Rm Min Research Articles

Flares in the Galactic centre – II. Polarization signatures of flares at mm-wavelengths

ABSTRACT Recent polarimetric mm-observations of the galactic centre showed sinusoidal loops in the $\mathcal {Q{\small --}U}$ plane with a duration of one hour. The loops coincide with a quasi-simultaneous X-ray flare. A promising mechanism to explain the flaring events are magnetic flux eruptions in magnetically arrested accretion flows (MAD). In our previous work, we studied the accretion flow dynamics during flux eruptions. Here, we extend our previous study by investigating whether polarization loops can be a signature produced by magnetic flux eruptions. We find that loops in the $\mathcal {Q{\small --}U}$ plane are robustly produced in MAD models as they lead to enhanced emissivity of compressed disc material due to orbiting flux bundles. A timing analysis of the synthetic polarized light curves demonstrate a polarized excess variability at time-scales of $\simeq 1~\rm h$. The polarization loops are also clearly imprinted on the cross-correlation of the Stokes parameters which allows us to extract a typical periodicity of $30~\rm min$ to $1~\rm h$ with some evidence for a spin dependence. These results are intrinsic to the MAD state and should thus hold for a wide range of astrophysical objects. A subset of general relativistic magnetohydrodynamic simulations without saturated magnetic flux, namely, single temperature standard and normal evolution models, also produces $\mathcal {Q{\small --}U}$ loops. However, in disagreement with the observations, loops in these simulations are quasi-continuous with a low polarization excess.

The minimum mass for star formation by dynamical fragmentation: dependence on epoch, dust abundance, and environment

ABSTRACT We estimate the minimum mass of a star formed by dynamical collapse and fragmentation, as a function of epoch, dust abundance, and environment. Epoch is parametrized by redshift, zred, through the variation in the temperature of the cosmic microwave background. The dust abundance is parametrized by the mass-fraction in dust, ZD, with the additional simplifying assumption that the intrinsic properties of dust do not change with ZD, only the amount of dust. Environment is parametrized by the energy-density of the ambient suprathermal radiation fields through a dilution factor ω⋆ (applied to a blackbody radiation field at $T_{\star }=10^4\, {\rm K}$). The critical condition is that a spherical proto-fragment should be able to cool, and therefore contract, fast enough to detach from neighbouring proto-fragments. The minimum mass increases with increasing redshift, increasing dust abundance, and increasing suprathermal background. Values in the range from $M_{{\rm MIN}}\sim 0.002\, {\rm M}_{\odot }$ to $M_{{\rm MIN}}\sim 0.2\, {\rm M}_{\odot }$ are obtained at the extremes of the parameter ranges we have considered (0 ≤ zred ≤ 8, 0.00016 < ZD < 0.04, and 10−15 ≤ ω⋆ ≤ 10−8). Our results agree quite well with the predictions of detailed numerical simulations invoking similar redshifts and dust abundances, but our estimates are somewhat lower; we attribute this difference to resolution issues and the small-number statistics from the simulations. The increased minimum masses predicted at high redshift and/or high suprathermal background result in significantly bottom-light initial mass functions, and therefore low mass-to-light ratios, provided that the dust abundance is not too low. The changes due to high suprathermal background may be particularly important for star formation in galactic nuclei and at high redshift.

The cluster mass function and the σ8 tension

ABSTRACT We use a large set of halo mass function (HMF) models in order to investigate their ability to represent the observational cluster mass function (CMF), derived from the $\tt {GalWCat19}$ cluster catalogue, within the Lambda cold dark matter (ΛCDM) cosmology. We apply the χ2 minimization procedure to constrain the free parameters of the models, namely Ωm and σ8. We find that all HMF models fit well the observational CMF, while the Bocquet et al. model provides the best fit, with the lowest χ2 value. Utilizing the index of inconsistency (IOI) measure, we further test the possible inconsistency of the models with respect to a variety of Planck 2018 ΛCDM cosmologies, resulting from the combination of different probes (CMB–BAO or CMB–DES). We find that the HMF models that fitted well the observed CMF provide consistent cosmological parameters with those of the Planck CMB analysis, except for the Press and Schechter, Yahagi et al., and Despali et al. models that return large IOI values. The inverse $\chi _{\rm min}^2$-weighted average values of Ωm and σ8, overall 23 theoretical HMF models are ${\bar{\Omega }_{m,0}}=0.313\pm 0.022$ and ${\bar{\sigma }_8}=0.798\pm 0.040$, which are clearly consistent with the results of Planck–CMB, providing S8 = σ8(Ωm/0.3)1/2 = 0.815 ± 0.05. Within the ΛCDM paradigm and independently of the selected HMF model in the analysis, we find that the current CMF shows no σ8 tension with the corresponding Planck–CMB results.

