Tracing the Giant Outer Halo of the Mysterious Massive Disk Galaxy M104 I. Photometry of the Extended Globular Cluster Systems

Abstract

M104 (NGC 4594, the Sombrero galaxy) is a mysterious massive early-type galaxy that shows a dominant bulge and a prominent disk. However, the presence of a halo in M104 has been elusive, and it is not yet known how M104 has acquired such a peculiar structure. Using wide ($\sim 2$ deg${}^2$) and deep $ugi$ images of M104 obtained with the CFHT/MegaCam, we detect a large number of globular clusters (GCs) found out to $R\approx 35^{\prime }$ ($\sim 100$ kpc). The color distribution of these GCs shows two subpopulations: a blue (metal-poor) system and a red (metal-rich) system. The total number of GCs is estimated to be $N_{GC}=1610\pm 30$ and the specific frequency to be $S_N=1.8\pm 0.1$. The radial number density profile of the GCs is steep in the inner region at $R<20^{\prime }$, and becomes shallow in the outer region at $20^{\prime }<R<35^{\prime }$. The outer region is dominated by blue GCs and is extended out to $R\approx 35^{\prime }$. This shows clearly the existence of a giant metal-poor halo in M104. The inner region is composed of a bulge hosting a disk, corresponding to a metal-rich halo as seen in early-type galaxies. At least two clumps of blue GCs are found in the outer region. One clump is overlapped with a faint stellar stream located in the south west, indicating that it may be a remnant of a disrupted dwarf galaxy. Our results imply that the metal-rich inner halo of M104 formed first via major mergers, and the metal-poor outer halo grew via numerous minor mergers.

Accepted for publication in ApJ, 19 pages, 13 figures, 7 tables

References in corpus (14)

• The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment
• A Classical Morphological Analysis of Galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G)
• HST/ACS Wide-Field Photometry of the Sombrero Galaxy Globular Cluster System
• A Search for "Dwarf" Seyfert Nuclei. VII. A Catalog of Central Stellar Velocity Dispersions of Nearby Galaxies
• An Ultra Compact Dwarf around the Sombrero galaxy (M104): the Nearest Massive UCD
• NGC 5128 globular cluster candidates out to 150 kpc: a comprehensive catalog from Gaia and ground based data
• Globular Cluster Systems and their Host Galaxies: Comparison of Spatial Distributions and Colors
• Globular Clusters As Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474
• The Strikingly Metal-Rich Halo of the Sombrero Galaxy
• A feather on the hat: Tracing the giant stellar stream around the Sombrero galaxy
• Distance and mass of the M104 (Sombrero) group
• A Wide-field Photometric Survey of Globular Clusters in the Peculiar Early-type Galaxy M85
• Globular Cluster Systems of Massive Compact Elliptical Galaxies in the Local Universe: Evidence for Relic Red Nuggets?
• Beyond the Brim of the Hat: Kinematics of Globular Clusters out to Large Radius in the Sombrero Galaxy

Cited by in corpus (3)

• Rubin Observatory LSST Stars Milky Way and Local Volume Star Clusters Roadmap
• New dwarf galaxy candidates in the sphere of influence of the Sombrero galaxy
• Globular clusters in M104: Tracing kinematics and metallicities from the centre to the halo