## If stars contribute significantly to Mlum, should use stellar velocity dispersion

- Will be higher than sHI for evolved populations

## Need to have a well-defined length scale

- If sHI constant and NHI constant, then Mlum grows like
*R*2. Mvir only grows like*R*, so Mlum/Mvir grows linearly with length scale

- If sHI constant and NHI constant, then Mlum grows like