ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED

By A. Romanowsky, S. M. Fall. 2012

201 citations recorded by the source corpus.

Motivated by a new wave of kinematical tracers in the outer regions of early-type galaxies (ellipticals and lenticulars), we re-examine the role of angular momentum in galaxies of all types. We present new methods for quantifying the specific angular momentum j, focusing mainly on the more challenging case of early-type galaxies, in order to derive firm empirical relations between stellar j⋆ and mass M⋆ (thus extending earlier work by Fall). We carry out detailed analyses of eight galaxies with kinematical data extending as far out as 10 effective radii, and find that data at two effective radii are generally sufficient to estimate total j⋆ reliably. Our results contravene suggestions that ellipticals could harbor large reservoirs of hidden j⋆ in their outer regions owing to angular momentum transport in major mergers. We then carry out a comprehensive analysis of extended kinematic data from the literature for a sample of ∼100 nearby bright galaxies of all types, placing them on a diagram of j⋆ versus M⋆. The ellipticals and spirals form two parallel j⋆–M⋆ tracks, with log-slopes of ∼0.6, which for the spirals are closely related to the Tully–Fisher relation, but for the ellipticals derives from a remarkable conspiracy between masses, sizes, and rotation velocities. The ellipticals contain less angular momentum on average than spirals of equal mass, with the quantitative disparity depending on the adopted K-band stellar mass-to-light ratios of the galaxies: it is a factor of ∼3–4 if mass-to-light ratio variations are neglected for simplicity, and ∼7 if they are included. We decompose the spirals into disks and bulges and find that these subcomponents follow j⋆–M⋆ trends similar to the overall ones for spirals and ellipticals. The lenticulars have an intermediate trend, and we propose that the morphological types of galaxies reflect disk and bulge subcomponents that follow separate, fundamental j⋆–M⋆ scaling relations. This provides a physical motivation for characterizing galaxies most basically with two parameters: mass and bulge-to-disk ratio. Next, in an approach complementary to numerical simulations, we construct idealized models of angular momentum content in a cosmological context, using estimates of dark matter halo spin and mass from theoretical and empirical studies. We find that the width of the halo spin distribution cannot account for the differences between spiral and elliptical j⋆, but that the observations are reproduced well if these galaxies simply retained different fractions of their initial j complement (∼60% and ∼10%, respectively). We consider various physical mechanisms for the simultaneous evolution of j⋆ and M⋆ (including outflows, stripping, collapse bias, and merging), emphasizing that the vector sum of all such processes must produce the observed j⋆–M⋆ relations. We suggest that a combination of early collapse and multiple mergers (major or minor) may account naturally for the trend for ellipticals. More generally, the observed variations in angular momentum represent simple but fundamental constraints for any model of galaxy formation.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/640b13b4aa3833e62866039dc4a2adb55c897844

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Electrical and Electronic Engineering

In Instrumentation

Citations in the corpus

Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge (2014, methodology): “The predictions based on the simplified models are in the ball park of observed AM in low-redshift galaxies (e.g. Romanowsky & Fall 2012; Fall & Romanowsky 2013).”
MORPHOLOGIES OF ∼190,000 GALAXIES AT z = 0–10 REVEALED WITH HST LEGACY DATA. I. SIZE EVOLUTION (2015, result): “Our jd/md values are comparable to the estimates with kinematical data for nearby disks (jd/md ∼ 0.8; Romanowsky & Fall 2012; Fall & Romanowsky 2013).”
The size evolution of star-forming and quenched galaxies in the IllustrisTNG simulation (2017, background): “…found very little size evolution with time at a fixed mass (Lilly et al. 1998; Barden et al. 2005; Ichikawa et al. 2012; Stott et al. 2013; Curtis-Lake et al. 2016). early-type galaxies (considering halo spin, for example, can at most partly account for this difference; Romanowsky & Fall 2012).”
3D BAROLO: a new 3D algorithm to derive rotation curves of galaxies (2015, background): “Finally, gas kinematics can also be used to infer the distribution of angular momentum in galaxies and study how it evolves with time (e.g. Romanowsky & Fall 2012).”
Galaxy And Mass Assembly (GAMA): mass–size relations of z < 0.1 galaxies subdivided by Sérsic index, colour and morphology (2014, background): “The close connection between size (or surface brightness) and angular momentum makes systematic size measurements in galaxy surveys an exquisite test of evolutionary models (Fall 1983; Romanowsky & Fall 2012).”
Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, methodology): “Since specific angular momentum scales with M2/3 (Romanowsky & Fall 2012), j∗/M 2/3 ∗ is a measure of relative rotational support.”
CONNECTING ANGULAR MOMENTUM AND GALACTIC DYNAMICS: THE COMPLEX INTERPLAY BETWEEN SPIN, MASS, AND MORPHOLOGY (2015, methodology): “The angular momentum of disk galaxies was found to be about six times higher than that of the ellipticals of equal mass. Romanowsky & Fall (2012) and Fall & Romanowsky (2013) revisited and extended this work, analyzing 67 spiral and 40 early-type galaxies.”