GALEX Ultraviolet Photometry of Globular Clusters in M31

Abstract

We present ultraviolet photometry for globular clusters (GCs) in M31 from 15 square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect 200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750 Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses, respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV, to an approximate limiting V magnitude of 19. Out of six clusters with [Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore, we find no candidate metal-rich clusters with significant FUV flux, because of the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC 6441, which are metal-rich Galactic GCs with hot HB stars. We show that our GALEX photometry follows the general color trends established in previous UV studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in the UV and with population synthesis models, we suggest that the age range of M31 and Galactic halo GCs are similar.

arXiv commentThis paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

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Cited by in corpus (16)

• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• Better age estimations using UV-optical colours: breaking the age-metallicity degeneracy
• Hot Populations in M87 Globular Clusters
• GALEX Ultraviolet Photometry of Globular Clusters in M31: Three Year Results and a Catalog
• Nonlinear Color-Metallicity Relations of Globular Clusters. III. On the Discrepancy in Metallicity between Globular Cluster Systems and their Parent Elliptical Galaxies
• A Comprehensive GALEX Ultraviolet Catalog of Star Clusters in M31 and a Study of the Young Clusters
• Yonsei Evolutionary Population Synthesis (YEPS) Model. I. Spectroscopic Evolution of Simple Stellar Populations
• Nonlinear Color-Metallicity Relations of Globular Clusters. II. A Test on the Nonlinearity Scenario for Color Bimodality Using the u-band Colors: The Case of M87 (NGC 4486)
• Age constraints for an M31 globular cluster from SEDs-fit
• The hot stars in orbit around the M31 central supermassive black hole: are they young or old?
• Compact stellar systems in the Fornax cluster: a UV perspective
• Old stellar population synthesis: New age and mass estimates for Mayall II = G1
• Probing the Intermediate-Age Globular Clusters in NGC 5128 from Ultraviolet Observations
• The ultraviolet colour of globular clusters in M31: a core density effect?
• Evidence for a Strong End-On Bar in the Ringed Sigma-Drop Galaxy NGC 6503