French's Primordial Study and Schramm & Turner, 1997

In a thread entitled "French's Primordial Study", Ned provided a reference
for 'current data' that is 'more definitive' than the French study that
failed to support Ned's position on primordial isotope generation.

http://www.google.com/groups?selm=vk....supernews.com

However, at the time I was swamped, and had no time to divert from the main
issue. The reference faded from my mind with time. I've since run across
French again, and it's now time to address Ned's claims about his reference.

{snip discussion of French paper never addressed by Ned Wright}

Claim made by Ned Wright:
===========================
"The current data is much more definitive. For example, see
Figure 4 of Schramm and Turner, http://arXiv.org/abs/astro-ph/9706069."

"One dataset gives Y_p = 0.232+/-0.003(stat)+/-0.005(sys); while another
gives Y_p = 0.243+/-0.003(stat). The systematic errors affect the
scaling of Y_p but not the level at which the zero-intercept model is
rejected. With this data the helium proportional to oxygen model is
rejected by more than 80 standard deviations."
===========================

The quote from S&T is:
"There have been two recent determinations of the primeval abundance based
upon the He/H ratio measured in regions of hot, ionized gas (HII regions)
found in metal-poor, dwarf emission-line galaxies. Using one sample and
extrapolating to zero metallicity, Olive and Steigman [33] infer YP = 0.232
+- 0.003 (stat) +- 0.005 (sys); using a new sample of objects Izotov et al
[34] infer YP = 0.243 +- 0.003 (stat). Both data sets are shown in Fig. 4.
In brief, the current situation is ambiguous, both as to the primeval 4He
abundance and as to the consistency of the big-bang prediction."


I got a good laugh out of the combination of the title: "Big Bang
Nucleosynthesis Enters the Precision Era" and Figure 4.

Figure 4 is described as follows: "Helium-4 abundance vs. oxygen abundance
in metal-poor, dwarf emission-line galaxies. Right panel (triangles) is the
sample analyzed by Olive and Steigman [33]; left panel (circles) is the new
sample of Izotov et al [34]." Both figures are pure shotgun scatter
measurements, where every uncertainty bar dwarfs the total range of the
data. The data is more scattered than similar data (taken 15 years earlier)
from French or Peimbert and Torres-Peimbert (French's references). Olive
and Steigman's data shows no obvious trend (hovering between .24 and .26 for
all values of metallicity), while Izotov et al shows a trend down to
..22 for lower metallicities.

[33] K.A. Olive and G. Steigman, Astrophys. J. (Suppl.), (1995).
[34] Y. Izotov, T.X. Thuan, and V.A. Lipovetsky, Astrophys. J. Suppl. 108, 1
(1997).

The S&T paper actually is a poor source for experimental primordial He
values. The actual sources of the data are Olive and Steigman and Izotov et
al. Of these two sets of carefully-selected data, S&T have this to say:
"Turning to the data themselves; the two samples are in general agreement,
except for the downturn at the lowest metallicities which is seen in the
data analyzed by Olive and Steigman. (Skillman has recently also expressed
concern about the use of the lowest metallicity object, IZw18 [38].)"

Izotov states: "The galaxy I Zw 18 ... 0930+554 is of special interest,
since it is the most metal-deficient BCG known." But despite this
importance, Izotov excludes it: "We find that the most metal-deficient BCG
known, IZw 18, cannot be used for this purpose because of its abnormally low
He I line intensities." In other words, efforts are made to exclude
discrepant low-range data. The results are in 'general agreement' only
because the error bars swamp the data.


I may as well look at the sources of the data in S&T, since S&T is a
primarily theoretical paper.......


On the paper of Izotov et al, 1997
= = = = = = = = = = = = = = = = = = = = = = = = = = =
Only one galaxy is shared between the French study and Izotov (I Zw 18 or
0930+554). French finds an He value of .052 (about 16%). Interestingly,
the only galaxy shared is is the lowest He value of the 14 galaxies plotted
on French's figure 6. (Izotov also excludes the other low-metallicity
galxies used in French.)

