Mass Inflow Rate Research Articles

Signatures of Inflowing Gas in Red Geyser Galaxies Hosting Radio Active Galactic Nuclei

Abstract We study cool neutral gas traced by NaD absorption in 140 local (z < 0.1) early-type red geyser galaxies. These galaxies show unique signatures in spatially resolved strong line emission maps that have been interpreted as large-scale active galactic nucleus–driven ionized winds. To investigate the possible fuel source for these winds, we examine the abundance and kinematics of cool gas (T ∼ 100–1000 K) inferred from Na i D absorption in red geysers and matched control samples drawn from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. We find that red geysers host greater amounts of NaD-associated material. Substantial cool gas components are detected in more than 50% of red geysers (compared to 25% of the control sample) going up to 78% for radio-detected red geysers. Our key result is that cool gas in red geysers is predominantly infalling. Among our 30 radio-detected red geysers, 86% show receding NaD absorption velocities (with respect to the systemic velocity) between 40 and 50 km s−1. We verify this result by stacking NaD profiles across each sample, which confirms the presence of infalling NaD velocities within red geysers (∼40 km s−1) with no velocity offsets detected in the control samples. Interpreting our observations as signatures of inflowing cool neutral clouds, we derive an approximate mass inflow rate of M ̇ in ∼ 0.1 M ⊙ yr − 1 , similar to that expected from minor merging and internal recycling. Some red geysers show much higher rates ( M ̇ in ∼ 5 M ⊙ yr − 1 ), which may indicate an ongoing accretion event.

Analysis of static and dynamic characteristics of aerostatic bearing with reflux orifices

Purpose The purpose of this paper is to provide a solution for Reynolds equation with both throttling term and reverse throttling term and provides a reference for changing damping of hydrostatic bearing. Design/methodology/approach The reverse throttling term is introduced into the Reynolds equation, and the adaptive damping factor is used in the Newton iteration method to improve convergence of numerical calculations. The static and dynamic performances of this bearing are numerically investigated by the finite-element method. Findings The results indicate that the reflux orifices lead to a decrease in load capacity at a high eccentricity ratio. Additionally, the mass inflow rate is increased; however, the additional inflow increase can be controlled by enhanced backpressure of the reflux orifice. Nevertheless, the bearing with the reflux orifice shows superiority in resisting high-frequency disturbances and enhances direct damping by 20% under a high backpressure. Originality/value This work presents an adaptive Newton damping iterative method for solving Reynolds equation with both throttling term and reverse throttling term. This work also provides a new idea for bearing structure design in improving damping.

Star Formation in Nuclear Rings with the TIGRESS Framework

Abstract Nuclear rings are sites of intense star formation at the centers of barred galaxies. To understand what determines the structure and star formation rate (SFR; ) of nuclear rings, we run semi-global, hydrodynamic simulations of nuclear rings subject to constant mass inflow rates . We adopt the TIGRESS framework of Kim & Ostriker to handle radiative heating and cooling, star formation, and related supernova (SN) feedback. We find that the SN feedback is never strong enough to destroy the ring or quench star formation everywhere in the ring. Under the constant , the ring star formation is very steady and persistent, with the SFR exhibiting only mild temporal fluctuations. The ring SFR is tightly correlated with the inflow rate as , for a range of . Within the ring, vertical dynamical equilibrium is maintained, with the midplane pressure (powered by SN feedback) balancing the weight of the overlying gas. The SFR surface density is correlated nearly linearly with the midplane pressure, as predicted by the pressure-regulated, feedback-modulated star formation theory. Based on our results, we argue that the ring SFR is causally controlled by , while the ring gas mass adapts to the SFR to maintain the vertical dynamical equilibrium under the gravitational field arising from both gas and stars.

