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Journal articles on the topic 'Active Galactic Nuclei, quasars, emission lines, Seyfert'

Author: Grafiati
Published: 10 March 2023

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1

Zhou, Yipeng, Lei Hao, Peng Jiang, et al. "Discovery of a Radio-loud Narrow-line Seyfert 1 Galaxy at z = 0.9 Reddened with a Strong 2175 Å Bump." Astrophysical Journal 941, no. 2 (2022): 111. http://dx.doi.org/10.3847/1538-4357/aca085.

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Abstract We present a broadband spectrophotometric analysis of an unusual quasar, SDSS J160558.86+474300.1, at z = 0.9, found in a systematic search for reddened radio-loud narrow-line Seyfert 1 galaxies (NLS1s). J1605+4743 qualifies for the conventional definition of an NLS1 in its permitted emission line widths and Hβ/[O iii] flux ratio. It also shows strong Fe ii emissions. J1605+4743 has a steep radio spectrum. With a radio loudness of ∼150 (70) before (after) reddening correction, it is among the most radio-loud NLS1s discovered. In addition, the blueshifted emission lines are also found
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Marziani, Paola, Marco Berton, Swayamtrupta Panda, and Edi Bon. "Optical Singly-Ionized Iron Emission in Radio-Quiet and Relativistically Jetted Active Galactic Nuclei." Universe 7, no. 12 (2021): 484. http://dx.doi.org/10.3390/universe7120484.

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The issue of the difference between optical and UV properties of radio-quiet and radio-loud (relativistically “jetted”) active galactic nuclei (AGN) is a long standing one, related to the fundamental question of why a minority of powerful AGN possess strong radio emission due to relativistic ejections. This paper examines a particular aspect: the singly-ionized iron emission in the spectral range 4400–5600 Å, where the prominent HI Hβ and [Oiii]λλ4959,5007 lines are also observed. We present a detailed comparison of the relative intensity of Feii multiplets in the spectral types of the quasar
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Liu, Chenxu, Karl Gebhardt, Erin Mentuch Cooper, et al. "The Active Galactic Nuclei in the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX). I. Sample Selection." Astrophysical Journal Supplement Series 261, no. 2 (2022): 24. http://dx.doi.org/10.3847/1538-4365/ac6ba6.

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Abstract We present the first active galactic nuclei (AGN) catalog of the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX) observed between 2017 January and 2020 June. HETDEX is an ongoing spectroscopic survey (3500–5500 Å) with no target preselection based on magnitudes, colors or morphologies, enabling us to select AGN based solely on their spectral features. Both luminous quasars and low-luminosity Seyferts are found in our catalog. AGN candidates are selected with at least two significant AGN emission lines, such as the Lyα and C iv λ1549 line pair, or with a single broad emis
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Lyu, Jianwei, and George H. Rieke. "Polar Dust Emission in Quasar IR SEDs and Its Correlation with Narrow-line Regions." Astrophysical Journal Letters 940, no. 2 (2022): L31. http://dx.doi.org/10.3847/2041-8213/ac9e5c.

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Abstract Polar dust has been found to play an important role in the mid-infrared emission of nearby Seyfert nuclei. If and how often polar dust exists among the quasar population is unknown due to the lack of spatially resolved observations. In this Letter, we report correlations between the prominence of active galactic nucleus (AGN) forbidden line emission (commonly associated with the narrow-line region) and the dust mid-IR energy output among the archetypal Palomar-Green quasar sample and other bright type-1 AGNs drawn from the Sloan Digital Sky Survey, Spitzer, and Wide-field Infrared Sur
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Maitra, Chandreyee, Frank Haberl, Valentin D. Ivanov, Maria-Rosa L. Cioni, and Jacco Th van Loon. "Identification of AGN in the XMM-Newton X-ray survey of the SMC." Astronomy & Astrophysics 622 (January 24, 2019): A29. http://dx.doi.org/10.1051/0004-6361/201833663.

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Context. Finding active galactic nuclei (AGN) behind the Magellanic Clouds (MCs) is difficult because of the high stellar density in these fields. Although the first AGN behind the Small Magellanic Cloud (SMC) were reported in the 1980s, it is only recently that the number of AGN known behind the SMC has increased by several orders of magnitude. Aims. The mid-infrared colour selection technique has proven to be an efficient means of identifying AGN, especially obscured sources. The X-ray regime is complementary in this regard and we use XMM-Newton observations to support the identification of
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Jha, Vivek Kumar, Hum Chand, Vineet Ojha, Amitesh Omar, and Shantanu Rastogi. "A comparative study of the physical properties for a representative sample of Narrow and Broad-line Seyfert galaxies." Monthly Notices of the Royal Astronomical Society 510, no. 3 (2021): 4379–93. http://dx.doi.org/10.1093/mnras/stab3700.

