Secular Evolution Research Articles

The McDonald Accelerating Stars Survey: Architecture of the Ancient Five-planet Host System Kepler-444

We present the latest and most precise characterization of the architecture for the ancient (≈11 Gyr) Kepler-444 system, which is composed of a K0 primary star (Kepler-444 A) hosting five transiting planets and a tight M-type spectroscopic binary (Kepler-444 BC) with an A–BC projected separation of 66 au. We have measured the system’s relative astrometry using the adaptive optics imaging from Keck/NIRC2 and Kepler-444 A’s radial velocities from the Hobby-Eberly Telescope and reanalyzed relative radial velocities between BC and A from Keck/HIRES. We also include the Hipparcos-Gaia astrometric acceleration and all published astrometry and radial velocities in an updated orbit analysis of BC’s barycenter. These data greatly extend the time baseline of the monitoring and lead to significant updates to BC’s barycentric orbit compared to previous work, including a larger semimajor axis ( au), a smaller eccentricity (e = 0.55 ± 0.05), and a more precise inclination (). We have also derived the first dynamical masses of B and C components. Our results suggest that Kepler-444 A’s protoplanetary disk was likely truncated by BC to a radius of ≈8 au, which resolves the previously noticed tension between Kepler-444 A’s disk mass and planet masses. Kepler-444 BC’s barycentric orbit is likely aligned with those of A’s five planets, which might be primordial or a consequence of dynamical evolution. The Kepler-444 system demonstrates that compact multiplanet systems residing in hierarchical stellar triples can form at early epochs of the universe and survive their secular evolution throughout cosmic time.

Long eccentricity forcing of the Late Pliensbachian to Early Toarcian (Jurassic) terrestrial wildfire activities in the Tarim Basin, northwestern China

Wildfires are an important disturbance driver for terrestrial ecosystems and even Earth systems, which reflect crucial information about the interactions between the atmosphere and the biosphere. However, the relatively long-term secular evolution controlled by climate change in the Early Jurassic wildfires are poorly understood. Here, we conduct cyclostratigraphic, chemostratigraphic, and molecular compound analyses on the Late Pliensbachian to Early Toarcian terrestrial stratigraphy of the Kuqa River section in the Tarim Basin, northwestern China, in order to obtain a holistic understanding the evolutionary processes of wildfire on long time scales during a past warming event, the Pliensbachian-Toarcian event (Pl-To). Based on the long eccentricity cycle identified in the time series analysis, we establish a ∼ 1.8 Ma high-resolution floating astronomical timescale (FATS) and reconstruct the variable lake level by using the sedimentary noise model. The Pl-To warming event associated with the Karoo-Ferrar Large Igneous Province (K-F LIP) may have led to a shift in climate from warm and wet to dry and hot, with a significant decrease in lake levels in the Tarim Basin. Besides, polycyclic aromatic hydrocarbons (PAHs), C29 sterane and dibenzofuran evidence indicates that the global warming event (Pl-To event) also may regulate the wildfires by affecting the fuel abundance (vegetation). Notably, the astrochronology and PAHs suggest that the periodically enhanced wildfires correspond to the long eccentricity cycles, indicating that astronomical forcing plays a key role in triggering the wildfires. Our results report the first documentation of multiple full long eccentricity cycles forced wildfires during the Late Pliensbachian to Early Toarcian and reveal orbital forcing as a driving mechanism for periodically enhanced wildfires superimposed on a long-time gradual weakening trend associated with Pl-To warming event.

