On the origin of the angular momentum properties of gas and dark matter in galactic halos and its implications

Abstract

We perform a set of non-radiative hydrodynamical simulations of merging spherical halos in order to understand the angular momentum (AM) properties of the galactic halos seen in cosmological simulations. The universal shape of AM distributions seen in simulations is found to be generically produced as a result of mergers. The universal shape is such that it has an excess of low AM material and hence cannot explain the exponential structure of disk galaxies. A resolution to this is suggested by the spatial distribution of low AM material which is found to be in the centre and a conical region close to the axis of rotation. A mechanism that preferentially discards the material in the centre and prevents the material along the poles from falling onto the disc is proposed as a solution. We implement a simple geometric criteria for selective removal of low AM material and show that in order for 90% of halos to host exponential discs one has to reject at least 40% of material. Next, we explore the physical mechanisms responsible for distributing the AM within the halo during a merger. For dark matter there is an inside-out transfer of AM, whereas for gas there is an outside-in transfer, which is due to differences between collisionless and gas dynamics. We also explain the apparent high spin of dark matter halos undergoing mergers and show that a criteria stricter than what is currently used, would be required to detect such unrelaxed halos. Finally, we demonstrate that the misalignment of AM between gas and dark matter only occurs when the intrinsic spins of the merging halos are not aligned with the orbital AM of the system. The self-misalignment (orientation of AM when measured in radial shells not being constant), which could be the cause of warps and anomalous rotation in disks galaxies, also occurs under similar conditions.

Accepted for publication in ApJ

References in corpus (13)

• CALIFA, the Calar Alto Legacy Integral Field Area survey: I. Survey presentation
• The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals
• The Sydney-AAO Multi-object Integral field spectrograph (SAMI)
• The spin and shape of dark matter haloes in the Millennium simulation of a LambdaCDM universe
• A Revised Model for the Formation of Disk Galaxies: Low Spin and Dark-Halo Expansion
• The Hidden Mass and Large Spatial Extent of a Poststarburst Galaxy Outflow
• The Impact of Feedback on Disk Galaxy Scaling Relations
• On the Origin of Exponential Galaxy Disks
• Probing the Intrinsic Shape and Alignment of Dark Matter Haloes using SDSS Galaxy Groups
• Dark Matter Halos of Disk Galaxies: Constraints from the Tully-Fisher Relation
• The Alignment between Satellites and Central Galaxies: Theory vs. Observations
• Angular distribution of satellite galaxies from the Sloan Digital Sky Survey Data Release 4
• Do Mergers Spin up Dark Matter Halos?

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• The role of mergers and halo spin in shaping galaxy morphology
• The SAMI Galaxy Survey: the link between angular momentum and optical morphology
• The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics
• The impact of baryons on the spins and shapes of dark matter haloes
• Is the dark-matter halo spin a predictor of galaxy spin and size?
• Kinematic modelling of the Milky Way using the RAVE and GCS stellar surveys
• Angular momentum properties of haloes and their baryon content in the Illustris simulation
• Fundamental relations for the velocity dispersion of stars in the Milky Way
• The origin of the atomic and molecular gas contents of early-type galaxies. II. Misaligned gas accretion
• How to get cool in the heat: comparing analytic models of hot, cold, and cooling gas in haloes and galaxies with EAGLE
• Galaxy and Mass Assembly (GAMA): galaxy radial alignments in GAMA groups
• First Science with SAMI: A Serendipitously Discovered Galactic Wind in ESO 185-G031
• Very Metal-Poor Outer-Halo Stars with Round Orbits
• The angular momentum of cosmological coronae and the inside-out growth of spiral galaxies
• Damped Lyα Absorption Systems in Semi-Analytic Models with Multiphase Gas
• Models of rotating coronae
• Angular Momentum of Early and Late Type Galaxies: Nature or Nurture?
• The segregation of baryons and dark matter during halo assembly
• The SAMI galaxy survey: Galaxy Interactions and Kinematic Anomalies in Abell 119
• Smoothing Rotation Curves and Mass Profiles
• The Hector Survey: integral field spectroscopy of 100,000 galaxies
• The MUSE Hubble Ultra Deep Field Survey XVI. The angular momentum of low-mass star-forming galaxies. A cautionary tale and insights from TNG50
• A random-walk model for dark matter halo spins
• HI angular momentum mass relation
• A universal angular momentum profile for dark matter haloes
• Tilted outer and inner structures in edge-on galaxies?
• Stellar angular momentum distribution linked to galaxy morphology
• Spin transfer from dark matter to gas during halo formation
• A Shallow Slope for the Stellar Mass--Angular Momentum Relation of Star-Forming Galaxies at $1.5<z<2.5$
• Hot accretion onto spiral galaxies: the origin of extended and warped HI discs
• Self-consistent dynamical models with a finite extent -- I. The uniform density sphere