Some people are expressing belief that the new rule will improve ATM because of the endless repetition by some ATM proponents. Certainly some threads cycle on way beyond their use because of an unwillingness by the ATM proponent to concede that they have been shown to be wrong.
However, my experience is that mainstreamers can be equally guilty of this same flaw. Here's an example of a single thread of discussion that has been intermixed in the Arp et al thread for the last 3 months. It is a simple enough concept to grasp and well enough explained in post #2628, but the thing keeps getting brought up.
Note that the quotes selected are only the portions of the posts relevant to this subtopic that keeps coming up. Many of the posts contain additional discussion on other subtopics.
Thanatos Dec 15th post #2625
NGC 4192 and 4569 have negative vvir values, according to LEDA. What algorithm did you apply in assigning them a redshift distance modulus?
Dgruss23 Dec 15th post #2628:
I didn't calculate a single redshift distance for Virgo Cluster Galaxies. The paper utilizes the Tully-Fisher Relation. The Tully-Fisher relation is a tight relationship between the absolute magnitude and the rotational velocity of a galaxy. No redshift distances are needed. So the negative redshifts are irrelevant to the distance calculation. The redshifts are used to calculate the PV72 value:
PV72 = Vvir - DistancexH0
where Vvir is the redshift corrected for Virgo infall; the distance is the TFR distance, and H0 is a Hubble constant of 72 km s-1 Mpc-1.
In that paper NGC 4192 was found to have a TFR distance of 15.1 Mpc and Vvir = -46 km s-1. So PV72 is found by:
PV72 = -46 -(15.1 x 72) = -1133 km s-1
Thanatos Dec 16th post #2635
I have no defense to that argument. I thought your paper was asserting a correlation between the redshift and TF distance modulus based on morphology. If not, I concede I do not know what I am talking about.
Thanatos Dec 17th post#2637
The question remains on the table . . . how do you derive a redshift distance from galaxies that exhibit negative vvir velocities? It appears your PV72 values require both a redshift and TF distance modulus.
TomT Dec 17th post#2638
Thanatos,
The reply by dgruss23 below, was given in his post #2628. It completely answered your objection. Look at the PV72 equation. Where is a redshift distance modulus calculated or needed? The negative Vvir velocity is used directly in the equation.
"I didn't calculate a single redshift distance for Virgo Cluster Galaxies. The paper utilizes the Tully-Fisher Relation. The Tully-Fisher relation is a tight relationship between the absolute magnitude and the rotational velocity of a galaxy. No redshift distances are needed. So the negative redshifts are irrelevant to the distance calculation. The redshifts are used to calculate the PV72 value:
PV72 = Vvir - DistancexH0
where Vvir is the redshift corrected for Virgo infall; the distance is the TFR distance, and H0 is a Hubble constant of 72 km s-1 Mpc-1.
In that paper NGC 4192 was found to have a TFR distance of 15.1 Mpc and Vvir = -46 km s-1. So PV72 is found by:
PV72 = -46 -(15.1 x 72) = -1133 km s-1"
Dgruss23 Dec 17th post #2639
You don't ... you can't calculate a redshift distance for a galaxy with a negative velocity. I explained this already. I did not calculate a single redshift distance for Virgo galaxies. You would never do that with Virgo galaxies because the mainstream view is that peculiar motions are too large at that distance for reliable redshift distances. The negative redshifts are a great example as to why.
Only a TFR distance modulus is required. The TFR distance modulus is converted to an actual distance in Mpc units and then PV72 is calculated using the following:
PV72 = Vvir - (Mpc x 72 km s-1 Mpc-1)
You don't need a redshift distance to calculate a PV72 value. It is simple the difference between the observed redshift and the cosmological redshift expected at the TFR distance.
Thanatos Dec 18th post#2643
I know the difference between redshift and TF distance. If that is in dispute, I offer my version vs yours on this forum - and let the chips fall where they may.
Dgruss23 Dec 18th post# 2644
I'm sure you do know the difference between the redshift and TFR as distance methods. What you seem not to understand is that you don't need to have a redshift distance to calculate a PV72 value. You only need a TFR distance and a measured redshift
Thanatos Dec19th post #2645
Your argument is not easily refuted: "you don't need to have a redshift distance to calculate a PV72 value. You only need a TFR distance and a measured redshift." Please explain and quantify the difference between a 'redshift distance' and 'measured redshift". The logic escapes me. I will not go away that easily.
Dgruss23 Dec19th post#2651
Logic has nothing to do with it Thanatos. I've already shown you the difference in prior posts. You can pick up any introductory astronomy textbook and read about it.
However, I'll try again. If you go to NED and look up the redshift of the Virgo ScI NGC 4254, you'll find it gives you a redshift of z=0.008029. This is the shift of the 21cm HI spectral lines relative to the expected value. Multiply z by the speed of light that becomes a redshift of 2407 km s-1. That is a heliocentric redshift which must be corrected to some proper reference frame such as Vvir which is corrected for Virgo cluster infall of the local group. The Vvir value for NGC 4254 in Table III is 2508 km s-1.
That is what I mean when I say "measured redshift". It is simply a velocity derived by multiplying the observed spectral shift of spectral lines by the speed of light.
A redshift distance is simply found by dividing the measured redshift by the value of the Hubble constant - in the case of the paper I used H0=72 km s-1 Mpc-1.
So for NGC 4254, the redshift distance is found as follows:
Redshift distance = 2508 km s-1/72 km s-1 Mpc-1
Redshift distance = 34.8 Mpc
The Tully-Fisher distance = 18.8 Mpc (Table III)
Of course it would be absurd to calculate a redshift distance for a galaxy in a large cluster because of the possibility for large peculiar motions. The value PV72 was calculated as shown in earlier posts assuming the TFR distance is correct.
Thanatos Dec24 post#2672
My apologies. I thought you were claiming an inexplicable difference between redshift and TFR distances, and assumed you meant 'peculiar velocity' was the difference between the two. I concede I missed your point.
So on December 24th the matter seems resolved ... right? Read on into the next post (too many words for the single post limit).






