Star formation in extreme environments: the effects of cosmic rays and mechanical heating

Meijerink, R.; Spaans, Marco; Loenen, A. F.; Werf, P. P. van der

doi:10.1051/0004-6361/201015136

Cited by 168 publications

(221 citation statements)

References 33 publications

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“…The OH/H 2 O ratio as predicted by XDR and CR models of high density molecular regions is >1, and χ OH easily exceeds 10 −6 (Maloney et al 1996;Meijerink et al 2011). 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.…”

Section: X-and Cosmic Raysmentioning

confidence: 95%

“…4.2.2), so OH photodissociation could produce significant columns of dense O i. Still, the C-shock models by Wardle et al (1999) with enhanced H 2 O photodissociation due to X-or cosmic rays produce little O i, with OH/Oi > 100, but models for XDRs and CRs by Meijerink & Spaans (2005) and Meijerink et al (2011) predict large amounts of oxygen in atomic form, though they use densities significantly lower than 3 × 10 6 cm −3 .…”

Section: Inflowing Gas In Ngc 4418?mentioning

confidence: 99%

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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: 95%

Section: Inflowing Gas In Ngc 4418?mentioning

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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“…The cosmic ray ionization rate of nitrogen (including the secondary photons generated by cosmic rays interacting with hydrogen) is about a factor of two larger than that of hydrogen (McElroy et al 2013), ∼few × 10 −15 s −1 , but is much lower than the values needed to offset the recombination by electrons. Although regions of intense cosmic ray ionization may exist with ionization rates ∼10 −14 s −1 (Bayet et al 2011;Meijerink et al 2011), rates ≥10 −12 s −1 would be required for cosmic rays to explain high fractional nitrogen ionization at densities n(e) ≥ 1 cm −3 . Indeed Meijerink et al (2011) consider rates almost that large in their models of photon dominated regions (PDRs) but only consider high atomic hydrogen densities, n(H) ≥ 10 3 cm −3 such that the fractional ionization is small.…”

Section: Cosmic Ray Ionizationmentioning

confidence: 99%

“…Although regions of intense cosmic ray ionization may exist with ionization rates ∼10 −14 s −1 (Bayet et al 2011;Meijerink et al 2011), rates ≥10 −12 s −1 would be required for cosmic rays to explain high fractional nitrogen ionization at densities n(e) ≥ 1 cm −3 . Indeed Meijerink et al (2011) consider rates almost that large in their models of photon dominated regions (PDRs) but only consider high atomic hydrogen densities, n(H) ≥ 10 3 cm −3 such that the fractional ionization is small. Their models cannot be applied to the ionized gas probed by our [N ii] observations 7 .…”

Section: Cosmic Ray Ionizationmentioning

confidence: 99%

Ionized gas at the edge of the central molecular zone

Langer

Goldsmith

Pineda

et al. 2015

A&A

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Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims. We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N + and C + .Methods. We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H 2 .Results. We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at −207 km s −1 associated with Sgr E and the other at −174 km s −1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ∼5 to 21 cm −3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H 2 layer in the −207 km s −1 cloud is ∼1−2× 10 21 cm −2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ∼7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions. The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N + and high electron density require an intense EUV field with a photon flux of order 10 6 to 10 7 photons cm −2 s −1 , and/or efficient proton charge exchange with nitrogen, at temperatures of order 10 4 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

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“…is the molecular abundance. While a single molecular abundance is not particularly informative, with reliable estimates of the abundances of several species significant progress can be made (Meijerink & Spaans 2005;Meijerink et al 2007Meijerink et al , 2011Bayet et al 2008;Viti et al 2014). An interesting question therefore is whether LVG models can in fact be used to reliably recover molecular abundances.…”

Section: A1 Free X Molmentioning

confidence: 99%

How Dense Is Your Gas? On the Recoverability of LVG Model Parameters

Tunnard

Greve

2016

ApJ

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We explore the recoverability of gas physical conditions with the Large Velocity Gradient (LVG) model, using the public code RADEX and the molecules HCN and CO. Examining a wide parameter range with a series of models of increasing complexity, we use both grid and Monte Carlo Markov Chain methods to recover the input conditions, and quantify the inherent and noise-induced uncertainties in the model results. We find that even with the benefit of generous assumptions, the LVG models struggle to recover any parameter better than to within half a dex, although we find no evidence of systemic offsets. Examining isotopologue lines, we demonstrate that it is always preferable to model the isotopologue abundance ratio as a free parameterdue to large biases introduced in all other parameters when an incorrect ratio is assumed. Finally, we explore the effects of the background radiation temperature on CO and HCN line ratios, with an emphasis on the effect of the CMB at > z 4, and show that while the effect on the line ratios is minor, the effect on the spectral line energy distribution peak is significant and that the CO(1-0) line luminosity to H 2 mass conversion factor (α CO ) needs to be altered to account for the loss of contrast against the hotter CMB as redshift increases.

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Star formation in extreme environments: the effects of cosmic rays and mechanical heating

Cited by 168 publications

References 33 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

Ionized gas at the edge of the central molecular zone

How Dense Is Your Gas? On the Recoverability of LVG Model Parameters

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Star formation in extreme environments: the effects of cosmic rays and mechanical heating

Cited by 168 publications

References 33 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

Ionized gas at the edge of the central molecular zone

How Dense Is Your Gas? On the Recoverability of LVG Model Parameters

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