Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMultiphase Signatures of AGN Feedback in Abell 2597
115
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present new Chandra X-ray observations of the brightest cluster galaxy (BCG) in the cool core cluster Abell 2597. The data reveal an extensive kpc-scale X-ray cavity network as well as a 15 kpc filament of soft-excess gas exhibiting strong spatial correlation with archival VLA radio data. In addition to several possible scenarios, multiwavelength evidence may suggest that the filament is associated with multiphase (10^3 - 10^7 K) gas that has been entrained and dredged-up by the propagating radio source. Stemming from a full spectral analysis, we also present profiles and 2D spectral maps of modeled X-ray temperature, entropy, pressure, and metal abundance. The maps reveal an arc of hot gas which in projection borders the inner edge of a large X-ray cavity. Although limited by strong caveats, we suggest that the hot arc may be (a) due to a compressed rim of cold gas pushed outward by the radio bubble or (b) morphologically and energetically consistent with cavity-driven active galactic nucleus (AGN) heating models invoked to quench cooling flows, in which the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas rushes to refill its wake. If confirmed, this would be the first observational evidence for this model.
rate research
Read More
Supermassive black hole (SMBH) feeding and feedback processes are often considered as disjoint and studied independently at different scales, both in observations and simulations. We encourage to adopt and unify three physically-motivated scales for feeding and feedback (micro - meso - macro ~ mpc - kpc - Mpc), linking them in a tight multiphase self-regulated loop. We pinpoint the key open questions related to this global SMBH unification problem, while advocating for the extension of novel mechanisms best observed in massive halos (such as chaotic cold accretion) down to low-mass systems. To solve such challenges, we provide a set of recommendations that promote a multiscale, multiwavelength, and interdisciplinary community.
We study the gas accretion onto a supermassive black hole (SMBH) using the 3D SPH code GADGET-3 on scales of 0.1-200 pc. First we test our code with spherically symmetric, adiabatic Bondi accretion problem. We find that our simulation can reproduce the expected Bondi accretion flow very well for a limited amount of time until the effect of outer boundary starts to be visible. We also find artificial heating of gas near the inner accretion boundary due to the artificial viscosity of SPH. Second, we implement radiative cooling and heating due to X-rays, and examine the impact of thermal feedback by the central X-ray source. The accretion flow roughly follows the Bondi solution for low central X-ray luminosities, however, the flow starts to exhibit non-spherical fragmentation due to thermal instability for a certain range of central L_X, and a strong overall outflow develops for greater L_X. The cold gas develops filamentary structures that fall into the central SMBH, whereas the hot gas tries to escape through the channels in-between the cold filaments. Such fragmentation of accreting gas can assist in the formation of clouds around AGN, induce star-formation, and contribute to the observed variability of narrow-line regions.
We present results from Chandra and XMM-Newton observations of Abell 98 (A98), a galaxy cluster with three major components: a relatively bright subcluster to the north (A98N), a disturbed subcluster to the south (A98S), and a fainter subcluster to the far south (A98SS). We find evidence for surface brightness and temperature asymmetries in A98N consistent with a shock-heated region to the south, which could be created by an early stage merger between A98N and A98S. Deeper observations are required to confirm this result. We also find that A98S has an asymmetric core temperature structure, likely due to a separate ongoing merger. Evidence for this is also seen in optical data. A98S hosts a wide-angle tail (WAT) radio source powered by a central active galactic nucleus (AGN). We find evidence for a cavity in the intracluster medium (ICM) that has been evacuated by one of the radio lobes, suggesting that AGN feedback is operating in this system. Examples of cavities in non-cool core clusters are relatively rare. The three subclusters lie along a line in projection, suggesting the presence of a large-scale filament. We observe emission along the filament between A98N and A98S, and a surface brightness profile shows emission consistent with the overlap of the subcluster extended gas haloes. We find the temperature of this region is consistent with the temperature of the gas at similar radii outside this bridge region. Lastly, we examine the cluster dynamics using optical data. We conclude A98N and A98S are likely bound to one another, with a 67% probability, while A98S and A98SS are not bound at a high level of significance.
The reionization of the Universe ends the dark ages that started after the recombination era. In the case of H, reionization finishes around $zsim 6$. Faint star-forming galaxies are the best candidate sources of the H-ionizing radiation, although active galactic nuclei may have also contributed. We have explored whether the termination regions of the jets from active galactic nuclei may have contributed significantly to the ionization of H in the late reionization epoch, around $zsim 6-7$. We assumed that, as it has been proposed, active galactic nuclei at $zsim 6$ may have presented a high jet fraction, accretion rate, and duty cycle, and that non-thermal electrons contribute significantly to the pressure of jet termination regions. Empirical black-hole mass functions were adopted to characterize the population of active galactic nuclei. From all this, estimates were derived for the isotropic H-ionizing radiation produced in the jet termination regions, at $zsim 6$, through inverse Compton scattering off CMB photons. We find that the termination regions of the jets of active galactic nuclei may have radiated most of their energy in the form of H-ionizing radiation at $zsim 6$. For typical black-hole mass functions at that redshift, under the considered conditions (long-lasting, common, and very active galactic nuclei with jets), the contribution of these jets to maintain (and possibly enhance) the ionization of H may have been non-negligible. We conclude that the termination regions of jets from active galactic nuclei could have had a significant role in the reionization of the Universe at $zgtrsim 6$.
We present a deep study of the average hard X-ray spectra of Seyfert galaxies. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the 165 Seyfert galaxies detected at z<0.2. Our final sample consists of 44 Seyfert 1s, 29 Seyfert 1.5s, 78 Seyfert 2s, and 14 Narrow Line Seyfert 1s. We derived the average hard X-ray spectrum of each subsample in the 17-250keV energy range. All classes of Seyfert galaxies show on average the same nuclear continuum, as foreseen by the zeroth order unified model, with a cut-off energy of Ec>200keV, and a photon index of Gamma ~1.8. Compton-thin Seyfert 2s show a reflection component stronger than Seyfert 1s and Seyfert 1.5s. Most of this reflection is due to mildly obscured (10^23 cm^-2 < NH < 10^24 cm^-2) Seyfert 2s, which have a significantly stronger reflection component (R=2.2^{+4.5}_{-1.1}) than Seyfert 1s (R<=0.4), Seyfert 1.5s (R<= 0.4) and lightly obscured (NH < 10^23 cm^-2) Seyfert 2s (R<=0.5). This cannot be explained easily by the unified model. The absorber/reflector in mildly obscured Seyfert 2s might cover a large fraction of the X-ray source, and have clumps of Compton-thick material. The large reflection found in the spectrum of mildly obscured Seyfert 2s reduces the amount of Compton-thick objects needed to explain the peak of the cosmic X-ray background. Our results are consistent with the fraction of Compton-thick sources being ~10%. The spectra of Seyfert 2s with and without polarized broad lines do not show significant differences, the only difference between the two samples being the higher hard X-ray and bolometric luminosity of Seyfert 2s with polarized broad lines. The average hard X-ray spectrum of Narrow line Seyfert 1s is steeper than those of Seyfert 1s and Seyfert 1.5s, probably due to a lower energy of the cutoff.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