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ABSTRACT We present a comparative study of the physical properties of a homogeneous sample of 144 Narrow line Seyfert 1 (NLSy1) and 117 Broad-line Seyfert 1 (BLSy1) galaxies. These two samples are in a similar luminosity and redshift range and have optical spectra available in the 16th data release of Sloan Digital Sky Survey (SDSS-DR16) and X-ray spectra in either XMM-NEWTON or ROSAT. Direct correlation analysis and a principal component analysis (PCA) have been performed using ten observational and physical parameters obtained by fitting the optical spectra and the soft X-ray photon indices
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7

Filippenko, Alexei V. "Low-Luminosity Active Galactic Nuclei." Symposium - International Astronomical Union 134 (1989): 495–512. http://dx.doi.org/10.1017/s0074180900141804.

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I review the basic properties of low-luminosity active galactic nuclei (LLAGNs) — objects in which activity similar to, but intrinsically milder than, that in QSOs and luminous Seyferts is believed to be present. Until recently, most LLAGNs were first recognized as such and studied at optical wavelengths, but evidence for activity and valuable information concerning its nature are now also being obtained in many other spectral ranges. Low-ionization nuclear emission-line regions (LINERs) are the most common LLAGNs; in a large fraction of them the emission lines come from clouds of gas probably
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8

Makishima, K., N. Iyomoto, Y. Ishisaki, and Y. Terashima. "X-Ray Observations of Low-Luminosity Active Galactic Nuclei." International Astronomical Union Colloquium 159 (1997): 52–53. http://dx.doi.org/10.1017/s0252921100039610.

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AbstractThrough X-ray observations with ASCA, low-luminosity active galactic nuclei have been found in at least seven near-by spiral galaxies. Some of them exhibit very intense, and possibly broad, Fe-K emission lines. Their time variability is relatively insignificant, in contrast to lowluminosity Seyfert galaxies.
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9

Foschini, Luigi, Matthew L. Lister, Heinz Andernach, et al. "A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei." Universe 8, no. 11 (2022): 587. http://dx.doi.org/10.3390/universe8110587.

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We considered the fourth catalog of gamma-ray point sources produced by the Fermi Large Area Telescope (LAT) and selected only jetted active galactic nuclei (AGN) or sources with no specific classification, but with a low-frequency counterpart. Our final list is composed of 2980 gamma-ray point sources. We then searched for optical spectra in all the available literature and publicly available databases, to measure redshifts and to confirm or change the original LAT classification. Our final list of gamma-ray emitting jetted AGN is composed of BL Lac Objects (40%), flat-spectrum radio quasars
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10

Moorwood, A. F. M., and E. Oliva. "Infrared [FeII] and H2 Line Emission in Active Galactic Nuclei." Symposium - International Astronomical Union 134 (1989): 365–71. http://dx.doi.org/10.1017/s007418090014135x.

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Infrared spectra around [FeII](1.644μm), H2 (v = 1-0 S(1) at 2.121μm) and Brγ (H 7-4 at 2.167μm) have been obtained of 35 emission line nuclei whose optical spectra range from pure HII regionlike to Seyfert 1. All three emission lines have been detected in a large fraction of those nuclei exhibiting starburst activity but not in “pure” Seyferts. The highest detection frequency, however, was found for composite nuclei showing evidence for both starburst and Seyfert activity. Several arguments suggest that both the [FeII] and H2 are shock excited and could be largely attributed to supernova remn
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11

Sales, D. A., M. G. Pastoriza та R. Riffel. "A 5.5–35 μm Spectral Analysis of Active Galactic Nuclei". Proceedings of the International Astronomical Union 5, S267 (2009): 137. http://dx.doi.org/10.1017/s1743921310005983.

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The spectroscopic properties of a sample of nine Seyfert 1, six NLS1, 26 Seyfert 2, and three starburst galaxies have been studied at mid-infrared wavelengths in order to determine if the frequency of detection of the brightest emission lines and the continuum shape are correlated with the degree of activity. The raw data were obtained from the Spitzer Infrared Spectrograph (IRS) archive and reduced with the pipeline (version 17.2). The spectra of the galaxies were grouped by type of activity. We conclude through this study that in general the continuum shape of the active galactic nuclei (AGN
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Genzel, R., D. Lutz, E. Sturm, L. Tacconi, N. Thatte, and A. Sternberg. "Infrared to Millimeter Spectroscopy and Imaging of Active Galactic Nuclei." International Astronomical Union Colloquium 159 (1997): 312–24. http://dx.doi.org/10.1017/s0252921100040355.

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AbstractObservations in the 1 µm to 1 cm wavelength band give important information on the physical processes occurring in and immediately around active galactic nuclei. Concentrating on recent results on ionic, atomic, and molecular emission lines, we discuss as examples the first ISO results on the nature of ultra-luminous infrared galaxies, and near-infrared and millimeter measurements of the central 100 parsecs of the Seyfert 2 galaxy NGC 1068.
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13

Persson, S. E. "High-density gas in bipolar outflow sources and active galactic nuclei." Canadian Journal of Physics 64, no. 4 (1986): 421–25. http://dx.doi.org/10.1139/p86-075.

