Globular cluster population of the HST frontier fields galaxy J07173724+3744224

TL;DR

This study measures and analyzes the globular cluster system of the elliptical galaxy J07173724+3744224 using HST data, revealing its population size, distribution, and color bimodality, which inform galaxy formation history.

Contribution

First measurement of the globular cluster population around J07173724+3744224, including its size, distribution, and color properties, using deep HST imaging.

Findings

Total globular clusters: 3441 +/- 1416

Radial distribution follows a power law with index -0.6

Color bimodality indicates in situ formation of red clusters and accreted blue clusters

Abstract

We present the first measurement of the globular cluster population surrounding the elliptical galaxy J07173724+3744224 (z=0.1546). This galaxy is located in the foreground in the field-of-view of the Hubble Space Telescope (HST) Frontier Fields observations of galaxy cluster MACS J0717.5+3745 (z=0.5458). Based on deep HST ACS F435W, F606W, and F814W images, we find a total globular cluster population of N_tot = 3441 +/- 1416. Applying the appropriate extinction correction and filter transformation from ACS F814W to the Johnson V-band, we determine that the host galaxy has an absolute magnitude of M_V = -22.2. The specific frequency was found to be S_N = 4.5 +/- 1.8. The radial profile of the globular cluster system was best fit using a powerlaw of the form $\sigma\sim R^{-0.6}$, with the globular cluster population found to be more extended than the halo light of the host galaxy ($\sigma_{halo}\sim R^{-1.7}$). The F435W-F814W colour distribution suggests a bimodal population, with red globular clusters 1-3x more abundant than blue clusters. These results are consistent with the host elliptical galaxy J07173724+3744224 having formed its red metal-rich GCs in situ, with the blue metal-poor globular clusters accreted from low-mass galaxies.