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Parsec-scale separation supermassive black hole binaries in the centre of gas-rich galaxy merger remnants could be surrounded by massive circumbinary discs (CBDs). Black hole mass and spin evolution during the gas-rich binary inspiral are crucial in determining the direction and power of relativistic jets that radio observations with LOFAR (Low-Frequency Array) and SKAO (Square Kilometer Array Observatory) will probe, and for predicting gravitational wave (GW) emission that the IPTA (International Pulsar Timing Array) and LISA (Laser Interferometer Space Antenna) will measure. We present 3D hydrodynamic simulations capturing gas-rich, self-gravitating CBDs around a |$2\times 10^6$| M |$_{\odot }$| supermassive black hole binary, that probe different mass ratios, eccentricities, and inclinations. We employ a subgrid Shakura–Sunyaev accretion disc to self-consistently model black hole mass and spin evolution together with super-Lagrangian refinement techniques to resolve gas flows, streams, and mini-discs within the cavity, which play a fundamental role in torquing and feeding the binary. We find that higher mass ratio and eccentric binaries result in larger cavities, while retrograde binaries result in smaller cavities. All of the simulated binaries are expected to shrink with net gravitational torques being negative. Unlike previous simulations, we do not find preferential accretion onto the secondary black hole. This implies smaller chirp masses at coalescence and hence a weaker GW background. Critically this means that spin alignment is faster than the binary inspiral time-scale even for low-mass ratios. When considering initially misaligned systems, the orientation of the mini-discs around each black hole can vary significantly. We discuss the implications of this behaviour for black hole spin alignment and highlight the need for broader parameter space studies of misaligned systems to understand the impact on black hole recoil velocities. [ABSTRACT FROM AUTHOR]

One of the most important questions in astrophysics is what causes galaxies to stop forming stars. Previous studies have shown a tight link between quiescence and black hole mass. Other studies have revealed that quiescence is also associated with 'starvation', the halting of gas inflows, which results in the remaining gas being used up by star formation and in rapid chemical enrichment. In this work, we find the missing link between these two findings. Using a large sample of galaxies, we uncover the intrinsic dependences of the stellar metallicity on galaxy properties. In the case of star-forming galaxies, stellar metallicity is primarily driven by stellar mass. However, for passive galaxies, the stellar metallicity is primarily driven by the stellar velocity dispersion. The latter is known to be tightly correlated with black hole mass. This result can be seen as connecting previous studies, where the integrated effect of black hole feedback (i.e. black hole mass, traced by the velocity dispersion) prevents gas inflows, starving the galaxy, which is seen by the rapid increase in the stellar metallicity, and leading to the galaxy becoming passive. [ABSTRACT FROM AUTHOR]

We present observational evidence for a stellar fundamental metallicity relation (FMR), a smooth relation between stellar mass, star formation rate, and the light-weighted stellar metallicity of galaxies, analogous to the well-established gas-phase FMR. We use the non-parametric software ppxf to reconstruct simultaneously the star formation and chemical-enrichment history of a representative sample of galaxies from the local MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) survey. We find that (i) the metallicity of individual galaxies increases with cosmic time and (ii) at all stellar masses, the metallicity of galaxies is progressively higher, moving from the starburst region above the main sequence (MS) towards the passive galaxies below the MS, manifesting the stellar FMR. The scatter is reduced when replacing the stellar mass |$M_{*}$| with |$M_{*}/R_{\rm e}$| (with |$R_{\rm e}$| being the effective radius), in agreement with previous results using the velocity dispersion |$\sigma _{\rm e}$|⁠ , which correlates with |$M_{*}/R_{\rm e}$|⁠. Our results point to starvation as the main physical process through which galaxies quench, showing that metal-poor gas accretion from the intergalactic medium/circumgalactic medium – or the lack thereof – plays an important role in galaxy evolution by simultaneously shaping both their star formation and their metallicity evolutions, while outflows play a subordinate role. This interpretation is further supported by the additional finding of a young stellar FMR, tracing only the stellar populations formed in the last 300 Myr. This suggests a tight co-evolution of the chemical composition of both the gaseous interstellar medium and the stellar populations, where the gas-phase FMR is continuously imprinted on to the stars over cosmic times. [ABSTRACT FROM AUTHOR]

We present an analysis of the quenching of local observed and simulated galaxies, including an investigation of the dependence of quiescence on both intrinsic and environmental parameters. We apply an advanced machine learning technique utilizing random forest classification to predict when galaxies are star forming or quenched. We perform separate classification analyses for three groups of galaxies: (a) central galaxies, (b) high-mass satellites (⁠|$M_{*} \gt 10^{10.5}\,{\rm {\rm M}_{\odot }}$|⁠), and (c) low-mass satellites (⁠|$M_{*} \lt 10^{10}\,{\rm {\rm M}_{\odot }}$|⁠) for three cosmological hydrodynamical simulations (Evolution and Assembly of GaLaxies and their Environments, Illustris, and IllustrisTNG), and observational data from the Sloan Digital Sky Survey. The simulation results are unanimous and unambiguous: quiescence in centrals and high-mass satellites is best predicted by intrinsic parameters (specifically central black hole mass), while it is best predicted by environmental parameters (specifically halo mass) for low-mass satellites. In observations, we find black hole mass to best predict quiescence for centrals and high-mass satellites, exactly as predicted by the simulations. However, local galaxy overdensity is found to be most predictive parameter for low-mass satellites. None the less, both simulations and observations do agree that it is environment which quenches low-mass satellites. We provide evidence which suggests that the dominance of local overdensity in classifying low-mass systems may be due to the high uncertainty in halo mass estimation from abundance matching, rather than it being fundamentally a more predictive parameter. Finally, we establish that the qualitative trends with environment predicted in simulations are recoverable in the observation space. This has important implications for future wide-field galaxy surveys. [ABSTRACT FROM AUTHOR]

