madbadgalaxyman
08-05-2014, 12:37 PM
Here are some recent papers with some interesting discoveries and possible discoveries. Pity that the likes of Sky & Telescope and Astronomy only report on a minuscule fraction of the discoveries that are made!
(the people who write in these magazines do not keep up with extragalactic research; this is a typical amateur thing, really)
PAPER 1
70,000 Globular Clusters discovered in the Coma Cluster of Galaxies, of which some 23,000 belong to the giant elliptical galaxy NGC 4874, but the rest of the globular clusters more properly belong to the Coma Cluster itself (that is, they are thought to be orbiting in the cluster potential, not around a specific galaxy) : :
http://m.iopscience.iop.org/0004-637X/730/1/23?rel=ref&relno=2
......
But this is not entirely unexpected;
- I have noticed that when CCDs were used to measure the very outermost light of certain specific cluster Elliptical galaxies, the total (integrated) magnitude of said galaxy kept increasing with progressively increasing radius to which the magn. was measured, but there was no radius at which the galaxy's total magnitude stopped increasing(!)......
obviously, there was optically-luminous "stuff" out there, even beyond any reasonable estimate of a galaxy's outermost outline. (M86 is a classic example....it doesn't seem to have a defined boundary!)
- intergalactic Globulars and planetary nebulae and Stars are already known in the Virgo Cluster. The very rich galaxy population in Coma, a population which is very densely arrayed, may have engaged in very multiple episodes of tidal stripping of objects from its member galaxies.
- the intracluster (inter-galaxy) light is very prominent near the centre of Coma, so there was already an expectation that there would be lots of inter-galaxy objects of various sorts.
I do note, however, that the Globular Cluster numbers in this paper are pretty rubbery, with the HST here stretched to its absolute limit, and a lot of assumptions and extrapolations being made in order to get these numbers.
[[ In the innermost being of a Globular Cluster aficionado, when he finally shuffles off this mortal coil, and his soul "floats upwards" (as it is destined to do) to the vast Globular Clusters System of the Coma Cluster of Galaxies, there will be awakened an ecstatic feeling similar to that which is enjoyed by the soul of the believer when he finally reaches heaven or paradise. ]
PAPER 2
Discovery of a new of type of galaxy in today's universe ?!??!?
(not at large look-back times) : :
http://arxiv.org/abs/1203.2623
These elliptical-galaxy-like systems seem to be of large mass and luminosity, but they are thought to be much more compact than the normal giant E galaxy.
Supposedly, it is now confirmed that giant ellipticals - when considered as a population - get progressively smaller, the further back we look in time, so perhaps these massive compact galaxies simply have not accreted extra matter in the way that normal big ellipticals have done. However, the new massive compact galaxies seem NOT to be just like standard ellipticals that have accreted further gas and stars from external sources.
This discovery is associated with a goodish European group of astronomers
( http://www.iac.es/proyecto/traces/ )
who have actually made meaningful progress in Elliptical galaxy & S0 galaxy evolution.
Hmmm......and Hmmm again.....
On reading the listed properties of these galaxies in the summary section of this paper:
- compact spheroids
- but elongated overall isophotes
- considerable star formation within the last 2Gyr
- dynamically significant rotation
- disky morphology
, one does wonder if this "new" type of galaxy really is unique..... perhaps these are just S0 galaxies which have undergone unequal-mass galaxy mergers (not just mergers with tiny galaxies, which, as we know, occur all the time)
There has been an absolute obsession with the idea that S0s are just gas-stripped spirals, but the alternative hypothesis of an origin in a galaxy merger is physically plausible for at least some S0 galaxies
Have they just "discovered" S0 galaxies??
PAPER 3
This paper pertains to the problem that a lot of the interstellar gas in dwarf galaxies may be undetectable using standard tracers;
specifically , transitions of the CO molecule (in the millimeter-wave radio regime ) are used to trace the cold molecular diatomic hydrogen gas that directly forms nearly all of the stars in a non-dwarf galaxy;
however, as dwarf galaxies have a very low content of C and O and other 'heavy' elements (presumably because they expel 'metal-enriched' ISM), their radio emission from the CO molecule is usually weak or non-existent. In other words, it is plausible that a dwarf galaxy could have a lot of diatomic hydrogen gas in it without astronomers being able to detect it.
However, as explained in this article, mid IR and Far-IR and sub-millimeter observations (specifically by Herschel and Spitzer ) perform the role of the US Cavalry in "coming to the rescue" of astronomers who are trying to make an inventory of the Interstellar Medium of a dwarf galaxy that includes all of the molecular hydrogen gas : :
http://arxiv.org/abs/1105.1006
PAPER 4 (hot off the presses!)
Nuclear star clusters are rather similar to globular clusters, so it is believed. However they commonly contain multiple stellar populations (non coeval populations).
(this is why Omega Cen may be the nucleus of a formerly existing galaxy; it has two parallel main sequences)
But why there should commonly be a regular and very rich star cluster at the centre of many galaxies is a difficult question.
