(MNRAS 327, 610, 2001 & 347, 1234, 2004) David Churches, Mike Edmunds, Alistair Nelson - Physics & Astronomy, Cardiff University - Physics & Astronomy, Cardiff University DLAs in simulated galaxies and dust obscuration 1) To investigate the plausibility of proto-galaxies as the originators of DLAs 2) To illuminate the effect of dust obscuration on DLA count statistics Objectives Requirements A code for resolved simulations of protogalaxy formation A Model for Generation of Heavy Elements via Star Formation A Model for Dust in the ISM of the galaxy Column density vs Zinc abundance for DLA sytems τ = 0.01 τ = 0.1 τ = 0.5 τ = 1.0 Mathlin et al MNRAS 321, 743, 2001

Aim of the Simulations CDM N-body simulation of a 240 Mpc box (Virgo consortium ApJ 499, 20, 1998) This is NOT the aim of our simulations Our Aim is to simulate the detailed development of structure and column density at the level of individual galaxies

Galaxy Formation Code Tree-Code/SPH [ with 1/(r + ε) potential ] Parallelised using mpi - both particle pushing and tree building Individual Particle Timesteps Fully dynamic Kernel Radius Star Formation via a Schmidt Law ( SF = k ρ 1.5 ) Isothermal Equation of State Peter Williams - Joint Astrophysical Institute, Shanghai Normal University - Joint Astrophysical Institute, Shanghai Normal University (Williams, Churches & Nelson ApJ 607, 1, 2004)

Sample Run - Initial Conditions Williams & Nelson, A.&A. 2001, 374, 860. Mass 5x10 11 M סּ – 90% non-baryonic DM, 10% baryonic gas Initial Radius = R i 175 kpc initially solid body rotation with Ω = 0.16 / Gyr (λ = 0.06) initially in Hubble expansion with V radial = H i R, H i = 560 km/sec per Mpc sound speed 7.5 km/sec, ε = 175 pc gas, DM particles, finally star particles Dark MatterGas

Gas, Star & DM movies all components face-on all components edge-on gas only face-on gas only face-on gas column density face-on gas column density face-on(

gas starsdark matter Sample run final state after 9 Gyrs In addition to Morphology, the model galaxies also match observations quantitatively

First - Spiral Shocks Isothermal shock Pre-shock velocity 38 km/s Sound speed 10 km/sec →Mach number 3.8 Density jumps by a factor of 20 Equivalent to Mach number 4.5 Gas velocity near central object showing shocks Another simulation

Other Galaxy Properties Rotation Curve Density Profiles Star Formation Rates DM Gas Stars Gas x vs v y - final stellar mass 3.75x10 10 M סּ - final gas mass 1.25x10 10 M סּ

Generation of heavy Elements Where Z = Metallicity ρ g = gas density p = fraction of the new stellar mass returned to ISM in heavy elements α = fraction of new stellar mass locked up as long- lived stellar remnants and dS/dt = rate of SF per unit volume and dS/dt = rate of SF per unit volume This formula is applied to all the gas particles, which carry the metallicity Z in the galaxy We apply the simple model (Pagel & Patchett MNRAS 172, 13, 1975) Z vs time, using Z~23(O/H) (Pagel et al MNRAS 255, 325, 1992) Z vs time, and radius using Z~23(O/H) (Pagel et al MNRAS 255, 325, 1992) 1 Gyear 2 Gyears 3 Gyears 4 Gyears 5 Gyears

Mini Survey of 5 Models First the column densities and Zinc abundances through vertical sight lines through the gas discs of the models were calculated On 16x16 grid 30 kpc square

Mini Survey of 5 Models Model parameters used :- Mass (10 11 M סּ ) Spin Parameter λ for the 5x10 11 M סּ case for the 5x10 11 M סּ case time (Gyears)redshift a12.2 b21.3 c30.8 d50.4 a c b d For each model the Column densities and Zinc abundances were calculated at 4 times from the start of the calculation For each model the Column densities and Zinc abundances were calculated at 4 times from the start of the calculation

Mini Survey of 5 Models M = 5x10 11 M סּ, λ=0.06 M = 5x10 11 M סּ, λ=0.09 M = 5x10 11 M סּ, λ=0.12 M = 2.5x10 11 M סּ, λ=0.09 M = M סּ, λ=0.09 observations All the models at t = 1 and 2 Gyears The models overlap the observations, but occupy a larger region, with many high column density sight lines But these have τ > 0.5, which means that they may not be observed (Pei & Fall Ap J,1995)

Dust Model The amount of dust is based on the metallicity From Mathlin, Baker, Churches, & Edmunds MNRAS, 321, 743, 2001 Edmunds & Eales MNRAS, 299, L29, Where N g = gas column density The Optical Depth τ for metallicity Z is given by :-

Varying inclination angle The sight line survey was repeated for 2 other angles of incidence 0o0o0o0o 60 o 80 o Fraction of sight lines with τ > 0.5 or >1.0 as a function of time for the M = 5x10 11 M סּ case Conclusions:- 1) The results support the idea that DLA’s originate in galaxy disks at different stages of evolution 2) Any observational survey which counts the number of DLA’s needs to recognise that up to a significant fraction of them may not have been detected 80 o 60 o 0o0o0o0o

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