Proper Motions of Stellar Streams Discovered in the Dark Energy Survey
N. Shipp, T. S. Li, A. B. Pace, D. Erkal, A. Drlica-Wagner, B. Yanny, V. Belokurov, W. Wester, S. E. Koposov, G. F. Lewis, J. D. Simpson, Z. Wan, D. B. Zucker, … 展开作者
N. Shipp, T. S. Li, A. B. Pace, D. Erkal, A. Drlica-Wagner, B. Yanny, V. Belokurov, W. Wester, S. E. Koposov, G. F. Lewis, J. D. Simpson, Z. Wan, D. B. Zucker, S. L. Martell, M. Y. Wang
We cross-match high-precision astrometric data from Gaia DR2 with accurate multi-band photometry from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar streams in the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra. We determine low-confidence proper motion measurements for four additional stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment between stream tracks and the systemic proper motion of streams that may suggest a systematic gravitational influence from the Large Magellanic Cloud. These proper motions, when combined with radial velocity measurements, will allow for detailed orbit modeling which can be used to constrain properties of the LMC and its affect on nearby streams, as well as global properties of the Milky Way's gravitational potential.
Context. As a fragile element, lithium is a sensitive probe of physical processes occurring in stellar interiors. Aims. We aim at investigating the relationship between lithium abundance and rotation rate in low-mass members of the newly discovered 125~Myr-old Psc-Eri stellar stream. Methods. We obtained high resolution optical spectra and measure the equivalent width of the 607.8 nm LiI line for 40 members of the Psc-Eri stream, whose rotational periods have been derived by arXiv:1905.10588. Results. We show that a tight correlation exists between lithium content and rotation rate among the l…
Tidal streams in newly discovered M32 analogues: evidence for the stripping scenario
我们提出了两个新发现的紧凑的椭圆（cE）星系，表现出明确的证据潮汐蒸汽，并发现在搜索的SDSS DR 7 cE候选人。的结构参数的CE使用GALFIT，给出有效半径，Re，388和263秒差距，和B波段平均表面亮度内Re的19.4和19.2的幅度每弧秒平方。我们重新分析了SDSS光谱，表明它们拥有年轻到中等年龄的恒星星族。这两个cE提供了直接的证据，一个“吸烟枪”，潮汐剥离的过程，被认为是M32型星系的起源。这两个星系都是在一个小的星系群中，有很大的螺旋部分，这表明我们可能会在动态年轻的环境中看到这样的cE星系的形成。更紧凑的星系是在一个与本星系群类似的小星系群中发现的，因此为理解M32提供了一个额外的模型。
AT2016dah and AT2017fyp are fairly typical Andromeda Galaxy (M31) classical novae. AT2016dah is an almost text book example of a 'very fast' declining, yet uncommon, Fe II'b' (broad-lined) nova, discovered during the rise to peak optical luminosity, and decaying with a smooth broken power-law light curve. AT2017fyp is classed as a 'fast' nova, unusually for M31, its early decline spectrum simultaneously shows properties of both Fe II and He/N spectral types - a 'hybrid'. Similarly, the light curve of AT2017fyp has a broken power-law decline but exhibits an extended flat-topped maximum. Both no…
The longest recognized stellar stream in the Milky Way Galaxy has an expanse of over more than half the north sky. There was a physical disturbance within the stream, 500 million years ago, which could have been the scar of a dark matter collision. Due to its proximity to the galactic center, the GD-1 stellar stream can act as an antenna for gravitational perturbations. In 2018, a significant gap in GD-1 was discovered due to perturbation. A stream gap occurs when a massive object collides with the stellar stream. Based on the chasm location and width, we can guess when and where the impact oc…
We perform a search for stellar streams around the Milky Way using the first three years of multi-band optical imaging data from the Dark Energy Survey (DES). We use DES data covering $\sim 5000$ sq. deg. to a depth of $g > 23.5$ with a relative photometric calibration uncertainty of $< 1 \%$. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of $\sim 50$ kpc. We search for stellar streams using a matched-filter in color-magnitude space derived from a synth…
