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 Hβ and [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.

Comparing the behavior of orbits in different 3D dynamical models for elliptical galaxies

We study the behavior of orbits in two different galactic dynamical models, describing the motion in the central parts of a triaxial elliptical galaxy with a dense nucleus. Numerical experiments show that both models display regular motion together with extended chaotic regions. A detailed investigation of the properties of motion is made for the 2D and 3D Hamiltonian systems, using a number of different dynamical parameters, such as the Poincare′ surface of a section, the maximal Lyapunov Characteristic Exponent, the S（c） spectrum, the S（w） spectrum and the P （f ） indicator. The numerical calculations suggest that the properties of motion in both potentials are very similar. Our results show that one may use different kinds of gravitational potentials in order to describe the motion in triaxial galaxies while obtaining quantitatively similar results.

Stellar ages and metallicities of nearby elliptical galaxies

Stellar ages and metallicities are crucial for understanding the formation and evolution of elliptical galaxies. However, due to the age-metallicity degeneracy, it is hard to measure these two parameters accurately with broad-band photometry. In this paper, we observed high-resolution spectra for a sample of 20 nearby elliptical galaxies （EGs） with the NAOC 2.16 m telescope, and determined stellar ages and metallicities by using the empirical population synthesis and Lick/IDS index system methods. We found that stellar ages from these two methods are consistent with each other for purely old EGs; however, stellar metallicities show a zeropoint offset of 0.5 Z⊙. Our results confirm that stellar populations in low-density environment galaxies are more diverse compared to their high-density counterparts. We also investigated the element abundance-galaxy mass relation for nearby elliptical galaxies.

Clumpy metal concentrations in elliptical galaxies NGC 4374 and NGC 4636

We present a high spatial resolution study of metal distributions in the nearby, gas-rich elliptical galaxies NGC 4374 and NGC 4636 with the Chandra ACIS archive data. We define the hardness ratio HRFeL as the ratio of the emission in 0.65- 1.4 keV to that in 0.3-0.6 keV and 1.4-3.5 keV （after the magnesium and silicon lines are excluded）, and HRcont as the ratio of the emission in 1.4-3.5keV to that in 0.3- 0.6 keV, so that the HRFeL and HRcont maps can be used to trace the iron abundance and gas temperature distributions, respectively. By applying the a Trous wavelet algorithm to the obtained emission hardness ratio maps, we reveal that the HRFeL distributions are highly irregular, exhibiting strong spatial variations on 0.1-1 Re scales, which do not follow the HRcont distributions. Since the effect of temperature variation is small, we conclude that most of the high-HRFeL regions are very likely to possess higher abundances than the ambient gas. We also find that these high-HRFeL substructures are not associated with either the LMXB or globular cluster populations, thus their origins should be related to AGN activity or mergers.

Elliptical Galaxies with Emission Lines from the Sloan Digital Sky Survey

As part of a study of star formation history along the Hubble sequence, we present here the results for 11 elliptical galaxies with strong nebular emission lines. After removing the dilution from the underlying old stellar populations by use of stellar population synthesis model, we derive the accurate fluxes of all the emission lines in these objects, which are then classified, using emission line ratios, into one Seyfert 2, six LINERs and four HII galaxies. We also identify one HII galaxy （A1216＋04） as a hitherto unknown Wolf-Rayet galaxy from the presence of the WolfRayet broad bump at 4650A. We propose that the star-forming activities in elliptical galaxies are triggered by either galaxy-galaxy interaction or the merging of a small satellite/a massive star cluster, as has been suggested by recent numerical simulations.

