A 21-year-old woman presented with a left-hand deformity that had been present since birth.She had no clear family or genetic history.Physical examination revealed absence of the left metacarpal phalanges and four sof...A 21-year-old woman presented with a left-hand deformity that had been present since birth.She had no clear family or genetic history.Physical examination revealed absence of the left metacarpal phalanges and four soft tissue bulges at the distal end of the wrist(Figure 1a).Digital radiography showed fusion of the lunate and triangular bones of the left wrist,fusion of the scaphoid with the distal row of carpal bones,and an irregular bone with an uneven distal margin.展开更多
In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded s...In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded sheets by covering the tailor-welded sheets with better plastic properties overlapping sheets.At the same time,the interface friction effect between the overlapping and tailor-welded sheets was utilized to control the stress magnitude and further improve the formability and quality of the tailor-welded sheets.In this work,the bulging process of the tailor-welded overlapping sheets was taken as the research object.Aluminum alloy tailor-welded overlapping sheets bulging specimens were studied by a combination of finite element analysis and experimental verification.The results show that the appropriate use of interface friction between tailor-welded and overlapping sheets can improve the formability of tailor-welded sheets and control the flow of weld seam to improve the forming quality.When increasing the interface friction coefficient on the side of tailor-welded sheets with higher strength and decreasing that on the side of tailor-welded sheets with lower strength,the deformation of the tailor-welded sheets are more uniform,the offset of the weld seam is minimal,the limit bulging height is maximal,and the forming quality is optimal.展开更多
The bulge test is a widely utilized method for assessing the mechanical properties of thin films,including metals,polymers,and semiconductors.However,as film thickness diminishes to nanometer scales,boundary condition...The bulge test is a widely utilized method for assessing the mechanical properties of thin films,including metals,polymers,and semiconductors.However,as film thickness diminishes to nanometer scales,boundary conditions dominated by weak van der Waals forces significantly impact mechanical responses.Instead of sample fracture,interfacial shear deformation and delamination become the primary deformation modes,thereby challenging the applicability of conventional bulge models.To accommodate the interfacial effect,a modified mechanical model based on the bulge test has been proposed.This review summarizes recent advancements in the bulge test to highlight the potential challenges and opportunities for future research.展开更多
The influences of strength coefficient K, work hardening exponent n and thickness t of the overlapping sheet on bulging process are analyzed based on hardening material model. Also, bulging experiments are carried out...The influences of strength coefficient K, work hardening exponent n and thickness t of the overlapping sheet on bulging process are analyzed based on hardening material model. Also, bulging experiments are carried out by taking the aluminum alloy LF21 as formed sheet metal, and selecting overlapping sheet with different thicknesses and material properties, by which accuracy of the above analysis result is verified in the aspects of geometric shape, thickness distribution and limit bulging height. The results show that higher strength coefficient K, larger work hardening exponent n and proper thickness of the overlapping sheet are helpful to improve the formability and forming uniformity of formed sheet metal.展开更多
The forming limit diagram of Ti-15-3 alloy sheet was constituted at room temperature. The effects of different punch and rubber hardness on the limit principal strain distributions were investigated experimentally. Fi...The forming limit diagram of Ti-15-3 alloy sheet was constituted at room temperature. The effects of different punch and rubber hardness on the limit principal strain distributions were investigated experimentally. Finite element analysis models of the samples with dimensions of 180 mm×180 mm were established to analyze the friction coefficients of different interfaces. Effects of various friction coefficients on the strain distributions were studied in detail. Finally, the friction coefficients in the cold forming were determined by contrasting the strain results between the experimental data and the simulated ones.展开更多
Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analys...Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analysis and experiments of viscous warm pressure bulging （VWPB） of AZ31B magnesium alloy were conducted to analyze the influence of different ellipticity dies on the formability of AZ31B magnesium alloy. At the same time, based on the grid strain rule, the forming limit diagram （FLD） of VWPB of AZ31B magnesium alloy was obtained through measuring the strain of bulging specimens. The results showed that at the temperature range of viscous medium thermal stability, the viscous medium can fit the geometry variation of sheet and generate non-uniform pressure field, and as the die ellipticity increases, the difference value of non-uniform pressure reduces. Meanwhile, according to the FLD, the relationship between part complexity and ultimate deformation was investigated.展开更多
Based on the elastoplastic mechanical properties of the weld and heat affected zone metals obtained by a nanoindentation test, a theoretical calculation model was established for the forming limit diagram（FLD） of ta...Based on the elastoplastic mechanical properties of the weld and heat affected zone metals obtained by a nanoindentation test, a theoretical calculation model was established for the forming limit diagram（FLD） of tailor-welded blanks（TWBs） on the basis of plastic constitutive relations and Hosford yield criteria. Hemispherical punch bulging tests were performed to verify the FLD theoretical calculation results. The results demonstrated that not only the FLD theoretical calculation of base materials but also that of TWBs had a good agreement with their experiments. Besides, poorer formability of TWBs caused its FLD significantly lower than that of base materials. The theoretical calculation model offers a reliable approach to obtain the specific FLD of TWBs.展开更多
Ring hoop tension test and tube bulging test were carried out at elevated temperatures up to 480 ℃to evaluate the formability of AZ31B extruded tube for internal high pressure forming （IHPF） process. The total elon...Ring hoop tension test and tube bulging test were carried out at elevated temperatures up to 480 ℃to evaluate the formability of AZ31B extruded tube for internal high pressure forming （IHPF） process. The total elongation along hoop direction and the maximum expansion ratio （MER） of the tube were obtained. The fracture surface after bursting was also analyzed. The results show that the total elongation along hoop direction and the MER value have a similar changing tendency as the testing temperature increases, which is quite different from the total elongation along axial direction. Both the total elongation along hoop direction and the MER value increase to a peak value at about 160 ℃. After that, they begin to decrease quickly until a certain rebounding temperature is reached. From the rebounding temperature, they begin to increase rapidly again. Burnt structure appears on the fracture surface when tested at temperatures higher than 420 ℃. Therefore, the forming temperature of the tested tube should be lower than 420 ℃, even though bigger formability can be achieved at higher temperature.展开更多
We investigate the MBH-σ＊ relation for radio-loud quasars with redshifl z 〈 0.83 in Data Release 3 of the Sloan Digital Sky Survey （SDSS）. The sample consists of 3772 quasars with better models of the H/4 and [O ...We investigate the MBH-σ＊ relation for radio-loud quasars with redshifl z 〈 0.83 in Data Release 3 of the Sloan Digital Sky Survey （SDSS）. The sample consists of 3772 quasars with better models of the H/4 and [O Ⅲ] lines and available radio luminosity, including 306 radio-loud quasars, 3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity （181 radio-quiet quasars with measured radio luminosity）. The virial supermassive black hole mass （MBH） is calculated from the broad Hβline, and the host stellar velocity dispersion （σ＊） is traced by the core [O Ⅲ] gaseous velocity dispersion. The radio luminosity and radio loudness are derived from the FIRST catalog. Our results are as follows： （1） For radio-quiet quasars, we confirm that there is no obvious deviation from the MBH-σ＊ relation defined for inactive galaxies when the uncertainties in ~IBH and the luminosity bias are concerned. （2） We find that the radio-loud quasars deviate more from the MBH-σ＊ relation than do the radio-quiet quasars. This deviation is only partly due to a possible cosmological evolution of the MBH-σ＊ relation and the luminosity bias. （3） The radio luminosity is proportional to MBH1.28＋0.23-0.16（LBol/LEdd） ^1.29＋0.31-0.24 for radio-quiet quasars and to -MBH3.10＋0.60-0.70（LBol/LEdd）^4.18＋1.40-1.10 - for radio-loud quasars. The weaker dependence of the radio luminosity on the mass and the Eddington ratio for radio-loud quasars shows that other physical effects would account for their radio luminosities, such as the spin of the black hole.展开更多
This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow e...This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.展开更多
