Local Surface Density of the Galactic Disk from a Three-Dimensional Stellar Velocity Sample

Корчагин, В. И.; Girard, Terrence M.; Borkova, T. V.; Dinescu, D. I.; Altena, W. F. van

doi:10.1086/379138

Cited by 71 publications

(99 citation statements)

References 37 publications

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“…−2 in agreement with the Korchagin et al (2003) determination 42 ± 6 M pc −2 , based on a sample of 1500 K giants from H observations, mainly first ascent giants rather than clump giants.…”

Section: The K Z Forcesupporting

confidence: 90%

Weighing the local dark matter with RAVE red clump stars

Bienaymé

Famaey

Siebert

et al. 2014

A&A

113

103

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We determine the Galactic potential in the solar neigbourhood from RAVE observations. We select red clump stars for which accurate distances, radial velocities, and metallicities have been measured. Combined with data from the 2MASS and UCAC catalogues, we build a sample of ∼4600 red clump stars within a cylinder of 500 pc radius oriented in the direction of the South Galactic Pole, in the range of 200 pc to 2000 pc distances. We deduce the vertical force and the total mass density distribution up to 2 kpc away from the Galactic plane by fitting a distribution function depending explicitly on three isolating integrals of the motion in a separable potential locally representing the Galactic one with four free parameters. Because of the deep extension of our sample, we can determine nearly independently the dark matter mass density and the baryonic disc surface mass density. We find (i) at 1 kpc K z /(2πG) = 68.5 ± 1.0 M pc −2 ; and (ii) at 2 kpc K z /(2πG) = 96.9 ± 2.2 M pc −2 . Assuming the solar Galactic radius at R 0 = 8.5 kpc, we deduce the local dark matter density ρ DM (z = 0) = 0.0143 ± 0.0011 M pc −3 = 0.542 ± 0.042 Gev cm −3 and the baryonic surface mass density Σ bar = 44.4 ± 4.1 M pc −2 . Our results are in agreement with previously published K z determinations up to 1 kpc, while the extension to 2 kpc shows some evidence for an unexpectedly large amount of dark matter. A flattening of the dark halo of order 0.8 can produce such a high local density in combination with a circular velocity of 240 km s −1 . It could also be consistent with a spherical cored dark matter profile whose density does not drop sharply with radius. Another explanation, allowing for a lower circular velocity, could be the presence of a secondary dark component, a very thick disc resulting either from the deposit of dark matter from the accretion of multiple small dwarf galaxies, or from the presence of an effective "phantom" thick disc in the context of effective galactic-scale modifications of gravity.

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Section: The K Z Forcesupporting

confidence: 90%

Weighing the local dark matter with RAVE red clump stars

Bienaymé

Famaey

Siebert

et al. 2014

A&A

113

103

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“…Depending on which local stellar volume mass density was assumed for the thin disc, the total dynamical mass density slightly changes. However, by taking into account the error bars, both values are in a good agreement with the results of Holmberg & Flynn (2000) and Korchagin et al (2003). Undoubtedly, the derived values are highly dependent on the density assumed for the ISM (see Sect.…”

Section: The Dynamical Mass and The Age-velocity Relationsupporting

confidence: 82%

“…The estimation of the local dynamical mass density by Crézé et al (1998) was 0.076 ± 0.015 M pc −3 . Holmberg & Flynn (2000) derives it to be 0.102 ± 0.010 M pc −3 and similarly Korchagin et al (2003) gives 0.100 M pc −3 , while van Leeuwen (2007) proposes a bit higher value 0.122 ± 0.019 M pc −3 . Table 7 presents the contribution of all mass components to the total dynamical mass Notes.…”

