We estimate the intrinsic luminosities and synchrotron peak frequencies using the derived Doppler factor for a sample of 170 BL Lac objects, of which the synchrotron peak frequency is derived by fitting the SED constr...We estimate the intrinsic luminosities and synchrotron peak frequencies using the derived Doppler factor for a sample of 170 BL Lac objects, of which the synchrotron peak frequency is derived by fitting the SED constructed with the collected multi-band data from the literature. We find that the debeamed radio and optical core luminosities follow the same correlation found for FR I radio galaxies, which is in support of the unification of the BL Lac objects and the FR I galaxies based on orientation. For the debeamed luminosity at the synchrotron peak frequency, we find a significant positive correlation between the luminosity and intrinsic synchrotron peak frequency. This implies that the more powerful sources may have the majority of jet emission at higher frequency. At the synchrotron peak frequency, the intrinsic luminosity and black hole mass show strong positive correlation, while mild correlation is found in the case of jet power, indicating that the more powerful sources may have more massive black holes.展开更多
Using a large sample of blazars of the Fermi observations presented by Abdo et al., we constructed a sample of blazars including high energy peaked BL Lac objects （HBLs）, low energy peaked BL Lac objects （LBLs） an...Using a large sample of blazars of the Fermi observations presented by Abdo et al., we constructed a sample of blazars including high energy peaked BL Lac objects （HBLs）, low energy peaked BL Lac objects （LBLs） and flat-spectral ra- dio quasars （FSRQs）. These unique characteristics make it possible to unambiguously address the question of how HBLs, LBLs and FSRQs are related. In this paper, we investigated the relationship between X-ray and 7-ray spectral indices （~^-aT）, as well as the relationship between the broadband spectral indices （~ro--ar~, ~ro--~ox, OZro--O^x7 and ~r^-~xT） for this sample. The color-color diagram shows that there is a significant correlation between both quantities when all three subclasses of blazars are considered, which suggests that there is a unified scheme for blazars. On the other hand, the a^-~7 diagram reveals that three kinds of blazars have different spectral energy distributions： the trend of HBLs is different from that of FSRQs and LBLs, whereas FSRQs and LBLs have a similar trend, which hints that FSRQs and LBLs have similar spectral properties, but HBLs have distinct spectral properties. In addi- tion, the broadband energy distributions also reveal the similar spectral properties with that of the Cx-C7 diagram. The spectral properties revealed from the Fermi sample do not support the blazar sequence reported by Fossati et al. and Ghisellini et al.展开更多
By analyzing the azimuthal variations of total gravitating mass profiles in the central 300 h^-1 71 kpc regions of four galaxy clusters with Chandra data, we find that the azimuthally-averaged mass profiles may have b...By analyzing the azimuthal variations of total gravitating mass profiles in the central 300 h^-1 71 kpc regions of four galaxy clusters with Chandra data, we find that the azimuthally-averaged mass profiles may have been systematically underestimated by 16^＋9 -8% at lσ significance in the 50-100 h^-1 71 kpc regions, probably due to the prevailing existence of 2-D hot gas substructures in 100-300h^-1 71 kpc. The mass biases become negligible（-7＋11 _9＋ %） at 〉 150 h^-1 71 kpc. We confirm the results that the gas temperature maps can be used to probe the departure from hydrostatic equilibrium and help quantify the systematic biases in X-ray mass measurements in the central regions of clusters.展开更多
By cross-correlating an archive sample of 542 extragalactic radio sources with the Fermi-LAT Third Source Catalog （3FGL）, we have compiled a sample of 80 γ-ray sources and 462 non-Fermi sources with available core ...By cross-correlating an archive sample of 542 extragalactic radio sources with the Fermi-LAT Third Source Catalog （3FGL）, we have compiled a sample of 80 γ-ray sources and 462 non-Fermi sources with available core dominance parameter （RcD）, and core and extended radio luminosity; all the parameters are directly measured or derived from available data in the literature. We found that RCD has significant correlations with radio core luminosity, γ-ray luminosity and γ-ray flux; the Fermi sources have on average higher RCD than non-Fermi sources. These results indicate that the Fermi sources should be more compact, and the beaming effect should play a crucial role in the detection of γ-ray emission. Moreover, our results also show Fermi sources have systematically larger radio flux than non-Fermi sources at fixed ReD, indicating larger intrinsic radio flux in Fermi sources. These results show a strong connection between radio and γ-ray flux for the present sample and indicate that the non-Fermi sources are likely due to the low beaming effect, and/or the low intrinsic γ-ray flux. This supports a scenario that has been published in the literature： a co-spatial origin of the activity for the radio and γ-ray emission, suggesting that the origin of the seed photons for the high-energy γ-ray emission is within the jet.展开更多
