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The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies  [PDF]
Y. Revaz,P. Jablonka,T. Sawala,V. Hill,B. Letarte,M. Irwin,G. Battaglia,A. Helmi,M. D. Shetrone,E. Tolstoy,K. A. Venn
Physics , 2009, DOI: 10.1051/0004-6361/200911734
Abstract: We present a large sample of fully self-consistent hydrodynamical Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It has enabled us to identify the key physical parameters and mechanisms at the origin of the observed variety in the Local Group dSph properties. The initial total mass (gas + dark matter) of these galaxies is the main driver of their evolution. Star formation (SF) occurs in series of short bursts. In massive systems, the very short intervals between the SF peaks mimic a continuous star formation rate, while less massive systems exhibit well separated SF bursts, as identified observationally. The delay between the SF events is controlled by the gas cooling time dependence on galaxy mass. The observed global scaling relations, luminosity-mass and luminosity-metallicity, are reproduced with low scatter. We take advantage of the unprecedentedly large sample size and data homogeneity of the ESO Large Programme DART, and add to it a few independent studies, to constrain the star formation history of five Milky Way dSphs, Sextans, LeoII, Carina, Sculptor and Fornax. For the first time, [Mg/Fe] vs [Fe/H] diagrams derived from high-resolution spectroscopy of hundreds of individual stars are confronted with model predictions. We find that the diversity in dSph properties may well result from intrinsic evolution. We note, however, that the presence of gas in the final state of our simulations, of the order of what is observed in dwarf irregulars, calls for removal by external processes.
The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies with GEAR  [PDF]
Yves Revaz,Pascale Jablonka
Physics , 2011, DOI: 10.1051/0004-6361/201117402
Abstract: We present a fully parallel chemo-dynamical Tree/SPH code, GEAR, which allows to perform high resolution simulations with detailed chemical diagnostics. Starting from the public version of Gadget-2, we included the complex treatment of the baryon physics: gas cooling, star formation law, chemical evolution and supernovae feedback. We qualified the performances of GEAR with the case of dSph galaxies. GEAR conserves the total energy budget of the systems to better than 5% over 14Gyr and proved excellent convergence of the results with numerical resolution. We showed that models of dSphs in a static Euclidean space, where the expansion of the universe is neglected are valid. In addition, we tackled some of the existing open questions in the field, like the stellar mass fraction of dSphs and its link with the predicted dark matter halo mass function, the effect of the supernova feedback, the spatial distribution of the stellar populations, and the origin of the diversity in star formation histories and chemical abundance patterns. Strong supernovae driven winds seem incompatible with the observed metallicities and luminosities. Despite the fact that newly formed stars are preferentially found in the galaxy central parts, turbulent motions in the gas can quickly erase any metallicity gradient. The variety in dSph properties result from a range of total masses as well as from a dispersion in central densities. The latter is also seen in the haloes emerging from a LCDM cosmogony.
The effect of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies  [PDF]
S. Recchi,G. Hensler
Physics , 2009, DOI: 10.1002/asna.200911261
Abstract: We study the effects of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies, in particular focusing on two model galaxies similar to IZw18 and NGC1569. We consider both scenarios, clouds put at the beginning of the simulation and continuously created infalling ones. Due to dynamical processes and thermal evaporation, the clouds survive only a few tens of Myr, but during this time they act as an additional cooling agent and the internal energy of cloudy models is typically reduced by 20 - 40% in comparison with models without clouds. The clouds delay the development of large-scale outflows, therefore helping to retain a larger amount of gas inside the galaxy. However, especially in models with continuous creation of infalling clouds, their bullet effect can pierce the expanding supershell and create holes through which the superbubble can vent freshly produced metals. Moreover, assuming a pristine chemical composition for the clouds, their interaction with the superbubble dilutes the gas, reducing the metallicity (by up to ~ 0.4 dex) with respect to the one attained by diffuse models.
Chemical and dynamical evolution in gas-rich dwarf galaxies  [PDF]
Simone Recchi,Francesca Matteucci,Annibale D'Ercole
Physics , 2000,
Abstract: We study the effect of a single, instantaneous starburst in a gas-rich dwarf galaxy on the dynamical and chemical evolution of its interstellar medium. We consider the energetic input and the chemical yields originating from SNeII, SNeIa and intermediate-mass stars. We find that a galaxy resembling IZw18 develops a galactic wind carrying out mostly the metal-rich gas. The various metals are lost differentially and the metals produced by the SNeIa are lost more efficiently than the others. As a consequence, we find larger [$\alpha$/Fe] ratios for the gas inside the galaxy than for the gas leaving the galaxy. Finally we find that a single burst occurring in primordial gas (without pre-enrichment), gives chemical abundances and dynamical structures in good agreement with what observed in IZw18 after $\sim$ 29 Myr from the beginning of star formation.
