Elusive active galactic nuclei

Maiolino, R.; Comastri, A.; Gilli, R.; Nagar, N. M.; Bianchi, S.; Böker, Torsten; Colbert, E. J. M.; Krabbe, A.; Marconi, A.; Matt, Giorgio; Salvati, M.

doi:10.1046/j.1365-8711.2003.07036.x

Cited by 148 publications

(161 citation statements)

References 41 publications

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“…Large amounts of OH can be formed through dissociative recombination of H 3 O + , which in turn is formed through the sequence O + → OH + → H 2 O + → H 3 O + (Maloney et al 1996); as we will report in a forthcoming paper, these molecular ions are indeed detected in absorption from excited levels in both sources. However, both NGC 4418 and Arp 220 have strong X-ray deficits relative to the FIR emission (Maiolino et al 2003;Iwasawa et al 2005). From the X-ray flux reported by Maiolino et al (2003) from NGC 4418, F X (0.3−8 keV) = 1.5 erg s −1 cm −2 , and assuming a point-like X-ray source located at the center of our C core component, the X-ray flux at the surface of C core (r ∼ 10 pc) is ∼0.1 erg s −1 cm −2 ; a similar estimate for Arp 220 with the fluxes reported by Iwasawa et al (2001) yields an X-ray (0.5−10 keV) flux at the surface of the western nucleus (r ∼ 50 pc) of ∼0.5 erg s −1 cm −2 .…”

Section: X-and Cosmic Raysmentioning

confidence: 99%

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

González-Alfonso

Fischer

Graciá-Carpio

et al. 2012

A&A

157

166

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Full range Herschel/PACS spectroscopy of the (ultra)luminous infrared galaxies NGC 4418 and Arp 220, observed as part of the SHINING key programme, reveals high excitation in H 2 O, OH, HCN, and NH 3 . In NGC 4418, absorption lines were detected with E lower > 800 K (H 2 O), 600 K (OH), 1075 K (HCN), and 600 K (NH 3 ), while in Arp 220 the excitation is somewhat lower. While outflow signatures in moderate excitation lines are seen in Arp 220 as have been seen in previous studies, in NGC 4418 the lines tracing its outer regions are redshifted relative to the nucleus, suggesting an inflow withṀ 12 M yr −1 . Both galaxies have compact and warm (T dust 100 K) nuclear continuum components, together with a more extended and colder component that is much more prominent and massive in Arp 220. A chemical dichotomy is found in both sources: on the one hand, the nuclear regions have high H 2 O abundances, ∼10 −5 , and high HCN/H 2 O and HCN/NH 3 column density ratios of 0.1−0.4 and 2−5, respectively, indicating a chemistry typical of evolved hot cores where grain mantle evaporation has occurred. On the other hand, the high OH abundance, with OH/H 2 O ratios of ∼0.5, indicates the effects of X-rays and/or cosmic rays. The nuclear media have high surface brightnesses ( 10 13 L /kpc 2 ) and are estimated to be very thick (N H 10 25 cm −2 ). While NGC 4418 shows weak absorption in H 18 2 O and 18 OH, with a 16 O-to-18 O ratio of 250−500, the relatively strong absorption of the rare isotopologues in Arp 220 indicates 18 O enhancement, with 16 O-to-18 O of 70−130. Further away from the nuclear regions, the H 2 O abundance decreases to 10 −7 and the OH/H 2 O ratio is reversed relative to the nuclear region to 2.5−10. Despite the different scales and morphologies of NGC 4418, Arp 220, and Mrk 231, preliminary evidence is found for an evolutionary sequence from infall, hot-core like chemistry, and solar oxygen isotope ratio to high velocity outflow, disruption of the hot core chemistry and cumulative high mass stellar processing of 18 O.

