Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Pairing of Accreting Massive Black Holes in Multiphase Circumnuclear Disks: the Interplay between Radiative Cooling, Star Formation, and Feedback Processes
217
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the orbital decay of a pair of massive black holes (BHs) with masses 5 * 10^5 and 10^7 M_sun, using hydrodynamical simulations of circumnuclear disks (CNDs) with the alternating presence of sub-grid physics such as radiative cooling, star formation, supernova feedback, BH accretion and feedback. In the absence of such processes, the orbit of the secondary BH decays over timescales of ~10 Myr to the center of the CND, where the primary BH resides. When strong dissipation operates in CNDs, fragmentation into massive objects the size of giant molecular clouds and with densities in the range 10^4 - 10^7 amu / cm^3 occurs, causing stochastic torques and hits that can eject the secondary BH from the midplane. Outside the plane, the low-density medium provides only weak drag, and the BH return is governed by inefficient dynamical friction. In rare cases, clump-BH interactions can lead to a faster decay. Feedback processes lead to outflows, but do not change significantly the overall density of the CND midplane. However, with a spherically distributed BH feedback a hot bubble is generated behind the secondary, which almost shuts off dynamical friction, a phenomenon we dub wake evacuation, leading to delays in the decay of possibly ~0.3 Gyr. We discuss the non-trivial implications on the discovery space of the eLISA telescope. Our results suggest the largest uncertainty in predicting BH merger rates lies in the potentially wide variety of galaxy host systems, with different degrees of gas dissipation and heating, yielding decay timescales from ~10 to ~300 Myr.
rate research
Read More
Recent advances in our understanding of massive star formation have made clear the important role of protostellar disks in mediating accretion. Here we describe a simple, semi-analytic model for young, deeply embedded, massive accretion disks. Our approach enables us to sample a wide parameter space of stellar mass and environmental variables, providing a means to make predictions for a variety of sources that next generation telescopes like ALMA and the EVLA will observe. Moreover we include, at least approximately, multiple mechanisms for angular momentum transport, a comprehensive model for disk heating and cooling, and a realistic estimate for the angular momentum in the gas reservoir. We make predictions for the typical sizes, masses, and temperatures of the disks, and describe the role of gravitational instabilities in determining the binarity fraction and upper mass cut-off.
Black hole accretion is widely thought to influence star formation in galaxies, but the empirical evidence for a physical correlation between star formation rate (SFR) and the properties of active galactic nuclei (AGNs) remains highly controversial. We take advantage of a recently developed SFR estimator based on the [O II] $lambda3727$ and [O III] $lambda5007$ emission lines to investigate the SFRs of the host galaxies of more than 5,800 type 1 and 7,600 type 2 AGNs with $z < 0.35$. After matching in luminosity and redshift, we find that type 1 and type 2 AGNs have a similar distribution of internal reddening, which is significant and corresponds to $sim 10^9,M_odot$ of cold molecular gas. In spite of their comparable gas content, type 2 AGNs, independent of stellar mass, Eddington ratio, redshift or molecular gas mass, exhibit intrinsically stronger star formation activity than type 1 AGNs, in apparent disagreement with the conventional AGN unified model. We observe a tight, linear relation between AGN luminosity (accretion rate) and SFR, one that becomes more significant toward smaller physical scales, suggesting that the link between the AGN and star formation occurs in the central kpc-scale region. This, along with a correlation between SFR and Eddington ratio in the regime of super-Eddington accretion, can be interpreted as evidence that star formation is impacted by positive feedback from the AGN.
There is mounting evidence for the coevolution of galaxies and their embedded massive black holes (MBHs) in a hierarchical structure formation paradigm. To tackle the nonlinear processes of galaxy-MBH interaction, we describe a self-consistent numerical framework which incorporates both galaxies and MBHs. The high-resolution adaptive mesh refinement (AMR) code Enzo is modified to model the formation and feedback of molecular clouds at their characteristic scale of 15.2 pc and the accretion of gas onto a MBH. Two major channels of MBH feedback, radiative feedback (X-ray photons followed through full 3D adaptive ray tracing) and mechanical feedback (bipolar jets resolved in high-resolution AMR), are employed. We investigate the coevolution of a 9.2e11 Msun galactic halo and its 1e5 Msun embedded MBH at redshift 3 in a cosmological LCDM simulation. The MBH feedback heats the surrounding ISM up to 1e6 K through photoionization and Compton heating and locally suppresses star formation in the galactic inner core. The feedback considerably changes the stellar distribution there. This new channel of feedback from a slowly growing MBH is particularly interesting because it is only locally dominant, and does not require the heating of gas globally on the disk. The MBH also self-regulates its growth by keeping the surrounding ISM hot for an extended period of time.
HD dominates the cooling of primordial clouds with enhanced ionization, e.g. shock-heated clouds in structure formation or supernova remnants, relic HII regions of Pop III stars, and clouds with cosmic-ray (CR) irradiation. There, the temperature decreases to several 10 K and the characteristic stellar mass decreases to $sim 10 {rm M}_{odot}$, in contrast with first stars formed from undisturbed pristine clouds ($sim 100 {rm M}_{odot}$). However, without CR irradiation, even weak far ultra-violet (FUV) irradiation suppresses HD formation/cooling. Here, we examine conditions for HD cooling in primordial clouds including both FUV and CR feedback. At the beginning of collapse, the shock-compressed gas cools with its density increasing, while the relic HII region gas cools at a constant density. Moreover, shocks tend to occur in denser environments than HII regions. Owing to the higher column density and the more effective shielding, the critical FUV intensity for HD cooling in a shock-compressed gas becomes $sim 10$ times higher than in relic HII regions. Consequently, in the shock-compressed gas, the critical FUV intensity exceeds the background level for most of the redshift we consider ($6 lesssim z lesssim 15$), while in relic HII regions, HD cooling becomes effective after the CR intensity increases enough at $z lesssim 10$. Our result suggests that less massive ($sim 10 {rm M}_{odot}$) Pop III stars may be more common than previously considered and could be the dominant population of Pop III stars.
We derive X-ray mass, luminosity, and temperature profiles for 45 galaxy clusters to explore relationships between halo mass, AGN feedback, and central cooling time. We find that radio--mechanical feedback power (referred to here as AGN power) in central cluster galaxies correlates with halo mass as P$_{rm mech}$ $propto$ M$^{1.55pm0.26}$, but only in halos with central atmospheric cooling times shorter than 1 Gyr. The trend of AGN power with halo mass is consistent with the scaling expected from a self-regulating AGN feedback loop, as well as with galaxy and central black hole co-evolution along the $M_{rm BH} - sigma$ relation. AGN power in clusters with central atmospheric cooling times longer than $sim 1$ Gyr typically lies two orders of magnitude below those with shorter central cooling times. Galaxies centred in clusters with long central cooling times nevertheless experience ongoing and occasionally powerful AGN outbursts. We further investigate the impact of feedback on cluster scaling relations. We find $L-T$, and $M-T$ relations in clusters with direct evidence of feedback which are steeper than self-similar, but not atypical compared to previous studies of the full cluster population. While the gas mass rises, the stellar mass remains nearly constant with rising total mass, consistent with earlier studies. This trend is found regardless of central cooling time, implying tight regulation of star formation in central galaxies as their halos grew, and long-term balance between AGN heating and atmospheric cooling. Our scaling relations are presented in forms that can be incorporated easily into galaxy evolution models.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
