Tracing Sagittarius Structure with SDSS and SEGUE Imaging and Spectroscopy
Brian Yanny, Heidi Jo Newberg, Jennifer A. Johnson, Young Sun Lee, Timothy C. Beers, Dmitry Bizyaev, Howard Brewington, Paola Re Fiorentin, Paul Harding, Elena … 展开作者
Brian Yanny, Heidi Jo Newberg, Jennifer A. Johnson, Young Sun Lee, Timothy C. Beers, Dmitry Bizyaev, Howard Brewington, Paola Re Fiorentin, Paul Harding, Elena Malanushenko, Viktor Malanushenko, Dan Oravetz, Kaike Pan, Audrey Simmons, Stephanie Snedden
备注：
19 figures, accepted for publication in ApJ, references updated
We show that the Sagittarius dwarf tidal stream can be traced with very red K/M-giant stars selected from SDSS photometry. A subset of these stars are spectroscopically confirmed with SEGUE and SDSS spectra, and the distance scale of 2MASS and SDSS M giants is calibrated to the RR Lyrae distance scale. The absolute g band magnitude of the K/M-giant stars at the tip of the giant branch is M_g=-1.0. The line-of-sight velocities of the M giant and BHB stars that are spatially coincident with the Sgr dwarf tidal stream are consistent with those of previous authors, reinforcing the need for new models that can explain all of the Sgr tidal debris stream observations. We estimate stellar densities along the tidal tails that can be used to help constrain future models. The K/M-giant, BHB, and F-turnoff stars in the lower surface brightness tidal stream that is adjacent to the main leading Sgr dwarf tidal tail have velocities and metallicities that are similar to those of the stars in the leading tidal tail. The ratio of K/M giants to BHBs and BHBs to F-turnoff stars are also similar for both branches of the leading tidal tail. We show that there is an additional low-metallicity tidal stream near the Sgr trailing tidal tail.
We apply the optimal filter technique to Sloan Digital Sky Survey photometry around Segue 1 and find that the outer parts of the cluster are distorted. There is strong evidence for ~ 1 degree elongations of extra-tidal stars, extending both eastwards and southwestwards of the cluster. The extensions have similar differential Hess diagrams to Segue 1. A Kolmogorov-Smirnov test suggests a high probability that both come from the same parent distribution. The location of Segue 1 is close to crossings of the tidal wraps of the Sagittarius stream. By extracting blue horizontal branch stars from Slo…
It is now known that minor mergers are capable of creating structure in the phase-space distribution of their host galaxy's disc. In order to search for such imprints in the Milky Way, we analyse the SEGUE F/G-dwarf and the Schuster et al. (2006) stellar samples. We find similar features in these two completely independent stellar samples, consistent with the predictions of a Milky Way minor-merger event. We next apply the same analyses to high-resolution, idealised N-body simulations of the interaction between the Sagittarius dwarf galaxy and the Milky Way. The energy distributions of stellar…
We employ abundances from the Sloan Digital Sky Survey (SDSS) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE) to study the alpha-element distribution of the stellar members of the Sagittarius stream. To test the reliability of SDSS/SEGUE abundances for the study of Sagittarius, we select high-likelihood samples tracing the different components of the Milky Way, and recover known literature alpha-element distributions. Using selection criteria based on the spatial position, radial velocity, distance and colours of individual stars, we obtain a robust sample of Sagitta…
We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 98.2% of the stars within 67 pc (10 arcmin, or 2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r=21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far out as 87 pc. After correcting for the influence of binary stars using repeated velocity measurements,…
This paper uses Gaussian mixture techniques to dissect the Milky Way (MW) stellar halo in angular momentum space. Application to a catalogue of 5389 stars near the plane of the Sagittarius (Sgr) stream with full 6D phase-space coordinates supplied by Gaia EDR3 and SEGUE returns four independent dynamical components. The broadest and most populated corresponds to the `smooth' MW halo. The narrowest and faintest contains 40 stars of the Orphan stream. We find a component with little or no angular momentum likely associated with the GSE substructure. We also identify 925 stars and 7 Globular Clus…
Tracing the very early disruption of the Sagittarius dwarf galaxy in the distant Milky Way halo
University of Groningen（格罗宁根大学）；University of Victoria（维多利亚大学）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森天体物理中心）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉古纳大学）
We present a chemical abundance analysis of 300S-1, the brightest likely member star of the 300 km/s stream near the faint satellite galaxy Segue 1. From a high-resolution Magellan/MIKE spectrum we determine a metallicity of [Fe/H] = -1.46 +- 0.05 +- 0.23 (random and systematic uncertainties) for star 300S-1, and find an abundance pattern similar to typical halo stars at this metallicity. Comparing our stellar parameters to theoretical isochrones, we estimate a distance of 18 +- 7 kpc. Both the metallicity and distance estimates are in good agreement with what can be inferred from comparing th…
