面向类旋涡星系盘有效厚度的获取及图像处理方法

面向类(face-on)旋涡星系盘的有效厚度或标高不能通过表面亮度测光的方式测量.为了获得面向类旋涡星系盘的厚度参数,将基于三维星系盘引力势Poisson方程在等角对数螺旋型物质密度扰动情形下的解,运用一种解析法对面向类旋涡星系盘的标高进行测算.为了去除星系核球的光污染而获得旋臂最内点位置(r0)的重要参数,使用了在星系观测图像中扣除双成份(盘+核球)测光模型的图像处理方法.通过对旋涡星系相关结构参数的拟合测量,各得到了一个普通旋涡星系(S)与棒旋星系(SB)的有效厚度与相关参数,并给出了它们的球盘比(rb/rd)和星系盘的标长与厚度之比(rd/H).采用这种在观测图像中扣除双成份测光模型的方法,将更容易看清旋臂结构的最内端,因而这里获得的禁区半径r0的数值往往比从原星系图像上直接测量的数值要小,获得的星系盘有效厚度将更薄.     

晚型旋涡星系及其盘的颜色星等关系

从Sloan数字巡天(Sloan Digital Sky Survey)第二批释放的数据(Data ReleaseTwo,简称DR2)中,选择了395个在r波段亮于15等的晚型旋涡星系作为样本,研究了这些星系及其盘的颜色星等关系.结果表明晚型旋涡星系及其盘的三个颜色g-r,r-z和g-z均与r波段的绝对星等有紧密的相关关系,越亮的星系(或盘),颜色越红,而且星系的相关性比盘的更强.     

X射线选射电噪活动星系核的多波段性质(英文)

基于被ROSAT全天区巡天观测和射电 4.85GHz巡天观测同时探测到的活动星系核的大样本 ,研究了X射线选的射电噪活动星系核的多波段性质 .通过分析该样本中的活动星系核的宽波段能量分布 ,确认了来自射电、光学和X射线波段的辐射光度之间的显著相关性 .这种相关性对于类星体、赛弗特、蝎虎座天体和射电星系是有区别的 .同时 ,探讨了从光学到X射线波段之间的谱指数与红移以及 50 0 0 和 4.85GHz处的单色光度的相关性     

卫星星系的数目与中央星系性质关系的研究

卫星星系是研究星系形成的有力探针.近期的研究指出,中央星系是椭圆星系时,其卫星星系数目比旋涡星系多.为了探究这种差异,采用了新一代流体动力学模型(The Next Generation Illustris Simulations,简称TNG模拟)中TNG300-1的数据,选择了恒星质量范围为1010M⊙·h-1Mc1012M⊙·h-1的中央星系,同时根据星系的核球质量与星系的恒星质量的比值(B/T)将这个范围的中央星系划分为旋涡星系和椭圆星系.使用统计学的方法进行分析后发现:当控制暗晕质量分布,使得不同形态的中央星系所处的暗晕的质量分布完全相同时,卫星星系分布存在新的差异,即旋涡星系的卫星星系数目更多.这一结论和观测结果相反,产生这一差异的主要原因是:旋涡星系的卫星星系包含更多的冷气体,使得旋涡星系的卫星星系恒星形成效率更高.     

星系群HCG 95中的星系群内光观测研究

星系团/群内光(ICL (Intra-Cluster Light)/IGL (Intra-Group Light))可以用来研究星系群和星系团的动力学演化. Hickson致密星系群密度高并且速度弥散低,其致密的环境可以用来研究星系并合和相互作用星系的性质,是研究IGL理想场所之一.利用中国近地天体巡天望远镜(Chinese Near Object Survey Telescope,CNEOST)的观测,获得了星系群HCG 95的g波段和r波段深度成像数据.采用模型拟合方法来测量HCG 95星系群中的IGL光度,并计算了IGL的光度占星系群总光度的比例fIGL,在g和r波段的结果分别为3.55%±0.38%和3.78%±0.59%.此外,利用常规的表面亮度阈值截取方法,在g和r波段的结果分别为1.9%–10%和1.5%–10%,与前述结果一致.估算的IGL颜色(g-r=0.78±0.37)与星系群中的HCG 95A和HCG 95C星系的颜色(g-r=0.82–0.85)一致,属于年老星族,表明HCG 95星系群中的IGL可能来自HCG 95A和HCG 95C相互作用剥离出来的物质,也有...     

