Radio Jets & Lobes -- proposed simple mechanism

A new paper is out, astro-ph/0603803, "Kinematics of the Narrow-Line
Region in the Seyfert 2 Galaxy" by Das, Crenshaw, Deo & Kraemer. They
use HST STIS on the radio jet of NGC1068. Their result, plainly, is
"an increase in radial velocity roughly proportional to distance from
the nucleus followed by a linear decrease after roughly 100 parsec
similar to that seen in other Seyfert galaxies, indicating common
acceleration/deceleration mechanisms."

So how does this happen? As the paper says, "The large scale outflow
itself is not well understood dynamically", which is polite for:
(1) they have no idea how it happens
(2) neither does anyone else
(3) the various proposed models all fail.

I would like to propose a simple mechanism: Gravity. An increasingly
popular model of the universe is that of gravity propagating via an
additional large dimension, e.g. the Randall-Sundrum AdS 5D model.
Such a model treats our universe as a membrane on the surface of a
higher-dimensional body, with attendant gravitational highlands and
lowlands, i.e. each place is characterized by a gravitational scalar.

Galaxies are typically modelled as condensing out of primordial space,
but James Jeans observed that galaxies appear as though they have been
poured into the universe, from the center. If our universe is
modelled as a membrane wrapped around a higher dimensional body, then
it's a quick extension to model that galaxy cores are where matter is
injected into our universe from the higher-dimensional body.

Such a point of injection would be like a volcano, in gravitational
terms. The eruption would be from a very high place, i.e. a place
where the gravitational scalar is very low. Matter would *fall* from
the point of injection into our universe. That it falls along the
galaxy's minor axis would be consequnetial to the overall
extra-dimensional gravitational contours of the galaxy, which would
also account for anomolous rotational profiles.

OK, it's a different view of the universe, but one consistent with
observation, and certainly provides the simplest possible explanation
for the velocity profiles of radio jets and lobes. For further
evidence of the gravitational topography surrounding galaxies, see HI
maps such as this 1979 one around NGC 3628 at
quasars.org/ngc3628/ngc3628-HI.htm . The HI gas fills an area
surrounding the galaxy, then dribbles over an edge and oozes into
space. The appearance is clearly that of the galaxy's gravitational
influence extending only so far into the IGM, and no further. This
would be fully explained, once again, by the presence of a
gravitational scalar which overcomes the galaxy's gravity past a
certain distance, else the gas would not ooze away like it does.

So I propose that it is gravity which accounts for the velocity
profile of radio jets and lobes: the material is simply falling away
from the galactic core source.

Eric Flesch

Eric Flesch writes:

A new paper is out, astro-ph/0603803, "Kinematics of the Narrow-Line
Region in the Seyfert 2 Galaxy" by Das, Crenshaw, Deo & Kraemer. They
use HST STIS on the radio jet of NGC1068. Their result, plainly, is
"an increase in radial velocity roughly proportional to distance from
the nucleus followed by a linear decrease after roughly 100 parsec
similar to that seen in other Seyfert galaxies, indicating common
acceleration/deceleration mechanisms."

So how does this happen? As the paper says, "The large scale outflow
itself is not well understood dynamically", which is polite for:
(1) they have no idea how it happens
(2) neither does anyone else
(3) the various proposed models all fail.

I would like to propose a simple mechanism: Gravity. An increasingly
popular model of the universe is that of gravity propagating via an
additional large dimension, e.g. the Randall-Sundrum AdS 5D model.
Such a model treats our universe as a membrane on the surface of a
higher-dimensional body, with attendant gravitational highlands and
lowlands, i.e. each place is characterized by a gravitational scalar.

Galaxies are typically modelled as condensing out of primordial space,
but James Jeans observed that galaxies appear as though they have been
poured into the universe, from the center. If our universe is
modelled as a membrane wrapped around a higher dimensional body, then
it's a quick extension to model that galaxy cores are where matter is
injected into our universe from the higher-dimensional body.

