NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/sci/astro/9228

Internet Message Format | 1992-08-25 | 7.1 KB

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From: [e-mail] (Mike Newberry)
Newsgroups: sci.astro
Subject: Re: B-O Effect (was Re: Proof of quasar non-locality?)
Message-ID: <[e-mail]>
Date: 25 Aug 92 20:38:13 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Sender: [e-mail]
Organization: University of Arizona, Tucson, AZ
Lines: 119

In article <[e-mail]> [e-mail] (Tom Van Flandern) writes:
>
>Earlier, I wrote:
>
>>> what I think is going on is that we have [an] extension of the blue giant
>>> branch.. into the ultraviolet, which would be not so easily observable
>>> through our atmosphere. ... When.. galaxies are farther away, the
>>> ultraviolet extension shifts into the visible range, making the net color
>>> blue.
>
>and [e-mail] (Don Wells) replied:
>
>> I described a spectrum of a B-O "blue" galaxy. The x-axis of that plot was
>> wavelength *in the rest frame*, i.e. it does not suffer from this technical
>> problem. A plot of any nearby object with the same type of spectrum would
>> look just the same. Therefore, the blue broadband color of the distant
>> (B-O) object cannot be due to a putative UV flux which would be hidden in
>> nearby objects.  ...  The B-O galaxies---just like nearby "late-type"
>> galaxies---simply contain some hot, young B and A stars and associated H-II
>> regions, in addition to the usual population of cooler, older stars. The
>> hot stars and emission lines imply recent star formation.
>
>     If luminous stars in galaxies covered a full range of temperatures, I
>would understand this argument.  But the luminous stars have two branches,
>one red and one blue; and galaxy spectra are a composite of these.  My
>argument is to assume that the B-O galaxies are "normal", and consisting of a
>composite of both branches.  They would then appear blue if the blue branch
>stars were more numerous or more luminous than the red branch stars.
>
>     Now consider one of those "normal" B-O galaxies, and bring it closer to
>us.  As its redshift decreases, more and more of the blue branch light
>disappears into the ultraviolet.  At the same time, more and more red branch
>light is brought into the visible range from the infrared.  Inevitably, the
>galaxy will get more yellow in appearance.  There must be a net shift of the
>peak intensity toward longer wavelengths.
>
>     If you can rule this out observationally, I haven't yet understood how.
>
>> New, high-resolution images (FWHM=0.45 arcsec) of the blue galaxies in A370
>> and Cl0024+1654 have been presented. These images reveal that a significant
>> fraction of these galaxies are multiple systems, unresolved by previous
>> ground-based observations. In addition, a number of these systems show
>> signs of significant morphological peculiarities, suggestive of
>> interactions/mergers.
>
>     First you tell me that the B-O objects must be galaxies, not
>supermassive stars, because they are resolved objects with composite spectra.
>Now apparently we learn that higher resolution shows each is a multiple
>source with peculiar morphologies.  I must point out that this sounds close
>to the multiple supermassive star systems imbedded in nebulosity which I
>originally suggested.
>
>     Can we really be sure we know what the B-O objects are at this early
>stage in our explorations of space?  -|Tom|-
>
>--
>Tom Van Flandern / Washington, DC / [e-mail]
>Meta Research was founded to foster research into ideas not otherwise
>supported because they conflict with mainstream theories in Astronomy.


All right, this has gone on long enough. Here's my 2 dollars' worth:

There is absolutely NO way that the spectrum of a Butcher-Oemler "blue"
galaxy can be a single star or a small group of stars.  If you make
theoretical models for the spectrum of these or other galaxies (and I have
actually done this), there is actually only a very small parameter space
of the mix of various stellar types that can give you a spectrum that
matches that observed for these galaxies.  It is unfortunate, but of
no direct consequence to the present argument, that the allowed parameter
space becomes redundant for two distinctly different stellar mixes: the
first being a truncation of active star formation in a system that had active
star formation just 1 or so Gyr before the light left the galaxy, and the
other being a system which was previously inactive and experienced a burst
of star formation turning a few percent of its mass into stars in the
period of about 1 Gyr before the light left the galaxy.  The question of
interest with regard to the "meta model" then becomes how long it took the
light from these systems to reach the earth, as this relates to whether
these galaxies are really small groups of not too distant stars (i.e., the
non-cosmological redshift idea) or are actually galaxies as luminous as
the Milky Way at the distance inferred from the redshifts of their
spectra (i.e., the cosmological redshift idea).

There are a number of types of observations which are completely inconsistent
with the non-cosmological redshift idea; only some of these are related to
the BO Effect. I will not present all lines of evidence as this would be
overkill:

(1) The composite spectra of stellar populations change as the stellar
population ages, and the spectra of the "blue" galaxies as well as those
of the other galaxies in these and other clusters appear the way they should
for stellar populations that are observed at about the look-back time that
corresponds to the redshifts of their spectra.

(2) The *spectra* of galaxies of similar morphology but observed at different
redshifts show a continuity of properties that is completely consistent
with redshift being interpreted as *age* only.

(3) Making arguments based upon the observed colors of galaxies is *always*
frought with ambiguity as one can make various combinations of stellar
population parameters (namely, the initial mass function, age, star formation
rate over time, metal abundance, and mix of different sub-populations) that
can produce the same color as another stellar population observed at some
other redshift. HOWEVER, when you use the spectra of stellar populations,
the population parameters/redshift ambiguity almost goes away.  I say
"almost" because there is still redundency at the level of, say 1 Gyr in
age or less than 0.05 in redshift, but there is just no way to have the
composite spectra of clumps of supermassive blue and red-branch stars
mimic the spectra of whole galaxies of more "conventional" stars. To be
honest about this, there is indeed much that we continue to argue about over
the detailed successes and failures of stellar population sythesis at matching
the spectra of galaxies.  However, these are relatively small points that
represent details of the models; the general picture is pinned down far
too well for the spectra of galaxies to be mimicked by a small number of
supermassive stars that produce non-cosmological redshifts.


Mike Newberry
Steward Observatory