Emission-line activity in type 2 quasars from the Sloan Digital Sky Survey

Villar-Martí,n, M.,Humphrey, A.,Martí,nez-Sansigre, A.,Pé,rez-Torres, M.,Binette, L.,Zhang, X. G. Blackwell Publishing Ltd 2008 Monthly notices of the Royal Astronomical Society Vol.390 No.1

<P>ABSTRACT</P><P>We have compared the optical emission-line ratios of type 2 quasars from Zakamska et al. with standard active galactic nucleus (AGN) photoionization model predictions, type 2 Seyfert galaxies, H <SMALL>II</SMALL> galaxies and narrow-line Fanaro–Riley type II radio galaxies. Moderate to high-ionization narrow-line radio galaxies and type 2 Seyfert galaxies are indistinguishable from type 2 quasars based on their optical line ratios. The standard AGN photoionization models, widely discussed for other type 2 AGN, can reproduce successfully the loci and trends of type 2 quasars in some of the main diagnostic diagrams. These models are not exempt of problems, and the discrepancies with the data are the same encountered for other type 2 AGN. As for these, realistic models must take into account a range of cloud properties, as widely demonstrated in the literature.</P><P>The Zakamska et al. sample is strongly biased towards objects with high line luminosities (L[O <SMALL>III</SMALL>] >10<SUP>42</SUP> erg s<SUP>−1</SUP>). We have found that stellar photoionization is obvious in a fraction of objects (3 out of 50) which are characterized by low [O <SMALL>III</SMALL>] luminosities compared with most type 2 quasars in the sample. We suggest that if the sample were expanded towards lower line luminosities (∼10<SUP>40–42</SUP> erg s<SUP>−1</SUP>) stellar photoionization might be evident much more frequently.</P><P>We explore an alternative scenario to pure AGN photoionization in which a varying contribution of stellar ionized gas contributes to the line fluxes. Although the models presented here are rather simplistic and not strong quantitative results can be extracted regarding the relative contribution of stellar versus AGN photoionization, our results suggest that adding a varying contribution of stellar photoionized gas works in the right direction to solve most of the problems affecting the standard AGN photoionization models. The ‘temperature problem’ on the other hand remains.</P>

OBJECTIVE-PRISM SEARCH OF EMISSION-LINE GALAXIES INSIDE THE HYDRA VOID

KIM CHULHEE The Korean Astronomical Society 2000 Journal of The Korean Astronomical Society Vol.33 No.2

In order to identify the candidates of emission-line galaxies inside the southern Hydra Void, photo-graphic objective-prism observations with the UK Schmidt Telescope were carried out using the Tech-Pan films for five fields. All observed prism plates were scanned with the APM Facility and the scanned data was processed to determine the APM plate parameters and to draw spectra. For all galaxy spectra, the emission features, the distance between emission features of H$\beta$4861, [OIII]${\lambda}{\lambda}$ 4959, 5007 and the overlapping by nearby objects were investigated by eyeballing. A total of 7 candidates of emission-line galaxies inside the Hydra Void were identified.

The black hole mass, Eddington ratio and <i>M</i>_BH–σ_{[O <small>III</small>]} relation in young radio galaxies

Blackwell Publishing Ltd 2009 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.398 No.4

<P>ABSTRACT</P><P>The masses of the central supermassive black holes (BHs) and the Eddington ratios for a sample of 65 young radio galaxies [27 gigahertz-peaked spectrum (GPS) and 38 compact steep-spectrum (CSS) sources] are estimated by various methods. We find that the average BH mass of these young radio galaxies is ⟨log <I>M</I><SUB>BH</SUB>⟩≃ 8.3, which is less than that of radio loud quasi-stellar objects (QSOs) and low-redshift radio galaxies (⟨log <I>M</I><SUB>BH</SUB>⟩≃ 9.0). The CSS/GPS sources have relatively high Eddington ratios with average ratio ⟨log <I>L</I><SUB>bol</SUB>/<I>L</I><SUB>Edd</SUB>⟩=−0.56, which are similar to those of narrow-line Seyfert 1 galaxies (NLS1s). It suggests that the CSS/GPS sources may not only be in the early stage of radio activities, but also in the early stage of their accretion activities.</P><P>We find that the young radio galaxies as a class deviate systematically from the <I>M</I><SUB>BH</SUB>–σ<SUB>*</SUB> relation defined by nearby inactive galaxies, when using σ<SUB>[O <SMALL>III</SMALL></SUB> as a surrogate for the stellar velocity dispersion σ<SUB>*</SUB>. There is no significant correlation between the deviation of the [O <SMALL>III</SMALL>] emission line width, Δσ≡σ<SUB>[O <SMALL>III</SMALL>]</SUB>−σ<SUB>[pred]</SUB> and the jet/accretion power, where σ<SUB>[pred]</SUB> are calculated from the Tremaine et al. relation using the estimated BH masses. However, we find that the deviation Δσ in young radio galaxies is well correlated with the Eddington ratio, and this correlation is found to be similar to that of radio quiet active galactic nuclei (AGN) (QSOs/NLS1s) where the radio jet is absent or weak. We suggest that the accretion activities may still play an important role in shaping the kinematics of [O <SMALL>III</SMALL>] narrow line in these young radio galaxies.</P>