Dynamical and chemical evolution of gas-rich dwarf galaxies  [PDF]
Simone Recchi,Francesca Matteucci,Annibale D'Ercole
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.04189.x
Abstract: We study the effect of a single, instantaneous starburst on the dynamical and chemical evolution of a gas-rich dwarf galaxy, whose potential well is dominated by a dark matter halo. We follow the dynamical and chemical evolution of the ISM by means of an improved 2-D hydrodynamical code coupled with detailed chemical yields originating from type II SNe, type Ia SNe and single low and intermediate mass stars (IMS). In particular we follow the evolution of the abundances of H, He, C, N, O, Mg, Si and Fe. We find that for a galaxy resembling IZw18, a galactic wind develops as a consequence of the starburst and it carries out of the galaxy mostly the metal-enriched gas. In addition, we find that different metals are lost differentially in the sense that the elements produced by type Ia SNe are more efficiently lost than others. As a consequence of that we predict larger [$\alpha$/Fe] ratios for the gas inside the galaxy than for the gas leaving the galaxy. A comparison of our predicted abundances of C, N, O and Si in the case of a burst occurring in a primordial gas shows a very good agreement with the observed abundances in IZw18 as long as the burst has an age of $\sim 31$ Myr and IMS produce some primary nitrogen. However, we cannot exclude that a previous burst of star formation had occurred in IZw18 especially if the preenrichment produced by the older burst was lower than $Z=0.01$ Z$_{\odot}$. Finally, at variance with previous studies, we find that most of the metals reside in the cold gas phase already after few Myr. This result is mainly due to the assumed low SNII heating efficiency, and justifies the generally adopted homogeneous and instantaneous mixing of gas in chemical evolution models.
Dynamical condition of neutral hydrogen envelopes of dwarf galaxies and their possible morphological evolution  [PDF]
Yuka Y. Tajiri,Hideyuki Kamaya
Physics , 2002, DOI: 10.1051/0004-6361:20020594
Abstract: We investigate the star-formation history of gas-rich dwarf galaxies, taking account of the dynamical evolution of their neutral hydrogen (H{\sc i}) envelope. Gas-rich dwarfs are classified into blue compact dwarfs (BCDs) and dwarf irregulars (dIrrs). In this paper, their H{\sc i} envelope is clearly shown not to be blown away by their stellar feedback. This is concluded since the observed star-formation rate (SFR) of gas-rich dwarfs is generally smaller than a critical SFR, $\psi_{\rm crit}$, at which stellar feedback accelerates the H{\sc i} envelope to the escape velocity. From this standpoint and the chemical property of sample BCDs, we suggest two possibilities; (1) The H{\sc i} gas in the envelope of BCDs is consumed to fuel their star-formation; and (2) BCDs have a similar star-formation history. We also discuss morphological evolution among dwarf galaxies. As long as gas-rich dwarfs are isolated, it is difficult for them to evolve into dwarf ellipticals (dEs). When the H{\sc i} envelope in gas-rich dwarfs is consumed in subsequent star-formation, a morphological exchange between BCDs and dIrrs is still expected, consistent with previous studies. If the SFR of gas-rich dwarfs was much higher than $\psi_{\rm crit}$ in the past, interestingly, an evolutionary scenario from dEs to gas-rich dwarfs is possible.
SPH code for dynamical and chemical evolution of disk galaxies  [PDF]
Peter Berczik
Physics , 1998,
Abstract: The problem of chemical and dynamical evolution of galaxies is one of the most attracting and complex problems of modern astrophysics. Within the framework of the given work the standard dynamic Smoothed Particle Hydrodynamics (SPH) code (Monaghan J.J. 1992, ARAA, 30, 543) is noticeably expanded. Our investigation concernes with the changes and incorporation of new ideas into the algorithmic inclusion of Star Formation (SF) and Super Novae (SN) explosions in SPH (Berczik P. & Kravchuk S.G., 1996, ApSpSci, 245, 27). The proposed energy criterion for definition of a place and efficiency of SF results in the successfully explain Star Formation History (SFH) in isolated galaxies of different types. On the base of original ideas we expand a code in a more realistic way of the description of effects of return of a hot, chemical enriched gas in Interstellar Matter (ISM). In addition to the account of SNII, we offer the self-agreed account of SNIa and PN. This allows to describe not only the ISM content of $ O^{16} $ but also the content of $ Fe^{56} $. This model will allow to investigate adequately also a well known $ G - dwarf $ problem. In the frame of this approach we are able to reproduce the presently observed kinematics of star and gaseous components as well as their distributions and heavy element abundances. The developed model provide the realistic description of dynamics and chemical evolution of typical disk -- like galaxies over the Hubble timescale.
