The Einstein ring GAL-CLUS-022058s: a Lensed Ultrabright Submillimeter Galaxy at z=1.4796

Abstract

We report an ultra-bright lensed submillimeter galaxy at $z_{spec}=1.4796$, identified as a result of a full-sky cross-correlation of the AllWISE and Planck compact source catalogs aimed to search for bright submillimeter galaxies at $z\sim 1.5-2.8$. APEX/LABOCA observations of the candidate galaxy reveal a source with flux (S${}_{870\hat{I}¼m}=54\pm 8$ mJy). The position of the APEX source coincides with the position of the AllWISE mid-IR source, and with the Einstein ring GAL-CLUS-022058s, observed with the HST. Archival VLT/FORS observations reveal the redshift of this Einstein ring, $z_{spec}=1.4796$, and detection of the CO(5-4) line at $z_{spec}=1.4802$ with APEX/nFLASH230 confirms the redshift of the submillimeter emission. The lensed source appears to be gravitationally magnified by a massive foreground galaxy cluster lens at $z=0.36$. We use Lenstool to model the gravitational lensing, which is near to a "fold arc" configuration for an elliptical mass distribution of the central halo, where four images of the lensed galaxy are seen; the mean magnification is $\hat{I}{¼}_{\mathrm{L}}=18\pm 4$. We have determined an intrinsic rest-frame infrared luminosity of $L_{IR}\approx 10^{12}{L}_{\odot }$ and a likely star formation rate of $\sim 70-170$ $M_{\odot }y{r}^{-1}$. The molecular gas mass is $M_{mol}\sim 2.6\times 10^{10}{M}_{\odot }$ and the gas fraction is $f=0.34\pm 0.07$. We also obtain a stellar mass log$(M_{\ast }/M_{\odot })=10.7\pm 0.1$ and a specific star formation rate log$(sSFR/Gy{r}^{-1})=0.15\pm 0.03$. This galaxy lies on the so-called main sequence of star-forming galaxies at this redshift.