Phases Of Interstellar Medium Research Articles

Diagnosing the interstellar medium of galaxies with far-infrared emission lines

Context. Gas cooling processes in the interstellar medium (ISM) are key to understanding how star formation occurs in galaxies. Far-infrared (FIR) fine-structure emission lines can be used to infer gas conditions and trace different phases of the ISM. Aims. We model eight of the most important FIR emission lines and explore their variation with star formation rate (SFR) out to z = 6 using cosmological hydrodynamical simulations. In addition, we study how different physical parameters, such as the interstellar radiation field (ISRF) and metallicity, impact the FIR lines and line ratios. Methods. We implemented a physically motivated multi-phase model of the ISM by post-processing the EAGLE cosmological simulation and using CLOUDY look-up tables for line emissivities. In this model we included four phases of the ISM: dense molecular gas, neutral atomic gas, diffuse ionised gas (DIG), and H II regions. Results. Our model shows reasonable agreement (to ∼0.5 dex) with the observed line luminosity–SFR relations up to z = 6 in the FIR lines analysed. For ease of comparison, we also provide linear fits to our model results. Our predictions also agree reasonably well with observations in diagnostic diagrams involving various FIR line ratios. Conclusions. We find that [C II] is the best SFR tracer of the FIR lines even though it arises from multiple ISM phases, while [O III] and [N II] can be used to understand the DIG–H II balance in the ionised gas. In addition, line ratios such as [C II]/[O III] and [N II]/[O I] are useful for deriving parameters such as ISRF, metallicity, and specific SFR. These results can help interpret the observations of the FIR lines from the local Universe to high redshifts.

Star Formation Variability as a Probe for the Baryon Cycle within Galaxies

We investigate the connection between the regulation of star formation and the cycling of baryons both within and in and out of galaxies. We use idealized numerical simulations of Milky Way–mass galaxies, in which we vary the galaxy morphology and stellar feedback strength. By following individual gas parcels through the disk, spiral arms, and massive star-forming clumps, we quantify how gas moves through the different phases of the interstellar medium (ISM) and forms stars. We show that the residence time of gas in the dense ISM phase (τ SF), the nature of spiral arms, and the clump properties depend on both the galaxy morphology and stellar feedback. We quantify signatures of the baryon cycle within galaxies using the temporal and spatial power spectrum density (PSD) of the star formation rate (SFR). Stronger stellar feedback leads to more bursty star formation while the correlation timescale of the SFH is longer, because stronger feedback dissolves the dense ISM phase, leading to a more homogeneous ISM and a decrease in τ SF. The bulge strength has a similar effect: the deep gravitational potential in a bulge-dominant galaxy imposes a strong shear force that breaks apart gas clumps in the ISM; this subsequently inhibits the fragmentation of gas and therefore the star formation in the disk, leading to a decrease in the spatial power on scales of ∼1 kpc. We conclude that measurements of the temporal and spatial PSD of the SFR can provide constraints on the baryon cycle and the star formation process.

Introducing TIGRESS-NCR. I. Coregulation of the Multiphase Interstellar Medium and Star Formation Rates

Massive, young stars are the main source of energy that maintains multiphase structure and turbulence in the interstellar medium (ISM), and without this “feedback” the star formation rate (SFR) would be much higher than is observed. Rapid energy loss in the ISM and efficient energy recovery by stellar feedback lead to coregulation of SFRs and the ISM state. Realistic approaches to this problem should solve for the dynamical evolution of the ISM, including star formation and the input of feedback energy self-consistently and accurately. Here, we present the TIGRESS-NCR numerical framework, in which UV radiation, supernovae, cooling and heating processes, and gravitational collapse are modeled explicitly. We use an adaptive ray-tracing method for UV radiation transfer from star clusters represented by sink particles, accounting for attenuation by dust and gas. We solve photon-driven chemical equations to determine the abundances of hydrogen (time dependent) and carbon/oxygen-bearing species (steady state), which then set cooling and heating rates self-consistently. Applying these methods, we present high-resolution magnetohydrodynamics simulations of differentially rotating local galactic disks representing typical conditions of nearby star-forming galaxies. We analyze ISM properties and phase distributions and show good agreement with existing multiwavelength galactic observations. We measure midplane pressure components (turbulent, thermal, and magnetic) and the weight, demonstrating that vertical dynamical equilibrium holds. We quantify the ratios of pressure components to the SFR surface density, which we call the feedback yields. The TIGRESS-NCR framework will allow for a wide range of parameter exploration, including in low-metallicity systems.

