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) 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)

Hierarchical Galaxy Formation 1 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

Mapping Galaxy Formation 2

1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDF s, GOODS, HUDF ) 2

2 Mapping Galaxy Formation 1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDF s, GOODS, HUDF )

Mapping Galaxy Formation 1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDF s, GOODS, HUDF ) 2. Stellar Archaeology studying nearby galaxies by resolving their present-day stellar populations 2

Mapping Galaxy Formation 1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDF s, GOODS, HUDF ) 2. Stellar Archaeology studying nearby galaxies by resolving their present-day stellar populations 2

Mapping Galaxy Formation 1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDF s, GOODS, HUDF ) 2. Stellar Archaeology studying nearby galaxies by resolving their present-day stellar populations 2 Courtesy Elena Sabbi (STScI)

Resolving Galaxies with HST Imaging 3

images in multiple bands BVI (optical) & JH (NIR) 3

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

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

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

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

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

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

What does it really mean to go outside the Local Group? Grebel (1999) 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 4

What is beyond the Local Group? Courtesy Tom Brown (STScI) 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 … 5

The Closest Giant Elliptical: NGC 5128 NGC 5128 WEH 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 6

The Closest Giant Elliptical: NGC 5128 NGC 5128 WEH 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 6 Rejkuba et al. 2005

The Closest Giant Elliptical: NGC 5128 NGC 5128 WEH 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 6 Rejkuba et al Metal-rich all the way out ! Mean [M/H] = – 0.64 Mean Age = 8.5 Gyrs

Similarities with M31 Halo in the LG 7 M31

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

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

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 8 NGC 1569 ACS/WFC

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 Grocholski, Aloisi et al. (in prep.) 8 NGC 1569 ACS/WFC V – I I Grocholski, Aloisi et al. (in prep.)

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 Grocholski, Aloisi et al. (in prep.) 8 NGC 1569 ACS/WFC V – I I Grocholski, Aloisi et al. (in prep.) I V – I [Fe/H] = – 1.0 NGC 1569 Halo 1Gyr 3Gyr 10Gyr

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 Morphology of RGB, presence of RC and lack (?) of HB suggest metal-rich and intermediate-age stars in the halo once again ! Grocholski, Aloisi et al. (in prep.) 8 NGC 1569 ACS/WFC V – I I Grocholski, Aloisi et al. (in prep.) I V – I [Fe/H] = – 1.0 NGC 1569 Halo 1Gyr 3Gyr 10Gyr

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

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

RGB Stars in I Zw Aloisi et al. 2007

Variable Stars in I Zw 18 Lowest metallicity Cepheids ever observed ! Z = 1/50 Z o days 8.6 days 130 days 139 or 186 days

Variable Stars in I Zw 18 Lowest metallicity Cepheids ever observed ! Z = 1/50 Z o days 8.6 days 130 days 139 or 186 days Aloisi et al P = 8.6 days

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

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

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

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

HST UV Spectroscopy after SM4 Aloisi et al 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 Å region Confirmation of the metallicity offset between neutral and ionized gas ? Constraints to chemical evolution models 15