Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15: I. Line profiles, physical conditions, and H2O abundance

Lars Egstrøm Kristensen; E. F. Van Dishoeck; J. C. Mottram; A. Karska; U. A. Ylldlz; E. A. Bergin; Per Bjerkeli; S. Cabrit; S. Doty; N. J. Evans; A. Gusdorf; D. Harsono; G. J. Herczeg; D. Johnstone; Jes Kristian Jørgensen; T. A. van Kempen; J. E. Lee; S. Maret; M. Tafalla; R. Visser; S. F. Wampfler

doi:10.1051/0004-6361/201630127

Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15: I. Line profiles, physical conditions, and H₂O abundance

Lars Egstrøm Kristensen, E. F. Van Dishoeck, J. C. Mottram, A. Karska, U. A. Ylldlz, E. A. Bergin, Per Bjerkeli, S. Cabrit, S. Doty, N. J. Evans, A. Gusdorf, D. Harsono, G. J. Herczeg, D. Johnstone, Jes Kristian Jørgensen, T. A. van Kempen, J. E. Lee, S. Maret, M. Tafalla, R. VisserS. F. Wampfler

Astrofysik og Planetforskning

10 Citationer (Scopus)

8 Downloads (Pure)

Abstract

Context. Through spectrally unresolved observations of high-J CO transitions, Herschel Photodetector Array Camera and Spectrometer (PACS) has revealed large reservoirs of warm (300 K) and hot (700 K) molecular gas around low-mass protostars. The excitation and physical origin of this gas is still not understood. Aims. We aim to shed light on the excitation and origin of the CO ladder observed toward protostars, and on the water abundance in different physical components within protostellar systems using spectrally resolved Herschel-HIFI data. Methods. Observations are presented of the highly excited CO line J = 16-15 (E_up/k_B = 750 K) with the Herschel Heterodyne Instrument for the Far Infrared (HIFI) toward a sample of 24 low-mass protostellar objects. The sources were selected from the Herschel "Water in Star-forming regions with Herschel" (WISH) and "Dust, Ice, and Gas in Time" (DIGIT) key programs. Results. The spectrally resolved line profiles typically show two distinct velocity components: a broad Gaussian component with an average FWHM of 20 km s^-1 containing the bulk of the flux, and a narrower Gaussian component with a FWHM of 5 km s^-1 that is often offset from the source velocity. Some sources show other velocity components such as extremely-high-velocity features or "bullets". All these velocity components were first detected in H₂O line profiles. The average rotational temperature over the entire profile, as measured from comparison between CO J = 16-15 and 10-9 emission, is ~300 K. A radiative-transfer analysis shows that the average H₂O/CO column-density ratio is ~0.02, suggesting a total H₂O abundance of ~2 × 10^-6, independent of velocity. Conclusions. Two distinct velocity profiles observed in the HIFI line profiles suggest that the high-J CO ladder observed with PACS consists of two excitation components. The warm PACS component (300 K) is associated with the broad HIFI component, and the hot PACS component (700 K) is associated with the offset HIFI component. The former originates in either outflow cavity shocks or the disk wind, and the latter in irradiated shocks. The low water abundance can be explained by photodissociation. The ubiquity of the warm and hot CO components suggest that fundamental mechanisms govern the excitation of these components; we hypothesize that the warm component arises when H₂ stops being the dominant coolant. In this scenario, the hot component arises in cooling molecular H₂-poor gas just prior to the onset of H₂ formation. High spectral resolution observations of highly excited CO transitions uniquely shed light on the origin of warm and hot gas in low-mass protostellar objects.

Originalsprog	Engelsk
Artikelnummer	A93
Tidsskrift	Astronomy and Astrophysics
Vol/bind	605
Antal sider	19
ISSN	0004-6361
DOI	https://doi.org/10.1051/0004-6361/201630127
Status	Udgivet - sep. 2017

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10.1051/0004-6361/201630127Licens: Andet

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Citationsformater

Kristensen, L. E., Van Dishoeck, E. F., Mottram, J. C., Karska, A., Ylldlz, U. A., Bergin, E. A., Bjerkeli, P., Cabrit, S., Doty, S., Evans, N. J., Gusdorf, A., Harsono, D., Herczeg, G. J., Johnstone, D., Jørgensen, J. K., van Kempen, T. A., Lee, J. E., Maret, S., Tafalla, M., ... Wampfler, S. F. (2017). Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15: I. Line profiles, physical conditions, and H₂O abundance. Astronomy and Astrophysics, 605, Artikel A93. https://doi.org/10.1051/0004-6361/201630127

Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15: I. Line profiles, physical conditions, and H₂O abundance. / Kristensen, Lars Egstrøm; Van Dishoeck, E. F.; Mottram, J. C. et al.
I: Astronomy and Astrophysics, Bind 605, A93, 09.2017.

Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review

Kristensen, LE, Van Dishoeck, EF, Mottram, JC, Karska, A, Ylldlz, UA, Bergin, EA, Bjerkeli, P, Cabrit, S, Doty, S, Evans, NJ, Gusdorf, A, Harsono, D, Herczeg, GJ, Johnstone, D, Jørgensen, JK, van Kempen, TA, Lee, JE, Maret, S, Tafalla, M, Visser, R & Wampfler, SF 2017, 'Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15: I. Line profiles, physical conditions, and H₂O abundance', Astronomy and Astrophysics, bind 605, A93. https://doi.org/10.1051/0004-6361/201630127

@article{72c433deeb43413fa26e51a89aaf23b6,

title = "Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15: I. Line profiles, physical conditions, and H2O abundance",

abstract = "Context. Through spectrally unresolved observations of high-J CO transitions, Herschel Photodetector Array Camera and Spectrometer (PACS) has revealed large reservoirs of warm (300 K) and hot (700 K) molecular gas around low-mass protostars. The excitation and physical origin of this gas is still not understood. Aims. We aim to shed light on the excitation and origin of the CO ladder observed toward protostars, and on the water abundance in different physical components within protostellar systems using spectrally resolved Herschel-HIFI data. Methods. Observations are presented of the highly excited CO line J = 16-15 (Eup/kB = 750 K) with the Herschel Heterodyne Instrument for the Far Infrared (HIFI) toward a sample of 24 low-mass protostellar objects. The sources were selected from the Herschel {"}Water in Star-forming regions with Herschel{"} (WISH) and {"}Dust, Ice, and Gas in Time{"} (DIGIT) key programs. Results. The spectrally resolved line profiles typically show two distinct velocity components: a broad Gaussian component with an average FWHM of 20 km s-1 containing the bulk of the flux, and a narrower Gaussian component with a FWHM of 5 km s-1 that is often offset from the source velocity. Some sources show other velocity components such as extremely-high-velocity features or {"}bullets{"}. All these velocity components were first detected in H2O line profiles. The average rotational temperature over the entire profile, as measured from comparison between CO J = 16-15 and 10-9 emission, is ~300 K. A radiative-transfer analysis shows that the average H2O/CO column-density ratio is ~0.02, suggesting a total H2O abundance of ~2 × 10-6, independent of velocity. Conclusions. Two distinct velocity profiles observed in the HIFI line profiles suggest that the high-J CO ladder observed with PACS consists of two excitation components. The warm PACS component (300 K) is associated with the broad HIFI component, and the hot PACS component (700 K) is associated with the offset HIFI component. The former originates in either outflow cavity shocks or the disk wind, and the latter in irradiated shocks. The low water abundance can be explained by photodissociation. The ubiquity of the warm and hot CO components suggest that fundamental mechanisms govern the excitation of these components; we hypothesize that the warm component arises when H2 stops being the dominant coolant. In this scenario, the hot component arises in cooling molecular H2-poor gas just prior to the onset of H2 formation. High spectral resolution observations of highly excited CO transitions uniquely shed light on the origin of warm and hot gas in low-mass protostellar objects.",

keywords = "Astrochemistry, ISM: jets and outflows, Line: profiles, Outflows, Stars: formation, Stars: jets, Stars: winds",

author = "Kristensen, {Lars Egstr{\o}m} and {Van Dishoeck}, {E. F.} and Mottram, {J. C.} and A. Karska and Ylldlz, {U. A.} and Bergin, {E. A.} and Per Bjerkeli and S. Cabrit and S. Doty and Evans, {N. J.} and A. Gusdorf and D. Harsono and Herczeg, {G. J.} and D. Johnstone and J{\o}rgensen, {Jes Kristian} and {van Kempen}, {T. A.} and Lee, {J. E.} and S. Maret and M. Tafalla and R. Visser and Wampfler, {S. F.}",

year = "2017",

month = sep,

doi = "10.1051/0004-6361/201630127",

language = "English",

volume = "605",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "E D P Sciences",

}

TY - JOUR

T1 - Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15

T2 - I. Line profiles, physical conditions, and H2O abundance

AU - Kristensen, Lars Egstrøm

AU - Van Dishoeck, E. F.

AU - Mottram, J. C.

AU - Karska, A.

AU - Ylldlz, U. A.

AU - Bergin, E. A.

AU - Bjerkeli, Per

AU - Cabrit, S.

AU - Doty, S.

AU - Evans, N. J.

AU - Gusdorf, A.

AU - Harsono, D.

AU - Herczeg, G. J.

AU - Johnstone, D.

AU - Jørgensen, Jes Kristian

AU - van Kempen, T. A.

AU - Lee, J. E.

AU - Maret, S.

AU - Tafalla, M.

AU - Visser, R.

AU - Wampfler, S. F.

