Broad Hα Emission Research Articles

Active Galactic Nuclei with a Low-metallicity Narrow-line Region

Abstract Low-metallicity active galactic nuclei (AGNs) are interesting to study for the early phase of AGN evolution. However, most AGNs are chemically matured, and accordingly, low-metallicity AGNs are extremely rare. One approach to search for low-metallicity AGNs systematically is utilizing the so-called BPT diagram that consists of the [O iii]λ5007/Hβ and [N ii] /Hα flux ratios. Specifically, photoionization models predict that low-metallicity AGNs show a high [O iii]λ5007/Hβλ4861 ratio and a relatively low [N ii]λ6584/Hαλ6563 ratio that corresponds to the location between the sequence of star-forming galaxies and that of usual AGNs on the BPT diagram (hereafter “the BPT valley”). However, other populations of galaxies such as star-forming galaxies and AGNs with a high electron density or a high-ionization parameter could be also located in the BPT valley, not only low-metallicity AGNs. In this paper, we examine whether most of the emission-line galaxies at the BPT valley are low-metallicity AGNs or not. We select 70 BPT-valley objects from 212,866 emission-line galaxies obtained by the Sloan Digital Sky Survey. Among the 70 BPT-valley objects, 43 objects show firm evidence of the AGN activity, i.e., the He ii λ4686 emission and/or weak but significant broad Hα emission. Our analysis shows that those 43 BPT-valley AGNs are not characterized by a very high gas density nor ionization parameter, inferring that at least 43 among 70 BPT-valley objects (i.e., %) are low-metallicity AGNs. This suggests that the BPT diagram is an efficient tool to search for low-metallicity AGNs.

Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey

Abstract We present a sample of 10 low-mass active galactic nuclei (AGNs) selected from the 40-month Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey. The sample is selected to have robust NuSTAR detections at , to be at , and to have optical r-band magnitudes at least 0.5 mag fainter than an galaxy at its redshift. The median values of absolute magnitude, stellar mass, and 2–10 X-ray luminosity of our sample are , , and erg s−1, respectively. Five objects have detectable broad Hα emission in their optical spectra, indicating black hole masses of . We find that of the galaxies in our sample do not show AGN-like optical narrow emission lines, and one of the 10 galaxies in our sample, J115851+4243.2, shows evidence for heavy X-ray absorption. This result implies that a non-negligible fraction of low-mass galaxies might harbor accreting massive black holes that are missed by optical spectroscopic surveys and X-ray surveys. The mid-IR colors of our sample also indicate that these optically normal low-mass AGNs cannot be efficiently identified with typical AGN selection criteria based on Wide Field Infrared Survey Explorer colors. While the hard ( keV) X-ray-selected low-mass AGN sample size is still limited, our results show that sensitive NuSTAR observations are capable of probing faint hard X-ray emission originating from the nuclei of low-mass galaxies out to moderate redshift ( ), thus providing a critical step in understanding AGN demographics in low-mass galaxies.

X-Ray and Ultraviolet Properties of AGNs in Nearby Dwarf Galaxies

Abstract We present new Chandra X-ray Observatory and Hubble Space Telescope observations of eight optically selected broad-line active galactic nucleus (AGN) candidates in nearby dwarf galaxies (z < 0.055). Including archival Chandra observations of three additional sources, our sample contains all 10 galaxies from Reines et al. (2013) with both broad Hα emission and narrow-line AGN ratios (six AGNs, four composites), as well as one low-metallicity dwarf galaxy with broad Hα and narrow-line ratios characteristic of star formation. All 11 galaxies are detected in X-rays. Nuclear X-ray luminosities range from L 0.5–7keV ≈ 5 × 1039 to 1 × 1042 ergs−1. In all cases except for the star-forming galaxy, the nuclear X-ray luminosities are significantly higher than would be expected from X-ray binaries, providing strong confirmation that AGNs and composite dwarf galaxies do indeed host actively accreting black holes (BHs). Using our estimated BH masses (which range from ∼7 × 104 to 1 × 106 M ⊙), we find inferred Eddington fractions ranging from ∼0.1% to 50%, i.e., comparable to massive broad-line quasars at higher redshift. We use the HST imaging to determine the ratio of UV to X-ray emission for these AGNs, finding that they appear to be less X-ray luminous with respect to their UV emission than more massive quasars (i.e., α OX values an average of 0.36 lower than expected based on the relation between α OX and 2500 Å luminosity). Finally, we discuss our results in the context of different accretion models onto nuclear BHs.

