scholarly journals MEGA: Merger graphs of structure formation

2020 ◽  
Vol 494 (3) ◽  
pp. 4509-4524
Author(s):  
William J Roper ◽  
Peter A Thomas ◽  
Chaichalit Srisawat
Keyword(s):  
Structure Formation ◽  
Galaxy Formation ◽  
Mass Growth ◽  
Catastrophic Failures ◽  
Growth Properties ◽  
The Universe ◽  
Galactic Haloes

ABSTRACT When following the growth of structure in the Universe, we propose replacing merger trees with merger graphs, in which haloes can both merge and split into separate pieces. We show that this leads to smoother mass growth and eliminates catastrophic failures in which massive haloes have no progenitors or descendants. For those who prefer to stick with merger trees, we find that trees derived from our merger graphs have similar mass growth properties to previous methods, but again without catastrophic failures. For future galaxy formation modelling, two different density thresholds can be used to distinguish host haloes (extended galactic haloes, groups, and clusters) from higher density subhaloes: sites of galaxy formation.

scholarly journals The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

2020 ◽  
Vol 495 (1) ◽  
pp. 743-757 ◽  
Author(s):  
Sownak Bose ◽  
Alis J Deason ◽  
Vasily Belokurov ◽  
Carlos S Frenk
Keyword(s):  
Galaxy Formation ◽  
Radial Distribution ◽  
Milky Way ◽  
Resolution Limit ◽  
Hydrodynamic Simulations ◽  
Tidal Interactions ◽  
History Of ◽  
The Universe ◽  
Very High ◽  
Galactic Haloes

ABSTRACT Ultrafaint dwarf galaxies ($M_\star \le 10^{5}\, {\rm M}_\odot$) are relics of an early phase of galaxy formation. They contain some of the oldest and most metal-poor stars in the Universe which likely formed before the epoch of hydrogen reionization. These galaxies are so faint that they can only be detected as satellites of the Milky Way. They are so small that they are not resolved in current cosmological hydrodynamic simulations. Here, we combine very high-resolution cosmological N-body simulations with a semi-analytic model of galaxy formation to study the demographics and spatial distribution of ultrafaint satellites in Milky Way-mass haloes. We show that the abundance of these galaxies is correlated with the assembly history of the host halo: at fixed mass, haloes assembled earlier contain, on average, more ultrafaint satellites today than haloes assembled later. We identify simulated galactic haloes that experience an ancient Gaia-Enceladus-Sausage-like and a recent LMC-like accretion event and find that the former occurs in 33 per cent of the sample and the latter in 9 per cent. Only 3 per cent experience both events and these are especially rich in ultrafaint satellites, most acquired during the ancient accretion event. Our models predict that the radial distribution of satellites is more centrally concentrated in early-forming haloes. Accounting for the depletion of satellites by tidal interactions with the central disc, we find a very good match to the observed radial distribution of satellites in the Milky Way over the entire radial range. This agreement is mainly due to the ability of our model to track ‘orphan’ galaxies after their subhaloes fall below the resolution limit of the simulation.

scholarly journals Are Cluster Dwarfs Recycled Galaxies?

2004 ◽  
Vol 217 ◽  
pp. 556-561
Author(s):  
Christopher J. Conselice
Keyword(s):  
Structure Formation ◽  
Hierarchical Structure ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Galaxy Cluster ◽  
Physical Processes ◽  
Galaxy Type ◽  
Luminosity Functions ◽  
Intracluster Light ◽  
The Universe

Although cluster dwarf galaxies are often neglected due to their faintness, recent observations demonstrate they may be critical for understanding the physical processes behind galaxy formation. Dwarfs are the most common galaxy type and are particularly abundant in clusters. Recent observational results suggest that dwarfs in dense environments do not all form early in the universe, as expected in hierarchical structure formation models. Many of these systems appear to be younger and more metal rich than dwarfs in lower density areas, suggesting they are possibly created by a tidal process. Several general galaxy cluster observations, including steep luminosity functions and the origin of intracluster light, are natural outcomes of these processes.

scholarly journals Ab Initio Formation of Galaxies, Groups and Large-Scale Structure

2000 ◽  
Vol 174 ◽  
pp. 434-444
Author(s):  
Antonaldo Diaferio
Keyword(s):  
Dark Matter ◽  
Ab Initio ◽  
Structure Formation ◽  
Galaxy Formation ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Global Properties ◽  
Small Scales ◽  
First Time ◽  
The Universe

