You are an expert at summarizing long articles. Proceed to summarize the following text: 
narrow line seyfert 1 galaxies ( nls1s ) are a special type of active galactic nuclei ( agn ) whose optical spectra are similar to seyfert1 type , but with much narrower balmer line width ; they also show weak [ oiii ] lines and strong feii emission in optical and uv ( osterbrock & pogge 1985 ) . the importance of nls1s lies in that their properties are at the extremity among seyfert1 family , including steep soft x - ray spectra ( @xmath0 ) and rapid x - ray variability , strong blue wings of emission lines ( e.g.  boroson & green 1992 ; laor et al . 1994 ; wang 1996 , boller et al . 1996 , grupe et al .  1999 , 2001 , xu , et al . observational data show that nls1 tend to have small black hole masses and the high eddington ratios @xmath1 ( e.g.  boroson 2002 ) . in fact , they were found to locate at one extreme end of eigenvector1 of the correlation matrix ( boroson & green 1992 , sulentic et al . 2000 ) , which is believed to be driven primarily by @xmath2 . radio - loud nls1s were also found to exist , though their number is still small ( e.g. komossa et al .  2006 ) . yet there are quite a few aspects about nls1s where controversies remain or little study has been given to . the reasons can be ascribed partly to the relatively small number of nls1 known ( a few hundreds ) before this work , as well as the heterogeneity of the objects as a whole . for example , little work has been done regarding broad band sed , associated outflows , radio - loud nls1s and their jets , host galaxies , optical variability , mean spectrum and dispersion , the @xmath3 relation , as well as their cosmic evolution . a much larger and homogeneously selected nls1 sample is required . with its large sky coverage and unprecedented sensitivity and uniformity , the spectroscopic survey of the sloan digital sky survey ( sdss ; york et al . 2000 ) provides us with the most suitable database for discovering nls1s . as a pioneer work , williams et al . ( 2002 ) have compiled a sample of  150 nls1 from the sdss early data release . we carried out an extensive and systematic search for nls1s by making use of the sdss dr3 data , which yielded 2011 nls1s , mostly previously unknown . the sample and preliminary statistical results are presented in zhou et al . ( 2006 ) . in this proceedings contribution , we summarize the sample properties and some of the significant results , with some new , preliminary development . our nls1s were drawn from the sdss dr3 spectroscopic databases of both galaxies and qsos . the data reduction procedure , as described in detail in zhou et al .  ( 2006 ) , consists of mainly two steps . firstly , star light contribution to fiber spectra from host galaxies is carefully removed by performing starlight - nuclear spectral decomposition using our algorithm ( lu et al . 2006 ) developed at university of science of technology of china . our technique has proved to be accurate and robust when performing extensive testing against results from independent observations and measurement , including hst spectroscopic measurements ( wang t. , et al .  in prep . ) . secondly , nuclear emission - line spectra  with the star - spectrum and continuum subtracted  are fitted to derive spectral parameters using the code as described in dong et al . in this process , the balmer emission lines are de - blended into a broad and a narrow component  this is essential as by doing so we could really measure the physical parameters of the broad line region . this process accounts for the difference in the results for some of the objects between our work and that of williams et al . ( 2002 ) . we selected nls1s as those having fwhm of the _ broad _ component of h@xmath4 or h@xmath5 ( detected at the @xmath6 confidence level ) narrow than @xmath7 . the 10% relaxed margin in the linewidth cutoff compared to the conventional @xmath8 ( goodrich 1989 ) is to recover those nls1s dropped out due to the uncertainty in linewidth measurement . our criteria resulted in 2011 nls1 candidates . using a stricter criterion of @xmath9 would reduce the sample to 1885 objects . all but one fulfill @xmath10/h\beta<3$]the second item of the conventional definition . we gave , along with the source list , measured spectral parameters and their error estimates . below we summarize some of the preliminary results directly based on statistical analysis of observed and derived parameters ; for details of these analysis please refer to zhou et al . ( 2006 ) . \1 ) nls1 fraction + we found