Aims. To validate the Einstein equivalence principle (local position invariance) by limiting the fractional changes in the electron-to-proton mass ratio, mu = m_e/m_p, measured in Galactic plane objects. Methods. High resolution spectral observations
of dark clouds in the inversion line of NH3(1,1) and pure rotational lines of other molecules (the so-called ammonia method) were performed at the Medicina 32-m and the Effelsberg 100-m radio telescopes to measure the radial velocity offsets, Delta RV = V_rot - V_inv, between the rotational and inversion transitions which have different sensitivities to the value of mu. Results. In our previous observations (2008-2010), a mean offset of <Delta RV> = 0.027+/-0.010 km/s [3 sigma confidence level (C.L.)] was measured. To test for possible hidden errors, we carried out additional observations of a sample of molecular cores in 2010-2013. As a result, a systematic error in the radial velocities of an amplitude ~0.02 km/s was revealed. The averaged offset between the radial velocities of the rotational transitions of HC3N(2-1), HC5N(9-8), HC7N(16-15), HC7N(21-20), and HC7N(23-22), and the inversion transition of NH3(1,1) <Delta RV> = 0.003+/-0.018 km/s (3 sigma C.L.). This value, when interpreted in terms of Delta mu/mu= (mu_obs - mu_lab)/mu_lab, constraints the mu-variation at the level of Delta mu/mu < 2*10^{-8} (3 sigma C.L.), which is the most stringent limit on the fractional changes in mu based on astronomical observations.
(Abridged) Aims. In the present part of our survey we search for ammonia emitters in the Aquila rift complex which trace the densest regions of molecular clouds. Methods. From a CO survey carried out with the Delingha 14-m telescope we selected ~150
targets for observations in other molecular lines. Here we describe the mapping observations in the NH3(1,1) and (2,2) inversion lines of the first 49 sources performed with the Effelsberg 100-m telescope. Results. The NH3(1,1) and (2,2) emission lines are detected in 12 and 7 sources, respectively. Among the newly discovered NH3 sources, our sample includes the following well-known clouds: the starless core L694-2, the Serpens cloud Cluster B, the Serpens dark cloud L572, the filamentary dark cloud L673, the isolated protostellar source B335, and the complex star-forming region Serpens South. Angular sizes between 40 and 80 (~0.04-0.08 pc) are observed for compact starless cores but as large as 9 (~0.5 pc) for filamentary dark clouds. The measured kinetic temperatures of the clouds lie between 9K and 18K. From NH3 excitation temperatures of 3-8K we determine H2 densities with typical values of ~(0.4-4) 10^4 cm^-3. The masses of the mapped cores range between ~0.05 and ~0.5M_solar. The relative ammonia abundance, X= [NH3]/[H2], varies from 10^-7 to 5 10^-7 with the mean <X> = (2.7+/-0.6) 10^-7 (estimated from spatially resolved cores assuming the filling factor eta = 1). In two clouds, we observe kinematically split NH3 profiles separated by ~1 km/s. The splitting is most likely due to bipolar molecular outflows for one of which we determine an acceleration of <~ 0.03 km/s/yr. A starless core with significant rotational energy is found to have a higher kinetic temperature than the other ones which is probably caused by magnetic energy dissipation.
