A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Research
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

An old galaxy at z=7.1



 
 
Thread Tools Display Modes
  #31  
Old March 12th 15, 09:13 PM posted to sci.astro.research
Steve Willner
external usenet poster
 
Posts: 1,172
Default An old galaxy at z=7.1

In article ,
Eric Flesch writes:
I wonder what you'd think of this paper: "The Temperature Of The z=8.4
Intergalactic Medium" -- http://arxiv.org/abs/1503.00045 .


They measure the "spin temperature" of the IGM at z=8.4


It's early days for this sort of observation, and I'd really like to
have an expert -- which I am not -- explain what the expectations
are. What's being measured, as you say, is the spin temperature T_S
of the neutral hydrogen, or rather the _difference_ between T_S and
the CMB temperature T_CMB. The measurement is complicated by the
unknown neutral fraction of the intergalactic gas and (to a lesser
extent) other physical parameters.

What isn't clear to me is what T_S "should" be, though I gather it
should equal the kinetic temperature T_g of the neutral hydrogen gas.
Apparently in a model with no heating by stars, the gas decouples
from the CMB at about z = 200 and then cools adiabatically faster
than the CMB. According to the preprint cited, T_g should reach
1.8 K at z = 8.4, where T_CMB = ~25 K, but I don't understand why T_g
isn't coupled to T_CMB.

One caution is that the preprint is apparently an unrefereed draft.
For all I know, there could be something horribly wrong that I can't
spot.

and are hard-pressed to reach as high as 10K.


I think that's backwards: the _weakness_ of observed fluctuations
requires either T_g is near T_CMB or the neutral fraction is either
very large or very small. (That last seems quite unlikely to me, but
the former might be the case as far as I can tell.) If the neutral
fraction is near 50%, T_g 10 K (and presumably 90 K).

The _high_ T_g, if you believe it, requires that there be some source
of gas heating, presumably X-rays from SNe, and that requires fairly
early star formation. However, I don't see how near-zero star
formation at z 8.4 with neutral fraction = 100% is ruled out by
these results. It may be ruled out by direct detection of z 8
galaxies, but that would take a quantitative argument.

As I say, early days, but the approach is extremely promising.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
  #32  
Old March 12th 15, 09:15 PM posted to sci.astro.research
Richard D. Saam
external usenet poster
 
Posts: 240
Default An old galaxy at z=7.1

On 3/7/15 2:47 AM, Steve Willner wrote:
In article ,
jacob navia writes:
http://www.eso.org/public/archives/r...8/eso1508a.pdf


This is an interesting paper, but because it's in _Nature_, not all
the information is given. In particular, it looks to me as though
the uncertainties on the physical quantities are underestimated, and
I don't see how the authors derive the expected equivalent width for
the C III] line. (It isn't in the reference cited.) A dust
temperature as low as 35 K also strikes me as unlikely; the CMBR
temperature is 23 K, after all. None of this changes the basic and
valuable result that there must be _some_ dust in the galaxy, and in
fact more of the galaxy's luminosity comes out in the rest-frame FIR
than in the UV.

Why is CMBR presently at 2.7 K and (1+7.1)*2.7 K = 22 K
considered dogma
when the temperatures thermodynamically approaching zero are available
not in thermal equilibrium with CMBR 2.7 K and (1+7.1)*2.7 K = 22 K
particularly in the context that dust thermal emissivity
may be an indicator of these low temperatures although
related extremely long wavelengths are not measurable at this time
as calculated by
established black body spectrum peak wave length theory.

wave length (cm) = h*c/(4.96536456*Boltzmann*T)

Emission T K Emission wave length (cm)
2.2E+01 1.3E-02
2.7E+00 1.1E-01
1.0E+00 2.9E-01
1.0E-01 2.9E+00
1.0E-02 2.9E+01
1.0E-03 2.9E+02
1.0E-04 2.9E+03
1.0E-05 2.9E+04
1.0E-06 2.9E+05
1.0E-07 2.9E+06
1.0E-08 2.9E+07
1.0E-09 2.9E+08
1.0E-10 2.9E+09
1.0E-11 2.9E+10
1.0E-12 2.9E+11
1.0E-13 2.9E+12
1.0E-14 2.9E+13
1.0E-15 2.9E+14
1.0E-16 2.9E+15
1.0E-17 2.9E+16

Paraphrasing and amplifying your statement:
more of the galaxy's luminosity comes out in the higher wave lengths
with the possibility that
non currently measurable long wave length luminosity
represents large portions of galactic and extra-galactic dust.

This concept is further amplified by introducing
experimentally available dimensionless material emissivity factors(F)
into black body spectrum peak wave length theory:

wave length (cm) = h*c/(F^(1/4)*4.96536456*Boltzmann*T)

Carbon and other dust candidates such as silicates or metal types
have emissivity factors(F) on the order of .1 - .9 .
I have looked for experimental emissivity factors(F) for gaseous types
such as hydrogen agglomerate particles
and have not found them
but anticipate their emissivity factors(F) .1
making their thermal emissivity detection further problematic.

Such anticipated increased dust would contribute
to a more rapid star formation within the context of BB theory.

