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Old 17-11-2020, 07:25 AM
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Weltevreden SA (Dana)
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The 'cinnamon bun' galaxy name isn't the only thing weird about it

NGC 12588 was a cosmic nobody till its image started showing up in SciTech Daily & all The Regular Suspects earlier today. Have any of you logged it, and what did you see?

So now that it's a somebody, what is it? It appears to have an unusual hexagonal morphology of 6 vestigial arms visible that emerge from a featureless surface only near the outer Lindblad resonance, where most gassy galaxies consist mainly of atomic hydrogen and shouldn't have young molecular HII clouds making scads of blue stars. It also appears to have a higher surface density in the 3:00 o'clock to 8 o'clock sector, possibly a remnant of ancient interaction with a galaxy not readily discernible here. This is a hard critter to track down—none of the papers in the 24 cited in Simbad provide any more than positional, proper/peculiar motion, and association data. The only published motion data is from 1988. No spectra available. The galaxy appears to have low H-alpha emission density and a marked absence of dust features. It could be an SO in mid-evolution between dusty spiral and featureless lenticular. If X-ray images were available we might see the telltale blue trail of ram pressure stripping. If it's an outlier member of the Perseus SSC (as its sky position suggests) it may be in rapid free-fall toward NGC 1275. However, the required velocity would have to have been imparted during a multi-body interaction in which 12588 was ejected at speed as the lowest-mass member. Its 2D sky position isn't its 3D position and there's no constraining distance data available. It might be one of the triple systems cited in KARACHENTSEVA V.E.1988, but that paper apparently hasn't been translated & in unavailable on ADS.

Any clues from you lads over there?



=Dana in S Africa
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Old 17-11-2020, 11:10 AM
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madbadgalaxyman (Robert)
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Hi Dana,
"long time no see".
That's in the UGC catalogue, not in the NGC.

The presence of two or three sub-systems within a galaxy, each of a distinctive age and kinematics and gas content, is not in itself unusual.

A good example of this is IC 5332, recently photographed by IIS members:
http://www.iceinspace.com.au/forum/s...d.php?t=186836

and there are many other galaxies which have this sort of "dual" internal structure, often with an old-aged (= 6-12 billion years old) disk that shows a spiral density wave, together with a young-aged blue-coloured disk structure which has semi-chaotic and open spiral structure.

In other cases, there seems to be a more profound decoupling between two (or even three, in some galaxies!) Different and Distinctive morphological+kinematic+age sub-components of a galaxy, which may well be indicative of a severe (ongoing, or in the past) perturbation.

A tremendous example of this is the Nearly Unclassifiable galaxy NGC 1316, which is Very Similar to an elliptical galaxy in its inner bright parts (albeit the inner region contains a small amount of dust, and also contains subtle low-contrast shells which are of such low contrast that they are hard to measure photometrically), but which also has a much much more Extended and Highly Peculiar component that extends vastly outside of the "elliptical-like" component.....Dr Kenneth Freeman of ANU wrote a paper indicating that this outermost part of N1316 is likely to be a kinematically-cold disk component which is currently (now.....) in the process of being formed in the outermost parts of NGC 1316.

( NGC 1316 has undergone more than one galaxy merger, in its history)
Here's a link to Mike Sidonio's superb pic of N1316::
http://www.iceinspace.com.au/forum/s...d.php?t=187524

But!.....the presence of two distinct and apparently-decoupled morphologies within the same extragalactic system does not have to be, in itself, evidence of a severe perturbation of a galaxy.

However, this sure is a weird (or at least "somewhat weird) galaxy that you have found , as the decoupling between the two evident sub-systems of UGC 12588, at least seems to be much much more evident than is usual in a normal spiral galaxy.

I will have a look , for comparison purposes , at my long-neglected database of 60 thousand galaxy images , as your idea that gas has been stripped from this galaxy by the effects of pressure from the inter-galactic or intra-GalaxyCluster medium has some merit.
But the separation between the two morphological sub-components of this interesting galaxy seems to be too profound for its appearance to be merely the result of gas being stripped from this galaxy. And why would the stripped gas have then formed itself into the pretty spiral pattern which is so very evident?

( one usually observes quite a lot of material which has been stripped from cluster galaxies;
for instance they Very Often lose lots of stars due to gravitational interactions between cluster members, and one does see modest amounts of HII patches that are part of the gas which has been lost by galaxies within galaxy clusters.)

Nonetheless, UGC 12588 may not(!!) actually be very far outside of the normal parameter space for galaxies, if (if!) it is actually a dwarf galaxy;
for instance, the inner component could be a somewhat dusty structure of intermediate-aged stars, and the outer component could simply be a Stochastic (= propagating)(by successive shocks to the interstellar medium) star formation process, leading to a Raggedy (entropic) spiral structure......
common enough in very large numbers of dwarf and low-luminosity galaxies.