Both French and Izotov provide oxygen values for this galaxy. Izotov in
Table 4 provides 7.22 +- .01*, or a chemical abundance of 1.7E-5 (with a 5%
error). French provides 1.8E-5 chemical abundance (with a 10% error). So
French and Izotov agree on oxygen (the primary heavy element marker). This
is not surprising -- as Izotov is using the same methodology used by French,
15 years earlier. Thus, we cannot simply ignore the prior French values,
simply because they are older.

*Log N(x) with H == 12.00

Isotov notes that he has thrown out some data when calculating his He
results:

"Our sample contains a large number of low-metallicity
galaxies with spectra obtained and reduced in a homoge-
neous way. We combine the data in the present paper with
the data in to improve statistics and increase the Paper I
range of oxygen and nitrogen abundances for regression
fitting to determine the primordial helium abundance.
However, we have not included 10 H II regions from the
present sample, using the following rejection criteria :"

So, Isotov is going to throw away data to 'improve statistics.' Classic
data selection. But let's see if there's any real rationale (i.e. errors in
the data).

"1. The H II region is faint and its spectrum is too noisy
for helium abundance determination. Using this criterion,
we rejected the galaxies 0749+568, 0749+582, 0907+543,
0943+561A, and 1116+583B."

Well, faint and noisy signals are valid reasons -- so long as the criteria
are determined before He values are calculated. However, if it is done to
arbitrarily 'improve' the chi-squared result (as Izotov admits), then this
is a textbook case of what Babbage calls 'clipping' the data. And looking
at Table 4 clearly shows that these regions have lower statistical error
from noise than other regions that Isotove kept.

"2. There is a large spread in the individual determinations
of the ionic helium abundance from the He I 4471, 5876,
and 6678 lines as compared to the mean value (Table 5).
A galaxy is rejected when the deviation of an individual
determination is more than 20% from the mean value.
Using this criterion, we removed 1358+576, 1441+294,
and 1535+554."

Variations from the mean are not valid reasons to exclude data. This is
another textbook case of 'clipping' data to arbitrarily improve the apparent
statistics.

"3. The galaxy shows strong Balmer underlying absorption
features and weak He I emission lines, which makes the
measurements of He I line intensities difficult. Using this
criterion, we rejected 1319+579B."

As in criterion 1, this may be valid so long as the criteria are determined
before He values are calculated. However, the error bars for this region
for both He and heavy element abundances is below that of galaxy data which
Izotov kept. Hence Izotov is simply 'clipping' another data point to
'improve' his statistics.


But now -- after all the quasi-valid 'clipping' criteria have been
performed, we come to that special case. The one that would disprove the
BBN -- if valid. Izotov creates a special section just to rationalize
removing I Zw 18 from the data pool:

"Finally, we have rejected the BCG I Zw 18. This galaxy has the lowest
oxygen abundance known and has played an important role in the past for the
(Z /50) determination of the primordial helium abundance. However, the He I
line intensities in this galaxy (Table 3) are unusually low as compared to
other very metal-deficient BCGs ... The derived helium mass fraction is
only Y=0.19 in the case of Brocklehurst's (1972) and Y=0.21 in the case of
emissivities Smits's (1996) emissivities (Table 5), significantly lower than
the values derived for other low-metallicity galaxies. ...."

And -- one might add -- significantly below the estimates of French of
0.16 -- which French declares an upper bound.

A VERY long section lists various authors have studied the problem with
care, observation and theory. Yet I Zw 18 refuses to respond to all
efforts. So Izotov concludes: "But these assumptions** are very uncertain,
and as long as they are not well understood, I Zw 18 CANNOT BE USED FOR THE
DETERMINATION OF THE PRIMORDIAL HELIUM ABUNDANCE." (emphasis in original)

** The various theoretical attempts to explain away an observation at odds
with the BBN.


One of the primary reasons for low-mettalicity galaxies is that the lower
the metallicity, the higher the quality of the data -- at least according to
O&S. Thus, deleting the best-studied, but lowest metallicity galaxy is
completely unjustifiable.

