Quenched Galaxies are Important Host Candidates of Binary Black Hole and Binary Neutron Star Mergers

In this work,we present the probabilities of mergers of binary black holes(BBHs)and binary neutron stars(BNSs)as functions of stellar mass,metallicity,specific star formation rate(sSFR),and age for galaxies with redshift z≤0.1.Using the binary-star evolution(BSE)code and some fitting formulae,we construct a phenomenological model of cosmic gravitational wave(GW)merger events.By using the Bayesian analysis method and the observations from Advanced LIGO and Virgo,we obtain the relevant parameters of the phenomenological model(such as the maximum black hole mass is 93_(-22)^(+73)M_(⊙)).Combining the above model results with the galaxy catalog given by the EMERGE empirical galaxy model,we find the normalized probability of occurrence of a merger event varying with log10 sSFR yr(-1)for galaxies with z≤0.1 is different from that in previous studies,that is,two peaks exist in this work while there is only one peak(log_(10)(sSFR/yr^(−1))=−10)in the previous work.The sSFR value corresponding to the new peak is log_(10)(sSFR/yr^(−1))=−12 and in line with the value(log_(10)(sSFR yr^-1)=-12.65_(-0.66)^(+0.44)of NGC 4493,the host galaxy of BNS merger event GW170817.The new peak is caused by today’s quenched galaxies,which give a large contribution to the total SFR at high redshift in the EMERGE empirical galaxy model.Moreover,we find that the BNS mergers are most likely detected in galaxies with age∼11 Gyr,which is greater than previous results(6−8Gyr)and close to the age of NGC 4993,13.2_(-0.9)^(+0.5)Gyr.

A Study of Binary Stellar Population Synthesis of Elliptical Galaxies

We determined the relative stellar ages and metallicities of about 80 elliptical galaxies in both low and high density environments using the latest binary stellar population (BSP) synthesis model and tested the predictions of a recent hierarchical formation model that adopted the new ACDM cosmology. The stellar ages and metallicities were estimated from two high-quality published spectra line indices, the Hβand [MgFe] indices. The results show that the stellar populations of elliptical galaxies are older than 3.9 Gyr and more metal rich than 0.02. Most of our results are in agreement with the model predictions: (1) elliptical galaxies in denser environment are redder and have older populations than field galaxies; (2) elliptical galaxies with more massive stellar components are redder and have older and more metal rich populations than less massive ones; (3) the most massive galaxies have the oldest and most metal rich stars. However, some of our results differ from the model predictions on the metallicity distributions of low- and high-density elliptical galaxies and the dependence on the distance to the cluster center.

GABE: Galaxy Assembly with Binary Evolution

We developed a new semi-analytic galaxy formation model: Galaxy Assembly with Binary Evolution(GABE). For the first time, we introduce binary evolution into semi-analytic models of galaxy formation by using the Yunnan-Ⅱ stellar population synthesis model, which includes various binary interactions. When implementing our galaxy formation model onto the merger trees extracted from the Millennium simulation, it can reproduce a large body of observational results. We find that in the local universe, the model including binary evolution reduces the luminosity at optical and infrared wavelengths slightly, but it increases the luminosity at ultraviolet wavelengths significantly, especially in FUV band. The resulting luminosity function does not change very much over SDSS optical bands and infrared band, but the predicted colors are bluer, especially when the FUV band is under consideration. The new model allows us to explore the physics of various high energy events related to the remnants of binary stars, such as type Ia supernovae, short gamma-ray bursts and gravitational wave events, and their relation with host galaxies in a cosmological context.

An upgraded interpolator of the radial basis function network for spectral calculation based on empirical stellar spectral library

Stellar population synthesis is an important method in galaxy and star-cluster studies.In stellar population synthesis models,a stellar spectral library is necessary for the integrated spectra of the stellar population.Usually,the stellar spectral library is utilized for the transformation between the stellar atmospheric parameters and stellar spectrum.The empirical stellar spectral library has distinct advantages over the theoretical library.However,for the empirical spectral library,the distribution of stars is irregular in the stellar atmospheric parameter space,which makes the traditional interpolator difficult to get accurate results.In this work,we will provide an improved radial basis function interpolator which is implemented to obtain the interpolated stellar spectra based on the empirical stellar spectral library.For this interpolator,we use the relation between the standard varianceσin the Gaussian radial basis function and the density distribution of stars in the stellar atmospheric parameter space to give the prior constraint on thisσ.Moreover,we also consider the anisotropic radial basis function by the advantage of the local dispersion of stars in the stellar atmospheric parameter space.Furthermore,we use the empirical stellar spectral library MILES to test this interpolator.On the whole,the interpolator has a good performance except for the edge of the low-temperature region.At last,we compare this interpolator with our work in 2018,and the interpolation result shows an obvious improvement.Users can apply this interpolator to retrieve the interpolated spectra based on the stellar spectral library quickly and easily.

Model-Synthesized Rate of Type Ia Supernovae and its Influence on the Chemical Enrichment of the ISM

Using Hurley's rapid binary stellar evolution code, we have studied the model- synthesized rate of Type Ia Supernovae (SNe Ia) and its influence on the chemical enrichment of the interstellar medium ejected by stellar populations. We adopt two popular scenarios, i.e., single degenerate scenario (SD) and double degenerate scenario (DD), for the progenitors of SNe Ia to calculate the rates of SNe Ia. Rates calculated in this work agree with that of Hachisu et al. and Han & Podsiadlowski, but are different from that usually adopted in chem- ical evolution models of galaxies. We apply the rates of SNe Ia to the chemical enrichment (especially Fe enrichment), then compare the results with previous studies. As known SNe Ia slightly affect the enrichment of C, N, O and Mg elements, while significantly affect the en- richment of Fe. We find that the occurrence and the value of the Fe enrichment in our models are earlier and smaller than that commonly adopted in chemical evolution models. We also study the evolution of [Mg/Fe] ratios, which are almost reciprocals of the Fe enrichment. The study may provide constraints on the free parameters of chemical evolution models of galaxies and evolutionary population synthesis.

Effects of α-Enhancement on Stellar Evolution

用 Eggleton 的代码，我们系统地基于规模太阳的混合和 α-enhanced 金属混合在在结果之间的星的进化显示出差别。作为输入， OPAL 高温度暗被用于木头(T/K )】 4.00，并且新 Wichita 州的低温度暗，为木头(T/K )≤4.00。我们的计算盖子星集中从 0.25 到 80.0M，在 Δlog M = 的 spaced 0.10 或 0.05。金属 licities Z 的价值是 0.0001， 0.0003， 0.001， 0.004， 0.01， 0.02， 0.03， 0.04， 0.06， 0.08 和 0.10。为给定的 Z，起始的氢团部分被 X = 给 0.76 −3.0Z。我们证明 α-enhancement 能提起星的有效温度和光明，并且减少进化年龄。与一些以前的工作相比， α-enhancement 的效果更显然在我们的计算被表明。