Stellar Debris Streams: New Probes of Galactic Structure and Formation

Grillmair, Carl J.

doi:10.1007/978-1-4419-7317-7_21

Cited by 5 publications

(1 citation statement)

References 70 publications

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“…Astronomers have found about 10-20 star streams so far in the Milky Way that may be good to observe for testing the theory of CDM [3]. Fortunately, they are likely to find even more star streams in the near future, bringing us closer to understanding dark matter.…”

Section: The Futurementioning

confidence: 99%

Using Bright Streams to Learn about Dark Matter

Ngan¹

2017

Front. Young Minds

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Matter is what we call all of the "stuff" that makes up the universe. Ordinary matter, such as atoms, makes up only about 15% of all the matter in the universe. The other 85% is called "dark matter"-it is invisible but important enough to hold our galaxy, the Milky Way, together so it does not break apart. What is dark matter? For decades, astronomers have been thinking of ideas and trying to test these ideas by observations. One popular theory called "cold dark matter (CDM)" has been widely successful in explaining dark matter in the universe as a whole, but it still needs to be tested inside our own galaxy. In this study, we show how computer simulations can help us use streams of stars in the galaxy to determine whether CDM is the correct theory to explain dark matter.

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Section: The Futurementioning

confidence: 99%

Using Bright Streams to Learn about Dark Matter

Ngan¹

2017

Front. Young Minds

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Distance estimates in the Milky Way using tidal streams

Fantin¹

2012

Proc. IAU

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During the past 20 years, numerous stellar streams have been discovered in both the Milky Way and the Local Group. These streams have been tidally torn from orbiting systems, which suggests that most should roughly trace the orbit of their progenitors around the Galaxy. As a consequence, they play a fundamental role in understanding the formation and evolution of our Galaxy. This project is based on the possibility of applying a technique developed by Binney to various tidal streams and overdensities in the Galaxy. The aim is to develop an efficient method to constrain the Galactic gravitational potential, to determine its mass distribution, and to test distance measurements. Here we apply the technique to the Grillmair & Dionatos GD-1 cold stellar stream. In the unrealistic case of noise-free data, the results show that the technique provides excellent discrimination against incorrect potentials and that it is possible to predict the heliocentric distance very accurately. This changes dramatically when errors are taken into account, which wash out most of the results. Nevertheless, it is still possible to rule out spherical potentials and set constraints on the distance of a given stream.

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Update on the Cetus Polar Stream and Its Progenitor

Yam

Carlin

Newberg

et al. 2013

ApJ

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We trace the Cetus Polar Stream (CPS) with blue horizontal branch (BHB) and red giant stars (RGBs) from Data Release 8 of the Sloan Digital Sky Survey (SDSS DR8). Using a larger dataset than was available previously, we are able to refine the measured distance and velocity to this tidal debris star stream in the south Galactic cap. Assuming the tidal debris traces the progenitor's orbit, we fit an orbit to the CPS and find that the stream is confined between ∼ 24 − 36 kpc on a rather polar orbit inclined 87 • to the Galactic plane. The eccentricity of the orbit is 0.20, and the period ∼ 700 Myr. If we instead matched N-body simulations to the observed tidal debris, these orbital parameters would change by 10% or less. The CPS stars travel in the opposite direction to those from the Sagittarius tidal stream in the same region of the sky. Through N-body models of satellites on the best-fitting orbit, and assuming that mass follows light, we show that the stream width, line-of-sight depth, and velocity dispersion imply a progenitor of 10 8 M ⊙ . However, the density of stars along the stream requires either a disruption time on the order of one orbit, or a stellar population that is more centrally concentrated than the dark matter. We suggest that an ultra-faint dwarf galaxy progenitor could reproduce a large stream width and velocity dispersion without requiring a very recent deflection of the progenitor into its current orbit. We find that most Cetus stars have metallicities of −2.5 < [Fe/H] < −2.0, similar to the observed metallicities of the ultra-faint dwarfs. Our simulations suggest that the parameters of the dwarf galaxy progenitors, including their dark matter content, could be constrained by observations of their tidal tails through comparison of the debris with N-body simulations. Newberg et al. (2009) used data from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) to confirm this discovery of a new stream in the south Galactic cap. The authors showed that this new stream of BHB stars crosses the Sagittarius trailing tidal tail at (l, b) ∼ (140 • , −70 • ), but is separated from Sgr by about 30 • in Galactic longitude at b ∼ −30 • . Because this newfound stream is located mostly in the constellation Cetus and is roughly distributed along constant Galactic longitude (i.e., the orbit is nearly polar), Newberg et al. (2009) dubbed it the Cetus Polar Stream. A slight gradient in the distance to the stream was detected, from ∼ 36 kpc at b ∼ −71 • to ∼ 30 kpc at b ∼ −46 • , where the distance nearer the South Galactic Pole places the CPS at approximately the same distance as the Sgr stream at that position. The authors examined BHB, red giant branch (RGB), and lower RGB (LRGB) stars identified by stellar parameters in the SEGUE spectroscopic database, and found a mean metallicity of [Fe/H] = -2.1 for the CPS. The ratio of blue straggler (BS) to BHB stars was shown to be much higher in Sgr than in the CPS,

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Stellar Debris Streams: New Probes of Galactic Structure and Formation

Cited by 5 publications

References 70 publications

Using Bright Streams to Learn about Dark Matter

Using Bright Streams to Learn about Dark Matter

Distance estimates in the Milky Way using tidal streams

Update on the Cetus Polar Stream and Its Progenitor

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