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Eliot Quataert

Publications and source records attributed to Eliot Quataert.

At least 91 records · Page 5Linked to original sources
arXiv2023

Period Evolution of Repeating Transients in Galactic Nuclei

Wide-field survery have recently detected recurring optical and X-ray sources near galactic nuclei, with period spanning hours to years. These phenomena could result from repeated partial tidal disruptions of stars by supermassive black holes (SMBHs) or by interaction between star and SMBH-accretion discs. We study the physical processes that produce period changes in such sources, highlighting the key role of the interaction between the orbiting star and the accretion disc. We focus on ASASSN-14ko - a repeatedly flaring optical source with a mean period $P_0 = 115 \, \rm d$ and a detected period decay $\dot{P} = -2.6\times 10^{-3}$ (Payne et al. 2022). We argue that the system's $\dot{P}$ is most compatible with true orbital decay produced by hydrodynamical drag as a star passes through the accretion disc on an inclined orbit, twice per orbit. The star is likely a sun-like star whose envelope is somewhat inflated, possibly due to tidal heating. Star-disc interaction inevitably leads to drag-induced stripping of mass from the star, which may be the dominant component in powering the observed flares. We discuss ASASSN-14ko's possible formation history and observational tests of our interpretation of the measured $\dot P$. Our results imply that partial tidal disruption events manifesting as repeating nuclear transients cannot be modeled without accounting for the cumulative impact of tidal heating over many orbits. We discuss the implications of our results for other repeating transients, and predict that the recurrence time of Quasi-Periodic Eruptions is expected to decay at a rate of order $|\dot{P}| \approx 10^{-6}-10^{-5}$.

astro-ph.HE↗
arXiv2023

Unraveling Jet Quenching Criteria Across L* Galaxies and Massive Cluster Ellipticals

In the absence of supplementary heat, the radiative cooling of halo gas around massive galaxies (Milky Way mass and above) leads to an excess of cold gas or stars beyond observed levels. AGN jet-induced heating is likely essential, but the specific properties of the jets remain unclear. Our previous work (Su et al. 2021) concludes from simulations of a halo with $10^{14} M_\odot$ that a successful jet model should have an energy flux comparable to the free-fall energy flux at the cooling radius and should inflate a sufficiently wide cocoon with a long enough cooling time. In this paper, we investigate three jet modes with constant fluxes satisfying the criteria, including high-temperature thermal jets, cosmic ray (CR)-dominant jets, and widely precessing kinetic jets in $10^{12}-10^{15}\,{\rm M}_{\odot}$ halos using high-resolution, non-cosmological MHD simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model, conduction, and viscosity. We find that scaling the jet energy according to the free-fall energy at the cooling radius can successfully suppress the cooling flows and quench galaxies without obviously violating observational constraints. We investigate an alternative scaling method in which we adjust the energy flux based on the total cooling rate within the cooling radius. However, we observe that the strong interstellar medium (ISM) cooling dominates the total cooling rate in this scaling approach, resulting in a jet flux that exceeds the amount needed to suppress the cooling flows. With the same energy flux, the CR-dominant jet is most effective in suppressing the cooling flow across all the surveyed halo masses due to the enhanced CR pressure support. We confirm that the criteria for a successful jet model, which we proposed in Su et al. (2021), work across a much wider range, encompassing halo masses of $10^{12}-10^{15} {\rm M_\odot}$.

