We create mock X-ray observations of hot gas in galaxy clusters with a new extension of the L-Galaxies semianalytic model of galaxy formation,which includes the radial distribution of hot gas in each halo.Based on the...We create mock X-ray observations of hot gas in galaxy clusters with a new extension of the L-Galaxies semianalytic model of galaxy formation,which includes the radial distribution of hot gas in each halo.Based on the model outputs,we first build some mock light cones,then generate mock spectra with the SOXS package and derive the mock images in the light cones.Using the mock data,we simulate mock X-ray spectra for the ROSAT all-sky survey,and compare the mock spectra with the observational results.Then,we consider the design parameters of the HUBS mission and simulate the observation of the halo hot gas for HUBS as an important application of our mock work.We find:(1)our mock data match the observations by current X-ray telescopes.(2)The survey of hot baryons in resolved clusters by HUBS is effective below redshift 0.5,and the observations of the emission lines in point-like sources at z>0.5 by HUBS help us understand the hot baryons in the early universe.(3)By taking advantage of the large simulation box and flexibility in semi-analytic models,our mock X-ray observations provide the opportunity to select targets and observation strategies for forthcoming X-ray facilities.展开更多
We present a study of a fossil cluster,SDSS J0150–1005（z 0.364）,with high spatial resolution based on the imaging spectroscopic analysis of Chandra observations.The Chandra X-ray image shows a relaxed and symmetric...We present a study of a fossil cluster,SDSS J0150–1005（z 0.364）,with high spatial resolution based on the imaging spectroscopic analysis of Chandra observations.The Chandra X-ray image shows a relaxed and symmetric morphology,which indicates that SDSS J0150–1005 is a well-developed galaxy cluster with no sign of a recent merger.According to the isothermal model,its global gas temperature is 5.73±0.80 keV,and the virial mass is 6.23±1.34×1014M⊙.Compared with the polytropic temperature model,the mass calculated based on the isothermal model is overestimated by 49%±11.The central gas entropy,S0.1 r200=143.9±18.3 keV cm2,is significantly lower than the average value of normal galaxy clusters with similar temperatures.Our results indicate that SDSS J0150–1005 formed during an early epoch.展开更多
In the ΛCDM cosmological model, based on observations of supernovae Ia, the cosmic dark energy density is assumed to be Ω_(Λ)~ 0.70 and the gravitational mass density is assumed to be Ω_(m)~ 0.30. Based on the ass...In the ΛCDM cosmological model, based on observations of supernovae Ia, the cosmic dark energy density is assumed to be Ω_(Λ)~ 0.70 and the gravitational mass density is assumed to be Ω_(m)~ 0.30. Based on the assumption that the observed cosmic microwave background(CMB) is a thermal relic of the early hot universe, the cosmic plasma density should be small, i.e., Ω_(b)~ 0.05(otherwise the Sunyaev-Zeldovich effect of the cosmic plasma would ruin the observed CMB's perfect blackbody spectrum). To fill the gap between Ω_(m) and Ω_(b), non-baryonic dark matter Ω_(c)~ 0.25 is introduced into the ΛCDM model. If the CMB is the result of a partial thermal equilibrium between cosmic radiation and cosmic plasma, then the observed perfect blackbody spectrum of the CMB can coexist with cosmic plasma. In this case, it is not necessary to introduce non-baryonic cold dark matter into cosmological models. A better candidate for dark matter is the cosmic plasma.展开更多
We construct a sample of 70 clusters using data from XMM-Newton and Planck to investigate the YSZ,Planck-YSZ,XMM scaling relation and the cool-core influences on this relation.YSZ,XMM is calculated by accurately de-pr...We construct a sample of 70 clusters using data from XMM-Newton and Planck to investigate the YSZ,Planck-YSZ,XMM scaling relation and the cool-core influences on this relation.YSZ,XMM is calculated by accurately de-projected temperature and electron number density profiles derived from XMMNewton.YSZ,Planckis the latest Planck data restricted to our precise X-ray cluster size θ500.To study the cool-core influences on the YSZ,Planck-YSZ,XMM scaling relation,we apply two criteria,namely the limits of central cooling time and classic mass deposition rate,to distinguish cool-core clusters(CCCs) from non-cool-core clusters(NCCCs).We also use YSZ,Planckfrom other papers,which are derived from different methods,to confirm our results.The intercept and slope of the YSZ,Planck-YSZ,XMM scaling relation are A =-0.86 ± 0.30 and B = 0.83 ± 0.06 respectively.The intrinsic scatter is σins= 0.14 ± 0.03.The ratio of YSZ,Planck/YSZ,XMM is 1.03 ± 0.05,which is in excellent statistical agreement with unity.Discrepancies in the YSZ,Planck-YSZ,XMM scaling relation between CCCs and NCCCs are found in the observation.They are independent of the cool-core classification criteria and YSZ,Planckcalculation methods,although the discrepancies are more significant under the classification criteria of classic mass deposition rate.The intrinsic scatter of CCCs(0.04) is quite small compared to that of NCCCs(0.27).The ratio of YSZ,Planck/YSZ,XMM for CCCs is 0.89 ± 0.05,suggesting that CCCs’ YSZ,XMM may overestimate the Sunyaev-Zel’dovich(SZ)signal.By contrast,the ratio of YSZ,Planck/YSZ,XMM for NCCCs is 1.14 ± 0.12,which indicates that NCCCs’ YSZ,XMM may underestimate the SZ signal.