星系中的形态特征，如旋臂、棒、环、潮汐尾等，携带着关于其结构、起源和演化的信息。因此，对这些特征进行编目和研究，并将它们与其他基本星系性质、星系所处的环境以及与其他星系的相互作用关联起来，是非常重要的。当前和未来的星系数据量如此之大，以至于由天文学家专家通过视觉检查来识别形态特征的传统方法已不再足够。因此，有必要使用基于人工智能的技术，如机器学习和深度学习，来快速高效地寻找形态结构。在本研究中，我们报告了应用深度学习从Sloan Digital Sky Survey (SDSS) 数据发布DR18的星系图像中寻找环状结构。我们使用Buta (2017) 编制的SDSS环星系目录来训练网络，达到了良好的准确率和召回率，并生成了一个包含29420个星系的目录，其中4855个星系具有预测置信度超过90%的环状结构。利用Abraham等人 (2018) 使用深度学习技术识别的棒状星系图像目录，我们识别出2087个同时具有棒和环的星系集合。该目录对于理解这些重要形态结构的起源应该非常有用。作为该目录实用性的一个例子，我们探索了样本中环星系的环境和恒星形成特征。
英文摘要：
Morphological features in galaxies, like spiral arms, bars, rings, tidal tails etc. carry information about their structure, origin and evolution. It is therefore important to catalog and study such features and to correlate them with other basic galaxy properties, the environment in which the galaxies are located and their interactions with other galaxies. The volume of present and future data on galaxies is so large that traditional methods, which involve expert astronomers identifying morphological features through visual inspection, are no longer sufficient. It is therefore necessary to use AI based techniques like machine learning and deep learning for finding morphological structures quickly and efficiently. We report in this study the application of deep learning for finding ring like structures in galaxy images from the Sloan Digital Sky Survey (SDSS) data release DR18. We use a catalog by Buta (2017) of ringed galaxies from the SDSS to train the network, reaching good accuracy and recall, and generate a catalog of 29420 galaxies of which 4855 have ring like structures with prediction confidence exceeding 90 percent. Using a catalog of barred galaxy images identified by Abraham et. al. (2018) using deep learning techniques, we identify a set of 2087 galaxies with bars as well as rings. The catalog should be very useful in understanding the origin of these important morphological structures. As an example of the usefulness of the catalog, we explore the environments and star formation characteristics of ring galaxies in our sample.
We present an analysis of Galactic halo structure and substructure traced by ~500 RR Lyrae stars in the SDSS stripe 82 region. The main result of this study is a 2D map of the Galactic halo that reaches distances of 100 kpc and traces previously known and new halo substructures, such as the Sagittarius and Pisces tidal streams. We also present strong direct evidence, based on both RR Lyrae and main sequence stars, that the halo stellar number density profile significantly steepens beyond 30 kpc from the Galactic center. Using a novel photometric metallicity method that simultaneously combines …
We present a homogeneous survey of the CN and CH bandstrengths in eight Galactic globular clusters observed during the course of the Sloan Extension for Galactic Understanding and Exploration (SEGUE) sub-survey of the SDSS. We confirm the existence of a bimodal CN distribution among RGB stars in all of the clusters with metallicity greater than [Fe/H] = -1.7; the lowest metallicity cluster with an observed CN bimodality is M53, with [Fe/H] ~ -2.1. There is also some evidence for individual CN groups on the subgiant branches of M92, M2, and M13, and on the red giant branches of M92 and NGC 5053…
Using a sample of 407 RR Lyrae stars extracted from SDSS Stripe 82, we study the degree of substructure in the Galactic halo. We identify overdensities associated with the known substructures of the Hercules-Aquila Cloud and the Sagittarius Stream, and find a further previously-unknown substructure, the Pisces Overdensity, at ~100 kpc from the Sun. Together, the three substructures account for ~80% of our RR Lyrae sample. We also study the density distribution of RR Lyraes in the halo and find that the profile is best fit by a broken power law with an inner slope of -2.4 and a break radius of …
We re-examine recent claims of observational evidence for a dual Galactic halo in SEGUE/SDSS data, and trace them back to improper error treatment and neglect of selection effects. In particular, the detection of a vertical abundance gradient in the halo can be explained as a metallicity bias in distance. A similar bias, and the impact of disk contamination, affect the sample of blue horizontal branch stars. These examples highlight why non-volume complete samples require forward-modelling from theoretical models or extensive bias-corrections. We also show how observational uncertainties produ…
We report results concerning the distribution and properties of galactic extinction at high galactic latitudes derived from stellar statistics using the Sloan Digital Sky Survey (SDSS). We use the classical Wolf diagram method to identify regions with extinction, and derive the extinction and the extinction law of the dust using all five SDSS spectral bands. We estimate the distance to the extinguishing medium using simple assumptions about the stellar populations in the line of sight. We report the identification of three extinguishing clouds, each a few tens of pc wide, producing 0.2-0.4 mag…
