Spectroscopic and photometric confirmation of 3 globular and 14 intermediate-age clusters in the Irr II galaxy NGC3077

TL;DR

This study confirms the ages, metallicities, and properties of 17 star clusters in NGC 3077, revealing a mix of old and intermediate-age clusters and providing insights into the galaxy's star formation history.

Contribution

It presents the first spectroscopic and photometric confirmation of both old and intermediate-age globular clusters in NGC 3077, highlighting a diverse cluster population.

Findings

Identified 3 old, metal-poor globular clusters similar to Milky Way GCs.

Most clusters are intermediate-age (3-4 Gyr) and metal-rich.

The galaxy has a low GC specific frequency, indicating active past star formation.

Abstract

We present the results from spectroscopic and photometric analysis of 17 globular cluster (GC) candidates in the Irr II galaxy NGC 3077. The GC candidates were selected on the Hubble Space Telescope (HST) images and were cleaned of foreground Galactic stars using the GAIA parameters. We carried out aperture photometry using the multi-band archival images from SDSS, and 2MASS of all candidates, and low resolution (R= 1000) spectroscopic observations of 12 GC candidates and three suspected foreground stars using the OSIRIS/MOS mode at the Gran Telescopio Canarias (GTC). Age, metallicity and extinction values were determined both using spectroscopic and photometric data, independently. We find three of the 17 candidates are old (age >10 Gyr), metal-poor ([Fe/H]<-1.0 dex), massive (mass>10^5 Msun) GCs with characteristics similar to the classical GCs in the Milky Way. The rest are intermediate-age clusters (IACs) with typical ages of 3 to 4 Gyr, and in general metal-rich clusters. The radial velocities of both populations are within 100 km/s of the recessional velocity of the host galaxy. A relatively large population of IACs and low value of GC specific frequency (Sn=0.7) suggest that the pre-interaction galaxy was actively forming stars and star clusters, and is unlikely to be a dE as suggested in some previous works.