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MILLIMETER-WAVE SPECTRAL LINE SURVEYS TOWARD THE GALACTIC CIRCUMNUCLEAR DISK AND Sgr A*

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Published 2014 August 12 • © 2014. The American Astronomical Society. All rights reserved.
, , Citation Shunya Takekawa et al 2014 ApJS 214 2 DOI 10.1088/0067-0049/214/1/2

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shunya@z2.keio.jp

Author affiliations

1 School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa 223-8522, Japan; shunya@z2.keio.jp

2 Department of Physics, Institute of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa 223-8522, Japan

3 Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Dates

  1. Received 2014 April 28
  2. Accepted 2014 July 16
  3. Published
Keywords

galaxies: nuclei; Galaxy: center; ISM: molecules; radio lines: ISM

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0067-0049/214/1/2

ABSTRACT

We have performed unbiased spectral line surveys at the 3 mm band toward the Galactic circumnuclear disk (CND) and Sgr A* using the Nobeyama Radio Observatory 45 m radio telescope. The target positions are two tangential points of the CND and the direction of Sgr A*. We have obtained three wide-band spectra that cover the frequency range from 81.3 GHz to 115.8 GHz, detecting 46 molecular lines from 30 species, including 10 rare isotopomers and 4 hydrogen recombination lines. Each line profile consists of multiple velocity components which arise from the CND, +50 km s−1 and +20 km s−1 giant molecular clouds (GMCs), and the foreground spiral arms. We define the specific velocity ranges that represent the CND and the GMCs toward each direction, and classify the detected lines into three categories: the CND, GMC, HBD types, based on the line intensities integrated over the defined velocity ranges. The CND and GMC types are the lines that mainly trace the CND and the GMCs, respectively. The HBD types possesses the both characteristics of the CND and GMC types. We also present lists of line intensities and other parameters, as well as intensity ratios, which must be useful to investigate the difference between the nuclear environments of our Galaxy and others.

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1. INTRODUCTION

Most galaxies are thought to have supermassive black holes (SMBHs) at their centers, some of which are observed as active galactic nuclei (AGNs). Recent observations have provided compelling evidence that the Milky Way also has an SMBH with a mass of (4.5 ± 0.4) × 106 M☉ at the dynamical center (Ghez et al. 2008; Gillessen et al. 2009), which is observed as the compact nonthermal radio source Sgr A* (Balick & Brown 1974). Despite its large mass, Sgr A* is extremely dim compared to extragalactic AGNs. The luminosity of the nucleus is only ∼1033–1035 erg s−1, which is far below the Eddington luminosity (6 × 1044 erg s−1). However, some authors suggested that Sgr A* had experienced highly active phases in the past. The widespread Fe 6.4 keV fluorescent line over the central 200 pc suggests that Sgr A* was one million times brighter in the X-ray than the present about several hundred years ago (Koyama et al. 1996; Murakami et al. 2000; Ryu et al. 2013). The pair of large gamma-ray lobes recently discovered by the Fermi Large Area Telescope is hypothesized to be a remnant of quasar activity at ∼107 yr ago (Su et al. 2010). It is possible that nuclear activities are transient in nature, and the currently inactive Sgr A* may turn active in future.

Sgr A* is located in the center of the extended radio source Sgr A, which consists of a thermal minispiral (Sgr A west) and a nonthermal supernova remnant shell (Sgr A east). The circumnuclear disk (CND), which is a dense, warm ring of molecular gas, encompasses the minispiral (e.g., Genzel et al. 1985; Güsten et al. 1987; Kaifu et al. 1987). The well-known 2 pc radius ring of the CND has a rotating velocity of ∼110 km s−1. The entity of the CND is possibly an infalling disk with a diameter of 10 pc, which includes the 2 pc radius ring and the negative longitude extension (Oka et al. 2011). The CND may have been formed by the tidal capture and disruption of a molecular cloud (Sanders 1998; Wardle & Yusef-Zadeh 2008), and is now a potential reservoir for material accreting into the central parsec. It is likely that the CND is not a stable but transient feature (Oka et al. 2011; Requena-Torres et al. 2012). Two giant molecular clouds (GMCs), M–0.13–0.08 (+20 km s−1 cloud) and M–0.02–0.07 (+50 km s−1 cloud), are located in the vicinity of the nuclear region. These GMCs are thought to be interacting with the nuclear region (e.g., Güsten et al. 1981; Genzel et al. 1990). In particular, it is suggested that the +20 km s−1 cloud is feeding the CND (Okumura et al. 1989; Coil & Ho 1999).

Properties of the molecular clouds in the central region are probably linked to the nuclear activities. It is possible that an outflow originating from the central SMBH and the mass-losing He stars may be interacting with the northern and southern lobes of the CND (Mužić et al. 2007). The chemical composition of the CND provides a useful guide for research on feedback from the activity of Sgr A*, as well as on the gas fueling through the CND. High-energy photons/particles generated by AGN activities form X-ray/cosmic-ray dissociation regions (XDRs/CRDRs). Intense UV radiation forms photodissociation regions (PDRs) in irradiated molecular clouds. Theoretical calculations predict a number of XDR/PDR discriminators, such as HCN/HCO+ and HNC/HCN ratios, and abundances of NO, HOC+, and HCO (Spaans & Meijerink 2005; Meijerink et al. 2007). Abundance of refractory molecules, such as SiO, are thought to be enhanced in shocked regions and X-ray-irradiated regions (Martín et al. 2012; Amo-Baladrón et al. 2009).

Most of these diagnostic probes have transitions in millimeter wavelength. Using some of the diagnostic probes with intense emission, several authors have studied the chemistry of the CND and adjacent GMCs (e.g., Amo-Baladrón et al. 2011; Martín et al. 2012). Amo-Baladrón et al. (2011) suggested a possible connection between the CND and the GMCs. In order to investigate their physical connection, a careful search for the best probes of the CND and the GMCs must be essential. Unbiased spectral lines surveys are useful to search for the probes, and to diagnose the physical conditions and chemical composition. However, no unbiased line surveys in the millimeter-wave range toward the CND and Sgr A* have been reported so far. Therefore, we have performed unbiased spectral line surveys at 3 mm band toward the CND and Sgr A*. This paper focuses on a full presentation of the obtained spectra and line parameters between characteristic velocity ranges. Detailed analyses of the physical conditions and chemical composition will be presented in forthcoming papers.

2. OBSERVATIONS

The observations were carried out in 2013 February and May with the Nobeyama Radio Observatory (NRO) 45 m radio telescope (RT). Target positions were chosen as (Δl, Δb) = (+ 46'', 0''), (0'', 0''), (− 40'', 0''), which are defined by offsets from the position of Sgr A*, (α2000, δ2000) = (17h45m$40\buildrel{\mathrm{s}}\over{.}0$, −29° 00' 27farcs9) (Reid & Brunthaler 2004). Hereafter, we refer those target positions to NE, SGA, SW, respectively (Figure 1).

Figure 1.

Figure 1. Target positions of our line surveys (circles) superimposed on a map of the velocity-integrated HCN J = 1–0 emission (Christopher et al. 2005). The star indicates the position of Sgr A*. Sizes of circles represent the half-power beam widths (HPBW) of the NRO 45 m radio telescope at 115 GHz and 86 GHz.

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For these line surveys, we used the TZ1 V/H receivers which were operated in the two-sideband mode. The beamwidth and the main-beam efficiency (ηMB) are listed in Table 1. We used the SAM45 spectrometer in the 2 GHz bandwidth (488.24 kHz resolution) mode. Using 14 arrays of SAM45, we obtained a 4 GHz instantaneous bandwidth for each sideband (LSB and USB). The system noise temperatures ranged from 120 to 360 K during the observations. The observations were made by the 3:1 on–off position switching mode. The reference positions were (l, b) = (0fdg0, +0fdg5), (0fdg0, −0fdg5), which were observed alternately. Pointing errors were corrected every 1.5 hr by observing the SiO maser emissions (43 GHz) from VX Sgr with the H40 receiver. The pointing accuracy was better than 3'' (rms) in both azimuth and elevation. Calibration of the antenna temperature was accomplished by the standard chopper-wheel method.