展开更多
By creating and analyzing two dimensional gas temperature and abundance maps of the RGH 80 compact galaxy group with high-quality Chandra data,we detect a high-abundance （ 0.7 Z⊙） arc,where the metal abundance is s...By creating and analyzing two dimensional gas temperature and abundance maps of the RGH 80 compact galaxy group with high-quality Chandra data,we detect a high-abundance （ 0.7 Z⊙） arc,where the metal abundance is significantly higher than the surrounding regions by 0.3Z⊙.This structure shows tight spatial correlations with the member galaxy PGC 046529,as well as with the arm-like feature identified on the X-ray image in the previous work of Randall et al.（2009）.Since no apparent signature of AGN activity is found to be associated with PGC 046529 in multi-band observations,and the gas temperature,metallicity,and mass of the high-abundance arc resemble those of the ISM of typical early-type galaxies,we conclude that this high-abundance structure is the remnant of the ISM of PGC 046529,which was stripped out of the galaxy by ram pressure stripping due to the motion of PGC 046529 in RGH 80.This novel case shows that ram pressure stripping can work as efficiently in the metal enrichment process in galaxy groups as it can in galaxy clusters.展开更多
We revisit the XMM-Newton observation of the galaxy cluster Abell 1650 with a deprojection technique. We find that the radial deprojected spectra of Abell 1650 can be marginally fitted by a single-temperature model. I...We revisit the XMM-Newton observation of the galaxy cluster Abell 1650 with a deprojection technique. We find that the radial deprojected spectra of Abell 1650 can be marginally fitted by a single-temperature model. In order to study the properties of the central gas, we fit the spectra of the central two regions with a two- temperature model. The fits then become significantly better and the cool gas about 1～2 keV can be connected with the gas cooling. Fitting the central spectrum （r≤1′） by using a cooling flow model with an isothermal component yields a small mass deposition rate of 10-7^＋11 M. yr^-1, while the standard cooling flow model can not fit this spectrum satisfactorily except that there exists a cut-off temperature having a level of about 3 keV. From the isothermal model we derive the deprojected electron density profile ne（r）, and then together with the deprojected temperature profile the total mass and gas mass fraction of cluster are also determined. We compare the properties of Abell 1650 with those of Abell 1835 （a large cooling flow cluster） and some other clusters, to explore the difference in properties between large and small cooling flow cluster, and what causes the difference in the cooling flow of different clusters. It has been shown that Abell 1835 has a steeper potential well and thus a higher electron density and a lower temperature in its center, indicating that the shape of the gravitational potential well in central region determines the cooling flow rates of clusters. We calculate the potential, internal and radiated energies of these two clusters, and find that the gas energies in both clusters are conserved during the collapsing stage.展开更多
Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clu...Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.展开更多
Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark c...Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.展开更多