astro-ph.GA↗
arXiv2023

A Unified Picture of Short and Long Gamma-ray Bursts from Compact Binary Mergers

The recent detections of the $\sim10$-s long $γ$-ray bursts (GRBs) 211211A and 230307A followed by softer temporally extended emission (EE) and kilonovae, point to a new GRB class. Using state-of-the-art first-principles simulations, we introduce a unifying theoretical framework that connects binary neutron star (BNS) and black hole-NS (BH-NS) merger populations with the fundamental physics governing compact-binary GRBs (cbGRBs). For binaries with large total masses $M_{\rm tot}\gtrsim2.8\,M_\odot$, the compact remnant created by the merger promptly collapses into a BH, surrounded by an accretion disk. The duration of the pre-magnetically arrested disk (MAD) phase sets the duration of the roughly constant power cbGRB and could be influenced by the disk mass, $M_d$. We show that massive disks ($M_d\gtrsim0.1\,M_\odot$), which form for large binary mass ratio $q\gtrsim1.2$ in BNS or $q\lesssim3$ in BH-NS mergers, inevitably produce 211211A-like long cbGRBs. Once the disk becomes MAD, the jet power drops with the mass accretion rate as $\dot{M}\sim t^{-2}$, naturally establishing the EE decay. Two scenarios are plausible for short cbGRBs. They can be powered by BHs with less massive disks, which form for other $q$ values. Alternatively, for binaries with $M_{\rm tot}\lesssim2.8\,M_\odot$, mergers should go through a hypermassive NS (HMNS) phase, as inferred for GW170817. Magnetized outflows from such HMNSs, which typically live for $\lesssim1\,{\rm s}$, offer an alternative progenitor for short cbGRBs. The first scenario is challenged by the bimodal GRB duration distribution and the fact that the Galactic BNS population peaks at sufficiently low masses that most mergers should go through a HMNS phase.

astro-ph.HE↗
arXiv2023

Local models of two-temperature accretion disc coronae. I. Structure, outflows, and energetics

We use local stratified shearing-box simulations to elucidate the impact of two-temperature thermodynamics on the thermal structure of coronae in radiatively efficient accretion flows. Rather than treating the coronal plasma as an isothermal fluid, we use a simple, parameterized cooling function that models the collisional transfer of energy from the ions to the rapidly cooling leptons. Two-temperature models naturally form temperature inversions, with a hot, magnetically dominated corona surrounding a cold disc. Simulations with net vertical flux (NF) magnetic fields launch powerful magnetocentrifugal winds that would enhance accretion in a global system. The outflow rates are much better converged with increasing box height than analogous isothermal simulations, suggesting that the winds into two-temperature coronae may be sufficiently strong to evaporate a thin disc and form a radiatively inefficient accretion flow under some conditions. We find evidence for multiphase structure in the corona, with broad density and temperature distributions, and we propose criteria for the formation of a multiphase corona. The fraction of cooling in the surface layers of the disc is substantially larger for NF fields compared to zero net-flux configurations, with moderate NF simulations radiating ${\gtrsim}30$ per cent of the flow's total luminosity above two midplane scale-heights. Our work shows that NF fields may efficiently power the coronae of luminous Seyfert galaxies and quasars, providing compelling motivation for future studies of the heating mechanisms available to NF fields and the interplay of radiation with two-temperature thermodynamics.

astro-ph.HE↗
arXiv2023

Quasi-periodic eruptions from mildly eccentric unstable mass transfer in galactic nuclei

We propose that the recently observed quasi-periodic eruptions (QPEs) in galactic nuclei are produced by unstable mass transfer due to Roche lobe overflow of a low-mass main-sequence star in a mildly eccentric (e ~ 0.5) orbit. We argue that the QPE emission is powered by circularization shocks, but not directly by black hole accretion. Our model predicts the presence of a time-steady accretion disk that is bolometrically brighter than the time-averaged QPE luminosity, but primarily emits in the extreme-UV. This is consistent with the quiescent soft X-ray emission detected in between the eruptions in eROSITA QPE1, QPE2, and GSN 069. Such accretion disks have an unusual $νL_ν\propto ν^{12/7}$ optical spectrum. The lifetime of the bright QPE phase, 100-1000 yrs, is set by mass-loss triggered by ram-pressure interaction between the star and the accretion disk fed by the star itself. We show that the stellar orbits needed to explain QPEs can be efficiently created by the Hills breakup of tight stellar binaries provided that (i) the stellar binary orbit is tidally hardened before the breakup due to diffusive growth of the f-mode amplitude, and (ii) the captured star's orbit decays by gravitational wave emission without significant orbital angular momentum diffusion (which is the case for black holes less than about a million Msun). We conclude by discussing the implications of our model for hyper-velocity stars, extreme mass ratio inspirals, repeating partial TDEs, and related stellar phenomena in galactic nuclei.

astro-ph.HE↗
arXiv2023

Constraints on the narrow-line region of the X-ray quasi-periodic eruption source GSN 069

