That they used 6 galaxies that are located in 6 different clusters is not in dispute. What is in dispute is your claim that they assumed that the galaxies are at the mean distance of their respective clusters, making their result "irrelevant". I have refuted this claim many times, noting that you have not given a quote that supports this assertion. You just gave the "only six galaxies beyond the Fornax cluster" quote, but it does not make such an assumption.

The cosmic velocity of a galaxy is the same as the cosmic velocity of the host cluster. If you think otherwise, you are promoting some bizarre ATM idea.

So you like to quote mine the papers for individual words. Why not quote the caption from figure 4 (The HKP final paper by Freedman et al.) that shows the Hubble diagram? There the distance vs. velocity results are given for "Tully-Fisher clusters", "fundamental plane clusters" and "surface brightness fluctuation galaxies".

http://www.journals.uchicago.edu/ApJ...52417.fg4.html

Galaxies, not clusters.

Or why not quote Table 10 from the same paper where the final SBF results are given. Galaxies, their flow corrected velocities and distances are given. Galaxies, not clusters. Or why not quote this from the Ferrarese paper: "Errors on H0 are given by the formulae listed in the notes to part 3 of Table 5, for the case in which errors on the velocities and distances (d in Mpc) are identical for the N galaxies used to derive H0." It says "the N galaxies used to derive H0". Galaxies, not clusters. Instead, you just quote mine the papers for everything where the word "cluster" appears without understanding what they are talking about. The reason the word "clusters" is used in the above quote is that the authors are reminding the readers that the target galaxies used to derive H0 are in different clusters.

That is indeed the heliocentric systemic velocity of the Coma cluster that they gave "for comparison" as it reads in the paper. However, it is not the redshift that was used to determine H0. And then you go and quote redshifts from sources that have nothing to do with this paper and leave out the only one that matters - the CfA redshift survey that was the one used in the papers... Besides, even if there were a 3% error (6965 km/s / 6750 km/s = 1.03) in the redshifts, it would not change the NGC 4881 derived value of H0 by much: 6965 km/s / 102.3 Mpc = 68.1 km/s/Mpc vs. 6750 / 102.3 = 66 km/s/Mpc. This is well within the quoted errors for NGC 4881.

So, the HKP did indeed use valid distances and flow corrected velocities for the galaxies to derive H0. They do not assume (and they do not need to) that the galaxies are at the mean cluster distance. In fact, the sample size is quite sufficient to keep the error reasonable - this is discussed in detail in Table 5 of the Ferrarese paper.

http://www.journals.uchicago.edu/ApJ...684/40684.html

Specifically, the sample size affects the error as follows:

Sqrt((R_3.1/d)²+(0.46*H₀*R_SBF)²)/Sqrt(N)

where R_3.1 is the random error on the flow velocities (+/- 400 km/s), R_SBF is the random error on the color-corrected magnitude and N is the sample size. This is perfectly valid statistics. Dgruss23 can't show what's wrong with it, because nothing is. The final SBF H0 result is reliable, the Ferrarese paper where it was presented is heavily cited (well over 100 citations) and none of those who cite it in the literature question (let alone dismiss) this result. You simply erred when declaring it "irrelevant".

I've already responded to every bit of this in post #69 and post #74 of this thread.

So it is agreed that they used 6 galaxies. It is also agreed that each of those galaxies was in a different cluster. However you continue to claim that they did not use the galaxy as a representation of the mean cluster distance. Let's look again at the Ferrarese et al (2000) paper in which the HKP presented the SBF analysis in detail.

From the first paragraph of section 8 of Ferrarese et al:

These are 4 of the 6 SBF galaxies used by the HKP. Note that they refer to these galaxies as the central galaxies in "clusters". Central galaxies are presumed to be at the mean cluster distance - otherwise they're not central!

Now - and I already quoted this before - later in the same section they state:

They go on to explain the corrections applied:

.

But note carefully here - Zahl is arguing that the redshifts were not the cluster redshift, but the redshift of the individual galaxy. However, we can see that they state column 6 is the velocity of the cluster and earlier in the paragraph they describe making corrections to the velocity in column 6! And they say straight out that their last difficulty is to find the "clusters" velocity - not the individual galaxy velocities. And I explained all this before in my earlier posts.

You tell me I'm quote mining and don't understand what I'm talking about. That's rich. I've repeatedly demonstrated that they used one galaxy per cluster and in calculating H0 they used the redshift of the cluster - not the individual galaxies. YOU actually are the one that is ignoring the larger context of what they did. The underlying analysis is in the Ferrarese et al paper - that is what you must look at to understand what they did.

Of course in Table 10 (Freedman etal) they listed galaxies - those are the galaxies from which the cluster distance was represented. Note in Table 4 of the Ferrarese paper not only did they include the galaxy ID, but also the cluster it belongs to ... and further more they noted that the heliocentric redshift they corrected with their flow model was a cluster redshift. All this backs up what I've been saying. What - you think that because they didn't list the cluster names in the final paper it means that all the analysis in the Ferrarese et al paper - analysis that demonstrates they used cluster redshifts - doesn't exist?

Of course Ferrarese et al simply followed what Lauer et al (1998) did. Here is what they say about the 4 SBF galaxies that the HKP adopted from their study(Section 3 first paragraph):

So let me ask you this Zahl: How is it that they define the 6 galaxies used as "central" galaxies and then use the mean redshift for the cluster (not those individual galaxies) and yet you claim that they were not using the individual SBF galaxies as the mean cluster distance?


It was the redshift that was corrected to the redshift used for calculating H0 through their flow model. Go back and read the paragraph again - or what I demonstrated above.

They cited "Chen et al in preparation" as the source of the CfA redshifts they used. Why don't you do an ADS search on Chen et al and tell me what you find? Then perhaps you'll understand why I had to quote redshifts from other sources.

Agreed, you've been making a huge deal about something insignificant - and in the process the discussion has been distracted from the point you seem not to grasp.

You are missing the point Zahl. I did not say that the SBF distances could not be accurate. They might be very accurate -- (although if you read Ferrarese et al you'll see some explanation as to why the Coma cluster SBF has a high uncertainty). The sample size is too small for a global determination of H0. Period. That is why I said their SBF is irrelevant. And I stand by that. If you think that 6 galaxy distances is sufficient to determine the global value of H0, then we simply will not agree.

The only way their SBF result would be compelling is if the assumption that the 6 "central" brightest cluster galaxies they used are actually central to the clusters is valid. And how would we establish that the 6 SBF galaxies are central to their clusters --- well we'd need distances to those clusters from other methods. For Coma their SBF distance is 102.3 Mpc. The HKP gets 85.6 Mpc from the I-band TFR (28 galaxies) and 85.8 Mpc from the FP (81 galaxies).

So is NGC 4881's SBF distance correct? Either it is correct and (1) NGC 4881 is on the backside of the cluster not at its center or (2) NGC 4881 is at the center and the TFR and FP distances to Coma are grossly inaccurate due to an unknown systematic error. The other option is that NGC 4881's distance is incorrect and the TFR and FP distances are the correct distances.

