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

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

JB Joseph Lazio wrote:

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

I'm not quite sure how you got to this result, but no matter.

JB It is quite simple. Assume mean star mass is 10 Sun, then star
JB quantity is 10^10 / galaxy. Mean time to supernova is 2 x 10^7
JB years, hence 500 supernovas per year.

May I gently suggest that a mean stellar mass of 10 solar masses
seems perhaps a bit high?

JB Certainly. But that is simply another reason for ruling out a
JB "preponderance" of such stars.

"Preponderance" is ill-defined. The luminosity of a hot star (O or B)
can exceed 10,000 solar luminosities. The number of O and B stars in
a galaxy will never dominate the total number of stars, but they can
make an important, potentially dominant, contribution to the luminosity.


[...]
As for the metal content, when hot stars run out of fuel, they
collapse and form supernovae, spraying metals all over their
surroundings.

JB Agreed. The question I am asking is whether there are enough of
JB them to give the observed concentrations of heavy metals, at the
JB observed z shifts, in the timescales currently predicted by GR.

Well, that's a topic of current, active research, particularly looking
at extreme low metallicity stars to see if their abundances can be
explained by a small number of supernovae.

By way of context, I'm not saying that there are not issues to
research or that we understand everything. However, I have yet to
be convinced that (1) the broad picture doesn't make sense,

JB I would agree that the broad picture certainly does make
JB sense. What I am particularly interested in is whether the
JB numbers really add up, within the believed timescales. This is
JB not because I am a Luddite. It is because I am investigating a
JB different relativistic field equation, which, in addition to
JB having other apparent advantages, also suggests that timescales
JB between high z epochs could be longer than established GR theory
JB predicts.

I think you have to be more specific about what aspects cause
difficulties. As an example, going from a redshift of 6 to 5, in the
current cosmology, is a span of about 0.3 Gyr. Broadly, that would
appear to be plenty of time to have multiple generations of hot stars
go supernovae. Now details like getting the abundance patterns
correct, worrying about whether the first generations blow the gas out
of a galaxy and quench star formation prohibiting additional
generations, and the like remain to be figured out. On the face of
it, though, simple timescales don't appear to be problematic.


[...]
Also, a quick ADS search finds a paper by Nugent et al., URL:
http://adsabs.harvard.edu/cgi-bin/np...pJ...645..841N
, which describes some of the difficulties in observing (...) Type
II supernovae. This suggests to me that high redshift supernovae
from early galaxies (e.g., at z ~ 3) are not detected because we
do not yet have the sensitivity, except when the supernovae also
produce GRBs.

JB I certainly did not get that impression from the abstract. They
JB say this study is "based on five events at redshift up to z~0.3"
JB and conclude "thus demonstrating the feasibility of measuring the
JB expansion history."

JB Are you referring to a specific location within the paper itself?

Sure, Section 4 discusses what one would have to do to push this
investigation to 0.5 and beyond. Recall that star formation in the
Universe is thought to peak at redshifts of 1--2 (and possibly
higher). In order to get to redshifts of 1 or higher, they state that
facilities such as the James Webb Space Telescope or the Thirty Meter
Telescope will be required.

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Kent Paul Dolan wrote:

http://www.google.com/search?q=%22Ge...Deep+Survey%22

==

http://www.gemini.edu/index.php?opti...ask=view&id=18

Thanks

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

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

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.

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

John

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

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.


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
JB 1 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.

Nonetheless, I think you've misinterpreted their comment. First, in
Section 3.1, they state that the median formation redshift is 2.4.
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. At
this redshift, the age of the Universe was 2.7 Gyr (though I think one
would want to be careful in interpreting "age" too literally).

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.


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.

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

http://www.google.com/search?q=3D%22...Deep+Survey%22

=3D=3D

http://www.gemini.edu/index.php?opti...3Dview&id=3D18

Thanks

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

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

From the 20 galaxies examined between z =3D 1.308 and z =3D 2.147, five =
had
'best fit' z at formation of 4.7 or higher.

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

John

Note also from
http://www.gemini.edu/index.php?opti...3Dview&id=3D22

"One related study of particular interest is the recent paper by R.
Pell=C3=B3, D. Shaerer, J. Richard, J.-F. Le Borgne and J.-P. Kneib,
"ISAAC/VLT observations of a lensed galaxy at z =3D 10.0" Astronomy &
Astrophysics, vol. 416, issue 3, p. L 35."

JB

[Mod. note: that candidate z=10 object has been fairly convincingly
debunked by followup observations; see Bremer et al 2004 ApJ 615 L1,
Weatherley et al 2004 A&A 428 L29, and Smith et al 2006 ApJ 636 575 --
mjh.]

[I don't normally correct my posts, because most of the posts in which
I catch errors I think that the meaning can still be inferred.
However, in some of my cutting-n-pasting, a clause ended up in the
wrong place in this post.]

"JL" == Joseph Lazio writes:

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

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.