Long term optical variability of bright X-ray point sources in elliptical galaxies

We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array （ACIS-S） and observations from the Hubble Space Telescope （HST） Advanced Camera for Surveys. Out of the 46 bright （X-ray counts 〉 60） sources that are in the common field of view of the Chandra and HST observations, 34 of them have potential optical counterparts, while the rest of them are optically dark. After taking into account systematic errors, estimated using optical sources in the field as a reference, we find that four of the X-ray sources （three in NGC 1399 and one in NGC 1427） have variable optical counterparts at a high level of significance. The X-ray luminosities of these sources are ～10^38 erg S^-1 and are also variable on similar time scales. The optical variability implies that the optical emission is asso- ciated with the X-ray source itself rather than being the integrated light from a host globular cluster. For one source, the change in optical magnitude is 〉 0.3, which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity. However, the optically variable sources in NGC 1399 have been reported to have blue colors （g - z 〉 1）. All four sources have been detected in the infrared （IR） by Spitzer as point sources, and their ratios of 5.8 to 3.6 μm flux are 〉 0.63, indicating that their IR spectra are like those of Active Galactic Nuclei （AGNs）. While spectroscopic confirmation is required, it is likely that all four sources are background AGNs. We find none of the X-ray sources having opticalfiR colors different from AGNs to be optically variable.

Morphological Classification of Infrared Galaxies Based on WISE

This study introduces a novel convolutional neural network,the WISE Galaxy Classification Network(WGC),for classifying spiral and elliptical galaxies using Wide-field Infrared Survey Explorer(WISE)images.WGC attains an accuracy of 89.03%,surpassing the combined use of K-means or SVM with the Color-Color method in more accurately identifying galaxy morphologies.The enhanced variant,WGC_mag,integrates magnitude parameters with image features,further boosting the accuracy to 89.89%.The research also delves into the criteria for galaxy classification,discovering that WGC primarily categorizes dust-rich images as elliptical galaxies,corresponding to their lower star formation rates,and classifies less dusty images as spiral galaxies.The paper explores the consistency and complementarity of WISE infrared images with SDSS optical images in galaxy morphology classification.The SDSS Galaxy Classification Network(SGC),trained on SDSS images,achieved an accuracy of 94.64%.The accuracy reached 99.30% when predictions from SGC and WGC were consistent.Leveraging the complementarity of features in WISE and SDSS images,a novel variant of a classifier,namely the Multi-band Galaxy Morphology Integrated Classifier,has been developed.This classifier elevates the overall prediction accuracy to 95.39%.Lastly,the versatility of WGC was validated in other data sets.On the HyperLEDA data set,the distinction between elliptical galaxies and Sc,Scd and Sd spiral galaxies was most pronounced,achieving an accuracy of 90%,surpassing the classification results of the Galaxy Zoo 2 labeled WISE data set.This research not only demonstrates the effectiveness of WISE images in galaxy morphology classification but also represents an attempt to integrate multi-band astronomical data to enhance understanding of galaxy structures and evolution.

Comparisons of Jet Properties between GeV Radio Galaxies and Blazars

We compile a sample of spectral energy distributions （SEDs） of 12 GeV radio galaxies （RGs）, including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification, as expected in the unification model, is found for the derived jet parameters between FR I RGs and BL Lacertae objects （BL Lacs） and between FR II RGs and flat spectrum radio quasars （FSRQs）. However, on average FR I RGs have a larger ＇Tb （break Lorentz factor of electrons） and lower B （magnetic field strength） than FR II RGs, analogous to the differences be- tween BL Lacs and FSRQs. The derived Doppler factors （~） of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent pop- ulations of blazars with smaller tS. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carded by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the ＂sequence＂ behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.

Luminosity Function of the Cluster of Galaxies Abell 566

We investigate the Luminosity Function （LF） of the cluster of galaxies Abell 566. The photometric data of 15 intermediate-bands are obtained from the Beijing-Arizona- Taiwan-Connecticut （BATC） photometric sky survey. For each of the 15 wavebands, the LF of cluster galaxies is well modelled by the Schechter function, with characteristic luminosities from -18.0 to -21.9 magnitude, from the α- to the p-band. Morphological dependence of the LF is investigated by separating the cluster members into ＇red＇ and ＇blue＇ subsamples. It is clear that late type galaxies have a steeper shape of LF than the early type galaxies. We also divided the sample galaxies by their local environment. It was found that galaxies in the sparser region have steeper shape of LF than galaxies in the denser region. Combining the results of morphological and environmental dependence of LFs, we show that Abell 566 is a well relaxed cluster with positive evidence of galaxy interaction and merger, and excess number of bright early type galaxies located in its denser region.

