On Mon, Mar 30, 2015 at 11:10 AM, Desika Narayanan <dnarayan@haverford.edu> wrote:

Hi All,

I'm trying to understand some of the stellar ages that the Tipsy example data (the isolated galaxy) at:

http://yt-project.org/data/

When I examine the formation time with the super-simple script:

http://paste.yt-project.org/show/5501/

I get: 

max star age:  100.000499852 Gyr

I thought normally the formation time was the current simulation time minus the stellar age for Tipsy outputs - am I interpreting this wrongly?

Hi Desika,

I encountered this before.  Take a look at the following section of the docs, which makes use of this dataset:

http://yt-project.org/docs/dev/analyzing/filtering.html#filtering-particle-fields

I don't have a copy of gasoline to confirm this, but the conclusion I came to is that the stars in the initial conditions for this simulation were given a creation time arbitrarily far in the future, generating spurious stellar ages.

If you instead define particle filters for formed stars like so:

def young_stars(pfilter, data):

    age = data.ds.current_time - data[pfilter.filtered_type, "creation_time"]

    filter = np.logical_and(age.in_units('Myr') <= 5, age >= 0)

    return filter

def old_stars(pfilter, data):

    age = data.ds.current_time - data[pfilter.filtered_type, "creation_time"]

    filter = np.logical_or(age.in_units('Myr') >= 5, age < 0)

    return filter

where I've arbitrarily chosen 5 Myr as the cutoff for old stars and young stars, you'll find that your results make more sense.

 

HTH,

Nathan

Thanks,
desika

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