TY - JOUR
T1 - A statistical study of giant molecular clouds traced by 13CO, C18O, CS, and CH3OH in the disk of NGC 1068 based on ALMA observations
AU - Tosaki, Tomoka
AU - Kohno, Kotaro
AU - Harada, Nanase
AU - Tanaka, Kunihiko
AU - Egusa, Fumi
AU - Izumi, Takuma
AU - Takano, Shuro
AU - Nakajima, Taku
AU - Taniguchi, Akio
AU - Tamura, Yoichi
N1 - Funding Information:
We thank the anonymous referee for helpful comments to improve the paper. Data analysis was in part carried out on the common use data analysis computer system at the Astronomy Data Center, ADC, of the National Astronomical Observatory of Japan (NAOJ). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00060.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. T.T. was supported by the ALMA Japan Research Grant of NAOJ Chile Observatory, NAOJ-ALMA-0156. K.K. acknowledges support from JSPS KAKENHI grant number 25247019.
PY - 2017
Y1 - 2017
N2 - We present 1″.4 (98 pc) resolution ALMA observations of 13CO(J = 1-0), C18O(J = 1-0), CS(J = 2-1), and CH3OH(JK = 2K-1K) molecular rotational lines in the central 1′ (4.2 kpc) diameter region of NGC 1068 to study the physical and chemical properties of giant molecular clouds (GMCs) and to test whether these GMC-scale properties are linked to the larger-scale galactic environment. Using the derived 13CO cube, we have identified 187 high-significance (>8σ) GMCs by employing the CLUMPFIND algorithm. The molecular gas masses of GMCs (M13CO), derived from the 13CO data, range from 1.8 × 104 M⊙ to 4.2 × 107 M⊙. A mass function of GMCs in NGC 1068 has been obtained for the first time at ∼100 pc resolution. We find the slope of the mass function γ = -1.25 ± 0.07 for a mass range of M13CO ≥ 105 M⊙. This is shallower than the GMCs in the disk regions of the Milky Way, M 51, and NGC 300. Further, we find that the high mass cut-off of the GMC mass function occurs at M13CO ∼ 6 × 107 M⊙, which is an order of magnitude larger than that in the nuclear bar region of M 51, indicating that the more massive clouds dominate the mass budget in NGC 1068. The observed C18O(J = 1-0)/13CO(J = 1-0) intensity ratios are found to be fairly uniform (0.27 ± 0.05) among the identified GMCs. In contrast, the CH3OH(JK = 2K-1K)/13CO(J = 1-0) ratios exhibit striking spatial variation across the disk, with the smallest values around the bar-end (<0.03), and larger ratios along the spiral arms (∼0.1-0.2). We find that GMCs with detectable methanol emission tend to have systematically larger velocity widths than those without methanol emission, suggesting that (relatively weak) shocks are responsible for the enhancement of the CH3OH/13CO ratios of GMCs in the disk of NGC 1068.
AB - We present 1″.4 (98 pc) resolution ALMA observations of 13CO(J = 1-0), C18O(J = 1-0), CS(J = 2-1), and CH3OH(JK = 2K-1K) molecular rotational lines in the central 1′ (4.2 kpc) diameter region of NGC 1068 to study the physical and chemical properties of giant molecular clouds (GMCs) and to test whether these GMC-scale properties are linked to the larger-scale galactic environment. Using the derived 13CO cube, we have identified 187 high-significance (>8σ) GMCs by employing the CLUMPFIND algorithm. The molecular gas masses of GMCs (M13CO), derived from the 13CO data, range from 1.8 × 104 M⊙ to 4.2 × 107 M⊙. A mass function of GMCs in NGC 1068 has been obtained for the first time at ∼100 pc resolution. We find the slope of the mass function γ = -1.25 ± 0.07 for a mass range of M13CO ≥ 105 M⊙. This is shallower than the GMCs in the disk regions of the Milky Way, M 51, and NGC 300. Further, we find that the high mass cut-off of the GMC mass function occurs at M13CO ∼ 6 × 107 M⊙, which is an order of magnitude larger than that in the nuclear bar region of M 51, indicating that the more massive clouds dominate the mass budget in NGC 1068. The observed C18O(J = 1-0)/13CO(J = 1-0) intensity ratios are found to be fairly uniform (0.27 ± 0.05) among the identified GMCs. In contrast, the CH3OH(JK = 2K-1K)/13CO(J = 1-0) ratios exhibit striking spatial variation across the disk, with the smallest values around the bar-end (<0.03), and larger ratios along the spiral arms (∼0.1-0.2). We find that GMCs with detectable methanol emission tend to have systematically larger velocity widths than those without methanol emission, suggesting that (relatively weak) shocks are responsible for the enhancement of the CH3OH/13CO ratios of GMCs in the disk of NGC 1068.
KW - Galaxies: ISM
KW - Galaxies: individual (NGC 1068)
KW - Radio lines: galaxies
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U2 - 10.1093/pasj/psw122
DO - 10.1093/pasj/psw122
M3 - Article
AN - SCOPUS:85019498137
VL - 69
JO - Publication of the Astronomical Society of Japan
JF - Publication of the Astronomical Society of Japan
SN - 0004-6264
IS - 2
M1 - 18
ER -