The origins of quasi-periodic eruptions (QPEs) are poorly understood, although most theoretical explanations invoke an accretion disk around a supermassive black hole. The gas and stellar environments in the galactic nuclei of these sources are also poorly constrained. In this paper, we present an analysis of archival Hubble Space Telescope (HST) images to study the narrow-line [O III] emission in the QPE source GSN 069. We find strong evidence for a compact nuclear [O III] emission region of size $\lesssim 35$ pc, overlaid on top of extended [O III] emission up to 2 kpc away from the nucleus. The age of the accretion system is estimated to be between 10 and 100 yr. The [O III] luminosity of the compact region was measured to be $(2.1 \pm 0.3) \times 10^{40}\,\rm erg\,s^{-1}$. Based on CLOUDY simulations, we constrain that the [O III] emitting gas has a hydrogen number density in the range $5 \times 10^{3} < n_{\rm H} \lesssim 10^{8}\,\rm cm^{-3}$ and volume filling factor $f_{\rm V} < 2 \times 10^{-3}$. We suggest that the dense gas in the nuclear region of GSN 069 originates from molecular clouds (with total mass $\gtrsim 3 \times 10^{3}\,M_{\odot}$), which are freshly ionised by the soft X-ray photons from the accretion disk. We predict possible evolution of the compact narrow-line region on emission-line diagnostic diagrams, and hence future HST or integral-field unit observations can be used to further pin down the age of this puzzling system.

astro-ph.HE↗
arXiv2023

The Origin of the Consistent Planetary Nebula Luminosity Function Bright-end Cutoff

The [O III] 5007 Angstrom line is typically the brightest line in planetary nebula (PN) spectra. Observations show that the brightest [O III] 5007 Angstrom PN in a galaxy -- the planetary nebula luminosity function (PNLF) bright-end cutoff -- is surprisingly independent of galaxy type. To understand the origin of this puzzling uniformity, we simulate PNe with a range of cloud and star parameters using the photoionization code CLOUDY. We find that the peak [O III] 5007 Angstrom luminosity depends weakly on both the central stellar effective temperature at high temperature and on the total PN ejecta mass; however, the peak [O III] 5007 Angstrom luminosity depends strongly on the central stellar luminosity and the PN dust-to-gas mass ratio. We explain these scalings physically. They imply that a higher dust-to-gas mass ratio at higher central stellar luminosity can help explain a constant bright-end cutoff in the PNLF across galaxy types. This prediction is testable with a survey of galactic PNe. The surviving remnants of double white dwarf mergers should also produce photoionized nebulae analogous to PNe. These may be preferentially present at the high luminosity end of the [O III] PLNF and could explain the existence of PNe in early-type galaxies that are more luminous in [O III] than expected from single-star evolutionary models. The presence of white dwarf mergers in both young and old stellar populations could contribute to the uniformity of the [O III] PNLF across galaxy types; such nebulae would lack the hydrogen lines otherwise characteristic of PNe.

astro-ph.SR↗
arXiv2023

Numerical simulations of the random angular momentum in convection II: delayed explosions of red supergiants following "failed'' supernovae

When collapse of the iron core in a massive red or yellow supergiant does not lead to an energetic supernova, a significant fraction of the convective hydrogen envelope will fall in towards the black hole formed from the collapsing core. The random velocity field in the convective envelope results in finite specific angular momentum in each infalling shell. Using 3D hydrodynamical simulations, we follow the infall of this material to small radii, resolving the circularization radii of the flow. We show that infall of the convective envelope leads to nearly complete envelope ejection in a $\gtrsim$ 10$^{48}$ erg explosion with outflow speeds of $\gtrsim$ 200 km/s. The light curve of such an explosion would show a characteristic, red plateau as the ejecta cools and a hydrogen recombination front recedes through the expanding ejecta. Adopting supernova IIp scalings, the event would have a plateau luminosity of $\gtrsim$ 10$^{40}$ erg/s and a duration of several hundreds of days. These events would appear quite similar to luminous red novae with red or yellow supergiant progenitors; some luminous red novae may, in fact, be signposts of black hole formation. The mechanism studied here produces more energetic explosions than the weak shock generated from the radiation of neutrino energy during the proto-neutron star phase. Because we cannot simulate all the way to the horizon, our results are likely lower limits on the energy and luminosity of transients produced during the collapse of a red or yellow supergiant to form a black hole.