Type Ia supernovae in NS+He star systems and the isolated mildly recycled pulsars

ABSTRACT Type Ia supernovae (SNe Ia) are successful cosmological distance indicators and important element factories in the chemical evolution of galaxies. They are generally thought to originate from thermonuclear explosions of carbon–oxygen white dwarfs in close binaries. However, the observed diversity among SNe Ia implies that they have different progenitor models. In this article, we performed the long-term evolution of NS+He star binaries with different initial He star masses ($M_{\rm He}^{\rm i}$) and orbital periods ($P_{\rm orb}^{\rm i}$) for the first time, in which the He star companions can explode as SNe Ia eventually. Our simulations indicate that after the He stars develop highly degenerate oxygen–neon (ONe) cores with masses near the Chandrasekhar limit, explosive oxygen burning can be triggered due to the convective Urca process. According to these calculations, we obtained an initial parameter space for the production of SNe Ia in the $\rm log\,$$P^{\rm i}_{\rm orb}{\text {--}}M^{\rm i}_{\rm He}$ plane. Meanwhile, we found that isolated mildly recycled pulsars can be formed after He stars explode as SNe Ia in NS+He star binaries, in which the isolated pulsars have minimum spin periods ($P_{\rm spin}^{\rm min}$) of ∼30–110 ms and final orbital velocities of ${\sim} \rm 60{\!-\!}360\, km\, s^{-1}$, corresponding to initial orbital periods of 0.07–10 d. Our work suggests that the NS+He star channel may contribute to the formation of isolated mildly recycled pulsars with velocity $\rm {\lesssim} 360\, km\, s^{-1}$ in observations, and such isolated pulsars should locate in the region of pulsars with massive white dwarf companions in the $P_{\rm spin} {\!-\!}\dot{P}_{\rm spin}$ diagram.

Ton S 415: a close binary containing an intermediate helium subdwarf discovered with SALT and TESS

ABSTRACT Hot subdwarfs are early-type low-mass stars lying between the main sequence and the white dwarf sequence. The majority have helium-burning cores and helium-poor surfaces. A minority have helium-rich surfaces. A few, including Ton S 415, have surfaces with between 10 per cent and 90 per cent helium (by number). Their properties are diverse and their origins mostly unknown. Ton S 415 was identified as a suspected binary in a Southern African Large Telescope (SALT) survey of hot subdwarfs from its large radial velocity. Using SALT spectroscopy and Transiting Exoplanet Survey Satellite light curves, we confirm that Ton S 415 is a close binary with an orbital period $p=84.6460\pm 0.0004\, {\rm min}$ and velocity semi-amplitude $K=175.5\pm 1.0\, {\rm km\, s^{-1}}$. Analysis of the SALT spectrum and broad-band spectral energy distribution shows the visible star to have an effective temperature $T_{\rm eff}=43\, 300\pm 1000\, {\rm K}$, surface gravity $\log g/{\rm cm\, s^{-2}}=5.89\pm 0.10$, surface helium-to-hydrogen ratio log y = −0.62 ± 0.10, radius $R=0.1074\pm 0.0025\, R_{\odot }$, and mass $M=0.33\pm 0.09\, {\rm {\rm M}_{\odot }}$. By modelling the light curve, we estimate the binary mass ratio to be q = 0.7 ± 0.3 and infer an unseen white dwarf companion with a mass of $M_{\rm WD}=0.47\pm 0.24\, {\rm {\rm M}_{\odot }}$. The results are consistent with a post-common-envelope binary that lost its hydrogen envelope before reaching the peak of the red giant branch, becoming a hot subdwarf with a non-canonical mass. We predict that the system will evolve into a double white dwarf binary before eventually either forming a stably accreting AM CVn system, or merging to form an R CrB star.

