Gas Filaments Research Articles

The warm-hot intergalactic medium in inter-cluster filaments. A forecast for HUBS observations based on eRASS1 superclusters

Cosmological simulations indicate that nearly half of the baryons in the nearby Universe are in the warm-hot intergalactic medium (WHIM) phase, and about a half them reside in cosmic filaments connecting galaxy clusters. Recent observational studies using stacked survey data and deep exposures of galaxy cluster outskirts have detected soft X-ray excesses associated with optically identified filaments. However, the physical characteristics of WHIM in filaments remain largely undetermined due to a lack of direct spectral diagnostics of individual targets, which are limited by the spectral resolution of current instruments in the soft X-ray band. We aim to select appropriate targets for WHIM characterization through pointing observations with the future Hot Universe Baryon Surveyor (HUBS) mission, which is designed with eV-level energy resolution in the 0.1-2.0 keV band and a one-square-degree field of view, thus complementing other planned microcalorimetry missions such as Athena. We built a sample of 1577 inter-cluster filaments based on the first eROSITA All-Sky Survey (eRASS1) supercluster catalog and estimated their soft X-ray emission. Their modeled emission and geometrical properties were used to select candidate targets for HUBS observations. Four inter-cluster filaments were selected as the most appropriate candidates. By simulating and analyzing their mock observations, we demonstrated that with 200 ks HUBS exposure for each candidate, the gas properties of individual filaments can be accurately determined, with the temperature constrained to ±0.01 keV, metallicity constrained to leq±0.03 solar, and density constrained to $<±10%$. Elemental abundances of O, Ne, Mg, and Fe can be measured separately, providing unprecedented insights into the chemical history of the filament gas. We also show that direct mapping of the WHIM distribution is promising with narrowband imaging of the O viii line. Our work forecasts that next-generation X-ray missions such as HUBS will provide substantial improvement in our understanding of the physical status and evolution history of the diffuse WHIM gas in the cosmic large-scale structure.

ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks

The central molecular zone (CMZ) of our Galaxy exhibits widespread emission from SiO and various complex organic molecules (COMs), yet the exact origin of such emission is uncertain. Here we report the discovery of a unique class of long (>0.5 pc) and narrow (<0.03 pc) filaments in the emission of SiO 5–4 and eight additional molecular lines, including several COMs, in our ALMA 1.3 mm spectral line observations toward two massive molecular clouds in the CMZ, which we name as slim filaments. However, these filaments are not detected in the 1.3 mm continuum at the 5σ level. Their line-of-sight velocities are coherent and inconsistent with being outflows. The column densities and relative abundances of the detected molecules are statistically similar to those in protostellar outflows but different from those in dense cores within the same clouds. Turbulent pressure in these filaments dominates over self gravity and leads to hydrostatic inequilibrium, indicating that they are a different class of objects than the dense gas filaments in dynamical equilibrium ubiquitously found in nearby molecular clouds. We argue that these newly detected slim filaments are associated with parsec-scale shocks, likely arising from dynamic interactions between shock waves and molecular clouds. The dissipation of the slim filaments may replenish SiO and COMs in the interstellar medium and lead to their widespread emission in the CMZ.

MUSEQuBES: Unveiling Cosmic Web Filaments at z ≈ 3.6 through Dual Absorption and Emission Line Analysis

Abstract According to modern cosmological models, galaxies are embedded within cosmic filaments, which supply a continuous flow of pristine gas, fueling star formation and driving their evolution. However, due to their low density, the direct detection of diffuse gas in cosmic filaments remains elusive. Here, we report the discovery of an extremely metal-poor ([X/H] ≈ −3.7), low-density ( log 10 n H / cm − 3 ≈ −4, corresponding to an overdensity of ≈5) partial Lyman limit system (pLLS) at z ≈ 3.577 along the quasar sightline Q1317–0507, probing cosmic filaments. Additionally, two other low-metallicity ([X/H] ≲ −2) absorption systems are detected at similar redshifts, one of which is also a pLLS. Very Large Telescope (VLT) MUSE observations reveal a significant overdensity of Lyα emitters (LAEs) associated with these absorbers. The spatial distribution of the LAEs strongly suggests the presence of an underlying filamentary structure. This is further supported by the detection of a large Lyα-emitting nebula with a surface brightness of ≥ 1 0 − 19 erg cm − 2 s − 1 arcsec − 2 , with a maximum projected linear size of ≈260 pkpc extending along the LAEs. This is the first detection of giant Lyα emission tracing cosmic filaments, linked to normal galaxies and likely powered by in situ recombination.

