We have obtained 1087 near-infrared ( NIR ; JHK _ { s } ) measurements of 21 Type Ia supernovae ( SNe Ia ) using PAIRITEL , the 1.3-m Peters Automated InfraRed Imaging TELescope at Mount Hopkins , Arizona .
This new set of observations nearly doubles the number of well-sampled NIR SN Ia light curves .
These data strengthen the evidence that SNe Ia are excellent standard candles in the NIR , even without correction for optical light-curve shape .
We construct fiducial NIR templates for normal SNe Ia from our sample , excluding only the three known peculiar SNe Ia : SN 2005bl , SN 2005hk , and SN 2005ke .
The H -band absolute magnitudes in this sample of 18 SNe Ia have an intrinsic RMS of only 0.15 mag with no correction for light-curve shape .
We found a relationship between the H -band extinction and optical color excess of A _ { H } = 0.2 E ( B - V ) .
This variation is as small as the scatter in distance modulus measurements currently used for cosmology that are based on optical light curves after corrections for light-curve shape Combining the homogeneous PAIRITEL measurements with 23 SNe Ia from the literature , these 41 SNe Ia have standard H -band magnitudes with an RMS scatter of 0.16 mag .
The good match of our sample with the literature sample suggests there are few systematic problems with the photometry .
We present a nearby NIR Hubble diagram that shows no correlation of the residuals from the Hubble line with light-curve properties .
Future samples that account for optical and NIR light-curve shapes , absorption , spectroscopic variation , or host-galaxy properties may reveal effective ways to improve the use of SNe Ia as distance indicators .
Since systematic errors due to dust absorption in optical bands remain the leading difficulty in the cosmological use of supernovae , the good behavior of SN Ia NIR light curves and their relative insensitivity to reddening make these objects attractive candidates for future cosmological work .