Geochemistry of Precambrian dyke swarms in the Singhbhum craton, India: Implications for recycled crustal components in the mantle source

The Singhbhum craton, eastern India records multiple stages of emplacement of Precambrian dyke swarms with contrasting petrogenetic models proposed for their formation. In this study, we document elemental and Sr-Nd isotopic data for three major dyke swarms in the southern part of the craton, including the ca. 2.7 Ga Ghatgaon dyke swarm, the Early Proterozoic Keonjhar dyke swarm and the ca. 1.76 Ga Pipilia dyke swarm. Dyke compositions are dominated by basalt and basaltic andesite with minor andesite, showing trace element signatures typical of continental crustal rocks. Age-corrected Nd isotopic data for Ghatgaon (εNdt = −4.8 to + 4.6), Keonjhar (εNdt = −11.9 to + 3.8), and Pipilia (a single sample with εNdt = −8.8) dyke swarms display substantial variations. The lack of magma compositions that could indicate the presence of elevated mantle potential temperature among the rocks suggests melting regime was likely similar to the ambient mantle. The Dy/Yb and Dy/Dy* systematics of the rocks indicates melting occurred between spinel-stable depths and the spinel-garnet transition zone. The dominantly mafic compositions of the rocks and ubiquitous continental crustal trace element signature are best explained by peridotite source with recycled crustal components, probably in the form of pyroxenites. Our new Nd isotopic data, which argue against any simple secular evolution trend invoked in previous studies, indicate that crustal recycling was likely an episodic phenomenon rather than a discrete, single-stage process since the Archean. Geochemical modelling indicates that a sublithospheric mantle source with (10% or less) recycled crustal components satisfactorily explains the trace element variations of the dyke swarms.

Plumbing the depths of magma crystallization using 176Lu/177Hf in zircon as a pressure proxy

AbstractExtensional tectonics are marked by shallow magma crystallization depths, whereas compressional tectonics are associated with deeper crystallization depths. This implies that variations in crystallization depths can be used to track changes in Earth’s dominant tectonic regimes through time. We therefore developed a new “pressure of crystallization” proxy based on the variation of the 176Lu/177Hf ratio in zircon. This ratio is controlled by zircon fractionation and residual garnet, and it can be used to monitor the evolution of a crystallizing magma ascending within the crust. The secular evolution of the 176Lu/177Hf ratio in zircon is characterized by cyclical oscillations that are broadly in tune with the δ18O record in zircon and with periods of continental collision and supercontinent amalgamation. The apparent mean depth of crystallization of zircon-bearing igneous rocks has decreased with time over the last ~3.0 b.y. This can be linked to shallowing of the primary crystallization depths and/or to the effect of time-integrated erosion in the geologic record. Prior to ca. 3.0 Ga, crystallization depth maxima and oscillations in apparent depth are less clear, perhaps suggesting that the nature of tectonic interactions was different in the Mesoarchean and earlier.

Development of Songliao Basin by Palaeo‐Pacific slab rollback: Evidence from Early Cretaceous rhyolites in SK2 Borehole, NE China

As the largest petroliferous basin in northeast (NE) China, Songliao Basin preserves continuous Cretaceous sedimentary‐volcanic records, providing an excellent opportunity to recover the palaeo‐environment. The Yingcheng Formation in the Songliao Basin contains ample gas reservoirs that attract widespread attention. Whereas the timing, petrogenesis and geodynamic mechanism of the volcanic rocks in the Yingcheng Formation are still controversial, which largely constrain our understanding of the formation and evolution of the Songliao Basin. Here, we present an integrated investigation of zircon U–Pb ages and Hf isotope, as well as whole‐rock elements and Sr‐Nd isotopes data for a suite of rhyolites of Yingcheng Formation from the SK2 Borehole of NE China. Zircon U–Pb age dating results of nine samples have yielded a concentrated age of ~110 Ma. These Yingcheng rhyolites are characterized by high SiO2 (66–78 wt%) and alkali (Na2O + K2O = 7.80–11.70 wt%) content, high 10000*Ga/Al (1.26–3.82, mostly >2.6) and FeOT/(FeOT + MgO) ratios (0.81–0.95), which show geochemical affinities with A‐type rhyolites. They have relatively low Y/Nb (0.69–1.78, average 1.19) and Rb/Nb (1.58–6.52, average 4.34) ratios, suggesting that the Yingcheng volcanic samples belong to A1‐type rhyolites which formed in an intraplate environment. These Yingcheng rhyolites show depleted Nd‐Hf isotopic compositions (εNd(t) = 2.43–4.87 and zircon εHf(t) = 4.22–9.88) comparable with the Early Cretaceous A‐type and I‐type rhyolites in the Songliao Basin, suggesting that they were originated from a juvenile continental crust. They were most likely derived from the partial melting of anhydrous lower crust instead of differentiation of mantle‐derived or mixing with alkaline basaltic magma, due to their low Mg# and absence of the coeval mafic rocks. Combined with the previous studies, A‐type rhyolites in the Yingcheng Formation erupted lasting at least 10 Myr and were widely distributed in the rifts of the Songliao Basin. We propose that the Yingcheng rhyolites were most likely generated from the rollback of the Palaeo‐Pacific Plate in the Early Cretaceous, thus highlighting the significance of the subduction of the Palaeo‐Pacific Plate during the secular evolution of the Songliao Basin.

