Context : The Galactic center is the closest region in which we can study star formation under extreme physical conditions like those in high-redshift galaxies .

Aims : We measure the temperature of the dense gas in the central molecular zone ( CMZ ) and examine what drives it .

Methods : We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3 - 2 para-formaldehyde ( \textrm { p - H } _ { 2 } \textrm { CO } ) transitions .
We used the 3 _ { 2 , 1 } -2 _ { 2 , 0 } / 3 _ { 0 , 3 } -2 _ { 0 , 2 } line ratio to determine the gas temperature in n \sim 10 ^ { 4 } -10 ^ { 5 } \textrm { cm } ^ { -3 } gas .
We have produced temperature maps and cubes with 30 ^ { \prime \prime } and 1 km s ^ { -1 } resolution and published all data in FITS form The data can be accessed from doi:10.7910/DVN/27601 and are available from CDS via anonymous ftp to cdsarc.u-strasbg.fr ( 130.79.128.5 ) or via http : //cdsweb.u-strasbg.fr/cgi-bin/qcat ? J/A+A/ .

Results : Dense gas temperatures in the Galactic center range from \sim 60 K to > 100 K in selected regions .
The highest gas temperatures T _ { G } > 100 K are observed around the Sgr B2 cores , in the extended Sgr B2 cloud , the 20 km s ^ { -1 } and 50 km s ^ { -1 } clouds , and in “ The Brick ” ( G0.253+0.016 ) .
We infer an upper limit on the cosmic ray ionization rate \zeta _ { CR } < 10 ^ { -14 } \mathrm { s } ^ { -1 } .

Conclusions : The dense molecular gas temperature of the region around our Galactic center is similar to values found in the central regions of other galaxies , in particular starburst systems .
The gas temperature is uniformly higher than the dust temperature , confirming that dust is a coolant in the dense gas .
Turbulent heating can readily explain the observed temperatures given the observed line widths .
Cosmic rays can not explain the observed variation in gas temperatures , so CMZ dense gas temperatures are not dominated by cosmic ray heating .
The gas temperatures previously observed to be high in the inner \sim 75 pc are confirmed to be high in the entire CMZ .