CGM/IGM Feedback Physics Weekly: July 27-August 2, 2026

Five qualifying arXiv preprints submitted from July 27 through August 2 examine different points in the CGM/IGM feedback chain: the gas retained by haloes, the survival of cold inflows, the geometry of cool CGM gas, the mass loading required by quasar winds, and a forecast for measuring feedback's imprint on the cosmic baryon field. Read together, they sharpen a practical question for simulations and observations: which reservoir records the coupling, at what scale, and for how long?

No qualifying standalone GitHub release or public astronomy dataset release was verified for this window. The code and dataset categories therefore remain empty rather than being filled with older activity or papers that reuse existing survey data.

Authors: Jonathan J. Davies, Joop Schaye, Filip Huško, Ruby J. Wright, Evgenii Chaikin, Matthieu Schaller, Robert J. McGibbon, Alejandro Benítez-Llambay, Sylvia Ploeckinger, Alexander J. Richings, and collaborators.

What it does: The paper uses the COLIBRE cosmological simulations to track how supernova and active-galactic-nucleus feedback shape the baryonic content of haloes across mass. It compares the simulated halo gas fraction–halo mass relation with observational constraints and with other simulation suites. 1

Method: The analysis follows the relation between gas fraction within the halo radius and halo mass, then separates the effects of supernova feedback in dwarf haloes from AGN feedback in group-scale systems. It also compares the fiducial model with a hybrid AGN prescription that combines thermal and jet-driven feedback, and examines differences relative to EAGLE and resolution effects. 1

Finding: The halo gas-fraction relation is non-monotonic, peaking near . Supernovae efficiently expel gas from lower-mass dwarf haloes, while AGN feedback depletes gas in galaxy groups. The fiducial model agrees with Chandra and XMM-Newton constraints for groups and clusters, but predicts higher gas fractions than eROSITA stacks and kinetic Sunyaev–Zel’dovich measurements; the hybrid AGN model lowers the fractions and improves agreement with those latter constraints. 1

Why it matters: Two simulations can produce similar galaxy populations while retaining substantially different amounts of halo gas. That makes the CGM and intragroup reservoir a useful independent calibration target: matching stellar masses or quenching alone does not tell us whether feedback coupled to surrounding gas at the right strength and location.

Caveat: The comparison remains prescription- and resolution-dependent, and the observational constraints themselves do not form one unanimous target: the fiducial model sits differently relative to X-ray and eROSITA/kSZ inferences. The paper shows why a hybrid prescription is worth testing; it does not identify a unique feedback model. 1

Authors: Ellis R. Owen, Nicolas Ledos, Evangelia Ntormousi, Shinsuke Takasao, Kentaro Nagamine, and Sebastiano Cantalupo.

What it does: This paper asks whether cosmic rays supplied from cosmic-web filaments can heat magnetised cold streams enough to change the gas supply of massive galaxies. It is a process-level test of selective inflow disruption, not a claim that cosmic rays universally shut off accretion. 2

Method: The authors couple spectrally resolved cosmic-ray transport to a redshift-dependent analytic model of cold streams in galaxy haloes. The calculation follows the competition between CR heating and radiative cooling across dense stream cores, diffuse stream material, and partially mixed gas at the stream–CGM interface. 2

Finding: Dense stream cores are resilient: their temperatures rise by less than a factor of ten, which is still insufficient to overcome radiative cooling at the interface. The response changes in diffuse streams and partially mixed interface gas in the most massive haloes near the virial radius, where CR heating can exceed cooling and raise gas toward or above the mixing-layer temperature. Complete evaporation is possible only in extreme cases. 2

Why it matters: The result replaces a binary picture of “cold flow” versus “no cold flow” with a spatially selective one. A feedback model may preserve the dense supply channel while weakening its envelope, so the observable consequence could be a change in the thermal structure and duty cycle of inflow rather than an immediate halt to galaxy growth.

Caveat: The strongest effects are confined to diffuse or partially mixed material, at larger radii and in higher-mass haloes, and the setup is an analytic model with externally supplied cosmic-web cosmic rays. The conclusion is therefore about where disruption is plausible, not a universal evaporation rate. 2

Authors: Xuanyi Wu and Cheng Li.

What it does: Using DESI DR1 luminous red galaxies and background quasar spectra, the paper measures the mean Mg II equivalent-width field around massive quiescent galaxies as a function of projected radius and azimuth relative to the galaxy major axis. The analysis is valuable here as an observational CGM diagnostic, even though it does not isolate feedback as the cause. 3

Method: A forced-measurement procedure assigns a Mg II doublet-window equivalent width to every LRG–quasar pair, including pairs without individually detected absorbers. The signal is corrected with a redshift-matched random control from the same normalized quasar spectra, over $0.01$–$1.0$ proper Mpc and (0.4<z_{\rm LRG}<1.1). 3

Finding: The all-angle absorption profile declines with radius, while sightlines near the major axis show enhanced absorption relative to the minor axis at roughly 30–80 kpc. Over –$0.077$ Mpc, the integrated major-minus-minor difference is Å, with a position-angle randomization probability of . The inner all-angle profile is stronger at lower redshift, but the anisotropy amplitude shows no significant redshift evolution. 3

Why it matters: The measurement demonstrates that cool/warm CGM structure around massive quiescent haloes can be tested geometrically rather than only through a radial average. That opens a route to compare feedback, satellite, and large-scale-structure predictions using the same observable and spatial scale.

