Statistical detection of a tidal stream associated with the globular cluster M68 using Gaia data

ABSTRACT A method to search for tidal streams and to fit their orbits based on maximum likelihood is presented and applied to the Gaia data. Tests of the method are performed showing how a simulated stream produced by tidal stripping of a star cluster is recovered when added to a simulation of the Gaia catalogue. The method can be applied to search for streams associated with known progenitors or to do blind searches in a general catalogue. As the first example, we apply the method to the globular cluster M68 and detect its clear tidal stream stretching over the whole North Galactic hemisphere, and passing within 5 kpc of the Sun. This is one of the closest tidal streams to us detected so far, and is highly promising to provide new constraints on the Milky Way gravitational potential, for which we present preliminary fits finding a slightly oblate dark halo consistent with other observations. We identify the M68 tidal stream with the previously discovered Fjörm stream by Ibata et al. The tidal stream is confirmed to contain stars that are consistent with the HR-diagram of M68. We provide a list of 115 stars that are most likely to be stream members, and should be prime targets for follow-up spectroscopic studies.

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Quantifying tidal stream disruption in a simulated Milky Way

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx1268 ◽

2017 ◽

Vol 470 (1) ◽

pp. 522-538 ◽

Cited By ~ 10

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.

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Using ground based data as a precursor for Gaia in getting proper motions of satellites

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005750 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 210-213

Author(s):

Tobias K. Fritz ◽

Sean T. Linden ◽

Paul Zivick ◽

Nitya Kallivayalil ◽

Jo Bovy

Keyword(s):

Adaptive Optics ◽

Globular Cluster ◽

Proper Motion ◽

Milky Way ◽

Dwarf Galaxy ◽

Optical Data ◽

Line Of Sight ◽

Wide Field ◽

Proper Motions ◽

Tidal Stream

AbstractWe present our effort to measure the proper motions of satellites in the halo of the Milky Way with mainly ground based telescopes as a precursor on what is possible with Gaia. For our first study, we used wide field optical data from the LBT combined with a first epoch of SDSS observations, on the globular cluster Palomar 5 (Pal 5). Since Pal 5 is associated with a tidal stream it is very useful to constrain the shape of the potential of the Milky Way. The motion and other properties of the Pal 5 system constrain the inner halo of the Milky Way to be rather spherical. Further, we combined adaptive optics and HST to get an absolute proper motion of the globular cluster Pyxis. Using the proper motion and the line-of-sight velocity we find that the orbit of Pyxis is rather eccentric with its apocenter at more than 100 kpc and its pericenter at about 30 kpc. The dynamics excludes an association with the ATLAS stream, the Magellanic clouds, and all satellites of the Milky Way at least down to the mass of Leo II. However, the properties of Pyxis, like metallicity and age, point to an origin from a dwarf of at least the mass of Leo II. We therefore propose that Pyxis originated from an unknown relatively massive dwarf galaxy, which is likely today fully disrupted. Assuming that Pyxis is bound to the Milky Way we derive a 68% lower limit on the mass of the Milky Way of 9.5 × 1011 M⊙.

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Globular Cluster Streams as Galactic High-Precision Scales

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006742 ◽

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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FOSSILs in the Galactic Halo

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318007111 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 73-76

Author(s):

Carl J. Grillmair

Keyword(s):

Galactic Halo ◽

Galactic Center ◽

Dwarf Galaxies ◽

Matched Filter ◽

The North ◽

History Of ◽

Tidal Streams ◽

North Galactic ◽

Size Scales

AbstractWe use a matched filter to detect compact groups of old, metal-poor stars that we term FOSSILs (Fragments of Old Stellar Systems in Limbo). With size scales on the order of 10 arcminutes, distances ranging from 2 to 200 kpc, and memberships ranging from a handful to several dozen stars, these FOSSILs stand out from the surrounding field and are presumably signatures of, or debris from, ancient star clusters and dwarf galaxies. They may be localized concentrations of stars within more extensive tidal streams, and in some cases may be the signatures of extant but heretofore undetected ultrafaint galaxies. Using magnitudes and colors from the Pan-STARRs survey, we detect ∼ 70 such FOSSILs at 5 σ or greater in a 2200 square degree region in the vicinity of the north Galactic pole. A subsample of more populous FOSSILs that could be candidate ultrafaint dwarf galaxies suggests a total population of 200 such objects within 200 kpc of the Galactic center. Spectroscopic and astrometric follow-up of these FOSSILs will be required to determine the nature of these structures, deepen our understanding of the make-up and accretion history of the Galactic halo, and perhaps alleviate the missing satellites problem.