By performing a two dimensional spectral analysis on the galaxy group NGC 533 with high-quality Chandra data, we find that the metal abundance distribution in this group is anisotropic. In the area around 2.5′ from t...By performing a two dimensional spectral analysis on the galaxy group NGC 533 with high-quality Chandra data, we find that the metal abundance distribution in this group is anisotropic. In the area around 2.5′ from the center, we find two concentrations of high abundance structures, in which the abundances are significantly higher than their surrounding regions at the 90% confidence level. We find that the total iron mass in these two regions agrees with the iron mass synthesized in the central dominant galaxy in n 19＋0.08 Gyr. The double-sided configuration of the high abun- 0.03 dance structure, together with the point-like radio emission in the center suggests that the abundance structures could have been transported from the center to their present positions by active galactic nucleus （AGN） activity. We further calculate the energy required for transport, and find that it could have been supplied during an AGN period. However, considering that this group is reported to have experienced a recent merger, the possibility that this merger is responsible for the abundance structures still cannot be excluded.展开更多
We propose a consistency test for some recent X-ray gas mass fraction （fgas） measurements in galaxy clusters, using the cosmic distance-duality relation, Ttneory = DL（1 ＋ Z）-2/DA, with luminosity distance （DL） ...We propose a consistency test for some recent X-ray gas mass fraction （fgas） measurements in galaxy clusters, using the cosmic distance-duality relation, Ttneory = DL（1 ＋ Z）-2/DA, with luminosity distance （DL） data from the Union2 compilation of type Ia supernovae. We set Z/theory = 1, instead of assigning any red- shift parameterizations to it, and constrain the cosmological information preferred by fga8 data along with supernova observations. We adopt a new binning method in the reduction of the Union2 data, in order to minimize the statistical errors. Four data sets of X-ray gas mass fraction, which are reported by Allen et al. （two samples）, LaRoque et al. and Ettori et al., are analyzed in detail in the context of two theoretical models of fgas. The results from the analysis of Alien et al.＇s samples demonstrate the feasibility of our method. It is found that the preferred cosmology by LaRoque et al.＇s sample is consistent with its reference cosmology within the 1σ confidence level. However, for Ettori et al.＇s fgas sample, the inconsistency can reach more than a 3σ confidence level and this dataset shows special preference to an ΩA = 0 cosmology.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the support from the National SKA Program of China No.2020SKA0110102the fund for key programs of Shanghai Astronomical Observatory(Grants E195121009 and E297091002)+1 种基金Shanghai Committee of Science and Technology Grant No.19ZR1466700supported in part by the Natural Science Foundation of China(Grants 12133008,12192220,and 12192223)。
文摘We create mock X-ray observations of hot gas in galaxy clusters with a new extension of the L-Galaxies semianalytic model of galaxy formation,which includes the radial distribution of hot gas in each halo.Based on the model outputs,we first build some mock light cones,then generate mock spectra with the SOXS package and derive the mock images in the light cones.Using the mock data,we simulate mock X-ray spectra for the ROSAT all-sky survey,and compare the mock spectra with the observational results.Then,we consider the design parameters of the HUBS mission and simulate the observation of the halo hot gas for HUBS as an important application of our mock work.We find:(1)our mock data match the observations by current X-ray telescopes.(2)The survey of hot baryons in resolved clusters by HUBS is effective below redshift 0.5,and the observations of the emission lines in point-like sources at z>0.5 by HUBS help us understand the hot baryons in the early universe.(3)By taking advantage of the large simulation box and flexibility in semi-analytic models,our mock X-ray observations provide the opportunity to select targets and observation strategies for forthcoming X-ray facilities.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10878001, 10973010 and 11125313)the National Basic Research Program of China (973 Program+2 种基金 Grant Nos. 2009CB824900 and 2009CB824904)the Shanghai Science and Technology Commission (Program of Shanghai Subject Chief Scientist Grant Nos. 12XD1406200 and 11DZ2260700)
文摘We present a study of a fossil cluster,SDSS J0150–1005（z 0.364）,with high spatial resolution based on the imaging spectroscopic analysis of Chandra observations.The Chandra X-ray image shows a relaxed and symmetric morphology,which indicates that SDSS J0150–1005 is a well-developed galaxy cluster with no sign of a recent merger.According to the isothermal model,its global gas temperature is 5.73±0.80 keV,and the virial mass is 6.23±1.34×1014M⊙.Compared with the polytropic temperature model,the mass calculated based on the isothermal model is overestimated by 49%±11.The central gas entropy,S0.1 r200=143.9±18.3 keV cm2,is significantly lower than the average value of normal galaxy clusters with similar temperatures.Our results indicate that SDSS J0150–1005 formed during an early epoch.
