Gaps in the GD-1 Star Stream

暗物质次亚晕与薄恒星流的半解析建模：在CDM框架下对GD-1类流的统计预测

Semi-Analytic Modeling of Dark Matter Subhalo Encounters with Thin Stellar Streams: Statistical Predictions for GD-1-like Streams in CDM

研究通过半解析方法建模暗物质次亚晕与GD-1类流的相互作用，分析次亚晕质量范围及影响参数对流中空洞形成的影响。

The spatial distribution of Milky Way satellites, gaps in streams and the nature of dark matter

The spatial distribution of Milky Way (MW) subhaloes provides an important set of observables for testing cosmological models. These include the radial distribution of luminous satellites, planar configurations, and the abundance of dark subhaloes whose existence or absence is key to distinguishing amongst dark matter models. We use the COCO $N$-body simulations of cold dark matter (CDM) and 3.3keV thermal relic warm dark matter (WDM) to predict the satellite spatial distribution in the limit that the impact of baryonic physics is minimal. We demonstrate that the radial distributions of CDM an…

Delayed star formation in high-redshift stream-fed galaxies

We propose that star formation is delayed relative to the inflow rate in rapidly-accreting galaxies at very high redshift (z > 2) because of the energy conveyed by the accreting gas. Accreting gas streams provide fuel for star formation, but they stir the disk and increase turbulence above the usual levels compatible with gravitational instability, reducing the star formation efficiency in the available gas. After the specific inflow rate has sufficiently decreased - typically at z < 3 - galaxies settle in a self-regulated regime with efficient star formation. An analytic model shows that this…

Star Stream Folding by Dark Galactic Sub-Halos

Star streams in galactic halos are long, thin, unbound structures that will be disturbed by the thousands dark matter sub-halos that are predicted to be orbiting within the main halo. A sub-halo generally induces a localized wave in the stream which often evolves into a "z-fold" as an initially trailing innermost part rotates faster than an initially leading outermost part. The folding, which becomes increasingly complex with time, leads to an apparent velocity dispersion increase and thickening of the stream. We measure the equivalent velocity dispersion around the local mean in the simulatio…

A Star in the M31 Giant Stream: the Highest Negative Stellar Velocity Known

We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km/s. Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-mainsequence close binary, a symbiotic nova, or less likely, a post-AGB star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.

Density Variations in the NW Star Stream of M31

The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the M31-M33 system has found a star stream which extends about 120 kpc NW from the center of M31. The great length of the stream, and the likelihood that it does not significantly intersect the disk of M31, means that it is unusually well suited for a measurement of stream gaps and clumps along its length as a test for the predicted thousands of dark matter sub-halos. The main result of this paper is that the density of the stream varies between zero and about three times the mean along its length on scales of 2 to 20 kpc…

The Influence of Streaming Velocities on the Formation of the First Stars

How, when and where the first stars formed are fundamental questions regarding the epoch of Cosmic Dawn. A second order effect in the fluid equations was recently found to make a significant contribution: an offset velocity between gas and dark matter, the so-called streaming velocity. Previous simulations of a limited number of low-mass dark matter haloes suggest that this streaming velocity can delay the formation of the first stars and decrease halo gas fractions and the halo mass function in the low mass regime. However, a systematic exploration of its effects in a large sample of haloes h…

C-19与炽热、宽阔的恒星流

C-19 and Hot, Wide, Star Streams

本研究通过含绕轨子晕的演化CDM银河系晕模拟，解释C-19恒星流异常炽热宽阔的成因，即低质量球状星团潮汐瓦解并处于远心点附近。

The critical dark matter halo mass for Population III star formation: dependence on Lyman-Werner radiation, baryon-dark matter streaming velocity, and redshift

A critical dark matter halo mass ($M_{\rm crit}$) for Population III (Pop III) stars can be defined as the typical minimum halo mass that hosts sufficient cold dense gas required for the formation of the first stars. The presence of Lyman-Werner (UV) radiation, which can dissociate molecular hydrogen, and the baryon-dark matter streaming velocity both delay the formation of Pop III stars by increasing $M_{\rm crit}$. In this work, we constrain $M_{\rm crit}$ as a function of Lyman-Werner flux (including self-shielding), baryon-dark matter streaming, and redshift using cosmological simulations …

Shepherding Tidal Debris with the Galactic Bar: The Ophiuchus Stream

The dynamics of stellar streams in rotating barred potentials is explained for the first time. Naturally, neighbouring stream stars reach pericentre at slightly different times. In the presence of a rotating bar, these neighbouring stream stars experience different bar orientations during pericentric passage and hence each star receives a different torque from the bar. These differing torques reshape the angular momentum and energy distribution of stars in the stream, which in turn changes the growth rate of the stream. For a progenitor orbiting in the same sense as the bar's rotation and sati…

Globular Clusters in a Cosmological N-body Simulation

Stellar dynamical model globular clusters are introduced into reconstituted versions of the dark matter halos of the Via-Lactea II (VL-2) simulation to follow the star cluster tidal mass loss and stellar stream formation. The clusters initially evolve within their local sub-galactic halo, later being accreted into the main halo. Stars are continually removed from the clusters, but those that emerged in the sub-galactic halos are dispersed in a wide stream when accreted into the main halo. Thin tidal streams that survive to the present can begin to form once a cluster is in the main halo. A hig…