QUASAR HOST GALAXIES AND THE MSMBH–σ* RELATION

ABSTRACT We analyze the emission line profiles detected in deep optical spectra of quasars to derive the mass of their super-massive black holes (SMBH) following the single-epoch virial method. Our sample consists in six radio-loud (RL) quasars and four radio-quiet (RQ) quasars. We carefully fit a broad and narrow Gaussian component for each emission line in both the Hβ (10 objects) and Hα regions (5 objects). A very good agreement of the derived SMBH masses, , is found using the fitted broad Hβ and Hα emission lines. We compare our results with those found by previous studies. We study the relationship between the of the quasar and the stellar velocity dispersion, , of the host galaxy. We use the measured and to investigate the – relation for both the RL and radio-quiet subsamples. Besides the scatter, we find a good agreement between radio-quiet quasars and AGN+quiescent galaxies and between RL quasars and AGN. Our analysis does not support the hypothesis of using σ([O iii] λ5007) as a surrogate for stellar velocity dispersions in high-mass, high-luminosity quasars. We also investigate the relationship between the 5 GHz radio-continuum luminosity, , of the quasar host galaxy with both and . We do not find any correlation between and , although we observe a trend that galaxies with larger stellar velocity dispersions have larger . Using the results of our fitting for the narrow emission lines of [O iii] λ5007 and [N ii] λ6583 we estimate the gas-phase oxygen abundance of six quasars, being sub-solar in all cases.

ASPHERICITY, INTERACTION, AND DUST IN THE TYPE II-P/II-L SUPERNOVA 2013EJ IN MESSIER 74

ABSTRACT SN 2013ej is a well-studied core-collapse supernova (SN) that stemmed from a directly identified red supergiant (RSG) progenitor in galaxy M74. The source exhibits signs of substantial geometric asphericity, X-rays from persistent interaction with circumstellar material (CSM), thermal emission from warm dust, and a light curve that appears intermediate between supernovae of Types II-P and II-L. The proximity of this source motivates a close inspection of these physical characteristics and their potential interconnection. We present multiepoch spectropolarimetry of SN 2013ej during the first 107 days and deep optical spectroscopy and ultraviolet through infrared photometry past ∼800 days. SN 2013ej exhibits the strongest and most persistent continuum and line polarization ever observed for a SN of its class during the recombination phase. Modeling indicates that the data are consistent with an oblate ellipsoidal photosphere, viewed nearly edge-on and probably augmented by optical scattering from circumstellar dust. We suggest that interaction with an equatorial distribution of CSM, perhaps the result of binary evolution, is responsible for generating the photospheric asphericity. Relatedly, our late-time optical imaging and spectroscopy show that asymmetric CSM interaction is ongoing, and the morphology of broad Hα emission from shock-excited ejecta provides additional evidence that the geometry of the interaction region is ellipsoidal. Alternatively, a prolate ellipsoidal geometry from an intrinsically bipolar explosion is also a plausible interpretation of the data but would probably require a ballistic jet of radioactive material capable of penetrating the hydrogen envelope early in the recombination phase. Finally, our latest space-based optical imaging confirms that the late interaction-powered light curve dropped below the stellar progenitor level, confirming the RSG star’s association with the explosion.

