(a) CO 1–0 integrated intensity map, naturally weighted with synthesized beam ﹩3\farcs 95\times 3\farcs 27﹩ and beam ﹩\mathrm{P.A.}\,=-42\fdg 8﹩. Contour levels are 1.1 Jy beam⁻¹ km s⁻¹ × (1.0, 2.5, 4.0, …, 17.5, 19.0). The peak flux is 29.04 Jy beam⁻¹ km s⁻¹ at ﹩\alpha =13^{\mathrm{h}\,}27^{\mathrm{m}\,}43\fs 715﹩; ﹩\delta =+47^{\circ }26^{\prime }52\farcs 25﹩ in the M1 arm. The lowest contour is at the 3 σ level. The total integrated flux in the map is ﹩2.7\times 10^{3}﹩ Jy km s⁻¹. The dotted lines mark the secondary arms B1 and B2, and the string of interarm D clouds (see text). Arrows indicate other features discussed in the text. The outer map cutoff is indicated with a dashed line. This cutoff is approximately 5^{﹩\arcsec﹩} inside the map's outer primary beam half‐power points. (b) CO 1–0 integrated intensity map robustly weighted with synthesized beam ﹩2\farcs 88\times 2\farcs 11﹩ and beam ﹩\mathrm{P.A.}\,=-80\fdg 7﹩. Contour levels are 0.4 Jy beam⁻¹ km s⁻¹ × (1.0, 4.0, 8.0, …, 32). The peak flux is 18.64 Jy beam⁻¹ km s⁻¹ at the same position as for the naturally weighted map. The lowest contour is at the 3 σ level. The total integrated flux in the map is ﹩2.0\times 10^{3}﹩ Jy km s⁻¹. The outer map cutoff is indicated with a dashed line. (c) Position‐velocity cut through the M1 and B1 features, at P.A. 242°. Zero velocity is at 472 km s⁻¹. (d) CO contours overlaid on an HST archive image of the center of M51 with Hα shown in red. The CO traces the main dust lanes, and the strong Hα is often seen on the downstream side of massive GMAs. The orientation angle of the image may be determined by comparison with a, which shows the CO contours on an equatorial coordinate reference frame.