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Lean Tutorial¶
This tutorial runs through all of the steps for doing a project with Marvin from start-to-finish with no extra fat. We recommend the use of ipython
or jupyter notebook
when using Marvin. You can start either from a terminal with ipython
or jupyter notebook
.
Project Description¶
Calculate the [NII]/H\(\alpha\) ratio for star-forming spaxels in galaxies with stellar mass between \(10^{10}\) and \(10^{11}\) .
Sample Selection¶
Marvin uses a simplified query syntax (in both Web and local queries) that understands the MaNGA database schema, so you don’t have to write complicated SQL queries.
Goal: Find galaxies with stellar mass between \(10^{10}\) and \(10^{11}\).
Create the query with doQuery()
and run it (limit to only 3 results for demo purposes):
>>> from marvin.tools.query import doQuery
>>> q, r = doQuery(search_filter='nsa.sersic_logmass >= 10 and nsa.sersic_logmass <= 11', limit=3)
Tip: see Marvin Query to learn the basics of querying. See Example Queries and Marvin Query Syntax Tutorial for help with designing search filters.
View the Results
. You may see a different set of results. That is ok as long as you see some set of results.:
>>> df = r.toDF()
>>> df
mangaid plateifu sersic_logmass
0 1-109056 8077-6103 10.200446
1 1-109081 8077-12705 10.862523
2 1-109112 8078-1901 10.128309
Convert into Maps objects:
>>> r.convertToTool('maps')
>>> r.objects
>>> galaxies = r.objects
Get the Maps¶
Alternatively, maybe we already knew our galaxy IDs, which we can use to create Maps
objects:
>>> from marvin.tools.maps import Maps
>>> mangaids = ['1-245458', '1-22301', '1-605884']
>>> galaxies = [Maps(mangaid=mangaid) for mangaid in mangaids]
Get the H\(\alpha\) maps:
>>> haflux_maps = [galaxy['emline_gflux_ha_6564'] for galaxy in galaxies]
Plot H\(\alpha\) map of the second galaxy:
>>> haflux_map = haflux_maps[1]
>>> fig, ax = haflux_map.plot()
Get Spectrum and Model Fit¶
Let’s take a look at the model fits a spaxel. The easiest way is to navigate to the Galaxy page for 7992-6101 and click on the red “Map/SpecView Off” button.
However, we can also plot the spectrum and model fits in Python. First, we can find the coordinates of a spaxel by moving our cursor around the interactive matplotlib plotting window. When the cursor is over the spaxel of interest, the coordinates will appear in the lower right.
Then we can create a Spaxel
object by accessing the parent Maps
object from the Map
object (haflux_map.maps
) and retrieve the model fit.
>>> spax = galaxies[1].getSpaxel(x=28, y=24, xyorig='lower', cube=True, modelcube=True)
Now let’s plot the spectrum and model fit:
>>> import matplotlib.pyplot as plt
>>> # Set matplotlib style sheet. Undo with matplotib.rcdefaults().
>>> plt.style.use('seaborn-darkgrid')
>>> ax = spax.flux.plot()
>>> ax.plot(spax.full_fit.wavelength, spax.full_fit.value)
>>> ax.legend(list(ax.get_lines()), ['observed', 'model'])
>>> ax.axis([7100, 7500, 0.3, 0.65])
Plot BPT Diagram¶
The get_bpt()
returns masks for spaxels of different ionization types and the Figure object.
>>> masks, fig, axes = galaxies[1].get_bpt()
For a detailed description see BPT Diagrams.
Select Star-forming Spaxels¶
Select the star-forming spaxels that are in the star-forming region of each diagnostic diagram (hence the “global” keyword):
>>> sf = masks['sf']['global']
Return the complement of the BPT global star-forming mask (True
means star-forming) using ~
and mark those spaxels as DONOTUSE since they are non-star-forming spaxels.
>>> mask_non_sf = ~sf * haflux_map.pixmask.labels_to_value('DONOTUSE')
Do a bitwise OR between the DAP mask and the non-star-forming mask:
>>> mask = haflux_map.mask | mask_non_sf
Plot with our new mask:
>>> haflux_map.plot(mask=mask)
Plot [NII]/H\(\alpha\) Flux Ratio for Star-forming Spaxels¶
Calculate [NII]6585/H\(\alpha\) flux ratio:
>>> maps_7992_6101 = galaxies[1]
>>> nii = maps_7992_6101['emline_gflux_nii_6585']
>>> ha = maps_7992_6101['emline_gflux_ha_6564']
>>> nii_ha = nii / ha
Plot the [NII]/H\(\alpha\) flux ratio for the star-forming spaxels:
>>> nii_ha.plot(mask=mask, cblabel='[NII]6585 / Halpha flux ratio')
Next Steps¶
- Getting Started (more general introduction to Marvin)
- Plotting Tutorial
- Download Data (avoid repeating the same remote API calls every time you run your script)