We present $g^\prime$ and $z^\prime$ aperture photometry for 96 Galactic Globular Clusters, making this the largest homogeneous catalog of photometry for these objects in the SDSS filter system. For a subset of 56 clusters we also provide photometry in $r^\prime$ and $i^\prime$. We carry out comparisons with previous photometry as well as with the SDSS dataset. The data will be useful for a series of applications in Galactic and extragalactic astrophysics. Future papers will analyse the colour-metallicity relation, colour-magnitude diagrams, and structural parameters. The compilation of result…
Aims: We used 12,530 photometrically-selected blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey (SDSS) to estimate the total extinction of the Milky Way at the high Galactic latitudes, $R_V$ and $A_V$ in each line of sight. Methods: A Bayesian method was developed to estimate the reddening values in the given lines of sight. Based on the most likely values of reddening in multiple colors, we were able to derive the values of $R_V$ and $A_V$. Results: We selected 94 zero-reddened BHB stars from seven globular clusters as the template. The reddening in the four SDSS colors for…
This is the first paper in a dedicated series to study the properties of the optically selected BLR-less AGNs (Active Galactic Nuclei with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136676 spectroscopic objects (galaxies and QSOs) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22693 pure narrow line objects without broad emissio…
Based on SDSS g, r and SCUSS (South Galactic Cap of u-band Sky Survey) $u$ photometry, we develop a photometric calibration for estimating the stellar metallicity from $u-g$ and $g-r$ colors by using the SDSS spectra of 32,542 F- and G-type main sequence stars, which cover almost $3700$ deg$^{2}$ in the south Galactic cap. The rms scatter of the photometric metallicity residuals relative to spectrum-based metallicity is $0.14$ dex when $g-r<0.4$, and $0.16$ dex when $g-r>0.4$. Due to the deeper and more accurate magnitude of SCUSS $u$ band, the estimate can be used up to the faint magnitude of…
Based on SDSS and South Galactic Cap of u-band Sky Survey (SCUSS) early data, we use star counts method to estimate the Galactic structure parameters in an intermediate latitude with 10,180 main-sequence (MS) stars in absolute magnitude interval of $4 \leq M_r \leq 13$. We divide the absolute magnitude into five intervals:$4 \leq M_r < 5$, $5 \leq M_r < 6$, $6 \leq M_r < 8$, $8 \leq M_r < 10$, $10 \leq M_r \leq 13$, and estimate the Galactic structure parameters in each absolute magnitude interval to explore their possible variation with the absolute magnitude. Our study shows the parameters d…
Using the integral field unit (IFU) data from Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we collect a sample of 36 star forming galaxies that host galactic-scale outflows in ionized gas phase. The control sample is matched in the three dimensional parameter space of stellar mass, star formation rate and inclination angle. Concerning the global properties, the outflows host galaxies tend to have smaller size, more asymmetric gas disk, more active star formation in the center and older stellar population than the control galaxies. Comparing the stellar population propert…
In Liu (2015), we propose selecting binary active galactic nuclei (AGNs) candidates using the centroid shift of the images, which is induced by the non-synchronous variations of the two nuclei. In this paper, a known binary AGN (SDSS J233635.75-010733.7) is employed to verify the ability of this method. Using 162 exposures in the $R$ band of \textit{Palomar Transient Factory} (PTF), an excess of dispersion in the positional distribution of the binary AGN is detected, though the two nuclei cannot be resolved in the images of PTF. We also propose a new method to compare the position of the binar…
We estimated the galactic model parameters for a set of 20 intermediate-latitude fields with galactic longitudes 0<l<100 and 160<l<240, included in the currently available Data Release 6 (DR6) of SDSS, to explore their possible variation with galactic longitude. The local space densities of the thick disc and halo are almost the same for all fields, <(n_{2}/n_{1})>=6.52% and <(n_{3}/n_{1})>=0.35%, respectively, a result different than the one cited for high-latitude fields. The thin disc's scaleheight is 325 pc in the galactic centre changes to 369 pc in the third quadrant, which confirms the …
