Paleoparasitology

Combes, Claude

doi:10.1590/s0074-02762003000900001

Cited by 10 publications

(11 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The correlation between Type IIIs and unbarred or weakly barred galaxies (EPB08) is consistent with the model presented here, as it is expected that bars are weakened (e.g., Athanassoula 2005; Debattista et al 2006) and even destroyed (Bournaud & Combes 2002;Combes 2011) in a gas accretion event.…”

Section: Type III Profilessupporting

confidence: 89%

See 1 more Smart Citation

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

Minchev

Famaey

Quillen

et al. 2012

A&A

186

208

View full text Add to dashboard Cite

We investigate the evolution of galactic discs in N-body tree-SPH simulations. We find that discs, initially truncated at three scalelengths, can triple their radial extent, solely driven by secular evolution. At the same time, the initial radial metallicity gradients are flattened and even reversed in the outer discs. Both Type I (single exponential) and Type II (down-turning) observed disc surfacebrightness profiles can be explained by our findings. We show that profiles with breaks beyond the bar's outer Lindblad resonance, at present only explained as the effect of star-formation threshold, can occur even if no star formation is considered. We explain these results with the strong angular momentum outward transfer, resulting from torques and radial migration associated with multiple patterns, such as central bars and spiral waves of different multiplicity. We find that even for stars ending up on cold orbits, the changes in angular momentum exhibit complex structure as a function of radius, unlike the expected effect of transient spirals alone. We show that the bars in all of our simulations are the most effective drivers of radial migration through their corotation resonance, throughout the 3 Gyr of evolution studied. Focussing on one of our models, we find evidence for non-linear coupling among m = 1, 2, 3 and 4 density waves, where m is the pattern multiplicity. In this way the waves involved conspire to carry the energy and angular momentum extracted by the first mode from the inner parts of the disc much farther out than a single mode could. We suggest that the naturally occurring larger resonance widths at galactic radii beyond four scale-lengths may have profound consequences on the formation and location of breaks in disc density profiles, provided spirals are present at such large distances. We also consider the effect of gas inflow and show that when in-plane smooth gas accretion of ∼5 M /yr is included, the outer discs become more unstable, leading to a strong increase in the stellar velocity dispersion. This, in turn, causes the formation of a Type III (up-turning) profile in the old stellar population. We propose that observations of Type III surface brightness profiles, combined with an up-turn in the stellar velocity dispersions beyond the disc break, could be a signature of ongoing gas-accretion. The results of this study suggest that disc outskirts comprised of stars migrated from the inner disc would have relatively large radial velocity dispersions (>30 km s −1 at 6 scale-lengths for Milky Way-size systems), and significant thickness when seen edge-on.

show abstract

Section: Type III Profilessupporting

confidence: 89%

“…Therefore, in this prescription both the gas and stellar particles can increase in mass. For more details we refer the reader to Combes (2011).…”

Section: Gas Accretionmentioning

confidence: 99%

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

Minchev

Famaey

Quillen

et al. 2012

A&A

186

208

View full text Add to dashboard Cite

show abstract

“…13, bottom panels), gas accumulates in the OLR region, but differently from the stellar component, gas is then able to dissipate part of its energy, shocks and forms rings of concentrated material at the OLR. Similarly, gas outside the OLR is not able to penetrate this resonance and access the inner region of the disc, until the barrier is removed (because of a significant change in the bar properties, see for example Combes 2011).…”

Section: Olr: a Barrier For Migratorsmentioning

confidence: 99%

Quantifying stellar radial migration in anN-body simulation: blurring, churning, and the outer regions of galaxy discs

Halle

Matteo

Haywood

et al. 2015

A&A

101

View full text Add to dashboard Cite

Radial stellar migration in galactic discs has received much attention in studies of galactic dynamics and chemical evolution, but remains a dynamical phenomenon that needs to be fully quantified. In this work, using a Tree-SPH simulation of an Sb-type disc galaxy, we quantify the effects of blurring (epicyclic excursions) and churning (change of guiding radius). We quantify migration (either blurring or churning) both in terms of flux (the number of migrators passing at a given radius), and by estimating the population of migrators at a given radius at the end of the simulation compared to non-migrators, but also by giving the distance over which the migration is effective at all radii. We confirm that the corotation of the bar is the main source of migrators by churning in a bardominated galaxy, its intensity being directly linked to the episode of a strong bar, in the first 1-3 Gyr of the simulation. We show that within the outer Lindblad resonance (OLR), migration is strongly dominated by churning, while blurring gains progressively more importance towards the outer disc and at later times. Most importantly, we show that the OLR limits the exchange of angular momentum, separating the disc in two distinct parts with minimal or null exchange, except in the transition zone, which is delimited by the position of the OLR at the epoch of the formation of the bar, and at the final epoch. We discuss the consequences of these findings for our understanding of the structure of the Milky Way disc. Because the Sun is situated slightly outside the OLR, we suggest that the solar vicinity may have experienced very limited churning from the inner disc.

show abstract

“…Combes (2008bCombes ( , 2010Combes ( , 2011 gives brief theoretical reviews of bar-to-lens evolution. She also reviews an additional important aspect of bar dissolution.…”

Section: Bar Suicide and The Origin Of Lens Components I N -Body Simentioning

confidence: 99%

Secular evolution in disk galaxies

Kormendy¹

2013

Secular Evolution of Galaxies

124

138

View full text Add to dashboard Cite

Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -the inner parts shrink while the outer parts expand -provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School.I begin with a review of the formation, growth and death of bars. Then I review the slow ("secular") rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark halos. The "existence-proof" phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the center. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure.

show abstract

Paleoparasitology

Cited by 10 publications

References 0 publications

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

Quantifying stellar radial migration in anN-body simulation: blurring, churning, and the outer regions of galaxy discs

Secular evolution in disk galaxies

Contact Info

Product

Resources

About