Using simple dimensional arguments for both spiral and elliptical galaxies, we present formulae to derive an estimate of the halo spin parameter λ for any real galaxy, in terms of common observational parameters. This allows a rough estimate of λ, which we apply to a large volume‐limited sample of galaxies taken from the Sloan Digital Sky Survey data base. The large numbers involved (11 597) allow the derivation of reliable λ distributions, as signal adds up significantly in spite of the errors in the inferences for particular galaxies. We find that if the observed distribution of λ is modelled with a lognormal function, as often done for this distribution in dark matter haloes that appear in cosmological simulations, we obtain parameters λ0= 0.04 ± 0.005 and σλ= 0.51 ± 0.05, interestingly consistent with values derived from simulations. For spirals, we find a good correlation between empirical values of λ and visually assigned Hubble types, highlighting the potential of this physical parameter as an objective classification tool.

We present a highly simplified model of the dynamical structure of a disc galaxy where only two parameters fully determine the solution, mass and angular momentum. We show through simple physical scalings that once the mass has been fixed, the angular momentum parameter λ is expected to regulate such critical galactic disc properties as colour, thickness of the disc and bulge-to-disc ratio. It is, hence, expected to be the determinant physical ingredient resulting in a given Hubble type. A simple analytic estimate of λ for an observed system is provided. An explicit comparison of the distribution of several galactic parameters against both Hubble type and λ is performed using observed galaxies. Both such distributions exhibit highly similar characteristics for all galactic properties studied, suggesting λ as a physically motivated classification parameter for disc galaxies.

We search for correlations between the spins in pairs of spiral galaxies, to study if the angular momentum gain for each galaxy was the result of tidal torques imprinted by the same tidal field. To perform our study we made use of a sample of galaxy pairs identified using the Sloan Digital Sky Survey. We find a weak, but statistically significant correlation between the spin magnitudes of neighbouring galaxies, but no clear alignment between their orientations. We show that events such as interactions with close neighbours play an important role in the value of the spin for the final configuration, as we find that these interactions tend to reduce the value of the λ spin parameter of late‐type galaxies considerably, with dependence on the morphology of the neighbour. This implies that the original tidal field for each pair could have been similar, but the redistribution of angular momentum at later stages of evolution is important.

We use a sample of galaxies from the Sloan Digital Sky Survey (SDSS) to search for correlations between the λ spin parameter and the environment and mass of galaxies. In order to calculate the total value of λ for each observed galaxy, we employed a simple model of the dynamical structure of the galaxies, which allows a rough estimate of the value of λ using only readily obtainable observables from the luminous galaxies. Use of a large volume‐limited sample (upwards of 11 000) allows reliable inferences of mean values and dispersions of λ distributions. We find, in agreement with some N‐body cosmological simulations, no significant dependence of λ on the environmental density of the galaxies. For the case of mass, our results show a marked correlation with λ, in the sense that low‐mass galaxies present both higher mean values of λ and associated dispersions, than high‐mass galaxies. These results provide interesting constrain on the mechanisms of galaxy formation and acquisition of angular momentum, a valuable test for cosmological models.