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Paper text:
the `` monolithic collapse '' versus `` satellite accretion '' debate surrounding galaxy formation is a classic one , and one which received attention once again at this euroconference iii .
the former scenario was best expressed by eggen , lynden - bell & sandage ( 1962 , hereafter els ) ; supporting evidence for the els picture came from the apparent positive correlation between eccentricity and metallicity of halo stars .
however , current cosmological theories of structure formation have more in common with accretion - style scenarios like that envisioned by searle & zinn ( 1978 ) .
evidence in support of the latter can be found in the observations of stellar phase space substructure in the galactic halo ( e.g. helmi et  al .
1999 ) .
we were motivated to run a grid of chemodynamical simulations with the intention of contrasting the effects of the two collapse scenarios on the evolution of the milky way .
the two models described here vary primarily in their degree of clustering , and we examine the properties of the resulting simulated galaxies , in order to uncover present - day `` signatures '' of the model initial conditions and evolution . here , we focus on the distribution of halo star orbital eccentricities .
our galactic chemodynamical code ( gcd+ ) models self - consistently the effects of gravity , gas dynamics , radiative cooling , and star formation . type  ia and type  ii supernova feedback is included .
we relax the instantaneous recycling approximation when monitoring the galactic chemical evolution .
details of gcd+ can be found in kawata & gibson ( 2003 , in prep ) ; an earlier version of the code is described in kawata ( 2001 ) .
the semi - cosmological version of gcd+ used here is based upon the code of katz & gunn ( 1991 ) .
the initial condition is an isolated sphere of dark matter and gas , onto which small scale density fluctuations are superimposed ( parameterised by @xmath0 ) .
these perturbations are the seeds for local collapse and subsequent star formation .
solid - body rotation is imparted to the initial sphere ; this determines whether a disk - like or elliptical galaxy results . for the models described here ,
relevant parameters include the total mass ( @xmath1  m@xmath2 ) , baryon fraction ( @xmath3 ) , and spin parameter ( @xmath4 ) ; we employed 38911 dark matter and 38911 gas / star particles .
again , the two models described here differ only in the value of @xmath0 . in model  1 , @xmath5 , as favoured in standard cdm
( @xmath6 ) cosmology . in model  2 ,
@xmath7 , a smaller value which results in a more rapid , dissipative , collapse .
plots of model 1 ( upper panels ) and model 2 ( lower panels ) .
the @xmath8 axis is the initial rotation axis .
grey dots represent gas particles , while black represent star particles .
epochs are chosen so that roughly the same stellar mass is present in corresponding upper & lower panels . gas collapse and star formation
are more centralised in model 2 . ]
figure  1 demonstrates the classical hierarchical merging in action in both models 1 ( upper panels ) and 2 ( lower panels ) . gas particles are marked in grey , while star particles are in black .
star formation occurs in overdense regions , seeded by the initial small - scale perturbation spectrum .
stars continue to form in sub - clumps , as well as in the central region of the disk galaxy as it is built up .
we see less clustering in model 2 with most of the star formation occurring in the central region of the galaxy .
we analysed the bulk properties of the models at @xmath8=0 and confirmed that they were consistent with those of berczik ( 1999 ) and bekki & chiba ( 2001 ) .
the predicted surface density profiles , metallicity gradients , and rotation curves for our two models did not differ significantly .
however , we did find a difference in the distribution of the eccentricities of the orbits of solar neighbourhood halo stars .    [ cols="^,^ " , ]     the histogram of figure  2a shows the eccentricity distribution of halo star particles ( [ fe / h]@xmath9@xmath100.6 ) in the solar neighbourhood for the two models .
each bin shows the fraction of such star particles falling in a given eccentricity range .
also shown are observations from chiba & beers ( 2000 , hereafter cb ) .
model 1 produced a greater number of high eccentricity ( ecc @xmath11 0.8 ) solar neighbourhood halo stars , and is in better agreement with observation .
we next examined the specific accretion history of each model , tracing the eccentricity distribution functions for the stars associated with each disrupted satellite .
we identified satellites at @xmath8=0.46 which have merged into the halo of the host galaxy by @xmath8=0 .
the histogram of figure 2b shows the eccentricity distribution of solar neighbourhood halo stars which originated in these recently accreted satellites .
the @xmath12-axis is normalised by the total number of solar neighbourhood halo stars in each eccentricity bin .
our primary conclusions are that the majority of these halo stars are of high - eccentricity , and that one satellite in particular contributes @xmath1320% of all high eccentricity halo stars in the solar neighbourhood at @xmath8=0 .
the reader is directed to the complementary study of steinmetz et  al .
( these proceedings ) which finds that stars from accreted satellites which were on polar orbits form part of the galaxies halo .
the key question we wish to address remains ... _ what are the implications for the competing galaxy formation paradigms ? _    a brief response is as follows : cb observationally found no correlation between eccentricity and metallicity for halo stars near the sun ( their figure 6a ) , obviating the need for a `` rapid collapse '' picture of the formation of the galaxy ( els ) .
however , cb do identify a clump of high - eccentricity low - metallicity ( [ fe / h]@xmath13@xmath101.7 ) stars in this observational plane . in terms of els
, they interpret this clump as a relic of a rapid collapse phase .
our simulations suggest that this clump is , more likely , evidence of recent satellite accretion in the galactic halo .
cbb thanks the organising committee for financial assistance , and appreciates the hospitality of gerhard hensler and andi burkert in arranging collaborative visits to kiel and mpifa , heidelberg .
bkg acknowledges the financial support of the australian research council through its large research grant program ( # a00105171 ) .
we acknowledge the generous support of the australian partnership for advanced computing through its merit allocation scheme .
the present - day chemical and dynamical properties of the milky way are signatures of the galaxy s formation and evolution . using a self consistent chemodynamical evolution code we examine these properties within the currently favoured paradigm for galaxy formation - hierarchical clustering within a cdm cosmology . 
 our tree n - body / smoothed particle hydrodynamics code includes a self - consistent treatment of gravity , hydrodynamics , radiative cooling , star formation , supernova feedback and chemical enrichment . 
 two models are described which explore the role of small - scale density perturbations in driving the evolution of structure within the milky way . 
 the relationship between metallicity and kinematics of halo stars are quantified and the implications for galaxy formation discussed . while high - eccentricity halo stars have previously been considered a signature of `` rapid collapse '' , we suggest that many such stars may have come from recently accreted satellites .