MULTI-EPOCH SPECTROSCOPY OF DWARF GALAXIES WITH AGN SIGNATURES: IDENTIFYING SOURCES WITH PERSISTENT BROAD Hα EMISSION

ABSTRACT We use time-domain optical spectroscopy to distinguish between broad emission lines powered by accreting black holes (BHs) and stellar processes (i.e., supernovae) for 16 galaxies identified as active galactic nucleus (AGN) candidates by Reines et al (2013). Our study is primarily focused on those objects with narrow emission line ratios dominated by star formation, for which the origin of the broad Hα emission was unclear. Based on follow-up spectroscopy, we find that the broad Hα emission has faded or was ambiguous for all of the star-forming objects (14/16), over baselines ranging from 5–14 years, suggesting a transient stellar process was responsible for the broad emission in previous Sloan Digital Sky Survey observations. For the two objects in our follow-up sample with narrow-line AGN signatures (RGG 9 and RGG 119), we find persistent broad Hα emission consistent with an AGN origin. Additionally, we use high spectral resolution observations to measure stellar velocity dispersions for 15 objects in the Reines et al. (2013) sample, all with narrow-line ratios indicating the presence of an AGN. Stellar masses range from to M ⊙, and we measure in the range of . These correspond to some of the lowest-mass galaxies with optical signatures of AGN activity. We show that RGG 119, the one object that has both a measured and persistent broad Hα emission, falls near the extrapolation of the relation to the low-mass end.

An effective selection method for low-mass active black holes and first spectroscopic identification

Abstract We present a new method for effectively selecting objects which may be low-mass active black holes (BHs) at galaxy centers using high-cadence optical imaging data, and our first spectroscopic identification of an active 2.7 × 106 M⊙ BH at z = 0.164. This active BH was originally selected due to its rapid optical variability, from a few hours to a day, based on Subaru Hyper Suprime-Cam g-band imaging data taken with a 1 hr cadence. Broad and narrow Hα lines and many other emission ones are detected in our optical spectra taken with Subaru FOCAS, and the BH mass is measured via the broad Hα emission line width (1880 km s−1) and luminosity (4.2 × 1040 erg s−1) after careful correction to the atmospheric absorption around 7580–7720 Å. We measure the Eddington ratio and find it to be as low as 0.05, considerably smaller than those in a previous SDSS sample with similar BH mass and redshift, which indicates one of the special potentials of our Subaru survey. The g − r color and morphology of the extended component indicate that the host galaxy is a star-forming galaxy. We also show the effectiveness of our variability selection for low-mass active BHs.

LOW-MASS ACTIVE GALACTIC NUCLEI WITH RAPID X-RAY VARIABILITY

ABSTRACT We present a detailed study of the optical spectroscopic properties of 12 active galactic nuclei (AGNs) with candidate low-mass black holes (BHs) selected by Kamizasa et al. through rapid X-ray variability. The high-quality, echellette Magellan spectra reveal broad Hα emission in all the sources, allowing us to estimate robust virial BH masses and Eddington ratios for this unique sample. We confirm that the sample contains low-mass BHs accreting at high rates: the median M BH = 1.2 × 106 M ⊙ and median L bol/L Edd = 0.44. The sample follows the M BH–σ * relation, within the considerable scatter typical of pseudobulges, the probable hosts of these low-mass AGNs. Various lines of evidence suggest that ongoing star formation is prevalent in these systems. We propose a new strategy to estimate star formation rates in AGNs hosted by low-mass, low-metallicity galaxies, based on modification of an existing method using the strength of [O ii] λ3727, [O iii] λ5007, and X-rays.

SDSS J085431.18+173730.5: THE FIRST COMPACT ELLIPTICAL GALAXY HOSTING AN ACTIVE NUCLEUS

ABSTRACT We report the discovery of a rare compact early-type galaxy, SDSS J085431.18+173730.5 (hereafter cE_AGN). It has a half-light radius of R e = 490 pc and a brightness of M r = −18.08 mag. Optical spectroscopy available from the Sloan Digital Sky Survey (SDSS) reveals the presence of prominent broad-line emissions with the Hα broad component width of FWHM = 2400 km s−1. The black hole (BH) mass, as estimated from the luminosity and width of the broad Hα emission, is 2.1 × 106 M ☉ ?> . With the help of surface photometry, we perform a detailed analysis of the structural properties. The observed light distribution is best modeled with a double Sérsic function. Fixing the outer component as an exponential disk, we find that the inner component has a Sérsic index of n = 1.4. Considering the inner component as bulge/spheroidal we find that cE_AGN remains consistent in both the BH mass–bulge mass relation and the BH mass–bulge Sérsic index relation. Given these observational properties, we discuss its possible origin investigating the surrounding environment where it is located.

Relativistic baryonic jets from an ultraluminous supersoft X-ray source.