Such a point of injection would be like a volcano, in gravitational
terms. The eruption would be from a very high place, i.e. a place
where the gravitational scalar is very low. Matter would *fall* from
the point of injection into our universe. That it falls along the
galaxy's minor axis would be consequnetial to the overall
extra-dimensional gravitational contours of the galaxy, which would
also account for anomolous rotational profiles.

OK, it's a different view of the universe, but one consistent with
observation, and certainly provides the simplest possible explanation
for the velocity profiles of radio jets and lobes. For further
evidence of the gravitational topography surrounding galaxies, see HI
maps such as this 1979 one around NGC 3628 at
quasars.org/ngc3628/ngc3628-HI.htm . The HI gas fills an area
surrounding the galaxy, then dribbles over an edge and oozes into
space. The appearance is clearly that of the galaxy's gravitational
influence extending only so far into the IGM, and no further. This
would be fully explained, once again, by the presence of a
gravitational scalar which overcomes the galaxy's gravity past a
certain distance, else the gas would not ooze away like it does.

So I propose that it is gravity which accounts for the velocity
profile of radio jets and lobes: the material is simply falling away
from the galactic core source.

Eric's post is the kind of thing that brings out the usenet kooks, even
on a moderated group such as sci.astro.research, and I suspect that I'm
going to look like one of those kooks. Thirty-five years I proposed a
similar process, although not necessarily directly supportive of Eric's
idea, but which was at least congruent, in a dissertation that I never
finished. If that last statement isn't enough to get you to stop
reading, nothing will.

When I was in graduate school, I began three doctoral programs at the
same time, one in evolutionary ecology, a second in electrical
engineering/artificial intelligence and a third in galactic astronomy. I
finished the first two, but never completed the third, for a reason no
more complicated than life became busy. But the idea of the astronomy
dissertation has continued to haunt me since, and Eric's posting was
similar enough for me to inflict this posting on you.

The notion underlying the proposed dissertation was simple enough: it
was a phenomological taxonomy of galactic morphologies, one that
strongly suggested a mechanism promoting the galactic constructions:
that there are episodic mass expulsions from instable galactic nuclei
onto a co-rotating plane. The basic idea was that Sandage had the the
taxonomy of galaxies wrong. He organized his galaxies as a "tuning fork":

http://nedwww.ipac.caltech.edu/level...s/figure2.jpeg

My argument was that Sandage had his diagram wrong in two ways: the
tuning fork notion should be more properly collapsed into a single
linear sequence, and that he had the order of the galaxies backwards.
The single-armed "c" galaxies in Sandage's diagram are the outermost
forms, but they actually should be the closest to the ellipticals. The
ellipticals are galaxies in which, in my taxonomy, mass expulsions never
occurred. In the "c" forms, one episode of mass expulsion from an
instable nucleus did occur, but the initial conditions of the galaxy
were such that a second or third expulsion never happened.

If episodic mass outflows (as indicated by the bars in some galaxies)
were indeed occurring, then the proper evolutionary sequence should be:

E0 - E7 - SBc - Sc - SBb - Sb - SBa - Sa

In this linear evolutionary sequence, a collimated bar of low-velocity,
low-luminosity, near-laminar mass initially flows out from the galactic
nucleus until it reaches that point where whatever force is collimating
the bar can no longer be maintained against the torques imposed by the
ambient gas environment. At that point, the laminar flow shock
terminates into a chaotic burst of star formation, "writing" the
characteristic scythe-like pattern of stars onto the background gas as
the bar rotates. As the nucleus continues to rotate faster than the
background gas, the bar's star formation shock termination point leaves
in its wake an increasingly more diffuse, older population of stars
farther out on the scythe's tips.

NGC 1300 is a good as an illustration of this process as any:

http://www.celestiamotherlode.net/ca...Reinhard_F.jpg

or

http://tinyurl.com/l3lqd

.....although NGC 1300 is more weakly collimated than most barred
galaxies, possibly because it is nearing the end of its barred phase and
will "soon" perhaps collapse from an SBc form into a standard Sc galaxy.

