Resolved Stellar Populations outside the Local Group
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Transcript of Resolved Stellar Populations outside the Local Group
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Resolved Stellar Populations outside the Local Group
Alessandra Aloisi (STScI/ESA)
Science with the New HST after SM4Bologna – 30 January 2008
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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)
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Hierarchical Galaxy Formation
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• 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
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Mapping Galaxy Formation
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Mapping Galaxy Formation
1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF)
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Mapping Galaxy Formation
1. High-Redshift Studies looking directly back in time by observing distant galaxies (e.g. HDFs, GOODS, HUDF)
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Mapping Galaxy Formation
1. 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
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Mapping Galaxy Formation
1. 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
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Mapping Galaxy Formation
1. 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
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Courtesy Elena Sabbi (STScI)
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Resolving Galaxies with HST Imaging
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Resolving Galaxies with HST Imaging
• images in multiple bands BVI (optical) & JH (NIR)
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Resolving Galaxies with HST Imaging
Sextans ACTIO• images in multiple bands
BVI (optical) & JH (NIR)
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Hunter (1997)
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Resolving Galaxies with HST Imaging
Sextans ACTIO
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Hunter (1997)
Sextans AHST/WFPC2
Dohm-Palmer et al. (2002)
• images in multiple bands BVI (optical) & JH (NIR)
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Resolving Galaxies with HST Imaging
Sextans A
Dolphin et al. (2003)
Sextans A
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• images in multiple bands BVI (optical) & JH (NIR)
• CMD of resolved stars
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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
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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)
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TO
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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
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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 !
dSphsdEsdSph/dIrrsdIrrs
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What is beyond the Local Group?
Courtesy Tom Brown (STScI)
closest giant EllipticalNGC 5128 (Centaurus group)
D = 3.8 Mpc
closest Starburst NGC 1569 (IC 342 group ? )
D = 3.2 Mpc
closest metal-poor BCDUGC 4483 (M81 group)
D = 3.4 Mpc
and more …
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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
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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
6Rejkuba et al. 2005
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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
6Rejkuba et al. 2005
Metal-rich all the way out !
Mean [M/H] = – 0.64
Mean Age = 8.5 Gyrs
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Similarities with M31 Halo in the LG
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M31
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Similarities with M31 Halo in the LG
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M31 haloACS/WFC
Brown et al. (2003)
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Similarities with M31 Halo in the LG
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M31 haloACS/WFC
Brown et al. (2003)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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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
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NGC 1569ACS/WFC
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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.)
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NGC 1569ACS/WFC
V – I
I
Grocholski, Aloisi et al. (in prep.)
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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.)
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NGC 1569ACS/WFC
V – I
I
Grocholski, Aloisi et al. (in prep.)Grocholski, Aloisi et al. (in prep.)
I
V – I
[Fe/H] = – 1.0 NGC 1569 Halo1Gyr 3Gyr 10Gyr
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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.)
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NGC 1569ACS/WFC
V – I
I
Grocholski, Aloisi et al. (in prep.)Grocholski, Aloisi et al. (in prep.)
I
V – I
[Fe/H] = – 1.0 NGC 1569 Halo1Gyr 3Gyr 10Gyr
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The Closest Metal-Poor BCD: UGC 4483• deep field observed with WFPC2 down to the RGB
Izotov & Thuan (2002)
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UGC 4483ACS/WFC
I
V – I
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The Most Metal-Poor BCD at the borders of the Local Volume: I Zw 18
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RGB Stars in I Zw 18
11Aloisi et al. 2007
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Variable Stars in I Zw 18
Lowest metallicity Cepheids
ever observed !
Z = 1/50 Zo
12
125 days
8.6 days
130 days
139 or 186 days
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Variable Stars in I Zw 18
Lowest metallicity Cepheids
ever observed !
Z = 1/50 Zo
12
125 days
8.6 days
130 days
139 or 186 days
Aloisi et al. 2007
P = 8.6 days
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Distance of I Zw 18
• Cepheids – theoretical reddening-free Wesenheit relation for the 3 confirmed Cepheids yields average distance D = 19 ± 2 Mpc
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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
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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
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PL Relation vs. Metallicity
Fiorentino et al. 2007 (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
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HST UV Spectroscopy after SM4
Aloisi et al. 2003
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 realO abundances from the 1300-
1350 Å region
Confirmation of the metallicity offset between neutral and ionized gas ?
Constraints to chemical evolution models
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