[Widdekind]

Cosmological computer simulations show, that large 'mother-ship' galaxies are accompanied by fleets of 'support craft' galaxies:

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Very high resolution simulations, of dark matter, predict that galaxies, such as the Milky Way, should be accompanied by thousands of lower-mass dwarf galaxies, buzzing around them, like bees around a hive. Although the Milky Way does have a few dwarf companions, they are far fewer than the simulations predict (Geach. The Lost Galaxies in Scientific American (May 2011), p.53).

And, indeed, local spiral galaxies have 100-500 GCs, and elliptical super-galaxies have over 10 thousand. Interpreting GCs, as 'mini-dwarf galaxies', goes far toward rectifying simulations w/ observations.

If GCs typically mass , then, by the 0.1% rule, GCs should swarm around central BHs with masses of . According to the M-sigma relation:

such systems should show velocity dispersions of order 4-6 km/sec. Is that accurate? Do GCs obey galactic laws?? According to Scarpa (2007 AD), "all [Globular] Clusters studied so far do behave like galaxies".

[Widdekind]

Globular Clusters obey galaxy scaling laws:

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Galactic globular clusters show tight correlations between velocity dispersion, luminosity and a physical scale, as expected from the Virial Theorem... These correlations are analogous to the fundamental plane correlations for elliptical galaxies...

New data for old LMC globular clusters show... global velocity dispersions range from 15 to 25 kms^-1 . These values fall almost perfectly on the extrapolation of the best Galactic cluster relation sigma ~ L^1/2. The validity of this relation is, therefore, extended to brighter globular clusters. This indicates similarities, in terms of structure and mass-to-light ratio, between the NGC 5128 and the Galactic globular clusters. Using the Galactic relation to estimate the absolute magnitude from the velocity dispersion, a distance modulus can be derived for each NGC 5128 globular cluster. Their average provide a NGC 5128 distance modulus consistent with the recent determinations from planetary nebula luminosity function or surface brightness fluctuation ( Dubarth (1994)).

source: Mordechai Milgrom. Ninety-five percent of the universe has gone missing, Or has it? in: Does Dark Matter Really Exist (Scientific American Special Report), p.2-ff. Also available online.

Addendum: galaxy scaling laws reflect origin of observed brightness in column density along LOS

According to Geach (2011), over half of all baryonic conventional matter, across our Cosmos, is so diffuse (optically thin) that it is, as yet, non-visible.

central BH masses, in GCs, range from One Hundred - Ten Thousand solar masses

Widdekind, on 24 April 2011 - 10:40 PM, said:

...If GCs typically mass ...

According to Rejkuba (2007 AD):

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masses range from , typical of Galactic globular clusters, to , similar to more massive DGTOs and nuclei of dE,N galaxies

Such implies central BH masses ranging from , and velocity dispersions ranging from .

This post has been edited by Widdekind: 25 April 2011 - 11:14 PM

[Widdekind]

Galactic growth-spurt (video):

attempt to understand Geach (2011) & galactic dark matter

The Inter-Galactic Medium (IGM) is filled with a diffuse, ultra-low surface-brightness, as-yet-un-human-detected gas, which accounts for half of all baryonic matter currently expected to exist (Geach (2011)). Now, the Milky Way galaxy resides, amidst a 'concentrated clump' of that diffuse matter. And, at the galactic core -- even as with Globular Clusters -- the visible matter, of stars with some gas & dust, can account, for the gravity, inferred from the motions of that matter (PPs). Yet, the visible matter component, of field stars & Globular Clusters, decreases in density rather rapidly with radius (); whereas, the inferred dark matter decreases much more slowly with radius () (Carroll & Ostlie. Intro to Mod. Astrophys., p.928-ff).

Thus, the galactic mass-to-light ratio, increases substantially, with increasing distance, from the galactic core. And, thereby, that ratio rises, from near nothing at the galactic core, to large values, approaching the invisible 'infinity' of the IGM, towards the periphery. And so, it may be possible, to 'connect' the two models, by envisioning the visible Milky Way galaxy, as residing inside a 'clump' of diffuse IGM, whose center has been evacuated, by the conversion of those baryons, into stars, but whose periphery remains un-converted, primordial, IGM. If so, then the Milky Way galaxy may exist inside a diffuse 'shell' of (un-converted baryonic) dark matter:

[Widdekind]

0.1% rule

(source: planet facts)

[Widdekind]

GCs are, still, star clusters. So, if other types of star clusters 'evaporate' over time (e.g., open clusters), due to dynamical, dispersive, interactions with their environment; and if GCs are amongst the most ancient structures still surviving, into the present epoch, in our galactic environment, from the deep archaic past >12 Gya; and if all the ~150 GCs still orbiting our galaxy, have plunged through our galaxy's disk numerous times, over their >12 Gyr lifetimes; then,

• in real life, GCs are 'dispersively evaporated' over time
  
• in simulations, GCs are static-and-fixed DM particles, which are 'computationally immune' to interactions

Thus, the discrepancy between (1) observations; and (2) simulations -- "the observed number of small satelite galaxies in galaxies disagrees with the expectations based on dark matter simmulations of galaxy formation" -- could be a numerical artifact, from the 'numerical immunity', of DM particles, once 'created' and inserted into the simulation's N-body 'particle list', to any-and-all further, and potentially disruptive-and-dispersive, interactions. Er go, there is no fundamental discrepancy, between observations & simulations on this point, save that, in real life, the number of GCs decreases over time, whereas they remain 'aloof and immune' in simulations.

