Gas Accretion Rate Research Articles

The VANDELS Survey: Star formation and quenching in two over-densities at 3<z<4

Exploring galaxy evolution in dense environments, such as proto-clusters, is pivotal for understanding the mechanisms that drive star formation and the quenching of star formation. This study provides insights into how two over-densities could have impacted the physical properties, such as the star formation rate, stellar mass, morphology, and the evolution of their members, particularly members characterised by a quenching of star formation. We focus on the over-densities identified at $3<z<4$ in the Chandra Deep Field South (CDFS) and in the Ultra Deep Survey (UDS) regions of the VIMOS (VIsible MultiObject Spectrograph) Ultra Deep Survey (VANDELS). Our methodology involves the analysis of the spectral energy distribution of the members of the over-densities and of the galaxies in the field. We relied on Bayesian analysis techniques BEAGLE and BAGPIPES to study the best-fit physical parameters and the rest-frame U-V and V-J colours (UVJ). This approach allowed us to separate quenched and star-forming galaxies based on the UVJ diagram and by estimating their specific star formation rate (sSFR). We used the TNG300 simulation to interpret our results. We find that two out of 13 over-densities host quenched galaxies, with red rest-frame U-V colour and low sSFR. The physical properties of them are consistent with those of massive passive galaxies from the literature. The quenched members are redder, older, more massive, and show a more compact morphology than the other galaxy members. The two over-densities, with the highest-density peaks at $z and $z respectively, have dark matter halo masses consistent with being proto-clusters at $z and they each host an active galactic nucleus (AGN). We found five AGNs in the structure at $z and three AGNs in the one at $z In comparison to quenched galaxies in the field, our massive quenched members show a higher local density environment. By using the IllustrisTNG simulation (TNG300), we find that proto-cluster structures with quenched galaxies at high redshift are likely to evolve into a structure with a higher fraction of passive galaxies by $z = The two over-densities studied here host massive quenched galaxies in their highest-density peaks and AGNs. By following the evolution of the passive galaxies in the simulated proto-clusters at $z = 3$ from the TNG300 simulation, we find that the median of their sSFRs was larger than 10$^ $ yr$^ $ at $z=6$ and the median mass growth rate was 96<!PCT!> from $z=6$ to $z=3$. In 20<!PCT!> of the simulated proto-clusters, the passive galaxy had already accreted 10-20<!PCT!> of the mass at $z=6$, with SFRs $>100$ M$_ odot $ yr$^ $ at $z=8$. The conditions for this favorable mass assembly could be the galaxy interactions and the high gas accretion rate in the dense environment. As a consequence, the quenching of the star formation at $z=3$ could be driven by the black hole mass growth and AGN feedback. This scenario is consistent with the properties of the two quenched galaxies we find in our two over-densities at $z sim3$.

Magnetized Accretion onto and Feedback from Supermassive Black Holes in Elliptical Galaxies

We present 3D magnetohydrodynamic simulations of the fueling of supermassive black holes in elliptical galaxies from a turbulent cooling medium on galactic scales, taking M87* as a typical case. We find that the mass accretion rate is increased by a factor of ∼10 compared with analogous hydrodynamic simulations. The scaling of Ṁ∼r1/2 roughly holds from ∼10 pc to ∼10−3 pc (∼10 r g) with the accretion rate through the event horizon being ∼10−2 M ⊙ yr−1. The accretion flow on scales ∼0.03–3 kpc takes the form of magnetized filaments. Within ∼30 pc, the cold gas circularizes, forming a highly magnetized (β ∼ 10−3) thick disk supported by a primarily toroidal magnetic field. The cold disk is truncated and transitions to a turbulent hot accretion flow at ∼0.3 pc (103 r g). There are strong outflows toward the poles driven by the magnetic field. The outflow energy flux increases with smaller accretor size, reaching ∼3 × 1043 erg s−1 for r in = 8 r g; this corresponds to a nearly constant energy feedback efficiency of η ∼ 0.05–0.1 independent of accretor size. The feedback energy is enough to balance the total cooling of the M87/Virgo hot halo out to ∼50 kpc. The accreted magnetic flux at small radii is similar to that in magnetically arrested disk models, consistent with the formation of a powerful jet on horizon scales in M87. Our results motivate a subgrid model for accretion in lower-resolution simulations in which the hot gas accretion rate is suppressed relative to the Bondi rate by ∼(10rg/rB)1/2 .