Under this hypothesis, the direction of rotation of the galaxy is made
obvious by two phenomena: the wake of the shock termination point and
the dust lanes in the bars. The dust lanes are presumed to be a leading
edge phenomenon.

The question has been for some time whether the dust lanes represent
flow inwards, towards the galactic center, or outwards. This hypothesis
obviously argues for flow outwards, but so do the simple pictures of
galaxies. If you look at the image of NGC 1300, the dust lanes can be
reliably tracked back through the chaos of the scythe blades almost to
their tips. No imaginable physical mechanism could spontaneously
organize a dust lane to gather itself together far out in the blades,
flow inwards towards the bar, change its direction of flow 90 degrees
when it nears the tip of the bar, and then flow in towards the center of
the galaxy.

Once the current expulsion episode ends, the bar disappears, and thus
the galaxy's morphology moves the alternate side of the tuning fork for
a time. Because the first episodic expulsion left the local nuclear
neighborhood with a more dense medium, the second expulsion event,
should it occur, shock terminates earlier, inside of the radius of the
first, and the same occurs for the third, fourth, etc. events, should
they occur.

The galactic nucleus need not be absolutely stable in its orientiation
during its lifetime. If it were to wobble, the second or third mass
expulsions may not be co-planar with the first, and the various
expulsive "writings" onto the background would be tilted slightly one to
another, as they appear they might be in Andromeda:

http://www.akhtarnama.com/images/Andromeda%20galaxi.jpg

In the 35 years since I first worked on this thesis, several things have
been learned that were not known at the time:

o black holes in galactic nuclei were unknown at the time, but
supermassive blackholes are now believed to inhabit the nucleus of every
spiral galaxy, either as singles or multiples. At least there is now a
plausible source for the nuclear instability.

o barred galaxies were estimated to represent about 10% of the
population in 1970. That estimate is now closer to 75%, for either
galaxies with fully-formed bars or bar remnants.

o the rotation curves of the galaxies are now known to be
non-Newtonian. Indeed, they now appear as if they were written on some
large, unseen co-rotating plane.

In the intervening 35 years of once in a blue moon thinking about this
idea, and occasionally looking at galactic images, I've yet to see an
image of a galaxy that is inconsistent with this taxonomy, but then
again, we're highly tuned to see what we want to see in an image.

Wirt Atmar


Wirt Atmar, Ph.D.
President
AICS Research, Inc.
University Park, NM 88003-4691
(505) 524-9800
(505) 526-4700 fax



http://aics-research.com/research/

Wirt Atmar wrote:
The basic idea was that Sandage had the the
taxonomy of galaxies wrong. He organized his galaxies as a "tuning fork":

Hubble, actually, though Sandage (and others) did a lot of subsequent
work.

My argument was that Sandage had his diagram wrong in two ways: the
tuning fork notion should be more properly collapsed into a single
linear sequence, and that he had the order of the galaxies backwards.
The single-armed "c" galaxies in Sandage's diagram are the outermost
forms, but they actually should be the closest to the ellipticals.

The Hubble classification isn't based on whether the arms are single or
double. It is instead the ratio of "bulge" to "disk." Or nearly
equivalently "stars" to "gas." Ellipticals can have a bit of residual
gas (and dust as well), but there is no organized disk. Sc types have
a large disk and relatively small bulge, and irregulars have
essentially no bulge at all. This is perhaps illustrated best in
Spitzer/IRAC data (OK, I'm prejudiced!), where the 3.6 micron channel
shows the stars, and the 8 micron channel (with stars subtracted) shows
the dust. Pahre et al. (2004 ApJS 154, 235) Fig. 2 is a good example
of the quantitative dependence of the star to dust ratio on Hubble
type.

