اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدAGN Feedback: Does it work?
368
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
While feedback is important in theoretical models, we do not really know if it works in reality. Feedback from jets appears to be sufficient to keep the cooling flows in clusters from cooling too much and it may be sufficient to regulate black hole growth in dominant cluster galaxies. Only about 10% of all quasars, however, have powerful radio jets, so jet-related feedback cannot be generic. The outflows could potentially be a more common form of AGN feedback, but measuring mass and energy outflow rates is a challenging task, the main unknown being the location and geometry of the absorbing medium. Using a novel technique, we made first such measurement in NGC 4051 using XMM data and found the mass and energy outflow rates to be 4 to 5 orders of magnitude below those required for efficient feedback. To test whether the outflow velocity in NGC 4051 is unusually low, we compared the ratio of outflow velocity to escape velocity in a sample of AGNs and found it to be generally less than one. It is thus possible that in most Seyferts the feedback is not sufficient and may not be necessary.
قيم البحث
اقرأ أيضاً
Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the strong light-matter interaction in nanophotonic resonators to determine the concentration of chiral molecules at ultra-low thresholds, which is highly a
ttractive for numerous applications in life science and chemistry. However, a thorough understanding of the underlying interactions is still missing. The theoretical description relies on either simple approximations or on purely numerical approaches. We close this gap and present a general theory of chiral light-matter interactions in arbitrary resonators. Our theory describes the chiral interaction as a perturbation of the resonator modes, also known as resonant states or quasi-normal modes. We observe two dominant contributions: A chirality-induced resonance shift and changes in the modes excitation and emission efficiencies. Our theory brings new and deep insights for tailoring and enhancing chiral light-matter interactions. Furthermore, it allows to predict spectra much more efficiently in comparison to conventional approaches. This is particularly true as chiral interactions are inherently weak and therefore perturbation theory fits extremely well for this problem.
The development of neural networks and pretraining techniques has spawned many sentence-level tagging systems that achieved superior performance on typical benchmarks. However, a relatively less discussed topic is what if more context information is
introduced into current top-scoring tagging systems. Although several existing works have attempted to shift tagging systems from sentence-level to document-level, there is still no consensus conclusion about when and why it works, which limits the applicability of the larger-context approach in tagging tasks. In this paper, instead of pursuing a state-of-the-art tagging system by architectural exploration, we focus on investigating when and why the larger-context training, as a general strategy, can work. To this end, we conduct a thorough comparative study on four proposed aggregators for context information collecting and present an attribute-aided evaluation method to interpret the improvement brought by larger-context training. Experimentally, we set up a testbed based on four tagging tasks and thirteen datasets. Hopefully, our preliminary observations can deepen the understanding of larger-context training and enlighten more follow-up works on the use of contextual information.
Black holes depend only on mass and spin, while what we see from the accretion flow in steady state depends also on mass accretion rate and (weakly) inclination. Hence we should be able to scale the accretion flow properties from the stellar to the s
upermassive black holes. But the data show significant differences between these two types of systems, suggesting that we are missing some crucial physics in AGN. One of these differences is the soft X-ray excess which is seen ubiquitously in bright AGN, but only occasionally in BHB. Another is the much faster variability seen in the high energy tail of high mass accretion rate AGN compared to that seen in the tail of BHB. We show that while this variability is not understood, it can be used via the new spectral-timing techniques to constrain the nature of the soft X-ray excess. The coherence, lag-frequency and lag-energy results strongly support this being an additional low temperature Comptonisation component rather than extreme relativistically smeared reflection in the simple Narrow Line Seyfert 1 PG1244+026.
Partial bosonisation of the two-dimensional Hubbard model focuses the functional renormalisation flow on channels in which interactions become strong and local order sets in. We compare the momentum structure of the four-fermion vertex, obtained on t
he basis of a patching approximation, to an effective bosonic description. For parameters in the antiferromagnetic phase near the onset of local antiferromagnetic order, the interaction of the electrons is indeed well described by the exchange of collective bosonic degrees of freedom. The residual four-fermion vertex after the subtraction of the bosonic exchange contribution is small. We propose that similar partial bosonisation techniques can improve the accuracy of renormalisation flow studies also for the case of competing order.
Mergers of galaxies have been suspected to be a major trigger of AGN activity for many years. However, when compared to carefully matched control samples, AGN host galaxies often show no enhanced signs of interaction. A common explanation for this la
ck of observed association between AGN and mergers has often been that while mergers are of importance for triggering AGN, they only dominate at the very high luminosity end of the AGN population. In this study, we compare the morphologies of AGN hosts to a carefully matched control sample and particularly study the role of AGN luminosity. We find no enhanced merger rates in AGN hosts and also find no trend for stronger signs of disturbance at higher AGN luminosities. While this study does not cover very high luminosity AGN, we can exclude a strong connection between AGN and mergers over a wide range of AGN luminosities and therefore for a large part of the AGN population.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