文摘In the ΛCDM cosmological model, based on observations of supernovae Ia, the cosmic dark energy density is assumed to be Ω_(Λ)~ 0.70 and the gravitational mass density is assumed to be Ω_(m)~ 0.30. Based on the assumption that the observed cosmic microwave background(CMB) is a thermal relic of the early hot universe, the cosmic plasma density should be small, i.e., Ω_(b)~ 0.05(otherwise the Sunyaev-Zeldovich effect of the cosmic plasma would ruin the observed CMB's perfect blackbody spectrum). To fill the gap between Ω_(m) and Ω_(b), non-baryonic dark matter Ω_(c)~ 0.25 is introduced into the ΛCDM model. If the CMB is the result of a partial thermal equilibrium between cosmic radiation and cosmic plasma, then the observed perfect blackbody spectrum of the CMB can coexist with cosmic plasma. In this case, it is not necessary to introduce non-baryonic cold dark matter into cosmological models. A better candidate for dark matter is the cosmic plasma.
基金supported by the Bureau of International Cooperation, Chinese Academy of Sciences (GJHZ1864)support from the National Natural Science Foundation of China (Grant No. 11703014)
文摘We construct a sample of 70 clusters using data from XMM-Newton and Planck to investigate the YSZ,Planck-YSZ,XMM scaling relation and the cool-core influences on this relation.YSZ,XMM is calculated by accurately de-projected temperature and electron number density profiles derived from XMMNewton.YSZ,Planckis the latest Planck data restricted to our precise X-ray cluster size θ500.To study the cool-core influences on the YSZ,Planck-YSZ,XMM scaling relation,we apply two criteria,namely the limits of central cooling time and classic mass deposition rate,to distinguish cool-core clusters(CCCs) from non-cool-core clusters(NCCCs).We also use YSZ,Planckfrom other papers,which are derived from different methods,to confirm our results.The intercept and slope of the YSZ,Planck-YSZ,XMM scaling relation are A =-0.86 ± 0.30 and B = 0.83 ± 0.06 respectively.The intrinsic scatter is σins= 0.14 ± 0.03.The ratio of YSZ,Planck/YSZ,XMM is 1.03 ± 0.05,which is in excellent statistical agreement with unity.Discrepancies in the YSZ,Planck-YSZ,XMM scaling relation between CCCs and NCCCs are found in the observation.They are independent of the cool-core classification criteria and YSZ,Planckcalculation methods,although the discrepancies are more significant under the classification criteria of classic mass deposition rate.The intrinsic scatter of CCCs(0.04) is quite small compared to that of NCCCs(0.27).The ratio of YSZ,Planck/YSZ,XMM for CCCs is 0.89 ± 0.05,suggesting that CCCs’ YSZ,XMM may overestimate the Sunyaev-Zel’dovich(SZ)signal.By contrast,the ratio of YSZ,Planck/YSZ,XMM for NCCCs is 1.14 ± 0.12,which indicates that NCCCs’ YSZ,XMM may underestimate the SZ signal.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10673008,10878001 and 10973010)the Ministry of Science and Technology of China (Grant No. 2009CB824900/2009CB24904)the Ministry of Education of China (the NCET Program)
文摘By creating and analyzing two dimensional gas temperature and abundance maps of the RGH 80 compact galaxy group with high-quality Chandra data,we detect a high-abundance （ 0.7 Z⊙） arc,where the metal abundance is significantly higher than the surrounding regions by 0.3Z⊙.This structure shows tight spatial correlations with the member galaxy PGC 046529,as well as with the arm-like feature identified on the X-ray image in the previous work of Randall et al.（2009）.Since no apparent signature of AGN activity is found to be associated with PGC 046529 in multi-band observations,and the gas temperature,metallicity,and mass of the high-abundance arc resemble those of the ISM of typical early-type galaxies,we conclude that this high-abundance structure is the remnant of the ISM of PGC 046529,which was stripped out of the galaxy by ram pressure stripping due to the motion of PGC 046529 in RGH 80.This novel case shows that ram pressure stripping can work as efficiently in the metal enrichment process in galaxy groups as it can in galaxy clusters.