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The highest density regions near the base of the outflow in young stellar objects with bipolar molecular outflows are discussed. Bright emission lines of Ca II and O I characterize the spectra and lead to estimates of n ~ 1010 cm−3, temperatures of a few thousand Kelvins, and mass motions of several hundred kilometres per second. Typically the rate of momentum transfer within this region fails by more than an order of magnitude to provide the force necessary to drive the molecular outflow on the parsec scale. The overall near-infrared spectra of these young stars are similar to those of certai
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14

Netzer, Hagai. "High-Energy Lines in Active Galactic Nuclei." International Astronomical Union Colloquium 159 (1997): 20–33. http://dx.doi.org/10.1017/s0252921100039567.

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AbstractThe recent observations of a highly ionized, X-ray absorbing gas in active galactic nuclei (AGN) suggest a new nuclear component, the so-called ‘warm absorber’. This gas is likely to be at a temperature of ~ 1–2 × 105 K and is most easily detected in the 0.5–10keV range, where several oxygen absorption edges are often observed.This review describes the properties of warm absorbers and the relation to other nuclear components, such as the broad-line emitting gas. The stability of the gas is a key issue and analysis shows that it is likely to be thermally stable, at the above mentioned t
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15

Doddamani, Vijayakumar H., and P. Vedavathi. "Ultraviolet Line-Continuum properties of Seyfert 1 galaxies and quasars." Proceedings of the International Astronomical Union 9, S304 (2013): 233–35. http://dx.doi.org/10.1017/s1743921314003883.

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AbstractActive galaxies are most luminous objects in the universe whose spectra are characterized by both permitted and forbidden emission line features. The spectra of Seyfert 1 galaxies and quasars contain strong and broad emission lines of wide ranging ionization potentials. The velocity widths of the lines range from a minimum of ≈ 500 km/s for narrow lines to a maximum of 20,000 km/sec for broad lines. The UV spectra of the active galaxies contain strong and broad emission lines such as Lyα, NV, SiIV, OIV], CIV, CIII] and MgII lines. The widths of the broad lines are attributed to the dif
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16

GHISELLINI, GABRIELE. "JETTED ACTIVE GALACTIC NUCLEI." International Journal of Modern Physics: Conference Series 08 (January 2012): 1–12. http://dx.doi.org/10.1142/s2010194512004345.

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Most of the electromagnetic output of blazars (BL Lac objects and Flat Spectrum Radio Quasars) comes out in the γ–ray band, making the Large Area Telescope [0.1–100 GeV] onboard the Fermi satellite and the Cherenkov telescopes crucial for gather crucial data and thus to understand their physics. These data are complemented by the observations of the Swift satellite in the X–ray and optical–UV bands, and by ground based optical and radio telescopes. This rich coverage of the spectrum allows a robust modelling, from which important trends start to emerge. In powerful sources we see the contribut
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17

Fricke, K. J., and W. Kollatschny. "Relationships of the Active Nucleus, Galaxy, and Environment." Symposium - International Astronomical Union 134 (1989): 425–44. http://dx.doi.org/10.1017/s0074180900141580.

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35 years ago Baade and Minkowski (1954) suggested that a galaxy collision - diagnosed from the peculiar appearance of the parent object and its strong emission lines - is responsible for the strong radio-source CygA. This was the first time that gravitational interactions between galaxies were suggested to trigger nuclear activity. Over the following decades after the detection of the quasars and the gradual realization that quasars, comparable to the Seyfert phenomenon, are events at the nuclei of seemingly isolated galaxies, the collision hypothesis was abandoned. Efforts concentrated on the
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18

García-Benito, Rubén, Enrique Pérez-Montero, Oli L. Dors, José M. Vlchez, Monica V. Cardaci, and Guillermo F. Hägele. "A new tool to derive chemical abundances in type-2 active galactic nuclei." Proceedings of the International Astronomical Union 15, S356 (2019): 61–65. http://dx.doi.org/10.1017/s1743921320002586.

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AbstarctWe present a new tool for the analysis of the optical emission lines of the gas in the Narrow Line Region (NLR) around Active Galactic Nuclei (AGNs). This new tool can be used in large samples of objects in a consistent way using different sets of optical emission-lines taking into the account possible variations from the O/H - N/O relation. The code compares certain observed emission-line ratios with the predictions from a large grid of photoionization models calculated under the most usual conditions in the NLR of AGNs to calculate the total oxygen abundance, nitrogen-to-oxygen ratio
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19

Binette, L., M. Villar Martín, G. Magris C., et al. "TEMPERATURE DISCREPANCY WITH PHOTOIONIZATION MODELS OF THE NARROW-LINE REGION." Revista Mexicana de Astronomía y Astrofísica 58, no. 1 (2022): 133–53. http://dx.doi.org/10.22201/ia.01851101p.2022.58.01.11.