Section: The Dynamical Mass and The Age-velocity Relationmentioning

confidence: 97%

The Besançon Galaxy model renewed

Czekaj

Robin

Figueras

et al. 2014

A&A

130

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Context. The understanding of Galaxy evolution can be facilitated by the use of population synthesis models, which allows us to test hypotheses on the star formation history, star evolution, and chemical and dynamical evolution of the Galaxy. Aims. The new version of the Besançon Galaxy model (BGM) aims to provide a more flexible and powerful tool to investigate the initial mass function (IMF) and star formation rate (SFR) of the Galactic disc. Methods. We present a new strategy for the generation of thin disc stars, which assumes the IMF, SFR and evolutionary tracks as free parameters. We have updated most of the ingredients for the star count production and, for the first time, binary stars are generated in a consistent way. The local dynamical self-consistency is maintained in this new scheme. We then compare simulations from the new model with Tycho-2 data and the local luminosity function, as a first test to verify and constrain the new ingredients. The effects of changing thirteen different ingredients of the model are systematically studied. Results. For the first time, a full sky comparison is performed between BGM and data. This strategy allows us to constrain the IMF slope at high masses, which is found to be close to 3.0 and excludes a shallower slope such as Salpeter's one. The SFR is found decreasing whatever IMF is assumed. The model is compatible with a local dark matter density of 0.011 M pc −3 implying that there is no compelling evidence for the significant amount of dark matter in the disc. While the model is fitted to Tycho-2 data, which is a magnitude limited sample with V < 11, we check that it is still consistent with fainter stars. Conclusions. The new model constitutes a new basis for further comparisons with large scale surveys and is being prepared to become a powerful tool for the analysis of the Gaia mission data.

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“…The local mass density was recently revised by van Leeuwen (2007) by using a re-reduction of the Hipparcos catalogue. In contrast to Crézé et al (1998) Korchagin et al (2003) of 0.100 M pc −3 are considered as the reference value. To match this value, we corrected the interstellar matter mass density and attributed to it 0.05 M pc −3 , in agreement with Binney & Tremaine (2008) and still within the error bars given by observational constraints.…”

Section: Thin-disc Local Density and Dynamical Self-consistencymentioning

confidence: 97%

Constraining the thick disc formation scenario of the Milky Way

Robin

Reylé

Fliri

et al. 2014

A&A

170

216

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Aims. More than 30 years after its discovery, the thick disc of the Milky Way is not fully explored. We examine the shape of the thick disc in order to gain insight into the process of its formation. Methods. The shape of the thick disc is studied in detail using photometric data at high and intermediate latitudes from SDSS and 2MASS surveys. We adopted the population synthesis approach using an approximate Bayesian computation -Markov chain Monte Carlo (ABC-MCMC) method to determine the potential degeneracies in the parameters that can be caused by the mixing with the halo and the thin disc. We characterised the thick-disc shape, scale height, scale length, local density, and flare, and we investigated the extent of the thick-disc formation period by simulating several formation episodes. Results. We find that the vertical variation in density is not exponential, but much closer to a hyperbolic secant squared. Assuming a single formation epoch, the thick disc is better fitted with a sech 2 scale height of 470 pc and a scale length of 2.3 kpc. However, if one simulates two successive formation episodes, which mimicks an extended formation period, the older episode has a higher scale height and a longer scale length than the younger episode, which indicates a contraction during the collapse phase. The scale height decreases from 800 pc to 340 pc, the scale length from 3.2 kpc to 2 kpc. The likelihood is much higher when the thick disc formation extends over a longer period. We also show that star formation increases from the old episode to the young and that there is no flare in the outskirt of the thick disc during the main episode. We compare our results with formation scenarios of the thick disc. During the fitting process, the halo parameters are determined as well. If a power-law density is assumed, it has an exponent of 3.3 and an axis ratio of 0.7. Alternatively, a Hernquist shape would have an exponent of 2.76, an axis ratio of 0.77, and a core radius of 2.1 kpc.The constraint on the halo shows that a transition between an inner and outer halo, if it exists, cannot be at a distance shorter than about 30 kpc, which is the limit of our investigation using turnoff halo stars. Finally, we show that extrapolating the thick disc towards the bulge region explains well the stellar populations observed there that there is no longer need to invoke a classical bulge. Conclusions. The facts that the thick-disc episode lasted for several billion years, that a contraction is observed during the collapse phase, and that the main thick disc has a constant scale height with no flare argue against the formation of the thick disc through radial migration. The most probable scenario for the thick disc is that it formed while the Galaxy was gravitationally collapsing from well-mixed gas-rich giant clumps that were sustained by high turbulence, which prevented a thin disc from forming for a time, as proposed previously. This scenario explains well the observations in the thick-disc region and in the bulge region.

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Local Surface Density of the Galactic Disk from a Three-Dimensional Stellar Velocity Sample

Cited by 71 publications

References 37 publications

Weighing the local dark matter with RAVE red clump stars

Weighing the local dark matter with RAVE red clump stars

The Besançon Galaxy model renewed

Constraining the thick disc formation scenario of the Milky Way

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