Still lower noise radio astronomy (was: low-noise amplifiers for radio astronomy )

"J(B" == John (Liberty) Bell writes:

JB Joseph Lazio wrote:

JB A number of these references, and links therefrom to published
JB papers, do confirm that my impression gleaned from the AIP
JB synopsis, was, in fact, correct.

JB Of the material I have read thus far, table1 (...) of
JB http://www.ociw.edu/lcirs/public/paperIV_astroph.pdf, is
JB particularly revealing.

I'm a bit leery of focussing too heavily on one paper. As others
have pointed out, this is an area of active work. For instance, a
quick ADS search finds over 200 papers having the words "galaxy,"
"formation," and "epoch" in their abstracts.

JB I think you are being a little unreasonable here. You first
JB criticised me for quoting an AIP synopsis of an important GDDS
JB press release, and now you criticise me for quoting one of the
JB appropriate peer reviewed papers which back up that press
JB release.

No, I'm not criticising you for looking at this paper. In fact,
looking at the paper is far better than the press release. I'm merely
cautioning that this paper may not tell the whole and final story.


From the 20 galaxies examined between z = 1.308 and z = 2.147,
five had 'best fit' z at formation of 4.7 or higher.

JB However, the body of the paper confirms this is a 'conservative'
JB estimate of age. On p 8, section 4, discussion, they state that
JB "more plausible models" produce best fit ages that are typically 1
JB Gyr larger than those in table 1. Using
JB http://www.astro.ucla.edu/~wright/CosmoCalc.html, that would give
JB formation times of 0.3 Gyr after the Big Bang, for all five
JB cases.

[...]
First, in Section 3.1, they state that the median formation
redshift is 2.4.

JB It is unfortunate that they lumped all these galaxies together
JB like this, when it is obvious, and explicitly stated, that some
JB are much older than others.

They provide a table of their results. If you don't like the way
they've sliced and diced them, you can choose whatever other sample
you'd like. The difficulty is, of course, their sample is only 20
objects. If you start taking subsets of their sample, the statistical
confidence in any results could degrade rapidly.

Checking that against Table 1, indeed, 10 of the 20 objects have
z_f 2.4, with a median inferred "age" of these galaxies of 1.5
Gyr.

JB Of course. That is because galaxy formation continued long after
JB the first observed galaxies, and long after the first galaxies
JB required to explain the metal content of the oldest galaxies in
JB this survey. Such newer galaxies would obviously also have been
JB found in the survey volume

Actually, my statement was largely just a sanity check. If you look
at the full sample, the median inferred formation redshift is indeed
2.4


The full statement from Section 4 is

More plausible models, those with star formation extended over one
or more dynamical times, produce best-fitting ages that are
typically 1 Gyr *larger* than those in Table 1, implying z_f ~
4 for a substantial fraction of the galaxies. (emphasis in
original)

They are saying that a more likely formation epoch was around z ~
4, when the age of the Universe was about 1.6 Gyr, or about 1 Gyr
earlier than z ~ 2.7.

JB No they are not. Read the final paragraph of their discussion.

Usually I credit myself with reasonable reading comprehension, but I
just don't see how you get any other meaning out of that sentence.
Table 1 gives a listing of ages for the galaxies, with the age for
each galaxy inferred by fitting the spectrum of that galaxy using a
model of a stellar population. You could go back through the table
and add 1 Gyr to each galaxy's age, then convert that to the implied
formation redshift. My guess, if you would do that, you'd find that
the resulting formation redshift would shift to have a median about 4.

JB Also read [...] the paragraph immediately below figure 1
JB at http://www.gemini.edu/index.php?opti...ask=view&id=18
JB They are unambiguously saying that different galaxies in their
JB survey formed at different times. They are saying, in addition,
JB that, on average, each galaxy would be 1 Gyr *older* than
JB conservatively given in table 1, using more plausible models.

I don't see that anything here contradicts what I said. This paper
stars by selecting red galaxies from their sample. The reddest
galaxies are the ones most likely to provide constraints on early star
formation. Your second sentence is exactly what the paper says and is
consistent with what I said.

JB Again, it is unfortunate that they did not break this information
JB down galaxy by galaxy, within the quoted paper, but I suspect the
JB reason for this could wll have been diplomacy.

I don't understand this at all. They do provide a listing for each
galaxy in Table 1.