M31的观测与研究进展

介绍了本星系群中最大的旋涡星系M31(仙女星系)的基本观测性质。与银河系结构类似，M31的基本成分包括：核、核球、盘和晕。对以上各个成分的观测和研究进展分别作了综述，重点是盘的星族成分和恒星形成历史，以及球状星团的分布和晕的形成历史。同时与银河系的各种观测特征和形成机制作了详细的比较。     

晚型旋涡星系盘的颜色梯度与结构参数的相关关系

从Sloan数字巡天第2批释放的数据(SDSS DR2)中选择了395个在r波段亮于15等的面向晚型旋涡星系作为样本,研究了盘的颜色梯度与结构参数的关系.结果表明:盘的颜色梯度与盘的绝对星等(质量)无关;盘的颜色梯度与盘的尺度有关,越大的盘颜色梯度越陡;盘的颜色梯度与盘的颜色有关,越蓝的盘颜色梯度越陡;盘的颜色梯度与盘的表面亮度有关,越亮的盘颜色梯度越陡,并简单讨论了盘的颜色梯度与各结构参数的相关关系对晚型旋涡星系盘恒星形成历史的约束.     

河外H_2O超脉泽辐射

介绍了近年来河外Ｈ２Ｏ超脉泽的主要观测结果。Ｈ２Ｏ超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在 Ｓｅｒｆｅｒｔ ２星系或低电离核区。至今为止，已有２０个星系探测到Ｈ２Ｏ超脉泽。脉泽辐射的各向同性光度为１０～６０００Ｌ⊙。所有超脉泽星系显示出核的活动，显然，脉泽是由核活动所产生的射电和Ｘ射线光子或激波来抽运的。Ｈ２Ｏ超脉泽倾向存在于高倾斜度的星系，这使得沿视线上的分子柱密度增高，产生足够大的放大光深。最有可能产生Ｈ２Ｏ超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。     

EGS场中高红移极亮红外星系的形态与结构

通过利用CANDELS-EGS(Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey-Extended Groth Strip)场中HST WFC3(Hubble Space Telescope Wide Field Camera 3)F160W高分辨率的观测图像,研究了9个光谱红极亮红外星系的形态结构特征.发现这些星系的形态表现出多样性(从椭圆到多个亮核或弥散的结构),如:双核,气体桥,双不对称体,不规则或椭圆结构.为了定量地研究这些极亮红外星系的形态,测量了它们在静止光学波段的形态参数(基尼系数G和矩指数M20).与近邻极亮红外星系相比,高红移极亮红外星系的G偏小而M20偏大,表明这些星系的星族分布聚集度小且不对称性大.基于对样本中极亮红外星系2维面亮度轮廓的拟合,得到这些星系的有效半径分布在2.4 kpc到5.8 kpc之间,其平均值是(3.9±1.1)kpc.相比较于近邻相似质量的恒星形成星系来说,高红移极亮红外星系的平均大小要小1到2倍.在类似红移和红外光度条件下,得出的这些结果也与其它文献中给出的结论相一致.     

M31中天体的光谱观测与研究

仙女星系(M31)是距离地球最近的大型旋涡星系,与银河系结构相似且质量相当,对M31天体的光谱观测与研究有助于理解银河系以及一般星系的形成与演化历史。整理了自20世纪以来天文学家对M31中天体的相关光谱观测与研究成果,共涉及了M31中5 000余个发射线天体、2 000余个星团、6 000余颗恒星、1 000余颗新星以及核球和盘上的星族的光谱。恒星光谱观测由早期的以超巨星为主发展到近20年更大样本以及更多类型,其中红巨星被用于研究M31星系盘和晕的性质及子结构。发射线天体通常被应用于M31质量测定、运动学分析和恒星演化的研究。M31星团的研究集中于金属丰度和运动学性质,以及利用视向速度测定M31位力质量。对M31中心星族的研究主要集中于核区的星族组成和运动学分析,其中运动学研究结果更支持核区的偏心盘模型。最后,介绍了郭守敬望远镜对M31天体的光谱观测与相关科学研究。     