astro-ph.HE↗
arXiv2023

Millimeter Observational Signatures of Flares in Magnetically Arrested Black Hole Accretion Models

In general relativistic magneto-hydrodynamic (GRMHD) simulations, accreted magnetic flux on the black hole horizon episodically decays, during which magnetic reconnection heats up the plasma near the horizon, potentially powering high-energy flares like those observed in M87* and Sgr A*. We study the mm observational counterparts of such flaring episodes. The change in 230 GHz flux during the expected high energy flares depends primarily on the efficiency of accelerating $γ\gtrsim 100$ ($T_e \gtrsim 10^{11}$ K) electrons. For models in which the electrons are heated to $T_e \sim 10^{11}$ K during flares, the hot plasma produced by reconnection significantly enhances 230 GHz emission and increases the size of the 230 GHz image. By contrast, for models in which the electrons are heated to higher temperatures (which we argue are better motivated), the reconnection-heated plasma is too hot to produce significant 230 GHz synchrotron emission, and the 230 GHz flux decreases during high energy flares. We do not find a significant change in the mm polarization during flares as long as the emission is Faraday thin. We also present expectations for the ring-shaped image as observed by the Event Horizon Telescope during flares, as well as multi-wavelength synchrotron spectra. Our results highlight several limitations of standard post-processing prescriptions for the electron temperature in GRMHD simulations. We also discuss the implications of our results for current and future observations of flares in Sgr A*, M87*, and related systems. Appendices contain detailed convergence studies with respect to resolution and plasma magnetization.

astro-ph.HE↗
arXiv2023

Polarized anisotropic synchrotron emission and absorption and its application to Black Hole Imaging

Low-collisionality plasma in a magnetic field generically develops anisotropy in its distribution function with respect to the magnetic field direction. Motivated by the application to radiation from accretion flows and jets, we explore the effect of temperature anisotropy on synchrotron emission. We derive analytically and provide numerical fits for the polarized synchrotron emission and absorption coefficients for a relativistic bi-Maxwellian plasma (we do not consider Faraday conversion/rotation). Temperature anisotropy can significantly change how the synchrotron emission and absorption coefficients depend on observing angle with respect to the magnetic field. The emitted linear polarization fraction does not depend strongly on anisotropy, while the emitted circular polarization does. We apply our results to black hole imaging of Sgr A* and M87* by ray-tracing a GRMHD simulation and assuming that the plasma temperature anisotropy is set by the thresholds of kinetic-scale anisotropy-driven instabilities. We find that the azimuthal asymmetry of the 230 GHz images can change by up to a factor of 3, accentuating ($T_\perp > T_\parallel$) or counteracting ($T_\perp < T_\parallel$) the image asymmetry produced by Doppler beaming. This can change the physical inferences from observations relative to models with an isotropic distribution function, e.g., by allowing for larger inclination between the line of sight and spin direction in Sgr A*. The observed image diameter and the size of the black hole shadow can also vary significantly due to plasma temperature anisotropy. We describe how the anisotropy of the plasma can affect future multi-frequency and photon ring observations. In Appendices we calculate kinetic anisotropy-driven instabilities (mirror, whistler, and firehose) for relativistically hot plasmas.

astro-ph.HE↗
arXiv2023

Tidal Disruption Event Demographics with the Zwicky Transient Facility: Volumetric Rates, Luminosity Function, and Implications for the Local Black Hole Mass Function