Towards a universal analytical model for Population III star formation: interplay between feedback and fragmentation

ABSTRACT JWST has brought us new insights into Cosmic Dawn with tentative detection of the unique signatures of metal-free Population III (Pop III) stars, such as strong He II emission, extremely blue ultraviolet spectrum, and enhanced nitrogen abundance. Self-consistent theoretical predictions of the formation rates, sites, and masses of Pop III stars are crucial for interpreting the observations, but are challenging due to complex physical processes operating over the large range of length-scales involved. One solution is to combine analytical models for the small-scale star formation process with cosmological simulations that capture the large-scale physics such as structure formation, radiation backgrounds, and baryon-dark matter streaming motion that regulate the conditions of Pop III star formation. We build an analytical model to predict the final masses of Pop III stars/clusters from the properties of star-forming clouds, based on the key results of small-scale star formation simulations and stellar evolution models. Our model for the first time considers the interplay between feedback and fragmentation and covers different modes of Pop III star formation ranging from ordinary small ($\sim\!{10{-}2000}\ \rm M_\odot$) clusters in molecular-cooling clouds to massive ($\gtrsim\!{10^{4}}\ \rm M_\odot$) clusters containing supermassive ($\sim\!{10^{4}{-}3}\times 10^{5}\ \rm M_\odot$) stars under violent collapse of atomic-cooling clouds with large gas accretion rates of $\gtrsim\!{0.1}\ \rm M_\odot \ yr^{-1}$. As an example, the model is applied to the Pop III star-forming clouds in the progenitors of typical haloes hosting high-z luminous quasars ($M_{\rm h}\sim 10^{12}\ \rm M_\odot$ at $z\sim 6$), which shows that formation of Pop III massive clusters is common ($\sim\!{20{-}70}{{\ \rm per\ cent}}$) in such biased ($\sim\!{4}\sigma$) regions, and the resulting heavy black hole seeds from supermassive stars can account for a significant fraction of observed luminous ($\gtrsim\!{10^{46}}\ \rm erg\ s^{-1}$) quasars at $z\sim 6$.

Entrainment of hot gas into cold streams: the origin of excessive star formation rates at cosmic noon

ABSTRACT We explore the evolution of cold streams from the cosmic web that feed galaxies through their shock-heated circumgalactic medium (CGM) at cosmic noon, $z\simeq 1-5$. In addition to the hydrodynamical instabilities and radiative cooling that we have incorporated in earlier works, we embed the stream and the hot CGM in the gravitational potential of the host dark matter halo, deriving equilibrium profiles for both. Self-gravity within the stream is tentatively ignored. We find that the cold streams gradually entrain a large mass of initially hot CGM gas that cools in the mixing layer and condenses onto the stream. This entrainment, combined with the acceleration down the gravitational potential well, typically triples the inward cold inflow rate into the central galaxy, compared to the original rate at the virial radius, which makes the entrained gas the dominant source of gas supply to the galaxy. The potential sources for the hot gas to be entrained are recycled enriched gas that has been previously ejected from the galaxy, and fresh virial-shock-heated gas that has accumulated in the CGM. This can naturally elevate the star formation rate in the galaxy by a factor of $\sim 3$ compared to the gas accretion rate onto the halo, thus explaining the otherwise puzzling observed excess of star formation at cosmic noon. When accounting for self-shielding of dense gas from the ultraviolet background, we find that the energy radiated from the streams, originating predominantly from the cooling of the entrained gas, is consistent with observed Lyman-$\alpha$ blobs around galaxies.

