Extremely Bright Submillimeter Galaxies beyond the Lupus-I Star-forming Region
Yun, M. S.; Wilner, D. J.; Shimajiri, Y.; Kohno, K.; Wilson, G. W.; Aretxaga, I.; Hughes, D. H.; Chandler, C. J.; Austermann, J. E.; Tamura, Y.; Goss, W. M.; Saigo, K.; Hayashi, M.; Scott, K. S.; Oasa, Y.; Hatsukade, B.; Ezawa, H.; Kawabe, R.; Tsukagoshi, T.; Ohashi, N.; Nakajima, Y.; Inutsuka, S.; Tomida, K.; Taniguchi, A.; Dickman, R.; Hiramatsu, M.; Ogasawara, R.; Oshima, T.
Japan, Chile, France, United States, Mexico
Abstract
We report detections of two candidate distant submillimeter galaxies (SMGs), MM J154506.4-344318 and MM J154132.7-350320, which are discovered in the AzTEC/ASTE 1.1 mm survey toward the Lupus-I star-forming region. The two objects have 1.1 mm flux densities of 43.9 and 27.1 mJy, and have Herschel/SPIRE counterparts as well. The Submillimeter Array counterpart to the former SMG is identified at 890 μm and 1.3 mm. Photometric redshift estimates using all available data from the mid-infrared to the radio suggest that the redshifts of the two SMGs are {z}{photo}≃ 4-5 and 3, respectively. Near-infrared objects are found very close to the SMGs and they are consistent with low-z ellipticals, suggesting that the high apparent luminosities can be attributed to gravitational magnification. The cumulative number counts at {S}1.1{mm}≥slant 25 mJy, combined with the other two 1.1 mm brightest sources, are {0.70}-0.34+0.56 deg-2, which is consistent with a model prediction that accounts for flux magnification due to strong gravitational lensing. Unexpectedly, a z\gt 3 SMG and a Galactic dense starless core (e.g., a first hydrostatic core) could be similar in the mid-infrared to millimeter spectral energy distributions and spatial structures at least at ≳ 1\prime\prime . This indicates that it is necessary to distinguish the two possibilities by means of broadband photometry from the optical to centimeter and spectroscopy to determine the redshift, when a compact object is identified toward Galactic star-forming regions.