Tracing cosmic gas in filaments and halos: Low-redshift insights from the kinematic Sunyaev-Zel’dovich effect

Tracing cosmic gas in filaments and halos: Low-redshift insights from the kinematic Sunyaev-Zel’dovich effect

Anomalous infrared conical emission during ordered multifilamentation in gases

We demonstrate that amplitude modulation of a high-peak-power femtosecond laser pulse allows to change fundamentally the frequency-angular structure (FAS) of the supercontinuum formed during the filamentation in both molecular and atomic gases. Particularly, modulation with a 4-hole mask forms an inverted pattern of conical emission (CE) with its predominance in the Stokes wing of the pulse spectrum. We explain this phenomenon as a joint effect of self-phase modulation and temporal pulse splitting of interfering beamlets formed by the modulating mask. Our results pave a way for tailoring the frequency-angular structure of a filament-generated supercontinuum.

Investigation of Entire-Space Terahertz Emission From Gas Filament Excited by a Two-Color Field

Investigation of Entire-Space Terahertz Emission From Gas Filament Excited by a Two-Color Field

THE THREE HUNDRED project: Estimating the dependence of gas filaments on the mass of galaxy clusters

Context. Galaxy clusters are located in the densest areas of the universe and are intricately connected to larger structures through the filamentary network of the cosmic web. In this scenario, matter flows from areas of lower density to higher density. As a result, the properties of galaxy clusters are deeply influenced by the filaments that are attached to them, which are quantified by a parameter known as connectivity. Aims. We explore the dependence of gas-traced filaments connected to galaxy clusters on the mass and dynamical state of the cluster. Moreover, we evaluate the effectiveness of the cosmic web extraction procedure from the gas density maps of simulated cluster regions. Methods. Using the DisPerSE cosmic web finder, we identify filamentary structures from the 3D gas particle distribution in 324 simulated regions of 30 h−1 Mpc side from THE THREE HUNDRED hydrodynamical simulation at redshifts z = 0, 1, and 2. We estimate the connectivity at various apertures for ∼3000 groups and clusters spanning a mass range from 1013 h−1 M⊙ to 1015 h−1 M⊙. Relationships between connectivity and cluster properties like radius, mass, dynamical state, and hydrostatic mass bias are explored. Results. We show that the connectivity is strongly correlated with the mass of galaxy clusters, with more massive clusters being on average more connected. This finding aligns with previous studies in the literature, both from observational and simulated datasets. Additionally, we observe a dependence of the connectivity on the aperture at which it is estimated. We find that connectivity decreases with cosmic time, while no dependencies on the dynamical state and hydrostatic mass bias of the cluster are found. Lastly, we observe a significant agreement between the connectivity measured from gas-traced and mock-galaxy-traced filaments in the simulation.

Tracing gaseous filaments connected to galaxy clusters: The case study of Abell 2744

Filaments connected to galaxy clusters are crucial environments for studying the build up of cosmic structures as they funnel matter towards the clusters' deep gravitational potentials. Identifying gas in filaments is a challenge, due to their lower density contrast, which produces faint signals. Therefore, the best opportunity to detect these signals is in the outskirts of galaxy clusters. We revisited the X-ray observation of the cluster Abell 2744, using statistical estimators of the anisotropic matter distribution to identify filamentary patterns around it. We report, for the first time, the blind detection of filaments connected to a galaxy cluster from X-ray emission using a filament-finder technique and a multipole decomposition technique. We compare this result with filaments extracted from the distribution of spectroscopic galaxies using the same two approaches. This allowed us to demonstrate the robustness and reliability of our techniques in tracing the filamentary structure of three and five filaments connected to Abell 2744, in two and three dimensions, respectively.

