scholarly journals Tidal Streams in the Galactic Halo: Evidence for the Sagittarius Northern Stream or Traces of a New Nearby Dwarf Galaxy

2001 ◽  
Vol 549 (2) ◽  
pp. L199-L202 ◽  
Author(s):  
David Martínez-Delgado ◽  
Antonio Aparicio ◽  
M. Ángeles Gómez-Flechoso ◽  
Ricardo Carrera
Keyword(s):  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Tidal Streams ◽  
Northern Stream

scholarly journals The course of the Orphan Stream in the Northern Galactic hemisphere traced with Gaia DR2

2019 ◽  
Vol 486 (1) ◽  
pp. 936-949 ◽  
Author(s):  
Mark A Fardal ◽  
Roeland P van der Marel ◽  
Sangmo Tony Sohn ◽  
Andres del Pino Molina
Keyword(s):  
Proper Motion ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Three Dimensional ◽  
Red Giants ◽  
Independent Evidence ◽  
Horizontal Branch Stars ◽  
Red Giant ◽  
Tidal Streams ◽  
Using Data

Abstract The Orphan Stream is one of the most prominent tidal streams in the Galactic halo. Using data on red giants, RR Lyrae, and horizontal branch stars from Gaia and other surveys, we determine the proper motion of the Orphan Stream over a path of more than 90° on the sky. We also provide updated tracks for the sky position, distance, and radial velocity of the stream. Our tracks in these latter dimensions mostly agree with previous results. However, there are significant corrections to the earlier distance and latitude tracks as the stream approaches the Galactic disc. Stream stars selected with three-dimensional kinematics display a very tight red giant sequence. Concordantly, we find that applying a proper motion cut removes the most metal-rich stars from earlier spectroscopic samples of stream stars, though a significant dispersion remains, indicating a dwarf galaxy origin. The deceleration of the stream towards its leading end suggests a circular velocity of $\sim \!200 \, \mbox{km}\, \mbox{s}^{-1}$ at a galactocentric radius $\sim \!30 \, \mbox{kpc}$, consistent with other independent evidence. However, the track of the stream departs significantly from an orbit; the spatial track does not point along the same direction as the velocity vector, and it exhibits a lateral wiggle that is unlikely to match any reasonable orbit. The low metallicity and small dispersion of the stream in the various coordinates point to a progenitor with a relatively low dynamical mass $\sim \!10^8 \, \mathrm{ M}_{\odot }$.

scholarly journals Creation/destruction of ultra-wide binaries in tidal streams

2020 ◽  
Author(s):  
Jorge Peñarrubia
Keyword(s):  
Globular Clusters ◽  
Galactic Halo ◽  
Local Density ◽  
Formation Rate ◽  
Semimajor Axis ◽  
Major Axis ◽  
Binding Energies ◽  
Semi Major Axis ◽  
The Mean ◽  
Tidal Streams

Abstract This paper uses statistical and N-body methods to explore a new mechanism to form binary stars with extremely large separations (≳ 0.1 pc), whose origin is poorly understood. Here, ultra-wide binaries arise via chance entrapment of unrelated stars in tidal streams of disrupting clusters. It is shown that (i) the formation of ultra-wide binaries is not limited to the lifetime of a cluster, but continues after the progenitor is fully disrupted, (ii) the formation rate is proportional to the local phase-space density of the tidal tails, (iii) the semimajor axis distribution scales as p(a)da ∼ a1/2da at a ≪ D, where D is the mean interstellar distance, and (vi) the eccentricity distribution is close to thermal, p(e)de = 2ede. Owing to their low binding energies, ultra-wide binaries can be disrupted by both the smooth tidal field and passing substructures. The time-scale on which tidal fluctuations dominate over the mean field is inversely proportional to the local density of compact substructures. Monte-Carlo experiments show that binaries subject to tidal evaporation follow p(a)da ∼ a−1da at a ≳ apeak, known as Öpik’s law, with a peak semi-major axis that contracts with time as apeak ∼ t−3/4. In contrast, a smooth Galactic potential introduces a sharp truncation at the tidal radius, p(a) ∼ 0 at a ≳ rt. The scaling relations of young clusters suggest that most ultra-wide binaries arise from the disruption of low-mass systems. Streams of globular clusters may be the birthplace of hundreds of ultra-wide binaries, making them ideal laboratories to probe clumpiness in the Galactic halo.

scholarly journals Quantifying tidal stream disruption in a simulated Milky Way

2017 ◽  
Vol 470 (1) ◽  
pp. 522-538 ◽  
Author(s):  
Emily Sandford ◽  
Andreas H. W. Küpper ◽  
Kathryn V. Johnston ◽  
Jürg Diemand
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Galactic Halo ◽  
Mass Range ◽  
Galactic Centre ◽  
High Dimensions ◽  
Density Profiles ◽  
Upper Limits ◽  
Tidal Stream ◽  
Tidal Streams