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Using published work on the narrow-line region of Active Galactic Nuclei, a comparison is carried out among the [OIII] λ4363Å/5007Å ratios (ROIII) observed in quasars, Seyfert 2's and the spatially resolved ENLR plasma. Using the weak [ArIV] λ4711Å/λ4740Å doublet observed by Koski (1978) among Seyfert 2's, we find evidence of a Narrow-Line Region (NLR) populated by low density emission clouds (≲ 104 cm-3). After considering calculations of the [Ar] and [OIII] ratios that assume a powerlaw distribution of plasma densities, no evidence of collisional deexcitation is found. The plasma t
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Binette, L., M. Villar Martín, G. Magris C., et al. "TEMPERATURE DISCREPANCY WITH PHOTOIONIZATION MODELS OF THE NARROW-LINE REGION." Revista Mexicana de Astronomía y Astrofísica 58, no. 1 (2022): 133–53. http://dx.doi.org/10.22201/ia.01851101p.2022.58.01.11.

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Using published work on the narrow-line region of Active Galactic Nuclei, a comparison is carried out among the [OIII] λ4363Å/5007Å ratios (ROIII) observed in quasars, Seyfert 2's and the spatially resolved ENLR plasma. Using the weak [ArIV] λ4711Å/λ4740Å doublet observed by Koski (1978) among Seyfert 2's, we find evidence of a Narrow-Line Region (NLR) populated by low density emission clouds (≲ 104 cm-3). After considering calculations of the [Ar] and [OIII] ratios that assume a powerlaw distribution of plasma densities, no evidence of collisional deexcitation is found. The plasma t
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21

Kheirandish, Ali, Kohta Murase, and Shigeo S. Kimura. "High-energy Neutrinos from Magnetized Coronae of Active Galactic Nuclei and Prospects for Identification of Seyfert Galaxies and Quasars in Neutrino Telescopes." Astrophysical Journal 922, no. 1 (2021): 45. http://dx.doi.org/10.3847/1538-4357/ac1c77.

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Abstract Particles may be accelerated in magnetized coronae via magnetic reconnections and/or plasma turbulence, leading to high-energy neutrinos and soft γ-rays. We evaluate the detectability of neutrinos from nearby bright Seyfert galaxies identified by X-ray measurements. In the disk-corona model, we find that NGC 1068 is the most promising Seyfert galaxy in the Northern sky, where IceCube is the most sensitive, and show prospects for the identification of aggregated neutrino signals from Seyfert galaxies bright in X-rays. Moreover, we demonstrate that nearby Seyfert galaxies are promising
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22

Agostino, Christopher J., Samir Salim, Sara L. Ellison, Robert W. Bickley, and S. M. Faber. "A New Physical Picture for Active Galactic Nuclei Lacking Optical Emission Lines." Astrophysical Journal 943, no. 2 (2023): 174. http://dx.doi.org/10.3847/1538-4357/acac99.

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Abstract In this work, we use ∼500 low-redshift (z ∼ 0.1) X-ray active galactic nuclei (AGNs) observed by XMM-Newton and the Sloan Digital Sky Survey (SDSS) to investigate the prevalence and nature of AGNs that apparently lack optical emission lines (“optically dull AGNs”). Although one quarter of spectra appear absorption-line dominated in visual assessment, line extraction with robust continuum subtraction from the MPA/JHU catalog reveals usable [O iii] measurements in 98% of the sample, allowing us to study [O iii]-underluminous AGNs together with more typical AGNs in the context of the L [
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Bochkarev, Nikolay G. "1–3-Day Variations of the Broad Emission Lines of Seyfert Nuclei." Symposium - International Astronomical Union 121 (1987): 219–22. http://dx.doi.org/10.1017/s0074180900155172.

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One of the principal problems of investigation of AGNs is to understand the nature of the central objects and the physical processes which yield their gigantic luminosities. This requires us to consider the innermost parts of AGNs (3–30 gravitational radii, i.e. ≲ 1016 cm: angular size less than 1 milliarcsecond).1–3d variations of the relative shape of broad emission line profiles of active galactic nuclei (AGN) are perhaps the most informative probe of the innermost parts of AGNs (r = 1015–16 cm from the centre). Optimal objects for these observations are Sy 1.5 with strong variations of the
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24

Filippenko, Alexei V., and Wallace L. W. Sargent. "A Search for Low-Level Seyfert Activity in the 500 Brightest Northern Galaxies." Symposium - International Astronomical Union 121 (1987): 451–60. http://dx.doi.org/10.1017/s0074180900155470.

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A sensitive search for intrinsically faint Seyfert nuclei in the 500 brightest northern galaxies is being conducted with the Hale 5.08 m telescope. The primary aim is to extend the luminosity function of active galactic nuclei (AGNs) to lower luminosities. Thus far, we have detected Hα emission having full-width near zero-intensity (FWZI) ≳ 4000 km s−1 in a significant fraction (≳10%) of nearby galaxies. Moreover, the narrow emission lines in a given nucleus often have markedly different widths, as shown in detail for M81. Those associated with high critical densities are generally the broades
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den Brok, Jakob S., Michael J. Koss, Benny Trakhtenbrot, et al. "BASS. XXVIII. Near-infrared Data Release 2: High-ionization and Broad Lines in Active Galactic Nuclei*." Astrophysical Journal Supplement Series 261, no. 1 (2022): 7. http://dx.doi.org/10.3847/1538-4365/ac5b66.

