Blazars with strong emission lines were found to be associated mostly with broad-line type 1 Active Galactic Nuclei (AGN). Hitherto, evidence for blazars identified with Narrow Line Seyfert 1 (NLS1) AGN was limited to very few individual cases. Here we present a comprehensive study of a sample of 23 genuine radio-loud NLS1 galaxies which have the radio-loudness parameters, the ratio of radio (21 cm) to optical (4400Å) luminosity, greater than 100. The sample, drawn from the SDSS and FIRST, is homogeneous and the largest of this kind. A significant fraction of the sample objects show interesting radio to X-ray properties that are unusual to most of the previously known radio-loud NLS1 AGN, but are reminiscent of blazars. These include flat radio spectra, large amplitude flux and spectral variability, compact VLBI cores, very high brightness temperatures (10 11−14 K) derived from variability, enhanced optical emission in excess of the normal ionising continuum, flat X-ray spectra, and blazar-like SEDs. We interpret them as evidence for the postulated blazar nature of these very radio-loud NLS1 AGN, which might possess at least moderately relativistic jets. We suggest that those steep spectrum radio-loud NLS1 AGN in the sample are of the same population but with their radio jets aligned at large angles to the lines-of-sight. Intrinsically, some of the objects have relatively low radio power and would have been classified as radio-intermediate AGN.The black hole masses, estimated from the broad Balmer line width and luminosity, are within 10 6−8 M ⊙ , and the inferred Eddington ratios are around unity. Unless the black hole masses are largely under-estimated, our result stretches the low mass end of the black holes of luminous, fast accreting radio-loud AGN to a smaller mass regime (the order of 10 6 M ⊙ ) in the black hole mass-radio-loudness space where other normal AGN are seldom found. The results imply that radio-loud AGN may be powered by black holes with moderate masses (∼ 10 6−7 M ⊙ ) accreting at high rates (Eddington ratios up to unity or higher). The host galaxies of a few nearby objects appear to be disk-like or merger; and some of the objects show imprints of young stellar populations in their SDSS spectra. We find that some of the objects, despite having strong emission lines, resemble high-energy peaked BL Lacs in their SED with the synchrotron component peaked at around the UV; such objects constitute an intriguingly high fraction of the sample. The radio sources of the sample are ubiquitously compact. They are smaller than at most several tens of kilo-parsecs, suggesting a possible link with compact steep-spectrum radio sources. Given the peculiarities of blazar-like NLS1 galaxies, questions arise as to whether they are plain downsizing extensions of normal radio-loud AGN, or whether they form a previously unrecognised population.

This is the first paper in a series dedicated to the study of the emission-line and continuum properties of narrow line Seyfert 1 galaxies (NLS1s). We carried out a systematic search for NLS1s from objects assigned as "QSOs" or "galaxies" in the spectroscopic sample of the Sloan Digital Sky Survey Data Release 3 (SDSS DR3) by a careful modeling of their emission lines and continua. The result is a uniform sample comprising ∼ 2 000 NLS1. This sample dramatically increases the number of known NLS1 by a factor of ∼ 10 over previous compilations. This paper presents the parameters of the prominent emission lines and continua, which were measured accurately with typical uncertainties < 10%. Taking advantage of such an unprecedented large and uniform sample with accurately measured spectral parameters, we carried out various statistical analysis, some of which were only possible for the first time. The main results found are as follows.(1) Within the overall Seyfert 1 population, the incidence of NLS1s is strongly dependent on the optical, X-ray, and radio luminosities as well as the radioloudness. The fraction of NLS1 peaks around SDSS g-band absolute magnitude M g ∼ −22 m in the optical and ∼ 10 43.2 erg s −1 in the soft X-ray band, and decreases quickly as the radio-loudness increases. (2) On average the relative FeII emission, R 4570 = F eII(4434 − 4684)/Hβ, in NLS1s is about twice that in normal AGNs, and is anti-correlated with the broad component width of the Balmer emission lines. (3) 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 F W HM ∼ 1 000 km s −1 in NLS1s, but the trend appears to

We investigate the relationship between the linewidths of broad Mg II λ2800 and Hβ in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping (RM). Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe II contamination. We show that, contrary to popular belief, the velocity width of Mg II tends to be smaller than that of Hβ, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from RM, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg II and Hβ lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature.

We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad Hα emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN-galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range 8 × 10 4 -2 × 10 6 M ⊙ (with a median of 1.2 × 10 6 M ⊙ ), using the virial mass estimator based on the broad Hα line. About half of our sample of low-mass BHs differs from that of Greene & Ho, with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from 0.01 to ∼ 1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local Universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of L * field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1 Gyr.

