scholarly journals Extracting Galaxy Merger Timescales II: A new fitting formula

2020 ◽  
Author(s):  
R J J Poulton ◽  
C Power ◽  
A S G Robotham ◽  
P J Elahi ◽  
C D P Lagos
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Structure Formation ◽  
Structural Properties ◽  
Galaxy Formation ◽  
Fundamental Problem ◽  
Dark Matter Halos ◽  
New Model ◽  
Orbital Parameters ◽  
Improved Model

Abstract Predicting the merger timescale (τmerge) of merging dark matter halos, based on their orbital parameters and the structural properties of their hosts, is a fundamental problem in gravitational dynamics that has important consequences for our understanding of cosmological structure formation and galaxy formation. Previous models predicting τmerge have shown varying degrees of success when compared to the results of cosmological N-body simulations. We build on this previous work and propose a new model for τmerge that draws on insights derived from these simulations. We find that published predictions can provide reasonable estimates for τmerge based on orbital properties at infall, but tend to underpredict τmerge inside the host virial radius (R200) because tidal stripping is neglected, and overpredict it outside R200 because the host mass is underestimated. Furthermore, we find that models that account for orbital angular momentum via the circular radius Rcirc underpredict (overpredict) τmerge for bound (unbound) systems. By fitting for the dependence of τmerge on various orbital and host halo properties, we derive an improved model for τmerge that can be applied to a merging halo at any point in its orbit. Finally, we discuss briefly the implications of our new model for τmerge for semi-analytical galaxy formation modelling.

scholarly journals Rotation of Galaxy Dark Matter Halos

2006 ◽  
Vol 2 (S235) ◽  
pp. 104-104
Author(s):  
Stéphane Herbert-Fort ◽  
Dennis Zaritsky ◽  
Yeun Jin Kim ◽  
Jeremy Bailin ◽  
James E. Taylor
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Numerical Simulations ◽  
Galaxy Formation ◽  
Spiral Galaxy ◽  
Observational Studies ◽  
Spiral Galaxies ◽  
Satellite System ◽  
Dark Matter Halos ◽  
The Mean

AbstractThe degree to which outer dark matter halos of spiral galaxies rotate with the disk is sensitive to their accretion history and may be probed with associated satellite galaxies. We use the Steward Observatory Bok telescope to measure the sense of rotation of nearby isolated spirals and combine these data with those of their associated satellites (drawn from SDSS) to directly test predictions from numerical simulations. We aim to constrain models of galaxy formation by measuring the projected component of the halo angular momentum that is aligned with that of spiral galaxy disks, Jz. We find the mean bulk rotation of the ensemble satellite system to be co-rotating with the disk with a velocity of 22 ± 13 km/s, in general agreement with previous observational studies and suggesting that galaxy disks could be formed by halo baryons collapsing by a factor of ≈10. We also find a prograde satellite fraction of 51% and Jz, of the satellite system to be positively correlated with the disk, albeit at low significance (2655 ± 2232 kpc km/s).

scholarly journals How galaxies gain and lose their angular momentum

2007 ◽  
Vol 3 (S245) ◽  
pp. 51-54
Author(s):  
Elena D'Onghia
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Minor Role ◽  
Dark Matter Halos ◽  
Tidal Interactions ◽  
Higher Spin ◽  
Tidal Torques ◽  
A Minor

AbstractSpiral, fast-rotating galaxies like the Milky Way are the most common type in the Universe. One of the most pressing challenges faced by current models of galaxy formation is the origin of their angular momentum and disk. According to the standard tidal-torque theory the galactic spin is originated by tidal interactions between dark halos around galaxies and neighboring structures in the expanding Universe. We use a large cosmological N-body simulation to study the origin of possible correlations between the merging history and spin of cold dark matter halos. In particular, we examine claims that remnants of major mergers tend to have higher-than-average spins, and find that the effect is driven largely by unrelaxed systems: equilibrium dark matter halos show no significant correlation between spin and merging history. Out-of-equilibrium halos have, on average, higher spin than relaxed systems, suggesting that the virialization process leads to a net decrease in the value of the spin parameter. We present also high-resolution N-body/SPH cosmological simulations including cold gas and dark matter to investigate the processes by which gas loses its angular momentum during the protogalactic collapse phase, leading to simulated disk galaxies that are too compact with respect to the observations. We show that the gas and the dark matter have similar specific angular momenta until a merger event occurs at redshift 2. All the gas involved in the merger loses a substantial fraction of its specific angular momentum due to tidal torques and falls quickly into the center. Dynamical friction by small infalling substructures plays a minor role, in contrast to previous claims.