Dwarf galaxies are Extremely! easily perturbed, by processes internal and external to a galaxy, so they can often seem to be extremely unusual, at least at first glance, because of the ease with which the interstellar medium, and the stellar body of such a galaxy, can be moved around by relatively modest inputs of energy.
And this galaxy has a Very low radial velocity of recession, in the CMB reference frame, so it is conceivably a nearby dwarf galaxy which is far in the foreground of the galaxy clusters that exist in this part of the sky.

It certainly looks a Whole Lot more normal when the HST image is viewed at large size and high resolution;
https://cdn.spacetelescope.org/archi.../potw2046a.jpg

But this is certainly a galaxy with two very distinct components, and I would very much agree with your proposition that both of the components have a very distinctive and very interesting look!!


P.S.
You are right that this galaxy might conceivably be on its "last gasp"when it comes to its ongoing star formation, leading eventually to the formation of a quiescent S0 morphology.

So, maybe......
here we are looking at the formation of a dwarf S0 galaxy?!?!?


P.P.S.
I do believe that we might conceivably find other galaxies that look like this, if we look in amongst the population of low-luminosity galaxies.

(As they are an incredibly diverse bunch.......

There are several Brand New (= recently posited) morphological classes of dwarf galaxies that I do not even know about, as my eyes have resolutely been pointed Down To The Ground for several years, especially towards fossils of the Ediacaran Geological Period!

So my suggestion is that we do try to assign a Hubble Class for this galaxy;
that is, to force this galaxy to fit into one of the existing (known) morphological classes of galaxy (e.g. Dwarf Sd/S0, dwarf S0, Sd, Sdm, Sm, BCD, etc), but then, if this doesn't work out, maybe to conclude that there is really and truly something weird going on here!!

But Orthodox galaxy classification can fail for dwarf galaxies.

(It was always based on galaxies of intermediate to high luminosity, though many are attempting to extend it to the dwarf end, with variable amounts of success)

I think some dwarfs could, for instance, be of a Mixed galaxy type of Irregular and also(!) Elliptical (E + Irr, E/Irr) . So maybe better to try to look at each galaxy as being the sum of various morphological components.

For instance, if we look in the SIMBAD galaxy database and then go to the ''Aladin Lite' image viewer , so as to view an image this galaxy, the PanSTARRS/Dr1 image appears to show an old (or oldish) stellar body of a roughly spheroidal appearance (though of course the 3-D morphology is highly uncertain) together with a highly-entropic (but organized) spiral structure.......= Hubble type E/Sd ?!?!?
(but of course Hubble himself knew little or nothing of the detailed morphology of these dwarfs. It was his disciples who extended the sequence to these systems)


[[[ Nonetheless, if this is a non-dwarf galaxy, then we would be looking at a different proposition!
( I do think it is likely to be a low luminosity galaxy)
]]]

Last edited by madbadgalaxyman; 17-11-2020 at 01:48 PM.
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Old 17-11-2020, 08:16 PM
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grad

Hey there, Dana!

The 'cinnamon bun galaxy' analogy holds!!

http://ps1images.stsci.edu/cgi-bin/p...00000&catlist=

Here is what appears to be a panel of several images of this galaxy, taken with successively longer wavelength bands, from blue light through to near-infrared light, left to right.

( Unfortunately, my knowledge of galaxy surveys stopped increasing fouir years ago, so I know little about this imaging survey of galaxies, and its images. But in defense of this "astro-dereliction"(and even of my abominable heresy against astronomy), I state that I now know a Whole Lot More about soil fungi and arthropods, and that I can give a good and extremely detailed account of the earliest evolution of animal life! )

Note how the shorter wavelength images (the leftmost panels) show that there is a very nice dusting of knotty blue Arm material, but that this blue knotty material becomes progressively less noticeable at longer wavelengths (going towards the right).
(Obviously, this is the population of OB stars within this galaxxy)

In the near-infrared images, more towards the right, which emphasize the older (probably the intermediate-aged) and mass-dominant stellar population of this galaxy, the relevant longer-wavelength image panels (which were taken in the i and z , photometric bands) show a nice and smooth (or , at least, a relatively smooth) distribution of stars,which is roughly circular in outline.

So the well-known idea of a dichotomy or a duality of structure, within a single galaxy, probably applies in this particular galaxy.
Thus my attempt at galaxy classification, yielding a Morphological Type of......Elliptical(or S0) plus(!) Sd(=late-type spiral), for this galaxy, seems to be a plausible way of looking at the morphology of this galaxy.

