Millimeter Interferometric HCN(1-0) and HCO<sup>+</sup>(1-0) Observations of Luminous Infrared Galaxies

Imanishi, Masatoshi; Nakanishi, Koichiro; Tamura, Motohide; Oi, Nagisa; Kohno, Kotaro

doi:10.1086/523598

Cited by 107 publications

(178 citation statements)

References 82 publications

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“…Line ratios of the dense gas tracers HCN, HNC, and HCO + have often been used in the literature to investigate the nature of the dominant energy source in LIRGs, either a compact starburst or an AGN (e.g., Imanishi et al 2007;Aalto et al 2007a;Krips et al 2008;Costagliola et al 2011).…”

Section: Standard Line Ratios: Hcn Hnc and Hco +mentioning

confidence: 99%

“…Line-ratio surveys have mostly focused on the brightest transitions of dense-gas tracers such as HCN, HNC, and HCO + , trying to compare the observed values to chemical models of photon-dominated regions (PDRs), X-ray dominated regions (XDRs), and hot-cores (e.g., Imanishi et al 2007;Loenen et al 2007;Krips et al 2008;Baan et al 2008;Costagliola et al 2011;Viti et al 2014). However, the line ratios of such bright tracers show only small variations and their theoretical interpretation is still controversial (e.g., Kohno et al 2001;Aalto et al 2007b;Meijerink et al 2007;Costagliola et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies

Costagliola

Sakamoto

Müller

et al. 2015

A&A

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Context. Extragalactic observations allow the study of molecular chemistry and excitation under physical conditions which may differ greatly from those found in the Milky Way. The compact, obscured nuclei (CON) of luminous infrared galaxies (LIRG) combine large molecular columns with intense infrared (IR), ultra-violet (UV), and X-radiation and represent ideal laboratories for the study of the chemistry of the interstellar medium (ISM) under extreme conditions. Aims. Our aim was to obtain for the first time a multi-band spectral scan of a LIRG, and to derive molecular abundances and excitation to be compared to other Galactic and extragalactic environments. Methods. We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418, spanning a total of 70.7 GHz in bands 3, 6, and 7. We use a combined local thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to identify the molecular species and to derive column densities and excitation temperatures. We derive molecular abundances and compare them with other Galactic and extragalactic sources by means of a principal component analysis. Results. We detect 317 emission lines from a total of 45 molecular species, including 15 isotopic substitutions and 6 vibrationally excited variants. Our LTE/NLTE fit find kinetic temperatures from 20 to 350 K, and densities between 10 5 and 10 7 cm −3 . The spectrum is dominated by vibrationally excited HC 3 N, HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find that the chemistry of NCG 4418 is characterized by high abundances of HC 3 N, SiO, H 2 S, and c-HCCCH but a low CH 3 OH abundance. A principal component analysis shows that NGC 4418 and Arp 220 share very similar molecular abundances and excitation, which clearly set them apart from other Galactic and extragalactic environments. Conclusions. Our spectral scan confirms that the chemical complexity in the nucleus of NGC 4418 is one of the highest ever observed outside our Galaxy. The similar molecular abundances observed toward NCG 4418 and Arp 220 are consistent with a hot gas-phase chemistry, with the relative abundances of SiO and CH 3 OH being regulated by shocks and X-ray driven dissociation. The bright emission from vibrationally excited species confirms the presence of a compact IR source, with an effective diameter smaller than 5 pc and brightness temperatures higher than 350 K. The molecular abundances and the vibrationally excited spectrum are consistent with a young AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind of chemistry and excitation, typical of CON. Because of the narrow line widths and bright molecular emission, NGC 4418 is the ideal target for further studies of the chemistry in CONs.

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Section: Standard Line Ratios: Hcn Hnc and Hco +mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies

Costagliola

Sakamoto

Müller

et al. 2015

A&A

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“…The dense molecular gas tracer HCN has been found to be enhanced (relative to HCO+ and CO) in systems with dominant AGNs (e.g., Imanishi et al 2007). Privon et al (2015) have shown that some pure starburst and composite sources show similarly enhanced HCN emission.…”

Section: Optical and Radio Emissionmentioning

confidence: 99%

NuSTAR UNVEILS A HEAVILY OBSCURED LOW-LUMINOSITY ACTIVE GALACTIC NUCLEUS IN THE LUMINOUS INFRARED GALAXY NGC 6286

Ricci

Bauer

Treister

et al. 2016

ApJ

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We report the detection of a heavily obscured active galactic nucleus (AGN) in the luminous infrared galaxy (LIRG) NGC 6286 identified in a 17.5 ks Nuclear Spectroscopic Telescope Array observation. The source is in an early merging stage and was targeted as part of our ongoing NuSTAR campaign observing local luminous and ultraluminous infrared galaxies in different merger stages. NGC 6286 is clearly detected above 10 keV and by including the quasi-simultaneous Swift/XRT and archival XMM-Newton and Chandra data, we find that the source is heavily obscured (N H ;(0.95−1.32) × 10 24 cm −2 ) with a column density consistent with being Compton-thick (CT, N log cm 24The AGN in NGC 6286 has a low absorption-corrected luminosity (L 2−10 keV ∼ 3 −20 × 10 41 erg s −1 ) and contributes 1% to the energetics of the system. Because of its low luminosity, previous observations carried out in the soft X-ray band (<10 keV) and in the infrared did not notice the presence of a buried AGN. NGC 6286 has multiwavelength characteristics typical of objects with the same infrared luminosity and in the same merger stage, which might imply that there is a significant population of obscured low-luminosity AGNs in LIRGs that can only be detected by sensitive hard X-ray observations.

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“…At millimeter wavelengths, HCN has been found to be enhanced over HCO + in ULIRGs (Graciá-Carpio et al 2006) and in Seyferts over starbursts (Imanishi et al 2007), and this has been proposed to be a diagnostic of AGN activity. Costagliola et al (2011), however, argue that for high densities and columns HCO + is expected to be stronger than HCN in XDRs (Meijerink et al 2007).…”

Section: Model Uncertaintiesmentioning

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

154

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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Millimeter Interferometric HCN(1-0) and HCO⁺(1-0) Observations of Luminous Infrared Galaxies

Cited by 107 publications

References 82 publications

Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies

Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies

NuSTAR UNVEILS A HEAVILY OBSCURED LOW-LUMINOSITY ACTIVE GALACTIC NUCLEUS IN THE LUMINOUS INFRARED GALAXY NGC 6286

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

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Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies

Cited by 107 publications

References 82 publications

Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies

Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies

NuSTAR UNVEILS A HEAVILY OBSCURED LOW-LUMINOSITY ACTIVE GALACTIC NUCLEUS IN THE LUMINOUS INFRARED GALAXY NGC 6286

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

Contact Info

Product

Resources

About

Millimeter Interferometric HCN(1-0) and HCO⁺(1-0) Observations of Luminous Infrared Galaxies

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