We present a study of low surface brightness galaxies(LSBGs) selected by fitting the images for all the galaxies inα.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models(...We present a study of low surface brightness galaxies(LSBGs) selected by fitting the images for all the galaxies inα.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models(disk+bulge):single exponential,single sersic,exponential+deVaucular(exp+deV),and exponential+sérsic(exp+ser).Under the criteria of the B band disk central surface brightness μ_(0,disk)(B)≥22.5 mag arcsec^(-2) and the axis ratio b/a> 0.3,we selected four none-edge-on LSBG samples from each of the models which contain 1105,1038,207,and 75 galaxies,respectively.There are 756 galaxies in common between LSBGs selected by exponential and sersic models,corresponding to 68.42% of LSBGs selected by the exponential model and 72.83% of LSBGs selected by the sersic model,the rest of the discrepancy is due to the difference in obtaining μ_(0) between the exponential and sersic models.Based on the fitting,in the range of 0.5≤n≤1.5,the relation of μ_(0) from two models can be written as μ_(0,sérsic)-μ_(0,exp)=-1.34(n-1).The LSBGs selected by disk+bulge models(LSBG_(2)comps) are more massive than LSBGs selected by single-component models(LSBG_1comp),and also show a larger disk component.Though the bulges in the majority of our LSBG_(2)comps are not prominent,more than 60% of our LSBG_(2)comps will not be selected if we adopt a single-component model only.We also identified 31 giant low surface brightness galaxies(gLSBGs) from LSBG_(2)comps.They are located at the same region in the color-magnitude diagram as other gLSBGs.After we compared different criteria of gLSBGs selection,we find that for gas-rich LSBGs,M_(*)> 10^(10)M_⊙ is the best to distinguish between gLSBGs and normal LSBGs with bulge.展开更多
We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is ...We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is limited to a narrow range in the color-stellar mass diagram. After splitting green valley galaxies into two parts—a bluer green valley(green 1) and a redder one(green 2) and three stellar mass bins,we investigate the variation of physical properties across the green valley region. Our main results are as follows:(i) The percentages of pure bulge and bulge-dominated/elliptical galaxies increase gradually from blue cloud to red sequence while the percentages of pure disk and disk-dominated/spiral galaxies decrease gradually in all stellar mass bins and different environments.(ii) With the analysis of morphological and structural parameters(e.g., concentration(C) and the stellar mass surface density within the central 1 kpc(Σ1)), red galaxies show more luminous and compact cores than both green valley and blue galaxies, while blue galaxies show the opposite behavior in all stellar mass bins.(iii) A strong negative(positive) relationship between bulge-to-total light ratio(B/T) and specific star formation rate(sSFR)(D_(4000)) is found from blue to red galaxies. Our results indicate that the growth in bulge plays an important role when the galaxies change from the blue cloud, to the green valley and to the red sequence.展开更多
In order to test a possible evolutionary scenario of high-z compact quiescent galaxies(cQGs)that they can survive as local compact cores embedded in local massive galaxies with different morphology classes, we explore...In order to test a possible evolutionary scenario of high-z compact quiescent galaxies(cQGs)that they can survive as local compact cores embedded in local massive galaxies with different morphology classes, we explore the star formation histories of local compact cores according to their spectral analysis.We build a sample of 182 massive galaxies with compact cores(M*,core> 10^10.6 M⊙) at 0.02 ≤ z ≤ 0.06 from SDSS DR7 spectroscopic catalogue. The STARLIGHT package is used to analyze the median stacked spectra and derive the stellar ages and metallicities. Our main results show that local compact cores have the average age of about 12.1 ± 0.6 Gyr, indicating their early formation at z > 3, which is consistent with the formation redshifts of cQGs at 1 < z < 3. Together with previous studies, our result that local compact cores have similar formation redshifts as those of high-z cQGs, supports that local massive galaxies with compact cores are possible descendants of cQGs. Morphological study of local galaxies with compact cores suggests that there would be multiple possible evolutionary paths for high-z cQGs: most of them(> 80%)will evolve into local massive early-type galaxies according to dry minor merger, while some of them(~ 15%) will build substantial stellar/gas discs according to the late-time gas accretion and sustaining star formation, and finally grow up into spiral galaxies.展开更多
文摘A 21-year-old woman presented with a left-hand deformity that had been present since birth.She had no clear family or genetic history.Physical examination revealed absence of the left metacarpal phalanges and four soft tissue bulges at the distal end of the wrist(Figure 1a).Digital radiography showed fusion of the lunate and triangular bones of the left wrist,fusion of the scaphoid with the distal row of carpal bones,and an irregular bone with an uneven distal margin.