Quantifying the informativity of emission lines to infer physical conditions in giant molecular clouds

Context. Observations of ionic, atomic, or molecular lines are performed to improve our understanding of the interstellar medium (ISM). However, the potential of a line to constrain the physical conditions of the ISM is difficult to assess quantitatively, because of the complexity of the ISM physics. The situation is even more complex when trying to assess which combinations of lines are the most useful. Therefore, observation campaigns usually try to observe as many lines as possible for as much time as possible. Aims. We have searched for a quantitative statistical criterion to evaluate the full constraining power of a (combination of) tracer(s) with respect to physical conditions. Our goal with such a criterion is twofold. First, we want to improve our understanding of the statistical relationships between ISM tracers and physical conditions. Secondly, by exploiting this criterion, we aim to propose a method that helps observers to make their observation proposals; for example, by choosing to observe the lines with the highest constraining power given limited resources and time. Methods. We propose an approach based on information theory, in particular the concepts of conditional differential entropy and mutual information. The best (combination of) tracer(s) is obtained by comparing the mutual information between a physical parameter and different sets of lines. The presented analysis is independent of the choice of the estimation algorithm (e.g., neural network or χ2 minimization). We applied this method to simulations of radio molecular lines emitted by a photodissociation region similar to the Horsehead Nebula. In this simulated data, we considered the noise properties of a state-of-the-art single dish telescope such as the IRAM 30m telescope. We searched for the best lines to constrain the visual extinction, AVtot, or the ultraviolet illumination field, G0. We ran this search for different gas regimes, namely translucent gas, filamentary gas, and dense cores. Results. The most informative lines change with the physical regime (e.g., cloud extinction). However, the determination of the optimal (combination of) line(s) to constrain a physical parameter such as the visual extinction depends not only on the radiative transfer of the lines and chemistry of the associated species, but also on the achieved mean signal-to-noise ratio. The short integration time of the CO isotopologue J = 1 − 0 lines already yields much information on the total column density for a large range of (AVtot, G0) space. The best set of lines to constrain the visual extinction does not necessarily combine the most informative individual lines. Precise constraints on the radiation field are more difficult to achieve with molecular lines. They require spectral lines emitted at the cloud surface (e.g., [CII] and [CI] lines). Conclusions. This approach allows one to better explore the knowledge provided by ISM codes, and to guide future observation campaigns.

Multi-epoch jet outbursts in Abell 496: Synchrotron ageing and buoyant X-ray cavities draped by warm gas filaments

Aims. The galaxy cluster Abell 496 has been extensively studied in the past for the clear sloshing motion of its hot intracluster medium (ICM) on large scales, but the interplay between the central radio galaxy and the surrounding cluster atmosphere is mostly unexplored. We present a dedicated radio, X-ray, and optical study of Abell 496 with the aim being to investigate this connection. Methods. We use deep radio images obtained with the Giant Metrewave Radio Telescope (GMRT) at 150, 330, and 617 MHz, the Very Large Array (VLA) at 1.4 and 4.8 GHz, and the VLA Low Band Ionosphere and Transient Experiment (VLITE) at 340 MHz, with angular resolutions ranging from 0.​″5 to 25″. Additionally, we use archival Chandra and Very Large Telescope (VLT) MUSE observations. Results. The radio images reveal three distinct periods of jet activity: an ongoing episode on subkiloparsec scales with an inverted radio spectrum; an older episode that produced lobes on scales of ∼20 kpc, which now have a steep spectral index (α = 2.0 ± 0.1); and an even older episode that produced lobes on scales of ∼50 − 100 kpc with an ultrasteep spectrum (α = 2.7 ± 0.2). Archival Chandra X-ray observations show that the older and oldest episodes excavated two generations of cavities in the hot gas of the cluster. The outermost X-ray cavity has a clear mushroom-head shape, likely caused by its buoyant rise in the cluster’s potential. Cooling of the hot gas is ongoing in the innermost 20 kpc, where warm, Hα-bright filaments are visible in VLT-MUSE data. The Hα-filaments are stretched toward the mushroom-head cavity, which may have stimulated ICM cooling in its wake. We conclude by discussing our nondetection of a radio mini-halo in this vigorously sloshing but low-mass galaxy cluster.