(actually, the sub-component of this galaxy with an old stellar population, more resembles a Dwarf Spheroidal galaxy)


Thus, madbadgalaxyman's tentative verdict on this galaxy is "indeed this is a very interesting system, but probably not perturbed in any significant way by external galaxies or influences"

Hmmm....
well, if I do get "a round tuit", I shall interrogate the fits files for this galaxy, in an endeavour to learn more about this interesting system.
But! I am Not at all in my prime for galaxy research at present, often spending much more time looking at soil samples in the microscope!

Last edited by madbadgalaxyman; 17-11-2020 at 08:37 PM.
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Old 18-11-2020, 08:53 AM
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The extreme Population I material in a galaxy ( dust, molecular hydrogen, OB stars, etc) behaves very differently from the mass-dominant component of old and/or intermediate -ages stars .

Particularly in dwarf galaxies, this young component can look highly chaotic and entropic and not entirely symmetric. This is "situation normal " for a star-forming dwarf galaxy .
Thus, the spiral structure in this galaxy is conceivably quite normal.
However, young Dana, as you are a bright boy, maybe you can disprove my hypothesis .

In a way, the "bun' of old stars that underlies the 'sprinkled cinnamon' of young stars, is more anomalous than the spiral component of this galaxy, as it looks to be a Dwarf Spheroidal Galaxy, that co-exists with a spiral galaxy ( or spiral component)

As Dana does , I suspect a low gas content and a low Star Formation Rate , in this galaxy .
So Dana's hypothesis that the pretty sprinkling of blue stars ( the Cinnamon!) is a transient phenomenon that is part of the settling down of this galaxy towards a quiescent state, has merit
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Old 18-11-2020, 05:28 PM
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The aforementioned images (in the webpage showing several images at various wavelengths) were from an initial survey that is associated with the ongoing PanSTARRS survey.

They are indeed in the photometric ugriz system.

Here is an attempt to display the g band image (approximately , this filter admits blue and visual wavelengths) at a realistic linear scale.
(We tend to lose the trend of changing surface brightness with increasing distance from the centre of a galaxy, in most displayed images)

Click image for larger version

Name:	g band_linear scale.jpg
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In this image, which tends to emphasize the younger material, such as the luminous OB stars in spiral arms, this galaxy looks pretty much like a normal dwarf spiral of type Sd or Sdm.
The spheroidal/elliptical component is not in evidence.
__________________________


Now here is the same image, this time displayed in a way that emphasizes some of the outer knots of blue supergiant stars, with this galaxy again looking pretty normal for a low luminosity spiral galaxy.

Click image for larger version

Name:	g band outer regins.jpg
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___________________________


Now here is the z band (near-infrared)(near 866nm) image of this galaxy, which tends rather to emphasize the space distribution of the older stars in a galaxy.
(the parallel lines are image artefacts)

Click image for larger version

Name:	Z band_.jpg
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ID:	268335

Voila!
The old stellar distribution looks like a completely different galaxy!

Indeed, if I only had this image, I might conceivably classify this as a dwarf spheroidal galaxy, albeit a dusty one with a certain amount of current star formation.
(not that I am in any way an authority on the classification of dwarf galaxies)


So you see what I mean about the duality or dichotomy of structure within a disk galaxy?


On balance, the visual appearance of this galaxy, in the standard blue/visual bandpass, is consistent with that of a spiral that is very late in the Hubble Sequence, but I don't know enough about these sorts of galaxies to say whether or not this particular galaxy is anomalous.

___________________________________ _________


Oh, and by the way, it is a commonplace for the near-infrared Hubble Class of a galaxy to be different from its Hubble Class as derived from Visual bandpass images.

Last edited by madbadgalaxyman; 18-11-2020 at 05:54 PM.
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Old 19-11-2020, 12:48 AM
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This image represents my attempt to enhance the blue knotty features and spiral arms, of this galaxy. I simply played around with the colour channels and the contrast , to make the blue features stand out more.
The original image is the Hubble Telescope one that is currently in the news, and I have tried to enhance its blue features without introducing morphology that does not exist in the real universe!
( I cannot guarantee that all of the structures in this version of the image are actually real.)

Click image for larger version

Name:	U12588_VplusI__w.HST__HIRES.jpg
Views:	25
Size:	197.8 KB
ID:	268339
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Old 20-11-2020, 07:45 AM
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Here is an HST image , taken with the F606W filter (approximately V band)("visual" wavelengths, so to speak)

Click image for larger version

Name:	U12588_F606W.jpg
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ID:	268376

The sprinkling of cinnamon (OB stars, chains of hot young luminous stars, spiral arms, etc.) is emphasized!
But , if there is any peculiarity in this galaxy, it would be the underlying spheroidal component, rather than the spiral structure.
____________________________

I am going to assume that this galaxy is no more than 10 megaparsecs (= 32.6 million light years) away, based on the degree of resolution of its brightest stars by HST and based on its redshift .

