Tully-Fisher relation?

Favorite Answer

Tully and Fischer used 535 km/s for Andromeda for their 1977 paper: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1977A%26A....54..661T&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf

L ∝ V^4, not L= V^4

You might want to back track and work with this how to: http://universe-review.ca/R02-07-candle.htm

Alternatively, you plug it back in to:
M= -9.5 x log(Rotational velocity in km/s)+2
(But I can't get a good number out of this formula...did you miss something in the copying)

Or you could do: (M.Androm/M.Milky)^9.5 *220km/s
but that only gives you 360km/s


**********************Addendum ******************

Got it all figured out.

the ΔV from the Tully-Fisher paper is the differential radial velocity (based on the width the H2 spectrum), not the radial velocity. Just divide by 2. Vr = 267 km/s

Further, you need to be sure to use log₁₀, not ln (I hang around too much with people who use log to mean ln). I made a plug in error when I first attempted this problem.

Answer

If we use the relationship you used:
M = - 9.5 log Vr + 2
we get Vr = 272 km/s
This is approximately what Tully Fisher used

However, if we use the Sa curve for M31 from this source ( ref: http://www.phys.unm.edu/~gbtaylor/astr422/09_A422_Galaxies_II.pdf )we get:

M = -9.5 log Vr + 3.15
-21.23 = -9.5 log Vr + 3.15
log Vr = 2.556
Vr = 360 km/s
This is close to the answer I got above for extrapolating based on the Milky Way Vr

Based on my review, the k values for the relationship
L = k V^4
will vary based on the type of galaxy. You will also get variations because this is an empirical formula so you will get a a gaussian distribution. Some things to consider would be age of galaxy, rate of new star formation, mass of galactic center, amount of dark matter halo, etc.

Hope this helps....Show more

This Site Might Help You.

RE:
Tully-Fisher relation?
The Tully Fisher relation can Be used to find the Distances to galaxies.
Tully Fisher relation: L= V^4
L is the luminosity
V is the rotational velocity of the galaxy in km/s

I went online and did a little research and found out that You can express the Luminosity as the Absolute magnitude. I......Show more

Why use the Tully - Fischer relationship on the Milky Way.
According to Wikipedia the Sun revolves at 220 KM/sec around the Milky Way. So according to the Tully- Fischer relationship (M = -9.5 x log (rotation velocity in km/s) + 2) the Milky Way has an absolute magnitude of -20.25 magnitude. So it seems reasonable that Andromeda Galaxy has an absolute magnitude of -21.23. Hope this helps...Show more