Accretion Rate Research Articles

The changing-look AGN SDSS J101152.98+544206.4 is returning to a type I state

Aims. We discovered that the changing-look active galactic nucleus (CLAGN) SDSS J101152.98+544206.4 (J1011+5442 for short) gradually returns to the type I state after a short period between 2014 and 2019 in the faint type 1.9 state. Methods. Motivated by the rebrightening in the optical and mid-infrared light curves from ZTF and WISE, we obtained new spectroscopic observations with the Xinglong 2.16 m, the Lijiang 2.4 m, and the MMT 6.5 m optical telescopes in 2024. Results. After changing its optical AGN type from 1 to 1.9 between 2003 and 2015 according to the repeat spectroscopy from the Time Domain Spectroscopic Survey, J1011+5442 returned to its type I state in 2024. We detect the significant and very broad Hβ lines (full width at half maximum of ≳5000 km/s) based on the new spectra, which suggests that J1011+5442 was in the intermediate state between the dim state in 2015 and the bright state in 2003. The long-term optical and mid-infrared light curves also show a brightening trend between 2019 and 2024 as the broad Hβ line appeared. The time lag of about 100 days between the mid-infrared and optical variability is consistent with the prediction of dust reverberation mapping. Conclusions. The behavior of the photometric and spectroscopic observations of J1011+5442 is consistent with the argument that the repeating changing-look phenomenon is regulated by the variation in the accretion rate.

Increased sea level rise accelerates carbon sequestration in a macro-tidal salt marsh.

Salt marshes are known as key ecosystems for nature-based climate mitigation through organic carbon sequestration into their sediment beds, but at the same time they are affected by accelerating sea level rise induced by climate warming. Consequently, an important question is how organic carbon accumulation rates (OCAR) of salt marshes will respond to future accelerating rates of relative sea level rise (RSLR). To date, existing insights are either based on (1) comparison of geographically distant marsh sites, differing in local RSLR rates but also in other environmental conditions that additionally can affect OCAR, or (2) experiments in given marsh sites, in which proxies for RSLR are manipulated, but run over periods of years instead of decades, the latter being the relevant time scale of marsh responses to RSLR. Here we bridge these shortcomings by studying the OCAR over four decades at two nearby salt marsh sites in the Netherlands, with similar environmental conditions, but with one site experiencing an accelerated RSLR rate of 9.7-11.7mmyr-1 (i.e., within the range of projected global mean sea level rise rates by 2100) due to local land subsidence induced by gas extraction, while the other site does not experience subsidence and has a low background RSLR rate of 2.0mmyr-1 (i.e. close to the current global mean sea level rise rate). Our results reveal that the salt marsh site experiencing the accelerated RSLR rates shows OCAR values that are on average twice as high as those found in the marsh site experiencing the low background RSLR rates. Moreover, the increase of OCAR in response to faster RSLR was even more pronounced (i.e. 63% increase) on marsh levees within 10m from tidal creeks, while this was more subtle (i.e. 27% increase) in marsh basins at a distance of 30-40m from the creeks. These observations of increased OCAR are mainly attributed to increased sediment accretion rates (SAR) in response to (1) increased tidal inundation due to accelerated RSLR and (2) larger sediment supply due to closer proximity to creeks, while sediment organic carbon content was relatively little affected. Our findings support expectations that nature-based climate mitigation actions, through salt marsh conservation and restoration, are sustainable on the long term of the coming decades, and are even likely to become more effective with future accelerations in global sea level rise, at least for macrotidal sites not limited by sediment supply.