How could we decide these options??? How about having a few more SBF distances to Coma? Which is my point - one SBF distance is not enough.

Zahl, even if you were correct (which you're not) that the SBF distances were individual distances not meant to be representative of the mean cluster distances, my primary objection would stand - 6 distances to individual galaxies is too small a sample for a global determination of H0.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Zahl,

Really, I think a lot of our disagreement about the clusters vs. individual galaxies issue comes from some inconsistency in the use of the terms in the HKP papers. As I've demonstrated in my previous post, they clearly identified clusters in Table 4 and Section 8 of the Ferrarese et al SBF analysis.

However, in the final report they only provide the galaxies in Table 10 - not the clusters. Then there is this quote from section 6.4 of the final report:

Note that they call them galaxies in the one sentence and refer to the clusters in the next sentence. That creates some ambiguity as to what table 10 represents.

Later in the same paragraph they resolve the ambiguity in the direction I've been arguing:

Now you made a big deal about the fact that table 10 doesn't say clusters. But in the text that refers to table 10 they do say clusters.

Are you going to continue to claim I'm mistaken about that which I've repeatedly demonstrated I'm not mistaken about, or could we perhaps address this issue about the sample size of the SBF and Type II SN samples?

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

"One galaxy per cluster" is not in dispute. Now answer these questions:

Why does Freedman write "Tully-Fisher clusters", "fundamental plane clusters" but instead of "surface brightness fluctuation clusters" there reads "surface brightness fluctuation galaxies" in the distance vs. velocity plot (Figure 4)? Why does table 4 in Ferrarese give location and magnitude data for galaxies if the velocity data is not valid for them as well? Why does the table say "H0, all galaxies ... 70 ± 4" and "H0, excluding NGC 4881 and NGC 4373 ... 69 ± 4"? Why doesn't it say "H0, all clusters ... " and "H0, excluding Coma..."? Why does the Ferrarese paper say that "Errors on H0 are given by the formulae listed in the notes to part 3 of Table 5, for the case in which errors on the velocities and distances (d in Mpc) are identical for the N galaxies used to derive H0."? Why doesn't it say "errors on the velocities and distances (d in Mpc) are identical for the N clusters used to derive H0."?

No, it means you don't understand that analysis. One would expect that in Freedman's final table where objects, distances, velocities and H0 values are listed, it is those objects that the given data refers to. But no, according to you they are just something from which the data was derived from and the objects that this data actually refers to were left out... Yeah, right. How logical.

The above formula directly addresses your "the sample size is too small" point. It gives statistically valid errors for H0 based on the 6 galaxies (the N refers to galaxies as it says in Ferrarese et al.). The H0 values given for the six galaxies in Ferrarese and Friedman papers are not global but are valid for the galaxies only. The global value is calculated from them and the above formula gives the error. NGC 4881 from Coma that you have made such a fuss about does not affect the calculated global H0 value at all. That formula would give invalid errors only if the six non-global H0 determinations were not drawn from a normal distribution, but they are and the result is thus valid. This is an inescapable fact, but I don't think you are going to get it anytime soon.

You ignore my questions and then demand I answer these:

Why do Freedman et al say "Flow corrected velocities, distances, and H0 values for the 6 clusters with SBF measurements are given in Table 10."? Why do they say clusters in Table 10 Zahl? Here, I'll answer for you since you have repeatedly refused to answer my direct questions: The answer is because they assumed the SBF galaxy is at the mean cluster distance and utilized the mean cluster redshift for calculating H0.

We've been over this and over this and you have ignored the quotes I've provided that clearly demonstrated what the HKP did in their SBF analysis. And you continue to ignore the larger point I made.

Here is the basic summary of the HKP SBF analysis:

1. Six brightest cluster galaxies had SBF distances determined utilizing the HKP Cepheid distances for absolute calibration. As I noted in the previous two posts, four of these these galaxies are described as "central galaxies in the Abell clusters A262, A3560, A3565, and A3742, ..." by Ferrarese et al. As "central" galaxies they are assumed to be a good representation of the mean cluster distance.

2. They utilized the mean redshifts of the clusters in which the SBF galaxies resided for determining H0. The mean heliocentric cluster redshifts were corrected to their flow model redshifts as discussed in Ferrarese et al. This was unquestionably established in my previous posts and Zahl continues to ignore my points. If the HKP did not assume that the SBF galaxies were at the mean cluster distance, then why use the mean cluster redshift for their analysis Zahl? Please justify such a procedure -- specifically.


This from you??? Who has been repeatedly shown to be wrong in this exchange?

Actually Zahl, the very same page that has Table 10 states that the H0 values for the "six clusters with SBF measurements are given in Table 10." And it is established, but you don't seem to grasp it, that mean cluster velocities were used for the SBF H0 calculation. Does everybody else besides Zahl see this? Here is the quote:

Why say "clusters" if it is really individual galaxies? How about this Zahl - could you provide a quote from either of the papers that trumps this quote above - that clearly demonstrates that the velocities used were the velocities of the individual galaxies and not the clusters? Your quote from the figure 4 caption doesn't cut it. It is superceded by all the other quotes and demonstrations I've provided.

But you ignored that point from my last post too. Why do they say clusters in the text and galaxies in the Table Zahl? Your wrong explanation is that they used the individual redshifts of the individual clusters and that the clusters were only mentioned because the galaxies were in clusters.

And you continue to ignore the larger point - Six galaxies is not enough galaxies to derive a global value for H0. Neither is the 4 galaxies utilized for the Type II SN sample.

Would you care to comment on the small sample size of the SBF and Type II SN samples. You were so offended by my use of the term irrelevant to describe the HKP SBF result (ironic that you would get offended by that considering how willingly you've chosen to be rude on this thread).

I've explained a number of times now that the problem I have with the SBF is what I've stated in bold above. Could you comment on that? Do you actually think that 6 galaxies is enough to determine the global value of H0?

And while you're at it, here is another point you ignored which I made in a post last week:

Will you respond to that point?

Or how about the related points I made here:

Will you respond to this larger issue please? You've already been shown to be wrong regarding your take on what the HKP did regarding the SBF analysis. To continue to beat that dead horse is wasting everyone's time.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Ever heard of small number statistics?

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

It seems unbearably difficult for you to comprehend that the velocities given in the V_flow column in Freedman's Table 10 are valid for both galaxies and their host clusters. This is why distances and velocities are plotted in Freedman's Hubble diagram (Figure 4) for "surface brightness galaxies" instead of "surface brightness clusters" and this is why Ferrarese writes that the velocities and distances for the N galaxies were used to derive H₀.

Do you disagree with the formula Sqrt((R_3.1/d)²+(0.46*H₀*R_SBF)²)/Sqrt(N) and the error it gives for a sample size of 6?

http://arxiv.org/PS_cache/astro-ph/p.../0505465v1.pdf

This is important, because it reflects directly upon the Expanding Photosphere Method (EPM) used by Hamuy. What is perfectly unclear is how this impacts Ho, as determined by Type II Supernova. It certainly widens the error bars.

__________________
jwj

It's a big universe out there...is it really unwinding, really burning out?