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Abstract We present the BAT AGN Spectroscopic Survey (BASS) Near-infrared Data Release 2 (DR2), a study of 168 nearby ( z ¯ = 0.04 , z < 0.6) active galactic nuclei (AGN) from the all-sky Swift Burst Array Telescope X-ray survey observed with the Very Large Telescope (VLT)/X-shooter in the near-infrared (NIR; 0.8–2.4 μm). We find that 49/109 (45%) Seyfert 2 and 35/58 (60%) Seyfert 1 galaxies observed with VLT/X-shooter show at least one NIR high-ionization coronal line (CL; ionization potential χ > 100 eV). Comparing the emission of the [Si vi] λ1.9640 CL with the X-ray emission for the
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Valencia-S., Mónica, G. Busch, S. Smajić, et al. "AGN with faint broad line regions: Some ‘True’-Seyfert 2s might be Narrow Line Seyfert 1s." Proceedings of the International Astronomical Union 9, S304 (2013): 274–77. http://dx.doi.org/10.1017/s1743921314004050.

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AbstractThe intriguing existence of ‘True’-Seyfert 2s has opened a debate on the validity of the unified model of active galactic nuclei (AGN). These objects, also called ‘Naked’-AGN, seem to lack a broad line region. In some cases, their X-ray emission is unabsorbed, typical of Seyfert 1 galaxies, indicating a clear view toward the nucleus, but no broad lines are seen in the optical. In ‘True’-Seyfert 2s with higher column densities, observations of polarized light have failed to reveal the hidden broad emission. We performed high-resolution near-infrared integral-field observations of two ‘T
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27

Cheng, F. H., J. H. You, and M. Yan. "Cerenkov redshift and the redshift difference among broad emission lines of quasars and active galactic nuclei." Physics Letters A 138, no. 4-5 (1989): 165–67. http://dx.doi.org/10.1016/0375-9601(89)90020-0.

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Matsuoka, Kenta, Tohru Nagao, Alessandro Marconi, Roberto Maiolino, and Yoshiaki Taniguchi. "The AGN-Starburst Connection traced by the Nitrogen Abundance." Proceedings of the International Astronomical Union 8, S290 (2012): 273–74. http://dx.doi.org/10.1017/s1743921312019977.

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AbstractThe connection between the active galactic nuclei (AGNs) and star formation activity is one of the most important issues in understanding the coevolution of supermassive black holes (SMBHs) and galaxies. In our recent study, by using SDSS quasar spectra we found that the emission-line flux rations involving a nitrogen line correlate with the Eddington ratio. This correlation suggests that the mass accretion in quasars is associated with a post-starburst phase, when AGB stars enrich the interstellar medium with the nitrogen. Moreover, we focused on nitrogen-loud quasars, that have promi
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Kim, Minjin, Luis C. Ho, Carol J. Lonsdale, Mark Lacy, Andrew W. Blain, and Amy E. Kimball. "Evidence of AGN-driven Outflows in Young Radio Quasars Selected from the Wide-field Infrared Survey Explorer." Proceedings of the International Astronomical Union 9, S304 (2013): 347–48. http://dx.doi.org/10.1017/s1743921314004268.

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AbstractWe present near-infrared spectra of young radio quasars selected by cross-correlating the Wide-field Infrared Survey Explorer (WISE) all-sky survey catalog with the radio catalog [Faint Images of the Radio Sky at Twenty cm (FIRST) and NRAO VLA Sky Survey (NVSS)]. The objects have typical redshifts of z ≈ 2 and [O III] luminosities of 107 erg s−1 comparable to those of luminous quasars. The observed flux ratios of narrow emission lines indicate that these objects appear to be powered by active galactic nuclei. The [O III] line is broad, with full width at half maximum ~1300 to 2100 km s
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Fernández-Ontiveros, Juan A., and Teo Muñoz-Darias. "X-ray binary accretion states in active galactic nuclei? Sensing the accretion disc of supermassive black holes with mid-infrared nebular lines." Monthly Notices of the Royal Astronomical Society 504, no. 4 (2021): 5726–40. http://dx.doi.org/10.1093/mnras/stab1108.

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ABSTRACT Accretion states, which are universally observed in stellar mass black holes in X-ray binaries, might be expected in active galactic nuclei (AGN). This is the case at low luminosities, when the jet–corona coupling dominates the energy output in both populations. Previous attempts to extend this framework to a wider AGN population have been extremely challenging due to heavy hydrogen absorption of the accretion disc continuum and starlight contamination from the host galaxies. We present the luminosity–excitation diagram (LED), based on the [O iv]25.9 μm and [Ne ii]12.8 μm mid-infrared
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Saikia, Payaswini, Elmar Körding, Deanne L. Coppejans, et al. "15-GHz radio emission from nearby low-luminosity active galactic nuclei." Astronomy & Astrophysics 616 (August 2018): A152. http://dx.doi.org/10.1051/0004-6361/201833233.

