Gravitational redshift is a classical effect of Einstein's General
Relativity, already measured in stars, quasars and clusters of galaxies. We
here identify the signature of gravitational redshift in the emission lines of
active galaxies due to supermassive black holes and discuss their impact on
cosmological inference from type Ia supernovae. Firstly, from the full width at
half maximum of HΞ²β lines of 75 Seyfert type I galaxies of the AGN
Black Hole Mass Database, we derive a gravitational redshift zgβ=(2.4Β±0.9)Γ10β4. Expanding this analysis to 86755 quasars from DR14 of
SDSS we have a mean value zgββ2.7Γ10β4. Then, by comparing
the redshifts of 34 lines measured at the central and outer regions of LINER
galaxies in the SAMI survey we obtain zgβ=(0.68Β±0.09)Γ10β4.
These numbers are compatible with central black holes of β109 solar
masses and broad line regions of β1~pc. For non-AGN galaxies the
gravitational redshift is compatible with zero and, as they constitute most of
SNe Ia host galaxies, the impact on the cosmological parameters is negligible.Comment: 5 pages, 5 figure