Monthly Notices of the Royal Astronomical Society

Kang, Shi-Ju; Zheng, Yong-Gang; Wu, Qingwen

doi: 10.1093/mnras/stad2456pmid: N/A

ABSTRACTAn equivalent–width-based classification may cause the erroneous judgement to the flat spectrum radio quasars (FSRQs) and BL Lacerate objects (BL Lac) due to the diluting the line features by dramatic variations in the jet continuum flux. To help address the issue, this work explores the possible intrinsic classification on the basis of a random forest supervised machine learning algorithm. In order to do so, we compile a sample of 1680 Fermi blazars that have both gamma-rays and radio-frequencies data available from the 4LAC-DR2 catalogue, which includes 1352 training and validation samples and 328 forecast samples. By studying the results for all of the different combinations of 23 characteristic parameters, we found that there are 178 optimal parameter combinations (OPCs) with the highest accuracy (≃98.89 per cent). Using the combined classification results from the nine combinations of these OPCs to the 328 forecast samples, we predict that there are 113 true BL Lacs (TBLs) and 157 false BL Lacs (FBLs) that are possible intrinsically FSRQs misclassified as BL Lacs. The FBLs show a clear separation from TBLs and FSRQs in the gamma-ray photon spectral index, Γph, and X-band radio flux, logFR, plot. Phenomenally, existence a BL Lac to FSRQ (B-to-F) transition zone is suggested, where the FBLs are in the stage of transition from BL Lacs to FSRQs. Comparing the LSP changing-look blazars (CLBs) reported in the literatures, the majority of LSP CLBs are located at the B-to-F zone. We argue that the FBLs located at B-to-F transition zone are the most likely candidates of CLBs.

Cinquegrana, Giulia C; Joyce, Meridith; Karakas, Amanda I

doi: 10.1093/mnras/stad2461pmid: N/A

ABSTRACTThe minimum initial mass required for a star to explode as an Fe core collapse supernova, typically denoted Mmas, is an important quantity in stellar evolution because it defines the border between intermediate mass and massive stellar evolutionary paths. The precise value of Mmas carries implications for models of galactic chemical evolution and the calculation of star formation rates. Despite the fact that stars with super-solar metallicities are commonplace within spiral and some giant elliptical galaxies, there are currently no studies of this mass threshold in super metal-rich models with Z > 0.05. Here, we study the minimum mass necessary for a star to undergo an Fe core collapse supernova when its initial metal content falls in the range 2.5 × 10−3 ≤ Z ≤ 0.10. Although an increase in initial Z corresponds to an increase in the Fe ignition threshold for Z ≈ 1 × 10−3 to Z ≈ 0.04, we find that there is a steady reversal in trend that occurs for Z > 0.05. Our super metal-rich models thus undergo Fe core collapse at lower initial masses than those required at solar metallicity. Our results indicate that metallicity-dependent curves extending to Z = 0.10 for the minimum Fe ignition mass should be utilized in galactic chemical evolution simulations to accurately model supernovae rates as a function of metallicity, particularly for simulations of metal-rich spiral and elliptical galaxies.

Zhu, Liming; Zhang, Hanjiu; Zhang, Liang; Duan, Xuefeng; Lu, Xinying; Liu, Ying; Li, Xuebin; Sun, Gang; Weng, Ningquan

doi: 10.1093/mnras/stad2493pmid: N/A

ABSTRACTThis paper presents a comprehensive site survey of the Delingha site on the northern Tibetan Plateau from 2012 to 2014. In this campaign, we investigated 24 h continuous astronomical seeing, meteorological properties, and $C_{n}^{2}$ in the ground layer (GL). The results show that the median seeing is 3.46 arcsec during the day and 1.80 arcsec during the night. The best nighttime seeing occurs in summer (1.66 arcsec), while the worst occurs in autumn (1.96 arcsec). Seeing exhibits obvious diurnal behaviour, with the worst seeing occurring around mid-day (11:00 to 14:00, Beijing time), and the best seeing just before sunset (18:00 to 20:00, Beijing time). Moreover, the Delingha site has good meteorological properties for astronomical observations during the measurement period, especially the low median wind speed (2.8 m s−1) and great temperature inversion (day: −0.3 K, night: 0.6 K). As for the vertical distribution of $C_{n}^{2}$, the exponential h−0.46 dependence of $C_{n}^{2}$ varying with height in the GL is also obtained, and its power index is significantly related to the seasons. Furthermore, we calculated the contribution of optical turbulence in the GL to the whole atmosphere. Turbulence within the GL contributes significantly in summer, and its contribution can reach more than 35 per cent. Finally, we present the complete dependence analysis of seeing on meteorological parameters at the Delingha site. The results show that the best seeing tends to occur when the temperature inversion is sufficiently large, but the dependence of seeing on wind speed is not significant.