The presence or absence of a bar is a separate issue, and I don't think
bars are well understood even now. (I am not an expert on this and
welcome corrections!) However, whatever causes them, they are seen in
the _stellar_ density, whereas disks and arms are seen in the gas+dust
density.

ellipticals are galaxies in which, in my taxonomy, mass expulsions never
occurred.

Lots of ellipticals show jets. Cen A is a familiar example. M87 is
another.

Under this hypothesis, the direction of rotation of the galaxy is made
obvious by two phenomena: the wake of the shock termination point and
the dust lanes in the bars. The dust lanes are presumed to be a leading
edge phenomenon.

I don't see any evidence for that in the Spitzer data, but take a look
for yourself at Fig. 1 of the article cited above.

o black holes in galactic nuclei were unknown at the time, but
supermassive blackholes are now believed to inhabit the nucleus of every
spiral galaxy, either as singles or multiples.

Black hole mass is thought to be proportional to _bulge_ mass, not
either disk or total mass.

Steve Willner writes:

Wirt Atmar wrote:

My argument was that [Hubble] had his diagram wrong in two ways: the
tuning fork notion should be more properly collapsed into a single
linear sequence, and that he had the order of the galaxies backwards.
The single-armed "c" galaxies in [Hubble]'s diagram are the outermost
forms, but they actually should be the closest to the ellipticals.

The Hubble classification isn't based on whether the arms are single or
double. It is instead the ratio of "bulge" to "disk." Or nearly
equivalently "stars" to "gas." Ellipticals can have a bit of residual
gas (and dust as well), but there is no organized disk. Sc types have
a large disk and relatively small bulge, and irregulars have
essentially no bulge at all. This is perhaps illustrated best in
Spitzer/IRAC data (OK, I'm prejudiced!), where the 3.6 micron channel
shows the stars, and the 8 micron channel (with stars subtracted) shows
the dust. Pahre et al. (2004 ApJS 154, 235) Fig. 2 is a good example
of the quantitative dependence of the star to dust ratio on Hubble
type.

Yes. A good part of the confusion in my descriptions stems from my
talking to myself for so long. As you mention in your paper (Pahre et
al. 2004 ApJS 154, 235), any number of classifactory schemes have been
proposed over the years, including a trained neural network. These
various schemes have demonstrated reasonably good correspondence among
themselves, but all of these classifications were accomplished by using
gross morphological attributes, so that correspondence should not be a
surprise.

Hubble also used the terms "early" and "late" for his subcategory
classifications, but Sandage, in interpreting Hubble's notes after his
death, said that Hubble did not mean to imply an evolutionary sequence
by those appellations. Unfortunately, that's exactly what I want to do,

What I wish to emphasize in my taxonomy is an underlying mechanism, not
simply a measured ratio. In the end, I believe that this taxonomy too
will likely be roughly correspondent to the more standard
classifications, but in this scheme, the number of arms do matter.
Single-armed morphologies will be approximately equivalent to Sc
galaxies, double-armed with Sb, and larger numbered with Sa.

The fundamental notion underlying this revised taxonomy is that *all*
spiral galaxies either currently have a bar or have had one in their
past. Moreover, the bars represent an extraordinary event, the
large-scale expulsion of mass from the galactic nucleus.

In that regard, I put together a PowerPoint presentation last night to
explain the proposed mechanism as simply and as quickly as I could using
just a very few high-resolution images of the nearby galaxies. It's at:

http://67.41.4.238/bar-properties.ppt

The slide set is composed of three parts: (i) the presumed decay of a
bar using three extant galaxies as a proxy for computer animation, (ii)
an outline of the obvious properties of a bar, and (iii) the nature of
the bar should it persist for more than one nuclear revolution. All of
the images used are those of single mass-expulsion galaxies, and are
thus Sc-like.



The presence or absence of a bar is a separate issue, and I don't think
bars are well understood even now. (I am not an expert on this and
welcome corrections!) However, whatever causes them, they are seen in
the _stellar_ density, whereas disks and arms are seen in the gas+dust
density.