We use our integrated SDSS photometry for 96 globular clusters in $g$ and $z$, as well as $r$ and $i$ photometry for a subset of 56 clusters, to derive the integrated colour-metallicity relation (CMR) for Galactic globular clusters. We compare this relation to previous work, including extragalactic clusters, and examine the influence of age, present-day mass function variations, structural parameters and the morphology of the horizontal branch on the relation. Moreover, we scrutinise the scatter introduced by foreground extinction (including differential reddening) and show that the scatter in…
Aims. We explore the outer Galactic disc up to a Galactocentric distance of 30 kpc to derive its parameters and measure the magnitude of its flare. Methods. We obtained the 3D density of stars of type F8V-G5V with a colour selection from extinction-corrected photometric data of the Sloan Digital Sky Survey - Sloan Extension for Galactic Understanding and Exploration (SDSS-SEGUE) over 1,400 deg^2 in off-plane low Galactic latitude regions and fitted it to a model of flared thin+thick disc. Results. The best-fit parameters are a thin-disc scale length of 2.0 kpc, a thin-disc scale height at sola…
We present the first detailed study of the behaviour of the stellar proper motion across the entire Galactic Anti-centre area visible in the Sloan Digital Sky Survey data. We use recalibrated SDSS astrometry in combination with positions from {\it Gaia} DR1 to provide tangential motion measurements with a systematic uncertainty $<$5 kms$^{-1}$ for the Main Sequence stars at the distance of the Monoceros Ring. We demonstrate that Monoceros members rotate around the Galaxy with azimuthal speeds of ~230 kms$^{-1}$, only slightly lower than that of the Sun. Additionally, both vertical and azimutha…
We explore the stellar metallicity distribution function of the Galactic halo based on SDSS ugriz photometry. A set of stellar isochrones is calibrated using observations of several star clusters and validated by comparisons with medium-resolution spectroscopic values over a wide range of metal abundance. We estimate distances and metallicities for individual main-sequence stars in the multiply scanned SDSS Stripe 82, at heliocentric distances in the range 5 - 8 kpc and |b| > 35 deg, and find that the in situ photometric metallicity distribution has a shape that matches that of the kinematical…
Although originally conceived as primarily an extragalactic survey, the Sloan Digital Sky Survey (SDSS-I), and its extensions SDSS-II and SDSS-III, continue to have a major impact on our understanding of the formation and evolution of our host galaxy, the Milky Way. The sub-survey SEGUE: Sloan Extension for Galactic Exploration and Understanding, executed as part of SDSS-II, obtained some 3500 square degrees of additional ugriz imaging, mostly at lower Galactic latitudes, in order to better sample the disk systems of the Galaxy. Most importantly, it obtained over 240,000 medium-resolution spec…
We present an absolute magnitude calibration for red giants with the colour magnitude diagrams of six Galactic clusters with different metallicities i.e. M92, M13, M3, M71, NGC 6791 and NGC 2158. The combination of the absolute magnitudes of the red giant sequences with the corresponding metallicities provides calibration for absolute magnitude estimation for red giants for a given $(g-r)_{0}$ colour. The calibration is defined in the colour interval 0.45 $\leq(g-r)_{0}\leq$ 1.30 mag and it covers the metallicity interval $-2.15\leq \lbrack Fe/H \rbrack \leq$ +0.37 dex. The absolute magnitude …
We test the ability of the TRILEGAL and Besancon models to reproduce the CMD of SDSS data at the north Galactic pole (NGP). We show that a Hess diagram analysis of colour-magnitude diagrams is much more powerful than luminosity functions (LFs) in determining the Milky Way structure. We derive a best-fitting TRILEGAL model to simulate the NGP field in the (g-r, g) CMD of SDSS filters via Hess diagrams. For the Besancon model, we simulate the LFs and Hess diagrams in all SDSS filters. We use a chi2 analysis and determine the median of the relative deviations in the Hess diagrams to quantify the …
The outer Galactic halo is home to a number of substructures which still have an uncertain origin, but most likely are remnants of former interactions between the Galaxy and its former satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as an overdensity of 2MASS M giants. We analyzed the region of Triangulum-Andromeda using photometric data from the Ninth Data Release of Sloan Digital Sky Survey (SDSS DR9). By comparing the observations with simulations from the TRILEGAL Galactic model, we were able to identify and map several scattered overdensities of main se…