Spectroscopic follow-up of black hole and neutron star candidates in ellipsoidal variables from Gaia DR3

ABSTRACT We present multi-epoch spectroscopic follow-up of a sample of ellipsoidal variables selected from Gaia Data Release 3 (DR3) as candidates for hosting quiescent black holes (BHs) and neutron stars (NSs). Our targets were identified as BH/NS candidates because their optical light curves – when interpreted with models that attribute variability to tidal distortion of a star by a companion that contributes negligible light – suggest that the companions are compact objects. From the likely BH/NS candidates identified in recent work accompanying Gaia DR3, we select 14 of the most promising targets for follow-up. We obtained spectra for each object at 2–10 epochs, strategically observing near conjunction to best constrain the radial velocity semi-amplitude. From the measured semi-amplitudes of the radial velocity curves, we derive minimum companion masses of $M_{2,\, \rm min} \le 0.5 \, {\rm M}_{\odot }$ in all cases. Assuming random inclinations, the typical inferred companion mass is $M_2 \sim 0.15\, {\rm M}_{\odot }$. This makes it unlikely that any of these systems contain a BH or NS, and we consider alternative explanations for the observed variability. We can best reproduce the observed light curves and radial velocities with models for unequal-mass contact binaries with star-spots. Some of the objects in our sample may also be detached main-sequence binaries, or even single stars with pulsations or star-spot variability masquerading as ellipsoidal variation. We provide recommendations for future spectroscopic efforts to further characterize this sample and more generally to search for compact object companions in close binaries.

Binary black holes population and cosmology in new lights: signature of PISN mass and formation channel in GWTC-3

ABSTRACT The mass, spin, and merger rate distribution of the binary black holes (BBHs) across cosmic redshifts provide a unique way to shed light on their formation channel. Along with the redshift dependence of the BBH merger rate, the mass distribution of BBHs can also exhibit redshift dependence due to different formation channels and dependence on the metallicity of the parent stars. We explore the redshift dependence of the BBH mass distribution jointly with the merger rate evolution from the third gravitational wave (GW) catalogue GWTC-3 of the LIGO–Virgo–KAGRA collaboration. We study possible connections between peak-like features in the mass spectrum of BBHs and processes related to supernovae physics and time delay distributions. We obtain a preference for short-time delays between star formation and BBH mergers. Using a power-law form for the time delay distribution ($(t^{\rm min}_d)^{d}$), we find d < −0.7 credible at 90 per cent interval. The mass distribution of the BBHs could be fitted with a power-law form with a redshift-dependent peak feature that can be linked to the pair instability supernovae (PISN) mass-scale MPISN(Z*) at a stellar metallicity Z*. For a fiducial value of the stellar metallicity Z* = 10−4, we find the $\rm M_{\rm PISN}(Z_*)=44.4^{+7.9}_{-6.3}$$\rm M_\odot$. This is in accordance with the theoretical prediction of the lower edge of the PISN mass-scale and differs from previous analyses. Although we find a strong dependence of the PISN value on metallicity, the model that we explored is not strongly favoured over those that do not account for metallicity as the Bayes factors are inconclusive. In the future with more data, evidence towards metallicity dependence of the PISN will have a significant impact on our understanding of stellar physics.

