Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting (EBM) and the other with direct laser metal ...sintering. Spatially indexed stress-free cubes were obtained by electrical discharge machining (EDM) equivalent prisms of similar shape. The (311) interplanar spacings from the EDM sectioned sample were compared to the interplanar spacings calculated to fulfill stress and moment balance. We have shown that applying stress and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. In addition, our work has shown that residual stresses in electron beam melted parts are much smaller than that of direct laser metal sintered parts most likely due to the powder preheating step in the EBM process.
ABSTRACT
We examine the connection between diffuse ionized gas (DIG), H ii regions, and field O and B stars in the nearby spiral M101 and its dwarf companion NGC 5474 using ultra-deep H α narrow-band ...imaging and archival GALEX UV imaging. We find a strong correlation between DIG H α surface brightness and the incident ionizing flux leaked from the nearby H ii regions, which we reproduce well using simple cloudy simulations. While we also find a strong correlation between H α and co-spatial far-ultraviolet (FUV) surface brightness in DIG, the extinction-corrected integrated UV colours in these regions imply stellar populations too old to produce the necessary ionizing photon flux. Combined, this suggests that H ii region leakage, not field OB stars, is the primary source of DIG in the M101 Group. Corroborating this interpretation, we find systematic disagreement between the H α- and FUV-derived star formation rates (SFRs) in the DIG, with SFRH α <SFRFUV everywhere. Within H ii regions, we find a constant SFR ratio of 0.44 to a limit of ∼10−5 M⊙ yr−1. This result is in tension with other studies of star formation in spiral galaxies, which typically show a declining SFRH α/SFRFUV ratio at low SFR. We reproduce such trends only when considering spatially averaged photometry that mixes H ii regions, DIG, and regions lacking H α entirely, suggesting that the declining trends found in other galaxies may result purely from the relative fraction of diffuse flux, leaky compact H ii regions, and non-ionizing FUV-emitting stellar populations in different regions within the galaxy.
Abstract
Benzene (C
6
H
6
), while stable under ambient conditions, can become chemically reactive at high pressures and temperatures, such as under shock loading conditions. Here, we report in situ ...x-ray diffraction and small angle x-ray scattering measurements of liquid benzene shocked to 55 GPa, capturing the morphology and crystalline structure of the shock-driven reaction products at nanosecond timescales. The shock-driven chemical reactions in benzene observed using coherent XFEL x-rays were a complex mixture of products composed of carbon and hydrocarbon allotropes. In contrast to the conventional description of diamond, methane and hydrogen formation, our present results indicate that benzene’s shock-driven reaction products consist of layered sheet-like hydrocarbon structures and nanosized carbon clusters with mixed
sp
2
-
sp
3
hybridized bonding. Implications of these findings range from guiding shock synthesis of novel compounds to the fundamentals of carbon transport in planetary physics.
Active galactic nuclei (AGN) are a key ingredient for understanding galactic evolution, as their activity is coupled to the host galaxy properties through feedback processes. AGN-driven outflows are ...one of the manifestations of this feedback. The laser guide star adaptive optics mode for MUSE at the VLT now permits us to study the innermost tens of parsecs of nearby AGN in the optical. We present a detailed analysis of the ionised gas in the central regions of NGC 7130, which is an archetypical composite Seyfert and nuclear starburst galaxy at a distance of 64.8 Mpc. We achieve an angular resolution of 0.″17, corresponding to roughly 50 pc. We performed a multi-component analysis of the main interstellar medium emission lines in the wavelength range of MUSE and identified nine kinematic components, six of which correspond to the AGN outflow. The outflow is biconic, oriented in an almost north–south direction, and has velocities of a few 100 km s
−1
with respect to the disc of NGC 7130. The lobe length is at least 3″(∼900 pc). We decomposed the approaching side of the outflow into a broad and a narrow component with typical velocity dispersions below and above ∼200 km s
−1
, respectively. The blueshifted narrow nomponent has a sub-structure, in particular a collimated plume traced especially well by O
III
. The plume is aligned with the radio jet, indicating that it may be jet powered. The redshifted lobe is composed of two narrow components and a broad component. An additional redshifted component is seen outside the main north-south axis, about an arcsecond east of the nucleus. Line ratio diagnostics indicate that the outflow gas in the north–south axis is AGN powered, whereas the off-axis component has LINER properties. We hypothesise that this is because the radiation field that reaches off-axis clouds has been filtered by clumpy ionised clouds found between the central engine and the low-ionisation emitting region. If we account for all the outflow components (the blueshifted components), the ionised gas mass outflow rate is
Ṁ
= 1.5 ± 0.9
M
⊙
yr
−1
(
Ṁ
= 0.55 ± 0.55
M
⊙
yr
−1
), and the kinetic power of the AGN is
Ė
kin
= (3.4 ± 2.5) × 10
41
erg s
−1
(
Ė
kin
= (8.8 ± 5.9) × 10
40
erg s
−1
), which corresponds to
F
kin
= 0.15 ± 0.11% (
F
kin
= 0.040 ± 0.027%) of the bolometric AGN power. The broad components, those with a velocity dispersion of
σ
> 200 km s
−1
, carry ∼2/3 (∼90%) of the mass outflow, and ∼90% (∼98%) of the kinetic power. The combination of high-angular-resolution integral field spectroscopy and a careful multi-component decomposition allows a uniquely detailed view of the outflow in NGC 7130, illustrating that AGN kinematics are more complex than those traditionally derived from less sophisticated data and analyses.