Not at all, what you don't comprehend is that the velocities are only valid for both the galaxies and the clusters if the galaxy is at the mean cluster distance. There is a whole lot of reality that you're leaving out of this picture.

Basic reality #1: Galaxies in clusters have peculiar motions.

Basic reality #2: The distance distribution in galaxies includes a depth effect -- not all galaxies in a cluster are at the same actual distance.

Basic reality #3: Clusters may experience bulk motions relative to the Hubble flow.

The procedure for calculating H0 must account for these realities. First, you can't just pick a galaxy in a cluster, determine it's distance and redshift and calculate H0 from that data. The individual galaxy may have a peculiar motion as large as 1500 km s-1.

Generally it is assumed that galaxy clusters themselves will have smaller deviations from the Hubble flow than the individual galaxies within the clusters.

So, the procedure most groups have adopted with the TFR, FP, and SBF locally, is to measure distances to multiple member galaxies in a cluster and get a mean distance for the cluster members. By getting a mean distance from multiple members one corrects for the distance distribution of the cluster.

The second part of this is to adopt a mean redshift for the members of the cluster - not the individual redshift of a single galaxy. Assuming a normal distribution of redshifts around the mean (usually redshift limits are set to eliminate foreground and background interlopers), the mean redshift will correct for the individual peculiar motions. In other words, the mean redshift is the cosmic redshift for the cluster assuming no net peculiar motion for the cluster (not always a correct assumption - but close enough for this discussion).

H0 is then derived from each cluster using the cluster's mean redshift and mean distance.

Now as we've already discussed, the HKP team did use the mean cluster redshift for the cluster the SBF galaxies reside in. The distance to the SBF galaxies were determined and utilized to calculate H0. But this procedure is only valid if the SBF galaxies are actually at (or very close to) the mean cluster distance. A key point you've continued to ignore is that the galaxies in the SBF analysis used by the HKP were Brightest Cluster Galaxies (BCG's). The assumption here is that BCG's are not only the brightest galaxies in the cluster, but are also at the center of the cluster. Again - Ferrarese et al stated:

"Central" is a key piece of this procedure that you have yet to acknowledge. It is the key assumption upon which any validity to their SBF analysis hinges.

For a SBF galaxy that is not in fact central, the cosmic velocity of the cluster is not the same as the cosmic velocity of the individual SBF galaxy. I'm well aware that the Coma cluster SBF distance is not as accurate as the rest, but it serves to illustrate my point.

For the sake of argument let's adopt the popular H0=70 km s-1 Mpc-1. Now NGC 4881 has a SBF distance of 102.3 Mpc. The I-band TFR distance is 85.6 Mpc and the FP is 85.8 Mpc. So here is the problem. If the NGC 4881 SBF distance is correct, and the value of the Hubble Constant is 70, then the cosmic redshift for NGC 4881 is 7161 km s-1.

But is NGC 4881 at the center (and hence the actual mean distance) of the cluster? According to the TFR and FP results it may not be. Now based upon the TFR and FP results, the cosmic velocity of the coma cluster (if H0=70) is 6000 km s-1 if the TFR and FP distances are correct.

If the SBF distance to NGC 4881 and the TFR and FP distances to the Coma cluster are all correct, then NGC 4881 is not central to the Coma cluster and there is a 1160 km s-1 difference between the cosmic redshift of NGC 4881 and the cosmic redshift of the Coma cluster.

So here is the concern with the HKP SBF result. They adopted the mean redshift of the clusters in which the SBF galaxies reside as the cosmological redshift of the galaxy at its SBF distance. They did this because they were using BCG, which are more likely to be central than any random elliptical galaxy within a cluster. But that mean redshift is only valid for calculating H0 if the SBF distance to the galaxy is the same distance as the distance to the cluster.

No, the formula is fine and the error it gives is fine. What you have is a very fine estimate of H0 and the uncertainty in that H0 estimate derived from 6 galaxies. I'm not saying that the H0 value they got is not the H0 value indicated from their sample. Nor am I saying that the uncertainty that they derived is not the correct uncertainty from their data.

What I am saying is that the sample size is too small to be certain that they have actually randomly sampled from the true distribution of H0 values. And I'm also saying that the validity of any of the individual H0 values from their SBF sample hinges critically upon the assumption that the SBF galaxies are in fact central galaxies within those clusters. And that assumption is not quantified in the above equation.

Sticking with basic cosmological models in which there is a global value for H0 that we can track down, it should be remembered that the correct global value of H0 does not have to fall within the systematic uncertainty of the method utilized to determine H0.

For example, the Sandage group comes up with H0=62.3 (+/-5 systematic error). The Sandage group uncertainty overlaps the HKP uncertainty. Does that mean the true value of H0 falls in the overlap?

Well what about the TFR study of Tully&Pierce (2000)? They found H0=77 +/-8. However, their study pre-dates the final metallicity corrected Cepheid distances in the HKP final report. Adopting the HKP final cepheid distances reduces their I-band TFR zero point from 21.57 to 21.50 and thus increases H0 to 79.5. This still overlaps with the uncertainty of the HKP TFR H0 estimate and overall H0 estimate ... but it doesn't overlap with the Sandage estimated uncertainty.

If Sandage et al are right, then the true value of H0 is outside the systematic uncertainty of the TP00 study and the reverse is true if Tully & Pierce are correct.

What it boils down to is that different studies adopt different procedures and you can't always capture those differences in procedure and assumptions into the systematic uncertainty you report.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

I am not sure what ATM theory you are proposing. In mainstream cosmology clusters are gravitationally bound and the expansion of the universe is stopped within them, resulting in the same expansion velocity (in kilometers per second) for all of their gravitationally bound objects after peculiar velocities have been corrected for. If the galaxies inside a cluster had different expansion velocities, they would be flying away from each other and the cluster would come apart. So what is this ATM theory you are proposing?

So are you disagreeing with the systematic error equation of 0.46*H₀*S_SBF and its given error (+/- 6 km/s/Mpc) then?

What evidence do you have that the sample is not actually random or are you just arguing that this could be the case?

dgruss is correct about this point, no ATM involved. Clusters are gravitationally bound, but that doesn't mean that all the galaxies within a cluster will have exactly the same redshift. The "fingers of god" are due to this large scatter in velocity between the cluster's members.

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

And you correct for peculiar motions by getting a mean redshift for the cluster and assuming that the cluster has a negligible bulk motion relative to the Hubble flow - which I already pointed out:

But let me ask you this. Since clusters are gravitationally bound, and individual galaxies have peculiar velocities that must be corrected for - and "expansion stops" within them ... it would be an incorrect procedure to take a single galaxy from one of those clusters and calculate H0 from that galaxy and the redshift of that galaxy ... right?

I ask because as this discussion has proceded you've steadily changed your position to that procedure I've advocated from the start - without acknowledging that I was right. I'm not talking about the "SBF irrelevant" opinion I stated. I know you don't agree with that, I'm talking about the correct procedure for calculating H0 using the SBF galaxies. Here was what you said early on in this exchange:


This is of course incorrect as I pointed out immediately and subsequently demonstrated. The HKP used mean cluster redshifts for the 6 SBF galaxies and described those 6 galaxies as "central" to the cluster.

