Clarification on the definition of j_z / j_circ in your TNG50 MW/M31-like galaxy catalogue
AMIT MONDAL
24 Oct
In my recent work, I use the TNG50 Milky Way/M31-like galaxy catalogue and aim to isolate the stellar halo component of each galaxy. I found that applying a cut on the circularity parameter can effectively select the spheroidal component of the galaxy, and by further applying a radial cut to exclude the bulge, one can identify the stellar halo stars.
However, I would like to clarify the following points:
What is the appropriate threshold for separating the spheroid — is it ϵ < 0.5, ϵ < 0.65, or |ϵ| < 0.5 (or 0.65)?
In the definition of the circularity parameter, ϵ = j_z / j_circ, does j_z correspond to the z-component of the angular momentum in Cartesian coordinates (i.e., j_z = x v_y − y v_x), or is it computed in cylindrical coordinates?
Is it physically acceptable to perform this analysis using the rotated coordinates and velocities provided in the TNG50 MW/M31-like galaxy catalogue?
In my recent work, I use the TNG50 Milky Way/M31-like galaxy catalogue and aim to isolate the stellar halo component of each galaxy. I found that applying a cut on the circularity parameter can effectively select the spheroidal component of the galaxy, and by further applying a radial cut to exclude the bulge, one can identify the stellar halo stars.
However, I would like to clarify the following points:
What is the appropriate threshold for separating the spheroid — is it ϵ < 0.5, ϵ < 0.65, or |ϵ| < 0.5 (or 0.65)?
In the definition of the circularity parameter, ϵ = j_z / j_circ, does j_z correspond to the z-component of the angular momentum in Cartesian coordinates (i.e., j_z = x v_y − y v_x), or is it computed in cylindrical coordinates?
Is it physically acceptable to perform this analysis using the rotated coordinates and velocities provided in the TNG50 MW/M31-like galaxy catalogue?