[[ I am assuming a ballpark estimate of its distance, based on its recession velocity, of 32 million light years. In other words, I am assuming this galaxy has a distance modulus of (m-M) = about 30 )

So, yeah, I do reckon that this extragalactic critter Really & Truly is a low luminosity Spiral Galaxy, as there exists a total (integrated) B magnitude of 13.93 in the Hyperleda database, and then we just apply the distance modulus to get an estimate of its Absolute Magnitude.
(nonetheless, the extant data on this galaxy is scant and of poor quality)

This seems to me to be the most parsimonious interpretation;
for I think that it is the safest bet (for now) to follow the limited available data; and thus to , at least initially, make the simplest interpretation.
(one which, of course, may later be modified)

But, Dana (my oracle on Stellar Astronomy), here is a question for you.....
are those actually resolved Red Supergiant stars in the HST image, as seen within the circular/spheroidal subcomponent of this galaxy?
( see the highest resolution version of the HST image at www.spacetelescope.org )
If so, this would be peculiar, as most of these dwarf galaxies have old or intermediate-aged spheroidal components.

In respect of your provocative hypothesis that this galaxy could have a very large peculiar velocity - that it is falling or orbiting at very high speed in the vicinity of a distant galaxy cluster -- I note that these 'peculiar' (non-cosmological) velocities of galaxy Infall and/or Orbit never seem to reach more than 2000-3000 kilometers per second, as measured spectroscopically (when we observe a galaxy from the direction of our line-of-sight).

So I conclude that this Interesting Extragalactic Critter is more likely to be a relatively nearby galaxy.

But I need to find more Hard Data on this galaxy!
......Not as easy as it used to be, as I have been entirely focused on the Ground Beneath My Feet for the last four years! (cataloguing soil arthropods, in particular!!!)

For, once upon a time, I knew (and used!) Every Source of galaxy data and galaxy imagery that exists in the whole entire known universe.....
but those days are well in the past.
( as for those galaxy Data Sources that are located somewhere in the Unknown Universe, who knows?)

Last edited by madbadgalaxyman; 20-11-2020 at 03:57 PM.
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Old 20-11-2020, 12:19 PM
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Karachentsev, who knows more about the "within 10 Megaparsecs" sample of galaxies than anyone else (having made a lifetime study of it!) gives the following parameters for this galaxy in his
''Updated Nearby Galaxy Catalog"
( see:
https://heasarc.gsfc.nasa.gov/W3Brow...istance_method
)

Apparent B (= "blue") magnitude = 14.11
(note: I wouldn't bet on this being particularly accurate. Could even be half a magnitude out. )

Distance = 7.9 Megaparsecs
(this distance measurement is based in its membership of a Galaxy Group which has other members with actual distance estimates)

B Absolute Magnitude (at the assumed distance) = -16.1
(note: this Absolute Magnitude estimate has to be regarded as merely an indicative figure for the luminosity of this galaxy......
The distance , and even the apparent B magnitude, both have considerable uncertainty. But the parameters of this galaxy are sufficiently well established to show that this is indeed a Small Galaxy that is very much in the foreground of the major clusters of galaxies )

(( The aforementioned catalog is one of the most useful, for relatively nearby galaxies.))


INFO ADDED IN EDIT::

Additional data on UGC 12588, taken from Tully's "Nearby Galaxies Catalogue"(1988)
(this catalogue is available at the ""VizieR" facility at the CDS Strasbourg website)

Hubble Type = type Sdm

Velocity distance (based on a Hubble Parameter of 75 km/s/Mpc)
= 9.3 Megaparsecs

Mass of HI (total mass of the neutral Atomic Hydrogen gas, in this galaxy)
, equals 2.88 x 10E8 solar masses.


madbadgalaxyman's commentary;
Tully's radio observations of the neutral Atomic Hydrogen gas in this galaxy, indicate that it contains a modest mass of neutral atomic hydrogen.
I would suppose that it is this gas that is forming the bright blue stars, rather than molecular hydrogen gas, as there is unlikely to be enough dust in this galaxy to shade the molecular hydrogen from starlight.
(low metallicity and low dust content, is a marker of a small galaxy!)

Last edited by madbadgalaxyman; 20-11-2020 at 03:59 PM.
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Old 21-11-2020, 05:42 AM
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Weltevreden SA (Dana)
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Robert, where have you been hiding?

Robert, you old fart, where the hell have you been hiding? I've been hoping to see your handle on this forum for years, wondering all this time what the dickens happened to you. And now that you DO turn up, what do I find? You've forsaken the glories of galaxies on high for ... looking down at your toenail fungus? Or whatever.

Could you do us all a great boon and look back up for awhile? I haven't had a halfway decent astronomical colloquy since you vanished into your Jurassic Park or whatever you call it. For heaven's sakes, my friend, lift thy eyes back to the skies. You'll hear bells pealing all over Australia, or at least the bells near Coonbarbaran or Melbourne. As I recall, you are from Melbourne, right? Well, that's at least one good thing I can say about the place.

