Orbital eccentricity as a probe of thick disc formation scenarios

Sales, Laura V.; Helmi, Amina; Abadi, Mario G.; Brook, Chris; Gómez, Facundo A.; Roškar, Rok; Debattista, Victor P.; House, Elisa; Steinmetz, Matthias; Villalobos, Álvaro

doi:10.1111/j.1745-3933.2009.00763.x

Cited by 95 publications

(155 citation statements)

References 22 publications

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“…This scenario was used, for example, in the analytical model of Schönrich & Binney (2009a, SB09a) and Schönrich & Binney (2009b, SB09b), where the authors managed to explain the MW thin-and thick-disk characteristics without the need of mergers or any discrete heating processes. Similarly, the increase of disk thickness with time found in the simulation by Roškar et al (2008) has been attributed to migration in the works by Sales et al (2009) and Loebman et al (2011).…”

Section: Radial Migration and Thick Disksmentioning

confidence: 91%

Chemodynamical evolution of the Milky Way disk

Minchev

Chiappini

Martig

2013

A&A

442

574

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In the first paper of this series, we present a new approach for studying the chemo-dynamical evolution in disk galaxies, which consists of fusing disk chemical evolution models with compatible numerical simulations of galactic disks. This method avoids known star formation and chemical enrichment problems encountered in simulations. Here we focus on the Milky Way, by using a detailed thindisk chemical evolution model (matching local observables, which are weakly affected by radial migration) and a simulation in the cosmological context, with dynamical properties close to those of our Galaxy. We examine in detail the interplay between in situ chemical enrichment and radial migration and their impact on key observables in the solar neighborhood, e.g., the age-metallicityvelocity relation, the metallicity distribution, and gradients in the radial and vertical directions. We show that, due to radial migration from mergers at high redshift and the central bar at later times, a sizable fraction of old metal-poor high-[α/Fe] stars can reach the solar vicinity. This naturally accounts for a number of recent observations related to both the thin and thick disks, despite the fact that we use thin-disk chemistry only. Although significant radial mixing is present, the slope in the age-metallicity relation is only weakly affected, with a scatter compatible with recent observational work. While we find a smooth density distribution in the [O/Fe]-[Fe/H] plane, we can recover the observed discontinuity by selecting particles according to kinematic criteria used in high-resolution samples to define the thin and thick disks. We outline a new method for estimating the birth place of the Sun and predict that the most likely radius lies in the range 4.4 < r < 7.7 kpc (for a current location at r = 8 kpc). A new, unifying model for the Milky Way thick disk is offered, where both mergers and radial migration play a role at different stages of the disk evolution. We show that in the absence of early-on massive mergers the vertical velocity dispersion of the oldest stars is underestimated by a factor of ∼2 compared with observations. We can, therefore, argue that the Milky Way thick disk is unlikely to have been formed through a quiescent disk evolution. An observational test involving both chemical and kinematic information must be devised to ascertain this possibility.

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Section: Radial Migration and Thick Disksmentioning

confidence: 91%

Chemodynamical evolution of the Milky Way disk

Minchev

Chiappini

Martig

2013

A&A

442

574

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“…We have also checked that none of the central galaxies has been, in the past, satellite of a more massive system; in other words, we do not consider dwarfs that might have been "ejected" from massive halos when the groups to which they belong are disrupted tidally (Balogh et al 2000;Gill et al 2004;Sales et al 2009;Ludlow et al 2010). Our sample of simulated galaxies therefore contains, by construction, only dwarf systems that have evolved in isolation in the periphery of the massive galaxies of the Local Group.…”

Section: Simulated Dwarf Samplementioning

confidence: 99%

The imprint of reionization on the star formation histories of dwarf galaxies

Benitez-Llambay

Navarro

Abadi

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We explore the impact of cosmic reionization on nearby isolated dwarf galaxies using a compilation of star formation histories estimated from deep HST data and a cosmological hydrodynamical simulation of the Local Group. The nearby dwarfs show a wide diversity of star formation histories; from ancient systems that have largely completed their star formation ∼ 10 Gyr ago to young dwarfs that have formed the majority of their stars in the past ∼ 5 Gyr to two-component systems characterized by the overlap of comparable numbers of old and young stars. Taken as an ensemble, star formation in nearby dwarfs dips to lower-thanaverage rates at intermediate times (4 < t/Gyr < 8), a feature that we trace in the simulation to the effects of cosmic reionization. Reionization heats the gas and drives it out of the shallow potential wells of low mass halos, affecting especially those below a sharp mass threshold that corresponds to a virial temperature of ∼ 2 × 10 4 K at z reion . The loss of baryons leads to a sharp decline in the star forming activity of early-collapsing systems, which, compounded by feedback from early star formation, empties halos of gas and leaves behind systems where a single old stellar component prevails. In halos below the threshold at z reion , reionization heating leads to a delay in the onset of star formation that lasts until the halo grows massive enough to allow some of the remaining gas to cool and form stars. Young stellar components therefore dominate in dwarfs whose halos assemble late and thus form few stars before reionization. Two-component systems may be traced to late mergers of individual examples of the two aforementioned cases. The relative dearth of intermediate-age stars in nearby dwarfs might thus be the clearest signature yet identified of the imprint of cosmic reionization on the star formation history of dwarf galaxies.

