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 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 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 The Connection Between Galaxies and Their Dark Matter Halos

2018 ◽  
Vol 56 (1) ◽  
pp. 435-487 ◽  
Author(s):  
Risa H. Wechsler ◽  
Jeremy L. Tinker
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cosmic Time ◽  
Stellar Mass ◽  
Dark Matter Halo ◽  
Strong Function ◽  
Galaxy Surveys ◽  
Narrow Region ◽  
Open Questions ◽  
Galaxy Halo

In our modern understanding of galaxy formation, every galaxy forms within a dark matter halo. The formation and growth of galaxies over time is connected to the growth of the halos in which they form. The advent of large galaxy surveys as well as high-resolution cosmological simulations has provided a new window into the statistical relationship between galaxies and halos and its evolution. Here, we define this galaxy–halo connection as the multivariate distribution of galaxy and halo properties that can be derived from observations and simulations. This galaxy–halo connection provides a key test of physical galaxy-formation models; it also plays an essential role in constraints of cosmological models using galaxy surveys and in elucidating the properties of dark matter using galaxies. We review techniques for inferring the galaxy–halo connection and the insights that have arisen from these approaches. Some things we have learned are that galaxy-formation efficiency is a strong function of halo mass; at its peak in halos around a pivot halo mass of 1012M⊙, less than 20% of the available baryons have turned into stars by the present day; the intrinsic scatter in galaxy stellar mass is small, less than 0.2 dex at a given halo mass above this pivot mass; below this pivot mass galaxy stellar mass is a strong function of halo mass; the majority of stars over cosmic time were formed in a narrow region around this pivot mass. We also highlight key open questions about how galaxies and halos are connected, including understanding the correlations with secondary properties and the connection of these properties to galaxy clustering.

scholarly journals Mass-Discrepancy Acceleration Relation: A Natural Outcome of Galaxy Formation in Cold Dark Matter Halos

2017 ◽  
Vol 118 (16) ◽  
Author(s):  
Aaron D. Ludlow ◽  
Alejandro Benítez-Llambay ◽  
Matthieu Schaller ◽  
Tom Theuns ◽  
Carlos S. Frenk ◽  
...  
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dark Matter Halos ◽  
Natural Outcome

THE LINK BETWEEN GALAXIES AND DARK MATTER

2011 ◽  
Vol 20 (10) ◽  
pp. 1771-1777
Author(s):  
HOUJUN MO
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Luminosity Function ◽  
The Other ◽  
Dark Matter Halos ◽  
Galaxy Formation And Evolution ◽  
The Galaxy ◽  
Galaxy Halo ◽  
Formation And Evolution ◽  
The Universe

Given that dark matter is gravitationally dominant in the universe, and that galaxy formation is closely related to dark matter halos, a key first step in understanding galaxy formation and evolution in the CDM paradigm is to quantify the galaxy-halo connection for galaxies of different properties. Here I will present results about the halo/galaxy connection obtained from two different methods. One is based on the conditional luminosity function, which describes the occupation of galaxies in halos of different masses, and the other is based on galaxy systems properly selected to represent dark halos.

scholarly journals An interesting case of the formation and evolution of a barred galaxy in the cosmological context

2020 ◽  
Vol 642 ◽  
pp. L12
Author(s):  
Ewa L. Łokas
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cosmic Time ◽  
Galaxy Cluster ◽  
Interesting Case ◽  
Massive Galaxies ◽  
Barred Galaxies ◽  
Tidal Interactions ◽  
The Galaxy ◽  
Formation And Evolution

Elongated, bar-like galaxies without a significant disk component, with little rotation support and no gas, often form as a result of tidal interactions with a galaxy cluster, as was recently demonstrated using the IllustrisTNG-100 simulation. Galaxies that exhibit similar properties are, however, also found to be infalling into the cluster for the first time. We use the same simulation to study in detail the history of such a galaxy over cosmic time in order to determine its origin. The bar appears to be triggered at t = 6.8 Gyr by the combined effect of the last significant merger with a subhalo and the first passage of another dwarf satellite, both ten times less massive than the galaxy. The satellites deposit all their gas in the galaxy, contributing to its third and last star-formation episode, which perturbs the disk and may also contribute to the formation of the bar. The galaxy then starts to lose its gas and dark matter due to its passage near a group of more massive galaxies. The strongest interaction involves a galaxy 22 times more massive, leaving the barred galaxy with no gas and half of its maximum dark matter mass. During this time, the bar grows steadily, seemingly unaffected by the interactions, although they may have aided its growth by stripping the gas. The studied galaxy, together with two other similar objects briefly discussed in this Letter, suggest the existence of a new class of early-type barred galaxies and thereby demonstrate the importance of interactions in galaxy formation and evolution.

