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 Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

2021 ◽  
Vol 8 ◽  
Author(s):  
Mauro D’Onofrio ◽  
Paola Marziani ◽  
Cesare Chiosi
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Galactic Nuclei ◽  
Scaling Relations ◽  
Short History ◽  
Physical Mechanisms ◽  
Galaxy Formation And Evolution ◽  
The Galaxy ◽  
History Of ◽  
Formation And Evolution

We review the properties of the established Scaling Relations (SRs) of galaxies and active galactic nuclei (AGN), focusing on their origin and expected evolution back in time, providing a short history of the most important progresses obtained up to now and discussing the possible future studies. We also try to connect the observed SRs with the physical mechanisms behind them, examining to what extent current models reproduce the observational data. The emerging picture clarifies the complexity intrinsic to the galaxy formation and evolution process as well as the basic uncertainties still affecting our knowledge of the AGN phenomenon. At the same time, however, it suggests that the detailed analysis of the SRs can profitably contribute to our understanding of galaxies and AGN.

scholarly journals Tips learned from panchromatic modeling of AGNs

2019 ◽  
Vol 15 (S341) ◽  
pp. 167-171
Author(s):  
Y. Sophia Dai
Keyword(s):  
Star Formation ◽  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Black Hole Mass ◽  
Formation History ◽  
History Of ◽  
The Relationship ◽  
Gas Supply

AbstractI will review the tips learned from panchromatic modeling of active galactic nuclei (AGNs), based on our recent work to study the relationship between AGN and star formation (SF). Several AGN SED models are compared, and a significant AGN contribution is found in the IR luminosities and corresponding star formation rates (SFRs). I will review the AGN-SF relation and how different parameters and sample selections affect the observed correlation. I will then report on the constant ratio discovered between the SFR and the black hole mass accretion rate (BHAR), and their implications on the gas supply and galaxy formation history of these systems. Caveats and important questions to answer are summarized at the end.

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 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 The Smithsonian Submillimeter Array

1994 ◽  
Vol 140 ◽  
pp. 384-391
Author(s):  
P. T. P. Ho
Keyword(s):  
Solar System ◽  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Milky Way ◽  
Angular Resolution ◽  
Galactic Nuclei ◽  
Circumstellar Disks ◽  
Concentric Ring ◽  
Submillimeter Wavelengths ◽  
Order Of Magnitude

SummaryThe Smithsonian Astrophysical Observatory is currently designing and constructing the Submillimeter Array (SMA). This instrument will consist of six 6-m telescopes, which can be moved and reconfigured in four concentric ring-like arrangements with maximum baselines of 500 m. Pending negotiations, the SMA will be sited on Mauna Kea at the 4000 m plateau, adjacent to the existing CSO and JCMT submillimeter telescopes. The goal of the SMA is to provide imaging at sub-arcsecond resolution for the wavelength range of 1.3 mm to 0.35 mm. This instrument will therefore improve the angular resolution achieved with present submillimeter telescopes by more than an order of magnitude. As the cool (10-100 K) dust and gas in the Milky Way and other external systems will radiate principally in the submillimeter wavelengths, we expect the SMA to provide unprecedented resolution and to make fundamental contributions to many different problems including the studies of our solar system, star formation and circumstellar disks, galaxies and molecular cloud structures, quasars and active galactic nuclei, and perhaps even galaxy formation in the early universe.

scholarly journals Re-ionization of the IGM — Massive Stars versus QSOs

2003 ◽  
Vol 212 ◽  
pp. 687-695 ◽  
Author(s):  
Piero Madau
Keyword(s):  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Mechanical Energy ◽  
Density Fluctuations ◽  
Atomic Processes ◽  
Feedback Mechanisms ◽  
Galaxy Formation And Evolution ◽  
History Of ◽  
Formation And Evolution ◽  
The Universe

In popular cold dark matter cosmological scenarios, stars may have first appeared in significant numbers around a redshift of 10 or so, as the gas within protogalactic halos with virial temperatures Tvir ≃ 20 000 K (corresponding to masses comparable to those of present-day dwarf ellipticals) cooled rapidly due to atomic processes and fragmented. It is this ‘second generation’ of subgalactic stellar systems, aided perhaps by an early population of accreting black holes in their nuclei, which may have generated the ultraviolet radiation and mechanical energy that ended the cosmic ‘dark ages’ and reheated and re-ionized most of the hydrogen in the universe by a redshift of z = 6. The detailed history of the universe during, and soon after these crucial formative stages, depends on the power-spectrum of density fluctuations on small scales and on a complex network of poorly understood feedback mechanisms, and is one of the missing links in galaxy formation and evolution studies.