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We present a sub-arcsec resolution radio imaging survey of a sample of 76 low-luminosity active galactic nuclei (LLAGN) that were previously not detected with the Very Large Array at 15 GHz. Compact, parsec-scale radio emission has been detected above a flux density of 40 μ Jy in 60% (45 of 76) of the LLAGN sample. We detect 20 out of 31 (64%) low-ionization nuclear emission-line region (LINER) nuclei, ten out of 14 (71%) low-luminosity Seyfert galaxies, and 15 out of 31 (48%) transition objects. We use this sample to explore correlations between different emission lines and the radio luminosi
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32

Hutsemékers, D., B. Agís González, F. Marin, D. Sluse, C. Ramos Almeida, and J. A. Acosta Pulido. "Polarization of changing-look quasars." Astronomy & Astrophysics 625 (May 2019): A54. http://dx.doi.org/10.1051/0004-6361/201834633.

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If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of l
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Singh, R., G. van de Ven, and K. Jahnke. "The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes." Proceedings of the International Astronomical Union 9, S304 (2013): 280–81. http://dx.doi.org/10.1017/s1743921314004074.

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AbstractGalaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus or AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher AGN-luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an A
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Pérez-Montero, E., O. L. Dors, J. M. Vílchez, R. García-Benito, M. V. Cardaci, and G. F. Hägele. "A bayesian-like approach to derive chemical abundances in type-2 active galactic nuclei based on photoionization models." Monthly Notices of the Royal Astronomical Society 489, no. 2 (2019): 2652–68. http://dx.doi.org/10.1093/mnras/stz2278.

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Abstract We present a new methodology for the analysis of the emission lines of the interstellar medium in the narrow-line regions around type-2 active galactic nuclei. Our aim is to provide a recipe that can be used for large samples of objects in a consistent way using different sets of optical emission lines that takes into the account possible variations from the O/H–N/O relation to use [N ii] lines. Our approach consists of a bayesian-like comparison between certain observed emission-line ratios sensitive to total oxygen abundance, nitrogen-to-oxygen ratio, and ionization parameter with t
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Qi, Yan-Qing, Tong Liu, Zhen-Yi Cai, and Mouyuan Sun. "Nucleosynthesis Contribution of Neutrino-dominated Accretion Flows to the Chemical Evolution of Active Galactic Nuclei." Astrophysical Journal 934, no. 1 (2022): 1. http://dx.doi.org/10.3847/1538-4357/ac7a43.

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Abstract Recent observations of quasars show high line-flux ratios in their broad emission lines and the ratios appear to be independent of redshift up to z ≳ 6, which indicates that the broad-line regions of these early quasars are surprisingly metal-rich. Here, we revisit the chemical evolution of high-redshift quasars by adding a new ingredient, i.e., the neutrino-dominated accretion flows (NDAFs) with outflows, on top of the conventional core-collapse supernovae (CCSNe). In the presence of the chemical contribution from NDAFs with outflows, the total metal mass (i.e., the summation of the
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Du, Pu, Shuo Zhai, and Jian-Min Wang. "Rarefied Broad-line Regions in Active Galactic Nuclei: Anomalous Responses in Reverberation Mapping and Implications for Weak Emission-line Quasars." Astrophysical Journal 942, no. 2 (2023): 112. http://dx.doi.org/10.3847/1538-4357/aca52a.

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Abstract Reverberation mapping (RM) is a widely used method for probing the physics of broad-line regions (BLRs) in active galactic nuclei (AGNs). There is increasing preliminary evidence that the RM behaviors of broad emission lines are influenced by BLR densities; however, the influences have not been investigated systematically from a theoretical perspective. In this paper, we adopt a locally optimally emitting cloud model and use CLOUDY to obtain the one-dimensional transfer functions of the prominent UV and optical emission lines for different BLR densities. We find that the influences of
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Berton, M., V. Braito, S. Mathur, et al. "Broadband X-ray observations of four gamma-ray narrow-line Seyfert 1 galaxies." Astronomy & Astrophysics 632 (December 2019): A120. http://dx.doi.org/10.1051/0004-6361/201935929.

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Narrow-line Seyfert 1 galaxies (NLS1s) is one of the few classes of active galactic nuclei harboring powerful relativistic jets and detected in γ-rays. NLS1s are well-known X-ray sources. While in non-jetted sources the origin of this X-ray emission may be a hot corona surrounding the accretion disk, in jetted objects, especially beamed ones, the contribution of corona and relativistic jet is difficult to disentangle without a proper sampling of the hard X-ray emission. For this reason, we observed with NuSTAR the first four NLS1s detected at high energy γ-rays. These data, along with XMM-Newt
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Ogawa, Shoji, Yoshihiro Ueda, Keiichi Wada, and Misaki Mizumoto. "Warm Absorbers in the Radiation-driven Fountain Model of Low-mass Active Galactic Nuclei." Astrophysical Journal 925, no. 1 (2022): 55. http://dx.doi.org/10.3847/1538-4357/ac3cb9.

