THE TWO-DIMENSIONAL SPATIAL DISTRIBUTIONS OF THE GLOBULAR CLUSTERS AND LOW-MASS X-RAY BINARIES OF NGC 4649

• Published in: The Astrophysical journal Vol. 783; no. 1; pp. 18 - 14
• Main Authors: D’Abrusco, R., Fabbiano, G., Mineo, S., Strader, J., Fragos, T., Kim, D.-W., Luo, B., Zezas, A.
• Format: Journal Article
• Language: English
• Published: United States 01.03.2014
• Subjects: Acquisitions; ANISOTROPY; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; COSMIC X-RAY SOURCES; GALAXIES; Globular clusters; INTERACTIONS; LUMINOSITY; MASS; SATELLITES; SPATIAL DISTRIBUTION; STARS; SYMMETRY; Two dimensional; TWO-DIMENSIONAL CALCULATIONS; X RADIATION; X-RAY SOURCES; X-ray stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/783/1/18

We report significant anisotropies in the projected two-dimensional (2D) spatial distributions of globular clusters (GCs) of the giant Virgo elliptical galaxy NGC 4649 (M60). Similar features are found in the 2D distribution of low-mass X-ray binaries (LMXBs), both associated with GCs and in the stellar field. Deviations from azimuthal symmetry suggest an arc-like excess of GCs extending north at 4-15 kpc galactocentric radii in the eastern side of major axis of NGC 4649. This feature is more prominent for red GCs, but still persists in the 2D distribution of blue GCs. High- and low-luminosity GCs also show some segregation along this arc, with high-luminosity GCs preferentially located in the southern end and low-luminosity GCs in the northern section of the arc. GC-LMXBs follow the anisotropy of red GCs, where most of them reside; however, a significant overdensity of (high-luminosity) field LMXBs is present to the south of the GC arc. These results suggest that NGC 4649 has experienced mergers and/or multiple accretions of less massive satellite galaxies during its evolution, of which the GCs in the arc may be the fossil remnant. We speculate that the observed anisotropy in the field LMXB spatial distribution indicates that these X-ray binaries may be the remnants of a star formation event connected with the merger, or maybe be ejected from the parent red GCs, if the bulk motion of these clusters is significantly affected by dynamical friction. We also detect a luminosity enhancement in the X-ray source population of the companion spiral galaxy NGC 4647. We suggest that these may be younger high mass X-ray binaries formed as a result of the tidal interaction of this galaxy with NGC 4649.