The Next Generation Virgo Cluster Survey - Infrared (NGVS-IR): I. A new Near-UV/Optical/Near-IR Globular Cluster selection tool

摘要

The NGVS-IR project (Next Generation Virgo Survey - Infrared) is a contiguousnear-infrared imaging survey of the Virgo cluster of galaxies. It complementsthe optical wide-field survey of Virgo (NGVS). The current state of NGVS-IRconsists of Ks-band imaging of 4 deg^2 centered on M87, and J and Ks-bandimaging of 16 deg^2 covering the region between M49 and M87. In this paper, wepresent the observations of the central 4 deg^2 centered on Virgo's coreregion. The data were acquired with WIRCam on the Canada-France-HawaiiTelescope and the total integration time was 41 hours distributed in 34contiguous tiles. A survey-specific strategy was designed to account forextended galaxies while still measuring accurate sky brightness within thesurvey area. The average 5\sigma limiting magnitude is Ks=24.4 AB mag and the50% completeness limit is Ks=23.75 AB mag for point source detections, whenusing only images with better than 0.7" seeing (median seeing 0.54"). Starclusters are marginally resolved in these image stacks, and Virgo galaxies with\mu_Ks=24.4 AB mag arcsec^-2 are detected. Combining the Ks data with opticaland ultraviolet data, we build the uiK color-color diagram which allows a veryclean color-based selection of globular clusters in Virgo. This diagnostic plotwill provide reliable globular cluster candidates for spectroscopic follow-upcampaigns needed to continue the exploration of Virgo's photometric andkinematic sub-structures, and will help the design of future searches forglobular clusters in extragalactic systems. Equipped with this powerful newtool, future NGVS-IR investigations based on the uiK diagram will address themapping and analysis of extended structures and compact stellar systems in andaround Virgo galaxies.