Abstract
Bolometric luminosities and Eddington ratios of both X-ray selected broad-line (Type-1) and narrow-line (Type-2) active galactic nuclei (AGN) from the XMM-Newton survey in the Cosmic ...Evolution Survey field are presented. The sample is composed of 929 AGN (382 Type-1 AGN and 547 Type-2 AGN) and it covers a wide range of redshifts, X-ray luminosities and absorbing column densities. About 65 per cent of the sources are spectroscopically identified as either Type-1 or Type-2 AGN (83 and 52 per cent, respectively), while accurate photometric redshifts are available for the rest of the sample. The study of such a large sample of X-ray selected AGN with a high-quality multiwavelength coverage from the far-infrared (now with the inclusion of Herschel data at 100 and 160 μm) to the optical-ultraviolet allows us to obtain accurate estimates of bolometric luminosities, bolometric corrections and Eddington ratios. The k
bol - L
bol relations derived in this work are calibrated for the first time against a sizable AGN sample, and rely on observed redshifts, X-ray luminosities and column density distributions. We find that k
bol is significantly lower at high L
bol with respect to previous estimates by Marconi et al. and Hopkins et al. Black hole (BH) masses and Eddington ratios are available for 170 Type-1 AGN, while BH masses for Type-2 AGN are computed for 481 objects using the BH mass-stellar mass relation and the morphological information. We confirm a trend between k
bol and λEdd, with lower hard X-ray bolometric corrections at lower Eddington ratios for both Type-1 and Type-2 AGN. We find that, on average, the Eddington ratio increases with redshift for all types of AGN at any given M
BH, while no clear evolution with redshift is seen at any given L
bol.
Investor-state disputes threaten the global green energy transition Tienhaara, Kyla; Thrasher, Rachel; Simmons, B Alexander ...
Science (American Association for the Advancement of Science),
2022-May-13, 2022-05-13, 20220513, Letnik:
376, Številka:
6594
Journal Article
Recenzirano
Global action on climate change could generate upward of $340 billion in legal claims from oil and gas in vestors.
Using multiwavelength surveys of active galactic nuclei (AGNs) across a wide range of bolometric luminosities (10 super(43) < L sub(bol) (erg s super(-1)) < 5 x 10 super(46)) and redshifts (0 < z < ...3), we find a strong, redshift-independent correlation between the AGN luminosity and the fraction of host galaxies undergoing a major merger. That is, only the most luminous AGN phases are connected to major mergers, while less luminous AGNs appear to be driven by secular processes. Combining this trend with AGN luminosity functions to assess the overall cosmic growth of black holes, we find that ~50% by mass is associated with major mergers, while only 10% of AGNs by number, the most luminous, are connected to these violent events. Our results suggest that to reach the highest AGN luminosities-where the most massive black holes accreted the bulk of their mass-a major merger appears to be required. The luminosity dependence of the fraction of AGNs triggered by major mergers can successfully explain why the observed scatter in the M-sigma relation for elliptical galaxies is significantly lower than in spirals. The lack of a significant redshift dependence of the L sub(bol)-functionof sub(merger) relation suggests that downsizing, i.e., the general decline in AGN and star formation activity with decreasing redshift, is driven by a decline in the frequency of major mergers combined with a decrease in the availability of gas at lower redshifts.
The similarities between gated quantum dots and the transistors in modern microelectronics--in fabrication methods, physical structure and voltage scales for manipulation--have led to great interest ...in the development of quantum bits (qubits) in semiconductor quantum dots. Although quantum dot spin qubits have demonstrated long coherence times, their manipulation is often slower than desired for important future applications, such as factoring. Furthermore, scalability and manufacturability are enhanced when qubits are as simple as possible. Previous work has increased the speed of spin qubit rotations by making use of integrated micromagnets, dynamic pumping of nuclear spins or the addition of a third quantum dot. Here we demonstrate a qubit that is a hybrid of spin and charge. It is simple, requiring neither nuclear-state preparation nor micromagnets. Unlike previous double-dot qubits, the hybrid qubit enables fast rotations about two axes of the Bloch sphere. We demonstrate full control on the Bloch sphere with π-rotation times of less than 100 picoseconds in two orthogonal directions, which is more than an order of magnitude faster than any other double-dot qubit. The speed arises from the qubit's charge-like characteristics, and its spin-like features result in resistance to decoherence over a wide range of gate voltages. We achieve full process tomography in our electrically controlled semiconductor quantum dot qubit, extracting high fidelities of 85 per cent for X rotations (transitions between qubit states) and 94 per cent for Z rotations (phase accumulation between qubit states).
Abstract
The deep connection between galaxies and their supermassive black holes is central to modern astrophysics and cosmology. The observed correlation between galaxy and black hole mass is ...usually attributed to the contribution of major mergers to both. We make use of a sample of galaxies whose disc-dominated morphologies indicate a major-merger-free history and show that such systems are capable of growing supermassive black holes at rates similar to quasars. Comparing black hole masses to conservative upper limits on bulge masses, we show that the black holes in the sample are typically larger than expected if processes creating bulges are also the primary driver of black hole growth. The same relation between black hole and total stellar mass of the galaxy is found for the merger-free sample as well as a sample that has experienced substantial mergers, indicating that major mergers do not play a significant role in controlling the co-evolution of galaxies and black holes. We suggest that more fundamental processes that contribute to galaxy assembly are also responsible for black hole growth.