Secular Evolution of Continents and the Earth System

AbstractUnderstanding of secular evolution of the Earth system is based largely on the rock and mineral archive preserved in the continental lithosphere. Based on the frequency and range of accessible data preserved in this record, we divide the secular evolution into seven phases: (a) “Proto‐Earth” (ca. 4.57–4.45 Ga); (b) “Primordial Earth” (ca. 4.45–3.80 Ga); (c) “Primitive Earth” (ca. 3.8–3.2 Ga); (d) “Juvenile Earth” (ca. 3.2–2.5 Ga); (e) “Youthful Earth” (ca. 2.5–1.8 Ga); (f) “Middle Earth” (ca. 1.8–0.8 Ga); and (g) “Contemporary Earth” (since ca. 0.8 Ga). Integrating this record with knowledge of secular cooling of the mantle and lithospheric rheology constrains the changes in the tectonic modes that operated through Earth history. Initial accretion and the Moon forming impact during the Proto‐Earth phase likely resulted in a magma ocean. The solidification of this magma ocean produced the Primordial Earth lithosphere, which preserves evidence for intra‐lithospheric reworking of a rigid lid, but which also likely experienced partial recycling through mantle overturn and meteorite impacts. Evidence for craton formation and stabilization from ca. 3.8 to 2.5 Ga, during the Primitive and Juvenile Earth phases, likely reflects some degree of coupling between the convecting mantle and a lithosphere initially weak enough to favor an internally deformable, squishy‐lid behavior, which led to a transition to more rigid, plate like, behavior by the end of the early Earth phases. The Youthful to Contemporary phases of Earth, all occurred within a plate tectonic framework with changes between phases linked to lithospheric behavior and the supercontinent cycle.

Effects of Inner Halo Angular Momentum on the Peanut/X Shapes of Bars

Cosmological simulations show that dark matter halos surrounding baryonic disks have a wide range of angular momenta, which is measured by the spin parameter (λ). In this study, we bring out the importance of inner angular momentum (<30 kpc), measured in terms of the halo spin parameter, on the secular evolution of the bar using N-body simulations. We have varied the halo spin parameter λ from 0 to 0.1, for corotating (prograde) spinning halos and one counterrotating (retrograde) halo spin (λ = −0.1) with respect to the disk. We report that as the halo spin increases the buckling is also triggered earlier and is followed by a second buckling phase in high-spin halo models. The timescale for the second buckling is significantly longer than the first buckling. We find that bar strength does not reduce significantly after the buckling in all of our models, which provides new insights about the role of inner halo angular momentum unlike previous studies. Also, the buckled bar can still transfer significant angular momentum to the halo in the secular evolution phase, but it reduces with increasing halo spin. In the secular evolution phase, the bar strength increases and saturates to nearly equal values for all the models irrespective of halo spin and the sense of rotation with respect to the disk. The final boxy/peanut shape is more pronounced (∼20%) in high-spin halos having higher angular momentum in the inner region compared to nonrotating halos. We explain our results with angular momentum exchanges between the disk and halo.

