The kinematics of late type stars in the solar cylinder studied with SDSS data
B. Fuchs, C. Dettbarn, H. -W. Rix, T. C. Beers, D. Bizyaev, H. Brewington, H. Jahreiss, R. Klement, E. Malanushenko, V. Malanushenko, D. Oravetz, K. Pan, A. Simmons, S. Snedden
We study the velocity distribution of Milky Way disk stars in a kiloparsec-sized region around the Sun, based on ~ 2 million M-type stars from DR7 of SDSS, which have newly re-calibrated absolute proper motions from combining SDSS positions with the USNO-B catalogue. We estimate photometric distances to all stars, accurate to ~ 20 %, and combine them with the proper motions to derive tangential velocities for this kinematically unbiased sample of stars. Based on a statistical de-projection method we then derive the vertical profiles (to heights of Z = 800 pc above the disk plane) for the first and second moments of the three dimensional stellar velocity distribution. We find that <W> = -7 +/- 1 km/s and <U> = -9 +/- 1 km/s, independent of height above the mid-plane, reflecting the Sun's motion with respect to the local standard of rest. In contrast, <V> changes distinctly from -20 +/- 2 km/s in the mid-plane to <V> = -32 km/s at Z = 800 pc, reflecting an asymmetric drift of the stellar mean velocity that increases with height. All three components of the M-star velocity dispersion show a strong linear rise away from the mid-plane, most notably σ_{ZZ}, which grows from 18 km/s (Z = 0) to 40 km/s (at Z = 800 pc). We determine the orientation of the velocity ellipsoid, and find a significant vertex deviation of 20 to 25 degrees, which decreases only slightly to heights of Z = 800 pc. Away from the mid-plane, our sample exhibits a remarkably large tilt of the velocity ellipsoid towards the Galactic plane, which reaches 20 deg. at Z = 800 pc and which is not easily explained. Finally, we determine the ratio σ^2_{ϕϕ}/σ^2_{RR} near the mid-plane, which in the epicyclic approximation implies an almost perfectly flat rotation curve at the Solar radius.
It has been often suggested that a tangible relation exists between relativistic jets in active galactic nuclei (AGN) and the morphology of their host galaxies. In particular, relativistic jets may commonly be related to merging events. Here we present for the first time a detailed spectroscopic and morphological analysis of a Seyfert galaxy, SDSS J211852.96-073227.5, at $z = 0.26$. This source has previously been classified as a gamma-ray emitting narrow-line Seyfert 1 galaxy. We re-observed it with the 6.5m Clay Telescope and these new, high-quality spectroscopic data have revealed that it i…
Motivated by the challenges of calculating the dynamical masses of late-type galaxies (LTGs) and the enormous amount of data from the Sloan Digital Sky Survey (SDSS), we calculate virial masses of a sample of approximately 126,000 LTGs from the sixteenth data release of the SDSS. The virial mass estimations were made considering Newtonian mechanics, virial equilibrium and velocity dispersion from stars and gas. The procedure gave as a result seven mass estimations for each galaxy. The calculated masses were calibrated using a sample of spiral galaxies with velocity rotation curves. Considering…
New ultracool subdwarfs identified in large-scale surveys using Virtual Observatory tools: II. SDSS DR7 vs UKIDSS LAS DR6, SDSS DR7 vs UKIDSS LAS DR8, SDSS DR9 vs UKIDSS LAS DR10, and SDSS DR7 vs 2MASS
我们的目标是发展一种有效的方法来寻找晚型次矮星（光谱类型>M5的金属耗尽矮星），以改善目前的统计。我们的目标是：提高我们对贫金属低质量矮星的认识，弥合晚M型和L型之间的差距，确定它们的表面密度，并了解金属丰度对恒星和亚恒星质量函数的影响。我们使用STILTS、Aladin和Topcat对SDSS、2 MASS和UKIDSS进行了交叉匹配搜索。我们考虑了不同的光度和自行标准，我们的选择。我们确定了29和71晚型亚矮星候选人在每个交叉相关超过8826和3679平方度，分别。我们获得了71个候选人的低分辨率光谱与GTC，NOT和VLT和检索光谱的30个候选人从SDSS光谱数据库。我们分类92候选人的101光谱的基础上使用两种方法：光谱指数和比较与模板已知的次矮星。我们分别从SDSS与2 MASS和SDSS与UKIDSS交叉匹配中确认了86%和94%的候选者为晚型次矮星。这些次矮星的光谱类型介于M5和L0.5之间，SDSS星等在r=19.4-23.3等范围内。我们新发现的晚型M包括49颗次矮星、25颗极端次矮星、6颗超次矮星、1颗次矮星/极端次矮星和2颗矮星/次矮星。在SDSS DR 7与UKIDSS LAS DR 10的交叉比对中，我们得出晚型次矮星的表面密度为每平方度0.040 $^{+0.012}_{-0.007}$。我们还检查了已知和新的亚矮星的AllWISE测光，发现M亚矮星的中…
