Nick Indriolo

Space Telescope Science Institute

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David A. Neufeld

Johns Hopkins University

Benjamin J. McCall

University of Illinois Urbana-Champaign

T. R. Geballe

Gemini North Observatory

Maryvonne Gérin

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

Takeshi Oka

University of Chicago

Matthew J. Richter

University of California, Davis

D. C. Lis

California Institute of Technology

Curtis DeWitt

Ames Research Center

Miwa Goto

University of Yamanashi

A. C. A. Boogert

University of Hawaiʻi at Mānoa

Cooperative Institutions

Max Planck Society

Space Telescope Science Institute

Max Planck Institute for Radio Astronomy

Centre National de la Recherche Scientifique

California Institute of Technology

University of Cologne

Ames Research Center

Center for Astrophysics Harvard & Smithsonian

Goddard Space Flight Center

Max Planck Institute for Extraterrestrial Physics

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H₃⁺ Spectroscopy and the Ionization Rate of Molecular Hydrogen in the Central Few Parsecs of the Galaxy

The Journal of Physical Chemistry A (2013)

Miwa Goto Nick Indriolo T. R. Geballe Tomonori Usuda

We report observations and analysis of infrared spectra of H3(+) and CO lines in the Galactic center, within a few parsecs of the central black hole, Sgr A*. We find a cosmic ray ionization rate typically an order of magnitude higher than outside the Galactic center. Notwithstanding, the elevated cosmic ray ionization rate is 4 orders of magnitude too short to match the proton energy spectrum, as inferred from the recent discovery of the TeV γ-ray source in the vicinity of Sgr A*.

10.1021/jp400017s

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Citations (33)

UBIQUITOUS ARGONIUM, ArH+, IN THE DIFFUSE INTERSTELLAR MEDIUM

Proceedings of the 74th International Symposium on Molecular Spectroscopy (2014)

H. S. P. Müller B. Winkel K. M. Menten John E. Pearson M. Wolfire

10.15278/isms.2014.tf02

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First time-dependent study of H2 and H3+ ortho-para chemistry in the diffuse ISM

arXiv (Cornell University) (2014)

T. Albertsson Nick Indriolo Holger Kreckel D. Semenov Kyle N. Crabtree

The chemistry in the diffuse interstellar medium initiates the gradual increase of molecular complexity during the life cycle of matter. A key molecule that enables build-up of new molecular bonds and new molecules via proton-donation is H3+. Its evolution is tightly related to molecular hydrogen and thought to be well understood. However, recent observations of ortho and para lines of H2 and H3+ in the diffuse ISM showed a puzzling discrepancy in nuclear spin excitation temperatures and populations between these two key species. H3+, unlike H2, seems to be out of thermal equilibrium, contrary to the predictions of modern astrochemical models. We conduct the first time-dependent modeling of the para-fractions of H2 and H3+ in the diffuse ISM and compare our results to a set of line-of-sight observations, including new measurements presented in this study. We isolate a set of key reactions for H3+ and find that the destruction of the lowest rotational states of H3+ by dissociative recombination largely control its ortho/para ratio. A plausible agreement with observations cannot be achieved unless a ratio larger than 1:5 for the destruction of (1,1)- and (1,0)-states of H3+ is assumed. Additionally, an increased CR ionization rate to 10(-15) 1/s further improves the fit whereas variations of other individual physical parameters, such as density and chemical age, have only a minor effect on the predicted ortho/para ratios. Thus our study calls for new laboratory measurements of the dissociative recombination rate and branching ratio of the key ion H3+ under interstellar conditions.