Melia, Fulvio

doi: 10.1093/mnras/stad2496pmid: N/A

ABSTRACTStudies of the Universe’s transition to smoothness in the context of Lambda cold dark matter (ΛCDM) have all pointed to a transition radius no larger than ∼300 Mpc. These are based on a broad array of tracers for the matter power spectrum, including galaxies, clusters, quasars, the Ly-α forest, and anisotropies in the cosmic microwave background. It is therefore surprising, if not anomalous, to find many structures extending out over scales as large as ∼2 Gpc, roughly an order of magnitude greater than expected. Such a disparity suggests that new physics may be contributing to the formation of large-scale structure, warranting a consideration of the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the Rh = ct universe. This model has successfully eliminated many other problems in ΛCDM. In this paper, we calculate the fractal (or Hausdorff) dimension in this cosmology as a function of distance, showing a transition to smoothness at ∼2.2 Gpc, fully accommodating all of the giant structures seen thus far. This outcome adds further observational support for Rh = ct over the standard model.

Shen, Xuejian; Vogelsberger, Mark; Boylan-Kolchin, Michael; Tacchella, Sandro; Kannan, Rahul

doi: 10.1093/mnras/stad2508pmid: N/A

ABSTRACTJWST observations have revealed a population of galaxies bright enough that potentially challenge standard galaxy formation models in the Λ cold dark matter (ΛCDM) cosmology. Using a minimal empirical framework, we investigate the influence of variability on the rest-frame ultra-violet (UV) luminosity function of galaxies at z ≥ 9. Our study differentiates between the median UV radiation yield and the variability of UV luminosities of galaxies at a fixed dark matter halo mass. We primarily focus on the latter effect, which depends on halo assembly and galaxy formation processes and can significantly increase the abundance of UV-bright galaxies due to the upscatter of galaxies in lower-mass haloes. We find that a relatively low level of variability, σUV ≈ 0.75 mag, matches the observational constraints at z ≈ 9. However, increasingly larger σUV is necessary when moving to higher redshifts, reaching $\sigma _{\rm UV} \approx 2.0\, (2.5)\, {\rm mag}$ at z ≈ 12 (16). This implied variability is consistent with expectations of physical processes in high-redshift galaxies such as bursty star formation and dust clearance during strong feedback cycles. Photometric constraints from JWST at z ≳ 9 therefore can be reconciled with a standard ΛCDM-based galaxy formation model calibrated at lower redshifts without the need for adjustments to the median UV radiation yield.

Becerra, R L; Klotz, A; Atteia, J L; Guetta, D; Watson, A M; De Colle, F; Angulo-Valdez, C; Butler, N R; Dichiara, S; Fraija, N; Garcia-Cifuentes, K; Kutyrev, A S; Lee, W H; Pereyra, M; Troja, E

doi: 10.1093/mnras/stad2513pmid: N/A

ABSTRACTWe collected the optical light-curve data of 227 gamma-ray bursts (GRBs) observed with the TAROT, COATLI, and RATIR telescopes. These consist of 133 detections and 94 upper limits. We constructed average light curves in the observer and rest frames in both X-rays (from Swift/X-Ray Telescope) and the optical. Our analysis focused on investigating the observational and intrinsic properties of GRBs. Specifically, we examined observational properties, such as the optical brightness function of the GRBs at T = 1000 s after the trigger, as well as the temporal slope of the afterglow. We also estimated the redshift distribution for the GRBs within our sample. Of the 227 GRBs analysed, we found that 116 had a measured redshift. Based on these data, we calculated a local rate of ρ0 = 0.2 Gpc−3 yr−1 for these events with z < 1. To explore the intrinsic properties of GRBs, we examined the average X-ray and optical light curves in the rest frame. We use the afterglowpy library to generate synthetic curves to constrain the parameters typical of the bright GRB jet, such as energy (〈E0〉 ∼ 1053.6 erg), opening angle (〈θcore〉 ∼ 0.2 rad), and density (〈n0〉 ∼ 10−2.1 cm−3). Furthermore, we analyse microphysical parameters, including the fraction of thermal energy in accelerated electrons (〈ϵe〉 ∼ 10−1.37) and in the magnetic field (〈ϵB〉 ∼ 10−2.26), and the power-law index of the population of non-thermal electrons (〈p〉 ∼ 2.2).

