PM2017 wrote:MAAAAC wrote:PM2017 wrote:I have the same issue. The closest things I've found thus far is this: http://astrosun2.astro.cornell.edu/~masters/lisadistances/tf.htm, but it hasn't been super useful.
I haven't had time to do it yet, but I was planning on looking into calibrating it using the milky way, to at least get a rough idea.
Ok, we're going to do this! So if we assume that those equations on the Cornell site are calibrated correctly for their respective bands (which I think is a pretty safe assumption, considering the credibility of the source and that they purportedly took the equations directly from Tully and Fisher?) then we have corrected equations that need 2 more things to be usable: input and output units and conversions to more useful quantities (ie. absolute magnitude in the B band isn't that useful, but it would be nice if we could have an equation for visual absolute magnitude or luminosity). From what I have seen through speed-reading random google-search results, the WR units ("rotationa rate for the galaxy") is the same thing as the "rotational velocity" (please correct me if I am wrong) which is typically in units of Km/s and can be found by taking half the measure of the difference in velocity between the two peaks of an H I 21 cm line graph. For the output units, well, its just absolute magnitude corrected for a band so it doesn't have "units" so we're all good there. Next is the matter of making the output values useful. I've hardly ever seen any questions ask for absolute magnitude corrected for the B band, etc. so, unless the test writers are super nice, it probably won't be that helpful. A more useful unit would be something like absolute magnitude in the visual band (which is your typical, normal "absolute magnitude") or Luminosity. This part is harder... and I don't know if it is even possible considering what the bands represent and their discrepancies for different types of stars, etc. From what I have read (https://en.wikipedia.org/wiki/Bolometric_correction, https://www.astro.umd.edu/~ssm/ASTR620/mags.html) It is possible to correct a band magnitude to convert it into bolometric magnitude (and thus, back into visual magnitude) for specific types of stars, but this wouldn't work for galaxies (unless you did something like change the bolometric corrections using the percentages of different stars in a galaxy, etc.) Perhaps it is a lost cause, and what we really need is a TF equation for the visual band or something bolometric. It's weird that we haven't been able to find one of these, as, being the most useful, you would think it would be the first equation to be created...
Actually, radio would be the most useful, since the Tully-Fischer relationship is really useful at distances where the redshift is enormous.
Yeah, I realized that shortly after posting this... But does this mean we're good?? If these are indeed calibrated equations with useful and known input and output values, we should be able to use them, right? Is there a problem with these equations that I'm not seeing?