Anyway, you got the picture. It's about time you showed up, and if it takes cosmic cinnamon buns to break you out of the woodwork, let's nibble on UGC 12588 and count its raisins.

Go to the HST website and download the 3.6 MB version of UGC 12588. Invert it to a inverted image of UGC 12588 extracted from the HST website 3.6 MB JPG. Inverting the image brings out structural features obscured by crowding in the HST 3.6 original. (This is why so many early astronomers made their notes directly on the glass plates of yore.) In the case of UGC 12588 one such feature is an apparent bar-like overdensity close to the 0°–180° axis. For another, there is no sign of a bulge or core/cusp central concentration. I tested both by fiddling with the image contrast settings and suspected what appears to be a coreless bar. So the next step up the learning ladder is a multiband ugriz and micron-to-microwave sweep. As Robert has shown us, optically, the PanSTARRS image set griz + y gives us a handful of mysteries to sort through. First, there no trace of a core or cusp-like centre—and also no bar. The pseudo-bar in the 606 nm HST image is possibly a processing artifact when the HST team reduced it from the HST 24.5 MB TIFF original. That leaves us with a diffuse cuspless core light profile. These are common in dwarf spheroidals, which is what that soft core does look like visually. A cross-check of the Aladin Lite image set basically confirms the PanSTARRS images, with the additional fillip that the DSS2/red image reveals a red, rather bright diffuse central luminosity with no traces of H-alpha activity. That too would be the signature of a dSph that hasn't formed new stars for multi-billions of years. Such a galaxy should also exhibit a large population of >2.2 solar mass red giants. If we invert the HST 24.5 MB TIFF using the same method, we find a central region peppered with a myriad of tiny low-luminosity dots—the low-mass red giant population we are looking for. Ergo, no doubt about it: this thing is dwarf spheroidal. So why the dickens do we have that expansive and very young starburst outside the corotation radius suddenly lighting up a huge reservoir of gas that has apparently snoozed for billions of years in an atomic hydrogen halo surrounding that dwarf, until now?

I have make confession here: My first post misidentified the diffuse boundary between the red starless centre and the active 6-arm spiral as 'outer Lindblad resonance' when I meant 'co-rotation circle'. My bad. Another wad of paper makes it to the wastebasket.

The term ‘co-rotation radius’ has real meaning here because in spiral galaxies it marks the point where the rotating mass of gas and stars on galaxy-wide scales moves as a unit body with respect to the forward velocity of a spiral arm density wave. Inside the corotation radius the stars move faster than the wave, which is why in most spirals the OB associations are on the inside curl of the spiral arm and reach full maturation by the time they cross the middle of the arm and go off as supernovae. That is why we find HII regions predominantly in the middle of spiral arms and not the outer edges. Inside a corotation circle it takes roughly 10 to 25 million years for a star-forming cloud complex to cross a spiral arm. At the corotation radius itself the wave and gas/stars move in step, so these regions are relatively quiescent. Lucky for us, because we live near the middle of the Milky Way’s co-rotation circle. Move us into the Scutum Cloud and we probably wouldn’t be here given the fulminous amount of shock turbulence, door slamming, yelling, boozing, and general mayhem that goes on in that cloud-dark of a household

UGC 12588’s starbursts are occurring outside the corotation radius, where the spiral waves move faster than the gas-star mass. We see evidence for this in UGC 12588’s spiral arms, where most of the bright O-B systems are near the front edge to middle of the arms—albeit with a couple of exceptions in the arm at 90° (west). For now we can overlook that anomaly because what we are really after is why so many stars have burst into life in such a rather brief recent era.

Something banged. What?

It would be awfully helpful at this point to have UV and X-ray bands which demonstrate copious low-mass protostar formation, and dust-revealing 3 to 6 micron bands which would reveal a long history of stellar outgassing. A lot of dust suggests multiple star-forming episodes; a dearth of it suggests we are looking a youngish initial outburst. That is pretty much what we are suspecting at this point—UGC 12588 is an old, lonesome dwarf spheroidal with a quiescent massive halo has suddenly come to life and we are keen to learn what happened. Alas for us, this galaxy has not been studied at high rez in the higher UV and X-ray bands (the Spitzer website draws a blank with this ID in the search box), nor in the dust-revealing micron bands that mm-to-micron systems like ALMA were built for.

That leaves us with the rest of the galaxy to explain and few tools to do it with. How do we reconcile a galaxy with a dSph light profile with a very recent >50 million year O-B star-forming burst in an unusual and hard to explain 6-arm spiral configuration if all we have is a simple visual-band image set?

