arXiv subjects

Misha Haywood

Publications and source records attributed to Misha Haywood.

At least 37 records · Page 2Linked to original sources

arXiv2023

The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers

Theory suggests that mergers play an important role in shaping galactic discs and stellar haloes, which was observationally confirmed in the MW thanks to Gaia data. In this work, aiming to probe the contribution of mergers to the in situ stellar halo formation, we analyse six M31/MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the LG. We found that all the HESTIA galaxies experience between one to four mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7-11Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase in the orbital eccentricity (and a corresponding decrease in the rotational velocity Vphi of pre-existing disc stars of the main progenitor, thus nicely reproducing the Splash-, Plume-like feature that was discovered in the MW. We do find a correlation between mergers and close pericentric passages of massive satellites and bursts of star formation in the in situ component. Massive mergers sharply increase the disc velocity dispersion of the in situ stars; however, the latest significant merger often heats up the disc up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In HESTIA galaxies, the in situ halo is an important component of the inner stellar halo where its fraction is about 30-40%, while in the outer parts it typically does not exceed ~5% beyond 15 kpc. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars that formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in Rmax-Zmax space are mainly populated by the stars born between significant mergers.

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arXiv2023

The stellar halo in Local Group Hestia simulations II. The accreted component

In the Milky Way, recent progress in the exploration of its assembly history is driven by the tremendous amount of high-quality data delivered by Gaia, which has revealed a number of substructures potentially linked to several ancient accretion events. In this work, aiming to explore the phase-space structure of accreted stars, we analyze six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience a few dozen mergers but only 1-4 mergers have the stellar mass ratio >0.2 where, depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo. Individual merger remnants show diverse density distributions at z=0, significantly overlapping with each other and with the in-situ stars in the ELz, UV and RVphi coordinates. The mergers debris often change their position in the ELz with time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct ELz features. In the UV plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features. We found an age gradient in Elz space for the individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host. The bulk of these stars is being formed during the last stages of accretion, making it possible to date the merger. In actions space (Jr, Jz, Jϕ), the mergers debris do not appear as isolated substructures but are instead scattered over a large parameters area and overlapping with the in-situ stars. We also introduce a purely kinematic space (Jz/Jr-eccentricity), where different merger debris can be disentangled better from each other and from the in-situ stars.

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arXiv2023

Stragglers of the thick disc

Young alpha-rich (YAR) stars have been detected in the past as outliers to the local age $\rm-$ [$α$/Fe] relation. These objects are enhanced in $α$-elements but apparently younger than typical thick disc stars. We study the global kinematics and chemical properties of YAR giant stars in APOGEE DR17 survey and show that they have properties similar to those of the standard thick disc stellar population. This leads us to conclude that YAR are rejuvenated thick disc objects, most probably evolved blue stragglers. This is confirmed by their position in the Hertzsprung-Russel diagram (HRD). Extending our selection to dwarfs allows us to obtain the first general straggler distribution in an HRD of field stars. We also compare the elemental abundances of our sample with those of standard thick disc stars, and find that our YAR stars are shifted in oxygen, magnesium, sodium, and the slow neutron-capture element cerium. Although we detect no sign of binarity for most objects, the enhancement in cerium may be the signature of a mass transfer from an asymptotic giant branch companion. The most massive YAR stars suggest that mass transfer from an evolved star may not be the only formation pathway, and that other scenarios, such as collision or coalescence should be considered.