JB The set of 20 galaxies spreads from one galaxy with a
JB conservative age of 0.5 Gyr (when observed at z=1.348), to one
JB galaxy with a conservative age of 4.0 Gyr (when observed at
JB z=1.396). Altogether there are 4 galaxies which thus give a
JB conservative z (formation) of 5 (thus giving an age of the
JB universe, at formation, of 1.2 Gyr).

You need to pay attention to the uncertainties. Galaxy 22-0948 has a
modeled age of 4 Gyr (+0.4 Gyr, -3.5 Gyr). That means that its "age"
could be anywhere from 0.5 to 4.4 Gyr. The same is true of the next
oldest galaxy (22-0674), it could be from 1.7 to 3.7 Gyr. That leads
me to suspect that the large z_f for these galaxies might be a bit
uncertain.

I'm also a bit uncertain why we're arguing about this. When they fit
for their ages, they explicitly constrained the stellar population age
to be less than the age of the Universe.

JB Now, if you have a conservative age spread from 0.5 Gyr to 4.0
JB Gyr with a mean increase of 1 Gyr for a more plausible age, it is
JB pretty obvious to me, that this would not mean a 200% increase
JB for the newest galaxy, and a mere 25% increase for the
JB oldest. However, if we take a more sensible interpretation, that
JB would probably place the formation time of the oldest galaxies
JB before the classically predicted big bang.

See my comments above.

I don't want to minimize the fact that stars, and galaxies, were
able to form quickly. After all, we know of quasars at redshifts z
6, when the Universe was less than 1 Gyr old. That's an
impressively rapid formation. However, I think that the gaps in
our understanding are more likely to be in what we know about
galaxy and star formation rather than in General Relativity.

JB Why?

Because we don't understand star formation in our own Galaxy?

JB As far as I can tell, classical GR does not have a particularly
JB illustrious record for the quantatitive accuracy in its
JB predictions at high z. The originally predicted deceleration in
JB the expansion of the universe has turned out to be completely
JB wrong, because what the multinational High-z Supernova Search
JB Team has confirmed in practice, is that the expansion of the
JB universe is accelerating.

Classical GR does accomodate an accelerated expansion of the Universe,
that's what the cosmological constant does, which is a term Einstein
himself inserted. Classical GR does not predict the value of the
cosmological constant, any more than it predicts the value of the
Hubble constant or the mean density of matter. These are quantities
that have to be determined experimentally.

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Kent Paul Dolan wrote:
John (Liberty) Bell wrote:

Now, if you have a conservative age spread from
0.5 Gyr to 4.0 Gyr with a mean increase of 1 Gyr
for a more plausible age, it is pretty obvious to
me, that this would not mean a 200% increase for
the newest galaxy, and a mere 25% increase for the
oldest.

*shudder*

Understand that one can move the mean or median of a
distribution _anywhere_ within the range of the
extremes while holding the end toward which one is
moving the mean or median, fixed.

So, the center of the 3.6 gigayear wide distribution
could move a gigayear closer to the big bang without
moving the end closest to the big bang, closer to
the big bang at all.

The issue might well be merely that the distribution
_compresses_ in time.

This argument might make some sense within an abstract discussion, but
I don't see how it can make any sense within the context of the known
physics and models of galactic evolution.

Could you explain?

Being told what happened to the mean or median tells
you very little about what happened to the
individual data points. Certainly basing conclusions
on what is surmised to have happened to some of the
data points is an exercise fraught with risk.

That is why I said:

"It is unfortunate that they lumped all these galaxies together like
this, when it is obvious, and explicitly stated, that some are much
older than others."

and,

"Again, it is unfortunate that they did not break this information down

galaxy by galaxy, within the quoted paper"


John Bell
http://global.accelerators.co.uk
(Change John to Liberty to bypass anti-spam email filter)

Joseph Lazio wrote:
"J(B" == John (Liberty) Bell writes:

I have snipped everything here where we appear to be arguing about
things we actually agree on. We do seem to be agreed on what the median
age is, and that different galaxies have different actual ages, within
the sample set.

JB Again, it is unfortunate that they did not break this information
JB down galaxy by galaxy, within the quoted paper, but I suspect the
JB reason for this could wll have been diplomacy.

I don't understand this at all.

By "this information", I am referring specifically to the longer than
'conservative' age which results from a 'more credible' model of galaxy
evolution. It would have been interesting to examine such consequences
of a more credible model, on a galaxy by galaxy basis.

