Garching, 19/05/2004 1

Modelling the PNLF: Population Effects on the Bright Cut-off

Paola Marigo – Dipartimento di Astronomia,Padova

Léo Girardi – Osservatorio Astronomico di Trieste

Achim Weiss – Max-Planck-Institut fur Astrophysik, Garching

Martin Groenewegen – Instituut voor Sterrenkunde, Leuven

Cesare Chiosi – Dipartimento di Astronomia,Padova

Abell 39

Garching, 19/05/2004 2

Ciardullo, Jacoby, et al.’s interpretative scenario:

I. Jacoby (1996): narrow CSPN mass distribution (0.58 ± 0.02 M) over the age range 3-10 Gyr , i.e. initial mass range 1-2 M.

II. Ciardullo & Jacoby (1999) : circumstellar extinction estinguishes the overluminous and massive-progenitor PNe below the cut-off.

III. Dopita et al. (1992) explains little dependence on metallicity.

Why is the PNLF cut-off magnitude constant?

So far no robust theoretical explanation

I. Dopita et al. (1992), Mendez et al. (1993) predict a strong dependence on population age.

I. Modelling full of hidden and implicit assumptions, rarely a population synthesis approach.

but

Garching, 19/05/2004 3

Synthetic model of PN evolution

AGB evolution (Marigo et al. 1996,1998, Marigo 2001)

central star mass (Mi, Z) [p] AGB wind velocity density and chemical comp. of the ejecta (r, t)

post-AGB evolution (Vassiliadis & Wood 1994)

logL-logTeff tracks (H-burn./He burn.) [p1] [p2] fast wind

dynamical evolution of the nebula

interacting-winds model [p] shell thickening due to ionisation

Ionisation and nebular emission lines

CLOUDY photoionisation code [p1] [p2]

(Marigo et al. 2001, A&A, 378, 958)

Garching, 19/05/2004 4

Garching, 19/05/2004 5

Vassiliadis & Wood (1994) Initial masses: 0.9 – 5.0 M

Metallicities: Z= 0.016, 0.008, 0.004, 0.001

H-burning central stars

He-burning central stars

loops less luminous longer evolutionary timescales

post-AGB evolutionary tracks

Garching, 19/05/2004 6

Interacting-winds model(Volk & Kwok 1985; Kahn 1983; Breitschwerdt & Kahn 1990)

I. MOMENTUM-DRIVEN PHASE

I. ENERGY-DRIVEN PHASE

radiative cooling > kinetic energy from the fast windIsothermal shock (RI RS)

radiative cooling << kinetic energy from the fast windFormation of the hot bubbleAdiabatic shock (RI << RS) (eqs)

Garching, 19/05/2004 7

Ionisation and line emission from CLOUDY(Ferland 2000, 2001)

INPUT • Expanding-sphere geometry• Rin, Rout• Uniform N(H) • Elemental abundances (H,He,C,N,O,etc.)• L and Teff of the CSPN

Mi=2.0 M; MCSPN=0.685 M; Z=0.008; H-burn.; Mion=0.091 M; tPN=3000 yr

OUTPUT• Te (volume average)• ionisation fractions• line fluxes

Garching, 19/05/2004 8

Mi=1.7 M; MCS= 0.6 M; Z=0.019

Output of the PN synthetic model

Time evolution of:

• Ionised mass

• Nebular radius

• Expansion velocity

• optical configuration

• emission line luminosities

Garching, 19/05/2004 9

NUCLEAR BURNING REGIME (H-/He-burning tracks)

TRANSITION TIME (500 to 10000 yr)

METALLICITY (Z=0.019, 0.008, 0.004)

STAR FORMATION HISTORY (mainly the age of last episode of SF)

FREE PARAMETERS

Monte Carlo + population synthesis of galaxies used to simulate PN samples for any distribution of parameters

Garching, 19/05/2004 10

PN central stars in the HR diagram

Simulated PN sample:

M5007 < 1; Ntot = 500SFR=const.; Z=0.019; ttr=500 yrH-burn. and He-burn. tracks optically thick ; optically thin

Garching, 19/05/2004 11

Ionised mass-radius relation

Observed data from Zhang (1995), Boffi & Stanghellini (1994)

Simulated PN sample:

M5007 < 1; Ntot = 500SFR=const.; Z=0.019; ttr=500 yrH-burn. and He-burn. tracks optically thick ; optically thin

Garching, 19/05/2004 12

Electron density-radius relation

Data from Phillips (1998)

Simulated PN sample:

M5007 < 1; Ntot = 500SFR=const.; Z=0.019; ttr=500 yrH-burn. and He-burn. tracks optically thick ; optically thin

Garching, 19/05/2004 13

Electron temperature distribution of Galactic PNe

Observed (ESO-Strasbourg Catalogue)

Predicted (H-burning tracks)

Predicted (He-burning tracks)

Garching, 19/05/2004 14

I([OIII]5007)/I(H) distribution of Galactic PNe

Observed (McKenna et al. 1996)

Predicted (H-burning tracks)

Predicted (He-burning tracks)

Garching, 19/05/2004 15

WHICH PNe FORM THE CUT-OFF?

MCSPN 0.70-0.75 M; Mi 2-3 M; age 0.5-1.0 Gyr

Garching, 19/05/2004 16

DEPENDENCE ON H-/He-BURNING TRACKS

• No dependence for young ages (i.e galaxies with continued SFR)• Strong dependence for old ages• Anyway both H- and He-burning tracks are expected to occur

Garching, 19/05/2004 17

DEPENDENCE ON TRANSITION TIME

• Some dependence for young ages – about 500 yr to reproduce observed cut-off of spirals• No dependence for old ages

Garching, 19/05/2004 18

DEPENDENCE ON METALLICITY

Ciardullo (2002) based on Dopita et al. (1992) photoionisation models

ASSUMPTION: at any Z, age of 0.8 Gyr (of the star at the PNLF cut-off)

6 Gyr

0.8 Gyr

• Not what expected from Dopita et al. (1992) models• Non-monotonic behaviour for young ages – caused by 3rd dredge-up of oxygen in intermediate-mass AGB stars• Monotonic behaviour at old ages (no 3rd dredge-up)

Garching, 19/05/2004 19

DEPENDENCE ON AGE OF THE LAST EPISODE OF SF

• Strong dependence after about 0.7 Gyr• Decline of about 5 mag for 10-Gyr old populations

Garching, 19/05/2004 20

PNLF IN TEMPLATE GALAXIES

t

t t

t

Z

Z

SFH AMR

Garching, 19/05/2004 21

M5007 -4.5 can be reproduced for galaxies with ongoing or recent star formation

difficulty to explain the observed invariance of the cut-off in galaxies from late to early types:

recent burst of SF in ellipticals?

something missing in the models? (yes, but e.g. extinction makes PNe fainter, not brighter)

could larger MCSPN or higher [O/H] at low Z produce such bright PNe at old ages? (under investigation)

some exotic type of PNe in ellipticals? (to be investigated)

MAIN CONCLUSIONS