, the high-resolution spectrograph for the ELT, in these key science fields, together with a brief, non-exhaustive overview of other extragalactic research topics that will be pursued by this instrument, and its synergistic use with other facilities that will become available in the early 2030s. [ABSTRACT FROM AUTHOR]

The scaling of galaxy properties with halo mass suggests that feedback loops regulate star formation, but there is no consensus yet about how those feedback loops work. To help clarify discussions of galaxy-scale feedback, Paper I presented a very simple model for supernova feedback that it called the minimalist regulator model. This follow-up paper interprets that model and discusses its implications. The model itself is an accounting system that tracks all of the mass and energy associated with a halo's circumgalactic baryons—the central galaxy's atmosphere. Algebraic solutions for the equilibrium states of that model reveal that star formation in low-mass halos self-regulates primarily by expanding the atmospheres of those halos, ultimately resulting in stellar masses that are insensitive to the mass-loading properties of galactic winds. What matters most is the proportion of supernova energy that couples with circumgalactic gas. However, supernova feedback alone fails to expand galactic atmospheres in higher-mass halos. According to the minimalist regulator model, an atmospheric contraction crisis ensues, which may be what triggers strong black hole feedback. The model also predicts that circumgalactic medium properties emerging from cosmological simulations should depend largely on the specific energy of the outflows they produce, and we interpret the qualitative properties of several numerical simulations in light of that prediction. [ABSTRACT FROM AUTHOR]

This paper presents a new framework for understanding the relationship between a galaxy and its circumgalactic medium (CGM). It focuses on how imbalances between heating and cooling cause either expansion or contraction of the CGM. It does this by tracking all of the mass and energy associated with a halo's baryons, including their gravitational potential energy, even if feedback has pushed some of those baryons beyond the halo's virial radius. We show how a star-forming galaxy's equilibrium state can be algebraically derived within the context of this framework, and we analyze how the equilibrium star formation rate depends on supernova feedback. We consider the consequences of varying the mass loading parameter η M ≡ M ̇ wind / M ̇ * relating a galaxy's gas mass outflow rate ( M ̇ wind ) to its star formation rate ( M ̇ * ) and obtain results that challenge common assumptions. In particular, we find that equilibrium star formation rates in low-mass galaxies are generally insensitive to mass loading, and when mass loading does matter, increasing it actually results in more star formation because more supernova energy is needed to resist atmospheric contraction. [ABSTRACT FROM AUTHOR]

We explore the influence of radio-mode feedback on the properties of the cool circumgalactic medium (CGM). To this end, we assemble a statistical sample of approximately 30,000 radio galaxies with background quasars by combining optical spectroscopic measurements of luminous red galaxies and quasars from the year 1 data set of the Dark Energy Spectroscopic Instrument and radio sources from the LOw-Frequency ARray Two-metre Sky Survey (LoTSS) DR2 catalog and the Very Large Array Sky Survey (VLASS) quick-look catalog. Galaxies with similar optical properties but with no radio counterparts in LoTSS and VLASS are selected as the control group. We measure the cool CGM properties of radio galaxies and their control samples traced by Mg ii absorption lines, including covering fraction, rest equivalent width, and gas kinematics. Our results show no significant difference in the properties of gas around radio galaxies and their control sample, indicating that the operating radio-mode feedback of massive galaxies does not produce detectable effects on the properties of the cool CGM. Finally, we show that the CGM of radio galaxies contains a nonnegligible amount of cool gas with approximately 1010 M ⊙. This abundance can place a stringent constraint on the radio-mode feedback models. [ABSTRACT FROM AUTHOR]

We have performed wide-field, ultra-low-surface-brightness H α emission-line mapping around NGC 1068 with the newly commissioned Circumgalactic H α Spectrograph. NGC 1068 is notable for its active galactic nucleus, which globally ionizes gas in the disk and halo. Line-emitting diffuse ionized gas is distributed throughout the galactic disk and large-scale ionized filaments are found well beyond the disk, aligned with the cone angle of the central jet. We report the discovery of a new ribbon of ionized gas around NGC 1068 beyond even the known outer filamentary structure, located 20 kpc from the galaxy. The H α surface brightness of this ribbon is on the order of the bright telluric lines, ranging from 4 to 16 R, with fainter regions on the order of the sky background continuum. Unlike previous extended emission, the ribbon is not as well aligned with the current axis of the central jet. It is not associated with any galactic structure or known tidal features in the halo of NGC 1068, though it may originate from a larger distribution of unmapped neutral atomic or molecular gas in the halo. The morphology of the ribbon emission in H α is correlated with extended UV emission around NGC 1068. H α -to-UV flux ratios in the ribbon are comparable to extended emission-line ratios in the halos of NGC 5128, NGC 253, and M82. The H α excess in the ribbon gas suggests ionization by slow shocks or a mixture of in situ star formation and photoionization and collisional ionization processes. [ABSTRACT FROM AUTHOR]

Using stacked emission-line flux measurements of cool circumgalactic gas (CGM) in lower-mass galaxies (109.0 ≤ M */ M ⊙ ≤ 1010.2), we measure the dependence of the emission characteristics on orientation relative to the disk plane as a function of radius and compare to what we found previously for massive (M * > 1010.4 M ⊙) early-type galaxies. Although the line ratios (the lower [N ii ]/H α and [O iii ]/H β) suggest an overall softer ionizing source than in the more massive galaxies, consistent with previous findings, we find the same ionization hardening signature (a higher [N ii ]/H α ratio in the inner polar region) along the polar direction at small radii that we found for the more massive galaxies. The line ratio in the inner polar bin is distinct from that measured for the inner planar bin with 99.99%, confidence and with >99.9% confidence we conclude that it lies outside the star formation regime. The effective hardening of the ionization of the CGM along the polar axis, at small radii, could indicate either relic effects of active galactic nucleus activity or shock ionization. In either case, this signature appears to be ubiquitous across the stellar mass range we are able to explore with our spectral stacking technique and currently available archival data. [ABSTRACT FROM AUTHOR]

The Fermi and eROSITA bubbles (FBs and eRBs), large diffuse structures in our Galaxy, can be the by-products of steady star formation activity. To simultaneously explain the star formation history of the Milky Way (MW) and the metallicity of ∼ Z ⊙ at the Galactic disk, a steady Galactic wind driven by cosmic rays (CRs) is required. For tenuous gases with a density of ≲10−3 cm−3, CR heating dominates over radiative cooling, and the gas can maintain the virial temperature of ∼0.3 keV, ideal for escape from the Galactic system as the wind. A part of the wind falls back onto the disk like a Galactic fountain flow. We model the wind dynamics according to the Galactic evolution scenario and find that the scale height and surface brightness of the X-ray and the hadronic gamma-ray emissions from such fountain flow region can be consistent with the observed properties of the FBs and eRBs. This implies that the bubbles are persistent structures of the MW existing over (at least) the last ∼1 Gyr rather than evanescent structures formed by nontrivial, ∼10 Myr past Galactic center transient activities. [ABSTRACT FROM AUTHOR]

