Serendipitously we have discovered a rare , bright submillimeter galaxy ( SMG ) with a flux density of 30 \pm 2 mJy at \lambda = 1.2 mm , using MAMBO2 at the IRAM 30-meter millimeter telescope .
Although no optical counterpart is known for MM18423+5938 , we were able to measure the redshift z = 3.92960 \pm 0.00013 from the detection of CO lines using the IRAM Eight MIxer Receiver ( EMIR ) .
In addition , by collecting all available photometric data in the far-infrared and radio to constrain its spectral energy distribution , we derive the FIR luminosity 4.8 10 ^ { 14 } / m L _ { \odot } and mass 6.0 10 ^ { 9 } / m M _ { \odot } for its dust , allowing for a magnification factor m caused by a probable gravitational lens .
The corresponding star-formation rate is 8.3 10 ^ { 4 } / m M _ { \odot } /yr .
The detection of three lines of the CO rotational ladder , and a significant upper limit for a fourth CO line , allow us to estimate an H _ { 2 } mass of between 1.9 10 ^ { 11 } / m M _ { \odot } and 1.1 10 ^ { 12 } / m M _ { \odot } .
The two lines C I ( ^ { 3 } P _ { 1 } - ^ { 3 } P _ { 0 } ) and C I ( ^ { 3 } P _ { 2 } - ^ { 3 } P _ { 1 } ) were clearly detected and yield a [ C I ] / [ H _ { 2 } ] number abundance of between 1.4 10 ^ { -5 } and 8.0 10 ^ { -5 } .
Upper limits are presented for emission lines of HCN , HCO ^ { + } , HNC , H _ { 2 } O , and of other molecules .
The moderate excitation of the CO lines is indicative of an extended starburst , and excludes the dominance of an AGN in heating this high-z SMG .