Methyl Formate as a probe of temperature and structure of Orion-KL

Transcription

1 Methyl Formate as a probe of temperature and structure of Orion-KL Cécile Favre Århus University - Institut for Fysik og Astronomy (IFA) N. Brouillet (LAB), D. Despois (LAB), A. Baudry (LAB), A. Wootten (NRAO), F. Combes (LERMA), M. Guélin (IRAM) & G. Wlodarczak (PhLAM) ESO Spectroscopy Extending the Limits of Astrophysical Spectroscopy 17 th of January 2011 (Victoria, British Columbia)

2 The Orion Kleinmann-Low nebula ν = 8.46 GHz 14.6 km/s 21.6 km/s Hot Core R. Y. Shuping, UCLA, W. M. Keck Observatory. Compact Ridge Hot Core VLA beam 0.26 x0.22 Gómez et al Rodríguez et al km/s Compact Ridge Level step : 150 µjy/beam First contour : 300 µjy/beam An explosive event : 500 years ago! See Laurent Loinard (P34) & Luis Zapata (P67) posters A very rich source of molecules Provides unique conditions for the study in interstellar chemistry : the release of molecules from grain mantles

3 D The Orion-KL nebula : a very rich source of molecules C D B B A A H U MHz 2 CS U MHz D C ( ) CH 3 CH 2 OH D C D C C A B A B A ~ 5000 AU CH 3 OCH 3 CH 3 CH 2 CN IRc2 ( ) ( ) ( ) M. Guélin, Nobel Symposium 2006 «Cosmic Chemistry» - A, B, C and D : hot core (or corinos) O-bearing and N-bearing species tend to peak at different locations

4 Data sets from the IRAM Plateau de Bure Interferometer Frequency (GHz) Spatial resolution ( x ) Spectral resolution (km/s) x x x x

5 Methyl formate HCOOCH 3 o An abundant O-bearing molecule toward Orion-KL o Probe of the temperature and structure of Orion-KL o Results obtained with the PdBI at very high angular resolution (1.8 x0.8 ) Strong emission in the Compact Ridge : an external heating Two major velocity components along a N-S structure Methyl formate is probably released from the ice mantle Other [C 2 H 4 O 2 ] isomers o Acetic acid: N CH3COOH 1.8x10 15 cm -2 o Glycolaldehyde: N CH2OHCHO 2.4x10 14 cm -2

6 Methyl Formate HCOOCH 3 Structure Theoretical spectrum (JPL& Ilyushin et al. 2009) 64 transitions up to E u 650 K 37 in fundamental state v t = 0 27 in the first torsionally excited state v t =1 Methyl Formate formation? (Garrod & Herbst 2006) On grain surfaces And/or in gas phase from precursor methanol (CH 3 OH)

7 Methyl Formate HCOOCH 3 A clumpy structure PdBI uv GHz Hot Core Compact Ridge Favre et al submitted to A&A Integrated intensity map obtained with PdBI Synthesized beam 1.79 x0.79 PA:14 ( MHz, MHz and MHz) Level step : 3.2 K.km/s (3σ)

8 The Compact Ridge an unusual region? MHz (Ix2K) MHz MHz (Ix5K) Frequency (GHz) Beam ( X ) Spectral resolution (GHz) (km.s -1 ) X X X The combination of high angular and spectral resolution yields kinematic ( ALMA!) Favre et al submitted to A&A

9 The Compact Ridge an unusual region? 7.6 km/s component 1.79 X km/s component 3.6 X 2.2 T = 79 K Favre et al submitted to A&A T = 119 K An external heating Shocks? Beam ( x ) Trot (K) N HCOOCH3 (cm -2 ) 1.79 X ±2 1.6x X ±10 3.0x10 16

10 The Compact Ridge an unusual region? 9.3 km/s component 1.79 X km/s component 3.6 X 2.2 T = 112 K Favre et al submitted to A&A T = 168 K An external heating Shocks? Beam ( x ) Trot (K) N HCOOCH3 (cm -2 ) 1.79 X ±50 6.8x X ±29 1.6x10 16

11 Relation to vibrationally excited H 2 A close correlation between the distributions of HCOOCH 3 and H 2 at several places Shocks destroy ice grain mantles Release of HCOOCH 3 (or a precursor) by shocks? Favre et al submitted to A&A Methyl Formate 8.7 km/s channel map overlaid over 2.12 μm excited H 2 emission (ESO-VLT) Lacombe et al. (2004)