The formation of relativistic jets by an accreting compact object is one of the fundamental mysteries of astrophysics. Although the theory is poorly understood, observations of relativistic jets from systems known as microquasars (compact binary stars) have led to a well established phenomenology. Relativistic jets are not expected to be produced by sources with soft or supersoft X-ray spectra, although two such systems are known to produce relatively low-velocity bipolar outflows. Here we report the optical spectra of an ultraluminous supersoft X-ray source (ULS) in the nearby galaxy M81 (M81 ULS-1; refs 9, 10). Unexpectedly, the spectra show blueshifted, broad Hα emission lines, characteristic of baryonic jets with relativistic speeds. These time-variable emission lines have projected velocities of about 17 per cent of the speed of light, and seem to be similar to those from the prototype microquasar SS 433 (refs 11, 12). Such relativistic jets are not expected to be launched from white dwarfs, and an origin from a black hole or a neutron star is hard to reconcile with the persistence of M81 ULS-1's soft X-rays. Thus the unexpected presence of relativistic jets in a ULS challenges canonical theories of jet formation, but might be explained by a long-speculated, supercritically accreting black hole with optically thick outflows.

A NEW CATALOG OF TYPE 1 AGNs AND ITS IMPLICATIONS ON THE AGN UNIFIED MODEL

We have recently identified a substantial number of type 1 active galactic nuclei (AGNs) featuring weak broad-line regions (BLRs) at from detailed analysis of galaxy spectra in the Sloan Digital Sky Survey Data Release 7. These objects predominantly show a stellar continuum but also a broad Hα emission line, indicating the presence of a low-luminosity AGN oriented so that we are viewing the central engine directly without significant obscuration. These accreting black holes have previously eluded detection due to their weak nature. The newly discovered BLR AGNs have increased the number of known type 1 AGNs by 49%. Some of these new BLR AGNs were detected with the Chandra X-ray Observatory, and their X-ray properties confirm that they are indeed type 1 AGNs. Based on our new and more complete catalog of type 1 AGNs, we derived the type 1 fraction of AGNs as a function of [O iii] emission luminosity and explored the possible dilution effect on obscured AGNs due to star formation. The new type 1 AGN fraction shows much more complex behavior with respect to black hole mass and bolometric luminosity than has been suggested previously by the existing receding torus model. The type 1 AGN fraction is sensitive to both of these factors, and there seems to be a sweet spot (ridge) in the diagram of black hole mass and bolometric luminosity. Furthermore, we present the possibility that the Eddington ratio plays a role in determining opening angles.

Confirming HD 23478 as a new magnetic B star hosting an Hα-bright centrifugal magnetosphere

In this paper, we report 23 magnetic field measurements of the B3IV star HD 23478: 12 obtained from high-resolution Stokes V spectra using the ESPaDOnS (Canada–France–Hawaii Telescope) and Narval (Télescope Bernard Lyot) spectropolarimeters, and 11 from medium-resolution Stokes V spectra obtained with the DimaPol spectropolarimeter (Dominion Astronomical Observatory). HD 23478 was one of two rapidly rotating stars identified as potential ‘centrifugal magnetosphere’ hosts based on IR observations from the Apache Point Observatory Galactic Evolution Experiment survey. We derive basic physical properties of this star including its mass (⁠|$M=6.1^{+0.8}_{-0.7}\,\mathrm{M}_{\odot }$|⁠), effective temperature (Teff = 20 ± 2 kK), radius (⁠|$R=2.7^{+1.6}_{-0.9}\,\mathrm{R}_{\odot }$|⁠), and age (⁠|$\tau _{\rm age}=3^{+37}_{-1}\,{\rm Myr}$|⁠). We repeatedly detect weakly variable Zeeman signatures in metal, He, and H lines in all our observations corresponding to a longitudinal magnetic field of 〈Bz〉 ≈ −2.0 kG. The rotational period is inferred from Hipparcos photometry (Prot = 1.0498(4) d). Under the assumption of the Oblique Rotator Model, our observations yield a surface dipole magnetic field of strength Bd ≥ 9.5 kG that is approximately aligned with the stellar rotation axis. We confirm the presence of strong and broad Hα emission and gauge the volume of this star's centrifugal magnetosphere to be consistent with those of other Hα emitting centrifugal magnetosphere stars based on the large inferred Alfvén to Kepler radius ratio.