As I mentioned earlier, I first began thinking about this problem 35
years ago in preparation for a dissertation in astronomy which I never
wrote. At that time, barred galaxies were believed to comprise
approximately 10% of the population, and were considered "non-normal."
When the observed population of barred galaxies rose to approx. 50% of
the observed spirals in the 1980's/90's, there were mentions in the
literature that they should stop being called abnormal, as they were now
known to be as abundant as "normal" spirals. Barred galaxies now
represent 75% of the observed population, thus they should perhaps be
now called the normal form.

Regardless of what they're called, the bars are such an extraordinary
feature that any proposed mechanism of galaxy evolution that doesn't
accurately account for their presence and behaviors must almost
certainly be wrong.

Mechanisms promoting spiral structures are relatively easy to imagine,
and any number of processes have been proposed to explain the presence
of spirals (density waves, close approach perturbations, etc.), but
devising a reasonable explanation for the presence and nature of a bar
has not proven itself nearly to be as simple.

Nonetheless, as grandiose as it sounds, I believe that the bars are the
singular key to a proper understanding of galactic morphological evolutions.



ellipticals are galaxies in which, in my taxonomy, mass expulsions never
occurred.

Lots of ellipticals show jets. Cen A is a familiar example. M87 is
another.

Yes, I know. I was undecided 35 years ago and I remain undecided now as
to whether the jets in Cen A and M87 are a qualitatively different
phenomenon than the mass expulsions that I associate with the bars, or
whether they are a faint echo, a "peep", of a bar-like phenomenon that
was too weak to really get going.

My predisposition is to believe that the phenomena are unrelated, but
neither would I be surprised if that supposition were wrong, given, of
course, the fact that the main hypothesis is eventually proven correct.

Wirt Atmar

Wirt Atmar wrote:
As you mention in your paper (Pahre et
al. 2004 ApJS 154, 235), any number of classifactory schemes have been
proposed over the years, including a trained neural network. These
various schemes have demonstrated reasonably good correspondence among
themselves, but all of these classifications were accomplished by using
gross morphological attributes, so that correspondence should not be a
surprise.

You should separate the _method_ (human eye, neural network,
quantitative measure) from the _scheme_ (shape, color, light profile).
But your basic point is correct: existing schemes all agree. That
isn't a content-free conclusion. One could imagine that, for example,
stellar colors might not be correlated with gas/stars ratio or with
galaxy shape. The existence of such correlations is telling us
something about galaxy evolution.

Single-armed morphologies will be approximately equivalent to Sc
galaxies, double-armed with Sb, and larger numbered with Sa.

If by Sa/Sb/Sc you mean the standard classification, I am aware of no
evidence that Sa galaxies have more arms than Sc. You are, of course,
free to propose a different classification scheme, but you should avoid
using standard terminology if you mean something entirely different.

There are people who measure how many spiral arms different galaxies
have.

As I mentioned earlier, I first began thinking about this problem 35
years ago in preparation for a dissertation in astronomy which I never
wrote.

There has been rather a lot of progress in galaxy studies since then.
I agree with you that despite all the progress, bars are not well
understood. There are gravitational models that produce bars,
including their kinematics, but I don't think these are yet entirely
general. As I wrote earlier, I could be wrong about this.

Despite that, I think you will have a hard time with any hypothesis
that ellipticals evolve to become Sc galaxies. The typical elliptical
is 100% Population 2 stars. The typical Sc is 10% Pop 2, 10% gas, and
80% Pop 1 stars. What mechanism turns Pop 2 stars into Pop 1 plus gas?

Steve Willner writes:

Wirt Atmar wrote:

As you mention in your paper (Pahre et
al. 2004 ApJS 154, 235), any number of classifactory schemes have been
proposed over the years, including a trained neural network. These
various schemes have demonstrated reasonably good correspondence among
themselves, but all of these classifications were accomplished by using
gross morphological attributes, so that correspondence should not be a
surprise.

