search

editeodoro / Bbarolo

Bbarolo is a 3D fitting tool to derive the kinematics of galaxies from emission-line observations.
http://editeodoro.github.io/Bbarolo/
GNU General Public License v2.0
30 stars 8 forks source link

Arcsec to kpc conversion #28

Closed 0ort9 closed 1 year ago

0ort9 commented 2 years ago

ello, i am using Bbarolo for my master thesis and it works great so far! I was just wondering how Barolo converts the radii to Kpc without having any information about the distance of the galaxies? The radii in kpc seem very of for my calculations. Or is there an option to set the distance? Thanks in advance!

editeodoro commented 2 years ago

Hello, you can specify the distance in Mpc with the parameter DISTANCE. If not specified, the code will estimate a putative distance from the systematic velocity, using the Hubble flow, and this can be extremely wrong! Thus, if you do not input your own distance, it is better not to trust the outputs in kpc.

0ort9 commented 2 years ago

Thank you for the answer! I could not find the option in the documentation but it seems to work now. I encountered another problem. Maybe you can help me out. If i leave Vsys as a free parameter the output is always 0 km/s for every ring. It works fine if i set it to a fixed value. Also i was curious about how barolo finds the initial guess for Vsys. I know that it uses the midpoint between 20% of the maxima of each side of the global spectrum. But does it determine the maxima based on some fits or will it just read out the max data point? And one last thing: Is it possible to get the masked moment map output in terms of other units? For example K*km/s for the mom0

Thank you again in advance!

editeodoro commented 2 years ago

About the VSYS that does not vary, it sounds like some kind of bug. Can you send me a private message with your datacube and parameter file, such that I can reproduce the problem and try to fix it?

For the initial guess of VSYS, it just uses the maximum values of the data.

Finally, currently it is not possible to change the units of the 0th moment map, which will be always in Jy/beamkm/s. However there is a trick you can use: if the code does not understand the BUNIT keyword in the FITS header, it will not make any conversion. For example if BUNIT='K', the map will be in Jy/beamkm/s (because it understands 'K'), but if you change it, for example, to BUNIT='K (Tmb)', the output will be in K*km/s (because it does not understand 'Tmb' and no flux conversion is done).

editeodoro commented 1 year ago

The problem of VSYS being always zero when left free has been fixed in e76e469a27c9e16e1a0fbfef53dee0eea31869d2. It was a bug that showed up only when VSYS and VRAD were kept free at the same time.

Closing this thread.