Table 1. Beamwidth and Main Beam Efficiency of the 45 m RT

Receiver Frequency Beamwidth ηMB
(GHz) (arcsec) (%)
  86 19.2 ± 0.2 36 ± 2
TZ1(H) 110 16.1 ± 0.1 31 ± 2
  115 15.4 ± 0.1 28 ± 1
  86 19.2 ± 0.2 36 ± 2
TZ1(V) 110 16.3 ± 0.1 32 ± 3
  115 14.9 ± 0.1 29 ± 2

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All data were reduced using the NEWSTAR reduction package. We subtracted baselines of each 2 GHz spectrum by fitting sixth- or seventh-degree polynomials. We composed wide-band spectra covering 81.3–115.8 GHz toward the observed three positions by averaging and merging all 2 GHz spectra (Figure 2). The spectral resolution of the resultant spectra was 1.0 MHz. Antenna temperatures ($T^*_{a}$) were converted into main-beam temperatures (TMB) by multiplying 1/ηMB(ν). For the frequency dependence of the efficiency ηMB, we adopted that ηMB(ν) = −0.236 × (νobs/GHz) + 56.47 (%), which was obtained by the least-square fitting to the ηMB measured at three frequencies (Table 1). The rms noise levels of the wide-band spectra were calculated by using data in emission/absorption-free frequency ranges (Figure 3).

Figure 2.

Figure 2. Spectral line zoos obtained at the three observed positions: NE, SW, and SGA.

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Figure 3.

Figure 3. Plots of rms noise of TMB at the three observed positions. Each value is calculated in relatively stable baseline without spectral lines.

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3. RESULTS

We show the wide-band spectra toward NE, SW, and SGA in Figure 2. A number of spectral lines appear in these wide-band spectra. The SGA spectrum is more rippled than the other positions, presumably because the intense continuum emission from Sgr A* manifests the non-linearity of the system. We identified 4 hydrogen recombination lines and 46 lines from 30 molecular species, including 10 rare isotopomers (Table 2). In addition to familiar diatomic and triatomic molecules, a few more complex molecules (e.g., HCCCN, c-C3H2, CH3OH, 13CH3OH, CH3CHO, and CH3CN) were detected.

Table 2. Peak Velocities and Velocity Dispersions of the Identified Spectral Lines

Species Transition Rest Freq. Vpeak (km s−1) σV (km s−1)
(GHz) NE SGA SW NE SGA SW
HNO 10, 1 − 00, 0 81.477490 35.65 35.65 24.98 ... ... ...
HCCCN J = 9–8 81.881463 52.22 37.94 34.28 31.37 25.13 41.16
c-C3H2 20, 2 − 11, 1 82.093555 63.74 52.79 −82.70 ... ... ...
CH3OH 5−1, 5 − 40, 4E 84.521206 52.16 34.78 34.78 24.70 27.42 19.58
OCS J = 7–6 85.139104 13.39 −17.59 13.39 ... ... ...
c-C3H2 21, 2 − 10, 1 85.338906 53.07 53.07 53.07 57.70 28.03 55.83
H 42α 85.688180 82.50 0.63 −74.59 31.44 ... 32.31
H13CN J = 1–0 86.340176 57.21 57.21 −37.58 42.37 49.27 54.49
H13CO+ J = 1–0 86.754288 54.21 47.30 −16.63 40.51 ... 62.09
SiO J = 2–1 86.846995 53.83 70.75 −20.38 48.00 57.09 52.24
HN13C J = 1–0 87.090859 49.43 45.99 52.87 21.47 39.47 45.28
CCH NJ, F = 13/2, 2 − 01/2, 1 87.316925 54.33 47.81 54.33 51.80 39.52 63.38
CCH NJ.F = 11/2, 1 − 01/2, 1 87.402004 54.89 48.03 54.89 55.99 42.15 60.36
HNCO 40, 4 − 30, 3 87.925238 37.29 34.23 37.29 33.81 34.60 32.56
HCN J = 1–0 88.631847 75.59 59.01 −40.09 44.96 44.17 65.52
HCO+ J = 1–0 89.188526 82.10 68.99 −36.22 47.24 39.32 60.43
HNC J = 1–0 90.663564 50.47 50.47 8.48 45.39 41.53 60.97
HCCCN J = 10–9 90.978993 50.39 34.25 30.95 25.35 42.54 26.91
CH3CN JK, F = 53, 6 − 43, 5 91.971310 2.97 18.94 −16.27 25.01 25.87 32.79
H 41α 92.034680 85.28 −22.87 85.28 11.17 37.96 71.98
13CS J = 2–1 92.494270 52.09 −17.28 8.01 36.52 52.87 52.29
N2H+ $J_{F_1,F}=1_{1,2}-0_{1,2}$ 93.171917 39.31 32.87 7.78 29.82 29.79 39.85
13CH3OH 20, 2 − 10, 1A++ 94.407129 66.78 66.78 38.83 ... ... ...
CH3OH 21, 2 − 11, 1A++ 95.914310 −12.16 15.35 33.79 ... ... ...
CH3CHO 50, 5 − 40, 4A++ 95.963465 40.82 40.82 49.88 ... ... ...
C34S J = 2–1 96.412950 50.84 47.73 8.24 38.64 32.53 56.44
CH3OH 20, 2 − 10, 1E 96.744549 61.51 46.32 46.32 32.96 31.11 42.92
OCS J = 8–7 97.301209 46.24 46.24 46.24 22.21 ... 15.04
CH3OH 21, 1 − 11, 0A−− 97.582808 44.57 44.57 11.39 ... ... 47.27
CS J = 2–1 97.980953 52.48 49.42 7.81 45.37 49.44 60.44
H 40α 99.022750 90.07 −37.09 −69.48 29.24 58.19 22.41
SO NJ = 23–12 99.299905 51.04 51.04 6.96 35.88 34.19 45.19
HCCCN J = 11–10 100.076386 52.08 46.09 34.11 26.50 29.91 29.07
CH3OH 8−2, 7 − 81, 7E 101.469719 28.71 28.71 5.08 ... ... ...
H2CS 30, 3 − 20, 2 103.040548 51.06 21.96 33.60 ... ... ...
H2CS 31, 2 − 21, 1 104.617109 51.89 26.10 26.10 40.34 ... ...
H 39α 106.737250 84.96 23.17 −72.32 37.68 68.65 50.55
13CN NJ, F = 11/2, 1 − 01/2, 2 108.658948 79.87 74.35 74.35 32.88 ... 60.37
13CN NJ, F = 13/2, 2 − 01/2, 1 108.782374 23.08 23.08 9.30 42.86 39.26 ...
CH3OH 00, 0 − 1−1, 1E 108.893929 49.36 46.61 30.09 13.98 ... 15.89
HCCCN J = 12–11 109.173638 51.18 37.45 31.96 22.29 14.04 47.41
OCS J = 9–8 109.463063 46.73 46.73 43.99 19.87 34.31 ...
C18O J = 1–0 109.782176 16.87 38.71 5.94 35.23 28.78 35.12
HNCO 50, 5–40, 4 109.905753 48.43 32.06 32.06 22.70 18.19 17.77
13CO J = 1–0 110.201354 25.45 36.33 33.61 49.48 56.14 61.16
CH3CN JK, F = 61, 7 − 51, 6 110.381404 44.55 36.40 33.69 20.01 ... 50.52
C17O JF = 17/2 − 05/2 112.358988 29.32 31.99 45.33 15.93 ... 33.45
CN NJ, F = 11/2, 3/2 − 01/2, 1/2 113.170528 51.73 49.08 9.35 74.18 78.30 78.62
CN NJ, F = 13/2, 5/2 − 01/2, 3/2 113.490982 73.92 23.73 39.58 53.15 47.99 70.70
CO J = 1–0 115.271202 52.54 34.34 29.13 58.03 66.88 73.84

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We extracted 50 line profiles for each position (Figure 4). Each extracted spectrum covers the LSR velocity range from −300 to +300 km s−1. After the extraction, we again subtracted baselines from the spectra by fitting up to third-degree polynomials, although a linear function was used in most cases. Flat lines in some extracted spectra denote the velocity range where the adjacent lines appear. The peak velocities (Vpeak), velocity dispersions (σV), peak temperatures (Tpeak), and 1σ rms noise levels (ΔTMB) of the detected lines are listed in Tables 2 and 3. The ΔTMB values were calculated for the velocity ranges from −300 to −200 km s−1 and from +200 to +300 km s−1. The σV values were calculated using pixels with TMB > 3ΔTMB. All the detected lines have larger velocity widths than those from typical molecular clouds in the Galactic disk. Because of their large velocity widths, some lines are blended and/or unresolved. The lines of common interstellar molecules (e.g., CO, CS, HCN, and HCO+) are intense (Tpeak ≳ 1 K) and have very large velocity widths at every position. In particular, CO J = 1–0 line exceeds 35 K and shows a number of velocity components. About a half of the lines from SGA show absorption features due to the foreground gas in the Galactic disk.

Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

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Figure 4.

Figure 4. Spectral line profiles toward three observed positions. Thick lines are smoothed spectra with grid widths of 10 km s−1. The flat lines in some extracted spectra denote velocity ranges where adjacent lines appear.

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Table 3. Peak Temperatures and 1σ rms Noise Levels of the Identified Spectral Lines

Species Transition Rest Freq. Tpeak (K) ΔTMB (K)
(GHz) NE SGA SW NE SGA SW
HNO 10, 1 − 00, 0 81.477490 0.089 0.063 0.082 0.023 0.022 0.023
HCCCN J = 9–8 81.881463 0.320 0.252 0.328 0.021 0.019 0.020
c-C3H2 20, 2 − 11, 1 82.093555 0.061 0.048 0.048 0.022 0.025 0.023
CH3OH 5−1, 5 − 40, 4E 84.521206 0.263 0.208 0.196 0.013 0.012 0.013
OCS J = 7–6 85.139104 0.077 0.056 0.052 0.019 0.019 0.020
c-C3H2 21, 2 − 10, 1 85.338906 0.208 0.192 0.173 0.019 0.021 0.018
H 42α 85.688180 0.122 0.091 0.158 0.025 0.027 0.025
H13CN J = 1–0 86.340176 0.679 0.484 0.594 0.022 0.023 0.021
H13CO+ J = 1–0 86.754288 0.194 0.123 0.197 0.016 0.040 0.015
SiO J = 2–1 86.846995 0.271 0.204 0.371 0.022 0.018 0.018
HN13C J = 1–0 87.090859 0.128 0.140 0.111 0.021 0.021 0.021
CCH NJ, F = 13/2, 2 − 01/2, 1 87.316925 0.720 0.608 0.631 0.022 0.024 0.021
CCH NJ.F = 11/2, 1 − 01/2, 1 87.402004 0.424 0.361 0.344 0.013 0.022 0.018
HNCO 40, 4 − 30, 3 87.925238 0.233 0.275 0.307 0.025 0.028 0.025
HCN J = 1–0 88.631847 5.775 4.782 5.802 0.033 0.052 0.030
HCO+ J = 1–0 89.188526 4.189 2.637 4.267 0.055 0.109 0.064
HNC J = 1–0 90.663564 1.773 0.996 1.194 0.014 0.014 0.016
HCCCN J = 10–9 90.978993 0.277 0.185 0.228 0.017 0.017 0.019
CH3CN JK, F = 53, 6 − 43, 5 91.971310 0.144 0.092 0.133 0.017 0.017 0.017
H 41α 92.034680 0.118 0.130 0.087 0.020 0.022 0.016
13CS J = 2–1 92.494270 0.273 0.136 0.142 0.017 0.019 0.016
N2H+ $J_{F_1,F}=1_{1,2}-0_{1,2}$ 93.171917 0.578 0.492 0.871 0.028 0.036 0.031
13CH3OH 20, 2 − 10, 1A++ 94.407129 0.055 0.052 0.060 0.019 0.022 0.019
CH3OH 21, 2 − 11, 1A++ 95.914310 0.043 0.062 0.051 0.013 0.011 0.012
CH3CHO 50, 5 − 40, 4A++ 95.963465 0.068 0.064 0.052 0.013 0.014 0.014
C34S J = 2–1 96.412950 0.289 0.115 0.162 0.016 0.017 0.015
CH3OH 20, 2 − 10, 1E 96.744549 0.908 0.720 0.788 0.014 0.013 0.014
OCS J = 8–7 97.301209 0.094 0.066 0.069 0.016 0.016 0.015
CH3OH 21, 1 − 11, 0A−− 97.582808 0.078 0.062 0.063 0.017 0.017 0.015
CS J = 2–1 97.980953 3.673 1.914 1.840 0.020 0.019 0.020
H 40α 99.022750 0.118 0.170 0.091 0.016 0.023 0.017
SO NJ = 23–12 99.299905 0.404 0.255 0.319 0.023 0.020 0.020
HCCCN J = 11–10 100.076386 0.308 0.240 0.191 0.022 0.020 0.023
CH3OH 8−2, 7 − 81, 7E 101.469719 0.115 0.067 0.106 0.026 0.024 0.025
H2CS 30, 3 − 20, 2 103.040548 0.090 0.029 0.061 0.016 0.015 0.017
H2CS 31, 2 − 21, 1 104.617109 0.125 0.091 0.069 0.019 0.021 0.019
H 39α 106.737250 0.164 0.217 0.127 0.023 0.034 0.025
13CN NJ, F = 11/2, 1 − 01/2, 2 108.658948 0.155 0.088 0.141 0.023 0.023 0.024
13CN NJ, F = 13/2, 2 − 01/2, 1 108.782374 0.118 0.103 0.114 0.021 0.021 ...a
CH3OH 00, 0 − 1−1, 1E 108.893929 0.143 0.107 0.132 0.019 0.025 0.023
HCCCN J = 12–11 109.173638 0.340 0.217 0.220 0.022 0.027 0.025
OCS J = 9–8 109.463063 0.124 0.088 0.130 0.021 0.022 0.023
C18O J = 1–0 109.782176 0.670 0.359 0.479 0.021 0.019 0.024
HNCO 50, 5 − 40, 4 109.905753 0.291 0.308 0.382 0.020 0.021 0.023
13CO J = 1–0 110.201354 6.017 4.448 4.649 0.019 0.020 0.020
CH3CN JK, F = 61, 7 − 51, 6 110.381404 0.179 0.127 0.134 0.026 0.032 0.026
C17O JF = 17/2 − 05/2 112.358988 0.180 0.123 0.165 0.035 0.032 0.038
CN NJ, F = 11/2, 3/2 − 01/2, 1/2 113.170528 1.625 0.817 1.348 0.072 0.061 0.045
CN NJ, F = 13/2, 5/2 − 01/2, 3/2 113.490982 2.883 2.300 2.319 0.071 0.074 0.073
CO J = 1–0 115.271202 47.155 36.323 36.888 0.141 0.285 0.234

Note. aWe could not calculate the rms noise here because of the interference of adjacent lines.

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The overall velocity structures of the line profiles vary mainly depending on the position. The profiles of the detected lines, except for the hydrogen recombination lines, contain similar velocity components in each position. Most molecular lines from NE peak at VLSR ∼ +50 km s−1, while those from SW peak at VLSR ∼ +20 km s−1. Molecular lines from SGA generally exhibit complex profiles. The hydrogen recombination lines toward SGA show very large velocity width, which may be attributed to the rapidly rotating minispiral. The biased velocities of the NE and SW recombination lines, which peak at VLSR ∼ +80 and ∼ − 80 km s−1, respectively (except for H41α from SW), may suggest that rotating ionized gas is associated with the CND.

4. DISCUSSION

4.1. Decomposition of Line Profiles

All the identified lines contain multiple velocity components which originate from the +50 km s−1 and +20 km s−1 clouds, foreground/background spiral arms, and the CND. The emission from the +50 km s−1 and +20 km s−1 clouds are dominant in many molecular lines toward NE and SW. The +50 km s−1 cloud appears in the NE spectra, while the +20 km s−1 cloud appears in the SW spectra.