The properties of magnetised cold filaments in a cool-core galaxy cluster

Filaments of cold gas ($T $ K) are found in the inner regions of many cool-core clusters. These structures are thought to play a major role in the regulation of feedback from active galactic nuclei (AGNs). We study the morphology of the filaments, their formation, and their impact on the propagation of the outflowing AGN jets. We present a set of GPU-accelerated 3D magnetohydrodynamic simulations of an idealised Perseus-like cluster using the performance portable code AthenaPK . We include radiative cooling and a self-regulated AGN feedback model that redistributes accreted material through kinetic, thermal, and magnetic feedback. We confirm that magnetic fields play an important role in both the formation and evolution of the cold material. These suppress the formation of massive cold discs and favour magnetically supported filaments over clumpy structures. Achieving resolutions of $25-50$ pc, we find that filaments are not monolithic as they contain numerous and complex magnetically supported sub-structures. We find that the mass distribution of these clumps follows a power law of slope of $ for all investigated filaments. Studying the evolution of individual filaments, we find that their formation pathways can be diverse. We find examples of filaments forming through a combination of gas uplifting and condensation, as well as systems of purely infalling clumps condensing out of the intracluster medium. The density contrast between the cold gas and the outflowing hot material leads to recurring deflections of the jets, favouring inflation of bubbles. Filaments in cool-core clusters are clumpy and contain numerous sub-structures, resulting from a complex interplay between magnetic fields, thermal instability, and jet-cloud interaction. Frequent deflections of the AGN outflows suppress jet collimation and favour the formation of large X-ray bubbles, and smaller off-axis cavities.

Filamentary Hierarchies and Superbubbles: Galactic Multiscale Magnetohydrodynamic Simulations of Giant Molecular Cloud to Star Cluster Formation

There is now abundant observational evidence that star formation is a highly dynamical process that connects filament hierarchies and supernova feedback from galaxy-scale kiloparsec filaments and superbubbles to giant molecular clouds (GMCs) on 100 pc scales and star clusters (1 pc). Here we present galactic multiscale MHD simulations that track the formation of structure from galactic down to subparsec scales in a magnetized, Milky Way–like galaxy undergoing supernova-driven feedback processes. We do this by adopting a novel zoom-in technique that follows the evolution of typical 3 kpc subregions without cutting out the surrounding galactic environment, allowing us to reach 0.28 pc resolution in the individual zoom-in regions. We find a wide range of morphologies and hierarchical structures, including superbubbles, turbulence, and kiloparsec atomic gas filaments hosting multiple GMC condensations that are often associated with superbubble compression, down to smaller-scale filamentary GMCs and star cluster regions within them. Gas accretion and compression ultimately drive filaments over a critical, scale-dependent line mass leading to gravitational instabilities that produce GMCs and clusters. In quieter regions, galactic shear can produce filamentary GMCs within flattened, rotating disklike structures on 100 pc scales. Strikingly, our simulations demonstrate the formation of helical magnetic fields associated with the formation of these disklike structures.

Properties of the diffuse gas component in filaments detected in the Dianoga cosmological simulations

Context. Cosmic filaments are observationally hard to detect. However, hydrodynamical cosmological simulations are ideal laboratories where the evolution of the cosmic web can be studied, and they allow for easier insight into the nature of the filaments. Aims. We investigate how the intrinsic properties of filaments are evolving in areas extracted from a larger cosmological simulation. We aim to identify significant trends in the properties of the warm-hot intergalactic medium (WHIM) and suggest possible explanations. Methods. To study the filaments and their contents, we selected a subset of regions from the Dianoga simulation. We analysed these regions that were simulated with different baryon physics, namely with and without AGN feedback. We constructed the cosmic web using the subspace constrained mean shift (SCMS) algorithm and the sequential chain algorithm for resolving filaments (SCARF). We examined the basic physical properties of filaments (length, shape, mass, radius) and analysed different gas phases (hot, WHIM, and colder gas components) within those structures. The evolution of the global filament properties and the properties of the gas phases were studied in the redshift range 0 < z < 1.48. Results. Within our simulations, the detected filaments have, on average, lengths below 9 Mpc. The filaments’ shape correlates with their length, as the longer they are, the more likely they are curved. We find that the scaling relation between mass M and length L of the filaments is well described by the power law M ∞ L1.7. The radial density profile widens with redshift, meaning that the radius of the filaments becomes larger over time. The fraction of gas mass in the WHIM phase does not depend on the model and rises towards lower redshifts. However, the included baryon physics has a strong impact on the metallicity of gas in filaments, indicating that the AGN feedback impacts the metal content already at redshifts of z ~ 2.

