old galaxies in a supposedly young universe

At z=4 (1.6Gy after the supposed bang) we see old galaxies that have
stopped their star formation since a long time.

http://xxx.lanl.gov/pdf/1312.4952.pdf

How can this be?

Of course it is very easy. Big Bang theory is not questioned and the
observers suppose a phenomenal star formation rate before the observed time.

Problem is, there is not a lot of time left, we are only 1600 million
years after the supposed bang.

In the Summary of the article we can read: (page 7)

quote
While rare (with number densities ~ 10 and ~ 80 x
lower than at z=2 and z=0.1),they make up a surprisingly high fraction
of the massive galaxy population at z ~ 4 (34 +/- 13%), higher than
expected based on the declining trend over 1 z 3, suggesting an
effective mechanism of suppressing star formation and short formation
timescales ( 1Gyr).
end quote

A third of the galaxies at z=4 are in fact OLD GALAXIES.

Can you imagine?
Indeed we need an "effective mechanism of suppressing star formation"
here. 1600 years after the supposed bang there is no star with more than
1.6 Gy age excuse me. Galaxies should be highly active very young
objects as we have been told since a long time. But a full THIRD of the
population is quite OLD!

quote
The implied SFRs(*) needed
to form galaxies with a mean stellar mass of 0.8 x 10e+011M0 in such a
short time exceeds that of similarly abundant UV-bright galaxies at z =
4, suggesting that most of the star formation in their progenitors was
obscured by dust.
end quote

(*) SFR= Star Formation Rate

Yes, dust is a big helper here. :-)

Those galaxies are BIG systems (10e+011 M0) and look quiescent, no star
formation and an OLD star population, as mentioned in the article.

What is incredible is that an OLD star population doesn't bother anyone
at only 1.6 Gy after the big bang when there is no star older than 1.6 GY!!!

The mass of the Milky Way is approx 1.5e+012 M0. After 13.7 Gy of efforts.

These galaxies have acquired a mass of 1e+011 M0 in only 1.6Gy!!

[Mod. note: non-ASCII characters removed. Please do not cut and paste
from papers or web sources -- mjh]

On Wednesday, March 12, 2014 4:28:54 AM UTC-4, jacob navia wrote:
Those galaxies are BIG systems (10e+011 M0) and look quiescent, no star
formation and an OLD star population, as mentioned in the article.

What is incredible is that an OLD star population doesn't bother anyone
at only 1.6 Gy after the big bang when there is no star older than 1.6 GY!!!

You use loaded terms like "BIG" and "OLD."

The reality is that these galaxies are about 1/10th the size of the
Milky Way in a universe that is ~1/10th of today's age[*], so not
"BIG" by present day standards. Typical ages of the stars are 0.8 Gy
based on measured spectra, which is less than the 1.6 Gy age of the
universe, so not "OLD" by today's standards.

CM
[*] Not that I'm saying that star formation or galaxy formation is
linear with time.

In article , jacob navia
writes:

At z=4 (1.6Gy after the supposed bang) we see old galaxies that have
stopped their star formation since a long time.

http://xxx.lanl.gov/pdf/1312.4952.pdf

Do not link to the PDF; link to the abstract.

Problem is, there is not a lot of time left, we are only 1600 million
years after the supposed bang.

That is a long time.

1600 years

1600 million years?

after the supposed bang there is no star with more than
1.6 Gy age

1600 million years = 1.6 Gy; looks consistent to me.

excuse me. Galaxies should be highly active very young
objects as we have been told since a long time. But a full THIRD of the
population is quite OLD!

Obviously, observations of high-redshift galaxies will more easily find
active than inactive galaxies.

Le 12/03/2014 23:00, Craig Markwardt a écrit :
The reality is that these galaxies are about 1/10th the size of the
Milky Way in a universe that is ~1/10th of today's age[*], so not
"BIG" by present day standards.

