fig = plt.figure(figsize=(8,5))
ax = fig.add_subplot(111)
# read in the spectra that were extracted from the line of sight along (35,0)
v_HI, T_HI = np.loadtxt('inner_galaxy_HI_spectrum.txt', unpack=True)
v_CO, T_CO = np.loadtxt('inner_galaxy_CO_spectrum.txt', unpack=True)
ax.plot(v_HI, T_HI, 'k-', lw=3, label='HI 21cm')
ax.plot(v_CO, 10*T_CO, 'k-', lw=5, alpha=0.3, label='CO 2.6mm x 10')
ax.set_xlim(-70, 130)
ax.set_xlabel('Velocity (km/s)', fontsize=14)
ax.set_ylabel(r'$T_{\rm B}$ (K)', fontsize=14)
ax.legend(handlelength=3.3, borderpad=0.5, labelspacing=0.5, fontsize='medium',loc=2)
plt.tight_layout()
plt.savefig('galaxy_HI_CO_spectrum.pdf')