JWST ERS Program Q3D: The pitfalls of virial black hole mass constraints shown for a z ∼ 3 quasar with an ultramassive host

We present observations with the Mid-InfraRed Instrument (MIRI) and Near-InfraRed Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST), targeting the extremely red quasar J165202.64+172852.3 at z = 2.948 (dubbed J1652). As one of the most luminous quasars known to date, it drives powerful outflows and hosts a clumpy starburst, in the midst of several interacting companions. We estimated the black hole (BH) mass of the system based on the broad Hα and Hβ lines, as well as the broad Paβ emission in the infrared and Mg II in the ultraviolet. We recovered a very broad range of mass estimates, with individual constraints ranging between log MBH ∼ 9 and 10.2, which is extended further if we impose a uniform broad line region geometry at all wavelengths. The large spread may be caused by several factors: uncertainties on measurements (insufficient sensitivity to detect the broadest component of the faint Paschen β line, spectral blending, ambiguities in the broad or narrow component distinction, etc.), lack of virial equilibrium, and uncertainties on the luminosity-inferred size of the broad line region (BLR). The exotic nature of our target (luminous, starburst, powerful outflows, high accretion rate, and dusty centre) is another likely contribution to the large uncertainties. We broadly constrained the stellar mass of J1652 by fitting the spectral energy distribution, which suggests that the host is extremely massive, at ∼1012.1 M⊙, with a 1.1 dex uncertainty at > 1 dex above the characteristic mass of the Schechter fit to the z = 3 stellar mass function. Notably, J1652’s central BH might be interpreted as being either over-massive or in line with the BH mass–stellar mass relation, depending on the choice of assumptions. The recovered Eddington ratio varies accordingly, but it exceeds 10% in any case. We set our results into context by providing an extensive overview and discussion of recent literature results and their associated assumptions. Our findings provide an important demonstration of the uncertainties inherent in the virial BH mass estimates of individual objects, which are of particular relevance in the JWST era, given the increasing number of studies on rapidly accreting quasars at high redshift.

The Three Hundred project: The relationship between the shock and splashback radii of simulated galaxy clusters

Abstract Observations of the intracluster medium (ICM) in the outskirts of galaxy clusters reveal shocks associated with gas accretion from the cosmic web. Previous work based on non-radiative cosmological hydrodynamical simulations have defined the shock radius, $r_{\text{shock}}$ , using the ICM entropy, $K \propto T/{n_\mathrm{e}}^{2/3}$ , where T and $n_{\text{e}}$ are the ICM temperature and electron density, respectively; the $r_{\text{shock}}$ is identified with either the radius at which K is a maximum or at which its logarithmic slope is a minimum. We investigate the relationship between $r_{\text{shock}}$ , which is driven by gravitational hydrodynamics and shocks, and the splashback radius, $r_{\text{splash}}$ , which is driven by the gravitational dynamics of cluster stars and dark matter and is measured from their mass profile. Using 324 clusters from The Three Hundred project of cosmological galaxy formation simulations, we quantify statistically how $r_{\text{shock}}$ relates to $r_{\text{splash}}$ . Depending on our definition, we find that the median $r_{\text{shock}} \simeq 1.38 r_{\text{splash}} (2.58 R_{200})$ when K reaches its maximum and $r_{\text{shock}} \simeq 1.91 r_{\text{splash}} (3.54 R_{200})$ when its logarithmic slope is a minimum; the best-fit linear relation increases as $r_{\text{shock}} \propto 0.65 r_{\text{splash}}$ . We find that $r_{\text{shock}}/R_{200}$ and $r_{\text{splash}}/R_{200}$ anti-correlate with virial mass, $M_{200}$ , and recent mass accretion history, and $r_{\text{shock}}/r_{\text{splash}}$ tends to be larger for clusters with higher recent accretion rates. We discuss prospects for measuring $r_{\text{shock}}$ observationally and how the relationship between $r_{\text{shock}}$ and $r_{\text{splash}}$ can be used to improve constraints from radio, X-ray, and thermal Sunyaev-Zeldovich surveys that target the interface between the cosmic web and clusters.