Constraints on PDS 70 b and c from the dust continuum emission of the circumplanetary discs considering in situ dust evolution

Context. The young T Tauri star PDS 70 has two gas accreting planets sharing one large gap in a pre-transitional disc. Dust continuum emission from PDS 70 c has been detected by Atacama Large Millimeter/submillimeter Array (ALMA) Band 7, considered as the evidence of a circumplanetary disc. However, there has been no detection of the dust emission from the CPD of PDS 70 b. Aims. We constrain the planet mass and the gas accretion rate of the planets by introducing a model of dust evolution in the CPDs and reproducing the detection and non-detection of the dust emission. Methods. We first develop a 1D steady gas disc model of the CPDs reflecting the planet properties. We then calculate the radial distribution of the dust profiles considering the dust evolution in the gas disc and calculate the total flux density of dust thermal emission from the CPDs. Results. We find positive correlations between the flux density of dust emission and three planet properties, the planet mass, gas accretion rate, and their product called ‘MMdot’. We then find that the MMdot of PDS 70 c is ≥4 × 10−7 MJ2 yr−1, corresponding to the planet mass of ≥5 MJ and the gas accretion rate of ≥2 × 10−8 MJ yr−1. This is the first case to succeed in obtaining constraints on planet properties from the flux density of dust continuum emission from a CPD. We also find some loose constraints on the properties of PDS 70 b from the non-detection of its dust emission. Conclusions. We propose possible scenarios for PDS 70 b and c explaining the non-detection respectively detection of the dust emission from their CPDs. The first explanation is that planet c has larger planet mass, larger gas accretion rate, or both than planet b. The other possibility is that the CPD of planet c has a larger amount of dust supply, weaker turbulence, or both than that of planet b. If the dust supply to planet c is larger than b due to its closeness to the outer dust ring, it is also quantitatively consistent with that planet c has weaker Hα line emission than planet b considering the dust extinction effect.

Accretion of primordial H–He atmospheres in mini-Neptunes: The importance of envelope enrichment

Context. Out of the more than 5000 detected exoplanets, a considerable number belong to a category called “mini-Neptunes”. Interior models of these planets suggest that they have primordial H–He-dominated atmospheres. As this type of planet is not found in the Solar System, understanding their formation is a key challenge in planet formation theory. Unfortunately, quantifying how much H–He planets have, based on their observed mass and radius, is impossible due to the degeneracy of interior models. Aims. Another approach to estimating the range of possible primordial envelope masses is to use formation theory. As different assumptions in planet formation can heavily influence the nebular gas accretion rate of small planets, it is unclear how large the envelope of a protoplanet should be. We explore the effects that different assumptions regarding planet formation have on the nebular gas accretion rate, particularly by exploring the way in which solid material interacts with the envelope. This allows us to estimate the range of possible post-formation primordial envelopes. Thereby, we demonstrate the impact of envelope enrichment on the initial primordial envelope, which can be used in evolution models. Methods. We applied formation models that include different solid accretion rate prescriptions. Our assumption is that mini-Neptunes form beyond the ice line and migrate inward after formation; thus, we formed planets in situ at 3 and 5 au. We considered that the envelope can be enriched by the accreted solids in the form of water. We studied how different assumptions and parameters influence the ratio between the planet’s total mass and the fraction of primordial gas. Results. The primordial envelope fractions for low- and intermediate-mass planets (total mass below 15 M⊕) can range from 0.1% to 50%. Envelope enrichment can lead to higher primordial mass fractions. We find that the solid accretion rate timescale has the largest influence on the primordial envelope size. Conclusions. Rates of primordial gas accretion onto small planets can span many orders of magnitude. Planet formation models need to use a self-consistent gas accretion prescription.

On the origin of outward migration of Population III stars

ABSTRACT Outward migration of massive binary stars or black holes in their circumbinary disc is often observed in simulations and it is key to the formation of wide black hole binaries. Using numerical simulations of Population III (Pop III) star formation, we study the angular momentum of Pop III binaries and the torques between stars and gas discs to understand the origin of outward migration and high ellipticity. The outward migration of protostars is produced by gravitational torques exerted on them by their circumstellar minidiscs. The minidiscs, on the other hand, migrate outward mainly by gaining angular momentum by accreting gas from the circumbinary disc. The angular momentum transfer is most efficient for rapidly accreting equal-mass binaries, and weaker when the secondary mass is small or the massive companion evaporates the gas disc via radiative feedback. We conclude that outward migration and the formation of wide equal-mass massive binaries is common in metal-free/metal-poor star formation, mainly driven by their large accretion rates. We expect that the lower gas temperature and accretion rates in metal-enriched circumstellar discs would lead more often to inward migration and closer binary separations. We also observe inward migration for smaller mass Pop III protostars/fragments, leading to the rapid merging of sink particles and likely the formation of close binary black holes that, however, reach separations below the resolution of our simulations. We discuss the implications that Pop III separations and ellipticity may have on the interpretation that gravitational wave signals from merging intermediate-mass black holes come from Pop III remnants.