Dissociative recombination

Branching fraction

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CONSTRAINING THE ENVIRONMENT OF CH⁺FORMATION WITH CH⁺₃OBSERVATIONS

The Astrophysical Journal (2010)

Nick Indriolo Takeshi Oka T. R. Geballe Benjamin J. McCall

The formation of CH+ in the interstellar medium has long been an outstanding problem in chemical models. In order to probe the physical conditions of the ISM in which CH+ forms, we propose the use of CH3+ observations. The pathway to forming CH3+ begins with CH+, and a steady state analysis of CH3+ and the reaction intermediary CH2+ results in a relationship between the CH+ and CH3+ abundances. This relationship depends on the molecular hydrogen fraction, f_H2, and gas temperature, T, so observations of CH+ and CH3+ can be used to infer the properties of the gas in which both species reside. We present observations of both molecules along the diffuse cloud sight line toward Cyg OB2 No. 12. Using our computed column densities and upper limits, we put constraints on the f_H2 vs. T parameter space in which CH+ and CH3+ form. We find that average, static, diffuse molecular cloud conditions (i.e. f_H2>0.2, T~60 K) are excluded by our analysis. However, current theory suggests that non-equilibrium effects drive the reaction C+ + H_2 --> CH+ + H, endothermic by 4640 K. If we consider a higher effective temperature due to collisions between neutrals and accelerated ions, the CH3+ partition function predicts that the overall population will be spread out into several excited rotational levels. As a result, observations of more CH3+ transitions with higher signal-to-noise ratios are necessary to place any constraints on models where magnetic acceleration of ions drives the formation of CH+.

Endothermic process

10.1088/0004-637x/711/2/1338

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Metastable Helium as a Probe of the Cosmic-Ray Ionization Rate

noao (2008)

Nick Indriolo Benjamin J. McCall L. M. Hobbs K. H. Hinkle

Metastability

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Performance of the CalCOS FUV WAVECORR Algorithm at Lifetime Position 4

James T. White Nick Indriolo Julia Román-Duval

Position (finance)

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CENTRAL 300 PC OF THE GALAXY PROBED BY THE INFRARED SPECTRA OF H3+ AND CO PART II. MORPHOLOGY AND DYNAMICS OF THE GAS

Proceedings of the 73rd International Symposium on Molecular Spectroscopy (2018)

Takeshi Oka Nick Indriolo Benjamin J. McCall Tomonori Usuda Miwa Goto

Velocity-resolved spectra of infrared lines of H + 3 at 3.7 µm and CO at 2.3 µm have been obtained toward ∼40 stars in the Central Molecular Zone (CMZ), a region of radius ∼150 pc centered on the Galactic center.Although the coverage of the region is limited by the available number of suitable stars for absorption spectroscopy, the rich Doppler profiles of the H + 3 lines in warm (T ∼250 K) and diffuse (n ≤100 cm -3 ) clouds a have allowed us to draw a longitude-velocity (l-v) plot to reach the following conclusions.(1) Based on the blue-shifted profiles of H + 3 absorption lines, which are dominantly in the velocity range from -200 km s -1 to 10 km s -1 , the warm diffuse gas is moving outward from the center.(2) Although limited in uniformity of longitudinal coverage, the observed (l-v) plot for H + 3 suggests that the outer surface of the expanding gas forms a ring of radius of ∼140 pc and has a velocity of expansion of ∼140 km s -1 .This finding revives the idea of the expanding molecule ring proposed by Kaifu et al.(1972) b and Scoville (1972) c which contrasts with a more recent interpretation of the overall gas kinematics as due to a barred gravitational potential (Binney et al. 1991).d (3) The results revive the idea of an explosion or overall expulsion of gas from the center within the last few million years.Unlike the original proposals that the EMR is also rotating, the H + 3 l-v plot indicates purely expanding gas.

Morphology

Gas dynamics

Dynamics

10.15278/isms.2018.rl11

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Herschel observations of interstellar chloronium. II - Detections toward G29.96-0.02, W49N, W51, and W3(OH), and determinations of the ortho-to-para and $^{35}$Cl/$^{37}$Cl isotopic ratios