Constraining cosmic ray transport with observations of the circumgalactic medium

ABSTRACT Recent theoretical studies predict that the circumgalactic medium (CGM) around low-redshift, ∼L* galaxies could have substantial non-thermal pressure support in the form of cosmic rays. However, these predictions are sensitive to the specific model of cosmic ray transport employed, which is theoretically and observationally underconstrained. In this work, we propose a novel observational constraint for calculating the lower limit of the radially averaged, effective cosmic ray transport rate, ${\kappa _{\rm eff}^{\rm min}}$. Under a wide range of assumptions (so long as cosmic rays do not lose a significant fraction of their energy in the galactic disc, regardless of whether the cosmic ray pressure is important or not in the CGM), we demonstrate a well-defined relationship between ${\kappa _{\rm eff}^{\rm min}}$ and three observable galaxy properties: the total hydrogen column density, the average star formation rate, and the gas circular velocity. We use a suite of Feedback in Realistic Environments 2 galaxy simulations with a variety of cosmic ray transport physics to demonstrate that our analytical model of ${\kappa _{\rm eff}^{\rm min}}$ is a robust lower limit of the true cosmic ray transport rate. We then apply our new model to calculate ${\kappa _{\rm eff}^{\rm min}}$ for galaxies in the COS-Halos sample, and confirm this already reveals strong evidence for an effective transport rate that rises rapidly away from the interstellar medium to values ${\kappa _{\rm eff}^{\rm min}}\gtrsim 10^{30\!-\!31}\, {\rm cm}^2\, {\rm s}^{-1}$ (corresponding to anisotropic streaming velocities of $v^{\rm stream}_{\rm eff} \gtrsim 1000\, {\rm km}\, {\rm s}^{-1}$) in the diffuse CGM, at impact parameters larger than 50–100 kpc. We discuss how future observations can provide qualitatively new constraints in our understanding of cosmic rays in the CGM and intergalactic medium.

Interferometric H i intensity mapping: perturbation theory predictions and foreground removal effects

ABSTRACT We provide perturbation theory predictions for the H i intensity mapping power spectrum multipoles using the Effective Field Theory of Large Scale Structure, which should allow us to exploit mildly non-linear scales. Assuming survey specifications typical of proposed interferometric H i intensity mapping experiments like Canadian Hydrogen Observatory and Radio transient Detector and PUMA, and realistic ranges of validity for the perturbation theory modelling, we run mock full shape Markov chain Monte Carlo (MCMC) analyses at z = 0.5, and compare with Stage-IV optical galaxy surveys. We include the impact of 21cm foreground removal using simulations-based prescriptions, and quantify the effects on the precision and accuracy of the parameter estimation. We vary 11 parameters in total: three cosmological parameters, seven bias and counter terms parameters, and the H i brightness temperature. Amongst them, the four parameters of interest are: the cold dark matter density, ωc, the Hubble parameter, h, the primordial amplitude of the power spectrum, As, and the linear H i bias, b1. For the best-case scenario, we obtain unbiased constraints on all parameters with $\lt 3{{\ \rm per\ cent}}$ errors at $68{{\ \rm per\ cent}}$ confidence level. When we include the foreground removal effects, the parameter estimation becomes strongly biased for ωc, h, and b1, while As is less biased (<2σ). We find that scale cuts $k_{\rm min} \ge 0.03 \ h\,\mathrm{Mpc}^{-1}$ are required to return accurate estimates for ωc and h, at the price of a decrease in the precision, while b1 remains strongly biased. We comment on the implications of these results for real data analyses.

Theoretical studies of low-frequency shear Alfvén waves in reversed shear tokamak plasmas

