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presented by Vianney Lebouteiller (IAP) coll. with Daniel Kunth

Is the ISM in Starburst galaxies well mixed?. presented by Vianney Lebouteiller (IAP) coll. with Daniel Kunth. Team / Collaborators. Thesis of Vianney Lebouteiller Team of the Institut d’Astrophysique de Paris (IAP)

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presented by Vianney Lebouteiller (IAP) coll. with Daniel Kunth

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  1. Is the ISM in Starburst galaxies well mixed? presented by Vianney Lebouteiller (IAP) coll. with Daniel Kunth

  2. Team / Collaborators • Thesis of Vianney Lebouteiller • Team of the Institut d’Astrophysique de Paris (IAP) french team (A. Lecavelier des Etangs, J.-M. Désert, G. Hébrard, R. Ferlet, A. Vidal-Madjar) • & LERMA - Obs. de Paris : J. Lequeux • & JHU Baltimore : A. Aloisi

  3. Outline • Problematic : self-enrichment of the HII regions ? • A new approach: study of the neutral gas • FUSE • method and analysis • Results on Blue Compact Dwarfs • The next step: Giant HII regions • the example of NGC 604 • Results on NGC 604 • neutral gas homogeneity • abundances ratio • modelling • Conclusions & Perspectives

  4. Origin of the problem IZw18 • The problem of mixing in the ISM is a genenal one • Moreover, Kunth & Sargent (1986) pointed out thelack of extremely metal-poorgalaxies in emission-line surveys hence proposed: • Self-enrichment hypothesis : Self–pollutionby fresh released metals in situ by SNe, providing rapid cooling of the hot gas during the lifetime of the starburst. Pristine gasin the outer regions ?

  5. Evidences against/for abundances discontinuities • Small scale abundances inhomogenities suspected in a few objects: • NGC5253(Walsh & Roy, 1989; Kobulnicky et al. 1997) • local pollution inIIZw40(Walsh & Roy, 1993) • andMkn 996(Thuan et al. 1996) : N/H overabundances attributed to WR winds. But not true in all young starburts (Kobulnicky, 1999; Oey & Schield, 2000) • Abundances are similar to those of young stars IZw18 • IZw18, SBS0035-052, SMC: 6 regions: log O/H=8.13 ±0.08 LMC:4 regions: log O/H=8.37 ±0.25 • (Russel & Dopita 1990) • α-elements inhot gasis often over solar e.g. in theLMC(Dennerl et al. 2001) Delayed mixing ?

  6. Two models … Recchi et al. 2002 Tenorio-Tagle 1996 ejecta and winds carry out metals but gas immediately cools down and enrich the ISM SNe expell the gas, creating a superbubble evolving in a low density spherical halo: disperse and mix few 109 yrs few 106 yrs Mixing timescale discontinuities no discontinuities

  7. FUSE • 900-1200 Å • HI, OI, NI, FeII, SiII, ArI, ...

  8. Studying the HI metal composition

  9. Abundances determination • Profile fitting procedure Owens(M. Lemoine) • returns most likely values (N, b, T, ...) • Owensderives an estimation of the errors (including uncertainties on the LSF, the continuum,...) • One homogeneous cloud • Deriving abundances from the column densities • ionization structure assumeda priori Fig: Example of fitted lines H N O Si P Ar Fe H I (13.60 eV) N I (14.53 eV) O I (13.62 eV) SiII (16.34 eV) P II (19.72 eV) Ar I (15.76 eV) FeII (16.18 eV)

  10. Results : Blue Compact Dwarfs HI region (UV abs. lines) HII region (opt. em. lines) log (X/H) log (X/H) Refs :Lebouteiller et al. (2003) for IZw36, Lecavelier et al. (2003) and Aloisi et al. ( 2003) for IZw18Thuan et al. (in preparation) for SBS 0335-052, Thuan et al. (2002) for Markarian 59 (+NGC1705 poster n°3 A. Aloisi and NGC253 poster n°14 J. Cannon)

  11. ? ? ?

  12.  Observations of individual HII regions in spiral galaxies M33 • Relatively high S/N, sightlines less complex • Avoid possible systematic errors, study the effects of the multiple sightlines, ... • Unique possibility to model, to know the ionization stucture, etc... 1’

  13. FUSE (metals) FUSE (metals) HST/STIS (HI, 2D) Mode 30’’x30’’ 4’’x20’’ G140L 52’’x2’’ Resolution ~0.07 Å ~0.07 Å ~2 Å FUSE LWRS Exp. time ~13 ksec ~7 ksec ~2 ksec HST/ STIS FUSE MDRS 20 pc The case of NGC604 • 3-5 Myrs (Hunter et al. 1996), 4-5 (Wilson & Matthews 1995) • ~200 pc HII region size

  14. NGC 604 spectrum CIII Pcygni feature OVI Pcygni feature Metals from M33 HI from M33

  15. HI column density determination Profiles before convolution Profiles after convolution Red: total profile • log N(HI) = 21.01±0.05

  16. HI withSTIS 20.73 ±0.15 star O4 Ia, V=17.0 20.86 ±0.18 star O4 Iab, V=18.2 Lyman α 20.52 ±0.19 star O4, V=19.2 (fig. of Bruhweiler at al. 2001) 23/18

  17. Mimic FUSE data • Construction of the global spectrum ≡ mean, weighted by the stars magnitudes • Do we overestimate HI column density ? • N(HI)=20.96

  18. Ionized gas (optical emission-lines) Diffuse neutral gas (FUSE LWRS & MDRS) Results: abundances X/H • Consistent determinations • Global underabundance in the neutral gas, even for Fe • Less enriched gas in the sightlines vs. enrichment of the HII gas log (X/H) X/H

  19. Results: abundances X/Y • N/O same as HII region  N primary, no ionization correction • Ar/O  little ionization correction may be needed log (X/Y) X/Y

  20. Modelling of NGC604 HII region PDR HI region => Coupling with HI

  21. Conclusions & perspectives • Difficult interpretation for BCDs needs to be validated  Giant HII Regions • Evidence for pockets of metal deficient neutral gas in NGC604 • less chemically evolved gas in the sight lines ? • are dustier regions invisible in far-UV more metallic ? • Is the neutral gas associated to the HII region ? • v(HI) always  v(HII) • Future work on other giant HII regions in M33 • Investigate hidden saturated lines (...resolution effects) See poster n°41 for more details

  22. end of the presentation

  23. Column densities

  24. NGC 604 : MDRS and LWRS observations  test LWRS MDRS HST/ STIS The derived broadenings are consistent with the size of the cluster 15’’ Total broadening/3 (px) 4’’ λ (Å)

  25. HI stellar contamination ? Stellar vs. interstellar HI ? O stars dominate  No significant stellar contamination is expected for Lyβ in hot stars stellar population (Robert et al. 2003) Observations Synth Mod Spec Theo model

  26. NGC 604, some facts

  27. C IV Si IV N V Stellar contamination evidences Synthetic model spectra (Robert et al. 2003) 0.5 Z IMF=-2.35 Instantaneous burst Uses a stellar library from observations Synthetic model spectra (Starburst 99) 0.5 Z IMF=-2.35 Instantaneous burst Uses a stellar library from observations C III

  28. Modelling of NGC604 HII region PDR • Cd fit LWRS independent compare with HIIR cd: • To come : PDR modelling NEUTRAL REGION

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