They do provide a listing for each
galaxy in Table 1.

That table covers only the 'conservative' figures per galaxy.

JB The set of 20 galaxies spreads from one galaxy with a
JB conservative age of 0.5 Gyr (when observed at z=1.348), to one
JB galaxy with a conservative age of 4.0 Gyr (when observed at
JB z=1.396). Altogether there are 4 galaxies which thus give a
JB conservative z (formation) of 5 (thus giving an age of the
JB universe, at formation, of 1.2 Gyr).

This *should* have read: Altogether there are 5 galaxies which thus
give a
conservative z (formation) of 4.7 or greater (thus giving an age of the
universe, at formation, of 1.3 Gyr).

You need to pay attention to the uncertainties.

I did, for my own personal analysis of the data.

Galaxy 12-8895 has z=1.646, Conservative age = 2.6 + - 0.3 Gyr, hence z
(formation) of 4.7
Galaxy 22-0189 has z=1.490, Conservative age = 3.0 + 0.7 - 0.2 Gyr,
hence z (formation) of 4.8

Translating this to age of universe at z formation, using default flat
setting of http://www.astro.ucla.edu/~wright/CosmoCalc.html gives a
time since Big Bang of

1.59 to 0.99 Gyr, and 1.46 to 0.56 Gyr respectively.

Adding 1 Gyr to their ages for the 'more plausible' evolution model
gives a creation time relative to Big Bang of:

+ 0.59 to - 0.01Gyr, and + 0.46 to - 0.44 Gyr respectively.

It is true, however, that the 3 further galaxies with conservative z
formation 5, do have much greater uncertainties.

I'm also a bit uncertain why we're arguing about this. When they fit
for their ages, they explicitly constrained the stellar population age
to be less than the age of the Universe.

Yes, that was a specific (and severe) constraint for the 'conservative'
model, which then required several implausible hypotheses for the (thus
required) galaxy evolution model..

JB Now, if you have a conservative age spread from 0.5 Gyr to 4.0
JB Gyr with a mean increase of 1 Gyr for a more plausible age, it is
JB pretty obvious to me, that this would not mean a 200% increase
JB for the newest galaxy, and a mere 25% increase for the
JB oldest. However, if we take a more sensible interpretation, that
JB would probably place the formation time of the oldest galaxies
JB before the classically predicted big bang.

See my comments above.

See mine too, for the more tightly constrained early galaxies.

I don't want to minimize the fact that stars, and galaxies, were
able to form quickly. After all, we know of quasars at redshifts z
6, when the Universe was less than 1 Gyr old. That's an
impressively rapid formation. However, I think that the gaps in
our understanding are more likely to be in what we know about
galaxy and star formation rather than in General Relativity.

JB Why?

Because we don't understand star formation in our own Galaxy?

This is probably more your area than mine. However, I don't think star
formation is the central problem here. It seems to be stellar
evolution, and supernova seeding of heavy elements, from a plausible
distribution of stellar masses. That does seem to be understood (or at
least modelled) quite well.

JB As far as I can tell, classical GR does not have a particularly
JB illustrious record for the quantatitive accuracy in its
JB predictions at high z. The originally predicted deceleration in
JB the expansion of the universe has turned out to be completely
JB wrong, because what the multinational High-z Supernova Search
JB Team has confirmed in practice, is that the expansion of the
JB universe is accelerating.

Classical GR does accomodate an accelerated expansion of the Universe,
that's what the cosmological constant does, which is a term Einstein
himself inserted.

Not really. Einstein inserted the cosmological constant as a widely
acknowledged "fudge factor" to stop the universe from expanding. He
removed it again, describing it as "the biggest blunder of my lifetime"
when Hubble showed the universe was, in fact, expanding. This "fudge
factor" had been pretty comprehensively debunked in the physics
community, by the 1970's, because it was not derivable from pure
theory.

Its recent resurrection in pure physics, and preservation in astronomy,
to allow any arbitrary 'fudging' of the predictions of pure theory
again, could be argued to be an endictment of the poor state of the
genuine predictive power of that pure theory (on the scale of the
universe).

Classical GR does not predict the value of the
cosmological constant, any more than it predicts the value of the
Hubble constant or the mean density of matter. These are quantities
that have to be determined experimentally.

