A 3 mm Spectral Line Survey toward the Barred Spiral Galaxy NGC 3627

Abstract

We conduct spectral line survey observations in the 3 mm band toward a spiral arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC 3627 with the IRAM 30 m telescope and the Nobeyama 45 m telescope. Additional observations are performed toward the spiral arm and the bar-end in the 2 mm band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end, and the nuclear region, respectively. Star-formation activities are different among the three regions, and in particular, the nucleus of NGC 3627 is known as a LINER/Seyfert 2 type nucleus. In spite of these physical differences, the chemical composition shows impressive similarities among the three regions. This result means that the characteristic chemical composition associated with 2. Observations IRAM 30 m TelescopeObservations toward SA and BE in NG 3627 were performed with the IRAM 30 m telescope at Pico Veleta in July, 2014 and December, 2014. The observed positions are shown in Figure 1 and Table 1. The beam sizes are 30-20 ′′ and 19-17 ′′ at the 3 mm and 2 mm band, respectively, which correspond to linear scales of 1.2-0.9 kpc and 0.8-0.7 kpc at the distance of 11.1 Mpc, respectively. The observed frequency range is from 85.0 to 116.0 GHz and from 140.0 to 148.0 GHz for SA, while it is from 85.0 to 100.5 GHz, from 108.4 to 116.0 GHz, and from 140.0 to 148.0 GHz for BE. The frequency range from 100.5 to 108.4 GHz does not involve strong spectral lines according to previous spectral line surveys toward the spiral arm of M51 (Watanabe et al. 2014). Therefore, we put a lower priority on this frequency range, and did not observe it for BE because of the limited observation time. Two EMIR (Eight MIxer Receivers) bands, E090 and E150, were used simultaneously with the dual polarization mode. The EMIR is the sideband separating receiver, which outputs the USB and LSB signals separately. The image rejection ratio is confirmed to be better than 13 dB and 10 dB for E090 and E150, respectively, according to the status report of the 30 m telescope 1 . The system noise temperature ranged from 75 to 310 K for E090 and from 100 to 210 K for E150. Detailed frequency settings and system noise temperatures are summarized in Table 3. Backends were eight FTS (Fourier Transform Spectrometers) autocorrelators whose bandwidth and channel width are 4050 MHz and 195 kHz, respectively. The telescope pointing was checked every hour by observing the continuum source 1055+018 near the target position, and was found to be better than ±5 ′′ . The wobbler switching mode was employed with beam throw of ±120 ′′ and switching frequency of 0.5 Hz. The wobbler throw is toward the azimuth direction, and hence, the absolute off-position depends on the hour angle. Nevertheless, the off-position was always out of the CO disk of NGC 3627. The intensity scale was calibrated to the antenna temperature (T * A ) scale by using cold and hot loads. T * A was converted to the main beam temperature T mb by multiplying F eff /B eff . Here, F eff is the forward efficiency, w...

CO(2-1)/CO(1-0) line ratio on $\sim$100 parsec scale in the nearby barred galaxy NGC1300

“…This is consistent with recent studies that show the presence of the dense gas or high gas density in bar-end regions of the Milky Way and nearby galaxies (e.g., Gallagher et al 2018;Yajima et al 2019;Kohno et al 2021;Bešlić et al 2021). For example, in NGC 3627, Watanabe et al (2019) showed that there is denser molecular gas in bar-end region than in the spiral arm by comparing the chemical composition. Kohno et al (2021) proposed the converging gas flow from the arm and bar causes the highly turbulent condition, which makes frequent cloud-cloud collisions (CCCs).…”

Differences in star formation activity between tidally triggered and isolated bars: a case study of NGC 4303 and NGC 3627

“…molecular gas and star formation activity, NGC 3627 shows significant differences in the SFR from region to region but the bar itself has very low observable star formation efficiency (Watanabe et al 2011). The bar ends, however, show the most intense star formation of any region with SFE for the three regions Spiral Arm, Bar-End, and the Nuclear Region determined by Watanabe et al (2019) to be 1.3 ± 0.4, 5.7 ± 1.7 and 1.8 ± 1.0 × 10 −9 yr −1 respectively. Despite this, the chemical composition in these regions appears to be quite similar, indicating that the characteristic chemistry on the observed scale is generally insensitive to physical conditions and local effects, such as the star formation rate (Watanabe et al 2019).…”

“…Despite this, the chemical composition in these regions appears to be quite similar, indicating that the characteristic chemistry on the observed scale is generally insensitive to physical conditions and local effects, such as the star formation rate (Watanabe et al 2019). Many studies of NGC 3627 are concerned by this significant variation between regions, particularly at the bar ends and have endeavoured to attribute physical effects to such results (Watanabe et al 2011;Casasola et al 2011;Law et al 2018;Beuther et al 2018;Watanabe et al 2019).…”

“…Regardless of which factors influence the formation of the central bar, it is widely accepted that the presence of such a feature has significant effect on a range of properties within the host galaxy (Sheth et al 2002;Fujii et al 2018;Zana et al 2019). For example, star formation rates for regions within morphological features, such as the bar and arms, are consistently observed to differ considerably, often showing significantly lower star forming efficiency in the bar compared to other areas of the disc (Downes et al 1996;Sheth et al 2002;Watanabe et al 2019). This variation is often attributed to the non-circular motions of stars and gas in the bar, usually induced by a non-axisymmetric bar potential that generates strong shock or shear motions along the bar and disrupts the bar-located molecular clouds, thus suppressing star formation in that region (Roberts et al 1979;Athanassoula 1992;Schinnerer et al 2002;Dobbs et al 2014;Beuther et al 2018).…”

Dense molecular gas properties on 100 pc scales across the disc of NGC 3627

“…The next logical step is to also map the denser gas content of individual molecular clouds. The single dish studies have provided an insight into how the dense molecular gas is distributed in nearby galaxies (Kepley et al 2018;Viaene et al 2018;Watanabe et al 2019). Moreover, despite the difficulties attaining sensitivity at high angular resolution, several works have begun to map high critical density lines down to cloud scales in nearby galaxies using interferometers (e.g.…”