AAS 199th meeting, Washington, DC, January 2002
Session 153. Stellar Populations and Dynamics in Extragalactic Systems
Oral, Thursday, January 10, 2002, 2:00-3:30pm, Georgetown West

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[153.02] Stellar populations and globular clusters in NGC 5128

Marina Rejkuba (ESO, Germany and PUC, Chile)

NGC 5128 (Cen A) is the closest high-luminosity AGN, radio galaxy, giant elliptical and one of the best examples of a merger remnant. Using the VLT+FORS1 deep U and V-band and ten epochs of the VLT+ISAAC K-band images, the ages and metallicities of the stars and globular clusters in the two fields have been derived. The majority of the halo of NGC 5128 consists of old metal-rich stars (Harris & Harris, 2000, AJ 119, 2423). However, we have detected a significant metal-poor component ([Fe/H]<-0.7 dex), as well as an extended giant branch (Rejkuba et al. 2001, A&A in press) with numerous Mira and semiregular long-period variable stars. This extended giant branch may be connected with an intermediate-age population.

With VLT and Magellan U and V-band data star formation regions in the north-eastern halo were investigated (Rejkuba et al. 2002, ApJ 535, in press). The young blue stars are associated with line-emitting filaments located between the inner radio lobe and the northern middle lobe. Around the outer filament, ~14 kpc from the center, stars as young as 10 Myr have been detected. They are principally aligned with the direction of the radio jet, but a vertical north-south alignment along the edge of the HI cloud is also present. We discovered that young stars are associated with the inner filaments and knots of photoionized gas at ~ 8 kpc too. The temperature of the brightest stars is insufficient to account alone for the high excitation of the surrounding ionized gas. The highly collimated star formation is present only in the north-eastern halo of the galaxy, suggesting the interaction of the jet with the gas clouds deposited by the last accretion event as the preferred triggering mechanism. This supports the hypothesis for jet induced star formation in the high redshift galaxies.

FONDECYT #01990440 and ESO studentship grants are acknowledged.

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