We explore the vertical light distribution as a function of galactocentric radius in the edge-on ( i =88 ^ { \circ } ) Sd “ superthin ” galaxy UGC 7321 .
UGC 7321 is a low-luminosity spiral ( M _ { B,i } = -17.0 ) with a diffuse , low surface brightness stellar disk and no discernible bulge component .
Within \sim 0 ^ { \prime } \hskip { -4.836969 pt } . \hskip { 0.0 pt } 25 ( \sim 725 pc ) of the disk center the global luminosity profile of UGC 7321 can be reasonably characterized by an exponential function with a scale height h _ { z } \sim 2 ^ { \prime \prime } \hskip { -4.836969 pt } . \hskip { 0.0 pt } 9 ( \sim 140 pc ) in H and h _ { z } \sim 3 ^ { \prime \prime } \hskip { -4.836969 pt } . \hskip { 0.0 pt } 1 ( \sim 150 pc ) in R , making this among the thinnest galaxy disks know .
Near the disk center we derive a ratio of disk scale length to global disk scale height h _ { r } / h _ { z } \sim 14 in both H and R ; near the edge of the disk , h _ { r } / h _ { z } \sim 10 .
At intermediate galactocentric radii ( 0 ^ { \prime } \hskip { -4.836969 pt } . \hskip { 0.0 pt } 25 \leq|r| \leq 1 ^ { \prime } \hskip { -4.836969 pt } . \hskip { 0.0 pt } 5 ) , the disk of UGC 7321 becomes less peaked than an exponential near the galactic plane .
At these radii the vertical luminosity profiles can be well reproduced by a linear combination of two isothermal disk components of differing scale heights .
These fits , together with the strong disk color gradients by Matthews , Gallagher , & van Driel ( 1999 ) , suggest that UGC 7321 has multiple disk subcomponents comprised of stellar populations with different ages and velocity dispersions .
Thus even examples of the thinnest pure disk galaxies exhibit complex structure and signatures of dynamical heating .