The evolutionary status of the Galaxy’s X-ray binary stars

The article is devoted to the analysis of the evolutionary status of the X-ray binary stars of the Galaxy. It is shown that the assumption of the conservative evolution of these binary systems leads to an overestimation of the X-ray luminosity of the Galaxy by 3–4 orders. The total observed rate of accretion of matter by relativistic components of X-ray binaries is close to ~10-6⊙/yr, while the theoretically possible rate reaches ~10-2⊙/yr. The contradiction between these estimates is eliminated if two factors are taken into account. The first of them is the formation of a common envelope in massive X-ray binary systems after filling the Roche lobe by the donor and the brief phase of a bright X-ray source. The common envelope eliminates the output of X-ray radiation generated during accretion, and also leads to the loss of part of the donor’s matter from the system. The second factor is the presence of intense stellar wind of donors in massive X-ray binary, as well as the occurrence of induced stellar wind in low-mass donors due to exposure to hard radiation from an accreting relativistic star. At the same time, the generally accepted assumption that donors of X-ray binaries fill their Roche lobes may not be fulfilled. A significant part of the donor’s wind matter may be lost from the system. In addition, radiation can enhance the stellar wind of the accretion disk, and part of this wind will also leave the system. There are other factors that reduce the total number of accreted matter: supernova explosions in X-ray binaries, destroying part of these systems, the impossibility of accretion onto rapidly rotating young neutron stars with a strong magnetic field, as well as a rapid drop in the rate of loss of matter by the donor as its mass decreases, characteristic for low-mass X-ray systems.

A jet-induced shock in a young, powerful radio galaxy at z = 3.00

Abstract The bright radio source, GLEAM J091734 $-$ 001243 (hereafter GLEAM J0917 $-$ 0012), was previously selected as a candidate ultra-high redshift ( $z \gt 5$ ) radio galaxy due to its compact radio size and faint magnitude ( $K(\mathrm{AB})=22.7$ ). Its redshift was not conclusively determined from follow-up millimetre and near-infrared spectroscopy. Here we present new HST WFC3 G141 grism observations which reveal several emission lines including [NeIII] $\lambda$ 3867, [NeV] $\lambda$ 3426 and an extended ( $\approx 4.8\,$ kpc), [OII] $\lambda$ 3727 line which confirm a redshift of $3.004\pm0.001$ . The extended component of the [OII] $\lambda$ 3727 line is co-spatial with one of two components seen at 2.276 GHz in high resolution ( $60\times 20\,$ mas) Long Baseline Array data, reminiscent of the alignments seen in local compact radio galaxies. The BEAGLE stellar mass ( $\approx 2\times 10^{11}\,\textit{M}_\odot$ ) and radio luminosity ( $L_{\mathrm{500MHz}}\approx 10^{28}\,$ W Hz $^{-1}$ ) put GLEAM J0917 $-$ 0012 within the distribution of the brightest high-redshift radio galaxies at similar redshifts. However, it is more compact than all of them. Modelling of the radio jet demonstrates that this is a young, $\approx 50\,$ kyr old, but powerful, $\approx 10^{39}\,$ W, compact steep spectrum radio source. The weak constraint on the active galactic nucleus bolometric luminosity from the [NeV] $\lambda$ 3426 line combined with the modelled jet power tentatively implies a large black hole mass, $\ge 10^9\,\textit{M}_\odot$ , and a low, advection-dominated accretion rate, i.e. an Eddington ratio $\le 0.03$ . The [NeV] $\lambda$ 3426/[NeIII] $\lambda$ 3867 vs [OII] $\lambda$ 3727/[NeIII] $\lambda$ 3867 line ratios are most easily explained by radiative shock models with precursor photoionisation. Hence, we infer that the line emission is directly caused by the shocks from the jet and that this radio source is one of the youngest and most powerful known at cosmic noon. We speculate that the star-formation in GLEAM J0917 $-$ 0012 could be on its way to becoming quenched by the jet.