The recently discovered S1 stream passes through the Solar neighbourhood on a low inclination, counter-rotating orbit. The progenitor of S1 is a dwarf galaxy with a total mass comparable to the present-day Fornax dwarf spheroidal, so the stream is expected to have a significant DM component. We compute the effects of the S1 stream on WIMP and axion detectors as a function of the density of its unmeasured dark component. In WIMP detectors the S1 stream supplies more high energy nuclear recoils so will marginally improve DM detection prospects. We find that even if S1 comprises less than 10% of …
Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20$^{\circ}$ across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from LAMOST and photometric rotation periods from the Zwicky Transient Facility (Z…
The recently discovered Indus stellar stream exhibits a diverse chemical signature compared to what is found for most other streams due to the abundances of two outlier stars, Indus$\_$0 and Indus$\_$13. Indus$\_$13, exhibits an extreme enhancement in rapid neutron-capture ($r$-)process elements with $\mathrm{[Eu/Fe]} = +1.81$. It thus provides direct evidence of the accreted nature of $r$-process enhanced stars. In this paper we present a detailed chemical analysis of the neutron-capture elements in Indus$\_$13, revealing the star to be slightly actinide poor. The other outlier, Indus$\_0$, d…
Nearby stellar streams carry unique information on the dynamical evolution and disruption of stellar systems in the Galaxy, the mass distribution in the disk, and provide unique targets for planet formation and evolution studies. We revisit the stream discovered in Meingast et al (2019) to search for new members, using Gaia DR2 data and a machine learning approach. We use a bagging classifier of one-class Support Vector Machines to perform a search in positions and proper motions for new stream members. We use the variable prediction frequency resulting from the multitude of classifiers to est…
Recently, a new cylindrical-shaped stream of stars up to 700 pc long was discovered hiding in the Galactic disk using kinematic data enabled by the Gaia mission. This stream of stars, dubbed Pisces-Eridanus (Psc-Eri), was initially thought to be as old as 1 Gyr, yet its stars shared a rotation period distribution consistent with a population that was 120-Myr-old. Here, we explore the detailed chemical nature of this stellar stream. We carried out high-resolution spectroscopic follow-up of 42 Psc-Eri stars using McDonald Observatory, and combined these data with information for 40 members obser…
Mergers and tidal interactions between massive galaxies and their dwarf satellites are a fundamental prediction of the Lambda-Cold Dark Matter cosmology. These events are thought to influence galaxy evolution throughout cosmic history and to provide important observational diagnostics of structure formation. Stellar streams in the Local Group are spectacular evidence for satellite disruption at the present day. However, constructing a significant sample of tidal streams beyond our immediate cosmic neighborhood has proven a daunting observational challenge and their potential for deepening our …
We observe two metal-poor main sequence stars that are members of the recently-discovered Sylgr stellar stream. We present radial velocities, stellar parameters, and abundances for 13 elements derived from high-resolution optical spectra collected using the Magellan Inamori Kyocera Echelle spectrograph. The two stars have identical compositions (within 0.13 dex or 1.2 sigma) among all elements detected. Both stars are very metal poor ([Fe/H] = -2.92 +/- 0.06). Neither star is highly enhanced in C ([C/Fe] < +1.0). Both stars are enhanced in the alpha elements Mg, Si, and Ca ([alpha/Fe] = +0.32 …
Stellar streams produced from dwarf galaxies provide direct evidence of the hierarchical formation of the Milky Way. Here, we present the first comprehensive study of the "LMS-1" stellar stream, that we detect by searching for wide streams in the Gaia EDR3 dataset using the STREAMFINDER algorithm. This stream was recently discovered by Yuan et al. (2020). We detect LMS-1 as a $60°$ long stream to the north of the Galactic bulge, at a distance of $\sim 20$ kpc from the Sun, together with additional components that suggest that the overall stream is completely wrapped around the inner Galaxy. Us…