Near-infrared bulge–disc correlations of lenticular galaxies

We consider the luminosity and environmental dependence of structural parameters of lenticular galaxies in the near-infrared K band. Using a 2D galaxy image decomposition technique, we extract bulge and disc structural parameters for a sample of 36 lenticular galaxies observed by us in the K band. By combining data from the literature for field and cluster lenticulars with our data, we study correlations between parameters that characterize the bulge and the disc as a function of luminosity and environment. We find that scaling relations such as the Kormendy relation, photometric plane and other correlations involving bulge and disc parameters show a luminosity dependence. This dependence can be explained in terms of galaxy formation models in which faint lenticulars  ( M _T > −24.5)  formed via secular formation processes that likely formed the pseudo-bulges of late-type disc galaxies, while brighter lenticulars  ( M _T < −24.5)  formed through a different formation mechanism most likely involving major mergers. On probing variations in lenticular properties as a function of environment, we find that faint cluster lenticulars show systematic differences with respect to faint field lenticulars. These differences support the idea that the bulge and disc components fade after the galaxy falls into a cluster, while simultaneously undergoing a transformation from spiral to lenticular morphologies.     

Triaxial stellar systems following the r1/n luminosity law: an analytical mass–density expression, gravitational torques and the bulge/disc interplay

We have investigated the structural and dynamical properties of triaxial stellar systems whose surface brightness profiles follow the   r ^{1/ n}   luminosity law – extending the analysis by Ciotti, who explored the properties of spherical   r ^{1/ n}   systems. A new analytical expression that accurately reproduces the spatial (i.e., deprojected) luminosity density profiles (error less than 0.1 per cent) is presented for detailed modelling of the Sérsic family of luminosity profiles. We evaluate both the symmetric and the non-axisymmetric components of the gravitational potential and force, and compute the torques as a function of position. For a given triaxiality, stellar systems with smaller values of n have a greater non-axisymmetric gravitational field component . We also explore the strength of the non-axisymmetric forces produced by bulges with differing n and triaxiality on systems having a range of bulge-to-disc ratios. The increasing disc-to-bulge ratio with increasing galaxy type (decreasing n ) is found to greatly reduce the amplitude of the non-axisymmetric terms, and therefore reduce the possibility that triaxial bulges in late-type systems may be the mechanism or perturbation for non-symmetric structures in the disc.
Using seeing-convolved   r ^{1/ n}   -bulge plus exponential-disc fits to the K -band data from a sample of 80 nearby disc galaxies, we probe the relations between galaxy type, Sérsic index n and the bulge-to-disc luminosity ratio. These relations are shown to be primarily a consequence of the relation between n and the total bulge luminosity. In the K band, the trend of decreasing bulge-to-disc luminosity ratio along the spiral Hubble sequence is predominantly, though not entirely, a consequence of the change in the total bulge luminosity; the trend between the total disc luminosity and Hubble type is much weaker.     

Testing model predictions of the cold dark matter cosmology for the sizes, colours, morphologies and luminosities of galaxies with the SDSS

The huge size and uniformity of the Sloan Digital Sky Survey (SDSS) make possible an exacting test of current models of galaxy formation. We compare the predictions of the galform semi-analytical galaxy formation model for the luminosities, morphologies, colours and scalelengths of local galaxies. galform models the luminosity and size of the disc and bulge components of a galaxy, and so we can compute quantities which can be compared directly with SDSS observations, such as the Petrosian magnitude and the Sérsic index. We test the predictions of two published models set in the cold dark matter cosmology: the Baugh et al. model, which assumes a top-heavy initial mass function (IMF) in starbursts and superwind feedback, and the Bower et al. model, which uses active galactic nucleus feedback and a standard IMF. The Bower et al. model better reproduces the overall shape of the luminosity function, the morphology–luminosity relation and the colour bimodality observed in the SDSS data, but gives a poor match to the size–luminosity relation. The Baugh et al. model successfully predicts the size–luminosity relation for late-type galaxies. Both models fail to reproduce the sizes of bright early-type galaxies. These problems highlight the need to understand better both the role of feedback processes in determining galaxy sizes, in particular the treatment of the angular momentum of gas reheated by supernovae, and the sizes of the stellar spheroids formed by galaxy mergers and disc instabilities.     

