Mapping the <sup>13</sup>CO/C<sup>18</sup>O abundance ratio in the massive star-forming region G29.96−0.02

Paron, S.; Areal, M. B.; Ortega, M. E.

doi:10.1051/0004-6361/201833658

Cited by 13 publications

(12 citation statements)

References 24 publications

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“…Since the column density calculation depends on τ, a similar issue arises toward the edge of the map, mainly seen for N( 13 CO) in both regions. The global values of column density found toward this region are in agreement with other star-forming regions (Shimajiri et al 2014;Paron et al 2018;Vazzano et al 2019). Inside the H II region, no 13 CO (3−2) and C 18 O (3−2) are detected.…”

Section: Physical Properties Of the Clumpssupporting

confidence: 88%

“…By looking at the ratio maps, we observed that the value for this latter ratio is lower towards the densest part of the region and higher toward the edges. Unfortunately, as noted by Shimajiri et al (2014), this ratio is affected by the beam filling factor which could be as low as 0.4 as well as being nonuniform over the area due to the different structures observed (Paron et al 2018). The resolution of our observations does not allow us to come to a conclusion as to the dissociation of C 18 O towards the PDR of RCW 120.…”

Section: Dynamics Of the Regionmentioning

confidence: 67%

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APEX CO observations towards the photodissociation region of RCW 120

Figueira

Zavagno

Bronfman

et al. 2020

A&A

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Context. The edges of ionized (H II) regions are important sites for the formation of (high-mass) stars. Indeed, at least 30% of the Galactic high-mass-star formation is observed there. The radiative and compressive impact of the H II region could induce star formation at the border following different mechanisms such as the collect and collapse or the radiation-driven implosion (RDI) models and change their properties. Aims. We aim to study the properties of two zones located in the photo dissociation region (PDR) of the Galactic H II region RCW 120 and discuss them as a function of the physical conditions and young star contents found in both clumps. Methods. Using the APEX telescope, we mapped two regions of size 1.5′ × 1.5′ toward the most massive clump of RCW 120 hosting young massive sources and toward a clump showing a protrusion inside the H II region and hosting more evolved low-mass sources. The 12CO (J = 3−2), 13CO (J = 3−2) and C18O (J = 3−2) lines observed, together with Herschel data, are used to derive the properties and dynamics of these clumps. We discuss their relation with the hosted star formation. Results. Assuming local thermodynamic equilibrium, the increase of velocity dispersion and Tex are found toward the center of the maps, where star-formation is observed with Herschel. Furthermore, both regions show supersonic Mach numbers (7 and 17 in average). No substantial information has been gathered about the impact of far ultraviolet radiation on C18O photodissociation at the edges of RCW 120. The fragmentation time needed for CC to be at work is equivalent to the dynamical age of RCW 120 and the properties of region B are in agreement with bright-rimmed clouds. Conclusions. Although conclusions from this fragmentation model should be taken with caution, it strengthens the fact that, together with evidence of compression, CC might be at work at the edges of RCW 120. Additionally, the clump located at the eastern part of the PDR is a good candidate pre-existing clump where star-formation may be induced by the RDI mechanism.

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Section: Physical Properties Of the Clumpssupporting

confidence: 88%

Section: Dynamics Of the Regionmentioning

confidence: 67%

APEX CO observations towards the photodissociation region of RCW 120

Figueira

Zavagno

Bronfman

et al. 2020

A&A

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“…Lin et al 2016). Therefore, the behaviour of the 13 CO/C 18 O abundance ratio (hereafter X 13/18 ) across molecular clouds could be used as a tool to indirectly evaluate the degree of photodissociation in the cloud (Paron et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Study of the ¹³CO/C¹⁸O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24

Areal

Paron

Ortega

et al. 2019

Publ. Astron. Soc. Aust.