We present the first study of spatially integrated higher-order stellar kinematics over cosmic time. We use deep rest-frame optical spectroscopy of quiescent galaxies at redshifts z  = 0.05, 0.3, and 0.8 from the SAMI, MAGPI, and LEGA-C surveys to measure the excess kurtosis h 4 of the stellar velocity distribution, the latter parametrized as a Gauss-Hermite series. Conservatively using a redshift-independent cut in stellar mass (⁠|$M_\star = 10^{11}\, \mathrm{M_\odot }$|⁠) and matching the stellar-mass distributions of our samples, we find 7σ evidence of h 4 increasing with cosmic time, from a median value of 0.019 ± 0.002 at z  = 0.8 to 0.059 ± 0.004 at z  = 0.06. Alternatively, we use a physically motivated sample selection based on the mass distribution of the progenitors of local quiescent galaxies as inferred from numerical simulations; in this case, we find 10σ evidence. This evolution suggests that, over the last 7 Gyr, there has been a gradual decrease in the rotation-to-dispersion ratio and an increase in the radial anisotropy of the stellar velocity distribution, qualitatively consistent with accretion of gas-poor satellites. These findings demonstrate that massive galaxies continue to accrete mass and increase their dispersion support after becoming quiescent. [ABSTRACT FROM AUTHOR]

Nebular He  ii  λ4686 Å line emission is useful to unveil active galactic nuclei (AGN) residing in actively star-forming (SF) galaxies, typically missed by the standard BPT classification. Here, we adopt the He  ii diagnostic to identify hidden AGN in the Local Universe using for the first time spatially resolved data from the Data Release 15 of the Mapping Nearby Galaxies at APO survey (MaNGA DR15). By combining results from He  ii and BPT diagnostics, we overall select 459 AGN host candidates (∼10 per cent in MaNGA DR15), out of which 27 are identified as AGN by the He  ii diagram only. The He  ii -only AGN population is hosted by massive (M * ≳ 1010 M⊙) SF Main Sequence galaxies and on average less luminous than the BPT-selected AGN. Given the He  ii line faintness, we revisit our census accounting for incompleteness effects due to the He  ii sensitivity limit of MaNGA. We thus obtain an overall increased fraction (11 per cent) of AGN in MaNGA compared to the BPT-only census (9 per cent), which further increases to 14 per cent for galaxies more massive than 1010 M⊙; interestingly, on the SF Main Sequence the increase is by about a factor of 2. A substantial number of AGN in SF galaxies points to significant, coeval star formation and black hole accretion, consistently with results from hydrodynamical simulations and with important implications on quenching scenarios. In view of exploring unprecedented high redshifts with JWST and new ground-based facilities, revisiting the standard BPT classification through novel emission-line diagnostics is fundamental to discover AGN in highly SF environments. [ABSTRACT FROM AUTHOR]

We analyse the chemical properties of three z∼ 8 galaxies behind the galaxy cluster SMACS J0723.3-7327, observed as part of the Early Release Observations programme of the James Webb Space Telescope. Exploiting [O  iii ]λ4363 auroral line detections in NIRSpec spectra, we robustly apply the direct T e  method for the very first time at such high redshift, measuring metallicities ranging from extremely metal poor (12 + log(O/H)≈ 7) to about one-third solar. We also discuss the excitation properties of these sources, and compare them with local strong-line metallicity calibrations. We find that none of the considered diagnostics match simultaneously the observed relations between metallicity and strong-line ratios for the three sources, implying that a proper re-assessment of the calibrations may be needed at these redshifts. On the mass–metallicity plane, the two galaxies at z ∼ 7.6 (⁠|$\rm log(M_*/M_{\odot }) = 8.1, 8.7$|⁠) have metallicities that are consistent with the extrapolation of the mass–metallicity relation at z ∼2–3, while the least massive galaxy at z ∼ 8.5 (⁠|$\rm log(M_*/M_{\odot }) = 7.8$|⁠) shows instead a significantly lower metallicity. The three galaxies show different level of offset relative to the Fundamental Metallicity Relation, with two of them (at z ∼ 7.6) being marginally consistent, while the z ∼ 8.5 source deviating significantly, being probably far from the smooth equilibrium between gas flows, star formation, and metal enrichment in place at later epochs. [ABSTRACT FROM AUTHOR]