scholarly journals Observing merger trees in a new light

2018 ◽  
Vol 35 ◽  
Author(s):  
Rhys J. J. Poulton ◽  
Aaron S. G. Robotham ◽  
Chris Power ◽  
Pascal J. Elahi
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Diagnostic Tool ◽  
Cosmic Time ◽  
Analytical Models ◽  
Dark Matter Halos ◽  
Assembly Simulation ◽  
Novel Method ◽  
Tree Building

AbstractMerger trees harvested from cosmologicalN-body simulations encode the assembly histories of dark matter halos over cosmic time and are a fundamental component of semi-analytical models of galaxy formation. The ability to compare the tools used to construct merger trees, namely halo finders and tree building algorithms, in an unbiased and systematic manner is critical to assess the quality of merger trees. In this paper, we present the dendrogram, a novel method to visualise merger trees, which provides a comprehensive characterisation of a halo’s assembly history—tracking subhalo orbits, halo merger events, and the general evolution of halo properties. We show the usefulness of thedendrogramas a diagnostic tool of merger trees by comparing halo assembly simulation analysed with three different halo finders—VELOCIraptor, AHF, and Rockstar—and their associated tree builders. Based on our analysis of the resulting dendrograms, we highlight how they have been used to motivate improvements to VELOCIraptor. Thedendrogramsoftware is publicly available online, at:https://github.com/rhyspoulton/MergerTree-Dendrograms.

scholarly journals Properties of Dark Matter Halos in Disk Galaxies

2004 ◽  
Vol 220 ◽  
pp. 281-286 ◽  
Author(s):  
Roelof S. de Jong ◽  
Susan Kassin ◽  
Eric F. Bell ◽  
Stéphane Courteau
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Momentum Distribution ◽  
Surface Brightness ◽  
High Surface ◽  
Large Set ◽  
Dark Matter Halos ◽  
Rotation Curves ◽  
Galaxy Assembly ◽  
Adiabatic Contraction

We present a simple technique to estimate mass-to-light (M/L) ratios of stellar populations based on two broadband photometry measurements, i.e. a colour-M/L relation. We apply the colour-M/L relation to galaxy rotation curves, using a large set of galaxies that span a great range in Hubble type, luminosity and scale size and that have accurately measured HI and/or Hα rotation curves. Using the colour-M/L relation, we construct stellar mass models of the galaxies and derive the dark matter contribution to the rotation curves.We compare our dark matter rotation curves with adiabatically contracted Navarro, Frenk, & White (1997, NFW hereafter) dark matter halos. We find that before adiabatic contraction most high surface brightness galaxies and some low surface brightness galaxies are well fit by a NFW dark matter profile. However, after adiabatic contraction, most galaxies are poorly fit in the central few kpc. the observed angular momentum distribution in the baryonic component is poorly matched by ACDM model predictions, indicating that the angular momentum distribution is not conserved during the galaxy assembly process. We find that in most galaxies the dark matter distribution can be derived by scaling up the HI gas contribution. However, we find no consistent value for the scaling factor among all the galaxies.

scholarly journals What is the Evidence for Dark Matter?

2004 ◽  
Vol 220 ◽  
pp. 27-37 ◽  
Author(s):  
J. A. Sellwood
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Alternative Hypothesis ◽  
Fine Tuning ◽  
Current Evidence ◽  
Newtonian Mechanics ◽  
Dark Matter Halos ◽  
Gravitational Fields ◽  
Decisive Advantage ◽  
Satisfactory Theory

Newtonian mechanics indicates that galaxies and galaxy clusters are much more massive than we would have guessed from their luminosities, with the discrepancy being generally attributed to dark matter halos. An alternative hypothesis is that accelerations in very weak gravitational fields are larger than predicted by Newton's laws, and there is no need for dark matter. Even though we do not currently have a satisfactory theory associated with this rival hypothesis, we can ask whether any observational tests could rule it out or prefer it over the dark matter hypothesis. Current evidence suggests that neither hypothesis enjoys a decisive advantage over the other. If dark matter turns out to be the correct interpretation however, then theories of galaxy formation face some quite severe fine-tuning problems.

scholarly journals Small-scale Substructure in Dark Matter Haloes: Where Does Galaxy Formation Come to an End?

