Cold Gas Accretion Research Articles

H i studies of extremely metal-poor dwarfs in voids – I

ABSTRACT We present and discuss the results of the Giant Metrewave Radio Telescope H i 21-cm line mapping for five isolated low-mass (M$_{\rm bary}$$\sim$(2–8)$\times 10^7$ M$\odot$) eXtremely Metal Poor dwarfs [12+$\log$(O/H) = 7.13–7.28], selected from the nearby void galaxy sample. All the studied void dwarfs show disturbed morphology in the H i maps with the angular resolutions of $\sim 11$ to $\sim 40\,{\rm arcsec}$. We examine the H i morphology and velocity field and the relative orientation of their stellar and gas body spins. We discuss the overall non-equilibrium state of their gas and the possible origin and evolution of the studied void dwarfs. The most straightforward interpretation of the ubiquitous phenomenon of the gas component non-equilibrium state in these and similar void dwarfs is the cold accretion from the void filaments and/or minor mergers. The cold gas accretion in voids could be linked to the presence of small filaments that constitute the substructure of voids.

A3COSMOS: Dissecting the gas content of star-forming galaxies across the main sequence at 1.2 ≤ z < 1.6

Aims. We aim to understand the physical mechanisms that drive star formation in a sample of mass-complete (>109.5 M⊙) star-forming galaxies (SFGs) at 1.2 ≤ ɀ < 1.6. Methods. We selected SFGs from the COSMOS2020 catalog and applied a uυ-domain stacking analysis to their archival Atacama Large Millimeter/submillimeter Array (ALMA) data. Our stacking analysis provides precise measurements of the mean molecular gas mass and size of SFGs down to a stellar mass of M★ ~ 109.5 M⊙, even though at these stellar mass galaxies on the main sequence (MS) are no longer detected individually in the archival ALMA data. We also applied an image-domain stacking analysis on their HST i-band and UltraVISTA J - and Ks-band images. This allowed us to trace the distribution of their stellar component. Correcting these rest-frame optical sizes using the Rhalf–stellar–light-to-Rhalf–stellar–mass conversion at rest 5000 Å, we obtain the stellar mass size of MS galaxies and compare them to the sizes of their star-forming component obtained from our ALMA stacking analysis. Results. Across the MS (−0.2 < ∆MS = log(SFR/SFRMS) < 0.2), the mean molecular gas fraction of SFGs increases by a factor of ~1.4, while their mean molecular gas depletion time decreases by a factor of ~1.8. The scatter of the MS could thus be caused by variations in both the star formation efficiency and molecular gas fraction of galaxies. The mean molecular gas fraction of MS galaxies decreases by a factor of ~7 from M★~ 109.7 M⊙ to ~1011.3 M⊙, while their mean molecular gas depletion time remains roughly the same at all stellar masses. This finding could be a hint that the bending of the MS at ɀ ~1.4 is primarily driven by variations in cold gas accretion. The majority of the galaxies lying on the MS have RFIR ≈ Rstellar. Their central regions are subject to large dust attenuation. Starbursts (SBs, ∆MS > 0.7) have a mean molecular gas fraction ~2.1 times larger and mean molecular gas depletion time ~3.3 times shorter than MS galaxies. Additionally, they have more compact star-forming regions (~2.5 kpc for MS galaxies vs. ~1.4 kpc for SBs) and systematically disturbed rest-frame optical morphologies, which is consistent with their association with major-mergers. SBs and MS galaxies follow the same relation between their molecular gas mass and star formation rate surface densities with a slope of ~ 1.1–1.2, that is, the so-called Kennicutt-Schmidt relation.

Jellyfish galaxies with the IllustrisTNG simulations – when, where, and for how long does ram pressure stripping of cold gas occur?