As I pointed out, you cannot select a galaxy from a cluster and calculate H0 from that galaxy's distance and redshift because (1) the redshift of the galaxy may be contaminated by peculiar motion and (2) the galaxy may not be representative of the mean cluster distance:

As of post#91 you seemed not yet to understand what the HKP did or why what you were proposing they did would be absurd:

It does appear that you now understand I was right in my earlier statements although you continue to suggest I don't know what I'm talking about. You're now talking about correcting for peculiar motions.

But do you understand that clusters have a depth effect? In other words, they're not all at the same distance. If you calculate the distances to multiple galaxies within a cluster you'll get a distribution of distances. With a large enough sample the mean and the median distance for the galaxies in the cluster will be very close.

So H0 is calculated from the mean distance and the mean redshift. With the SBF analysis, the HKP takes the SBF galaxy to be at the center because it is a brightest cluster galaxy. You said earlier (quoted above) that there was no need for them to do so - but there is because they are using the mean redshift of the cluster for calculating H0. If the SBF galaxies are not at the mean cluster distance, then the H0 value derived is not correct.

No, the statistics are properly applied to their sample. But as I pointed out Sandage et al find 62.3 +/-5 while Tully&Pierce find 79.5 +/-8. The statistical uncertainties do not overlap. Both studies cannot be correct - even though their statistical calculations of their uncertainty is valid.

This is what I said:

What evidence do you have that it is random? You could strengthen any evidence you do have with a larger sample of SBF galaxies.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

No, he is not. If you had read the article you linked to, you would have learned that the fingers are caused by peculiar velocities. In the above quote I wrote after the peculiar velocities have been corrected for. Once this is done, the fingers collapse to points and all gravitationally bound objects within the cluster have the same expansion velocity (given in the V_flow column in Freedman's table 10), contrary to what dgruss23 claims.

You apparently think that because the preceding sentence reads "a distance is determined to a galaxy (not cluster)" that the following sentence "Redshift is then found" means that they just take the radial velocity of that galaxy, but the quote doesn't actually say that. In fact, that passage does not describe at all how the redshift is determined for H0 calculation, because the point of contention back then was not redshifts but distances and specifically your claim that the SBF galaxies were assumed to be at the mean cluster distance - a notion which the above passage refutes. But none of this is relevant to the following which you apparently now finally accept:

So you either accept the above or you are proposing some ATM theory. Which is it?

Huh? The above clearly says "flow corrected". Do you happen to have dyslexia or something?

Your argumentation makes no sense in the slightest. First you argue for significant systematic errors and then you agree with the given (small) systematic errors. Make up your mind. Do you agree with the latter or the former? Because you can't agree with both and still claim to be logical.

I have qualitative and quantitative evidence. The qualitative evidence is that the result is not subject to systematic undetected biases in a single cluster environment (such as undetected dust in front of the target galaxy) because different cluster environments are sampled. The target galaxies are also in different general directions so that undetected systematics in the local flow field do not give rise to systematic errors. In fact, working in the context of your own argument, you have not given any reason why the galaxies would be systematically located on the far side of their host clusters as required by your case. Again working in the context of your own argument, if there would be a systematic bias in galaxy locations, it would be more likely that the galaxies would be on the near side of the clusters, because galaxies on the near side are not as much obstructed from our point of view by other clusters structures and dust as those on the far side, potentially leading to a selection effect that prefers galaxies on the near side.

The quantative evidence comes from Jarque-Bera normality test (done with R 2.5.0 & fBasics statistics package) run on the sample of six H0 values. It gives the following results:

LM p-value: 0.946
ALM p-value: 0.723
Asymptotic: 0.919

This is in very good agreement with the distribution expected if the sample was indeed random and had no outliers. Therefore we can be confident that the values do not come from a mixture distribution (true and a biased one). This leaves the possibility that the parameter µ is biased by a constant systematic error that equally affects all H0 values in the sample. But this is unlikely as I qualitatively argued above. Moreover, such as error would not be lessened or even detected by increasing the sample size (because increasing the sample size does not help to reduce the systematic error when that systematic error is constant), thus refuting dgruss23's insufficient sample size argument.

Now let's hear dgruss23's evidence for systematic errors.

If this is true, since V = H0 * D, wouldn't it then be true that all gravitationally bound objects within the cluster are the same distance from us?
In other words, if H0 is a constant, and the expansion velocities of the objects are all the same, then the distances D = V/H0, would also all be the same.

That's my point. Your summary is so general as to be misleading. And perhaps you could explain the incorrect reference to the Cepheid part of the description?



This is clearly incorrect. The Cepheid galaxies used to calibrate the SBF galaxies are not the same SBF galaxies used to calculate H0. The table 10 galaxies do not have Cepheid distances. Given this error it is not hard to understand why I would take your meaning to be that you were saying redshift is found for the galaxy -- especially when you emphasize the incorrect notion that you think there was no need for the galaxy to be representative of the mean cluster distance.


You've offered nothing that refutes my "claim". The SBF galaxies are assumed to be central, are stated by Ferrarese et al to be central and it would make no sense to calculate H0 from the mean cluster redshift if the galaxies were not assumed to be central. You still refuse to acknowledge whether or not you understand that clusters have a depth effect.


You obviously don't know what dyslexia means any more than you understand what "flow corrected" is. Flow corrected velocities are adjustments to the heliocentric redshifts to account for the following motions: First the centroid of the local group correction is applied, then infall for three attractors: Virgo, The Great Attractor, and the Shapley Concentration. This flow corrected model has absolutely nothing to do with the intracluster peculiar motions of the individual galaxies within the cluster - that is what I'm referring to. The flow model that you're referring to is a set of corrections for bulk motions of groups and clusters due to other major mass concentrations. See section 8 of the Ferrarese paper for the discussion on the flow model and for more details they refer the reader to Mould et al (2000).

In the context of this discussion my point is that you cannot calculate H0 from the distance to an individual galaxy in a cluster and its individual redshift. You must use the mean cluster distance and the mean cluster redshift because the individual galaxies have varying distances and random peculiar motions that can be a sizeable fraction of the cosmological redshift.

And this is where my objection to the number of galaxies comes in. They used a single galaxy to define a cluster distance. As I've stated a number of times now - and you continue to fail to see the relevance of the point because you have mistaken notions about how this was done - the only reason they could reasonably use a single galaxy to determine the cluster distance is because they selected the BCG's - which are traditionally assumed to be central - the very word Ferrarese et al used.


You have such a narrow understanding. Zahl, as I pointed out - it is not always easy or possible to capture all the systematic errors. The equation captures what they think they know about the systematic errors and if they are right that the galaxies are at the cluster center, then their systematic error is just fine.

You continue to selectively respond to my examples and ignore those that you don't have an answer for.



The part in bold is completely inapplicable to this situation. These are brightest cluster galaxies - obstruction is not an issue!