We present an analysis of the structure, kinematics and orbit of a newly found stellar stream emanating from the globular cluster M92 (NGC 6341). This stream was discovered in an improved matched-filter map of the outer Galaxy, based on a "color-color-magnitude" diagram, created using photometry from the Canada-France Imaging Survey (CFIS) and the Pan-STARRS 1 3$π$ survey (PS1). We find the stream to have a length of 17° (2.5 kpc at the distance of M92), a width dispersion of $0.29$°(42 pc) and a stellar mass of $[3.17 \pm{0.89}] \times 10^{4} $ M$_\odot$ ($10 \%$ of the stellar mass of the cu…
We combine the power of two stream-searching tools, STREAMFINDER and StarGO applied to the Gaia EDR3 data, to detect stellar debris belonging to the Cetus stream system that forms a complex, nearly polar structure around the Milky Way. In this work, we find the southern extensions of the northern Cetus stream as the Palca stream and a new southern stream, which overlap on the sky but have different distances. These two stream wraps extend over more than $\sim100°$ on the sky ($-60°<δ<+40°$). The current N-body model of the system reproduces both wraps in the trailing arm. We also show that the…
We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors, using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey ($S^5$), proper motions from $Gaia$ EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ${\sim}10-50$ kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwa…
In this paper, we present a holistic view of the detection, characterization, and origin of stellar streams in the disk of a simulated Milky Way-like galaxy. The star-by-star simulation of the Galaxy evolves stars born in clusters in a realistic galactic potential that includes spiral arms, a bar, and giant molecular clouds over $5$ Gyr. We first devise a new hybrid method to detect stellar streams that combines phase space density information along with the action-angle space spanned by stars in our simulation. We find that streams' progenitor star clusters and associations are all preferenti…
Omega Centauri is the most massive globular cluster of the Milky Way, and possesses many peculiar properties. In particular, the cluster contains distinct multiple stellar populations, with a large spread in metallicity and different kinematics as a function of light elements abundance, implying that it formed over an extended period of time. This has lead to the suggestion that $ω$ Cen is the remnant core of an accreted dwarf galaxy. If this scenario is correct, $ω$ Cen should be tidally limited, and one should expect to find tidal debris spread along its orbit. Here we use N-body simulations…
The GD-1 stream is one of the longest and coldest stellar streams discovered to date, and one of the best objects for constraining the dark matter properties of the Milky Way. Using data from {\it Gaia} DR2 we study the proper motions, distance, morphology and density of the stream to uncover small scale perturbations. The proper motion cleaned data shows a clear distance gradient across the stream, ranging from 7 to 12 kpc. However, unlike earlier studies that found a continuous gradient, we uncover a distance minimum at $φ_{1}\approx$-50 deg, after which the distance increases again. We can …
We aim to measure the proper motion along the Sagittarius stream that is the missing piece to determine its full 6D phase space coordinates. We conduct a blind search of over-densities in proper motion from Gaia DR2 in a broad region around the Sagittarius stream by applying wavelet transform techniques. We find that for most of the sky patches, the highest intensity peaks delineate the path of the Sagittarius stream. The 1500 peaks identified depict a continuous sequence spanning almost $2π$ in the sky, only obscured when the stream crosses the Galactic disk. Altogether, around $100\,000$ sta…
