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First detection of THz water maser in NGC7538-IRS1 with SOFIA and new 22 GHz e-MERLIN maps
Astrophysics of Galaxies · Submitted 20 Jun 2017
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to IRS1b outflow, in a star-forming region.
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The abstract, sentence by sentence
The formation of massive stars is still not well understood. Accumulating a large amount of mass infalling within a single entity in spite of radiation pressure is possible if, among several other conditions, enough thermal energy is released. Despite numerous water line observations, with the Herschel Space Observatory, in most of the sources observations were not able to trace the emission from the hot core around the newly forming protostellar object. We want to probe the physical conditions and water abundance in the inner layers of the host protostellar object NGC7538-IRS1 using a highly excited H2O line. Water maser models predict that several THz water masers should be detectable in these objects. We present SOFIA observations of the o-H2O 8(2,7)-7(3,4) line at 1296.41106 GHz and a 6(1,6)-5(2,3) 22 GHz e-MERLIN map of the region (first-ever 22 GHz images made after the e-MERLIN upgrade). In order to be able to constrain the nature of the emission - thermal or maser - we use near-simultaneous observations of the 22 GHz water maser performed with the Effelsberg radiotelescope and e-MERLIN. A thermal water model using the RATRAN radiative transfer code is presented based on HIFI pointed observations. Molecular water abundances are derived for the hot core. The H2O 8(2,7)- 7(3,4) line is detected toward NGC7538-IRS1 with one feature at the source velocity (-57.7 km/s) and another one at -48.4 km/s. We propose that the emission at the source velocity is consistent with thermal excitation and is excited in the innermost part of the IRS1a massive protostellar object's closest circumstellar environment. The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to IRS1b outflow, in a star-forming region. Assuming thermal excitation of the THz line, the water abundance in NGC7538-IRS1's hot core is estimated to be 5.2x10^{-5} with respect to H2.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The formation of massive stars is still not well understood. | background 0.94 | 0.03 | 0.01 | asserted 0.99 |
| s1 | Accumulating a large amount of mass infalling within a single entity in spite of radiation pressure is possible if, among several other conditions, enough thermal energy is released. | background 1.00 | 0.04 | 0.02 | hedged possibility 0.84 |
| s2 | Despite numerous water line observations, with the Herschel Space Observatory, in most of the sources observations were not able to trace the emission from the hot core around the newly forming protostellar object. | gap 0.90 | 0.09 | 0.02 | asserted 0.98 |
| s3 | We want to probe the physical conditions and water abundance in the inner layers of the host protostellar object NGC7538-IRS1 using a highly excited H2O line. | contribution 0.73 | 0.21 | 0.03 | asserted 0.54 |
| s4 | Water maser models predict that several THz water masers should be detectable in these objects. | background 0.99 | 0.05 | 0.05 | hedged possibility 0.70 |
| s5 | We present SOFIA observations of the o-H2O 8(2,7)-7(3,4) line at 1296.41106 GHz and a 6(1,6)-5(2,3) 22 GHz e-MERLIN map of the region (first-ever 22 GHz images made after the e-MERLIN upgrade). | contribution 0.63 | 0.96 | 0.06 | asserted 1.00 |
| s6 | In order to be able to constrain the nature of the emission - thermal or maser - we use near-simultaneous observations of the 22 GHz water maser performed with the Effelsberg radiotelescope and e-MERLIN. | method 0.99 | 0.89 | 0.03 | asserted 0.91 |
| s7 | A thermal water model using the RATRAN radiative transfer code is presented based on HIFI pointed observations. | method 0.97 | 0.88 | 0.03 | asserted 0.99 |
| s8 | Molecular water abundances are derived for the hot core. | result 0.82 | 0.93 | 0.05 | asserted 0.98 |
| s9 | The H2O 8(2,7)- 7(3,4) line is detected toward NGC7538-IRS1 with one feature at the source velocity (-57.7 km/s) and another one at -48.4 km/s. | result 1.00 | 0.96 | 0.11 | asserted 1.00 |
| s10 | We propose that the emission at the source velocity is consistent with thermal excitation and is excited in the innermost part of the IRS1a massive protostellar object's closest circumstellar environment. | interpretation 1.00 | 0.69 | 0.14 | hedged possibility 0.99 |
| s11 | The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to IRS1b outflow, in a star-forming region. | interpretation 0.82 | 0.85 | 0.78 | hedged possibility 0.97 |
| s12 | Assuming thermal excitation of the THz line, the water abundance in NGC7538-IRS1's hot core is estimated to be 5.2x10^{-5} with respect to H2. | result 1.00 | 0.91 | 0.15 | asserted 0.61 |
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The paper
Original abstract
The formation of massive stars is still not well understood. Accumulating a large amount of mass infalling within a single entity in spite of radiation pressure is possible if, among several other conditions, enough thermal energy is released. Despite numerous water line observations, with the Herschel Space Observatory, in most of the sources observations were not able to trace the emission from the hot core around the newly forming protostellar object. We want to probe the physical conditions and water abundance in the inner layers of the host protostellar object NGC7538-IRS1 using a highly excited H2O line. Water maser models predict that several THz water masers should be detectable in these objects. We present SOFIA observations of the o-H2O 8(2,7)-7(3,4) line at 1296.41106 GHz and a 6(1,6)-5(2,3) 22 GHz e-MERLIN map of the region (first-ever 22 GHz images made after the e-MERLIN upgrade). In order to be able to constrain the nature of the emission - thermal or maser - we use near-simultaneous observations of the 22 GHz water maser performed with the Effelsberg radiotelescope and e-MERLIN. A thermal water model using the RATRAN radiative transfer code is presented based on HIFI pointed observations. Molecular water abundances are derived for the hot core. The H2O 8(2,7)- 7(3,4) line is detected toward NGC7538-IRS1 with one feature at the source velocity (-57.7 km/s) and another one at -48.4 km/s. We propose that the emission at the source velocity is consistent with thermal excitation and is excited in the innermost part of the IRS1a massive protostellar object's closest circumstellar environment. The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to IRS1b outflow, in a star-forming region. Assuming thermal excitation of the THz line, the water abundance in NGC7538-IRS1's hot core is estimated to be 5.2x10^{-5} with respect to H2.
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