In order to investigate physical conditions and chemical composition of the CND, it is necessary to decompose the line profiles into their constituents. However, it is not easy to perform the decomposition by spectral fitting, since each profile has a complicated shape suffering from the absorption and contamination of the disk gas. Hence, we define velocity ranges that represent the CND and the GMCs, and calculate integrated intensities for each range at each position (Table 4). Figure 5 shows the defined velocity ranges in the HCN, CS, and CH3OH line profiles. Since the CND is rotating at a velocity of ∼110 km s−1, the lines that trace the CND should be prominent in velocities around ∼+110 km s−1 at NE and ∼ −110 km s−1 at SW. This is well illustrated in the HCN and HCO+ profiles. The +50 km s−1 and +20 km s−1 clouds should be prominent in velocities around +50 km s−1 at NE, and around +20 km s−1 at SW, respectively. These components are apparent in several optically thin lines such as the N2H+, CH3OH, and HCCCN lines.

Figure 5.

Figure 5. Line profiles of the HCN, CS, and C3OH lines toward NE, SW, and SGA. The red and green bands show the velocity ranges that represent the CND and GMCs, respectively. The HCN, CS, and CH3OH lines are typical of the CND, HBD, and GMC types, respectively (see Section 4.3).

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Table 4. Velocity Ranges for Integration

  NE SGA SW
  Total GMC CND Total GMC CND Total GMC CND
Vmin (km s−1) −150 30 120 −200 20 70 −200 10 −120
Vmax (km s−1) 200 60 90 200 50 100 150 40 −90
Symbola $I^{\rm NE}_{\rm total}$ $I^{\rm NE}_{\rm GMC}$ $I^{\rm NE}_{\rm CND}$ $I^{\rm SGA}_{\rm total}$ $I^{\rm SGA}_{\rm GMC}$ $I^{\rm SGA}_{\rm CND}$ $I^{\rm SW}_{\rm total}$ $I^{\rm SW}_{\rm GMC}$ $I^{\rm SW}_{\rm CND}$

Note. aSymbol denotes the intensity integrated over Vmin to Vmax.

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4.2. Line Intensities

We list the velocity-integrated line intensities (Tables 5–7) calculated for the velocity ranges listed in Table 4. Figure 6 shows a correlation plot between the integrated intensities at NE and SW for the CND velocity range ($I^{\rm NE}_{\rm CND}$ and $I^{\rm SW}_{\rm CND}$, respectively). The good correlation may support our choice of the velocity ranges that represent the same entity, the CND. We hence define that $I_{\rm CND} \equiv I^{\rm NE}_{\rm CND} + I^{\rm SW}_{\rm CND}$. Figure 7 shows a correlation plot between the integrated intensities at NE and SW for the GMC velocity range ($I^{\rm NE}_{\rm GMC}$ and $I^{\rm SW}_{\rm GMC}$, respectively). The line intensities from the GMCs in NE are generally more intense than those in SW. In other words, the +50 km s−1 cloud is brighter than the +20 km s−1 cloud in most of the detected lines. This plot also shows a tight correlation, although $I^{\rm NE}_{\rm GMC}$ is generally larger than $I^{\rm SW}_{\rm GMC}$. This fact indicates that the +50 km s−1 and +20 km s−1 clouds have roughly similar chemical composition and physical conditions. Thus, we also define that $I_{\rm GMC} \equiv I^{\rm NE}_{\rm GMC} + I^{\rm SW}_{\rm GMC}$. We list ICND and IGMC in Table 8, the values of which are most likely to represent the typical intensities from the CND and the GMCs.

Figure 6.

Figure 6. Correlation plot between the integrated intensities $I^{\rm NE}_{\rm CND}$ and $I^{\rm SW}_{\rm CND}$ for each lines. A solid line shows where $I^{\rm NE}_{\rm CND}=I^{\rm SW}_{\rm CND}$.

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Figure 7.

Figure 7. Correlation plot between the integrated intensities $I^{\rm NE}_{\rm GMC}$ and $I^{\rm SW}_{\rm GMC}$ for each lines. A solid line shows where $I^{\rm NE}_{\rm GMC}=I^{\rm SW}_{\rm GMC}$.

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Table 5. Velocity-integrated Intensities of the Identified Lines toward NE

Species Transition Rest Freq. $I^{\rm NE}_{\rm total}$ $I^{\rm NE}_{\rm GMC}$ $I^{\rm NE}_{\rm CND}$
(GHz) (K km s−1) (K km s−1) (K km s−1)
HNO 10, 1 − 00, 0 81.477490 4.03 ± 0.81 1.24 ± 0.24 0.12 ± 0.24
HCCCN J = 9–8 81.881463 18.35 ± 0.75 7.00 ± 0.22 1.15 ± 0.22
c-C3H2 20, 2 − 11, 1 82.093555 1.34 ± 0.78 0.76 ± 0.23 0.29 ± 0.23
CH3OH 5−1, 5 − 40, 4E 84.521206 13.15 ± 0.47 5.56 ± 0.14 0.58 ± 0.14
OCS J = 7–6 85.139104 4.18 ± 0.68 1.17 ± 0.20 ...
c-C3H2 21, 2 − 10, 1 85.338906 16.41 ± 0.64 3.86 ± 0.19 2.08 ± 0.19
H 42α 85.688180 9.55 ± 0.84 1.25 ± 0.25 2.13 ± 0.25
H13CN J = 1–0 86.340176 54.17 ± 0.76 13.41 ± 0.22 8.50 ± 0.22
H13CO+ J = 1–0 86.754288 11.41 ± 0.36 2.96 ± 0.11 2.52 ± 0.11
SiO J = 2–1 86.846995 27.57 ± 0.66 5.80 ± 0.19 3.92 ± 0.19
HN13C J = 1–0 87.090859 7.88 ± 0.73 2.53 ± 0.21 0.48 ± 0.21
CCH NJ, F = 13/2, 2 − 01/2, 1 87.316925 68.32 ± 0.53 16.30 ± 0.16 5.77 ± 0.16
CCH NJ.F = 11/2, 1 − 01/2, 1 87.402004 36.51 ± 0.34 9.75 ± 0.10 2.57 ± 0.10
HNCO 40, 4 − 30, 3 87.925238 14.29 ± 0.85 5.73 ± 0.25 0.43 ± 0.25
HCN J = 1–0 88.631847 545.85 ± 1.15 106.92 ± 0.34 120.44 ± 0.34
HCO+ J = 1–0 89.188526 366.98 ± 1.88 56.86 ± 0.55 93.21 ± 0.55
HNC J = 1–0 90.663564 143.29 ± 0.47 39.48 ± 0.14 23.03 ± 0.14
HCCCN J = 10–9 90.978993 12.71 ± 0.58 5.65 ± 0.17 0.83 ± 0.17
CH3CN JK, F = 53, 6 − 43, 5 91.971310 7.99 ± 0.37 1.23 ± 0.12 0.25 ± 0.12
H 41α 92.034680 4.17 ± 0.42 1.16 ± 0.14 0.53 ± 0.14
13CS J = 2–1 92.494270 17.00 ± 0.57 4.70 ± 0.17 1.24 ± 0.17
N2H+ $J_{F_1,F}=1_{1,2}-0_{1,2}$ 93.171917 38.15 ± 0.67 14.05 ± 0.20 1.54 ± 0.20
13CH3OH 20, 2 − 10, 1A++ 94.407129 2.45 ± 0.65 1.09 ± 0.19 0.13 ± 0.19
CH3OH 21, 2 − 11, 1A++ 95.914310 1.40 ± 0.26 0.65 ± 0.09 ...
CH3CHO 50, 5 − 40, 4A++ 95.963465 2.19 ± 0.26 0.82 ± 0.09 0.41 ± 0.09
C34S J = 2–1 96.412950 13.55 ± 0.50 4.69 ± 0.15 0.81 ± 0.15
CH3OH 20, 2 − 10, 1E 96.744549 63.34 ± 0.45 23.02 ± 0.13 3.72 ± 0.13
OCS J = 8–7 97.301209 5.19 ± 0.51 1.53 ± 0.15 0.57 ± 0.15
CH3OH 21, 1 − 11, 0A−− 97.582808 3.00 ± 0.54 0.95 ± 0.16 0.19 ± 0.16
CS J = 2–1 97.980953 252.75 ± 0.66 69.36 ± 0.19 24.95 ± 0.19
H 40α 99.022750 9.91 ± 0.51 1.57 ± 0.15 1.91 ± 0.15
SO NJ = 23–12 99.299905 27.81 ± 0.74 8.00 ± 0.22 2.42 ± 0.22
HCCCN J = 11–10 100.076386 13.16 ± 0.62 5.17 ± 0.18 0.69 ± 0.18
CH3OH 8−2, 7 − 81, 7E 101.469719 4.17 ± 0.82 0.77 ± 0.24 ...
H2CS 30, 3 − 20, 2 103.040548 ... 0.72 ± 0.15 ...
H2CS 31, 2 − 21, 1 104.617109 7.52 ± 0.61 2.08 ± 0.18 0.58 ± 0.18
H 39α 106.737250 11.80 ± 0.72 1.88 ± 0.21 1.39 ± 0.21
13CN NJ, F = 11/2, 1 − 01/2, 2 108.658948 11.95 ± 0.54 1.93 ± 0.16 2.11 ± 0.16
13CN NJ, F = 13/2, 2 − 01/2, 1 108.782374 9.85 ± 0.51 2.23 ± 0.15 0.96 ± 0.15
CH3OH 00, 0 − 1−1, 1E 108.893929 2.67 ± 0.42 2.48 ± 0.12 −0.40 ± 0.12
HCCCN J = 12–11 109.173638 13.42 ± 0.29 6.44 ± 0.08 0.56 ± 0.08
OCS J = 9–8 109.463063 6.02 ± 0.64 1.86 ± 0.19 0.09 ± 0.19
C18O J = 1–0 109.782176 32.21 ± 0.54 12.36 ± 0.16 0.60 ± 0.16
HNCO 50, 5 − 40, 4 109.905753 14.25 ± 0.48 6.70 ± 0.14 0.27 ± 0.14
13CO J = 1–0 110.201354 425.35 ± 0.58 149.80 ± 0.17 13.10 ± 0.17
CH3CN JK, F = 61, 7 − 51, 6 110.381404 9.24 ± 0.81 3.09 ± 0.24 1.44 ± 0.24
C17O JF = 17/2 − 05/2 112.358988 9.49 ± 1.08 3.62 ± 0.32 0.09 ± 0.32
CN NJ, F = 11/2, 3/2 − 01/2, 1/2 113.170528 207.06 ± 2.21 35.41 ± 0.65 20.46 ± 0.65
CN NJ, F = 13/2, 5/2 − 01/2, 3/2 113.490982 274.16 ± 2.15 47.48 ± 0.63 47.22 ± 0.63
CO J = 1–0 115.271202 4203.28 ± 4.26 1290.94 ± 1.25 250.78 ± 1.25