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Abstract To investigate the origins of the warm absorbers in active galactic nuclei (AGNs), we study the ionization-state structure of the radiation-driven fountain model in a low-mass AGN and calculate the predicted X-ray spectra utilizing the spectral synthesis code Cloudy. The spectra show many absorption and emission line features originating in the outflowing ionized gas. The O viii 0.654 keV lines are produced mainly in the polar region much closer to the supermassive black hole than the optical narrow-line regions. The absorption measure distribution of the ionization parameter (ξ) at a
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Zhen-Guo, Ma. "Iron K Emission Lines in Seyfert(-Like) Active Galactic Nuclei: Revelation of a Rapidly Spinning Central Black Hole." Chinese Physics Letters 19, no. 10 (2002): 1537–39. http://dx.doi.org/10.1088/0256-307x/19/10/342.

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Marziani, Paola, Ascension del Olmo, Jaime Perea, Mauro D’Onofrio, and Swayamtrupta Panda. "Broad UV Emission Lines in Type-1 Active Galactic Nuclei: A Note on Spectral Diagnostics and the Excitation Mechanism." Atoms 8, no. 4 (2020): 94. http://dx.doi.org/10.3390/atoms8040094.

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This paper reviews several basic emission properties of the UV emission lines observed in the spectra of quasars and type-1 active galactic nuclei, mainly as a function of the ionization parameter, metallicity, and density of the emitting gas. The analysis exploits a general-purpose 4D array of the photoionization simulations computed using the code CLOUDY, covering ionization parameter in the range 10−4.5–10+1.0, hydrogen density nH∼107–1014 cm−3, metallicity Z between 0.01 and 100 Z⊙, and column density in the range 1021–1023 cm−2. The focus is on the most prominent UV emission lines observe
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41

Xie, Yanxia, and Luis C. Ho. "The Ionization and Destruction of Polycyclic Aromatic Hydrocarbons in Powerful Quasars." Astrophysical Journal 925, no. 2 (2022): 218. http://dx.doi.org/10.3847/1538-4357/ac32e2.

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Abstract We reanalyze the mid-infrared (5–40 μm) Spitzer spectra of 86 low-redshift (z < 0.5) Palomar–Green quasars to investigate the nature of polycyclic aromatic hydrocarbon (PAH) emission and its utility as a star formation rate (SFR) indicator for the host galaxies of luminous active galactic nuclei (AGNs). We decompose the spectra with our recently developed template-fitting technique to measure PAH fluxes and upper limits, which we interpret using mock spectra that simulate the effects of AGN dilution. While luminous quasars can severely dilute and affect the detectability of emissio
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Guo, Hengxiao, Aaron J. Barth, Kirk T. Korista, et al. "The Paschen Jump as a Diagnostic of the Diffuse Nebular Continuum Emission in Active Galactic Nuclei*." Astrophysical Journal 927, no. 1 (2022): 60. http://dx.doi.org/10.3847/1538-4357/ac4bc6.

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Abstract Photoionization modeling of active galactic nuclei (AGN) predicts that diffuse continuum (DC) emission from the broad-line region makes a substantial contribution to the total continuum emission from ultraviolet through near-infrared wavelengths. Evidence for this DC component is present in the strong Balmer jump feature in AGN spectra, and possibly from reverberation measurements that find longer lags than expected from disk emission alone. However, the Balmer jump region contains numerous blended emission features, making it difficult to isolate the DC emission strength. In contrast
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43

Park, Daeseong, Aaron J. Barth, Luis C. Ho та Ari Laor. "A New Iron Emission Template for Active Galactic Nuclei. I. Optical Template for the Hβ Region*". Astrophysical Journal Supplement Series 258, № 2 (2022): 38. http://dx.doi.org/10.3847/1538-4365/ac3f3e.

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Abstract We present a new empirical template for iron emission in active galactic nuclei (AGNs) covering the 4000–5600 Å range. The new template is based on a spectrum of the narrow-line Seyfert 1 galaxy Mrk 493 obtained with the Hubble Space Telescope. In comparison with the canonical iron template object I Zw 1, Mrk 493 has narrower broad-line widths, lower reddening, and a less extreme Eddington ratio, making it a superior choice for template construction. We carried out a multicomponent spectral decomposition to produce a template incorporating all the permitted and forbidden lines of Fe i
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Dors, O. L., M. Contini, R. A. Riffel, et al. "Chemical abundances of Seyfert 2 AGNs – IV. Composite models calculated by photoionization + shocks." Monthly Notices of the Royal Astronomical Society 501, no. 1 (2020): 1370–83. http://dx.doi.org/10.1093/mnras/staa3707.

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ABSTRACT We build detailed composite models of photoionization and shock ionization based on the suma code to reproduce emission lines emitted from the Narrow Line Regions (NLR) of Seyfert 2 nuclei. The aim of this work is to investigate diagram active galactic nucleus (AGN) positions according to shock parameters, shock effects on the gas temperature and ionization structures and derive a semi-empirical abundance calibration based on emission-line ratios little sensitive to the shock presence. The models were used to reproduce optical (3000 < λ(Å) < 7000) emission line intensiti
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Temple, Matthew J., Gary J. Ferland, Amy L. Rankine, et al. "Fe iii emission in quasars: evidence for a dense turbulent medium." Monthly Notices of the Royal Astronomical Society 496, no. 3 (2020): 2565–76. http://dx.doi.org/10.1093/mnras/staa1717.