You should separate the _method_ (human eye, neural network,
quantitative measure) from the _scheme_ (shape, color, light profile).
But your basic point is correct: existing schemes all agree. That
isn't a content-free conclusion. One could imagine that, for example,
stellar colors might not be correlated with gas/stars ratio or with
galaxy shape. The existence of such correlations is telling us
something about galaxy evolution.

Yes, I very much agree. The correlations in colors, stellar ages, and
gas and dust ratios among the galaxy shapes are telling us something
quite profound about galactic evolution, and that's been something
that's been said for nearly a half century now, but by itself it is not
explanatory.

These correlations are nonetheless a pattern that strongly suggests an
underlying evolutionary process, that the galaxies are not just random
hodge-podge collections of attributes, but rather that there is a
relatively strictly predefined sequence to their evolution, whatever it
might be.



Single-armed morphologies will be approximately equivalent to Sc
galaxies, double-armed with Sb, and larger numbered with Sa.

If by Sa/Sb/Sc you mean the standard classification, I am aware of no
evidence that Sa galaxies have more arms than Sc. You are, of course,
free to propose a different classification scheme, but you should avoid
using standard terminology if you mean something entirely different.

Yes, I agree. My apologies. My terminology results from me talking to
myself too long.


As I mentioned earlier, I first began thinking about this problem 35
years ago in preparation for a dissertation in astronomy which I never
wrote.

There has been rather a lot of progress in galaxy studies since then.
I agree with you that despite all the progress, bars are not well
understood. There are gravitational models that produce bars,
including their kinematics, but I don't think these are yet entirely
general. As I wrote earlier, I could be wrong about this.

Despite that, I think you will have a hard time with any hypothesis
that ellipticals evolve to become Sc galaxies. The typical elliptical
is 100% Population 2 stars. The typical Sc is 10% Pop 2, 10% gas, and
80% Pop 1 stars. What mechanism turns Pop 2 stars into Pop 1 plus gas?

Let me apologize for not explaining the basic hypothesis more clearly.
Ellipticals, in my theology, don't evolve into spirals, at least not any
longer. They are the remnant protogalaxies for which the process of
evolving into "grand design" galaxies never began. Ellipticals are
"normal" galaxies, but for reasons of their initial conditions (which
are probably nothing more complicated than their initial masses and
angular momenta), never underwent the process of what I consider to the
central feature of galactic evolution: at least one large-scale,
collimated nuclear mass expulsion. As a consequence, 13 Ga later, they
are now composed solely of old, metal-poor Population II stars, and they
will remain this way for all time, barring a close approach or a
collision with another galaxy.

Centaurus A, which you mentioned earlier, is an elliptical that is most
likely a "transitional form" between the completely quiescent
ellipticals and the spirals, but only by accident. In this image, the
VLA's radio lobe map has been superimposed on an optical image of Cen A:

http://imgsrc.hubblesite.org/hu/db/1...s/full_jpg.jpg

The weak mass arms evident in the VLA data are undoubtedly the result of
the "recent collision" of an elliptical with a spiral, but the radio
arms appear to be too weak, too low mass, or are now perhaps too old, to
currently promote new (Pop I) star formation where they shock terminal
into the IGM.

Leaving the ellipticals aside, in the hypothesis I wish to promote,
those protogalaxies whose nuclei originally exceeded some minimum set of
conditions regarding initial mass and angular momentum, episodically
create a collimated mass expulsion, resulting in a bar. This expulsion
is astoundingly rigid along is axis, collimated presumably by some sort
of magnetic solenoid.

The nuclei of these galaxies exist in some sort of co-rotating frame of
unseen matter (hot gas, dark matter, etc.), but the nuclei are rotating
somewhat faster than the frame itself. When the large-scale mass
expulsion occurs, the bar rotates in lock-step with its nucleus, faster
than the co-rotating frame, at or near its nucleus' rotational speed.