A study of the long-term activity of five intermediate polars with accretion discs

ABSTRACT Intermediate polars (IPs) are cataclysmic variables with mildly magnetized white dwarfs (WDs). This analysis of the long-term optical activity of five examples of IPs with accretion discs used data from the Catalina Real-time Transient Survey, Digital Access to a Sky Century @ Harvard (DASCH) and the American Association of Variable Star Observers (AAVSO). It is shown that each of these IPs had their most preferred value of absolute magnitude Mopt, even if it significantly varied on the superorbital time-scale. The values of Mopt of these IPs were in the zone of thermal-viscous instability (TVI) of the disc most of the time. The properties of a series of outbursts of V426 Oph can be explained by an intermittently operating TVI. The activity of TV Col and DW Cnc is interpreted as caused by a gradually variable mass inflow rate from the secondary to a cool disc. The mass transfer rate from the secondary varied on a well-determined time-scale. It is shown that Mopt of EI UMa, close to the peaks of outbursts of non-magnetic dwarf novae, fluctuated on the time-scale of days; it also produced short flares, ascribed to the bursts of matter from the donor. HY Leo, with a presumably cool disc, fluctuated between its high and low states. A temporary brightening from an extended low state is ascribed to a short, intense burst of matter from the donor to the remaining cool disc or torus.

Multi-transonic spherical-type flows around massive black holes: galactic potential induced standing isothermal shocks

Accretion on length-scales of interstellar or even intergalactic is particularly relevant, in the context of spherical or quasi-spherical hot mode accretion, supposedly powering low excitation radio galaxies in the maintenance-mode feedback paradigm. In the present study, we aim to analyze such a spherical-type flow around the host active nucleus in the backdrop of a five-component galactic system (SMBH, stellar, dark matter, diffuse hot gas, Λ), with the principal intent to address the issue of galactic potential induced shock formation in the flow, that may contain (dissipative) isothermal standing shocks. The present paper is an extension of Raychaudhuri et al. (2018) [83], who conducted a preliminary investigation of such a problem. The galactic potential, not only renders the flow to be multi-transonic in nature, the flow topology resembles `Xα' and `α X' type trajectories of advective flows in the vicinity of the BHs/compact objects. Owing to the influence of the galactic potential, the entire range of galactic mass-to-light ratio (ΥB) allows shock formation in central to the outer radial regions of our wind-type flows, with the strength of those galactic induced shocks found to be comparable to that of the shocks one would expect in the advective flows in the vicinity of a BH. We also observe that the shock parameters remain sensitive to ΥB. We discussed the possible implication of these shocks in the context of radio source dynamics as well as their potential association with flaring in radio jets. Our study also reveals that galactic potential could substantially augment the mass inflow rate.

Morphological and kinematical analysis of the double-barred galaxy NGC 3504 using ALMA CO (2–1) data

ABSTRACT We present results obtained from ALMA CO (2–1) data of the double-barred galaxy NGC 3504. With three times higher angular resolution (∼0${_{.}^{\prime\prime}}$8) than previous studies, our observations reveal an inner molecular gas bar, a nuclear ring, and four inner spiral arm-like structures in the central 1-kpc region. Furthermore, the CO emission is clearly aligned with the two dust lanes in the outer bar region, with differences in shape and intensity between them. The total molecular gas mass in the observed region (50 arcsec × 57 arcsec) is estimated to be ${\sim}3. 1\times 10^9 \, {\rm M}_{\odot }$, which is 17 per cent of the stellar mass. We used the Kinemetry package to fit the velocity field and found that circular motion strongly dominates at R = 0.3–0.8 kpc, but radial motion becomes important at R < 0.3 kpc and R = 1.0–2.5 kpc, which is expected due to the presence of the inner and outer bars. Finally, assuming that the gas moves along the dust lanes in the bar rotating frame, we derived the pattern speed of the outer bar to be 18 ± 5 km s−1 kpc−1, the average streaming velocities on each of the two dust lanes to be 165 and 221 km s−1, and the total mass inflow rate along the dust lanes to be $12\, {\rm M}_{\odot }$ yr−1. Our results give a new example of an inner gas bar within a gas-rich double-barred galaxy and suggest that the formation of double-barred galaxies could be associated with the existence of such gas structures.

A natural boundary of dark matter haloes revealed around the minimum bias and maximum infall locations

ABSTRACT We explore the boundary of dark matter haloes through their bias and velocity profiles. Using cosmological N-body simulations, we show that the bias profile exhibits a ubiquitous trough that can be interpreted as created by halo accretion that depletes material around the boundary. The inner edge of the active depletion region is marked by the location of the maximum mass inflow rate that separates a growing halo from the draining environment. This inner depletion radius can also be interpreted as the radius enclosing a highly complete population of splashback orbits, and matches the optimal exclusion radius in a halo model of the large-scale structure. The minimum of the bias trough defines a characteristic depletion radius, which is located within the infall region bounded by the inner depletion radius and the turnaround radius, while approaching the turnaround radius in low-mass haloes that have stopped mass accretion. The characteristic depletion radius depends the most on halo mass and environment. It is approximately 2.5 times the virial radius and encloses an average density of ∼40 times the background density of the universe, independent on halo mass but dependent on other halo properties. The inner depletion radius is smaller by 10–20 per cent and encloses an average density of ∼63 times the background density. These radii open a new window for studying the properties of haloes.

