Spectra of Two Bright Candidate Globular Clusters in the Merger Galaxy NGC 7252
Session 17 -- Normal Galaxies
Oral presentation, Monday, 10:30-12:00, Wheeler Room

## [17.08] Spectra of Two Bright Candidate Globular Clusters in the Merger Galaxy NGC 7252

Francois Schweizer (Carnegie--DTM), Patrick Seitzer (U.\ Michigan)

Spectra of the two brightest, unresolved bluish knots'' surrounding the nucleus of the merger remnant NGC 7252 are presented. Seven of these knots were already found by Schweizer (1982: ApJ, 252, 455), who surmised that the brightest knot might be a galactic foreground star while the other six knots might represent young star clusters formed during the merger. These knots are just the brightest of a population of about 40 blue pointlike objects discovered by Whitmore et al.\ (this meeting) on frames taken with the Planetary Camera of the Hubble Space Telescope. The spectra were obtained with the Double Spectrograph of the Palomar 5-m telescope and cover $\lambda\lambda$4600--5500 in the blue and $\lambda\lambda$6300--6950 in the red at 2--4\AA\ resolution. These spectra feature H$\alpha$, H$\beta$, and Mg~I absorption lines characteristic of late A-type to mid F-type stars at the redshift of NGC 7252, but no emission lines. Therefore, these spectra show unambiguously that (1) despite its apparent bightness, the brightest knot is a cluster in NGC 7252 rather than a galactic foreground star, and (2) even the two brightest unresolved knots are not H~II regions, but have ceased forming stars. The spectra strongly support the notion that these knots are relatively young ($<$1 Gyr), very luminous ($M_V$~$\approx$ $-$17 and $-$15.5 for $H_0$~= 50 according to Whitmore et al.) clusters of nearly coeval stars. Because these clusters remain barely resolved by HST, they are most likely globular clusters that will fade by 3--7 mag during the next 15 Gyr, depending on their exact present age (Charlot \& Bruzual, 1991: ApJ, 367, 126). Both clusters have measured radial velocities within 150 km/s of that of the center of the galaxy.