The low-frequency Alfvénic fluctuations in the kinetic thermal-ion gap frequency range have aroused the interest of researchers since they can interact with background thermal particles and/or energetic particles. In the theoretical framework of the general fishbone-like dispersion relation (GFLDR), we theoretically investigate and delineate the linear wave properties of the low-frequency shear Alfvén wave excited by energetic and/or thermal particles observed in tokamak experiments with reversed magnetic shear. These low-frequency shear Alfvén waves are closely related to the dedicated experiment on energetic ion-driven low-frequency instabilities conducted on DIII-D in 2019. Therefore, adopting the representative experimental equilibrium parameters of DIII-D, in this work we demonstrate that the experimentally observed low-frequency modes and beta-induced Alfvén eigenmodes (BAEs) are, respectively, the reactive-type unstable mode and dissipative-type unstable mode, each with dominant Alfvénic polarization, thus the former being more precisely called low-frequency Alfvén modes (LFAMs). More specifically, due to diamagnetic and trapped particle effects, the LFAM can be coupled with the beta-induced Alfvén-acoustic mode (BAAE) in the low-frequency range (frequency much less than the thermal-ion transit frequency and/or bounce frequency), or with the BAE in the high frequency range (frequency higher than or comparable to the thermal-ion transit frequency), resulting in reactive-type instabilities. Moreover, due to different instability mechanisms, the maximal drive of BAEs occurs in comparison with LFAMs, when the minimum of the safety factor (<inline-formula><tex-math id="M1">\begin{document}$ q_{\rm min} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230255_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230255_M1.png"/></alternatives></inline-formula>) deviates from a rational number. Meanwhile, the BAE eigenfunction peaks at the radial position of the maximum energetic particle pressure gradient, resulting in a large deviation from the <inline-formula><tex-math id="M2">\begin{document}$ q_{\rm min} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230255_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230255_M2.png"/></alternatives></inline-formula> surface. The ascending frequency spectrum patterns of the experimentally observed BAEs and LFAMs can be theoretically reproduced by varying <inline-formula><tex-math id="M3">\begin{document}$ q_{\rm min} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230255_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230255_M3.png"/></alternatives></inline-formula>, and they can also be well explained based on the GFLDR. In particular, it is confirmed that the stability of the BAAE is not affected by energetic ions, which is consistent with the first-principle-based theory predictions and simulation results. The present analysis illustrates the solid predictive capability of the GFLDR and its practical applications in enhancing the ability to explain experimental and numerical simulation results.

Modelling repetition in zDM: A single population of repeating fast radio bursts can explain CHIME data

Abstract Regardless of whether or not all fast radio bursts (FRBs) repeat, those that do form a population with a distribution of rates. This work considers a power-law model of this population, with rate distribution $\Phi_r \sim R^{{\gamma_r}}$ between ${R_{\rm min}}$ and ${R_{\rm max}}$ . The zDM code is used to model the probability of detecting this population as either apparently once-off or repeat events as a function of redshift, z, and dispersion measure, DM. I demonstrate that in the nearby Universe, repeating sources can contribute significantly to the total burst rate. This causes an apparent deficit in the total number of observed sources (once-off and repeaters) relative to the distant Universe that will cause a bias in FRB population models. Thus instruments with long exposure times should explicitly take repetition into account when fitting the FRB population. I then fit data from The Canadian Hydrogen Intensity Mapping Experiment (CHIME). The relative number of repeat and apparently once-off FRBs, and their DM, declination, and burst rate distributions, can be well explained by 50–100% of CHIME single FRBs being due to repeaters, with ${R_{\rm max}} > 0.75$ d $^{-1}$ above $10^{39}$ erg, and ${{\gamma_r}} = -2.2_{-0.8}^{+0.6}$ . This result is surprisingly consistent with follow-up studies of FRBs detected by the Australian Square Kilometre Array Pathfinder (ASKAP). Thus the evidence suggests that CHIME and ASKAP view the same repeating FRB population, which is responsible not just for repeating FRBs, but the majority of apparently once-off bursts. For greater quantitative accuracy, non-Poissonian arrival times, second-order effects in the CHIME response, and a simultaneous fit to the total FRB population parameters, should be treated in more detail in future studies.

Neutrino fast flavor pendulum. II. Collisional damping

In compact astrophysical objects, the neutrino density can be so high that neutrino-neutrino refraction can lead to fast flavor conversion of the kind $\nu_e \bar\nu_e \leftrightarrow \nu_x \bar\nu_x$ with $x=\mu,\tau$, depending on the neutrino angle distribution. Previously, we have shown that in a homogeneous, axisymmetric two-flavor system, these collective solutions evolve in analogy to a gyroscopic pendulum. In flavor space, its deviation from the weak-interaction direction is quantified by a variable $\cos\vartheta$ that moves between $+1$ and $\cos\vartheta_{\rm min}$, the latter following from a linear mode analysis. As a next step, we include collisional damping of flavor coherence, assuming a common damping rate $\Gamma$ for all modes. Empirically we find that the damped pendular motion reaches an asymptotic level of pair conversion $f=A+(1-A)\cos\vartheta_{\rm min}$ (numerically $A\simeq 0.370$) that does not depend on details of the angular distribution (except for fixing $\cos\vartheta_{\rm min}$), the initial seed, nor $\Gamma$. On the other hand, even a small asymmetry between the neutrino and antineutrino damping rates strongly changes this picture and can even enable flavor instabilities in otherwise stable systems.