We characterize the kinematic and chemical properties of $\sim$3,000 Sagittarius (Sgr) stream stars, including K-giants, M-giants, and BHBs, select from SEGUE-2, LAMOST, and SDSS separately in Integrals-of-Motion space. The orbit of Sgr stream is quite clear from the velocity vector in $X$-$Z$ plane. Stars traced by K-giants and M-giants present the apogalacticon of trailing steam is $\sim$ 100 kpc. The metallicity distributions of Sgr K-, M-giants, and BHBs present that the M-giants are on average the most metal-rich population, followed by K-giants and BHBs. All of the K-, M-giants, and BHBs…
We characterise the radial density, metallicity and flattening profile of the Milky Way's stellar halo, based on the large sample of 1757 spectroscopically confirmed giant stars from SDSS/SEGUE-2 after excising stars that were algorithmically attributed to apparent halo substructure (including the Sagittarius stream). Compared to BHB stars or RR Lyrae, giants are more readily understood tracers of the overall halo star population, with less bias in age or metallicity. The well-characterized selection function of the sample enables forward modelling of those data, based on ellipsoidal stellar d…
We assemble 121 spectroscopically-confirmed halo carbon stars, drawn from the literature, exhibiting measurable variability in the Catalina Surveys. We present their periods and amplitudes, which are used to estimate distances from period-luminosity relationships. The location of the carbon stars - and their velocities when available - allow us to trace the streams of the Sagittarius (Sgr) dwarf spheroidal galaxy. These are compared to a canonical numerical simulation of the accretion of Sgr. We find that the data match this model well for heliocentric distances of 15-50 kpc, except for a virt…
We present the kinematics of Blue Straggler (BS) stars identified in the Canada-France-Imaging-Survey (CFIS), covering 4000 deg$^2$ on the sky in the $u$-band. The BS sample, characterised through CFIS and Pan-STARRS photometry, has been kinematically decomposed into putative halo and disc populations after cross-matching with Gaia astrometry and SDSS/SEGUE/LAMOST spectroscopy. This decomposition clearly reveals the strong flaring of the outer Milky Way disc. In particular, we show that we can detect this flaring up to a vertical height of $|Z| \simeq 8$ kpc at a Galactocentric distance of $R\…
We present mean absolute proper motion measurements for seven ultra-faint dwarf galaxies orbiting the Milky Way, namely Boötes III, Carina II, Grus II, Reticulum II, Sagittarius II, Segue 2 and Tucana IV. For four of these dwarfs our proper motion estimate is the first ever provided. The adopted astrometric data come from the second data release of the Gaia mission. We determine the mean proper motion for each galaxy starting from an initial guess of likely members, based either on radial velocity measurements or using stars on the Horizontal Branch identified in the Gaia ($G_{\rm BP}$-$G_{\rm…
We present evidence for globular cluster stellar debris in a dwarf galaxy system (Sagittarius: Sgr) based on an analysis of high-resolution \textit{H}-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We add [N/Fe], [Ti/Fe], and [Ni/Fe] abundance ratios to the existing sample of potential members of M~54; this is the first time that [N/Fe] abundances are derived for a large number of stars in M~54. Our study reveals the existence of a significant population of nitrogen- (with a large spread, $\gtrsim1$ dex) and aluminum-enriched stars with moderate M…
We use the SDSS/SEGUE spectroscopic sample of stars in the leading and trailing streams of the Sagittarius (Sgr) to demonstrate the existence of two sub-populations with distinct chemistry and kinematics. The metallicity distribution function (MDF) of the trailing stream is decomposed into two Gaussians describing a metal-rich sub-population with means and dispersions (-0.74, 0.18) dex and a metal-poor with (-1.33, 0.27) dex. The metal-rich sub-population has a velocity dispersion ~ 8 km/s, whilst the metal-poor is nearly twice as hot ~13 km/s. For the leading stream, the MDF is again well-des…
The fraction of stars forming in compact, gravitationally bound clusters (the `cluster formation efficiency' or CFE) is an important quantity for deriving the spatial clustering of stellar feedback and for tracing star formation using stellar clusters across the Universe. Observations of clusters in nearby galaxies have revealed a strong dependence of the CFE on the local gas density, indicating that more stars form in star clusters when the star formation rate surface density is higher. Previously, it has not been possible to test this relation at very young ages and in clusters with individu…
The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of SgrB2, we encounter the SgrB2(DS) region which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended HII region. We use the Very Large Array in its CnB and D configurations, and in the frequency bands C (4--8 GHz) and X (8--12 GHz) to observe the whole SgrB2 complex. Continuum and radio recombination line maps are obtained. We detect radio continuum emission in Sg…
