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On the radial extent of the dwarf irregular galaxy IC 10 N. Sanna et al. 2010, ApJ, 722, L244

On the radial extent of the dwarf irregular galaxy IC 10 N. Sanna et al. 2010, ApJ, 722, L244 20 11 Jun 2 김 상 철 (Sang Chul KIM). 2MASS JHK image. 11.7’ x 11.7’. Dwarf galaxies. dwarf elliptical (dE). Dwarf spheroidal (dSph). compact elliptical (cE). Dwarf irregular (dI, dIrr).

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On the radial extent of the dwarf irregular galaxy IC 10 N. Sanna et al. 2010, ApJ, 722, L244

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  1. On the radial extent of the dwarf irregular galaxy • IC 10 • N. Sanna et al. 2010, ApJ, 722, L244 • 2011 Jun2 • 김 상 철 (Sang Chul KIM)

  2. 2MASS JHK image 11.7’ x 11.7’

  3. Dwarf galaxies dwarf elliptical (dE) Dwarf spheroidal (dSph) compact elliptical (cE) Dwarf irregular (dI, dIrr) Blue compact dwarf (BCD)

  4. 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’

  5. IC 10 – basic parameters (from NED mostly) • 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

  6. HI envelope 80’ 1˚ 62’ Huchtmeier (1979) Cohen (1979)

  7. Photometric data • Space : HST/ACS, HST/WFPC2 • α, βγ, δ • Ground : Subaru 8.2m/Suprime-Cam, CFHT 3.6m/Mega-Cam • εζ

  8. Fig 1 ζ (CFHT) r~30’ ε (Subaru) r ~ 18’/23’ Fig 1 δ α,β,γ D = 13’ Subaru/Suprime-Cam : shallow (VRI) and deep (VRI) images CFHT/Mega-Cam : g (3 x 700 s), i (3 x 400 s)

  9. Results Fig 2

  10. Fig 2 • 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

  11. Fig 2 2. Young MS stars : strong radial gradient 18 ≤ I ≤ 25.5, 1 ≤ V-I ≤ 1.5 N : decreases rapidly as r ↑

  12. 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)

  13. Field stars 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

  14. 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)

  15. Radial extent of IC 10 • Significantly underestimated! • Subaru data  r > 18’ – 23’ • CFHT data  probably D > 1°

  16. Simulated CMDsfor the field stars Fig 3 E(B-V) = 0.63 ± 0.10 sky area = 1˚× 1˚ Pisa MW model (Castellani+ 02, Cignoni+ 06) Padova MW model (Girardi+ 05) 1.74 1.53 1.59 1.38 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) 4σ 3σ

  17. E(B-V) = 0.78±0.06 0.63±0.09 Fig 4 Fig 4 : stars within r < 6.5’  To select member stars Young MS Intermediate-age Space data Old- & intermediate-age RGs Subaru/Suprime-Cam data Pietrinferni et al. (2004) isochrones

  18. 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

  19. E(B-V) = 0.78±0.06 0.63±0.09 Fig 4 Fig 4 : stars within r < 6.5’  To select member stars Young MS Intermediate-age Space data Old- & intermediate-age RGs Candidate field stars Subaru/Suprime-Cam data Pietrinferni et al. (2004) isochrones

  20. 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…

  21. Thank You!

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