NGC 7172: an obscured active nucleus

Sharpies, Ray; Longmore, A. J.; Hawarden, T. G.; Carter, D.

doi:10.1093/mnras/208.1.15

Cited by 29 publications

(18 citation statements)

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“…A radio core was detected with VLA data (Unger et al 1987). At IR frequencies, Sharples et al (1984) found variations on timescales of about three months. The nucleus of this galaxy is not detected at UV frequencies with the OM (see Table A.1).…”

Section: Appendix B: Notes and Comparisons With Previous Results For mentioning

confidence: 95%

“…NGC 7172 is an early type galaxy located in the HCG 90 group, which shows dust lanes (Sharples et al 1984, see also Appendix C.1). Optically classified as a Seyfert 2 (see an optical spectrum in Appendix C.1), no broad lines have been observed in polarized light (Lumsden et al 2001).…”

Section: Appendix B: Notes and Comparisons With Previous Results For mentioning

confidence: 99%

“…Flux variations are indeed a property of AGN, and they have been reported at different frequencies for Seyfert 2s, such as in radio (Nagar et al 2002;Neff & de Bruyn 1983) or infrared (Sharples et al 1984;Hönig et al 2012). In the present work we used data from the OM onboard XMM-Newton to study UV variability.…”

Section: Flux Variationsmentioning

confidence: 99%

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X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

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Context. Variability across the electromagnetic spectrum is a property of active galactic nuclei (AGN) that can help constrain the physical properties of these galaxies. Nonetheless, the way in which the changes happen and whether they occur in the same way in every AGN are still open questions. Aims. This is the third in a series of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern(s) in a sample of optically selected Seyfert 2 galaxies. Methods. We use the 26 Seyfert 2s in the Véron-Cetty and Véron catalog with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source were simultaneously fitted, and we let different parameters vary in the model. Whenever possible, short-term variations from the analysis of the light curves and/or long-term UV flux variations were studied. We divided the sample into Compton-thick and Compton-thin candidates to account for the degree of obscuration. When transitions between Compton-thick and thin were obtained for different observations of the same source, we classified it as a changing-look candidate. Results. Short-term variability at X-rays was studied in ten cases, but variations are not found. From the 25 analyzed sources, 11 show long-term variations. Eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related to absorbers at hard X-rays are less common, and in many cases these variations are accompanied by variations in the nuclear continuum. At UV frequencies, only NGC 5194 (out of six sources) is variable, but the changes are not related to the nucleus. We report two changing-look candidates, MARK 273 and NGC 7319. Conclusions. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results. Within this scenario, the Compton-thick candidates are dominated by reflection, which suppresses their continuum, making them seem fainter, and they do not show variations (except MARK 3), while the Compton-thin and changing-look candidates do.

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Section: Appendix B: Notes and Comparisons With Previous Results For mentioning

confidence: 95%

Section: Appendix B: Notes and Comparisons With Previous Results For mentioning

confidence: 99%

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X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

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“…Marshall et al (1979) identified NGC 7172 with the X-ray source H2158-321. Rubin (1974) stated that NGC 7172 is a normal galaxy, however, Sharples et al (1984) analyzed X-ray, optical, NIR, and radio data and concluded that NGC 7172 is far more than a normal galaxy. They detected a steep rise in the continuum from J band up to the L band and an NIR excess typical of Seyfert galaxies.…”

Section: Ngc 7172mentioning

confidence: 99%

“…Additionally, they registered a spatial offset in the flux peaks between the optical and NIR data. According to Sharples et al (1984), the NIR flux peak is situated 2 −3 north of the optical flux peak. Veron-Cetty & Veron (1986) obtained optical spectra with the 3.6m ESO telescope.…”

Section: Ngc 7172mentioning

confidence: 99%

Unveiling the nucleus of NGC 7172

Smajić

Fischer

Zuther

et al. 2012

A&A

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Aims. We present the results of near-infrared (NIR) H + K European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 7172. We investigate the central 800 pc, concentrating on excitation conditions, morphology, and stellar content. NGC 7172 was selected from a sample of the ten nearest Seyfert 2 galaxies from the Veron-Cetty & Veron catalogue. All objects were chosen as test cases for adaptive optics (AO) assisted observations that allow a detailed study (at high spatial and spectral resolution) of the nuclear and host environments. NGC 7172 has a prominent dustlane crossing the central galaxy region from east to west, which makes it an ideal candidate to investigate the effect of obscuration by strong galactic extinction on (active) galaxies and their classification. Methods. The NIR is less influenced by dust extinction than optical light and is sensitive to the mass-dominating stellar populations. SINFONI integral field spectroscopy combines NIR imaging and spectroscopy and provides us with the opportunity to analyze several emission and absorption lines to investigate the stellar populations and ionization mechanisms over the 4 × 4 field of view (FOV). is predominantly inhabited by gas, dust, and an old K-M type giant stellar population. The gaseous, molecular, and stellar velocity maps show a related disturbed disk structure and similar velocities. Conclusions. We find evidence of nuclear activity located behind the prominent dustlane crossing the central region of the galaxy. The nucleus of NGC 7172, which is optically classified as a Seyfert 2 nucleus without any trace of broad emission lines, is a Seyfert 1 nucleus either surrounded by a molecular dust torus or hidden behind the strong galactic extinction. Our observation provides support for the unified model scheme. However, an evolutionary scenario cannot be ruled out by our observation.

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Surveys of Local AGN’s

Véron

1986

Structure and Evolution of Active Galactic Nuclei

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NGC 7172: an obscured active nucleus

Cited by 29 publications

References 0 publications

X-ray spectral variability of Seyfert 2 galaxies

X-ray spectral variability of Seyfert 2 galaxies

Unveiling the nucleus of NGC 7172

Surveys of Local AGN’s

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