A proto-pseudobulge in ESO 320-G030 fed by a massive molecular inflow driven by a nuclear bar

Galaxies with nuclear bars are believed to efficiently drive gas inward, generating a nuclear starburst and possibly an active galactic nucleus. We confirm this scenario for the isolated, double-barred, luminous infrared galaxy ESO 320-G030 based on an analysis of Herschel and ALMA spectroscopic observations. Herschel/PACS and SPIRE observations of ESO 320-G030 show absorption or emission in 18 lines of H2O, which we combine with the ALMA H2O 423 − 330 448 GHz line (Eupper ∼ 400 K) and continuum images to study the physical properties of the nuclear region. Radiative transfer models indicate that three nuclear components are required to account for the multi-transition H2O and continuum data. An envelope, with radius R ∼ 130 − 150 pc, dust temperature Tdust ≈ 50 K, and NH2 ∼ 2 × 1023 cm−2, surrounds a nuclear disk with R ∼ 40 pc that is optically thick in the far-infrared (τ100 μm ∼ 1.5 − 3, NH2 ∼ 2 × 1024 cm−2). In addition, an extremely compact (R ∼ 12 pc), warm (≈100 K), and buried (τ100 μm > 5, NH2 ≳ 5 × 1024 cm−2) core component is required to account for the very high-lying H2O absorption lines. The three nuclear components account for 70% of the galaxy luminosity (SFR ∼ 16 − 18 M⊙ yr−1). The nucleus is fed by a molecular inflow observed in CO 2-1 with ALMA, which is associated with the nuclear bar. With decreasing radius (r = 450 − 225 pc), the mass inflow rate increases up to Ṁinf ∼ 20 Ṁ yr−1, which is similar to the nuclear star formation rate (SFR), indicating that the starburst is sustained by the inflow. At lower r, ∼100 − 150 pc, the inflow is best probed by the far-infrared OH ground-state doublets, with an estimated Ṁinf ∼ 30 Ṁ yr−1. The inferred short timescale of ∼20 Myr for nuclear gas replenishment indicates quick secular evolution, and indicates that we are witnessing an intermediate stage (< 100 Myr) proto-pseudobulge fed by a massive inflow that is driven by a strong nuclear bar. We also apply the H2O model to the Herschel far-infrared spectroscopic observations of H218O, OH, 18OH, OH+, H2O+, H3O+, NH, NH2, NH3, CH, CH+, 13CH+, HF, SH, and C3, and we estimate their abundances.

The dynamics of the broad-line region in NGC 3227

ABSTRACT Archival Hubble Space Telescope (HST) observations of the Seyfert 1 nucleus of NGC 3227 obtained with the Space Telescope Imaging Spectrograph (STIS) are re-examined in order to constrain a viable photoionization model for the broad-line region (BLR). The results imply that the BLR is a partially ionized, dust-free, spherical shell that is collapsing, supersonically, at the free-fall velocity due to its proximity to a supermassive black hole. The BLR is ionization bounded at the outer radius, coincident with the dust reverberation radius, and transforms into an X-ray emitting plasma inside the Balmer reverberation radius as the central UV–X-ray source is approached. Only 40 M⊙ of Hydrogen are required to explain the Balmer emission-line luminosity, but it is compressed by gravity into a column measuring 5.5 × 1024 atoms cm−2. Assuming radiatively inefficient accretion, the X-ray luminosity requires ∼10−2 M⊙ yr−1. However, the mass inflow rate required to explain the luminosity of the broad H α emission line is ∼1 M⊙ yr−1. The very large disparity between these two estimates indicates that 99 per cent of the inflowing gas must be re-directed into an outflow, and on a very short time-scale corresponding to ∼40 yr. Alternatively, the radiative efficiency of the inflow has been overestimated, or the X-ray luminosity has been underestimated, a distinct possibility if the BLR is indeed Compton-thick.