基金Funded by the National Natural Science Foundation of China(Nos.52075347,51575364)and the Natural Science Foundation of Liaoning Provincial(No.2022-MS-295)。
文摘In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded sheets by covering the tailor-welded sheets with better plastic properties overlapping sheets.At the same time,the interface friction effect between the overlapping and tailor-welded sheets was utilized to control the stress magnitude and further improve the formability and quality of the tailor-welded sheets.In this work,the bulging process of the tailor-welded overlapping sheets was taken as the research object.Aluminum alloy tailor-welded overlapping sheets bulging specimens were studied by a combination of finite element analysis and experimental verification.The results show that the appropriate use of interface friction between tailor-welded and overlapping sheets can improve the formability of tailor-welded sheets and control the flow of weld seam to improve the forming quality.When increasing the interface friction coefficient on the side of tailor-welded sheets with higher strength and decreasing that on the side of tailor-welded sheets with lower strength,the deformation of the tailor-welded sheets are more uniform,the offset of the weld seam is minimal,the limit bulging height is maximal,and the forming quality is optimal.
基金supported by the National Natural Science Foundation of China(Grant Nos.22072031,12372107,11832010,and 11890682)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB36000000).
文摘The bulge test is a widely utilized method for assessing the mechanical properties of thin films,including metals,polymers,and semiconductors.However,as film thickness diminishes to nanometer scales,boundary conditions dominated by weak van der Waals forces significantly impact mechanical responses.Instead of sample fracture,interfacial shear deformation and delamination become the primary deformation modes,thereby challenging the applicability of conventional bulge models.To accommodate the interfacial effect,a modified mechanical model based on the bulge test has been proposed.This review summarizes recent advancements in the bulge test to highlight the potential challenges and opportunities for future research.
基金Project(51205260)supported by the National Natural Science Foundation of ChinaProject(L2012046)supported by the Liaoning Provincial Committee of Education,China
文摘The influences of strength coefficient K, work hardening exponent n and thickness t of the overlapping sheet on bulging process are analyzed based on hardening material model. Also, bulging experiments are carried out by taking the aluminum alloy LF21 as formed sheet metal, and selecting overlapping sheet with different thicknesses and material properties, by which accuracy of the above analysis result is verified in the aspects of geometric shape, thickness distribution and limit bulging height. The results show that higher strength coefficient K, larger work hardening exponent n and proper thickness of the overlapping sheet are helpful to improve the formability and forming uniformity of formed sheet metal.
文摘The forming limit diagram of Ti-15-3 alloy sheet was constituted at room temperature. The effects of different punch and rubber hardness on the limit principal strain distributions were investigated experimentally. Finite element analysis models of the samples with dimensions of 180 mm×180 mm were established to analyze the friction coefficients of different interfaces. Effects of various friction coefficients on the strain distributions were studied in detail. Finally, the friction coefficients in the cold forming were determined by contrasting the strain results between the experimental data and the simulated ones.
基金Project(51575364)supported by the National Natural Science Foundation of ChinaProject(2013024014)supported by the Natural Foundation of Liaoning Province,China
文摘Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analysis and experiments of viscous warm pressure bulging （VWPB） of AZ31B magnesium alloy were conducted to analyze the influence of different ellipticity dies on the formability of AZ31B magnesium alloy. At the same time, based on the grid strain rule, the forming limit diagram （FLD） of VWPB of AZ31B magnesium alloy was obtained through measuring the strain of bulging specimens. The results showed that at the temperature range of viscous medium thermal stability, the viscous medium can fit the geometry variation of sheet and generate non-uniform pressure field, and as the die ellipticity increases, the difference value of non-uniform pressure reduces. Meanwhile, according to the FLD, the relationship between part complexity and ultimate deformation was investigated.