Bulge–disc decompositions and structural bimodality of Ursa Major cluster spiral galaxies

We present bulge and disc (B/D) decompositions of existing   K '  surface brightness profiles for 65 Ursa Major (UMa) cluster spiral galaxies. This improves upon the disc-only fits of Tully et al. The 1996 disc fits were used by Tully & Verheijen for their discovery of the bimodality of structural parameters in the UMa cluster galaxies. It is shown that our new one-dimensional B/D decompositions yield disc structural parameters that differ only slightly from the basic fits of Tully et al. and evidence for structural bimodality of UMa galaxies is maintained. Our B/D software for the decomposition of one-dimensional surface brightness profiles of galaxies uses a non-linear minimization scheme to recover the best-fitting Sérsic bulge and the exponential disc while accounting for the possible presence of a compact nucleus and spiral arms and for the effects of seeing and disc truncations. In agreement with Tully & Verheijen, we find that the distribution of near-infrared disc central surface brightnesses is bimodal with an F-test confidence of 80 per cent. There is also strong evidence for a local minimum in the luminosity function at     . A connection between the brightness bimodality and a dynamical bimodality, based on new H  i linewidths, is identified. The B/D parameters are presented in Table 1 .  

  Table 1.  B/D parameters.     

15.

Morphology and Structure of High-redshift Massive Galaxies in the CANDELS Fields     

Fang Guan-wen  Lin Ze-sen  Kong Xu 《Chinese Astronomy and Astrophysics》2018,42(1):20-29

Using the multi-band photometric data of all five CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) fields and the near-infrared (F125W and F160W) high-resolution images of HST WFC3 (Hubble Space Telescope Wide Field Camera 3), a quantitative study of morphology and structure of mass-selected galaxies is presented. The sample includes 8002 galaxies with a redshift 1 < z < 3 and stellar mass M_*> 10¹⁰M_⊙. Based on the Convolutional Neural Network (ConvNet) criteria, we classify the sample galaxies into SPHeroids (SPH), Early-Type Disks (ETD), Late-Type Disks (LTD), and IRRegulars (IRR) in different redshift bins. The findings indicate that the galaxy morphology and structure evolve with redshift up to z ～ 3, from irregular galaxies in the high-redshift universe to the formation of the Hubble sequence dominated by disks and spheroids. For the same redshift interval, the median values of effective radii (r_e) of different morphological types are in a descending order: IRR, LTD, ETD, and SPH. But for the Sérsic index (n), the order is reversed (SPH, ETD, LTD, and IRR). In the meantime, the evolution of galaxy size (r_e) with the redshift is explored for the galaxies of different morphological types, and it is confirmed that their size will enlarge with time. However, such a phenomenon is not found in the relations between the redshift (1 < z < 3) and the mean axis ratio (b/a), as well as the Sérsic index (n).     

16.

Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model     

Zhi-Jian Luo Cheng-Gang Shu 《中国天文和天体物理学报》2007,7(4):590-594

According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.     

17.

Elliptical galaxies from mergers of discs     

Antonio César González-García  Marc Balcells 《Monthly notices of the Royal Astronomical Society》2005,357(2):753-772

We analyse N -body galaxy merger experiments involving disc galaxies. Mergers of disc–bulge–halo models are compared to those of bulgeless, disc–halo models to quantify the effects of the central bulge on merger dynamics and the structure of the remnant. Our models explore galaxy mass ratios 1:1 through 3:1, and use higher bulge mass fractions than previous studies. A full comparison of the structural and dynamical properties with our observations is carried out. The presence of central bulges results in longer tidal tails, oblate final intrinsic shapes, surface brightness profiles with a higher Sérsic index, steeper rotation curves and oblate-rotator internal dynamics. Mergers of bulgeless galaxies do not generate long-lasting tidal tails, and their strong triaxiality seems inconsistent with observations; these remnants show shells, which we do not find in models including central bulges. Giant ellipticals with boxy isophotes and anisotropic dynamics cannot be produced by the mergers modelled here; they could be the result of mergers between lower luminosity ellipticals, themselves plausibly formed in disc-disc mergers.     

18.

