Discussion session Galactic v. Extra-galactic PNe: two different views of the same phenomenon? J. R. Walsh, ST-ECF, ESO (G. H. Jacoby, WIYN) PNe as Astronomical Tools 1st July 2005
!Success of [O III] PNLF – excellent secondary distance indicator for galaxies of all types, luminosities, ages, metallicities. Comparable to e.g. SBF (within 0.15mag.) ? No theoretical understanding why the PNLF works so well. (Dopita et al. 1992 - quantified effect of Z; Mendez et al. 1997, Marigo et al. 2001, 2004). Why should young and old populations with different mass stars at the AGB-PN stage have same M[OIII] cuttoff?
Virgo distance rungs Feldmeier, Ciardullo, Jacoby (1998), Feldmeier et al. (2003, 2004)
The Problem • Bright arm of PNLF is same shape in all galaxies • Constancy of PN luminosity in the brightest 0.5 mag. to the PNLF cut-off at M[OIII] -4.47 • Peak luminosity of the PNLF provided by stars with core masses > 0.6 Msun (Ciardullo et al. 2005; Marigo, 2001, 2004) M33 PNLF (Ciardullo et al 2004) Shoulder N -4.5 M[OIII] Cut off State-of-the art models of evolution of PNe provided by Marigo et al. papers (C.f. XPN Schoenberner et al.) Consider parameterized AGB – WD evolution including H and He burning, mass loss prescriptions, abundance of shell, photoionization. Acceptable matches to e.g. mass-radius relation, line ratio trends (e.g. HeII/Hβ v. [O III]), expansion velocities, etc. No treatment of circumstellar dust
The theoretical challenge • Bright end of PNLF formed by stars in a very narrow mass range ~ 2.5MSun • Similar result for He burners but slower evolution broadens age width of peak L Latest models (Marigo et al. 2004) construct PNLF by Monte Carlo simulations of PN populations of varying age and metallicity. Salpeter IMF. Now using Cloudy to produce spectra from the evolution models (instead of assuming Te) (tr = time TP-AGB to post-AGB at 104K)
Old populations – fainter PNe • Considering constant SFR with cut-off, construct sample from grid of pre + post AGB evolutionary models => PNLF v. age • Excellent match for young systems (spirals) but PNLF cut-off too faint for old galaxies (ellipticals) => distance too short
PNLF of spirals and ellipticals 1012MSun elliptical; * formation <4Gyr MW model - * formation rapid rise <3Gyr then declining (Portinari et al. 1998)
GalacticPNe • Detailed morphologies • Detailed velocity fields → hydrodynamic models • Nebular diagnostics and abundances • Central star spectra → temperatures, gravities, mass loss, abundances, masses • Reliable distances (< factor 2) in general, hence luminosities & masses only for selected few (parallaxes, pm distances, binaries, GC PNe, …) • > 2000 (and rising) confirmed – perhaps changing the picture (Corradi, Frew)
Extra-galactic PNe • Barely extended / Point-like • Expansion velocity only (Richer – correlated with PN L[OIII] or Z ?) • Limited diagnostics and abundances ([O III]4363Å only possible < 10Mpc) • No central star spectra (except for Magellanic Clouds) • Reliable distances → luminosities for all • > 6000 known (Acker & Jacoby preparing catalogue) PN spectra in NGC 5128
Selection effects • Extra-gal • [O~III] Brightness • Low extinction • Low stellar background Galactic • Extended – usually resolved to be included in imaging surveys • Low extinction regions (but can image in IR) • High surface brightness (usually not [O III])
Solutions … • Selection effects between Galactic and extra-galactic PNe not well understood – are bright Galactic and extra-galactic PNe the same? • Is there a ‘hidden’ fraction of evenly-distributed younger stars (< 2Gyr) in early type galaxies supplying the bright end cut-off PN • But young stars bright so should be evident in stellar age indicators (e.g. Hβ index) but not distinguished in integrated populations (e.g. NGC 5128, but for NGC 4697 c.f. Sambhus) • Our understanding of AGB and PN single star evolution needs revision – route for PN in early type galaxies different to Milky Way. Possible reasons:- differing IMF, extended star formation history, super-metal rich stars, … stellar masses for MW PNe under-estimated (c.f. Pauldrach) • Binary star solutions – high luminosity extra-gal PN from merged binaries (1*+1* = 2L* = 1PN, Ciardullo) ?
PNLF for SMC • PNLF for SMC from Jacoby (2005) should be complete • Feature 4 mags down PNLF may be evidence of PN on falling track or possibly a signature of a previous star formation event
Observational disciminants • Search for more PN in globular clusters to better quantify PN as arising from blue straggler scenario (3 PN detected in NGC 5128 GC’s) • Can we discriminate single star from merged binary star PN – abundances, morphology (e.g. Galactic Bulge). • Are non-spherical PN restricted to binary progenitors? How can line profiles of unresolved PN help? • Search for more examples of kinematic coupling to PNLF (decompose the PNLF by population age) • Try to age model the PNLF by applying star formation history analysis as done for Colour-Magnitude diagrams