On bursty star formation during cosmological reionisation – how does it influence the baryon mass content of dark matter halos?

Abstract The baryon mass content (i.e. stellar and gas mass) of dark matter halos in the early Universe depends on both global factors – for example, ionising ultraviolet (UV) radiation background – and local factors – for example, star formation efficiency and assembly history. We use a lightweight semi-analytical model to investigate how both local and global factors impact the halo baryon mass content at redshifts of $z\geq 5$ . Our model incorporates a time delay between when stars form and when they produce feedback of $0\leq t^d/\mathrm{Myr} \leq 30$ , which can drive bursts of star formation, and a mass and redshift-dependent UV background, which captures the influence of cosmological reionisation on gas accretion onto halos. We use statistically representative halo assembly histories and assume that the cosmological gas accretion rate is proportional to the halo mass accretion rate. Delayed ( $t^d$ >0) feedback leads to oscillations in gas mass with cosmic time, behaviour that cannot be captured with instantaneous feedback ( $t^d$ =0). Highly efficient star formation drives stronger oscillations, while strong feedback impacts when oscillations occur; in contrast, inefficient star formation and weak feedback produce similar long-term behaviour to that observed in instantaneous feedback models. If the delayed feedback timescale is too long, a halo retains its gas reservoir but the feedback suppresses star formation. Our model predicts that lower mass systems (halo masses $m_\mathrm{h} \leq 10^7 \mathrm{M}_\odot$ ) at $z \leq 10$ should be strongly gas deficient ( $m_\mathrm{g}\rightarrow 0$ ), whereas higher mass systems retain their gas reservoirs because they are sufficiently massive to continue accreting gas through cosmological reionisation. Interestingly, in higher mass halos, the median $m_\star/(m_\star+m_\mathrm{g}) \simeq 0.01-0.05$ , but is a factor of 3–5 smaller when feedback is delayed. Our model does not include seed supermassive black hole feedback, which is necessary to explain massive quenched galaxies in the early Universe.

The impact of gas accretion and AGN feedback on the scatter of the mass–metallicity relation

ABSTRACT The gas-phase metallicity of galaxies encodes important information about galaxy evolution processes, in particular star formation, feedback, outflows, and gas accretion, the relative importance of which can be extracted from systematic trends in the scatter of the mass–metallicity relation (MZR). Here, we use a sample of low-redshift (0.02 < z < 0.055) galaxies from SDSS to investigate the nature of the scatter around the MZR, the observables and physical processes causing it, and its dependence on galaxy mass. We use cold gas masses inferred from optical emission lines using the technique of Scholte & Saintonge (2023) to confirm that at fixed stellar mass, metallicity and gas mass are anticorrelated, but only for galaxies up to M* = 1010.5 M⊙. In that mass regime, we find a link between the offset of a galaxy from the MZR and halo mass, using the amplitude of the two-point correlation function as a proxy for halo mass; at fixed stellar mass, the most gas-poor galaxies reside in the most massive haloes. This observation is consistent with changes in gas accretion rates onto galaxies as a function of halo mass, with environmental effects acting on satellite galaxies also contributing. At higher stellar masses, the scatter of the MZR does no longer correlate with gas or halo mass. Instead, there is some indication of a link with AGN activity, as expected from models and simulations that metallicity is set by the interplay between gas in- and outflows, star formation, and AGN feedback, shaping the MZR and its scatter.

