Supermassive black holes as the regulators of star formation in central galaxies

We present a relationship between the black hole mass, stellar mass, and star formation rate of a diverse group of 91 galaxies with dynamically-measured black hole masses. For our sample of galaxies with a variety of morphologies and other galactic properties, we find that the specific star formation rate is a smoothly decreasing function of the ratio between black hole mass and stellar mass, or what we call the specific black hole mass. In order to explain this relation, we propose a physical framework where the gradual suppression of a galaxy's star formation activity results from the adjustment to an increase in specific black hole mass and, accordingly, an increase in the amount of heating. From this framework, it follows that at least some galaxies with intermediate specific black hole masses are in a steady state of partial quiescence with intermediate specific star formation rates, implying that both transitioning and steady-state galaxies live within this region known as the "green valley." With respect to galaxy formation models, our results present an important diagnostic with which to test various prescriptions of black hole feedback and its effects on star formation activity.Comment: 15 pages, 4 figures, 2 tables. Accepted for publication in The Astrophysical Journa

The origin of the mass scales for maximal star formation efficiency and quenching: the critical role of Supernovae

We use the Henriques et al. (2015) version of the Munich galaxy formation model (L-GALAXIES) to investigate why the halo and stellar mass scales above which galaxies are quenched are constant with redshift and coincide with the scale where baryons are most efficiently converted into stars. This model assumes that central galaxies are quenched by AGN feedback when hot halo gas accretes onto a supermassive black hole. Nevertheless, we find that supernova (SN) feedback sets both mass scales. As haloes grow above a threshold mass, SNe can no longer eject material so their hot gas content increases, enhancing the cooling rate onto the central galaxy, its cold gas content, its star formation rate and the growth rate of its central black hole. Strong AGN feedback terminates this short-lived phase by suppressing the fuel supply for star formation. Despite strong evolution of the halo mass - temperature relation, quenching occurs at a redshift-independent halo and stellar mass which coincides with the mass where baryons have been converted into stars with maximal efficiency. These regularities and coincidences are a result of the specific parameters selected by MCMC tuning of the model to fit the observed abundance and passive fraction of galaxies over the redshift range 0<z<3. Thus they are required by the observed evolution of the galaxy population, at least in the context of models of this type.Comment: 12 pages, 8 figures, submitted to MNRA

The relationship between black hole mass and galaxy properties: Examining the black hole feedback model in IllustrisTNG

Supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. We explore how observable correlations between the specific star formation rate (sSFR), stellar mass (M$_{\rm{star}}$), and black hole mass (M$_{\rm{BH}}$) are sensitive to the physics of black hole feedback in a galaxy formation model. We use the IllustrisTNG simulation suite, specifically the TNG100 simulation and ten model variations that alter the parameters of the black hole model. Focusing on central galaxies at $z = 0$ with M$_{\rm{star}} > 10^{10}$ M$_{\odot}$, we find that the sSFR of galaxies in IllustrisTNG decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. This occurs at a particular M$_{\rm{BH}}$ threshold above which galaxies are found to sharply transition from being mostly star-forming to mostly quiescent. As a result of this behavior, the fraction of quiescent galaxies as a function of M$_{\rm{star}}$ is sensitive to both the normalization of the M$_{\rm{BH}}$-M$_{\rm{star}}$ relation and the M$_{\rm{BH}}$ threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical M$_{\rm{BH}}$ measurements with the caveat that this sample is not representative of the whole galaxy population. While IllustrisTNG reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in M$_{\rm{BH}}$ at a given M$_{\rm{star}}$ and show a smoother decline in sSFR with M$_{\rm{BH}}$.Comment: 20 pages, submitted to MNRA

Dense stellar clump formation driven by strong quasar winds in the FIRE cosmological hydrodynamic simulations

We investigate the formation of dense stellar clumps in a suite of high-resolution cosmological zoom-in simulations of a massive, star forming galaxy at $z \sim 2$ under the presence of strong quasar winds. Our simulations include multi-phase ISM physics from the Feedback In Realistic Environments (FIRE) project and a novel implementation of hyper-refined accretion disk winds. We show that powerful quasar winds can have a global negative impact on galaxy growth while in the strongest cases triggering the formation of an off-center clump with stellar mass ${\rm M}_{\star}\sim 10^{7}\,{\rm M}_{\odot}$, effective radius ${\rm R}_{\rm 1/2\,\rm Clump}\sim 20\,{\rm pc}$, and surface density $\Sigma_{\star} \sim 10^{4}\,{\rm M}_{\odot}\,{\rm pc}^{-2}$. The clump progenitor gas cloud is originally not star-forming, but strong ram pressure gradients driven by the quasar winds (orders of magnitude stronger than experienced in the absence of winds) lead to rapid compression and subsequent conversion of gas into stars at densities much higher than the average density of star-forming gas. The AGN-triggered star-forming clump reaches ${\rm SFR} \sim 50\,{\rm M}_{\odot}\,{\rm yr}^{-1}$ and $\Sigma_{\rm SFR} \sim 10^{4}\,{\rm M}_{\odot}\,{\rm yr}^{-1}\,{\rm kpc}^{-2}$, converting most of the progenitor gas cloud into stars in $\sim$2\,Myr, significantly faster than its initial free-fall time and with stellar feedback unable to stop star formation. In contrast, the same gas cloud in the absence of quasar winds forms stars over a much longer period of time ($\sim$35\,Myr), at lower densities, and losing spatial coherency. The presence of young, ultra-dense, gravitationally bound stellar clumps in recently quenched galaxies could thus indicate local positive feedback acting alongside the strong negative impact of powerful quasar winds, providing a plausible formation scenario for globular clusters.Comment: 14 pages, 12 figure