To start with, large spiral arm systems usually presume a large core mass to anchor a density wave structure, plus a large gas mass to populate an entire galaxy arm structure in the sub-50 million year age bin of a large O-B starforming region. For the central mass, our earlier cross-check of the Aladin Lite image set basically confirmed the PanSTARRS results, with the additional fillip that the DSS2/red image revealed a red central luminosity with no traces of H-alpha activity (a sure sign of a dSph morphology). We already knew this, so no news there. Resorting to the higher authority of the HST 24.5 MB hi-rez TIFF, we see that OB formation does extend into the central region, albeit at less furious a rate. We also see the central region peppered with a multitude of low-mass red giants, as one would expect in a middle-aged dSph. Even at this high a resolution the featureless matte of a dSph is unmistakable—but so is the very young blaze of rapid-onset star formation across the entire galaxy.

Back to Square One, then: how does a multi-billion year old quiescent galaxy hold onto enough gas reserve to suddenly burst forth into a youngish spiral with 3 times the radius and perhaps half the mass of the old galaxy? Moreover, what happened to spontaneously initiate this level of star formation? UGC 12588 exists in near isolation in the outskirts of the Local Group. The WikiSky field of this galaxy shows just how lonely it is out there. There just ain't nothin' to hit out on those realms of nowhere in particular. Can’t go Boom without a fuse.


This post truncated here due to IIS length limits. Continuation in following post ...
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Old 21-11-2020, 05:48 AM
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Weltevreden SA (Dana)
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Robert, where have you been hiding?

Robert, you old fart, where the hell have you been hiding? I've been hoping to see your handle on this forum for years, wondering all this time what the dickens happened to you. And now that you DO turn up, what do I find? You've forsaken the glories of galaxies on high for ... looking down at your toenail fungus? Or whatever.

Could you do us all a great boon and look back up for awhile? I haven't had a halfway decent astronomical colloquy since you vanished into your Jurassic Park or whatever you call it. For heaven's sakes, my friend, lift thy eyes back to the skies. You'll hear bells pealing all over Australia, or at least the bells near Coonbarbaran or Melbourne. As I recall, you are from Melbourne, right? Well, that's at least one good thing I can say about the place.

Anyway, you got the picture. It's about time you showed up, and if it takes cosmic cinnamon buns to break you out of the woodwork, let's nibble on UGC 12588 and count its raisins.

Go to the HST website and download the 3.6 MB version of UGC 12588. Invert it to a inverted image of UGC 12588 extracted from the HST website 3.6 MB JPG. Inverting the image brings out structural features obscured by crowding in the HST 3.6 original. (This is why so many early astronomers made their notes directly on the glass plates of yore.) In the case of UGC 12588 one such feature is an apparent bar-like overdensity close to the 0°–180° axis. For another, there is no sign of a bulge or core/cusp central concentration. I tested both by fiddling with the image contrast settings and suspected what appears to be a coreless bar. So the next step up the learning ladder is a multiband ugriz and micron-to-microwave sweep. As Robert has shown us, optically, the PanSTARRS image set griz + y gives us a handful of mysteries to sort through. First, there no trace of a core or cusp-like centre—and also no bar. The pseudo-bar in the 606 nm HST image is possibly a processing artifact when the HST team reduced it from the HST 24.5 MB TIFF original. That leaves us with a diffuse cuspless core light profile. These are common in dwarf spheroidals, which is what that soft core does look like visually. A cross-check of the Aladin Lite image set basically confirms the PanSTARRS images, with the additional fillip that the DSS2/red image reveals a red, rather bright diffuse central luminosity with no traces of H-alpha activity. That too would be the signature of a dSph that hasn't formed new stars for multi-billions of years. Such a galaxy should also exhibit a large population of >2.2 solar mass red giants. If we invert the HST 24.5 MB TIFF using the same method, we find a central region peppered with a myriad of tiny low-luminosity dots—the low-mass red giant population we are looking for. Ergo, no doubt about it: this thing is dwarf spheroidal. So why the dickens do we have that expansive and very young starburst outside the corotation radius suddenly lighting up a huge reservoir of gas that has apparently snoozed for billions of years in an atomic hydrogen halo surrounding that dwarf, until now?

I have make confession here: My first post misidentified the diffuse boundary between the red starless centre and the active 6-arm spiral as 'outer Lindblad resonance' when I meant 'co-rotation circle'. My bad. Another wad of paper makes it to the wastebasket.