Periodically repeating fast radio bursts: Lense–Thirring precession of a debris disk?

Abstract Recently, repeating fast radio bursts (FRBs) with a period of PFRB = 16.35 ± 0.18 d from FRB 180916.J0158+65 were reported. It still remains controversial how such a periodicity might arise for this FRB. In this Letter, based on an assumption of a young pulsar surrounding by a debris disk, we attempt to diagnose whether Lense–Thirring precession of the disk on the emitter can produce the observed periodicity. Our calculations indicate that the Lense–Thirring effect of a tilted disk can result in a precession period of 16 d for a mass inflow rate of 0.5–1.5 × 1018 g s−1, a pulsar spin period of 1–20 ms, and an extremely low viscous parameter α = 10−8 in the disk. The disk mass and the magnetic field of the pulsar are also constrained to be ∼10−3 M⊙ and <2.5 × 1013 G. In our model, a new-born pulsar with normal magnetic field and millisecond period would successively experience the accretion and propeller phases, and is visible as a strong radio source in the current stage. The rotational energy of such a young neutron star can provide the observed radio bursting luminosity for 400 yr.

Experimental study on thermal hazard and facade flame characterization induced by incontrollable combustion of indoor energy usage

Abstract Fire accidents induced by indoor energy combustion occurred frequently and caused tremendous loss. This paper investigated the evolution laws of important fire risk parameters for quantitatively assessing the thermal hazard of room with triangular windows by reduced-scale experiments. The fire hazard was characterized by the risk parameters of hot gas temperature inside the room and facade flame height. Results show that the neutral plane position is hardly affected by total heat release rate of fire source, and it mainly depends on triangular opening height rather than base width. The ratios of neutral plane height above opening bottom to opening height are about 0.25, 0.25 and 0.61 for isosceles, right and inverted right triangular openings respectively. Based on theoretical derivation, an appropriate ventilation factor for triangular opening was defined to describe air mass inflow rate during under-ventilated condition. The hot gas temperature inside the room can be predicted based on the newly defined ventilation factor. Finally, a non-dimensional correlation was proposed to characterize facade flame height as a 0.53 power function of a normalized excess heat release rate. This work is of benefits to evaluate the fire hazard of buildings and then to provide calculation basis for building fire protection design.

On the Cooling Flow Problem in the Gaseous Halo of the Milky Way

Abstract Theoretical and observational arguments suggest that there is a large amount of hot (∼106 K) diffuse gas residing in the Milky Way (MW) halo, but its total mass and spatial distribution are still unclear. In this work, we present a general model for the gas density distribution in the Galactic halo, and investigate the gas evolution under radiative cooling with a series of 2D hydrodynamic simulations. We find that the mass inflow rate in the developed cooling flow increases with gas metallicity and the total gas mass in the halo. For a fixed halo gas mass, the spatial gas distribution affects the onset time of the cooling catastrophe, which starts earlier when the gas distribution is more centrally peaked, but does not substantially affect the final mass inflow rate. The gravity from the Galactic bulge and disk affects gas properties in the inner regions, but has little effect on the final inflow rate either. We confirm our results by investigating cooling flows in several density models adopted from the literature, including the Navarro–Frenk–White (NFW) model, the cored-NFW model, the Maller & Bullock model, and the β model. Typical mass inflow rates in our simulations range from ∼5 M ⊙ yr−1 to ∼60 M ⊙ yr−1, and are much higher than the observed star formation rate in our Galaxy, suggesting that stellar and active galactic nucleus feedback processes may play important roles in the evolution of the MW and MW-type galaxies.

Two-dimensional Inflow–Outflow Solution of Supercritical Accretion Flow

Abstract We present the two-dimensional inflow–outflow solutions of radiation hydrodynamic equations of supercritical accretion flows. Compared with prior studies, we include all components of the viscous stress tensor. We assume steady-state flow and use self-similar solutions in the radial direction to solve the equations in the r–θ domain of spherical coordinates. The set of differential equations have been integrated from the rotation axis to the equatorial plane. We find that the self-similarity assumption requires that the radial profile of density is described by ρ(r) ∝ r −0.5. Correspondingly, the radial profile of the mass inflow rate decreases with decreasing radius as . An inflow–outflow structure has been found in our solution. Inflow exists in the region θ > 65°, while above that the flow moves outward and outflow could launch. The driving forces of the outflow are analyzed and it is found that the radiation force is dominant and pushes the gas particles outward with poloidal velocity ∼0.25c. The properties of the outflow are also studied. The results show that the mass flux-weighted angular momentum of the inflow is lower than that of the outflow, thus the angular momentum of the flow can be transported by the outflow. We also analyze the convective stability of the supercritical disk and find that in the absence of a magnetic field, the flow is convectively unstable. Our analytical results are fully consistent with the previous numerical simulations of supercritical accretion flow.