Effects of Thermodynamics on the Concurrent Accretion and Migration of Gas Giants in Protoplanetary Disks

Accretion and migration usually proceeds concurrently for giant planet formation in the natal protoplanetary disks. Recent works indicate that the concurrent accretion onto a giant planet imposes significant impact on the planetary migration dynamics in the isothermal regime. In this work, we carry out a series of 2D global hydrodynamical simulations with Athena++ to explore the effect of thermodynamics on the concurrent accretion and migration process of the planets in a self-consistent manner. The thermodynamics effect is modeled with a thermal relaxation timescale using a β-cooling prescription. Our results indicate that radiative cooling has a substantial effect on the accretion and migration processes of the planet. As cooling timescales increase, we observe a slight decrease in the planetary accretion rate, and a transition from the outward migrating into inward migration. This transition occurs approximately when the cooling timescale is comparable to the local dynamical timescale (β∼1), which is closely linked to the asymmetric structures from the circumplanetary disk (CPD) region. The asymmetric structures in the CPD region which appear with an efficient cooling provide a strong positive torque driving the planet migrate outward. However, such a positive torque is strongly suppressed, when the CPD structures tend to disappear with a relatively long cooling timescale (β≳10). Our findings may also be relevant to the dynamical evolution of accreting stellar-mass objects embedded in disks around active galactic nuclei.

The Surprising Long‐Term Evolution of the ULXP NGC 7793 P13

ABSTRACTThe ultra‐luminous x‐ray pulsar (ULXP) NGC 7793 P13 has been regularly monitored with XMM‐Newton, NuSTAR, and Swift for the last 8 years. Here, we present the latest results of this monitoring campaign with respect to the pulse period evolution and spectral variability. We find that since the source recovered from an x‐ray low state in 2020–2022 the spin‐up rate has increased significantly compared with before the off‐state, even though the x‐ray luminosity has not shown an equivalent increase. We find that the x‐ray and optical/UV flux are anti‐correlated, and speculate that this variability might be driven by a large accretion disk, precessing at a super‐orbital period of 7–8 years. We study the spectral behavior in the XMM‐Newton and NuSTAR data, and find very little changes in the spectral shape, despite the large flux variability. This spectral consistency provides further indication that the observed flux variability is a geometric effect and not due to intrinsic changes of the accretion rate.

Accretion onto WD 2226-210, the central star of the Helix Nebula

ABSTRACT The central star of the Helix Nebula, WD 2226$-$210 presents enigmatic hard X-ray emission and mid-IR excess. The latter has been attributed to a dusty disc or a cloud-like structure around WD 2226$-$210 formed from material of Kuiper Belt-like or comet-like objects in highly eccentric orbits. We present here a detailed analysis of multi-epoch Chandra and XMM–Newton X-ray observations of WD 2226$-$210, comparing these to previous Einstein and ROSAT data. The luminosity of the hard X-ray component of WD 2226$-$210 has remained basically constant in the decade from 1992 to 2002, with very subtle evidence for variability in time-scales of hours. Under the assumption that the X-ray emission from WD 2226$-$210 is due to accretion of material, an accretion rate of $\dot{M}\approx 10^{-10}$ M$_\odot$ yr$^{-1}$ is estimated. The origin of the material accreted by WD 2226$-$210 is uncertain, and can be attributed to the disc-like structure around it or to a substellar donor companion. The accretion rate proposed for the continuous replenishment by bombardment of the mid-IR-emitting structure around WD 2226$-$210 cannot match that required by the X-ray emission.