Really? All systematic errors are distance independent? Have you actually compared the SBF distances with other distance estimates? We'll go in order of increasing SBF distance:

NGC 4373 (ESO 322-6) - a member of the centaurus cluster. The HKP finds 36.3 Mpc for this galaxy. Tonry et al find a SBF distance to the nearby galaxy ESO 322-8 of 36.3 Mpc - in exact agreement. Newman et al (1999) find a Cepheid distance to NGC 4603 in centaurus of 33.3 Mpc. Tully&Pierce (2000) find an I-band TFR distance of 38.9 Mpc. So the HKP SBF distance is in excellent agreement with the other estimates.

Next out are the neighbor galaxies NGC 5193 and IC 4296 for which the HKP find distances of 51.5 and 55.5 Mpc respectively. These galaxies are members of clusters which would be part of a larger structure of clusters encompassing Abell 3574. Abell 3574 has a Fundamental plane distance of 51.6 Mpc and using the K-band TFR a distance of 57.5 Mpc is found. Again the SBF distance is in good agreement with the other methods.

Next up NGC 7014 with a SBF distance of 67.3 Mpc. The K-band TFR for 4 neighbors of NGC 7014 gives a distance of 58.3 Mpc. The NGC 7014 distance modulus is larger by +0.31 mag.

NGC 708 in Abell 262 has a SBF distance of 68.2 Mpc. Tully&Pierce (2000) find a I-band TFR distance of 58.3 Mpc to the Pisces filament which A262 belongs. The NGC 708 SBF distance modulus is larger by +0.34 mag.

Finally there is the Coma cluster galaxy NGC 4881 for which the SBF distance is 102.3 Mpc. This compares with 83.6 Mpc for the Tully&Pierce I-band TFR and 85.8 Mpc for the HKP Fundamental Plane distance. The SBF distance modulus is larger by +0.37 to +0.44 mag.

This suggests a possible systematic difference that increases with distance. For the galaxies with SBF distances less than 60 Mpc the SBF is in agreement with the other distance methods. For the two galaxies at ~68 Mpc, the SBF distance moduli are greater by +0.31 to +0.34 mag. For the Coma cluster the SBF distance modulus is greater by +0.37 to +0.44 mag.

Do I have an explanation for this? No.

Can we be certain there is a systematic error in the SBF distances? No.

Why can't we be certain there is a systematic error that increases with distance? The sample is too small! Only 6 galaxies! More SBF work is needed beyond 60 Mpc to figure this out.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Tom,

Zahl doesn't understand the application of peculiar motions to this scenario. If you look at his/her comments as I noted in my previous post you'll see he thinks that peculiar motions within the cluster (fingers of god effect) are accounted for by the flow model.

That is simply not the case. The Flow model corrects for large scale motions of the local group and infall from nearby attractors. It has nothing to do with the individual motions of galaxies within a cluster. You "correct" for peculiar motions by taking a mean redshift for the cluster. If the cluster redshifts have a normal distribution, then the mean of the cluster redshifts essentially cancels out the random peculiar motions.

Then if you calculate a mean distance by determining the distances to multiple galaxies in the cluster you have a distance that is "corrected" for the depth of the cluster.

Using the mean redshift and mean distance gives you H0.

This is all very basic stuff and yet for all my patience and effort to explain this to Zahl, I might as well be doing this:

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

In general I agree with Dgruss, but Zahl makes a good point when he suggests luminosity bias should favor selection of galaxies within a cluster that are closer rather than further. So the reason Dgruss suggest that the SBF distances may be suspect is counter-intuitive.

In any case, since the calculated total systemic errors do not overlap, something is systemically wrong with at least one study. I think it is premature to state, at this time, that there is a convergence of observational evidence that is consistent with lower values of Ho. I think it is more correct to say lower values of Ho are more compatible with current cosmological theory.

__________________
jwj

It's a big universe out there...is it really unwinding, really burning out?

Jerry, Zahl is correct that luminosity bias can be an issue. However, it is not an issue with the HKP SBF analysis because they only used a single galaxy - the brightest cluster galaxy. The BCG's in these relatively local clusters (<150 Mpc) are well within the detection limits of the surveys.

You have to watch out for luminosity bias when you survey multiple galaxies within a cluster. As you include fainter galaxies from the luminosity function, the chances of preferentially selecting the near-side galaxies increases. If the near-side galaxies in the survey outnumber the far-side galaxies, then the calculated cluster distance will be too small and the resulting H0 will be too large.

This is similar to the Malmquist bias in which for a magnitude limited sample, as one includes galaxies at steadily larger distances, the sample will preferentially include the galaxies from the brighter end of the luminosity function. For secondary distance indicators this will lead to a trend of systematically underestimating distances as distance increases and results in a steadily increasing value of H0 as distance increases.

Just how significant Malmquist bias is also depends critically upon the intrinsic scatter of the secondary distance indicator. Distance indicators with small intrinsic scatter will have smaller effects from Malmquist bias.

At any rate, luminosity bias is not an issue with BCG's of the HKP SBF sample.

I would agree that the current cosmological theory favors a lower value of H0. That's why it is so important to periodically examine whether or not the empirically derived value of H0 can be improved.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

All gravitationally bound objects within clusters are not at the same distance from us and the global value of H0 is constant, but H0 from a single bound target galaxy in a cluster is not global even if there are no measurement errors. There will be intrinsic scatter in such values following straight from the fact that the expansion of the universe is stopped within clusters. However, a few independent measurements beat down this scatter (random error can be reduced by increasing the sample size) unless there are systematic errors. Besides, such scatter is small because as big as clusters are, they are still pretty small in the grand scheme of things and the universe wouldn't expand much over a cluster size slab of space anyway. A galaxy located somewhere near the center, having an expansion redshift of (say) 7000 km/s at 100 Mpc from us would give an estimate of 7000/100=70 km/s/Mpc for H0. If that galaxy was located on the outskirts of the cluster in the radial direction, at a distance of 5 Mpc (about the characteristic radius of clusters) from the core, the intrinsic error in the H0 determination would be only about 3 km/s/Mpc (7000/105=66.7 km/s/Mpc -> 70-66.7=3.3 km/s/Mpc) compared with the case where the galaxies were two free streaming galaxies in the Hubble flow separated by that same 5 Mpc (7000/100=70 km/s/Mpc & 7350/105=70 km/s/Mpc). This is why it does not matter much where the target galaxy is located in the cluster - a few independent measurements of individual galaxies in different clusters beat down the random error and the error would not amount to much anyway.

So dgruss23, you have twice dodged this question. Your answer?

I am not going to debate semantics with you as they have no relevance to your claim that the HKP SBF results are subject to significant systematics that render them irrelevant, a notion for which you have so far offered no evidence. This is the only thing that interests me in this exchange. I just note that there is nothing wrong with phrases like "flow corrected velocities for the galaxies" as evidenced by the fact that Freedman herself used such in the final HKP paper: "The galaxy velocities have been corrected for the flow-field model described above."

So (according to you) they were not able to capture all the systematic errors. Therefore (again according to you) the formula and the systematic errors given in the paper are wrong. What are the correct systematic errors then and how are they derived? You can't expect to be taken seriously if you argue that the real systematic errors are larger than those reported and declare the result irrelevant but not offer the corrected error treatment.