Caveat: The signal is localized to tens of kiloparsecs and disappears when averaged over the full 0.01–1.0 Mpc range. The local is not a global significance after searching windows, and the authors state that the measurement cannot distinguish among gas from feedback, satellites, or surrounding structure without additional satellite catalogues, galaxy properties, and absorber kinematics. 3

Author: James H. Matthews.

What it does: This paper asks how massive and clumpy a quasar wind must be to produce the large C IV emission-line blueshifts observed in some quasars. Its main scale is the nuclear line-forming wind, so it is a lower-priority CGM item; its value for this digest is the upstream constraint it places on the mass and power available to quasar feedback. 4

Method: The study combines one-dimensional analytic calculations with two-dimensional numerical models. It asks how much mass must pass through the line-forming region to maintain the density and ionization conditions required for blueshifted C IV emission. 4

Finding: The required wind mass-outflow rate is about times the accretion rate, where is the volume filling factor that represents clumping. A smooth wind is therefore disfavored by the line-formation requirement. If the same wind is the broad-absorption-line outflow with terminal velocity near $10,000$ km s, its power is significant for feedback because outflow power scales as the square of terminal velocity. 4

Why it matters: Feedback models often pass from an unresolved nuclear wind to a larger-scale energy or momentum coupling prescription. This paper identifies a physical input that cannot be hidden inside a single efficiency parameter: the mass loading, filling factor, and terminal velocity jointly determine whether the wind can carry substantial power outward.

Caveat: The wind-driving and clump-formation physics remain uncertain, and the physical conditions in the line-forming region need better observational constraints. The paper does not directly measure the wind's eventual effect on the CGM, so readers should treat it as an upstream energetics constraint rather than a CGM detection. 4

Authors: Ryan Raikman, Haochen Wang, Kiyoshi Masui, and Shion Andrew.

What it does: This paper proposes a cross-correlation statistic in dispersion space that uses fast-radio-burst dispersion measures and galaxy overdensities to separate free-electron clustering from the clustering of the FRB sources themselves. Its feedback relevance is on IGM and large-scale baryon structure, and the result is a forecast rather than a current measurement. 5

Method: Fisher forecasts combine FRB samples representative of CHIME and CHORD with DESI Legacy Survey bright galaxies and Euclid galaxies. The proposed statistic contains more information than the dispersion-measure moment , because the latter can be recovered from the former while the full distribution retains additional information. 5

Finding: The forecast signal-to-noise is about 12 for CHIME × DESI and 54 for CHORD × Euclid. In the paper's simple parameterization, the logarithmic cutoff scale for baryon clustering caused by feedback, , could be constrained to about 26% precision with CHIME and 14% with CHORD. The statistic is designed to work even when most FRBs lack host-galaxy redshifts. 5

Why it matters: Most feedback diagnostics in this week's set are local to a halo or wind. This proposal reaches a larger scale and asks whether feedback-induced suppression of baryon clustering can be inferred from the free-electron field. It is a possible bridge between CGM-scale baryon loss and the statistics of the IGM.

Caveat: These are survey forecasts, not detections. Their precision depends on the assumed FRB populations, galaxy surveys, and redshift or host-identification uncertainties; the authors note that reliable FRB redshifts will remain unavailable for most events for the foreseeable future. 5

Start with COLIBRE if you need a direct model-to-observable test: it places feedback prescriptions against the retained gas reservoir and exposes disagreement between galaxy-population success and halo-gas success. Read the cosmic-ray cold-stream paper next if your question is process-level: it says where inflow is likely to be weakened and where dense cores remain resilient.

Then use the DESI Mg II result as a concrete geometry measurement, while keeping its origin ambiguity intact. The quasar-wind paper is most useful for readers connecting nuclear line formation to the mass and velocity inputs of larger-scale feedback models. The FRB paper belongs on the forward-looking list for IGM and survey-design work, not in the evidence column beside an observed CGM signal.

The common lesson is narrower than “feedback is stronger” or “feedback is weaker.” A useful model must preserve the coupling location, the gas phase, and the lifetime of the tracer relevant to the measurement. Halo gas fractions, cold-stream interfaces, Mg II anisotropy, nuclear wind lines, and FRB dispersion do not measure the same quantity; their value is that they constrain different links in the same baryon-cycle problem.