We investigate the scaling relations of bulge and disk structural parameters for a sample of 108 disk galaxies .
Structural parameters of individual galaxies are obtained from two-dimensional bulge/disk decomposition of their H-band surface brightness distributions Table 1 is only available in electronic form at the 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/ .
Bulges are modelled with a generalized exponential ( Sérsic ) with variable integer shape index n .
We find that bulge effective scalelengths r _ { e } ^ { B } and luminosity M ^ { B } increase with increasing n , but disk properties are independent of bulge shape .
As Hubble type T increases , bulges become less luminous and their mean effective surface brightness < \mu _ { e } ^ { B } > gets fainter ; disk < \mu _ { e } ^ { D } > shows a similar , but much weaker , trend .
When bulge parameters ( < \mu _ { e } ^ { B } > , r _ { e } ^ { B } , M ^ { B } ) are compared with disk ones ( < \mu _ { e } ^ { D } > , r _ { e } ^ { D } , M ^ { D } ) , they are tightly correlated for n = 1 bulges .
The correlations gradually worsen with increasing n such that n = 4 bulges appear virtually independent of their disks .
The Kormendy relation , < \mu _ { e } ^ { B } > vs . r _ { e } ^ { B } , is shown to depend on bulge shape n ; the two parameters are tightly correlated in n = 4 bulges ( r = 0.8 ) , and increasingly less so as n decreases ; disk < \mu _ { e } ^ { D } > and r _ { e } ^ { D } are well correlated ( r = 0.7 ) .
Bulge-to-disk size ratios r _ { e } ^ { B } / r _ { e } ^ { D } are independent of Hubble type , but smaller for exponential bulges ; the mean r _ { e } ^ { B } / r _ { e } ^ { D } for n = 1 bulges is 4 times smaller than that for n = 4 , with a spread which is 9 times smaller .
Strongly barred SB galaxies with exponential bulges are more luminous than their unbarred counterparts .
Exponential bulges appear to be closely related to their underlying disks , while bulges with higher n values are less so ; n = 4 bulges and their disks apparently have no relation .
We interpret our results as being most consistent with a secular evolutionary scenario , in which dissipative processes in the disk are responsible for building up the bulges in most spirals .