This has nothing to do with the luminosity of the SBF galaxy. They have to be confident that the measured fluctuation power really comes from the SBF galaxy and not from the intervening structures. If the (well visible) SBF galaxy is behind a foreground galaxy or dust that can't be reliably removed, they have to reject the SBF galaxy and choose another. This creates a potential selection effect favoring the near side SBF candidate galaxies because the far side SBF candidate galaxies are more likely to have their faces partially covered by one of the galaxies in the cluster, contaminating the SBF fluctuation spectrum.

Yes.

No, but I addressed just such a possibility before the bolded part.

I have. What kind of person gives distance estimates and argues for systematic errors, but does not give the errors in those distance estimates? Well, let's be courteous and not characterize such an individual. No reference, distance errors or names for these "4 neighbors of NGC 7014" were given so I have no choice but to dismiss the given 58.3 Mpc figure until the missing info is given.

Tully & Pierce (2000) give 60.3 +/- 2 Mpc for Pisces Filament vs. 68.2 +/- 6.7 Mpc for NGC 708 in A262 from Freedman. Tully & Pierce (2000) give 86.3 +/- 4 Mpc for Coma vs. 102.3 +/- 24.8 Mpc for NGC 4881 in Coma from Freedman. These can be added in quadrature to give a difference of +16 +/- 25.1 Mpc for NGC 7014/Coma and +7.9 +/- 7 Mpc for NGC 708/A262/Pisces.

As can be seen, neither of these differences is statistically significant. Together they give a reduced chi-square of 1.68 for two degrees of freedom and p=0.43. There is no statistically significant difference between Tully & Pierce TFR distance estimates and those from Freedman's SBF sample even when considering only the largest claimed differences. Including the targets that show even less difference in the analysis, the p-value goes even higher. We can conclude that there is still no evidence of systematic errors, just like Jarque-Bera told us.

These questions?

I've spent considerable time showing why you're wrong. These questions are rooted in profound misunderstandings on your part as to what the HKP did. You have refused to respond to key points in my explanations throughout this discussion.

parejkoj tried to explain your error to you as well and again you failed to grasp the point.

The whole basis for you asking this question is rooted in your own misunderstanding. You claimed that the HKP used the individual redshifts of the individual SBF galaxies to calculate H0 and that the SBF did not need to represent the mean cluster distance:



There are several facts about the process that you have not understood:

1. The HKP used the mean redshift of the cluster members to calculate H0, not the individual redshift of the galaxy with a SBF distance.
2. Part of the reason that they did this was that they selected the brightest cluster galaxies which might reasonably be assumed to be near the cluster center.
3. Galaxies within clusters have a depth effect (not all clusters are at the same distance from the Milky Way) and therefore H0 should not be calculated from the distance to an individual galaxy, but rather the mean cluster distance. The reason the HKP was willing to use a single galaxy to calculate H0 was that it was a BCG.

More recently we can add the following facts that you have a misunderstanding about:

4. Peculiar motions of individual cluster members are corrected for by taking a mean cluster redshift.
5. The Flow model used by the HKP corrects for large scale flows outside the cluster's internal dynamics not intracluster peculiar motions.

That is five very profound misunderstandings that you have either persisted with, dropped, or eventually adopted view on without acknowledging that you were initially incorrect.

So I'll break apart your "questions" and explain where you are right, where you are mistaken, and where you are not specific enough:

Quote:

Originally Posted by Zahl It seems unbearably difficult for you to comprehend that the velocities given in the Vflow column in Freedman's Table 10 are valid for both galaxies and their host clusters.

You are incorrect here. The Vflow column is valid as the mean cluster redshift for the mean cluster distance, not the individual galaxies at their individual distances. I'm not sure why you cannot understand this. It connects to your failure to acknowledge misunderstanding #3 above.

You are correct on this - gravitational dynamics and peculiar motions should dominate over the Hubble flow in a cluster


You are not specific enough here. Yes, all galaxies within a cluster should have the same cosmological redshift, but they're not all at the exact same distance due to the depth effect. Since you have been advocating that you can calculate H0 from a single galaxy within a cluster, it is not clear to me that you understand the potential influence of the depth effect on the H0 calculation from an individual galaxy within a cluster.

The Hubble relation is linear. For the Coma cluster the individual galaxy distances calculated from the Tully-Fisher relation range from ~70 Mpc to ~100 Mpc. The HKP adopted 7143 km s-1 for the Coma cluster. If I only pick one galaxy in the cluster to calculate H0, then if it is the 70 Mpc galaxy I get H0=102.0. If my single galaxy happens to be the galaxy at 100 Mpc I get H0=71.4.

Again, that is why we take multiple galaxies to get both the redshift and the distance for the cluster - and that is why it is so important to note that the HKP used the BCG's. They would not have just selected some galaxy at random. They had to pick a galaxy they could be pretty sure was very close to the cluster center.

Depending upon how much of the above you actually understand - which from what I can tell from your various statements was not much before we started this discussion - but meant by your above statement, then your statement could be correct or incorrect.

This is correct. That's why the peculiar motions within the cluster suggest the presences of DM.


Zahl, either you have not understood my explanation as to the difference between peculiar motions and the flow model, or you're dodging admitting you made an error here. I don't know which it is, but neither possibility is very good for you.

The difference between correcting the mean cluster redshift for a flow model and correcting for peculiar motions is not "semantics". It is a genuine important difference. Peculiar motions are "corrected" for by finding the mean cluster redshift. That mean cluster redshift is the raw heliocentric redshifts. The heliocentric redshift is corrected for important influences external to the cluster using the flow model. The galaxies within the cluster still have peculiar motions relative to the cluster mean regardless of what flow model is adopted. Most researchers adopt the CMB reference frame for their corrected redshift - not the flow model of the HKP.


There is nothing wrong with the phrase, just the way you've used it.


What I pointed out (and provided examples of) is that different studies take different approaches and sometimes the systematic errors for the different approaches don't overlap. One of the possibilities is a systematic difference between two different methods. You can look for a systematic difference in the global H0 result. In that case the SBF method result agrees with most other results. You can also look at the specific distances and compare those with the distances derived from other methods to see if any systematic differences exist.

I pointed to some other distance determinations and noted that - for the small sample of only 6 SBF galaxies - the SBF agrees with the other methods for distances <60 Mpc, but when the SBF distance is above 60 Mpc, the SBF distance is larger than the other distance estimate and possibly such that the difference increases with distance.

And as was my point from the very beginning of our disagreement. We cannot be sure whether or not such a systematic effect is real because we're only working with 6 SBF galaxies. You need a larger sample to pin down whether or not this possible systematic effect is a real systematic effect. And if larger samples ultimately show that it is a real effect, then you have to go back and refigure the value of H0 from the SBF method - or possibly the other methods - because you'll have to identify a reason for the systematic difference and correct for it.

But you cannot do that with only 6 galaxies and be certain about what you're doing. You need a larger sample - which has been one of my themes throughout our discussion.