Multi-scale analysis of the Monoceros OB 1 star-forming region

Context. We started a multi-scale analysis of star formation in G202.3+2.5, an intertwined filamentary sub-region of the Monoceros OB1 molecular complex, in order to provide observational constraints on current theories and models that attempt to explain star formation globally. In the first paper (Paper I), we examined the distributions of dense cores and protostars and found enhanced star formation activity in the junction region of the filaments. Aims. In this second paper, we aim to unveil the connections between the core and filament evolutions, and between the filament dynamics and the global evolution of the cloud. Methods. We characterise the gas dynamics and energy balance in different parts of G202.3+2.5 using infrared observations from the Herschel and WISE telescopes and molecular tracers observed with the IRAM 30-m and TRAO 14-m telescopes. The velocity field of the cloud is examined and velocity-coherent structures are identified, characterised, and put in perspective with the cloud environment. Results. Two main velocity components are revealed, well separated in radial velocities in the north and merged around the location of intense N2H+ emission in the centre of G202.3+2.5 where Paper I found the peak of star formation activity. We show that the relative position of the two components along the sightline, and the velocity gradient of the N2H+ emission imply that the components have been undergoing collision for ~105 yr, although it remains unclear whether the gas moves mainly along or across the filament axes. The dense gas where N2H+ is detected is interpreted as the compressed region between the two filaments, which corresponds to a high mass inflow rate of ~1 × 10−3 M⊙ yr−1 and possibly leads to a significant increase in its star formation efficiency. We identify a protostellar source in the junction region that possibly powers two crossed intermittent outflows. We show that the H II region around the nearby cluster NCG 2264 is still expanding and its role in the collision is examined. However, we cannot rule out the idea that the collision arises mostly from the global collapse of the cloud. Conclusions. The (sub-)filament-scale observables examined in this paper reveal a collision between G202.3+2.5 sub-structures and its probable role in feeding the cores in the junction region. To shed more light on this link between core and filament evolutions, one must characterise the cloud morphology, its fragmentation, and magnetic field, all at high resolution. We consider the role of the environment in this paper, but a larger-scale study of this region is now necessary to investigate the scenario of a global cloud collapse.

The Mass Inflow and Outflow Rates of the Milky Way

Abstract We present new calculations of the mass inflow and outflow rates around the Milky Way (MW), derived from a catalog of ultraviolet metal-line high-velocity clouds (HVCs). These calculations are conducted by transforming the HVC velocities into the Galactic standard of rest (GSR) reference frame, identifying inflowing (v GSR < 0 km s−1) and outflowing (v GSR > 0 km s−1) populations, and using observational constraints on the distance, metallicity, dust content, covering fractions, and total silicon column density of each population. After removing HVCs associated with the Magellanic Stream and the Fermi Bubbles, we find inflow and outflow rates in cool (T ∼ 104 K) ionized gas of dM in/dt ≳ (0.53 ± 0.23)(d/12 kpc)(Z/0.2Z ⊙)−1 M ⊙ yr−1 and dM out/dt ≳ (0.16 ± 0.07)(d/12 kpc)(Z/0.5Z ⊙)−1 M ⊙ yr−1. The apparent excess of inflowing over outflowing gas suggests that the MW is currently in an inflow-dominated phase, but the presence of substantial mass flux in both directions supports a Galactic fountain model, in which gas is constantly recycled between the disk and the halo. We also find that the metal flux in both directions (in and out) is indistinguishable. By comparing the outflow rate to the Galactic star formation rate, we present the first estimate of the mass loading factor (η HVC) of the disk-wide MW wind, finding η HVC ≳ (0.10 ± 0.06)(d/12 kpc)(Z/0.5Z ⊙)−1. Including the contributions from low- and intermediate-velocity clouds and from hot gas would increase these inflow and outflow estimates.