We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete sample of 33 TDEs is constructed using the Zwicky Transient Facility over three years (from October 2018 to September 2021). We infer the black hole (BH) mass ($M_{\rm BH}$) with host galaxy scaling relations, showing that the sample $M_{\rm BH}$ ranges from $10^{5.1}\,M_\odot$ to $10^{8.2}\,M_\odot$. We developed a survey efficiency corrected maximum volume method to infer the rates. The rest-frame $g$-band luminosity function (LF) can be well described by a broken power-law of $ϕ(L_g)\propto [(L_g / L_{\rm bk})^{0.3} + (L_g / L_{\rm bk})^{2.6}]^{-1}$, with $L_{\rm bk}=10^{43.1}\,{\rm erg\,s^{-1}}$. In the BH mass regime of $10^{5.3}\lesssim (M_{\rm BH}/M_\odot) \lesssim 10^{7.3}$, the TDE mass function follows $ϕ(M_{\rm BH})\propto M_{\rm BH}^{-0.25}$, which favors a flat local BH mass function ($dn_{\rm BH}/d{\rm log}M_{\rm BH}\approx{\rm constant}$). We confirm the significant rate suppression at the high-mass end ($M_{\rm BH}\gtrsim 10^{7.5}\,M_\odot$), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of $M_{\rm gal}\sim 10^{10}\,M_\odot$, the average optical TDE rate is $\approx 3.2\times 10^{-5}\,{\rm galaxy^{-1}\,yr^{-1}}$. We constrain the optical TDE rate to be [3.7, 7.4, and 1.6$]\times 10^{-5}\,{\rm galaxy^{-1}\,yr^{-1}}$ in galaxies with red, green, and blue colors.

astro-ph.HE↗
arXiv2023

Multiphase condensation in cluster halos: interplay of cooling, buoyancy and mixing

Gas in the central regions of cool-core clusters and other massive halos has a short cooling time ($\lesssim1~\mathrm{Gyr}$). Theoretical models predict that this gas is susceptible to multiphase condensation, in which cold gas is expected to condense out of the hot phase if the ratio of the thermal instability growth time scale ($t_{\mathrm{ti}}$) to the free-fall time ($t_{\mathrm{ff}}$) is $t_{\mathrm{ti}}/t_{\mathrm{ff}}\lesssim10$. The turbulent mixing time $t_{\mathrm{mix}}$ is another important time scale: if $t_{\mathrm{mix}}$ is short enough, the fluctuations are mixed before they can cool. In this study, we perform high-resolution ($512^2\times768$--$1024^2\times1536$ resolution elements) hydrodynamic simulations of turbulence in a stratified medium, including radiative cooling of the gas. We explore the parameter space of $t_{\mathrm{ti}}/t_{\mathrm{ff}}$ and $t_{\mathrm{ti}}/t_{\mathrm{mix}}$ relevant to galaxy and cluster halos. We also study the effect of the steepness of the entropy profile, the strength of turbulent forcing and the nature of turbulent forcing (natural mixture vs. compressive modes) on multiphase gas condensation. We find that larger values of $t_{\mathrm{ti}}/t_{\mathrm{ff}}$ or $t_{\mathrm{ti}}/t_{\mathrm{mix}}$ generally imply stability against multiphase gas condensation, whereas larger density fluctuations (e.g., due to compressible turbulence) promote multiphase gas condensation. We propose a new criterion $\min(t_{\mathrm{ti}}/\min(t_{\mathrm{mix}},t_\mathrm{ff}))\lesssim c_2\times\exp(c_1σ_s)$ for when the halo becomes multiphase, where $σ_s$ denotes the amplitude of logarithmic density fluctuations and $c_1\simeq6$, $c_2\simeq1.8$ from an empirical fit to our results.

astro-ph.GA↗
arXiv2023

What Causes The Formation of Disks and End of Bursty Star Formation?

As they grow, galaxies can transition from irregular/spheroidal with 'bursty' star formation histories (SFHs), to disky with smooth SFHs. But even in simulations, the direct physical cause of such transitions remains unclear. We therefore explore this in a large suite of numerical experiments re-running portions of cosmological simulations with widely varied physics, further validated with existing FIRE simulations. We show that gas supply, cooling/thermodynamics, star formation model, Toomre scale, galaxy dynamical times, and feedback properties do not have a direct causal effect on these transitions. Rather, both the formation of disks and cessation of bursty star formation are driven by the gravitational potential, but in different ways. Disk formation is promoted when the mass profile becomes sufficiently centrally-concentrated in shape (relative to circularization radii): we show that this provides a well-defined dynamical center, ceases to support the global 'breathing modes' which can persist indefinitely in less-concentrated profiles and efficiently destroy disks, promotes orbit mixing to form a coherent angular momentum, and stabilizes the disk. Smooth SF is promoted by the potential or escape velocity (not circular velocity) becoming sufficiently large at the radii of star formation that cool, mass-loaded (momentum-conserving) outflows are trapped/confined near the galaxy, as opposed to escaping after bursts. We discuss the detailed physics, how these conditions arise in cosmological contexts, their relation to other correlated phenomena (e.g. inner halo virialization, vertical disk 'settling'), and observations.

