Merger Mass Movements

Class providing models of the movements of mass during galaxy mergers—the prescription for where the gas and stellar components of the satellite and host galaxies are redistributed after a merger event. Implementations specify the destination (disc, spheroid, or dominant component) for the gas and stars of both the satellite and the host, and whether the merger should be classified as major or minor. This drives the morphological transformation of merging galaxies, controlling bulge growth and triggering starbursts during coalescence.

Default implementation: mergerMassMovementsSimple

Methods

get → void

Determine the movements of stellar and gaseous mass components during a galaxy merger event, returning the destination (disk, spheroid, or dominant component) for each component of the satellite and host galaxies, and whether the merger should be classified as major or minor.

  • type (treeNode ), intent(inout), target :: node

  • type (enumerationDestinationMergerType), intent( out) :: destinationGasSatellite, destinationStarsSatellite, destinationGasHost, destinationStarsHost

  • logical , intent( out) :: mergerIsMajor

mergerMassMovementsBaugh2005

A merger mass movements class which implements mass movements according to:

  • If \(M_\mathrm{satellite} > f_\mathrm{major} M_\mathrm{central}\) then all mass from both satellite and central galaxies moves to the spheroid component of the central galaxy;

  • Otherwise:

    • If \(M_\mathrm{central, spheroid} < f_\mathrm{burst} M_\mathrm{central}\) and the gas fraction in the host equals or exceeds \(f_\mathrm{gas,crit}\) then all gas is moved to the host spheroid, while the host stellar disk remains in place.

    • Otherwise, gas from the satellite moves to the component of the central specified by the [destinationGasMinorMerger] parameter (either “disk” or “spheroid”), stars from the satellite moves to the spheroid of the central and mass in the central does not move.

Here, \(f_\mathrm{major}=\)[massRatioMajorMerger] is the mass ratio above which a merger is considered to be “major”, while \(f_\mathrm{burst}=\)[ratioMassBurst] and \(f_\mathrm{gas,crit}=\)[fractionGasCriticalBurst].

Parameters

  • [massRatioMajorMerger] (real; default 0.25d0) — The mass ratio above which mergers are considered to be “major”.

  • [ratioMassBurst] (real; default 0.05d0) — The mass ratio above which mergers are considered to trigger a burst.

  • [fractionGasCriticalBurst] (real; default 0.75d0) — The host gas fraction above which mergers are considered to trigger a burst.

  • [destinationGasMinorMerger] (string; one of unmoved, dominant, disk, spheroid; default spheroid) — The component to which satellite galaxy gas moves to as a result of a minor merger.

mergerMassMovementsSimple

A merger mass movements class which implements mass movements according to:

  • If \(M_\mathrm{satellite} > f_\mathrm{major} M_\mathrm{central}\) then all mass from both satellite and central galaxies moves to the spheroid component of the central galaxy;

  • Otherwise: Gas from the satellite moves to the component of the central specified by the [minorMergerGasMovesTo] parameter (either “disk” or “spheroid”), stars from the satellite moves to the spheroid of the central and mass in the central does not move.

Here, \(f_\mathrm{major}=\)[majorMergerMassRatio] is the mass ratio above which a merger is considered to be “major”.

(Default implementation)

Methods

  • calculationReset — Reset memoized calculations.

Parameters

  • [massRatioMajorMerger] (real; default 0.25d0) — The mass ratio above which mergers are considered to be “major”.

  • [destinationGasMinorMerger] (string; one of unmoved, dominant, disk, spheroid; default spheroid) — The component to which satellite galaxy gas moves to as a result of a minor merger.

  • [destinationStarsMinorMerger] (string; one of unmoved, dominant, disk, spheroid; default spheroid) — The component to which satellite galaxy stars move to as a result of a minor merger.

mergerMassMovementsVerySimple

A merger mass movements class which assumes that the satellite material is always added to the disk of the host, while the host mass is not moved.

Parameters

  • [massRatioMajorMerger] (real; default 0.25d0) — The mass ratio above which mergers are considered to be “major”.