AbstractFor the first time, the combination of semi-analytic modelling of galaxy formation and N-body simulations of cosmic structure formation enables us to model, at the same time, both the photometric and the clustering properties of galaxies. Two Cold Dark Matter Universes provide a reasonable fit to the observed properties of galaxies, groups and clusters, including luminosities, colours, density and velocity biases. We show how the properties of galaxies and groups on small scales are inextricably connected with the global properties of the Universe.

scholarly journals New methods for identifying Lyman continuum leakers and reionization-epoch analogues

2020 ◽  
Vol 498 (1) ◽  
pp. 164-180 ◽  
Author(s):  
Harley Katz ◽  
Dominika Ďurovčíková ◽  
Taysun Kimm ◽  
Joki Rosdahl ◽  
Jeremy Blaizot ◽  
...  
Keyword(s):  
Emission Line ◽  
Galaxy Formation ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Indirect Methods ◽  
High Redshift Galaxies ◽  
Lyman Continuum ◽  
The Universe ◽  
Ionization Parameter ◽  
Redshift Galaxies

ABSTRACT Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly ‘analogues’ of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ∼ 3 and z ∼ 0. We find that the simulated galaxies with high LyC escape fractions (fesc) often exhibit high O32 and populate the same regions of the R23–O32 plane as z ∼ 3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32–fesc plane. Based on emission line diagnostics and how they correlate with fesc, lower metallicity LyC leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. In contrast, local [S ii]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the S ii Baldwin–Phillips–Terlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [C ii]158 μm and [O iii]88 μm can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe.

scholarly journals Anisotropy of the Microwave Background and Biased Galaxy Formation

1988 ◽  
Vol 130 ◽  
pp. 43-50
Author(s):  
Nick Kaiser
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Microwave Background ◽  
Galaxy Clustering ◽  
Clear View ◽  
Hot Gas ◽  
Density Perturbations ◽  
The Universe ◽  
Theoretical Developments

Fluctuations in the microwave background will have been imprinted at z ≃ 1000, when the photons and the plasma decoupled. On angular scales greater than a few degrees these fluctuations provide a clear view of any primordial density perturbations, and therefore a clean test of theories which invoke such fluctuations from which to form the structure we see in the universe. On smaller angular scales the predictions are less certain: reionization of the gas may modify the spectrum of the primordial fluctuations, and secondary fluctuations may be generated.Here I shall review some recent theoretical developments. A brief survey is made of the currently popular theories for the primordial perturbations, with emphasis on the predictions for large scale anisotropy. One major uncetainty in the predictions arises from the normalisation of the fluctuations to e.g. galaxy clustering, and much attention is given to the question of ‘biased’ galaxy formation. The effect of reionization on the primordial fluctuations is discussed, as is the anisotropy generated from scattering off hot gas in clusters, groups and galaxies.

scholarly journals Supercomputer simulations of structure formation in the Universe

2016 ◽  
Vol 12 (S325) ◽  
pp. 10-16
Author(s):  
Tomoaki Ishiyama
Keyword(s):  
Domain Decomposition ◽  
Structure Formation ◽  
Short Range ◽  
Large Scale ◽  
Massively Parallel ◽  
Average Performance ◽  
And Performance ◽  
Performance Results ◽  
The Universe ◽  
Peak Speed

AbstractWe describe the implementation and performance results of our massively parallel MPI†/OpenMP‡ hybrid TreePM code for large-scale cosmological N-body simulations. For domain decomposition, a recursive multi-section algorithm is used and the size of domains are automatically set so that the total calculation time is the same for all processes. We developed a highly-tuned gravity kernel for short-range forces, and a novel communication algorithm for long-range forces. For two trillion particles benchmark simulation, the average performance on the fullsystem of K computer (82,944 nodes, the total number of core is 663,552) is 5.8 Pflops, which corresponds to 55% of the peak speed.

The First Stars

2013 ◽  
Author(s):  
Abraham Loeb ◽  
Steven R. Furlanetto
Keyword(s):  
Phase Transition ◽  
Early Universe ◽  
Galaxy Formation ◽  
Big Bang ◽  
First Stars ◽  
Complex Chemical ◽  
Radiative Processes ◽  
Complex Processes ◽  
The Big Bang ◽  
The Universe

This chapter considers the emergence of the complex chemical and radiative processes during the first stages of galaxy formation. It studies the appearance of the first stars, their feedback processes, and the resulting ionization structures that emerged during and shortly after the cosmic dawn. The formation of the first stars tens or hundreds of millions of years after the Big Bang had marked a crucial transition in the early Universe. Before this point, the Universe was elegantly described by a small number of parameters. But as soon as the first stars formed, more complex processes entered the scene. To illustrate this, the chapter provides a brief outline of the prevailing (though observationally untested) theory for this cosmological phase transition.

Sign in / Sign up

Export Citation Format

Share Document