Is there any field in the subfind subhalos that can give me the age of a galaxy?
If not, what is the recommended way of calculating the age of a galaxy?
Thank You.
Dylan Nelson
3 Jul
You perhaps mean either "dark matter halo formation time", usually defined as when a halo has assembled half its mass, or perhaps "stellar age", often defined as the mean (weighted in some way) age of all the stars that make up a galaxy.
Siddharth Dutta
3 Jul
Could you kindly point me towards how to calculate these two values (and which properties to use).
Bryanne McDonough
16h
Hi Siddharth,
This is a problem I ran into in grad school. Age of a galaxy is complicated to measure because of merger history. Which age you want to use depends somewhat on what you are interested in measuring.
For stellar ages, I've used luminosity weighted age (see section 3.4 of my paper. For that you need from the star particle data luminosity in some band (I used r-band) and GFM_StellarFormationTime. Sum the product of formation time and luminosity, then divide by the sum of luminosities. Another stellar-based metric I know at least one person has used is just the age of the oldest stellar particle, although that's tracking the age of the age of the oldest progenitor.
I've not computed dark matter halo formation time before, but you would probably want to grab the mass history from one of the merger catalogs then grab the redshift at which the halo was half its present day mass.
Hello
Is there any field in the subfind subhalos that can give me the age of a galaxy?
If not, what is the recommended way of calculating the age of a galaxy?
Thank You.
You perhaps mean either "dark matter halo formation time", usually defined as when a halo has assembled half its mass, or perhaps "stellar age", often defined as the mean (weighted in some way) age of all the stars that make up a galaxy.
Could you kindly point me towards how to calculate these two values (and which properties to use).
Hi Siddharth,
This is a problem I ran into in grad school. Age of a galaxy is complicated to measure because of merger history. Which age you want to use depends somewhat on what you are interested in measuring.
For stellar ages, I've used luminosity weighted age (see section 3.4 of my paper. For that you need from the star particle data luminosity in some band (I used r-band) and GFM_StellarFormationTime. Sum the product of formation time and luminosity, then divide by the sum of luminosities. Another stellar-based metric I know at least one person has used is just the age of the oldest stellar particle, although that's tracking the age of the age of the oldest progenitor.
I've not computed dark matter halo formation time before, but you would probably want to grab the mass history from one of the merger catalogs then grab the redshift at which the halo was half its present day mass.