The Gas Accretion Rate of Galaxies over z ≈ 0–1.3

We present here estimates of the average rates of accretion of neutral gas onto main-sequence galaxies and the conversion of atomic gas to molecular gas in these galaxies at two key epochs in galaxy evolution: (i) z ≈ 1.3–1.0, toward the end of the epoch of peak star formation activity in the Universe, and (ii) z ≈ 1–0, when the star formation activity declines by an order of magnitude. We determine the net gas accretion rate R Acc and the molecular gas formation rate R Mol by combining the relations between the stellar mass and the atomic gas mass, the molecular gas mass, and the star formation rate (SFR) at three epochs, z = 1.3, z = 1.0, and z = 0, with the assumption that galaxies evolve continuously on the star-forming main sequence. We find that, for all galaxies, R Acc is far lower than the average SFR R SFR at z ≈ 1.3–1.0; however, R Mol is similar to R SFR during this interval. Conversely, both R Mol and R Acc are significantly lower than R SFR over the later interval, z ≈ 1–0. We find that massive main-sequence galaxies had already acquired most of their present-day baryonic mass by z ≈ 1.3. At z ≈ 1.3–1.0, the rapid conversion of the existing atomic gas to molecular gas was sufficient to maintain a high average SFR, despite the low net gas accretion rate. However, at later times, the combination of the lower net gas accretion rate and the lower molecular gas formation rate leads to a decline in the fuel available for star formation and results in the observed decrease in the SFR density of the Universe over the last 8 Gyr.

Formation of giant planets around intermediate-mass stars

ABSTRACT To understand giant planet formation, we need to focus on host stars close to $M_{\star }{=}1.7\, \rm M_\odot$, where the occurrence rate of these planets is the highest. In this initial study, we carry out pebble-driven core accretion planet formation modelling to investigate the trends and optimal conditions for the formation of giant planets around host stars in the range of $1\!-\!2.4\ \rm {\rm M}_{\odot }$. We find that giant planets are more likely to form in systems with a larger initial disc radius; higher disc gas accretion rate; pebbles of ∼millimeter in size; and birth location of the embryo at a moderate radial distance of ∼10 au. We also conduct a population synthesis study of our model and find that the frequency of giant planets and super-Earths decreases with increasing stellar mass. This contrasts the observational peak at $1.7\, \rm M_\odot$, stressing the need for strong assumptions on stellar mass dependencies in this range. Investigating the combined effect of stellar mass dependent disc masses, sizes, and lifetimes in the context of planet population synthesis studies is a promising avenue to alleviate this discrepancy. The hot-Jupiter occurrence rate in our models is $\sim 0.7\!-\!0.8~{{\ \rm per\ cent}}$ around $1\, \rm M_\odot$ – similar to RV observations around Sun-like stars, but drastically decreases for higher mass stars.

The Gas Accretion Rate of Star-forming Galaxies over the Last 4 Gyr

Star-forming galaxies are believed to replenish their atomic gas reservoir, which is consumed in star formation, through accretion of gas from their circumgalactic mediums (CGMs). However, there are few observational constraints today on the gas accretion rate in external galaxies. Here, we use our recent measurement of the scaling relation between the atomic hydrogen (H i) mass M H I and the stellar mass M * in star-forming galaxies at z ≈ 0.35, with the relations between the star formation rate (SFR) and M *, and the molecular gas mass M Mol and M *, and the assumption that star-forming galaxies evolve along the main sequence, to determine the evolution of the neutral gas reservoir and the average net gas accretion rate onto the disks of star-forming galaxies over the past 4 Gyr. For galaxies with M * ≳ 109 M ⊙ today, we find that both M * and M H I in the disk have increased, while M Mol has decreased, since z ≈ 0.35. The average gas accretion rate onto the disk over the past 4 Gyr is similar to the average SFR over this period, implying that main-sequence galaxies have maintained a stable H i reservoir, despite the consumption of gas in star formation. We obtain an average net gas accretion rate (over the past 4 Gyr) of ≈6 M ⊙ yr−1 for galaxies with the stellar mass of the Milky Way. At low redshifts, z ≲ 0.4, the reason for the decline in the cosmic SFR density thus appears to be the inefficiency in the conversion of atomic gas to molecular gas, rather than insufficient gas accretion from the CGM.

