We present Atacama Large Millimiter/submillimiter Array ( ALMA ) observations of eight highly excited CO ( { J _ { up } } > 8 ) lines and continuum emission in two z \sim 6 quasars : SDSS J231038.88+185519.7 ( hereafter J2310 ) , for which CO ( 8-7 ) , CO ( 9-8 ) , and CO ( 17-16 ) lines have been observed , and ULAS J131911.29+095951.4 ( J1319 ) , observed in the CO ( 14-13 ) , CO ( 17-16 ) and CO ( 19-18 ) lines .
The continuum emission of both quasars arises from a compact region ( < 0.9 kpc ) .
By assuming a modified black-body law , we estimate dust masses of Log ( M _ { dust } / M _ { \odot } ) = 8.75 \pm 0.07 and Log ( M _ { dust } / M _ { \odot } ) = 8.8 \pm 0.2 and dust temperatures of T _ { dust } = 76 \pm 3 ~ { } { K } and T _ { dust } = 66 ^ { +15 } _ { -10 } ~ { } { K } , respectively for J2310 and J1319 .
Only CO ( 8-7 ) and CO ( 9-8 ) in J2310 are detected , while 3 \sigma upper limits on luminosities are reported for the other lines of both quasars .
The CO line luminosities and upper limits measured in J2310 and J1319 are consistent with those observed in local AGN and starburst galaxies , and other z \sim 6 quasars , except for SDSS J1148+5251 ( J1148 ) , the only quasar at z = 6.4 with a previous CO ( 17-16 ) line detection .
By computing the CO SLEDs normalised to the CO ( 6-5 ) line and FIR luminosities for J2310 , J1319 , and J1149 , we conclude that different gas heating mechanisms ( X-ray radiation and/or shocks ) may explain the different CO luminosities observed in these z \sim 6 quasar .
Future { J _ { up } } > 8 CO observations will be crucial to understand the processes responsible for molecular gas excitation in luminous high- z quasars .