检索结果-南通市图书馆

Photometric redshifts of galaxies from SDSS and 2MASS

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2009年第4期9卷 390-400页

作者： Tao Wang Jia-sheng Huang qiu-sheng gu Department of Astronomy Nanjing University Nanjing 210093 China Harvard-Smithsonian Center for Astrophysics 60 Garden Street Cambridge MA 02138

In order to find the physical parameters which determine the accuracy of pho- tometric redshifts, we compare the spectroscopic and photometric redshifts （photo-z＇s） for a large sample of -80000 SDSS-2MASS galaxies. Photo-z＇s in this paper are estimated by using the artificial neural network photometric redshift method （ANNz）. For a subset of -40000 randomly selected galaxies, we find that the photometric redshift recovers the spectroscopic redshift distribution very well with rms of 0.016. Our main results are as follows：（1） Using magnitudes directly as input parameters produces more accurate photo-z＇s than using colors; （2） The inclusion of 2MASS （J, H, Ks） bands does not improve photo-z＇s significantly, which indicates that near infrared data might not be important for the low-redshift sample; （3） Adding the concentration index （essentially the steepness of the galaxy brightness profile） as an extra input can improve the photo-z＇s estimation up to -10 percent; （4） Dividing the sample into early- and late-type galaxies by using the concentration index, normal and abnormal galaxies by using the emission line flux ratios, and red and blue galaxies by using color index （g - r）, we can improve the accuracy of photo-z＇s significantly; （5） Our analysis shows that the outliers （where there is a big difference between the spectroscopic and photometric redshifts） are mainly correlated with galaxy types, e.g., most outliers are late-type （blue） galaxies.

关键词： galaxies distances and redshifts-methods statistical-techniques pho-tometric

The physical properties of galaxies with unusually high gas-phase metallicity

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2020年第2期20卷 53-66页

作者： Yong-Yun Chen qiu-sheng gu Xue Ge School of Astronomy and Space Science Nanjing University

We use 1221 galaxies with unusually high gas-phase metallicity to study their physical *** scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase *** goal is to understand the physical origins of the high gas-phase *** address this study,we select a control sample matching similar redshift and stellar *** main results are as follows.(i) Compared with the control sample,the high-metallicity sample shows lower ionization parameter,higher electron density and more dust content.(ii) We also find that the high-metallicity sample has older stellar age and higher [Mgb/] ratio,which indicates that the high-metallicity sample has shorter timescale of star formation.(iii) According to the plane of Hδ_A vs.D_n4000,we can see that the control sample has higher HδAand lower D_n4000 than the high-metallicity sample,which may imply that the control sample experiences recent star formation.(iv) There is a significant difference in gas distribution between the highmetallicity and control *** high-metallicity sample has lower gas fraction than control sample,which indicates that galaxies have high gas-phase metallicity probably due to their low HI gas fraction.(v) There is no significant difference between the high-metallicity and control samples in environment,which may suggest that the environment has no effect on gas-phase metallicity.

关键词： galaxies:evolution galaxies:formation galaxies:abundance galaxies:ISM galaxies:star formation

Surface photometry and radial color gradients of nearby luminous early-type galaxies in SDSS Stripe 82

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2011年第3期11卷 309-326页

作者： Fang-Zhou Jiang Song Huang qiu-sheng gu Department for Intensive Instruction Kuang Yaming Honors School Nanjing University Nanjing 210093 China Department of Astronomy Nanjing University Nanjing 210093 China

