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-0.1 in    dynamically cold , large galaxy disks seen today appear to have formed early or gradually ; they are easily destroyed through strong interactions or mergers .
for example , wyse ( these proceedings ) argues the milky way has not suffered a major merger in the last 10 gyr .
the nearly constant co - moving number of large disks out to @xmath1 ( e.g. lilly et al .
1998 ) and the subtle changes with redshift in the scaling relations for large , field spirals corroborate a picture of early formation or slow , quiescent growth , but infrequent death .
the mass accretion rate onto disks is not known directly , however , at any epoch .
direct measurements of disk mass as a function of time , e.g. , from measurement of disk scale - heights and stellar velocity dispersions , are desirable , but currently unavailable  except for a handful of local systems .
photometric estimates of disk mass based on colors are uncertain and incomplete .
another approach is to use the evolution of the zeropoint and scatter in disk scaling - relations as a diagnostic of _ changes _ in mass accretion rates .
here we focus on the correlations with , and cause of the scatter in the tully - fisher relation .    for gradual formation , we assume that discrete , but small accretion events perturb otherwise axisymmetric systems . were we to obtain a complete census of galaxies at difference epochs , the relative number of perturbed systems should then reflect changes in the minor - merger rate .
zaritsky & rix ( 1997 ) estimated the minor - merger rate for nearby galaxies by comparing the amplitude of photometric @xmath2 modes to @xmath3 and offsets in luminosity from a fiducial tf relation .
kinematic measures of disturbance would be preferred , however , since the long - term morphological perturbation may be subtle ( haynes 2000 ) , and photometric effects may evolve with look back - time due to changing gas fractions and star - formation rates ( mihos , these proceedings ) . here
we give two examples of how spatially resolved kinematics can directly link disk asymmetries to scatter in the tf relation .
this , in turn , points to a tractable method for measuring the growth rate of spiral disks .
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-0.1 in    using high signal - to - noise , integral - field , echelle spectroscopy and surface photometry of seven apparently face - on spirals , we have been able to construct h@xmath4 velocity fields out to 3 scale lengths , and compare kinematic to photometric position angles , and kinematic inclinations to photometric axis - ratios ( andersen et al .
2000 , and these proceedings ) . from mismatches between these quantities
, we find that normal , non - barred , intermediate - type spiral disks are non - circular , with a model - dependent estimate of mean ellipticity at the 6% level . considering the effects of our observed distribution of intrinsic ellipticity only on the inferred photometric inclination , we estimate this accounts for @xmath5 mag of scatter in the tf - relation for samples selected within @xmath6 ( figure 1a ) , consistent with franx & de zeeuw s expectations ( 1992 ) .
evidence that intrinsic ellipticity predominantly effects photometric but not kinematic measures of inclination is shown in figure 1b .
we establish a tight , @xmath7-band tf relation for galaxies with @xmath8 by using kinematic inclinations . not only is our zeropoint in agreement with courteau ( 1997 ) , but our scatter is smaller ( albeit with a much smaller sample ) .
hence , it is now possible to study the tf relation for nearly face - on samples , where photometric projection effects and internal extinction are minimized , and the perpendicular component of the disk velocity dispersion can be measured to estimate disk mass .
-0.1 in    an outstanding question is whether local disk non - circularity is caused primarily by small amounts of lopsided matter accretion , triaxial halos , or other dynamical processes . in principle
one might hope to determine this from a detailed analysis of disk velocity fields . alternatively
, we look here to higher - redshift systems to see if greater ellipticity or asymmetry is evident , as we might expect if minor mergers are the dominant source of this perturbation .
we recently acquired high - resolution , wiyn telescope images of a representative sample of luminous , field spirals at intermediate redshifts for which we have h@xmath4 rotation - curves ( e.g. , bershady et al . 1999 ) .
we find that significantly over - luminous galaxies in the @xmath9 @xmath10-band tf relation tend to appear optically distorted in the wiyn images  something we were unable to determine during the selection process based on lower - resolution images .
our definition of `` over - luminous '' accounts for the well - exhibited correlation of tf offsets with color ( figure 2b ) .
some of the most extreme outliers exhibiting pronounced optical distortions are even accompanied by clear signatures of kinematic asymmetry .
a representative sequence is shown in figure 3 .
the physical connection arising here is between bluer colors and higher luminosity ( i.e. enhanced star - formation ) , which is accompanied by increased asymmetry at extreme offsets from a fiducial tf relation . the next step is to establish a statistical trend with redshift of increased asymmetry and tf offsets above and beyond changes in stellar m / l .
to do so requires further observations . at intermediate redshifts ,
higher angular resolution is needed to detect and quantify the asymmetry in less extreme systems ; precision bi - dimensional spectroscopy is needed to determine reliable inclinations .
locally , representative kinematic surveys are needed to understand the link between tf scatter and asymmetry .
we explore how the growth rate of spiral disks can be measured via analyses of the scatter in the tully - fisher ( tf ) relation of local and intermediate redshift galaxies . as an initial step , 
 we show it is possible to construct a low - dispersion tf relation for nearly face - on , nearby spirals . 
 we find these spiral disks are non - circular , ( a mean ellipticity of 6% ) , which accounts for @xmath00.1 mag of the intrinsic scatter in the nearby tf relation of even the most `` normal '' looking spirals . 
 if this ellipticity is induced by matter accretion , we expect to find greater disk ellipticity or disturbance in the past . 
 we find evidence that more extreme outliers of the intermediate - redshift tf relation are more morphologically and kinematically disturbed . 
 whether this effect reflects a redshift trend or selection bias of local samples needs to be addressed .    
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