Lithium, masses, and kinematics of young Galactic dwarf and giant stars with extreme [α/Fe] ratios

Context. Recent spectroscopic explorations of large Galactic stellar samples stars have revealed the existence of red giants with [α/Fe] ratios that are anomalously high, given their relatively young ages. Aims. We revisit the GALAH DR3 survey to look for both dwarf and giant stars with extreme [α/Fe] ratios, that is, the upper 1% in the [α/Fe]–[Fe/H] plane over the range in [Fe/H] between −1.1 and +0.4 dex. We refer to these outliers as “exαfe” stars. Methods. We used the GALAH DR3 data along with their value-added catalog to trace the properties (chemical abundances, masses, ages, and kinematics) of the exαfe stars. We applied strict criteria to the quality of the determination of the stellar parameters, abundances, and age determinations to select our sample of single stars. We investigated the effects of secular stellar evolution and the magnitude limitations of the GALAH survey to understand the mass and metallicity distributions of the sample stars. Here, we also discuss the corresponding biases in previous studies of stars with high – albeit not extreme – [α/Fe] in other spectroscopic surveys. Results. We find both dwarf and giant exαFe stars younger than 3 Gyr, which we refer to as “y-exαfe” stars. Dwarf y-exαFe stars exhibit lithium abundances similar to those of young [α/Fe]-normal dwarfs at the same age and [Fe/H]. In particular, the youngest and most massive stars of both populations exhibit the highest Li abundances, A(Li) ∼ 3.5 dex (i.e., a factor of 2 above the protosolar value), while cooler and older stars exhibit the same Li depletion patterns increasing with both decreasing mass and increasing age. In addition, the [Fe/H] and mass distributions of both the dwarf and giant y-exαFe stars do not differ from those of their [α/Fe]-normal counterparts found in the thin disk and they share the same kinematic properties, with lower eccentricities and velocities with respect to the local standard of rest than old stars of the thick disk. Conclusions. We conclude that y-exαFe dwarf and giant stars are indeed young, their mass distribution shows no peculiarity, and they differ from young [α/Fe]-normal stars by their extreme [α/Fe] content only. However, their origins still remain unclear.

Examining the dust of the tailless Oort-cloud comet C/2020 T2

We report our latest analysis of the Oort-cloud comet C/2020 T2 (also named Palomar or T2) observed at 2.06 au from the Sun (phase angle of 28.°5) roughly two weeks before perihelion. It lacks a significant dust tail in scattered light, showing a strong central condensation of the coma throughout the apparition that is reminiscent of so-called Manx comets. Its spectral slope of polarized light increases and decreases in the J (1.25 μm) and H (1.65 μm) bands, respectively, resulting in an overall negative (blue) slope (−0.31 ±0.14% μm−1 ) in contrast to the red polarimetric color of active comets observed at similar geometries. The average polarization degree of T2 is 2.86±0.17% for the J and 2.75±0.16% for the H bands. Given that near-infrared wavelengths are sensitive to the intermediate-scale structure of cometary dust (i.e., dust aggregates), our light-scattering modeling of ballistic aggregates with different porosities and compositions shows that the polarimetric properties of T2 are compatible with low-porosity (~66%), absorbing dust aggregates with negligible ice contents on a scale of 10–100 μm (density of ~652 kg m−3). This is supported by the coma morphology of T2 which has a viable β (the relative importance of solar radiation pressure on dust particles) range of ≲10−4. The secular evolution of r-band activity of T2 from archival data reveals that the increase in its brightness accelerates around 2.4 au pre-perihelion, with its overall dust production rate that is about 100 times smaller than those of active Oort-cloud comets. We also found an apparent concentration of T2 and Manx comets toward ecliptic orbits. This paper underlines the heterogeneous nature of Oort-cloud comets, which may be investigated in the near future with dedicated studies of their dust characteristics.

Investigation of the dynamical evolution of planetary systems with isotropically varying masses

AbstractIn this work, the secular evolution of exoplanetary systems is investigated, when the variability of the masses of celestial bodies is the leading factor of dynamical evolution. The masses of the parent star and the planets change due to the particles leaving the bodies and falling on them. At the same time, bodies masses are assumed to change isotropically at different rates. The law of mass change is considered to be known and given function of time. The relative motions of the planets are investigated by the methods of the canonical perturbation theory in the absence of resonances. It is assumed that the orbits of the planets do not intersect. Evolutionary equations in analogues of Poincaré variables (Λi, λi, ξi, ηi, pi, qi) are obtained and used to study the K2-3 exoplanetary system. All analytical and numerical calculations are performed with the aid of the Wolfram Mathematica.

