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Resolved Stellar Populations outside the Local Group

Resolved Stellar Populations outside the Local Group. Alessandra Aloisi (STScI/ESA). Science with the New HST after SM4 Bologna – 30 January 2008. Collaborators. F. Annibali, A. Grocholski, C. Leitherer, J. Mack, M. Sirianni, & R. van der Marel (STScI)

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Resolved Stellar Populations outside the Local Group

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  1. Resolved Stellar Populations outside the Local Group Alessandra Aloisi (STScI/ESA) Science with the New HST after SM4 Bologna – 30 January 2008

  2. Collaborators F. Annibali, A. Grocholski, C. Leitherer, J. Mack, M. Sirianni, & R. van der Marel (STScI) L. Angeretti, G. Clementini, R. Contreras, G. Fiorentino, M. Maio, D. Romano, & M. Tosi (INAF-OAB) M. Marconi & I. Musella (INAF-OAC) E. Held & L. Greggio (INAF-OAP) A. Saha (NOAO)

  3. Hierarchical Galaxy Formation • dwarf galaxies first to form stars • bigger galaxies form by merging of these building blocks High-mass galaxies’ oldest pop must be as old as low-mass galaxies’ pop or younger 1

  4. Mapping Galaxy Formation 2

  5. Mapping Galaxy Formation High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF) 2

  6. Mapping Galaxy Formation High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF) 2

  7. Mapping Galaxy Formation High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF) 2. Stellar Archaeology studying nearby galaxies by resolving their present-day stellar populations 2

  8. Mapping Galaxy Formation High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF) 2. Stellar Archaeology studying nearby galaxies by resolving their present-day stellar populations 2

  9. Mapping Galaxy Formation High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF) 2. Stellar Archaeology studying nearby galaxies by resolving their present-day stellar populations Courtesy Elena Sabbi (STScI) 2

  10. Resolving Galaxies with HST Imaging 3

  11. Resolving Galaxies with HST Imaging • images in multiple bands BVI (optical) &JH (NIR) 3

  12. Resolving Galaxies with HST Imaging Sextans A CTIO • images in multiple bands BVI (optical) &JH (NIR) Hunter (1997) 3

  13. Resolving Galaxies with HST Imaging Sextans A HST/WFPC2 Sextans A CTIO • images in multiple bands BVI (optical) &JH (NIR) Hunter (1997) Dohm-Palmer et al. (2002) 3

  14. Resolving Galaxies with HST Imaging Sextans A Sextans A • images in multiple bands BVI (optical) &JH (NIR) • CMD of resolved stars Dolphin et al. (2003) 3

  15. Resolving Galaxies with HST Imaging Sextans A • images in multiple bands BVI (optical) &JH (NIR) • CMD of resolved stars • distance • RGBT, TP-AGB, Cepheids Cepheids TP-AGB (C stars) RGBT Dolphin et al. (2003) 3

  16. Resolving Galaxies with HST Imaging Sextans A • images in multiple bands BVI (optical) &JH (NIR) • CMD of resolved stars • distance • RGBT, TP-AGB, Cepheids • star formation history Cepheids TP-AGB (C stars) RGBT TO Aparicio & Gallart (2004) 3

  17. Resolving Galaxies with HST Imaging Sextans A • images in multiple bands BVI (optical) &JH (NIR) • CMD of resolved stars • distance • RGBT, TP-AGB, Cepheids • star formation history Cepheids TP-AGB (C stars) RGBT TO Aparicio & Gallart (2004) All galaxies studied in sufficient detail so far contain ancient populations 3

  18. What does it really mean to go outside the Local Group? • distance > 1 Mpc • different types of • galaxies accessible: • Giant Ellipticals • Active Galaxies • (starbursts & BCDs) • only filters F606W • & F814W really • feasible ! dSphs dEs dSph/dIrrs dIrrs Grebel (1999) 4

  19. What is beyond the Local Group? closest giant Elliptical NGC 5128 (Centaurus group) D = 3.8 Mpc closest Starburst NGC 1569 (IC 342 group ? ) D = 3.2 Mpc closest metal-poor BCD UGC 4483 (M81 group) D = 3.4 Mpc and more … Courtesy Tom Brown (STScI) 5

  20. The Closest Giant Elliptical: NGC 5128 • some fields (r < 30 kpc) observed with WFPC2 down to the RGBT • deepest field (r ~ 37 kpc) observed with ACS/WFC down to the RC NGC 5128 WEH 6

  21. The Closest Giant Elliptical: NGC 5128 • some fields (r < 30 kpc) observed with WFPC2 down to the RGBT • deepest field (r ~ 37 kpc) observed with ACS/WFC down to the RC NGC 5128 WEH Rejkuba et al. 2005 6

