盘状星系的颜色星等关系

在Sloan数字巡天计划第二批释放的数据中选择了15257个面向的盘状星系,统计研究它们的颜色星等关系．结果表明3个颜色g-r、r-i、r-z均与r波段的绝对星等有紧密的相关关系,即:越亮的星系,颜色越红,而且色指数弥散越小．并且简单讨论了观测到的颜色星等关系对盘状星系的恒星形成历史的约束．     

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.     

晚型旋涡星系盘的颜色梯度

从Sloan巡天第二批释放的数据(Sloan Digital Sky Survey, Data Release Two)中选择了395个在r波段亮于15 mag的晚型旋涡星系作为样本，对样本星系的表面亮度轮廓进行一维两成分(核球与盘)拟合，并着重讨论了盘的颜色梯度，分别用Δc／ΔR和Δc／Δlg R两种形式来拟合。结果表明，对于波长相距较大的颜色r-z和g-z，颜色梯度更符合Δc／ΔR为常数的线性变化形式，而g-r则符合Δc／ΔlgR为线性的情形；用Δc／ΔlgR拟合的梯度值分别为Δ(9-r)／ΔlgR=-0.152±0.010，Δ(r-z)／ΔlgR=-0.377±0.019，Δ(g-z)／ΔlgR=-0.590±0.026，均与前人的研究结果一致。     

旋涡星系颜色梯度的研究进展

旋涡星系的颜色梯度反映了其星族构成沿径向的分布,包含了星系恒星形成历史的信息.因此,对旋涡星系颜色梯度的研究有助于理解星系的形成和演化过程.大部分旋涡星系存在负的颜色梯度,其主要原因是旋涡星系存在星族梯度.颜色梯度与星系的面亮度之间存在内禀的相关,表明质量面密度在星系的形成和演化过程中具有重要作用.     

早型旋涡星系M81 (NGC 3031)的形态学解构研究

利用星系解构软件GALFIT通过面亮度轮廓拟合对近邻早型旋涡星系M81 (NGC 3031)进行形态学解构,旨在探究M81星系的结构组成并对其进行形态学量化.通过6种解构模式,对M81进行了不同复杂程度的结构分解,其中最复杂的解构模式包含核球、盘、外旋臂、内旋臂、星系核5个子结构.研究结果显示, M81有一个Sérsic指数约为5.0的经典核球,其形态和光度在不同解构模式中均保持稳定; M81星系盘的Sérsic指数约为1.2,但它的形态参数和光度与是否分解内旋臂相关.不同子结构的组合对作为混合体的星系整体的形态有不可忽视的影响.星系解构的结果提供了不同解构模式适用性的建议:其中核球+盘+星系核的三成分解构适用于大样本星系的核-盘研究;而考虑旋臂的复杂解构则适合于对星系子结构的精确测量,如小样本(或个源)研究.基于Spitzer-The Infrared Array Camera (IRAC) 4.5μm的单波段图像的形态学解构研究是后续一系列研究的开始,在此基础上未来将会对M81进行多波段解构,同时研究不同子结构的光谱能量分布和星族性质,并推断M81各子结构的形成历史和演化过程.     

同等质量下盘状星系的颜色-尺度关系

挑选Sloan数字巡天第7次释放数据(SDSS DR7)的主星系样本中近邻的、面向的盘状星系作为星系样本,统计研究了在恒星总质量相等的情况下盘状星系的颜色和尺度之间的相关性,并对相关性的真实性进行了检验.发现对于同等质量的盘状星系,u-r颜色与尺度相关性很弱,而g-r、r-i、r-z颜色与尺度负相关,即星系的尺度越大,颜色越蓝.该结果意味着盘状星系的质量分布对其恒星形成历史影响很大,物质分布越延展的星系,其演化越慢.     

The Color-Magnitude Relations of Late-type Spiral Galaxies and Their Disks

The 395 late-type spiral galaxies brighter than 15^m in r-band are selected from the Data Release 2 of Sloan Digital Sky Survey and the colormagnitude relations of these galaxies and their disks are investigated. It is found that the colors g − r, r − z and g − z of these galaxies and their disks are strongly correlated with the r-band absolute magnitudes, i.e., the more luminous galaxies (or disks) have the redder colors than the less luminous galaxies (or disks). And the correlation of galaxies is stronger than that of their disks.     