Vacuum UV photodesorption of organics in the interstellar medium: an experimental study of formic acid HCOOH and methyl formate HCOOCH3-containing ices.

Being a potential process that could explain gas phase abundances of so-called complex organic molecules (COMs) in the cold interstellar medium (ISM), the UV photon-induced desorption from organics-containing molecular ices has been experimentally studied. In this work, we focused on the observation of the photodesorbed products and the measurement of the associated photodesorption yields from pure and mixed molecular ices, each containing organic molecules whose detection has been achieved in the gas phase of the cold ISM, namely formic acid HCOOH and methyl formate HCOOCH3. Each molecule, in pure ice or in ice mixed with CO or water, was irradiated at 15 K with monochromatic vacuum UV photons in the 7-14 eV range using synchrotron radiation from the SOLEIL synchrotron facility, DESIRS beamline. Photodesorption yields of the intact molecules and of the photoproducts were derived as a function of the incident photon energy. Experiments have revealed that the desorbing species match the photodissociation pattern of each isolated molecule, with little influence of the kind of ice (pure or mixed in CO or H2O-rich environment). For both species, the photodesorption of the intact organics is found to be negligible in our experimental conditions, resulting in yields typically below 10-5 ejected molecules per incident photon. The results obtained on HCOOH and HCOOCH3-containing ices are similar to what has already been found for methanol-containing ices, but contrast with the case of another complex molecule, CH3CN, photodesorption of which has been recently studied. Such experimental results may be linked to the observation of COMs in protoplanetary disks, in which CH3CN is commonly observed whereas HCOOH or methanol are detected only in some sources, HCOOCH3 not being detected at all.

Photochemistry and Heating/Cooling of the Multiphase Interstellar Medium with UV Radiative Transfer for Magnetohydrodynamic Simulations

We present an efficient heating/cooling method coupled with chemistry and UV radiative transfer that can be applied to numerical simulations of the interstellar medium (ISM). We follow the time-dependent evolution of hydrogen species (H2, H, H+), assume carbon/oxygen species (C, C+, CO, O, and O+) are in formation–destruction balance given the nonsteady hydrogen abundances, and include essential heating/cooling processes needed to capture the thermodynamics of all ISM phases. UV radiation from discrete point sources and the diffuse background is followed through adaptive ray tracing and a six-ray approximation, respectively, allowing for H2 self-shielding; cosmic-ray heating and ionization are also included. To validate our methods and demonstrate their application for a range of density, metallicity, and radiation fields, we conduct a series of tests, including the equilibrium curves of thermal pressure versus density, the chemical and thermal structure in photodissociation regions, H i-to-H2 transitions, and the expansion of H ii regions and radiative supernova remnants. Careful treatment of photochemistry and cosmic-ray ionization is essential for many aspects of ISM physics, including identifying the thermal pressure at which cold and warm neutral phases coexist. We caution that many current heating and cooling treatments used in galaxy formation simulations do not reproduce the correct thermal pressure and ionization fraction in the neutral ISM. Our new model is implemented in the MHD code Athena and incorporated in the TIGRESS simulation framework, for use in studying the star-forming ISM in a wide range of environments.