12 Velocity structure: a North-South component at 9.3 km/s N-S Structure 8.71 BN Hot Core Compact Ridge Most signal at 8 km/s No emission at 4-5 km/s (even toward the Hot Core) North-South Structure : 9-10 km/s two spectral components GHz GHz (Ix2K) GHz (Ix1.5K) Compact Ridge emission peak T (K) HCOOCH3 channel MHz Synthesized PdBI beam: 1.79 x0.79 PA:14 Level step : 50 mjy/beam Velocity (km/s) Favre et al submitted to A&A

13 HOCH 2 -CH 2 OH Ethylene Glycol HCOOCH 3 Methyl formate ALMA and molecular observations towards Orion-KL CH 2 OHCHO Glycolaldehyde CH 3 COOH Acetic Acid

14 Spectral confusion in Orion-KL: a major problem Many lines (almost all peaks are real lines) Many unidentified Many with a low intensity such molecules have relatively low abundances Tercero, B. et al mm molecular survey (IRAM-30m)

15 Spectral Confusion a major problem toward Orion-KL! Hot Core 30% of real detected lines 40% of real detected lines Detected: 14 Blended : 40 Part. Blended : 3 Not detected : 7 N = 1.6x10 17 cm K Compact Ridge HCOOCH 3 Integrated intensity map obtained with PdBI ( MHz, MHz et MHz) Level step (3σ): 3.2 K.km/s Detected: 8 Blended : 28 Part. Blended : 5 Not detected : 23 N = 4.5x10 16 cm K 49% of real detected lines Detected: 20 Blended : 33 Part. Blended : 2 Not detected : 9 N = 1.6x10 17 cm K ALMA should allow the reduction of spectral confusion

16 ALMA may reduce the confusion problem Line identification / Remove lines blends Beam of PdBI Ethylene glycol? 30m Beam of 30 m T T Ethylene glycol? Ethylene glycol? Formamide IRAM 30m telescope (11 ) Importance of spatial resolution Formamide Frequency (MHz) SO 2 SO 2 Plateau de Bure Interferometer (2.52 x 1.64 ) U-line PdBI Frequency (MHz)

17 ALMA may reduce the confusion problem Frequency (MHz) Beam ( X ) Spectral Resolution (MHz) (km.s -1 ) X X Reveal new molecules Δv = 1.1 km/s Δv = 3.6 km/s Importance of spectral resolution

18 What ALMA will make easier Multi-molecule / line studies Present PdBI data : 2 GHz of bandwidth in total! Detection ratio : o Methyl formate HCOOCH3 : 49% PdBI Needed several observing run Inhomogeneous data ALMA Bandwidth 2 GHz or more in one run

19 Summary Orion-KL nebula is a very molecular rich source high line confusion HCOOCH3 is a probe of the temperature and structure of Orion-KL o Temperatures cover the range 80 to 170 K o 28 emission peaks o Compact Ridge: an external heating o Two velocity components and a velocity gradient o MF production involves the release of molecules from ice mantles Detection of low abundance molecules is difficult High angular and spectral resolutions of ALMA : lower the spectral confusion limit Bandwidth vs spectral resolution multi molecular lines

20 Thank you for your attention

21 Compromise between resolution / bandwidth 0.5km.s ν(ghz) 8 GHz of bandwidth 0.008km.s ν(ghz) 125 MHz of bandwidth Frequency (GHz) Beam ( X ) PdBI Spectral Resolution (GHz) (km.s -1 ) ALMA Bandwidth 8 GHz ALMA Bandwidth 125 MHz X km/s 0.02 km/s X km/s 0.01 km/s Bandwidth 2 GHz :

22 Methyl Formate HCOOCH 3 : data analysis Source I Hot Core Compact Ridge Lines are optically thin τ << 0.05 in general At most 20% of flux is missing Lines are thermalized n H2 ~ 3-7x10 8 cm -3 >> n cr ~ cm -3 Tex = Tkin = Trot LTE is reached HCOOCH 3 Integrated intensity map obtained with PdBI Synthesized beam 1.79 x0.79 PA:14 ( MHz, MHz and MHz) Level step : 3.2 K.km/s (3σ) Favre et al submitted to A&A