晚型星系金属丰度与自转速度的关系

星系物质化学组成的研究不仅对于理解有关星系形成和演化的各种物理过程具有重要意义，而且还可以对星系形成和演化的各种理论模型提供重要的约束。随着观测技术及理论工作水平的不断提高，利用星系的大量观测资料来系统地研究星系化学组成与星系宏观性质之间的关系将成为可能。星系金属丰度与光度之间的强相关性以及晚型星系金属丰度与自转速度的关系即是其中最有意义的内容之一。全面回顾了星系金属丰度与星系宏观观测性质间关系的研究历史，重点评述了晚型星系金属丰度与自转速度关系的最新研究进展，详细讨论了目前对此类关系的物理解释及其对星系形成和演化模型的影响。     

The CO to H2 Conversion Factor in Normal Late-Type Galaxies

The molecular gas mass in nearby galaxies is generally estimated using ¹²CO(1-0) line intensities and assuming the X conversion factor between I(CO) and N(H₂) measured in the solar neighborhood. It is however known that this X conversion factor is not universal since it changes with metallicity, cosmic ray density and UV radiation field. Far-IR data in the spectral range 100-1000 μm can be used to estimate the molecular gas content of late-type galaxies in an independent way of CO line measurements once a metallicity-dependent dust to gas ratio is assumed, allowing a direct estimate of X. This exercise is presented here for a large sample of galaxies with available multifrequency data. X spans from ∼ 10²⁰ mol cm^-2 (K km s^-1)^-1 in giant spirals to ∼ 10²¹ mol cm^-2 (K km s^-1)^-1 in dwarf irregulars. This revised version was published online in September 2006 with corrections to the Cover Date.     

[CII] Emission and Star Formation in Late-Type Galaxies

A linear correlation between the ratio of the[CII( $^{\text{2}}$ P A linear correlation between the ratio of the[CII( P → P )] line intensity to the [ CO(J:1 →0)] line emission, I /I and the equivalent width (EW) is found, over the range 2–71 ? in EW, for a sample of 21late-Type= galaxies. The latter is comprised of an optically selected sample of 12 normal Virgo Cluster spiral galaxies with [CII] detections obtained by us with ISOLWS, plus nine late-Type= galaxies with higher star formation rates (SFRs), for which [CII] data and, especially, EW data are available in the literature. As a result we infer I /I to be a reliable tracer of the current mass-normalized global SFR for non-starburst spiral galaxies. Moreover, the ratio of the [CII] line to the total far-infrared (FIR) continuum intensity, I /I , is found to decrease from ∼0.5% to ∼0.1% with decreasing SFR which we propose is due to a `[CII]-quiet' component of I from dust heated by the general interstellar radiation field (ISRF). The more `quiescent' galaxies in the sample have values of I /I different from those observed in `compact' Galactic interstellar regions. Their [CII]-emission is interpreted to be dominated by diffuse regions of the interstellar medium (ISM). For normal `star-forming' galaxies the diffuse component of the [CII] emission is estimated to account for at least 50% of the total. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Number-diameter Relation of Galaxies

Contrary to the number-magnitude relation, the number-angular diameter relation is influenced by the luminosity function. The number-diameter counts by DODD et al. (1975) are in agreement with the normal luminosity function and a homogeneous space distribution without a local density excess. Almost all the faint small (<18 arcsec) galaxies may be first-ranked cluster members.     

Spiral-Vortex Structure in the Gaseous Disks of Galaxies

General ideas, as well as experimental and theoretical efforts concerning the prediction and discovery of new structures in the disks of spiral galaxies – giant anticyclones - are reviewed. A crucial point is the development of a new method to restore the full vector velocity field of the galactic gas from the line-of-sight velocity field. This method can be used to get self-consistent solutions for the following problems: 1) determination of non-circular velocities associated with spiral-vortex structure; 2) determination of fundamental parameters of this structure: pattern speed, corotation radius, location of giant anticyclones; 3) refinement of galactic rotation curves taking into account regular non-circular motion in the spiral density wave, which makes it possible to build more accurate models of the mass distribution in the galaxy; 4) refinement of parameters of the rotating gaseous disk: inclination angle, center of rotation and position angle of the major dynamical axis, systematic velocity. The method is demonstrated using the restoration of the velocity field of the galaxy NGC 157 as an example. Results for this and some other spiral galaxies suggest that giant anticyclones are a universal property of galaxies with grand design structure.     

The Halo Concentration and Mass Relation Traced by Satellite Galaxies

We study the relation between halo concentration and mass(c-M relation) using galaxy catalogs of the Seventh and Eighth Data Releases of the Sloan Digital Sky Survey(SDSS DR7 and DR8). Assuming that the satellite galaxies follow the distribution of dark matter, we derive the halo concentration by fitting the satellite radial profile with a Nararro Frank and White(NFW) format. The derived c-M relation covers a wide halo mass range from10^11.6to 10^14.1M_⊙. We confirm the anti-...     

Correlations Between Color Gradients and Structural Parameters of Disks in Late-type Spiral Galaxies

From the second group of the data released by the Sloan numerical patrol survey (SDSS DR2), 395 face-on late-type spiral galaxies brighter than 15-th magnitude in the waveband r are selected as the sample. The relations between the color gradients and structural parameters of disks are studied. The results indicate the following: (1) The color gradient is independent of the absolute magnitude (mass) of the disk. (2) The color gradient of disk is concerned with the size of disk. The larger the disk, the steeper the color gradient. (3) The color gradient of disk is concerned with the color of disk. The bluer the disk color, the steeper the gradient. (4) The color gradient of disk is related with the surface brightness of disk. The brighter the disk, the steeper the color gradient. Moreover, the historical constraint formed by the relations between the color gradients of disks and various structural parameters is briefly discussed.