We consider the refractive lensing effects of ionized cool (T ~ 104 K) gas cloudlets in the circumgalactic medium (CGM) of galaxies. In particular, we discuss the combined effects of lensing from these cloudlets and scintillation from plasma screens in the Milky Way interstellar medium (ISM). We show that, if the CGM comprises a mist of subparsec cloudlets with column densities of order 1017 cm-2 (as predicted by [M. McCourt, S. P. Oh, R. O'Leary, A. M. Madigan, MNRAS 473, 5407-5431 (2018)]), then fast radio bursts (FRBs) whose sightlines pass within a virial radius of a CGM halo will may be lensed into tens of refractive images with a -10 ms scattering timescale. When these images are formed, they will be resolved by scintillating screens in the Milky Way ISM and will suppress the observed scintillation. We illustrate this effect in refractive lensing and argue that positive detections of FRB scintillation may constrain the properties of these cool-gas cloudlets, with current scintillation observation weakly disfavoring the cloudlet model. We propose that sheet-like geometries for the cool gas in the CGM can reconcile quasar absorption measurements (from which we infer the presence of the cool gas with structure on subparsec scales) and the unexpected lack of lensing signals from this gas thus far observed. [ABSTRACT FROM AUTHOR]

We present CloudFlex, an open-source tool for predicting absorption-line signatures of cool gas in galaxy halos with small-scale structure. Motivated by analyses of ∼104 K material in hydrodynamical simulations of turbulent, multiphase media, we model cool gas structures as complexes of cloudlets sampled from a power-law distribution of mass ∝ m cl − α with velocities drawn from a turbulent velocity field. The user may specify α, the lower limit of the cloudlet mass distribution ( m cl , min ), and several other parameters that set the mass, size, and velocity distribution of the complex. This permits investigation of the relation between these parameters and absorption-line observables. As a proof-of-concept, we calculate the Mg ii λ 2796 absorption induced by the cloudlets in background quasi-stellar object (QSO) spectra. We demonstrate that, at fixed metallicity, the covering fraction of sight lines with equivalent widths W 2796 < 0.3 Å increases significantly with decreasing m cl , min , cloudlet number density (n cl), and complex size. We then use this framework to predict the halo-scale W 2796 distribution around ∼ L * galaxies. We show that the observed incidences of W 2796 > 0.3 Å sight lines with impact parameters 10 kpc < R ⊥ < 50 kpc in projected QSO–galaxy studies are consistent with our model over much of parameter space. However, they are underpredicted by models with m cl , min ≥ 100 M ⊙ and n cl ≥ 0.03 cm−3, in keeping with a picture in which the inner cool circumgalactic medium (CGM) is dominated by numerous low-mass cloudlets (m cl ≲ 100 M ⊙) with a volume filling factor ≲1%. When used to model absorption-line data sets built from multi-sight line and/or spatially extended background probes, CloudFlex enables detailed constraints on the size and velocity distributions of structures comprising the photoionized CGM. [ABSTRACT FROM AUTHOR]

Jetted active galactic nuclei (AGN) hosting extended photoionized nebulae provide us with a unique view of the timescales associated with AGN activity. Here, we present a new green bean galaxy at z = 0.304458 ± 0.000007 with large-scale jet-induced radio emission. The spectral energy distributions of the radio components show steep spectral indices (α = −0.85 to −0.92 for the extended regions, and α = −1.02 for the faint radio core), and spectral age modeling of the extended radio emission indicates that the lobes are >6 Myr old. It is unclear whether the jet is active, or is a remnant with an off-time of 2–3 Myr. Several detached clouds lie around the host galaxy up to 37.8 kpc away from the nucleus, and their ionization profile indicates a decline (∼2 dex) in the AGN ionizing photon production over the past ∼0.15 Myr. Furthermore, we measure a blueshift for one of the clouds that is spatially coincident with the path of the radio jet. The cloud is likely illuminated by the photoionizing AGN, and potentially underwent an interaction with the relativistic jet. Our multiwavelength analysis suggests that RGB1 was in a phase of jet production prior to the radiatively efficient accretion phase traced by the detached cloud emission. It is unclear whether RGB1 transitioned into a low-excitation radio galaxy or an inactive galaxy over the past ∼0.15 Myr, or whether the extended radio and optical emission trace distinct accretion phases that occurred in succession. [ABSTRACT FROM AUTHOR]

We present statistics of z ∼ 6–9 galaxy outflows indicated by spatially extended gas emission and broad lines. With a total of 61 spectroscopically confirmed galaxies at z ∼ 6–9 in the JWST CEERS, GLASS, and ERO data, we find four galaxies with [O iii ] + H β ionized gas emission significantly extended beyond the kiloparsec-scale stellar components on the basis of the emission line images constructed by the subtraction of NIRCam broadband (line on/off-band) images. By comparison with low- z galaxies, the fraction of galaxies with spatially extended gas, 4/18, at z ∼ 6–9 is an order of magnitude higher than that at z ∼ 0–1, which can be explained by events triggered by frequent major mergers at high redshift. We also investigate medium- and high-resolution NIRSpec spectra of 30 galaxies at z ∼ 6–9, and identify five galaxies with broad (140−800 km s−1) lines in the [O iii ] forbidden line emission, suggestive of galaxy outflows. One galaxy at z = 6.38 shows both spatially extended gas emission and the broad lines, while none of the galaxies with spatially extended gas emission or broad lines present a clear signature of active galactic nuclei (AGN) in either the line diagnostics or type 1 AGN line broadening (>1000 km s−1), which suggests that outflows are mainly driven by stellar feedback. The existence of galaxies with/without spatially extended gas emission or broad lines may be explained by different viewing angles toward outflows or the fact that these are galaxies in the early, late, or post phases of galaxy outflows at high redshift, where relatively large fractions of such galaxies indicate longer-duration and/or more frequent outflows at early cosmic epochs. [ABSTRACT FROM AUTHOR]

The interaction between supermassive black hole (SMBH) feedback and the circumgalactic medium (CGM) continues to be an open question in galaxy evolution. In our study, we use smoothed particle hydrodynamics simulations to explore the impact of SMBH feedback on galactic metal retention and the motion of metals and gas into and through the CGM of L* galaxies. We examine 140 galaxies from the 25 Mpc cosmological volume Romulus25, with stellar masses between log(M */ M ⊙) = 9.5–11.5. We measure the fraction of metals remaining in the interstellar medium (ISM) and CGM of each galaxy and calculate the expected mass of each SMBH based on the M BH– σ relation (Kormendy & Ho 2013). The deviation of each SMBH from its expected mass, Δ M BH, is compared to the potential of its host via σ. We find that SMBHs with accreted mass above M BH– σ are more effective at removing metals from the ISM than undermassive SMBHs in star-forming galaxies. Overall, overmassive SMBHs suppress the total star formation of their host galaxies and more effectively move metals from the ISM into the CGM. However, we see little to no evacuation of gas from the CGM out of their halos, in contrast with other simulations. Finally, we predict that C iv column densities in the CGM of L* galaxies are unlikely to depend on host galaxy SMBH mass. Our results show that the scatter in the low-mass end of the M BH– σ relation may indicate how effective an SMBH is in the local redistribution of mass in its host galaxy. [ABSTRACT FROM AUTHOR]