Impact of star formation models on the growth of simulated galaxies at high redshifts

Star formation is a key process that governs the baryon cycle within galaxies, however, the question of how it controls their growth remains elusive due to modeling uncertainties. To understand the impact of star formation models on galaxy evolution, we performed cosmological zoom-in radiation-hydrodynamic simulations of a dwarf dark matter halo, with a virial mass of $ at $z=6$. We compared two different star formation models: a multi-freefall model combined with a local gravo-thermo-turbulent condition and a more self-consistent model based on a sink particle algorithm, where gas accretion and star formation are directly controlled by the gas kinematics. As the first study in this series, we used cosmological zoom-in simulations with different spatial resolutions and found that star formation is more bursty in the runs with the sink algorithm, generating stronger outflows than in the runs with the gravo-thermo-turbulent model. The main reason for the increased burstiness is that the gas accretion rates on the sinks are high enough to form stars on very short timescales, leading to more clustered star formation. As a result, the star-forming clumps are disrupted more quickly in the sink run due to more coherent radiation and supernova feedback. The difference in burstiness between the two star formation models becomes even more pronounced when the supernova explosion energy is artificially increased. Our results suggest that improving the modeling of star formation on small, sub-molecular cloud scales can significantly impact the global properties of simulated galaxies.

A dynamics-based density profile for dark haloes – III. Parameter space

Abstract In the previous paper of this series, we proposed a new function to fit halo density profiles out to large radii. This truncated Einasto profile models the inner, orbiting matter as ρorb∝exp [ − 2/α (r/rs)α − 1/β (r/rt)β] and the outer, infalling term as a power-law overdensity. In this paper, we analyse the resulting parameter space of scale radius rs, truncation radius rt, steepening α, truncation sharpness β, infalling normalisation δ1, and infalling slope s. We show that these parameters are non-degenerate in averaged profiles, and that fits to the total profiles generally recover the underlying properties of the orbiting and infalling terms. We study the connection between profile parameters and halo properties such as mass (or peak height) and accretion rate. We find that the commonly cited dependence of α on peak height is an artefact of fitting Einasto profiles to the actual, truncated profiles. In our fits, α is independent of mass but dependent on accretion rate. When fitting individual halo profiles, the parameters exhibit significant scatter but otherwise follow the same trends. We confirm that the entire profiles are sensitive to the accretion history of haloes, and that the two radial scales rs and rt particularly respond to the formation time and recent accretion rate. As a result, rt is a more accurate measure of the accretion rate than the commonly used radius where the density slope is steepest.

Multi-wavelength monitoring and Reverberation Mapping of NGC 2617 at deepest minimum with a Sharp Upward Turn During 2021–2024

Abstract We present the results of a new X-ray to near-IR photometric and spectroscopic monitoring of the changing look AGN NGC 2617 carried out from March 2022 to March 2024. We found significant variability at all wavelengths and in the intensities and profiles of the broad Balmer lines. Reverberation mapping was carried out for three observing seasons during 2021-2024. We obtained time delays of ∼4 d for the response of the Hβ line to optical continuum variations. The X-ray variations correlate well with the UV and optical, with a few days lag for longer wavelengths. The K band lagged the B band by ∼ 15 d during the last 3 seasons, which is significantly shorter than the delays reported previously by the 2016 and 2017–2019 campaigns. Near-IR variability arises from two different emission regions: the outer part of the accretion disc and a more distant dust component. The HK-band variability is governed primarily by dust. The Hβ/Hα ratio variations (for broad components only) correlate with the X-ray and UV fluxes. The spectral type changed from type 1.8 to type 1.9 during October 2023–January 2024 and then a more rapid change to type 1.5 occurred in February 2024. We interpret these changes as a combination of two factors: changes in the accretion rate as a dominant cause but also the sublimation or recovery of dust along the line of sight.

Investigation of Floating Peat Wetlands, Sacramento–San Joaquin Delta, California