We performed spectroscopic observations of the small-separation lensed quasar SDSS J1001+5027, whose images have an angular separation $θ\sim 2.^{\!\!\prime\prime}86$, and placed constraints on the physical properties of gas clouds in the vicinity of the quasar (i.e., in the outflowing wind launched from the accretion disk). The two cylinders of sight to the two lensed images go through the same region of the outflowing wind and they become fully separated with no overlap at a very large distance from the source ($\sim 330$ pc). We discovered a clear difference in the profile of the CIV broad …
We derive ages, metallicities, and individual element abundances of early- and late-type galaxies (ETGs and LTGs) out to 1.5 R$_e$. We study a large sample of 1900 galaxies spanning $8.6 - 11.3 \log M/M_{\odot}$ in stellar mass, through key absorption features in stacked spectra from the SDSS-IV/MaNGA survey. We use mock galaxy spectra with extended star formation histories to validate our method for LTGs and use corrections to convert the derived ages into luminosity- and mass-weighted quantities. We find flat age and negative metallicity gradients for ETGs and negative age and negative metal…
Methods. We used different galaxy classification techniques: human labeling, multi-photometry diagrams, Naive Bayes, Logistic Regression, Support Vector Machine, Random Forest, k-Nearest Neighbors, and k-fold validation. Results. We present results of a binary automated morphological classification of galaxies conducted by human labeling, multiphotometry, and supervised Machine Learning methods. We applied its to the sample of galaxies from the SDSS DR9 with 0.02 < z < 0.1 and 24m < Mr < 19.4m. To study the classifier, we used absolute magnitudes: Mu, Mg, Mr , Mi, Mz, Mu-Mr , Mg-Mi, Mu-Mg, Mr-…
High resolution galaxy spectra contain much information about galactic physics, but the high dimensionality of these spectra makes it difficult to fully utilize the information they contain. We apply variational autoencoders (VAEs), a non-linear dimensionality reduction technique, to a sample of spectra from the Sloan Digital Sky Survey. In contrast to Principal Component Analysis (PCA), a widely used technique, VAEs can capture non-linear relationships between latent parameters and the data. We find that a VAE can reconstruct the SDSS spectra well with only six latent parameters, outperformin…
In this work we make use of DR14 APOGEE spectroscopic data to study a sample of 92 known OB stars. We developed a near-infrared semi-empirical spectral classification method that was successfully used in case of four new exemplars, previously classified as later B-type stars. Our results agree well with those determined independently from ECHELLE optical spectra, being in line with the spectral types derived from the "canonical" MK blue optical system. This confirms that the APOGEE spectrograph can also be used as a powerful tool in surveys aiming to unveil and study large number of moderately…
We study the radial acceleration relation (RAR) for early-type galaxies (ETGs) in the SDSS MaNGA MPL5 dataset. The complete ETG sample show a slightly offset RAR from the relation reported by McGaugh et al. (2016) at the low-acceleration end; we find that the deviation is due to the fact that the slow rotators show a systematically higher acceleration relation than the McGaugh's RAR, while the fast rotators show a consistent acceleration relation to McGaugh's RAR. There is a 1σsignificant difference between the acceleration relations of the fast and slow rotators, suggesting that the accelerat…