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arXiv2023

The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy

Reconstructing how all the stellar components of the Galaxy formed and assembled over time, by studying the properties of the stars which make it, is the aim of Galactic archeology. In these last years, thanks to the launch of the ESA Gaia astrometric mission, and the development of many spectroscopic surveys, we are for the first time in the position to delve into the layers of the past of our galaxy. Globular clusters (GCs) play a fundamental role in this research field since they are among the oldest stellar systems in the Milky Way (MW) and so bear witness of its entire past. In the recent years, there have been several attempts to constrain the nature of clusters (accreted or formed in the MW itself) through the analysis of kinematic spaces and to reconstruct from this the properties of the accretions events experienced by the MW through time. This work aims to test a widely-used assumption about the clustering of the accreted populations of GCs in the integrals of motions space. We analyze a set of dissipation-less N-body simulations that reproduce the accretion of one or two satellites with their GC population on a MW-type galaxy. Our results demonstrate that a significant overlap between accreted and "kinematically-heated" in-situ GCs is expected in kinematic spaces, for mergers with mass ratios of 1:10. In contrast with standard assumptions made in the literature so far, we find that accreted GCs do not show dynamical coherence, that is they do not cluster in kinematic spaces. In addition, GCs can also be found in regions dominated by stars which have a different origin (i.e. different progenitor). This casts doubt on the association between GCs and field stars that is generally made in the literature to assign them to a common origin. Our findings severely question the recovered accretion history of the MW based on the phase-space clustering of the GC population.

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arXiv2023

The e-TidalGCs Project: Modeling the extra-tidal features generated by Galactic globular clusters

We present the e-TidalGCs Project which aims at modeling and predicting the extra-tidal features surrounding all Galactic globular clusters for which 6D phase space information, masses and sizes are available (currently 159 globular clusters). We focus the analysis and presentation of the results on the distribution of extra-tidal material on the sky, and on the different structures found at different heliocentric distances. We emphasize the wide variety of morphologies found: beyond the canonical tidal tails, our models reveal that the extra-tidal features generated by globular clusters take a wide variety of shapes, from thin and elongated shapes, to thick, and complex halo-like structures. We also compare some of the most well studied stellar streams found around Galactic globular clusters to our model predictions, namely those associated to the clusters NGC 3201, NGC 4590, NGC 5466 and Pal 5. Additionally, we investigate how the distribution and extension in the sky of the simulated streams vary with the Galactic potential by making use of three different models, containing or not a central spheroid, or a stellar bar. Overall, our models predict that the mass lost by the current globular cluster population in the field from the last 5 Gyrs is between $0.3-2.1\times10^{7}M_{\odot}$, an amount comparable between 7-55 % of current mass. Most of this lost mass is found in the inner Galaxy, with the half-mass radius of this population being between 4-6 kpc. The outputs of the simulations will be publicly available, at a time when the ESA Gaia mission and complementary spectroscopic surveys are delivering exquisite data to which these models can be compared.

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arXiv2021

Rapid early gas accretion for the inner Galactic disc

Recent observations of the Milky Way and galaxies at high redshifts suggest that galaxy discs were already in place soon after the Big Bang. While the gas infall history of the Milky Way in the inner disc has long been assumed to be characterised by a short accretion time scale, this has not been directly constrained using observations. Using the unprecedented amount and quality of data of the inner regions of the Milky Way that has recently been produced by APOGEE and Gaia, we aim to derive strong constraints on the infall history of the inner (less than 6 kpc) Galaxy (with a focus on stars between 4-6 kpc, which we show is an appropriate proxy for the entire inner disc). We have implemented gas infall into a chemical evolution model of the Galaxy disc, and used a Schmidt-Kennicutt law to connect the infall to the star formation. We explore a number of models, and two different formulations of the infall law. In one formulation, the infall is non-parametric, and in the other the infall has an explicitly exponential form. We fit the model parameters to the time-[Si/Fe] distribution of solar vicinity stars, and the metallicity and [Si/Fe] distribution function of stars with a galactocentric radius between 4-6 kpc from APOGEE. Our results point to a fast early gas accretion, with an upper limit of accretion timescale of around 2 Gyr in the inner disc of the Milky Way. This suggests that at least half the baryons were in place within 2-3 Gyr of the Big Bang, and that half the stars of the inner disc formed within the first 5 Gyr, during the thick disc formation phase. This implies that the stellar mass of the inner disc is dominated by the thick disc, supporting our previous work, and that the gas accretion onto the inner disc was rapid and early.