The Galactic Center in Color: Measuring Extinction with High-proper-motion Stars

The Milky Way’s central parsec is a highly extinguished region with a population of high-proper-motion stars. We have tracked 145 stars for ∼10 yr at wavelengths between 1 and 4 μm to analyze extinction effects in color–magnitude space. Approximately 30% of this sample dims and reddens over the course of years, likely from the motion of sources relative to an inhomogeneous screen of dust. We correct previous measurements of the intrinsic variability fraction for differential extinction effects, resulting in a reduced stellar variability fraction of 34%. The extinction variability subsample shows that the extinguishing material has subarcsecond scales, much smaller variations than previously reported. The observed extinction events imply a typical cross section of 500 au and a density of around 3 × 104 atoms cm−3 for the extinguishing material, which are consistent with measurements of filamentary dust and gas at the Galactic center. Furthermore, given that the stars showing extinction variability tend to be more highly reddened than the rest of the sample, the extinction changes are likely due to material localized to the Galactic center region. We estimate the relative extinction between 1 and 4 μm as AH:AK′:AL′=1.67±0.05:1:0.69±0.03 . Our measurement of extinction at longer wavelengths—L’ (3.8 μm)—is inconsistent with recent estimations of the integrated extinction toward the central parsec. One interpretation of this difference is that the dust variations this experiment are sensitive to—which are local to the Galactic center—are dominated by grains of larger radius than the foreground.

The SRG/eROSITA all-sky survey. X-ray emission from the warm-hot phase gas in long cosmic filaments

The properties of the warm-hot intergalactic medium (WHIM) in cosmic filaments are among the least quantified units in modern astrophysics. The Spectrum Roentgen Gamma/eROSITA All Sky Survey ((SRG/eRASS) provides a unique opportunity to study the X-ray emission of the WHIM. We applied both imaging and spectroscopic stacking techniques to the data of the first four eRASS scans to inspect the X-ray emissions from 7817 cosmic filaments identified from Sloan Digital Sky Survey (SDSS) optical galaxy samples. We obtained a $9 significant detection of the total X-ray signal from filaments in the 0.3--1.2 keV band. Here, we introduce a novel method to estimate the contamination fraction from unmasked X-ray halos, active galactic nuclei, and X-ray binaries associated with filament galaxies. We found an approximately 40<!PCT!> contamination fraction for these unmasked sources, suggesting that the remaining 60<!PCT!> of the signal could be coming from the WHIM and a $5.4 detection significance of the WHIM. Moreover, we modeled the temperature and baryon density contrast of the detected WHIM by fitting the stacked spectrum and surface brightness profile. The best-fit temperature $ K obtained by using a single temperature model, is marginally higher than in the simulation results. This could be due to the fitting of a single temperature model on a multi-temperature spectrum. Assuming a 0.2 solar abundance, the best-fit baryon density contrast $ b is in general agreement with the X-ray emitting phases in the IllustrisTNG simulation. This result suggests that the broadband X-ray emission traces the high end of the temperature and density values that characterize the entire WHIM population.

Improving the beam pointing and intensity stability of the third harmonic generated in air filament

Third harmonic generation (THG) by laser filamentation in gases is immune to the damage threshold and phase matching limit for UV and EUV pulse generation. Here, we report on the jitter measurements of the beam pointing and the intensity of the THG through filamentation with different repetition rates in air. The THG jitters are stronger at the high repetition rates (1 kHz) filaments. A technique of applying an external DC electric field on the filament was found to suppress the jitters. The beam pointing and intensity jitters of the 1 kHz THG from laser filament in air were reduced by about 1 fold with the extreme external electric field electric field applied on the filament. This technique provides a way to generate a stable, high repetition rate UV and EUV sources.

