The faint stellar halos of galaxies contain key information about the oldest stars and the process of galaxy formation. A previous study of stacked SDSS images of disk galaxies has revealed a halo with an abnormally red r-i colour, seemingly inconsistent with our current understanding of stellar halos. Here, we investigate the statistical properties of the faint envelopes of low surface brightness disk galaxies to look for further support for a red excess. 1510 edge-on low surface brightness galaxies were selected from the SDSS Data Release 5, rescaled to the same apparent size, aligned and stacked. This procedure allows us to reach a surface brightness of mu_g ~ 31 mag arcsec^-2. After a careful assessment of instrumental light scattering effects, we derive median and average radial surface brightness and colour profiles in g,r and i. The sample is then divided into 3 subsamples according to g-r colour. All three samples exhibit a red colour excess in r-i in the thick disk/halo region. The halo colours of the full sample, g-r = 0.60+-0.15 and r-i = 0.80+-0.15, are found to be incompatible with the colours of any normal type of stellar population. The fact that no similar colour anomaly is seen at comparable surface brightness levels along the disk rules out a sky subtraction residual as the source of the extreme colours. A number of possible explanations for these abnormally red halos are discussed. We find that two different scenarios -- dust extinction of extragalactic background light and a stellar population with a very bottom-heavy initial mass function -- appear to be broadly consistent with our observations and with similar red excesses reported in the halos of other types of galaxies.
We built r-band surface brightness profiles by SDSS data for 16 Seyfert galaxies observed in Crimean Astrophysical Observatory. Obtained profiles can be used for finding more accurate lightcurves for these galaxies.
A number of recent estimates of the total luminosities of galaxies in the SDSS are significantly larger than those reported by the SDSS pipeline. This is because of a combination of three effects: one is simply a matter of defining the scale out to which one integrates the fit when defining the total luminosity, and amounts on average to < 0.1 mags even for the most luminous galaxies. The other two are less trivial and tend to be larger; they are due to differences in how the background sky is estimated and what model is fit to the surface brightness profile. We show that PyMorph sky estimates…
The Sloan Digital Sky Survey pipeline photometry underestimates the brightnesses of the most luminous galaxies. This is mainly because (i) the SDSS overestimates the sky background and (ii) single or two-component Sersic-based models better fit the surface brightness profile of galaxies, especially at high luminosities, than does the de Vaucouleurs model used by the SDSS pipeline. We use the PyMorph photometric reductions to isolate effect (ii) and show that it is the same in the full sample as in small group environments, and for satellites in the most massive clusters as well. None of these …
Colour gradients within SDSS DR7 galaxies: hints of recent evolution
星系的演化路径塑造了它的内部结构,特别是它的内部颜色变化。本文介绍了斯隆数字巡天(SDSS DR 7)第七次数据发布的星系内部颜色变化的研究。我们统计研究的内部颜色变化和全球星系的属性之间的联系,寻找最近的星系演化的线索。考虑到只有良好的光度和光谱测量的星系,我们定义了四个亮度阈值样本的红移范围内0.01<z<0.17,每个包含超过48000个星系。这些星系的颜色梯度是根据SDSS DR 7提供的表面亮度测量结果计算出来的。在其测定可能的系统性影响进行了分析。我们发现,平均而言,星系的核心比它们的外部更红。我们还发现,在晚型星系中更有可能发现陡峭的颜色梯度。这一结果适用于一系列基于形态和光谱特征的分类。事实上,我们的研究结果平均而言与陡峭的颜色梯度有关,因为星系中存在更多的年轻恒星。我们的研究结果还表明,核活动是在大质量星系中产生陡峭颜色梯度的边缘驱动因素。我们选择了相互作用的星系对,在投影半径上间隔为5角秒,红移差为100 km/s,发现它们呈现出比平均种群更陡峭的梯度,偏向更蓝的核心。我们的分析表明,颜色梯度可以用于选择最近遭受恒星形成(小)爆发的星系。
An enhancement in the number of galaxies as function of the redshift is visible on the SDSS Photometric Catalogue DR 12 at z=0.383. This over-density of galaxies is named the Great Wall. This variable number of galaxies as a function of the redshift can be explained in the framework of the luminosity function for galaxies. The differential of the luminosity distance in respect to the redshift is evaluated in the framework of the LCDM cosmology.