Diffuse x-ray and gamma-ray limits on boson stars that interact with nuclei

Light bosonic dark matter can form gravitationally bound states known as boson stars. In this work, we explore a new signature of these objects interacting with the interstellar medium (ISM). We show how small effective couplings between the bosonic dark matter and the nucleon lead to a potential that accelerates ISM baryons as they transit the boson star, making the ISM within radiate at a high rate and energy. The low ISM density, however, implies the majority of Galactic boson stars will be too faint to be observable through this effect. By contrast, the diffuse photon flux, in hard x-rays and soft gamma-rays, produced by boson stars interacting with the ionized ISM phases can be sizable. We compute this diffuse flux and compare it to existing observations from HEAO-1, INTEGRAL and COMPTEL to infer limits on the fraction of these objects. This novel method places constraints on boson star dark matter while avoiding back-action effects from ambient baryons on the boson star configuration, unlike terrestrial searches where it has been noted that back-action can screen light bosonic fields. In addition, this study could be extended to other couplings and structures formed from light dark matter. For dark matter masses (10-14, 10-8) eV and boson star masses (10-10, 10-1) M ⊙, we find the constraints on the fraction can go down to f* ≲ 10-9 for dark matter in boson stars that is directly coupled to the Standard Model.

Inferring the HII region escape fraction of ionizing photons from infrared emission lines in metal-poor star-forming dwarf galaxies

Local metal-poor galaxies stand as ideal laboratories for probing the properties of the interstellar medium (ISM) in chemically unevolved conditions. Detailed studies of this primitive ISM can help gain insights into the physics of the first primordial galaxies that may be responsible for the reionization. Quantifying the ISM porosity to ionizing photons in nearby galaxies may improve our understanding of the mechanisms leading to Lyman continuum photon leakage from galaxies. The wealth of infrared (IR) tracers available in local galaxies and arising from different ISM phases allows us to constrain complex models in order to estimate physical quantities.

Low-power jet–interstellar medium interaction in NGC 7319 revealed by JWST/MIRI MRS

We present JWST/MIRI MRS spectroscopy of NGC 7319, the largest galaxy in the Stephan’s Quintet, observed as part of the Early Release Observations (ERO). NGC 7319 hosts a type 2 active galactic nucleus (AGN) and a low-power radio jet (L1.4 GHz = 3.3 × 1022 W Hz−1) with two asymmetric radio hotspots at 430 pc (N2) and 1.5 kpc (S2) projected distances from the unresolved radio core. The MRS data suggest that the molecular material in the disk of the galaxy decelerates the jet and causes this length asymmetry. We find enhanced emission from warm and hot H2 (Tw = 330 ± 40 K, Th = 900 ± 60 K) and ionized gas at the intersection between the jet axis and dust lanes in the disk. This emission is coincident with the radio hotspot N2, the hotspot closer to the core, suggesting that the jet–interstellar medium (ISM) interaction decelerates the jet. Conversely, the mid-infrared emission at the more distant hotspot is fainter, more highly ionized, and with lower H2 excitation, suggesting a more diffuse atomic environment where the jet can progress to farther distances. At the N2 radio hotspot, the ionized gas mass (Mion = (2.4–12)×105 M⊙) is comparable to that of the warm H2, but the former is more turbulent (σion ∼ 300 vs. σH2 ∼ 150 km s−1), so the mechanical energy of the ionized gas is ∼1.3–10 times higher. From these estimates, we find that only < 1% of the jet energy remains as mechanical energy in these two ISM phases at N2. We also find extended (r > 0.3–1.5 kpc) high-ionization emission ([Mg V], [Ne VI], and [Ne V]) close to the radio hotspots. This initial analysis of NGC 7319 shows the potential of MIRI/MRS to investigate the AGN feedback mechanisms due to radio jets and their radiation field in the, often heavily dust-enshrouded, central regions of galaxies. Understanding these mechanisms is an essential ingredient in the development of cosmological simulations of galaxy evolution.