A new estimation of manganese distribution for local dwarf spheroidal galaxies

The distribution of abundance for iron-peak elements in dwarf spheroidal galaxies （dSphs） is important for galaxy evolution and supernova （SN） nucleosynthesis. Nowadays, manganese （Mn） is one of the most observed iron-peak elements in local dSphs. Studies of its distributions allow us to derive and understand the evolution history of these dSphs. We improve a phenomenological model by a two-curve model including a new initial condition, that includes detailed calculations of SN explosion rates and yields. We compare the results with the observed Mn distribution data for three dSphs： Fornax, Sculpture and Sextans. We find that the model can describe the observed Fe and Mn distributions well simultaneously for the three dSphs. The results also indicate that the initial conditions should be determined by the low metallicity sam- ples in the beginning time of the galaxies and the previous assumption of metellicity-dependant Mn yield of SNIa is not needed when a wide mass range of core-collapse SNe is included. Our method is applicable to the chemical evolution of other iron-peak elements in dSphs and can be modified to provide more detailed processes for the evolution of dSphs.

Are Seyfert 2 Galaxies without Polarized Broad Emission Lines More Obscured?

New XMM-Newton data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. An analysis of the 0.5 - 10 keV spectra shows that four Seyfert 2 galaxies with polarized broad lines （PBLs） are absorbed by NH 〈 1024 cm^-2, while two of three Seyfert 2 galaxies without PBLs show evidence of Compton-thick obscuration, supporting the conclusion that Seyfert 2 galaxies without PBLs are more obscured than those with PBLs, Adding the measured obscuration indicators （NH, T ratio, and Fe Kα line EW） of six luminous AGNs to our previous sample improves the significance level of the difference in absorption from 92.3% to 96.3% for NH, 99.1% to 99.4% for T ratio, and 95.3% to 97.4% for Fe Kα line EW. The present results support and enhance the suggestions that the absence of PBLs in Seyfert 2 galaxies can be explained by larger viewing angles of the line of sight to the putative dusty toms, which leads to the obscuration of the broad-line scattering screen, as expected in the unification model.

Lensing clusters of galaxies in the SDSS-Ⅲ

We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey Ⅲ （SDSS DR8） by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing giant arcs in addition to 30 known lensing systems. Among 68 cases, 13 clusters are ＂almost certain＂ lensing systems with tangential giant arcs, 22 clusters are ＂probable＂ and 31 clusters are ＂pos- sible＂ lensing systems. We also find two exotic systems with blue rings. The giant arcs have angular separations of 2.0jj - 25.7j~ from the bright central galaxies. We note that the rich clusters are more likely to be lensing systems and the separations between the arcs and the central galaxies increase with cluster richness.

Correlation between excitation index and Eddington ratio in radio galaxies

We use a sample of 111 radio galaxies with redshift z 〈 0.3 to investigate their nuclear properties. The black hole masses of the sources in this sample are estimated with the velocity dispersion/luminosity of the galaxies, or the width of the broad-lines. We find that the excitation index, the relative intensity of low and high excitation lines, is correlated with the Eddington ratio for this sample. The size of the narrow-line region （NLR） was found to vary with ionizing luminosity as RNLR ∝ Lion^0.25 （Liu et al. 2013）. Using this empirical relation, we find that the correlation between the excitation index and the Eddington ratio can be reproduced by photoionization models. We adopt two sets of spectral energy distributions （SEDs）, with or without a big blue bump in ultraviolet as the ionizing continuum, and infer that the modeled correlation between the excitation index and the Eddington ratio is insensitive to the applied SED. This means that the difference between high excitation galaxies and low excitation galaxies is not caused by the different accretion modes in these sources. Instead, it may be caused by the size of the NLR.