基金Project(51275444) supported by the National Natural Science Foundation of ChinaProject(20121333110003) supported by the Specialized Research Fund for the Doctoral Program of Higher Education,China+1 种基金Project(E2014203271) supported by the Natural Science Foundation–Steel and Iron Foundation of Hebei ProvinceChina
文摘Based on the elastoplastic mechanical properties of the weld and heat affected zone metals obtained by a nanoindentation test, a theoretical calculation model was established for the forming limit diagram（FLD） of tailor-welded blanks（TWBs） on the basis of plastic constitutive relations and Hosford yield criteria. Hemispherical punch bulging tests were performed to verify the FLD theoretical calculation results. The results demonstrated that not only the FLD theoretical calculation of base materials but also that of TWBs had a good agreement with their experiments. Besides, poorer formability of TWBs caused its FLD significantly lower than that of base materials. The theoretical calculation model offers a reliable approach to obtain the specific FLD of TWBs.
基金Project(50805033)supported by the National Natural Science Foundation of ChinaProject(E200804)supported by the Natural Science Foundation of Heilongjiang Province of China
文摘Ring hoop tension test and tube bulging test were carried out at elevated temperatures up to 480 ℃to evaluate the formability of AZ31B extruded tube for internal high pressure forming （IHPF） process. The total elongation along hoop direction and the maximum expansion ratio （MER） of the tube were obtained. The fracture surface after bursting was also analyzed. The results show that the total elongation along hoop direction and the MER value have a similar changing tendency as the testing temperature increases, which is quite different from the total elongation along axial direction. Both the total elongation along hoop direction and the MER value increase to a peak value at about 160 ℃. After that, they begin to decrease quickly until a certain rebounding temperature is reached. From the rebounding temperature, they begin to increase rapidly again. Burnt structure appears on the fracture surface when tested at temperatures higher than 420 ℃. Therefore, the forming temperature of the tested tube should be lower than 420 ℃, even though bigger formability can be achieved at higher temperature.
基金the National Natural Science Foundation of China
文摘We investigate the MBH-σ＊ relation for radio-loud quasars with redshifl z 〈 0.83 in Data Release 3 of the Sloan Digital Sky Survey （SDSS）. The sample consists of 3772 quasars with better models of the H/4 and [O Ⅲ] lines and available radio luminosity, including 306 radio-loud quasars, 3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity （181 radio-quiet quasars with measured radio luminosity）. The virial supermassive black hole mass （MBH） is calculated from the broad Hβline, and the host stellar velocity dispersion （σ＊） is traced by the core [O Ⅲ] gaseous velocity dispersion. The radio luminosity and radio loudness are derived from the FIRST catalog. Our results are as follows： （1） For radio-quiet quasars, we confirm that there is no obvious deviation from the MBH-σ＊ relation defined for inactive galaxies when the uncertainties in ~IBH and the luminosity bias are concerned. （2） We find that the radio-loud quasars deviate more from the MBH-σ＊ relation than do the radio-quiet quasars. This deviation is only partly due to a possible cosmological evolution of the MBH-σ＊ relation and the luminosity bias. （3） The radio luminosity is proportional to MBH1.28＋0.23-0.16（LBol/LEdd） ^1.29＋0.31-0.24 for radio-quiet quasars and to -MBH3.10＋0.60-0.70（LBol/LEdd）^4.18＋1.40-1.10 - for radio-loud quasars. The weaker dependence of the radio luminosity on the mass and the Eddington ratio for radio-loud quasars shows that other physical effects would account for their radio luminosities, such as the spin of the black hole.
文摘This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.
