Eulerian Vs Lagrangian

EulerianVs Lagrangian●●Difficult to refine a gridanticipating the fluid behaviourNot clear if turbulent cascadesare correctly recovered whenAMR is truncated at a givenresolution●Seem to suppress instabilities incertain conditions, due to aspusious surface tension andinacurate gradient estimatesacross density jumps●Problems to treat structureformation from growinggravitational instabilities, giventhat scales are always ½, and½ , and ½....

Arbitrarily curved boundary conditions

Excessive mixing in eulerian methods...Faster grow of instability and galilean invariance inAREPO...

Formation of galaxies in simulations andthe low-angular-momentum problem:●●●In first simulations, most of the gas lost angularmomentum when accretedBig bulgesSolution? Heating? ---> UV bckgrnd + stllr fdbck● SPH cause sporious loose of A.M !!●●Resolution related problem ---> zoom in ^^'Not possible in big simulations... so... would it reproducevariety of galaxies and constrained observables?● SPH also creates 'blobs' =/

GADGET Vs AREPO●●Same gravity solver and sub-resolution physics: radiativecooling, heating background, star formation and feedback.Refinement/de-refinement in AREPO

GADGETAREPO

Gas Disk Analysis● Find structures with SUBFIND → 1367matching halos●Distinguish hot halo from colder, denser gasdisk:●●Cold gas clumps remain...Should be removed??

GADGETAREPO

Disks do rotate more in AREPO

Disk fitting and comparison●●Steeper central regionsFits including/excludingcentral 2.8 h -1 kpc

Disk fitting and comparisonIncludingExcluding

Disk fitting and comparison●●AREPO disks are between 1.5 and 2 times largerBlobs cause continued and dashed lines to bedifferent in GADGET

How about rotation...●●AREPO galaxies are more rotationally supportedThey lie closer to where they are supposed to be

Origin of the discrepanciesSpurious hidrodynamical torques...●●●●SPH transport angular momentum from thedisk to the hot haloDecouple the two phases?Increase the resolution?But galaxy assembly is a hierarchicalprocess...

Origin of the discrepanciesGas Heating and Cooling...●Coolong in AREPO is more efficient for tworeasons:– Dissipative heating in haloes driven by thepresence of turbulent energy– Difference in mixing at phase densityboundaries: in-falling substructures, diskhalo

Origin of the discrepanciesCold clumps...●They exist

Origin of the discrepanciesCold clumps...●Cold gas patches from the IGM that do not mix/disruptwhen infalling into the hot halo