Our Galaxy - Structure & Evolution - recent review

[madbadgalaxyman]

Here is a recent review paper, by Professor Kenneth C. Freeman of ANU, about the structure and evolution of our own Galaxy:

137456


Cheers,
Bad Galaxy Man

[Weltevreden SA]

It's exciting to see yet another method of verifying a huge body of stellar data at accuracies and extensibilities hardly dreamed of a decade ago. Here's a handy arXiv paper (http://arxiv.org/abs/1303.1957v1) to understand how ASM (accepted acronym for astroseismology?) translates into quanitifiable content. See also Astroseismology.org (http://www.asteroseismology.org/) for a close look at the science. When we think of red giants, about the last thing we'd expect out of those soft, diffuse, flaring stellar surfaces driven by a rapid-rotation dynamo beneath, would be reliable seismic signals. HERMES is a very valuable Aussie addition to advancing the field. Congrats to Mr. Freeman and the folks at AAT. Must make you all proud. And thanks to Robert for bringing Mr. Freeman's paper to us. =Dana

[madbadgalaxyman]

Dana,

Here is a bit more about Ken Freeman.
He has little name recognition in Australia, so I remarked to him once that if he was as good at cricket as he is at astronomy, he would be a household name in Australia.

Dr Kenneth C. Freeman is, in every way, comparable to any of the great extragalactic astronomers of the past.
Some of his recent papers, e.g. on NGC 1316 (arxiv: 1201.6010), come close to actually understanding galaxy formation and evolution, which is more than can be said for most of the other extragalactic astronomers!

Now in his early 70s, it seems possible that Dr Freeman will soon be turned into an "emeritus", which is bizarre and unfair, as he is still extremely scientifically productive.

I like Dr Freeman, as he is something of an "old school" gentleman, polite and slightly self-effacing, who is happy to answer some of my questions about galaxies.
Fortunately, there is no need for Ken to feel, like some other professional astronomers do, that I have no business (as an amateur astronomer) being an expert on galaxy morphology, because he knows gigantically more about galaxies than I do.

Ken Freeman is regarded as something of a renaissance man in astronomy, due to the fact that he has made major contributions in many and diverse areas:
- observational astronomy, and also theoretical astronomy
- Milky Way structure and evolution
- stellar astronomy
- disk galaxies and their structures
- bar structures, their evolution and dynamics
- the study of dark matter
- the structure and evolution of elliptical galaxies
- the evolution of galaxies

Best regards,
Robert

[Weltevreden SA]

Wow, Robert, thanks again for the leads to Mr. Freeman's papers. You're certainly spot-on about his stature in astrophysics in general and stellar pops in particular. I looked him up on The Usual Suspects (arXiv, IOP, Simbad & pals) and was delighted to see he's done major and very recent research on our MW bulge. A fortuitous find for me, as I'm in the middle of reading up on the bulge globulars & their metals/distribution. About 10 days ago we had several really good nights over here. I gave NGC 6256, 6380, Ton 2, and HP1 a shot, and was delighted to bag all in one night. N6256 has been one of my favorites for a long time because my 180mm and 200mm can resolve about 10-15 right at the edge of seeing (vm14.5 - 15.5). It's a grand sight: the higher the power the less the faint subluminal glow and the more the specks. Now, armed with Mr. Freeman's bulge data, I can better put these and other bulge globulars in the same picture. A fun winter project will be to log all the bulge globs and then go back to read his papers again.

I can see why he's so keen to ferret astroseismology data out of the red clump stars there. At metallicities apparently falling into two pops of [Fe/H] < -0.5 and + 0.15, these RGB clumps point to the bulge having a much more complex history than suspected. Harder data on the borders of those stellar pops will be most welcome in his group.

I wonder what software they use to weed out IR and speckle chatter in astroseismology involving such remote and dense fields. I always thought ASM was useful to only about 1 or 2 kpc out and relatively nondense fields.

=Thanks again, Dana

[madbadgalaxyman]

If anyone could solve the problem of how galaxies form, it would be Dr Freeman, as his knowledge is broader than that of the typical extragalactic astronomer. You would be surprised how overspecialized some of these people are.

[madbadgalaxyman]

Dana,
do you know the globular cluster catalog of Bill Harris?
He has been obsessed with globulars throughout his long professional career, and his catalog is quite up-to-date

Here is the link:

http://physwww.mcmaster.ca/~harris/mwgc.dat

[Weltevreden SA]

Thanks for the reference, Robert. I use the Harris catalog to look up data on GCs I observe, e.g. HB magnitude to determine if the same-magnitude specks I see are really cluster members, and extinction to explain why a large-diameter GC in the eyepiece is so faint in my eye. N6366, 5466, 6380, & 6256 are so reddened they have the curious property of resolving into individual stars at small exit pupils, while losing their glow completely. N5053's size, absolute magnitude, and HB magnitude is not much different than nearby M53's, yet it can be impossible in any but the clearest air (in scopes that I have, anyway) while M53 is easily resolved.

