Handle "Boundary Conditions" generally

zhafen / linefinder

A tool for finding and classifying the worldlines of Lagrangian parcels of mass, in the context of hydrodynamic simulations of galaxy formation.

https://zhafen.github.io/linefinder

MIT License

0 stars 1 forks source link

Handle "Boundary Conditions" generally #46

Closed zhafen closed 7 years ago

zhafen commented 7 years ago

Originally reported by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

At some point, early in the simulation, the halo finder successfully resolves what galaxy is the main galaxy. However, under our classification scheme, the moment the halo finder resolves our main galaxy everything that was previously actually inside the galaxy (which the halo finder couldn't resolve) is suddenly classified as "merger". This clearly isn't correct.

The proposed solution:

Count the main galaxy as being resolved when n_star_main_gal >= 100.
Manually classify anything that is accreted onto the galaxy the first neg snapshots after the galaxy is resolved as pristine gas.

Bitbucket: https://bitbucket.org/zhafen/pathfinder/issue/46

zhafen commented 7 years ago

Original comment by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

Fixed as of the latest commit.

zhafen commented 7 years ago

Original comment by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

To mark this uncertainty, I'll be storing main_mt_halo_first_snap in the output files.

zhafen commented 7 years ago

Original comment by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

$updated_stellar_mass_fractions.png$

The above is what happens when I increase neg to 10. It looks okay.

Honestly, though, the best option might be honesty: we don't know what happens to gas at high redshifts... This is something we should be aware of, going forward.

zhafen commented 7 years ago

Original comment by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

While boundary conditions should be applied as described above, after doing so there is still a suspicious high-z population, the "merger-gas" population in the above figure.

Particles in this population were in a galaxy for at least 100 Myr before accreting but were not in the main galaxy in the first few snapshots after the main galaxy was officially resolved. This means that they have the potential to actually be fresh accretion/recycled gas. In fact, given previous knowledge, they likely are (especially because there's no accompanying merger-star component).

There are two ways I can think of addressing this:

Don't count anything as being in a galaxy prior to when the main galaxy is resolved.
Increase neg (the number of snapshots to which we apply the boundary condition) to a larger value.

zhafen commented 7 years ago

Original comment by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

Boundary conditions need to be applied in two places:

Nothing should be counted as being in the main galaxy before it is resolved (this will also take care of accretion and ejection events, which are derived from this).
Anything that "accretes" onto the main galaxy in the first neg snapshots it's resolved should be counted as pristine gas.

zhafen commented 7 years ago

Original comment by Zachary Hafen (Bitbucket: zhafen, GitHub: zhafen)

Issue #44 was marked as a duplicate of this issue.