scholarly journals Stream-orbit misalignment & a new algorithm for constraining the Galactic potential with streams

2013 ◽  
Vol 9 (S298) ◽  
pp. 195-200
Author(s):  
Jason L. Sanders ◽  
James Binney
Keyword(s):  
Action Space ◽  
Galactic Potential ◽  
Alternative Algorithm ◽  
Orbit Fitting ◽  
Tidal Stream ◽  
Tidal Streams

AbstractIn general, a tidal stream is misaligned with the orbit of its progenitor. Here we present the formation of tidal streams in angle-action space to discuss the effect of this misalignment on orbit-fitting algorithms for constraining the Galactic potential. We close by presenting and testing an alternative algorithm which more fully accounts for the dynamics of streams by using the angle-action formalism.

scholarly journals ACTION-SPACE CLUSTERING OF TIDAL STREAMS TO INFER THE GALACTIC POTENTIAL

2015 ◽  
Vol 801 (2) ◽  
pp. 98 ◽  
Author(s):  
Robyn E. Sanderson ◽  
Amina Helmi ◽  
David W. Hogg
Keyword(s):  
Action Space ◽  
Galactic Potential ◽  
Tidal Streams

scholarly journals Action-space clustering of tidal streams to map the Galactic potential

2013 ◽  
Vol 9 (S298) ◽  
pp. 207-212 ◽  
Author(s):  
Robyn E. Sanderson ◽  
Amina Helmi ◽  
David W. Hogg
Keyword(s):  
Action Space ◽  
Leibler Divergence ◽  
Galactic Potential ◽  
Stellar Halo ◽  
Observational Errors ◽  
Tidal Streams ◽  
Potential Parameters ◽  
Best Fit ◽  
Membership Information ◽  
Input Potential

AbstractGiven a parametrized model of the Galactic potential, the best-fit parameters can be obtained by maximizing the Kullback-Leibler divergence of the action distribution of a set of stars initially clustered in action space (e.g. stars in tidal streams). This method will allow us to map the Milky Way's gravitational potential by simultaneously fitting multiple tidal streams without requiring stream membership information. With 20 streams of at least 20 stars each, including observational errors consistent with predictions for Gaia, this technique recovers the input potential parameters to a precision of 10-60% and an accuracy of 10%. With all the observed streams in our mock stellar halo (about 40) that fit the error criteria, the precision improves to 10%.

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.

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

2019 ◽  
Vol 488 (2) ◽  
pp. 1535-1557 ◽  
Author(s):  
Carles G Palau ◽  
Jordi Miralda-Escudé
Keyword(s):  
Globular Cluster ◽  
Milky Way ◽  
Spectroscopic Studies ◽  
Dark Halo ◽  
General Catalogue ◽  
Tidal Stream ◽  
Statistical Detection ◽  
Tidal Streams ◽  
North Galactic

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.

scholarly journals SUBSTRUCTURE FORMATION IN TIDAL STREAMS OF GALACTIC MINOR MERGERS

2019 ◽  
Vol 55 (2) ◽  
pp. 273-288
Author(s):  
D. A. Noreña ◽  
J. C. Muñoz-Cuartas ◽  
L. F. Quiroga ◽  
N. Libeskind
Keyword(s):  
Dark Matter ◽  
Dynamical Stability ◽  
Stellar Clusters ◽  
Tidal Stream ◽  
Substructure Formation ◽  
Satellite Galaxies ◽  
Minor Mergers ◽  
Tidal Streams

In this work, we explore the idea that substructures like stellar clusters could be formed from the tidal stream produced in galactic minor mergers. We use N -body and SPH simulations of satellite galaxies interacting with a larger galaxy. We study the distribution of mass in streams to identify overdensity regions in which a substructure could be formed. We find that without gas, no substructure forms as none of the overdensities shows a definite morphology nor dynamical stability. Including gas we find that several clumps appear and prove to be real long standing physical structures (t ≥ 1 Gyr). We analyze the orbits, ages and masses of these structures, finding their correspondence with the halo subsystems. We conclude that it is possible to form cluster-like structures from the material in tidal streams and find evidence in favour of the presence of dark matter in these systems.

scholarly journals Bardsey – an island in a strong tidal stream: underestimating coastal tides due to unresolved topography

Ocean Science ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1337-1345
Author(s):  
J. A. Mattias Green ◽  
David T. Pugh
Keyword(s):  
Satellite Altimetry ◽  
Energy Resource ◽  
Tidal Energy ◽  
Small Scale ◽  
Phase Lag ◽  
Wake Effect ◽  
Tidal Dissipation ◽  
Tidal Energetics ◽  
Tidal Stream ◽  
Tidal Streams