We make use of the images from the Sloan Digital Sky Survey Stripe 82（Stripe 82） to present an analysis of r band surface brightness profiles and radial color gradients（g-r,u-r） in our sample of 111 nearby early-type galaxies（ETGs） .Thanks to the Stripe 82 images,each of which is co-added from about 50 single frames,we are able to pay special attention to the low-surface-brightness areas（LSB areas） of the *** LSB areas affect the Sérsic fittings and concentration indices by making both of the indices less than the typical values for *** the Sérsic fits to all the surface brightness profiles,we found some Sérsic indices that range from 1.5 to 2.5,much smaller than those of typical de Vaucouleur profiles and relatively close to those of exponential disks,and some others much larger than four but still with accurate *** galaxies cannot be fitted with a single Sérsic profile,but once we try double Sérsic profiles,the fittings are improved：one with a profile relatively close to the de Vaucouleur law in the inner area and a profile relatively close to an exponential law in the LSB area,the other with a nice fitting in the inner area but still having a failed fitting in the outer *** 60%of the sample has negative color gradients（red-core） within 1.5Re,much more than the approximately 10%positive ones（blue-core） within the same ***,taking into account the LSB areas,we find that the color gradients are not necessarily monotonic：about one third of the red-core（or blue-core） galaxies have positive（or negative） color gradients in the outer areas. So LSB areas not only make ETGs’Sérsic profiles deviate from de Vaucouleur ones and shift to the disk end,but also reveal that quite a number of ETGs have opposite color gradients in inner and outer *** outcomes remind us of the necessity of double-Sérsic *** LSB phenomena may be interpreted by mergers and thus have different metallicity in the outer *** parameters ar

关键词： galaxies:early-type galaxies—galaxies:surface brightness profiles and color gradients—techniques:photometric

Stellar ages and metallicities of nearby elliptical galaxies

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2009年第11期9卷 1215-1229页

作者： Bai-Tian Tang qiu-sheng gu Song Huang Department of Astronomy Nanjing University Nanjing 210093 China

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

关键词： galaxies elliptical and lenticular, cD -- galaxies statistics -- galaxies stellar content

Circumnuclear Star Forming Activity in NGC 3982

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2008年第5期8卷 555-565页

作者： Shui-Nai Zhang qiu-sheng gu Yi-Peng Wang Department of Astronomy Nanjing University Nanjing 210093 China

We present a study of the nearby Seyfert galaxy NGC 3982 using optical, infrared and X-ray data acquired by SDSS, Spitzer and Chandra. Our main results are as follows：（1） A simple stellar population synthesis on the nuclear and circumnuclear SDSS spectra gives unambiguous evidence of young stellar components in both the nuclear and circumnuclear regions. （2） The Spitzer Infrared Spectrograph （IRS） spectrum of the central region （∽ 3＂） shows a power-law continuum, a silicate emission feature at 9.7μm, and significant PAH emission features at 7.7, 8.6, 11.3 and 12.7 pro, suggesting the coexistence of AGN and starburst activities in the central region of NGC 3982. （3） We estimate the star formation rate （SFR） of the circumnuclear （∽ 5＂ - 20＂） region from the Hα luminosity to be SFRHα = 0.52 M⊙ yr^-1, which is consistent with the result from the Spitzer IRAC 8 μm luminosity, SFR8.0μm = 0.57 M⊙ yr^-1. （4） We measure the spectral energy distribution for the active nucleus of NGC 3982 from radio to X-ray, and obtain a bolometric luminosity of Lbol 4.5 × 10^42 erg s-1, corresponding to an Eddington ratio （Lbol//LEdd） of 0.014 The HST image of NGC 3982 shows a nuclear mini-spiral between the circumnuclear starforming region and the nucleus, which could be the channel through which gas is transported to the supermassive black hole from the circumnuclear star-forming region.

关键词： galaxies Seyfert - galaxies starburst - galaxies nuclei - galaxies individual (NGC 3982)

Conditions for galaxy quenching at 0.5

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2020年第8期20卷 143-156页

作者： Xue Ge Feng-Shan Liu qiu-sheng gu Emanuele Contini Yi-Zhou gu School of Astronomy and Space Science Nanjing UniversityNanjing 210093China Key Laboratory of Modern Astronomy and Astrophysics Nanjing UniversityNanjing 210093China Collaborative Innovation Center of Modern Astronomy and Space Exploration Nanjing 210093China Key Laboratory of Space Astronomy and Technology National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Department of Physics and Institute of Theoretical Physics Nanjing Normal UniversityNanjing 210023China

