The giant elliptical galaxy NGC 1275, at the centre of the Perseus cluster, is surrounded by a well-known giant nebulosity of emission-line filaments, which are plausibly in excess of 10(8) years ...old. The filaments are dragged out from the centre of the galaxy by radio-emitting 'bubbles' rising buoyantly in the hot intracluster gas, before later falling back. They act as markers of the feedback process by which energy is transferred from the central massive black hole to the surrounding gas. The mechanism by which the filaments are stabilized against tidal shear and dissipation into the surrounding extremely hot (4 x 10(7) K) gas has been unclear. Here we report observations that resolve thread-like structures in the filaments. Some threads extend over 6 kpc, yet are only 70 pc wide. We conclude that magnetic fields in the threads, in pressure balance with the surrounding gas, stabilize the filaments, so allowing a large mass of cold gas to accumulate and delay star formation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
We present the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey. We fit HST NUV to NIR broad-band and H α fluxes to derive star cluster ages, masses, and extinctions ...and determine the star formation rate (SFR) of six merging galaxies. These systems are excellent laboratories to trace cluster formation under extreme gas physical conditions, rare in the local Universe, but typical for star-forming galaxies at cosmic noon. We detect clusters with ages of 1–500 Myr and masses that exceed 107 M⊙. The recent cluster formation history and their distribution within the host galaxies suggest that systems such as NGC 34, NGC 1614, and NGC 4194 are close to their final coalescing phase, while NGC 3256, NGC 3690, and NGC 6052 are at an earlier/intermediate stage. A Bayesian analysis of the cluster mass function in the age interval 1–100 Myr provides strong evidence in four of the six galaxies that an exponentially truncated power law better describes the observed mass distributions. For two galaxies, the fits are inconclusive due to low number statistics. We determine power-law slopes β ∼ −1.5 to −2.0 and truncation masses, Mc, between 106 and a few times 107 M⊙, among the highest values reported in the literature. Advanced mergers have higher Mc than early/intermediate merger stage galaxies, suggesting rapid changes in the dense gas conditions during the merger. We compare the total stellar mass in clusters to the SFR of the galaxy, finding that these systems are among the most efficient environments to form star clusters in the local Universe.
We present optical integral field unit (IFU) observations (VLT/VIMOS-IFU and WIYN/SparsePak), and associated archival deep Hα imaging (MPG/ESO 2.2 m WFI), of the nearby starburst galaxy NGC 253. With ...VIMOS we observed the nuclear region and southern superwind outflow in detail with five pointings, and with the WIYN/SparsePak IFU we observed two partially overlapping regions covering the central disc and northern halo. The high signal-to-noise ratio of the data and spectral resolution (80-90 km s−1) enable us to accurately decompose the emission line profiles into multiple components.
The combination of these data sets, together with the wealth of information on NGC 253 available in the literature, allows us to study the starburst-driven superwind in great detail. We investigate the known minor axis outflow cone, which is well-defined in the Hα imaging and kinematics between radii of 280 and 660 pc from the nucleus. Kinematic modelling indicates a wide opening angle (∼60°), an inclination consistent with that of the disc and deprojected outflow speeds of a few 100 km s−1 that increase with distance above the plane. The N ii/Hα and S ii/Hα line ratio maps imply that a significant fraction of the wind optical emission lines arise from shocked gas, with localized pockets/filaments of strongly shocked gas. From the kinematics, the cone appears partially closed in at least one place, and very broad Hα linewidths (>400 km s−1 full width at half maximum) suggest there is material filling the cone in some regions. Extrapolation of the cone to its apex shows it is not centred on the starburst nucleus, suggesting the wind is deflected and collimated by the dense circumnuclear material. We discuss the implications of these findings on our understanding of the origins and evolution of the superwind. No evidence for an outflow is found on the north-western side of the disc out to >2 kpc in our optical data, due to obscuration by the foreground disc. The lack of an obvious connection between the inner (r < 1 kpc) Hα and X-ray bright outflow cone and the large-scale (r≲ 10 kpc) X-ray 'horns' is also discussed.
The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using x-ray magnetic linear dichroism microscopy, we show that staggered effective fields generated ...by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multidomain antiferromagnetic films.
Electrical switching of an antiferromagnet Wadley, P.; Howells, B.; Železný, J. ...
Science (American Association for the Advancement of Science),
02/2016, Letnik:
351, Številka:
6273
Journal Article
Recenzirano
Odprti dostop
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, ...relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10⁶ ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
ABSTRACT The observed scale heights of extraplanar diffuse ionized gas (eDIG) layers exceed their thermal scale heights by a factor of a few in the Milky Way and other nearby edge-on disk galaxies. ...Here, we test a dynamical equilibrium model of the eDIG layer in NGC 891, where we ask whether the thermal, turbulent, magnetic field, and cosmic-ray pressure gradients are sufficient to support the layer. In optical emission-line spectroscopy from the SparsePak integral field unit on the WIYN 3.5 m telescope, the H emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of , where . We find that the thermal ( km s−1) and turbulent ( km s−1) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of . Using a literature analysis of radio continuum observations from the CHANG-ES survey, we demonstrate that the magnetic field and cosmic-ray pressure gradients are sufficient to stably support the gas at kpc if the cosmic rays are sufficiently coupled to the system ( ). Thus, a stable dynamical equilibrium model is viable only if the eDIG is found in a thin ring around R = 8 kpc, and nonequilibrium models such as a galactic fountain flow are of interest for further study.