Well, I asked an astrophysicist and the answer is:

http://imagine.gsfc.nasa.gov/docs/as...s/001205a.html

The Question

(Submitted December 05, 2000)
What is the average size of a galaxy?

The Answer

Thank you for your question. Our Milky Way galaxy is a pretty typical
large galaxy. Most of the stars are in a disk that is about 100,000
light years across in diameter and 3000 light years thick. Most of the
galaxies in the universe are actually smaller than the Milky Way. For
example, most of the dozens of galaxies in our Local Group are at least
ten times smaller in diameter.
-- Michael Loewenstein and David Marsden for "Ask an Astrophysicist"

OK?

Those galaxies aren't the size of the Milky Way but then, our galaxy is
a big one. They are the size of an average galaxy in our local universe,
and they are BIG since in only 1.6 Gy they have reached sizes similar to
the galaxies in the local group...

Le 12/03/2014 23:00, Craig Markwardt a écrit :
Typical ages of the stars are 0.8 Gy
based on measured spectra, which is less than the 1.6 Gy age of the
universe, so not "OLD" by today's standards.

The age of the stars were deduced from the colors of the galaxies.
Spectra weren't taken since

quote
..... the sample is too faint for spectrographs on large telescopes.
end quote

Prediction:

These galaxies will be confirmed as plain old galaxies in a few years
with better scopes.

[Mod. note: the 'spectrum' of a galaxy may refer to its SED rather
than to high-resolution spectroscopy -- mjh]

Le 12/03/2014 23:04, Phillip Helbig---undress to reply a écrit :
Problem is, there is not a lot of time left, we are only 1600 million
years after the supposed bang.
That is a long time.

We are speaking about galaxies and stars. A normal star like the sun
lives around 10Gy. After 1.6Gy a normal star is still in its youth.

Supposing a human being lives for 90 years, the correspondig age would
be around 14.4 years.

A galaxy lives even longer (unless swallowed by another one).

So, 1.6 Gy is nothing really. Our own galaxy makes only 6 revolutions in
that time. If we set a "day" as a revolution of a body around itself,
1.6 Gy is just a bit more than 6 days.

Conclusion: "A long time" depends on the size of the body. For galaxies,
1.6Gy is just about a week.

jacob

On Thursday, March 13, 2014 1:16:01 PM UTC-4, jacob navia wrote:
Le 12/03/2014 23:00, Craig Markwardt a écrit :

Typical ages of the stars are 0.8 Gy
based on measured spectra, which is less than the 1.6 Gy age of the
universe, so not "OLD" by today's standards.


The age of the stars were deduced from the colors of the galaxies.
Spectra weren't taken since
[ etc. ]

Please read the Straatman et al paper again. With enough "colors" a
broadband spectrum is possible. See Fig 2. of the paper you cite. They
are consistent with stars of age ~0.8 Gy.

Furthermore, if you had read the Straatman paper, you would have found
the discussion of even higher redshift objects (z~10) with heavy UV
emission that could be the early high star formation rate progenitors
of the z~4 objects in question.


Well, I asked an astrophysicist and the answer is:
[ ... ]

Ask an Astronomer is great for basic qualitative questions, but the
response you quoted says nothing quantitative about whether the z~4
galaxies are "BIG." In fact, if we look at real estimates of galaxy
mass distributions (Tomczak et al 2014; Fontana et al 2006), these
galaxies are at the upper end of the mass distribution for high
redshift galaxies, but are not outliers. This is not a surprise
because the Straatman objects were selected on that basis for follow
up studies. There were many galaxies with lower masses that were not
studied in detail because they were not interesting for the purposes
of the paper.

We are speaking about galaxies and stars. A normal star like the sun
lives around 10Gy. After 1.6Gy a normal star is still in its youth.

Thanks for arguing by analogy, but our sun is not a good analogy for
star formation history. There are much more massive stars that can
form, evolve and die within tens of millions of years.

CM

References
Fontana et al, 2006 A&A 459 745
Tomczak et al 2006, ApJ 783 85