The distribution and origin of C<sub>2</sub>H in NGC 253 from ALCHEMI

Holdship, Jonathan; Viti, S.; Martín, S.; Harada, Nanase; Mangum, J. G.; Sakamoto, Kazushi; Müller, S.; Tanaka, K.; Yoshimura, Yuki; Nakanishi, Koji; Herrero-Illana, R.; Mühle, S.; Aladro, R.; Colzi, L.; Emig, K. L.; García‐Burillo, S.; Henkel, C.; Humire, P. K.; Meier, David S.; Rivilla, V. M.; Werf, P. van der

doi:10.1051/0004-6361/202141233

Cited by 25 publications

(46 citation statements)

References 42 publications

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“…The high value of cosmic-ray ionization rate we derived in Section 6.3 is consistent with another work from our team that concluded that ζ > 10 −14 s −1 because C 2 H is somewhat abundant even in extremely high A V regions (Holdship et al 2021). The derived value of the cosmic-ray ionization rate is higher than those usually obtained in our Galaxy.…”

Section: Derived Physical Parameterssupporting

confidence: 92%

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Harada

Martín

Mangum

et al. 2021

ApJ

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Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1−0) integrated intensity shows its association with “superbubbles,” cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are ∼10–150, and the fractional abundance of HOC+ relative to H2 is ∼1.5 × 10−11–6 × 10−10, which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G 0 ≳ 103 if the maximum visual extinction is ≳5, or a cosmic-ray ionization rate of ζ ≳ 10−14 s−1 (3–4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.

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Section: Derived Physical Parameterssupporting

confidence: 92%

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Harada

Martín

Mangum

et al. 2021

ApJ

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“…The gas densities are consistent with previous measurements. The range of likely density values for each region overlaps very well with those derived from the ALCHEMI observations of C 2 H (Holdship et al 2021). They also fall well within the range of 1 × 10 5 -1 × 10 6 cm −3 found in other ALCHEMI work (Harada et al 2021) and elsewhere (Leroy et al 2018).…”

Section: The Gmc Propertiessupporting

confidence: 85%

“…Points that do not overlap tend to be low-E U SO transitions, which are underpredicted by the model. This is perhaps a similar effect to that seen in C 2 H emission in the same GMCs (Holdship et al 2021), where low-E U emission was clearly excited by an additional gas component. However, because these deficiencies are small, we consider that the majority of the gas emitting these species is well characterized by our model.…”

Section: Model Spectral Line Intensitiessupporting

confidence: 70%

“…Finally, a prior distribution p(θ) must be chosen. The large amount of previous work on NGC 253 provides a fantastic opportunity to set informed priors on the density (Leroy et al 2018), column density (Mangum et al 2019), and CRIR (Harada et al 2021;Holdship et al 2021). Despite this, we chose in the first instance to use uninformative priors that are uniform within limits based on those works.…”

Section: Parameter Inferencementioning

confidence: 99%

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Energizing Star Formation: The Cosmic-Ray Ionization Rate in NGC 253 Derived from ALCHEMI Measurements of H₃O⁺ and SO

Holdship

Mangum

Viti

et al. 2022

ApJ

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The cosmic-ray ionization rate (CRIR) is a key parameter in understanding the physical and chemical processes in the interstellar medium. Cosmic rays are a significant source of energy in star formation regions, impacting the physical and chemical processes that drive the formation of stars. Previous studies of the circum-molecular zone of the starburst galaxy NGC 253 have found evidence for a high CRIR value: 103–106 times the average CRIR within the Milky Way. This is a broad constraint, and one goal of this study is to determine this value with much higher precision. We exploit ALMA observations toward the central molecular zone of NGC 253 to measure the CRIR. We first demonstrate that the abundance ratio of H3O+ and SO is strongly sensitive to the CRIR. We then combine chemical and radiative transfer models with nested sampling to infer the gas properties and CRIR of several star-forming regions in NGC 253 from emission from their transitions. We find that each of the four regions modeled has a CRIR in the range (1–80) × 10−14 s−1 and that this result adequately fits the abundances of other species that are believed to be sensitive to cosmic rays, including C2H, HCO+, HOC+, and CO. From shock and photon-dominated/X-ray dominated region models, we further find that neither UV-/X-ray-driven nor shock-dominated chemistry is a viable single alternative as none of these processes can adequately fit the abundances of all of these species.

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“…For the non-LTE analysis, we use the radiative transfer code RADEX (van der Tak et al 2007) via the Python package Spec-tralRadex 4 (Holdship et al 2021) using HNCO and SiO molecular data (Niedenhoff et al 1995;Sahnoun et al 2018;Balança et al 2018) from the LAMDA database (Schöier et al 2005). This allows us to account for how the gas density and temperature affect the excitation of the transitions and to fit three parameters of interest: n H2 , T kin , and N as well as the beam filling factor.…”

Section: Non-lte Analysis With Radexmentioning

confidence: 99%

The chemical footprint of AGN feedback in the outflowing circumnuclear disk of NGC 1068

Huang¹,

Viti²,

Holdship³

et al. 2022

Preprint

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Context. In the nearby (D=14 Mpc) AGN-starburst composite galaxy NGC 1068, it has been found that the molecular gas in the Circum-nuclear Disk (CND) is outflowing, which is a manifestation of ongoing AGN feedback. The outflowing gas has a large spread of velocities, which likely drive different shock chemistry signatures at different locations in the CND. Aims. We perform a multi-line molecular study using two shock tracers, SiO and HNCO, with the aim to determine the gas properties traced by these two species, and explore the possibility of reconstructing the shock history in the CND. Methods. Five SiO transitions and three HNCO transitions were imaged at high resolution 0 .5 − 0 .8 with the Atacama Large Millimeter/submillimeter Array (ALMA). We performed both LTE and non-LTE radiative transfer analysis coupled with Bayesian inference process in order to characterize the gas properties, such as molecular gas density and gas temperature. Results. We found clear evidence of chemical differentiation between SiO and HNCO, with the SiO/HNCO ratio ranging from greater than one on the east of CND to lower than one on the west side. The non-LTE radiative transfer analysis coupled with Bayesian inference confirms that the gas traced by SiO has different densities -and possibly temperatures -than that traced by HNCO. We find that SiO traces gas affected by fast shocks while the gas traced by HNCO is either just affected by slow shocks or not shocked at all. Conclusions. A distinct differentiation between SiO and HNCO has been revealed in our observations and the further analysis of the gas properties traced by both species, which confirms the results from previous chemical modelings.

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The distribution and origin of C₂H in NGC 253 from ALCHEMI

Cited by 25 publications

References 42 publications

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Energizing Star Formation: The Cosmic-Ray Ionization Rate in NGC 253 Derived from ALCHEMI Measurements of H₃O⁺ and SO

The chemical footprint of AGN feedback in the outflowing circumnuclear disk of NGC 1068

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The distribution and origin of C2H in NGC 253 from ALCHEMI

Cited by 25 publications

References 42 publications

Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO+/HOC+ Emission in NGC 253 from ALCHEMI

Energizing Star Formation: The Cosmic-Ray Ionization Rate in NGC 253 Derived from ALCHEMI Measurements of H3O+ and SO

The chemical footprint of AGN feedback in the outflowing circumnuclear disk of NGC 1068

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The distribution and origin of C₂H in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Starburst Energy Feedback Seen through HCO⁺/HOC⁺ Emission in NGC 253 from ALCHEMI

Energizing Star Formation: The Cosmic-Ray Ionization Rate in NGC 253 Derived from ALCHEMI Measurements of H₃O⁺ and SO