We select a large volume-limited sample of low surface brightness galax- ies （LSBGs, 2021） to investigate in detail their statistical properties and their dif- ferences from high surface brightness galaxies （HSBGs,...We select a large volume-limited sample of low surface brightness galax- ies （LSBGs, 2021） to investigate in detail their statistical properties and their dif- ferences from high surface brightness galaxies （HSBGs, 3639）. The distributions of stellar masses of LSBGs and HSBGs are nearly the same and they have the same me- dian values. Thus this volume-limited sample has good completeness and is further removed from the effect of stellar masses on their other properties when we compare LSBGs to HSBGs. We found that LSBGs tend to have lower stellar metallicities and lower effective dust attenuations, indicating that they have lower dust than HSBGs. The LSBGs have relatively higher stellar mass-to-light ratios, higher gas fractions, lower star forming rates （SFRs）, and lower specific SFRs than HSBGs. Moreover, with the decreasing surface brightness, gas fraction increases, but the SFRs and spe- cific SFRs decrease rapidly for the sample galaxies. This could mean that the star formation histories between LSBGs and HSBGs are different, and HSBGs may have stronger star forming activities than LSBGs.展开更多
The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could ...The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AGNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi Gamma-ray Space Telescope）.展开更多
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 Te...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.展开更多
We present periodicity search analyses on long-term radio light curves at 4.8,8,and 14.5 GHz of blazar PKS 0607–157 observed by the University of Michigan Radio Astronomical Observatory telescope.The highly variable ...We present periodicity search analyses on long-term radio light curves at 4.8,8,and 14.5 GHz of blazar PKS 0607–157 observed by the University of Michigan Radio Astronomical Observatory telescope.The highly variable radio emissions are approximately distributed as a log-normal probability distribution function.The Power Spectral Density for the radio light curves can be well characterized by a power-law model.Using the Weighted Wavelet Z-transform and Lomb-Scargle periodogram methods,significant Quasi-periodic Oscillation(QPO)of∼4.6 yr in the radio light curve has been observed above the 3σconfidence level,which presents an interesting case among blazar QPO phenomena.We explore three plausible physical models to explain the observed QPOs:a supermassive binary black hole system,Lense-Thirring precession of the disk,and helical motion of plasma blobs within the jet.展开更多
Active galactic nuclei （AGNs） have two major classes, namely radio loud AGNs and radio quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which display extreme observational properties, such as rap...Active galactic nuclei （AGNs） have two major classes, namely radio loud AGNs and radio quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which display extreme observational properties, such as rapid variability, high luminosity, high and variable polarization, and superluminal motion. All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight. Observations suggest that the orientation can be expressed by a core-dominance parameter, R. The R, to some extent, is associated with the beaming effect. Blazars are believed to be unified with Fanaroff ＆ Riley type I/II （FRI/II） radio galaxies. In this work, we collected relevant observations from the literature for a sample of 1223 AGNs including 77 BL Lacertae objects, 495 quasars, 460 galaxies, 119 FRs and 72 unidentified sources, and calculated the core-dominance parameters and spectral indexes, discussed the relationship between the two parameters, and gave some discussions. Our analysis suggests that the core-dominance parameters in BL Lacertae objects are larger than those in quasars and galaxies, and the radio spectral indexes in BL Lacertae objects are lower than those in quasars and galaxies. We also found that the core-dominance parameter-spectral index correlation exists for a large sample presented in this work, which may come from a relativistic beaming effect.展开更多
We report our identification of three gigaelectronvoltγ-ray sources,4FGL J0502.6+0036,4FGL J1055.9+6507,and 4FGL J1708.2+5519,as Active Galactic Nuclei(AGNs).They are listed in the latest Fermi-Large Area Telescope s...We report our identification of three gigaelectronvoltγ-ray sources,4FGL J0502.6+0036,4FGL J1055.9+6507,and 4FGL J1708.2+5519,as Active Galactic Nuclei(AGNs).They are listed in the latest Fermi-Large Area Telescope source catalog as unidentified ones.We find that the sources all showedγ-ray flux variations in recent years.Using different survey catalogs,we are able to find a radio source within the error circle of each source's position.Further analysis of optical sources in the fields allows us to determine the optical counterparts,which showed similar variation patterns to those seen inγ-rays.The optical counterparts have reported redshifts of 0.6,1.5,and 2.3,respectively,estimated from photometric measurements.In addition,we also obtain an X-ray spectrum of 4FGL J0502.6+0036 and a flux upper limit on the X-ray emission of 4FGL J1055.9+6507 by analyzing the archival data.The broadband spectral energy distributions of the three sources from radio toγ-rays are constructed.Comparing mainly theγ-ray properties of the three sources with those of different sub-classes of AGNs,we tentatively identify them as blazars.Followup optical spectroscopy is highly warranted for obtaining their spectral features and thus verifying the identification.展开更多
