Abridged: We measured photometric and spectroscopic Prot for a large
sample of nearby bright M dwarfs with spectral types from M0 to M9, as part of
our continual effort to fully characterize the Guaranteed Time Observation
programme stars of the CARMENES survey. We determine Prot for 129
stars. Combined with the literature, we tabulate Prot for 261 stars,
or 75% of our sample. We evaluate the plausibility of all periods available for
this sample by comparing them with activity signatures and checking for
consistency between multiple measurements. We find that 166 of these stars have
independent evidence that confirmed their Prot. There are
inconsistencies in 27 periods, which we classify as debated. A further 68
periods are identified as provisional detections that could benefit from
independent verification. We provide an empirical relation for the Prot uncertainty as a function of the Prot value, based on the
dispersion of the measurements. We show that published formal errors seem to be
often underestimated for periods ≳10 d. We highlight the importance of
independent verification on Prot measurements, especially for inactive
M dwarfs. We examine rotation-activity relations with emission in X-rays,
Hα, Ca II H & K, and surface magnetic field strengths. We find overall
agreement with previous works, as well as tentative differences in the
partially versus fully convective subsamples. We show Prot as a
function of stellar mass, age, and galactic kinematics. With the notable
exception of three transiting planet systems and TZ Ari, all known planet hosts
in this sample have Prot≳15 d. This indicates that important
limitations need to be overcome before the radial velocity technique can be
routinely used to detect and study planets around young and active stars.Comment: Accepted for publication in A&