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“…The shape of eccentricity (e) distribution of thick disk stars can be used to constrain the main physical mechanism responsible for their formation (Sales et al 2009). Recent studies (e.g., Dierickx et al 2010;Wilson et al 2011;Lee et al 2011;Kordopatis et al 2011), which used the Sales et al (2009) eccentricity test, reached a general conclusion that the eccentricity distribution is inconsistent with the accretion scenario, but could not distinguish between other published models, i.e., heating, migration or merger scenarios.…”

Section: Stellar Orbital Eccentricitiesmentioning

confidence: 99%

“…In this paper, to provide constraints on the various suggested formation models, we explore the stellar orbital eccentricity distributions (e.g., Sales et al 2009;Di Matteo et al 2011), a possible correlation between the eccentricities and metallicity (see Lee et al 2011), and rotational velocity gradients with metallicity in the thin and thick disks (e.g., Lee et al 2011;Kordopatis et al 2011;Navarro et al 2011;Liu & van de Ven 2012).…”

Section: Introductionmentioning

confidence: 99%

Kinematics and chemical properties of the Galactic stellar populations

Adibekyan

Figueira

Santos

et al. 2013

A&A

159

202

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Aims. We analyzed chemical and kinematical properties of about 850 FGK solar neighborhood long-lived dwarfs observed with the HARPS high-resolution spectrograph. The stars in the sample have log g ≥ 4 dex, 5000 ≤ T eff ≤ 6500 K, and −1.39 ≤ [Fe/H] ≤ 0.55 dex. The aim of this study is to characterize and explore the kinematics and chemical properties of stellar populations of the Galaxy in order to understand their origins and evolution. Methods. We applied a purely chemical analysis approach based on the [α/Fe] vs. [Fe/H] plot to separate Galactic stellar populations into the thin disk, thick disk, and high-α metal-rich (hαmr). Then, we explored the population's stellar orbital eccentricity distributions, their correlation with metallicity, and rotational velocity gradients with metallicity in the Galactic disks to provide constraints on the various formation models. Results. We identified a gap in the [α/Fe]-[Fe/H] plane for the α-enhanced stars, and by performing a bootstrapped Monte Carlo test we obtained a probability higher than 99.99% that this gap is not due to small-number statistics. Our analysis shows a negative gradient of the rotational velocity of the thin disk stars with [Fe/H] (-17 km s −1 dex −1 ), and a steep positive gradient for both the thick disk and hαmr stars with the same magnitude of about +42 km s −1 dex −1 . For the thin disk stars we observed no correlation between orbital eccentricities and metallicity, but observed a steep negative gradient for the thick disk and hαmr stars with practically the same magnitude (≈-0.18 dex −1 ). The correlations observed for the nearby stars (on average 45 pc) using high-precision data, in general agree well with the results obtained for the SDSS sample of stars located farther from the Galactic plane. Conclusions. Our results suggest that radial migration played an important role in the formation and evolution of the thin disk. For the thick disk stars it is not possible to reach a firm conclusion about their origin. Based on the eccentricity distribution of the thick disk stars only their accretion origin can be ruled out, and the heating and migration scenario could explain the positive steep gradient of V φ with [Fe/H]. When we analyzed the hαmr stellar population we found that they share properties of both the thin and thick disk population. A comparison of the properties of the hαmr stars with those of the subsample of stars from the N-body/SPH simulation using radial migration suggest that they may have originated from the inner Galaxy. Further detailed investigations would help to clarify their exact nature and origin.

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Orbital eccentricity as a probe of thick disc formation scenarios

Cited by 95 publications

References 22 publications

Chemodynamical evolution of the Milky Way disk

Chemodynamical evolution of the Milky Way disk

The imprint of reionization on the star formation histories of dwarf galaxies

Kinematics and chemical properties of the Galactic stellar populations

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