Constraint on the cosmological f(R) model from the multipole power spectrum of the SDSS luminous red galaxy sample and prospects for a future redshift survey
Because of the 3D nature of galaxies, an algorithm for constructing spatial density distribution models of galaxies on the basis of galaxy images has many advantages over surface density distribution approximations. We present a method for deriving spatial structure and overall parameters of galaxies from images and estimate its accuracy and derived parameter degeneracies on a sample of idealised model galaxies. The test galaxies consist of a disc-like component and a spheroidal component with varying proportions and properties. Both components are assumed to be axially symmetric and coplanar.…
We introduce a method for producing a galaxy sample unbiased by surface brightness and stellar mass, by selecting star-forming galaxies via the positions of core-collapse supernovae (CCSNe). Whilst matching $\sim$2400 supernovae from the SDSS-II Supernova Survey to their host galaxies using IAC Stripe 82 legacy coadded imaging, we find $\sim$150 previously unidentified low surface brightness galaxies (LSBGs). Using a sub-sample of $\sim$900 CCSNe, we infer CCSN-rate and star-formation rate densities as a function of galaxy stellar mass, and the star-forming galaxy stellar mass function. Result…
We have analyzed multi-band light curves of 328 intermediate redshift (0.05 <= z < 0.24) type Ia supernovae (SNe Ia) observed by the Sloan Digital Sky Survey-II Supernova Survey (SDSS-II SN Survey). The multi-band light curves were parameterized by using the Multi-band Stretch Method, which can simply parameterize light curve shapes and peak brightness without dust extinction models. We found that most of the SNe Ia which appeared in red host galaxies (u - r > 2.5) don't have a broad light curve width and the SNe Ia which appeared in blue host galaxies (u - r < 2.0) have a variety of light cur…
The large-scale environment of low surface brightness galaxies
导致低表面亮度星系(LSB)存在的确切形成场景和演化过程尚未完全了解。由于LSB的环境以前只在小尺度(低于2 Mpc)上进行过研究,因此在更大尺度上研究LSB星系附近的星系内容可以为我们对这类星系起源的理解增加很多。我们使用SDSS DR 4的光谱主星系样本来研究LSB星系的环境星系密度,并与高表面亮度星系(HSB)附近的星系密度进行比较。环境研究,分为两个红移箱,表明低质量和更大质量的LSB都拥有比HSB更低的星系密度的环境。在2和5百万秒差距之间的尺度上,集团和细丝的尺度上,LSB和HSB之间的星系密度的差异是显着的。为了量化这一点,我们首次推出了LSB-HSB抗偏置器件。得到的LSB-HSB抗偏参数值为10%~ 15%。从这些结果中,我们得出结论,LSB形成于初始宇宙的低密度区域,直到现在一直漂移到大尺度结构的细丝和壁的外部。此外,我们的研究结果以及实际的宇宙学模拟表明,LSB是由先天和后天的混合造成的。
We describe the algorithm used to select the Luminous Red Galaxy (LRG) sample for the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV) using photometric data from both the SDSS and the Wide-Field Infrared Survey Explorer (WISE). LRG targets are required to meet a set of color selection criteria and have z-band and i-band MODEL magnitudes z < 19.95 and 19.9 < i < 21.8, respectively. Our algorithm selects roughly 50 LRG targets per square degree, the great majority of which lie in the redshift range 0.6 < z < 1.0 (median redshift 0.71). We dem…
It has been shown, both in simulations and observationally, that the tidal field of a large galaxy can torque its satellites such that the major axis of satellite galaxies points towards their hosts. This so-called `shape alignment' has been observed in isolated Milky Way-like galaxies but not in `Local Group'-like pairs. In this study, we investigate the shape alignment of satellite galaxies in galaxy pairs similar to the Local Group identified in the Sloan Digital Sky Survey Data Release 13 (SDSS DR13). By stacking tens of thousands of satellite galaxies around primary galaxy pairs, we find …
We study the properties of galaxies with very thin discs using a sample of 85 objects whose stellar disc radial-to-vertical scale ratio determined from photometric decomposition, exceeds nine. We present evidences of similarities between the very thin disc galaxies (VTD galaxies) and low surface brightness (LSB) disc galaxies, and conclude that both small and giant LSB galaxies may reveal themselves as VTD, edge-on galaxies. Our VTD galaxies are mostly bulgeless, and those with large radial scale length tend to have redder colors. We performed spectral observations of 22 VTD galaxies with the …
We describe the SDSS-IV MaNGA PyMorph Photometric (MPP-VAC) and MaNGA Deep Learning Morphology (MDLM-VAC) Value Added Catalogs. The MPP-VAC provides photometric parameters from Sérsic and Sérsic+Exponential fits to the 2D surface brightness profiles of the MaNGA DR15 galaxy sample. Compared to previous PyMorph analyses of SDSS imaging, our analysis of the MaNGA DR15 incorporates three improvements: the most recent SDSS images; modified criteria for determining bulge-to-disk decompositions; and the fits in MPP-VAC have been eye-balled, and re-fit if necessary, for additional reliability. A comp…