We investigate two classes of conditions for galaxy quenching at 0.510^10 M⊙)have much higher stellar mass surface densities within the central 1 kpc(∑1)and smaller sizes than star-forming galaxies in the same stellar mass *** addition,the quiescent fractions significantly increase with the increase of∑1 regardless of whether galaxies are centrals or *** contrast,we find that the overall lower-mass quiescent galaxies(M*<~10^10M⊙)have slightly higher E1 and comparable sizes compared to starforming galaxies of the same mass and at the same *** z<1.5,satellites have higher halo masses and larger quiescent fractions than those of centrals at a given∑1(stellar mass).Our findings indicate that the significant growth of the galaxy cores is closely related to the quenching of massive galaxies since z^2.5,while the environmental effect plays an important role in the quenching of low-mass galaxies at z≤1.5.

关键词： galaxies:evolution galaxies:formation galaxies:high-redshift

Variation of physical properties across the green valley for local galaxies

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2019年第2期19卷 133-142页

作者： Xue Ge qiu-sheng gu Yong-Yun Chen Nan Ding School of Astronomy and Space Science Nanjing University Key Laboratory of Modern Astronomy and Astrophysics Nanjing University Collaborative Innovation Center of Modern Astronomy and Space Exploration

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 *** 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.

关键词： galaxies:structure galaxies:star formation galaxies:bulges

A Study of the Star-forming Dwarf Galaxy NGC 855 with Spitzer

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2007年第6期7卷 764-770页

作者： sheng-Peng Li qiu-sheng gu Ying-He Zhao Jia-sheng Huang Xin-Lian Luo Department of Astronomy Nanjing University Nanjing 210093 Harvard-Smithsonian Center for Astrophysics 60 Garden Street Cambridge MA 02138

We present a study of the dwarf elliptical galaxy NGC 855 using the narrow-band Hα and Spitzer data. Both the Hα and Spitzer IRAC images confirm star-forming activity in the center of NGC 855. We obtained a star formation rate （SFR） of 0.022 and 0.025Mo yr^-1, respectively, from the Spitzer IRAC 8.0 μm and MIPS 24 #m emission data. The HI observation suggests that the star-forming activity might be triggered by a minor merger. We also find that there is a distinct IR emission region in 5.8 and 8.0 μm bands, located at about 10＂ away from the nucleus of NGC 855. Given the strong 8.0 μm but faint Hα emission, we expect that it is a heavily obscured star-forming region, which needs to be confirmed by further optical spectroscopic observations.

关键词： galaxies elliptical -- galaxies individual NGC 855

Quasar SDSS J142507.32+323137.4: dual AGNs?

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2011年第4期11卷 411-418页

作者： Zhi-Xin Peng Yan-Mei Chen qiu-sheng gu Chen Hu Department of Astronomy Nanjing University Nanjing 210093 China Key Laboratory of Modem Astronomy and Astrophysics （Nanjing University） Ministry of Education Nanjing 210093 China Key Laboratory for Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China

We analyze the optical spectrum of type 1 QSO SDSS J1425＋3231. This object is interesting since its narrow emission lines, such as [O Ⅲ]λλ4959, 5007, are double-peaked, and the line structure can be modeled well by three Gaussian components： two components for the two peaks （we refer to the peaks at low/high redshift as ＂the blue/red component＂） and another one for the line wing which has the same line center as that of the blue component, but is- 3 times broader. The separation between the blue and red components is -500km s-1 with the blue component being -2 times broader than the red one. The Hβ emission can be separated into four components： two for the double-peaked narrow line and two for the broad line which comes from the broad line regions. The black hole mass estimated from the broad Hβ emission line using the typical reverberation mapping relation is 0.85 × 108 M⊙, which is consistent with that derived from parameters of [O Ⅲ]λ 5007 of the blue component. We suggest that this QSO might be a dual AGN system; the broad Hβ emission line is mainly contributed by the primary black hole （traced by the blue component） while the broad Hβ component of the secondary black hole （traced by the red component） is hard to be separated out considering a resolution of - 2 000 for SDSS spectra or it may be totally obscured by the dusty torus.

关键词： galaxie active -- galaxies individual (SDSS J142507.32+323137.4)-- quasars emission lines