Narrow-line AGN in the ISO-2MASS survey

Leipski, C.; Haas, Martín; Meusinger, H.; Siebenmorgen, R.; Chini, R.; Drass, H.; Albrecht, M.; Wilkes, B. J.; Huchra, J. P.; Ott, Stephan; Césarsky, C. J.; Cutri, R. M.

doi:10.1051/0004-6361:20066168

Cited by 10 publications

(12 citation statements)

References 37 publications

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“…J2341 turns out to be almost a factor of 10 less luminous in the MIR than type-2 AGN at similar redshift which were found in the ISO-2MASS survey (Leipski et al 2007).…”

Section: The Quasarsupporting

confidence: 57%

The reddest ISO-2MASS quasar

Leipski¹,

Haas²,

Siebenmorgen

et al. 2007

A&A

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Context. While there is growing consensus on the existence of numerous dust-enshrouded red quasars, their discovery and detailed exploration is still an observational challenge. In the course of the near-mid-infrared AGN search combining the 6.7 µm ISOCAM Parallel Survey and 2MASS we have discovered 24 type-1 quasars about a third of which are too red to be discriminated by optical/UV search techniques. Aims. Here we report on a detailed case study of the reddest type-1 quasar of our sample, 2MASS J23410667−0914327 (for short J2341) at redshift z = 0.236 with M K = −25.8 and J − K s = 1.95. This source has a very red optical appearance but lacks the far-infrared emission typically seen in known dust enshrouded AGN. Therefore we here explore its enigmatic nature. Methods. We performed spectroscopy in the optical with VLT/FORS1 and in the mid-infrared (5-38 µm) with the Spitzer Space Telescope as well as near-infrared (NIR) imaging with ISPI at the CTIO 4m-telescope. To explain the red optical continuum of the quasar we examine nuclear dust reddening of an intrinsically blue quasar continuum in combination with dilution by stellar light of the host galaxy. Results. The optical and NIR observations reveal a star forming emission-line galaxy at the same redshift as the quasar with a projected linear separation of 1. 8 (6.7 kpc). The quasar and its companion are embedded in diffuse extended continuum emission. Compared with its companion the quasar exhibits redder optical-NIR colours, which we attribute to hot nuclear dust. The mid-infrared spectrum shows only few emission lines superimposed on a power-law spectral energy distribution typically seen in type-1 AGN. However, the lack of strong far-infrared emission suggests that our potentially interacting object contains much less gas and dust and is in a stage different from dust reddened ULIRG-AGN like Mrk 231. The optical spectrum shows signatures for reddening in the emission-lines and no post-starburst stellar population is detected in the host galaxy of the quasar. The optical continuum emission of the active nucleus appears absorbed and diluted. Conclusions. Even the combination of absorption and host dilution is not able to match J2341 with standard quasar templates. While the BLR shows only a rather moderate absorption of E B−V = 0.3, the continuum shorter than 4500 Å requires strong obscuration with E B−V = 0.7, clearly exceeding the constraints from the low upper limit on the silicate 9.7 µm absorption. This leads us to conclude that the continuum of the quasar J2341 is intrinsically redder than that of typical quasars.

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“…J2341 turns out to be almost a factor of 10 less luminous in the MIR than type-2 AGN at similar redshift which were found in the ISO-2MASS survey (Leipski et al 2007).…”

Section: The Quasarsupporting

confidence: 57%

The reddest ISO-2MASS quasar

Leipski¹,

Haas²,

Siebenmorgen

et al. 2007

A&A

Self Cite

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“…They found that ∼45% of the sources have strong silicate absorption with S 9.7 > 0.5. Differing from Leipski et al (2007), Goulding et al (2012) argued that the dominant contribution to the observed silicate absorption is made by the dust located in the host galaxy and not necessarily in a compact obscuring torus surrounding the central engine. We note that the discussions on the low A V /Δτ 9.7 ratio presented in this work are based on the assumption that both the optical extinction and the silicate absorption are from the torus.…”

Section: Discussionmentioning

confidence: 99%

Dust in Active Galactic Nuclei: Anomalous Silicate to Optical Extinction Ratios?

Lyu

Hao

2014

ApJ

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Dust plays a central role in the unification theory of active galactic nuclei (AGNs). However, little is known about the nature (e.g., size, composition) of the dust that forms a torus around the AGN. In this Letter, we report a systematic exploration of the optical extinction (A V ) and the silicate absorption optical depth (Δτ 9.7 ) of 110 type 2 AGNs. We derive A V from the Balmer decrement based on the Sloan Digital Sky Survey data, and Δτ 9.7 from the Spitzer/InfraRed Spectrograph data. We find that with a mean ratio of A V /Δτ 9.7 5.5, the optical-to-silicate extinction ratios of these AGNs are substantially lower than that of the Galactic diffuse interstellar medium (ISM) for which A V /Δτ 9.7 ≈ 18.5. We argue that the anomalously low A V /Δτ 9.7 ratio could be due to the predominance of larger grains in the AGN torus compared to that in the Galactic diffuse ISM.

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“…We refer to these sources as elusive AGNs (Maiolino et al 2003). These sources belong to the SF class and might have many properties in common with known categories of elusive AGNs found in the literature, such as the optically dull AGNs discovered in optical samples (Maiolino et al 2003;Elvis et al 1981;Rigby et al 2005), the X-ray bright optically normal galaxies (XBONGs) discovered in X-ray samples (Comastri et al 2002), and the type 3 QSOs found in IR-selected samples Leipski et al 2007). The rich taxonomy of these categories reflects mostly the wavelengths at which they were discovered, while the scenarios proposed to explain their nature are similar.…”

Section: The Nature Of Elusive Agnsmentioning

confidence: 97%

Spectral Energy Distributions of Hard X‐Ray Selected Active Galactic Nuclei in theXMM‐NewtonMedium Deep Survey

Polletta

Tajer

Maraschi

et al. 2007

ApJ

836

1,088

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We present the SEDs of a hard X-ray selected sample containing 136 sources with F 2Y10 keV > 10 À14 erg cm À2 s À1 ; 132 are AGNs. The sources are detected in a 1 deg 2 area of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with (1 þ z) ¼ 0:11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17 þ9 À6 % of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33 þ6 À1 %) and AGN2 (50 þ6 À11 %). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L 3Y20 m /L corr 0:5Y10 keV ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-rayYradio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E > 10 keV are too faint to be detected even in the deepest current radio surveys.

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Narrow-line AGN in the ISO-2MASS survey

Cited by 10 publications

References 37 publications

The reddest ISO-2MASS quasar

The reddest ISO-2MASS quasar

Dust in Active Galactic Nuclei: Anomalous Silicate to Optical Extinction Ratios?

Spectral Energy Distributions of Hard X‐Ray Selected Active Galactic Nuclei in theXMM‐NewtonMedium Deep Survey

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