Role of feedback in AGN-host coevolution: A study from partially obscured active galactic nuclei

Partially obscured AGNs within a redshift range z=0.011∼0.256 are used to re-study the role of feedback in the AGN-host coevolution issue in terms of their [OIII]λ5007 emission line profile. The spectra of these objects enable us to determine the AGN’s accretion properties directly from their broad Hα emission. This is essential for getting rid of the “circular reasoning” in our previous study of narrow emission-line galaxies, in which the [OIII] emission line was used not only as a proxy of AGN’s bolometric luminosity, but also as a diagnostic of outflow. In addition, the measurement of Dn(4000) index is improved by removing an underlying AGN’s continuum according to the corresponding broad Hα emission. With these improvements, we confirm and reinforce the correlation between L/LEdd and stellar population age. More important is that this correlation is found to be related to both [OIII] line blue asymmetry and bulk blueshift velocity, which suggests a linkage between SMBH growth and host star formation through the feedback process. The current sample of partially obscured AGNs shows that the composite galaxies have younger host stellar population, higher Eddington ratio, less significant [OIII] blue wing and smaller bulk [OIII] line shift than do the Seyfert galaxies.

SDSS1133: an unusually persistent transient in a nearby dwarf galaxy

While performing a survey to detect recoiling supermassive black holes, we have identified an unusual source having a projected offset of 800 pc from a nearby dwarf galaxy. The object, SDSS J113323.97+550415.8, exhibits broad emission lines and strong variability. While originally classified as a supernova (SN) because of its non-detection in 2005, we detect it in recent and past observations over 63 yr and find over a magnitude of rebrightening in the last 2 yr. Using high-resolution adaptive optics observations, we constrain the source emission region to be ≲12 pc and find a disturbed host-galaxy morphology indicative of recent merger activity. Observations taken over more than a decade show narrow [O iii] lines, constant ultraviolet emission, broad Balmer lines, a constant putative black hole mass over a decade of observations despite changes in the continuum, and optical emission-line diagnostics consistent with an active galactic nucleus (AGN). However, the optical spectra exhibit blueshifted absorption, and eventually narrow Fe ii and [Ca ii] emission, each of which is rarely found in AGN spectra. While this peculiar source displays many of the observational properties expected of a potential black hole recoil candidate, some of the properties could also be explained by a luminous blue variable star (LBV) erupting for decades since 1950, followed by a Type IIn SN in 2001. Interpreted as an LBV followed by an SN analogous to SN 2009ip, the multidecade LBV eruptions would be the longest ever observed, and the broad Hα emission would be the most luminous ever observed at late times (>10 yr), larger than that of unusually luminous SNe such as SN 1988Z, suggesting one of the most extreme episodes of pre-SN mass-loss ever discovered.

Investigating the AGN activity and black hole masses in low surface brightness galaxies

AbstractWe present an analysis of the optical nuclear spectra from the active galactic nuclei (AGN) in a sample of giant low surface brightness (GLSB) galaxies. GLSB galaxies are extreme late type spirals that are large, isolated and poorly evolved compared to regular spiral galaxies. Earlier studies have indicated that their nuclei have relatively low mass black holes. Using data from the Sloan Digital Sky Survey (SDSS), we selected a sample of 30 GLSB galaxies that showed broad Hα emission lines in their AGN spectra. In some galaxies such as UGC 6284, the broad component of Hα is more related to outflows rather than the black hole. One galaxy (UGC 6614) showed two broad components in Hα, one associated with the black hole and the other associated with an outflow event. We derived the nuclear black hole (BH) masses of 29 galaxies from their broad Hα parameters. We find that the nuclear BH masses lie in the range 105 – 107 M⊙. The bulge stellar velocity dispersion σe was determined from the underlying stellar spectra. We compared our results with the existing BH mass - velocity dispersion (MBH–σe) correlations and found that the majority of our sample lie in the low BH mass regime and below the MBH–σe correlation. The effects of galaxy orientation in the measurement of σe and the increase of σe due to the effects of bar are probable reasons for the observed offset for some galaxies, but in many galaxies the offset is real. A possible explanation for the MBH–σe offset could be lack of mergers and accretion events in the history of these galaxies which leads to a lack of BH-bulge co-evolution.

