UNVEILING SOURCES OF HEATING IN THE VICINITY OF THE ORION BN/KL HOT CORE AS TRACED BY HIGHLY EXCITED INVERSION TRANSITIONS OF AMMONIA

Journal Article · Tue Sep 20 04:00:00 EDT 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/739/1/L13· OSTI ID:21565446

Goddi, C; Humphreys, E M. L. ^[1]; Greenhill, L J ^[2]; Chandler, C J ^[3]

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1. European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany)
2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
3. National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)

Using the Expanded Very Large Array, we have mapped the vicinity of the Orion BN/KL Hot Core with subarcsecond angular resolution in seven metastable inversion transitions of ammonia (NH{sub 3}): (J, K) = (6,6) to (12,12). This emission comes from levels up to 1500 K above the ground state, enabling identification of source(s) responsible for heating the region. We used this multi-transition data set to produce images of the rotational/kinetic temperature (T {sub rot}/T {sub kin}) and the column density N {sub col} of NH{sub 3} for ortho and para species separately and on a position-by-position basis. We find T {sub rot} and N {sub col} in the range 160-490 K and (1-4) x 10{sup 17} cm{sup -2}, respectively. Our spatially resolved images show that the highest (column) density and hottest gas is found in a northeast-southwest elongated ridge to the southeast of Source I. We have also measured the ortho-para ratio of ammonia, estimated to vary in the range 0.9-1.6. Enhancement of ortho with respect to para and the offset of hot NH{sub 3} emission peaks from known (proto)stellar sources provide evidence that the NH{sub 3} molecules have been released from dust grains into the gas phase through the passage of shocks and not by stellar radiation. We propose that the combined effect of Source I's proper motion and its low-velocity outflow impinging on a pre-existing dense medium is responsible for the excitation of NH{sub 3} and the Orion Hot Core. Finally, we found for the first time evidence of a slow ({approx}5 km s{sup -1}) and compact ({approx}1000 AU) outflow toward IRc7.

• OSTI ID: 21565446
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 739; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AMMONIA
EMISSION
ENERGY-LEVEL TRANSITIONS
EXCITATION
HEATING
HYDRIDES
HYDROGEN COMPOUNDS
IMAGES
MOTION
NEBULAE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PROPER MOTION
VELOCITY