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 Thousands of Milky Ways: galaxy satellites and building blocks

2009 ◽  
Vol 5 (S262) ◽  
pp. 240-243
Author(s):  
Nelson Padilla ◽  
Claudia Lagos ◽  
Sofía Cora
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Galactic Nuclei ◽  
Building Blocks ◽  
Chemical Enrichment ◽  
Stellar Formation ◽  
History Of ◽  
The Universe

AbstractA semi-analytic model of galaxy formation with and without active galactic nuclei feedback is used to study the nature of possible building blocks (BBs) of z = 0 galaxies, including those of Milky-Way types. We find that BBs can show an important range of properties arising from environmental variables such as host halo mass, and whether a galaxy is a satellite within its host halo; the stellar formation histories are comparatively faster and the chemical enrichment is more efficient in BBs than in surviving satellites, in accordance with recent metallicity measurements for the Milky Way. These results can be used in combination with observational constraints to continue probing the ability of the cold dark-matter scenario to reproduce the history of galaxy demography in the Universe.

scholarly journals A new model for including galactic winds in simulations of galaxy formation – I. Introducing the Physically Evolved Winds (PhEW) model

2020 ◽  
Vol 497 (3) ◽  
pp. 2586-2604 ◽  
Author(s):  
Shuiyao Huang ◽  
Neal Katz ◽  
Evan Scannapieco ◽  
J'Neil Cottle ◽  
Romeel Davé ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Thermal Conduction ◽  
Ambient Medium ◽  
Hydrodynamic Simulations ◽  
Numerical Resolution ◽  
Physical Conditions ◽  
Galactic Winds ◽  
Wide Range ◽  
Very High ◽  
Galactic Haloes

ABSTRACT The propagation and evolution of cold galactic winds in galactic haloes is crucial to galaxy formation models. However, modelling of this process in hydrodynamic simulations of galaxy formation is oversimplified owing to a lack of numerical resolution and often neglects critical physical processes such as hydrodynamic instabilities and thermal conduction. We propose an analytic model, Physically Evolved Winds, that calculates the evolution of individual clouds moving supersonically through a uniform ambient medium. Our model reproduces predictions from very high resolution cloud-crushing simulations that include isotropic thermal conduction over a wide range of physical conditions. We discuss the implementation of this model into cosmological hydrodynamic simulations of galaxy formation as a subgrid prescription to model galactic winds more robustly both physically and numerically.

scholarly journals Shaping Disk Galaxy Stellar Populations via Internal and External Processes

2012 ◽  
Vol 10 (H16) ◽  
pp. 372-372
Author(s):  
Rok Roškar
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Stellar Populations ◽  
Radial Migration ◽  
Disk Formation ◽  
Process Understanding ◽  
History Of ◽  
Nearby Galaxies ◽  
Gas Accretion

AbstractIn recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

scholarly journals Origin of strong magnetic fields in Milky Way-like galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 274-275
Author(s):  
Alexander M. Beck
Keyword(s):  
Magnetic Fields ◽  
Galaxy Formation ◽  
Milky Way ◽  
Cosmic Time ◽  
Strong Magnetic Fields ◽  
Origin And Evolution ◽  
The Universe

AbstractMagnetic fields are observed on all scales in the Universe (see e.g. Kronberg 1994), but little is known about the origin and evolution of those fields with cosmic time. Seed fields of arbitrary source must be amplified to present-day values and distributed among cosmic structures. Therefore, the emergence of cosmic magnetic fields and corresponding dynamo processes (see e.g. Zel'dovich et al. 1983; Kulsrud et al. 1997) can only be jointly understood with the very basic processes of structure and galaxy formation (see e.g. Mo et al. 2010).

Intergalactic Matter and Radiation and its Bearing on Galaxy Formation and Evolution

1974 ◽  
Vol 58 ◽  
pp. 93-108
Author(s):  
G. R. Burbidge
Keyword(s):  
Galaxy Formation ◽  
High Mass ◽  
Clusters Of Galaxies ◽  
X Ray ◽  
Hot Gas ◽  
Galaxy Formation And Evolution ◽  
Formation And Evolution ◽  
The Universe ◽  
Very High ◽  
Theoretical Standpoint

An up-dated review is given of the evidence for the presence of intergalactic matter and radiation in the Universe. It is concluded that the only important constituents which may make a sizable contribution to the total mass-energy are intergalactic gas and condensed objects with a very high mass-to-light ratio. If the QSOs are not at cosmological distances, cold atomic hydrogen may still be the most important constituent and may contribute much more mass than do the galaxies. The X-ray observations still do not unambiguously show that very hot gas is present, though it is very likely on general grounds that some hot gas is present in clusters of galaxies.The question of whether or not large amounts of matter, enough to close the Universe, are present, remains unsettled. From the theoretical standpoint the answer depends almost completely on the approach taken to the problem of galaxy formation and to the cosmological model which is favoured.

