More than 50 \% of Active Galactic Nuclei ( AGNs ) are suspected to be red and affected by dust-obscuration .
Meanwhile , popular spectral diagnostics of AGNs are based on optical or ultraviolet light , making the dust obscuration as a primary concern for understanding the general nature of AGNs and supermassive black holes residing in them .
To provide with a method of investigating properties of the dusty AGNs , we derive new black hole ( BH ) mass estimators based on velocity widths and luminosities of Near Infrared ( NIR ) hydrogen emission lines such as P \alpha and P \beta , and also investigate the line ratios of these Hydrogen lines .
To derive the BH mass ( M _ { BH } ) estimators , we used a sample of 37 unobscured Type-1 AGNs with a M _ { BH } range of 10 ^ { 6.8 } – 10 ^ { 9.4 } ~ { } M _ { \odot } , where M _ { BH } come from either reverberation mapping method or single-epoch measurement method using Balmer lines .
Our work shows that M _ { BH } can be estimated from the Paschen line luminosities and the velocity widths to the accuracy of 0.18 - 0.24 dex ( rms scatter ) .
We also show that the mean line ratios of the Paschen lines and the Balmer lines are \mathrm { \frac { H \alpha } { P \alpha } } \simeq 9.00 , \mathrm { \frac { H \beta } { P \alpha } } \simeq 2.70 , which are consistent with a Case B recombination under a typical AGN broad line region environment .
These ratios can be used as reference points when estimating the amount of dust extinction over the broad line region ( BLR ) for red AGNs .
We expect the future application of the new BH mass estimators on red , dusty AGNs to provide a fresh view of obscured AGNs .