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Great Circle Tidal Streams: Evidence for a Nearly Spherical Massive Dark Halo around the Milky Way

The Astrophysical Journal ◽

10.1086/320060 ◽

2001 ◽

Vol 551 (1) ◽

pp. 294-311 ◽

Cited By ~ 344

Author(s):

Rodrigo Ibata ◽

Geraint F. Lewis ◽

Michael Irwin ◽

Edward Totten ◽

Thomas Quinn

Keyword(s):

Milky Way ◽

Great Circle ◽

Dark Halo ◽

Tidal Streams

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Electrochemical behaviour and ESR spectra of nitro substituted mono- and dibenzoylmethylenebenzthiazolines and selenazolines

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19791540 ◽

1979 ◽

Vol 44 (5) ◽

pp. 1540-1551 ◽

Cited By ~ 3

Author(s):

Jaro Komenda ◽

Jiří Huzlík

Keyword(s):

Electron Transfer ◽

Esr Spectroscopy ◽

Electrochemical Behaviour ◽

Spectroscopic Studies ◽

Esr Spectra ◽

Slow Electron

Compounds of the type of 2-(4'-nitrobenzoyl)methylene-3-ethylbenzothiazoline (I) and 2-bis-(p-nitrobenzoyl)methylene-3-ethylbenzothiazoline (II) were studied polarographically and by ESR spectroscopy to obtain informations about their electrochemical and follow-up reactions and their conformation. Whereas with compounds of the type I the conjugation in their molecules is preserved, with type II the coplanarity of the molecules is disturbed, which is manifested in the values of the splitting constants of the ESR spectra and a slow electron transfer between both nitrophenyl substituents. These conclusions are supported by NMR spectroscopic studies.

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The globular cluster system of the Auriga simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1380 ◽

2020 ◽

Vol 496 (1) ◽

pp. 638-648 ◽

Cited By ~ 1

Author(s):

Timo L R Halbesma ◽

Robert J J Grand ◽

Facundo A Gómez ◽

Federico Marinacci ◽

Rüdiger Pakmor ◽

...

Keyword(s):

Globular Cluster ◽

Milky Way ◽

Cluster Formation ◽

Solar Radius ◽

High Mass ◽

Formation Model ◽

The Galaxy ◽

High Mass Loss ◽

Globular Cluster System ◽

Varying Mass

ABSTRACT We investigate whether the galaxy and star formation model used for the Auriga simulations can produce a realistic globular cluster (GC) population. We compare statistics of GC candidate star particles in the Auriga haloes with catalogues of the Milky Way (MW) and Andromeda (M31) GC populations. We find that the Auriga simulations do produce sufficient stellar mass for GC candidates at radii and metallicities that are typical for the MW GC system (GCS). We also find varying mass ratios of the simulated GC candidates relative to the observed mass in the MW and M31 GCSs for different bins of galactocentric radius metallicity (rgal–[Fe/H]). Overall, the Auriga simulations produce GC candidates with higher metallicities than the MW and M31 GCS and they are found at larger radii than observed. The Auriga simulations would require bound cluster formation efficiencies higher than 10 per cent for the metal-poor GC candidates, and those within the Solar radius should experience negligible destruction rates to be consistent with observations. GC candidates in the outer halo, on the other hand, should either have low formation efficiencies, or experience high mass-loss for the Auriga simulations to produce a GCS that is consistent with that of the MW or M31. Finally, the scatter in the metallicity as well as in the radial distribution between different Auriga runs is considerably smaller than the differences between that of the MW and M31 GCSs. The Auriga model is unlikely to give rise to a GCS that can be consistent with both galaxies.

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The Milky Way globular cluster system within the context of a closed box

Astrophysics and Space Science ◽

10.1007/s10509-020-03897-0 ◽

2020 ◽

Vol 365 (12) ◽

Author(s):

Graeme H. Smith

Keyword(s):

Globular Cluster ◽

Milky Way ◽

Cluster System ◽

Globular Cluster System

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On the origin of the helium-rich population in the peculiar globular cluster Omega Centauri

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310004114 ◽

2009 ◽

Vol 5 (S268) ◽

pp. 187-188

Author(s):

Donatella Romano ◽

M. Tosi ◽

M. Cignoni ◽

F. Matteucci ◽

E. Pancino ◽

...

Keyword(s):

Chemical Composition ◽

Globular Cluster ◽

Main Sequence ◽

Milky Way ◽

Dwarf Galaxy ◽

Potential Well ◽

Galactic Winds ◽

Supernova Explosions

AbstractIn this contribution we discuss the origin of the extreme helium-rich stars which inhabit the blue main sequence (bMS) of the Galactic globular cluster Omega Centauri. In a scenario where the cluster is the surviving remnant of a dwarf galaxy ingested by the Milky Way many Gyr ago, the peculiar chemical composition of the bMS stars can be naturally explained by considering the effects of strong differential galactic winds, which develop owing to multiple supernova explosions in a shallow potential well.

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