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arXiv2020

Bimodality of [α/Fe]-[Fe/H] distributions is a natural outcome of dissipative collapse and disc growth in Milky Way-type galaxies

We present a set of self-consistent chemo-dynamical simulations of MW-type galaxies formation to study the origin of the bimodality of $α$-elements in stellar populations. We explore how the bimodality is related to the geometrically and kinematically defined stellar discs, gas accretion and radial migration. We find that the two $α$-sequences are formed in quite different physical environments. The high-$α$ sequence is formed early from a burst of star formation (SF) in a turbulent, compact gaseous disc which forms a thick disc. The low-$α$ stellar populations is the result of quiescent SF supported by the slow accretion of enriched gas onto a radially extended thin disc. Stellar feedback-driven outflows during the formation of the thick disc are responsible for the enrichment of the surrounding gaseous halo, which subsequently feeds the disc on a longer time-scale. During the thin disc phase, chemical evolution reaches an equilibrium metallicity and abundance, where the stars pile-up. This equilibrium metallicity decreases towards the outer disc, generating the ridgeline that forms the low-$α$ sequence. We identify a second mechanism capable of creating a low-$α$ sequence in one of our simulations. Rapid shutdown of the SF, provoked by the feedback at the end of the thick disc phase, suppresses the chemical enrichment of the halo gas, which, once accreted onto the star-forming disc, dilutes the ISM at the beginning of the thin disc formation. Both mechanisms can operate in a galaxy, but the former is expected to occur when SF efficiency ceases to be dominated by the formation of the thick disc, while the latter can occur in the inner regions. Being the result of the presence of low and high gas density environments, the bimodality is independent of any particular merger history, suggesting that it could be much more widespread than has been claimed.

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arXiv2019

The Canada-France Imaging Survey: Reconstructing the Milky Way Star Formation History from its White Dwarf Population

As the remnants of stars with initial masses $\lesssim$ 8 M$_{\odot}$, white dwarfs contain valuable information on the formation histories of stellar populations. In this paper, we use deep, high-quality, u-band photometry from the Canada France Imaging Survey (CFIS), griz photometry from Pan-STARRS 1 (PS1), as well as proper motions from Gaia DR2, to select 25,156 white dwarf candidates over $\sim$4500 deg$^2$ using a reduced proper motion diagram. We develop a new white dwarf population synthesis code that returns mock observations of the Galactic field white dwarf population for a given star formation history, while simultaneously taking into account the geometry of the Milky Way, survey parameters, and selection effects. We use this model to derive the star formation histories of the thin disk, thick disk, and stellar halo. Our results show that the Milky Way disk began forming stars (11.3 $\pm$ 0.5) Gyr ago, with a peak rate of (8.8 $\pm$ 1.4) M$_{\odot}$yr$^{-1}$ at (9.8 $\pm$ 0.4) Gyr, before a slow decline to a constant rate until the present day --- consistent with recent results suggesting a merging event with a satellite galaxy. Studying the residuals between the data and best-fit model shows evidence for a slight increase in star formation over the past 3 Gyr. We fit the local fraction of helium-atmosphere white dwarfs to be (21 $\pm$ 3) %. Incorporating this methodology with data from future wide-field surveys such as LSST, Euclid, CASTOR, and WFIRST should provide an unprecedented view into the formation of the Milky Way at its earliest epoch through its white dwarfs.

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arXiv2019

Chronos --- Taking the pulse of our Galactic neighbourhood (ESA Voyage 2050 White Paper)