Edge‐on disk galaxies in the SDSS DR6: Fractions of bulgeless and other disk galaxies     

S.J. Kautsch 《Astronomische Nachrichten》2009,330(1):100-106

The aim of this study is to determine the fractions of different spiral galaxy types, especially bulgeless disks, from a complete and homogeneous sample of 15 127 edge‐on disk galaxies extracted from the sixth data release from the Sloan Digital Sky Survey. The sample is divided in broad morphological classes and sub types consisting of galaxies with bulges, intermediate types and galaxies which appear bulgeless. A small fraction of disky irregulars is also detected. The morphological separation is based on automated classification criteria which resemble the bulge sizes and the flatness of the disks. Each of these broad classes contains about 1/3 of the total sample. Using strict criteria for selecting pure bulgeless galaxies leads to a fraction of 15% of simple disk galaxies. We compare this fraction to other galaxy catalogs and find an excellent agreement of the observed frequency of bulgeless galaxies. Although the fraction of simple disk galaxies in this study does not represent a “cosmic” fraction of bulgeless galaxies, it shows that the relative abundance of pure disks is comparable to other studies and offers a profound value of the frequency of simple disks in the local Universe. This fraction of simple disks emphasizes the challenge for formation and evolution models of disk galaxies since these models are hard pressed to explain the observed frequency of these objects (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

19.

Formation of giant low surface brightness galaxies through disc instability     

Masafumi Noguchi 《Monthly notices of the Royal Astronomical Society》2001,328(2):353-358

It is shown that the giant low surface brightness galaxies (GLSBs), characterized by a large but diffuse disc component, can result from ordinary spiral galaxies through dynamical evolution. Numerical simulations indicate that the formation of a bar in a gravitationally unstable disc with high surface density induces non-circular motions and radial mixing of disc matter, leading to the flattening of the disc density profile. The resulting decrease in the disc central surface brightness is ∼1.5 magnitude, while the disc scalelength is nearly doubled, transforming a typical high surface brightness galaxy to a GSLB. This scenario seems promising especially for the GSLBs possessing a significant bulge, which are difficult to incorporate into the traditional Hubble sequence. Namely, because this disc transmutation can operate even if a moderate bulge component exists, the GSLBs with a bulge are argued to have resulted from the high surface brightness galaxies which had already possessed a bulge. The current picture naturally explains other observed characteristics of the GSLBs as well, including the propensity for having grand-design spiral arms and a bar, a high incidence of active nuclei, and galaxy environments.     

20.

Quantitative Study of Galaxy Morphology     

Dajana Džanović  R.M. Sharples  A.J. Benson  C.S. Frenk 《Astrophysics and Space Science》2003,285(1):73-77

We use an automatic algorithm to fit two-dimensional bulge and disk surface brightness profiles to a sample of 200 Sloan Digital Sky Survey Early Data Release (SDSS EDR) galaxies of known redshift and brighter than r=16. The bulge-to-disk (B/D) luminosity ratios can be combined with an estimate of the galaxy's local environment to address a number of key issues that are central to our understanding of galaxy formation:– How do B/D ratios depend upon galaxy luminosity?– What are the disk and spheroid luminosity functions for field galaxies?– How does the total luminosity in bulges and disks depend on environment?     

Morphology and Structure of High-redshift Massive Galaxies in the CANDELS Fields

Using the multi-band photometric data of all five CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) fields and the near-infrared (F125W and F160W) high-resolution images of HST WFC3 (Hubble Space Telescope Wide Field Camera 3), a quantitative study of morphology and structure of mass-selected galaxies is presented. The sample includes 8002 galaxies with a redshift 1 < z < 3 and stellar mass M_*> 10¹⁰M_⊙. Based on the Convolutional Neural Network (ConvNet) criteria, we classify the sample galaxies into SPHeroids (SPH), Early-Type Disks (ETD), Late-Type Disks (LTD), and IRRegulars (IRR) in different redshift bins. The findings indicate that the galaxy morphology and structure evolve with redshift up to z ～ 3, from irregular galaxies in the high-redshift universe to the formation of the Hubble sequence dominated by disks and spheroids. For the same redshift interval, the median values of effective radii (r_e) of different morphological types are in a descending order: IRR, LTD, ETD, and SPH. But for the Sérsic index (n), the order is reversed (SPH, ETD, LTD, and IRR). In the meantime, the evolution of galaxy size (r_e) with the redshift is explored for the galaxies of different morphological types, and it is confirmed that their size will enlarge with time. However, such a phenomenon is not found in the relations between the redshift (1 < z < 3) and the mean axis ratio (b/a), as well as the Sérsic index (n).     

Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model

According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.     

Elliptical galaxies from mergers of discs

We analyse N -body galaxy merger experiments involving disc galaxies. Mergers of disc–bulge–halo models are compared to those of bulgeless, disc–halo models to quantify the effects of the central bulge on merger dynamics and the structure of the remnant. Our models explore galaxy mass ratios 1:1 through 3:1, and use higher bulge mass fractions than previous studies. A full comparison of the structural and dynamical properties with our observations is carried out. The presence of central bulges results in longer tidal tails, oblate final intrinsic shapes, surface brightness profiles with a higher Sérsic index, steeper rotation curves and oblate-rotator internal dynamics. Mergers of bulgeless galaxies do not generate long-lasting tidal tails, and their strong triaxiality seems inconsistent with observations; these remnants show shells, which we do not find in models including central bulges. Giant ellipticals with boxy isophotes and anisotropic dynamics cannot be produced by the mergers modelled here; they could be the result of mergers between lower luminosity ellipticals, themselves plausibly formed in disc-disc mergers.     

Edge‐on disk galaxies in the SDSS DR6: Fractions of bulgeless and other disk galaxies

The aim of this study is to determine the fractions of different spiral galaxy types, especially bulgeless disks, from a complete and homogeneous sample of 15 127 edge‐on disk galaxies extracted from the sixth data release from the Sloan Digital Sky Survey. The sample is divided in broad morphological classes and sub types consisting of galaxies with bulges, intermediate types and galaxies which appear bulgeless. A small fraction of disky irregulars is also detected. The morphological separation is based on automated classification criteria which resemble the bulge sizes and the flatness of the disks. Each of these broad classes contains about 1/3 of the total sample. Using strict criteria for selecting pure bulgeless galaxies leads to a fraction of 15% of simple disk galaxies. We compare this fraction to other galaxy catalogs and find an excellent agreement of the observed frequency of bulgeless galaxies. Although the fraction of simple disk galaxies in this study does not represent a “cosmic” fraction of bulgeless galaxies, it shows that the relative abundance of pure disks is comparable to other studies and offers a profound value of the frequency of simple disks in the local Universe. This fraction of simple disks emphasizes the challenge for formation and evolution models of disk galaxies since these models are hard pressed to explain the observed frequency of these objects (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of giant low surface brightness galaxies through disc instability

It is shown that the giant low surface brightness galaxies (GLSBs), characterized by a large but diffuse disc component, can result from ordinary spiral galaxies through dynamical evolution. Numerical simulations indicate that the formation of a bar in a gravitationally unstable disc with high surface density induces non-circular motions and radial mixing of disc matter, leading to the flattening of the disc density profile. The resulting decrease in the disc central surface brightness is ∼1.5 magnitude, while the disc scalelength is nearly doubled, transforming a typical high surface brightness galaxy to a GSLB. This scenario seems promising especially for the GSLBs possessing a significant bulge, which are difficult to incorporate into the traditional Hubble sequence. Namely, because this disc transmutation can operate even if a moderate bulge component exists, the GSLBs with a bulge are argued to have resulted from the high surface brightness galaxies which had already possessed a bulge. The current picture naturally explains other observed characteristics of the GSLBs as well, including the propensity for having grand-design spiral arms and a bar, a high incidence of active nuclei, and galaxy environments.     

Quantitative Study of Galaxy Morphology

We use an automatic algorithm to fit two-dimensional bulge and disk surface brightness profiles to a sample of 200 Sloan Digital Sky Survey Early Data Release (SDSS EDR) galaxies of known redshift and brighter than r=16. The bulge-to-disk (B/D) luminosity ratios can be combined with an estimate of the galaxy's local environment to address a number of key issues that are central to our understanding of galaxy formation:– How do B/D ratios depend upon galaxy luminosity?– What are the disk and spheroid luminosity functions for field galaxies?– How does the total luminosity in bulges and disks depend on environment?