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 significa...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.展开更多
We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broadband spectral indices. The distribution of luminosities show...We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broadband spectral indices. The distribution of luminosities shows that the averaged luminosity of flat spectrum radio quasars（FSRQs） is larger than that of BL Lacertae（BL Lac） objects. On the other hand, the broadband spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects have similar spectral properties,but high energy peaked BL Lac objects have a distinct spectral property. This may be due to the fact that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme is also revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameters.展开更多
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...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 gala展开更多
We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample con...We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample contains 166 sources. The statistical analysis based on this sample confirms positive correlations between these two bands, but the correlations become weaker as the γ-ray energy increases. The statistical results between various parameters show negative correla- tions of γ-ray photon spectral index with γ-ray loudness for both Flat Spectrum Radio Quasars （FSRQs） and BL Lacertae objects, positive correlations of γ-ray variability index with the γ-ray loudness for FSRQs, a negative correlation of the γ-ray variabil- ity index with the γ-ray photon spectral index for FSRQs, and negative correlations of γ-ray photon spectral index with γ-ray luminosity for FSRQs. These results suggest that the γ-ray variability may be due to changes inside the γ-ray emission region like the injected power, rather than changes in the photon density of the external radiation fields, and the variability amplitude tends to be larger as the γ-rays are closer to the high energy peak of the spectral energy distribution （SED）. No correlation of variabil- ity index found for BL Lacertae objects implies that variability behavior may differ below and above the peak energy.展开更多
Binary stars are common in star clusters and galaxies, but the detailed ef- fects of binary evolution are not taken into account in some color-magnitude diagram （CMD） studies. This paper studies the CMDs of twelve g...Binary stars are common in star clusters and galaxies, but the detailed ef- fects of binary evolution are not taken into account in some color-magnitude diagram （CMD） studies. This paper studies the CMDs of twelve globular clusters via binary- star stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of binary and single stars on CMD studies. It is shown that binaries can better fit the observational CMDs of the sample globular clusters compared to single stars. This suggests that the effects of binary evolution should be considered when modeling the CMDs and stellar populations of star clusters and galaxies.展开更多
Because of the 3D nature of galaxies, an algorithm for constructing spatial density distribution models of galaxies on the basis of galaxy images has many advan- tages over approximations of the surface density distri...Because of the 3D nature of galaxies, an algorithm for constructing spatial density distribution models of galaxies on the basis of galaxy images has many advan- tages over approximations of the surface density distribution. We present a method for deriving the spatial structure and overall parameters of galaxies from images and estimate its accuracy and derived parameter degeneracies on a sample of idealised model galaxies. The test galaxies consist component with varying proportions and of a disc-like component and a spheroidal properties. Both components are assumed to be axially symmetric and coplanar. We simulate these test galaxies as if they had been observed in the SDSS project through ugriz filters, thus gaining a set of realis- tically imperfect images of galaxies with known intrinsic properties. These artificial SDSS galaxies were thereafter remodelled by approximating the surface brightness distribution with a 2D projection of a bulge＋disc spatial distribution model and the restored parameters were compared to the initial ones. Down to the r-band limiting magnitude of 18, errors in the restored integral luminosities and colour indices re- main within 0.05 mag and errors in the luminosities of individual components within 0.2 mag. Accuracy of the restored bulge-to-disc luminosity ratio （B/D） is within 40% in most cases, and becomes worse for galaxies with low B/D, but the general balance between bulges and discs is not shifted systematically. Assuming that the intrinsic disc axial ratio is ≤ 0.3, then the inclination angles can be estimated with errors 〈 5° for most of the galaxies with B/D 〈 2 and with errors 〈 15° up to B/D = 6. Errors in the recovered sizes of the galactic components are below 10% in most cases. The axial ratios and the shape parameter N of Einasto＇s distribution （similar to the Sersic index） are relatively inaccurate, but can provide statistical estimates for large samples. In general, models of disc components are more accurate than models of spheroidal compo展开更多
Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The major- ity of identif...Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The major- ity of identified extragalactic sources in γ-ray catalogs of EGRET and Fermi are blazars. Observationally, blazars can be divided into two classes： fiat spectrum radio quasars （FSRQs） and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in ＂7-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in 7-ray luminosity between the two classes is significantly reduced. In order to ex- plain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.展开更多
We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have b...We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have been interpreted as relativistically broad Fe Lc~ lines. Such features are not clearly observed in other active galactic nuclei despite sometimes having high iron abundance required by the best fitted blurred reflection models. Given the importance of these lines, we explore whether the rapid variability of spectral parameters may introduce broad bumps/dips artificially in the time averaged spectrum, which may then be mistaken as broadened lines. We tested this hypothesis by performing time resolved spectroscopy using long （〉 100 ks） XMM-Newton observations and by dividing them into segments with typical exposures of a few ks. We extracted spectra from each such segment and modeled them using a two component phenomenological model consisting of a power law to represent the hard component and a black body to represent the soft emission. As expected, both the sources showed variations in the spectral parameters. Using these variation trends, we simulated model spectra for each segment and then co-added to get a combined simulated spectrum. In the simulated spectra, we found no broad features below 1 keV and in particular no deviation near 0.9 keV as seen in the real averaged spectra. This implies that the broad Fe Lα line that is seen in the spectra of these sources is not an artifact of the variation of spectral components and, hence, provides evidence that the line is indeed genuine.展开更多
We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM ...We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent- heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.展开更多
We study ten galaxy groups and clusters suggested in the literature to be ＂fossil systems（FSs）＂based on Chandra observations. According to the M（500）- T and LX- T relations, the gas properties of FSs are not phy...We study ten galaxy groups and clusters suggested in the literature to be ＂fossil systems（FSs）＂based on Chandra observations. According to the M（500）- T and LX- T relations, the gas properties of FSs are not physically distinct from ordinary galaxy groups or clusters. We also first study the f（gas, 2500）- T relation and find that the FSs exhibit the same trend as ordinary systems. The gas densities of FSs within 0.1r200 are - 10^-3cm^-3, which is the same order of magnitude as galaxy clusters. The entropies within 0.1r200（S（0.1r200）） of FSs are systematically lower than those in ordinary galaxy groups, which is consistent with previous reports, but we find their S（0.1r200）- T relation is more similar to galaxy clusters. The derived mass profiles of FSs are consistent with the Navarro, Frenk and White model in（0.1- 1）（r200）, and the relation between scale radius rs and characteristic mass density δc indicates self-similarity of dark matter halos of FSs. The ranges of rs and δc for FSs are also close to those of galaxy clusters. Therefore, FSs share more common characteristics with galaxy clusters. The special birth place of the FS makes it a distinct type of galaxy system.展开更多
基金Supported by the National Natural Science Foundation of ChinaThis work is supported by theNSFC under grants 10373019,10633010 and 10703009
文摘We estimate the intrinsic luminosities and synchrotron peak frequencies using the derived Doppler factor for a sample of 170 BL Lac objects, of which the synchrotron peak frequency is derived by fitting the SED constructed with the collected multi-band data from the literature. We find that the debeamed radio and optical core luminosities follow the same correlation found for FR I radio galaxies, which is in support of the unification of the BL Lac objects and the FR I galaxies based on orientation. For the debeamed luminosity at the synchrotron peak frequency, we find a significant positive correlation between the luminosity and intrinsic synchrotron peak frequency. This implies that the more powerful sources may have the majority of jet emission at higher frequency. At the synchrotron peak frequency, the intrinsic luminosity and black hole mass show strong positive correlation, while mild correlation is found in the case of jet power, indicating that the more powerful sources may have more massive black holes.