ABSTRACT Jellyfish galaxies are prototypical examples of satellite galaxies undergoing strong ram pressure stripping (RPS). We analyse the evolution of 512 unique, first-infalling jellyfish galaxies from the TNG50 cosmological simulation. These have been visually inspected to be undergoing RPS sometime in the past 5 Byr (since z = 0.5), have satellite stellar masses $M_\star ^{\rm sat}\sim 10^{8\!-\!10.5}\, {\rm M}_\odot$, and live in hosts with $M_{\rm 200c}\sim 10^{12\!-\!14.3}\, {\rm M}_\odot$ at z = 0. We quantify the cold gas (T ≤ 104.5 K) removal using the tracer particles, confirming that for these jellyfish, RPS is the dominant driver of cold gas loss after infall. Half of these jellyfish are completely gas-less by z = 0, and these galaxies have earlier infall times and smaller satellite-to-host mass ratios than their gaseous counterparts. RPS can act on jellyfish galaxies over long time-scales of ≈1.5–8 Gyr. Jellyfish in more massive hosts are impacted by RPS for a shorter time span and, at a fixed host mass, jellyfish with less cold gas at infall and lower stellar masses at z = 0 have shorter RPS time spans. While RPS may act for long periods of time, the peak RPS period – where at least 50 per cent of the total RPS occurs – begins within ≈1 Gyr of infall and lasts ≲2 Gyr. During this period, the jellyfish are at host-centric distances ∼0.2–2R200c, illustrating that much of RPS occurs at large distances from the host galaxy. Interestingly, jellyfish continue forming stars until they have lost ≈98 per cent of their cold gas. For groups and clusters in TNG50 $(M_{\rm 200c}^{\rm host}\sim 10^{13\!-\!14.3}\, {\rm M}_\odot)$, jellyfish galaxies deposit more cold gas ($\sim 10^{11\!-\!12}\, {\rm M}_\odot$) into haloes than what exists in them at z = 0, demonstrating that jellyfish, and in general satellite galaxies, are a significant source of cold gas accretion.

Anatomy of galactic star formation history: roles of different modes of gas accretion, feedback, and recycling

ABSTRACT We investigate how the diverse star formation histories observed across galaxy masses emerged using models that evolve under gas accretion from host haloes. They also include ejection of interstellar matter by supernova feedback, recycling of ejected matter and preventive feedback that partially hinders gas accretion. We consider three schemes of gas accretion: the fiducial scheme that includes the accretion of cold gas in low-mass haloes and high-redshift massive haloes as hinted by cosmological simulations; the flat scheme in which high-mass cold accretion is removed; and finally, the shock-heating scheme that assumes radiative cooling of the shock-heated halo gas. The fiducial scheme reproduces dramatic diminishment in star formation rate (SFR) after its peak as observed for the present halo mass $M_{\rm vir}\gt 10^{12.5}\, {\rm M}_\odot$ , while other two schemes show reduced or negligible quenching. This scheme reproduces the high-mass slope in the SFR versus stellar mass relation decreasing towards recent epochs, whereas other two schemes show opposite trend that contradicts observation. Success in the fiducial scheme originates in the existence of high-mass cold-mode accretion, which retards transition to the slow hot-mode accretion, thereby inducing a larger drop in SFR. Aided by gas recycling, which creates monotonically increasing SFR in low-mass haloes, this scheme can reproduce the downsizing galaxy formation. Several issues remain, suggesting non-negligible roles of missing physics. Feedback from active galactic nuclei could mitigate upturn of SFR in low-redshift massive haloes, whereas galaxy mergers could remedy early inefficient star formation.

Toward Horizon-scale Accretion onto Supermassive Black Holes in Elliptical Galaxies

We present high-resolution, three-dimensional hydrodynamic simulations of the fueling of supermassive black holes in elliptical galaxies from a turbulent medium on galactic scales, taking M87* as a typical case. The simulations use a new GPU-accelerated version of the Athena++ AMR code, and they span more than six orders of magnitude in radius, reaching scales similar to that of the black hole horizon. The key physical ingredients are radiative cooling and a phenomenological heating model. We find that the accretion flow takes the form of multiphase gas at radii less than about a kpc. The cold gas accretion includes two dynamically distinct stages: the typical disk stage in which the cold gas resides in a rotationally supported disk, and relatively rare chaotic stages (≲10% of the time) in which the cold gas inflows via chaotic streams. Though cold gas accretion dominates the time-averaged accretion rate at intermediate radii, accretion at the smallest radii is dominated by hot virialized gas at most times. The accretion rate scales with radius as when hot gas dominates, and we obtain near the event horizon, similar to what is inferred from EHT observations. The orientation of the cold gas disk can differ significantly on different spatial scales. We propose a subgrid model for accretion in lower-resolution simulations in which the hot gas accretion rate is suppressed relative to the Bondi rate by . Our results can also provide more realistic initial conditions for simulations of black hole accretion at the event horizon scale.