Dragging the bar through the frame creates an obvious torque requirement
for the bar. When the torque requirement is exceeded at some distance
from the nucleus, the bar breaks and the internal mass of the bar, which
has up to now been flowing essentially laminarly outward through the
axis of the bar, shock terminates against the frame and creates regions
of new metal-rich, hot, young Pop I star formation.

During it's lifetime, the bar "paints" its new stars and dust lanes onto
the co-rotating frame. The properties of the frame are such that
surprisingly little dissipation of the "bar-written" arms appears to
occur over the 10+ Ga history of the galaxies.

We now know that the disks of the spirals rotate as a
non-Keplerian/non-Newtonian constant frame due to Vera Rubin's and
colleagues' measurements, but that wasn't known when I first starting
thinking about this 35 years ago. I said to myself then, "Self, if all
what I am telling you is true, then this too must be true, no matter how
radical it sounds." That it has proven to be true, I take to be a
significant validation, but it is of course not proof in and of itself
of the correctness of the general hypothesis. It's only satisfying.

If you have the time, look at the PowerPoint slides that I spent just a
few minutes preparing:

http://67.41.4.238/bar-properties.ppt

NGC 1300 is used as the protypical barred galaxy in the slides, simply
because we have such extraordinarily detailed images of it now, but also
because it's not rare. Whatever the initial distribution of masses and
momenta among the protogalaxies, most resulting spirals seem to have
inherited only enough "oomph" for one mass expulsion (one set of arms),
but a few galaxies do appear as if they have undergone one or several
more subsequent mass expulsions/bar formations during their lifetimes.

Each expulsion event is going to change the color, the age & metalicity
of the disc stars, the gas/dust ratios, and the disc/nuclear bulge
ratios in a predictable manner, thus the obvious correlations we
observe. Indeed, I would not be surprised if the galactic nuclei in the
most actively "armed" galaxies we now observe had not contracted from
their original masses and sizes, redistributing their initial mass out
into their discs, further altering those ratios.

Wirt Atmar

Steve Willner writes:

Wirt Atmar wrote:

As you mention in your paper (Pahre et
al. 2004 ApJS 154, 235), any number of classifactory schemes have been
proposed over the years, including a trained neural network. These
various schemes have demonstrated reasonably good correspondence among
themselves, but all of these classifications were accomplished by using
gross morphological attributes, so that correspondence should not be a
surprise.

You should separate the _method_ (human eye, neural network,
quantitative measure) from the _scheme_ (shape, color, light profile).
But your basic point is correct: existing schemes all agree. That
isn't a content-free conclusion. One could imagine that, for example,
stellar colors might not be correlated with gas/stars ratio or with
galaxy shape. The existence of such correlations is telling us
something about galaxy evolution.

Yes, I very much agree. The correlations in colors, stellar ages, and
gas and dust ratios among the galaxy shapes are telling us something
quite profound about galactic evolution, and that's been something
that's been said for nearly a half century now, but by itself it is not
explanatory.

These correlations are nonetheless a pattern that strongly suggests an
underlying evolutionary process, that the galaxies are not just random
hodge-podge collections of attributes, but rather that there is a
relatively strictly predefined sequence to their evolution, whatever it
might be.



Single-armed morphologies will be approximately equivalent to Sc
galaxies, double-armed with Sb, and larger numbered with Sa.

If by Sa/Sb/Sc you mean the standard classification, I am aware of no
evidence that Sa galaxies have more arms than Sc. You are, of course,
free to propose a different classification scheme, but you should
avoid using standard terminology if you mean something entirely
different.

Yes, I agree. My apologies. My terminology results from me talking to
myself too long.



As I mentioned earlier, I first began thinking about this problem 35
years ago in preparation for a dissertation in astronomy which I never
wrote.

There has been rather a lot of progress in galaxy studies since then.
I agree with you that despite all the progress, bars are not well
understood. There are gravitational models that produce bars,
including their kinematics, but I don't think these are yet entirely
general. As I wrote earlier, I could be wrong about this.

