The ALMaQUEST Survey: V. The non-universality of kpc-scale star
  formation relations and the factors that drive them
  Using a sample of ~15,000 kpc-scale star-forming spaxels in 28 galaxies drawn
from the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey, we
investigate the galaxy-to-galaxy variation of the `resolved' Schmidt-Kennicutt
relation (rSK; Sigma_H2 - Sigma_SFR), the `resolved' star forming main sequence
(rSFMS; Sigma_* - Sigma_SFR) and the `resolved' molecular gas main sequence
(rMGMS; Sigma_* - Sigma_H2). The rSK relation, rSFMS and rMGMS all show
significant galaxy-to-galaxy variation in both shape and normalization,
indicating that none of these relations is universal between galaxies. The
rSFMS shows the largest galaxy-to-galaxy variation and the rMGMS the least. By
defining an `offset' from the average relations, we compute a Delta_rSK,
Delta_rSFMS, Delta_rMGMS for each galaxy, to investigate correlations with
global properties. We find the following correlations with at least 2 sigma
significance: the rSK is lower (i.e. lower star formation efficiency) in
galaxies with higher M_*, larger Sersic index and lower specific SFR (sSFR);
the rSFMS is lower (i.e. lower sSFR) in galaxies with higher M_* and larger
Sersic index; the rMGMS is lower (i.e. lower gas fraction) in galaxies with
lower sSFR. In the ensemble of all 15,000 data points, the rSK relation and
rMGMS show equally tight scatters and strong correlation coefficients, compared
with a larger scatter and weaker correlation in the rSFMS. Moreover, whilst
there is no correlation between Delta_rSK and Delta_rMGMS in the sample, the
offset of a galaxy's rSFMS does correlate with both of the other two offsets.
Our results therefore indicate that the rSK and rMGMS are independent
relations, whereas the rSFMS is a result of their combination.
