(MNRAS 327, 610, 2001 & 347, 1234, 2004)(MNRAS 327, 610, 2001 & 347, 1234, 2004)

David Churches, Mike Edmunds, Alistair NelsonDavid Churches, Mike Edmunds, Alistair Nelson - Physics & Astronomy, Cardiff University- Physics & Astronomy, Cardiff University

DLAs in simulated galaxies and DLAs in simulated galaxies and dust obscurationdust 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

ObjectivesObjectives

RequirementsRequirements

A code for resolved simulations of protogalaxy formationA code for resolved simulations of protogalaxy formation

A Model for Generation of Heavy Elements via Star FormationA Model for Generation of Heavy Elements via Star Formation

A Model for Dust in the ISM of the galaxyA Model for Dust in the ISM of the galaxy

Column density vs Zinc abundance for DLA sytemsColumn density vs Zinc abundance for DLA sytems

ττ = 0.01 = 0.01

ττ = 0.1 = 0.1

ττ = 0.5 = 0.5

ττ = 1.0 = 1.0

Mathlin et al MNRAS 321, 743, 2001Mathlin et al MNRAS 321, 743, 2001

AimAim of the Simulations of the SimulationsCDM 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 CodeGalaxy 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 ρ1.5)

Isothermal Equation of State

Peter WilliamsPeter Williams - Joint Astrophysical Institute, Shanghai Normal University- Joint Astrophysical Institute, Shanghai Normal University

(Williams,(Williams, Churches & Nelson ApJ 607, 1, 2004)Churches & Nelson ApJ 607, 1, 2004)

Sample Run - Initial ConditionsSample Run - Initial ConditionsWilliams & Nelson,Williams & Nelson, A.&A. 2001, 374, 860A.&A. 2001, 374, 860..

Mass 5x1011 M 90% – ּס non-baryonic DM, 10% baryonic gas Initial Radius = Ri 175 kpc initially solid body rotation with Ω = 0.16 / Gyr (λ = 0.06) initially in Hubble expansion with Vradial = Hi R , Hi = 560 km/sec per Mpc sound speed 7.5 km/sec , ε = 175 pc 33552 gas , 33401 DM particles, finally 46016 star particles

Dark Matter Gas

Gas, Star & DM moviesGas, Star & DM movies

all components face-on

all components edge-on

gas only face-ongas only face-on

gas column density face-on

(http://www.cf.ac.uk/pub/Alistair.Nelson/index.html)(http://www.cf.ac.uk/pub/Alistair.Nelson/index.html)

gas stars dark matter

Sample run final state after 9 GyrsIn addition to Morphology, In addition to Morphology, the model galaxies also match observations quantitativelythe model galaxies also match observations quantitatively

First - Spiral ShocksFirst - Spiral Shocks

Isothermal shock

Pre-shock velocity 38 km/sSound speed 10 km/sec→Mach number 3.8

Density jumps by a factor of 20Equivalent to Mach number 4.5

Gas velocity near central object showing shocksAnother simulation

Other Galaxy PropertiesOther Galaxy Properties

Rotation Curve

Density Profiles

Star Formation Rates

DM

Gas Stars

Gas x vs vGas x vs vyy

- final stellar mass 3.75x1010 Mּס - final gas mass 1.25x1010 Mּס

Generation of heavy ElementsGeneration of heavy Elementsdt

dSZp

dt

Zgd )()(

dt

dSZp

dt

Zgd )()(

dt

dSZp

dt

Zgd )()(

dt

dSZp

dt

Zd g )()(

Where Where Z Z = Metallicity = Metallicity

ρρgg = gas density = gas density

p p = fraction of the new stellar mass = fraction of the new stellar mass returned to ISM in heavy returned to ISM in heavy elementselements

αα = fraction of new stellar mass locked = fraction of new stellar mass locked up as up as long- long- lived stellar remnantslived stellar remnants

and and dS/dt = rate of SF per unit volumedS/dt = rate of SF per unit volumeThis formula is applied to all the gas particles, This formula is applied to all the gas particles, which carry the metallicity Z in the galaxywhich carry the metallicity Z in the galaxy