Subducted oceanic plateau fed crustal growth: Insights from Amdo dacites in central Tibetan Plateau

The oceanic lithosphere subduction has been attested to exert the first-order control on the formation of the continental crust, but the role of oceanic plateaus on the crustal growth is elusive. It is difficult to identify the component of the oceanic plateaus in the continental crust because of their disappearance after subduction into deep mantle or obduction to be a part of the ophiolite mélanges in the ancient orogenic belts. Amdo microcontinent in the central Tibetan Plateau is an ideal place to assess the role of oceanic plateaus on crustal growth as it preserves the well-exposed arc magmatic rocks and fragments of the Meso-Tethyan oceanic plateaus to its south. Here, we present an integrated investigation of zircon U Pb ages and Hf isotope, as well as whole-rock elements and Sr-Nd-Hf isotopes for a suit of dacites in the Amdo microcontinent. Zircon U Pb dating indicates that the Amdo dacites formed at ca. 117 Ma, postdated the major formation period of the Meso-Tethyan oceanic plateaus. The Amdo dacites have relatively high SiO 2 (63.45–66.82 wt%) and low Mg# values (20.0–36.1), belonging to calc-alkaline series. The zircon thermometer and oxybarometer give an estimated temperature and oxygen fugacity of crystallization as ca. 700–720 °C and ΔFMQ = + 0.98, respectively. They have low Y (5.51–6.61 ppm) and Yb (0.44–0.53 ppm) contents and high La/Yb ratios (28.4–30.3). Despite their low Sr/Y ratios (6.86–13.5) caused by a small degree of fractionation of plagioclase, the Amdo dacites have an adakitic geochemical affinity, which was most likely derived from the thickened continental lower crust. These dacites have more depleted Sr-Nd-Hf isotope compositions (whole-rock 87 Sr/ 86 Sr i = 0.709796–0.710563, ε Nd (t) = −3.27 to −2.82, ε Hf (t) = 4.20–4.83 and zircon ε Hf (t) = 4.2–8.8) than the Neoproterozoic and Cambrian orthogneisses, as well as the Jurassic magmatic rocks. Simple binary mixing modeling reveals that the Amdo dacites could represent the hybrid melts of 50–60% of the subducted Meso-Tethyan oceanic plateau materials with 50–40% of the Amdo ancient continental crustal materials. The decoupled whole-rock Nd Hf isotopes (Δε Hf (t) = 7.55–8.43) of the Amdo dacites could be explained by the addition of zircon-free sediments overlie on the oceanic plateaus. These results indicate that subduction of the Meso-Tethyan oceanic plateaus with/without the overlying sediments made a substantial contribution to continental crustal growth. In conjunction with previous studies, the subduction of the Meso-Tethyan oceanic plateaus may discontinuously occur for about 37 million years, thus highlighting the significance of subduction of the Meso-Tethyan oceanic plateaus during the secular evolution of the central Tibetan Plateau. • ~117 Ma Amdo dacites first reported here formed under arc magmas-like oxidized environment. • Amdo dacites were most likely derived from the thickened continental lower crust. • Amdo dacites represent a hybrid melt of the ancient crustal basement and oceanic plateau materials. • Subduction of the oceanic plateau has an enormous potential for crust growth.