The period 2035-50 considered in the ESA Voyage long-term plan will coincide with a series of foreseeable advances in the characterization of the stellar content of the Milky Way. The Gaia mission, combined with large-scale spectroscopic surveys, is helping to build an unprecedented census in terms of the astrometric, kinematic and chemical properties of Galactic stellar populations. Within a decade, precise measurements of such properties will be available for hundreds of millions of stars. Meanwhile, time-domain surveys initiated with CoRoT and Kepler/K2 and carried on by space missions such as TESS and PLATO or ground-based projects like the LSST, will have brought asteroseismology to a high level of maturity. The combination of precise ages from asteroseismology with astrometric and spectroscopic data, on large stellar samples, is allowing Galactic archaeologists to gain new insight into the assembly history of the Milky Way. Recent breakthroughs --- based on the detection of solar-like oscillations in tens of thousands of red-giant stars --- demonstrate the potential of such approach. Therefore, we are convinced that an all-sky, high-cadence, long-duration stellar variability survey will become a scientific priority in the 2035-50 period. The Chronos concept presented here consists in a time-domain extension to Gaia. It will allow for mass and age estimates for half a million red giants within 1.7 kpc from the Sun and hence shed a new light on our understanding of the Galactic dynamics and archaeology. In terms of the targeted pulsators, Chronos will bridge the gap between PLATO and the LSST by surveying stars all the way from the subgiant branch to the early AGB. Finally, it will surpass all previous surveys capable of conducting asteroseismology in terms of the combined sky coverage and duration of the observations (2 x 3.75 months over the whole sky and >5 years in the CVZ).

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arXiv2019

The Detailed Science Case for the Maunakea Spectroscopic Explorer, 2019 edition

(Abridged) The Maunakea Spectroscopic Explorer (MSE) is an end-to-end science platform for the design, execution and scientific exploitation of spectroscopic surveys. It will unveil the composition and dynamics of the faint Universe and impact nearly every field of astrophysics across all spatial scales, from individual stars to the largest scale structures in the Universe. Major pillars in the science program for MSE include (i) the ultimate Gaia follow-up facility for understanding the chemistry and dynamics of the distant Milky Way, including the outer disk and faint stellar halo at high spectral resolution (ii) galaxy formation and evolution at cosmic noon, via the type of revolutionary surveys that have occurred in the nearby Universe, but now conducted at the peak of the star formation history of the Universe (iii) derivation of the mass of the neutrino and insights into inflationary physics through a cosmological redshift survey that probes a large volume of the Universe with a high galaxy density. MSE is positioned to become a critical hub in the emerging international network of front-line astronomical facilities, with scientific capabilities that naturally complement and extend the scientific power of Gaia, the Large Synoptic Survey Telescope, the Square Kilometer Array, Euclid, WFIRST, the 30m telescopes and many more.

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arXiv2019

The echo of the bar buckling: phase-space spirals in Gaia DR2

Using a single N-body simulation ($N=0.14\times 10^9$) we explore the formation, evolution and spatial variation of the phase-space spirals similar to those recently discovered by Antoja et al. in the Milky Way disk, with Gaia DR2. For the first time in the literature, we use a self-consistent N-body simulation of an isolated Milky Way-type galaxy to show that the phase-space spirals develop naturally from vertical oscillations driven by the buckling of the stellar bar. We claim that the physical mechanism standing behind the observed incomplete phase-space mixing process can be internal and not necessarily due to the perturbation induced by a massive satellite. In our model, the bending oscillations propagate outwards and produce axisymmetric variations of the mean vertical coordinate and of the vertical velocity component. As a consequence, the phase-space wrapping results in the formation of patterns with various morphology across the disk, depending on the bar orientation, distance to the galactic center and time elapsed since the bar buckling. Once bending waves appear, they are supported for a long time via disk self-gravity. The underlying physical mechanism implies the link between in-plane and vertical motion that leads directly to phase-space structures whose amplitude and shape are in remarkable agreement with those of the phase-space spirals observed in the Milky Way disk. In our isolated galaxy simulation, phase-space spirals are still distinguishable, at the solar neighbourhood, 3 Gyr after the buckling phase. The long-lived character of the phase-space spirals generated by the bar buckling instability cast doubts on the timing argument used so far to get back at the time of the onset of the perturbation: phase-space spirals may have been caused by perturbations originated several Gyrs ago, and not as recent as suggested so far.

