[[Mod. note -- This post arrived at my moderation inbox with lots of
hex-encoded 8-bit characters. I have hand-repaired those whose meaning
seemed obvious from context. -- jt]]

Le 15/05/2017 =C3=A0 07:10, jacobnavia a =C3=A9crit :
ZF-COSMOS-20115

[snip]

[[Mod. note --
1. It would be very nice if you would provide references, e.g., to
just which observations of ZF-20115 you're referring to.

arXiv:1702.01751v2 [astro-ph.GA] 29 Mar 2017
A massive, quiescent galaxy at redshift of z=3.717

The authors of that paper say:

"...Here, we report the spectroscopic confirmation of one of these
galaxies at redshift z=3.717 with a stellar mass of 1.7*10^11 M_sun
whose absorption line spectrum shows no current star-formation"

Further down, they say:

"It takes at least 100--200 Myr of quiescence to reach the line
strengths needed and the quiescent star-formation rate has to be
at least a 100=C3=97 less than during the formation period."

Next page:

"There are a number of significant implications from this spectroscopic
confirmation of the existence of a quiescent galaxy population at
z =E2=88=BC 4
with stellar masses of =E2=88=BC 10^11M=E2=8A=99 and a space density of 1.8 =C2=B1 0.7 =C3=97 10=E2=88=925
Mpc=E2=88=923 . These are not seen in modern hydrodynamical (i.e. dark matter
and baryon physics) simulations of galaxy formation, whose volumes now
approach =E2=88=BC 106 Mpc."

So, we have a dead galaxy, probably the successors of the early quasars.

And all that: the merger of two big galaxies, the ensuing quasar and its
demise, and 200 My of cooling of the ashes, all that in just 1625 My?

Galaxies are big and their movements are slow. In 1625 My the milky way
(much less massive than ZF-20115) manages to make just around 6 turns.

A series of ad hoc explanations are presented in other papers to explain
this galaxy away. The quasar (not seen, apparently in a quiscent state
then) should have heated the gas, quenched star formation, and leave a
dead corpse of stars still shining. All that, in just 1.6 Gy.

Nobody here has definitely answered how much time after the bang should
have passed until star formation was at all possible.

Let's assume 150-200 My.

In just 1.3Gy (1600 - 200 quiescent period and - 200 cooling after the
bang) two huge galaxies collided, their nucleous merged what provoked a
quasar that heated the gas and stopped star formation.

I think that it is obvious that all that happened maybe, the galaxies
did collide, their two huge black holes fused and started a big quasar
that heated the gas.

But that takes at least 4-5 Gy. The collision of our galaxy with
Andromeda will happen in 4 Gy. And when galaxies collide they do not
fuse instantaneously but dance around for a long while before their
central black holes merge.

The precursor galaxies could not have so many stars anyway since the
universe had just begun a few hundred million years before. Supposing
that the precursor galaxies were both around 200 My old, just babys in
galaxy time, the collision would have happened at 400-500 My after the
BB.. That leaves only 600 My available to

1) Build that quasar, i.e. a black hole fusion with all the time needed
for that: the time to pass around each other, get into orbit, approach,
etc. Let's say that happens hyper quickly: just 100 My.

2) Quasar built, it must heat the gas incredibly fast to stop any
further star formation, i.e. just 500 My to blow away all the gas of the
galaxy and make it a dead one.

Let's be reasonable, this looks like a film seen in fast forward, to
keep bending reality to theory.

At the same time you have to build stars at huge rates to be able to
weight 3*10^11 solar masses in a few hundred My...

To completely quench star formation you have to heat a lot of gas and
that takes a lot of time.

Yes, anyone here can point to my idiotic "common sense" but the story of
all that happening in 1.625 Gy seems (to me) completely preposterous.


2. I don't see any reason why a high-redshift (= young) galaxy with
a very low star-formation rate would be inconsistent with big-bang
cosmology.

Because there is no time to produce dead galaxies yet.

In fact, I rather doubt that we understand star formation
well enough to make such a statement.

So, we do not understand star formation but we do understand how the
universe started etc.

I have a different interpretation of the observations. This is a dead
galaxy, probably the remnants of a quasar that heated all the gas and
extinguished itself, leaving a bright core of stars, very dense. And
that can't be done in 1625 My.


3. arXiv:1704.03868 suggests that ZF-20115 may in fact have lots of
ongoing star formation, but that this activity is heavily obscured
and thus invisible to optical surveys. In fact, the authors write
"We conclude that the ZF20015 system does not pose a
challenge to current models of galaxy formation [[...]]"
-- jt]]


Of course.

The authors said:

"The stellar mass we see is relatively unobscured."

and further down:

"We note the non-detection by Herschel at 100=E2=80=93160=CE=BCm
limits current obscured star-formation to 70=E2=80=93100 M=E2=8A=99
yr=E2=88=921"

Of course you can tweak the models, build unlikely scenarios, make yet
another twist.

ALMA will make more spectroscopic observations but this thing is too big
to hide now.

A dead galaxy in an infant universe?

And beyond this one there are many others galaxies waiting to be discovered.

jacob