Combination of CN(1-0), HCN(1-0), and HNC(1-0): A possible indicator for a high-mass star formation sequence in the Milky Way

Han, Xiaohong; Zhou, Jianjun; Wang, J. Z.; Esimbek, Jarken; Zhang, J. S.; Wang, N.

doi:10.1051/0004-6361/201423791

Cited by 11 publications

(7 citation statements)

References 44 publications

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“…Simon et al (2001) determined a kinematic distance of 6 kpc for the GRSMC 45.46+0.05 complex containing the two UC HII regions. Fish et al (2003) and Han et al (2015) obtained near and far kinematic distances for both G45.07+0.13 and G45.12+0.13 of ∼4.0 and ∼8.0 kpc. The estimated far distance is consistent with the previous estimate by Hunter et al (1997) and a more recent one based on the trigonometric parallax method (7.75 ± 0.45 kpc, Wu et al 2019).…”

Section: Introductionmentioning

confidence: 93%

Infrared study of the star-forming region associated with the UC HII regions G45.07+0.13 and G45.12+0.13

Azatyan

Nikoghosyan

Harutyunian

et al. 2022

Publ. Astron. Soc. Aust.

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Ultra-compact H ii (UC HII) regions are an important phase in the formation and early evolution of massive stars and a key component of the interstellar medium (ISM). The main objectives of this work are to study the young stellar population associated with the G45.07+0.13 and G45.12+0.13 UC HII regions, as well as the ISM in which they are embedded. We determined the distribution of the hydrogen column density (N( $\mathrm{H}_2$ )) and dust temperature ( $T_d$ ) in the molecular cloud using Modified blackbody fitting on Herschel images obtained in four bands: 160, 250, 350, and $500\,\unicode{x03BC}\mathrm{m}$ . We used near-, mid-, and far-infrared photometric data to identify and classify the young stellar objects (YSOs). Their main parameters were determined by the radiation transfer models. We also constructed a colour-magnitude diagram and K luminosity functions (KLFs) to compare the parameters of stellar objects with the results of the radiative transfer models. We found that N( $\mathrm{H}_2$ ) varies from ${\sim}3.0 \times 10^{23}$ to $5.5 \times 10^{23}\,\mathrm{cm}^{-2}$ within the G45.07+0.13 and G45.12+0.13 regions, respectively. The maximum $T_d$ value is 35 K in G45.12+0.13 and 42 K in G45.07+0.13. $T_d$ then drops significantly from the centre to the periphery, reaching about 18–20 K at distances of ${\sim}2.6$ and ${\sim}3.7\,\mathrm{pc}$ from InfraRed Astronomical Satellite (IRAS) 19110+1045 (G45.07+0.13) and IRAS 19111+1048 (G45.12+0.13), respectively. The gas plus dust mass value included in G45.12+0.13 is ${\sim}3.4 \times 10^5\,\mathrm{M}_\odot$ and ${\sim}1.7 \times 10^5\,\mathrm{M}_\odot$ in G45.07+0.13. The UC HII regions are connected through a cold ( $T_d = 19\,\mathrm{K}$ ) bridge. The radial surface density distribution of the identified 518 YSOs exhibits dense clusters in the vicinity of both IRAS sources. The parameters of YSOs in the IRAS clusters (124 objects) and 394 non-cluster objects surrounding them show some differences. About 75% of the YSOs belonging to the IRAS clusters have an evolutionary age greater than $10^6$ yr. Their slope $\alpha$ of the KLF agrees well with a Salpeter-type initial mass function (IMF) ( $\gamma = 1.35$ ) for a high mass range (O–F stars, $\beta \sim 2$ ) at 1 Myr. The non-cluster objects are uniformly distributed in the molecular cloud, 80% of which are located to the right of the 0.1 Myr isochrone. The slope $\alpha$ of the KLF of non-cluster objects is $0.55\,\pm\,0.09$ , corresponding better to a Salpeter-type IMF for low-mass objects (G–M stars, $\beta \sim 1$ ). Our results show that two dense stellar clusters are embedded in these two physically connected UC HII regions. The clusters include several high- and intermediate-mass zero-age main sequence stellar objects. Based on the small age spread of the stellar objects, we suggest that the clusters originate from a single triggering shock. The extended emission observed in both UC HII regions is likely due to the stellar clusters.

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Section: Introductionmentioning

confidence: 93%

Infrared study of the star-forming region associated with the UC HII regions G45.07+0.13 and G45.12+0.13

Azatyan

Nikoghosyan

Harutyunian

et al. 2022

Publ. Astron. Soc. Aust.