A super-linear ‘radio-AGN main sequence’ links mean radio-AGN power and galaxy stellar mass since z ∼ 3

Mapping the average active galactic nucleus (AGN) luminosity across galaxy populations and over time reveals important clues regarding the interplay between supermassive black hole and galaxy growth. This paper presents the demography, mean power, and cosmic evolution of radio AGN across star-forming galaxies (SFGs) of different stellar masses (ℳ*). We exploit deep VLA-COSMOS 3 GHz data to build the rest-frame 1.4 GHz AGN luminosity functions at 0.1 ≤ z ≤ 4.5 hosted in SFGs. Splitting the AGN luminosity function into different ℳ* bins reveals that, at all redshifts, radio AGN are both more frequent and more luminous in higher ℳ* than in lower ℳ* galaxies. The cumulative kinetic luminosity density exerted by radio AGN in SFGs peaks at z ∼ 2, and it is mostly driven by galaxies with 10.5 ≤ log(ℳ*/ℳ⊙) < 11. Averaging the cumulative radio AGN activity across all SFGs at each (ℳ*,z) results in a ‘radio-AGN main sequence’ that links the time-averaged radio-AGN power ⟨L1.4AGN⟩ and galaxy stellar mass, in the form: log ⟨[L1.4AGN/ W Hz−1]⟩ = (20.97 ± 0.16) + (2.51 ± 0.34)⋅ log(1+z) + (1.41 ± 0.09)⋅(log[ℳ*/ℳ⊙] – 10). The super-linear dependence on ℳ*, at fixed redshift, suggests enhanced radio-AGN activity in more massive SFGs as compared to star formation. We ascribe this enhancement to both a higher radio AGN duty cycle and a brighter radio-AGN phase in more massive SFGs. A remarkably consistent ℳ* dependence is seen for the evolving X-ray AGN population in SFGs. This similarity is interpreted as possibly driven by secular cold gas accretion fuelling both radio and X-ray AGN activity in a similar fashion over the galaxy’s lifetime.

MaNGA 8313-1901: Gas Accretion Observed in a Blue Compact Dwarf Galaxy?

Gas accretion is an important process in the evolution of galaxies, but it has limited direct observational evidences. In this paper, we report the detection of a possible ongoing gas accretion event in a blue compact dwarf (BCD) galaxy, MaNGA 8313-1901, observed by the Mapping Nearby Galaxies and Apache Point Observatory (MaNGA) program. This galaxy has a distinct off-centered blue clump to the northeast (the NE clump) that shows low metallicity and enhanced star formation. The kinematics of the gas in the NE clump also seems to be detached from the host BCD galaxy. Together with the metallicity drop of the NE clump, it suggests that the NE clump likely has an external origin, such as gas accretion or galaxy interaction, rather than an internal origin, such as an H II complex in the disk. After removing the underlying host component, we find that the spectrum of the “pure” clump can match very well with a modeled spectrum containing a stellar population of the young stars (≤7 Myr) only. This may imply that the galaxy is experiencing an accretion of cold gas, instead of a merger event involving galaxies with significant preexisting old stars. We also find signs of another clump (the SW clump) at the southwest corner of the host galaxy, and the two clumps may share the same origin of gas accretion.

Multiple gas acquisition events in galaxies with dual misaligned gas disks

Frequent accretion of external cold gas is thought to play an important role in galaxy assembly. However, almost all known kinematically misaligned galaxies identify only one gas disk that is misaligned with the stellar disk, implying a single gas acquisition event. Here we report a new configuration in two galaxies where both contain two gas disks misaligned with each other and also with the stellar disk. Such systems are not expected to be stable or long-lasting, challenging the traditional picture of gas accretion of galaxies and their angular momentum build-up. The differences in kinematic position angles are larger than 120{\deg} between the two gas disks, and 40{\deg} between each gas disk and the stellar component. The star formation activity is enhanced at the interface of the two gas disks compared with the other regions within the same galaxy. Such systems illustrate that low-redshift galaxies can still experience multiple gas acquisition events, and provide a new view into the origins of galactic gas.