The Harris catalog provides much data, but no images or CMDs. I fill in that info using Marco Castellani's (http://gclusters.altervista.org/) website. He really keeps it up to date: little-visited GCs like te Djorgovskis and Haute Province 1 are there. I'm impressed by how many 'amateurs' and semi-pros go to such enormous effort to collect and update info that very few will use on serious projects. Unsung heros, the whole lot.

Re Dr. Freeman and his plans to do astroseismology on Galactic bulge stars, this paper (http://arxiv.org/pdf/1304.6084v1.pdf) just showed up on arXiv to demonstrate where Dr. Freeman's info might shed light (literally) on some problem areas. The 'boxy bulge' has had astronomers devising explanations for quite awhile now. The current one is two distinct disrupted dwarfs that came in from mid latitudes above the galactic plane about a Gyr apart. I still wonder how Dr. Freeman and associates can weed out the signal-to-noise chatter from atmospheric scintillation close by and the myriad filaments of gas and dust lying between us and the bulge. With metallicities, filtration is affected similarly across the spectrum, but I wonder how reliable an astroseismic signal will be when so many waveforms from so many stars are so tightly packed across a box of even a few arcsecs.

Thanks again for the tips & links. We're all grateful for the many references you provide. =Dana

[madbadgalaxyman]

[QUOTE=Weltevreden SA;969896]

The Harris catalog provides much data, but no images or CMDs. I fill in that info using Marco Castellani's (http://gclusters.altervista.org/) website. He really keeps it up to date: little-visited GCs like te Djorgovskis and Haute Province 1 are there. I'm impressed by how many 'amateurs' and semi-pros go to such enormous effort to collect and update info that very few will use on serious projects. Unsung heros, the whole lot.

Re Dr. Freeman and his plans to do astroseismology on Galactic bulge stars, this paper (http://arxiv.org/pdf/1304.6084v1.pdf) just showed up on arXiv to demonstrate where Dr. Freeman's info might shed light (literally) on some problem areas. The 'boxy bulge' has had astronomers devising explanations for quite awhile now. [QUOTE]

You obviously know and understand globular clusters much better than the typical advanced amateur astronomer. Keep on looking at this data, as I am sure you will find something interesting, anomalous, or unusual! A lot of things are discovered simply by prolonged brooding about data.
(e.g. I have had some definite success finding some unusual galaxy morphology, to the degree that it has been thought worthy of further investigation by professional astronomers. Obviously, galaxy morphology and classification is the area where I have detailed knowledge)

Apparent Bulges, as observed in two-dimensional images of disk galaxies, are not necessarily spheroidal in shape, and even where they are spheroidal, they can be either oblate spheroids or they can be prolate spheroids (or even triaxial spheroids!).

Some so-called 'bulges', for instance, while looking like strong central brightenings that are observed in a face-on galaxy, actually turn out to be planar structures that are essentially a phenomenon of the central part of the planar disk of a galaxy;
this sort of inner structure is called a pseudo-bulge. (e.g. NGC 6946 and M101 do not have real bulges, as the central bright part of the galaxy is simply an extension of the disk, inwards). (It looks to me like the recent image of NGC 2997 in our imaging forum shows a pseudo-bulge or spiralling inner-disk, which is perhaps(?) superposed on a small 'classical' spheroidal bulge)
(as we know from the stellar population concept, several different kinematic, structural, and age, components can be superposed in a single part of a galaxy, so things can get very complex)

Three-dimensional Bulge Shape and the actual bulge size cannot be determined using old-fashioned qualitative methods such as Hubble classification, but instead require detailed modelling of isophotes, mass distribution, stellar orbits, etc. (many of the bulge prominence estimates made using visual galaxy classification turn out to be entirely wrong, for technical reasons which I won't go into!)

Ken Freeman, Francois Combes, Martin Bureau, and other workers such as Ron Buta and David Block, have found, on kinematic grounds, that a bar structure, when seen in an edge-on galaxy, looks like a Boxy or Boxy/X-shaped bulge. When they say there is a 'boxy/X-shaped, or peanut shaped' bulge, there exists a co-existence of an X-shape and a box (or peanut) shape in the observed two-dimensional bulge morphology that is seen in an image of a galaxy.

On the other hand, very large examples of boxy/x-shaped bulges have been explained as resulting from merger or cannibalization of galaxies.

Small boxy bulge examples:
The Milky Way, and also here is a photo of NGC 5746....
137878

Boxy/X-shaped bulge example:
NGC 3628 (optical image, and an NIR image)
137879
137880
Note that the extreme extensions of the arms of the 'X' make the overall structure to seem very extended indeed; a challenge for theorists to understand. Is the 'X' actually a bulge at all?

Large Boxy/X-shaped bulge example :
NGC 6771
137881
This is a common S0 galaxy morphology in some galaxy cluster environments, though it is not very familiar in the local population of bright galaxies. Some people would call this bulge peanut-shaped.

[Weltevreden SA]

Robert, you've probably seen this Simmons 2012 paper re. SMBH activity in bulgeless AGNs, but if other IIS folks haven't and are interested, here's the link (http://arxiv.org/abs/1207.4190). Sometimes I need a night-long eyepiece session just to clear the clutter of what's going on down here. =Dana