The term ‘co-rotation radius’ has real meaning here because in spiral galaxies it marks the point where the rotating mass of gas and stars on galaxy-wide scales moves as a unit body with respect to the forward velocity of a spiral arm density wave. Inside the corotation radius the stars move faster than the wave, which is why in most spirals the OB associations are on the inside curl of the spiral arm and reach full maturation by the time they cross the middle of the arm and go off as supernovae. That is why we find HII regions predominantly in the middle of spiral arms and not the outer edges. Inside a corotation circle it takes roughly 10 to 25 million years for a star-forming cloud complex to cross a spiral arm. At the corotation radius itself the wave and gas/stars move in step, so these regions are relatively quiescent. Lucky for us, because we live near the middle of the Milky Way’s co-rotation circle. Move us into the Scutum Cloud and we probably wouldn’t be here given the fulminous amount of shock turbulence, door slamming, yelling, boozing, and general mayhem that goes on in that cloud-dark of a household

UGC 12588’s starbursts are occurring outside the corotation radius, where the spiral waves move faster than the gas-star mass. We see evidence for this in UGC 12588’s spiral arms, where most of the bright O-B systems are near the front edge to middle of the arms—albeit with a couple of exceptions in the arm at 90° (west). For now we can overlook that anomaly because what we are really after is why so many stars have burst into life in such a rather brief recent era.

Something banged. What?

It would be awfully helpful at this point to have UV and X-ray bands which demonstrate copious low-mass protostar formation, and dust-revealing 3 to 6 micron bands which would reveal a long history of stellar outgassing. A lot of dust suggests multiple star-forming episodes; a dearth of it suggests we are looking a youngish initial outburst. That is pretty much what we are suspecting at this point—UGC 12588 is an old, lonesome dwarf spheroidal with a quiescent massive halo has suddenly come to life and we are keen to learn what happened. Alas for us, this galaxy has not been studied at high rez in the higher UV and X-ray bands (the Spitzer website draws a blank with this ID in the search box), nor in the dust-revealing micron bands that mm-to-micron systems like ALMA were built for.

That leaves us with the rest of the galaxy to explain and few tools to do it with. How do we reconcile a galaxy with a dSph light profile with a very recent >50 million year O-B star-forming burst in an unusual and hard to explain 6-arm spiral configuration if all we have is a simple visual-band image set?

To start with, large spiral arm systems usually presume a large core mass to anchor a density wave structure, plus a large gas mass to populate an entire galaxy arm structure in the sub-50 million year age bin of a large O-B starforming region. For the central mass, our earlier cross-check of the Aladin Lite image set basically confirmed the PanSTARRS results, with the additional fillip that the DSS2/red image revealed a red central luminosity with no traces of H-alpha activity (a sure sign of a dSph morphology). We already knew this, so no news there. Resorting to the higher authority of the HST 24.5 MB hi-rez TIFF, we see that OB formation does extend into the central region, albeit at less furious a rate. We also see the central region peppered with a multitude of low-mass red giants, as one would expect in a middle-aged dSph. Even at this high a resolution the featureless matte of a dSph is unmistakable—but so is the very young blaze of rapid-onset star formation across the entire galaxy.

Back to Square One, then: how does a multi-billion year old quiescent galaxy hold onto enough gas reserve to suddenly burst forth into a youngish spiral with 3 times the radius and perhaps half the mass of the old galaxy? Moreover, what happened to spontaneously initiate this level of star formation? UGC 12588 exists in near isolation in the outskirts of the Local Group. The WikiSky field of this galaxy shows just how lonely it is out there. There just ain't nothin' to hit out on those realms of nowhere in particular. Can’t go Boom without a fuse.


This post truncated here due to IIS length limits. Continuation in following post ...
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Old 21-11-2020, 06:01 AM
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Weltevreden SA (Dana)
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Continuation of Dana in S Africa post re. UGC 12588

... Can’t go Boom without a fuse ...


If UGC's enigmatic mixed-morphology structure wasn't pain enough in the neck as it is, its UGC classification rubs salt into it. There’s no PGC cross-classification, and most PhD theses use PGC classifications because of their positional accuracy. All the 24 Simbad citations referencing this galaxy are membership identity papers, not a galactic assembly studie. They don't address the question of how dwarf galaxies can hold on to huge gas reserves in their halos until some impetus like a swerve-by shock or acoustic wave from a void-to-filament turbulent infall triggers the kind of rapid-onset formation we seem to see in UGC 12588.

My best guess at this point is that UGC 12588, traveling at about 400 km/sec as part of a local density field, encountered one or more of the multitude of high-mass atomic hydrogen clouds known to inhabit the Local Group and Andromeda M31 dark matter haloes. Such clouds are not rare, but receive scant notice because of their extreme low luminosity in the 21 cm band and absence of any other markers such as dust density or CO emission. They lack oomph in our world where oomph is usually what gets PhD students’ attention via the beaming approval of their advisors

One analogous situation does come to mind: the dSph IC 1613, which coasted along placidly in the LG outskirts for 10 billion years until about 150 million years ago it encountered a succession of 2 and possibly 3 massive atomic hydrogen clouds that may have been primordial overdensities that were never shocked into free fall to become star-forming molecular clouds. IC 1613’s outer H1 halo sideswiped the first of these between 100 and 150 million years ago, then more abruptly into the second and possibly a third. That is why we see IC 1613’s distantly offset ferocious HII collapse fronts some 6 kpc from the old dSph core. Those collisional shocks in turn triggered secondary collect-and-collapse shocks closer to the IC 1613 core, which is why the galaxy today has its messy dual-morphology appearance.