David A. Neufeld J. H. Black Maryvonne Gérin J. R. Goicoechea P. F. Goldsmith

We report additional detections of the chloronium molecular ion, H$_2$Cl$^+$, toward four bright submillimeter continuum sources: G29.96, W49N, W51, and W3(OH). With the use of the HIFI instrument on the Herschel Space Observatory, we observed the $2_{12}-1_{01}$ transition of ortho-H$_2^{35}$Cl$^+$ at 781.627 GHz in absorption toward all four sources. Much of the detected absorption arises in diffuse foreground clouds that are unassociated with the background continuum sources and in which our best estimates of the $N({\rm H_2Cl^+})/N({\rm H})$ ratio lie in the range $(0.9 - 4.8) \times 10^{-9}$. These chloronium abundances relative to atomic hydrogen can exceed the predictions of current astrochemical models by up to a factor of 5. Toward W49N, we have also detected the $2_{12}-1_{01}$ transition of ortho-H$_2^{37}$Cl$^+$ at 780.053 GHz and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ at 485.418 GHz. These observations imply $\rm H_2^{35}Cl^+/H_2^{37}Cl^+$ column density ratios that are consistent with the solar system $^{35}$Cl/$^{37}$Cl isotopic ratio of 3.1, and chloronium ortho-to-para ratios consistent with 3, the ratio of spin statistical weights.

Hydrogen molecule

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High-resolution Infrared Spectroscopy of Hot Molecular Gas in AFGL 2591 and AFGL 2136: Accretion in the Inner Regions of Disks around Massive Young Stellar Objects

The Astrophysical Journal (2020)

Andrew G. Barr A. C. A. Boogert Curtis DeWitt Edward Montiel Matthew J. Richter

Abstract We have performed a high-resolution 4–13 μ m spectral survey of the hot molecular gas associated with the massive protostars AFGL 2591 and AFGL 2136, utilizing the Echelon Cross Echelle Spectrograph (EXES) on board the Stratospheric Observatory for Infrared Astronomy, and the iSHELL instrument and Texas EchelonCross Echelle Spectrograph (TEXES) on the NASA Infrared Telescope Facility (IRTF). Here we present the results of this survey with analysis of CO, HCN, C 2 H 2 , NH 3 , and CS, deriving the physical conditions for each species. Also from the IRTF, iSHELL data at 3 μ m for AFGL 2591 are presented that show HCN and C 2 H 2 in emission. In the EXES and TEXES data, all species are detected in absorption, and temperatures and abundances are found to be high (600 K and 10 −6 , respectively). Differences of up to an order of magnitude in the abundances of transitions that trace the same ground-state level are measured for HCN and C 2 H 2 . The mid-infrared continuum is known to originate in a disk, hence we attribute the infrared absorption to arise in the photosphere of the disk. As absorption lines require an outwardly decreasing temperature gradient, we conclude that the disk is heated in the midplane by viscous heating due to accretion. We attribute the near-IR emission lines to scattering by molecules in the upper layers of the disk photosphere. The absorption lines trace the disk properties at 50 au where high-temperature gas-phase chemistry is taking place. Abundances are consistent with chemical models of the inner disk of Herbig disks.

Protostar

Infrared telescope

Spectral resolution

10.3847/1538-4357/abab05

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Salt-bearing disk candidates around high-mass young stellar objects

arXiv (Cornell University) (2022)

Adam Ginsburg Brett A. McGuire Patricio Sanhueza Fernando A. Olguin Luke T Maud

Molecular lines tracing the orbital motion of gas in a well-defined disk are valuable tools for inferring both the properties of the disk and the star it surrounds. Lines that arise only from a disk, and not also from the surrounding molecular cloud core that birthed the star or from the outflow it drives, are rare. Several such emission lines have recently been discovered in one example case, those from NaCl and KCl salt molecules. We studied a sample of 23 candidate high-mass young stellar objects (HMYSOs) in 17 high-mass star-forming regions to determine how frequently emission from these species is detected. We present five new detections of water, NaCl, KCl, PN, and SiS from the innermost regions around the objects, bringing the total number of known briny disk candidates to nine. Their kinematic structure is generally disk-like, though we are unable to determine whether they arise from a disk or outflow in the sources with new detections. We demonstrate that these species are spatially coincident in a few resolved cases and show that they are generally detected together, suggesting a common origin or excitation mechanism. We also show that several disks around HMYSOs clearly do not exhibit emission in these species. Salty disks are therefore neither particularly rare in high-mass disks, nor are they ubiquitous.

Outflow

Young stellar object

High mass

10.48550/arxiv.2211.02502

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