基金supported by the National Natural Science Foundation of China(Grant No. 10878013)the Natural Science Foundation of Yunnan Province (2007A230M,2011FZ081)the Program for Innovative Research Team (in Scienceand Technology) in University of Yunnan Province (IRTSTYN)
文摘Using a large sample of blazars of the Fermi observations presented by Abdo et al., we constructed a sample of blazars including high energy peaked BL Lac objects （HBLs）, low energy peaked BL Lac objects （LBLs） and flat-spectral ra- dio quasars （FSRQs）. These unique characteristics make it possible to unambiguously address the question of how HBLs, LBLs and FSRQs are related. In this paper, we investigated the relationship between X-ray and 7-ray spectral indices （~^-aT）, as well as the relationship between the broadband spectral indices （~ro--ar~, ~ro--~ox, OZro--O^x7 and ~r^-~xT） for this sample. The color-color diagram shows that there is a significant correlation between both quantities when all three subclasses of blazars are considered, which suggests that there is a unified scheme for blazars. On the other hand, the a^-~7 diagram reveals that three kinds of blazars have different spectral energy distributions： the trend of HBLs is different from that of FSRQs and LBLs, whereas FSRQs and LBLs have a similar trend, which hints that FSRQs and LBLs have similar spectral properties, but HBLs have distinct spectral properties. In addi- tion, the broadband energy distributions also reveal the similar spectral properties with that of the Cx-C7 diagram. The spectral properties revealed from the Fermi sample do not support the blazar sequence reported by Fossati et al. and Ghisellini et al.
基金supported by National Natural Science Foundation of China(Grant Nos.10673008,10878001and10973010)the Ministry of Science and Technology of China(Grant No.2009CB824900/2009CB24904)the Ministry of Education of China(the NCET Program)
文摘By analyzing the azimuthal variations of total gravitating mass profiles in the central 300 h^-1 71 kpc regions of four galaxy clusters with Chandra data, we find that the azimuthally-averaged mass profiles may have been systematically underestimated by 16^＋9 -8% at lσ significance in the 50-100 h^-1 71 kpc regions, probably due to the prevailing existence of 2-D hot gas substructures in 100-300h^-1 71 kpc. The mass biases become negligible（-7＋11 _9＋ %） at 〉 150 h^-1 71 kpc. We confirm the results that the gas temperature maps can be used to probe the departure from hydrostatic equilibrium and help quantify the systematic biases in X-ray mass measurements in the central regions of clusters.
基金supported by the National Natural Science Foundation of China(Nos.U1431111,11163002,11473054 and U1531245)the Science and Technology Commission of Shanghai Municipality(Grant 14ZR1447100)
文摘By cross-correlating an archive sample of 542 extragalactic radio sources with the Fermi-LAT Third Source Catalog （3FGL）, we have compiled a sample of 80 γ-ray sources and 462 non-Fermi sources with available core dominance parameter （RcD）, and core and extended radio luminosity; all the parameters are directly measured or derived from available data in the literature. We found that RCD has significant correlations with radio core luminosity, γ-ray luminosity and γ-ray flux; the Fermi sources have on average higher RCD than non-Fermi sources. These results indicate that the Fermi sources should be more compact, and the beaming effect should play a crucial role in the detection of γ-ray emission. Moreover, our results also show Fermi sources have systematically larger radio flux than non-Fermi sources at fixed ReD, indicating larger intrinsic radio flux in Fermi sources. These results show a strong connection between radio and γ-ray flux for the present sample and indicate that the non-Fermi sources are likely due to the low beaming effect, and/or the low intrinsic γ-ray flux. This supports a scenario that has been published in the literature： a co-spatial origin of the activity for the radio and γ-ray emission, suggesting that the origin of the seed photons for the high-energy γ-ray emission is within the jet.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10933001, 10973006, 10973015 and 10673002)the National Basic Research Program of China (973 Program+1 种基金 Nos. 2007CB815404 and 2007CB815406)the Young Researcher Grant of National Astronomical Observatories, Chinese Academy of Sciences
文摘We select a large volume-limited sample of low surface brightness galax- ies （LSBGs, 2021） to investigate in detail their statistical properties and their dif- ferences from high surface brightness galaxies （HSBGs, 3639）. The distributions of stellar masses of LSBGs and HSBGs are nearly the same and they have the same me- dian values. Thus this volume-limited sample has good completeness and is further removed from the effect of stellar masses on their other properties when we compare LSBGs to HSBGs. We found that LSBGs tend to have lower stellar metallicities and lower effective dust attenuations, indicating that they have lower dust than HSBGs. The LSBGs have relatively higher stellar mass-to-light ratios, higher gas fractions, lower star forming rates （SFRs）, and lower specific SFRs than HSBGs. Moreover, with the decreasing surface brightness, gas fraction increases, but the SFRs and spe- cific SFRs decrease rapidly for the sample galaxies. This could mean that the star formation histories between LSBGs and HSBGs are different, and HSBGs may have stronger star forming activities than LSBGs.