Spatially-Resolved View of High-Redshift Starbursts: the case of Sub-mm Galaxies

AbstractUltra-luminous infrared galaxies (LIR > 1012 L⊙) are locally rare, but appear to dominate the co-moving energy density at higher redshifts (z>2). Many of these are optically-faint, dust-obscured galaxies that have been identified by the detection of their thermal dust emission at sub-mm wavelengths. Multi-wavelength spectroscopic follow-up observations of these sub-mm galaxies (SMGs) have shown that they are massive (Mstellar ~ 1011 M⊙) objects undergoing intense star-formation (SFRs ~ 102−103 M⊙ yr−1) with a mean redshift of z ~ 2, coinciding with the epoch of peak quasar activity. The large fraction of AGNs in SMGs and the derived SMBH masses (M• < 108 M⊙) in these galaxies suggest that the submm phase may play an important role in the rapid growth of SMBHs. When both AGN and star-formation activity are present, long-slit spectroscopic techniques face difficulties in disentangling their contributions and may result in SFR and mass overestimates. We present an integral field view of the Hα emission in a sample of 3 SMGs at z~1.4–2.4 with the IFU instrument OSIRIS on Keck. Designed to be used with Laser Guide Star Adaptive Optics, OSIRIS allows a spatial resolution of up to 10× higher than what has been possible in previous seeing-limited studies of the ionized gas in these galaxies. Our main results are the following: (1) We detect multiple galactic-scale sub-components: the compact, broad Hα emission (FWHM >1000 km s−1) likely associated with an AGN, the more extended narrow-line Hα emission (FWHM ≲500 km s−1) of star-forming regions; the latter are dominated by multiple 1–2 kpc sized Hα-bright clumps, each contributing 1-25% of the total clump-integrated Hα emission. (2) We derive clump dynamical masses ~1–10×109M⊙, 1–2 orders of magnitude larger than the kpc-scaled stellar clumps uncovered in optically-selected z ~ 2 star-forming galaxies. (3) We determine high star-formation rate surface densities (ΣSFR~1–50 M⊙yr−1 kpc−2, after extinction correction), similar to local starbursts and luminous infrared galaxies. In contrast to these local environments, SMGs undergo such intense activity on significantly larger spatial scales as revealed by extended Hα emission over 4–16 kpc. (4) We find no evidence of ordered global motion as it would be found in a disk, but rather large velocity offsets (~ few × 100 km s−1) between the distinct stellar clumps. The merger interpretation is likely the most accurate scenario for the SMGs in our sample. However, the final test of whether an underlying disk structure is present will come from studies of the cold gas at the high spatial resolutions possible with ALMA.We refer the reader to Menéndez-Delmestre et al. (2012) for more details.

The broad line emission from the AGN 3C 390.3: complex broad-line region and perturbation in accretion disk

AbstractFrom 13-years of the spectral optical monitoring of a well-known broad-line radio galaxy 3C 390.3 we concluded that the geometry of the broad emission-line region is complex, while still the main part of the emission is coming from the accretion disk. Here we present part of the analysis of the broad Hα and Hβ emission lines, which are showing highly variable double-peaked profiles during the monitoring period (1995-2007), with the aim to probe the accretion disk properties. The disk-like geometry plays a dominant role, but the variability of Hα and Hβ line profiles and intensities shows a presence of an additional emission-line region, that has a different nature for different periods, e.g. in one period the observed variation can be well modeled if one assumes changes in position and size of the emitting disk along the accretion disk.

