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

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

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

10’ HI distribution map[1]

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

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

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

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

PEGASE IMF: Salpeter 1955 SFR: Instantaneous Burst Model N(M) ~ M -2.35 0.1 < M < 120 Msun SFR: Instantaneous Burst Model Only relative age distribution is needed Initial Metallicity: 0.02, 0.008 and 0.0001 Intrinsic Reddening by Inclination: NGC 3623: 71° NGC 3627: 60° NGC 3628: 89° Data from NED

Results: relative age distribution

Age Histograms

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.

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