We present high-quality ( high signal-to-noise ratio and moderate spectral resolution) near-infrared (near-IR) spectroscopic observations of 23 well-known broad emission line active galactic nuclei (AGNs). In addition, we obtained simultaneous (within 2 months) optical spectroscopy of similar quality. The near-IR broad emission line spectrum of AGNs is dominated by permitted transitions of hydrogen, helium, oxygen, and calcium, and by the rich spectrum of singly ionized iron. In this paper we present the spectra, line identifications, and measurements, and we address briefly some of the important issues regarding the physics of AGN broad emission line regions. In particular, we investigate the excitation mechanism of neutral oxygen and confront for the first time theoretical predictions of the near-IR iron emission spectrum with observations.

We use statistical results from a large sample of about 500 blazars, based on two surveys, the Deep X-ray Radio Blazar Survey (DXRBS), nearly complete, and the RASS-Green Bank survey (RGB), to provide new constraints on the spectral energy distribution of blazars, particularly flat-spectrum radio quasars (FSRQ). This reassessment is prompted by the discovery of a population of FSRQ with spectral energy distribution similar to that of high-energy peaked BL Lacs. The fraction of these sources is sample dependent, being ∼ 10% in DXRBS and ∼ 30% in RGB (and reaching ∼ 80% for the Einstein Medium Sensitivity Survey). We show that these "X-ray strong" radio quasars, which had gone undetected or unnoticed in previous surveys, indeed are the strong-lined counterparts of high-energy peaked BL Lacs and have synchrotron peak frequencies, ν peak , much higher than "classical" FSRQ, typically in the UV band for DXRBS. Some of these objects may be 100 GeV -TeV emitters, as are several known BL Lacs with similar broadband spectra. Our large, deep, and homogeneous DXRBS sample does not show anti-correlations between ν peak and radio, broad line region, or jet power, as expected in the so-called "blazar sequence" scenario. However, the fact that FSRQ do not reach X-ray-to-radio flux ratios and ν peak values as extreme as BL Lacs and the elusiveness of high ν peak -high-power blazars suggest that there might be an intrinsic, physical limit to the synchrotron peak frequency that can be reached by strong-lined, powerful blazars. Our findings have important implications for the study of jet formation and physics and its relationship to other properties of active galactic nuclei.

Our knowledge of the blazar surface densities and luminosity functions, which are fundamental parameters, relies still on samples at relatively high flux limits. As a result, our understanding of this rare class of active galactic nuclei is mostly based on relatively bright and intrinsically luminous sources. We present the radio number counts, evolutionary properties, and luminosity functions of the faintest blazar sample with basically complete ($95%) identifications. Based on the Deep X-Ray Radio Blazar Survey (DXRBS), it includes 129 flat-spectrum radio quasars (FSRQs) and 24 BL Lac objects down to a 5 GHz flux and power $50 mJy and $10 24 W Hz À1 , respectively, an order of magnitude improvement as compared to previously published (radio-selected) blazar samples. DXRBS FSRQs are seen to evolve strongly, up to redshift %1.5, above which high-power sources show a decline in their comoving space density. DXRBS BL Lac objects, on the other hand, do not evolve. High-energy and low-energy peaked BL Lac objects (HBLs and LBLs, respectively) share the same lack of cosmological evolution, which is at variance with some previous results. The observed luminosity functions are in good agreement with the predictions of unified schemes, with FSRQs getting close to their expected minimum power. Despite the fact that the large majority of our blazars are FSRQs, BL Lac objects are intrinsically $50 times more numerous. Finally, the relative numbers of HBLs and LBLs in the radio and X-ray bands are different from those predicted by the so-called blazar sequence and support a scenario in which HBLs represent a small minority (%10%) of all BL Lac objects.

We investigate why BL Lacertae objects (BL Lacs) have values of the Ca H&K break (a stellar absorption feature) lower than low-power radio galaxies and if its use is justified to separate the two classes. For this purpose we relate this parameter to the radio and optical core emissions, as well as to the X-ray powers, for a sample of ~90 radio sources. We find that the Ca H&K break value decreases with increasing jet powers, and that it also anti-correlates with the radio core dominance parameter but not with extended radio emission. Based on this we conclude that the Ca H&K break value of BL Lacs and radio galaxies is a suitable indicator of orientation. From the luminosity ratios between objects with low and high Ca H&K break values we constrain the average Lorentz factors for BL Lacs and low-power radio galaxies in the radio and X-ray band to Gamma ~ 2 -- 4 and derive average viewing angles for the galaxies. Our values are in agreement with results from independent methods. We find that the correlations between Ca H&K break and radio core and X-ray luminosity hold independently for low- (LBL) and high-energy peaked BL Lacs (HBL). We derive average viewing angles for their parent populations, which turn out to be similar to the ones for our entire sample, and compare for the first time the luminosities of LBL and HBL at different orientations.Comment: 14 pages, 12 figures. Accepted for publication in MNRA