astro-ph.GA↗
arXiv2023

Large-scale Evolution of Seconds-long Relativistic Jets from Black Hole-Neutron Star Mergers

We present the first numerical simulations that track the evolution of a black hole-neutron star (BH-NS) merger from pre-merger to $r\gtrsim10^{11}\,{\rm cm}$. The disk that forms after a merger of mass ratio $q=2$ ejects massive disk winds ($3-5\times10^{-2}\,M_{\odot}$). We introduce various post-merger magnetic configurations and find that initial poloidal fields lead to jet launching shortly after the merger. The jet maintains a constant power due to the constancy of the large-scale BH magnetic flux until the disk becomes magnetically arrested (MAD), where the jet power falls off as $L_j\sim t^{-2}$. All jets inevitably exhibit either excessive luminosity due to rapid MAD activation when the accretion rate is high or excessive duration due to delayed MAD activation compared to typical short gamma-ray bursts (sGRBs). This provides a natural explanation for long sGRBs such as GRB 211211A but also raises a fundamental challenge to our understanding of jet formation in binary mergers. One possible implication is the necessity of higher binary mass ratios or moderate BH spins to launch typical sGRB jets. For post-merger disks with a toroidal magnetic field, dynamo processes delay jet launching such that the jets break out of the disk winds after several seconds. We show for the first time that sGRB jets with initial magnetization $σ_0>100$ retain significant magnetization ($σ\gg1$) at $r>10^{10}\,{\rm cm}$, emphasizing the importance of magnetic processes in the prompt emission. The jet-wind interaction leads to a power-law angular energy distribution by inflating an energetic cocoon whose emission is studied in a companion paper.

astro-ph.HE↗
arXiv2023

Cosmic-Ray Driven Galactic Winds from the Warm Interstellar Medium

We study the properties of cosmic-ray (CR) driven galactic winds from the warm interstellar medium using idealized spherically symmetric time-dependent simulations. The key ingredients in the model are radiative cooling and CR-streaming-mediated heating of the gas. Cooling and CR heating balance near the base of the wind, but this equilibrium is thermally unstable, leading to a multiphase wind with large fluctuations in density and temperature. In most of our simulations, the heating eventually overwhelms cooling, leading to a rapid increase in temperature and a thermally-driven wind; the exception to this is in galaxies with the shallowest potentials, which produce nearly isothermal $T \approx 10^4$ K winds driven by CR pressure. Many of the time-averaged wind solutions found here have a remarkable critical point structure, with two critical points. Scaled to real galaxies, we find mass outflow rates $\dot M$ somewhat larger than the observed star formation rate in low mass galaxies, and an approximately "energy-like" scaling $\dot M \propto v_{\rm esc}^{-2}$. The winds accelerate slowly and reach asymptotic wind speeds of only $\sim 0.4 v_{\rm esc}$. The total wind power is $\sim 1\%$ of the power from supernovae, suggesting inefficient preventive CR feedback for the physical conditions modeled here. We predict significant spatially extended emission and absorption lines from $10^4 - 10^{5.5}$ K gas; this may correspond to extraplanar diffuse ionized gas seen in star-forming galaxies.

astro-ph.GA↗
arXiv2023

Hours-long Near-UV/Optical Emission from Mildly Relativistic Outflows in Black Hole-Neutron Star Mergers