Using ~1,700,000 target- and sky-fiber spectra from the SDSS, we have carried out a systematic search for Galactic planetary nebulae (PNe) via detections of the [OIII] 4959, 5007 lines. Thanks to the excellent sensitivity of the SDSS spectroscopic surveys, this is by far the deepest search for PNe ever taken, reaching a surface brightness of the [OIII] 5007 line down to about 29.0 mag./arcsec^2. The search recovers 13 previously known PNe in the Galactic Caps. In total, 44 new PN candidates are identified, including 7 candidates of multiple detections and 37 candidates of single detection. The…
The Sloan Digital Sky Survey III/Apache Point Observatory Galactic Evolution Experiment (SDSS-III/APOGEE) is a large-scale spectroscopic survey of Galactic stars and star clusters. The SDSS-III/APOGEE survey is designed to produce high-S/N, R = 27,500-31,000 spectra that cover a wavelength range of 1.51 to 1.68 microns. By utilizing APOGEE's excellent kinematics (error <= 0.5 km/s) and abundances (errors ~ 0.1 dex), we will be able to study star cluster kinematics and chemical properties in detail. Over the course of the 3-year survey beginning in 2011, APOGEE will target 25-30 key open and gl…
The Open Cluster Chemical Analysis and Mapping (OCCAM) Survey aims to produce a comprehensive, uniform, infrared-based dataset for hundreds of open clusters, and constrain key Galactic dynamical and chemical parameters from this sample. This first contribution from the OCCAM survey presents analysis of 141 members stars in 28 open clusters with high-resolution metallicities derived from a large uniform sample collected as part of the SDSS-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE). This sample includes the first high-resolution metallicity measurements for 22 open clus…
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 AGNs. The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44<z<0.6, which will lead to statistical conclusions in the CMASS sample being less likely robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the lowest density regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note …
This paper describes an automatic isophotal fitting procedure that succeeds, without the support of any visual inspection of neither the images nor the ellipticity/P.A. radial profiles, at extracting a fairly pure sample of barred LTGs among thousands of optical images from the SDSS. The procedure relies on the methods described in Consolandi et al. (2016) to robustly extract the photometrical properties of a large sample of local SDSS galaxies and is tailored to extract bars on the basis of their well-known peculiarities in their P.A. and ellipticity profiles. It has been run on a sample of 5…
Studies of stellar populations, understood to mean collections of stars with common spatial, kinematic, chemical, and/or age distributions, have been reinvigorated during the last decade by the advent of large-area sky surveys such as SDSS, 2MASS, RAVE, and others. We review recent analyses of these data that, together with theoretical and modeling advances, are revolutionizing our understanding of the nature of the Milky Way, and galaxy formation and evolution in general. The formation of galaxies like the Milky Way was long thought to be a steady process leading to a smooth distribution of s…
We use our Galactic Globular Cluster Catalog (G2C2) photometry for 111 Galactic globular clusters (GC) in g and z, as well as r and i photometry for a subset of 60 GCs and u photometry for 22 GCs, to determine the structural parameters assuming King (1962) models. In general, the resulting core radii are in good comparison with the current literature values. However, our half-light radii are slightly lower than the literature. The concentrations (and therefore also the tidal radii) are poorly constrained mostly because of the limited radial extent of our imaging. Therefore, we extensively disc…
Kiloparsec-scale dual active galactic nuclei (AGNs) are active supermassive black hole pairs co-rotating in galaxies with separations of less than a few kpc. Expected to be a generic outcome of hierarchical galaxy formation, their frequency and demographics remain uncertain. We have carried out an imaging survey with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) of AGNs with double-peaked narrow [O III] emission lines. HST/WFC3 offers high image quality in the near-infrared (NIR) to resolve the two stellar nuclei, and in the optical to resolve [O III] from ionized gas in the narr…
Stellar feedback-driven outflows regulate the stellar formation and chemical enrichment of galaxies, yet the underlying dependence of mass outflow rate on galaxy properties remains largely unknown. We develop a simple yet comprehensive non-equilibrium chemical evolution model~(NE-CEM) to constrain the mass-loading factor $η$ of outflows using the metallicity-stellar mass-SFR relation observed by SDSS at $z{=}0$. Our NE-CEM predicts the chemical enrichment by explicitly tracking both the histories of star formation and mass-loading. After exploring the EAGLE simulation, we discover a compact ye…