Richard D Saam
  #33  
Old March 16th 15, 12:40 PM posted to sci.astro.research
Jonathan Thornburg [remove -animal to reply][_3_]
external usenet poster
 
Posts: 137
Default An old galaxy at z=7.1

Robert L. Oldershaw wrote:
Here is a direct, straightforward question that I would like to have answered.

What quantitative or unique qualitative empirical result would lead us
to think that there is a problem with our theoretical model of the
early period of expansion?

I presume that there are some limits to what the existing model could
account for. So what are these "lines in the sand" that do offer clear
and definitive tests of the model?


The standard big bang model requires that the mass distribution in the
universe should become more and more anisotropic over time. We have good
evidence from CMBR observations that the universe was isotropic to within
a few parts per million at the CMBR-last-scattering time (redshift
somewhere around 1100 or so if I recall correctly).

So....

Hypothetical case #1:
If we were to observe some mass tracer to be highly *anisotropic* at
times *earlier* (i.e., redshifts higher) than the CMBR-last-scattering time,
that would be very hard to explain in (i.e., it would be a big problem for)
the big bang model.

Hypothetical case #2:
If we were to observe some mass tracer to be *more* isotropic than
the CMBR at a time *later* than (i.e., at a redshift lower than) the
CMBR-last-scattering time, that would be also be very hard to explain in
(i.e., it would be a big problem for) the big bang model.

Hypothetical case #3:
If we were to observe the distribution of some mass tracer (say,
galaxies, as measured by their 2-point correlation function) to become
*more* isotropic with increasing time over some redshift range, that
would also be hard to explain, i.e., it would be a big problem for,
the big bang model.


[Technically, #2 and #3 might be better characterized as big problems
for our theories of the evolution of anisotropies in an expanding
universe, rather than for the big bang model itself.]

[I suppose there might actually be some theoretical wiggle room around
each of my cases if the "mass tracers" turn out not to accurately trace
mass. One way to reduce that wiggle-room might be to use (galaxy-cluster)
gravitational lensing measurements for #2 and #3, since these directly
sample the mass distribution (at least in theory; in practice these are
very delicate observations to make, and they require elaborate theoretical
modelling of a type of which I don't think Robert Oldershaw approves).]

ciao,

--
-- "Jonathan Thornburg [remove -animal to reply]"
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
"There was of course no way of knowing whether you were being watched
at any given moment. How often, or on what system, the Thought Police
plugged in on any individual wire was guesswork. It was even conceivable
that they watched everybody all the time." -- George Orwell, "1984"
  #34  
Old March 18th 15, 08:33 AM posted to sci.astro.research
Robert L. Oldershaw
external usenet poster
 
Posts: 617
Default An old galaxy at z=7.1

On Monday, March 16, 2015 at 7:40:24 AM UTC-4, Jonathan Thornburg [remove -animal to reply] wrote:

The standard big bang model requires that the mass distribution in the
universe should become more and more anisotropic over time. We have good
evidence from CMBR observations that the universe was isotropic to within
a few parts per million at the CMBR-last-scattering time (redshift
somewhere around 1100 or so if I recall correctly).


If I remember correctly, the Planck results at some point generated
talk of an inherent "directionality" to the observable portion of the
cosmos. If deeper and more sensitive observations turned up a dipole
anisotropy that was not due to our relative motion, but rather due to
the distribution of matter, would that require a qualitatively
different model for the global expansion?

[Mod. note: reformatted -- mjh]
  #35  
Old March 18th 15, 12:44 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default An old galaxy at z=7.1

In article , "Robert L.
Oldershaw" writes:

The standard big bang model requires that the mass distribution in the
universe should become more and more anisotropic over time. We have good
evidence from CMBR observations that the universe was isotropic to within
a few parts per million at the CMBR-last-scattering time (redshift
somewhere around 1100 or so if I recall correctly).


If I remember correctly, the Planck results at some point generated
talk of an inherent "directionality" to the observable portion of the
cosmos. If deeper and more sensitive observations turned up a dipole
anisotropy that was not due to our relative motion, but rather due to
the distribution of matter, would that require a qualitatively
different model for the global expansion?


You are confusing two different things. The directionality refers to
the fact that the "direction" (not obvious what is meant for multipoles
higher than 2) of some multipoles appear to be correlated. While this
effect appears to be real, it is a very-few-sigma result. It is also
not clear if it is primordial. However, it has nothing to do with the
dipole direction. The primordial dipole is essentially unobservable,
since there is a dipole due to our own motion. Only if one knew the
latter precisely could one correct for it and hence see the primordial
dipole.

One DOES expect a primordial dipole. However, most people don't worry
about it since it is essentially unobservable, which is why most plots
of the power spectrum start at the quadrupole.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Our galaxy heading for collision with Andromeda Galaxy signifiespost Amateur Astronomy 9 June 22nd 12 07:10 AM
Our galaxy heading for collision with Andromeda Galaxy signifiespost Policy 12 June 14th 12 06:55 AM
Our galaxy heading for collision with Andromeda Galaxy signifiespost Space Science Misc 0 June 13th 12 02:22 AM
Our galaxy heading for collision with Andromeda Galaxy signifiespost Astronomy Misc 0 June 9th 12 04:56 AM
Galaxy Seen Colliding with Invisible Dark Matter Galaxy! Double-A[_1_] Misc 0 June 17th 07 12:56 PM


All times are GMT +1. The time now is 12:12 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.