meeting 2025 11 04 gw - JacobPilawa/TriaxSchwarzschild_wiki_6 GitHub Wiki

For complete clarify, here are the data going into the plots below. Note that this page specifies that all the WISE magntiudes are reported in Vega magntiudes, and that page provides the official references for the conversion between systems.

AllWISE:

• Quotes "w1mpro" and "w2mpro" directly. These are the "magnitude measured with profile-fitting photometry"

unWISE:

• Doesn't quote magntiudes but rather fluxes (flux_1 and flux_2 for the W1 and W2 channels; they also have a "local background substracted flux," but I haven't touched those).
• On page 19 of their paper, they discuss converting from flux to different systems. Specifically, they say that the Vega magntiudes are given by m_{vega} = 22.5-2.5*log10(flux). Once the Vega magntiudes are calculated, m_{AB} = m_{vega} + C, where C = 2.699 for W1 and C = 3.339 for W2.
• They also state that the "As noted in §5.3, the agreement between unWISE and AllWISE magnitudes can be improved by subtracting 4 mmag and 32 mmag from W1 and W2" which I have not done just yet, but will attempt that at a later time. Should be very minor differences

• Note that two galaxies in unWISE appear to have INCREDIBLY bright W1 magntiudes. These galaxies are NGC 4649 and NGC 4427. I've double checked that the fluxes from their online catalog, and the W1 fluxes in unWISE do appear to be monstrously large. Their full data are listed below, but the punchline is that the M/L's that are inferred from the colors are enormous, blowing up the unWISE mass estimates.
• I've included the two points in the first plot showing the W1/W2/color comparsion, but I've clipped these from the remaining analysis for now. Since we're not likely to use the unWISE data, I thought it best to move on for now.
• There's also one additional galaxy (NGC 910) for which unWISE W1 appears to be brighter. I've also removed this from the remaining analysis until I figure out why that might be the case, since it's in direct opposition to the other trends. I suspect there's just something strange about the W1 photometry for these sources.

With the magnitudes in hand, I can apply the Cluver+14 method to produce stellar mass estimates. The Cluver+14 method. The Cluver+14 paper does not mention k-corrections, so I chose to leave them off for this comparison. This should not impact our results appreciably since the MASSIVE galaxies have negligible k-corrections.

In brief, the steps are:

• There's excellent agreement between the unWISE and AllWISE results, with the AllWISE data resulting in slightly higher masses than the unWISE data. I think this makes sense (especially given Section 6.8 in the unWISE paper)-- the unWISE data force photometry on all sources assuming they're point sources, so for extended sources, fluxes and locations will be biased. However for most sources, the large FWHM of the WISE PSF makes this negligible, but for the closest, largest galaxies, this problem is worse.

I have to look into this in much more detail, but I quickly ran through the various corrections described in the unWISE paper. Two corrections stood out to me:

• One can estimate using the FWHM of WISE and the FWHM of the galaxy, how much flux is being lost when doing the photometry in unWISE. They discuss this in section 6.8 for extended sources;
• Most of the MASSIVE galaxies have FWHM of ~2.5arcsec or so, which is a roughly ~10% effect. We can convert the fraction of missing flux into magnitude corrections, which I've done and plotted here:
• They also state that, due to difference in calibrations, one should subtract an additional 4 mmag and 32 mmag from W1 and W2 respectively.

The result is this set of comparisons for the magnitudes:

110/115 of the MASSIVE Galaxies are in WISE2MBH, but the final sample I'm comparing here is 107/115 of the galaxies. I've removed three additional galaxies which had weird looking W1 measurements from above along with the 5 non-matches. The galaxies which are removed are:

• NGC 0910 (strange W1)
• NGC 4472 (strange W1)
• NGC 4649 (strange W1)
• UGC 01389 (non-match)
• NGC 0890 (non-match)
• NGC 1497 (non-match)
• NGC 2256 (non-match)
• NGC 7426 (non-match)

From the 107/115 sample, two galaxies stood out as having very discrepant stellar masses compared with the WISE2MBH values. I've also removed these two from the comparison below, since there's likely something going on with them that I don't fully understand yet. These galaxies are listed below along with their data:

• NGC 5252
• NGC 4486

• NOTE: THIS IS STILL A WORK IN PROGRESS FRIDAY AFTERNOON!