G = 6.67 x 10-8 cm3 s-2 g-1 = 1.327 x 1011 km3 s-2 M⊙-1 = 4.3 x 10-6 kpc km2 s-2 M⊙-1
Surface brightness conversion between linear Σ in
L⊙ pc-2 and logarithmic μ in
μ = 21.57 + M⊙ -2.5logΣ
where M⊙ is the absolute magnitude of the sun in the relevant band, not to be confused with the solar mass M⊙.
Distance modulus: m-M⊙ = 5logD-5 when D is in pc; becomes 5logD+25 when D is in Mpc. There is also a term for the k-correction due to the redshifting of the source spectrum when the cosmic redshift becomes substantial.
HI flux-to-mass conversion: MHI = 2.36 x 105 D2 FHI
gives the mass of atomic hydrogen in M⊙ given D, the distance in Mpc and FHI, the 21 cm flux integral in Jy km s-1
Baryonic Tully-Fisher Relation:
Mb = A*Vf4
with A ≈ 50 M⊙ km-4 s4
In MOND, A = X/(Ga0) with the geometric factor X ≈ 0.8 and (Ga0)-1 = 63 M⊙ km-4 s4.
MOND acceleration constant:
a0 = 1.2 x 10-10 m s-2 = 3700 km2 s-2 kpc-1
Critical surface density
Σ* = a0/G = 860 M⊙ pc-2 = 1.8 kg m-2 (about the surface density of a stiff piece of construction paper)