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arXiv2018

Mergers, tidal interactions, and mass exchange in a population of disc globular clusters: II. Long-term evolution

Globular clusters (GCs), the oldest stellar systems observed in the Milky Way, have for long been considered single stellar populations. As such, they provided an ideal laboratory to understand stellar dynamics and primordial star formation processes. However, during the last two decades, observations unveiled their real, complex nature. Beside their pristine stars, GCs host one or more helium enriched and possibly younger stellar populations whose formation mechanism is still unknown. Even more puzzling is the existence of GCs showing star by star iron spreads. Using detailed N-body simulations we explore the hypothesis that these anomalies in metallicity could be the result of mutual stripping and mergers between a primordial population of disc GCs. In the first paper of this series we proved, both with analytical arguments and short-term N-body simulations, that disc GCs have larger fly-by and close encounter rates with respect to halo clusters. These interactions lead to mass exchange and even mergers that form new GCs, possibly showing metallicity spreads. Here, by means of long-term direct N-body simulations, we provide predictions on the dynamical properties of GCs that underwent these processes. The comparison of our predictions with available and future observational data could provide insights on the origin of GCs and on the Milky Way build-up history as a whole.

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arXiv2018

Mergers, tidal interactions, and mass exchange in a population of disc globular clusters

We present the results of a self-consistent $N$-body simulation following the evolution of a primordial population of thick disc globular clusters (GCs). We study how the internal properties of such clusters evolve under the action of mutual interactions, while they orbit a Milky Way-like galaxy. For the first time, through analytical and numerical considerations, we find that physical encounters between disc GCs are a crucial factor that contributed to the shape of the current properties of the Galactic GC system. Close passages or motion on similar orbits may indeed have a significant impact on the internal structure of clusters, producing multiple gravitationally bound sub-populations through the exchange of mass and even mergers. Our model produces two major mergers and a few small mass exchanges between pairs of GCs. Two of our GCs accrete stars from two companions, ending up with three internal sub-populations. We propose these early interactions and mergers between thick disc GCs with slightly different initial chemical compositions as a possible explanation for the presence of the spreads in metallicity observed in some of the massive Milky Ways GCs.

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arXiv2018

In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2

We investigate the nature of the double color-magnitude sequence observed in the Gaia DR2 HR diagram of stars with high transverse velocities. The stars in the reddest-color sequence are likely dominated by the dynamically-hot tail of the thick disk population. Information from Nissen & Schuster (2010) and from the APOGEE survey suggests that stars in the blue-color sequence have elemental abundance patterns that can be explained by this population having a relatively low star-formation efficiency during its formation. In dynamical and orbital spaces, such as the `Toomre diagram', the two sequences show a significant overlap, but with a tendency for stars on the blue-color sequence to dominate regions with no or retrograde rotation and high total orbital energy. In the plane defined by the maximal vertical excursion of the orbits versus their apocenters, stars of both sequences redistribute into discrete wedges. We conclude that stars which are typically assigned to the halo in the solar vicinity are actually both accreted stars lying along the blue sequence in the HR diagram, and the low velocity tail of the old Galactic disk, possibly dynamically heated by past accretion events. Our results imply that a halo population formed in situ and responsible for the early chemical enrichment prior to the formation of the thick disk is yet to be robustly identified, and that what has been defined as the stars of the in situ stellar halo of the Galaxy may be in fact fossil records of its last significant merger.

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arXiv2018

Galactic planetary nebulae as probes of radial metallicity gradients and other abundance patterns