基金Supported by the National Natural Science Foundation of China.
文摘We revisit the XMM-Newton observation of the galaxy cluster Abell 1650 with a deprojection technique. We find that the radial deprojected spectra of Abell 1650 can be marginally fitted by a single-temperature model. In order to study the properties of the central gas, we fit the spectra of the central two regions with a two- temperature model. The fits then become significantly better and the cool gas about 1～2 keV can be connected with the gas cooling. Fitting the central spectrum （r≤1′） by using a cooling flow model with an isothermal component yields a small mass deposition rate of 10-7^＋11 M. yr^-1, while the standard cooling flow model can not fit this spectrum satisfactorily except that there exists a cut-off temperature having a level of about 3 keV. From the isothermal model we derive the deprojected electron density profile ne（r）, and then together with the deprojected temperature profile the total mass and gas mass fraction of cluster are also determined. We compare the properties of Abell 1650 with those of Abell 1835 （a large cooling flow cluster） and some other clusters, to explore the difference in properties between large and small cooling flow cluster, and what causes the difference in the cooling flow of different clusters. It has been shown that Abell 1835 has a steeper potential well and thus a higher electron density and a lower temperature in its center, indicating that the shape of the gravitational potential well in central region determines the cooling flow rates of clusters. We calculate the potential, internal and radiated energies of these two clusters, and find that the gas energies in both clusters are conserved during the collapsing stage.
基金Supported by the National Natural Science Foundation of Chinasupported by the National Science Foundation of China under the Distinguished Young Scholar Grant 10825313by the Ministry of Science and Technology's National Basic Science Program(Project 973)under grant No.2007CB815401
文摘Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.
文摘Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10878001,10973010,and 11125313)the National Basic Research Program of China (973 Program+1 种基金Grant Nos.2009CB824900 and 2009CB824904)Shanghai Jiao Tong University Innovation Fund For Postgraduates
文摘By performing a two dimensional spectral analysis on the galaxy group NGC 533 with high-quality Chandra data, we find that the metal abundance distribution in this group is anisotropic. In the area around 2.5′ from the center, we find two concentrations of high abundance structures, in which the abundances are significantly higher than their surrounding regions at the 90% confidence level. We find that the total iron mass in these two regions agrees with the iron mass synthesized in the central dominant galaxy in n 19＋0.08 Gyr. The double-sided configuration of the high abun- 0.03 dance structure, together with the point-like radio emission in the center suggests that the abundance structures could have been transported from the center to their present positions by active galactic nucleus （AGN） activity. We further calculate the energy required for transport, and find that it could have been supplied during an AGN period. However, considering that this group is reported to have experienced a recent merger, the possibility that this merger is responsible for the abundance structures still cannot be excluded.
基金supported by the National Basic Research Program of China (973 program Grant Nos. 2009CB824800 and 2012CB821804)+1 种基金the National Natural Science Foundation of China (Grant Nos. 11033002 and 11173006)the Fundamental Research Funds for the Central Universities
文摘We propose a consistency test for some recent X-ray gas mass fraction （fgas） measurements in galaxy clusters, using the cosmic distance-duality relation, Ttneory = DL（1 ＋ Z）-2/DA, with luminosity distance （DL） data from the Union2 compilation of type Ia supernovae. We set Z/theory = 1, instead of assigning any red- shift parameterizations to it, and constrain the cosmological information preferred by fga8 data along with supernova observations. We adopt a new binning method in the reduction of the Union2 data, in order to minimize the statistical errors. Four data sets of X-ray gas mass fraction, which are reported by Allen et al. （two samples）, LaRoque et al. and Ettori et al., are analyzed in detail in the context of two theoretical models of fgas. The results from the analysis of Alien et al.＇s samples demonstrate the feasibility of our method. It is found that the preferred cosmology by LaRoque et al.＇s sample is consistent with its reference cosmology within the 1σ confidence level. However, for Ettori et al.＇s fgas sample, the inconsistency can reach more than a 3σ confidence level and this dataset shows special preference to an ΩA = 0 cosmology.
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.