Despite that, I think you will have a hard time with any hypothesis
that ellipticals evolve to become Sc galaxies. The typical elliptical
is 100% Population 2 stars. The typical Sc is 10% Pop 2, 10% gas, and
80% Pop 1 stars. What mechanism turns Pop 2 stars into Pop 1 plus
gas?

Let me apologize for not explaining the basic hypothesis more clearly.
Ellipticals, in my thesis, don't evolve into spirals, at least not any
longer. They are the remnant protogalaxies for which the process of
evolving into "grand design" galaxies never began. Ellipticals are
"normal" galaxies, but for reasons of their initial conditions (which
may be no more complicated than their initial masses and angular
momenta), never underwent the process that I consider to the central
feature of galactic evolution: at least one large-scale, collimated
nuclear mass expulsion. As a consequence, 13 Ga later, they are now
composed solely of old, metal-poor Population II stars, and they will
remain this way for all time, barring a close approach or a collision
with another galaxy.

Centaurus A, which you mentioned earlier, is an elliptical that is most
likely a "transitional form" between the completely quiescent
ellipticals and the spirals, but only by accident. In this image, the
VLA's radio lobe map has been superimposed on an optical image of Cen A:

http://imgsrc.hubblesite.org/hu/db/1...s/full_jpg.jpg

The weak mass arms evident in the VLA data are undoubtedly the result of
the "recent collision" of an elliptical with a spiral, but the radio
arms appear to be too weak, too low mass, or are now perhaps too old, to
currently promote new (Pop I) star formation where they shock terminal
into the IGM.

Leaving the ellipticals aside, in the hypothesis I wish to promote,
those protogalaxies whose nuclei originally exceeded some minimum set of
conditions regarding initial mass and angular momentum, episodically
create collimated mass expulsions, resulting in the formation of bars.
This expulsion is astoundingly rigid along is axis, collimated
presumably by some sort of magnetic solenoid.

The nuclei of these galaxies are presumed to exist within some form of
co-rotating frame of unseen matter (hot gas, dark matter, ...), but the
nuclei are rotating somewhat faster than the frames themselves. When the
large-scale mass expulsion occurs, their bars rotate in lock-step with
their nuclei, faster than the co-rotating frame, at or near their
nuclei's rotational speeds.

Dragging these bars through the frame creates an obvious torque on the
bars. When the torque strength of the bar is exceeded some distance from
the nucleus, the bar breaks and the internal mass of the bar, which has
up to now been flowing essentially laminarly outward through the central
axis of the bar, shock terminates against the frame and creates regions
of new metal-rich, hot, young Pop I star formation.

During it's lifetime, the bar "paints" its new stars and dust lanes onto
the co-rotating frame. The properties of the frame are such that
surprisingly little dissipation of the "bar-written" arms appears to
occur over the 10+ Ga history of the galaxies.

If you have the time, look at the PowerPoint slides that I spent just a
few minutes preparing:

http://67.41.4.238/bar-properties.ppt

These few slides detail the further evolution of the bar.

NGC 1300 is used as the protypical barred galaxy in the slides, simply
because we have such extraordinarily detailed images of it now, but also
because it's not rare. Whatever the initial distribution of masses and
momenta among the protogalaxies, most resulting spirals seem to have
inherited only enough "oomph" for one mass expulsion (one set of arms),
but a few galaxies do appear as if they have undergone one or several
more subsequent mass expulsions/bar formations during their lifetimes.

Each expulsion event is going to change the color, the age & metalicity
of the disc stars, the gas/dust ratios, and the disc/nuclear bulge
ratios in a predictable manner, thus creating the obvious correlations
we observe. Indeed, I would not be surprised if the galactic nuclei in
the most active multi-armed galaxies we now observe had not contracted
from their original masses and sizes, redistributing their initial
central mass out into their discs, further altering those ratios.

Wirt Atmar