REFs:

Inglis. Observer's Guide to Stellar Evolution.
Nicolson. Dark Side of the Universe.

[Widdekind]

Observationally, humans have detected comparatively few 'Intermediate Mass Black Holes' (IMBH), having masses of a thousand to a million solar masses, in the centers of galaxies. For example, only three dozen IMBHs (so defined) have been detected, amidst half-a-million galaxies analyzed. And, this dirth of IMBHs, i.e. an 'IMBH desert', between numerous stellar-mass BHs & numerous galactic-mass SMBH, suggests that SMBH form via some sort of "direct collapse" scenario, above a mass threshold near a million solar masses -- as opposed to some sort of "gradual growth" scenario, which would presumably produce a continuous distribution of BH masses, rather than the observed 'bimodal' distribution (SciAm 2012, cp. SciAm 2012)

Now, the observed 'IMBH desert', of M_BH~10^3-6M_sun objects, corresponds, according to the '0.1% rule', to an observed dirth, of M~10^6-9M_sun spheroidal galaxy objects, i.e. the observed 'gap', between Globular Clusters (GC,UCD) of 10^5-7M_sun, and small Ellipticals & spiral Bulges (CE) of 10^9-10M_sun:

"rogue SMBHs" are indicated, according to where their presumed 'un-imploded' precursor "super-GCs" would have resided
(Mo. Galaxy Formation & Evolution, p.58)

Now, small spheroidal galaxy components, i.e. disk-less 'Compact Ellipticals' & spiral Bulges (CE), of absolute bolometric magnitude M_B>-18, typically do not have central SMBHs. Instead, such CEs typically have central, compact, 'Nuclear Star Clusters' (NSC), which obey the same '0.1%' scaling relation, as the SMBHs, in bigger-and-brighter E galaxies, of M_B<-18, suggesting that both NSCs, and SMBHs, stem from the same source. Thus, the transition dwarfish to full-sized Es, in the above figure, typically represents a parallel & qualitative transition, from central NSC, to central SMBH -- i.e. CE = GC + star halo, E = SMBH + star halo. Note, for a given mass-to-light ratio, a 1000x increase in mass, translates to 7.5 magnitudes. Thus, that explains the 'gap' between GCs & bulges, corresponding to the 'gap' between GC/UCDs of M_B>-10, and CEs of M_B~-17, in the above figures.

Now, presuming a hierarchical formation of structures, smaller CEs would merge, to make larger Es. And, in parallel, the compact NSCs in the CEs, must merge, into single central SMBHs, in resulting Es. Therefore, there is an apparent transition, near M_B~-18, M_gal~10⁹M_sun, M_BH~10⁶M_sun, above which E galaxies host central SMBHs, and below which CE dwarf galaxies still host central NSCs. Such suggests, that compact star clusters, which are typically R~5-10pc in size, become gravitationally unstable, at masses >10⁶M_sun, above which threshold, they 'implode', forming SMBHs, by a "direct collapse" mechanism (cp. discover 2009). Note that million solar mass BHs have 'radii of influence' r = GM_BH/<v_*>² ~5 pc (Ryden. Foundations of Astrophysics, p.480). Perhaps, then, compact clusters of stars 'implode' when their masses increases to a 'threshold', where-at the radius-of-influence, of an equally-massive BH, is comparable to the actual size, of said star cluster?

And now, if compact star clusters can exist on their own, e.g. GCs & UCDs, up to that maximum mass threshold of a million solar masses; then perhaps 'imploded' star clusters, i.e. "rogue SMBHs", can also exist, on their own, above that mass threshold ? If so, then the 'gap', between UCDs, and CEs, could be occupied by "dark objects", i.e. "rogue SMBHs", of millions to billions of solar masses, yet existing independently, i.e. without a surrounding stellar halo:

This post has been edited by Widdekind: 4 January 2012 - 09:47 AM

[Widdekind]

Faber-Jackson (spheroidals) & Tully-Fisher (disks)

if

then (dividing by R²)

relating the surface brightness (I) to the square of the surface density (). i understand that relation to be the crucial core of the FJ/TF relations, linking light-generation & star-formation (I) to physical characteristics of galaxies (M,R). The fact that star-formation increases with the square of the disk density underlies the TF relation for disk-galaxies. Something similar occurs for spheroidals.

Note too

the contours of constant surface-brightness and mass-to-light ratio have the form M ~ R²; the contours of constant total luminosity have the form M ~ R. These lines can be plotted on the (M,R) plane; and the positions of various galaxy types can be over-plotted, adapting from the figure from Galaxy Formation & Evolution:

Given the correlation between Irregulars evolving into Spirals (Ir --> S), perhaps the presence of large, luminous (high L), but dim (low I), spiral-type LSB galaxies, e.g. Malin 1, implies the presence of a corresponding class of irregular-type LSBs ? Because LSB are "crouching giants", lurking below the ambient background sky surface-brightness, pattern recognition techniques may only extract "nice neat spirals" from the noise. But, even as conventional Irregulars disk down into Spirals, perhaps there exist large but dim LSB Irregulars slowly disking down into LSB Spirals like Malin 1 ??