Actually, classical GR did 'predict' the 'value' of the cosmological
constant.
Its value was whatever we required to prevent the universe from
expanding (or contracting).
(See also my earlier response to Kent Paul Dolan.)

You have, in reality, now explicitly stated several more reasons why
Einstein's field equation is less than completely satisfactory, as a
genuinely predictive theory.


John Bell
http://global.accelerators.co.uk
(Change John to Liberty to bypass anti-spam email filter)

"JB" == John (Liberty) Bell writes:

JB Joseph Lazio wrote:

[To recap, are the inferred ages of the red galaxies reported by
McCarthy et al. problematic?]

JB Galaxy 12-8895 has z=1.646, Conservative age = 2.6 + - 0.3 Gyr,
JB hence z (formation) of 4.7
JB Galaxy 22-0189 has z=1.490, Conservative age = 3.0 + 0.7 - 0.2
JB Gyr, hence z (formation) of 4.8

JB Translating this to age of universe at z formation, using default
JB flat setting [...] gives a time since Big Bang of

JB 1.59 to 0.99 Gyr, and 1.46 to 0.56 Gyr respectively.

JB Adding 1 Gyr to their ages for the 'more plausible' evolution
JB model gives a creation time relative to Big Bang of:

JB + 0.59 to - 0.01Gyr, and + 0.46 to - 0.44 Gyr respectively.

So at this point, you have two choices.
1) It is non-physical for objects to be older than the Universe.
That some portion of the uncertainty on their inferred ages
implies ages older than that of the Universe indicates that we do
not understand how to model in detail the evolution of stellar
populations (and/or there may be some unrecognized systematic
effect lurking in the analysis).
2) That some portion of the uncertainty on their inferred ages
implies ages older than that of the Universe indicates that we do
not know the age of the Universe.

You seem to adopt #2. However, the authors of the stellar evolution
model used (PEGASE) identify a number of uncertainties in that model,
including uncertainties in the stellar evolutionary tracks, the
effects of extinction, effects of metallicity, and possible effects
from the IMF. Given these various uncertainties, I certainly see no
reason to favor #2 over #1, and perhaps some reason to favor #1 over #2.

Also, near the start of my comments in this thread, I cautioned about
relying too heavily on this paper. I note this morning's astro-ph
includes a paper by Lai et al. (astro-ph/0610572) discussing galaxies
at z ~ 5.7. The stellar populations of these galaxies have
model-dependent ages potentially as old as 100 to 700 Myr. Given that
the age of the Universe at z ~ 5.7 was 1 Gyr, even an age of 700 Myr
still allows 300 Myr for the stars to form. Again, this doesn't seem
wildly out of whack.

------------------------------

I don't want to minimize the fact that stars, and galaxies, were
able to form quickly. After all, we know of quasars at
redshifts z 6, when the Universe was less than 1 Gyr old.
That's an impressively rapid formation. However, I think that
the gaps in our understanding are more likely to be in what we
know about galaxy and star formation rather than in General
Relativity.

JB Why?

Because we don't understand star formation in our own Galaxy?

JB This is probably more your area than mine. However, I don't think
JB star formation is the central problem here. It seems to be
JB stellar evolution, and supernova seeding of heavy elements, from
JB a plausible distribution of stellar masses. That does seem to be
JB understood (or at least modelled) quite well.

What's the correct distribution of stellar masses? To what extent is
dust absorption affecting the measurements? To what extent does
metallicity affect either stellar formation or evolution? ...?


JB As far as I can tell, classical GR does not have a particularly
JB illustrious record for the quantatitive accuracy in its
JB predictions at high z. The originally predicted deceleration in
JB the expansion of the universe has turned out to be completely
JB wrong, because what the multinational High-z Supernova Search Team
JB has confirmed in practice, is that the expansion of the universe
JB is accelerating.

Classical GR does accomodate an accelerated expansion of the
Universe, that's what the cosmological constant does, which is a
term Einstein himself inserted.

JB Not really. Einstein inserted the cosmological constant as a
JB widely acknowledged "fudge factor" to stop the universe from
JB expanding.

The cosmological constant is not a "fudge factor." It's a natural
product of the derivation of GR, somewhat akin to an integration
constant in elementary calculus. Einstein adopted a non-zero value
because that's what he thought was required to match the data. Once
Hubble showed the recession of galaxies, a value of zero was perfectly
acceptable.