We have searched the archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X‐ray data base with several publicly available radio catalogues, restricting our candidate list to serendipitous X‐ray sources with a flat radio spectrum (αr≤0.70, where S∝ν−α). This makes up the Deep X‐ray Radio Blazar Survey (DXRBS). Here we present new identifications and spectra for 106 sources, including 86 radio‐loud quasars, 11 BL Lacertae objects, and nine narrow‐line radio galaxies. Together with our previously published objects and already‐known sources, our sample now contains 298 identified objects: 234 radio‐loud quasars [181 flat‐spectrum quasars: FSRQ (αr≤0.50) and 53 steep‐spectrum quasars: SSRQ], 36 BL Lacs and 28 narrow‐line radio galaxies. Redshift information is available for 96 per cent of these. Thus our selection technique is ∼90 per cent efficient at finding radio‐loud quasars and BL Lacs. Reaching 5‐GHz radio fluxes ∼50 mJy and 0.1–2.0 keV X‐ray fluxes a few ×10−14 erg cm−2 s−1, DXRBS is the faintest and largest flat‐spectrum radio sample with nearly complete (∼85 per cent) identification. We review the properties of the DXRBS blazar sample, including redshift distribution and coverage of the X‐ray‐radio–power plane for quasars and BL Lacs. Additionally, we touch upon the expanded multiwavelength view of blazars provided by DXRBS. By sampling for the first time the faint end of the radio and X‐ray luminosity functions, this sample will allow us to investigate the blazar phenomenon and the validity of unified schemes down to relatively low powers.

We use quasi‐simultaneous near‐infrared (near‐IR) and optical spectroscopy from four observing runs to study the continuum around 1 μm in 23 well‐known broad emission line active galactic nuclei (AGN). We show that, after correcting the optical spectra for host galaxy light, the AGN continuum around this wavelength can be approximated by the sum of mainly two emission components, a hot dust blackbody and an accretion disc. The accretion disc spectrum appears to dominate the flux at ∼ 1 μm, which allows us to derive a relation for estimating AGN black hole masses based on the near‐IR virial product. This result also means that a near‐IR reverberation programme can determine the AGN state independent of simultaneous optical spectroscopy. On average we derive hot dust blackbody temperatures of ∼1400 K, a value close to the sublimation temperature of silicate dust grains, and relatively low hot dust covering factors of ∼7 per cent. Our preliminary variability studies indicate that in most sources, the hot dust emission responds to changes in the accretion disc flux with the expected time lag; however, a few sources show a behaviour that can be attributed to dust destruction.

We provide a comprehensive census of the near-Infrared (NIR, 0.8-2.4 µm) spectroscopic properties of 102 nearby (z < 0.075) active galactic nuclei (AGN), selected in the hard X-ray band (14-195 keV) from the Swift-Burst Alert Telescope (BAT) survey. With the launch of the James Webb Space Telescope this regime is of increasing importance for dusty and obscured AGN surveys. We measure black hole masses in 68% (69/102) of the sample using broad emission lines (34/102) and/or the velocity dispersion of the Ca II triplet or the CO band-heads (46/102). We find that emission line diagnostics in the NIR are ineffective at identifying bright, nearby AGN galaxies because ([Fe ii] 1.257µm/Paβ and H 2 2.12µm/Brγ) identify only 25% (25/102) as AGN with significant overlap with star forming galaxies and only 20% of Seyfert 2 have detected coronal lines (6/30). We measure the coronal line emission in Seyfert 2 to be weaker than in Seyfert 1 of the same bolometric luminosity suggesting obscuration by the nuclear torus. We find that the correlation between the hard X-ray and the [Si vi] coronal line luminosity is significantly better than with the [O iii] λ 5007 luminosity. Finally, we find 3/29 galaxies (10%) that are optically classified as Seyfert 2 show broad emission lines in the NIR. These AGN have the lowest levels of obscuration among the Seyfert 2s in our sample (log N H < 22.43 cm −2 ), and all show signs of galaxy-scale interactions or mergers suggesting that the optical broad emission lines are obscured by host galaxy dust.

Aims. The multi-frequency sedentary survey is a flux-limited, statistically well-defined sample of highly X-ray dominated (i.e., with a very high X-ray to radio flux ratio) BL Lacertae objects, which includes 150 sources. In this paper, the third of the series, we report the results of a dedicated optical spectroscopy campaign that, together with results from other independent optical follow-up programs, led to the spectroscopic identification of all sources in the sample. Methods. We carried out a systematic spectroscopic campaign for the observation of all unidentified objects of the sample using the ESO 3.6 m, the KPNO 4 m, and the TNG optical telescopes.Results. We present new identifications and optical spectra for 76 sources, 50 of which are new BL Lac objects, 18 are sources previously referred as BL Lacs but for which no redshift information was available, and 8 are broad emission-line AGNs. We find that the multi-frequency selection technique used to build the survey is highly efficient (∼90%) in selecting BL Lacs objects. We present positional and spectroscopic information for all confirmed BL Lac objects. Our data allowed us to determine 36 redshifts out of the 50 new BL Lacs and 5 new redshifts for the previously known objects. The redshift distribution of the complete sample is presented and compared with that of other BL Lacs samples. For 26 sources without recognizable absorption features, we calculated lower limits to the redshift using a method based on simulated optical spectra with different ratios between jet and galaxy emission. For a subsample of 38 object with high-quality spectra, we find a correlation between the optical spectral slope, the 1.4 GHz radio luminosity, and the Ca H&K break value, indicating that for powerful/beamed sources the optical light is dominated by the non-thermal emission from the jet.