Diagnosing 0.1–10 au Scale Morphology of the FU Ori Disk Using ALMA and VLTI/GRAVITY

Abstract We report new Atacama Large Millimeter/submillimeter Array Band 3 (86–100 GHz; ∼80 mas angular resolution) and Band 4 (146–160 GHz; ∼50 mas angular resolution) observations of the dust continuum emission toward the archetypal and ongoing accretion burst young stellar object FU Ori, which simultaneously covered its companion, FU Ori S. In addition, we present near-infrared (2–2.45 μm) observations of FU Ori taken with the General Relativity Analysis via VLT InTerferometrY (GRAVITY; ∼1 mas angular resolution) instrument on the Very Large Telescope Interferometer (VLTI). We find that the emission in both FU Ori and FU Ori S at (sub)millimeter and near-infrared bands is dominated by structures inward of ∼10 au radii. We detected closure phases close to zero from FU Ori with VLTI/GRAVITY, which indicate the source is approximately centrally symmetric and therefore is likely viewed nearly face-on. Our simple model to fit the GRAVITY data shows that the inner 0.4 au radii of the FU Ori disk has a triangular spectral shape at 2–2.45 μm, which is consistent with the H2O and CO absorption features in a 10−4 M ⊙ yr−1, viscously heated accretion disk. At larger (∼0.4–10 au) radii, our analysis shows that viscous heating may also explain the observed (sub)millimeter and centimeter spectral energy distribution when we assume a constant, ∼10−4 M ⊙ yr−1 mass inflow rate in this region. This explains how the inner 0.4 au disk is replenished with mass at a modest rate, such that it neither depletes nor accumulates significant masses over its short dynamic timescale. Finally, we tentatively detect evidence of vertical dust settling in the inner 10 au of the FU Ori disk, but confirmation requires more complete spectral sampling in the centimeter bands.

Hot Accretion Flow in Two-Dimensional Spherical Coordinates: Considering Pressure Anisotropy and Magnetic Field

For systems with extremely low accretion rate, such as Galactic Center Sgr A* and M87 galaxy, the ion collisional mean free path can be considerably larger than its Larmor radius. In this case, the gas pressure is anisotropic to magnetic field lines. In this paper, we pay attention to how the properties of outflow change with the strength of anisotropic pressure and the magnetic field. We use an anisotropic viscosity to model the anisotropic pressure. We solve the two-dimensional magnetohydrodynamic (MHD) equations in spherical coordinates and assume that the accretion flow is radially self-similar. We find that the work done by anisotropic pressure can heat the accretion flow. The gas temperature is heightened when anisotropic stress is included. The outflow velocity increases with the enhancement of strength of the anisotropic force. The Bernoulli parameter does not change much when anisotropic pressure is involved. However, we find that the energy flux of outflow can be increased by a factor of 20 in the presence of anisotropic stress. We find strong wind (the mass outflow is about 70% of the mass inflow rate) is formed when a relatively strong magnetic field is present. Outflows from an active galactic nucleus can interact with gas in its host galaxies. Our result predicts that outflow feedback effects can be enhanced significantly when anisotropic pressure and a relatively powerful magnetic field is considered.

Cooling flow solutions for the circumgalactic medium

ABSTRACT In several models of galaxy formation feedback occurs in cycles or mainly at high redshift. At times and in regions where feedback heating is ineffective, hot gas in the galaxy halo is expected to form a cooling flow, where the gas advects inward on a cooling timescale. Cooling flow solutions can thus be used as a benchmark for observations and simulations to constrain the timing and extent of feedback heating. Using analytic calculations and idealized 3D hydrodynamic simulations, we show that for a given halo mass and cooling function, steady-state cooling flows form a single-parameter family of solutions, while initially hydrostatic gaseous haloes converge on one of these solutions within a cooling time. The solution is thus fully determined once either the mass inflow rate ${\dot{M}}$ or the total halo gas mass are known. In the Milky Way halo, a cooling flow with ${\dot{M}}$ equal to the star formation rate predicts a ratio of the cooling time to the free-fall time of ∼10, similar to some feedback-regulated models. This solution also correctly predicts observed $\rm{O\,{\small VII}}$ and $\rm{O\,{\small VIII}}$ absorption columns, and the gas density profile implied by $\rm{O\,{\small VII}}$ and $\rm{O\,{\small VIII}}$ emission. These results suggest ongoing heating by feedback may be negligible in the inner Milky-Way halo. Extending similar solutions out to the cooling radius however underpredicts observed $\rm{O\,{\small VI}}$ columns around the Milky-Way and around other low-redshift star-forming galaxies. This can be reconciled with the successes of the cooling flow model with either a mechanism which preferentially heats the $\rm{O\,{\small VI}}$-bearing outer halo, or alternatively if $\rm{O\,{\small VI}}$ traces cool photoionized gas beyond the accretion shock. We also demonstrate that the entropy profiles of some of the most relaxed clusters are reasonably well described by a cooling flow solution.