If you want to know how common or not-common these oddball dwarf spheroidal morphologies (and therefore histories) can be, check Dan Weisz's 2014 paper, Fig. 2.

My current sheet of paper awaiting the wastebasket says that the UGC 12588 chance interaction with a primeval remnant cloud occurred as a pass-through direct- or near-direct collision. That would also explain the somewhat lopsided density differences between the 2nd and 4th quadrants as we look at it. For an example of head-on cloud-galaxy collisions, see this simulation from the CLUES Project.

Nice theory. I wonder if it's true.

Over to you, Mr. Lang ...



And hey, stick around, OK?

=Dana in S Africa
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Old 21-11-2020, 06:48 AM
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Ha ha!

Pungent and Powerful and Provoking Prose, as usual, from Mr Dana!
Incidentally, you mention that I am now stuck somewhere in Jurassic Park, and that consequently I am apparently unwilling to look up into the sky;
but I note that I am actually not that interested in the Jurassic Period.

Look up the North Pole Dome geological structure and The Strelley Pool Formation, in the Pilbara of Western Australia, some 3.5 billion years ago, and you will find one of the two places and times that I most commonly hang out in , looking for clues as to the origin of life on Earth, and as to complex and eventful co-evolution of the Earth Environment and its biota.
(by the way, this particular geological formation has become a "no go zone" for non-professional palaeontologists such as myself, due to its scientific importance. So I am combing the rocks of W.A. and the N.T. to find a site that is not so well defended by the pros)

The other place that I most love to walk around in, is the earliest part of the Ediacaran Geological Period, looking for clues as to the origin and Very earliest evolution of the Metazoans.
( indeed, I have discovered my very own personal Ediacaran Fossil Site (!) in Oz, which I will not reveal even when subjected to torture, as it is not crawling with hostile and aggressively defensive professional palaeontologists, as is that very famous site in the Flinders Ranges)

So, just maybe, you are more than a little 'over the top' in your commentary about me, for I think it is true to say that my intellect always goes where my curiosity leads, and my curiosity has lead me to exploring (in great detail) some Interesting and Mysterious and Extremely Complex issues connected with various signal events in the co-evolution of the Earth's biota and bio-geo-chemical-atmospheric systems.

And what's so wrong about following one's curiosity?

Hmmmm.....I perceive that you feel that I have "forsaken" something, but in my defense I will say to you that I think I find sufficient interest and intellectual stimulation, and a powerful sense of discovery and of widening vistas, in my current intellectual preoccupation.
So I think it more important that one continues on in the spirit of that Holy Curiosity so prized by Einstein, as there are so very many mysteries to explore, in the heavens and on the Earth.

cheers, Robert
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Old 21-11-2020, 08:37 AM
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The implication of your (seemingly) dismissive attitude to the sciences that I currently chase, at least seems to be that they are somehow less worthy than astronomy and less interesting than astronomy.

I have always read very many papers in many other sciences apart from astronomy, and currently attend graduate-level lectures in neurobiology and molecular biology, so I am well qualified to opine that there do indeed exist other sciences which are as interesting as astronomy!

Robert

P.S. I can quite understand intellectual arrogance, indeed I tolerate it very well, in people that are as bright as Dr Dana. For it must surely be that these types of people actually do have a justifiable intellectual pride. But the flipside of this is the less admirable quality of scorn.
_________________

ADDED IN EDIT
Your assertion of the primacy of the science of astronomy is undoubtedly the viewpoint that one should get from an astronomer! But these complex arguments about which of the sciences is the most grand and beautiful and complex and interesting and significant , tend to go on forever .
So, suffice it to say that there are extremely interesting and beautiful and fiendishly complicated problems to solve in each and every one of the sciences
( But I note the familiar disparagement of mycology and phycology in your post)
__________

P.P.S.
I haven't actually lost interest in astronomy, as evidenced by this mugshot of Yours Truly about to use his 25x100 Binos to chase down some RCW nebulae.
Click image for larger version

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I recently got two 6 inch Refractor tube assemblies, with a view towards building a pair of 6 inch binoculars, so as to expand these visual studies of southern HII regions!

Last edited by madbadgalaxyman; 22-11-2020 at 07:29 AM.
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Old 22-11-2020, 08:38 AM
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Weltevreden SA (Dana)
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My comments were made in loving joy at seeing your name back on this forum, writing as vividly and deeply informed as before. I apologise that they offended.
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