Abstract Simulations of tidal streams show that close encounters with dark matter subhaloes induce density gaps and distortions in on-sky path along the streams. Accordingly, observing disrupted streams in the Galactic halo would substantiate the hypothesis that dark matter substructure exists there, while in contrast, observing collimated streams with smoothly varying density profiles would place strong upper limits on the number density and mass spectrum of subhaloes. Here, we examine several measures of stellar stream ‘disruption' and their power to distinguish between halo potentials with and without substructure and with different global shapes. We create and evolve a population of 1280 streams on a range of orbits in the Via Lactea II simulation of a Milky Way-like halo, replete with a full mass range of Λcold dark matter subhaloes, and compare it to two control stream populations evolved in smooth spherical and smooth triaxial potentials, respectively. We find that the number of gaps observed in a stellar stream is a poor indicator of the halo potential, but that (i) the thinness of the stream on-sky, (ii) the symmetry of the leading and trailing tails and (iii) the deviation of the tails from a low-order polynomial path on-sky (‘path regularity') distinguish between the three potentials more effectively. We furthermore find that globular cluster streams on low-eccentricity orbits far from the galactic centre (apocentric radius ∼30–80 kpc) are most powerful in distinguishing between the three potentials. If they exist, such streams will shortly be discoverable and mapped in high dimensions with near-future photometric and spectroscopic surveys.

Stellar Populations of the Outer Milky-Way Halo

2017 ◽  
Vol 13 (S334) ◽  
pp. 29-33
Author(s):  
Baslio Santiago ◽  
Elmer Luque ◽  
Adriano Pieres ◽  
Anna Bárbara Queiroz
Keyword(s):  
Galaxy Evolution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Building Blocks ◽  
Early Stages ◽  
Dark Energy Survey ◽  
Stellar Streams ◽  
The Galaxy

AbstractThe stellar spheroidal components of the Milky-Way contain the oldest and most metal poor of its stars. Inevitably the processes governing the early stages of Galaxy evolution are imprinted upon them. According to the currently favoured hierarchical bottom-up scenario of galaxy formation, these components, specially the Galactic halo, are the repository of most of the mass built up from accretion events in those early stages. These events are still going on today, as attested by the long stellar streams associated to the Sagittarius dwarf galaxy and several other observed tidal substructure, whose geometry, extent, and kinematics are important constraints to reconstruct the MW gravitational potential and infer its total (visible + dark) mass. In addition, the remaining system of MW satellites is expected to be a fossil record of the much larger population of Galactic building blocks that once existed and got accreted. For all these reasons, it is crucial to unravel as much of this remaining population as possible, as well as the current stellar streams that orbit within the halo. The best bet to achieve this task is to carry out wide, deep, and multi-band photometric surveys that provide homogeneous stellar samples. In this contribution, we summarize the results of several years of work towards detecting and characterizing distant MW stellar systems, star clusters and dwarf spheroidals alike, with an emphasis on the analysis of data from the Dark Energy Survey (DES). We argue that most of the volume in distance, size and luminosity space, both in the Galaxy and in the Clouds, is still unprobed. We then discuss the perspectives of exploring this outer MW volume using the current surveys, as well as other current and future surveys, such as the Large Synoptic Survey Telescope (LSST).

scholarly journals The Canis Major Dwarf Galaxy

2004 ◽  
Vol 21 (4) ◽  
pp. 371-374
Author(s):  
Geraint F. Lewis ◽  
Rodrigo A. Ibata ◽  
Michael J. Irwin ◽  
Nicolas F. Martin ◽  
Michele Bellazzini ◽  
...  
Keyword(s):  
Building Block ◽  
Milky Way ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Dwarf Galaxy ◽  
Observational Evidence ◽  
Thick Disk ◽  
Equatorial Orbit ◽  
Satellite Galaxy

AbstractRecent observational evidence suggests that the Sagittarius dwarf galaxy represents the only major ongoing accretion event in the Galactic halo, accounting for the majority of stellar debris identified there. This paper summarises the recent discovery of another potential Milky Way accretion event, the Canis Major dwarf galaxy. This dwarf satellite galaxy is found to lie just below the Galactic plane and appears to be on an equatorial orbit. Unlike Sagittarius, which is contributing to the Galactic halo, the location and eventual demise of Canis Major suggests that it represents a building block of the thick disk.

scholarly journals RR Lyrae Stars in the Newly Discovered Ultra-faint Dwarf Galaxy Centaurus I*

2021 ◽  
Vol 162 (6) ◽  
pp. 253
Author(s):  
C. E. Martínez-Vázquez ◽  
W. Cerny ◽  
A. K. Vivas ◽  
A. Drlica-Wagner ◽  
A. B. Pace ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Relative Rate ◽  
Distance Modulus ◽  
Rr Lyrae Stars ◽  
Full Sample ◽  
Rr Lyrae ◽  
The One ◽  
Lyrae Stars

