(mnras 327, 610, 2001 & 347, 1234, 2004) david churches, mike edmunds, alistair nelson - physics...
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(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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