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Table 6. Velocity-integrated Intensities of the Identified Lines Toward SGA

Species Transition Rest Freq. $I^{\rm SGA}_{\rm total}$ $I^{\rm SGA}_{\rm GMC}$ $I^{\rm SGA}_{\rm CND}$
(GHz) (K km s−1) (K km s−1) (K km s−1)
HNO 10, 1 − 00, 0 81.477490 5.21 ± 0.59 0.71 ± 0.23 0.26 ± 0.23
HCCCN J = 9–8 81.881463 14.89 ± 0.60 5.23 ± 0.20 1.94 ± 0.20
c-C3H2 20, 2 − 11, 1 82.093555 1.69 ± 0.70 0.29 ± 0.27 0.38 ± 0.27
CH3OH 5−1, 5 − 40, 4E 84.521206 10.64 ± 0.38 3.90 ± 0.12 1.36 ± 0.12
OCS J = 7–6 85.139104 4.46 ± 0.57 0.73 ± 0.20 0.53 ± 0.20
c-C3H2 21, 2 − 10, 1 85.338906 14.98 ± 0.62 2.74 ± 0.20 1.49 ± 0.20
H 42α 85.688180 7.06 ± 0.79 0.75 ± 0.26 0.07 ± 0.26
H13CN J = 1–0 86.340176 36.08 ± 0.73 7.93 ± 0.23 6.67 ± 0.23
H13CO+ J = 1–0 86.754288 7.28 ± 0.69 0.75 ± 0.27 1.56 ± 0.27
SiO J = 2–1 86.846995 19.64 ± 0.43 3.80 ± 0.14 3.54 ± 0.14
HN13C J = 1–0 87.090859 9.62 ± 0.67 2.21 ± 0.22 1.21 ± 0.22
CCH NJ, F = 13/2, 2 − 01/2, 1 87.316925 38.95 ± 0.50 11.59 ± 0.17 5.80 ± 0.17
CCH NJ.F = 11/2, 1 − 01/2, 1 87.402004 20.10 ± 0.43 6.89 ± 0.16 2.79 ± 0.16
HNCO 40, 4 − 30, 3 87.925238 20.67 ± 0.91 5.69 ± 0.28 2.15 ± 0.28
HCN J = 1–0 88.631847 307.64 ± 1.55 71.94 ± 0.52 81.32 ± 0.52
HCO+ J = 1–0 89.188526 149.07 ± 2.83 11.43 ± 1.09 53.28 ± 1.09
HNC J = 1–0 90.663564 59.06 ± 0.38 19.78 ± 0.14 9.76 ± 0.14
HCCCN J = 10–9 90.978993 9.77 ± 0.50 3.61 ± 0.17 1.16 ± 0.17
CH3CN JK, F = 53, 6 − 43, 5 91.971310 7.31 ± 0.33 1.17 ± 0.12 0.84 ± 0.12
H 41α 92.034680 17.28 ± 0.54 2.76 ± 0.17 0.99 ± 0.17
13CS J = 2–1 92.494270 18.65 ± 0.59 2.80 ± 0.19 2.77 ± 0.19
N2H+ $J_{F_1,F}=1_{1,2}-0_{1,2}$ 93.171917 35.10 ± 0.93 11.66 ± 0.29 1.51 ± 0.29
13CH3OH 20, 2 − 10, 1A++ 94.407129 3.05 ± 0.54 0.73 ± 0.22 0.10 ± 0.22
CH3OH 21, 2 − 11, 1A++ 95.914310 2.27 ± 0.16 0.69 ± 0.08 0.15 ± 0.08
CH3CHO 50, 5 − 40, 4A++ 95.963465 2.54 ± 0.24 0.92 ± 0.09 0.39 ± 0.09
C34S J = 2–1 96.412950 8.31 ± 0.45 1.85 ± 0.15 1.12 ± 0.15
CH3OH 20, 2 − 10, 1E 96.744549 41.49 ± 0.40 14.13 ± 0.13 6.85 ± 0.13
OCS J = 8–7 97.301209 4.48 ± 0.42 0.83 ± 0.15 0.67 ± 0.15
CH3OH 21, 1 − 11, 0A−− 97.582808 3.55 ± 0.43 0.57 ± 0.16 0.47 ± 0.16
CS J = 2–1 97.980953 169.51 ± 0.60 37.88 ± 0.18 31.44 ± 0.18
H 40α 99.022750 28.90 ± 0.76 2.95 ± 0.21 1.41 ± 0.21
SO NJ = 23–12 99.299905 19.18 ± 0.56 5.03 ± 0.19 2.87 ± 0.19
HCCCN J = 11–10 100.076386 15.87 ± 0.59 4.51 ± 0.18 1.75 ± 0.18
CH3OH 8−2, 7 − 81, 7E 101.469719 4.16 ± 0.63 0.76 ± 0.23 0.11 ± 0.23
H2CS 30, 3 − 20, 2 103.040548 2.16 ± 0.34 0.18 ± 0.14 0.08 ± 0.14
H2CS 31, 2 − 21, 1 104.617109 6.32 ± 0.58 1.52 ± 0.20 0.70 ± 0.20
H 39α 106.737250 29.72 ± 1.11 3.76 ± 0.31 2.00 ± 0.31
13CN NJ, F = 11/2, 1 − 01/2, 2 108.658948 5.75 ± 0.60 0.56 ± 0.21 0.96 ± 0.21
13CN NJ, F = 13/2, 2 − 01/2, 1 108.782374 5.60 ± 0.37 0.98 ± 0.14 0.97 ± 0.14
CH3OH 00, 0 − 1−1, 1E 108.893929 7.85 ± 0.67 1.92 ± 0.22 0.57 ± 0.22
HCCCN J = 12–11 109.173638 12.25 ± 0.73 4.59 ± 0.25 0.63 ± 0.25
OCS J = 9–8 109.463063 7.73 ± 0.63 1.58 ± 0.20 0.38 ± 0.20
C18O J = 1–0 109.782176 20.23 ± 0.46 6.92 ± 0.15 1.69 ± 0.15
HNCO 50, 5 − 40, 4 109.905753 16.13 ± 0.55 6.40 ± 0.17 0.88 ± 0.17
13CO J = 1–0 110.201354 294.15 ± 0.67 91.72 ± 0.18 29.57 ± 0.18
CH3CN JK, F = 61, 7 − 51, 6 110.381404 10.91 ± 0.76 2.33 ± 0.25 1.59 ± 0.25
C17O JF = 17/2 − 05/2 112.358988 8.82 ± 0.80 1.58 ± 0.28 0.68 ± 0.28
CN NJ, F = 11/2, 3/2 − 01/2, 1/2 113.170528 74.99 ± 1.67 15.00 ± 0.54 6.05 ± 0.54
CN NJ, F = 13/2, 5/2 − 01/2, 3/2 113.490982 113.44 ± 1.82 29.51 ± 0.66 19.16 ± 0.66
CO J = 1–0 115.271202 3046.59 ± 9.15 891.18 ± 2.51 300.58 ± 2.51