We obtained deep Gemini GMOS-S $g,r$ photometry of the ultra-faint dwarf galaxy candidate Cetus II with the aim of providing stronger constraints on its size, luminosity and stellar population. Cetus II is an important object in the size-luminosity plane as it occupies the transition zone between dwarf galaxies and star clusters. All known objects smaller than Cetus II ($r_h \sim 20$ pc) are reported to be star clusters, while most larger objects are likely dwarf galaxies. We found a prominent excess of main-sequence stars in the colour-magnitude diagram of Cetus II, best described by a single…
Whilst young massive clusters (YMCs; $M$ $\gtrsim$ 10$^{4}$ M$_{\odot}$, age $\lesssim$ 100 Myr) have been identified in significant numbers, their progenitor gas clouds have eluded detection. Recently, four extreme molecular clouds residing within 200 pc of the Galactic centre have been identified as having the properties thought necessary to form YMCs. Here we utilise far-IR continuum data from the Herschel Infrared Galactic Plane Survey (HiGAL) and millimetre spectral line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90) to determine their global physical and kinematic …
Using Gaia DR2, we trace the Anticenter Stream (ACS) in various stellar populations across the sky and find that it is kinematically and spatially decoupled from the Monoceros Ring. Using stars from {\sc lamost} and {\sc segue}, we show that the ACS is systematically more metal-poor than Monoceros by $0.1$ dex with indications of a narrower metallicity spread. Furthermore, the ACS is predominantly populated of old stars ($\sim 10\,\rm{Gyr}$), whereas Monoceros has a pronounced tail of younger stars ($6-10\, \rm{Gyr}$) as revealed by their cumulative age distributions. Put togehter, all of this…
We fit an Extended Distribution Function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. These stars are detected to radii ~80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ~-2 to ~-4 at large radii. The halo's axis ratio increases with rad…
We present the first results of a project aiming to trace the spatial structure of the Milky Way using detached eclipsing binaries (DEBs) as distance indicators. A sample of DEBs from the OGLE-II catalogue was selected and their near infrared photometry was taken from the Vista Variables in the Via Lactea (VVV) survey. The I band OGLE-II light curves are used to create models of the DEBs, which together with the VVV photometry are compared with a set of theoretical isochrones. After correcting for stellar reddening, we find a set of absolute physical parameters of components of a given binary,…
Neighbors, Not Kin: Kinematic evidence for tidal tails from NGC 7492 along the Sagittarius stream
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心，拉格朗日实验室）；Centro de Investigación en Ciencias del Espacio y Física Teórica, Universidad Central de Chile（智利中央大学空间科学与理论物理研究中心）；Departamento de Física, Universidad de Santiago de Chile（智利圣地亚哥大学物理系）；Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS), Universidad de Santiago de Chile（智利圣地亚哥大学天体物理与空间探索跨学科研究中心）；Instituto Interdisciplinario de Ciencias Básicas (ICB), CONICET-UNCuyo（CONICET-门多萨大学基础科学跨研究所）；Consejo Nacional de Investigaciones Científicas y Técnicas（阿根廷国家科学研究委员会）；Instituto de Alta Investigación, Universidad de Tarapacá（塔拉帕卡大学高等研究院）；ESO–European Southern Observatory（欧洲南方天文台）；Miranda House, University of Delhi（德里大学米兰达学院）；Inter University Centre for Astronomy and Astrophysics（大学间天文与天体物理中心）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）
We present a large homogeneous set of stellar parameters and abundances across a broad range of metallicities, involving $13$ classical dwarf spheroidal (dSph) and ultra-faint dSph (UFD) galaxies. In total this study includes $380$ stars in Fornax, Sagittarius, Sculptor, Sextans, Carina, Ursa Minor, Draco, Reticulum II, Bootes I, Ursa Major II, Leo I, Segue I, and Triangulum II. This sample represents the largest, homogeneous, high-resolution study of dSph galaxies to date. With our homogeneously derived catalog, we are able to search for similar and deviating trends across different galaxies.…
Unveiling the Milky Way with a Gaia DR3 census of OB-type stars within 2 kpc. I. Tracing local Galactic structure, massive star-forming regions and core-collapse supernova progenitors
Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，CY塞吉-蓬图瓦兹大学，法国国家科学研究中心）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；INAF – Osservatorio Astrofisico di Torino（意大利国家天体物理研究所都灵天文台）；University of Vienna（维也纳大学）；Keele University（基尔大学）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；European Southern Observatory（欧洲南方天文台）
We use the Pristine survey CaHK narrow-band photometry, combined with the SDSS ugr photometry, to provide a cleaner sample of blue horizontal branch stars in the Galactic halo out to large distances. We demonstrate a completeness of 91% and a purity of 93% with respect to available spectroscopic classifications. We subsequently use our new clean sample of these standard candles to investigate the substructure in the Galactic halo over the Pristine footprint. Among other features, this allows for a careful tracing of multiple parts of the Sagittarius stream, providing a measurement independent …