Galaxy and Mass Assembly (GAMA): probing galaxy-group correlations in redshift space with the halo streaming model

ABSTRACT We have studied the galaxy-group cross-correlations in redshift space for the Galaxy And Mass Assembly (GAMA) Survey. We use a set of mock GAMA galaxy and group catalogues to develop and test a novel ‘halo streaming’ model for redshift-space distortions. This treats 2-halo correlations via the streaming model, plus an empirical 1-halo term derived from the mocks, allowing accurate modelling into the non-linear regime. In order to probe the robustness of the growth rate inferred from redshift-space distortions, we divide galaxies by colour, and divide groups according to their total stellar mass, calibrated to total mass via gravitational lensing. We fit our model to correlation data, to obtain estimates of the perturbation growth rate, fσ8, validating parameter errors via the dispersion between different mock realizations. In both mocks and real data, we demonstrate that the results are closely consistent between different subsets of the group and galaxy populations, considering the use of correlation data down to some minimum projected radius, rmin. For the mock data, we can use the halo streaming model to below $r_{\rm min} = 5{\, h^{-1}\, \rm Mpc}$, finding that all subsets yield growth rates within about 3 per cent of each other, and consistent with the true value. For the actual GAMA data, the results are limited by cosmic variance: fσ8 = 0.29 ± 0.10 at an effective redshift of 0.20; but there is every reason to expect that this method will yield precise constraints from larger data sets of the same type, such as the Dark Energy Spectroscopic Instrument (DESI) bright galaxy survey.

Perturbation theory models for LSST-era galaxy clustering: Tests with subpercent mock catalog measurements in Fourier and configuration space

We analyze the clustering of galaxies using the z=1.006 snapshot of the CosmoDC2 simulation, a high-fidelity synthetic galaxy catalog designed to validate analysis methods for the Large Synoptic Survey Telescope (LSST). We present sub-percent measurements of the galaxy auto-correlation and galaxy-dark matter cross correlations in Fourier space and configuration space for a magnitude-limited galaxy sample. At these levels of precision, the statistical errors of the measurement are comparable to the systematic effects present in the simulation and measurement procedure; nevertheless, using a hybrid-PT model, we are able to model non-linear galaxy bias with 0.5% precision up to scales of $k_{\rm max}= 0.5 \ h/{\rm Mpc}$ and $r_{\rm min}= 4 \ {\rm Mpc}/h$. While the linear bias parameter is measured with 0.01% precision, other bias parameters are determined with considerably weaker constraints and sometimes bimodal posterior distributions. We compare our fiducial model with lower dimensional models where the higher-order bias parameters are fixed at their co-evolution values and find that leaving these parameters free provides significant improvements in our ability to model small scale information. We also compare bias parameters for galaxy samples defined using different magnitude bands and find agreement between samples containing equal numbers of galaxies. Finally, we compare bias parameters between Fourier space and configuration space and find moderate tension between the two approaches. Although our model is often unable to fit the CosmoDC2 galaxy samples within the 0.1% precision of our measurements, our results suggest that the hybrid-PT model used in this analysis is capable of modeling non-linear galaxy bias within the percent level precision needed for upcoming galaxy surveys.

Backbone and shortest-path exponents of the two-dimensional Q-state Potts model.

We present a Monte Carlo study of the backbone and the shortest-path exponents of the two-dimensional Q-state Potts model in the Fortuin-Kasteleyn bond representation. We first use cluster algorithms to simulate the critical Potts model on the square lattice and obtain the backbone exponents d_{B}=1.7320(3) and 1.794(2) for Q=2,3, respectively. However, for large Q, the study suffers from serious critical slowing down and slowly converging finite-size corrections. To overcome these difficulties, we consider the O(n) loop model on the honeycomb lattice in the densely packed phase, which is regarded to correspond to the critical Potts model with Q=n^{2}. With a highly efficient cluster algorithm, we determine from domains enclosed by the loops d_{B}=1.64339(5),1.73227(8),1.7938(3),1.8384(5),1.8753(6) for Q=1,2,3,2+sqrt[3],4, respectively, and d_{min}=1.0945(2),1.0675(3),1.0475(3),1.0322(4) for Q=2,3,2+sqrt[3],4, respectively. Our estimates significantly improve over the existing results for both d_{B} and d_{min}. Finally, by studying finite-size corrections in backbone-related quantities, we conjecture an exact formula as a function of n for the leading correction exponent.