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Table 7. Velocity-integrated Intensities of the Identified Lines toward SW

Species Transition Rest Freq. $I^{\rm SW}_{\rm total}$ $I^{\rm SW}_{\rm GMC}$ $I^{\rm SW}_{\rm CND}$
(GHz) (K km s−1) (K km s−1) (K km s−1)
HNO 10, 1 − 00, 0 81.477490 1.89 ± 0.83 1.17 ± 0.24 0.11 ± 0.24
HCCCN J = 9–8 81.881463 17.84 ± 0.71 5.98 ± 0.21 1.16 ± 0.21
c-C3H2 20, 2 − 11, 1 82.093555 1.99 ± 0.81 0.68 ± 0.24 0.21 ± 0.24
CH3OH 5−1, 5 − 40, 4E 84.521206 10.53 ± 0.45 3.81 ± 0.13 0.45 ± 0.13
OCS J = 7–6 85.139104 1.86 ± 0.72 0.75 ± 0.21 0.49 ± 0.21
c-C3H2 21, 2 − 10, 1 85.338906 14.91 ± 0.59 3.20 ± 0.17 1.02 ± 0.17
H 42α 85.688180 11.07 ± 0.77 1.08 ± 0.23 1.57 ± 0.23
H13CN J = 1–0 86.340176 75.62 ± 0.75 8.71 ± 0.22 8.86 ± 0.22
H13CO+ J = 1–0 86.754288 24.49 ± 0.33 2.77 ± 0.10 2.56 ± 0.10
SiO J = 2–1 86.846995 40.71 ± 0.44 4.72 ± 0.13 4.49 ± 0.13
HN13C J = 1–0 87.090859 9.91 ± 0.72 1.95 ± 0.21 0.39 ± 0.21
CCH NJ, F = 13/2, 2 − 01/2, 1 87.316925 66.69 ± 0.50 13.68 ± 0.15 4.99 ± 0.15
CCH NJ.F = 11/2, 1 − 01/2, 1 87.402004 31.61 ± 0.40 6.76 ± 0.12 3.14 ± 0.12
HNCO 40, 4 − 30, 3 87.925238 15.24 ± 0.88 5.39 ± 0.26 0.36 ± 0.26
HCN J = 1–0 88.631847 601.92 ± 1.02 90.43 ± 0.30 94.43 ± 0.30
HCO+ J = 1–0 89.188526 316.63 ± 2.20 56.29 ± 0.65 39.47 ± 0.65
HNC J = 1–0 90.663564 153.53 ± 0.53 27.81 ± 0.16 17.37 ± 0.16
HCCCN J = 10–9 90.978993 10.91 ± 0.64 3.95 ± 0.19 0.84 ± 0.19
CH3CN JK, F = 53, 6 − 43, 5 91.971310 9.14 ± 0.34 1.49 ± 0.12 ...
H 41α 92.034680 7.84 ± 0.35 0.86 ± 0.11 0.86 ± 0.11
13CS J = 2–1 92.494270 14.72 ± 0.53 2.67 ± 0.16 1.16 ± 0.16
N2H+ $J_{F_1,F}=1_{1,2}-0_{1,2}$ 93.171917 47.24 ± 1.04 14.41 ± 0.30 2.45 ± 0.30
13CH3OH 20, 2 − 10, 1A++ 94.407129 ... 0.86 ± 0.19 ...
CH3OH 21, 2 − 11, 1A++ 95.914310 0.81 ± 0.19 0.73 ± 0.08 ...
CH3CHO 50, 5 − 40, 4A++ 95.963465 3.06 ± 0.31 0.58 ± 0.10 0.13 ± 0.10
C34S J = 2–1 96.412950 16.09 ± 0.48 2.76 ± 0.14 1.62 ± 0.14
CH3OH 20, 2 − 10, 1E 96.744549 50.68 ± 0.48 15.93 ± 0.14 1.19 ± 0.14
OCS J = 8–7 97.301209 3.05 ± 0.48 1.04 ± 0.14 ...
CH3OH 21, 1 − 11, 0A−− 97.582808 3.22 ± 0.47 0.82 ± 0.14 0.20 ± 0.14
CS J = 2–1 97.980953 259.57 ± 0.66 41.77 ± 0.19 23.79 ± 0.19
H 40α 99.022750 6.47 ± 0.51 0.43 ± 0.15 1.06 ± 0.15
SO NJ = 23–12 99.299905 30.64 ± 0.65 5.05 ± 0.19 2.36 ± 0.19
HCCCN J = 11–10 100.076386 13.72 ± 0.71 3.37 ± 0.21 0.73 ± 0.21
CH3OH 8−2, 7 − 81, 7E 101.469719 3.77 ± 0.79 1.19 ± 0.23 0.42 ± 0.23
H2CS 30, 3 − 20, 2 103.040548 2.94 ± 0.55 0.96 ± 0.16 0.18 ± 0.16
H2CS 31, 2 − 21, 1 104.617109 2.02 ± 0.59 1.00 ± 0.17 0.18 ± 0.17
H 39α 106.737250 9.18 ± 0.77 1.38 ± 0.23 2.05 ± 0.23
13CN NJ, F = 11/2, 1 − 01/2, 2 108.658948 16.02 ± 0.54 1.88 ± 0.16 1.37 ± 0.16
13CN NJ, F = 13/2, 2 − 01/2, 1 108.782374 13.87 ± 0.69 1.92 ± 0.22 1.67 ± 0.22
CH3OH 00, 0 − 1−1, 1E 108.893929 7.42 ± 0.49 2.53 ± 0.15 0.23 ± 0.15
HCCCN J = 12–11 109.173638 11.81 ± 0.65 4.27 ± 0.19 1.40 ± 0.19
OCS J = 9–8 109.463063 4.44 ± 0.61 1.58 ± 0.18 0.26 ± 0.18
C18O J = 1–0 109.782176 29.53 ± 0.64 8.41 ± 0.19 0.67 ± 0.19
HNCO 50, 5 − 40, 4 109.905753 15.91 ± 0.66 7.12 ± 0.19 0.31 ± 0.19
13CO J = 1–0 110.201354 336.54 ± 0.62 103.36 ± 0.18 8.86 ± 0.18
CH3CN JK, F = 61, 7 − 51, 6 110.381404 13.36 ± 0.69 2.73 ± 0.20 0.32 ± 0.20
C17O JF = 17/2 − 05/2 112.358988 14.24 ± 1.15 2.22 ± 0.34 1.31 ± 0.34
CN NJ, F = 11/2, 3/2 − 01/2, 1/2 113.170528 202.10 ± 1.38 22.66 ± 0.40 24.86 ± 0.40
CN NJ, F = 13/2, 5/2 − 01/2, 3/2 113.490982 252.42 ± 2.21 37.26 ± 0.65 42.22 ± 0.65
CO J = 1–0 115.271202 3576.56 ± 7.07 971.28 ± 2.07 249.15 ± 2.07