蛇夫座流是最近在银河系中发现的恒星潮汐流。我们提出了高质量的光谱数据的14个流成员星获得的凯克和MMT望远镜。我们确认流作为一个快速移动（$v_{los}\sim290$ km s $^{-1}$），运动学冷组（$σ_{v_{los}}\lesssim1$ km s $^{-1}$）的$α$增强和金属贫星（${\rm [α/Fe]\sim0.4}$ dex，${\rm [Fe/H]\sim-2.0}$ dex）。使用概率技术，我们同时在视线速度，颜色幅度，坐标和自行空间中对流进行建模，从而确定其在6D相空间中的分布。我们发现，这条流延伸到距离太阳7.5 ~ 9 kpc的地方;它的长度是宽度的50倍，只是在投影中看起来高度缩短。对这条星流中恒星的分析表明，它的年龄是$\sim12$ Gyr，其初始恒星质量是$\sim2\times10^4$ $M_{\odot}$（或至少是$\gtrsim7\times10^3$ $M_{\odot}$）。假设一个基准的银河系势，我们拟合一个与观测到的相空间分布相匹配的流轨道，除了在自行中的一些张力：流的轨道周期为$\sim350$ Myr，并且在一个相当偏心的轨道（$e\sim0.66$）上，近心为$\sim3.5$ kpc，远心为$\sim17$ kpc。该流的相空间结构和恒星数量表明，它的前身一定是一个球状星团，它在百万年前只被$\sim240…
There is increasing evidence that a substantial fraction of Milky Way satellite galaxies align in a rotationally-supported plane of satellites, a rare configuration in cosmological simulations of galaxy formation. It has been suggested that other Milky Way substructures (namely young halo globular clusters and stellar/gaseous streams) similarly tend to align with this plane, accordingly dubbed the Vast Polar Structure (VPOS). Using systemic proper motions inferred from Gaia data, we find that globular cluster orbital poles are not clustered in the VPOS direction, though the population with the…
Detectability of dark matter subhalo impacts in Milky Way stellar streams
University of California, San Diego（加利福尼亚大学圣地亚哥分校）；Institute of High Energy Physics, Austrian Academy of Sciences（奥地利科学院高能物理研究所）；The Observatories of the Carnegie Institution for Science（卡内基科学机构天文台）
We introduce the Southern Stellar Stream Spectroscopy Survey (${S}^5$), an on-going program to map the kinematics and chemistry of stellar streams in the Southern Hemisphere. The initial focus of ${S}^5$ has been spectroscopic observations of recently identified streams within the footprint of the Dark Energy Survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky W…
Thin stellar streams, formed from the tidal disruption of globular clusters, are important gravitational tools, sensitive to both global and small-scale properties of dark matter. The Palomar 5 stellar stream (Pal 5) is an exemplar stream within the Milky Way: Its $\sim 20^\circ$ tidal tails connect back to the progenitor cluster, and the stream has been used to study the shape, total mass, and substructure fraction of the dark matter distribution of the Galaxy. However, most details of the phase-space distribution of the stream are not fully explained, and dynamical models that use the stream…
Stellar ejecta gradually enrich the gas out of which subsequent stars form, making the least chemically enriched stellar systems direct fossils of structures formed in the early universe. Although a few hundred stars with metal content below one thousandth of the solar iron content are known in the Galaxy, none of them inhabit globular clusters, some of the oldest known stellar structures. These show metal content of at least ~0.2 percent of the solar metallicity ([Fe/H] > -2.7). This metallicity floor appears universal and it has been proposed that proto-galaxies that merge into the galaxies …
The C-19 stream is the most metal poor stellar system ever discovered, with a mean metallicity $[Fe/H] = -3.38\pm0.06$. Its low metallicity dispersion ($σ_{\rm [Fe/H]}$ $<$ 0.18 at the 95\% confidence level) as well as variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use VLT/UVES spectra of seven C-19 stars to derive more precise velocity measurements for member stars, and to identify two new members with radial velocities and metallicities consistent with the stream's properties. One of these new member stars is located 30 $°$ away from the previous…
We present the discovery of a large population of stellar streams that surround the inner Galaxy, found in the Gaia DR2 catalog using the new STREAMFINDER algorithm. Here we focus on the properties of eight new high-significance structures found at Heliocentric distances between 1 and 10 kpc and at Galactic latitudes $|b|>20°$, named Slidr, Sylgr, Ylgr, Fimbulthul, Svöl, Fjörm, Gjöll and Leiptr. Spectroscopic measurements of seven of the streams confirm the detections, which are based on Gaia astrometry and photometry alone, and show that these streams are predominantly metal-poor. The sample …