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ABSTRACT Recent improvements to atomic energy-level data allow, for the first time, accurate predictions to be made for the Fe iii line emission strengths in the spectra of luminous, $L_\text{bol}\simeq 10^{46}\!-\!10^{48}\mbox{${\rm \, erg}{\rm \, s}^{-1}\, $}$, active galactic nuclei. The Fe iii emitting gas must be primarily photoionized, consistent with observations of line reverberation. We use cloudy models exploring a wide range of parameter space, together with ≃26 000 rest-frame ultraviolet spectra from the Sloan Digital Sky Survey, to constrain the physical conditions of the line emi
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46

Nakata, Ryo, Kiyoshi Hayashida, Hirofumi Noda, Tomokage Yoneyama, Hironori Matsumoto, and Masatoshi Imanishi. "Spatially resolved X-ray spectroscopy of the archetype type 2 active galactic nucleus NGC 1068 with Chandra." Publications of the Astronomical Society of Japan 73, no. 2 (2021): 338–49. http://dx.doi.org/10.1093/pasj/psab001.

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Abstract We investigate spatial distributions of iron Kα (Fe-Kα) lines in the cental 100 pc of the Seyfert 2 galaxy NGC 1068 observed with Chandra. The spatial distributions of Fe-Kα lines, neutral and highly ionized, around the center of the galactic nucleus are not isotropic, as consistently confirmed in both image and spectral analyses. The hydrogen number density of the gas clouds responsible for the neutral Fe-Kα line emission is estimated to be 102–103 cm−3 for the sampled regions near the galactic core. The photo-ionization model, where iron is assumed to be ionized by X-rays from the g
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47

Joh, Kazuma, Tohru Nagao, Keiichi Wada, Koki Terao, and Takuji Yamashita. "Do gas clouds in narrow-line regions of Seyfert galaxies come from their nuclei?" Publications of the Astronomical Society of Japan 73, no. 4 (2021): 1152–65. http://dx.doi.org/10.1093/pasj/psab065.

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Abstract The narrow-line region (NLR) consists of gas clouds ionized by the strong radiation from the active galactic nucleus (AGN), distributed in the spatial scale of AGN host galaxies. The strong emission lines from the NLR are useful to diagnose physical and chemical properties of the interstellar medium in AGN host galaxies. However, the origin of the NLR is unclear; the gas clouds in NLRs may originally be in the host and photoionized by the AGN radiation, or they may be transferred from the nucleus with AGN-driven outflows. In order to study the origin of the NLR, we systematically inve
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Greenwell, Claire, Poshak Gandhi, Daniel Stern, et al. "A candidate optically quiescent quasar lacking narrow emission lines." Monthly Notices of the Royal Astronomical Society: Letters 503, no. 1 (2021): L80—L84. http://dx.doi.org/10.1093/mnrasl/slab019.

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ABSTRACT Many active galactic nuclei (AGN) surveys rely on optical emission line signatures for robust source classification. There are, however, examples of luminous AGN candidates lacking such signatures, including those from the narrow-line region, which are expected to be less susceptible to classical nuclear (torus) obscuration. Here, we seek to formalize this subpopulation of AGN with a prototypical candidate, SDSS J075139.06+402810.9. This shows infrared (IR) colours typical for AGN, an optical spectrum dominated by an early type galaxy continuum, an [O iii] λ5007Å limiting flux about t
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Gupta, N., G. Shukla, R. Srianand, et al. "MALS SALT-NOT Survey of MIR-selected Powerful Radio-bright AGN at 0 < z < 3.5." Astrophysical Journal 929, no. 1 (2022): 108. http://dx.doi.org/10.3847/1538-4357/ac4220.

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Abstract We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased sample of powerful radio-bright (&gt;200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median z = 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δi = 0.6 mag) and redder (Δ(g−i) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar pop
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Green, Paul J., Lina Pulgarin-Duque, Scott F. Anderson, et al. "The Time Domain Spectroscopic Survey: Changing-look Quasar Candidates from Multi-epoch Spectroscopy in SDSS-IV." Astrophysical Journal 933, no. 2 (2022): 180. http://dx.doi.org/10.3847/1538-4357/ac743f.

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Abstract Active galactic nuclei (AGN) can vary significantly in their rest-frame optical/UV continuum emission, and with strong associated changes in broad line emission, on much shorter timescales than predicted by standard models of accretion disks around supermassive black holes. Most such changing-look or changing-state AGN—and at higher luminosities, changing-look quasars (CLQs)—have been found via spectroscopic follow-up of known quasars showing strong photometric variability. The Time Domain Spectroscopic Survey of the Sloan Digital Sky Survey IV (SDSS-IV) includes repeat spectroscopy o
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