Study of Interstellar Molecular Clouds Using Formaldehyde Absorption Toward Extragalactic Radio Sources

Araya, E. D.; Dieter-Conklin, Nan; Goss, W. M.; Andreev, N.

doi:10.1088/0004-637x/784/2/129

Cited by 6 publications

(6 citation statements)

References 37 publications

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“…As in the case of 3C111, 69 observed H 2 CO in absorption in the direction of BL Lac. They estimated rough bounds on the density, 10 2 cm −3 ≲ n H ≲ 10 5 cm −3 , on the basis of the H 2 CO absorption properties (see explanation above for 3C111).…”

Section: Localizing Absorption Featuressupporting

confidence: 61%

“…We first attempt to find density estimates from the literature in the direction of our background sources. Araya et al (2014) observed H 2 CO in absorption in the directions of 3C111 and BL Lac. They argued that the excitation temperature of H 2 CO implies an upper limit to the density of n H < 10 5 cm −3 in these directions, while the relatively weak absorption by H 2 CO compared to CO and HCO + suggests that the density probably exceeds n H 10 2 cm −3 .…”

Section: Density Constraintsmentioning

confidence: 93%

“…The estimate of X SiO would change only by a factor of ∼ 2 in this case from the single-component fit. 69 observed H 2 CO in absorption in the direction of 3C111. They argued that the excitation temperature of H 2 CO implies an upper limit to the density of n H < 10 5 cm −3 in this direction, while the relatively weak absorption by H 2 CO-thought to be a denser gas tracer-compared to CO and HCO + suggests that the density probably exceeds n H ≳ 10 2 cm −3 in this direction.…”

Section: Localizing Absorption Featuresmentioning

confidence: 95%

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Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Stanimirović

Rybarczyk²

2022

Preprint

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Stellar feedback, in the form of interstellar shocks, shapes the structure of the interstellar medium (ISM) and is essential for the chemistry, structure, thermodynamics, and kinematics of interstellar gas. Stellar winds, young supernova explosions, and protostellar outflows drive powerful, high-velocity shocks, while the origin of much-lower-velocity shocks (< 10 km/s) in the diffuse and translucent ISM is not understood. Direct observational evidence for interstellar shocks caused by mechanisms other than stellar winds and supernovae, as well as constraints for their importance in the diffuse ISM, have been lacking. The SiO molecule is often considered an unambiguous way to trace interstellar shocks. We present the most sensitive survey to date of SiO in absorption, obtained with the Northern Extended Millimeter Array interferometer. We detect SiO in 5/8 directions probing diffuse and translucent environments without ongoing star formation. Our results demonstrate that SiO formation in the diffuse ISM (i.e., in the absence of significant star formation and stellar feedback) is more widespread and effective than previously reported. The observed SiO linewidths are all <4 km/s, which can be formed via low-velocity shocks, i.e., not outflows, stellar winds, or supernovae. Yet, the SiO abundances we detect are typically 1 to 2 orders of magnitude higher than previously reported in quiescent environments. The detection of SiO in diffuse and translucent environments where standard, UV-dominated chemical models have failed to account for high chemical abundances suggests that non-equilibrium effects are important to diffuse interstellar chemistry and that low-velocity shocks are effective in stirring up diffuse gas and dust. Our results also emphasize the need for observational constrains on the distribution of Si in the gas phase and grain mantles, which are crucial for understanding the physics of grain processing and diffuse interstellar chemistry.

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Section: Localizing Absorption Featuressupporting

confidence: 61%

Section: Density Constraintsmentioning

confidence: 93%

Section: Localizing Absorption Featuresmentioning

confidence: 95%

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Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Stanimirović

Rybarczyk²

2022

Preprint

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“…Specifically, 60″ resolution observations have been reported toward only a handful of late-type stars (Forster et al 1985;Araya et al 2003), regions of low-mass star formation (including prestellar cores; Colgan et al 1986;Zhou et al 1990;Kalenskii et al 2004;Young et al 2004;Araya et al 2006b), and diffuse molecular clouds (Marscher et al 1993;Araya et al 2014), all resulting in no detection of H 2 CO emission.…”