Ionised gas outflows driven by active galactic nuclei (AGN) are ubiquitous in high luminosity AGN with outflow speeds apparently correlated with the total bolometric luminosity of the AGN. This empirical relation and theoretical work suggest that in the range L_bol ~ 10^43-45 erg/s there must exist a threshold luminosity above which the AGN becomes powerful enough to launch winds that will be able to escape the galaxy potential. In this paper, we present pilot observations of two AGN in this transitional range that were taken with the Gemini North Multi-Object Spectrograph Integral Field Unit …
Studies of the kinematics and chemical compositions of Galactic globular clusters (GCs) enable the reconstruction of the history of star formation, chemical evolution, and mass assembly of the Galaxy. Using the latest data release (DR16) of the SDSS/APOGEE survey, we identify 3,090 stars associated with 46 GCs. Using a previously defined kinematic association, we break the sample down into eight separate groups and examine how the kinematics-based classification maps into chemical composition space, considering only $α$ (mostly Si and Mg) elements and Fe. Our results show that: (i) The loci of…
The stars SDSS J064655.6+411620.5 and SDSS J193712.01+502455.5 are relatively bright stars that were initially observed as part of the SDSS/MARVELS pre-survey. They were selected, on the basis of their weak CH $G$-bands, along with a total of 60 others, in the range of halo globular cluster metallicities for high-resolution spectroscopic follow-up as a part of the HESP-GOMPA survey (Hanle Echelle SPectrograph -- Galactic survey Of Metal Poor stArs). The stars exhibit typical nucleosynthesis signatures expected from the so-called second-generation stars of globular clusters. The light-element a…
The prevalence of outflow and feedback signatures in active galactic nuclei (AGN) is a major unresolved question which large integral field unit (IFU) surveys now allow to address. In this paper, we present a kinematic analysis of the ionised gas in 2778 galaxies at z $\sim$ 0.05 observed by SDSS-IV MaNGA. Specifically, we measure the kinematics of the [OIII] λ5007Å emission line in each spatial element and fit multiple Gaussian components to account for possible non-gravitational motions of gas. Comparing the kinematics of the ionised gas between 308 MaNGA-selected AGN that have been previous…
Unsupervised Chemo-Dynamical Dissection of the Inner Galactic Halo: Discovery of Five Accreted Substructures with SDSS-V and Gaia
Institute of Graduate Studies in Science, Istanbul University（伊斯坦布尔大学研究生科学学院）；Faculty of Science, Department of Astronomy and Space Sciences, Istanbul University（伊斯坦布尔大学理学院天文与空间科学系）
We conduct a systematic study of galactic outflows in star-forming galaxies at $z\sim0$-$2$ based on the absorption lines of optical spectra taken from SDSS DR7, DEEP2 DR4, and Keck Erb et al. We carefully make stacked spectra of homogeneous galaxy samples with similar stellar mass distributions at $z\sim0$-$2$, and perform the multi-component fitting of model absorption lines and stellar continua to the stacked spectra. We obtain the maximum ($v_\rm{max}$) and central ($v_\rm{out}$) outflow velocities, and estimate the mass loading factors ($η$), a ratio of the mass outflow rate to the star f…
We have identified 105 galaxy pairs at z ~ 0.04 with the MaNGA integral-field spectroscopic data. The pairs have projected separations between 1 kpc and 30 kpc, and are selected to have radial velocity offsets less than 600 km/s and stellar mass ratio between 0.1 and 1. The pair fraction increases with both the physical size of the integral-field unit and the stellar mass, consistent with theoretical expectations. We provide the best-fit analytical function of the pair fraction and find that ~3% of M* galaxies are in close pairs. For both isolated galaxies and paired galaxies, active galactic …
F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful, luminous, and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey (SDSS). We describe the absolute magnitude distribution of color-selected F turnoff stars, as measured from SDSS data, for eleven globular clusters in the Milky Way halo. We find that the M_g distribution of turnoff stars is intrinsically the same for all clusters studied, and is well fit by two half Gaussian functions, centered at mu=4.18, with a bright-side sigma=0.36, a…