scholarly journals Dwarf Galaxies as Cosmological Probes

2018 ◽  
Vol 14 (S344) ◽  
pp. 455-463
Author(s):  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dark Matter Halos ◽  
Too Big To Fail ◽  
Sharp Minimum ◽  
Luminous Galaxies ◽  
Small Scales ◽  
Low Mass

AbstractThe Lambda Cold Dark Matter (LCDM) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. These predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. A number of potential challenges to LCDM have been identified when confronting the expected properties of dwarfs with observation. I review our understanding of a few of these issues, including the “missing satellites” and the “too-big-to-fail” problems, and argue that neither poses an insurmountable challenge to LCDM. Solving these problems requires that most dwarf galaxies inhabit halos of similar mass, and that there is a relatively sharp minimum halo mass threshold to form luminous galaxies. These predictions are eminently falsifiable. In particular, LCDM predicts a large number of “dark” low-mass halos, some of which should have retained enough primordial gas to be detectable in deep 21 cm or Hα surveys. Detecting this predicted population of “mini-halos” would be a major discovery and a resounding success for LCDM on small scales.

scholarly journals Hi and Galaxy Formation in Loose Groups

2004 ◽  
Vol 21 (4) ◽  
pp. 390-392
Author(s):  
Daniel J. Pisano
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Local Group ◽  
Dark Matter Halos ◽  
Early Results ◽  
Large Numbers ◽  
The Galaxy ◽  
Order Of Magnitude ◽  
Low Mass ◽  
High Velocity Clouds

AbstractModels of hierarchical galaxy formation predict that large numbers of low-mass, dark matter halos remain around galaxies today. These models predict an order of magnitude more halos than observed stellar satellites in the Local Group. One possible solution to this discrepancy is that the high-velocity clouds (HVCs) around the Milky Way may be associated with the excess dark matter halos and be the gaseous remnants of the galaxy formation process. If this is the case, then analogues to the HVCs should be visible in other groups. In this paper, I review the observations of Hi clouds lacking stars around other galaxies and in groups, present early results from our Hi survey of loose groups analogous to the Local Group, and discuss implications for the nature of HVCs and galaxy formation.

scholarly journals Galaxy formation from dry and hydro simulations

2009 ◽  
Vol 5 (H15) ◽  
pp. 85-85
Author(s):  
Luca Ciotti
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Scaling Laws ◽  
High Redshift ◽  
Elliptical Galaxies ◽  
Dark Matter Halos ◽  
Galaxy Mergers ◽  
Lower Redshift

AbstractThe effects of dry and wet merging on the Scaling Laws (SLs) of elliptical galaxies (Es) are discussed. It is found that the SLs, possibly established at high redshift by the fast collapse of gas-rich and clumpy stellar distributions in preexisting dark matter halos following the cosmological SLs, are compatible with a (small) number of galaxy mergers at lower redshift.

scholarly journals The tidal evolution of dark matter substructure – I. subhalo density profiles

2019 ◽  
Vol 490 (2) ◽  
pp. 2091-2101 ◽  
Author(s):  
Sheridan B Green ◽  
Frank C van den Bosch
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Structural Parameters ◽  
Structural Evolution ◽  
Mass Function ◽  
Analytical Models ◽  
Analytical Treatment ◽  
Density Profiles ◽  
Tidal Evolution ◽  
Wide Range

ABSTRACT Accurately predicting the abundance and structural evolution of dark matter subhaloes is crucial for understanding galaxy formation, modelling galaxy clustering, and constraining the nature of dark matter. Due to the non-linear nature of subhalo evolution, cosmological N-body simulations remain its primary method of investigation. However, it has recently been demonstrated that such simulations are still heavily impacted by artificial disruption, diminishing the information content on small scales, and reducing the reliability of all simulation-calibrated semi-analytical models. In this paper, we utilize the recently released DASH library of high-resolution, idealized simulations of the tidal evolution of subhaloes, which are unhindered by numerical overmerging due to discreteness noise or force softening, to calibrate an improved, more accurate model of the evolution of the density profiles of subhaloes that undergo tidal heating and stripping within their host halo. By testing previous findings that the structural evolution of a tidally truncated subhalo depends solely on the fraction of mass stripped, independent of the details of the stripping, we identify an additional dependence on the initial subhalo concentration. We provide significantly improved fitting functions for the subhalo density profiles and structural parameters (Vmax and rmax) that are unimpeded by numerical systematics and applicable to a wide range of parameter space. This model will be an integral component of a future semi-analytical treatment of substructure evolution, which can be used to predict key quantities, such as the evolved subhalo mass function and annihilation boost factors, and validate such calculations performed with cosmological simulations.

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