Fluorescent H2 Emission Lines from the Reflection Nebula NGC 7023 Observed with IGRINS
Present at IGRINS workshop 2017 – Kyung Hee University 2017.07.28 by Huynh Anh N. Le1 and Soojong Pak2
1Department of Physics and Astronomy, Seoul National University 2School of Space Research, Kyung Hee University
Image from http://www.cosmotography.com/images/lrg_ngc7023.html Molecular Hydrogen Observations in Molecular Clouds Horse head Iris
Orion M1 Crab Molecular Hydrogen
• The most abundant molecular
Structure of H2 • Tracing interaction bet, the star and rotation the cloud. – Shocked Region – Photodissociation Region H H
vibration H2 Excitation Mechanism
Thermal Non-Thermal
Electrically Excited Collisional Excitation by Absorbing far-UV by shock and Radiates in IR bands in far-UV and IR bands Thermal
Collisional Excitation by shock in IR bands
Rosenthal et al. (2000) Non-Thermal
Electrically Excited by Absorbing far-UV and Radiates in far-UV and IR bands
Hora & Latter (1996) H2 Excitation – Line Intensity & Ratio
Thermal by shocks Non-thermal by Far-UV
Line ratio (2-1 / 1-0)
C-shocks : ~ 0.2 4 3 PDR (nH2 < 5 x 10 /cm ): ~ 0.6 J-shocks : < 0.5 dense PDR : < 0.6 slow J-shocks (< 24 km/s): < 0.3 Measured ratio = 0.3 ~ 0.5 possible mechanism: pure dense PDR pure J-shocks, C+J-shocks PDR + shocks MOLECULAR HYDROGEN IN STAR-FORMING REGIONS 795
Fig. 1.—Full set of energy levelsfor all electronicstatesincludedin our cal- culation. The configuration (with the other 1s el ectron suppressed for conve- nience) isgiven above each group of levels, and the shorthand notation for the level is below. isreversed; orthoiseven andparaisodd. Notethat thereareno Fig. 3.—Lowest rotational levelswithin thefirst threevibration levelsof the rotational J ¼ 0 statesin theC and D electronicstates, because groundelectronicstate. Theenergy scalesareinboth wavenumbersandkelvin. ¼ 1, and J ,where is the projection of the total elec- tronicorbital angular momentum onto the internuclear axis. Linewavelengthsarederived by differencing theselevel en- J ¼ 0.Thereisnosuch selection rulefor vibrational quantum ergies and correcting for the index of refraction of air for k > numbers. 2000 8 . Comparison of these theoretical wavelengths with the 2.2. Bound-bound Transitions observed wavelengths given in Timmermann et al. (1996) and Rosenthal et al.(2000) show that our wavelengthsderivedfrom 2.2.1. Tr ansitions within the Ground Electronic State electronictransition energiesagreewith theobserved valuesto Quadrupole radiative transition probabilities for rovibrational typically within k/k 2 ; 10 5. levelswithinthegroundelectronicstatearetakenfromWolniewicz Spectroscopicnotations, such as‘‘2–1 S(1),’’ are commonly et al. (1998). Thisdataset iscomplete; i.e., transition probabili- used to identify the transitions. The first numbers indicate the ties are given for all allowed transitions between the 301 rovi- change in vibrational levels.The capital letter indicatesthebranch, brational levels. whichspecifiesthechangeinJ,asshowninTable1.Thenumber Rate coefficient fits for collisi onal excitation processes within in parentheses is the lower J level of the transition. Radiative the X state are given by Le Bourlot et al. (1999)5 and adopted decays between ortho and para are not possible because of the here. Theseinclude rovibrational excitation of H2 by collisions 0 different nuclear spin. Within the ground electronic state, lines with H ,He,andH2,but only for nonreactive transitions,i.e., have the selection rule J ¼ 0, 2. For electronic transitions those that do not involve changes in nuclear spin. between and ,theselectionruleis J ¼ 0, 1, whereasthe TheLeBourlot et al . (1999) compilation, obtained with quan- correspondingrulefor to is J ¼ 1. For C+ theselection tum mechanical methods, should be appropriate to temperatures rule is J ¼ 1, whereas the corresponding rule for C is as low as 10 K. However, thiscompilation containsonly rate coefficientsof 500 transitions, roughly 4% of the12,535 pos- sible transitions within X. The data set presented by Martin & Mandy (1995, 1998) includesfar moretransitions but werenot intended to be applied to the low temperatures needed for the photodissociation region (PDR) models, since they were ob- tained with classical trajectory methods. Figure4 comparestheir ratewith theLeBourlot et al. (1999) valuesfor ratecoefficients
5 See also http://ccpH7.du2r.ac.uExcitationk /cooling_ by _ h2. – Ortho and Para Ratio
TA BLE 1 Br anch Notat ion
Branch Jup Jlo
O...... 2 P...... 1 Q...... 0 Fig. 2.—Energy levels within the ground el ectronic state. The ex ci tation R...... +1 1 energiesaregivenincm relativetothelowest level (v ¼ 0, J ¼ 0).The equiv- S...... +2 alent temperature is given on the right-hand axis. Shaw et al. (2005) Ortho-to-para-H2 ratio (OPR) OPR = 3 OPR < 3
Thermal by shock Non-thermal by Far-UV Constellation: Cepheus NGC 7023 (Iris Nebula) NGC 7023 (Iris Nebula)
• Illuminated by HD 200775 (Herbig B3Ve-B5,
Teff = 17,000 K)
• PDRs in North and South from HD 200775
• D = 430 (+160/-90) pc
• Clumpy structure ? (Martini+1999;1997)
• Advancing PDR ? (Fuente +2000)
• Existing of shock ? (Fuente +2000) IGRINS - observations
• Target: NGC 7023 • Date: 2014 July 12 (Commissioning) • Exposures: 2 x 600s / frame
• Positions (Ra, Dec)J2000 = (21:01:36.9, +68:09:47.8) • Total exposure time: t = 1200 s, ON position t = 1200 s, OFF position Le et al. 2017
Lemaire et al. (1996)
H2 spectra H2 spectra
• 68 H2 rovibrational emission lines (v = 1 – 13 and J = 1 – 11) from Regions A, B, and C Analysis
• Dynamical Information from H2 Lines
• Emission line ratios
• Ortho-to-para ratios
• H2 level population De-convolution of Line Width
V ΔVFWHM
Region A 3.64 0.16 4.63 0.34
Region B 3.46 0.11 3.29 0.26
Region C 3.39 0.22 3.20 0.27
Sample Spectra: H2 1-0 S(1) Line Analysis
Ortho-to-Para Ratio 2-1 S(1) / 1-0 S(1) (OPR)
Region A 0.41 0.01 1.82 0.11
Region B 0.48 0.02 1.75 0.09
Region C 0.56 0.03 1.63 0.12 Exc. Diag. of H2 level Column Density: Region A Exc. Diag. of H2 level Column Density: Region B Exc. Diag. of H2 level Column Density: Region C Comparison Data to PDR Model Comparison Data to PDR Model Comparison Data to PDR Model Comparison Data to PDR Model Derived Densities
5 = 0.01 pc
1 = 0.002 pc Summary and Conclusion
• We observed the NW filament of NGC Line ratio 7023 in H- and K-bands using the high (2-1 / 1- OPR V ΔVFWHM nH 0) spectral resolution spectrograph, IGRINS. 0.41 ± 1.82 ± 3.64 ± 4.63 ± 105 • We detected 68 H2 rovibration lines 0.01 0.11 0.16 0.34 which are mostly UV excited. Dense regions show collisional de- 0.48 ± 1.75 ± 3.46 ± 3.29 ± 103-104 excitation. 0.02 0.09 0.11 0.26 • We suggest that: The presence of the
0.56 ± 1.63 ± 3.39 ± 3.20 ± dynamic PDR front relative to the molecular 103-104 0.03 0.12 0.22 0.27 cloud. • We suggest that a high density (n 105 cm-3) clump with H 2.5 ± 0.3 – position offset 10′′ to the north a size of ~ 0.002 pc embedded in lower from ours (Martini+1997) 3 4 -3 density (nH 10 10 cm ) regions. Thank you!