Bar pattern speed at z∼1–2 to explore challenges of the Standard Cosmology

AbstractStellar bars drive the galaxy secular evolution. While rotating around the galaxy centre with a given angular frequency, the bar pattern speed, they sweep material and modify the galaxy structure. In the LCDM model, bars are expected to slow down by exchanging angular momentum with the other omponents and/or through dynamical friction exerted by the dark matter halo. The only direct method to derive the bar pattern speed, the Tremaine-Weinberg method, revealed that real bars rotate fast, stressing a tension between the observations, conducted to date in the local universe, and the LCDM model. Measuring the bar pattern speed to bars up to z∼1-2 will reveal if the expected bar evolutionary path is actually taking place and/or to confirm if the dark matter is able to exert friction. Using high resolution N-body simulations we tested the applicability of the Tremaine-Weinberg method to deep spectroscopy of the NIRSpec@JWST for a sample of bars at z∼1-2. Our analysis can be used to prepare an observational proposal to get dedicated data.

The SPHERE view of three interacting twin disc systems in polarized light

ABSTRACT Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic, or parabolic passages (a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared polarized light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems: AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarized intensity and put particular attention to the presence of multiple light sources in these systems. The local angle of linear polarization indicates the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show that the polarized intensity from scattering with multiple relevant light sources results from an incoherent summation of the individuals’ contribution. This can produce nulls of polarized intensity in an image, as potentially observed in AS 205. We discuss the geometry and content of the systems by comparing the polarized light observations with other data at similar resolution, namely with ALMA continuum and gas emission. Collective observational data can constrain the systems’ geometry and stellar trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.

Investigation of tidal evolution in the Bohai Sea using the combination of satellite altimeter records and numerical models

Understanding secular tidal variability is fundamental for many practical purposes such as navigation, coastal engineering and flood warning. Observational tidal evolution is primarily based on coastal tide gauge records whose location and number are extremely limited. Tides undergo significant changes in the Bohai Sea mainly due to coastline changes induced by human activities while there are no publicly accessible long-term hourly tide gauges in the Bohai Sea. In this paper, we investigate secular tidal evolution of four major constituents (M2, S2, O1, and K1) in the Bohai Sea based on multi-satellite altimeter records and the numerical model. Both satellite results and model results indicate consistent feature of tidal changes for M2 tide in the Bohai Sea: M2 amplitudes remarkably increase in the Bohai Bay and Liaodong Bay while noticeably decrease in the Laizhou Bay; M2 phases significantly decrease in the Bohai Bay and Laizhou Bay while substantially increase in the south of the Liaodong Bay. The tidal changes of S2, K1, and O1 constituents revealed by multi-satellite altimeters and the numerical model are contradictory in many parts in the Bohai Sea. Such inconsistency may be related to residual mesoscale ocean variability in satellite results and the ignored contribution of water depth changes to tidal evolution in model results.

Possible merger signatures of the bulges of non-dwarf galaxies in the core of the Coma Cluster

In this paper, we discuss a method to study virialised clusters of galaxies with no-interaction features, like tails and bridges, using diagnostics of bulge classification and their properties, namely Sérsic index (n) and the Kormendy relation. We study a sample of non-dwarf galaxies in the core of the Coma Cluster using HST/ACS data. We divided our galaxy sample into 4 categories based on bulge to total light ratio (B/T): B/T<0.3 (12%), 0.3<B/T≤0.6 (38%), 0.6<B/T≤0.8 (29%) and B/T>0.8 (21%). We classified the galaxy bulges using Sérsic index (n) and the Kormendy relation, where classical bulges are a result of mergers and pseudo bulges are a result of secular evolution. Using Sérsic index we found that 75% galaxies in our sample had classical bulges (n>2) and 25% galaxies had pseudo-bulges (n<2). From the Kormendy diagram we found that 90% galaxies had classical and 10% galaxies had pseudo-bulges. We observed that classical bulges with B/T≥0.3 galaxies in the central region of Coma Cluster (within 0.4 Mpc from NGC 4874) are redder in colour (F475W−F814W≥1.17). Pseudo-bulges and B/T≤0.3 galaxies are within 0.6 to 1.1 Mpc from NGC 4874 and are bluer in colour (F475W−F814W≤1.13). We find that the majority of galaxies with classical bulges have B/T≥0.3 and those with pseudo-bulges have B/T≤0.3. With our study of the Kormendy relation and colour, B/T and distance from centre relations, we infer that galaxies in the central region of Coma Cluster with B/T≥0.3 may have formed by mergers and those with B/T≤0.3 may have formed by secular process.

