Narrow-line Seyfert 1 Galaxies from the Sloan Digital Sky Survey Early Data Release

We present a sample of 150 narrow-line Seyfert 1 galaxies (NLS1's) found within the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR), only two of which were previously identified as such. This substantially increases the known number of NLS1's and provides a basic method by which to identify many more with subsequent releases of SDSS data. With its large size and homogeneous, well-defined selection criteria, this sample will help alleviate two major problems that have plagued NLS1 research in the past; namely, their relative rarity and significant differences in selection algorithms between the known samples. Forty-five of these SDSS-selected NLS1's are detected at energies of 0.1-2 keV in the ROSAT All-Sky Survey (RASS) and are found to have ultrasoft X-ray spectra with photon indices of Γ>~2, in agreement with previous results for NLS1's. However, about 10-20 of those NLS1's that were not detected by ROSAT have optical properties very similar to the detected objects and so should also have been detected by the RASS. This may be due to either significant intrinsic absorption in many NLS1's, or a significant subclass of NLS1's that have uncharacteristic, intrinsically flatter (hence harder) X-ray spectral energy distributions.