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Section: X-and Cosmic Raysmentioning

confidence: 99%

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

González-Alfonso

Fischer

Graciá-Carpio

et al. 2012

A&A

157

166

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“…However, only about 30% of AGN are radio-loud (Urry & Padovani 1995). Hard X-rays enabled the discoveries of elusive AGN completely hidden in starburst nuclei (Maiolino et al 2003). However, there exists also a significant fraction of X-ray faint AGN (Wilkes et al 2002), suggesting that also other search techniques should be considered.…”

Section: Introductionmentioning

confidence: 99%

The ISO-2MASS AGN survey: on the type-1 sources

Leipski¹,

Haas²,

Meusinger

et al. 2005

A&A

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Abstract. We combined the ISOCAM Parallel Mode Survey at 6.7 µm (LW2 filter) with the Two Micron All Sky Survey in order to obtain a powerful tool to search for AGN independent of dust extinction. Using moderate colour criteria H − K > 0.5 and K − LW2 > 2.7 we have selected a sample of 77 AGN candidates in an effective area of ∼10 square degrees. By means of optical spectroscopy we find 24 (∼30%) type-1 QSOs at redshifts 0.1 < z < 2.3; nine of them have z > 0.8. About one third of the ISO-2MASS QSOs show so red optical colours, that they are missed in optical and UV AGN surveys like SDSS, 2DF, or HES. With a surface density of about 2 deg −2 down to R < 18 mag the ISO-2MASS QSOs outnumber the 1.35 deg −2 of the SDSS quasar survey by 50%; we find a combined optical-IR QSO surface density of 2.7 deg −2 . Since only two of the ISO-2MASS QSOs have also J − K > 2, the inclusion of the ISO mid-infrared photometry significantly extends the capabilities of the pure 2MASS red AGN survey. We suggest that the newly found red AGN resemble young members of the quasar population, and that quasars spend much of their lifetime in a dust enshrouded phase.

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“…Fiore et al 2000;Comastri et al 2002;La Franca et al 2005 and references therein). Combining Chandra and archival X-ray data, Maiolino et al (2003) have found that the local total density of AGN may be a factor ∼2 higher than estimated from optical spectroscopic surveys. Up to now the exact proportion of AGN-dominated MIR galaxies is actually not known.…”

Section: Introductionmentioning

confidence: 94%

“…Indeed higher luminosities are typical of AGN activity (see e.g. Ranalli et al 2003;Maiolino et al 2003), while the most X-rayluminous star-forming galaxy known, NGC 3256, has a total X-ray luminosity of L X 8 × 10 41 erg s −1 (Lira et al 2002).…”

Section: X-ray Properties Of the 15 µM Sourcesmentioning

confidence: 99%

AGN counts at 15$\mu{\rm m}$

Franca¹,

Puccetti²,

Sacchi³

et al. 2007

A&A

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Context. The counts of galaxies and AGN in the mid infra-red (MIR) bands are important instruments for studying their cosmological evolution. However, the classic spectral line ratios techniques can become misleading when trying to properly separate AGN from starbursts or even from apparently normal galaxies. Aims. We use X-ray band observations to discriminate AGN activity in previously classified MIR-selected starburst galaxies and to derive updated AGN1 and (Compton thin) AGN2 counts at 15 µm. Methods. XMM observations of the ELAIS-S1 15 µm sample down to flux limits ∼2 × 10 −15 erg cm −2 s −1 (2-10 keV band) were used. We classified as AGN all those MIR sources with a unabsorbed 2-10 keV X-ray luminosity higher that ∼10 42 erg s −1 . Results. We find that at least about 13 ± 6% of the previously classified starburst galaxies harbor an AGN. According to these figures, we provide an updated estimate of the counts of AGN1 and (Compton thin) AGN2 at 15 µm. It turns out that at least 24% of the extragalactic sources brighter than 0.6 my at 15 µm are AGN (∼13% contribution to the extragalactic background produced at fluxes brighter than 0.6 mJy).

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Elusive active galactic nuclei

Cited by 148 publications

References 41 publications

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

The ISO-2MASS AGN survey: on the type-1 sources

AGN counts at 15$\mu{\rm m}$

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Elusive active galactic nuclei

Cited by 148 publications

References 41 publications

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H218O, OH,18OH, O I, HCN, and NH3

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H218O, OH,18OH, O I, HCN, and NH3

The ISO-2MASS AGN survey: on the type-1 sources

AGN counts at 15$\mu{\rm m}$

Contact Info

Product

Resources

About

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