We report the identification of a very radio loud, narrow-line quasar, SDSS J094857.3+002225, discovered in the Sloan Digital Sky Survey (SDSS) early data release (EDR). With FWHM ðH Þ % 1500 km s À1 and undetected [O iii] 4959, 5007 SDSS J094857.3+002225 is consistent with the conventional definition of narrow-line Seyfert 1 galaxies (NLS1s). Its strong optical Fe ii emission [R 4570 f ðFe ii 4570Þ= f ðH Þ % 1:59] is also typical of NLS1s. With a radio loudness RL ð f ;4:85 GHz =f ;B Þe1000 and radio power of P 4:85 GHz $ ð3:6 5:2Þ Â 10 26 W Hz À1 , it is the first bona fide, very radio loud NLS1. The inverted radio spectrum and very high brightness temperature (e10 13 K) derived from variation of the radio flux suggest the presence of a relativistic jet beaming toward the observer in this NLS1.

We have investigated the broad-line Balmer decrements (Hα/Hβ) for a large, homogeneous sample of Seyfert 1 galaxies and quasi-stellar objects (QSOs) using spectroscopic data obtained in the Sloan Digital Sky Survey. The sample, drawn from the Fourth Data Release, comprises 446 low-redshift (z 0.35) active galactic nuclei (AGN) that have blue optical continua as indicated by the spectral slopes in order to minimize the effect of dust extinction. We find that (i) the distribution of the intrinsic broad-line Hα/Hβ ratio can be well described by log-Gaussian, with a peak at Hα/Hβ = 3.06 and a standard deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate with AGN properties such as luminosity, accretion rate and continuum slope, etc.; (iii) on average, the Balmer decrements are found to be only slightly larger in radio-loud sources (3.37) and sources having double-peaked emission-line profiles (3.27) compared to the rest of the sample. We therefore suggest that the broad-line Hα/Hβ ratio can be used as a good indicator for dust extinction in the AGN broad-line region; this is especially true for radio-quiet AGN with regular emission-line profiles, which constitute the vast majority of the AGN population.

A new, complete sample of 14,584 broad-line active galactic nuclei (AGNs) at z < 0.35 is presented, which are uncovered homogeneously from the complete database of galaxies and quasars observed spectroscopically in the Sloan Digital Sky Survey Seventh Data Release. The stellar continuum is properly removed for each spectrum with significant host absorption line features, and careful analyses of the emission line spectra, particularly in the Hα and Hβ wavebands, are carried out. The broad Balmer emission line, particularly Hα, is used to indicate the presence of an AGN. The broad Hα lines have luminosities in a range of 10 38.5 -10 44.3 erg s −1 , and line widths (FWHMs) of 500-34,000 km s −1 . The virial black hole masses, estimated from the broad-line measurements, span a range of 10 5.1 -10 10.3 M , and the Eddington ratios vary from −3.3 to 1.3 in logarithmic scale. Other quantities such as multiwavelength photometric properties and flags denoting peculiar line profiles are also included in this catalog. We describe the construction of this catalog and briefly discuss its properties. The catalog is publicly available online. This homogeneously selected AGN catalog, along with the accurately measured spectral parameters, provides the most updated, largest AGN sample data, which will enable further comprehensive investigations of the properties of the AGN population in the low-redshift universe.

We used a large, homogeneous sample of 4178 z ≤ 0.8 Seyfert 1 galaxies and QSOs selected from the Sloan Digital Sky Survey to investigate the strength of Fe II emission and its correlation with other emission lines and physical parameters of active galactic nuclei. We find that the strongest correlations of almost all the emission-line intensity ratios and equivalent widths (EWs) are with the Eddington ratio (L/L Edd ), rather than with the continuum luminosity at 5100 Å (L 5100 ) or black hole mass (M BH ); the only exception is the EW of ultraviolet Fe II emission, which does not correlate at all with broad-line width, L 5100 , M BH , or L/L Edd . By contrast, the intensity ratios of both the ultraviolet and optical Fe II emission to Mg II λ2800 correlate quite strongly with L/L Edd . Interestingly, among all the emission lines in the near-UV and optical studied in this paper (including Mg II λ2800, Hβ, and [O III] λ5007), the EW of narrow optical Fe II emission has the strongest correlation with L/L Edd . We hypothesize that the variation of the emission-line strength in active galaxies is regulated by L/L Edd because it governs the global distribution of the hydrogen column density of the clouds gravitationally bound in the line-emitting region, as well as its overall gas supply. The -2systematic dependence on L/L Edd must be corrected when using the Fe II/Mg II intensity ratio as a measure of the Fe/Mg abundance ratio to study the history of chemical evolution in QSO environments.