Multiwavelength study of nearly face-on low surface brightness disk galaxies

We study the ages of a large sample （1802） of nearly face-on disk low surface brightness galaxies （LSBGs） using the evolutionary population synthesis （EPS） model PEGASE with an exponentially decreasing star formation rate to fit their mul- tiwavelength spectral energy distributions （SEDs） from far-ultraviolet （FUV） to nearinfrared （NIR）. The derived ages of LSBGs are 1-5 Gyr for most of the sample no matter if constant or varying dust extinction is adopted, which are similar to most of the previous studies on smaller samples. This means that these LSBGs formed the majority of their stars quite recently. However, a small part of the sample （~2%-3%） has larger ages of 5-8 Gyr, meaning their major star forming process may have occurred earlier. At the same time, a large sample （5886） of high surface brightness galaxies （HSBGs） are selected and studied using the same method for comparisons. The de- rived ages are 1-5 Gyr for most of the sample （97%） as well. These results probably mean that these LSBGs have not much different star formation histories from their HSBGs counterparts. However, we should notice that the HSBGs are generally about 0.2 Gyr younger, which could mean that the HSBGs may have undergone more recent star forming activities than the LSBGs.

Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies

We present an efficient, robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies. With appropriate mathematical treatments, the apparent numerical difficulties associated with singularities in computing elliptic integrals are completely removed. Using a boundary element discretization procedure, the governing equations are transformed into a linear algebra matrix equation that can be solved by straightforward Gauss elimination in one step without further iterations. The numerical code implemented according to our algorithm can accurately determine the surface mass density distribution in a disk galaxy from a measured rotation curve （or vice versa）. For a disk galaxy with a typical flat rotation curve, our modeling results show that the surface mass density monotonically decreases from the galactic center toward the periphery, according to Newtonian dynamics. In a large portion of the galaxy, the surface mass density follows an approximately exponential law of decay with respect to the galactic radial coordinate. Yet the radial scale length for the surface mass density seems to be generally larger than that of the measured brightness distribution, suggesting an increasing mass-tolight ratio with the radial distance in a disk galaxy. In a nondimensionalized form, our mathematical system contains a dimensionless parameter which we call the ＂galactic rotation number＂ that represents the gross ratio of centrifugal force and gravitational force. The value of this galactic rotation number is determined as part of the numerial solution. Through a systematic computational analysis, we have illustrated that the galactic rotation number remains within 4-10% of 1.70 for a wide variety of rotation curves. This implies that the total mass in a disk galaxy is proportional to V02 Rg, with V0 denoting the characteristic rotation velocity （such as the ＂flat＂ value in a typical ro- tation curve） and Rg the radius of the galactic disk. The predicted total galactic mass of the Milky Way is in good agreement with the star-count data.

The fundamental plane relation of early-type galaxies:environmental dependence

Using a sample of 70 793 early-type galaxies from SDSS DR7, we study the environmental dependence of the fundamental plane relation. With the help of the galaxy group catalog based on SDSS DR7, we calculate the fundamental planes in different dark matter halo mass bins for both central and satellite galaxies. We find the environmental dependence of the fundamental plane coefficients is similar in the g, r, i and z bands. The environmental dependence for central and satellite galaxies is significantly different. Although the fundamental plane coefficients for centrals vary systematically with the halo mass, those of satellites are similar in different halo mass bins. The discrepancy between centrals and satellites is significant in small halos, but negligible in the largest halo mass bins. These results remain the same when we only keep red galaxies, or galaxies with b/a 〉 0.6, or galaxies in a specific radius range in the sample. After the correction for the sky background, the results are still similar. We suggest that the different environmental effects of the halo mass on centrals and satellites may arise from their different quenching processes.

Chandra Observation of Point Sources in the X-Ray Elliptical Galaxy NGC 1407

With the Chandra pointing observation of about 50 ks, we have detected 41 point sources in the X-ray relatively faint elliptical galaxy NGC 1407, most of which appear to be low mass X-ray binaries. In luminosity flux units, these resolved point sources contribute about 17.8 % of the total emission of the galaxy in 0.3–10 keV. Of the remaining diffuse emission, about 53.4 % (or 43.9 % of total) may arise from unresolved point sources. We find six ultraluminous X-ray sources with luminosities above 1039 erg s?1. This number is less than has been found in NGC 720, but more than in NGC 4697 and NGC 1553, so suggesting a possible correlation between the number of ULXs and the total X-ray luminosity of early-type galaxies. A central point-like source is detected whose luminosity (2.36 ± 0.14×1039 erg s?1) is the highest among all resolved sources. However, because of its relatively low hardness ratio, we speculate that it is not likely to be a low luminosity AGN.