JB [...] This "fudge factor" had been pretty comprehensively
JB debunked in the physics community, by the 1970's, because it was
JB not derivable from pure theory.

So which do you believe, theory or observation?


JB Its recent resurrection in pure physics, and preservation in
JB astronomy, to allow any arbitrary 'fudging' of the predictions of
JB pure theory again, could be argued to be an endictment of the
JB poor state of the genuine predictive power of that pure theory
JB (...).

The cosmological constant has always been around. I'm sure that if
you go back to a classical text, like _Gravitation_, you'll see
discussion of the cosmological constant. What's new is that the data
have improved to the point that a non-zero value seems to be demanded.


Classical GR does not predict the value of the cosmological
constant, any more than it predicts the value of the Hubble
constant or the mean density of matter. These are quantities that
have to be determined experimentally.

JB Actually, classical GR did 'predict' the 'value' of the
JB cosmological constant. Its value was whatever we required to
JB prevent the universe from expanding (or contracting). (...)

Somebody else has already asked this question, but in your scheme it
seems that no theory with a free parameter can be considered acceptable.

--
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Joseph Lazio wrote:

So at this point, you have two choices.
1) It is non-physical for objects to be older than the Universe.
That some portion of the uncertainty on their inferred ages
implies ages older than that of the Universe indicates that we do
not understand how to model in detail the evolution of stellar
populations (and/or there may be some unrecognized systematic
effect lurking in the analysis).
2) That some portion of the uncertainty on their inferred ages
implies ages older than that of the Universe indicates that we do
not know the age of the Universe.

A) You are mistaken. There is a third logical choice:

3) Both #1 and #2 are true.

B) We don't know the age of the Universe. All we know is how old EFE
says it is, and then only approximately, once all the relevant
parameters of the theory have been tweaked to give the (current) best
fit from those things we do know. Figures in the past have ranged from
2 Gyr[1] to 100 Gyr. As knowledge accumulates, the tweaking has already
continued, into the 21st century.

Although EFE represents a vast improvement over what went before, it
would be na=EFve to assume it will continue to be a vast improvement
over everything that can possibly come subsequently. Even its own
internal contradictions indicate it is not perfect. Einstein touched on
this in "The Meaning of Relativity" and MTW devoted the whole of
the final chapter of "GRAVITATION" to this subject.

You seem to adopt #2.

No, I prefer to keep an open mind, and accept that #3 could be a
plausible option.

JB [...] This "fudge factor" had been pretty comprehensively
JB debunked in the physics community, by the 1970's, because it was
JB not derivable from pure theory.

So which do you believe, theory or observation?

Again, this is not an either or scenario. I place more trust in
theories which are elegant, and which predicts observation. The
'cosmological constant' has an appalling record in this respect.

JB Its recent resurrection in pure physics, and preservation in
JB astronomy, to allow any arbitrary 'fudging' of the predictions of
JB pure theory again, could be argued to be an indictment of the
JB poor state of the genuine predictive power of that pure theory

The cosmological constant has always been around. I'm sure that if
you go back to a classical text, like _Gravitation_, you'll see
discussion of the cosmological constant.

That was, in fact, the primary reference I read before referring to the
debunking of the CC by the 70's. MTW even quote Einstein on the CC as:
"The biggest blunder of my lifetime".

What's new is that the data
have improved to the point that a non-zero value seems to be demanded.

A cynic could equally well say: Hubble's observations showed EFE got it
drastically wrong, so the CC was removed. Subsequent observations
showed EFE got it drastically wrong again, so the latest patch is
putting it back in again 'upside down'. We do not yet know the next
catastrophe the CC will be responsible for, since this latest patch is
practically brand new.

Somebody else has already asked this question, but in your scheme it
seems that no theory with a free parameter can be considered acceptable.

A possible free parameter in a new theory is one thing. Turning a known
loose cannon round by 180 degrees in an old theory that has already
failed twice could look more like an act of desperation.

John Bell
http://global.accelerators.co.uk
(Change John to Liberty to bypass anti-spam email filter)

[1] Einstein A (1954) Fifteenth edition of his "Popular Exposition"

"J(B" == John (Liberty) Bell writes:

JB John (Liberty) Bell wrote:
Joseph Lazio wrote:

Suppose one starts with a group of stars all born at essentially
the same time. In 0.01 Gyr, all of the stars more massive than
about 20 solar masses will be gone, in 0.02 Gyr all of the stars
more massive than about 10 solar masses will be gone,

Well, that certainly seems to rule out a preponderance of such
stars in the observed galaxies. Assuming a typical galaxy of stars
of ~ 10^11 solar masses, and 1 month for the visibility persistence
of a supernova, that would work out at 40 supernovas
simultaneously visible per galaxy. That would have been noticed.