But that's not what happened - they used 6 brightest cluster galaxies. At no point did they reject the brightest cluster galaxy and pick a fainter galaxy in the same cluster.

And actually if you go back further into this - you'll see they adopted four of their SBF galaxies from the Lauer et al study. Lauer et al didn't actually use those 4 galaxies to find H0, they used those 4 galaxies as zero point calibrators for the Hubble diagram of 114 brightest cluster galaxies out to redshifts of ~15,000 km s-1.


Two things - First, that potential selection effect never actually happened. They adopted the data for the 4 Lauer et al galaxies and added two more of their own. Second, you're talking about multiple sight lines. You could - following your proposal - select a galaxy, find it is too obstructed, and then the next galaxy you select is actually suitably unobstructed but deeper in the cluster. Obstruction can be very patchy.


I'm sorry, but the K-band data is from a paper currently under review. Some people put their papers on astro-ph before they're accepted. I try to wait until it is the final accepted version.

Of course it's not statistically significant. The sample is too small. If a systematic offset persists for a larger sample - which we don't have available because only 6 galaxies were used - then you have something that becomes statistically significant. And if it persists for a larger sample you cannot just hide behind the errors overlapping.

And of course if you want to ignore a possible trend in which the difference increases with increasing distance, you can add in the lower distance galaxies where no difference shows up and really hide a real possibility for a systematic effect.

But I don't suppose you have any interest in a larger sample. Your position has been that none is needed - we can be very confident in an H0 value derived from 6 galaxies. Adding more galaxies won't change the result. Let's just do a chi-square test with 2 galaxies and call it a proof that no systematic errors would exist if we had a larger sample. I guess it's hard to imagine why scientists are always seeking more data points and larger samples!

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Let's summarize your claims in your most recent post:

You claim that "The Vflow column is valid as the mean cluster redshift for the mean cluster distance, not the individual galaxies at their individual distances." You agree with the statements "In mainstream cosmology clusters are gravitationally bound and the expansion of the universe is stopped within them" and "If the galaxies had different expansion velocities, they would be expanding away from each other and the cluster would fly apart."

You claim that the statement "resulting in the same expansion velocity (in kilometers per second) for all gravitationally bound objects inside them [clusters] after peculiar velocities have been corrected for." is not specific enough and start to ramble about distances and H0 calculation, but admit that "Yes, all galaxies within a cluster should have the same cosmological redshift".

Now, the cosmological redshift that you correctly say is the same for all galaxies within a cluster is caused by the expansion of space and is identified by the letter z in the well known formula d*H0 = c*z. Since it is caused by the expansion of space, the cosmological redshift is obtained after peculiar velocities of galaxies and perturbations caused by mass concentrations outside the cluster have been corrected for. What we have then is the cosmological redshift that can be converted to velocity by multiplying it with c.

But wait. This is the same velocity as what is given in the Vflow column in Freedman's Table 10! This is evidenced by the fact that the Vflow velocities have been corrected for peculiar velocities of galaxies and perturbations caused by mass concentrations outside the cluster and are actually used in the final calculation of H0 estimates in table 10, e.g., Vflow = 7441 +/- 300 km/s and D = 102.3 +/- 24.8 Mpc gives H0 = 72.7 +/- 18.7 km/s/Mpc. Thus we can see dgruss23's error - no wonder that he didn't describe how the determinations of cosmological redshifts and Vflow velocities differ because they don't. Both are the same for all gravitationally bound galaxies within a cluster. And it could not be any other way, because otherwise the galaxies would be flying away from each other and the cluster would come apart just as dgruss23 admitted.

Now let's look at what dgruss23 had to say about distances: "Yes, all galaxies within a cluster should have the same cosmological redshift, but they're not all at the exact same distance due to the depth effect. Since you have been advocating that you can calculate H0 from a single galaxy within a cluster, it is not clear to me that you understand the potential influence of the depth effect on the H0 calculation from an individual galaxy within a cluster.

The Hubble relation is linear. For the Coma cluster the individual galaxy distances calculated from the Tully-Fisher relation range from ~70 Mpc to ~100 Mpc. The HKP adopted 7143 km s-1 for the Coma cluster. If I only pick one galaxy in the cluster to calculate H0, then if it is the 70 Mpc galaxy I get H0=102.0. If my single galaxy happens to be the galaxy at 100 Mpc I get H0=71.4.

Again, that is why we take multiple galaxies to get both the redshift and the distance for the cluster"

Again you are giving distance estimates without their errors in the usual crackpot fashion. I really don't understand why you repeatedly mislead BAUT readers like this. If you had ever taken a freshman physics laboratory course you would have been taught that just giving a result without its error is useless. It should read in the forum rules that you are not allowed to compare different results without giving their errors to prevent the kind of atrocity dgruss23 is committing above. I won't do dgruss23's work for him (again!), but I just note that when the errors are given, the above estimates are consistent with each other and the HKP value for the Hubble constant. Tully-Fisher method has very large error bars for single galaxies.

They used Brightest Cluster Galaxies for SBF because these galaxies have narrow photometric and color distributions and are the brightest galaxies in their respective clusters, giving the best possible signal to noise ratio and the farthest reach possible with the SBF method, not because BCGs are near the cluster centers. As I demonstrated in post #111 with step-by-step calculations, it does not matter where the SBF galaxies are located in their respective clusters. I reproduce the post here:

"All gravitationally bound objects within clusters are not at the same distance from us and the global value of H0 is constant, but H0 from a single bound target galaxy in a cluster is not global even if there are no measurement errors. There will be intrinsic scatter in such values following straight from the fact that the expansion of the universe is stopped within clusters. However, a few independent measurements beat down this scatter (random error can be reduced by increasing the sample size) unless there are systematic errors. Besides, such scatter is small because as big as clusters are, they are still pretty small in the grand scheme of things and the universe wouldn't expand much over a cluster size slab of space anyway. A galaxy located somewhere near the center, having an expansion redshift of (say) 7000 km/s at 100 Mpc from us would give an estimate of 7000/100=70 km/s/Mpc for H0. If that galaxy was located on the outskirts of the cluster in the radial direction, at a distance of 5 Mpc (about the characteristic radius of clusters) from the core, the intrinsic error in the H0 determination would be only about 3 km/s/Mpc (7000/105=66.7 km/s/Mpc -> 70-66.7=3.3 km/s/Mpc) compared with the case where the galaxies were two free streaming galaxies in the Hubble flow separated by that same 5 Mpc (7000/100=70 km/s/Mpc & 7350/105=70 km/s/Mpc). This is why it does not matter much where the target galaxy is located in the cluster - a few independent measurements of individual galaxies in different clusters beat down the random error and the error would not amount to much anyway."

We have no choice but to accept the error treatment given by Ferrarese as you are unable to provide for a replacement and too incompetent to even try.

Let's make one point absolutely clear - the HKP SBF determinations agree with the (given by you) TFR determinations for all distances. You just naively eye-balled the figures without comprehending that the error bars become larger with increasing distance, leaving no evidence of any difference between the two data sets as I demonstrated in my previous post.