In this paper, we build from previous work and present simulations of recent (within the past Gyr), magnetized, cosmic-ray driven outflows from the Large Magellanic Cloud (LMC), including our first ...attempts to explicitly use the derived star formation history of the LMC to seed outflow generation. We run a parameter set of simulations for different LMC gas masses and cosmic-ray transport treatments, and we make preliminary comparisons to published outflow flux estimates, neutral and ionized hydrogen observations, and Faraday rotation measure maps. We additionally report on the gas mass that becomes unbound from the LMC disk and swept by ram pressure into the Trailing Magellanic Stream. We find that, even for our largest outburst, the mass contribution to the Stream is still quite small, as much of the outflow-turned-halo gas is shielded on the LMCs far-side due to the LMCs primarily face-on infall through the Milky Way halo over the past Gyr. On the LMC's near-side, past outflows have fought an uphill battle against ram pressure, with the near-side halo mass being at least a factor of a few smaller than that of the far-side. Absorption-line studies probing only the LMC foreground, then, may be severely underestimating the total mass of the LMC halo formed by outflows.
Abstract
We present the first kinematic study of extraplanar diffuse ionized gas (eDIG) in the nearby, face-on disk galaxy M83 using optical emission-line spectroscopy from the Robert Stobie ...Spectrograph on the Southern African Large Telescope. We use a Markov Chain Monte Carlo method to decompose the N
ii
6548, 6583, H
α
, and S
ii
6717, 6731 emission lines into H
ii
region and diffuse ionized gas emission. Extraplanar, diffuse gas is distinguished by its emission-line ratios (N
ii
λ
6583/H
α
) and its rotational velocity lag with respect to the disk (
km s
−1
in projection). With interesting implications for isotropy, the velocity dispersion of the diffuse gas,
km s
−1
, is a factor of a few higher in M83 than in the Milky Way and nearby, edge-on disk galaxies. The turbulent pressure gradient is sufficient to support the eDIG layer in dynamical equilibrium at an electron scale height of
kpc. However, this dynamical equilibrium model must be finely tuned to reproduce the rotational velocity lag. There is evidence of local bulk flows near star-forming regions in the disk, suggesting that the dynamical state of the gas may be intermediate between a dynamical equilibrium and a galactic fountain flow. As one of the first efforts to study eDIG kinematics in a face-on galaxy, this study demonstrates the feasibility of characterizing the radial distribution, bulk velocities, and vertical velocity dispersions in low-inclination systems.
We present an analysis of the positions and ages of young star clusters in eight local galaxies to investigate the connection between the age difference and separation of cluster pairs. We find that ...star clusters do not form uniformly but instead are distributed so that the age difference increases with the cluster pair separation to the 0.25-0.6 power, and that the maximum size over which star formation is physically correlated ranges from ∼200 pc to ∼1 kpc. The observed trends between age difference and separation suggest that cluster formation is hierarchical both in space and time: clusters that are close to each other are more similar in age than clusters born further apart. The temporal correlations between stellar aggregates have slopes that are consistent with predictions of turbulence acting as the primary driver of star formation. The velocity associated with the maximum size is proportional to the galaxy's shear, suggesting that the galactic environment influences the maximum size of the star-forming structures.
This study aimed to determine whether the COVID-19 pandemic had an impact on essential primary healthcare services at public primary healthcare facilities.
The number of weekly consultations for ...antenatal care (ANC), outpatient (OPD), immunisations (EPI), family planning (FP) and HIV services, between January 2018 and December 2020, were collected from 25 facilities in Masaka district, Uganda, 21 in Goma, and 29 in Kambia district, Sierra Leone. Negative binomial regression models accounting for clustering and season were used to analyse changes in activity levels between 2018, 2019 and 2020.
In Goma, we found no change in OPD, EPI or ANC consultations, FP was 17% lower in March-July 2020 compared to 2019, but this recovered by December 2020. New diagnoses of HIV were 34% lower throughout 2020 compared to 2019. In Sierra Leone, compared to the same periods in 2019, facilities had 18-29% fewer OPD consultations throughout 2020, and 27% fewer DTP3 doses in March-July 2020. There was no evidence of differences in other services. In Uganda there were 20-35% fewer under-5 OPD consultations, 21-66% fewer MCV1 doses, and 48-51% fewer new diagnoses of HIV throughout 2020, compared to 2019. There was no difference in the number of HPV doses delivered.
The level of disruption varied across the different settings and qualitatively appeared to correlate with the strength of lockdown measures and reported attitudes towards the risk posed by COVID-19. Mitigation strategies such as health communications campaigns and outreach services may be important to limit the impact of lockdowns on primary healthcare services.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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