On the radial extent of the dwarf irregular galaxy IC 10 N. Sanna et al. 2010, ApJ, 722, L244
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On the radial extent of the dwarf irregular galaxy
IC 10
N. Sanna et al. 2010, ApJ, 722, L244
2011 Jun 2
김 상 철 (Sang Chul KIM)
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2MASS JHK image
11.7’ x 11.7’
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Dwarf galaxies
Dwarf spheroidal (dSph)dwarf elliptical (dE)
compact elliptical (cE)
Dwarf irregular (dI, dIrr) Blue compact dwarf (BCD)
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Tidal radius of IC 10
- Dwarf irregular galaxy- Recent and strong star formation the only local group
(LG) analog of starburst galaxies
- previous : rt ≤ 10’ Massey & Armandroff (1995) : D ∼ 7’ Jarrett et al. (2003) : D ∼ 6’ Tikhonov & Galazutdinova (2009) : thick disk, minor axis ~
10.5’ Demers et al. (2004) : halo D ∼ 30’- HI cloud : covers > 1° (62’ x 80’)
- This study : red giant (RG) stars at r = 18’ – 23’ excess of stars (compared to model) at r = 34’ – 42’
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IC 10 – basic parameters- α(J2000) = 00:20:17.3, δ= +59:18:14, l = 118.96, b = -
3.33- Vel = -348 km/s, B = 11.8 mag- IBm V-VI- Diameter = 6.8’ x 5.9’- (m-M)0 = 24.56 ± 0.58, d = 846 ± 274 kpc (NED)- (m-M)0 = 24.60 ± 0.15, d = 830 kpc (TRGB, Sanna et al.
2008)- Galactic extinction E(B-V) = 1.527, AB=6.588 mag
M. Kim et al. (2009, ApJ, 703, 816)
d = 715 ± 10 ± 60 kpc
(from NED mostly)
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HI envelope
Huchtmeier (1979)
62’
80’1˚
Cohen (1979)
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Photometric data
- Space : HST/ACS, HST/WFPC2 α, β γ, δ
- Ground : Subaru 8.2m/Suprime-Cam, CFHT 3.6m/Mega-Cam
ε ζ
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Fig 1
Fig 1 α,β,γδ
ε (Subaru) r ~
18’/23’
ζ (CFHT)
r~30’
Subaru/Suprime-Cam : shallow (VRI) and deep (VRI) imagesCFHT/Mega-Cam : g (3 x 700 s), i (3 x 400 s)
D = 13’
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Results
Fig 2
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Fig 2
1. Limiting magnitude HST : deep, accurate C, W : limiting mag of I~25.5 – 26, V ~ 26.5 – 27 Subaru : same I ~ 25, V ~ 26 CFHT : shallow I ~ 22.5, V ~ 24.5
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Fig 2
2. Young MS stars : strong radial gradient 18 ≤ I ≤ 25.5, 1 ≤ V-I ≤ 1.5 N : decreases rapidly as r ↑
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Fig 2
3. Different apparent colors of RGB stars differential reddening W, RGB ridge line estimate in Subaru data S4, blue field stars’ ridge line estimate in CFHT data along the semimajor axis : E(B-V) = 0.78 ± 0.10 Subaru data regions : constant at E(B-V) = 0.63 ± 0.10 CFHT data regions : similar (E(B-V) = 0.63 ± 0.10) or smaller (E(B-V) = 0.40 ± 0.10)
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Fig 2
4. Old RGB stars : ubiquitous α-enhanced isochrone of 13 Gyr, [M/H] = -0.66, Y = 0.251 (Pietrinferni+ 06) stars in 21 ≤ I ≤ 26, 1 ≤ V-I ≤ 2.5 : bona fide old- and intermediate-age RGB
stars
Field stars
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Fig 2
5. CFHT data - same field contamination as the Subaru data - small overdensity of stars in the TRGB region (21 ≤ I ≤ 22, 2 ≤ V-I ≤
3.5)
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Radial extent of IC 10
- Significantly underestimated!
- Subaru data r > 18’ – 23’- CFHT data probably D > 1°
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Simulated CMDsfor the field stars
Fig 3E(B-V) = 0.63 ± 0.10sky area = 1˚ × 1˚
Pisa MW model (Castellani+ 02, Cignoni+ 06)
Padova MW model (Girardi+ 05)
Star count ratios
N(observed stars) /N(candidate field
stars)
Evidence of IC 10 stars at the position of the TRGB
(I = 21.66 ± 0.25)
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Fig 4
Space data
Subaru/Suprime-Cam data
E(B-V) = 0.78±0.06 0.63±0.09
Young MS
Old- & intermediate-
age RGs
Fig 4 : stars within r < 6.5’ To select member stars
Pietrinferni et al. (2004) isochrones
Intermediate
-age
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Total luminosity
- LV ~ 9.13 × 107 L⊙, MV = -15.11 : outermost regions (ζ) are not included lower limit
- LV ~ 1.6 × 108 L⊙ (Mateo 1998), MV = -16.0 (Richer+ 01) : literature – only covers the innermost regions
Difference robust identification of field stars in this study blue arrow in panel (c) adopted distance and reddening
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Fig 4
Space data
Subaru/Suprime-Cam data
E(B-V) = 0.78±0.06 0.63±0.09
Young MSIntermediate
-age
Old- & intermediate-
age RGs
Candidate field stars
Fig 4 : stars within r < 6.5’ To select member stars
Pietrinferni et al. (2004) isochrones
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M/L ratio
- Only in the regions where rotational velocity measurements are available (D = 13’)
- LV ~ 5.88 × 107 L⊙ (MV = -14.63)- Mtot ~ 6.2 × 108 M⊙
M/L ~ 10 M⊙/L⊙
※ Woo et al. (2008) : M/L ∼0.9
HI cloud (> 1°) association…
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Thank You!