Trying to plot on top of an all-sky fermi map

[Josh Tan]

Hello All:

We have a list of sources we would like to plot on top of an All-Sky Fermi Map. Unfortunately, we cannot figure out how to do this straightforwardly. From the tutorials and docs we've got the following code to produce the All-Sky Fermi map:

gc_pos = SkyCoord(0, 0, unit="deg", frame="galactic")


energy_axis = MapAxis.from_edges(
    [1e4, 3e4, 1e5, 3e5, 2e6], name="energy", unit="MeV", interp="log"
)


counts = Map.create(
    skydir=gc_pos,
    npix=(3600, 1800),
    proj="AIT",
    frame="galactic",
    binsz=0.1,
    axes=[energy_axis],
    dtype=float,
)


_,ax,_=counts.sum_over_axes().smooth(2).plot(stretch="log", vmax=30);

The intent is to creat a matplotlib axes object called ax that we can then plot against. However, this doesn't seem to actually work in this fashion.

Instead, we can use pyplot to overlay pixel coordinates which makes it pretty difficult to plot the sources. It seems other plotting functions don't have this issue, or maybe there is something simple we're missing?

Cheers,

Josh Tan

[Atreyee Sinha]

Hello Josh,

If I understand your question correctly, adding the following lines to your script should work (eg: If you want to plot Sgr A).

gc_pos = SkyCoord(0, 0, unit="deg", frame="galactic")

energy_axis = MapAxis.from_edges( [1e4, 3e4, 1e5, 3e5, 2e6], name="energy", unit="MeV", interp="log")

counts = Map.create( 

    skydir=gc_pos,   

    npix=(3600, 1800),  proj="AIT",  frame="galactic",    binsz=0.1,    axes=[energy_axis],    dtype=float,)

_,ax,_=counts.sum_over_axes().smooth(2).plot(stretch="log", vmax=30);

 

## Lines to be added

wcs = counts.geom.wcs

src_pos = SkyCoord.from_name("Sgr A").galactic 

ax.plot(src_pos.to_pixel(wcs=wcs)[0], src_pos.to_pixel(wcs=wcs)[1],  "o", color="red")

Let us know if this helps or if you have further questions!

regards,

Atreyee

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