The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by optical/UV lines beyond the stellar extent of galaxies. We herein introduce a novel multislit narrow-band spectroscopy method to conduct spatially resolved spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies (eDIG-CHANGES). In this paper, we introduce the project design and major scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is detected to a vertical extent of a few kiloparsecs above the disk, comparable to the X-ray and radio images. We do not see significant vertical variation of the [N ii ]/H α line ratio. A rough examination of the pressure balance between different circumgalactic medium phases indicates the magnetic field is in a rough pressure balance with the X-ray emitting hot gas and may play an important role in the global motion of both the eDIG and the hot gas in the lower halo. At the location of an Hubble Space Telescope/Cosmic Origins Spectrograph observed UV bright background active galactic nucleus ∼29 kpc from the center of NGC 3556, the magnetic pressure is much lower than that of the hot gas and the ionized gas traced by UV absorption lines, although the extrapolation of the pressure profiles may cause some biases in this comparison. By comparing the position–velocity diagrams of the optical and CO lines, we also find the dynamics of the two gas phases are consistent with each other, with no evidence of a global inflow/outflow and a maximum rotation velocity of ∼150 km s−1. [ABSTRACT FROM AUTHOR]

This paper presents the multiscale temperature structures in the Milky Way (MW) hot gas, as part of the XMM-Newton Line Emission Analysis Program, surveying the O vii, O viii, and Fe-L band emission features in the XMM-Newton archive. In particular, we define two temperature tracers, I OVIII/ I OVII (O87) and I FeL/(I OVII + I OVIII) (FeO). These two ratios cannot be explained simultaneously using single-temperature collisional ionization models, which indicates the need for multitemperature structures in hot gas. In addition, we show three large-scale features in the hot gas: the eROSITA bubbles around the Galactic center (GC), the disk, and the halo. In the eROSITA bubbles, the observed line ratios can be explained by a log-normal temperature distribution with a median of log T / K ≈ 6.4 and a scatter of σ T ≈ 0.2 dex. Beyond the bubbles, the line ratio dependence on the Galactic latitude suggests higher temperatures around the midplane of the MW disk. The scale height of the temperature variation is estimated to be ≈2 kpc assuming an average distance of 5 kpc for the hot gas. The halo component is characterized by the dependence on the distance to the GC, showing a temperature decline from log T / K ≈ 6.3 to 5.8. Furthermore, we extract the autocorrelation and cross-correlation functions to investigate the small-scale structures. O87 and FeO ratios show a consistent autocorrelation scale of ≈5° (i.e., ≈400 pc at 5 kpc), which is consistent with the expected physical sizes of X-ray bubbles associated with star-forming regions or supernova remnants. Finally, we examine the cross-correlation between the hot and UV-detected warm gas and show an intriguing anticorrelation. [ABSTRACT FROM AUTHOR]

Milky Way-type galaxies are surrounded by a warm-hot gaseous halo containing a considerable amount of baryons and metals. The kinematics and spatial distribution of highly ionized ion species such as O vi can be significantly affected by supernova (SN) explosions and early (pre-SN) stellar feedback (e.g., stellar winds, radiation pressure). Here we investigate effects of stellar feedback on O vi absorptions in Milky Way−like galaxies by analyzing the suites of high-resolution hydrodynamical simulations under the framework of SMUGGLE, a physically motivated subgrid interstellar medium and stellar feedback model for the moving-mesh code Arepo. We find that the fiducial run with the full suite of stellar feedback and moderate star formation activities can reasonably reproduce Galactic O vi absorptions observed by space telescopes such as the Far-Ultraviolet Spectroscopic Explorer, including the scale height of low-velocity (∣ v LSR∣ < 100 km s−1) O vi, the column density–line width relation for high-velocity (100 km s−1 ≤ ∣ v LSR∣ < 400 km s−1) O vi, and the cumulative O vi column densities. In contrast, model variations with more intense star formation activities deviate from observations further. Additionally, we find that the run considering only SN feedback is in broad agreement with the observations, whereas in runs without SN feedback this agreement is absent, which indicates a dominant role of SN feedback in heating and accelerating interstellar O vi. This is consistent with the current picture that interstellar O vi is predominantly produced by collisional ionization where mechanical feedback can play a central role. In contrast, photoionization is negligible for O vi production owing to the lack of high-energy (≳114 eV) photons required. [ABSTRACT FROM AUTHOR]

We explore the growth of the stellar disks in 14 nearby spiral galaxies as part of the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey. We study the radial distribution of specific star formation rates (sSFRs) and investigate the ratio of the difference in the outer and inner sSFRs (ΔsSFR = sSFRout – sSFRin) of the disk and the total sSFR, ΔsSFR/sSFR, to quantify disk growth. We find ΔsSFR/sSFR and the H i gas fraction to show a mild correlation of Spearman's ρ = 0.30, indicating that star formation and disk growth are likely to proceed outward in galactic disks with high H i gas fractions. The H i gas fractions and ΔsSFR/sSFR of the galaxies also increase with the distance to the nearest L ⋆ neighbor, suggesting that galaxies are likely to sustain the cold gas in their interstellar medium and exhibit inside-out growth in isolated environments. However, the H i content in their circumgalactic medium (CGM), probed by the Ly α equivalent width (W Ly α ) excess, is observed to be suppressed in isolated environments, as is apparent from the strong anticorrelation between the W Ly α excess and the distance to the fifth nearest L ⋆ neighbor (Spearman's ρ = −0.62). As expected, W Ly α is also found to be suppressed in cluster galaxies. We find no relation between the W Ly α excess of the detected CGM absorber and ΔsSFR/sSFR, implying that the enhancement and suppression of the circumgalactic H i gas does not affect the direction in which star formation proceeds in a galactic disk or vice versa. [ABSTRACT FROM AUTHOR]

Quenching of star formation in the central galaxies of cosmological halos is thought to result from energy released as gas accretes onto a supermassive black hole. The same energy source also appears to lower the central density and raise the cooling time of baryonic atmospheres in massive halos, thereby limiting both star formation and black hole growth, by lifting the baryons in those halos to greater altitudes. One predicted signature of that feedback mechanism is a nearly linear relationship between the central black hole's mass (M BH) and the original binding energy of the halo's baryons. We present the increasingly strong observational evidence supporting a such a relationship, showing that it extends up to halos of mass M halo ∼ 1014 M ⊙. We then compare current observational constraints on the M BH– M halo relation with numerical simulations, finding that black hole masses in IllustrisTNG appear to exceed those constraints at M halo < 1013 M ⊙ and that black hole masses in EAGLE fall short of observations at M halo ∼ 1014 M ⊙. A closer look at IllustrisTNG shows that quenching of star formation and suppression of black hole growth do indeed coincide with black hole energy input that lifts the halo's baryons. However, IllustrisTNG does not reproduce the observed M BH– M halo relation because its black holes gain mass primarily through accretion that does not contribute to baryon lifting. We suggest adjustments to some of the parameters in the IllustrisTNG feedback algorithm that may allow the resulting black hole masses to reflect the inherent links between black hole growth, baryon lifting, and star formation among the massive galaxies in those simulations. [ABSTRACT FROM AUTHOR]