Dynamical friction in dwarf galaxies  [PDF]
X. Hernandez,Gerard Gilmore
Physics , 1998, DOI: 10.1046/j.1365-8711.1998.01511.x
Abstract: We present a simplified analytic approach to the problem of the spiraling of a massive body orbiting within the dark halo of a dwarf galaxy. This dark halo is treated as the core region of a King distribution of dark matter particles, in consistency with the observational result of dwarf galaxies having solid body rotation curves. Thus we derive a simple formula which provides a reliable and general first order solution to the problem, totally analogous to the one corresponding to the dynamical friction problem in an isothermal halo. This analytic approach allows a clear handling and a transparent understanding of the physics and the scaling of the problem. A comparison with the isothermal case shows that in the core regions of a King sphere, dynamical friction proceeds at a different rate, and is sensitive to the total core radius. Thus, in principle, observable consequences may result. In order to illustrate the possible effects, we apply this formula to the spiraling of globular cluster orbits in dwarf galaxies, and show how present day globular cluster systems could in principle be used to derive better limits on the structure of dark halos around dwarf galaxies, when the observational situation improves. As a second application, we study the way a massive black hole population forming a fraction of these dark halos would gradually concentrate towards the centre, with the consequent deformation of an originally solid body rotation curve. This effect allows us to set limits on the fraction/mass of any massive black hole minority component of the dark halos of dwarf galaxies. In essence, we take advantage of the way the global matter distribution fixes the local distribution function for the dark matter particles, which in turn determines the dynamical friction problem.
Chemo-dynamical evolution of tidal dwarf galaxies. II. The long-term evolution and influence of a tidal field  [PDF]
Sylvia Ploeckinger,Simone Recchi,Gerhard Hensler,Pavel Kroupa
Physics , 2014, DOI: 10.1093/mnras/stu2629
Abstract: In a series of papers, we present detailed chemo-dynamical simulations of tidal dwarf galaxies (TDGs). After the first paper, where we focused on the very early evolution, we present in this work simulations on the long-term evolution of TDGs, ranging from their formation to an age of 3 Gyr. Dark-matter free TDGs may constitute a significant component of the dwarf galaxy (DG) population. But it remains to be demonstrated that TDGs can survive their formation phase given stellar feedback processes, the time-variable tidal field of the post-encounter host galaxy and its dark matter halo and ram-pressure wind from the gaseous halo of the host. For robust results the maximally damaging feedback by a fully populated invariant stellar IMF in each star cluster is assumed, such that fractions of massive stars contribute during phases of low star-formation rates. The model galaxies are studied in terms of their star-formation history, chemical enrichment and rotational curves. All models evolve into a self-regulated long-term equilibrium star-formation phase lasting for the full simulation time, whereby the TDGs become significantly more compact and sustain significantly higher SFRs through compressive tides than the isolated model. None of the models is disrupted despite the unphysical extreme feedback, and none of the rotation curves achieves the high values observed in real TDGs, despite non-virial gas accretion phases.
Dynamical processes, element mixing and chemodynamical cycles in dwarf galaxies  [PDF]
Andreas Rieschick,Gerhard Hensler
Physics , 2000,
Abstract: Since the chemical evolution of galaxies seems to differ between morphological types and deviates in many details from the standard scenario the question has to be addressed when, how and to what amount metal-enriched ejecta from Supernovae and Planetary Nebulae polute their environment. Since recent observations of dwarf galaxies show no significant metal abundance gradients throughout the galaxies while enhancement of metals happens in isolated HII regions, an effective mixing process has to be assumed. Chemodynamical evolution models can provide a possible explanation by demonstrating that strong evaporation of gas clouds by hot gas and following condensation leads to an almost perfect mixing of the gas. We focus on the different phases of chemodynamical evolution that are experienced by a representative dwarf irregular galaxy model and present a quantitative analysis of the chemodynamical gas flow cycles.
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