We present Arecibo 21 cm spectroscopy , Keck HIRES H \beta spectroscopy , and WIYN R-band imaging of 11 nearby blue compact galaxies with effective B-band surface brightness SBe = 19.4-21.2 mag arcsec ^ { -2 } and effective radii R _ { eff } = 0.6-1.9 kpc .
This sample was selected to test the reliablility of mass estimates derived using optical emission linewidths , particularly for the blue compact star-forming galaxies observed at intermediate redshifts ( 0.1 < z < 1 ) .
In addition , we also measure the H i content and gas depletion timescales for the nearby blue , compact galaxies in an attempt to infer the present nature and possible future evolution of their intermediate redshift analogs .
We detected H i in 10 of 11 sample galaxies .
They have H i masses of 0.3–4 \times 10 ^ { 9 } ~ { } M _ { \odot } , H i linewidths , W _ { 20 } , of 133–249 km~ { } s ^ { -1 } , dynamical masses of 0.5–5 \times 10 ^ { 10 } M _ { \odot } , gas depletion timescales , \tau _ { gas } , of 0.3–7 Gyr , H i mass fractions of 0.01–0.58 , and mass-to-light ratios of 0.1–0.8 .
These values span the range of values typical of nearby H ii galaxies , irregulars and spirals .
Despite the restricted morphological selection , our sample of galaxies is quite heterogeneous in terms of H i content , dynamical mass , and gas depletion timescale .
Therefore , these galaxies have a variety of evolutionary paths and should look very different from each other in 5 Gyr .
Those with high masses and gas depletion timescales are likely to retain their ISM for future star formation while the lower mass objects with small gas depletion timescales may be undergoing their last major event of star-formation .
Hence , the fading of intermediate-redshift luminous blue compact galaxies into NGC205-type spheroidals is a viable evolutionary scenario , but only for the least massive , most gas-poor objects in this sample .

The most consistent characteristic of our morphologically-selected sample is that the ratios of H ii linewidths to H i 21 cm linewidths , ℛ = \frac { W _ { 20 } ( \hbox { H { \sc ii } } ) } { W _ { 20 } ( \hbox { H { \sc i } } ) } , are systematically less than unity , with an average value of ℛ =0.66 \pm 0.16 ; similar to findings for local H ii galaxies .
The simplest explanation for this result is that the ionized gas is more centrally concentrated than the neutral gas within the gravitational potential .
We find that ℛ is a function of linewidth , such that smaller linewidth galaxies have smaller values of ℛ .
Correcting optical linewidths by this factor not only raises the derived masses of these galaxies , but also makes them consistent with the local luminosity–linewidth ( Tully-Fisher ) relation as well .
If this ratio applies to intermediate-redshift galaxies , then the masses of intermediate redshift blue compact galaxies can be obtained from optical linewidths after applying a small correction factor , and the proposed luminosity evolution of the Tully-Fisher relation is much smaller and more gradual than suggested by studies using optical emission line width measurements .