a strong dependence of the nls1 fraction among all seyfert1 agns . with increasing optical luminosity , the fraction of nls1s first increases and peaks at @xmath11 , and then drops again rapidly . the nls1 fraction also depends on radio - loudness , dropping from @xmath1215% in radio - quiet to only 5% in radio - loud objects . the nls1 fraction in optically selected agn sample is much lower than that in soft x - ray ( rosat ) selected agn samples . \2 ) emission line properties + on average the relative feii emission , @xmath13 , in nls1s is about twice that in normal agns , and is anti - correlated with the broad component width of the balmer emission lines . the equivalent width of h@xmath4 and feii emission lines are strongly positively correlated with the h@xmath4 and continuum luminosities ( the inverse baldwin effect ) . we do not find any difference between nls1s and normal agns in regard to the narrow line region . \3 ) @xmath14@xmath15 relation + we have examined the black hole mass vs.stellar velocity dispersion ( @xmath16 ) relation for a subsample of 308 nls1s for which @xmath16 could be measured directly from fitting the starlight in the sdss spectra with our stellar spectral templates . a significant correlation between @xmath17 and @xmath16 is found , but with the bulk of black hole masses falling below the values expected from the @xmath18 relation for normal galaxies and normal agns ( figure1 , left panel ) . this result indicates that nls1s are underage agns , where the growth of the smbh lags behind the formation of the galactic bulge ( see also , e.g.  mathur et al . 2001 , grupe et al . 2004 , bian & zhao 2004 , botte et al . we also find that the width of [ nii ] is well correlated with @xmath16 . \4 ) x - ray properties + 635 nls1s in the sample have x - ray counterparts detected in the rass . the well - known anti - correlation between the width of broad low - ionization lines and the soft x - ray spectral slope for broad line agns extends down to @xmath19 in nls1s , but the trend appears to reverse at still smaller line widths . there are 28 nls1s being observed by xmm - newton either as targets or serendipitously , for which their spectra were analyzed . for most of the objects the 0.310kev x - ray continuum can be fitted with a power law plus a soft x - ray excess , mostly well parameterized by a blackbody component . no significant fe k@xmath5 line was detected . in figure1 ( right panel ) we plot the distribution of the photon indices of the underlying continuum derived from xmm - newton data . the spectral slopes are systematically steeper than those for broad line seyfert 1 galaxies , confirming previous results ( e.g.  leighly 2000 ) . \5 ) radio - loud nls1s + of the sample 142 ( 7% ) nls1s were detected in radio in the first survey . about two dozen are very radio loud ( radio - loudness @xmath20100 , zhou et al .  in prep . ) . of particular interest , some objects show hybrid properties of nls1 and blazar  with 2masxj0324 + 3410 being an extreme example ( zhou et al . 2007 , apj in press ) . a detailed investigation of radio - loud fraction of nls1s is underway , by taking into account various selection effects in the sdss spectroscopic survey . we are currently working on updating the nls1 agn sample using the latest sdss dr5 data . other work currently undertaken includes : analyzing the x - ray spectral and temporal data for those having xmm - newton and rosat observations , examining optical variability of nls1 using the sdss supernovae survey data ( ai et al . this proceedings ) , radio - loud nls1s , broad - band sed . as for the future , we also plan to work on , as example , nls1s host galaxies and their stellar populations and comparisons with those of broad line seyfert agns , high - redshift nls1s .
this proceedings contribution summarizes first results obtained from a systematic study of 2011 nls1 galaxies , as presented in zhou et al . 
 ( 2006 , apjs 166 , 128 ) . 
 the sample was compiled by examining the spectral parameters of galaxies and qsos derived from sdss dr3 data . 
 we discuss some preliminary results on the statistic properties of the sample , such as the fraction of nls1 , the properties of broad and narrow emission lines , and emission in other wavebands . 
 the black hole mass  velocity dispersion relation for nls1s was re - examined using the velocity dispersion values estimated from the stellar absorption spectra of the host galaxies . 
 preliminary result from an x - ray study for a small subset using data obtained by xmm - newton is briefly discussed .