Influence of Ion–Neutral Damping on the Cosmic-Ray Streaming Instability: Magnetohydrodynamic Particle-in-cell Simulations

Abstract We explore the physics of the gyroresonant cosmic-ray streaming instability (CRSI) including the effects of ion–neutral (IN) damping. This is the main damping mechanism in (partially ionized) atomic and molecular gas, which are the primary components of the interstellar medium (ISM) by mass. Limitation of CRSI by IN damping is important in setting the amplitude of Alfvén waves that scatter cosmic rays (CRs) and control galactic-scale transport. Our study employs the magnetohydrodynamic (MHD)–particle-in-cell hybrid fluid-kinetic numerical technique to follow linear growth as well as post-linear and saturation phases. During the linear phase of the instability—where simulations and analytical theory are in good agreement—IN damping prevents wave growth at small and large wavelengths, with the unstable bandwidth lower for higher IN collision rates ν in. Purely MHD effects during the post-linear phase extend the wave spectrum toward larger k. In the saturated state, the CR distribution evolves toward greater isotropy (lower streaming velocity) by scattering off of Alfvén waves excited by the instability. In the absence of low-k waves, CRs with sufficiently high momentum are not isotropized. The maximum wave amplitude and rate of isotropization of the distribution function decrease at higher ν in. When the IN damping rate approaches the maximum growth rate of CRSI, wave growth and isotropization are suppressed. Implications of our results for CR transport in partially ionized ISM phases are discussed.

Nitrogen X-ray absorption in the local ISM

ABSTRACT Nitrogen is one of the most abundant metals in the interstellar medium (ISM), and thus it constitutes an excellent test to study a variety of astrophysical environments, ranging from nova to active galactic nuclei. We present a detailed analysis of the gaseous component of the N K-edge using high-resolution XMM–Newton spectra of 12 Galactic and 40 extragalactic sources. For each source, we have estimated column densities for N i, N ii, N iii, N v, N vi, and N vii ionic species, which trace the cold, warm, and hot phases of the local Galactic ISM. We have found that the cold-warm component column densities decrease with the Galactic latitude, while the hot component does not. Moreover, the cold column density distribution is in good agreement with UV measurements. This is the first detailed analysis of the nitrogen K-edge absorption due to ISM using high-resolution X-ray spectra.

Diagnosing the interstellar medium of galaxies with far-infrared emission lines

Context. Atomic fine structure lines have been detected in the local Universe and at high redshifts over the past decades. The [C II] emission line at 158 μm is an important observable as it provides constraints on the interstellar medium (ISM) cooling processes. Aims. We develop a physically motivated framework to simulate the production of far-infrared line emission from galaxies in a cosmological context. This first paper sets out our methodology and describes its first application: simulating the [C II] 158 μm line emission in the local Universe. Methods. We combine the output from EAGLE cosmological hydrodynamical simulations with a multi-phase model of the ISM. Gas particles are divided into three phases: dense molecular gas, neutral atomic gas, and diffuse ionised gas (DIG). We estimate the [C II] line emission from the three phases using a set of CLOUDY cooling tables. Results. Our results agree with previous findings regarding the contribution of these three ISM phases to the [C II] emission. Our model shows good agreement with the observed L[C II–star formation rate (SFR) relation in the local Universe within 0.4 dex scatter. Conclusions. The fractional contribution to the [C II] line from different ISM phases depends on the total SFR and metallicity. The neutral gas phase dominates the [C II] emission in galaxies with SFR ∼ 0.01–1 M⊙ yr−1, but the ionised phase dominates at lower SFRs. Galaxies above solar metallicity exhibit lower L[C II/SFR ratios for the neutral phase. In comparison, the L[C II/SFR ratio in the DIG is stable when metallicity varies. We suggest that the reduced size of the neutral clouds, caused by increased SFRs, is the likely cause for the L[C II deficit at high infrared luminosities, although EAGLE simulations do not reach these luminosities at z = 0.

Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium

ABSTRACT Utilizing several instruments on 4–8 m telescopes, we have observed a large sample of objects in the mid-infrared (8–13 μm). These comprise a few evolved stars, multiple envelopes of embedded young stellar objects (YSOs) or compact H-II regions, and several sightlines through the interstellar medium (ISM). The latter is where dust resides – and is potentially modified – between its formation in evolved stellar outflows and deposition in molecular clouds. In most objects, we detect not only the well-known 9.7 μm absorption feature of amorphous silicates but also a second absorption band around 11.1 μm whose carrier is attributed to crystalline forsterite. We propose that crystalline silicates are essentially ubiquitous in the ISM and earliest phases of star formation, and are evolutionary precursors to T-Tauri and Herbig stars where such silicates have been commonly found. Modelling shows that in most YSOs, H-II regions and ISM cases, the forsterite mass fraction is between 1 and 2 per cent, suggesting that the younger phases inherit their abundance from the ISM. However, several sources show much stronger features (abundances ≥3 per cent). This suggests that significant processing, perhaps crystallization by thermal annealing, occurs early on in star formation. Most intriguing is the first detection of crystalline silicate in the diffuse ISM. We propose that our observed abundance is consistent with a mass fraction of crystalline silicates of 10–20 per cent injected into the ISM, along with commonly accepted lifetimes against their destruction, but only if cosmic ray-induced amorphization is insignificant over a few Giga years.

Simulations of the star-forming molecular gas in an interacting M51-like galaxy

ABSTRACT We present here the first of a series of papers aimed at better understanding the evolution and properties of giant molecular clouds (GMCs) in a galactic context. We perform high-resolution, three-dimensional arepo simulations of an interacting galaxy inspired by the well-observed M51 galaxy. Our fiducial simulations include a non-equilibrium, time-dependent, chemical network that follows the evolution of atomic and molecular hydrogen as well as carbon and oxygen self-consistently. Our calculations also treat gas self-gravity and subsequent star formation (described by sink particles), and coupled supernova feedback. In the densest parts of the simulated interstellar medium (ISM), we reach sub-parsec resolution, granting us the ability to resolve individual GMCs and their formation and destruction self-consistently throughout the galaxy. In this initial work, we focus on the general properties of the ISM with a particular focus on the cold star-forming gas. We discuss the role of the interaction with the companion galaxy in generating cold molecular gas and controlling stellar birth. We find that while the interaction drives large-scale gas flows and induces spiral arms in the galaxy, it is of secondary importance in determining gas fractions in the different ISM phases and the overall star formation rate. The behaviour of the gas on small GMC scales instead is mostly controlled by the self-regulating property of the ISM driven by coupled feedback.

A Self-consistent Framework for Multiline Modeling in Line Intensity Mapping Experiments

Abstract Line intensity mapping (LIM) is a promising approach to study star formation and the interstellar medium (ISM) in galaxies by measuring the aggregate line emission from the entire galaxy population. In this work, we develop a simple yet physically motivated framework for modeling the line emission as would be observed in LIM experiments. It is done by building on analytic models of the cosmic infrared background that connect total infrared luminosity of galaxies to their host dark matter halos. We present models of the 21 cm, CO (1−0), [ ] 158 μm, and [ ] 122 and 205 μm lines consistent with current observational constraints. With four case studies of various combinations of these lines that probe different ISM phases, we demonstrate the potential for reliably extracting physical properties of the ISM, and the evolution of these properties with cosmic time, from auto- and cross-correlation analysis of these lines as measured by future LIM experiments.