Tidal wetland restoration is integral to achieving the Delta coequal goals. Deeply subsided islands limit the potential for tidal wetland restoration. Floating peats may offer an opportunity to create tidal habitat in the subsided western and central Delta. We conducted a mesocosm experiment to assess the feasibility of floating peat blocks, and the potential food-web benefits, biomass production, carbon sequestration, methane emissions, and water-quality effects. We evaluated the effect of varying water residence time and initial peat-block density. The peat blocks floated during the entire experiment, and accreted biomass at rates consistent with those reported for Delta non-tidal managed wetlands. Peat blocks placed in mesocosms with 45% open water expanded horizontally about 21% per year. We estimated average vertical accretion rates of 5.5 to 8.6 cm yr – 1 for all the mesocosms. Vertical and horizontal expansion increase floating peat-block stability. We measured a 3-fold zooplankton population increase during the first year after deployment, relative to the Mokelumne River, which was the mesocosm’s water source. Measured and modeled methane emissions were lower than those reported in Delta non-tidal managed wetlands. Aqueous methane concentrations and methane fluxes were significantly lower for the shorter water-residence-time of about 5 days compared to longer residence times of about 11 days. Elevated dissolved oxygen (DO) concentrations generally corresponded with low methane concentrations. Our estimated net ecosystem carbon balance of – 820 +/– 137 g C m – 2 yr – 1 indicates that the floating wetlands are potentially greater carbon sinks than Delta non-tidal wetlands. Nitrogen data indicated consumption by wetland plants, and denitrification and dissimilatory nitrate reduction in the mesocosms. Our preliminary results point to potential ecosystem benefits of floating peats on a larger scale.

A pluton-dike system as an incomplete assembled pluton: field geology, petrography and geochemistry of the Rodríguez dike swarm and the Kranck pluton, Fuegian Andes

Dikes extending into the host-rock are a common feature at pluton roofs. Typically, the dikes are considered offshoots from differentiated magma reservoirs within the pluton, i.e. late-stage intrusions of the successive discrete magma pulses that built the pluton. We evaluate this hypothesis on a dike swarm and associated pluton, the Kranck-Rodríguez pluton-dike system, by analyzing its field geology, petrography and geochemistry (whole-rock and mineral). This system was emplaced in the shallow crust (∼1.7 kbar) within the fold-and-thrust belt of the Fuegian Andes. The Kranck pluton is a small (∼4.4 km2), composite body composed of a diverse range of lithologies, from mafic to felsic. Internal contacts are mainly sharp and subvertical, suggesting diking as a mode of assembly. The Rodríguez dike swarm extends up to 6 km from the pluton, mainly exposed adjacent to it. This swarm also displays a wide variety of lithotypes, encompassing a set of dikes affected by ductile deformation, and a younger set without it. Geochemical and petrographic analyses, along with thermobarometry, suggest that the Rodríguez dikes and lithotypes within the pluton were fed from different, deeper magma reservoirs, in an inferred trans-crustal plumbing system. We propose that the dikes represent discrete increments of the growing pluton, in a protracted process of successive injections. This ultimately led to the assembly of the pluton in the sector of the system with greater magma flux. The system developed in two major episodes, pre- and post-ductile deformation, each characterized by multiple, discrete magma injections. We consider this system as an embryonic stage of a broader model that would evolve from sheets separated by host-rock, to bodies with sheeted margins containing host-rock rafts, and eventually to relatively inclusion-free plutons, potentially forming larger bodies if provided with a greater magma supply and/or higher accretion rates.

Detailed Calculations of the Efficiency of Planetesimal Accretion in the Core-accretion Model. III. The Contribution of Planetesimals beyond Saturn

Continuing our initiative on advancing the calculations of planetesimal accretion in the core-accretion model, we present here the results of our recent study of the contributions of planetesimals around and beyond the orbit of Saturn. In our first two papers, where our focus was on the effects of the Sun and Saturn, the initial distribution of planetesimals was limited to the regions around the accretion zone of a growing Jupiter. In this paper, we expanded that distribution to regions beyond the accretion zone of Saturn. We integrated the orbits of a large ensemble of planetesimals and studied the rate of their capture by the growing proto-Jupiter. In order to be consistent with our previous studies, we did not consider the effect of the nebular gas. Results demonstrated that the exterior planetesimals, especially those beyond 8 au, have only slight contributions to the growth and metallicity of the growing Jupiter. The final mass and composition of this planet is mainly due to the planetesimals inside and around its accretion zone. Our study shows that although the rate of capture varies slightly by the size and composition of planetesimals, in general, the final results are independent of the size and material of these bodies. Results also pointed to a new finding: the rate of accretion follows the same trend as that of the evolution of Jupiter’s envelope, with the largest accretion occurring during the envelope’s collapse. We present details of our analysis and discuss the implications of its results.