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“…This can serve as further evidence that they belong to the same star-forming region and form a physically connected system. According to the results obtained in Han et al (2015), the near and far kinematic distances of G45.07+0.13 and G45.12+0.13 regions are ∼ 4.0 and ∼ 8.0 kpc with tangent point distance of ∼ 6 kpc. The last, far distance estimation, is better consistent with a more recent estimate according to the trigonometric parallax (7.75 ± 0.45 kpc) in Wu et al (2019).…”

Section: Introuctionmentioning

confidence: 63%

Properties of ISM in two star-forming regions

Nikoghosyan

Azatyan

Harutyunian

et al. 2020

ComBAO

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The Hi-GAL provides an opportunity to make a complete and unbiased view of the continuum emission in the Galactic plane in five bands: 70, 160, 250, 350, and 500 μm. Our research focuses on two of star-forming regions. The first one is the molecular cloud, which includes G45.12+0.13 and G45.07+0.13 UCHII regions. Using the Modified blackbody fitting on Herschel images obtained in four bands: 160, 250, 350, and 500 μm, we determined the distribution of N(H2) hydrogen column density and Td dust temperature. The maps of N(H2) and Td show that UCHII regions clearly stand out against the general background of the molecular cloud with a relatively low density (from 1.0 x 1023 to 3.0 x 1023 cm-2) and significantly higher temperature (up to 100 K), what is fully consistent with the basic concept of UCHII regions about the presence of a hot, high mass stellar source and stellar wind, which leads to the blowing out of matter. The second one is the elongated star-forming region, which includes five stellar subgroups around IRAS 05184+3635, 05177+3636, 05168+3634, 05162+3639 and 05156+3643 sources. Here, on the contrary, the N(H2) is noticeably higher (from 1.0 x 1023 to 5.0 x 1023 cm-2) than in the surrounding molecular cloud and the Td does not exceed 25 K.

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“…A molecule that can help differentiate between these scenarios is CN. This molecule can be formed from HCN as a result of intense UV radiation in photodissociation regions (PDRs; e.g., Aalto et al 2002;Baan et al 2008;Han et al 2015). Costagliola et al (2011) found that in the Medusa, globally, CN 1−0 is found at higher intensity than HCN 1−0.…”

Section: Cn As a Tracer Of Radiative Feedbackmentioning

confidence: 99%

Major impact from a minor merger

König

Aalto

Müller

et al. 2018

A&A

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Context. Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on the growth of supermassive black holes and star formation is profound – about half of the star formation activity in the local Universe is the result of minor mergers. Aims. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales – from whole galaxies to giant molecular clouds in their molecular gas-rich centers. Methods. We use observations of HCN and HCO+ 1−0 with NOEMA and of CO3−2 with the SMA to study the properties of the dense molecular gas in the Medusa merger (NGC 4194) at 1′′ resolution. In particular, we compare the distribution of these dense gas tracers with CO2−1 high-resolution maps in the Medusa merger. To characterize gas properties, we calculate the brightness temperature ratios between the three tracers and use them in conjunction with a non-local thermodynamic equilibrium (non-LTE) radiative line transfer model. Results. The gas represented by HCN and HCO+ 1−0, and CO3−2 does not occupy the same structures as the less dense gas associated with the lower-J CO emission. Interestingly, the only emission from dense gas is detected in a 200 pc region within the “Eye of the Medusa”, an asymmetric 500 pc off-nuclear concentration of molecular gas. Surprisingly, no HCN or HCO+ is detected for the extended starburst of the Medusa merger. Additionally, there are only small amounts of HCN or HCO+ associated with the active galactic nucleus. The CO3−2/2−1 brightness temperature ratio inside “the Eye” is ~2.5 – the highest ratio found so far – implying optically thin CO emission. The CO2−1/HCN 1−0 (~9.8) and CO2−1/HCO+ 1−0 (~7.9) ratios show that the dense gas filling factor must be relatively high in the central region, consistent with the elevated CO3−1/2−1 ratio. Conclusions. The line ratios reveal an extreme, fragmented molecular cloud population inside the Eye with large bulk temperatures (T > 300 K) and high gas densities (n(H2) > 104 cm-3). This is very different from the cool, self-gravitating structures of giant molecular clouds normally found in the disks of galaxies. The Eye of the Medusa is found at an interface between a large-scale minor axis inflow and the central region of the Medusa. Hence, the extreme conditions inside the Eye may be the result of the radiative and mechanical feedback from a deeply embedded, young and massive super star cluster formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas entering the central region of the Medusa may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form newstars. Thus, caution is advised in taking the detection of emission from dense gas tracers as evidence of ongoing or imminent star formation.

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Combination of CN(1-0), HCN(1-0), and HNC(1-0): A possible indicator for a high-mass star formation sequence in the Milky Way

Cited by 11 publications

References 44 publications

Infrared study of the star-forming region associated with the UC HII regions G45.07+0.13 and G45.12+0.13

Infrared study of the star-forming region associated with the UC HII regions G45.07+0.13 and G45.12+0.13

Properties of ISM in two star-forming regions

Major impact from a minor merger

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