Detection of pairwise kSZ effect with DESI galaxy clusters and Planck

ABSTRACT We report a 5σ detection of the pairwise kinematic Sunyaev–Zel’dovich (kSZ) effect, combining galaxy clusters in DESI imaging surveys and the Planck temperature maps. The detection is facilitated by both improvements in the data and in the analysis method. For the data, we adopt the recently released DESI galaxy group catalog with ∼106 robustly identified groups, and construct various galaxy cluster samples for the kSZ measurement. The DESI group catalogue also provides estimation of halo mass, which further improves the kSZ measurement by $\sim 10{{\ \rm per\ cent}}$. For the analysis method, we derive an optimal estimator of pairwise kSZ through the maximum likelihood analysis. It also handles potential systematic errors self-consistently. The baseline cluster sample, containing the 1.2 × 105 richest galaxy clusters of typical mass ∼1014 M⊙/h at typical redshift 0.2–0.5, rules out the null hypothesis at 5σ. When fitting with a pairwise kSZ template from simulations, the signal is detected at 4.7σ and the average optical depth is constrained as $\bar{\tau }_e=(1.66\pm 0.35)\times 10^{-4}$. We perform various internal checks, with different cluster selection criteria, different sky coverage, and redshift range, different CMB maps, different filter sizes, different treatments of potential systematics, and the covariance matrix. The kSZ effect is consistently detected with 2.5 ≤S/N≤5.6 and acceptable $\chi ^2_{\rm min}$, across a variety of cluster samples. The S/N is limited by both the Planck resolution and the photo-z accuracy, and therefore, can be significant improved with DESI spectroscopic redshift information and with other CMB experiments.

Joint analyses of 2D CMB lensing and 3D galaxy clustering in the spherical Fourier-Bessel basis

Cross-correlating cosmic microwave background (CMB) lensing and galaxy clustering has been shown to greatly improve the constraints on the local primordial non-Gaussianity (PNG) parameter $f_{\rm NL}$ by reducing sample variance and also parameter degeneracies. To model the full use of the 3D information of galaxy clustering, we forecast $f_{\rm NL}$ measurements using the decomposition in the spherical Fourier-Bessel (SFB) basis, which can be naturally cross-correlated with 2D CMB lensing in spherical harmonics. In the meantime, such a decomposition would also enable us to constrain the growth rate of structure, a probe of gravity, through the redshift-space distortion (RSD). As a comparison, we also consider the tomographic spherical harmonic (TSH) analysis of galaxy samples with different bin sizes. Assuming galaxy samples that mimic a few future surveys, we perform Fisher forecasts using linear modes for $f_{\rm NL}$ and the growth rate exponent $\gamma$, marginalized over standard $\Lambda$ cold dark matter ($\Lambda$CDM) cosmological parameters and two nuisance parameters that account for clustering bias and magnification bias. Compared to TSH analysis using only one bin, SFB analysis could improve $\sigma(f_{\rm NL})$ by factors 3 to 12 thanks to large radial modes. With future wide-field and high-redshift photometric surveys like the LSST, the constraint $\sigma(f_{\rm NL}) < 1$ could be achieved using linear angular multipoles up to $\ell_{\rm min}\simeq 20$. Compared to using galaxy auto-power spectra only, joint analyses with CMB lensing could improve $\sigma(\gamma)$ by factors 2 to 5 by reducing degeneracies with other parameters, especially the clustering bias. For future spectroscopic surveys like the DESI or $\textit{Euclid}$, using linear scales, $\gamma$ could be constrained to $3\,\%$ precision assuming the GR fiducial value.