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Table 8. Velocity-integrated Intensities in the GMCs and CND, CND Parameters, and Spectral Types

Species Transition Rest Freq. IGMC ICND Error (1σ) ξCND Type
(GHz) (K km s−1) (K km s−1) (K km s−1)
HNO 10, 1 − 00, 0 81.477490 2.40 0.23 0.34 0.13 GMC
HCCCN J = 9–8 81.881463 12.98 2.31 0.30 0.25 GMC
c-C3H2 20, 2 − 11, 1 82.093555 1.43 0.51 0.33 0.50 HBD
CH3OH 5−1, 5 − 40, 4E 84.521206 9.38 1.03 0.19 0.16 GMC
OCS J = 7–6 85.139104 1.92 ... 0.29 ... ...
c-C3H2 21, 2 − 10, 1 85.338906 7.05 3.10 0.25 0.63 HBD
H 42α 85.688180 2.33 3.70 0.33 2.24 CND
H13CN J = 1–0 86.340176 22.11 17.36 0.31 1.20 CND
H13CO+ J = 1–0 86.754288 5.73 5.08 0.15 1.26 CND
SiO J = 2–1 86.846995 10.52 8.41 0.23 1.17 CND
HN13C J = 1–0 87.090859 4.47 0.87 0.30 0.28 GMC
CCH NJ, F = 13/2, 2 − 01/2, 1 87.316925 29.98 10.75 0.22 0.51 HBD
CCH NJ.F = 11/2, 1 − 01/2, 1 87.402004 16.51 5.70 0.16 0.53 HBD
HNCO 40, 4 − 30, 3 87.925238 11.11 0.79 0.36 0.10 GMC
HCN J = 1–0 88.631847 197.35 214.87 0.45 1.54 CND
HCO+ J = 1–0 89.188526 113.16 132.68 0.85 1.78 CND
HNC J = 1–0 90.663564 67.29 40.40 0.21 0.85 HBD
HCCCN J = 10–9 90.978993 9.60 1.67 0.25 0.26 GMC
CH3CN JK, F = 53, 6 − 43, 5 91.971310 2.73 ... 0.17 ... ...
H 41α 92.034680 2.01 1.39 0.18 1.10 CND
13CS J = 2–1 92.494270 7.37 2.41 0.23 0.51 HBD
N2H+ $J_{F_1,F}=1_{1,2}-0_{1,2}$ 93.171917 28.46 3.99 0.36 0.20 GMC
13CH3OH 20, 2 − 10, 1A++ 94.407129 1.95 ... 0.27 ... ...
CH3OH 21, 2 − 11, 1A++ 95.914310 1.38 ... 0.12 ... ...
CH3CHO 50, 5 − 40, 4A++ 95.963465 1.40 0.54 0.13 0.55 HBD
C34S J = 2–1 96.412950 7.45 2.44 0.20 0.61 HBD
CH3OH 20, 2 − 10, 1E 96.744549 38.95 4.91 0.19 0.18 GMC
OCS J = 8–7 97.301209 2.57 0.56 0.21 0.37 ...
CH3OH 21, 1 − 11, 0A−− 97.582808 1.77 0.39 0.21 0.32 GMC
CS J = 2–1 97.980953 111.13 48.75 0.27 0.67 HBD
H 40α 99.022750 2.01 2.97 0.21 2.72 CND
SO NJ = 23–12 99.299905 13.05 4.78 0.29 0.56 HBD
HCCCN J = 11–10 100.076386 8.55 1.42 0.28 0.25 GMC
CH3OH 8−2, 7 − 81, 7E 101.469719 1.96 ... 0.33 ... ...
H2CS 30, 3 − 20, 2 103.040548 1.68 ... 0.22 ... ...
H2CS 31, 2 − 21, 1 104.617109 3.09 0.76 0.25 0.33 GMC
H 39α 106.737250 3.25 3.44 0.31 1.66 CND
13CN NJ, F = 11/2, 1 − 01/2, 2 108.658948 3.80 3.48 0.22 1.32 CND
13CN NJ, F = 13/2, 2 − 01/2, 1 108.782374 4.16 2.63 0.26 0.97 HBD
CH3OH 00, 0 − 1−1, 1E 108.893929 5.00 ... 0.19 ... ...
HCCCN J = 12–11 109.173638 10.71 1.96 0.21 0.34 GMC
OCS J = 9–8 109.463063 3.44 0.35 0.26 0.17 GMC
C18O J = 1–0 109.782176 20.77 1.27 0.24 0.09 GMC
HNCO 50, 5 − 40, 4 109.905753 13.82 0.58 0.24 0.06 GMC
13CO J = 1–0 110.201354 253.15 21.96 0.25 0.12 GMC
CH3CN JK, F = 61, 7 − 51, 6 110.381404 5.83 1.76 0.31 0.48 GMC
C17O JF = 17/2 − 05/2 112.358988 5.84 1.41 0.46 0.59 HBD
CN NJ, F = 11/2, 3/2 − 01/2, 1/2 113.170528 58.08 45.31 0.76 1.24 CND
CN NJ, F = 13/2, 5/2 − 01/2, 3/2 113.490982 84.74 89.44 0.90 1.51 CND
CO J = 1–0 115.271202 2262.22 499.92 2.42 0.32 GMC

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4.3. Line Classification

Figure 8 shows a plot of $I^{\rm NE}_{\rm CND}/I^{\rm NE}_{\rm GMC}$ versus $I^{\rm SW}_{\rm CND}/I^{\rm SW}_{\rm GMC}$ for each lines. The lines in the upper right corner are enhanced toward the CND. In order to search for prominent probes for the CND, we define the CND parameter:

Equation (1)
Figure 8.

Figure 8. Plot of $I^{\rm NE}_{\rm CND}/I^{\rm NE}_{\rm GMC}$ vs. $I^{\rm SW}_{\rm CND}/I^{\rm SW}_{\rm GMC}$ for each lines. The green region satisfies ξCND < 0.5 and species in this region are classified as GMC-type. The turquoise region satisfies 0.5 ⩽ ξCND < 1 and species in this region are classified as HBD-type. Species out of arcs (ξCND ⩾ 1) are classified as CND-type.

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We classify the identified lines into three categories according to ξCND:

  • 1.  
    ξCND ⩾ 1 : CND type;
  • 2.  
    0.5 ⩽ ξCND < 1 : Hybrid (HBD) type;
  • 3.  
    ξCND < 0.5 : GMC type.

The CND and GMC types are the lines that mainly trace the CND and the GMCs, respectively. The HBD-type possesses both characteristics of the CND and GMC types. These types are also listed in Table 8. For example, HCN, HCO+, and SiO belong to the CND type, HCCCN, N2H+ and CH3OH belong to the GMC type, and CS, HNC, CCH, and SO belong to the HBD type. The lines of large molecules tend to be of GMC-type. The HBD-type lines arise from both the CND and the GMCs, and thus these lines could probe the physical connection between the CND and the GMCs. The line profiles of HCN, CS, and CH3OH are shown in Figure 5 as representative examples of the CND, HBD, and GMC types, respectively.

4.4. Line Intensity Ratios

Spectral line intensity ratios are used as indicators of physical conditions of molecular gas and chemical diagnosis, such as XDR/PDR/CRDR/shock-diagnosis. We list several line intensity ratios which were calculated using ICND and IGMC in Table 9.

