ABSTRACT We present a model describing the evolution of Fanaroff-Riley type I and II radio active galactic nuclei (AGNs) and the transition between these classes. We quantify galactic environments ...using a semianalytic galaxy formation model and apply our model to a volume-limited low-redshift ( ) sample of observed AGNs to determine the distribution of jet powers and active lifetimes at the present epoch. Radio sources in massive galaxies are found to remain active for longer, spend less time in the quiescent phase, and inject more energy into their hosts than their less massive counterparts. The jet power is independent of the host stellar mass within uncertainties, consistent with maintenance-mode AGN feedback paradigm. The environments of these AGNs are in or close to long-term heating-cooling balance. We also examine the properties of high- and low-excitation radio galactic subpopulations. The HERGs are younger than LERGs by an order of magnitude, whereas their jet powers are greater by a factor of four. The Eddington-scaled accretion rates and jet production efficiencies of these populations are consistent with LERGs being powered by radiatively inefficient advection-dominated accretion flows, whereas HERGs are fed by a radiatively efficient accretion mechanism.
Halophytes are defined as plants that are adapted to live in soils containing high concentrations of salt and benefiting from it, and thus represent an ideal model to understand complex physiological ...and genetic mechanisms of salinity stress tolerance. It is also known that oxidative stress signalling and reactive oxygen species (ROS) detoxification are both essential components of salinity stress tolerance mechanisms. This paper comprehensively reviews the differences in ROS homeostasis between halophytes and glycophytes in an attempt to answer the questions of whether stress-induced ROS production is similar between halophytes and glycophytes; is the superior salinity tolerance in halophytes attributed to higher antioxidant activity; and is there something special about the specific ‘pool’ of enzymatic and non-enzymatic antioxidants in halophytes. We argue that truly salt-tolerant species possessing efficient mechanisms for Na+ exclusion from the cytosol may not require a high level of antioxidant activity, as they simply do not allow excessive ROS production in the first instance. We also suggest that H2O2 ‘signatures’ may operate in plant signalling networks, in addition to well-known cytosolic calcium ‘signatures’. According to the suggested concept, the intrinsically higher superoxide dismutase (SOD) levels in halophytes are required for rapid induction of the H2O2 ‘signature’, and to trigger a cascade of adaptive responses (both genetic and physiological), while the role of other enzymatic antioxidants may be in decreasing the basal levels of H2O2, once the signalling has been processed. Finally, we emphasize the importance of non-enzymatic antioxidants as the only effective means to prevent detrimental effects of hydroxyl radicals on cellular structures.
The kinetic power of radio jets is a quantity of fundamental importance to studies of the AGN feedback process and radio galaxy physics. A widely used proxy for jet power is the extended radio ...luminosity. A number of empirical methods have been used to calibrate a scaling relationship between jet power (Q) and radio luminosity (L) of the form log (Q) = β
L
log (L) + C. The regression slope has typically been found to be β
L
∼ 0.7–0.8. Here we show that the previously reported scaling relations are strongly affected by the confounding variable, distance. We find that in a sample of FRI X-ray cavity systems, after accounting for the mutual distance dependence, the jet power and radio luminosity are only weakly correlated, with slope β
L
≈ 0.3: significantly flatter than previously reported. We also find that in previously used samples of high-power sources, no evidence for an intrinsic correlation is present when the effect of distance is accounted for. Using a simple model we show that β
L
is expected to be significantly lower in samples of FRI radio galaxies than it is for FRIIs, due to the differing dynamics for these two classes of radio source. For FRI X-ray cavity systems the model predicts β
L
(FRI) ≳ 0.5 in contrast to FRII radio galaxies, for which β
L
(FRII) ≳ 0.8. We discuss the implications of our finding for studies of radio mode feedback, and radio galaxy physics.
Recent results based on the analysis of radio galaxies and their hot X-ray emitting atmospheres suggest that non-radiating particles dominate the energy budget in the lobes of FR I radio galaxies, in ...some cases by a factor of more than 1000, while radiating particles dominate the energy budget in FR II radio galaxy lobes. This implies a significant difference in the radiative efficiency of the two morphological classes. To test this hypothesis, we have measured the kinetic energy flux for a sample of 3C FR II radio sources using a new method based on the observed parameters of the jet terminal hotspots, and compared the resulting Q sub(jet)-L sub(radio) relation to that obtained for FR I radio galaxies based on X-ray cavity measurements. Contrary to expectations, we find approximate agreement between the Q sub(jet)-L sub(radio) relations determined separately for FR I and FR II radio galaxies. This result is ostensibly difficult to reconcile with the emerging scenario in which the lobes of FR I and FR II radio galaxies have vastly different energy budgets. However, a combination of lower density environment, spectral aging and strong shocks driven by powerful FR II radio galaxies may reduce the radiative efficiency of these objects relative to FR Is and counteract, to some extent, the higher radiative efficiency expected to arise due to the lower fraction of energy in non-radiating particles. An unexpected corollary is that extrapolating the Q sub(jet)-L sub(radio) relation determined for low power FR I radio galaxies provides a reasonable approximation for high power sources, despite their apparently different lobe compositions.