Our knowledge of galaxy formation and evolution has incredibly progressed through multi-wavelength observational constraints of the interstellar medium (ISM) of galaxies at all cosmic epochs. However, little is known about the physical properties of the more diffuse and lower surface brightness reservoir of gas and dust that extends beyond ISM scales and fills dark matter haloes of galaxies up to their virial radii, the circumgalactic medium (CGM). New theoretical studies increasingly stress the relevance of the latter for understanding the feedback and feeding mechanisms that shape galaxies across cosmic times, whose cumulative effects leave clear imprints into the CGM. Recent studies are showing that a – so far unconstrained – fraction of the CGM mass may reside in the cold (T < 104 K) molecular and atomic phase, especially in high-redshift dense environments. These gas phases, together with the warmer ionised phase, can be studied in galaxies from z ∼ 0 to z ∼ 10 through bright far-infrared and sub-millimeter emission lines such as [C ii] 158µm, [O iii] 88 µm, [C I] 609µm, [C i] 370µm, and the rotational transitions of CO. Imaging such hidden cold CGM can lead to a breakthrough in galaxy evolution studies but requires a new facility with the specifications of the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). In this paper, we use theoretical and empirical arguments to motivate future ambitious CGM observations with AtLAST and describe the technical requirements needed for the telescope and its instrumentation to perform such science.

The baryon cycle is crucial for understanding galaxy formation, as gas inflows and outflows vary throughout a galaxy’s lifetime and affect its star formation rate. Despite the necessity of accretion for galaxy growth at high redshifts, direct observations of inflowing gas have proven elusive, especially at z ≳ 2. We present a spectroscopic analysis of a galaxy at redshift z = 2.45, which exhibits signs of inflow in several ultraviolet interstellar absorption lines, with no clear outflow signatures. The absorption lines are redshifted by ∼250 km s ^−1 with respect to the systemic redshift, and C iv shows a prominent inverse P-Cygni profile. Simple stellar population models suggest that this galaxy has a low metallicity (∼5% solar), with a very young starburst of age ∼4 Myr dominating the ultraviolet luminosity. The gas inflow velocity and nebular velocity dispersion suggest an approximate halo mass of order ∼10 ^11 M _⊙ , a regime in which simulations predict that bursty star formation is common at this redshift. We conclude that this system is likely in the beginning of a cycle of bursty star formation, where inflow and star formation rates are high, but where supernovae and other feedback processes have not yet launched strong outflows. In this scenario, we expect the inflow-dominated phase to be observable (e.g., with net redshifted interstellar medium absorption) for only a short timescale after a starburst onset. This result represents a promising avenue for probing the full baryon cycle, including inflows, during the formative phases of low-mass galaxies at high redshifts.

We report the first detection of nonthermal broadening of O vii lines in the warm-hot ≈10 ^6 K circumgalactic medium of the Milky Way. We use z = 0 absorption of O vii K α , O vii K β , and O viii K α lines in archival grating data of b > 15° quasar sightlines from Chandra and XMM-Newton. Nonthermal line broadening is evident in two-thirds of the sightlines considered, and on average is constrained at 4.6 σ significance. Nonthermal line broadening dominates over thermal broadening. We extensively test whether the appearance of nonthermal line broadening could instead be because of multiple thermally broadened velocity components and robustly rule it out. Nonthermal line broadening is more evident toward sightlines at lower galactic latitude indicating the Galactic disk origin of the nonthermal sources. There is weak/no correlation between nonthermal line broadening and the angular separation of sightlines from the Galactic center, indicating that the nuclear region might not be a major source of nonthermal factors.

We characterize the multiphase circumgalactic medium (CGM) and galaxy properties at z = 6.0–6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305–3150 to identify one new metal absorber at z = 6.2713 with multiple transitions (O i , Mg ii , Fe ii, and C ii ). They are combined with the published absorbing systems in Davies et al. at the same redshift range to form a sample of nine metal absorbers at z = 6.03–6.49. We identify eight galaxies within 1000 km s ^−1 and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [O iii ] ( λ λ 4959, 5007) doublets and H β emission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar masses ranging from 10 ^7.2 to 10 ^8.8 M _⊙ and metallicity between 0.02 and 0.4 solar. Notably, the z = 6.2713 system in the J0305–3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances of α elements to iron ([ α /Fe]) and find that the CGM gas in the most overdense region exhibits a lower [ α /Fe] ratio. Our modeling of the galaxy’s chemical abundance favors a top-heavy stellar initial mass function and hints that we may be witnessing the contribution of the first generation of Population III stars to the CGM at the end of the reionization epoch.

Understanding the physical mechanisms that control galaxy formation is a fundamental challenge in contemporary astrophysics. Recent advances in the field of astrophysical feedback strongly suggest that cosmic rays (CRs) may be crucially important for our understanding of cosmological galaxy formation and evolution. The appealing features of CRs are their relatively long cooling times and relatively strong dynamical coupling to the gas. In galaxies, CRs can be close to equipartition with the thermal, magnetic, and turbulent energy density in the interstellar medium, and can be dynamically very important in driving large-scale galactic winds. Similarly, CRs may provide a significant contribution to the pressure in the circumgalactic medium. In galaxy clusters, CRs may play a key role in addressing the classic cooling flow problem by facilitating efficient heating of the intracluster medium and preventing excessive star formation. Overall, the underlying physics of CR interactions with plasmas exhibit broad parallels across the entire range of scales characteristic of the interstellar, circumgalactic, and intracluster media. Here we present a review of the state-of-the-art of this field and provide a pedagogical introduction to cosmic ray plasma physics, including the physics of wave–particle interactions, acceleration processes, CR spatial and spectral transport, and important cooling processes. The field is ripe for discovery and will remain the subject of intense theoretical, computational, and observational research over the next decade with profound implications for the interpretation of the observations of stellar and supermassive black hole feedback spanning the entire width of the electromagnetic spectrum and multi-messenger data. [ABSTRACT FROM AUTHOR]

