Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe interaction between feedback from active galactic nuclei and supernovae
235
0
0.0
(
0
)
Authors
C. M. Booth
Ask ChatGPT about the research
No Arabic abstract
Energetic feedback from supernovae (SNe) and from active galactic nuclei (AGN) are both important processes that are thought to control how much gas is able to condense into galaxies and form stars. We show that although both AGN and SNe suppress star formation, they mutually weaken one anothers effect by up to an order of magnitude in haloes in the mass range for which both feedback processes are efficient (10^11.25 M_sun < m_200 < 10^12.5 M_sun). These results demonstrate the importance of the simultaneous, non-independent inclusion of these two processes in models of galaxy formation to estimate the total feedback strength. These results are of particular relevance to semi-analytic models, which implicitly assume the effects of the two feedback processes to be independent, and also to hydrodynamical simulations that model only one of the feedback processes.
rate research
Read More
We present results from a new set of 30 cosmological simulations of galaxy clusters, including the effects of radiative cooling, star formation, supernova feedback, black hole growth and AGN feedback. We first demonstrate that our AGN model is capable of reproducing the observed cluster pressure profile at redshift, z~0, once the AGN heating temperature of the targeted particles is made to scale with the final virial temperature of the halo. This allows the ejected gas to reach larger radii in higher-mass clusters than would be possible had a fixed heating temperature been used. Such a model also successfully reduces the star formation rate in brightest cluster galaxies and broadly reproduces a number of other observational properties at low redshift, including baryon, gas and star fractions; entropy profiles outside the core; and the X-ray luminosity-mass relation. Our results are consistent with the notion that the excess entropy is generated via selective removal of the densest material through radiative cooling; supernova and AGN feedback largely serve as regulation mechanisms, moving heated gas out of galaxies and away from cluster cores. However, our simulations fail to address a number of serious issues; for example, they are incapable of reproducing the shape and diversity of the observed entropy profiles within the core region. We also show that the stellar and black hole masses are sensitive to numerical resolution, particularly the gravitational softening length; a smaller value leads to more efficient black hole growth at early times and a smaller central galaxy.
(Abridged) We present a method that tracks the growth of supermassive black holes (BHs) and the feedback from AGN in cosmological simulations. Our model is a substantially modified version of the one by Springel et al. (2005). Because cosmological simulations lack both the resolution and the physics to model the multiphase interstellar medium, they tend to strongly underestimate the Bondi-Hoyle accretion rate. To allow low-mass BHs to grow, it is therefore necessary to increase the predicted Bondi-Hoyle rates in dense gas by large, ad-hoc factors. We explore the physical regimes where the use of such factors is reasonable, and through this introduce a new prescription for gas accretion. Feedback from AGN is modeled by coupling a fraction of the rest-mass energy of the accreted gas thermally into the surrounding medium. We describe the implementation as well as the limitations of the model and motivate all the changes relative to previous work. We investigate the robustness of the predictions for the cosmic star formation history, the redshift zero cosmic BH density, BH scaling relations, and galaxy specific star formation rates. We find that the freedom introduced by the need to increase the predicted accretion rates, the standard procedure in the literature, is the most significant source of uncertainty. Our simulations demonstrate that supermassive BHs are able to regulate their growth by releasing a fixed amount of energy for a given halo mass, independent of the assumed efficiency of AGN feedback, which sets the normalization of the BH scaling relations. Regardless of whether BH seeds are initially placed above or below the BH scaling relations they grow onto the same relations. AGN feedback efficiently suppresses star formation in high-mass galaxies.
The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. Cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. Outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source preventing runaway cooling by carving cavities and driving shocks across the medium. The AGN feedback loop is a key feature of all modern galaxy evolution models. Here we review our knowledge of the AGN feedback process in the specific context of galaxy groups. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling-heating balance. Unlike in more massive halos, the energy supplied by the central AGN to the hot intragroup medium can exceed the gravitational binding energy of halo gas particles. We report on the state-of-the-art in observations of the feedback phenomenon and in theoretical models of the heating-cooling balance in galaxy groups. We also describe how our knowledge of the AGN feedback process impacts on galaxy evolution models and on large-scale baryon distributions. Finally, we discuss how new instrumentation will answer key open questions on the topic.
Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionise the Universe. We assess the viability of this scenario using a semi-numerical framework for modeling reionisation, to which we add a quasar contribution by constructing a Quasar Halo Occupation Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth $tau_e$, neutral fraction, and ionising emissivity. Such a model predicts $tau_e$ too low by $sim 2sigma$ relative to Planck constraints, and reionises the Universe at $zlesssim 5$. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionising emissivity at $zsim 5$. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match $tau_e$ albeit with late reionisation, however such evolution is inconsistent with observations at $zsim 4-6$ and poorly motivated physically. These results arise because AGN are more biased towards massive halos than typical reionising galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionising bubbles that are reflected in $simtimes 2$ more 21cm power on all scales. A model with equal parts galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21cm experiments HERA and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionising photon budget for reionisation.
The observed relation between the X-ray radiation from AGNs, originating in the corona, and the optical/UV radiation from the disk is usually described by the anticorrelation between the UV to X-ray slope alpha_ox and the UV luminosity. Many factors can affect this relation, including: enhanced X-ray emission associated with the jets of radio-loud AGNs; X-ray absorption associated with the UV Broad Absorption Line (BAL) outflows; other X-ray absorption not associated with BALs; intrinsic X-ray weakness; UV and X-ray variability, and non-simultaneity of UV and X-ray observations. The separation of these effects provides information about the intrinsic alpha_ox-L_UV relation and its dispersion, constraining models of disk-corona coupling. We extract simultaneous data from the second XMM-Newton serendipitous source catalogue and the XMM-Newton Optical Monitor Serendipitous UV Source Survey Catalog, and derive the single-epoch alpha_ox indices. We use ensemble structure functions to analyse multi-epoch data. We confirm the anticorrelation of alpha_ox with L_UV, and do not find any evidence of a dependence of alpha_ox on z. The dispersion in our simultaneous data (0.12) is not significantly smaller than in previous non-simultaneous studies, suggesting that artificial alpha_ox variability introduced by non-simultaneity is not the main cause of dispersion. Intrinsic alpha_ox variability, i.e., the true variability of the X-ray to optical ratio, is instead important, and accounts for ~30% of the total variance, or more. Inter-source dispersion, due to intrinsic differences in the average alpha_ox values from source to source, is also important. The dispersion introduced by variability is mostly caused by the long timescale variations, which are expected to be driven by the optical variations.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