ABSTRACT
The optical Fundamental Plane of black hole activity relates radio continuum luminosity of active galactic nuclei (AGNs) to O iii luminosity and black hole mass. We examine the environments ...of low-redshift (z< 0.2) radio-selected AGNs, quantified through galaxy clustering, and find that halo mass provides similar mass scalings to black hole mass in the Fundamental Plane relations. AGN properties are strongly environment-dependent: massive haloes are more likely to host radiatively inefficient (low-excitation) radio AGN, as well as a higher fraction of radio luminous, extended sources. These AGN populations have different radio–optical luminosity scaling relations, and the observed mass scalings in the parent AGN sample are built up by combining populations preferentially residing in different environments. Accounting for environment-driven selection effects, the optical Fundamental Plane of supermassive black holes is likely to be mass-independent, as predicted by models.
We present an analysis of optical spectroscopically identified active galactic nuclei (AGN) down to a cluster magnitude of M
+ 1 in a sample of six self-similar Sloan Digital Sky Survey galaxy ...clusters at z ∼ 0.07. These clusters are specifically selected to lack significant substructure at bright limits in their central regions so that we are largely able to eliminate the local action of merging clusters on the frequency of AGN. We demonstrate that the AGN fraction increases significantly from the cluster centre to 1.5R
virial, but tails off at larger radii. If only comparing the cluster core region to regions at ∼ 2R
virial, no significant variation would be found. We compute the AGN fraction by mass and show that massive galaxies (log (stellarmass) > 10.7) are host to a systematically higher fraction of AGN than lower mass galaxies at all radii from the cluster centre. We attribute this deficit of AGN in the cluster centre to the changing mix of galaxy types with radius. We use the WHAN diagnostic to separate weak AGN from 'retired' galaxies in which the main ionization mechanism comes from old stellar populations. These retired AGN are found at all radii, while the mass effect is much more pronounced: we find that massive galaxies are more likely to be in the retired class. Further, we show that our AGN have no special position inside galaxy clusters - they are neither preferentially located in the infall regions nor situated at local maxima of galaxy density as measured with Σ5. However, we find that the most powerful AGN (with O iii equivalent widths <−10 Å) reside at significant velocity offsets in the cluster, and this brings our analysis into agreement with previous work on X-ray-selected AGN. Our results suggest that if interactions with other galaxies are responsible for triggering AGN activity, the time lag between trigger and AGN enhancement must be sufficiently long to obfuscate the encounter site and wipe out the local galaxy density signal.
The Darwin plantDionaea muscipulais able to grow on mineral-poor soil, because it gains essential nutrients from captured animal prey. Given that no nutrients remain in the trap when it opens after ...the consumption of an animal meal, we here asked the question of howDionaeasequesters prey-derived potassium. We show that prey capture triggers expression of a K⁺ uptake system in the Venus flytrap. In search of K⁺ transporters endowed with adequate properties for this role, we screened aDionaeaexpressed sequence tag (EST) database and identified DmKT1 and DmHAK5 as candidates. On insect and touch hormone stimulation, the number of transcripts of these transporters increased in flytraps. After cRNA injection of K⁺-transporter genes intoXenopusoocytes, however, both putative K⁺ transporters remained silent. Assuming that calcium sensor kinases are regulatingArabidopsisK⁺ transporter 1 (AKT1), we coexpressed the putative K⁺ transporters with a large set of kinases and identified the CBL9-CIPK23 pair as the major activating complex for both transporters inDionaeaK⁺ uptake. DmKT1 was found to be a K⁺-selective channel of voltage-dependent high capacity and low affinity, whereas DmHAK5 was identified as the first, to our knowledge, proton-driven, high-affinity potassium transporter with weak selectivity. When the Venus flytrap is processing its prey, the gland cell membrane potential is maintained around −120 mV, and the apoplast is acidified to pH 3. These conditions in the green stomach formed by the closed flytrap allow DmKT1 and DmHAK5 to acquire prey-derived K⁺, reducing its concentration from millimolar levels down to trace levels
The SOS signal-transduction pathway is known to be important for ion homeostasis and salt tolerance in plants. However, there is a lack of in planta electrophysiological data about how the changes in ...signalling and ion transport activity are integrated at the cellular and tissue level. In this study, using the non-invasive ion flux MIFE technique, we compared net K⁺, H⁺ and Na⁺ fluxes from elongation and mature root zones of Arabidopsis wild type Columbia and sos mutants. Our results can be summarised as follows: (1) SOS mutations affect the function of the entire root, not just the root apex; (2) SOS signalling pathway is highly branched; (3) Na⁺ effects on SOS1 may by-pass the SOS2/SOS3 complex in the root apex; (4) SOS mutation affects H⁺ transport even in the absence of salt stress; (5) SOS1 mutation affects intracellular K⁺ homeostasis with a plasma membrane depolarisation-activated outward-rectifying K⁺ channel being a likely target; (6) H⁺ pump also may be a target of SOS signalling. We provide an improved model of SOS signalling and discuss physiological mechanisms underlying salt stress perception and signalling in plants. Our work shows that in planta studies are essential for understanding the functional genomics of plant salt tolerance.
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