1

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)

2

2MASS JHK image

11.7’ x 11.7’

3

Dwarf galaxies

Dwarf spheroidal (dSph)dwarf elliptical (dE)

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- 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)

6

HI envelope

Huchtmeier (1979)

62’

80’1˚

Cohen (1979)

7

Photometric data

- Space : HST/ACS, HST/WFPC2 α, β γ, δ

- Ground : Subaru 8.2m/Suprime-Cam, CFHT 3.6m/Mega-Cam

ε ζ

8

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’

9

Results

Fig 2

10

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

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

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

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 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)

18

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

19

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

20

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

21

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…

22

Thank You!