The Ancient Globular Clusters of NGC 1291

TL;DR

This study catalogs 81 ancient globular clusters in NGC 1291, revealing their bimodal color distribution, spatial segregation, and a higher overall specific frequency, supporting the universality of halo GCs in spiral galaxies.

Contribution

It provides the first detailed catalog of GCs in NGC 1291, analyzing their properties and distribution, and compares these with other galaxy types to understand galaxy formation.

Findings

Bimodal color distribution of GCs with 65% blue and 35% red.

Red GCs are more centrally concentrated, blue GCs are more broadly distributed.

Higher overall specific frequency of GCs compared to other spirals.

Abstract

We present a new catalog of 81 ancient globular clusters (GCs) in the early-type spiral (SB0/a) galaxy NGC 1291. Candidates have been selected from B,V, and I band images taken with the Hubble Space Telescope, which also reveal 17 younger (t < few x 100Myr) clusters. The luminosity function shows a peaked shape similar to that found for GC systems in other spiral and elliptical galaxies. The ancient clusters have a bimodal color distribution, with approximately 65% (35%) of the population having blue (red) colors. The red, presumably metal-rich GCs are more centrally concentrated, as expected for a bulge population; while the blue, presumably metal-poor GCs, are more broadly distributed, consistent with expectations of a halo population. The specific frequency of GCs in NGC 1291 is higher than found previously in most spiral galaxies. However, if we consider just the blue subpopulation, we find Sn,blue=0.50 +/- 0.06, quite similar to that found for other spirals. This result supports the hypothesis of a universal population of halo GCs in spirals. The fraction of red GCs in NGC 1291, when compared with those found in other galaxies, suggests that these correlate with host galaxy type rather than with host galaxy luminosity.