Using [C ii] 158 μm Emission from Isolated ISM Phases as a Star Formation Rate Indicator

Abstract The brightest observed emission line in many star-forming galaxies is the 158 μm line, making it detectable up to z ∼ 7. In order to better understand and quantify the emission as a tracer of star formation, the theoretical ratio between the 205 μm emission and the 158 μm emission has been employed to empirically determine the fraction of emission that originates from the ionized and neutral phases of the interstellar medium (ISM). Sub-kiloparsec measurements of the 158 μm and 205 μm lines in nearby galaxies have recently become available as part of the Key Insights in Nearby Galaxies: a Far Infrared Survey with Herschel (KINGFISH) and Beyond the Peak programs. With the information from these two far-infrared lines along with the multi-wavelength suite of KINGFISH data, a calibration of the emission line as a star formation rate (SFR) indicator and a better understanding of the deficit are pursued. emission is also compared to polycyclic aromatic hydrocarbon (PAH) emission in these regions to compare photoelectric heating from PAH molecules to cooling by in the neutral and ionized phases of the ISM. We find that the emission originating in the neutral phase of the ISM does not exhibit a deficit with respect to the infrared luminosity and is therefore preferred over the emission originating in the ionized phase of the ISM as an SFR indicator for the normal star-forming galaxies included in this sample.

The Herschel Dwarf Galaxy Survey

The sensitive infrared telescopes, Spitzer and Herschel, have been used to target low-metallicity star-forming galaxies, allowing us to investigate the properties of their interstellar medium (ISM) in unprecedented detail. Interpretation of the observations in physical terms relies on careful modeling of those properties. We have employed a multiphase approach to model the ISM phases (H II region and photodissociation region) with the spectral synthesis code Cloudy. Our goal is to characterize the physical conditions (gas densities, radiation fields, etc.) in the ISM of the galaxies from the Herschel Dwarf Galaxy Survey. We are particularly interested in correlations between those physical conditions and metallicity or star-formation activity. Other key issues we have addressed are the contribution of different ISM phases to the total line emission, especially of the [C II]157 μm line, and the characterization of the porosity of the ISM. We find that the lower-metallicity galaxies of our sample tend to have higher ionization parameters and galaxies with higher specific star-formation rates have higher gas densities. The [C II] emission arises mainly from PDRs and the contribution from the ionized gas phases is small, typically less than 30% of the observed emission. We also find a correlation – though with scatter – between metallicity and both the PDR covering factor and the fraction of [C II] from the ionized gas. Overall, the low metal abundances appear to be driving most of the changes in the ISM structure and conditions of these galaxies, and not the high specific star-formation rates. These results demonstrate in a quantitative way the increase of ISM porosity at low metallicity. Such porosity may be typical of galaxies in the young Universe.

Metal Mixing and Ejection in Dwarf Galaxies Are Dependent on Nucleosynthetic Source

Abstract Using a high-resolution simulation of an isolated dwarf galaxy, accounting for multichannel stellar feedback and chemical evolution on a star-by-star basis, we investigate how each of 15 metal species is distributed within our multiphase interstellar medium (ISM) and ejected from our galaxy by galactic winds. For the first time, we demonstrate that the mass fraction probability distribution functions (PDFs) of individual metal species in the ISM are well described by a piecewise log-normal and power-law distribution. The PDF properties vary within each ISM phase. Hot gas is dominated by recent enrichment, with a significant power-law tail to high metal fractions, while cold gas is predominantly log-normal. In addition, elements dominated by asymptotic giant branch (AGB) wind enrichment (e.g., N and Ba) mix less efficiently than elements dominated by supernova enrichment (e.g., α elements and Fe). This result is driven by the differences in source energetics and source locations, particularly the higher chance compared to massive stars for AGB stars to eject material into cold gas. Nearly all of the produced metals are ejected from the galaxy (only 4% are retained), but over 20% of metals dominated by AGB enrichment are retained. In dwarf galaxies, therefore, elements synthesized predominantly through AGB winds should be both overabundant and have a larger spread compared to elements synthesized in either core-collapse or Type Ia supernovae. We discuss the observational implications of these results, their potential use in developing improved models of galactic chemical evolution, and their generalization to more massive galaxies.