基金supported by the National Key R&D Program of China (grant No.2022YFA1602901)support of the National Natural Science Foundation of China(NSFC) grant Nos. 12090040, 12090041, and 12003043+5 种基金supported by the Youth Innovation Promotion AssociationCAS (No. 2020057)the science research grants of CSST from the China Manned Space Projectsupport of the NSFC grant Nos.11733006 and U1931109supported by the Strategic Priority Research Program of the Chinese Academy of Sciences,Grant No. XDB0550100partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences。
文摘We present a study of low surface brightness galaxies(LSBGs) selected by fitting the images for all the galaxies inα.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models(disk+bulge):single exponential,single sersic,exponential+deVaucular(exp+deV),and exponential+sérsic(exp+ser).Under the criteria of the B band disk central surface brightness μ_(0,disk)(B)≥22.5 mag arcsec^(-2) and the axis ratio b/a> 0.3,we selected four none-edge-on LSBG samples from each of the models which contain 1105,1038,207,and 75 galaxies,respectively.There are 756 galaxies in common between LSBGs selected by exponential and sersic models,corresponding to 68.42% of LSBGs selected by the exponential model and 72.83% of LSBGs selected by the sersic model,the rest of the discrepancy is due to the difference in obtaining μ_(0) between the exponential and sersic models.Based on the fitting,in the range of 0.5≤n≤1.5,the relation of μ_(0) from two models can be written as μ_(0,sérsic)-μ_(0,exp)=-1.34(n-1).The LSBGs selected by disk+bulge models(LSBG_(2)comps) are more massive than LSBGs selected by single-component models(LSBG_1comp),and also show a larger disk component.Though the bulges in the majority of our LSBG_(2)comps are not prominent,more than 60% of our LSBG_(2)comps will not be selected if we adopt a single-component model only.We also identified 31 giant low surface brightness galaxies(gLSBGs) from LSBG_(2)comps.They are located at the same region in the color-magnitude diagram as other gLSBGs.After we compared different criteria of gLSBGs selection,we find that for gas-rich LSBGs,M_(*)> 10^(10)M_⊙ is the best to distinguish between gLSBGs and normal LSBGs with bulge.
基金supported by the National Key Research and Development Program of China (No. 2017YFA0402703)by the National Natural Science Foundation of China (No. 11733002)
文摘We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is limited to a narrow range in the color-stellar mass diagram. After splitting green valley galaxies into two parts—a bluer green valley(green 1) and a redder one(green 2) and three stellar mass bins,we investigate the variation of physical properties across the green valley region. Our main results are as follows:(i) The percentages of pure bulge and bulge-dominated/elliptical galaxies increase gradually from blue cloud to red sequence while the percentages of pure disk and disk-dominated/spiral galaxies decrease gradually in all stellar mass bins and different environments.(ii) With the analysis of morphological and structural parameters(e.g., concentration(C) and the stellar mass surface density within the central 1 kpc(Σ1)), red galaxies show more luminous and compact cores than both green valley and blue galaxies, while blue galaxies show the opposite behavior in all stellar mass bins.(iii) A strong negative(positive) relationship between bulge-to-total light ratio(B/T) and specific star formation rate(sSFR)(D_(4000)) is found from blue to red galaxies. Our results indicate that the growth in bulge plays an important role when the galaxies change from the blue cloud, to the green valley and to the red sequence.
基金supported by National Key R&D Program of China (No.2017YFA0402703)support from the National Natural Science Foundation of China (NSFC+9 种基金Grant Nos.1182230311773020 and 11421303)Shandong Provincial Natural Science Foundation,China(ZR2017QA001 and JQ201801)Funding for the SDSS and SDSS-II has been provided by the Alfred P.Sloan Foundationthe Participating Institutions,the National Science Foundationthe U.S.Department of Energythe National Aeronautics and Space Administrationthe Japanese Monbukagakushothe Max Planck Societythe Higher Education Funding Council for England。
文摘In order to test a possible evolutionary scenario of high-z compact quiescent galaxies(cQGs)that they can survive as local compact cores embedded in local massive galaxies with different morphology classes, we explore the star formation histories of local compact cores according to their spectral analysis.We build a sample of 182 massive galaxies with compact cores(M*,core> 10^10.6 M⊙) at 0.02 ≤ z ≤ 0.06 from SDSS DR7 spectroscopic catalogue. The STARLIGHT package is used to analyze the median stacked spectra and derive the stellar ages and metallicities. Our main results show that local compact cores have the average age of about 12.1 ± 0.6 Gyr, indicating their early formation at z > 3, which is consistent with the formation redshifts of cQGs at 1 < z < 3. Together with previous studies, our result that local compact cores have similar formation redshifts as those of high-z cQGs, supports that local massive galaxies with compact cores are possible descendants of cQGs. Morphological study of local galaxies with compact cores suggests that there would be multiple possible evolutionary paths for high-z cQGs: most of them(> 80%)will evolve into local massive early-type galaxies according to dry minor merger, while some of them(~ 15%) will build substantial stellar/gas discs according to the late-time gas accretion and sustaining star formation, and finally grow up into spiral galaxies.