Abstract We report the detection of three RR Lyrae (RRL) stars (two RRc and one RRab) in the ultra-faint dwarf (UFD) galaxy Centaurus I (Cen I) and two Milky Way (MW) δ Scuti/SX Phoenicis stars based on multi-epoch giz DECam observations. The two RRc stars are located within two times the half-light radius (r h ) of Cen I, while the RRab star (CenI-V3) is at ∼6 r h . The presence of three distant RRL stars clustered this tightly in space represents a 4.7σ excess relative to the smooth distribution of RRL in the Galactic halo. Using the newly detected RRL stars, we obtain a distance modulus to Cen I of μ 0 = 20.354 ± 0.002 mag (σ = 0.03 mag), a heliocentric distance of D ⊙ = 117.7 ± 0.1 kpc (σ = 1.6 kpc), with systematic errors of 0.07 mag and 4 kpc. The location of the Cen I RRL stars in the Bailey diagram is in agreement with other UFD galaxies (mainly Oosterhoff II). Finally, we study the relative rate of RRc+RRd (RRcd) stars (f cd) in UFD and classical dwarf galaxies. The full sample of MW dwarf galaxies gives a mean of f cd = 0.28. While several UFD galaxies, such as Cen I, present higher RRcd ratios, if we combine the RRL populations of all UFD galaxies, the RRcd ratio is similar to the one obtained for the classical dwarfs (f cd ∼ 0.3). Therefore, there is no evidence for a different fraction of RRcd stars in UFD and classical dwarf galaxies.

scholarly journals Mapping the Galactic Halo. III. Simulated Observations of Tidal Streams

2001 ◽  
Vol 122 (3) ◽  
pp. 1397-1419 ◽  
Author(s):  
Paul Harding ◽  
Heather L. Morrison ◽  
Edward W. Olszewski ◽  
John Arabadjis ◽  
Mario Mateo ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Tidal Streams

scholarly journals Resonant Trapping of the Moving Groups G18-39 and G21-22 in the Galactic Halo

2018 ◽  
Vol 14 (S344) ◽  
pp. 134-138
Author(s):  
W. J. Schuster ◽  
E. Moreno ◽  
J. G. Fernández-Trincado
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Rotation Speed ◽  
Dwarf Galaxy ◽  
Mass Model ◽  
The Mean ◽  
Moving Groups ◽  
Orbital Resonances ◽  
Two Peaks

AbstractOrbital resonances in the Galactic halo have been studied using the Galactic mass model of Pichardo et al. (2003, 2004), including a Galactic bar. For the two moving groups of the Galactic halo, G18-39 and G21-22 (Silva et al. 2012), the majority of stars in both groups appear trapped in two resonances over the Galactic plane, generated by the bar. We have taken the rotation speed of the bar, Ωb, as 45-55 km s-1 kpc-1. So, these two moving groups are part of stellar supergroups which populate these two resonances. The position of these two groups in the Bottlinger diagram can be explained by the mean (U,V) field generated by these two resonances crossing the solar vicinity, in contrast with the alternate explanation of Silva et al. (2012), based on the simulations of Meza et al. (2005), that these two groups, seen as two peaks in the U Galactic velocity, have been created by the accretion of a dwarf galaxy by the Milky Way, such as that of Ω Centauri.

scholarly journals The Milky Way, the Galactic Halo, and the Halos of Galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 266-271
Author(s):  
Ortwin Gerhard
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Large Fraction ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Galaxy Halos ◽  
The Subject ◽  
Hierarchical Nature ◽  
Tidal Streams ◽  
The Many

AbstractThe Milky Way, “our” Galaxy, is currently the subject of intense study with many ground-based surveys, in anticipation of upcoming results from the Gaia mission. From this work we have been learning about the full three-dimensional structure of the Galactic box/peanut bulge, the distribution of stars in the bar and disk, and the many streams and substructures in the Galactic halo. The data indicate that a large fraction of the Galactic halo has been accreted from outside. Similarly, in many external galaxy halos there is now evidence for tidal streams and accretion of satellites. To study these features requires exquisite, deep photometry and spectroscopy. These observations illustrate how galaxy halos are still growing, and sometimes can be used to “time” the accretion events. In comparison with cosmological simulations, the structure of galaxy halos gives us a vivid illustration of the hierarchical nature of our Universe.

scholarly journals Globular Cluster Streams as Galactic High-Precision Scales

2015 ◽  
Vol 11 (S317) ◽  
pp. 140-144
Author(s):  
Andreas H.W. Küpper ◽  
Eduardo Balbinot ◽  
Ana Bonaca ◽  
Kathryn V. Johnston ◽  
David W. Hogg ◽  
...  
Keyword(s):  
High Precision ◽  
Gravitational Potential ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Orbital Motion ◽  
Dwarf Galaxy ◽  
Tidal Streams

AbstractTidal streams of globular clusters are ideal tracers of the Galactic gravitational potential. Compared to the few known, complex and diffuse dwarf-galaxy streams, they are kinematically cold, have thin morphologies and are abundant in the halo of the Milky Way. Their coldness and thinness in combination with potential epicyclic substructure in the vicinity of the stream progenitor turns them into high-precision scales. With the example of Palomar 5, we demonstrate how modeling of a globular cluster stream allows us to simultaneously measure the properties of the disrupting globular cluster, its orbital motion, and the gravitational potential of the Milky Way.

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