We discuss whether modern machine learning methods can be used to characterize the physical nature of the large number of objects sampled by the modern multi-band digital surveys. In particular, we applied the MLPQNA (Multi Layer Perceptron with Quasi Newton Algorithm) method to the optical data of the Sloan Digital Sky Survey - Data Release 10, investigating whether photometric data alone suffice to disentangle different classes of objects as they are defined in the SDSS spectroscopic classification. We discuss three groups of classification problems: (i) the simultaneous classification of ga…
We present a new database of our two-dimensional bulge-disk decompositions for 14,233 galaxies drawn from SDSS DR12 in order to examine the properties of bulges residing in the local universe ($0.005 < z < 0.05$). We performed decompositions in $g$ and $r$ bands by utilizing the {\sc{galfit}} software. The bulge colors and bulge-to-total ratios are found to be sensitive to the details in the decomposition technique, and hence we hereby provide full details of our method. The $g-r$ colors of bulges derived are almost constantly red regardless of bulge size except for the bulges in the low bulge…
The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based spectroscopic dataset for hundreds of open clusters, and to constrain key Galactic dynamical and chemical parameters from this sample. This second contribution from the OCCAM survey presents analysis of 259 member stars with [Fe/H] determinations in 19 open clusters, using Sloan Digital Sky Survey Data Release 14 (SDSS/DR14) data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and ESA Gaia. This analysis, which includes clusters with R_{GC} ranging f…
The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to constrain key Galactic dynamical and chemical evolution parameters by the construction of a large, comprehensive, uniform, infrared-based spectroscopic data set of hundreds of open clusters. This fourth contribution from the OCCAM survey presents analysis using SDSS/APOGEE DR16 of a sample of 128 open clusters, 71 of which we designate to be "high quality" based on the appearance of their color-magnitude diagram. We find the APOGEE DR16 derived [Fe/H] abundances to be in good agreement with previous high resolution spectro…
We assemble a sample of 696 type 1 AGN up to a redshift of $z=2.5$, all of which have an SDSS spectrum containing at least one broad emission line (H $α$, H $β$ or Mg II) and an XMM-Newton X-ray spectrum containing at least 250 counts in addition to simultaneous optical/ultraviolet photometry from the XMM Optical Monitor. Our sample includes quasars and narrow-line Seyfert 1s: thus our AGN span a wide range in luminosity, black hole mass and accretion rate. We determine single-epoch black hole mass relations for the three emission lines and find that they provide broadly consistent mass estima…
Changing-Look Active Galactic Nuclei in SDSS-V: Host-Galaxy Properties and Black-Hole Scaling Relations
Tel Aviv University（特拉维夫大学）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；Excellence Cluster ORIGINS（ORIGINS卓越集群）；The Pennsylvania State University（宾夕法尼亚州立大学）；University of Washington（华盛顿大学）；University of Geneva（日内瓦大学）；Universidad Diego Portales（迭戈·波特莱斯大学）；Peking University（北京大学）
Photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) and the Sloan Digital Sky Survey (SDSS) are used to derive the global structure parameters of the smooth components of the Milky Way. The data, which cover nearly 11,000 deg$^2$ sky area and the full range of Galactic latitude, allow us to construct a globally representative Galactic model. The number density distribution of Galactic halo stars is fitted with an oblate spheroid that decays by power law. The best-fit yields an axis ratio and a power law index $κ=0.65$ and $p=2.79$, respect…
Modern sky surveys, such as the Sloan Digital Sky Survey and the Two-Micron All Sky Survey, have revolutionized the study of low-mass stars. With millions of photometric and spectroscopic observations, intrinsic stellar properties can be studied with unprecedented statistical significance. Low-mass stars dominate the local Milky Way and are ideal tracers of the Galactic potential and the thin and thick disks. Recent efforts, driven by SDSS observations, have sought to place the local low-mass stellar population in a broader Galactic context. I highlight a recent measurement of the luminosity a…
The widely accepted active galactic nucleus (AGN) paradigm has been recently challenged by the discovery of the so-called ``changing-look'' (CL) phenomenon characterized by spectral-type transitions. By comparing the SDSS-V and SDSS DR16 spectroscopic datasets, here we report the identification of 14 new CL-AGNs (redshift $z<0.5$) exhibiting spectral-type changes on a timescale of $\sim 10$yr. Follow-up spectroscopy was conducted with the Lick Shane 3m and Keck 10m telescopes for three of the objects. Detailed analysis of these spectra enables us to arrive at the following two main results. (1…