JL [...] I think you've misinterpreted their comment. First, in
JL Section 3.1, they state that the median formation redshift is 2.4.
JL Checking that against Table 1, indeed, 10 of the 20 objects have
JL z_f 2.4, with a median inferred "age" of these galaxies of 1.5
JL Gyr. At this redshift, the age of the Universe was 2.7 Gyr
JL (though I think one would want to be careful in interpreting "age"
JL too literally).

That should read:

[...] I think you've misinterpreted their comment. First, in Section
3.1, they state that the median formation redshift is 2.4. 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 (though I
think one would want to be careful in interpreting "age" too
literally). At this redshift, the age of the Universe was 2.7 Gyr.

Namely, I was commenting on the inferred "age" of the galaxies, not
the Universe.

JL 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)

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

--
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John (Liberty) Bell wrote:
Note also from
http://www.gemini.edu/index.php?opti...3Dview&id=3D22

"One related study of particular interest is the recent paper by R.
Pell=C3=B3, D. Shaerer, J. Richard, J.-F. Le Borgne and J.-P. Kneib,
"ISAAC/VLT observations of a lensed galaxy at z =3D 10.0" Astronomy &
Astrophysics, vol. 416, issue 3, p. L 35."

JB

[Mod. note: that candidate z=10 object has been fairly convincingly
debunked by followup observations; see Bremer et al 2004 ApJ 615 L1,
Weatherley et al 2004 A&A 428 L29, and Smith et al 2006 ApJ 636 575 --
mjh.]

Fair enough. Do you have equivalent arXiv refs for this? (I am assuming
if I follow these refs through, I will be blocked by no subscription)

JB

[Mod. note: if you search ADS for a paper these days, it is usually
quite good at finding you the astro-ph version if one exists. But I'll
do it for you this time: astro-ph/0409485, astro-ph/0407150, and
astro-ph/0601181 -- mjh]

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

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.

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

Why do *you* think the American Institute of Physics decided that the
bulk
of those other 200 papers were not sufficiently noteworthy to warrant a

"Physics News Update"?

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
JB 1 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.

Nonetheless, I think you've misinterpreted their comment.

No. If you check again, I think you will find that you have.

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

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.

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.

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

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.

No they are not. Read the final paragraph of their discussion.
Also read, for example, the paragraph immediately below figure 1 at
http://www.gemini.edu/index.php?opti...ask=view&id=18
They are unambiguously saying that different galaxies in their survey
formed at different times. They are saying, in addition, that, on
average, each galaxy would be 1 Gyr *older* than conservatively given
in table 1, using more plausible models.

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

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

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. However, if we take a more
sensible interpretation, that would probably place the formation time
of the
oldest galaxies before the classically predicted big bang.

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.

Why?

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

If I remember correctly, even with the much heralded observational
verification of GR's CMBR prediction, it turned out that the
originally predicted peak wavelength was out by a factor of about 3.


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

In message , "John
(Liberty) Bell" writes

If I remember correctly, even with the much heralded observational
verification of GR's CMBR prediction, it turned out that the
originally predicted peak wavelength was out by a factor of about 3.

I'm a complete amateur here, but does GR say anything about the CMBR, or
indeed the Big Bang?
Early predictions of the temperature of the background were wildly
inaccurate.

Jonathan Silverlight wrote:
In message , "John
(Liberty) Bell" writes

If I remember correctly, even with the much heralded observational
verification of GR's CMBR prediction, it turned out that the
originally predicted peak wavelength was out by a factor of about 3.

I'm a complete amateur here, but does GR say anything about the CMBR, or
indeed the Big Bang?

In one sense, Einstein's Field Equation (EFE) is contrived to say
anything you want it to say, because the cosmological constant was
introduced to (1) preserve a static universe, and its removal results
in (2) an expanding universe, or (3) a collapsing universe, or (4)
options 2 and 3 in sequence.

The second option starts with the Big Bang. The third option ends in
the Big Crunch.

The cosmological constant (described by Einstein as "the biggest
blunder of my lifetime"), was removed for reasons of mathematical
elegance and, in conjunction with adoption of the second option (and,
potentially, the fourth option too), to achieve compatibility with
Hubble's subsequently discovered data.

If I understand correctly, ts later reintroduction (as a variable) was
because of EFE's failure to correctly describe changes in the expansion
of the universe over time. Similarly, tinkering with the variables
within the equation permit an open universe, a flat universe, or a
closed universe, according to taste. Astronomers are at liberty to
change such variables as they see fit, to obtain an optimised match to
observational evidence.

It is true that CMBR is not a prediction of GR in the sense that its
*source* is a prediction of high energy physics. However, it *is* a
prediction of GR in the senses that:
a) EFE predicts those higher energy phases earlier in time once option
2 is adopted.
b) EFE then predicts the subsequent downward shifting in CMBR
wavelength to a value something like what we observe in practice.

Early predictions of the temperature of the background were wildly
inaccurate.

And why would that be?


John Bell
(Change John to Liberty to bypass anti-spam email filter)

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.

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.

xanthian.