We study outflows driven by active galactic nuclei (AGNs) using high-resolution simulations of idealized z ∼ 2 isolated disc galaxies. Episodic accretion events lead to outflows with velocities >1000 ...km s−1 and mass outflow rates of about the star formation rate (several tens of M⊙ yr−1). Outflowing winds escape perpendicular to the disc with wide opening angles, and are typically asymmetric (i.e. unipolar) because dense gas above or below the AGN in the resolved disc inhibits outflow. Owing to rapid variability in the accretion rates, outflowing gas may be detectable even when the AGN is effectively ‘off’. The highest velocity outflows are sometimes, but not always, concentrated within 2–3 kpc of the galactic centre during the peak accretion. With our purely thermal AGN feedback model – standard in previous literature – the outflowing material is mostly hot (≳106 K) and diffuse (n
H ≲ 10− 2 cm−3), but includes a cold component entrained in the hot wind. Despite the powerful bursts and high outflow rates, AGN feedback has little effect on the dense gas in the galaxy disc. Thus AGN-driven outflows in our simulations do not cause rapid quenching of star formation, although they may remove significant amounts of gas over long (≳Gyr) time-scales.
Observations suggest that a large fraction of black hole growth occurs in normal star-forming disc galaxies. Here we describe simulations of black hole accretion in isolated disc galaxies with ...sufficient resolution (∼5 pc) to track the formation of giant molecular clouds that feed the black hole. Black holes in z ∼ 2 gas-rich discs (f
gas 50 per cent) occasionally undergo ∼10 Myr episodes of Eddington-limited accretion driven by stochastic collisions with massive, dense clouds. We predict that these gas-rich discs host weak AGNs ∼1/4 of the time and moderate/strong AGNs ∼10 per cent of the time. Averaged over ∼100 Myr time-scales and the full distribution of accretion rates, the black holes grow at a few per cent of the Eddington limit - sufficient to match observations and keep the galaxies on the M
BH-M
bulge relation. This suggests that dense cloud accretion in isolated z 2 discs could dominate cosmic black hole growth. In z ∼ 0 discs with f
gas 10 per cent, Eddington-limited growth is extremely rare because typical gas clouds are smaller and more susceptible to disruption by active galactic nucleus (AGN) feedback. This results in an average black hole growth rate in high-f
gas galaxies that is up to 103 times higher than that in low-f
gas galaxies. In all our simulations, accretion shows variability by factors of ∼104 on a variety of time-scales, with variability at ∼1 Myr scales driven by the structure of the interstellar medium.
We study the connection between the large-scale dynamics and the gas fuelling towards a central black hole via the analysis of a Milky Way-like simulation at subparsec resolution. This allows us to ...follow a set of processes at various scales (e.g. the triggering of inward gas motion towards inner resonances via the large-scale bar, the connection to the central black hole via minispirals) in a self-consistent manner. This simulation provides further insights on the role of shear for the inhibition of star formation within the bar in regions with significant amount of gas. We also witness the decoupling of the central gas and nuclear cluster from the large-scale disc, via interactions with the black hole. This break of symmetry in the mass distribution triggers the formation of gas clumps organized in a time-varying 250 pc ring-like structure, the black hole being offset by about 70 pc from its centre. Some clumps form stars, while most get disrupted or merge. Supernovae feedback further create bubbles and filaments, some of the gas being expelled to 100 pc or higher above the galaxy plane. This helps remove angular momentum from the gas, which gets closer to the central dark mass. Part of the gas raining down is being accreted, forming a 10 pc polar disc-like structure around the black hole, leading to an episode of star formation. This gives rise to multiple stellar populations with significantly different angular momentum vectors, and may lead to a natural intermittence in the fuelling of the black hole.
Abstract
We examine the cosmic growth of the red sequence in a cosmological hydrodynamic simulation that includes a heuristic prescription for quenching star formation that yields a realistic passive ...galaxy population today. In this prescription, haloes dominated by hot gas are continually heated to prevent their coronae from fuelling new star formation. Hot coronae primarily form in haloes above ∼1012 M⊙, so that galaxies with stellar masses ∼1010.5 M⊙ are the first to be quenched and move on to the red sequence at z > 2. The red sequence is concurrently populated at low masses by satellite galaxies in large haloes that are starved of new fuel, resulting in a dip in passive galaxy number densities around ∼1010 M⊙. Stellar mass growth continues for galaxies even after joining the red sequence, primarily through minor mergers with a typical mass ratio ∼1:5. For the most massive systems, the size growth implied by the distribution of merger mass ratios is typically approximately two times the corresponding mass growth, consistent with observations. This model reproduces mass-density and colour-density trends in the local Universe, with essentially no evolution to z = 1, with the hint that such relations may be washed out by z ∼ 2. Simulated galaxies are increasingly likely to be red at high masses or high local overdensities. In our model, the presence of surrounding hot gas drives the trends with both mass and environment.