Multi-line Herschel/HIFI observations of water reveal infall motions and chemical segregation around high-mass protostars

Context. The physical conditions during high-mass star formation are poorly understood. Outflow and infall motions have been detected around massive protostellar objects, but their dependence on mass, luminosity, and age is unclear. In addition, physical conditions and molecular abundances are often estimated using simple assumptions such as spherical shape and chemical homogeneity, which may limit the accuracy of the results. Aims. We aim to characterize the dust and gas distribution and kinematics of the envelopes of high-mass protostars. In particular, we search for infall motions, abundance variations, and deviations from spherical symmetry, using Herschel data from the WISH program. Methods. We used HIFI maps of the 987 GHz H2O 202–111 emission to measure the sizes and shapes of 19 high-mass protostellar envelopes. To identify infall, we used HIFI spectra of the optically thin C18O 9–8 and H218O 111–000 lines. The high-J C18O line traces the warm central material and redshifted H218O 111–000 absorption indicates material falling onto the warm core. We probe small-scale chemical differentiation by comparing H2O 752 and 987 GHz spectra with those of H218O. Results. Our measured radii of the central part of the H2O 202–111 emission are 30–40% larger than the predictions from spherical envelope models, and axis ratios are <2, which we consider good agreement. For 11 of the 19 sources, we find a significant redshift of the H218O 111–000 line relative to C18O 9–8. The inferred infall velocities are 0.6–3.2 km s−1, and estimated mass inflow rates range from 7 × 10−5 to 2 × 10−2 M⊙ yr−1. The highest mass inflow rates seem to occur toward the sources with the highest masses, and possibly the youngest ages. The other sources show either expanding motions or H218O lines in emission. The H218O 111–000 line profiles are remarkably similar to the differences between the H2O 202–111 and 211–202 profiles, suggesting that the H218O line and the H2O 202–111 absorption originate just inside the radius where water evaporates from grains, typically 1000–5000 au from the center. In some sources, the H218O line is detectable in the outflow, where no C18O emission is seen. Conclusions. Together, the H218O absorption and C18O emission profiles show that the water abundance around high-mass protostars has at least three levels: low in the cool outer envelope, high within the 100 K radius, and very high in the outflowing gas. Thus, despite the small regions, the combination of lines presented in this work reveals systematic inflows and chemical information about the outflows.

How Gas Accretion Feeds Galactic Disks

Abstract Numerous observations indicate that galaxies need a continuous gas supply to fuel star formation and explain the star formation history. However, direct observational evidence of gas accretion remains rare. Using the EAGLE cosmological hydrodynamic simulation suite, we study cold gas accretion onto galaxies and the observational signatures of the cold gas kinematics. For EAGLE galaxies at z = 0.27, we find that cold gas accretes onto galaxies anisotropically with typical inflow speeds between 20 and 60 km s−1. Most of these galaxies have comparable mass inflow rates and star formation rates, implying that the cold inflowing gas plausibly accounts for sustaining the star-forming activities of the galaxies. As motivation for future work to compare the cold gas kinematics with measurements from quasar sightline observations, we select an EAGLE galaxy with an extended cold gas disk, and we probe the cold gas using mock quasar sightlines. We demonstrate that by viewing the disk edge on, sightlines at azimuthal angles below 10° and impact parameters out to 60 pkpc can detect cold gas that corotates with the galaxy disk. This example suggests that cold gas disks extending beyond the optical disks possibly explain the sightline observations that detect corotating cold gas near galaxy major axes.