We present a comparative study of active galactic nuclei (AGN) between galaxy pairs and isolated galaxies with the final data release of the MaNGA integral field spectroscopic survey. We build a sample of 391 kinematic galaxy pairs within the footprint of the survey and select AGN using the survey's spectra. We use the comoving volume densities of the AGN samples to quantify the effects that tidal interactions have on the triggering of nuclear accretion. Our hypothesis is that the pair sample contains AGN that are triggered by not only stochastic accretion but also tidally induced accretion an…
We re-examine the fraction of low-redshift Sloan Digital Sky Survey satellites and centrals in which star formation has been quenched, using the environment quenching efficiency formalism that separates out the dependence of stellar mass. We show that the centrals of the groups containing the satellites are responding to the environment in the same way as their satellites (at least for stellar masses above 10^10.3 Msun), and that the well-known differences between satellites and the general set of centrals arise because the latter are overwhelmingly dominated by isolated galaxies. The widespre…
A new, complete sample of 14,584 broad-line AGNs at $z<0.35$ is presented, which are uncovered homogeneously from the complete database of galaxies and quasars observed spectroscopically in the Sloan Digital Sky Survey Seventh Data Release. The stellar continuum is properly removed for each spectrum with significant host absorption line features, and careful analyses of the emission-line spectra, particularly in the H$\rm α$ and H$\rm β$ wavebands, are carried out. The broad Balmer emission line, particularly, H$\rm α$, is used to indicate the presence of an AGN. The broad H$\rm α$ lines have …
The shape of emission lines in the optical spectra of star-forming galaxies reveals the kinematics of the diffuse gaseous component. We analyse the shape of prominent emission lines in a sample of ~53,000 star-forming galaxies from the Sloan Digital Sky Survey, focusing on departures from gaussianity. Departures from a single gaussian profile allow us to probe the motion of gas and to assess the role of outflows. The sample is divided into groups according to their stellar velocity dispersion and star formation rate. The spectra within each group are stacked to improve the signal-to-noise rati…
Double-peaked narrow emission lines in active galactic nucleus (AGN) spectra can be produced by AGN outflows, rotation, or dual AGNs, which are AGN pairs in ongoing galaxy mergers. Consequently, double-peaked narrow AGN emission lines are useful tracers of the coevolution of galaxies and their supermassive black holes, as driven by AGN feedback and AGN fueling. We investigate this concept further with follow-up optical longslit observations of a sample of 95 Sloan Digital Sky Survey (SDSS) galaxies that have double-peaked narrow AGN emission lines. Based on a kinematic analysis of the longslit…
We use the Sloan Digital Sky Survey Data Release 12, which is the largest available white dwarf catalog to date, to study the evolution of the kinematical properties of the population of white dwarfs in the Galactic disc. We derive masses, ages, photometric distances and radial velocities for all white dwarfs with hydrogen-rich atmospheres. For those stars for which proper motions from the USNO-B1 catalog are available the true three-dimensional components of the stellar space velocity are obtained. This subset of the original sample comprises 20,247 objects, making it the largest sample of wh…
Stars ejected from the Galactic centre can be used to place important constraints on the Milky Way potential. Since existing hypervelocity stars are too distant to accurately determine orbits, we have conducted a search for nearby candidates using full three-dimensional velocities. Since the efficacy of such studies are often hampered by deficiencies in proper motion catalogs, we have chosen to utilize the reliable, high-precision SDSS Stripe 82 proper motion catalog. Although we do not find any candidates which have velocities in excess of the escape speed, we identify 226 stars on orbits tha…
The presence of Galactic cirrus is an obstacle for studying both faint objects in our Galaxy and low surface brightness extragalactic structures. With the aim of studying individual cirrus filaments in SDSS Stripe 82 data, we develop techniques based on machine learning and neural networks that allow one to isolate filaments from foreground and background sources in the entirety of Stripe 82 with a precision similar to that of the human expert. Our photometric study of individual filaments indicates that only those brighter than 26 mag arcsec$^{-2}$ in the SDSS $r$ band are likely to be identi…