SPATIALLY RESOLVED KINEMATICS OF GAS AND STARS IN HIDDEN TYPE 1 AGNS

Son, Donghoon,Woo, Jong-Hak,Eun, Da-In,Cho, Hojin,Karouzos, Marios,Park, Songyeon The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.5

We analyze the spatially resolved kinematics of gas and stars for a sample of ten hidden type 1 AGNs in order to investigate the nature of their central sources and the scaling relation with host galaxy stellar velocity dispersion. We select our sample from a large number of hidden type 1 AGNs, which are identified based on the presence of a broad (full width at half maximum ≳1000 km s^-1) component in the Hα line profile and which are frequently mis-classified as type 2 AGNs because AGN continuum and broad emission lines are weak or obscured in the optical spectral range. We used the Blue Channel Spectrograph at the 6.5-m Multiple Mirror Telescope to obtain long-slit data with a spatial scale of 0.3 arcsec pixel^-1. We detected broad Hβ lines for only two targets; however, the presence of strong broad Hα lines indicates that the AGNs we selected are all low-luminosity type 1 AGNs. We measured the velocity, velocity dispersion, and flux of stellar continuum and gas emission lines (i.e., Hβ and [O III]) as a function of distance from the center. The spatially resolved gas kinematics traced by Hβ or [O III] are generally similar to the stellar kinematics except for the inner center, where signatures of gas outflows are detected. We compare the luminosity-weighted effective stellar velocity dispersions with the black hole masses and find that our hidden type 1 AGNs, which have relatively low back hole masses, follow the same scaling relation as reverberation-mapped type 1 AGN and more massive inactive galaxies.

BRACKETT LINE-BASED M_BH ESTIMATORS AND HOT DUST TEMPERATURES OF TYPE 1 AGNs FROM AKARI SPECTROSCOPIC DATA

KIM, DOHYEONG,IM, MYUNGSHIN The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We provide results of near-infrared (NIR) spectroscopic observations of 83 nearby (0.002< z <0.48) and bright (K <14 mag) type 1 active galactic nuclei (AGNs). For the observations, we used the Infrared Camera (IRC) on AKARI allowing us to obtain the spectrum in the rarely studied spectral range of $2.5-5.0{\mu}m$. The $2.5-5.0{\mu}m$ spectral region suffers less dust extinction than ultra violet (UV) or optical wavelength ranges, and contains several important emission lines such as $Br{\beta}$ ($2.63{\mu}m$), $Br{\alpha}$ ($4.05{\mu}m$), and polycyclic aromatic hydrocarbon (PAH; $3.3{\mu}m$). The sample is selected from the bright quasar surveys of Palomar Green and SNUQSO, and AGNs with black hole (BH) masses estimated from reverberation mapping method. We measure the Brackett line properties for 11 AGNs, which enable us to derive BH mass estimators and investigate circum-nuclear environments. Moreover, we perform spectral modeling to fit the hot and warm dust components by adding photometric data from SDSS, 2MASS, WISE, and ISO to the AKARI spectra, and estimate hot and warm dust temperatures of ~1100K and ~220 K, respectively.

AGN BROAD LINE REGIONS SCALE WITH BOLOMETRIC LUMINOSITY

Sascha Trippe 한국천문학회 2015 Journal of The Korean Astronomical Society Vol.48 No.3

The masses of supermassive black holes in active galactic nuclei (AGN) can be derived spec- troscopically via virial mass estimators based on selected broad optical/ultraviolet emission lines. These estimates commonly use the line width as a proxy for the gas speed and the monochromatic continuum luminosity, λLλ, as a proxy for the radius of the broad line region. However, if the size of the broad line region scales with the bolometric AGN luminosity rather than λLλ, mass estimates based on different emission lines will show a systematic discrepancy which is a function of the color of the AGN continuum. This has actually been observed in mass estimates based on Hα/Hβ and Civ lines, indicating that AGN broad line regions indeed scale with bolometric luminosity. Given that this effect seems to have been overlooked as yet, currently used single-epoch mass estimates are likely to be biased.