A galaxy group candidate at z ≈ 3.7 in the COSMOS field

We report a galaxy group candidate HPC1001 at z ≈ 3.7 in the COSMOS field. This structure was selected as a high galaxy overdensity at z > 3 in the COSMOS2020 catalog. It contains ten candidate members, of which eight are assembled in a 10″ × 10″ area with the highest sky density among known protoclusters and groups at z > 3. Four out of ten sources were also detected at 1.2 mm with Atacama Large Millimeter Array continuum observations. Photometric redshifts, measured by four independent methods, fall within a narrow range of 3.5 < z < 3.9 and with a weighted average of z = 3.65 ± 0.07. The integrated far-IR-to-radio spectral energy distribution yields a total UV and IR star formation rate SFR ≈ 900 M⊙ yr−1. We also estimated a halo mass of ∼1013 M⊙ for the structure, which at this redshift is consistent with potential cold gas inflow. Remarkably, the most massive member has a specific star formation rate and dust to stellar mass ratio of Mdust/M* that are both significantly lower than that of star-forming galaxies at this redshift, suggesting that HPC1001 could be a z ≈ 3.7 galaxy group in maturing phase. If confirmed, this would be the earliest structure in maturing phase to date, and an ideal laboratory to study the formation of the earliest quiescent galaxies as well as cold gas accretion in dense environments.

Cosmological evolution of gas and supermassive black holes in idealized isolated haloes

ABSTRACT We study the evolution of baryonic gas in cosmologically growing dark matter haloes. To accurately model both the inner and outer regions of the haloes, we use a dark matter density profile that transitions smoothly from the Navarro–Frenk–White profile within the virial radius to a more realistic flat profile far beyond the halo. We construct a dark matter gravitational potential consistent with this density profile, and we use a ‘cosmological’ potential that accounts for gas evolution consistent with Hubble expansion at large radii. Gas is initialized with a density ≈ 0.2 times the dark matter density, consistent with the universal baryon fraction ρg/(ρg + ρDM) ≈ 0.17. We study the formation of the virial shock and evolution of the baryon fraction, including the effects of radiative cooling and active galactic nucleus jet feedback. The feedback is powered by the accretion of cold gas on to a central supermassive black hole (SMBH). The cores of the halo exhibit heating and cooling cycles, whose strength and duration depend on the feedback efficiency and the halo mass. The central SMBH initially grows exponentially with time in the early quasar phase, but the growth slows down at later times. The baryon fraction in the core decreases with increasing feedback efficiency and decreasing halo mass. While the halo outskirts evolve self-similarly, the core density is non-evolving, in agreement with cluster observations. We analyse the correlations between the properties of the gas and the central SMBH, and explore the existence of a Fundamental Plane.

Detections of inflowing gas from narrow absorption lines at parsec scales

The detection of inflows at the scale of the dusty torus and smaller is crucial for investigating the process of supermassive black hole (SMBH) accretion. However, only a few cases of inflowing gas at small scales have been reported through redshifted broad absorption lines so far. Here we report nine redshifted narrow absorption lines (NALs) of Mg+ions with inflowing speeds of 1071–1979 km s−1, which are likely along the directions close to the axes of accretion disks. The quasars showing inflowing Mg IINALs have, on average, slightly smaller Eddington ratios than the sources with outflowing Mg IINALs. The upper limits on the locations of the detected NALs are at parsec scale, that is, the distance from dusty tori to their central SMBHs. One possible origin of these infalling NALs is from dusty tori. However, these infalling NALs could also be naturally explained by chaotic cold accretion resulting from the nonlinear interaction of active galactic nucleus (AGN) jets with the interstellar medium (ISM), and these cold gaseous blobs may originally precipitate in metal-rich trailing outflows uplifted by AGN jet ejecta. The infalling NALs may therefore provide direct evidence for cold gas precipitation and accretion in AGN feedback processes, and provide direct evidence of inflowing gas along the directions close to quasar jets and at parsec scale. Regardless of whether these infalling NALs are from the dusty tori or the interaction of AGN jets with the ISM, the infalling NALs cannot provide sufficient fuel to power the quasars.