Multizone Modeling of Black Hole Accretion and Feedback in 3D GRMHD: Bridging Vast Spatial and Temporal Scales

Simulating accretion and feedback from the horizon scale of supermassive black holes (SMBHs) out to galactic scales is challenging because of the vast range of scales involved. Elaborating on H. Cho et al., we describe and test a “multizone” technique, which is designed to tackle this difficult problem in three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations. While short-timescale variability should be interpreted with caution, the method is demonstrated to be well-suited for finding dynamical steady states over a wide dynamic range. We simulate accretion on a nonspinning SMBH (a * = 0) using initial conditions and the external galactic potential from a large-scale galaxy simulation and achieve a steady state over eight decades in radius. As found in H. Cho et al., the density scales with radius as ρ ∝ r −1 inside the Bondi radius R B , which is located at R B = 2 × 105 r g (≈60 pc for M87), where r g is the gravitational radius of the SMBH; the plasma-β is ∼ unity, indicating an extended magnetically arrested state; the mass accretion rate Ṁ is ≈1% of the analytical Bondi accretion rate ṀB; and there is continuous energy feedback out to ≈100R B (or beyond > kpc) at a rate ≈0.02Ṁc2 . Surprisingly, no ordered rotation in the external medium survives as the magnetized gas flows to smaller radii, and the final steady solution is very similar to when the exterior has no rotation. Using the multizone method, we simulate GRMHD accretion over a wide range of Bondi radii, R B ∼ 102−107 r g, and find that Ṁ/ṀB≈(RB/6rg)−0.5 .

Thermal solutions of strongly magnetized disks and the hysteresis in X-ray binaries

Context. X-ray binaries (XRBs) exhibit a spectral hysteresis for luminosities in the range 10−2 ≲ L/LEdd ≲ 0.3, with a hard X-ray spectral state that persists from quiescent luminosities up to ≳0.3LEdd, transitioning to a soft spectral state that survives with decreasing luminosities down to ∼10−2LEdd. Aims. We present a possible approach to explain this behavior based on the thermal properties of a magnetically arrested disk simulation. Methods. By post-processing the simulation to include radiative effects, we solved for all the thermal equilibrium solutions as the accretion rate, Ṁ, varies during the XRB outburst. Results. For an assumed scaling of the disk scale height and accretion speed with temperature, we find that two solutions exist in the range of 10−3 ≲ Ṁ/ṀEddington ≲ 0.1 at r = 8 rg (4 × 10−2 ≲ Ṁ/ṀEddington ≲ 0.5 at r = 3 rg): a cold, optically thick solution, and a hot, optically thin one. This opens the possibility of a natural thermal hysteresis in the right range of luminosities for XRBs. We stress that our scenario for the hysteresis does not require us to invoke the strong advection-dominated accretion flow principle, nor does it require the magnetization of the disk to change during the XRB outburst. In fact, our scenario requires a highly magnetized disk in the cold soft state to reproduce the transition from soft to hard state at the right luminosities. Our scenario therefore predicts a jet, although possibly very weakly dissipative, in the soft state of XRBs. We also predict that if active galactic nuclei have similar hysteresis cycles and are strongly magnetized, they undergo a transition from soft to hard state at much lower L/LEdd than XRBs.