Partial stellar explosions – ejected mass and minimal energy

ABSTRACT Many massive stars appear to undergo enhanced mass-loss during late stages of their evolution. In some cases, the ejected mass likely originates from non-terminal explosive outbursts, rather than continuous winds. Here we study the dependence of the ejecta mass, mej, on the energy budget E of an explosion deep within the star, using both analytical arguments and numerical hydrodynamics simulations. Focusing on polytropic stellar models, we find that for explosion energies smaller than the stellar binding energy, the ejected mass scales as $m_{\rm ej} \propto E^{\varepsilon _{\rm m}}$, where εm = 2.4–3.0 depending on the polytropic index. The loss of energy due to shock breakout emission near the stellar edge leads to the existence of a minimal mass-shedding explosion energy, corresponding to a minimal ejecta mass. For a wide range of progenitors, from Wolf–Rayet stars to red supergiants (RSGs), we find a similar limiting energy of $E_{\rm min} \approx 10^{46}\!-\!10^{47} \rm \, erg$, almost independent of the stellar radius. The corresponding minimal ejecta mass varies considerably across different progenitors, ranging from ${\sim } 10^{-8} \, \rm M_\odot$ in compact stars, up to ${\sim } 10^{-2} \, \rm M_\odot$ in RSGs. We discuss implications of our results for pre-supernova outbursts driven by wave heating, and complications caused by the non-constant opacity and adiabatic index of realistic stars.

Exact solution of the Boltzmann equation for low-temperature transport coefficients in metals. II. Scattering by ferromagnons

In a previous paper (Paper I) we developed a technique for exactly solving the linearized Boltzmann equation for the electrical and thermal transport coefficients in metals in the low-temperature limit. Here we adapt this technique to determine the magnon contribution to the electrical and thermal conductivities, and to the thermopower, in metallic ferromagnets. For the electrical resistivity $\rho$ at asymptotically low temperatures we find $\rho \propto \exp{(-T_{\rm min}/T)}$, with $T_{\rm min}$ an energy scale that results from the exchange gap and a temperature independent prefactor of the exponential. The corresponding result for the heat conductivity is $\sigma_h \propto T^3\,\exp{(T_{\rm min}/T)}$, and thermopower is $S \propto T$. All of these results are exact, including the prefactors.

Tidally excited oscillations in hot white dwarfs

ABSTRACT We study the flux variation in helium white dwarfs (WDs) induced by dynamical tides for a variety of WD models with effective temperatures ranging from $T=10\, {\rm kK}$ to $T=26\, {\rm kK}$. At linear order, we find the dynamical tide can significantly perturb the observed flux in hot WDs. If the temperature $T\gtrsim 14\, {\rm kK}$, then the dynamical tide may induce a fractional change in the flux by $\gt 1{{\ \rm per\ cent}}$ when the orbital period is $P_{\rm orb}\simeq 20{\!-\!}60\, {\rm min}$. The ratio between the flux modulation due to the dynamical tide and that due to the equilibrium tide (i.e. ellipsoidal variability) increases as the WD’s radius decreases, and it could exceed $\mathcal {O}(10)$ if the WD has a radius R ≲ 0.03 R⊙. Unlike the ellipsoidal variability which is in phase with the orbital motion, the pulsation caused by the dynamical tide may have a substantial phase shift. A cold WD with $T\simeq 10\, {\rm kK}$, on the other hand, is unlikely to show observable pulsations due to the dynamical tide. At shorter orbital periods, the dynamical tide may break and become highly non-linear. We approximate this regime by treating the waves as one-way travelling waves and find the flux variation is typically reduced to 0.1–1 per cent and the excess phase is ∼90° (though with large uncertainty). Even in the travelling-wave limit, the flux perturbation due to dynamical tide could still exceed the ellipsoidal variability for compact WDs with R ≲ 0.02 R⊙. We further estimate the non-linear flux perturbations oscillating at four times the orbital frequency dominated by a self-coupled parent g-mode driving low-order daughter p modes. The non-linear flux variation could be nearly $50{{\ \rm per\ cent}}$ of the linear variation for very hot WD models with $T\gtrsim 26\, {\rm kK}$ and $1{{\ \rm per\ cent}}$ linear flux variation. We thus predict that both the linear and non-linear flux variations due to dynamical tides are likely to have significant observational signatures.