A cold accretion flow onto one component of a multiple protostellar system

Context. Gas accretion flows transport material from the cloud core onto the protostar. In multiple protostellar systems, it is not clear if the delivery mechanism is preferential or more evenly distributed among the components. Aims. The distribution of gas accretion flows within the cloud core of the deeply embedded, chemically rich, low-mass multiple protostellar system IRAS 16293−2422 is explored out to 6000 AU. Methods. Atacama Large Millimeter/submillimeter Array Band 3 observations of low-J transitions of various molecules, such as HNC, cyanopolyynes (HC3N, HC5N), and N2H+, are used to probe the cloud core structure of IRAS 16293−2422 at ~100 AU resolution. Additional Band 3 archival data provide low-J HCN and SiO lines. These data are compared with the corresponding higher-J lines from the PILS Band 7 data for excitation analysis. The HNC/HCN ratio is used as a temperature tracer. Results. The low-J transitions of HC3N, HC5N, HNC, and N2H+ trace extended and elongated structures from 6000 AU down to ~100 AU, without any accompanying dust continuum emission. Two structures are identified: one traces a flow that is likely accreting toward the most luminous component of the IRAS 16293−2422 A system. Temperatures inferred from the HCN/HNC ratio suggest that the gas in this flow is cold, between 10 and 30 K. The other structure is part of an uv-irradiated cavity wall entrained by one of the outflows driven by the source. The two outflows driven by IRAS 16293−2422 A present different molecular gas distributions. Conclusions. Accretion of cold gas is seen from 6000 AU scales onto IRAS 16293−2422 A but not onto source B, indicating that cloud core material accretion is competitive due to feedback onto a dominant component in an embedded multiple protostellar system. The preferential delivery of material could explain the higher luminosity and multiplicity of source A compared to source B. The results of this work demonstrate that several different molecular species, and multiple transitions of each species, are needed to confirm and characterize accretion flows in protostellar cloud cores.

Do Current X-Ray Observations Capture Most of the Black-hole Accretion at High Redshifts?

Abstract The cosmic black hole accretion density (BHAD) is critical for our understanding of the formation and evolution of supermassive black holes (BHs). However, at high redshifts (z > 3), X-ray observations report BHADs significantly (∼10 times) lower than those predicted by cosmological simulations. It is therefore paramount to constrain the high-z BHAD using independent methods other than direct X-ray detections. The recently established relation between star formation rate and BH accretion rate among bulge-dominated galaxies provides such a chance, as it enables an estimate of the BHAD from the star formation histories (SFHs) of lower-redshift objects. Using the CANDELS Lyα Emission At Reionization (CLEAR) survey, we model the SFHs for a sample of 108 bulge-dominated galaxies at z = 0.7–1.5, and further estimate the BHAD contributed by their high-z progenitors. The predicted BHAD at z ≈ 4–5 is consistent with the simulation-predicted values, but higher than the X-ray measurements (by ≈3–10 times at z = 4–5). Our result suggests that the current X-ray surveys could be missing many heavily obscured Compton-thick active galactic nuclei (AGNs) at high redshifts. However, this BHAD estimation assumes that the high-z progenitors of our z = 0.7–1.5 sample remain bulge-dominated where star formation is correlated with BH cold-gas accretion. Alternatively, our prediction could signify a stark decline in the fraction of bulges in high-z galaxies (with an associated drop in BH accretion). JWST and Origins will resolve the discrepancy between our predicted BHAD and the X-ray results by constraining Compton-thick AGN and bulge evolution at high redshifts.

Star Formation and Quenching of Central Galaxies from Stacked Hi Measurements

Abstract We quantitatively investigate the dependence of central galaxy Hi mass (M Hi ) on the stellar mass (M *), halo mass (M h ), star formation rate (SFR), and central stellar surface density within 1 kpc (Σ1), taking advantage of the Hi spectra stacking technique using both the Arecibo Fast Legacy ALFA Survey and the Sloan Digital Sky Survey. We find that the shapes of M Hi –M h and M Hi –M * relations are remarkably similar for both star-forming and quenched galaxies, with massive quenched galaxies having constantly lower Hi masses of around 0.6 dex. This similarity strongly suggests that neither halo mass nor stellar mass is the direct cause of quenching, but rather the depletion of the Hi reservoir. While the Hi reservoir for low-mass galaxies of M * < 1010.5 M ☉ strongly increases with M h , more massive galaxies show no significant dependence of M Hi with M h , indicating that the main effect of halo is to determine the smooth cold gas accretion. We find that the star formation and quenching of central galaxies are directly regulated by the available Hi reservoir, with an average relation of SFR ∝ M H I 2.75 / M * 0.40 , implying a quasi-steady state of star formation. We further confirm that galaxies are depleted of their Hi reservoir once they drop off the star formation main sequence and there is a very tight and consistent correlation between M Hi and Σ1 in this phase, with M H I ∝ Σ 1 − 2 . This result is consistent with the compaction-triggered quenching scenario, with galaxies going through three evolutionary phases of cold gas accretion, compaction and post-compaction, and quenching.