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Nowadays, there are several observational studies about the 13CO/C18O abundance ratio ( $X^{13/18}$ ) towards nearby molecular clouds. These works give observational support to the C18O selective photodissociation due to the interaction between the far ultraviolet (FUV) radiation and the molecular gas. It is necessary to increase the sample of molecular clouds located at different distances and affected in different ways by nearby or embedded H ii regions and OB associations to study the selective photodissociation. Using 12CO, 13CO, and C18O J = 1–0 data obtained from the FOREST unbiased Galactic plane imaging survey performed with the Nobeyama 45-m telescope, we analyse the filamentary infrared dark cloud IRDC $34.43+0.24$ located at the distance of about 3.9 kpc. This infrared dark cloud (IRDC) is related to several H ii regions and young stellar objects. Assuming local thermodynamic equilibrium, we obtain: $0.8 \times 10^{16} <$ N(13CO) $<4 \times 10^{17}$ cm–2 (average value $= 4.2 \times 10^{16}$ cm–2), $0.6 \times 10^{15} <$ N(C18O) $<4.4 \times 10^{16}$ cm–2 (average value $= 5.0 \times 10^{15}$ cm–2), and 3 $<$ $X^{13/18}$ $<$ 30 (average $= 8$ ) across the whole IRDC. Larger values of $X^{13/18}$ were found towards portions of the cloud related to the H ii regions associated with the N61 and N62 bubbles and with the photodissociation regions, precisely the regions in which FUV photons are strongly interacting with the molecular gas. Our result represents an observational support to the C18O selectively photodissociation phenomenon occurring in a quite distant filamentary IRDC. Additionally, based on IR data from the Hi-GAL survey, the FUV radiation field was estimated in Habing units, and the dust temperature (T $_{dust}$ ) and H2 column density (N(H2)) distribution were studied. Using the average of N(H2), values in close agreement with the ‘canonical’ abundance ratios [H2]/[13CO] and [H2]/[C18O] were derived. However, the obtained ranges in the abundance ratios show that if an accurate analysis of the molecular gas is required, the use of the ‘canonical’ values may introduce some bias. Thus, it is important to consider how the gas is irradiated by the FUV photons across the molecular cloud. The analysis of $X^{13/18}$ is a good tool to perform that. Effects of beam dilution and clumpiness were studied.

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“…Finally, N ( 13 CO) and N (C 18 O) were estimated under the LTE condition for simplicity by using equation (11) in Nishimura et al (2015), as only single transitions of the CO isotopologues are available. R 13/18 estimated under LTE and non-LTE assumptions are coincident within a factor of ∼2 in the massive star-forming region G29.96-0.02 (Paron et al 2018). In our estimation, N ( 13 CO) and N (C 18 O) are not reliably determined behind the PDR shell and near the systemic velocity (V lsr =3.7 km s −1 ).…”

Section: ρ Oph a Pdrmentioning

confidence: 66%

ALMA observations of layered structures due to CO selective dissociation in the $ρ$ Ophiuchi A plane-parallel PDR

Yamagishi,

Hara,

Kawabe

et al. 2019

Preprint

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We analyze 12 CO(J=2-1), 13 CO(J=2-1), C 18 O (J=2-1), and 1.3 mm continuum maps of the ρ Ophiuchi A photo-dissociation region (PDR) obtained with ALMA. Layered structures of the three CO isotopologues with an angular separation of 10 ′′ = 6.6×10 −3 pc = 1400 au are clearly detected around the Be star, S1 (i.e., each front of emission shifts from the near to far side in order of 12 CO, 13 CO, and C 18 O). We estimate the spatial variations of X( 13 CO)/X(C 18 O) abundance ratios, and find that the abundance ratio is as high as 40 near the emission front, and decreases to the typical value in the solar system of 5.5 in a small angular scale of 4 ′′ = 2.6×10 −3 pc = 560 au. We also find that the I( 12 CO(2-1))/I( 13 CO(2-1)) intensity ratio is very high (>21) in the flat-spectrum young stellar object, GY-51, located in the PDR. The enhancement of the ratios indicates that the UV radiation significantly affects the CO isotopologues via selective dissociation in the overall ρ Ophiuchi A PDR, and that the ρ Ophiuchi A PDR has a plane-parallel structure.

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Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Cited by 13 publications

References 24 publications

APEX CO observations towards the photodissociation region of RCW 120

APEX CO observations towards the photodissociation region of RCW 120

Study of the ¹³CO/C¹⁸O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24

ALMA observations of layered structures due to CO selective dissociation in the $ρ$ Ophiuchi A plane-parallel PDR

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Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

Cited by 13 publications

References 24 publications

APEX CO observations towards the photodissociation region of RCW 120

APEX CO observations towards the photodissociation region of RCW 120

Study of the 13CO/C18O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24

ALMA observations of layered structures due to CO selective dissociation in the $ρ$ Ophiuchi A plane-parallel PDR

Contact Info

Product

Resources

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Mapping the ¹³CO/C¹⁸O abundance ratio in the massive star-forming region G29.96−0.02

Study of the ¹³CO/C¹⁸O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24