The Galactic population of canonical pulsars

Context. Current wisdom suggests that the observed population of neutron stars are manifestations of their birth scenarios and their thermal and magnetic field evolution. Neutron stars can be observed at various wavebands as pulsars, and radio pulsars represent by far the largest population of neutron stars. Aims. In this paper, we aim to constrain the observed population of the canonical neutron star period, its magnetic field, and its spatial distribution at birth in order to understand the radio and high-energy emission processes in a pulsar magnetosphere. For this purpose we design a population synthesis method, self-consistently taking into account the secular evolution of a force-free magnetosphere and the magnetic field decay. Methods. We generated a population of pulsars and evolved them from their birth to the present time, using the force-free approximation. We assumed a given initial distribution for the spin period, surface magnetic field, and spatial Galactic location. Radio emission properties were accounted for by the polar cap geometry, whereas the gamma-ray emission was assumed to be produced within the striped wind model. Results. We find that a decaying magnetic field gives better agreement with observations compared to a constant magnetic field model. Starting from an initial mean magnetic field strength of B = 2.5 × 108 T with a characteristic decay timescale of 4.6 × 105 yr, a neutron star birth rate of 1/70 yr and a mean initial spin period of 60 ms, we find that the force-free model satisfactorily reproduces the distribution of pulsars in the P−Ṗ diagram with simulated populations of radio-loud, radio-only, and radio quiet gamma-ray pulsars similar to the observed populations.

Cool interstellar medium as an evolutionary tracer in ALMA-observed local dusty early-type galaxies

ABSTRACT The content and distribution of cool interstellar medium (&amp;lt;30 K) can indicate the evolutionary mechanisms that transform late-type to early-type galaxies (ETGs). To investigate this, ALMA observations of 12CO[2-1] line emission were obtained for five dusty ETGs from a complete sample in low-density environments. Four of the ETGs have massive (∼109 M⊙), extended molecular gas reservoirs with effective radii ∼3–5 kpc. This work provides a kinematic and structural analysis of these observations, to explore possible evolutionary mechanisms. Axisymmetric or bisymmetric kinematic models were fitted to observations of molecular gas discs, to quantify the dominant structures present and highlight additional structures or asymmetries. Integral field unit observations of these ETGs were also examined where available. Two of the ETGs, GAMA64646 and 622305, appear to have undergone tidal disturbance leading to molecular gas discs and/or star-forming inner rings. GAMA272990 may have undergone a merger, leading to an elliptical galaxy with an embedded star-forming molecular gas disc. GAMA622429 has probably undergone a minor merger, indicated by asymmetry in molecular gas distribution and disturbance in optical images. The remaining ETG, GAMA177186, was affected by source confusion from an offset source which could be a high-mass dust- and gas-rich object at high redshift. Overall, it appears that a high proportion of dusty ETGs in low-density environments have massive, extended molecular gas reservoirs, and have undergone some kind of interaction as part of their recent evolution. Secular evolution can then (re-)transform the ETGs from star-forming to passive galaxies.

The EDGE-CALIFA survey: The role of spiral arms and bars in driving central molecular gas concentrations

Shocks and torques produced by non-axisymmetric structures such as spiral arms and bars may transport gas to galaxy central regions. We test this hypothesis by studying the dependence of the concentration of CO luminosity (CCO) and molecular gas (Cmol) and the star formation rate (CSFR) in the central ∼2 kpc on the strength of non-axisymmetric disk structure using a sample of 57 disk galaxies selected from the EDGE-CALIFA survey. The Cmol is calculated using a CO-to-H2 conversion factor that decreases with higher metallicity and higher stellar surface density. We find that Cmol is systematically 0.22 dex lower than CCO. We confirm that high Cmol and strong non-axisymmetric disk structure are more common in barred galaxies than in unbarred galaxies. However, we find that spiral arms also increase Cmol. We show that there is a good correlation between Cmol and the strength of non-axisymmetric structure (which can be due to a bar, spiral arms, or both). This suggests that the stronger the bars and spirals, the more efficient the galaxy is at transporting cold gas to its center. Despite the small subsample size, the Cmol of the four Seyferts are not significantly reduced compared to inactive galaxies of similar disk structure, implying that the active galactic nucleus feedback in Seyferts may not notably affect the molecular gas distribution in the central ∼2 kpc. We find that CSFR tightly correlates with Cmol in both unbarred and barred galaxies. Likewise, elevated CSFR is found in galaxies with strong disk structure. Our results suggest that the disk structure, either spirals or bars, can transport gas to the central regions, with higher inflow rates corresponding to stronger structure, and consequently boost central star formation. Both spirals and bars play, therefore, an essential role in the secular evolution of disk galaxies.

