PGC54等三维旋涡星系盘等效厚度的测定

利用改进的Peng的方法,对Sloan Digital Sky Survey(SDSS)最新发布的旋涡星系的图像进行了处理和旋臂拟合,得到了73个旋涡星系的等效厚度和旋臂的切向角,这些物理量对以后星系性质的进一步研究非常重要.     

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.     

NGC864等10个旋涡星系盘的等值高度测定

使用北京天台兴隆观测站６０ｃｍ望远镜对１０个旋涡星系进行ＣＣＤ照相观测,通过对图像的处理及利用彭秋和提出的方法,得到了这１０星系盘的等值高度和用对数螺线拟合旋臂时对数螺线的切向角等一些重要参数。     

旋涡星系随uUbble序列的一些统计性质

对发表在A＆Ap Supplement Series上的365个旋涡星系的一些参数(如表示旋臂缠卷松紧程度的参数A、切向角μ、盘的扁度H／D25以及厚度等)随Hubble序列变化的关系进行了统计研究．首次得到这些参量的平均值;并且从统计结果可以明显地看到Hubble对旋涡星系的分类只是一种定性的、只有统计意义上的分类;另外,从我们的统计结果看,密度波理论的色散关系对大多数旋涡星系是成立的,即大多数旋涡星系的旋臂满足紧卷螺旋波的要求．     

旋涡星系的厚度的估算

本文利用文[1]中所求得的扰动引力势的严格解,当此解由无旋臂区向有旋臂区连续过渡时,在解中出现一非波动项,对此项作出估计,可得出厚度(H=2/α)与开始形成旋臂处的半径的r_0关系:αr_0=7(α为星系半厚度的倒数).我们由[2]选出了50颗旋涡星系,并测定了它们的r_0,由此定出了星系盘的平均厚度.     

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.     

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.     

旋涡星系中对任意旋臂倾角一致有效的密度-引力势渐近关系

本文给出对于臂数m≥2的旋涡星系(正常旋涡星系或棒旋星系),对任意旋臂倾角(0≤|β|≤π/2)一致有效的扰动密度-扰动引力势渐近关系。在|β|≤1的特殊情形,它回到紧卷波的各种已知渐近关系;在|β|不小的情形,这一新结果适用于讨论构成棒旋星系的“开展模式”(open mode)。     

星系盘中的磁重平衡:星系贮留原初磁场的观测证据

邻近旋涡星系中观测到的磁场被理论学家解释为发电机作用的结果.而我们发现,在邻近的星系中,磁场的强度与中性氢的柱密度紧密相关.星系盘中的磁场处于磁重平衡状态.这一结果与发电机放大机制相悖,从而支持星系磁场是原初起源的假说.     

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.     

A Chandra study of the massive,distant galaxy cluster SDSS J0150–1005

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.     

Comparison of some properties of star forming galaxies and active galactic nuclei between two BOSS galaxy samples from SDSS DR9

Using the LOWZ and CMASS samples of the ninth data release(DR9)from the SDSS-III Baryon Oscillation Spectroscopic Survey(BOSS), I investigate properties of star forming galaxies and active galactic nuclei(AGNs). The CMASS sample seriously suffers from the radial selection effect, even within the redshift0.44 ≤ z ≤ 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same.     

Relations between stellar mass and electron temperature-based metallicity for star-forming galaxies in a wide mass range

We select 947 star-forming galaxies from SDSS-DR7 with [O III]λ4363emission lines detected at a signal-to-noise ratio larger than 5σ. Their electron temperatures and direct oxygen abundances are then determined. We compare the results from different methods. t2, the electron temperature in the low ionization region, estimated from t3, that in the high ionization region, is compared using three analysis relations between t2- t3. These show obvious differences, which result in some different ionic oxygen abundances. The results of t3, t2, O++/H+and O+/H+derived by using methods from IRAF and literature are also compared. The ionic abundances O++/H+are higher than O+/H+for most cases. The different oxygen abundances derived from Teand the strong-line ratios show a clear discrepancy, which is more obvious following increasing stellar mass and strong-line ratio R23. The sample of galaxies from SDSS with detected [O III]λ4363 have lower metallicites and higher star formation rates, so they may not be typical representatives of the whole population of galaxies. Adopting data objects from Andrews Martini, Liang et al. and Lee et al. data, we derive new relations of stellar mass and metallicity for star-forming galaxies in a much wider stellar mass range: from 106 M to 1011 M.     

The star formation history of redshift z ~ 2 galaxies： the role of the infrared prior

We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.     

New estimates of scale heights and spiral structures for non-edge-on spiral galaxies

On the basis of Poisson＇s equation for the logarithmic perturbation of matter density, we provide improved estimates of scale heights and spiral structures for non-edge-on spiral galaxies by subtracting the surface brightness distributions from observed images. As examples, the non-edge-on spiral galaxies PGC 24996, which is face-on, and M31, which is inclined, are studied. The scale height, pitch angle and inclination angle of M31, our nearest neighbor, that are presented in this work, agree well with previous research.