A molecular line survey toward the nearby galaxies NGC 1068, NGC 253, and IC 342 at 3 mm with the Nobeyama 45 m radio telescope: The data

Abstract

AbstractWe present observational data of a molecular line survey toward the nearby galaxies NGC 1068, NGC 253, and IC 342 at wavelengths of 3 mm (∼85–116 GHz) obtained with the Nobeyama 45 m radio telescope. Regarding IC 342, a line survey with high spectral resolution in the 3 mm region was reported for the first time. NGC 1068 is a nearby gas-rich galaxy with X-rays from an active galactic nucleus (AGN), and NGC 253 and IC 342 are nearby gas-rich galaxies with prototypical starbursts. These galaxies are useful for studying the impacts of X-rays and ultraviolet radiation on molecular abundances. The survey was carried out with a resulting rms noise level of a few mK ($T\rm {_A^*}$). As a result we could obtain almost complete data of these galaxies in the 3 mm region: we detected 19–23 molecular species, depending on the galaxies, including several new detections (e.g., cyclic-C3H2 in IC 342). We found that the intensities of HCN, CN, and HC3N relative to 13CO are significantly strong in NGC 1068 compared with those in NGC 253 and IC 342. On the other hand, CH3CCH was not detected in NGC 1068. We obtained these results with the narrow beam (${15{^{\prime\prime}_{.}}2}$–${19{^{\prime\prime}_{.}}1}$) of the 45 m telescope, among single-dish telescopes, and in particular selectively observed molecular gas close to the circumnuclear disk (CND) in NGC 1068. The present line intensities in NGC 1068 were compared with those obtained with the IRAM 30 m radio telescope already reported. As a result, the intensity ratio of each line was found to have information on the spatial distribution. Our observations revealed the line intensities and stringent constraints on the upper limit for the three galaxies with such a narrow beam; consequently, the present data will be a basis for further observations with high spatial resolution.