Precise determination of the isotopic ratios of HC3N in the massive star-forming region Sgr B2(M) Takahiro Oyama, Rin Abe, Ayane Miyazaki, Mitsunori Araki, Shuro Takano, Nobuhiko Kuze, Yoshihiro Sumiyoshi, and Koichi Tsukiyama

・ Isotopic ratios of HC3N in Sgr B2(M) Main topic ・ Isotopic ratios of HC3N in Sgr B2(M) Additional topic ・ Vibrational excited states in hot core ・ HC315N as a potentially good probe to investigate 14N/15N ratio

Cyanoacetylene HC3N About 40% of the interstellar molecules Important to understand Galactic chemical evolution Carbon chain species HC3N: A relatively simple carbon chain species Large amount in interstellar medium Isotopic ratio: Reflecting its formation mechanism Starless dark cloud TMC-1 H13CCCN:HC13CCN:HCC13CN Takano et al., Astron. Astrophys. 329, 1156 (1998) 1 : 1.0(1) : 1.4(2) • Precursor with two equivalent carbon atoms Ex. HCCH, HCCH+ • Isotopic fractionation CN + 13C+ → 13CN + C+

Previous studies of HC3N in Sgr B2 What about other astronomical objects? • Wannier et al. (1978) H13CCCN : HC13CCN : HCC13CN = 1.1(3) : 1.0(3) : 1 Sagittarius B2 (Sgr B2) • Mangum et al. (1988) H13CCCN : HC13CCN : HCC13CN = 0.9(1) : 1.1(1) : 1 Insufficient to discuss the isotopic fractionation Reported ratios: Present study: Determination of the accurate isotopic ratios of HC3N in Sgr B2

Observation position Sgr B2(M) Massive star-forming region Distance from sun: 8.5 kpc ≒ 2.8×104 ly Radial velocity: 62 km/s Features: Many interstellar molecules cm wave continuum source　　　

Results ≈ ≈ • HCCCN: J =10－9, 11－10 Total ON time: 4 hours r.m.s ~13 mK ≈ HCCCN J = 10−9 J = 10−9 6 0.2 HCCC15N J = 10−9 4 HC13CCN HCC13CN H13CCCN Brightness temperature TB/K 0.1 2 ≈ 0.0 88.2 90.6 90.8 91.0 88.30 88.35 Frequency/GHz Frequency/GHz • HCCCN: J =10－9, 11－10 • H13CCCN, HC13CCN, HCC13CN: J =10－9 • Excited states: n4, n6, n7, 2n7, 3n7 or n5, 4n7 or n5 + n7 • HCCC15N: J =10－9 First detection in Sgr B2

13C isotopic ratio • 13C isotopomers HC3N Trot fixed to 163 K 24 25 26 27 28 29 12.25 12.26 Trot fixed to 163 K • 13C isotopomers HC3N 163 K N(H13CCCN)=8.2×1013 cm−2 N(HC13CCN)=8.2×1013 cm−2 N(HCC13CN)=8.1×1013 cm−2 log L Ratios 1 : 1.03(4) : 0.99(3) Eu/k Starless dark cloud TMC-1 1 : 1.0(1) : 1.4(2) Takano et al., Astron. Astrophys. 329, 1156(1998) • Rotational temperature Trot=163 K • Column density N =1.6×1015 cm－2

Isotopic fractionation Relatively hot • Kinetic temperatures (Tk) TMC-1: Tk =10 K (Tölle et al. 1981) Sgr B2 (M): Tk =175 K (Hüttemeister et al. 1995) • Isotopic exchange → exothermic reaction Ex. CN + 13C+ → 13CN + C+ + DE(35 K) • Energy difference between CN and 13CN Sufficiently small for Tk in Sgr B2(M) No contribution to make difference among the column densities of the 13C isotopomers The first report of the precise 13C isotopic ratios of HC3N in the warm region such as Sgr B2(M).

・ Isotopic ratios of HC3N in Sgr B2(M) Main topic ・ Isotopic ratios of HC3N in Sgr B2(M) Additional topic ・ Vibrational excited states in hot core ・ HC315N as a potentially good probe to investigate 14N/15N

Excited vibrational states • Vibrational excited states: T = 362 K Ground state 163 K • Ground state: T = 163 K 12.0 Clearly different 362 K Vibrational excitation induced by Mid-IR 11.0 log L Beam width 10.0 Ground state Hot core Mid-IR Excited molecules 400 800 1200 Eu/k Vicente et al., Astron. Astrophys. 361, 1058 (2000).

Absorption lines • Absorptions on both sides of lines Radial velocity km/s 100 200 ｰ200 ｰ100 K 4 0.2 0.0 0.08 0.00 0.04 0.03 Ground state n7 n6 n5 or 3n7 n4 n5 + n7 or 4n7 236.7 676.73 512.5 879.36 900.73 El(cm－1) J=10−9 62 km/s Excited vibrational state of HC3N only There are two clouds in front of Sgr B2(M) Velocity: ~50 km/s Cloud 1 Tvib: High Trot: Low Velocity: ~70 km/s Cloud 2 Tvib: High Trot: Low

Molecular clouds in Sgr B2(M) Emissions　 from Hot core Absorptions on both sides of lines Due to the Clouds between Galactic center and the Solar system Our Galaxy Sgr B2(M) cm wave continuum source Cloud 1, 2 Tvib: High Trot: Low Our Solar System Molecules populate the excited vibrational states 銀河中心 Radial velocity km/s 100 200 ｰ200 ｰ100 K 0.04 0.00 n5 or 3n7 There is a excitation source in the clouds

・ Isotopic ratios of HC3N in Sgr B2(M) Main topic ・ Isotopic ratios of HC3N in Sgr B2(M) Additional topic ・ Vibrational excited states in hot core ・ HC315N as a potentially good probe to investigate 14N/15N

14N/15N ratio • In GCE model, 14N/15N ratio Depending on the Galactocentric distance HCCC15N J = 10−9 88.30 88.35 0.0 0.1 0.2 Frequency/GHz C2H5CN 10010−909 In the galactic center, Dahmen et al.(1995) (288.6±65.1) Brightness temperature TB/K Adande et al.(2012) (123.8±37.1) N =1.5×1013 cm－2 Considerable difference Trot fixed to 163 K Lack of accurate data for the 14N/15N ratio in Galactic center N(HC3N)/N(HC315N) = 14N/15N ~ 99(tentative)

14N/15N ratio 14N/15N ratio is estimated with the column densities of HCN, HNC and so on. HC3N Cyanoacetylene　 • No disturbed lines Many absorption lines caused by envelope in Sgr B2(M) −2 4 Ta* (K) 2 90.9 91.0 91.1 91.2 91.3 Frequency (GHz) No disturbance 88.5 88.6 88.7 88.8 88.9 −2 2 4 HCN J = 1−0 Ta* (K) Frequency (GHz) Absorption lines Potentially good probe to investigate 14N/15N in Galactic center region

Summary • Precise determination of the 13C isotopic ratios H13CCCN : HC13CCN : HCC13CN = 1 : 1.03 : 0.99 • Observations of transitons in the exited states Determination of temperature, 362 K • Observations of J = 10−9 transition for HC315N Tentative determination of 14N/15N ratio, ~99 Future work • Observations of other transitions for HC315N Determination of accurate 14N/15N in Sgr B2(M)

Appendix

Telescope and Observing period 2016/4/8~11, and 5/10~11 • Receiver TZ1(H/V) • Autocorrelator FX-type SAM45 • Freq.resolution 488.24 kHz • Bandwidth 1600 MHz Nobeyama 45-m telescope