Measuring the physical imprints of gas flows in galaxies

Context. Galaxies are expected to accrete pristine gas from their surroundings to sustain their star formation over cosmic timescales. This mechanism is well established in models and simulations, but evidence from observations is mostly indirect. These gas inflows leave distinct traces in the chemical composition of newborn stars and alter the distribution of stellar abundances compared to what would be expected from a closed-box model of chemical evolution. Aims. The goal of this work is to measure the amount of pristine gas that galaxies accrete during their lifetime, using information on the ages and abundances of their stellar populations and a chemical evolution model. We also aim to determine the efficiency of star formation over time. Methods. We derived star formation histories and metallicity histories for a sample of 8523 galaxies from the MaNGA survey. We use the former to predict the evolution of the metallicity in a closed-box scenario, and estimate for each epoch the gas accretion rate required to match these predictions with the measured stellar metallicity. Results. Using only chemical parameters, we find that the history of gas accretion depends on the mass of galaxies. More massive galaxies accrete more gas and at higher redshifts than less massive galaxies, which accrete their gas over longer periods. We also find that galaxies with a higher star formation rate at z = 0 have a more persistent accretion history for a given mass. We characterize the individual accretion histories in terms of two parameters: the total accreted gas mass and the 80 of the accretion history, a measure of when most of the accretion occurred. As expected, there is a strong correlation between the integrated star formation history and the total accreted gas mass, such that more massive galaxies accreted more gas during their lifetime. Currently star-forming galaxies lie above this correlation, so they tend to accrete more gas than average. The relationship between 80, the current stellar mass, and the current specific star formation rate is split such that star-forming galaxies (as now observed) may be found in a population with persistent gas accretion regardless of their stellar mass. The star formation efficiency shows similar correlations: early-type galaxies and higher-mass galaxies had a higher efficiency in the past, and it declined such that they are less efficient in the present. Our analysis of individual galaxies shows that compactness affects the peak star formation efficiency that galaxies reach, and that the slope of the efficiency history of galaxies with current star formation is flat. Conclusions. We show throughout the article that we can obtain information about the processes that regulate the chemical composition of the interstellar medium during the lifetime of a galaxy from the properties of stellar populations. Our results support the hypothesis that a steady and substantial supply of pristine gas is required for persistent star formation in galaxies. Once they lose access to this gas supply, star formation comes to a halt.

The correlation between the 500 pc scale molecular gas masses and AGN powers for massive elliptical galaxies

Abstract Massive molecular clouds have been discovered in massive elliptical galaxies at the center of galaxy clusters. Some of this cold gas is expected to flow in the central supermassive black holes and activate galactic nucleus (AGN) feedback. In this study, we analyze archival Atacama Large Millimeter Array (ALMA) data of nine massive elliptical galaxies, focusing on CO line emissions, to explore the circumnuclear gas. We show that the mass of the molecular gas within a fixed radius (500 pc) from the AGNs (Mmol ∼ 107–108 M⊙) is correlated with the jet power estimated from X-ray cavities (Pcav ∼ 1042–1045 erg s−1). The mass accretion rate of the circumnuclear gas $\dot{M}$ also has a correlation with Pcav. On the other hand, the continuum luminosities at ∼1.4 GHz and ∼100–300 GHz have no correlation with Mmol. These results indicate that the circumnuclear gas is sustaining the long-term AGN activities (∼107 yr) rather than the current ones. The circumnuclear gas mass is a better indicator of the jet power than the continuum luminosity, which probably changes on a shorter time scale. We also study the origin of the continuum emission from the AGNs at ∼100–300 GHz and find that it is mostly synchrotron radiation. For low-luminosity AGNs, however, dust emission appears to contaminate the continuum.

The maximum accretion rate of a protoplanet: how fast can runaway be?