Dense stellar clump formation driven by strong quasar winds in the FIRE cosmological hydrodynamic simulations

We investigate the formation of dense stellar clumps in a suite of high-resolution cosmological zoom-in simulations of a massive, star-forming galaxy at z ∼ 2 under the presence of strong quasar winds. Our simulations include multiphase ISM physics from the Feedback In Realistic Environments (FIRE) project and a no v el implementation of hyper-refined accretion disc winds. We show that powerful quasar winds can have a global negative impact on galaxy growth while in the strongest cases triggering the formation of an off-centre clump with stellar mass M ∼ 10 7 M , effective radius R 1 / 2 Clump ∼ 20 pc , and surface density ∼10 4 M pc −2 . The clump progenitor gas cloud is originally not star -forming, b ut strong ram pressure gradients driven by the quasar winds (orders of magnitude stronger than experienced in the absence of winds) lead to rapid compression and subsequent conversion of gas into stars at densities much higher than the average density of star-forming gas. The AGN-triggered star-forming clump reaches SFR ∼ 50 M yr −1 and SFR ∼ 10 4 M yr −1 kpc −2 , converting most of the progenitor gas cloud into stars in ∼2 Myr, significantly faster than its initial free-fall time and with stellar feedback unable to stop star formation. In contrast, the same gas cloud in the absence of quasar winds forms stars over a much longer period of time ( ∼35 Myr), at lower densities, and losing spatial coherency. The presence of young, ultra-dense, gravitationally bound stellar clumps in recently quenched galaxies could thus indicate local positive feedback acting alongside the strong negative impact of powerful quasar winds, providing a plausible formation scenario for globular clusters

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.Comment: 17 pages, 12 figure

The First Quiescent Galaxies in TNG300

We identify the first quiescent galaxies in TNG300, the largest volume of the IllustrisTNG cosmological simulation suite, and explore their quenching processes and time evolution to z=0. We find that the first quiescent galaxies with stellar masses M_* > 3 x 10^{10} M_sun and specific star formation rates sSFR < 10^{-11} yr^{-1} emerge at z~4.2 in TNG300. Suppression of star formation in these galaxies begins with a thermal mode of AGN feedback at z~6, and a kinetic feedback mode acts in each galaxy by z~4.7 to complete the quenching process, which occurs on a time-scale of ~0.35 Gyr. Surprisingly, we find that the majority of these galaxies are not the main progenitors of their z=0 descendants; instead, four of the five galaxies fall into more massive galaxies in subsequent mergers at a range of redshifts 2.5 < z < 0.2. By z=0, these descendants are the centres of galaxy clusters with average stellar masses of 8 x 10^{11} M_sun. We make predictions for the first quenched galaxies to be located by the James Webb Space Telescope (JWST).Comment: 6 pages, 4 figure

JWST Reveals Widespread AGN-Driven Neutral Gas Outflows in Massive z ~ 2 Galaxies

We use deep JWST/NIRSpec R~1000 slit spectra of 113 galaxies at 1.7 < z < 3.5, selected from the mass-complete Blue Jay survey, to investigate the prevalence and typical properties of neutral gas outflows at cosmic noon. We detect excess Na I D absorption (beyond the stellar contribution) in 46% of massive galaxies ($\log$ M$_*$/M$_\odot >$ 10), with similar incidence rates in star-forming and quenching systems. Half of the absorption profiles are blueshifted by at least 100 km/s, providing unambiguous evidence for neutral gas outflows. Galaxies with strong Na I D absorption are distinguished by enhanced emission line ratios consistent with AGN ionization. We conservatively measure mass outflow rates of 3 - 100 $M_\odot$ yr$^{-1}$; comparable to or exceeding ionized gas outflow rates measured for galaxies at similar stellar mass and redshift. The outflows from the quenching systems (log(sSFR)[yr$^{-1}$] $\lesssim$ -10) have mass loading factors of 4 - 360, and the energy and momentum outflow rates exceed the expected injection rates from supernova explosions, suggesting that these galaxies could possibly be caught in a rapid blowout phase powered by the AGN. Our findings suggest that AGN-driven ejection of cold gas may be a dominant mechanism for fast quenching of star formation at z~2.Comment: 16 pages, 8 figures, submitted to MNRA