scholarly journals Galactic archeology with extremely metal-poor stars

2008 ◽  
Vol 4 (S255) ◽  
pp. 330-335
Author(s):  
Yutaka Komiya ◽  
Takuma Suda ◽  
Asao Habe ◽  
Masayuki Fujimoto
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Early Stage ◽  
Building Blocks ◽  
Low Mass Stars ◽  
History Of ◽  
Low Mass ◽  
Milky Way Halo

AbstractExtremely metal-poor (EMP) stars are thought to be formed in the low-mass protogalaxies as building blocks of the Milky Way and can be probes to investigate the early stage of galaxy formation and star formation in the early universe. We study the formation history of EMP stars in the Milky Way halo using a new model of chemical evolution based on the hierarchical theory of the galaxy formation. We construct the merging history of the Milky Way halo based on the extended Press-Schechter formalism, and follow the star formation and chemical evolution along the merger tree. The abundance trends and number of low-mass stars predicted in our model are compared with those of observed EMP stars. Additionally, in order to clarify the origin of hyper metal poor stars, we investigate the change of the surface metal abundances of stars by accretion of interstellar matter. We also investigate the pre-enrichment of intergalactic matter by the first supernovae.

scholarly journals On the Mass Assembly History of the Local Group

2019 ◽  
Author(s):  
Edoardo Carlesi ◽  
Yehuda Hoffman ◽  
Stefan Gottlöber ◽  
Noam I Libeskind ◽  
Alexander Knebe ◽  
...  
Keyword(s):  
Large Scale ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Local Group ◽  
Cosmological Parameters ◽  
Major Merger ◽  
History Of ◽  
Mass Assembly ◽  
Theoretical Considerations ◽  
The Universe

Abstract In this work an ensemble of simulated Local Group analogues is used to constrain the properties of the mass assembly history of the Milky Way (MW) and Andromeda (M31) galaxies. These objects have been obtained using the constrained simulation technique, which ensures that simulated LGs live within a large scale environment akin to the observed one. Our results are compared against a standard Λ Cold Dark Matter (ΛCDM) series of simulations which use the same cosmological parameters. This allows us to single out the effects of the constraints on the results. We find that (a) the median constrained merging histories for M31 and MW live above the standard ones at the 1-σ level, (b) the median formation time takes place ≈0.5 Gyr earlier than unconstrained values, while the latest major merger happens on average 1.5 Gyr earlier and (c) the probability for both LG haloes to have experienced their last major merger in the first half of the history of the Universe is $\approx 50\%$ higher for the constrained pairs. These results have been estimated to be significant at the $99\%$ confidence level by means of a Kolmogorov-Simirnov test. These results suggest that the particular environment in which the Milky Way and Andromeda form plays a role in shaping their properties, and favours earlier formation and last major merger time values in agreement with other observational and theoretical considerations.

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 Symmetry and the Arrow of Time in Theoretical Black Hole Astrophysics

2015 ◽  
Vol 2015 ◽  
pp. 1-5
Author(s):  
David Garofalo
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Time Reversal ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Arrow Of Time ◽  
Time Symmetry ◽  
The Universe

While the basic laws of physics seem time-reversal invariant, our understanding of the apparent irreversibility of the macroscopic world is well grounded in the notion of entropy. Because astrophysics deals with the largest structures in the Universe, one expects evidence there for the most pronounced entropic arrow of time. However, in recent theoretical astrophysics work it appears possible to identify constructs with time-reversal symmetry, which is puzzling in the large-scale realm especially because it involves the engines of powerful outflows in active galactic nuclei which deal with macroscopic constituents such as accretion disks, magnetic fields, and black holes. Nonetheless, the underlying theoretical structure from which this accreting black hole framework emerges displays a time-symmetric harmonic behavior, a feature reminiscent of basic and simple laws of physics. While we may expect such behavior for classical black holes due to their simplicity, manifestations of such symmetry on the scale of galaxies, instead, surprise. In fact, we identify a parallel between the astrophysical tug-of-war between accretion disks and jets in this model and the time symmetry-breaking of a simple overdamped harmonic oscillator. The validity of these theoretical ideas in combination with this unexpected parallel suggests that black holes are more influential in astrophysics than currently recognized and that black hole astrophysics is a more fundamental discipline.

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