Molecular line survey observations toward nearby galaxies with IRAM 30 m

Transcription

1 Molecular line survey observations toward nearby galaxies with IRAM 30 m Yuri Nishimura IoA/The University of Tokyo, NAOJ

2 IRAM 30 m: 32 GHz in only two tunings FTS 200 khz resolution: simultaneously observing 8 GHz 4 3 mm-band line survey: GHz in only two tunings E090 c-c3h2 N2H+ C18O CH3OH O 84 O CO 116 GHz HCN CN HCO+ 12CO The other option: GHz, GHz, and GHz E090 c-c3h2 N2H+ C18O CH3OH O 85 O CO 116 GHz HCN CN HCO+ o- 12CO CH3OH E p- 148 GHz 2 of 16

3 3 mm- and 2 mm-band line survey toward M51 Watanabe et al revealed the molecular composition of GMCs in the spiral arm of M51. HCN O HCO + N2H + CH3OH as well as 13CO, CN, and 12 CO ortho- M51 spiral arm P1 CH3OH para- 3 of 16

4 Our interest: Low-metallicity dwarf galaxies Nearby dwarf galaxies as a laboratory of low metallicity environment similar to first star-forming systems in the early universe molecular composition must be differentiated Elemental abundances of each galaxy Values in HII regions dwarfs Galaxy Z/Z sun O/H 10 4 C/H 10 4 N/H 10 5 S/H 10 5 LMC IC IRAM NGC /10 Solar/Galactic M51 ~ LMC&Solar/Galactic: Dufour et al. 1982, IC10: Magrini et al. 2009, Bolatto et al. 2000, Lequeux et al. 1979, NGC6822: Esteban et al. 2014, M51: Bresolin et al. 2004, Garnett et al of 16

5 Previous studies: LMC and IC10 Large Magellanic Cloud at the distance of 50 kpc from the sun observed with Mopra 22 m, 450 hours Spitzer/MIPS, Herschel-PA, SPIRE 7 molecular clouds with different star-forming activities IC10 at the distance of 950 kpc from the sun observed with NRO 45 m, 55 hours the CO brightest cloud Spitzer/MIPS, IRAC; Lebouteiller et al of 16

6 3 mm-band line survey toward LMC and IC10 The spectral intensity patterns of LMC and IC10 are found to be similar to one another! HCN HCO + LMC N44C as well as 13CO and 12 CO Nishimura et al. 2016b ApJ, 818, 161 HCN HCO + IC10 as well as 13CO and 12 CO Nishimura et al. 2016a ApJ, 829, 94 6 of 16

7 IRAM observations: NGC6822 Hα (grey) + HI (orange) image of NGC6822 Dwarf irregular Distance of 500 kpc from the sun Target: Hubble V, the brightest HII region 3 mm & 2 mm observation with IRAM 30 m Total observing time of 29 hours Schruba et al Previous studies: CO 2-1 & 3-2: Petitpas & Wilson 1998 HCO +,, and H 2 CO: Israel et al CO with ALMA: Schruba et al of 16

8 Results: 3 mm-band spectra HCN HCO + NGC6822 Hubble V as well as 13CO and 12 CO HPBW 29 ~ 71 pc Similar spectral intensity pattern! HCN HCO + LMC N44C as well as 13CO and 12 CO HPBW 38 ~ 10 pc Nishimura et al. 2016b ApJ, 818, 161 HCN HCO + IC10 as well as 13CO and 12 CO HPBW 17 ~ 80 pc Nishimura et al. 2016a ApJ, 829, 94 8 of 16

9 Comparison with metal-rich environments To understand the effect of low metallicity, we compared dwarf galaxies with our Galaxy and a spiral galaxy M51. HCN HCO + LMC N44C deficient N-bearing species HCN O HCO + M51 spiral arm P1 N2H + CH3OH Watanabe et al enhanced deficient CH 3 OH 9 of 16

10 Deficient Nitrogen-bearing species as a direct impact of lower elemental N abundances elemental 0.25 molecular N/O HCN/HCO similar trend! N6822 IC10 LMC MW M51 N6822 IC10 LMC MW M51 10 of 16

11 Enhanced & Deficient CH 3 OH Enhancement of is not due to elemental abundances! elemental molecular C/O /HCO enhanced! N6822 IC10 LMC MW M51 N6822 IC10 LMC MW M51 11 of 16

12 Enhanced & Deficient CH 3 OH reflecting extended photon dominated region in cloud peripheries due to the lower abundance of dust grains PDR is rich in C + : main ingredient of. less efficient on-dust reaction: CH 3 OH is produced on dust grains. deeper UV penetration extended PDR in cloud peripheries CO HCO H 2 CO CH 3 O CH 3 OH CO x dust grain H higher than 20 K shorter resident time 12 of 16

13 Results: 2 mm-band spectra We observed 2mm-band simultaneously with the 3mm band. Detection: ortho-/para-h 2 CO,, non-detection: CH 3 OH ortho- NGC6822 Hubble V CH3OH para- ortho- M51 spiral arm P1 Watanabe et al CH3OH para- 13 of 16

14 Results: 2 mm-band spectra CH 3 OH para-h 2 CO ortho- NGC6822 Hubble V CH3OH para- ortho- M51 spiral arm P1 Watanabe et al CH3OH para- 14 of 16

15 Summary We have conducted 3 mm- and 2 mm-band line survey observation toward the brightest HII region Hubble V in low-metallicity dwarf NGC6822 with IRAM 30 m telescope. The identified species are: 3 mm-band:, HCN, HCO +,, 13 CO, 12 CO 2 mm-band: ortho-/para-h 2 CO, The similar spectral pattern to the LMC and IC10 is confirmed. Nitrogen-bearing species are deficient, reflecting the lower elemental abundance of nitrogen. Due to the less abundant dust grains, is enhanced and CH 3 OH are deficient. While CH 3 OH is absent, H 2 CO is detected in the 2 mm band spectrum. In spite of general resemblance, 13 CO is found to be weak in NGC6822, compared with the LMC and IC of 16

16 Our future plan Recent progress of mapping line survey toward Galactic molecular cloud To understand molecular-cloud-scale (10 pc-scale) chemistry Orion B (Pety et al. 2017) W51 (Watanabe et al. 2017) W3(OH) (Nishimura et al. 2017) and more to come Importance of diffuse parts of a molecular cloud in the spectrum averaged over the entire cloud Similar mapping observations across an entire disk of a galaxy The EMPIRE survey (Bigiel et al. 2016) with IRAM 30 m More molecular species to be mapped 16 of 16