Tilted black hole accretion disc models of Sagittarius A*: time-variable
  millimetre to near-infrared emission
  High-resolution, multi-wavelength, and time-domain observations of the
Galactic centre black hole candidate, Sgr A*, allow for a direct test of
contemporary accretion theory. To date, all models have assumed alignment
between the accretion disc and black hole angular momentum axes, but this is
unjustified for geometrically thick accretion flows like that onto Sgr A*.
Instead, we calculate images and spectra from a set of simulations of accretion
flows misaligned ('tilted') by 15 degrees from the black hole spin axis and
compare them with millimetre (mm) to near-infrared (NIR) observations.
Non-axisymmetric standing shocks from eccentric fluid orbits dominate the
emission, leading to a wide range of possible image morphologies. These effects
invalidate previous parameter estimates from model fitting, including estimates
of the dimensionless black hole spin, except possibly at low values of spin or
tilt. At 1.3mm, the images have crescent morphologies, and the black hole
shadow may still be accessible to future mm-VLBI observations. Shock heating
leads to high energy electrons (T > 10^12 K), which can naturally produce the
observed NIR flux, spectral index, and rapid variability ('flaring'). This NIR
emission is uncorrelated with that in the mm, which also agrees with
observations.
  These are the first models to self-consistently explain the time-variable mm
to NIR emission of Sgr A*. Predictions of the model include significant
structural changes observable with mm-VLBI on both the dynamical (hour) and
Lense-Thirring precession (day-year) timescales; and ~30-50 microarcsecond
changes in centroid position from extreme gravitational lensing events during
NIR flares, detectable with the future VLT instrument GRAVITY. If the observed
NIR emission is caused by shock heating in a tilted accretion disc, then the
Galactic centre black hole has a positive, non-zero spin parameter (a > 0).
