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jzuhone / pyxsim

Simulating X-ray observations from astrophysical sources.
http://hea-www.cfa.harvard.edu/~jzuhone/pyxsim
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The emissivity calculation #33

Closed qinyuxian closed 3 years ago

qinyuxian commented 3 years ago

Hi John,

In my opinion, the emissivity (\epsilon = n_e n_H \Lambda_E(T,Z)) should be calculated in the comoving frame. However, it seems that pyXSIM uses the proper density to calculate the emission measure directly. The physical picuture what I understand may be can illustrated in the following figure. What do you think about it?

Thank you and best wishes.

t16_three_distances

qinyuxian commented 3 years ago

I think I was wrong. Sorry for troubling you.

qinyuxian commented 3 years ago

However, I think of another question. If I use the data from the snapshot of z = 0.1 and observer them at z=0.2. The comoving density is constant. Which physical densities shall I use, at z=0.1 or at z=0.2? Thank you.

jzuhone commented 3 years ago

Which redshift does the source emit at?

qinyuxian commented 3 years ago

It emits at z=0.2. However, I do not have snapshot at z=0.2. So I used the snapshot of z=0.1 instead of z=0.2.

jzuhone commented 3 years ago

If it emits at z = 0.2 you need the snapshot at z = 0.2.

qinyuxian commented 3 years ago

In fact, the positions, velocities and physical properties of the simulation are stored only at a discrete set of redshifts. If I want to make the light cone, such problem will arises.

jzuhone commented 3 years ago

This is always the case with light cone simulations--nothing unusual.

Unless you have another question pertinent to the emissivity I'll be closing this issue.

qinyuxian commented 3 years ago

It is OK to close.