The ongoing LIGO-Virgo-KAGRA observing run O4 provides an opportunity to discover new multi-messenger events, including binary neutron star (BNS) mergers such as GW170817, and the highly anticipated first detection of a multi-messenger black hole-neutron star (BH-NS) merger. While BNS mergers were predicted to exhibit early optical emission from mildly relativistic outflows, it has remained uncertain whether the BH-NS merger ejecta provides the conditions for similar signals to emerge. We present the first modeling of early near-ultraviolet/optical emission from mildly relativistic outflows in BH-NS mergers. Adopting optimal binary properties: a mass ratio of $q=2$ and a rapidly rotating BH, we utilize numerical relativity and general relativistic magnetohydrodynamic (GRMHD) simulations to follow the binary's evolution from pre-merger to homologous expansion. We use an M1 neutrino transport GRMHD simulation to self-consistently estimate the opacity distribution in the outflows and find a bright near-ultraviolet/optical signal that emerges due to jet-powered cocoon cooling emission, outshining the kilonova emission at early time. The signal peaks at an absolute magnitude of $\sim -15$ a few hours after the merger, longer than previous estimates, which did not consider the first principles-based jet launching. By late 2024, the Rubin Observatory will have the capability to track the entire signal evolution or detect its peak up to distances of $\gtrsim1$ Gpc. In 2026, ULTRASAT will conduct all-sky surveys within minutes, detecting some of these events within $\sim 200$ Mpc. The BH-NS mergers with higher mass ratios or lower BH spins would produce shorter and fainter signals.

astro-ph.HE↗
arXiv2023

Local positive feedback in the overall negative: the impact of quasar winds on star formation in the FIRE cosmological simulations

Negative feedback from accreting supermassive black holes is regarded as a key ingredient in suppressing star formation and quenching massive galaxies. However, several models and observations suggest that black hole feedback may have a positive effect, triggering star formation by compressing interstellar medium gas to higher densities. We investigate the dual role of black hole feedback using cosmological hydrodynamic simulations from the Feedback In Realistic Environments (FIRE) project, including a novel implementation of hyper-refined accretion-disc winds. Focusing on a massive, star-forming galaxy at $z \sim 2$ ($M_{\rm halo} \sim 10^{12.5} \, {\rm M}_{\odot}$), we show that strong quasar winds with kinetic power $\sim$10$^{46}$ erg/s acting for $>$20$\,$Myr drive the formation of a central gas cavity and can dramatically reduce the star formation rate surface density across the galaxy disc. The suppression of star formation is primarily driven by reducing the amount of gas that can become star-forming, compared to directly evacuating the pre-existing star-forming gas reservoir (preventive feedback dominates over ejective feedback). Despite the global negative impact of quasar winds, we identify several plausible signatures of local positive feedback, including: (1) spatial anti-correlation of wind-dominated regions and star-forming clumps, (2) higher local star formation efficiency in compressed gas near the edge of the cavity, and (3) increased local contribution of outflowing material to star formation. Stars forming under the presence of quasar winds tend to do so at larger radial distances. Our results suggest that positive and negative AGN feedback can coexist in galaxies, but local positive triggering of star formation plays a minor role in global galaxy growth.

astro-ph.GA↗
arXiv2023

Pressure anisotropy and viscous heating in weakly collisional plasma turbulence

Pressure anisotropy can strongly influence the dynamics of weakly collisional, high-beta plasmas, but its effects are missed by standard magnetohydrodynamics (MHD). Small changes to the magnetic-field strength generate large pressure-anisotropy forces, heating the plasma, driving instabilities, and rearranging flows, even on scales far above the particles' gyroscales where kinetic effects are traditionally considered important. Here, we study the influence of pressure anisotropy on turbulent plasmas threaded by a mean magnetic field (Alfvénic turbulence). Extending previous results that were concerned with Braginskii MHD, we consider a wide range of regimes and parameters using a simplified fluid model based on drift kinetics with heat fluxes calculated using a Landau-fluid closure. We show that viscous (pressure-anisotropy) heating dissipates between a quarter and half of the turbulent cascade power injected at large scales; this does not depend strongly on either plasma beta or the ion-to-electron temperature ratio. This will in turn influence the plasma's thermodynamics by regulating energy partition between different dissipation channels (e.g., electron and ion heat). Due to the pressure anisotropy's rapid dynamical feedback onto the flows that create it -- an effect we term `magneto-immutability' -- the viscous heating is confined to a narrow range of scales near the forcing scale, supporting a nearly conservative, MHD-like inertial-range cascade, via which the rest of the energy is transferred to small scales. Despite the simplified model, our results -- including the viscous heating rate, distributions, and turbulent spectra -- compare favourably to recent hybrid-kinetic simulations. This is promising for the more general use of extended-fluid (or even MHD) approaches to model weakly collisional plasmas such as the intracluster medium, hot accretion flows, and the solar wind.

astro-ph.HE↗