I think I've posted previously a reference to a paper that claimed
that Type II supernovae are difficult to detect beyond z ~ 0.5. The
most distant Type Ia supernova is about 1.7, IIRC.

Moreover, don't forget about extinction. I have some vague memories
about reports of supernova remnants being detected in M82 with no
corresponding supernova, presumably because the extinction is so high.

and in 0.1 Gyr, all of the stars more massive than about 5
solar masses will be gone.

Ditto. That would work out to 16 supernovas simultaneously
visible per galaxy. That too would have been noticed.

Heck, wait a full 1 Gyr and all of the stars more massive than
*2 solar masses* will be gone.

Ditto. Even that appears to work out as 4 supernovas simultaneously
visible per galaxy. That too should have been noticed.

JB Incidentally, the above figure appears to hit or surpass the
JB lowest limit on the rate of supernovas required to explain galaxy
JB observations at ~ 3 Gyr. These require stars constructed from
JB material that has passed through "repeated" supernova stages, to
JB explain percentages of matter beyond iron. Even if we assume this
JB merely means just over 2 supernovas per star mass, over that
JB timespan, that still works out at~ 2 x 10^11 / 2 x 10^9 = 100 Sun
JB masses of supernova per galaxy per year.

Once you start getting into the metallicity of stars, and its
cosmological evolution, I think you're into a thicket of uncertainty.
How much material gets blown out of a galaxy vs. recirculating in it?
Does the material blown out of a galaxy help "quench" the star
formation within it? What's the IMF? Etc.

JB Consequently, it still seems to me that we should see something
JB like commensurate light from supernovas as from galaxies, at high
JB z, if galactic evolution is to fit comfortably into the alloted
JB timespan.

As others have said, this is indeed a topic of current, intense
research. I wouldn't call many of us complacent, but I think Steve
Willner described it correctly, the numbers don't look completely out
of whack.

I'd return to a point I've made before, galaxy and star formation is
messy business. It requires dissipation, might involve magnetic
fields; against this backdrop, the basic assumptions involved in
estimating the age of the Universe seem reasonbly secure and the
problem looks to be much more simple, and the answer correspondingly
more robust.

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Thus spake Joseph Lazio
"J(B" == John (Liberty) Bell writes:

JB John (Liberty) Bell wrote:
I think I've posted previously a reference to a paper that claimed
that Type II supernovae are difficult to detect beyond z ~ 0.5. The
most distant Type Ia supernova is about 1.7, IIRC.

Yes, that's right. SN1997ff is at z=1.755. In the Riess gold set there
are only nine useful data points above z=1. Current surveys like the
Supernova Legacy Survey aren't even looking above about z=1, because of
measurement problems and risk of statistical bias in the data. We have
to wait for SNAP which should turn up hundreds, or even thousands of SN
at red shifts up to 2.

I'd return to a point I've made before, galaxy and star formation is
messy business. It requires dissipation, might involve magnetic
fields; against this backdrop, the basic assumptions involved in
estimating the age of the Universe seem reasonbly secure and the
problem looks to be much more simple, and the answer correspondingly
more robust.

No, that is where I think we do have a problem. It's early days, and all
the data is too preliminary to be sure, but galaxy evolution models do
not tie in well with the age of the universe, when one looks at galaxies
at z=6 and above. There are even large galaxies at z=10, though the
image we get of them is a bit inconclusive in terms of saying what kind
of stars they contain. I think we really have to wait for the next
generation of Very Large Telescopes before we can expect any conclusive
data, but if current trends continue we will start seeing galaxies which
do create a timescale problem for current cosmology. Anyway, I hope so,
because that is what I am predicting.



Regards

--
Charles Francis
substitute charles for NotI to email

Thus spake Joseph Lazio
I think I've posted previously a reference to a paper that claimed that
Type II supernovae are difficult to detect beyond z ~ 0.5. The most
distant Type Ia supernova is about 1.7, IIRC.