基金supported by a project (Grant No.SR/S2/HEP12/2007)the Department of Space and Technology, India.
文摘The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AGNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi Gamma-ray Space Telescope）.
基金financial support from the Council of Scientific and Industrial Research(CSIR) through the SRF schemepartially funded from the ISRO-RESPOND program
文摘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.
基金funded by the National Natural Science Foundation of China (NSFC) under No.11903028the support from the “Yunnan Revitalization Talent Support Program” of Yunnan province, China+2 种基金the University of Michigan Radio Astronomy Observatory, which is supported by the University of Michiganby a series of grants from the National Science Foundation, most recently AST-0607523NASA Fermi grants NNX09AU16G, NNX10AP16G, and NNX11AO13G.
文摘We present periodicity search analyses on long-term radio light curves at 4.8,8,and 14.5 GHz of blazar PKS 0607–157 observed by the University of Michigan Radio Astronomical Observatory telescope.The highly variable radio emissions are approximately distributed as a log-normal probability distribution function.The Power Spectral Density for the radio light curves can be well characterized by a power-law model.Using the Weighted Wavelet Z-transform and Lomb-Scargle periodogram methods,significant Quasi-periodic Oscillation(QPO)of∼4.6 yr in the radio light curve has been observed above the 3σconfidence level,which presents an interesting case among blazar QPO phenomena.We explore three plausible physical models to explain the observed QPOs:a supermassive binary black hole system,Lense-Thirring precession of the disk,and helical motion of plasma blobs within the jet.
基金supported by the National Natural Science Foundationof China (NSFC, Grant Nos. 10633010, 11173009)the National Basic Research Program (973 program, 2007CB815405)+3 种基金the Bureau of Education of Guangzhou Municipality (No.11 Sui-Jiao-Ke[2009])Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme(GDUPS)(2009)Yangcheng Scholar Funded Scheme (10A027S)the Joint Laboratory for Optical Astronomy of Chinese Academy of Sciences
文摘Active galactic nuclei （AGNs） have two major classes, namely radio loud AGNs and radio quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which display extreme observational properties, such as rapid variability, high luminosity, high and variable polarization, and superluminal motion. All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight. Observations suggest that the orientation can be expressed by a core-dominance parameter, R. The R, to some extent, is associated with the beaming effect. Blazars are believed to be unified with Fanaroff ＆ Riley type I/II （FRI/II） radio galaxies. In this work, we collected relevant observations from the literature for a sample of 1223 AGNs including 77 BL Lacertae objects, 495 quasars, 460 galaxies, 119 FRs and 72 unidentified sources, and calculated the core-dominance parameters and spectral indexes, discussed the relationship between the two parameters, and gave some discussions. Our analysis suggests that the core-dominance parameters in BL Lacertae objects are larger than those in quasars and galaxies, and the radio spectral indexes in BL Lacertae objects are lower than those in quasars and galaxies. We also found that the core-dominance parameter-spectral index correlation exists for a large sample presented in this work, which may come from a relativistic beaming effect.
