Dark Matter and Galaxy Formation

ABSTRACT We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the response of cold dark matter (CDM) haloes to baryonic processes. Previous work has shown that the halo response is primarily a function of the ratio between galaxy stellar mass and total virial mass, and the density threshold above which gas is eligible to form stars, n[cm−3]. At low n all simulations in the literature agree that dwarf galaxy haloes are cuspy, but at high n ≳ 100 there is no consensus. We trace halo contraction in dwarf galaxies with n ≳ 100 reported in some previous simulations to insufficient spatial resolution. Provided the adopted star formation threshold is appropriate for the resolution of the simulation, we show that the halo response is remarkably stable for n ≳ 5, up to the highest star formation threshold that we test, n = 500. This free parameter can be calibrated using the observed clustering of young stars. Simulations with low thresholds n ≤ 1 predict clustering that is too weak, while simulations with high star formation thresholds n ≳ 5, are consistent with the observed clustering. Finally, we test the CDM predictions against the circular velocities of nearby dwarf galaxies. Low thresholds predict velocities that are too high, while simulations with n ∼ 10 provide a good match to the observations. We thus conclude that the CDM model provides a good description of the structure of galaxies on kpc scales provided the effects of baryons are properly captured.

Download Full-text

The Large Range of Dark Matter content in Dwarf Galaxies and its Implications

Symposium - International Astronomical Union ◽

10.1017/s0074180900233536 ◽

1996 ◽

Vol 171 ◽

pp. 435-435

Author(s):

S.A. Pustilnik ◽

V.A. Lipovetsky ◽

J.-M. Martin ◽

T.X. Thuan

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Large Range ◽

Dwarf Galaxy ◽

Rotational Velocity ◽

Matter Content ◽

Optical Observations ◽

Strong Interactions ◽

Formation Mechanisms ◽

Mass Ratio

We present the analysis of a new set of radio and optical observations of a large sample of Byurakan Blue Compact Galaxies. HI spectra were obtained with the Nançay 300-m and Green Bank 43-m radio telescopes. CCD-images were taken with the KPNO 0.9-m and Whipple Observatory 1.2-m telescopes. Dark Matter (DM) to luminous mass ratios in these BCGs were found to vary from about less than 0.5 up to 14. Recent data taken from the literature indicate this same range. This result has important consequences on models of dwarf galaxy formation, indicating possibly different formation mechanisms. The standard CDM model of dwarfs formation requires large DM halos. However the formation of dwarfs as tidal debris resulting from strong interactions of massive spirals leads naturally to dwarfs with low content of DM. On Fig.1 we show DM to luminous mass ratio versus rotational velocity for our BCGs and some other galaxies.

Download Full-text

Rotation of Galaxy Dark Matter Halos

Proceedings of the International Astronomical Union ◽

10.1017/s1743921306005394 ◽

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).

Download Full-text

Observing merger trees in a new light

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2018.34 ◽

2018 ◽

Vol 35 ◽

Cited By ~ 8

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.

Download Full-text

Galaxy Formation and Dark Matter

Invisible Matter and the Fate of the Universe ◽

10.1007/978-1-4899-6469-4_10 ◽

1989 ◽

pp. 163-181

Author(s):

Barry Parker

Keyword(s):

Dark Matter ◽

Galaxy Formation

Download Full-text

The weak lensing radial acceleration relation: Constraining modified gravity and cold dark matter theories with KiDS-1000

Astronomy and Astrophysics ◽

10.1051/0004-6361/202040108 ◽

2021 ◽

Vol 650 ◽

pp. A113

Author(s):

Margot M. Brouwer ◽

Kyle A. Oman ◽

Edwin A. Valentijn ◽

Maciej Bilicki ◽

Catherine Heymans ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Modified Gravity ◽

Cold Dark Matter ◽

Weak Lensing ◽

Mass Relation ◽

Gravitational Acceleration ◽

Radial Acceleration ◽

The Galaxy ◽

The Difference

We present measurements of the radial gravitational acceleration around isolated galaxies, comparing the expected gravitational acceleration given the baryonic matter (gbar) with the observed gravitational acceleration (gobs), using weak lensing measurements from the fourth data release of the Kilo-Degree Survey (KiDS-1000). These measurements extend the radial acceleration relation (RAR), traditionally measured using galaxy rotation curves, by 2 decades in gobs into the low-acceleration regime beyond the outskirts of the observable galaxy. We compare our RAR measurements to the predictions of two modified gravity (MG) theories: modified Newtonian dynamics and Verlinde’s emergent gravity (EG). We find that the measured relation between gobs and gbar agrees well with the MG predictions. In addition, we find a difference of at least 6σ between the RARs of early- and late-type galaxies (split by Sérsic index and u − r colour) with the same stellar mass. Current MG theories involve a gravity modification that is independent of other galaxy properties, which would be unable to explain this behaviour, although the EG theory is still limited to spherically symmetric static mass models. The difference might be explained if only the early-type galaxies have significant (Mgas ≈ M⋆) circumgalactic gaseous haloes. The observed behaviour is also expected in Λ-cold dark matter (ΛCDM) models where the galaxy-to-halo mass relation depends on the galaxy formation history. We find that MICE, a ΛCDM simulation with hybrid halo occupation distribution modelling and abundance matching, reproduces the observed RAR but significantly differs from BAHAMAS, a hydrodynamical cosmological galaxy formation simulation. Our results are sensitive to the amount of circumgalactic gas; current observational constraints indicate that the resulting corrections are likely moderate. Measurements of the lensing RAR with future cosmological surveys (such as Euclid) will be able to further distinguish between MG and ΛCDM models if systematic uncertainties in the baryonic mass distribution around galaxies are reduced.

Download Full-text