Morphology and structure of BzK-selected galaxies at z ～ 2 in the CANDELS-COSMOS field

Utilizing a BzK-selecfion technique, we obtain 14 550 star-forming galaxies （sBzKs） and 1763 passive galaxies （pBzKs） at z - 2 from the K-selected （KAB 〈 22.5） catalog in the COSMOS/UltraVISTA field. The differential number counts of sBzKs and pBzKs are consistent with the results from the literature. Compared to the observed results, semi-analytic models of galaxy formation and evolution provide too few （many） galaxies at the high （low） mass end. Moreover, we find that the star formation rate and stellar mass of sBzKs follow the relation of the main sequence. Based on HST/Wide Field Camera 3 F160W imaging, we find a wide range of morphological diversities for sBzKs, from diffuse to early-type spiral structures, with relatively high M20, large size and low G, while pBzKs have elliptical-like compact morphologies with lower M20, smaller size and higher G, indicating a more concentrated and symmetric spatial extent of stellar population distribution in pBzKs than sBzKs. Furthermore, the sizes of pBzKs （sBzKs） at z - 2 are on average two to three （one to two） times smaller than those of local early-type （late-type） galaxies with similar stellar mass. Our findings imply that the two classes have different evolution models and mass assembly histories.

Revisiting the dichotomy of early-type galaxies

We study the relationship between isophotal shapes, central light profiles and kinematic properties of early-type galaxies （ETGs） based on a compiled sample of 184 ETGs. These sample galaxies are included in Data Release 8 of the Sloan Digital Sky Survey and have central light profiles and kinematic properties available from the literature, which were compiled from observations by the Hubble Space Telescope and the ATLAS3D integral-field spectrograph, respectively. We find that there is only a weak correlation between the isophotal shape （a4/a） and the central light profile （within 1 kpc） of ETGs. About two-fifths of ＂core＂ galaxies have disky isophotes, and one-third of ＂power-law＂ galaxies are boxy. Our statistical results also show that there are weak correlations between galaxy luminosity and dynamical mass with a4/a, but such correlations are tighter with a central light profile. Moreover, no clear link has been found between the isophotal shape and the Sersic index. Comparisons show that there are similar correlations between a4/a and ellipticity, and between a4/a and specific angular momentum ARo/2 for ＂power-law＂ ETGs, but there are no such correlations for ＂core＂ ETGs. Therefore, we speculate that the bimodal classifications of ETGs are not as simple as previously thought, though we also find that the disky ETGs with highest a4/a are more elongated and fast rotators.

Structural Properties of Early-Type Galaxies from the SDSS DR2

Two-dimensional bulge/disk light decomposition with GIM2D in both the r- and g-bands has been applied to a sample of 129 early-type galaxies brighter than 13.5 magnitude in the r-band, selected from the Sloan Digital Sky Survey Data Release 2. Intensity-weighted Fourier coefficient （α4/α） was also derived for each sample galaxy. Our analysis shows that there are correlations between bulge-to-total light ratio （B/T） with bulge Sersic index nB and between bulge and disk scale sizes. Isophotal shape parameter （α4/α） is not correlated with BIT and riB. Both bulge and disk components satisfy a color-magnitude relation. The space Fundamental Plane analysis shows that galaxies with larger B/T tend to lie tighter and closer to the line of k1 ＋ k2 = 8 （the so-called ＂zone of avoidance＂） than the galaxies with smaller B/T. It indicates that existence of the disk component may lead to scatter of the distribution on the Fundamental Plane. Our analysis also shows that k1 ＋ k2 correlates with （g-r） color and B/T, but does not correlate with （α4/α） for early-type galaxies. The fitted parameters and other retrieved parameters used in this paper for all sample galaxies are available online.