ABSTRACT The hunt is on for dozens of protoplanets hypothesized to reside in protoplanetary discs with imaged gaps. How bright these planets are, and what they will grow to become, depend on their accretion rates, which may be in the runaway regime. Using 3D global simulations, we calculate maximum gas accretion rates for planet masses Mp from 1$\, \mathrm{ M}_{{\oplus }}$ to $10\, \mathrm{ M}_{\rm J}$. When the planet is small enough that its sphere of influence is fully embedded in the disc, with a Bondi radius rBondi smaller than the disc’s scale height Hp – such planets have thermal mass parameters qth ≡ (Mp/M⋆)/(Hp/Rp)3 ≲ 0.3, for host stellar mass M⋆ and orbital radius Rp – the maximum accretion rate follows a Bondi scaling, with $\max \dot{M}_{\rm p} \propto \rho _{\rm g}M_{\rm p}^2 / (H_{\rm p}/R_{\rm p})^3$ for ambient disc density ρg. For more massive planets with 0.3 ≲ qth ≲ 10, the Hill sphere replaces the Bondi sphere as the gravitational sphere of influence, and $\max \dot{M}_{\rm p} \propto \rho _{\rm g}M_{\rm p}^1$, with no dependence on Hp/Rp. In the strongly superthermal limit when qth ≳ 10, the Hill sphere pops well out of the disc, and $\max \dot{M}_{\rm p} \propto \rho _{\rm g}M_{\rm p}^{2/3} (H_{\rm p}/R_{\rm p})^1$. Applied to the two confirmed protoplanets PDS 70b and c, our numerically calibrated maximum accretion rates imply that their Jupiter-like masses may increase by up to a factor of ∼2 before their parent disc dissipates.

Galactic coronae in Milky Way-like galaxies: the role of stellar feedback in gas accretion

ABSTRACT Star-forming galaxies like the Milky Way are surrounded by a hot gaseous halo at the virial temperature – the so-called galactic corona – that plays a fundamental role in their evolution. The interaction between the disc and the corona has been shown to have a direct impact on accretion of coronal gas onto the disc with major implications for galaxy evolution. In this work, we study the gas circulation between the disc and the corona of star-forming galaxies like the Milky Way. We use high-resolution hydrodynamical N-body simulations of a Milky Way-like galaxy with the inclusion of an observationally motivated galactic corona. In doing so, we use SMUGGLE, an explicit interstellar medium (ISM), and stellar feedback model coupled with the moving-mesh code arepo. We find that the reservoir of gas in the galactic corona is sustaining star formation: the gas accreted from the corona is the primary fuel for the formation of new stars, helping in maintaining a nearly constant level of cold gas mass in the galactic disc. Stellar feedback generates a gas circulation between the disc and the corona (the so-called galactic fountain) by ejecting different gas phases that are eventually re-accreted onto the disc. The accretion of coronal gas is promoted by its mixing with the galactic fountains at the disc–corona interface, causing the formation of intermediate temperature gas that enhances the cooling of the hot corona. We find that this process acts as a positive feedback mechanism, increasing the accretion rate of coronal gas onto the galaxy.

Giants are bullies: How their growth influences systems of inner sub-Neptunes and super-Earths

Observational evidence points to an unexpected correlation between outer giant planets and inner sub-Neptunes, which has remained unexplained by simulations so far. We utilize N-body simulations including pebble and gas accretion as well as planetary migration to investigate how the gas accretion rates, which depend on the envelope opacity and the core mass, influence the formation of systems of inner sub-Neptunes and outer gas giants as well as the eccentricity distribution of the outer giant planets. We find that less efficient envelope contraction rates allow for a more efficient formation of systems with inner sub-Neptunes and outer gas giants. This is caused by the fact that the cores that formed in the inner disk are too small to effectively accrete large envelopes and only cores growing in the outer disk, where the cores are more massive due to the larger pebble isolation mass, can become giants. As a result, instabilities between the outer giant planets do not necessarily destroy the inner systems of sub-Neptunes unlike simulations with more efficient envelope contraction where giant planets can form closer in. Our simulations show that up to 50% of the systems of cold Jupiters could have inner sub-Neptunes, in agreement with observations. At the same time, our simulations show a good agreement with the eccentricity distribution of giant exoplanets, even though we find a slight mismatch to the mass and semi-major axes’ distributions. Synthetic transit observations of the inner systems (r < 0.7 AU) that formed in our simulations reveal an excellent match to the Kepler observations, where our simulations can especially match the period ratios of adjacent planet pairs. As a consequence, the breaking the chains model for super-Earth and sub-Neptune formation remains consistent with observations even when outer giant planets are present. However, simulations with outer giant planets produce more systems with mostly only one inner planet and with larger eccentricities, in contrast to simulations without outer giants. We thus predict that systems with truly single close-in planets are more likely to host outer gas giants. We consequently suggest radial velocity follow-up observations of systems of close-in transiting sub-Neptunes to understand if these inner sub-Neptunes are truly alone in the inner systems or not.