China can help solve the debt and environmental crises Simmons, B Alexander; Ray, Rebecca; Yang, Hongbo ...
Science (American Association for the Advancement of Science),
01/2021, Letnik:
371, Številka:
6528
Journal Article
Recenzirano
Odprti dostop
China could implement debt-for-nature and debt-for-climate swaps to protect the environment and reduce global debt
Many developing countries are experiencing mounting external debt distress owing to ...the economic consequences of COVID-19. G20 Finance Ministers were swift to adopt the Debt Service Suspension Initiative (DSSI) in 2020, suspending bilateral debt payments through July 2021 for 73 low-income countries. Globally, Chinese government–sponsored banks have emerged as the largest bilateral creditors (
1
). For the 46 participating DSSI countries thus far, payments due to China constitute 68% ($8.4 billion) of all official bilateral payments originally due by the end of 2020 (
2
). G20 countries have now come to realize that they will need to go beyond debt suspension to include the cancellation of some portion of debt. Without substantial debt relief, developing countries will face pressure to exploit natural capital to pay short-term debt, placing conservation and climate change ambitions aside. It is therefore of paramount importance to align debt restructuring efforts with climate, biodiversity, and development goals. Although China has only recently become a major creditor, it has already built a strong record of bilateral debt relief and has begun to advocate for linking biodiversity, climate change, and international finance (
3
). Here, we conduct an exploratory analysis of opportunities for China to alleviate debt burdens in exchange for debtor nation commitments to climate change mitigation and/or adaptation and environmental protection through “debt-for-climate” and “debt-for-nature” swaps.
Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by inflammatory, demyelinating lesions localized in the brain and spinal cord. Experimental autoimmune ...encephalomyelitis (EAE) is an animal model of MS that is induced by activating myelin‐specific T cells and exhibits immune cell infiltrates in the CNS similar to those seen in MS. Both MS and EAE exhibit disease heterogeneity, reflecting variations in clinical course and localization of lesions within the CNS. Collectively, the differences seen in MS and EAE suggest that the brain and spinal cord function as unique microenvironments that respond differently to infiltrating immune cells. This review addresses the roles of the cytokines interferon‐γ and interleukin‐17 in determining the localization of inflammation to the brain or spinal cord in EAE.
Does galaxy evolution proceed through the green valley via multiple pathways or as a single population? Motivated by recent results highlighting radically different evolutionary pathways between ...early- and late-type galaxies, we present results from a simple Bayesian approach to this problem wherein we model the star formation history (SFH) of a galaxy with two parameters, t, τ and compare the predicted and observed optical and near-ultraviolet colours. We use a novel method to investigate the morphological differences between the most probable SFHs for both disc-like and smooth-like populations of galaxies, by using a sample of 126 316 galaxies (0.01 < z < 0.25) with probabilistic estimates of morphology from Galaxy Zoo. We find a clear difference between the quenching time-scales preferred by smooth- and disc-like galaxies, with three possible routes through the green valley dominated by smooth- (rapid time-scales, attributed to major mergers), intermediate- (intermediate time-scales, attributed to minor mergers and galaxy interactions) and disc-like (slow time-scales, attributed to secular evolution) galaxies. We hypothesize that morphological changes occur in systems which have undergone quenching with an exponential time-scale τ < 1.5 Gyr, in order for the evolution of galaxies in the green valley to match the ratio of smooth to disc galaxies observed in the red sequence. These rapid time-scales are instrumental in the formation of the red sequence at earlier times; however, we find that galaxies currently passing through the green valley typically do so at intermediate time-scales.
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ABSTRACT
Recent observations and simulations have revealed the dominance of secular processes over mergers in driving the growth of both supermassive black holes (SMBHs) and galaxy evolution. Here, ...we obtain narrow-band imaging of AGN powered outflows in a sample of 12 galaxies with disc-dominated morphologies, whose history is assumed to be merger-free. We detect outflows in 10/12 sources in narrow-band imaging of the $\mathrm{O\, \small {III} }$ $5007~\mathring{\rm A}$ emission using filters on the Shane-3m telescope. We calculate a mean outflow rate for these AGNs of $0.95\pm 0.14~\rm {M}_{\odot }~\rm {yr}^{-1}$. This exceeds the mean accretion rate of their SMBHs ($0.054\pm 0.039~\rm {M}_{\odot }~\rm {yr}^{-1}$) by a factor of 18. Assuming that the galaxy must provide at least enough material to power both the AGN and outflow, this gives a lower limit on the average inflow rate of $1.01\pm 0.14~\rm {M}_{\odot }~\rm {yr}^{-1}$, a rate which simulations show can be achieved by bars, spiral arms, and cold accretion. We compare our disc-dominated sample to a sample of nearby AGNs with merger dominated histories and show that the black hole accretion rates in our sample are five times higher (4.2σ) and the outflow rates are five times lower (2.6σ). We suggest that this could be a result of the geometry of the smooth, planar inflow in a secular dominated system, which is both spinning up the black hole to increase accretion efficiency and less affected by feedback from the outflow, than in a merger-driven system with chaotic quasi-spherical inflows. This work provides further evidence that secular processes are sufficient to fuel SMBH growth.
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