基金supported by the Basic Research Program of Yunnan Province(No.202201AS070005)the National Natural Science Foundation of China(NSFC,grant No.12273033)+1 种基金the Original Innovation Program of the Chinese Academy of Sciences(E085021002)support of the science research program for graduate students of Yunnan University(KC-23234629)。
文摘We report our identification of three gigaelectronvoltγ-ray sources,4FGL J0502.6+0036,4FGL J1055.9+6507,and 4FGL J1708.2+5519,as Active Galactic Nuclei(AGNs).They are listed in the latest Fermi-Large Area Telescope source catalog as unidentified ones.We find that the sources all showedγ-ray flux variations in recent years.Using different survey catalogs,we are able to find a radio source within the error circle of each source's position.Further analysis of optical sources in the fields allows us to determine the optical counterparts,which showed similar variation patterns to those seen inγ-rays.The optical counterparts have reported redshifts of 0.6,1.5,and 2.3,respectively,estimated from photometric measurements.In addition,we also obtain an X-ray spectrum of 4FGL J0502.6+0036 and a flux upper limit on the X-ray emission of 4FGL J1055.9+6507 by analyzing the archival data.The broadband spectral energy distributions of the three sources from radio toγ-rays are constructed.Comparing mainly theγ-ray properties of the three sources with those of different sub-classes of AGNs,we tentatively identify them as blazars.Followup optical spectroscopy is highly warranted for obtaining their spectral features and thus verifying the identification.
基金supported by the National Natural Science Foundation of China(grants 11573034,11533003,11373036 and 11133002)the National Basic Research Program(973 Program)of China(grant 2014CB845800)the Guangxi Science Foundation(2013GXNSFFA019001)
文摘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.
基金Supported by the National Natural Science Foundation of China
文摘We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broadband spectral indices. The distribution of luminosities shows that the averaged luminosity of flat spectrum radio quasars（FSRQs） is larger than that of BL Lacertae（BL Lac） objects. On the other hand, the broadband spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects have similar spectral properties,but high energy peaked BL Lac objects have a distinct spectral property. This may be due to the fact that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme is also revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameters.
文摘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 gala
基金the National Natural Science Foundation of China (Grant Nos. 10903025, 10973034, 11103060 and 11133006) for financial supportthe support of the National Basic Research Program of China (973 Program, 2009CB824800)
文摘We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample contains 166 sources. The statistical analysis based on this sample confirms positive correlations between these two bands, but the correlations become weaker as the γ-ray energy increases. The statistical results between various parameters show negative correla- tions of γ-ray photon spectral index with γ-ray loudness for both Flat Spectrum Radio Quasars （FSRQs） and BL Lacertae objects, positive correlations of γ-ray variability index with the γ-ray loudness for FSRQs, a negative correlation of the γ-ray variabil- ity index with the γ-ray photon spectral index for FSRQs, and negative correlations of γ-ray photon spectral index with γ-ray luminosity for FSRQs. These results suggest that the γ-ray variability may be due to changes inside the γ-ray emission region like the injected power, rather than changes in the photon density of the external radiation fields, and the variability amplitude tends to be larger as the γ-rays are closer to the high energy peak of the spectral energy distribution （SED）. No correlation of variabil- ity index found for BL Lacertae objects implies that variability behavior may differ below and above the peak energy.
基金supported by the National Natural Science Foundation of China (Grant No. 10963001)Yunnan Science Foundation(2009CD093)the Scientific Research Foundation of Dali University (DYKF2009 No. 1)
文摘Binary stars are common in star clusters and galaxies, but the detailed ef- fects of binary evolution are not taken into account in some color-magnitude diagram （CMD） studies. This paper studies the CMDs of twelve globular clusters via binary- star stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of binary and single stars on CMD studies. It is shown that binaries can better fit the observational CMDs of the sample globular clusters compared to single stars. This suggests that the effects of binary evolution should be considered when modeling the CMDs and stellar populations of star clusters and galaxies.