Type 1 AGN at low z. I. Emission properties

We analyze the emission properties of a new sample of 3 596 type 1 AGN, selected from the SDSS DR7 based on the detection of broad Hα emission. The sample extends over a broad Hα luminosity LbHα of 1040–1044 erg s−1 and a broad Hα FWHM of 1 000–25 000 km s−1, which covers the range of black hole mass 106 < MBH/M⊙ < 109.5 and luminosity in Eddington units 10−3 < L/LEdd < 1. We combine ROSAT, GALEX and 2MASS observations to form the SED from 2.2 μm to 2 keV. We find the following: 1. The distribution of the Hα FWHM values is independent of luminosity. 2. The observed mean optical-UV SED is well matched by a fixed shape SED of luminous quasars, which scales linearly with LbHα, and a host galaxy contribution. 3. The host galaxy r-band (fibre) luminosity function follows well the luminosity function of inactive non-emission line galaxies (NEG), consistent with a fixed fraction of ∼ 3% of NEG hosting an AGN, regardless of the host luminosity. 4. The optical-UV SED of the more luminous AGN shows a small dispersion, consistent with dust reddening of a blue SED, as expected for thermal thin accretion disc emission. 5. There is a rather tight relation of νLν(2 keV) and LbHα, which provides a useful probe for unobscured (true) type 2 AGN.

Type 1 AGN at low z- I. Emission properties

We analyse the emission properties of a new sample of 3579 type 1 AGN, selected from Sloan Digital Sky Survey (SDSS) Data Release 7 based on the detection of broad Hα emission. The sample extends over a broad Hα luminosity LbHα of and a broad Hα full width at half-maximum (FWHM) of ⁠, which covers the range of black hole mass 106 < MBH/M⊙ < 109.5 and luminosity in Eddington units 10−3 < L/LEdd < 1. We combine ROSAT, GALEX and 2MASS observations to form the spectral energy distribution (SED) from 2.2 m to 2 keV. We find the following. (1) The distribution of the Hα FWHM values is independent of luminosity. (2) The observed mean optical–ultraviolet (optical–UV) SED is well matched by a fixed-shape SED of luminous quasars, which scales linearly with LbHα, and a host galaxy contribution. (3) The host galaxy r-band (fibre) luminosity function follows well the luminosity function of inactive non-emission-line galaxies (NEGs), consistent with a fixed fraction of ∼3 per cent of NEGs hosting an AGN, regardless of the host luminosity. (4) The hosts of lower luminosity AGN have a mean z-band luminosity and u−z colour which are identical to NEGs with the same redshift distribution. With increasing LbHα the AGN hosts become bluer and less luminous than NEGs. The implied increasing star formation rate with LbHα is consistent with the relation for SDSS type 2 AGN of similar bolometric luminosity. (5) The optical–UV SED of the more luminous AGN shows a small dispersion, consistent with dust reddening of a blue SED, as expected for thermal thin accretion disc emission. (6) There is a rather tight relation between and LbHα, which provides a useful probe for unobscured (true) type 2 AGN. (7) The primary parameter that drives the X-ray to UV emission ratio is luminosity, rather than MBH or L/LEdd.

SPACE TELESCOPE IMAGING SPECTROGRAPH SPECTROSCOPY OF THE CENTRAL 14 pc OF NGC 3998: EVIDENCE FOR AN INFLOW

Prior imaging of the lenticular galaxy, NGC 3998, with the Hubble Space Telescope revealed a small, highly inclined, nuclear ionized gas disk, the kinematics of which indicate the presence of a 270 million solar mass black hole. Plausible kinematic models are used to constrain the size of the broad emission line region (BELR) in NGC 3998 by modeling the shape of the broad Hα, Hβ, and Hγ emission line profiles. The analysis indicates that the BELR is large with an outer radius ~7 pc, regardless of whether the kinematic model is represented by an accretion disk or a spherically symmetric inflow. The electron temperature in the BELR is ≤ 28,800 K consistent with photoionization by the active galactic nucleus (AGN). Indeed, the AGN is able to sustain the ionization of the BELR, albeit with a high covering factor ranging between 20% and 100% depending on the spectral energy distribution adopted for the AGN. The high covering factor favors a spherical distribution for the gas as opposed to a thin disk. If the gas density is ≥7 × 103 cm–3 as indicated by the broad forbidden [S II] emission line ratio, then interpreting the broad Hα emission line in terms of a steady state spherically symmetric inflow leads to a rate ≤ 6.5 × 10–2 M ☉ yr–1 which exceeds the inflow requirement to explain the X-ray luminosity in terms of a radiatively inefficient inflow by a factor of ≤18.