Misclassified Type 1 AGNs in the Local Universe

우종학,김지강,박대성,배현진,김재혁,이승언,김상철,권홍진 한국천문학회 2014 Journal of The Korean Astronomical Society Vol.47 No.5

We search for misclassified type 1 AGNs among type 2 AGNs identified with emission line flux ratios, and investigate the properties of the sample. Using 4 113 local type 2 AGNs at 0.02<z<0.05 selected from Sloan Digital Sky Survey Data Release 7, we detected a broad component of the Hα line with a Full-Width at Half-Maximum (FWHM) ranging from 1 700 to 19 090 kms-1 for 142 objects, based on the spectral decomposition and visual inspection. The fraction of the misclassified type 1 AGNs among type 2 AGN sample is ~3.5%, implying that a large number of missing type 1 AGN population may exist. The misclassified type 1 AGNs have relatively low luminosity with a mean broad Hα luminosity, log LHα = 40.50±0.35 ergs-1, while black hole mass of the sample is comparable to that of the local black hole population, with a mean black hole mass, log MBH = 6.94±0.51 M⊙. The mean Eddington ratio of the sample is log Lbol/LEdd = -2.00±0.40, indicating that black hole activity is relatively weak, hence, AGN continuum is too weak to change the host galaxy color. We find that the OIII lines show significant velocity offsets, presumably due to outflows in the narrow-line region, while the velocity offset of the narrow component of the Hα line is not prominent, consistent with the ionized gas kinematics of general type 1 AGN population.

LINEAR POLARIZATION OF A DOUBLE PEAKED BROAD EMISSION LINE IN ACTIVE GALACTIC NUCLEI

Lee, Hee-Won The Korean Astronomical Society 2011 Journal of The Korean Astronomical Society Vol.44 No.2

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with ${\Delta}{\mu}=0.1$. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.

Eddington Ratios of Dust-Obscured Quasars at <i>z</i> ~ 2

김도형,임명신,임구,김용정 한국천문학회 2024 Journal of The Korean Astronomical Society Vol.57 No.1

In the merger-driven galaxy evolution scenario, dust-obscured quasars are considered to be an intermediate population between merger-driven star-forming galaxies and unobscured quasars; however, this scenario is still controversial. To verify this, it is necessary to investigate whether dust-obscured quasars have higher Eddington ratio (λ_Edd) values than those of unobscured quasars, as expected in the merger-driven galaxy evolution scenario. In this study, we derive black hole (BH) masses of 10 dust-obscured quasars at <i>z</i> ~ 2, during the peak period of star-formation and BH growth in the Universe, using a newly derived mid-infrared (MIR) continuum luminosity <i>L</i>_MIR-based estimator that is highly resistant to dust extinction. Then, we compare the λ_Edd values of these dust-obscured quasars to those of unobscured type-1 quasars at similar redshifts. We find that the measured log(λ_Edd) values of the dust-obscured quasars, –0.06±0.10, are significantly higher than those of the unobscured quasars, -0.86±0.01. This result remains consistent across the redshift range from 1.5 to 2.5. Our results show that the dust-obscured quasars are at their maximal growth, consistent with the expectation from the merger-driven galaxy evolution scenario at the epoch quasar activities were most prominent in the cosmic history.

The kinematics of the Seyfert 2 galaxy NGC 5728 circumnuclear region

Son, D.-H.,Hyung, S.,Ferruit, P.,Pé,contal, E.,Lee, W.-B. Blackwell Publishing Ltd 2009 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.395 No.2

<P>ABSTRACT</P><P>We secured spectral images of the circumnuclear, 12 × 10 arcsec<SUP>2</SUP> region of the Seyfert 2 galaxy NGC 5728 with the Optically Adaptive System for Imaging Spectroscopy at the Canada–France–Hawaii Telescope 3.6-m telescope. The radial velocity distribution of the two bright zones, main central (C) core and north-west (NW) core, and strategically important points along the position angles, PA 33°, 90°, 123° and 143°, are analysed. The large-scale reconstructed monochromatic images of the Hα, Hβ, [O <SMALL>III</SMALL>] and [N <SMALL>II</SMALL>] lines show a bipolar morphology along PA ∼ 123°. The prominent elliptical ring is seen in the Hα and Hβ monochromatic images. Our analysis implies that this ring is rotating in the same clockwise direction as that of the galactic disc; this elliptical ring is in fact a projected result of a circular ring of radius ∼5.4 arcsec, with <I>i</I>∼ 50° (nearly aligned with the host galactic plane).</P><P>We used the [O <SMALL>III</SMALL>]5007 line profiles for a detailed analysis of kinematics in the circumnuclear region of the NGC 5728. The [O <SMALL>III</SMALL>]5007 line profiles reveal distinct kinematical structures. (1) The strongest component of Doppler peaks: two core components, consisting of the receding main C-core and the approaching NW-core with the radial velocities, <I>V</I><SUB>r</SUB>≃+250 and −240 (or −250) km s<SUP>−1</SUP>, respectively. These two cores consist of a roughly spherically symmetric distribution of the gas with radii of <I>r</I>∼ 1.0 arcsec (at <I>V</I><SUB>r</SUB>≃+240 km s<SUP>−1</SUP>) and 0.9 arcsec (at <I>V</I><SUB>r</SUB>≃−240 km s<SUP>−1</SUP>), respectively. Hints of the presence of inflows around these cores are observed. (2) The next strong line profile component: this component corresponds to the bipolar cone aligned PA ∼ 123°. (3) The reverse S-shaped kinematical boundary which runs through the double-peaked zone of 6–7 arcsec long in the galactic major axis direction is likely to be caused by a combination of the disc rotation of the host galaxy and the revolution of the two central cores.</P>