Astrophys. J., 788, L23 (2014/June-3)
Evidence for a gas-rich major merger in a proto-cluster at z = 2.5.
TADAKI K.-I., KODAMA T., TAMURA Y., HAYASHI M., KOYAMA Y., SHIMAKAWA R., TANAKA I., KOHNO K., HATSUKADE B. and SUZUKI K.
Abstract (from CDS):
Gas-rich major mergers in high-redshift proto-clusters are important events, perhaps leading to the creation of the slowly rotating remnants seen in the cores of clusters in the present day. Here, we present a deep Jansky Very Large Array observation of CO J = 1-0 emission line in a proto-cluster at z = 2.5, USS1558-003. The target field is an extremely dense region, where 20 Hα emitters (HAEs) are clustering. We have successfully detected the CO emission line from three HAEs and discovered a close pair of red and blue CO-emitting HAEs. Given their close proximity (∼30 kpc), small velocity offset (∼300 km/s), and similar stellar masses, they could be in the early phase of a gas-rich major merger. For the red HAE, we derive a total infrared luminosity of LIR= 5.1x1012 L☉ using MIPS 24 µm and radio continuum images. The LIR/L'CO ratio is significantly enhanced compared to local spirals and high-redshift disks with a similar CO luminosity, which is indicative of a starburst mode. We find the gas depletion timescale is shorter than that of normal star-forming galaxies regardless of adopted CO-H2 conversion factors. The identification of such a rare event suggests that gas-rich major mergers frequently take place in proto-clusters at z > 2 and may involve the formation processes of slow rotators seen in local massive clusters.
galaxies: evolution - galaxies: high-redshift - galaxies: ISM
Table 1: [TKT2014] bHAE-191 N=1 (No 191), [TKT2014] rHAE-191 N=2 (Nos 193 and 213).
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