Table 9. Line Intensity Ratios

Ratio GMC CND
CO/13CO 8.94 ± 0.01 22.8 ± 0.3
HCN/H13CN 8.9 ± 0.1 12.4 ± 0.2
HCN/CO 0.0872 ± 0.0002 0.430 ± 0.002
HCN/13CO 0.780 ± 0.002 9.8 ± 0.1
H13CN/13CO 0.087 ± 0.001 0.79 ± 0.02
CS/CO 0.0491 ± 0.0001 0.0975 ± 0.0007
CS/13CO 0.439 ± 0.001 2.22 ± 0.03
13CS/13CO 0.0291 ± 0.0009 0.11 ± 0.01
HNC/HCN 0.341 ± 0.001 0.188 ± 0.001
HNC/H13CN 3.04 ± 0.04 2.33 ± 0.04
HN13C/H13CN 0.20 ± 0.01 0.05 ± 0.02
HCN/HCO+ 1.74 ± 0.01 1.62 ± 0.01
H13CN/H13CO+ 3.9 ± 0.1 3.4 ± 0.1
SiO/H13CN 0.48 ± 0.01 0.48 ± 0.02
SiO/H13CO+ 1.84 ± 0.06 1.66 ± 0.07

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The CO/13CO and HCN/H13CN ratios can be used as opacity probes. Both of the ratios are lower in the GMCs than in the CND, reflecting the higher optical depth of the CO and HCN lines in the GMCs.

The ratios between dense gas and less dense gas probes are good indicators of gas density. The HCN/CO, HCN/13CO, H13CN/13CO, CS/CO, CS/13CO, and 13CS/13CO ratios can be used as density probes. All these ratios are significantly higher in the CND than in the GMCs, likely indicating very high density in the CND. In the Galactic disk (3.5 kpc <R < 7 kpc) and the central 600 pc, the HCN/CO ratios are 0.026 ± 0.008 and 0.081 ± 0.004, respectively (Helfer & Blitz 1997). In the nuclear environment, the HCN/CO ratios are 0.0872 ± 0.0002 in the GMCs and 0.430 ± 0.002 in the CND. The CS/CO ratios in the disk and the central 500 pc are 0.018 ± 0.008 and 0.027 ± 0.006, respectively (Helfer & Blitz 1993, 1997). The CS/CO ratios are 0.0491 ± 0.0001 in the nuclear GMCs and 0.0975 ± 0.0007 in the CND. These trends in the ratios indicate a steep density gradient in molecular gas toward the nucleus.

Several authors (e.g., Goldsmith et al. 1981; Churchwell et al. 1984; Schilke et al. 1992) predict that the HNC/HCN abundance ratio decreases with increasing temperature, so that the HNC/HCN ratio can be used as an indicator of gas temperature. In nearby molecular clouds, the HNC/HCN ratio is known to range from ∼0.01 in hot cores (Schilke et al. 1992) up to ∼4 in dark clouds (Hirota et al. 1998). In our data, the HNC/HCN ratios in the GMCs and the CND are 0.341 ± 0.001 and 0.188 ± 0.001, respectively. The HNC/HCN ratio, which is significantly lower in the CND than in the GMCs, may indicate a higher temperature of the CND. The HNC/H13CN and HN13C/H13CN ratios show the same trends.

The HCN/HCO+ ratio exceeds unity (>1) in AGN, while the ratio is below unity (<1) in starburst galaxies (e.g., Kohno et al. 2004). X-ray photons from AGN dissociate and ionize molecular gas, increasing the abundances of ions, radicals, and several molecular species. These regions are called XDRs (Lepp & Dalgarno 1996; Maloney et al. 1996; Spaans & Meijerink 2005; Meijerink et al. 2007). In our data, the HCN/HCO+ ratios are 1.74 ± 0.01 and 1.62 ± 0.01 in the GMCs and CND, respectively. They are comparable to each other and significantly exceed unity. Christopher et al. (2005) found that the ratio in the CND was typically ∼2.5 with interferometric observations. The ratios in the l = 1fdg3 complex and the Sgr B1 complex are ∼2.3 and ∼1.5, respectively (Tanaka et al. 2007, 2009). Such a high HCN/HCO+ ratio is found over the whole of the central molecular zone (e.g., Jones et al. 2012).

The SiO abundance is thought to be enhanced in shocked regions, and its intensity ratios to H13CN and H13CO+ are often used as shock probes. The SiO abundance in the CND does not seem to be particularly enhanced, although the SiO line was categorized as CND-type. The SiO/H13CO+ ratios in the GMCs and the CND are 1.84 ± 0.06 and 1.66 ± 0.07, respectively. These values are typical for the Sgr A molecular cloud complex (e.g., Tsuboi et al. 2011).

4.5. Spectra from Sgr A*

Suffering from severe absorption features against the intense continuum radiation from Sgr A*, decomposition of line profiles toward SGA is highly difficult. Based on previous works (e.g., Güsten et al. 1987; Kaifu et al. 1987; Oka et al. 2011), we define VLSR = +70 to +100 km s−1 as the CND range, and VLSR = +20 to +50 km s−1 as the GMC range (Figure 5). We calculated the velocity-integrated intensities of SGA ($I^{\rm SGA}_{\rm tot}$, $I^{\rm SGA}_{\rm GMC}$, and $I^{\rm SGA}_{\rm CND}$), using data with TMB > 0 K in order to minimize the effect of the absorption by the foreground. These intensities are listed in Table 6. Figure 9 shows a correlation plot of the GMC contribution ($I^{\rm SGA}_{\rm GMC}/I^{\rm SGA}_{\rm tot}$) versus the CND contribution ($I^{\rm SGA}_{\rm CND}/I^{\rm SGA}_{\rm tot}$). The GMC types prefer the top left of the plot, while the CND types roughly prefer the bottom right. The HBD types are distributed between the CND and GMC types. This may support the validity of our line classification and that of our definition of velocity ranges on the SGA spectra.

Figure 9.

Figure 9. Correlation plot between $I^{\rm SGA}_{\rm GMC}/I^{\rm SGA}_{\rm total}$ and $I^{\rm SGA}_{\rm CND}/I^{\rm SGA}_{\rm total}$ for each lines. The red, blue, and green circles represent the CND-, HBD-, and GMC-type lines, respectively.

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5. SUMMARY

We performed unbiased spectral line surveys at 3 mm band toward the Galactic CND and Sgr A* using the NRO 45 m RT. The target positions were two tangential points of the CND and the direction of Sgr A* (NE, SW, and SGA). With these surveys, we obtained 3 wide-band spectra that cover the frequency range from 81.3 GHz to 115.8 GHz, detecting 46 molecular lines from 30 species including 10 rare isotopomers and 4 hydrogen recombination lines. The detected lines consist of multiple velocity components that arise from the CND, GMCs (+50 km s−1 and +20 km s−1 clouds), and the foreground spiral arms. Many of the line profiles toward SGA severely suffer from absorption features.

We defined the specific velocity ranges that represent the CND and the GMCs toward each direction. Based on the line intensities integrated over the defined velocity ranges, we classified the detected lines into three categories: the CND, HBD, and GMC types. The rotational lines of HCN, H13CN, HCO+, H13CO+, SiO, CN, and 13CN, and hydrogen recombination lines are classified as CND-type. The detected lines include many diagnostic probes, i.e., opacity, density, temperature, XDR, and shock. We presented the lists of the line intensities and intensity ratios, which must be useful to investigate the difference between nuclear environments of our Galaxy and of others. Deep mapping observations in the CND-type lines with a single dish would reveal the accurate distribution and kinematics of molecular gas in the vicinity of our Galactic nucleus. We have already conducted such mapping observations with the NRO 45 m telescope. These results and detailed analyses will be presented in forthcoming papers.

We are grateful to the NRO staff for their excellent support of the 45 m observations. The Nobeyama Radio Observatory is a branch of the National Astronomical Observatory of Japan, National Institutes of Natural Sciences. We thank the anonymous referee for constructive comments which improved this paper.

10.1088/0067-0049/214/1/2