We study ultraviolet H i and metal-line transitions in the circumgalactic medium (CGM) of 15 massive, quenched luminous red galaxies (LRGs) at redshift z ∼ 0.5 and with impact parameters up to 400 kpc. We selected eight LRG–CGM systems to study general properties of the CGM around LRGs, while the other seven are already known to contain cool CGM gas from Mg ii optical studies (Mg ii -LRGs). In the general LRG population, we detect H i in four of eight LRGs, in all cases with N H I < 1016.7cm−2. In contrast, all Mg ii -LRGs show H i ; for four LRGs, the H i column density is N H I ≳ 1018cm−2. The CGM of LRGs also shows low and intermediate ionized lines (such as C iii, C ii, Si iii, and Si ii) and highly ionized lines of O vi (we detect O vi around five of seven Mg ii -LRGs and one of eight in the random sample). Next, we combine our sample with literature LRGs and ≲ L * galaxies, and we find that while for ≲ L * galaxies CGM H i Ly α absorption is stronger as galaxies are more massive, the cool CGM traced by H i Ly α is suppressed above stellar masses of M * ∼ 1011.5 M ☉. While most LRG–CGM systems show weak or nondetectable O vi (equivalent width < 0.2 Å), a few LRG–CGM systems show strong O vi 1031, which in most cases likely originates from groups containing both an LRG and a blue star-forming neighboring galaxy. [ABSTRACT FROM AUTHOR]

Drechsler et al. reported the unexpected discovery of a 1.°5 long [O iii ] emission nebula 1.°2 southeast of the M31 nucleus. Here we present additional images of this large emission arc, called the Strottner–Drechsler–Sainty Object (SDSO), along with radial velocity and flux measurements from low-dispersion spectra. Independent sets of [O iii ] images show SDSO to be composed of broad streaks of diffuse emission aligned northeast–southwest. Deep H α images reveal no strong coincident emission suggesting a high [O iii ]/H α ratio. We also find no other [O iii ] emission nebulosity as bright as SDSO within several degrees of M31 and no filamentary H α emission connected to SDSO. Optical spectra taken along the nebula's northern limb reveal [O iii ] λ λ 4959, 5007 emissions matching the location and extent seen in our [O iii ] images. The heliocentric velocity of this [O iii ] nebulosity is −9.8 ± 6.8 km s−1 with a peak surface brightness of (4 ± 2) × 10−18 erg s−1 cm−2 arcsec−2 (∼0.55 Rayleigh). We discuss SDSO as a possible unrecognized supernova remnant, a large and unusually nearby planetary nebula, a stellar bow shock nebula, or an interaction of M31's outer halo with Local Group circumgalactic gas. We conclude that galactic origins for SDSO are unlikely and favor instead an extragalactic M31 halo–circumgalactic cloud interaction scenario, despite the nebula's low radial velocity. We then describe new observations that may help resolve the nature and origin of this large nebulosity so close to M31 in the sky. [ABSTRACT FROM AUTHOR]

We present an analytic model for the cool, T ∼ 104 K, circumgalactic medium (CGM), describing the gas distribution, and thermal and ionization states. Our model assumes (total) pressure equilibrium with the ambient warm/hot CGM, photoionization by the metagalactic radiation, and allows for nonthermal pressure support, parameterized by the ratio of thermal pressures, η = P hot,th/ P cool,th. We apply the model to the COS-Halos measurements and find that a nominal model with η = 3, gas distribution out to r ≈ 0.6 R vir, and M cool = 3 × 109 M ⊙, corresponding to a volume filling fraction of f V,cool ≈ 1%, reproduces the H i and low/intermediate metal ions (C ii, C iii, Si ii, Si iii, and Mg ii) mean column densities. Variation of ±0.5 dex in η or M cool encompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured C iv and Si iv columns, and these can be reproduced with (i) a cool phase with M cool ∼ 1010 M ⊙ and η ≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, with M ∼ 1.5 × 1010 M ⊙ and occupying ∼1/2 of the total CGM volume. For cool gas with f V,cool ≈ 1%, we estimate an upper limit on the cloud sizes, R cl ≲ 0.5 kpc. Our results suggest that for the average galaxy CGM, the mass and nonthermal support in the cool phase are lower than previously estimated, and extreme scenarios are not necessary. We estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be offset, allowing M ̇ cool ≈ 0 over long timescales. [ABSTRACT FROM AUTHOR]

Spiral galaxies, including the Milky Way, have large-scale magnetic fields with significant energy densities. The dominant theory attributes these magnetic fields to a large-scale dynamo. We review the current status of dynamo theory and discuss various numerical simulations designed either to explain particular aspects of the problem or to reproduce galactic magnetic fields globally. Our main conclusions can be summarized as follows: Idealized direct numerical simulations produce mean magnetic fields, whose saturation energy density tends to decline with increasing magnetic Reynolds number. This is still an unsolved problem. Large-scale galactic magnetic fields of microgauss strengths can probably be explained only if helical magnetic fields of small or moderate length scales can be rapidly ejected or destroyed. Small-scale dynamos are important throughout a galaxy's life and probably provide strong seed fields at early stages. The circumgalactic medium (CGM) may play an important role in driving dynamo action at small and large length scales. These interactions between the galactic disk and the CGM may provide important insights into our understanding of galactic dynamos. We expect future research in galactic dynamos to focus on the cosmological history of galaxies and the interaction with the CGM as means of replacing the idealized boundary conditions used in earlier work. [ABSTRACT FROM AUTHOR]

Galaxy evolution is an important topic, and our physical understanding must be complete to establish a correct picture. This includes a thorough treatment of feedback. The effects of thermal–mechanical and radiative feedback have been widely considered; however, cosmic rays (CRs) are also powerful energy carriers in galactic ecosystems. Resolving the capability of CRs to operate as a feedback agent is therefore essential to advance our understanding of the processes regulating galaxies. The effects of CRs are yet to be fully understood, and their complex multi-channel feedback mechanisms operating across the hierarchy of galaxy structures pose a significant technical challenge. This review examines the role of CRs in galaxies, from the scale of molecular clouds to the circumgalactic medium. An overview of their interaction processes, their implications for galaxy evolution, and their observable signatures is provided and their capability to modify the thermal and hydrodynamic configuration of galactic ecosystems is discussed. We present recent advancements in our understanding of CR processes and interpretation of their signatures, and highlight where technical challenges and unresolved questions persist. We discuss how these may be addressed with upcoming opportunities. [ABSTRACT FROM AUTHOR]

We present XMM-Newton observations around the sight line of Mrk 421. The emission spectrum of the Milky Way (MW) circumgalactic medium (CGM) shows that a two-phase model is a better fit to the data compared to a single-phase model; in addition to the warm-hot virial phase at log (T /K) = 6.30 ± 0.02, a hot super-virial phase at log (T /K) = 6.88 − 0.06 + 0.07 is required. Furthermore, we present observations of five fields within 5 degrees of the primary field. Their spectra also require a two-phase model at warm-hot and hot temperatures. The hot phase, which was first discovered in Das et al. in 2019, appears to be widespread. By chemical tagging, we show that the emission from the supevirial phase comes from the L-shell transitions of Fe xviii –Fe xxii, and that the range of temperatures probed in emission is distinct from that in absorption. We detect scatter in temperature and emission measure in both the phases, and deduce that there is small-scale density inhomogeneity in the MW CGM. The emitting gas likely has higher density, possibly from regions close to the disk of the MW, while the absorption in the virial phase may arise from low-density gas extended out to the virial radius of the MW. The presence of the super-virial phase far from the regions around the Galactic center implicates physical processes unrelated to the activity at the Galactic center. Hot outflows resulting from star formation activity throughout the Galactic disk are likely to be responsible for producing this phase. [ABSTRACT FROM AUTHOR]

