DISCOVERY OF THE MOST ISOLATED GLOBULAR CLUSTER IN THE LOCAL UNIVERSE

Journal Article · Sun May 20 04:00:00 EDT 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/751/1/L19· OSTI ID:22047800

Jang, In Sung; Lim, Sungsoon; Park, Hong Soo

We report the discovery of two new globular clusters in the remote halos of M81 and M82 in the M81 Group based on Hubble Space Telescope archive images. They are brighter than typical globular clusters (M{sub V} = -9.34 mag for GC-1 and M{sub V} = -10.51 mag for GC-2), and much larger than known globular clusters with similar luminosity in the Milky Way Galaxy and M81. Radial surface brightness profiles for GC-1 and GC-2 do not show any features of tidal truncation in the outer part. They are located much farther from both M81 and M82 in the sky, compared with previously known star clusters in these galaxies. Color-magnitude diagrams of resolved stars in each cluster show a well-defined red giant branch (RGB), indicating that they are metal-poor and old. We derive a low metallicity with [Fe/H] Almost-Equal-To -2.3 and an old age {approx}14 Gyr for GC-2 from the analysis of the absorption lines in its spectrum in the Sloan Digital Sky Survey in comparison with the simple stellar population models. The I-band magnitude of the tip of the RGB for GC-2 is 0.26 mag fainter than that for the halo stars in the same field, showing that GC-2 is {approx}400 kpc behind the M81 halo along our line of sight. The deprojected distance to GC-2 from M81 is much larger than any other known globular clusters in the local universe. This shows that GC-2 is the most isolated globular cluster in the local universe.

• OSTI ID: 22047800
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 751; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTRA
ASTRONOMY
ASTROPHYSICS
BRIGHTNESS
COLOR
COMPARATIVE EVALUATIONS
DIAGRAMS
LUMINOSITY
METALS
MILKY WAY
RED GIANT STARS
STAR CLUSTERS
TELESCOPES
UNIVERSE