A CO isotopologue Line Atlas within the Whirlpool galaxy Survey (CLAWS)

We present the CO isotopologue Line Atlas within Whirpool galaxy Survey (CLAWS) based on an IRAM 30-m large programme which provides a benchmark study of numerous, faint isotopologues in mm-wavelength regime across full disc M51 (NGC 5194). The survey's core goal is to use low-J lines constrain excitation and chemistry, therefrom local physical conditions gas. In this survey paper, we describe CLAWS observing data reduction strategies. map J=1-0 2-1 transitions $^{12}$CO,$^{13}$CO, C$^{18}$O C$^{17}$O, as well several supplementary 1 mm 3 window (CN(1-0), CS(2-1), CH$_3$OH(2-1), N$_2$H$^+$(1-0), HC$_3$N(10-9)) at ~1 kpc resolution. A total observation time 149 h offers unprecedented sensitivity. these explore line ratios detail, their radial (and azimuthal) trends investigate whether changes stem from ISM properties such gas temperatures, densities or chemical abundances. For example, find negative for $^{13}$CO}/$^{12}$CO, C$^{18}$O/$^{12}$CO C$^{18}$O/$^{13}$CO transitions. also variations with environment, higher $^{12}$CO(2-1)/(1-0) $^{13}$CO/$^{12}$CO(1-0) interarm regions compared spiral arm regions. propose that aforementioned are most likely due variation optical depth, while abundance selective nucleosynthesis galaxy-wide scale could play role. spectral energy distribution (SLED) using archival JCMT $^{12}$CO(3-2) SLED shape environmental parameters further underlying temperatures densities.