Further to my post yesterday nasa has just issued a press release

http://www.nasa.gov/home/hqnews/2006...rk_Energy.html

This talks of an analysis of twenty four of the most distant supernovae,
many found in the last two years. I can't find any preprint that suggests
any of these are at greater than z=1.4, but await with interest. I did find,
pertinent to this thread

http://arxiv.org/abs/astro-ph/0503093

which states in the abstract:

We present the optical photometric data for the four supernovae. We also
show that the low frequency of Type Ia supernovae observed at z1.4 is
statistically consistent with current estimates of the global star formation
history combined with the non-trivial assembly time of SN Ia progenitors.


Regards

--
Charles Francis
substitute charles for NotI to email

Oh No wrote:

Thus spake Joseph Lazio
"J(B" == John (Liberty) Bell writes:

JB John (Liberty) Bell wrote:
I think I've posted previously a reference to a paper that claimed
that Type II supernovae are difficult to detect beyond z ~ 0.5. The
most distant Type Ia supernova is about 1.7, IIRC.

Yes, that's right. SN1997ff is at z=1.755. In the Riess gold set there
are only nine useful data points above z=1. Current surveys like the
Supernova Legacy Survey aren't even looking above about z=1, because of
measurement problems and risk of statistical bias in the data. We have
to wait for SNAP which should turn up hundreds, or even thousands of SN
at red shifts up to 2.

The reference (ApJ, 649, 563-569, 2006) provided by

(http://groups.google.com/group/sci.a...7a781e67a3a2/#)
indicates that there is no conclusive _observational_ evidence of q
becoming positive at z0.5.

If you are aware of different information, please clarify, with
appropriate references.

No, that is where I think we do have a problem. It's early days, and all
the data is too preliminary to be sure, but galaxy evolution models do
not tie in well with the age of the universe, when one looks at galaxies
at z=6 and above. There are even large galaxies at z=10, though the
image we get of them is a bit inconclusive in terms of saying what kind
of stars they contain.

A reference for this too, would also be appreciated

JB

Thus spake "John (Liberty) Bell"
Oh No wrote:

Thus spake Joseph Lazio
"J(B" == John (Liberty) Bell writes:

JB John (Liberty) Bell wrote:
I think I've posted previously a reference to a paper that claimed
that Type II supernovae are difficult to detect beyond z ~ 0.5. The
most distant Type Ia supernova is about 1.7, IIRC.

Yes, that's right. SN1997ff is at z=1.755. In the Riess gold set there
are only nine useful data points above z=1. Current surveys like the
Supernova Legacy Survey aren't even looking above about z=1, because of
measurement problems and risk of statistical bias in the data. We have
to wait for SNAP which should turn up hundreds, or even thousands of SN
at red shifts up to 2.

The reference (ApJ, 649, 563-569, 2006) provided by

(http://groups.google.com/group/sci.a..._frm/thread/1a
777a781e67a3a2/#)
indicates that there is no conclusive _observational_ evidence of q
becoming positive at z0.5.

That leads to a post by you, not by Rob. If you provide a complete ref,
with author and preferably arxiv, I will look at it. Although, actually
The cosmological parameters are pretty well tied down by supernova
observations, and that should tie q=q(t) down too. The only thing is, q
is used in a series expansion, which we don't much use any more, and it
makes not a lot of sense to use q(t) for any purpose I can think of.
What is usually discussed is q0=q(t0), i.e. now.

If you are aware of different information, please clarify, with
appropriate references.

No, that is where I think we do have a problem. It's early days, and all
the data is too preliminary to be sure, but galaxy evolution models do
not tie in well with the age of the universe, when one looks at galaxies
at z=6 and above. There are even large galaxies at z=10, though the
image we get of them is a bit inconclusive in terms of saying what kind
of stars they contain.

A reference for this too, would also be appreciated
#
I already gave you references in response to the above mentioned post.

I would refer you to two review papers in Natu

Glazebrook K. et. al., 2004, Nature, 430, 181-184.
http://www.pha.jhu.edu/~kgb/MiscPub/...iii-nature.pdf

Cimatti. et. al., 2004, Old Galaxies in the Young Universe, Nature, 430,
184-188. astro-ph/0407131

I'll let you search arxiv yourself for galaxies around z=10. I don't
think there are many found so far. I didn't use the reference when I had
it, because it seemed far too preliminary; the data is so thin it barely
admits more analysis than to say the thing exists.




Regards

--
Charles Francis
substitute charles for NotI to email