Context. Maser lines from different molecular species, including water, hydroxyl, and methanol, are common observational phenomena associated with massive star-forming regions. In particular, since its discovery, the 6.7 GHz methanol maser has been recognized as one of the clearest signposts in the formation of young high-mass stars. Aims. The methanol maser thus appears as an ideal tool for studying the early phases of massive star formation. However, it is difficult to establish the exact start of the methanol maser phase, and it would then be interesting to detect and study low flux-density methanol masers (i.e., 0.1 Jy or even 0.1 Jy), in order to determine if they can be used effectively to mark a specific evolutionary phase in high-mass star formation. Methods. Past surveys have been unable to systematically detect many low flux-density methanol masers, and thus we do not yet know how many such masers exist in the Galaxy and what their physical nature is. A large sample of massive cores can now be found in the Herschel infrared GALactic Plane Survey (Hi-GAL), which we have used to search for methanol and excited OH masers toward a sample of starless and protostellar high-mass clumps using the Arecibo telescope. Results. Out of a sample of 107 observed Hi-GAL sources, we detected a total of 37 methanol masers, with 22 sources being new and weak (median peak flux density 0.07 Jy) detections, in the Galactic longitude range [32.• 0, 59.• 8]. We also detected 12 6.035 GHz OH maser regions, with 9 new detections. Our survey covers a similar range of source distances to the "Arecibo Methanol Maser Galactic Plane Survey" (or AMGPS, ), but the methanol masers detected by us are clearly shifted toward lower integrated flux densities. Conclusions. The newly detected methanol masers mostly have low luminosity (assuming isotropic emission), and except for some sources, their weakness is not due to distance effects or positional offsets. No specific correlation is found with the physical parameters of the Hi-GAL clumps, except for sources with both CH 3 OH and OH masers, which tend to have higher mass and luminosity. The intensity of the methanol masers correlates well with the velocity range of the maser emission, which suggests that the low brightness of these masers is related to the number of maser spots in the emitting region and to their evolution with time.

The detection of four formaldehyde (H 2 CO) maser regions toward young high-mass stellar objects in the last decade, in addition to the three previously known regions, calls for an investigation of whether H 2 CO masers are an exclusive tracer of young high-mass stellar objects. We report the first survey specifically focused on the search for 6 cm H 2 CO masers toward non high-mass star-forming regions (non HMSFRs). The observations were conducted with the 305 m Arecibo Telescope toward 25 low-mass star-forming regions, 15 planetary nebulae and post-AGB stars, and 31 late-type stars. We detected no H 2 CO emission in our sample of non HMSFRs. To check for the association between high-mass star formation and H 2 CO masers, we also conducted a survey toward 22 high-mass star-forming regions from a Hi-GAL (Herschel infrared Galactic Plane Survey) sample known to harbor 6.7 GHz CH 3 OH masers. We detected a new 6 cm H 2 CO emission line in G32.74−0.07. This work provides further evidence that supports an exclusive association between H 2 CO masers and young regions of high-mass star formation. Furthermore, we detected H 2 CO absorption toward all Hi-GAL sources, and toward 24 low-mass starforming regions. We also conducted a simultaneous survey for OH (4660, 4750, 4765 MHz), H110α (4874 MHz), HCOOH (4916 MHz), CH 3 OH (5005 MHz), and CH 2 NH (5289 MHz) toward 68 of the sources in our sample of non HMSFRs. With the exception of the detection of a 4765 MHz OH line toward a pre-planetary nebula (IRAS 04395+3601), we detected no other spectral line to an upper limit of 15 mJy for most sources.