ABSTRACT
We use a complete, unbiased sample of 257 dwarf (10$^{8}\, {\rm M}_{\odot } \lt M_{\rm {\star }} \lt 10^{9.5}\, {\rm M}_{\odot }$) galaxies at z < 0.08, in the COSMOS field, to study the ...morphological mix of the dwarf population in low-density environments. Visual inspection of extremely deep optical images and their unsharp-masked counterparts reveals three principal dwarf morphological classes. 43 per cent and 45 per cent of dwarfs exhibit the traditional ‘early-type’ (elliptical/S0) and ‘late-type’ (spiral) morphologies, respectively. However, 10 per cent populate a ‘featureless’ class, that lacks both the central light concentration seen in early-types and any spiral structure – this class is missing in the massive-galaxy regime. 14 per cent, 27 per cent, and 19 per cent of early-type, late-type, and featureless dwarfs respectively show evidence for interactions, which drive around 20 per cent of the overall star formation activity in the dwarf population. Compared to their massive counterparts, dwarf early-types show a much lower incidence of interactions, are significantly less concentrated and share similar rest-frame colours as dwarf late-types. This suggests that the formation histories of dwarf and massive early-types are different, with dwarf early-types being shaped less by interactions and more by secular processes. The lack of large groups or clusters in COSMOS at z < 0.08, and the fact that our dwarf morphological classes show similar local density, suggests that featureless dwarfs in low-density environments are created via internal baryonic feedback, rather than by environmental processes. Finally, while interacting dwarfs can be identified using the asymmetry parameter, it is challenging to cleanly separate early and late-type dwarfs using traditional morphological parameters, such as ‘CAS’, M20, and the Gini coefficient (unlike in the massive-galaxy regime).
Manipulations that increase the expression of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus (e.g. peripheral administration of lipopolysaccharide, i.c.v. glycoprotein 120, ...social isolation) as well as the intrahippocampal injection of IL-1β following a learning experience, dramatically impair the memory of that experience if the formation of the memory requires the hippocampus. Here we employed social isolation to further study this phenomenon, as well as its relation to brain-derived neurotrophic factor (BDNF). BDNF was studied because of its well-documented role in the formation of hippocampally based memory. A 6 h period of social isolation immediately after contextual fear conditioning impaired memory for context fear measured 48 h later, and decreased BDNF mRNA in the dentate gyrus and the CA3 region of the hippocampus assessed immediately after the isolation. Moreover, an intrahippocampal injection of the IL-1 receptor antagonist prior to the isolation period prevented both the BDNF downregulation and the memory impairments produced by the isolation. These data suggest that hippocampal-dependent memory impairments induced by elevated levels of brain IL-1β may occur via an IL-1β-induced downregulation in hippocampal BDNF.
The structure of the edge plasma in a magnetic confinement system has a strong impact on the overall plasma performance. We uncover for the first time a magnetic-field-direction dependent density ...shelf, i.e., local flattening of the density radial profile near the magnetic separatrix, in high confinement plasmas with low edge collisionality in the DIII-D tokamak. The density shelf is correlated with a doubly peaked density profile near the divertor target plate, which tends to occur for operation with the ion B×∇B drift direction away from the X-point, as currently employed for DIII-D advanced tokamak scenarios. This double-peaked divertor plasma profile is connected via the E×B drifts, arising from a strong radial electric field induced by the radial electron temperature gradient near the divertor target. The drifts lead to the reversal of the poloidal flow above the divertor target, resulting in the formation of the density shelf. The edge density shelf can be further enhanced at higher heating power, preventing large, periodic bursts of the plasma, i.e., edge-localized modes, in the edge region, consistent with ideal magnetohydrodynamics calculations.
