1. Multicolor study of the interacting galaxies of Leo Triplet
Zhiyu Duan
8/12/2005

2. Leo Triplet
NGC3628
Dist：6.7Mpc
de Vaucoulers 1975
NGC3623
NGC3627

3. Previous Studies Interaction of NGC 3627 and NGC 3628
Dynamical distortion
Great Impact on gas content - infall
Formation of the plume

4. 10’
HI distribution map[1]

5. Dynamical model of the interaction by Rots, 1978
View from Earth
View from North
Interaction happened 0.8Gyr ago.

6. Questions
Perturbation of gas  any impact on the stellar content (star formation)?
Is NGC 3623 interacting with the other two?

7. Approach Stellar population synthesis: Mapping:
Age  the SRH of the galaxies
Mapping:
spatial distribution of age & SFH
Looking for similar evolutionary history and
Determining the relationship of the 3 galaxies

8. Observation More than 220 images of U, d-p bands:
>70 hours exposure.

10. PEGASE IMF: Salpeter 1955 SFR: Instantaneous Burst Model
N(M) ~ M < M < 120 Msun
SFR: Instantaneous Burst Model
Only relative age distribution is needed
Initial Metallicity:
0.02, and
Intrinsic Reddening by Inclination:
NGC 3623: 71°
NGC 3627: 60°
NGC 3628: 89°
Data from NED

11. Results: relative age distribution

12. Age Histograms

15. Conclusions
NGC 3623 is the oldest among the 3 galaxies, but its weak age gradient might indicate recent star formation in its bulge.  This galaxy is not isolated.
A potential bar is identified within the bulge of NGC 3623.
NGC 3627 & 3628 exhibit strong evidence of synchronized evolution.  interaction may have triggered star formation in them both.

16. END!