Precipitation is potentially a mechanism through which the circumgalactic medium (CGM) can regulate a galaxy's star formation. Here, we present idealized simulations of isolated Milky Way–like galaxies intended to examine the ability of galaxies to self-regulate their star formation, in particular via precipitation. We also examine the impact of rotation in the CGM. Using six simulations, we explore variations in the initial CGM t cool/ t ff ratio and rotation profile. Those variations affect the amount of gas accretion and star formation within the galactic disk. To encourage this accretion and better study its dependence on CGM structure, we gradually increase the efficiency of stellar feedback during the first half of our simulations. Yet despite this gradual increase, the resulting outflows quickly evacuate large, hot cavities within the CGM and even beyond r 200. Some of the CGM gas avoids interacting with the cavities and is able to feed the disk along its midplane, but the cooling of feedback-heated gas far from the midplane is too slow to supply the disk with additional gas. Our simulations illustrate the importance of physical mechanisms in the outer CGM and IGM for star formation regulation in Milky Way–scale halos. [ABSTRACT FROM AUTHOR]

As cosmic microwave background (CMB) photons traverse the universe, anisotropies can be induced via Thomson scattering (proportional to the electron density; optical depth) and inverse Compton scattering (proportional to the electron pressure; thermal Sunyaev–Zel'dovich effect). Measurements of anisotropy in optical depth τ and Compton y parameters are imprinted by the galaxies and galaxy clusters and are thus sensitive to the thermodynamic properties of the circumgalactic medium and intergalactic medium. We use an analytic halo model to predict the power spectrum of the optical depth (τ τ), the cross-correlation between the optical depth and the Compton y parameter (τ y), and the cross-correlation between the optical depth and galaxy clustering (τ g), and compare this model to cosmological simulations. We constrain the optical depths of halos at z ≲ 3 using a technique originally devised to constrain patchy reionization at a higher redshift range. The forecasted signal-to-noise ratio is 2.6, 8.5, and 13, respectively, for a CMB-S4-like experiment and a Vera C. Rubin Observatory–like optical survey. We show that a joint analysis of these probes can constrain the amplitude of the density profiles of halos to 6.5% and the pressure profiles to 13%. These constraints translate to astrophysical parameters, such as the gas mass fraction, f g, which can be constrained to 5.3% uncertainty at z ∼ 0. The cross-correlations presented here are complementary to other CMB and galaxy cross-correlations since they do not require spectroscopic galaxy redshifts and are another example of how such correlations are a powerful probe of the astrophysics of galaxy evolution. [ABSTRACT FROM AUTHOR]

One of the leading explanations for the origin of Fermi Bubbles is past jet activity in the Galactic center supermassive black hole Sgr A*. The claimed jets are often assumed to be perpendicular to the Galactic plane. Motivated by the orientation of pc-scale nuclear stellar disk and gas streams, as well as a low inclination of the accretion disk around Sgr A* inferred by the Event Horizon Telescope, we perform hydrodynamical simulations of nuclear jets significantly tilted relative to the Galactic rotation axis. The observed axisymmetry and hemisymmetry (north–south symmetry) of Fermi/eROSITA bubbles (FEBs) due to quasi-steady jets in Sgr A* could be produced if the jet had a super-Eddington power (≳5 × 1044 erg s−1) for a short time (jet active period ≲6 kyr) for a reasonable jet opening angle (≲10°). Such powerful explosions are, however, incompatible with the observed O viii /O vii line ratio toward the bubbles, even after considering electron–proton temperature nonequilibrium. We argue that the only remaining options for producing FEBs are (i) a low-luminosity (≈1040.5–41 erg s−1) magnetically dominated jet or accretion wind from the Sgr A*, or (ii) a supernovae or tidal disruption event driven wind of a similar luminosity from the Galactic center. [ABSTRACT FROM AUTHOR]

Observed breakBRD ("break bulges in red disks") galaxies are a nearby sample of face-on disk galaxies with particularly centrally concentrated star formation: they have red disks but recent star formation in their centers as measured by the D n 4000 spectral index. In Kopenhafer et al., a comparable population of breakBRD analogs was identified in the TNG simulation, in which the central concentration of star formation was found to reflect a central concentration of dense, star-forming gas caused by a lack of dense gas in the galaxy outskirts. In this paper, we examine the circumgalactic medium of the central breakBRD analogs to determine if the extended halo gas also shows differences from that around comparison galaxies with comparable stellar mass. We examine the circumgalactic medium gas mass, specific angular momentum, and metallicity in these galaxy populations. We find less gas in the circumgalactic medium of breakBRD galaxies, and that the breakBRD circumgalactic medium is slightly more concentrated than that of comparable M * galaxies. In addition, we find that the angular momentum in the circumgalactic medium of breakBRD galaxies tends to be low for their stellar mass, and shows more misalignment to the angular momentum vector of the stellar disk. Finally, we find that the circumgalactic medium metallicity of breakBRD galaxies tends to be high for their stellar mass. Together with their low star formation rate, we argue that these circumgalactic medium properties indicate a small amount of disk feeding concentrated in the central regions and a lack of low-metallicity gas accretion from the intergalactic medium. [ABSTRACT FROM AUTHOR]

Low-ionization-state Mg ii gas has been extensively studied in quasar sightline observations to understand the cool, ∼104 K gas in the circumgalactic medium. Motivated by recent observations showing that the Mg ii gas around low-redshift galaxies has significant angular momentum, we use the high-resolution EAGLE cosmological simulation to analyze the morphological and rotation structures of the z 0.3 circumgalactic Mg ii gas and examine how they change with the host galaxy properties. Around star-forming galaxies, we find that the Mg ii gas has an axisymmetric instead of a spherical distribution, and the axis of symmetry aligns with that of the Mg ii gas rotation. A similar rotating structure is less commonly found in the small sample of simulated quiescent galaxies. We also examine how often Mg ii gas around galaxies selected using a line-of-sight velocity cut includes gas physically outside of the virial radius (r vir). For example, we show that at an impact parameter of 100 pkpc, a ±500 km s-1 velocity cut around galaxies with stellar masses of 109-109.5 M o (1010-1010.5 M o) selects Mg ii gas beyond the virial radius 80% (6%) of the time. Because observers typically select Mg ii gas around target galaxies using such a velocity cut, we discuss how this issue affects the study of circumgalactic Mg ii gas properties, including the detection of corotation. While the corotating Mg ii gas generally extends beyond 0.5r vir, the Mg ii gas outside of the virial radius contaminates the corotation signal and makes observers less likely to conclude that gas at large impact parameters (e.g., 0.25r vir) is corotating.

