Personal tools
You are here: Home / H=1 Histories


Obtaining FITS file(s) of stochastic growth histories

Here is the link to the folder in Dr. Daniel Kelson’s Google Drive that contains a FITS file with 10^5 histories of 10^4 timesteps each.

The file we made available is “raw” from the stand point of being generated as a stochastic process with a σ of unity. That means that if you want to turn the contents into something physical, you have a few options. One option is—and the easiest of all—is to use it to ask questions about a particular regime, like, say, galaxies experiencing unabated fueling, like low and intermediate mass galaxies at late times, or all galaxies at early times.

For example, if you wanted to think about galaxies at late times with stellar masses in the range of 10^9 Msun to 10^10 Msun, where the quiescent fraction is still more-or-less about 15%-20%, and the median specific star formation rates are about log sSFR ~ -9.55 dex. You would take this FITS file and add up the array along the x axis (where the dimension is 10^4), and use that to normalize every row (each row is a possible “galaxy” out of the 10^5). Now every row acts like a star formation history normalized to unity at the final timestep. If you multiply each row by, say, 10^9 then each row then is a star formation history that ends up at 10^9 Msun. Note that if you then want to turn each element into an SFR you have to divide by the time span of a pixel. So if you are thinking about, say, these 10^9 Msun galaxies at z=0.1 and you think the star formation process began at z=20, you just take the difference in look back time for z=20 and z=0.1 using your favorite cosmological parameters, and divide that time span by 10^4. That’s 12x10^9 yrs divided by 10^4, so then each timestep is 1.2 Myr.