Dust-to-Gas and Dust-to-Metal Ratios

Dust-to-gas (D/G) and dust-to-metal (D/Z) ratios are simple-looking diagnostics that are highly sensitive to aperture and bookkeeping choices.

Dust-to-gas

For a stated aperture,

\[ D/G = M_\mathrm{dust}/M_\mathrm{gas}. \]

Use integrated component masses when quoting an integrated ratio. A mean of pixel-by-pixel ratios is generally not the same quantity.

Dust-to-metal

Always state which metal reservoir appears in the denominator. Gas-phase metals, total metals, and gas+dust metals are not interchangeable definitions. CosmicGrain analyses should preserve this distinction explicitly.

Comparing with observations

Match the observational aperture and metallicity convention as closely as possible. Record the adopted solar metallicity or abundance scale when converting between mass metallicity and oxygen abundance.