meeting 2025 10 31 gw - JacobPilawa/TriaxSchwarzschild_wiki_6 GitHub Wiki

Context

  • I've got some more diagnostics on the Zou vs. WISE vs. WISE2MBH discussions we've been having, as well as a reply from Hu Zou on the Zou W1 and W2 magnitudes. Maybe it's best to start there.

Cleaning up some of the recent results

  • I've been a bit scattered and wanted to briefly organize all of the latest results in a clearer, more concise bullet.

Email exchange with Hu Zou

First, here's my email to Hu, followed by his reply: ```

In particular, I was wondering how exactly the MAG_W1 and MAG_W2 (the WISE W1 and W2 apparent magnitudes) are obtained for each source as they are quoted in your "desidr9_galaxy_cspcat.fits" file from the 2022 paper.

From what I understand from your 2019 paper, the W1 and W2 fluxes are obtained from the unWISE catalog (the "unWISE" catalog on this page: https://irsa.ipac.caltech.edu/cgi-bin/Gator/nph-scan?submit=Select&projshort=WISE), and are then converted to AB magnitude and corrected for galactic extinction, but I was having trouble reproducing the magnitudes for a few of the galaxies I'm concerned about.

For example, M87 appears to have W1=10.3995 AB mag, W2=10.2882 AB mag in your "desidr9_galaxy_cspcat.fits" catalog. If I search for M87 in unWISE, it seems like the W1 flux and W2 flux are 273620 and 312930 nanomaggy, respectively (from the site above). This gives me:

m_{W1,AB} = 22.5 - 2.5log10(273620) + 2.699 = 11.606 AB mag m_{W2,AB} = 22.5 - 2.5log10(312930) + 3.339 = 12.100 AB mag

Neglecting the extinction correction here which should be rather small, I'm not sure how to reconcile the MAG_W1 or MAG_W2 listed in the catalog vs. my attempts at computing the values from the unWISE source catalog itself. Am I missing something in your calculation here? Any advice or guidance would be much appreciated.


 </details>
 
* And his reply:

The WISE magnitudes in the catalog are AB mag and the Galactic extinction is not corrected. The Galactic reddening value should be included in the catalog. But it is different from the official unWISE data, the DESI team (including us) has reprocessing the unWISE coadd and do Tractor photometry using the prior knowledge of optical morphology from DESI legacy surveys. You can find information from the website of Legacy Surveys (https://www.legacysurvey.org/; at present the website is down, I think it would be recovered soon) . Note that large galaxies like M87 wouldn’t never have good photometry. If any further questions, don’t hesitate to contact me.


* A few things stand out to me about this:
	* This email seems to imply to me that they went to the raw unWISE image co-adds, and then did their own tractor photomerty on the sources based on optical morphology; so maybe there's no public way for me to get the raw fluxes/magntiudes? But this is still quite offset from the other magntiudes.
	* Somewhat frustratingly, Hu says that the magntiudes are NOT extinction corrected, but both his 2019 and 2022 paper say the exact opposite:
		* Zou+19: "Table 3 gives a detailed description of our catalog. The magnitudes are in AB magnitude system and are corrected for Galactic extinction."
		* Zou+22: "Note that all the photometric magnitudes used in the following of this paper are corrected for the Galactic extinction."
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