We study the relationship between Galactic location ($R, Z$) and photometric activity for 3.6 million M dwarf stars within 1 kpc of the Sun. For this purpose, we identify 906 unique flare events as a proxy for magnetic activity from the SkyMapper Southern Survey DR3. We adopt vertical distance $|Z|$ from the Galactic disc as a proxy for age and confirm a strong trend of flaring fraction decreasing with growing stellar age. Among M dwarfs within 50 pc of the Sun, we find a flaring fraction of 1-in-1,500, independent of spectral type from M2 to M7, suggesting that these stars are all in a flare-…
Based on a large sample of 254 220 galaxies in 81 089 groups, which are selected from the spectroscopic galaxy sample of the SDSS DR12, we investigate the radial distribution of incidences, morphologies, environmental densities, and star formation properties of the active galactic nucleus (AGN) host galaxies and star-forming galaxies (SFGs) in the groups at z<0.2, as well as their changes with group richness ($N_{\rm rich}$). It is found that AGN fraction slightly declines with richness for the groups/clusters. The SFG fraction is on average about 2 times larger than the AGN fraction, with a s…
We present maps of the ionized gas flux distributions, excitation, star-formation rate SFR, surface mass density $Σ_{H+}$, and obtain total values of SFR and ionized gas masses {\it M} for 62 Active Galactic Nuclei (AGN) observed with SDSS-IV MaNGA and compare them with those of a control sample of 112 non-active galaxies. The most luminous AGN -- with $L(\rm{[OIII]}λ5007) \ge 3.8\times 10^{40}\,\mbox{erg}\,\mbox{s}^{-1}$, and those hosted by earlier-type galaxies are dominated by Seyfert excitation within 0.2 effective radius $R_e$ from the nucleus, surrounded by LINER excitation or transitio…
We present a detailed visual morphological classification for the 4614 MaNGA galaxies in SDSS Data Release 15, using image mosaics generated from a combination of r-band (SDSS and deeper DESI Legacy Surveys) images and their digital post-processing. We distinguish 13 Hubble types and identify the presence of bars and bright tidal debris. After correcting the MaNGA sample for volume completeness, we calculate the morphological fractions, the bi-variate distribution of type and stellar mass M*-where we recognise a morphological transition "valley" around S0a-Sa types- and the variations of the g…
The white dwarf SDSS J124043.01+671034.68 (SDSS J1240+6710) was previously found to have an oxygen-dominated atmosphere with significant traces of neon, magnesium, and silicon. A possible origin via a violent late thermal pulse or binary interactions have been suggested to explain this very unusual photospheric composition. We report the additional detection of carbon, sodium, and aluminium in far-ultraviolet and optical follow-up spectroscopy. No iron-group elements are detected, with tight upper limits on iron, cobalt and nickel, suggesting that the star underwent partial oxygen burning, but…
Genus statistics using the Delaunay tessellation field estimation method: (I) tests with the Millennium Simulation and the SDSS DR7
我们研究宇宙大尺度结构的拓扑结构，通过属统计，使用银河星表产生的千年模拟和观测数据，从最新的斯隆数字巡天数据发布（SDSS DR 7）。本文介绍了一种构造星系密度场和测量其等密度面亏格统计量的新方法。它是基于Delaunay曲面细分场估计（DTFE）技术，允许分段连续密度场的定义和精确计算其多边形等密度轮廓的拓扑结构，而不引入任何自由的数值参数。除了这种新的方法，我们还采用了传统的方法，平滑的星系分布与高斯的固定宽度，或自适应平滑的内核，包围了一个常数数量的相邻星系。我们的研究结果表明，基于Delaunay的方法提取的拓扑信息量最大。与传统的属统计方法不同，它能够区分不同的理论星系表分析在这里，无论是在真实空间和红移空间，即使它们是基于相同的基础模拟模型。特别是，DTFE方法检测与高置信度的半分析模型之一，在这里研究的SDSS数据相比，差异，而其他模型被发现是一致的。
By combining spectroscopic data from the LAMOST DR7, SDSS DR12, and corrected photometric data from the Gaia EDR3, we apply the Stellar Color Regression (SCR; Yuan et al. 2015a) method to recalibrate the SDSS Stripe 82 standard stars catalog of Ivezić et al. (2007). With a total number of about 30,000 spectroscopically targeted stars, we have mapped out the relatively large and strongly correlated photometric zero-point errors present in the catalog, $\sim$2.5 per cent in the $u$ band and $\sim$ 1 per cent in the $griz$ bands. Our study also confirms some small but significant magnitude depend…