Here is the latest information about the nuclear star cluster at the centre of our own Galaxy : :
http://arxiv.org/abs/1311.5258
____________________________
(the people who write in these magazines do not keep up with extragalactic research; this is a typical amateur thing, really)
PAPER 1
70,000 Globular Clusters discovered in the Coma Cluster of Galaxies, of which some 23,000 belong to the giant elliptical galaxy NGC 4874, but the rest of the globular clusters more properly belong to the Coma Cluster itself (that is, they are thought to be orbiting in the cluster potential, not around a specific galaxy) : :
http://m.iopscience.iop.org/0004-637X/730/1/23?rel=ref&relno=2
......
But this is not entirely unexpected;
- I have noticed that when CCDs were used to measure the very outermost light of certain specific cluster Elliptical galaxies, the total (integrated) magnitude of said galaxy kept increasing with progressively increasing radius to which the magn. was measured, but there was no radius at which the galaxy's total magnitude stopped increasing(!)......
obviously, there was optically-luminous "stuff" out there, even beyond any reasonable estimate of a galaxy's outermost outline. (M86 is a classic example....it doesn't seem to have a defined boundary!)
- intergalactic Globulars and planetary nebulae and Stars are already known in the Virgo Cluster. The very rich galaxy population in Coma, a population which is very densely arrayed, may have engaged in very multiple episodes of tidal stripping of objects from its member galaxies.
- the intracluster (inter-galaxy) light is very prominent near the centre of Coma, so there was already an expectation that there would be lots of inter-galaxy objects of various sorts.
I do note, however, that the Globular Cluster numbers in this paper are pretty rubbery, with the HST here stretched to its absolute limit, and a lot of assumptions and extrapolations being made in order to get these numbers.
[[ In the innermost being of a Globular Cluster aficionado, when he finally shuffles off this mortal coil, and his soul "floats upwards" (as it is destined to do) to the vast Globular Clusters System of the Coma Cluster of Galaxies, there will be awakened an ecstatic feeling similar to that which is enjoyed by the soul of the believer when he finally reaches heaven or paradise. ]
PAPER 2
Discovery of a new of type of galaxy in today's universe ?!??!?
(not at large look-back times) : :
http://arxiv.org/abs/1203.2623
These elliptical-galaxy-like systems seem to be of large mass and luminosity, but they are thought to be much more compact than the normal giant E galaxy.
Supposedly, it is now confirmed that giant ellipticals - when considered as a population - get progressively smaller, the further back we look in time, so perhaps these massive compact galaxies simply have not accreted extra matter in the way that normal big ellipticals have done. However, the new massive compact galaxies seem NOT to be just like standard ellipticals that have accreted further gas and stars from external sources.
This discovery is associated with a goodish European group of astronomers
( http://www.iac.es/proyecto/traces/ )
who have actually made meaningful progress in Elliptical galaxy & S0 galaxy evolution.
Hmmm......and Hmmm again.....
On reading the listed properties of these galaxies in the summary section of this paper:
- compact spheroids
- but elongated overall isophotes
- considerable star formation within the last 2Gyr
- dynamically significant rotation
- disky morphology
, one does wonder if this "new" type of galaxy really is unique..... perhaps these are just S0 galaxies which have undergone unequal-mass galaxy mergers (not just mergers with tiny galaxies, which, as we know, occur all the time)
There has been an absolute obsession with the idea that S0s are just gas-stripped spirals, but the alternative hypothesis of an origin in a galaxy merger is physically plausible for at least some S0 galaxies
Have they just "discovered" S0 galaxies??
PAPER 3
This paper pertains to the problem that a lot of the interstellar gas in dwarf galaxies may be undetectable using standard tracers;
specifically , transitions of the CO molecule (in the millimeter-wave radio regime ) are used to trace the cold molecular diatomic hydrogen gas that directly forms nearly all of the stars in a non-dwarf galaxy;
however, as dwarf galaxies have a very low content of C and O and other 'heavy' elements (presumably because they expel 'metal-enriched' ISM), their radio emission from the CO molecule is usually weak or non-existent. In other words, it is plausible that a dwarf galaxy could have a lot of diatomic hydrogen gas in it without astronomers being able to detect it.
However, as explained in this article, mid IR and Far-IR and sub-millimeter observations (specifically by Herschel and Spitzer ) perform the role of the US Cavalry in "coming to the rescue" of astronomers who are trying to make an inventory of the Interstellar Medium of a dwarf galaxy that includes all of the molecular hydrogen gas : :
http://arxiv.org/abs/1105.1006
PAPER 4 (hot off the presses!)
Nuclear star clusters are rather similar to globular clusters, so it is believed. However they commonly contain multiple stellar populations (non coeval populations).
(this is why Omega Cen may be the nucleus of a formerly existing galaxy; it has two parallel main sequences)
But why there should commonly be a regular and very rich star cluster at the centre of many galaxies is a difficult question.
Here is the latest information about the nuclear star cluster at the centre of our own Galaxy : :
http://arxiv.org/abs/1311.5258
____________________________