Galaxy rotation curve

Summary

The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each side are averaged to create the curve. A significant discrepancy exists between the experimental curves observed, and a curve derived by applying gravity theory to the matter observed in a galaxy. Theories involving dark matter are the main postulated solutions to account for the variance. The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances. In contrast, the orbital velocities of planets in planetary system

Official source

https://en.wikipedia.org/wiki/Galaxy_rotation_curve

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Simulations of galactic disks including a dark baryonic component

Daniel Pfenniger, Yves Revaz

The near proportionality between HI and dark matter in outer galactic disks prompted us to run N-body simulations of galactic disks in which the observed gas content is supplemented by a dark gas component representing between zero and five times the visible gas content. While adding baryons in the disk of galaxies may solve some issues, it poses the problem of disk stability. We show that the global stability is ensured if the ISM is multiphased, composed of two partially coupled phases, a visible warm gas phase and a weakly collisionless cold dark phase corresponding to a fraction of the unseen baryons. The phases are subject to stellar and UV background heating and gas cooling, and their transformation into each other is studied as a function of the coupling strength. This new model, which still possesses a dark matter halo, fits the rotation curves as well as the classical CDM halos, but is the only one to explain the existence of an open and contrasting spiral structure, as observed in the outer HI disks

2009

, ,

Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravitohydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e. g., radiative cooling and UV background by the standardized package GRACKLE) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of similar to 3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

Iop Publishing Ltd2016

Model BOSS and eBOSS luminous red galaxies at 0.2 < z < 1.0 using SubHalo Abundance Matching with three parameters

Ginevra Favole, Jean-Paul Richard Kneib, Anand Stéphane Raichoor, Jiaxi Yu, Cheng Zhao

SubHalo Abundance Matching (SHAM) is an empirical method for constructing galaxy catalogues based on high-resolution N-body simulations. We apply SHAM on the UNIT simulation to simulate SDSS BOSS/eBOSS luminous red galaxies (LRGs) within a wide redshift range of 0.2 < z < 1.0. Besides the typical SHAM scatter parameter sigma, we include v(smear) and V-ceil to take into account the redshift uncertainty and the galaxy incompleteness, respectively. These two additional parameters are critical for reproducing the observed 2PCF multipoles on 5-25 h(-1). The redshift uncertainties obtained from the best-fitting v(smear) agree with those measured from repeat observations for all SDSS LRGs except for the LOWZ sample. We explore several potential systematics but none of them can explain the discrepancy found in LOWZ. Our explanation is that the LOWZ galaxies might contain another type of galaxies that needs to be treated differently. The evolution of the measured sigma and V-ceil also reveals that the incompleteness of eBOSS galaxies decreases with the redshift. This is the consequence of the magnitude lower limit applied in eBOSS LRG target selection. Our SHAM also set upper limits for the intrinsic scatter of the galaxy-halo relation, given a complete galaxy sample: sigma(int) < 0.31 for LOWZ at 0.2 < z < 0.33, sigma(int) < 0.36 for LOWZ at 0.33 < z < 0.43, and sigma(int) < 0.46 for CMASS at 0.43 < z < 0.51. The projected 2PCFs of our SHAM galaxies also agree with the observational ones on the 2PCF fitting range.

OXFORD UNIV PRESS2022