You don't know if it happened or not as it is not known how many Brightest Cluster Galaxies were on top of the list, but had to be rejected due to contamination. If this is what happened, they would ditch that cluster because it does not have other targets that could give them a signal to noise ratio as high as a clean BCG can. They have to go for another cluster. I am not saying that this is what actually happened (it probably didn't), but at least I have described a mechanism that can plausibly result in the near side galaxies to be preferentially targeted for SBF. You have still not given any reason why far side galaxies would be preferentially targeted for SBF. But as my above calculations demonstrate, it would not matter anyway.

Once the proper error treatment is given, there is no "systematic offset" between the two samples, period. It is not difficult to think of ways things could be. After testing the sample with two quantitative methods we have found that there is no evidence of systematic errors in the SBF sample and the sample size is large enough to keep the random error reasonably small. Therefore we must conclude that the HKP SBF result for H0 is a good estimate and not "irrelevant".

I put in my 2-cents worth back on page 1, and don't see any particularly good reason to change my mind. The long discussion thus far is indicative of a strange phenomenon I have encountered, and been bemused by quite a bit over the years: People can be surprisingly emotional about cosmology, which seems to me to be about the least deserving topic of emotional impact that I can think of.

The title question reads, Is the value of the Hubble constant locked down?. Personally, I would say "no", simply because "locked down" has a ring of finality to it in my ears, which seems undeserved. Thereafter, the thread is devoted to the possibliity that the Hubble constant might be in the mid 80's. Considering all the argument about the value published in Freedman, et al., 2001, I would like to make an observation. Here is a list of H₀ values cribbed from their own abstract, where the uncertainties are first random, then systematic (all in km/sec/Mpc):

• 70 +/-5 +/-6 (surface brightness fluctuations)
• 71 +/-2 +/-6 (Type Ia supernovae)
• 71 +/-3 +/-7 (Tully-Fisher relation)
• 72 +/-9 +/-7 (Type II supernovae)
• 82 +/-6 +/-9 (fundamental plane)

The final reported value of 72+/-8 is statistically derived from this list of values. In this discussion so far, the final reported value has been treated, I think, with rather more a sense of certainty than it deserves. Just looking at the list, those values span a range from 59 to 97 km/sec/Mpc. Based on this alone, it would be absurd to insist that it was impossible for H₀ to reside in the region of the mid 80's. But it would not be absurd to suggest that it would be improbable, and my own judgement that it is improbable seems justified by these, and other data.

Furthermore, the list above is prima facie evidence that the value of the Hubble constant is far from "locked down", even if we think we can assign probabilities. Also, the Hubble Key Project is hardly the final word on the matter, although one might think it were, judging from its place in this discussion. Consider Sandage, et al., 2006. This is the final report for their 15 year program using HST observations of Cepheid variables to calibrate the luminosity of type Ia supernovae. They report H₀ = 62.3+/-1.3 (random) +/-5.0 (systematic), which certainly overlaps the bottom end of the list above, and overlaps comfortably with the lower part of the final value reported above by the Hubble Key Project. And, as Huchra's list of H₀ values shows, a value in the mid 80's remains well outside the range of reported values since then (although my earlier statement that this list contained all published values may not be correct).

As I see it, there has been no point made in this discussion to dissuade me from the obvious conclusion that a value in the mid 80's is improbable, but not at all impossible. I see no point in a thread devoted to the idea that we need to read & critically evaluate every single paper published on the Hubble constant, and ourselves decide whether or not the authors have done the right thing.

__________________
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

That conclusion was unanimously agreed on by the second page. For the last few pages the discussion has been on the Hubble Key Project SBF result (contaminated by systematic errors or not?) and my objections to dgruss23's habit of comparing distance measurements and claiming there is a "systematic offset" without giving error bars and not doing any error analysis.

I am trying to learn from this discussion, and have a couple questions if that is OK.

How does one calculate the galaxy pecular velocities, and how many galaxies within the cluster should be used to obtain a representative value (average for the galaxy) of the cosmological redshift?

I don't quite follow this. Are you saying the Vflows, calculated by the method you say is correct, give a solution for H0 = 72.7 +/- 18.7? In other words H0 lies between 64.0 and 91.4?

An aside comment: I agree with Tim Thompson's statement that it is surprising that people get emotional over cosmology.

TomT

Zahl, I never said that the cosmological redshifts and the Vflow redshifts were different. YOU - yes YOU Zahl, incorrectly stated that the Vflow model corrects for the peculiar motions within the cluster. It does not. You can correct the mean redshift of the cluster using the Vflow model. You can also correct individual galaxies within the cluster using the Vflow model. The cosmological redshift for a cluster is found in two steps. First, the mean redshift of the cluster members is found. This averaging of the individual galaxies redshifts corrects for the effect of peculiar motions. Second, the Vflow model was applied to correct the mean cluster redshift for motions external to the galaxy.

You misunderstood this from the beginning and you continue to refuse to admit your errors. You do not understand the difference between corrections to a heliocentric redshift and correction for peculiar motions within a cluster. And you want people to take seriously anything you say.




Yep, that's a very accurate explanation. Too bad you don't get it.

That's it Zahl. I am done reading anything you post. You've been wrong repeatedly and refused to admit it - despite being clearly shown to be wrong. And you've been insulting, rude, obnoxious.... You're on my ignore list - a list exactly one person long. Blather on all you wish. Your repeated inaccuracy and failure to grasp basic concepts and acknowledge them when you're corrected make it an irrelevant exercise to even try to discuss anything with you.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

I agree - Zahl's reaction has been emotional and knee-jerk to my suggestion that the SBF and Type II SN samples adopted by the HKP were too small to be compelling. The word I used that Zahl has reacted so childishly too was "irrelevant".

Any emotion on my part stems from being repeatedly insulted and forced to repeatedly point out errors on Zahl's part that Zahl refused to acknowledge - not from the cosmology issue itself.


Agreed, but the reason I started the thread is sometimes in these discussions people treat the value as if it is "locked down" - as if the HKP final report provides a written in stone answer. Stupendousman pointed out that researchers themselves often do not see it that way.

And that was my point for starting the thread.

I understand why people would feel that H0 in the mid-80's is improbable, but this is why it is worth looking at the details of the samples utilized. My biggest concern with the SBF and Type II SN samples is the very small sample sizes and the small number of calibrators - which I pointed out in the OP.

Things got so hung up on the SBF, that potential problems with the HKP I-band TFR distances were not explored.

They also adopted a steeper slope for the Cepheid P-L relation than the HKP. The van Leeuwen paper I linked to earlier confirms the HKP Cepheid slope over the Sandage teams slope - which means that the Sandage result is suspect.

I've certainly not advocated that we look at every single Hubble Constant paper - but I see no reason why those that are interested should not critically evaluate papers that they consider most relevant. The focus has remained on the HKP papers.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

For galaxies in a cluster, you can calculate the peculiar velocity relative to the cluster mean where

Vpec = Vobserved - Vmean

Since the mean redshift should be close to the cosmological redshift at the cluster's distance, this should give you a pretty good estimate of the peculiar motion of the galaxy within the cluster - and it will be independent of the cluster's distance in this case too.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982