We constrain gas inflow speeds in star-forming galaxies with color gradients consistent with inside-out disk growth. Our method combines new measurements of disk orientation with previously described circumgalactic absorption in background quasar spectra. Two quantities, a position angle and an axis ratio, describe the projected shape of each galactic disk on the sky, leaving an ambiguity about which side of the minor axis is tipped toward the observer. This degeneracy regarding the 3D orientation of disks has compromised previous efforts to measure gas inflow speeds. We present Hubble Space Telescope and Keck/LGSAO imaging that resolves the spiral structure in five galaxies at redshift z ≈ 0.2. We determine the sign of the disk inclination for four galaxies, under the assumption that spiral arms trail the rotation. We project models for both radial infall in the disk plane and circular orbits onto each quasar sightline. We compare the resulting line-of-sight velocities to the observed velocity range of Mg ii absorption in spectra of background quasars, which intersect the disk plane at radii between 69 and 115 kpc. For two sightlines, we constrain the maximum radial inflow speeds as 30-40 km s-1. We also rule out a velocity component from radial inflow in one sightline, suggesting that the structures feeding gas to these growing disks do not have unity covering factor. We recommend appropriate selection criteria for building larger samples of galaxy-quasar pairs that produce orientations sensitive to constraining inflow properties.

We present a first sample of 117 [O iii ] λλ 4960, 5008–selected star-forming galaxies at 5.33 < z < 6.93 detected in JWST/NIRCam 3.5 μ m slitless spectroscopy of a 6.′ 5 × 3.′ 4 field centered on the hyperluminous quasar SDSS J0100+2802, obtained as part of the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) survey. Three prominent galaxy overdensities are observed, one of them at the redshift of the quasar. Galaxies are found within 200 pkpc and 105 km s−1 of four known metal absorption-line systems. We focus on the role of the galaxies in ionizing the intergalactic medium (IGM) during the later stages of cosmic reionization and construct the mean Ly α and Ly β transmission as a function of distance from the galaxies. At the lowest redshifts in our study, 5.3 < z < 5.7, the IGM transmission rises monotonically with distance from the galaxies, as seen previously at lower redshifts. In contrast, at 5.7 < z < 6.14, the transmission of both Ly α and Ly β first increases with distance but then peaks at a distance of 5 cMpc before declining. Finally, in the region 6.15 < z < 6.26, where the additional ionizing radiation from the quasar dominates, the monotonic increase in transmission with distance is reestablished. This result is interpreted to represent evidence that the transmission of the IGM at z ∼ 5.9 toward J0100+2802 results from the "local" ionizing radiation of galaxies that dominates over the much-reduced cosmic background. [ABSTRACT FROM AUTHOR]

This study addresses how the incidence rate of strong O vi absorbers in a galaxy's circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure O vi absorption within 400 projected kpc and 300 km s−1 of 52 galaxies with M * ∼ 3 × 1010 M ⊙. The galaxies have redshifts 0.12 < z < 0.6, stellar masses 1010.1 M ⊙ < M * < 1010.9 M ⊙, and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O vi absorption (N O VI ≥ 1014.3 cm−2) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the O vi covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3 σ -equivalent statistical significance. On average, the CGM of star-forming galaxies with M * ∼ 3 × 1010 M ⊙ contains more O vi than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass. [ABSTRACT FROM AUTHOR]

We combine data sets from the CGM2 and CASBaH surveys to model a transition point, R cross, between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data consist of 7244 galaxies at z < 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01–20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover H i Ly α. Our best-fitting model is a two-component model that combines a 3D absorber–galaxy cross-correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination of R cross as a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 108 ≤ M ⋆/ M ⊙ ≤ 1010.5, we find that R cross(M ⋆) ≈ 2.0 ± 0.6 R vir. Additionally, we find excellent agreement between R cross(M ⋆) and the theoretically determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution at z < 0.5 that distribute T ≈ 104K gas to distances beyond the virial radius. [ABSTRACT FROM AUTHOR]

The CHIME/FRB project has detected hundreds of fast radio bursts (FRBs), providing an unparalleled population to statistically probe the foreground media that they illuminate. One such foreground medium is the ionized halo of the Milky Way (MW). We estimate the total Galactic electron column density from FRB dispersion measures (DMs) as a function of Galactic latitude using four different estimators, including ones that assume spherical symmetry of the ionized MW halo and ones that imply more latitudinal variation in density. Our observation-based constraints of the total Galactic DM contribution for ∣ b ∣ ≥ 30°, depending on the Galactic latitude and selected model, span 87.8–141 pc cm−3. This constraint implies upper limits on the MW halo DM contribution that range over 52–111 pc cm−3. We discuss the viability of various gas density profiles for the MW halo that have been used to estimate the halo's contribution to DMs of extragalactic sources. Several models overestimate the DM contribution, especially when assuming higher halo gas masses (∼3.5 × 1012 M ⊙). Some halo models predict a higher MW halo DM contribution than can be supported by our observations unless the effect of feedback is increased within them, highlighting the impact of feedback processes in galaxy formation. [ABSTRACT FROM AUTHOR]

Metals in the diffuse, ionized gas at the boundary between the Milky Way’s interstellar medium (ISM) and circumgalactic medium, known as the disk–halo interface (DHI), are valuable tracers of the feedback processes that drive the Galactic fountain. However, metallicity measurements in this region are challenging due to obscuration by the Milky Way ISM and uncertain ionization corrections that affect the total hydrogen column density. In this work, we constrain ionization corrections to neutral hydrogen column densities using precisely measured electron column densities from the dispersion measures of pulsars that lie in the same globular clusters as UV-bright targets with high-resolution absorption spectroscopy. We address the blending of absorption lines with the ISM by jointly fitting Voigt profiles to all absorption components. We present our metallicity estimates for the DHI of the Milky Way based on detailed photoionization modeling of the absorption from ionized metal lines and ionization-corrected total hydrogen columns. Generally, the gas clouds show a large scatter in metallicity, ranging between 0.04 and 3.2 Z _⊙ , implying that the DHI consists of a mixture of gaseous structures having multiple origins. We estimate the inflow and outflow timescales of the DHI ionized clouds to be 6–35 Myr. We report the detection of an infalling cloud with supersolar metallicity that suggests a Galactic fountain mechanism, whereas at least one low-metallicity outflowing cloud ( Z < 0.1 Z _⊙ ) poses a challenge for Galactic fountain and feedback models.