Mohammadi, S; Yusofi, E; Mohsenzadeh, M; Salem, M K

doi: 10.1093/mnras/stad2514pmid: N/A

ABSTRACTIn this study, we use the merger process of clusters/voids in the role of variable dark energy fluid to alleviate the Hubble tension, which can lead to a balance in the cosmological expansion rate. To reach this target, we will introduce a modified form of energy density for cosmic fluid with the quadratic equation of state, and then we obtain Hubble, deceleration parameters, and luminosity distance for this fluid. To obtain the merger factor and other parameters of our model, we utilize the NONLINEARMODELFIT function within MATHEMATICA. By consideration of the local and global measurements of $\rm H_0$, and the equation of state parameter w as the priory values, and fitting our model with observational Hubble data measurements, we will show that the merger of clusters/voids plays the role of balancing the cosmic expansion rate. Also, it will be shown that the model is more compatible than wCDM with the standard model to describe the accelerating Universe

Baliukin, I I; Izmodenov, V V; Alexashov, D B

doi: 10.1093/mnras/stad2518pmid: N/A

ABSTRACTThe hydrogen atoms penetrate the heliosphere from the local interstellar medium, and while being ionized, they form the population of pickup protons. The distribution of pickup protons is modified by the adiabatic heating (cooling) induced by the solar wind plasma compression (expansion). In this study, we emphasize the importance of the adiabatic energy change in the inner heliosheath that is usually either neglected or considered improperly. The effect of this process on the energy and spatial distributions of pickup protons and energetic neutral atoms (ENAs), which originate in the charge exchange of pickup protons, has been investigated and quantified using a kinetic model. The model employs the global distributions of plasma and hydrogen atoms in the heliosphere from the simulations of a kinetic-magnetohydrodynamic model of solar wind interaction with the local interstellar medium. The findings indicate that the adiabatic energy change is responsible for the broadening of the pickup proton velocity distribution and the significant enhancement of ENA fluxes (up to ∼5 and ∼20 times in the upwind and downwind directions at energies ∼1–2 keV for an observer at 1 au). It sheds light on the role of adiabatic energy change in explaining the discrepancies between the ENA flux observations and the results of numerical simulations.

Melnik, A M; Podzolkova, E N; Dambis, A K

doi: 10.1093/mnras/stad2520pmid: N/A

ABSTRACTWe study the periodic enhancement of either trailing or leading segments of the resonance elliptical rings in the dynamical model of the Galaxy which reproduces distributions of observed velocities derived from Gaia DR3 (EDR3) data along the Galactocentric distance. The model disc forms a nuclear ring, an inner combined ring, and outer resonance rings R1 and R2. The backbone of the inner combined ring is banana-type orbits around the Lagrange equilibrium points L4 and L5. Orbits associated with the unstable equilibrium points L1 and L2 also support the inner ring. We have found the changes of the morphology of the inner ring with a period of P = 0.57 ± 0.02 Gyr, which is close to the period of revolution along the long-period orbits around the points L4 and L5. A possible explanation of these morphological changes is the formation of an overdensity which then begins circulating along the closed contour. In the region of the Outer Lindblad Resonance (OLR), we have found the changes of the morphology of the outer rings with a period of P = 2.0 ± 0.1 Gyr. Probably, the morphological changes of the outer rings are due to the orbits trapped by the OLR. These orbits exhibit librations of the direction of orbital elongation with respect to the minor axis of the bar as well as the long-term variations in the stellar angular momentum, energy, average radius of the orbit, and eccentricity. Among many librating orbits, we discovered orbits with the libration period of P = 1.91 ± 0.01 Gyr, which may cause the morphological changes of the outer rings.

Kramarev, Nikita; Yudin, Andrey

doi: 10.1093/mnras/stad2529pmid: N/A

ABSTRACTIn this paper, we use analytical methods to study the last stages of the double neutron star (NS) system evolution. Depending on the initial masses of the components, this evolution can occur either in the framework of the merging scenario or in the NS stripping model. The main new ingredient of this work, compared with previous calculations, is accounting for accretion spin-up of the massive component. This effect leads to a significant decrease in the duration of the stable mass transfer of matter in the stripping mechanism. Within the framework of the Newtonian approximation, we determine the boundary between the merging and stripping scenarios. It is shown that this boundary weakly depends on the total mass of the system and the specific form of the NS equation of state, and is determined mainly by the initial mass ratio of the components. The stripping scenario is realized at M2/M1 ≲ 0.8, so it should make a large contribution to the population of gravitational wave events from NS–NS coalescing binaries that are close to us, and their accompanying short gamma-ray bursts. Nevertheless, the value obtained requires further clarification, taking into account relativistic effects, possible non-conservative mass transfer, etc.