Mass-Metallicity Relation for the Local Group Dwarf Spheroidal Galaxies: A New Picture for the Chemical Enrichment of Galaxies in the Lowest Mass Range

Tamura, Naoyuki; Hirashita, Hiroyuki; Takeuchi, Tsutomu T.

doi:10.1086/320329

Cited by 20 publications

(15 citation statements)

References 22 publications

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“…It is evident then that some mechanism for gas loss must be adopted. Therefore galactic winds as proposed in our scenario and already suggested by other authors to also explain the observed relation between [O/H] and the mean velocity dispersions in several types of dynamically hot galaxies as well as the massmetallicity relation in dSph galaxies (Richer et al 1998;Tamura et al 2001), seem to be a reasonable solution.…”

Section: Discussionsupporting

confidence: 84%

Chemical evolution models for the dwarf spheroidal galaxies Leo 1 and Leo 2

Lanfranchi

Matteuccí

2010

A&A

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Aims. We investigate the chemical evolutionary history of the dwarf spheroidal galaxies Leo 1 and Leo 2 by means of predictions from a detailed chemical evolution model compared to observations. The model adopts up to date nucleosynthesis and takes into account the role played by supernovae of different types (Ia, II), allowing us to follow in detail the evolution of several chemical elements (H, D, He, C, N, O, Mg, Si, S, Ca, Fe, Ba, and Eu). Methods. Each galaxy model is specified by the prescriptions of the star formation rate and by the galactic wind efficiency chosen to reproduce the main features of these galaxies, in particular the stellar metallicity distributions and several abundance ratios. These parameters are constrained by the star formation histories of the galaxies as inferred by the observed color-magnitude diagrams, indicating extended star formation episodes occurring at early epochs, but also with hints of intermediate stellar populations. Results. The main observed features of the galaxies Leo 1 and Leo 2 can be very well explained by chemical evolution models according to the following scenarios: the star formation occurred in two long episodes at 14 Gyr and 9 Gyr ago that lasted 5 and 7 Gyr, respectively, with a low efficiency (ν = 0.6 Gyr −1 ) in Leo 1, whereas the star formation history in Leo 2 is characterized by one episode at 14 Gyr ago that lasted 7 Gyr, also with a low efficiency (ν = 0.3 Gyr −1 ). In both galaxies an intense wind (nine and eight times the star formation rate -w i = 9 and 8 in Leo 1 and Leo 2, respectively) takes place which defines the pattern of the abundance ratios and the shape of the stellar metallicity distribution at intermediate to high metallicities. Conclusions. The observational constraints can only be reproduced with the assumption of gas removal by galactic winds.

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Section: Discussionsupporting

confidence: 84%

Chemical evolution models for the dwarf spheroidal galaxies Leo 1 and Leo 2

Lanfranchi

Matteuccí

2010

A&A

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“…Consistent with the results of Teyssier et al (2009) obtained via cosmological simulations we find that a tiny minority of massive satellites produces the overwhelming majority of HVSs. Given that more massive galaxies are usually also more metal-rich (Tamura et al 2001) we conclude that an intragalactic stellar population should have at least on average a higher metalicities than the surviving dwarf galaxy population.…”

Section: Discussionmentioning

confidence: 80%

Kinematics in galactic tidal tails

Piffl¹,

Williams²,

Steinmetz³

2011

A&A

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Context. Recent observations of stars with unusually high radial velocities in the Galactic stellar halo have raised new interest in so-called hypervelocity stars. Traditionally, it is assumed that the velocities of these stars could only come from an interaction with the supermassive black hole in the Galactic center. It was suggested that stars stripped off a disrupted satellite galaxy could reach similar velocities and leave the Galaxy. Aims. In this work we study the kinematics of tidal debris stars in detail to investigate the implications of the new scenario and the probability that the observed sample of hypervelocity stars could partly develop out of such a galaxy collision. Methods. We used a suite of N-body simulations following the encounter of a satellite galaxy with its Milky Way-type host galaxy to gather statistics on the properties of stripped-off stars. We study especially the orbital energy distribution of this population. Results. We quantify the typical pattern in angular and phase space formed by the debris stars. We further develop a simple stripping model to predict the kinematics of stripped-off stars. We show that the distribution of orbital energies in the tidal debris takes a typical form that can be described quite accurately by a simple function. Based on this we develop a method predicting the energy distribution that allows us to evaluate the significance and the implications of highvelocity stars in satellite tidal debris. Conclusions. Generally the tidal collisions of satellite galaxy produce stars that escape into intragalactic space even if the satellite itself is on a bound orbit. The main parameters determining the maximum energy kick a tidal debris star can get is the initial mass of the satellite and only to a lower extent its orbit. Main contributors to an unbound stellar population created in this way are massive satellites (M sat > 10 9 M ). We thus expect intragalactic stars to have a metallicity higher than the surviving satellite population of the Milky Way. However, the probability that the observed HVS population is significantly contaminated by tidal debris stars appears low in light of our results.

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“…A possible link between dSphs and giant ellipticals was suggested by Tamura et al (2001), who showed that both the mass-metallicity and mass-luminosity relations of some dSph galaxies may be understood as a low-mass extension of giant elliptical galaxies.…”

Section: Implications For the Formation Of The Giant Galaxiesmentioning

confidence: 99%

The evolution of the photometric properties of Local Group dwarf spheroidal galaxies

Calura¹,

Lanfranchi

Matteuccí

2008

A&A

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Aims. We investigate the present-day photometric properties of the dwarf spheroidal galaxies in the Local Group. From the analysis of their integrated colours, we consider a possible link between dwarf spheroidals and giant ellipticals. From the analysis of the M V vs. (B− V) plot, we search for a possible evolutionary link between dwarf spheroidal galaxies (dSphs) and dwarf irregular galaxies (dIrrs). Methods. By means of chemical evolution models combined with a spectro-photometric model, we study the evolution of six Local Group dwarf spheroidal galaxies (Carina, Draco, Sagittarius, Sculptor, Sextans and Ursa Minor). The chemical evolution models, which adopt up-to-date nucleosynthesis from low and intermediate mass stars as well as nucleosynthesis and energetic feedback from supernovae type Ia and II, reproduce several observational constraints of these galaxies, such as abundance ratios versus metallicity and the metallicity distributions. The proposed scenario for the evolution of these galaxies is characterised by low star formation rates and high galactic wind efficiencies. Results. Such a scenario allows us to predict integrated colours and magnitudes which agree with observations. Our results strongly suggest that the first few Gyrs of evolution, when the star formation is most active, are crucial to define the luminosities, colours, and other photometric properties as observed today. After the star formation epoch, the galactic wind sweeps away a large fraction of the gas of each galaxy, which then evolves passively. Our results indicate that it is likely that at a certain stage of their evolution, dSphs and dIrrs presented similar photometric properties. However, after that phase, they evolved along different paths, leading them to their disparate present-day properties.

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Mass-Metallicity Relation for the Local Group Dwarf Spheroidal Galaxies: A New Picture for the Chemical Enrichment of Galaxies in the Lowest Mass Range

Cited by 20 publications

References 22 publications

Chemical evolution models for the dwarf spheroidal galaxies Leo 1 and Leo 2

Chemical evolution models for the dwarf spheroidal galaxies Leo 1 and Leo 2

Kinematics in galactic tidal tails

The evolution of the photometric properties of Local Group dwarf spheroidal galaxies

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