Abstract. Bardsey Island is located at the western end of the Llŷn Peninsula in northwestern Wales. Separated from the mainland by a channel that is some 3 km wide, it is surrounded by reversing tidal streams of up to 4 m s−1 during spring tides. These local hydrodynamic details and their consequences are unresolved by satellite altimetry and are not represented in regional tidal models. Here we look at the effects of the island on the strong tidal stream in terms of the budgets for tidal energy dissipation and the formation and shedding of eddies. We show, using local observations and a satellite-altimetry-constrained product (TPXO9), that the island has a large impact on the tidal stream and that even in this latest altimetry-constrained product the derived tidal stream is under-represented due to the island not being resolved. The effect of the island leads to an underestimate of the current speed in the TPXO9 data in the channel of up to a factor of 2.5, depending on the timing in the spring–neap cycle, and the average tidal energy resource is underestimated by a factor up to 14. The observed tidal amplitudes are higher at the mainland than at the island, and there is a detectable phase lag in the tide across the island; this effect is not seen in the TPXO9 data. The underestimate of the tide in the TPXO9 data has consequences for tidal dissipation and wake effect computation and shows that local observations are key to correctly estimating tidal energetics around small-scale coastal topography.

Tidal eddies and coastal discharge

1977 ◽  
Vol 57 (3) ◽  
pp. 869-875 ◽  
Author(s):  
R. D. Pingree ◽  
Linda Maddock
Keyword(s):  
Coastal Waters ◽  
Water Movement ◽  
Numerical Models ◽  
Relevant Information ◽  
Sea Surface ◽  
Public Interests ◽  
Additional Information ◽  
Tidal Stream ◽  
Surface Drifters ◽  
Tidal Streams

Radioactive wastes and sewage discharged into coastal waters may be largely dispersed by tidal streams. Before authorization for sea discharges can be granted by responsible authorities representing public interests, as much information as possible must be obtained on water movement in the chosen area. Comprehensive data on tidal conditions around the British Isles can be found from the Admiralty Tidal Stream Atlases (Hydrographic Department). The method by which these currents are measured is explained in the Admiralty Manual of Hydrographic Surveying (Hydrographic Department, 1948). Further, special surveys using sea surface drifters and current meters are usually necessary to provide additional information in the neighbourhood of a proposed release. The purpose of this note is to point out that further relevant information can be obtained using numerical models and that these results should also be taken into account when decisions have to be made.

scholarly journals Current Patterns in the Inner Sound (Pentland Firth) from Underway ADCP Data*

2013 ◽  
Vol 30 (1) ◽  
pp. 96-111 ◽  
Author(s):  
Lonneke Goddijn-Murphy ◽  
David K. Woolf ◽  
Matthew C. Easton
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Tidal Energy ◽  
Current Data ◽  
Northern Coast ◽  
Orkney Islands ◽  
The North ◽  
Tidal Changes ◽  
Current Profiler ◽  
Tidal Stream ◽  
Tidal Streams

AbstractNumerous acoustic Doppler current profiler (ADCP) surveys were performed in the Inner Sound of the Pentland Firth, a channel between the Orkney Islands and the northern coast of Scotland connecting the Atlantic Ocean to the west and the North Sea to the east. The Pentland Firth has the highest tidal streams of the British Isles, and one of the highest that can be found around the globe. Here, the tidal energy industry is in its demonstration phase, but not many real current measurements are in the public domain. The authors present real current data, measured during different phases of the tidal cycle, using a vessel-mounted ADCP. The tidal changes can be rapid, and because the underway measurements take time, the apparent spatial patterns are affected by temporal variation. A method is described that estimated and corrected this temporal distortion using a hydrodynamic model. It appeared that ebb and flood streams did not fully overlap, and that the tidal streams were more complicated, turbulent, and variable than existing models suggest. The data were analyzed for characteristics pertinent to practical tidal stream energy exploitation, and two favorable sites in the Inner Sound are identified. All original current data are available from the British Oceanographic Data Centre (BODC).

scholarly journals A STATISTICAL METHOD FOR MEASURING THE GALACTIC POTENTIAL AND TESTING GRAVITY WITH COLD TIDAL STREAMS

2012 ◽  
Vol 760 (1) ◽  
pp. 2 ◽  
Author(s):  
Jorge Peñarrubia ◽  
Sergey E. Koposov ◽  
Matthew G. Walker
Keyword(s):  
Statistical Method ◽  
Galactic Potential ◽  
Tidal Streams

Generation of UK Tidal Stream Atlases from Regularly Gridded Hydrodynamic Modelled Data

1998 ◽  
Vol 51 (1) ◽  
pp. 73-78 ◽  
Author(s):  
Colin Bell ◽  
Lisa Carlin
Keyword(s):  
Continental Shelf ◽  
Data Sets ◽  
Tidal Stream ◽  
Tidal Streams ◽  
The Uk ◽  
Hydrodynamic Data

Accurate charts of tidal streams are needed in many fields of science and industry. The Proudman Oceanographic Laboratory's numerically modelled hydrodynamic data sets provide a suitable source for the production of such charts. Different methods of producing data in ‘tidal diamond’ format were investigated and the most suitable was selected for implementation over the UK continental shelf.

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