基金supported by the Estonian Science Foundationprojects IUT26-2 and IUT40-2support by the Centre of Excellence of Dark Matter in(Astro)particle Physics and Cosmology(TK120)+3 种基金Funding for SDSS-Ⅲ has been provided by the Alfred P.Sloan Foundationthe Participating Institutionsthe National Science Foundationthe U.S.Department of Energy Office of Science
文摘Because of the 3D nature of galaxies, an algorithm for constructing spatial density distribution models of galaxies on the basis of galaxy images has many advan- tages over approximations of the surface density distribution. We present a method for deriving the spatial structure and overall parameters of galaxies from images and estimate its accuracy and derived parameter degeneracies on a sample of idealised model galaxies. The test galaxies consist component with varying proportions and of a disc-like component and a spheroidal properties. Both components are assumed to be axially symmetric and coplanar. We simulate these test galaxies as if they had been observed in the SDSS project through ugriz filters, thus gaining a set of realis- tically imperfect images of galaxies with known intrinsic properties. These artificial SDSS galaxies were thereafter remodelled by approximating the surface brightness distribution with a 2D projection of a bulge＋disc spatial distribution model and the restored parameters were compared to the initial ones. Down to the r-band limiting magnitude of 18, errors in the restored integral luminosities and colour indices re- main within 0.05 mag and errors in the luminosities of individual components within 0.2 mag. Accuracy of the restored bulge-to-disc luminosity ratio （B/D） is within 40% in most cases, and becomes worse for galaxies with low B/D, but the general balance between bulges and discs is not shifted systematically. Assuming that the intrinsic disc axial ratio is ≤ 0.3, then the inclination angles can be estimated with errors 〈 5° for most of the galaxies with B/D 〈 2 and with errors 〈 15° up to B/D = 6. Errors in the recovered sizes of the galactic components are below 10% in most cases. The axial ratios and the shape parameter N of Einasto＇s distribution （similar to the Sersic index） are relatively inaccurate, but can provide statistical estimates for large samples. In general, models of disc components are more accurate than models of spheroidal compo
基金partially supported by projects SB/S2HEP-001/2013funded by DST(DB)+1 种基金ISRO/RES/2/367/10-11funded by ISRO,India
文摘Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The major- ity of identified extragalactic sources in γ-ray catalogs of EGRET and Fermi are blazars. Observationally, blazars can be divided into two classes： fiat spectrum radio quasars （FSRQs） and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in ＂7-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in 7-ray luminosity between the two classes is significantly reduced. In order to ex- plain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.
基金financial support from CSIR, New Delhifinancial support from DST, New Delhi through the INSPIRE Scheme
文摘We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have been interpreted as relativistically broad Fe Lc~ lines. Such features are not clearly observed in other active galactic nuclei despite sometimes having high iron abundance required by the best fitted blurred reflection models. Given the importance of these lines, we explore whether the rapid variability of spectral parameters may introduce broad bumps/dips artificially in the time averaged spectrum, which may then be mistaken as broadened lines. We tested this hypothesis by performing time resolved spectroscopy using long （〉 100 ks） XMM-Newton observations and by dividing them into segments with typical exposures of a few ks. We extracted spectra from each such segment and modeled them using a two component phenomenological model consisting of a power law to represent the hard component and a black body to represent the soft emission. As expected, both the sources showed variations in the spectral parameters. Using these variation trends, we simulated model spectra for each segment and then co-added to get a combined simulated spectrum. In the simulated spectra, we found no broad features below 1 keV and in particular no deviation near 0.9 keV as seen in the real averaged spectra. This implies that the broad Fe Lα line that is seen in the spectra of these sources is not an artifact of the variation of spectral components and, hence, provides evidence that the line is indeed genuine.
文摘We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent- heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.
基金supported by the Research Fund for the Doctoral Program of the Southwest University of Science and Technology (No. 14zx7102)
文摘We study ten galaxy groups and clusters suggested in the literature to be ＂fossil systems（FSs）＂based on Chandra observations. According to the M（500）- T and LX- T relations, the gas properties of FSs are not physically distinct from ordinary galaxy groups or clusters. We also first study the f（gas, 2500）- T relation and find that the FSs exhibit the same trend as ordinary systems. The gas densities of FSs within 0.1r200 are - 10^-3cm^-3, which is the same order of magnitude as galaxy clusters. The entropies within 0.1r200（S（0.1r200）） of FSs are systematically lower than those in ordinary galaxy groups, which is consistent with previous reports, but we find their S（0.1r200）- T relation is more similar to galaxy clusters. The derived mass profiles of FSs are consistent with the Navarro, Frenk and White model in（0.1- 1）（r200）, and the relation between scale radius rs and characteristic mass density δc indicates self-similarity of dark matter halos of FSs. The ranges of rs and δc for FSs are also close to those of galaxy clusters. Therefore, FSs share more common characteristics with galaxy clusters. The special birth place of the FS makes it a distinct type of galaxy system.