Remodelling the evolution of grain size distribution in galaxies

We revisit the evolution model of grain size distribution in a galaxy for the ultimate purpose of implementing it in hydrodynamical simulations. We simplify the previous model in such a way that some model-dependent assumptions are replaced with simpler functional forms. For the first test of the developed framework, we apply it to a one-zone chemical evolution model of a galaxy, confirming that our new model satisfactorily reproduces the previous results and that efficient coagulation of small grains produced by shattering and accretion is essential in reproducing the so-called MRN grain size distribution. For the next step, in order to test if our model can be treated together with the hydrodynamical evolution of the interstellar medium (ISM), we post-process a hydrodynamical simulation of an isolated disc galaxy using the new grain evolution model. We sample hydrodynamical particles representing each of the dense and diffuse ISM phases. By this post-processing, we find that the processes occurring in the dense gas (grain growth by accretion and coagulation) are important in reproducing the grain size distribution consistent with the Milky Way extinction curve. In our model, the grain size distributions are similar between the dense and diffuse ISM, although we observe a larger dispersion in the dense ISM. Moreover, we also show that even if we degrade the grain radius resolution (with 16 grid points), the overall shape of grain size distribution (and of resulting extinction curve) can be captured.

Magnetically aligned straight depolarization canals and the rolling Hough transform

Aims. We aim to characterize the properties of the straight depolarization canals detected in the Low Frequency Array (LOFAR) polarimetric observations of a field centered on the extragalactic source 3C 196. We also compare the canal orientations with magnetically aligned HI filaments and the magnetic field probed by polarized dust emission. Methods. We used the rolling Hough transform (RHT) to identify and characterize the orientation of the straight depolarization canals in radio polarimetric data and the filaments in HI data. Results. The majority of the straight depolarization canals and the Hi filaments are inclined by ~10° with respect to the Galactic plane and are aligned with the plane-of-sky magnetic field orientation probed by the Planck dust polarization data. The other distinct orientation, of −65° with respect to the Galactic plane, is associated with the orientation of a bar-like structure observed in the 3C 196 field at 350 MHz. Conclusions. An alignment between three distinct tracers of the (local) interstellar medium (ISM) suggests that an ordered magnetic field plays a crucial role in confining different ISM phases. The majority of the straight depolarization canals are a result of a projection of the complicated 3D distribution of the ISM. The RHT analysis is a robust method for identifying and characterizing the straight depolarization canals observed in radio-polarimetric data.

The VLT/MUSE view of the central galaxy in Abell 2052

We report observations of the radio galaxy 3C 317 (at z = 0.0345) located at the center of the Abell cluster A2052, obtained with the VLT/MUSE integral field spectrograph. The Chandra images of this cluster show cavities in the X-ray emitting gas, which were produced by the expansion of the radio lobes inflated by the active galactic nucleus (AGN). Our exquisite MUSE data show with unprecedented detail the complex network of line emitting filaments enshrouding the northern X-ray cavity. We do not detect any emission lines from the southern cavity, with a luminosity asymmetry between the two regions higher than ~75. The emission lines produced by the warm phase of the interstellar medium (WIM) enable us to obtain unique information on the properties of the emitting gas. We find dense gas (up to 270 cm−3) that makes up part of a global quasi spherical outflow that is driven by the radio source, and obtain a direct estimate of the expansion velocity of the cavities (265 km s−1). The emission lines diagnostic rules out ionization from the AGN or from star-forming regions, suggesting instead ionization from slow shocks or from cosmic rays. The striking asymmetric line emission observed between the two cavities contrasts with the less pronounced differences between the north and south sides in the hot gas; this represents a significant new ingredient for our understanding of the process of the exchange of energy between the relativistic plasma and the external medium. We conclude that the expanding radio lobes displace the hot tenuous phase of the interstellar medium (ISM), but also impact the colder and denser ISM phases. These results show the effects of the AGN on its host and the importance of radio mode feedback.