ABSTRACT
Dwarf galaxies are excellent cosmological probes, because their shallow potential wells make them very sensitive to the key processes that drive galaxy evolution, including baryonic ...feedback, tidal interactions, and ram pressure stripping. However, some of the key parameters of dwarf galaxies, which help trace the effects of these processes, are still debated, including the relationship between their sizes and masses. We re-examine the Fornax Cluster dwarf population from the point of view of isomass-radius–stellar mass relations (IRSMRs) using the Fornax Deep Survey Dwarf galaxy Catalogue, with the centrally located (among dwarfs) $3.63 \mathcal {M}_{\odot }$ pc−2 isodensity radius defining our fiducial relation. This relation is a powerful diagnostic tool for identifying dwarfs with unusual structure, as dwarf galaxies’ remarkable monotonicity in light profile shapes, as a function of stellar mass, reduces the relation’s scatter tremendously. By examining how different dwarf properties (colour, 10th nearest neighbour distance, etc.) correlate with distance from our fiducial relation, we find a significant population of structural outliers with comparatively lower central mass surface density and larger half-light-radii, residing in locally denser regions in the cluster, albeit with similar red colours. We propose that these faint, extended outliers likely formed through tidal disturbances, which make the dwarfs more diffuse, but with little mass-loss. Comparing these outliers with ultra-diffuse galaxies (UDGs), we find that the term UDG lacks discriminatory power; UDGs in the Fornax Cluster lie both on and off of IRSMRs defined at small radii, while IRSMR outliers with masses below $\sim 10^{7.5} \mathcal {M}_{\odot }$ are excluded from the UDG classification due to their small effective radii.
ABSTRACT Given their dominance of the galaxy number density, dwarf galaxies are central to our understanding of galaxy formation. While the incidence of active galactic nuclei (AGN) and their impact ...on galaxy evolution have been extensively studied in massive galaxies, much less is known about the role of AGN in the evolution of dwarfs. We search for radiatively efficient AGN in the nearby (0.1 < z < 0.3) dwarf (108 M⊙ < M⋆ < 1010 M⊙) population, using spectral energy distribution fitting (via prospector) applied to deep ultraviolet to mid-infrared photometry of 508 dwarf galaxies. Around a third (32 ± 2 per cent) of our dwarfs show signs of AGN activity. We compare the properties of our dwarf AGN to control samples, constructed from non-AGN, which have the same distributions of redshift and stellar mass as their AGN counterparts. Kolmogorov–Smirnov tests between the AGN and control distributions indicate that the AGN do not show differences in their distances to nodes, filaments, and nearby massive galaxies from their control counterparts. This indicates that AGN triggering in the dwarf regime is not strongly correlated with local environment. The fraction of AGN hosts with early-type morphology and those that are interacting are also indistinguishable from the controls within the uncertainties, suggesting that interactions do not play a significant role in inducing AGN activity in our sample. Finally, the star formation activity in dwarf AGN is only slightly lower than that in their control counterparts, suggesting that the presence of radiatively efficient AGN does not lead to significant, prompt quenching of star formation in these systems.
ABSTRACT
Tidal features in the outskirts of galaxies yield unique information about their past interactions and are a key prediction of the hierarchical structure formation paradigm. The Vera C. ...Rubin Observatory is poised to deliver deep observations for potentially millions of objects with visible tidal features, but the inference of galaxy interaction histories from such features is not straightforward. Utilizing automated techniques and human visual classification in conjunction with realistic mock images produced using the NewHorizon cosmological simulation, we investigate the nature, frequency, and visibility of tidal features and debris across a range of environments and stellar masses. In our simulated sample, around 80 per cent of the flux in the tidal features around Milky Way or greater mass galaxies is detected at the 10-yr depth of the Legacy Survey of Space and Time (30–31 mag arcsec−2), falling to 60 per cent assuming a shallower final depth of 29.5 mag arcsec−2. The fraction of total flux found in tidal features increases towards higher masses, rising to 10 per cent for the most massive objects in our sample (M⋆ ∼ 1011.5 M⊙). When observed at sufficient depth, such objects frequently exhibit many distinct tidal features with complex shapes. The interpretation and characterization of such features varies significantly with image depth and object orientation, introducing significant biases in their classification. Assuming the data reduction pipeline is properly optimized, we expect the Rubin Observatory to be capable of recovering much of the flux found in the outskirts of Milky Way mass galaxies, even at intermediate redshifts (z < 0.2).
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