Fast Methods for Computing Photometric Variability of Eccentric Binaries: Boosting, Lensing, and Variable Accretion

We analyze accretion-rate time series for equal-mass binaries in coplanar gaseous disks spanning a continuous range of orbital eccentricities up to 0.8 for both prograde and retrograde systems. The dominant variability timescales match those of previous investigations; the binary orbital period is dominant for prograde binaries with e ≳ 0.1, with a 5 × longer “lump” period taking over for e ≲ 0.1. This lump period fades and drops from 5 × to 4.5 × the binary period as e approaches 0.1, where it vanishes. For retrograde orbits, the binary orbital period dominates at e ≲ 0.55 and is accompanied by a 2 × longer timescale periodicity at higher eccentricities. The shape of the accretion-rate time series varies with binary eccentricity. For prograde systems, the orientation of an eccentric disk causes periodic trading of accretion between the binary components in a ratio that we report as a function of binary eccentricity. We present a publicly available tool, binlite, that can rapidly (≲0.01 s) generate templates for the accretion-rate time series onto either binary component for choice of binary eccentricity below 0.8. As an example use case, we build lightcurve models where the accretion rate through the circumbinary disk and onto each binary component sets contributions to the emitted specific flux. We combine these rest-frame, accretion-variability lightcurves with observer-dependent Doppler boosting and binary self-lensing. This allows a flexible approach to generating lightcurves over a wide range of binary and observer parameter space. We envision binlite as the access point to a living database that will be updated with state-of-the-art hydrodynamical calculations as they advance.

Variability of the inner dead zone edge in 2D radiation hydrodynamic simulations

Context. The inner regions of protoplanetary discs are prone to thermal instability (TI), which can significantly impact the thermal and dynamical evolution of planet-forming regions. Observable as episodic accretion outbursts, such periodic disturbances shape the disc’s vertical and radial structure. Aims. We have investigated the stability of the inner disc edge around a Class II T Tauri star and analysed the consequences of TI on the thermal and dynamic evolution in both the vertical and radial dimensions. A particular focus is laid on the emergence and destruction of solid-trapping pressure maxima. Methods. We conducted 2D axisymmetric radiation hydrodynamic simulations of the inner disc in a radial range of 0.05 AU to 10 AU. The models include a highly turbulent inner region, the transition to the dead zone, heating by both stellar irradiation and viscous dissipation, vertical and radial radiative transport, and tracking of the dust-to-gas mass ratio at every location. The simulated time frames include both the TI phase and the quiescent phase between TI cycles. We tracked the TI on S-curves of thermal stability. Results. Thermal instability can develop in discs with accretion rates of ≥3.6 ⋅ 10−9 M⊙ yr−1 and results from the activation of mag-netorotational instability (MRI) in the dead zone after the accumulation of material beyond the MRI transition. The TI creates an extensive MRI active region around the midplane and disrupts the stable pebble and migration trap at the inner edge of the dead zone. Our simulations consistently show the occurrence of TI reflares that, together with the initial TI, produce pressure maxima in the inner disc within 1 AU, possibly providing favourable conditions for streaming instability. During the TI phase, the dust content in the ignited regions adapts itself in order to create a new thermal equilibrium manifested in the upper branch of the S-curve. In these instances, we find a simple relation between the gas and dust-surface densities. Conclusions. On a timescale of a few thousand years, TI regularly disrupts the radial and vertical structure of the disc within 1 AU. While several pressure maxima are created, stable migration traps are destroyed and reinstated after the TI phase. Our models provide a foundation for more detailed investigations into phenomena such as the short-term variability of accretion rates.

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

Context. 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. Aims. 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. Methods. 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. 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 ≃ 3.55 and z ≃ 3.43, respectively, have dark matter halo masses consistent with being proto-clusters at z ∼ 3 and they each host an active galactic nucleus (AGN). We found five AGNs in the structure at z ≃ 3.55 and three AGNs in the one at z ≃ 3.43. 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 = 1. Conclusions. 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 10−8 yr−1 at z = 6 and the median mass growth rate was 96% from z = 6 to z = 3. In 20% of the simulated proto-clusters, the passive galaxy had already accreted 10–20% of the mass at z = 6, with SFRs > 100 M⊙ yr−1 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 ∼ 3.