scholarly journals Characterisation of the Galactic thick disk

2013 ◽  
Vol 9 (S298) ◽  
pp. 17-27
Author(s):  
Thomas Bensby
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Thin Disk ◽  
Thick Disk ◽  
Host Galaxy ◽  
Galaxy Formation And Evolution ◽  
Formation History ◽  
History Of ◽  
Formation And Evolution

AbstractThick disks appear to be common in external large spiral galaxies and our own Milky Way also hosts one. The existence of a thick disk is possibly directly linked to the formation history of the host galaxy and if its properties is known it can constrain models of galaxy formation and help us to better understand galaxy formation and evolution. This brief review attempts to highlight some of the characteristics of the Galactic thick disk and how it relates to other stellar populations such as the thin disk and the Galactic bulge. Focus has been put on results from high-resolution spectroscopic data obtained during the last 10 to 15 years.

NIHAO-UHD: High-resolution Simulations of MW mass galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 209-212
Author(s):  
Tobias Buck ◽  
Andrea Macciò ◽  
Melissa Ness ◽  
Aura Obreja ◽  
Aaron Dutton
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Satellite System ◽  
The Galaxy ◽  
First Results ◽  
History Of ◽  
Galaxy Center ◽  
Hydrodynamical Simulations ◽  
Very High ◽  
Disc Galaxies

AbstractHigh resolution cosmological and hydrodynamical simulations have reached a resolution able to resolve in a self consistent way the disc of our galaxy, the galaxy center and the satellites orbiting around it. We present first results from the NIHAO-UHD project, a set of very high-resolution baryonic zoom-in simulations of Milky Way mass disc galaxies. These simulations model the full cosmological assembly history of the galaxies and their satellite system using the same, well tested physics as the NIHAO project. We show that these simulations can self-consistently reproduce the observed kinematical and morphological features of the X-shaped bulge observed in our own Milky Way.

scholarly journals Distances and ages of globular clusters

2007 ◽  
Vol 3 (S248) ◽  
pp. 440-442 ◽  
Author(s):  
B. Chaboyer
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Formation History ◽  
Minimum Age ◽  
History Of ◽  
The Mean ◽  
Age Of The Universe ◽  
The Universe ◽  
Age Determinations

AbstractAs the oldest objects whose ages can be accurately determined, Galactic globular clusters can be used to establish the minimum age of the universe (and hence, to constrain cosmological models) and to study the early formation history of the Milky Way. The largest uncertainty in the determination of globular cluster ages is the distance scale. The current uncertainty in the distances to globular clusters is ~ 6%, which leads to a 13% uncertainty in the absolute ages of globular clusters. I am the PI on a SIM-Planetquest key project to determine the distances of 21 globular clusters with an accuracy of ranging from 1 to 4%. This will lead to age determinations accurate to 5 − 9%. The mean age of the oldest, most metal-poor globular clusters will be determined with an accuracy of ±3%.

scholarly journals Building Blocks of the Milky Way's Stellar Halo

2015 ◽  
Vol 11 (S317) ◽  
pp. 373-374
Author(s):  
Pim van Oirschot ◽  
Else Starkenburg ◽  
Amina Helmi ◽  
Gijs Nelemans
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Building Blocks ◽  
Formation Model ◽  
Halo Stars ◽  
Stellar Halo ◽  
History Of ◽  
Dynamical Properties ◽  
Star Formation Histories

AbstractWe study the assembly history of the stellar halo of Milky Way-like galaxies using the six high-resolution Aquarius dark matter simulations combined with the Munich-Groningen semi-analytic galaxy formation model. Our goal is to understand the stellar population contents of the building blocks of the Milky Way halo, including their star formation histories and chemical evolution, as well as their internal dynamical properties. We are also interested in how they relate or are different from the surviving satellite population. Finally, we will use our models to compare to observations of halo stars in an attempt to reconstruct the assembly history of the Milky Way's stellar halo itself.

scholarly journals Surveys for Metal-Poor Stars in the Galaxy: A New Window on the Low-Abundance Universe

1998 ◽  
Vol 11 (1) ◽  
pp. 58-61
Author(s):  
T.C. Beers
Keyword(s):  
Milky Way ◽  
High Signal ◽  
Signal To Noise ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
History Of ◽  
Chemical History ◽  
Low Metallicity ◽  
New Generation ◽  
The Universe

Measurement of the abundances of the light and heavy elements in stars of the Milky Way galaxy is the cornerstone for the study of numerous aspects of chemical evolution in galaxies and the Universe. We stand poised to enter an era of rapid understanding, as new-generation telescopes with apertures in the 8m-10m class enable astronomers to obtain high-resolution, high-signal-to-noise near-UV, optical, and IR spectra of the stars which have locked up the chemical history of our Galaxy in their outer atmospheres. It is thus appropriate to review present surveys for the low-metallicity stars of our Galaxy, as the stars we uncover today will be studied so intensively in the coming decades.

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