PY - 2017/9

Y1 - 2017/9

N2 - Context. Through spectrally unresolved observations of high-J CO transitions, Herschel Photodetector Array Camera and Spectrometer (PACS) has revealed large reservoirs of warm (300 K) and hot (700 K) molecular gas around low-mass protostars. The excitation and physical origin of this gas is still not understood. Aims. We aim to shed light on the excitation and origin of the CO ladder observed toward protostars, and on the water abundance in different physical components within protostellar systems using spectrally resolved Herschel-HIFI data. Methods. Observations are presented of the highly excited CO line J = 16-15 (Eup/kB = 750 K) with the Herschel Heterodyne Instrument for the Far Infrared (HIFI) toward a sample of 24 low-mass protostellar objects. The sources were selected from the Herschel "Water in Star-forming regions with Herschel" (WISH) and "Dust, Ice, and Gas in Time" (DIGIT) key programs. Results. The spectrally resolved line profiles typically show two distinct velocity components: a broad Gaussian component with an average FWHM of 20 km s-1 containing the bulk of the flux, and a narrower Gaussian component with a FWHM of 5 km s-1 that is often offset from the source velocity. Some sources show other velocity components such as extremely-high-velocity features or "bullets". All these velocity components were first detected in H2O line profiles. The average rotational temperature over the entire profile, as measured from comparison between CO J = 16-15 and 10-9 emission, is ~300 K. A radiative-transfer analysis shows that the average H2O/CO column-density ratio is ~0.02, suggesting a total H2O abundance of ~2 × 10-6, independent of velocity. Conclusions. Two distinct velocity profiles observed in the HIFI line profiles suggest that the high-J CO ladder observed with PACS consists of two excitation components. The warm PACS component (300 K) is associated with the broad HIFI component, and the hot PACS component (700 K) is associated with the offset HIFI component. The former originates in either outflow cavity shocks or the disk wind, and the latter in irradiated shocks. The low water abundance can be explained by photodissociation. The ubiquity of the warm and hot CO components suggest that fundamental mechanisms govern the excitation of these components; we hypothesize that the warm component arises when H2 stops being the dominant coolant. In this scenario, the hot component arises in cooling molecular H2-poor gas just prior to the onset of H2 formation. High spectral resolution observations of highly excited CO transitions uniquely shed light on the origin of warm and hot gas in low-mass protostellar objects.

AB - Context. Through spectrally unresolved observations of high-J CO transitions, Herschel Photodetector Array Camera and Spectrometer (PACS) has revealed large reservoirs of warm (300 K) and hot (700 K) molecular gas around low-mass protostars. The excitation and physical origin of this gas is still not understood. Aims. We aim to shed light on the excitation and origin of the CO ladder observed toward protostars, and on the water abundance in different physical components within protostellar systems using spectrally resolved Herschel-HIFI data. Methods. Observations are presented of the highly excited CO line J = 16-15 (Eup/kB = 750 K) with the Herschel Heterodyne Instrument for the Far Infrared (HIFI) toward a sample of 24 low-mass protostellar objects. The sources were selected from the Herschel "Water in Star-forming regions with Herschel" (WISH) and "Dust, Ice, and Gas in Time" (DIGIT) key programs. Results. The spectrally resolved line profiles typically show two distinct velocity components: a broad Gaussian component with an average FWHM of 20 km s-1 containing the bulk of the flux, and a narrower Gaussian component with a FWHM of 5 km s-1 that is often offset from the source velocity. Some sources show other velocity components such as extremely-high-velocity features or "bullets". All these velocity components were first detected in H2O line profiles. The average rotational temperature over the entire profile, as measured from comparison between CO J = 16-15 and 10-9 emission, is ~300 K. A radiative-transfer analysis shows that the average H2O/CO column-density ratio is ~0.02, suggesting a total H2O abundance of ~2 × 10-6, independent of velocity. Conclusions. Two distinct velocity profiles observed in the HIFI line profiles suggest that the high-J CO ladder observed with PACS consists of two excitation components. The warm PACS component (300 K) is associated with the broad HIFI component, and the hot PACS component (700 K) is associated with the offset HIFI component. The former originates in either outflow cavity shocks or the disk wind, and the latter in irradiated shocks. The low water abundance can be explained by photodissociation. The ubiquity of the warm and hot CO components suggest that fundamental mechanisms govern the excitation of these components; we hypothesize that the warm component arises when H2 stops being the dominant coolant. In this scenario, the hot component arises in cooling molecular H2-poor gas just prior to the onset of H2 formation. High spectral resolution observations of highly excited CO transitions uniquely shed light on the origin of warm and hot gas in low-mass protostellar objects.

KW - Astrochemistry

KW - ISM: jets and outflows

KW - Line: profiles

KW - Outflows

KW - Stars: formation

KW - Stars: jets

KW - Stars: winds

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U2 - 10.1051/0004-6361/201630127

DO - 10.1051/0004-6361/201630127

M3 - Journal article

AN - SCOPUS:85029653875

SN - 0004-6361

VL - 605

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A93

ER -