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

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

Gas accretion onto Jupiter mass planets in discs with laminar accretion flows

Context. Numerous studies have shown that a gap-forming Jovian mass planet embedded in a protoplanetary disc, in which a turbulent viscosity operates, can accrete gas efficiently through the gap, and for typical parameters it doubles its mass in ~0.1 Myr. The planet also migrates inwards on a timescale that is closely related to the local viscous evolution timescale, which is also typically 0.1 Myr. These timescales are short compared to protoplanetary disc lifetimes, and raise questions about the origins of the cold gas giant exoplanets that have been discovered in abundance. It is understood that protoplanetary discs are unlikely to be globally turbulent, and instead they may launch magnetised winds such that accretion towards the star occurs in laminar accretion flows located in narrow layers near the surfaces of the disc. Aims. The aim of this study is to examine the rate at which gas accretes onto Jovian mass planets that are embedded in layered protoplanetary discs, and to compare the results with those obtained for viscous models. Methods. We use 3D hydrodynamical simulations of planets embedded in protoplanetary discs, in which a constant radial mass flux towards the star of ṁ = 10−8 M⊙ yr−1 is sustained. We consider a classical viscous α disc model, and also models in which an external torque is applied in narrow surface layers to mimic the effects of a magnetised wind. The accreting layers have a variety of depths, as parameterised by their column densities ΣA, and we consider values of ΣA in the range 0.1−10 g cm−2. Results. The viscous disc model gives results in agreement with previous studies. In accord with our recent work that examines the migration of Jovian mass planets in layered models, we find the accretion rate onto the planet in the layered models crucially depends on the ability of the planet to block the wind-induced mass flow towards the star. For ΣA = 10 g cm−2, the planet torque can block the mass flow in disc, accretion onto the planet is slow, and a mass doubling time of 10 Myr is obtained. For ΣA = 0.1 g cm−2, the flow is not blocked, accretion is fast, and the mass doubling time is 0.2 Myr. Conclusions. Our results show that although the radial mass flow through the layered disc models is always 10−8 M⊙ yr−1, adopting different values of ΣA leads to very different gas accretion rates onto embedded gas giant planets.

Star formation histories of dwarf and giant galaxies with different supernovae-driven outflows: NGC 2403, NGC 628

The star formation histories and chemical evolution of a dwarf spiral galaxy NGC 2403 and a massive spiral galaxy NGC 628 are studied in this work through a simple chemical evolutionary model under the influence of several supernovae-driven galactic outflows. The galactic disk of each galaxy is considered as a collection of some concentric rings each of which evolves independently without exchanging matters among themselves. The disk is formed through continuous accretion of pristine gas from halo. A classical Kennicutt–Schmidt star formation law is taken into account with an exponential gas accretion rate. In order to analyze the impact of outflow, we have taken into account two separate types of supernovae-driven gas outflow, namely supernovae momentum-driven outflow and supernovae energy-driven outflow, both of which depend on the circular velocity of the disk. By comparing our model’s anticipated result with observational data, the most viable models are chosen. For the dwarf galaxy NGC 2403, the supernovae energy-driven outflow model yields a better result which indicates that the supernovae energy-driven outflow mechanism plays a major role in driving the outflows in low mass galaxies. However, for NGC 628, both the outflow models adequately account for the observed features, suggesting that both momentum-driven and energy-driven outflows contribute equally to the outflows of the massive galaxy NGC 628. Furthermore, we contrasted the evolution of radial and global properties of these galaxies.