After 'clipping' 10 'outlier' observations, this leaves Izotov with only 19
remaining observations. (Izotov has thrown out over a third of his data.)
To make up for this wholesale emasculation of the data set, he brings in 8
results from other papers (without discussing the details). Babbage calls
this 'padding' the data. It's not quite drylabbing, but Isotov has had a
free hand in selecting only those data points that further 'improve' his
statistics.

= = = = = = = = = = = = = = = = = = = = = = = = = = =


On the paper of Olive and Steigman et al, 1995
= = = = = = = = = = = = = = = = = = = = = = = = = = =
Unlike Isotov, O&S do not provide any actual data for direct evaluation.

Olive and Steigman do not obtain their own data. They borrow data from
"Skillman, et al (1994)"***, claiming 49 H II regions, including "11 new,
very metal-poor H II regions." However, O&S's Figures 5 & 6 (the source of
Figure 4 in T&S) only include 41 data points. This is because O&S have also
'clipped' the data -- removing various 'outliers' in order to 'improve' the
statistics. An interesting exception is the case of the eight 'N/O vs O/H
outliers'. O&S have kept these 'outliers,' because they are closer to the
desired He/H vs. O/H (and N/H) fit. And while O&S considers this to be a
bit discrepant from theory, since the inclusion of these 'problem'
observations improve the statistical fit, O&S keeps them.

*** The reference is "Elemental Abundances from Extremely Low Metallicity H
II Regions: A Higher Primordial He Abundance?", Skillman et al, 1994, ADS,
(1994dwga.work..519S). Neither abstract nor paper is available on ADS. Nor
is it found on an arxiv search. Nor was the abstract or content of a
similar paper found on ADS on the same subject. (Terlevich, E.; Skillman, E.
D.; Terlevich, R, "Primordial Helium from Extremely Metal-Poor Galaxies",
The Light Element Abundances, Proceedings of an ESO/EIPC Workshop).
Possibly, this paper was not actually published. If so, there is no
documentation backing up Olive and Steigman's paper.

{Boy this is such an 'improvement' over French. }

O&S simply ignores French's study -- though it lists several other studies
going all the way back to Peimbert and Torres-Peimbert (upon which French
also based his work). This is interesting. Despite the importance that Ned
Wright attached to the French study, both his 'modern' references avoid
French like the plague....

The reason for this is straightforward when you read on: "Virtually all
analyses agree that 0.22 = Yp = 0.24. The problems -- and
disagreements -- arise from the quest for the third significant figure in
Yp." French -- of course -- is one of those irritating results that
necessitated O&S to use the word 'virtually'. This is just another form of
'clipping' of unwanted observations. The attitude is obvious, because if
there is disagreement about the second significant figure (a range of .22 to
..24), then O&S's statement is transparently specious on disagreements of the
'third significant figure.'
= = = = = = = = = = = = = = = = = = = = = = = = = = =


One of the subjects discussed in French (and P&TP) -- but ignored in S&T,
Izotov and Olive and Steigman -- is that the He concentration data is an
*upper bound*. This is a significant oversight in S&T. (French observed
young galaxies with He abundances as low as 11%, and provided reasoning that
these abundances were 'real'. Even though they are far below the
theoretical Big Bang 'primordial' values.)


It is quite clear that the institutional pressure to conform the BBN model
is overwhelming. French began the process by simply avoiding his own data
when calculating the metallicity slope (back-calculating from the BBN
theory). The three later authors (S&T, O&S and Izotov) are more devious --
simply clipping discrepant data, and padding the dataset when clipping alone
won't provide sufficient adjustment.


So, it seems that Ned's claims about 'more definitive' recent work is even
more at sea than his claims about French.

Courtesy copy provided to Ned Wright.

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}