We use planetary nebulae (PNe) as probes to determine the Galactic radial oxygen gradients, and other abundance patterns. We select data homogeneously from recent data sets, including PNe at large Galactocentric distances. The radial oxygen gradient calculated for the general PN population, which probes the region between the Galactic center and out to $\sim$28 kpc, is shallow, with slope $\sim$-0.02 dex kpc$^{-1}$, in agreement with previous findings. We looked for time evolution of the metallicity gradient using PNe with different age progenitors as metallicity probes. We identify PNe whose progenitor stars are younger than 1 Gyr (YPPNe), and those whose progenitor stars are older than 7.5 Gyr (OPPNe), based on the comparison between evolutionary yields and elemental abundances of the PNe. By studying OPPNe and YPPNe separately we found that: (i) The OPPNe oxygen gradient is shallower ($\sim-0.015$ dex kpc$^{-1}$) than that derived from YPPNe ($\sim-0.027$ dex kpc$^{-1}$); (ii) the OPPNe inner radial distribution of oxygen is compatible with no gradient to the radial extent of the thick disk population ($\sim$10 kpc), similarly to what has been observed in thick disk stars; (iii) planetary nebulae (especially OPPNe) indicate that significant gradient slope is limited to Galactocentric distances between $\sim$10 to $\sim$13.5 kpc, as observed for open clusters and field stars. Outside this range, the distribution is almost flat. We found that the radial oxygen gradient is steeper for a PN population closer to the Galactic disk, similarly to what is observed in the general stellar population by the SEGUE survey. We use our novel population dating to compare our results with current chemical evolutionary models, and with gradients from other Galactic populations, for insight on galaxy chemical evolution.

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arXiv2018

Star formation history of the Galactic bulge from deep HST imaging of low reddening windows

Despite the huge amount of photometric and spectroscopic efforts targetting the Galactic bulge over the past few years, its age distribution remains controversial owing to both the complexity of determining the age of individual stars and the difficult observing conditions. Taking advantage of the recent release of very deep, proper-motion-cleaned colour--magnitude diagrams (CMDs) of four low reddening windows obtained with the Hubble Space Telescope (HST), we used the CMD-fitting technique to calculate the star formation history (SFH) of the bulge at -2deg > b > -4deg along the minor axis. We find that over 80 percent of the stars formed before 8 Gyr ago, but that a significant fraction of the super-solar metallicity stars are younger than this age. Considering only the stars that are within reach of the current generation of spectrographs (i.e. V < 21), we find that 10 percent of the bulge stars are younger than 5 Gyr, while this fraction rises to 20-25 percent in the metal-rich peak. The age-metallicity relation is well parametrized by a linear fit implying an enrichment rate of dZ/dt ~ 0.005 Gyr$^{-1}$. Our metallicity distribution function accurately reproduces that observed by several spectroscopic surveys of Baade's window, with the bulk of stars having metal-content in the range [Fe/H] ~ -0.7 to ~0.6, along with a sparse tail to much lower metallicities.

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arXiv2018

Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity ($Δ\rm V_{\rm GC}$) between metal-rich stars ([Fe/H] $\ge$ 0) and moderately metal-poor stars (-1.0 $\le$ [Fe/H] $<$ 0) in two models, one containing a thin disc and a small classical bulge (B/D=0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate $Δ\rm V_{\rm GC}$ at different latitudes ($b=0^\circ$, $-2^\circ$, $-4^\circ$,$-6^\circ$, $-8^\circ$ and $-10^\circ$) and longitudes ($l=0^\circ$, $\pm5^\circ$, $\pm10^\circ$ and $\pm15^\circ$) and show that the $Δ\rm V_{\rm GC}$ trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] $<$ -1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.

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arXiv2018

Radial migration in a stellar galactic disc with thick components

We study how migration affects stars of a galaxy with a thin stellar disc and thicker stellar components. The simulated galaxy has a strong bar and lasting spiral arms. We find that the amplitude of the churning (change in angular momentum) is similar for thin and thick components, and of limited amplitude, and that stars of all components can be trapped at the corotation of the bar. At the exception of those stars trapped at the corotation, we find that stars that are far from their initial guiding radius are more likely so due to blurring rather than churning effects. We compare the simulation to orbits integration with a fixed gravitational potential rotating at a constant speed. In the latter case, stars trapped at corotation are churned periodically outside and inside the corotation radius, with a zero net average. However, as the bar speed of the simulated galaxy decreases and its corotation radius increases, stars trapped at corotation for several Gyrs can be churned outwards on average. We study the location of extreme migrators (stars experimenting the largest churning) and find that extreme migrators come from regions on the leading side of the effective potential local maxima.

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