Section: Introductionmentioning

confidence: 99%

Formaldehyde Masers: Exclusive Tracers of High-Mass Star Formation

Araya

Olmi

Ortiz

et al. 2015

ApJS

Self Cite

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The detection of four formaldehyde (H 2 CO) maser regions toward young high-mass stellar objects in the last decade, in addition to the three previously known regions, calls for an investigation of whether H 2 CO masers are an exclusive tracer of young high-mass stellar objects. We report the first survey specifically focused on the search for 6 cm H 2 CO masers toward non high-mass star-forming regions (non HMSFRs). The observations were conducted with the 305 m Arecibo Telescope toward 25 low-mass star-forming regions, 15 planetary nebulae and post-AGB stars, and 31 late-type stars. We detected no H 2 CO emission in our sample of non HMSFRs. To check for the association between high-mass star formation and H 2 CO masers, we also conducted a survey toward 22 high-mass star-forming regions from a Hi-GAL (Herschel infrared Galactic Plane Survey) sample known to harbor 6.7 GHz CH 3 OH masers. We detected a new 6 cm H 2 CO emission line in G32.74−0.07. This work provides further evidence that supports an exclusive association between H 2 CO masers and young regions of high-mass star formation. Furthermore, we detected H 2 CO absorption toward all Hi-GAL sources, and toward 24 low-mass starforming regions. We also conducted a simultaneous survey for OH (4660, 4750, 4765 MHz), H110α (4874 MHz), HCOOH (4916 MHz), CH 3 OH (5005 MHz), and CH 2 NH (5289 MHz) toward 68 of the sources in our sample of non HMSFRs. With the exception of the detection of a 4765 MHz OH line toward a pre-planetary nebula (IRAS 04395+3601), we detected no other spectral line to an upper limit of 15 mJy for most sources.

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“…For the central position this results in T rot ≈130 ± 100 K versus T myXCLASS ≈ 70 K 12 using the rotational diagram and myXCLASS, respectively, 11 In position 2 (southeast) and position 3 (north) the H 2 CO line is also partly seen in absorption. Absorption features of H 2 CO at radio wavelengths were seen as early as 1969 (see Palmer et al 1969) and are still in use as diagnostic tool (see Araya et al 2014). In our case the absorption happens against the radio continuum at the mentioned source positions.…”

Section: H 2 Co Observationsmentioning

confidence: 53%

Simulating the circumstellar H₂CO and CH₃OH chemistry of young stellar objects using a spherical physical-chemical model

Fuchs

Witsch

Herberth

et al. 2020

A&A

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Context. Young stellar objects (YSOs) and their environments are generally geometrically and dynamically challenging to model, and the corresponding chemistry is often dominated by regions in non-thermal equilibrium. In addition, modern astrochemical models have to consider not only gas-phase reactions, but also solid-state reactions on icy dust grains. Solving the geometrical, physical, and chemical boundary conditions simultaneously requires a high computational effort and still runs the risk of false predictions due to the intrinsically non-linear effects that can occur. As a first step, solving problems of reduced complexity is helpful to guide more sophisticated approaches. Aims. The objective of this work is to test a model that uses shell-like structures (i.e., assuming a power-law number density and temperature gradient of the environment surrounding the YSO) to approximate the geometry and physical structure of YSOs, that in turn utilizes an advanced chemical model that includes gas-phase and solid-state reactions to model the chemical abundances of key species. A special focus is set on formaldehyde (H2CO) and methanol (CH3OH) as these molecules can be traced in the gas phase but are produced on icy dust grains. Furthermore, this kind of molecule is believed to be key to understanding the abundance of more complex species. We compare the influence of the geometry of the object on the molecular abundances with the effect induced by its chemistry. Methods. We set up a model that combines a grain-gas phase chemical model with a physical model of YSOs. The model ignores jets, shocks, and external radiation fields and concentrates on the physical conditions of spherically symmetric YSOs with a density and temperature gradient derived from available spectral energy distribution observations in the infrared. In addition, new observational data are presented using the APEX 12 m and the IRAM 30 m telescopes. Formaldehyde and methanol transitions have been searched for in three YSOs (R CrA-IRS 5A, C1333-IRAS 2A, and L1551-IRS 5) that can be categorized as Class 0 and Class 1 objects, and in the pre-stellar core L1544. The observed abundances of H2CO and CH3OH are compared with those calculated by the spherical physical-chemical model. Results. Compared to a standard “ρ and T constant” model, i.e., a homogeneous (flat) density and temperature distribution, using number density and temperature gradients results in reduced abundances for the CO hydrogenation products formaldehyde and methanol. However, this geometric effect is generally not large, and depends on the source and on the molecular species under investigation. Although the current model uses simplified geometric assumptions the observed abundances of H2CO and CH3OH are well reproduced for the quiescent Class 1 object R CrA-IRS 5A. Our model tends to overestimate formaldehyde and methanol abundances for sources in early evolutionary stages, like the pre-stellar core L1544 or NGC 1333-IRS 2A (Class 0). Observational results on hydrogen peroxide and water that have also been predicted by our model are discussed elsewhere.

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Study of Interstellar Molecular Clouds Using Formaldehyde Absorption Toward Extragalactic Radio Sources

Cited by 6 publications

References 37 publications

Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Formaldehyde Masers: Exclusive Tracers of High-Mass Star Formation

Simulating the circumstellar H₂CO and CH₃OH chemistry of young stellar objects using a spherical physical-chemical model

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Study of Interstellar Molecular Clouds Using Formaldehyde Absorption Toward Extragalactic Radio Sources

Cited by 6 publications

References 37 publications

Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Formaldehyde Masers: Exclusive Tracers of High-Mass Star Formation

Simulating the circumstellar H2CO and CH3OH chemistry of young stellar objects using a spherical physical-chemical model

Contact Info

Product

Resources

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Simulating the circumstellar H₂CO and CH₃OH chemistry of young stellar objects using a spherical physical-chemical model