We compare line emission calculated from theoretical disk models with optical to sub-millimeter wavelength observational data of the gas disk surrounding TW Hya and infer the spatial distribution of mass in the gas disk .
The model disk that best matches observations has a gas mass ranging from \sim 10 ^ { -4 } -10 ^ { -5 } M _ { \odot } for 0.06 { AU } < r < 3.5 AU and \sim 0.06 M _ { \odot } for 3.5 { AU } < r < 200 AU .
We find that the inner dust hole ( r < 3.5 AU ) in the disk must be depleted of gas by \sim 1 - 2 orders of magnitude compared to the extrapolated surface density distribution of the outer disk .
Grain growth alone is therefore not a viable explanation for the dust hole .
CO vibrational emission arises within r \sim 0.5 AU from thermal excitation of gas .
[ OI ] 6300Å and 5577Å forbidden lines and OH mid-infrared emission are mainly due to prompt emission following UV photodissociation of OH and water at r \lesssim 0.1 AU and at r \sim 4 AU .
[ NeII ] emission is consistent with an origin in X-ray heated neutral gas at r \lesssim 10 AU , and may not require the presence of a significant EUV ( h \nu > 13.6 eV ) flux from TW Hya .
H _ { 2 } pure rotational line emission comes primarily from r \sim 1 - 30 AU .
[ OI ] 63 \mu m , HCO ^ { + } and CO pure rotational lines all arise from the outer disk at r \sim 30 - 120 AU .
We discuss planet formation and photoevaporation as causes for the decrease in surface density of gas and dust inside 4 AU .
If a planet is present , our results suggest a planet mass \sim 4 - 7 M _ { J } situated at \sim 3 AU .
Using our photoevaporation models and the best surface density profile match to observations , we estimate a current photoevaporative mass loss rate of 4 \times 10 ^ { -9 } M _ { \odot } yr ^ { -1 } and a remaining disk lifetime of \sim 5 million years .