2004 ◽  
Vol 220 ◽  
pp. 91-98 ◽  
Author(s):  
J. E. Taylor ◽  
J. Silk ◽  
A. Babul
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Structure Formation ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Small Scale ◽  
Analytic Model ◽  
Model Predictions ◽  
Low Mass

Models of structure formation based on cold dark matter predict that most of the small dark matter haloes that first formed at high redshift would have merged into larger systems by the present epoch. Substructure in present-day haloes preserves the remains of these ancient systems, providing the only direct information we may ever have about the low-mass end of the power spectrum. We describe some recent attempts to model halo substructure down to very small masses, using a semi-analytic model of halo formation. We make a preliminary comparison between the model predictions, observations of substructure in lensed systems, and the properties of local satellite galaxies.

scholarly journals Angular Momentum Transfer in Dark Matter Halos: Erasing the Cusp

2006 ◽  
Vol 649 (2) ◽  
pp. 591-598 ◽  
Author(s):  
C. Tonini ◽  
A. Lapi ◽  
P. Salucci
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Momentum Transfer ◽  
Dark Matter Halos ◽  
Angular Momentum Transfer

scholarly journals The Angular Momentum Dichotomy

2014 ◽  
Vol 10 (S309) ◽  
pp. 349-349
Author(s):  
Adelheid Teklu ◽  
Rhea-Silvia Remus ◽  
Klaus Dolag ◽  
Andreas Burkert
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Lognormal Distribution ◽  
Spiral Galaxies ◽  
Disk Galaxies ◽  
Dark Matter Halos ◽  
Central Galaxy ◽  
Relative Angular Momentum ◽  
Spin Parameter ◽  
Spheroidal Galaxies

AbstractIn the context of the formation of spiral galaxies the evolution and distribution of the angular momentum of dark matter halos have been discussed for more than 20 years, especially the idea that the specific angular momentum of the halo can be estimated from the specific angular momentum of its disk (e.g. Fall & Efstathiou (1980), Fall (1983) and Mo et al. (1998)). We use a new set of hydrodynamic cosmological simulations called Magneticum Pathfinder which allow us to split the galaxies into spheroidal and disk galaxies via the circularity parameter ϵ, as commonly used (e.g. Scannapieco et al. (2008)). Here, we focus on the dimensionless spin parameter λ = J |E|1/2 / (G M5/2) (Peebles 1969, 1971), which is a measure of the rotation of the total halo and can be fitted by a lognormal distribution, e.g. Mo et al. (1998). The spin parameter allows one to compare the relative angular momentum of halos across different masses and different times. Fig. 1 reveals a dichotomy in the distribution of λ at all redshifts when the galaxies are split into spheroids (dashed) and disk galaxies (dash-dotted). The disk galaxies preferentially live in halos with slightly larger spin parameter compared to spheroidal galaxies. Thus, we see that the λ of the whole halo reflects the morphology of its central galaxy. For more details and a larger study of the angular momentum properties of disk and spheroidal galaxies, see Teklu et al. (in prep.).

scholarly journals The Origin of Angular Momentum in Dark Matter Halos

2002 ◽  
Vol 581 (2) ◽  
pp. 799-809 ◽  
Author(s):  
Maya Vitvitska ◽  
Anatoly A. Klypin ◽  
Andrey V. Kravtsov ◽  
Risa H. Wechsler ◽  
Joel R. Primack ◽  
...  
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Dark Matter Halos

scholarly journals THE STRUCTURE OF COLD DARK MATTER HALOS: RECENT INSIGHTS FROM HIGH RESOLUTION SIMULATIONS

2009 ◽  
Vol 24 (29) ◽  
pp. 2291-2305 ◽  
Author(s):  
MARCEL ZEMP
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Structure Formation ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Dark Matter Halos ◽  
General Properties

We review results from recent high resolution cosmological structure formation simulations, namely the Via Lactea I & II and GHALO projects. These simulations study the formation of Milky Way sized objects within a cosmological framework. We discuss the general properties of cold dark matter halos at redshift z = 0 and focus on new insights into the structure of halos we got due to the unprecedented high resolution in these simulations.

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