Observed galaxies with high stellar masses or in dense environments have low specific star formation rates, i.e. they are quenched. Based on cosmological hydrodynamic simulations that include a ...prescription where quenching occurs in regions dominated by hot (>105.4 K) gas, we argue that this hot gas quenching in haloes >1012 M⊙ drives both mass quenching (i.e. central quenching) and environment quenching (i.e. satellite quenching). These simulations reproduce a broad range of locally observed trends among quenching, halo mass, stellar mass, environment, and distance to halo centre. Mass quenching is independent of environment because ∼1012–1013 M⊙ ‘mass quenching haloes’ inhabit a large range of environments. On the other hand, environment quenching is independent of stellar mass because galaxies of all stellar masses may live in dense environments as satellites of groups and clusters. As in observations, the quenched fraction of satellites increases with halo mass and decreases with distance to the centre of the group or cluster. We investigate pre-processing in group haloes, ejected former satellites, and hot gas that extends beyond the virial radius. The agreement of our model with key observational trends suggests that hot gas in massive haloes plays a leading role in quenching low-redshift galaxies.
We observed highly efficient generation of electron-hole pairs due to impact excitation in single-walled carbon nanotube p-n junction photodiodes. Optical excitation into the second electronic ...subband E₂₂ leads to striking photocurrent steps in the device$I - V_{SD} $characteristics that occur at voltage intervals of the band-gap energy$E_{GAP} /e$. Spatially and spectrally resolved photocurrent combined with temperature-dependent studies suggest that these steps result from efficient generation of multiple electron-hole pairs from a single hot E₂₂ carrier. This process is both of fundamental interest and relevant for applications in future ultra-efficient photovoltaic devices.
Brillouin light scattering (BLS), complemented by ferromagnetic resonance (FMR) characterization, has been used for studying spin-wave (SW) propagation in Py(L)/Pt(6-mn) bilayers of various Py ...thicknesses (4mn < or = L < or = 10 nm). The FMR measurements allowed determination of the pertinent magnetic parameters and revealed the existence of a normal surface anisotropy. A pronounced asymmetry of Damon-Eshbach (DE) wave frequencies has been evidenced by BLS. Therefore, the difference between Stokes and anti-Stokes DE frequencies has been measured versus SW wave number for all the samples. A detailed discussion about the origin of this frequency difference is reported, which concludes that this is due to interface Dzyaloshinskii-Moriya interaction (IDMI).
OBJECTIVE:We sought to quantify and compare angular vestibulo-ocular reflex (aVOR) gain and compensatory saccade properties elicited by the head impulse test (HIT) in pontine-cerebellar stroke (PCS) ...and vestibular neuritis (VN).
METHODS:Horizontal HIT was recorded ≤7 days from vertigo onset with dual-search coils in 33 PCS involving the anterior inferior, posterior inferior, and superior cerebellar arteries (13 AICA, 17 PICA, 3 SCA) confirmed by MRI and 20 VN. We determined the aVOR gain and asymmetry, and compensatory overt saccade properties including amplitude asymmetry and cumulative amplitude (ipsilesional trials I; contralesional trials C).
RESULTS:The aVOR gain (normal0.96; asymmetry = 2%) was bilaterally reduced, greater in AICA (I = 0.39, C = 0.57; asymmetry = 20%) than in PICA/SCA strokes (I = 0.75, C = 0.74; asymmetry = 7%), in contrast to the unilateral deficit in VN (I = 0.22, C = 0.76; asymmetry = 54%). Cumulative amplitude (normal1.1°) was smaller in AICA (I = 4.2°, C = 3.0°) and PICA/SCA strokes (I = 2.1°, C = 3.0°) compared with VN (I = 8.5°, C = 1.3°). Amplitude asymmetry in AICA and PICA/SCA strokes was comparable, but favored the contralesional side in PICA/SCA strokes and the ipsilesional side in VN. Saccade asymmetry <61% was found in 97% of PCS and none of VN. Gain asymmetry <40% was found in 94% of PCS and 10% of VN.
CONCLUSION:HIT gains and compensatory saccades differ between PCS and VN. VN was characterized by unilateral gain deficits with asymmetric large saccades, AICA stroke by more symmetric bilateral gain reduction with smaller saccades, and PICA stroke by contralesional gain bias with the smallest saccades. Saccade and gain asymmetry should be investigated further in future diagnostic accuracy studies.
CLASSIFICATION OF EVIDENCE:This study provides Class II evidence that aVOR testing accurately distinguishes patients with PCS from VN (sensitivity 94%–97%, specificity 90%–100%).
•The winged helix domain is a versatile nucleic-acid-binding structural element.•This domain can exploit various nucleic acid structural features for recognition.•Transcription factors use this ...domain for sequence-specific DNA recognition.•DNA recombination and repair helicases use this domain as a strand-separating wedge.•Winged helix domains also mediate protein–protein interactions.
The winged helix domain (WHD) is a widespread nucleic-acid-binding protein structural element found in all kingdoms of life. Although the overall structure of the WHD is conserved, its functional properties and interaction profiles are extremely versatile. WHD-containing proteins can exploit nearly the full spectrum of nucleic acid structural features for recognition and even covalent modification or noncovalent rearrangement of target molecules. WHD functions range from sequence-recognizing keys in transcription factors and bulldozer-like strand-separating wedges in helicases to mediators of protein–protein interactions (PPIs). Further investigations are needed to understand the contribution of WHD structural dynamics to nucleic-acid-modifying enzymatic functions.
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