In this paper, we investigate how massive central galaxies cease their star formation by comparing theoretical predictions from cosmological simulations: EAGLE, Illustris, and IllustrisTNG with observations of the local Universe from the Sloan Digital Sky Survey (SDSS). Our machine learning (ML) classification reveals supermassive black hole mass (M BH) as the most predictive parameter in determining whether a galaxy is star forming or quenched at redshift z  = 0 in all three simulations. This predicted consequence of active galactic nucleus (AGN) quenching is reflected in the observations, where it is true for a range of indirect estimates of M BH via proxies as well as its dynamical measurements. Our partial correlation analysis shows that other galactic parameters lose their strong association with quiescence, once their correlations with M BH are accounted for. In simulations, we demonstrate that it is the integrated power output of the AGN, rather than its instantaneous activity, which causes galaxies to quench. Finally, we analyse the change in molecular gas content of galaxies from star-forming to passive populations. We find that both gas fractions (f gas) and star formation efficiencies (SFEs) decrease upon transition to quiescence in the observations but SFE is more predictive than f gas in the ML passive/star-forming classification. These trends in the SDSS are most closely recovered in IllustrisTNG and are in direct contrast with the predictions made by Illustris. We conclude that a viable AGN feedback prescription can be achieved by a combination of preventative feedback and turbulence injection which together quench star formation in central galaxies. [ABSTRACT FROM AUTHOR]

We investigate how star formation quenching proceeds within central and satellite galaxies using spatially resolved spectroscopy from the SDSS-IV MaNGA DR15. We adopt a complete sample of star formation rate surface densities (ΣSFR), derived in Bluck et al. (2020), to compute the distance at which each spaxel resides from the resolved star forming main sequence (ΣSFR − Σ* relation): ΔΣSFR. We study galaxy radial profiles in ΔΣSFR, and luminosity weighted stellar age (AgeL), split by a variety of intrinsic and environmental parameters. Via several statistical analyses, we establish that the quenching of central galaxies is governed by intrinsic parameters, with central velocity dispersion (σc) being the most important single parameter. High mass satellites quench in a very similar manner to centrals. Conversely, low mass satellite quenching is governed primarily by environmental parameters, with local galaxy overdensity (δ5) being the most important single parameter. Utilizing the empirical M BH − σc relation, we estimate that quenching via AGN feedback must occur at |$M_{\rm BH} \ge 10^{6.5-7.5} \, \mathrm{M}_{\odot }$|⁠ , and is marked by steeply rising ΔΣSFR radial profiles in the green valley, indicating 'inside-out' quenching. On the other hand, environmental quenching occurs at overdensities of 10–30 times the average galaxy density at z ∼ 0.1, and is marked by steeply declining ΔΣSFR profiles, indicating 'outside-in' quenching. Finally, through an analysis of stellar metallicities, we conclude that both intrinsic and environmental quenching must incorporate significant starvation of gas supply. [ABSTRACT FROM AUTHOR]

We present an analysis of star formation and quenching in the SDSS-IV MaNGA-DR15, utilizing over 5 million spaxels from ∼3500 local galaxies. We estimate star formation rate surface densities (ΣSFR) via dust corrected H α flux where possible, and via an empirical relationship between specific star formation rate (sSFR) and the strength of the 4000 Å break (D4000) in all other cases. We train a multilayered artificial neural network (ANN) and a random forest (RF) to classify spaxels into 'star-forming' and 'quenched' categories given various individual (and groups of) parameters. We find that global parameters (pertaining to the galaxy as a whole) perform collectively the best at predicting when spaxels will be quenched, and are substantially superior to local/spatially resolved and environmental parameters. Central velocity dispersion is the best single parameter for predicting quenching in central galaxies. We interpret this observational fact as a probable consequence of the total integrated energy from active galactic neucleus (AGN) feedback being traced by the mass of the black hole, which is well known to correlate strongly with central velocity dispersion. Additionally, we train both an ANN and RF to estimate ΣSFR values directly via regression in star-forming regions. Local/spatially resolved parameters are collectively the most predictive at estimating ΣSFR in these analyses, with stellar mass surface density at the spaxel location (Σ*) being by far the best single parameter. Thus, quenching is fundamentally a global process but star formation is governed locally by processes within each spaxel. [ABSTRACT FROM AUTHOR]

In order to investigate the importance of different proposed quenching mechanisms, we use an indirect method to estimate gas masses for ∼62 000 SDSS DR7 galaxies. We infer gas surface densities from dust column densities as traced by extinction within the fibre, applying a metallicity correction to account for varying dust-to-gas ratios. We find that both gas fraction and star formation efficiency (SFE) decrease moving away from the star-forming main sequence (MS) towards quiescence for all galaxy masses. We further show that both quantities correlate similarly strongly with the departure from the MS, implying the need for any physical model of quenching to invoke a change in both gas fraction and SFE. Our results call for a better understanding of the physical processes driving the decrease in SFE, which has received relatively little attention in the theory of quenching until now. [ABSTRACT FROM AUTHOR]