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getTree()
getTree(whichSubhalo, simulation='Illustris-1', snapshot=135)
Returns all the data needed to follow this subhalo, and it's mergers, forward and backward across all time.
More specifically, returns the snapshot numbers and subhalo IDs (also called "whichSubhalo" throughout these docs) needed to find the progenitor/ descendant of any galaxy and the galaxies that merge with it.
See Rodriguez-Gomez et al 2015 for more details about how the trees are made and structured (though note that this function takes a lot of complexity out of the tree structure whilst hopefully retaining all the information, or at least still allowing access to it via other functions in this package).
NOTE: Some subhalos may not have entries in the merger trees at certain snapshots (which is basically just bad luck + the difficulty of following these things) and this command will likely fail. This should be a rare event, especially at low redshift, but be aware.
whichSubhalo - the INTEGER subhalo number of the galaxy you want to track
snapshot - INTEGER snapshot number
simulation - which simulation to draw from
A dictionary with 2 numpy arrays, "Main" and "Mergers".
"Main" - The main progenitor branch of a galaxy, in broad terms the most massive (though other criteria are also used) galaxy in each branch and thus the thread to follow to see the evolution of a single galaxy. This starts when a subhalo is first classified (i.e. has collapsed enough to be noticeable) and ends either at z=0, or at some earlier time if the galaxy merges with a larger galaxy and is subsumed.
"Mergers" - Smaller galaxies will can collide with and become part of the main galaxy, this records their last snapshot and subhalo ID before merging (allowing you to go back and find their properties/ follow their history as well if you wish). If the "Main" branch terminates before z=0 (i.e. the galaxy we're following merges into a larger body) the first entry will point to the galaxy which has subsumed ours.
Also note that, as suggested in Rodriguez-Gomez et al 2015, the moment that two galaxies finally merge is not the best time to examine their pre-merger properties (many have been spiraling inwards for sometime, changing shape and losing material). Instead, the moment of maximum stellar mass of the smaller, merging, galaxy is a more representative time to examine the properties, Right now you'd have to follow the tree to find this moment yourself (very doable with these tools) but at some point I may even add these to the output of this function.
General Concepts
Intro to the Data An overview of the structure of the data and how best to use it
Installing and troubleshooting Quick rundown of what's needed to run the package and some common problems
Unit Conversion All values returned are converted to a user-specified unit system (default SI)
Naming Conventions OLD! - most useful information moved to Intro to the Data
Saving to File To save some download time data can be saved to file and accessed offline
Commands
getGalaxy Returns some properties of particles in a galaxy (i.e. a subhalo)
getSubhaloData Returns all properties of a particular subhalo
getHaloData Returns all properties of a particular halo
getSubhaloField Returns a single property of all subhalos
getHaloField Returns a single property of all halos
getSimData Returns general properties of a given simulation (including a conversion table for times, redshifts and snapshot numbers)
getSnapData Returns general properties for a given snapshot
getTree Returns the indexes needed to follow the galaxy, and it's mergers, across time