Astronomers unveil complex globular cluster system in giant elliptical galaxy NGC 4696

Using the advanced capabilities of the Magellan Telescopes in Chile, astronomers have conducted detailed photometric observations of the giant elliptical NGC 4696. These observations have uncovered a complex globular cluster system within the galaxy, as detailed in a paper published on June 12 on the pre-print server arXiv.

NGC 4696, positioned approximately 145 million away, stands as the brightest galaxy in the Centaurus Cluster. It spans an apparent size of 4.5 by 3.2 arcminutes and exhibits a heliocentric velocity of about 2,958 km/s. Prior investigations revealed a filamentary structure traversing its central region and extending towards a neighboring galaxy, NGC 4696B, suggesting historical mergers or material acquisition via ram-pressure stripping from NGC 4696B.

Studying the globular clusters (GCs) associated with NGC 4696 can offer significant insights into the galaxy's history, particularly its formation and evolutionary processes. Recognizing this potential, a team led by Sara Federle from the Andrés Bello National University in Chile delved into the globular cluster system (GCS) of NGC 4696.

“We presented the analysis of the GCS of the giant elliptical NGC 4696. The measurements are based on deep Magellan 6.5m/MegaCam (g′, r′, i′) photometry,” the researchers reported.

Federle's team began by selecting a sample of 3,973 globular cluster candidates within NGC 4696's field. By applying a two-color selection method, they refined this to 3,818 globular cluster candidates. Analysis of these candidates revealed that NGC 4696's GCS is notably disturbed, indicative of a complex interaction history with other members of the Centaurus Cluster.

The GCS exhibited a bimodal color distribution, with peaks at 0.763 mag (blue) and 1.012 mag (red), divided at approximately 0.905 mag. Interestingly, the study noted the absence of a significant blue tilt—a where blue clusters appear redder at higher luminosities—but found a radial trend suggesting a shift from a bimodal to a unimodal distribution at smaller galactocentric distances, hinting at an intermediate globular cluster population.

Additionally, the GCS's metallicity distribution mirrored the bimodal color trend. The radial density profiles differed between blue and red populations, while azimuthal distributions for the total, red, and blue globular cluster populations fit well with an asymmetrical sinusoidal distribution. This asymmetry suggests that interactions between NGC 4696 and its neighboring galaxies have significantly influenced its GCS.

“All these results point toward a complex GCS, strongly influenced by the interaction history of NGC 4696 with the other galaxies of the Centaurus cluster,” the authors concluded.

These findings not only enhance our understanding of NGC 4696 but also contribute to the broader knowledge of galactic formation and in cluster environments, emphasizing the intricate dynamics at play in the .