The Control of Sea Level Change over the Development of Favorable Sand Bodies in the Pinghu Formation, Xihu Sag, East China Sea Shelf Basin

The Pinghu Formation consists primarily of marine-continental transitional deposits. The widely distributed fluvial and tidal transgressive sand bodies comprise the main reservoirs of the Baochu slope zone in the Xihu Sag in the East China Sea Shelf Basin. These sand bodies are deeply buried, laterally discontinuous, and are frequently interrupted by coal-bearing intervals, thereby making it extremely difficult for us to characterize their hydrocarbon potential quantitatively via seismic inversion techniques, such as multi-attribute seismic analysis and post-stack seismic inversion, hindering further hydrocarbon exploration in the Xihu Sag. Here, a prestack seismic inversion approach is applied to the regional seismic data to decipher the spatiotemporal distribution pattern of the sand bodies across the four sequences, i.e., SQ1, SQ2, SQ3, and SQ4, from bottom up, within the Pinghu Formation. In combination with detailed petrology, well log, and seismic facies analysis, the secular evolution of the sedimentary facies distribution pattern during the accumulation of the Pinghu Formation is derived from the sand body prediction results. It is concluded that the sedimentary facies and sand body distribution pattern rely on the interplay between the hydrodynamics of fluvial and tidal driving forces from the continent and open ocean, respectively. Drops in the sea level led to the gradual weakening of tidal driving forces and relative increases in riverine driving forces. The direction of the sand body distribution pattern evolves from NE–SW oriented to NW–SE oriented, and the dominant sand body changes from tidal facies to fluvial facies. In addition, the sea level drop led to the decrease in the water column salinity, redox condition, organic matter composition, and the development of coal seams, all of which directly influenced the quality of reservoir and source rocks. The sand bodies in SQ2 and SQ3 are favorable reservoirs in the Pinghu Formation due to their good reservoir properties and great thickness. The high-quality source rock in SQ1 could provide significant hydrocarbons and get preserved in the sand body within SQ2 and SQ3. This contribution provides an insight into the control of the sea level change over the development of hydrocarbon reservoirs in the petroleum system from marginal-marine environments such as the Xihu Sag.

Will Earth's next supercontinent assemble through the closure of the Pacific Ocean?

Earth's known supercontinents are believed to have formed in vastly different ways, with two endmembers being introversion and extroversion. The former involves the closure of the internal oceans formed during the break-up of the previous supercontinent, whereas the latter involves the closure of the previous external superocean. However, it is unclear what caused such diverging behavior of supercontinent cycles that involved first-order interaction between subducting tectonic plates and the mantle. Here we address this question through 4D geodynamic modeling using realistic tectonic set-ups. Our results show that the strength of the oceanic lithosphere plays a critical role in determining the assembly path of a supercontinent. We found that high oceanic lithospheric strength leads to introversion assembly, whereas lower strength leads to extroversion assembly. A theoretically estimated reduction in oceanic crustal thickness, and thus its strength, during Earth's secular cooling indicates that introversion was only possible for the Precambrian time when the oceanic lithosphere was stronger, thus predicting the assembling of the next supercontinent Amasia through the closure of the Pacific Ocean instead of the Indian-Atlantic oceans. Our work provides a new understanding of the secular evolution of plate tectonics and geodynamics as the Earth cooled.