We apply the simple modelWe apply the simple model (Pagel & Patchett MNRAS 172, 13, 1975)(Pagel & Patchett MNRAS 172, 13, 1975)

Z vs time, using Z~23(O/H) Z vs time, using Z~23(O/H) (Pagel et al MNRAS 255, 325, 1992)(Pagel et al MNRAS 255, 325, 1992)Z vs time, and radius using Z~23(O/H) Z vs time, and radius using Z~23(O/H) (Pagel et al MNRAS 255, 325, 1992)(Pagel et al MNRAS 255, 325, 1992)

1 Gyear1 Gyear

2 Gyears2 Gyears

3 Gyears3 Gyears

4 Gyears4 Gyears

5 Gyears5 Gyears

Mini Survey of 5 ModelsMini Survey of 5 Models

First the column densities and Zinc First the column densities and Zinc abundances through vertical sight lines abundances through vertical sight lines through the gas discs of the models were through the gas discs of the models were calculatedcalculated

On 16x16 grid 30 On 16x16 grid 30 kpc squarekpc square

Mini Survey of 5 ModelsMini Survey of 5 ModelsModel parameters used :-Model parameters used :-

Mass (10Mass (101111 M Mּסּס)) 55 55 55 2.52.51010

Spin Parameter Spin Parameter λλ 0.060.06 0.090.09 0.120.12 0.090.090.090.09

for the 5x10for the 5x101111 M M ּסּס casecase

time (Gyears)time (Gyears) redshiftredshift

aa 11 2.22.2

bb 22 1.31.3

cc 33 0.80.8

dd 55 0.40.4

aa

cc

bb

dd

For each model the Column densities and For each model the Column densities and Zinc abundances were calculated at 4 times Zinc abundances were calculated at 4 times from the start of the calculation from the start of the calculation

Mini Survey of 5 ModelsMini Survey of 5 ModelsM = 5x10M = 5x101111MMּסּס, , λλ=0.06=0.06

M = 5x10M = 5x101111MMּסּס, , λλ=0.09=0.09

M = 5x10M = 5x101111MMּסּס, , λλ=0.12=0.12

M = 2.5x10M = 2.5x101111MMּסּס, , λλ=0.09=0.09

M = 10M = 101212MMּסּס, , λλ=0.09=0.09

observationsobservations

All the models All the models

atat t = 1 and 2 Gyearst = 1 and 2 Gyears

The models overlapThe models overlap the observations, but the observations, but occupy a larger region, with many high occupy a larger region, with many high column density sight linescolumn density sight lines

But these have But these have ττ > 0.5, which means that > 0.5, which means that they may not be observedthey may not be observed(Pei & Fall Ap J ,1995)(Pei & Fall Ap J ,1995)

Dust ModelDust Model

The amount of dust is based on the metallicityThe amount of dust is based on the metallicity

FromFrom Mathlin, Baker, Churches, & Edmunds MNRAS, 321, 743, 2001Mathlin, Baker, Churches, & Edmunds MNRAS, 321, 743, 2001Edmunds & Eales MNRAS, 299, L29, 1998.Edmunds & Eales MNRAS, 299, L29, 1998.

gZN201007.4

Where NWhere Ngg = gas column density = gas column density

The Optical Depth The Optical Depth ττ for metallicity Z is given by :- for metallicity Z is given by :-

Varying inclination angleVarying inclination angleThe sight line survey was repeated for 2 other angles of incidenceThe sight line survey was repeated for 2 other angles of incidence

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Fraction of sight lines Fraction of sight lines with with ττ > 0.5 or >1.0 as > 0.5 or >1.0 as a function of time for a function of time for the M = 5x10the M = 5x101111MMּסּס casecase

Conclusions:-Conclusions:-

1) The results support the idea that DLA’s originate in 1) The results support the idea that DLA’s originate in galaxy disks at different stages of evolutiongalaxy disks at different stages of evolution

2) Any observational survey which counts the number of 2) Any observational survey which counts the number of DLA’s needs to recognise that up to a significant fraction DLA’s needs to recognise that up to a significant fraction of them may not have been detectedof them may not have been detected

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The EndThe End