MUSE Analysis of Gas around Galaxies (MAGG) - VI. The cool and enriched gas environment of z≳3 Lyα emitters

We present a novel dataset that extends our view of the cosmic gas around $z 3-4$ Lyalpha emitters (LAEs) in the Muse Analysis of Gas around Galaxies (MAGG) survey by tracing a cool and enriched gas phase through 47 absorbers identified in newly obtained VLT/X-shooter near-infrared quasar spectra. Jointly with the more ionized gas traced by systems and the neutral from previous work, we find that LAEs are distributed inside cosmic structures that contain multiphase gas in composition and temperature. All gas phases are a strong function of the large-scale galaxy environment: the and the strength and kinematics positively correlate with the number of associated galaxies, and it is $ times more likely to detect metal absorbers around groups of LAEs than isolated ones. Exploring the redshift evolution, the covering factor of around groups of LAEs and isolated ones remains approximately constant from $z to $z but the one of around group galaxies drops by $z Adding the cool enriched gas traced by the absorbers to the results that we obtained for the and gas, we put forward a picture in which LAEs lie along gas filaments that contain high column-density systems and are enriched by strong and absorbers. While the gas appears to be more centrally concentrated near LAEs, weaker systems instead trace a more diffuse gas phase extended up to larger distances around the galaxies.

Splitting behavior and breakup mechanism of bubbles in the split‐and‐recombine microchannel

AbstractSplit‐and‐recombine (SAR) microreactor is an advanced reactor for chemical process intensification. Bubble flow in the SAR microchannel is an important phenomenon that affects reaction efficiency, however drew little attention before. This study aims to explore the underlying mechanisms of bubble splitting, retraction, and breakup behaviors in a compact SAR microchannel. Two breakup flow patterns, unilateral flow and unilateral alternate flow were identified with symmetric or asymmetric splitting, respectively. Mechanism analysis indicates that the splitting symmetry issue is related to liquid slug size, viscous effect and novel retraction behavior of a splitting filament. The retraction is induced by the interconnection and unequal pressures between the splitting filaments. The correlation between normalized breakup time and Ca number confirms the Capillary‐pressure breakup mechanism for the splitting gas filaments. Two empirical correlations for the two breakup flow patterns were proposed, which illustrate the significant contribution of bubble retraction to the breakup degree.

The hydrodynamic response of small-scale structure to reionization drives large IGM temperature fluctuations that persist to z = 4

ABSTRACT The thermal history and structure of the intergalactic medium (IGM) at $z \ge 4$ is an important boundary condition for reionization, and a key input for studies using the Ly $\alpha$ forest to constrain the masses of alternative dark matter candidates. Most such inferences rely on simulations that lack the spatial resolution to fully resolve the hydrodynamic response of IGM filaments and minihaloes to H i reionization heating. In this letter, we use high-resolution hydrodynamic + radiative transfer simulations to study how these affect the IGM thermal structure. We find that the adiabatic heating and cooling driven by the expansion of initially cold gas filaments and minihaloes sources significant small-scale temperature fluctuations. These likely persist in much of the IGM until $z \le 4$. Capturing this effect requires resolving the clumping scale of cold, pre-ionized gas, demanding spatial resolutions of ${\le} 2$ $h^{-1}$kpc. Pre-heating of the IGM by X-rays can slightly reduce the effect. Our preliminary estimate of the effect on the Ly $\alpha$ forest finds that, at $\log (k /[{\rm km^{-1} s}]) = -1.0$, the Ly $\alpha$ forest flux power (at fixed mean flux) can increase ${\approx} 10~{{\ \rm per\ cent}}$ going from 8 and 2 $h^{-1}$kpc resolution at $z = 4{\!-\!}5$ for gas ionized at $z \ \lt\ 7$. These findings motivate more careful analyses of how the effects studied here affect the Ly $\alpha$ forest.

Generation and Implementation of Continuum Infrared Pulses for Broadband Detection in 2D IR Spectroscopy.

In recent years, new methods of generating continuum mid-infrared pulses through filamentation in gases have been developed for ultrafast time-resolved infrared vibrational spectroscopy. The generated infrared pulses can have thousands of wavenumbers of bandwidth, spanning the entire mid-IR region while retaining pulse length below 100 fs. This technology has had a significant impact on problems involving ultrafast structural dynamics in congested spectra with broad features, such as those found in aqueous solutions and molecules with strong intermolecular interactions. This study describes the recent advances in generating and characterizing these pulses and the practical aspects of implementing these sources for broadband detection in transient absorption and 2D IR spectroscopy.