Host galaxies of high-redshift quasars: SMBH growth and feedback

ABSTRACT The properties of quasar-host galaxies might be determined by the growth and feedback of their supermassive black holes (SMBHs, 108−10 M⊙). We investigate such connection with a suite of cosmological simulations of massive (halo mass ≈1012 M⊙) galaxies at z ≃ 6 that include a detailed subgrid multiphase gas and accretion model. BH seeds of initial mass 105 M⊙ grow mostly by gas accretion, and become SMBH by z = 6 setting on the observed MBH−M⋆ relation without the need for a boost factor. Although quasar feedback crucially controls the SMBH growth, its impact on the properties of the host galaxy at z = 6 is negligible. In our model, quasar activity can both quench (via gas heating) or enhance (by interstellar medium overpressurization) star formation. However, we find that the star formation history is insensitive to such modulation as it is largely dominated, at least at z > 6, by cold gas accretion from the environment that cannot be hindered by the quasar energy deposition. Although quasar-driven outflows can achieve velocities $\gt 1000~\rm km~s^{-1}$, only ≈4 per cent of the outflowing gas mass can actually escape from the host galaxy. These findings are only loosely constrained by available data, but can guide observational campaigns searching for signatures of quasar feedback in early galaxies.

Three Lyman-α-emitting filaments converging to a massive galaxy group at z = 2.91: discussing the case for cold gas infall

We have discovered a 300 kpc-wide giant Lyman-α (Lyα) nebula centered on the massive galaxy group RO-1001 at z = 2.91 in the Cosmic Evolution Survey field. Keck Cosmic Web Imager observations reveal three cold gas filaments converging into the center of the potential well of its ∼4 × 1013 M⊙ dark matter halo, hosting 1200 M⊙ yr−1 of star formation as probed by Atacama Large Millimeter Array and NOrthern Extended Millimeter Array observations. The nebula morphological and kinematics properties and the prevalence of blueshifted components in the Lyα spectra are consistent with a scenario of gas accretion. The upper limits on active galactic nuclei activity and overall energetics favor gravity as the primary Lyα powering source and infall as the main source of gas flows to the system. Although interpretational difficulties remain, with outflows and likely also photoionization with ensuing recombination still playing a role, this finding provides arguably an ideal environment to quantitatively test models of cold gas accretion and galaxy feeding inside an actively star-forming massive halo at high redshift.

The radio galaxy population in the simba simulations

ABSTRACT We examine the 1.4 GHz radio luminosities of galaxies arising from star formation and active galactic nuclei (AGNs) within the state-of-the-art cosmological hydrodynamic simulation Simba. Simba grows black holes via gravitational torque limited accretion from cold gas and Bondi accretion from hot gas, and employs AGN feedback including jets at low Eddington ratios. We define a population of radio loud AGNs (RLAGNs) based on the presence of ongoing jet feedback. Within RLAGN, we define high and low excitation radio galaxies (HERGs and LERGs) based on their dominant mode of black hole accretion: torque limited accretion representing feeding from a cold disc, or Bondi representing advection-dominated accretion from a hot medium. Simba predicts good agreement with the observed radio luminosity function (RLF) and its evolution, overall as well as separately for HERGs and LERGs. Quiescent galaxies with AGN-dominated radio flux dominate the RLF at $\gtrsim 10^{22-23}$ W Hz−1, while star formation dominates at lower radio powers. Overall, RLAGNs have higher black hole accretion rates and lower star formation rates than non-RLAGN at a given stellar mass or velocity dispersion, but have similar black hole masses. Simba predicts an LERG number density of 8.53 Mpc−3, ∼10× higher than for HERGs, broadly as observed. While LERGs dominate among most massive galaxies with the largest black holes and HERGs dominate at high specific star formation rates, they otherwise largely populate similar-sized dark matter haloes and have similar host galaxy properties. Simba thus predicts that deeper radio surveys will reveal an increasing overlap between the host galaxy demographics of HERGs and LERGs.

