1,721,107 research outputs found
Intracluster and intragroup entropy from quasar activity
No full textWe investigate how the hierarchical merging of dark matter halos, the radiative cooling of baryons, and the energy feedback from supernovae and active galactic nuclei or quasars combine to govern the amount and the thermal state of the hot plasma pervading groups and clusters of galaxies. We show that, by itself, supernova preheating of the external gas flowing into clusters falls short of explaining the observed X-ray scaling relations of the plasma luminosity LX or the plasma entropy K versus the X-ray temperature T. To account for the scaling laws from rich to poor clusters takes preheating enhanced by the energy input from active galactic nuclei. In groups, on the other hand, the internal impacts of powerful quasars going off in member galaxies can blow some plasma out of the structure. So they depress LX and raise K to the observed average levels; meanwhile, the sporadic nature of such impulsive events generates the intrinsic component of the wide scatter apparent in the data. The same quasar feedback gives rise in groups to entropy profiles as steep as observed, a feature hard to explain with simple preheating schemes. Finally, we argue a close connection of the LX-T or the K-T relation with the M•-σ correlation between the host velocity dispersion and the masses of the black holes, relics of the quasar activity
Quasar Feedback on the Intracluster Medium
Full text linkGalaxy groups are quite underluminous in X-rays compared to clusters, so the intracluster medium (ICM) has to be considerably underdense in the former. We consider this to be due to substantial energy fed back into the ICM when the baryons in the member galaxies condense into stars ending up in supernovae (SNe) or accrete onto central supermassive black holes energizing active galactic nuclei (AGNs). We compute the outflow and the blowout effects driven by the AGNs and the resulting steep luminosity-temperature correlation LX-T. We compare this with the SN contribution and with the X-ray data; the latter require the AGN energy to be coupled to the surrounding ICM at fractional levels around 5×10-2. We link the LX-T behavior with the parallel effects of the AGN feedback on the gas in the host galaxy; we find that these yield a correlation steep up to MBH~σ5 between the galactic velocity dispersions and the central black hole masses
Probing scale-variance from clusters to groups of galaxies
No full textWe discuss need, levels and origins of non-gravitational heating in groups of galaxies, and how these may be probed not only with X-ray observation, but also with the SZ effect
Outflows in the gaseous discs of active galaxies and their impact on black hole scaling relations
No full textTo tackle the still unsolved and fundamental problem of the role of Active Galactic Nuclei (AGN) feedback in shaping galaxies, in this work we implement a new physical treatment of AGN-driven winds into our semi-analytic model of galaxy formation. To each galaxy in our model, we associate solutions for the outflow expansion and the mass outflow rates in different directions, depending on the AGN luminosity, on the circular velocity of the host halo, and on gas content of the considered galaxy. To each galaxy we also assign an effective radius derived from energy conservation during merger events, and a stellar velocity dispersion self-consistently computed via Jeans modelling. We derive all the main scaling relations between Black hole (BH) mass and total/bulge stellar mass, velocity dispersion, host halo dark matter mass, and star formation efficiency. We find that our improved AGN feedback mostly controls the dispersion around the relations but plays a subdominant role in shaping slopes and/or normalizations of the scaling relations. Including possible limited-resolution selection biases in the model provides better agreement with the available data. The model does not point to any more fundamental galactic property linked to BH mass, with velocity dispersion playing a similar role with respect to stellar mass, in tension with present data. In line with other independent studies carried out on comprehensive semi-analytic and hydrodynamic galaxy-BH evolution models, our current results signal either an inadequacy of present cosmological models of galaxy formation in fully reproducing the local scaling relations, in terms of both shape and residuals, and/or point to an incompleteness issue affecting the local sample of dynamically-measured BHs
The thermal state of the ICM probed with the SZ effect
No full textOrigins, levels and effects of non-gravitational energy inputs into the ICM pervading groups and clusters of galaxies. The role of the SZ effect as a probe of these processes
Probing AGN feedback on the ICM with the Sunyaev-Zel’dovich effect
No full textThe twentieth century witnessed some remarkable discoveries: the 1917 publication of Einstein's general theory of relativity, Carnegie astronomer Edwin Hubble's 1929 discovery of the expansion of the universe, evidence for the existence of dark matter, and the discovery of a mysterious dark energy, which is causing the universe to speed up its expansion. This comprehensive volume reviews the theory and measurement of various parameters related to the evolution of the universe. Topics include inflation, string theory, the history of cosmology in the context of measurements being made of the Hubble constant, the matter density, and dark energy, including observational results from the Sloan, Digital Sky Survey, Keck, Magellan, cosmic microwave background experiments, Hubble space telescope and Chandra. With chapters by leading authorities in the field, this book is a valuable resource for graduate students and professional research astronomers.
Review: Review of the hardback: '... this book is an excellent description of the state of cosmology at the beginning of the 21st Century and can be used as a very useful tool for a graduate course in cosmology.
X-Ray Evolution of Active Galactic Nuclei and Hierarchical Galaxy Formation
No full textWe have incorporated the description of the X-ray properties of aActive gGalactic nNuclei (AGNs) into a semi-analytic model of galaxy formation, adopting physically motivated scaling laws for accretion triggered by galaxy encounters. Our model reproduces the level of the cosmic X-ray background at 30 keV; we predict that the largest contribution (around two-thirds) comes from sources with intermediate X-ray luminosity 1043.51044.5 ergs s-1 in the 2-10 keV band) peaks at z~2, with a decline of around 3 dex to z=0; for the low- luminosity sources (1043<LX/ergss-1<1044), it has a broader and less pronounced maximum around z~1.5. The comparison with the data shows a generally good agreement. The model predictions slightly exceed the observed number of low-luminosity AGNs at z~1.5, with the discrepancy progressively extending to intermediate-luminosity objects at higher redshifts; we discuss possible origins offor the mismatch. Finally, we predict the source counts and the flux distribution at different redshifts in the hard (20--100 keV) X-ray band for the sources contributing to the X- ray background
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