The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

Roche, P. F.; Alonso‐Herrero, A.; González‐Martín, O.

doi:10.1093/mnras/stv495

Cited by 29 publications

(32 citation statements)

References 38 publications

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“…An additional problem is the ubiquitous presence of the 9.7 and 18 μm silicate absorption features toward the Galactic Center (McCarthy et al 1980;Fritz et al 2011;Roche et al 2015, and references therein). The features are attributed to the Si-O stretching and O-Si-O bending modes in silicates comprised of SiO 4 tetrahedra (Khanna et al 1981).…”

Section: Discussionmentioning

confidence: 99%

Iron: A Key Element for Understanding the Origin and Evolution of Interstellar Dust

Dwek

2016

ApJ

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The origin and depletion of iron differ from all other abundant refractory elements that make up the composition of interstellar dust. Iron is primarily synthesized in Type Ia supernovae (SNe Ia) and in core collapse supernovae (CCSN), and is present in the outflows from AGB stars. Only the latter two are observed to be sources of interstellar dust since searches for dust in SN Ia have provided strong evidence for the absence of any significant mass of dust in their ejecta. Consequently, more than 65% of the iron is injected into the ISM in gaseous form. Yet ultraviolet and X-ray observations along many lines of sight in the ISM show that iron is severely depleted in the gas phase as compared to expected solar abundances. The missing iron, comprising about 90% of the total, is believed to be locked up in interstellar dust. This suggests that most of the missing iron must have precipitated from the ISM gas by a cold accretion onto preexisting silicate, carbon, or composite grains. Iron is thus the only element that requires most of its growth to occur outside the traditional stellar condensation sources. This is a robust statement that does not depend on our evolving understanding of the dust destruction efficiency in the ISM. Reconciling the physical, optical, and chemical properties of such composite grains with their many observational manifestations is a major challenge for understanding the nature and origin of interstellar dust.

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Section: Discussionmentioning

confidence: 99%

Iron: A Key Element for Understanding the Origin and Evolution of Interstellar Dust

Dwek

2016

ApJ

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“…The optical depth of the 9.7 μm silicate absorption feature is τ 9.7 =2.52 (Stierwalt et al 2014), corresponding to A V ≈23 following the relationship found by Roche & Aitken (1985) for τ 9.7 and A V for the galactic center. We note the obscuration giving rise to the silicate absorption likely occurs outside of the nucleus but within the host galaxy (e.g., González-Martín et al 2013;Roche et al 2015) or from absorption within the starburst . The [C II] emission is suppressed relative to the far-infrared…”

Section: Target: Iras 13120-5453mentioning

confidence: 93%

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120–5453

Privon

Aalto

Falstad

et al. 2017

ApJ

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We present new Atacama Large Millimeter/submillimeter Array Band 7 (∼340 GHz) observations of the dense gas tracers HCN, HCO + , and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120-5453. We find centrally enhanced HCN (4-3) emission, relative to HCO + (4-3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of ∼1.2 yr −1 , the high HCN/HCO + ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds may also contribute additional mechanical heating. The starburst size implies a high Σ IR of 4.7×1012 L e kpc −2 , slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the Galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H 2 O lines and find a nuclear dust temperature of ∼40 K. IRAS 13120-5453 has a lower dust temperature and Σ IR than is inferred for the systems termed "compact obscured nuclei (CONs)" (such as Arp 220 and Mrk 231). If IRAS 13120-5453 has undergone a CON phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/active galactic nucleus core.

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“…As explained in Alonso-Herrero et al (2016b), for the deepest silicate feature the χ 2 values worsen. Roche et al (2015) compared the IRS and T-ReCS spectra of NGC 4418 and found that T-ReCS spectrum only shows the deep silicate absorption whereas the larger IRS aperture spectrum shows additionally other spectral features that may be due to the diffuse emission of the host galaxy. This causes differences in the spectral shape, which are not captured by the IRS templates, explaining the high value of χ 2 .…”

Section: The Methodsmentioning

confidence: 99%

A mid-infrared statistical investigation of clumpy torus model predictions

García‐González

Alonso‐Herrero

Hönig

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present new calculations of the CAT3D clumpy torus models, which now include a more physical dust sublimation model as well as AGN anisotropic emission. These new models allow graphite grains to persist at temperatures higher than the silicate dust sublimation temperature. This produces stronger near-infrared emission and bluer mid-infrared (MIR) spectral slopes. We make a statistical comparison of the CAT3D model MIR predictions with a compilation of sub-arcsecond resolution ground-based MIR spectroscopy of 52 nearby Seyfert galaxies (median distance of 36 Mpc) and 10 quasars. We focus on the AGN MIR spectral index α MIR and the strength of the 9.7 µm silicate feature S Sil . As with other clumpy torus models, the new CAT3D models do not reproduce the Seyfert galaxies with deep silicate absorption (S Sil < −1). Excluding those, we conclude that the new CAT3D models are in better agreement with the observed α MIR and S Sil of Seyfert galaxies and quasars. We find that Seyfert 2 are reproduced with models with low photon escape probabilities, while the quasars and the Seyfert 1-1.5 require generally models with higher photon escape probabilities. Quasars and Seyfert 1-1.5 tend to show steeper radial cloud distributions and fewer clouds along an equatorial line-of-sight than Seyfert 2. Introducing AGN anisotropic emission besides the more physical dust sublimation models alleviates the problem of requiring inverted radial cloud distributions (i.e., more clouds towards the outer parts of the torus) to explain the MIR spectral indices of type 2 Seyferts.

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The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

Cited by 29 publications

References 38 publications

Iron: A Key Element for Understanding the Origin and Evolution of Interstellar Dust

Iron: A Key Element for Understanding the Origin and Evolution of Interstellar Dust

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120–5453

A mid-infrared statistical investigation of clumpy torus model predictions

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