As a part of the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey, we investigate indirect evidence of gas inflow into the disk of the galaxy NGC 99. We combine optical spectra from the Binospec spectrograph on the MMT telescope with optical imaging data from the Vatican Advanced Technology Telescope, radio H i 21 cm emission images from the NSF Karl G. Jansky’s Very Large Array, and UV spectroscopy from the Cosmic Origins Spectrograph on the Hubble Space Telescope. We measure emission lines (H α , H β , [O iii ] λ 5007, [N ii ] λ 6583, and [S ii ] λ 6717, 31) in 26 H ii regions scattered about the galaxy and estimate a radial metallicity gradient of −0.017 dex kpc ^−1 using the N2 metallicity indicator. Two regions in the sample exhibit an anomalously low metallicity (ALM) of 12 + log(O/H) = 8.36 dex, which is ∼0.16 dex lower than other regions at that galactocentric radius. They also show a high difference between their H i and H α line of sight velocities on the order of 35 km s ^−1 . Chemical evolution modeling indicates gas accretion as the cause of the ALM regions. We find evidence for corotation between the interstellar medium of NGC 99 and Ly α clouds in its circumgalactic medium, which suggests a possible pathway for low metallicity gas accretion. We also calculate the resolved Fundamental Metallicity Relation (rFMR) on subkiloparsec scales using localized gas-phase metallicity, stellar mass surface density, and star formation rate surface density. The rFMR shows a similar trend as that found by previous localized and global FMR relations.

We present the design and first results of the inner circumgalactic medium (CGM) of QSO line-of-sight emitting galaxies at z ∼ 2–3, Keck Baryonic Structure Survey (KBSS)-InCLOSE. The survey will connect galaxy properties (e.g., stellar mass M _* , interstellar medium, hereafter ISM, metallicity) with the physical conditions of the inner CGM (e.g., kinematics, metallicity) to directly observe the galaxy-scale baryon cycle. We obtain deep Keck/KCWI optical IFU pointings of KBSS QSOs to discover new star-forming galaxies at small projected distances b ≲ 12″ (98 kpc, $\overline{z}=2.3$ ), then obtain follow-up Keck/MOSFIRE near-IR spectra to confirm their redshifts. We leverage KBSS images and Keck/High Resolution Echelle Spectrometer QSO spectra to model stellar populations and inner CGM absorption. In this paper, we analyze two QSO fields and discover more than 15 new galaxies with KCWI, then use MOSFIRE for two galaxies Q2343-G1 ( z = 2.43; G1) and Q2233-N1 ( z = 3.15; N1), which are both associated with damped Lyα absorbers. We find that G1 has typical M _* , UV/optical emission properties. N1 has lower M _* with very strong nebular emission. We jointly analyze neutral phase CGM and ionized ISM in N/O (for the first time at this z ), dust extinction, and high-ionization CGM finding that G1's CGM is metal poor and less evolved than its ISM, while N1's CGM and ISM abundances are comparable; their CGM shows ∼1 dex less dust extinction than the ISM; and G1's CGM has direct evidence of hot, metal-rich galactic outflow ejecta. These findings support that metals and dust are driven into the CGM from outflows, but may also be, e.g., stripped ISM gas or satellite enrichment. The full KBSS-InCLOSE sample will explore these scenarios.

The scaling of galaxy properties with halo mass suggests that feedback loops regulate star formation, but there is no consensus yet about how those feedback loops work. To help clarify discussions of galaxy-scale feedback, Paper I presented a very simple model for supernova feedback that it called the minimalist regulator model. This follow-up paper interprets that model and discusses its implications. The model itself is an accounting system that tracks all of the mass and energy associated with a halo’s circumgalactic baryons—the central galaxy’s atmosphere. Algebraic solutions for the equilibrium states of that model reveal that star formation in low-mass halos self-regulates primarily by expanding the atmospheres of those halos, ultimately resulting in stellar masses that are insensitive to the mass-loading properties of galactic winds. What matters most is the proportion of supernova energy that couples with circumgalactic gas. However, supernova feedback alone fails to expand galactic atmospheres in higher-mass halos. According to the minimalist regulator model, an atmospheric contraction crisis ensues, which may be what triggers strong black hole feedback. The model also predicts that circumgalactic medium properties emerging from cosmological simulations should depend largely on the specific energy of the outflows they produce, and we interpret the qualitative properties of several numerical simulations in light of that prediction.

Circumgalactic Ly α nebulae are gaseous halos around galaxies exhibiting luminous extended Ly α emission. This work investigates Ly α nebulae from deep imaging of ∼12 deg ^2 sky, targeted by the MAMMOTH-Subaru survey. Utilizing the wide-field capability of Hyper Suprime-Cam, we present one of the largest blind Ly α nebula selections, including QSO nebulae, Ly α blobs, and radio galaxy nebulae down to the typical 2 σ Ly α surface brightness of $(5-10)\times {10}^{-18}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$ . The sample contains 117 nebulae with Ly α sizes of 40–400 kpc, and the most gigantic one spans about 365 kpc, and is referred to as the Ivory Nebula. Combining multiwavelength data, we investigate diverse nebula populations and associated galaxies. We find a small fraction of Ly α nebulae have QSOs (∼7%), luminous infrared galaxies (LIRGs; ∼1%), and radio galaxies (∼2%). Remarkably, among the 28 enormous Ly α nebulae (ELANe) exceeding 100 kpc, about 80% are associated with UV-faint galaxies ( M _UV > −22), and are categorized as Type II ELANe. We underscore that Type II ELANe constitute the majority but remain largely hidden in current galaxy and QSO surveys. Dusty starburst and obscured AGN activity are proposed to explain the nature of Type II ELANe. The spectral energy distribution of stacking all Ly α nebulae also reveals signs of massive dusty star-forming galaxies with obscured AGNs. We propose a model to explain the dusty nature where the diverse populations of Ly α nebulae capture massive galaxies at different evolutionary stages undergoing violent assembly. Ly α nebulae provide critical insights into the formation and evolution of today’s massive cluster galaxies at cosmic noon.

This paper presents a new framework for understanding the relationship between a galaxy and its circumgalactic medium (CGM). It focuses on how imbalances between heating and cooling cause either expansion or contraction of the CGM. It does this by tracking all of the mass and energy associated with a halo’s baryons, including their gravitational potential energy, even if feedback has pushed some of those baryons beyond the halo’s virial radius. We show how a star-forming galaxy’s equilibrium state can be algebraically derived within the context of this framework, and we analyze how the equilibrium star formation rate depends on supernova feedback. We consider the consequences of varying the mass loading parameter ${\eta }_{M}\equiv {\dot{M}}_{\mathrm{wind}}/{\dot{M}}_{* }$ relating a galaxy’s gas mass outflow rate ( ${\dot{M}}_{\mathrm{wind}}$ ) to its star formation rate ( ${\dot{M}}_{* }$ ) and obtain results that challenge common assumptions. In particular, we find that equilibrium star formation rates in low-mass galaxies are generally insensitive to mass loading, and when mass loading does matter, increasing it actually results in more star formation because more supernova energy is needed to resist atmospheric contraction.

The shallow potential wells of star-forming dwarf galaxies make their surrounding circumgalactic and intergalactic medium (CGM/IGM) sensitive laboratories for studying the inflows and outflows thought to regulate galaxy evolution. We present new absorption-line measurements in quasar sight lines, probing within projected distances of