  22. The Closest Giant Elliptical: NGC 5128 • some fields (r < 30 kpc) observed with WFPC2 down to the RGBT • deepest field (r ~ 37 kpc) observed with ACS/WFC down to the RC NGC 5128 WEH Metal-rich all the way out ! Mean [M/H] = – 0.64 Mean Age = 8.5 Gyrs Rejkuba et al. 2005 6

  23. Similarities with M31 Halo in the LG M31 7

  24. Similarities with M31 Halo in the LG M31 halo ACS/WFC 7 Brown et al. (2003)

  25. Similarities with M31 Halo in the LG M31 halo ACS/WFC 7 Brown et al. (2003)

  26. The Closest Starburst: NGC 1569 • deep field observed with ACS/WFC • down to the RC • distance is 1 Mpc larger than previously believed • D = 3.2 Mpc • RC/HB at the detection limit NGC 1569 ACS/WFC 8

  27. The Closest Starburst: NGC 1569 Grocholski, Aloisi et al. (in prep.) • deep field observed with ACS/WFC • down to the RC • distance is 1 Mpc larger than previously believed • D = 3.2 Mpc • RC/HB at the detection limit NGC 1569 ACS/WFC I Grocholski, Aloisi et al. (in prep.) V – I 8

  28. The Closest Starburst: NGC 1569 Grocholski, Aloisi et al. (in prep.) Grocholski, Aloisi et al. (in prep.) [Fe/H] = – 1.0 NGC 1569 Halo 1Gyr3Gyr10Gyr • deep field observed with ACS/WFC • down to the RC • distance is 1 Mpc larger than previously believed • D = 3.2 Mpc • RC/HB at the detection limit NGC 1569 ACS/WFC I I V – I Grocholski, Aloisi et al. (in prep.) V – I 8

  29. The Closest Starburst: NGC 1569 Grocholski, Aloisi et al. (in prep.) Grocholski, Aloisi et al. (in prep.) [Fe/H] = – 1.0 NGC 1569 Halo 1Gyr3Gyr10Gyr • deep field observed with ACS/WFC • down to the RC • distance is 1 Mpc larger than previously believed • D = 3.2 Mpc • RC/HB at the detection limit NGC 1569 ACS/WFC I I V – I Grocholski, Aloisi et al. (in prep.) V – I Morphology of RGB, presence of RC and lack (?) of HB suggest metal-rich and intermediate-age stars in the halo once again ! 8

  30. The Closest Metal-Poor BCD: UGC 4483 • deep field observed with WFPC2 down to the RGB UGC 4483 ACS/WFC I Izotov & Thuan (2002) V – I 9

  31. The Most Metal-Poor BCD at the borders of the Local Volume: I Zw 18 10

  32. RGB Stars in I Zw 18 Aloisi et al. 2007 11

  33. Variable Stars in I Zw 18 125 days Lowest metallicity Cepheids ever observed ! Z = 1/50 Zo 130 days 8.6 days 139 or 186 days 12

  34. Variable Stars in I Zw 18 125 days P = 8.6 days Lowest metallicity Cepheids ever observed ! Z = 1/50 Zo 130 days 8.6 days 139 or 186 days Aloisi et al. 2007 12

  35. Distance of I Zw 18 • Cepheids – theoretical reddening-free Wesenheit relation for the 3 confirmed Cepheids yields average distance D = 19 ± 2 Mpc 13

  36. Distance of I Zw 18 • Cepheids – theoretical reddening-free Wesenheit relation for the 3 confirmed Cepheids yields average distance D = 19 ± 2 Mpc • TRGB – TRGB filtering technique gives D = 18 ± 2 Mpc 13

  37. Distance of I Zw 18 • Cepheids – theoretical reddening-free Wesenheit relation for the 3 confirmed Cepheids yields average distance D = 19 ± 2 Mpc • TRGB – TRGB filtering technique gives D = 18 ± 2 Mpc Distance larger than previously believed; contributed to difficulty in detecting RGB 13

  38. PL Relation vs. Metallicity Fiorentino et al. 2007 (to be submitted) Closer metal-poor BCDs need to be additionally investigated in order tobetter constrain PL relation at low metallicity Several BCDs available within the Local Volume ! 14

  39. HST UV Spectroscopy after SM4 COS & STIS will allow studies of the neutral ISM in star-forming systems (e.g., FUSE study of I Zw 18) In particular, COS will be crucial in the FUV to characterize the real O abundances from the 1300-1350 Å region Confirmation of the metallicity offset between neutral and ionized gas ? Constraints to chemical evolution models Aloisi et al. 2003 15

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