Feedback factory: multiple faint radio jets detected in a cluster at z = 2

ABSTRACT We report the detection of multiple faint radio sources, that we identify as active galactic nucleus (AGN) jets, within CLJ1449+0856 at z = 2 using 3 GHz Very Large Array observations. We study the effects of radio-jet-based kinetic feedback at high redshifts, which has been found to be crucial in low-redshift clusters to explain the observed thermodynamic properties of their intracluster medium (ICM). We investigate this interaction at an epoch featuring high levels of AGN activity and a transitional phase of ICM in regards to the likelihood of residual cold gas accretion. We measure a total flux of $\rm 30.6 \pm 3.3\, \mu Jy$ from the six detected jets. Their power contribution is estimated to be $1.2 \, (\pm 0.6)\, \times 10^{44} \, \rm erg\, s^{-1}$, although this value could be up to $4.7 \, \times 10^{44} \, \rm erg\, s^{-1}$. This is a factor of ∼0.25–1.0 of the previously estimated instantaneous energy injection into the ICM of CLJ1449+0856 from AGN outflows and star formation that have already been found to be sufficient in globally offsetting the cooling flows in the cluster core. In line with the already detected abundance of star formation, this mode of feedback being distributed over multiple sites, contrary to a single central source observed at low redshifts, points to accretion of gas into the cluster centre. This also suggests a ‘steady state’ of the cluster featuring non-cool-core-like behaviour. Finally, we also examine the total infrared–radio luminosity ratio for the known sample of galaxies within the cluster core and find that dense environments do not have any serious consequence on the compliance of galaxies to the infrared–radio correlation.

Dust and star formation in the centre of NGC 3311

Context. NGC 3311 is the central galaxy of the Hydra I galaxy cluster. It has a hot interstellar medium and hosts a central dust lane with emission lines. These dust lanes are frequent in elliptical galaxies, but the case of NGC 3311 might be particularly interesting for problems of dust lifetime and the role of cool gas in the central parts. Aims. We aim to use archival HST images and MUSE data to investigate the central dust structure of NGC 3311. Methods. We used the tool PyParadise to model the stellar population and extract the emission lines. Results. The HST/ACS colour map reveals the known dust structures, but also blue spots, which are places of strong line emission. A dusty “mini-jet” emanates from the centre. The distribution of the emission line gas matches the dust silhouette almost exactly. Close to the brightest Hα emission, the ratio [NII]/Hα resembles that of HII-regions; in the outer parts, [NII] gets stronger and is similar to LINERLow-ionization nuclear emission-line region -like spectra. The gas kinematics is consistent with that of a rotating disc. The Doppler shifts of the strongest line emissions, which indicate the areas of highest star formation activity, smoothly fit into the disc symmetry. The metallicity is supersolar. The presence of neutral gas is indicated by the fit residuals of the stellar NaI D absorption line, which we interpret as interstellar absorption. We estimate the mass of the neutral gas to be of the order of the X-ray mass. The dynamical mass infers a stellar population of intermediate age, whose globular clusters have already been identified. Conclusions. Our findings can be harmonised in a scenario in which the star formation is triggered by the accretion of cold gas onto a pre-existing gas/dust disc or ring. Newly produced dust then contributes to the longevity of the dust.

Interaction of a cold cloud with a hot wind: the regimes of cloud growth and destruction and the impact of magnetic fields

ABSTRACT Multiphase galaxy winds, the accretion of cold gas through galaxy haloes, and gas stripping from jellyfish galaxies are examples of interactions between cold and hot gaseous phases. There are two important regimes in such systems. A sufficiently small cold cloud is destroyed by the hot wind as a result of Kelvin–Helmholtz instabilities, which shatter the cloud into small pieces that eventually mix and dissolve in the hot wind. In contrast, stripped cold gas from a large cloud mixes with the hot wind to intermediate temperatures, and then becomes thermally unstable and cools, causing a net accretion of hot gas to the cold tail. Using the magneto-hydrodynamical code arepo, we perform cloud crushing simulations and test analytical criteria for the transition between the growth and destruction regimes to clarify a current debate in the literature. We find that the hot-wind cooling time sets the transition radius and not the cooling time of the mixed phase. Magnetic fields modify the wind–cloud interaction. Draping of wind magnetic field enhances the field upstream of the cloud, and fluid instabilities are suppressed by a turbulently magnetized wind beyond what is seen for a wind with a uniform magnetic field. We furthermore predict jellyfish galaxies to have ordered magnetic fields aligned with their tails. We finally discuss how the results of idealized simulations can be used to provide input to subgrid models in cosmological (magneto-)hydrodynamical simulations, which cannot resolve the detailed small-scale structure of cold gas clouds in the circumgalactic medium.