gjdonatiello
Andromeda Galaxy - M31 (nomenclature structures in the outer halo of the galaxy)
Andromeda Galaxy - M31 (nomenclature structures in the outer halo of the galaxy)
Credit: Giuseppe Donatiello
(revision 2023)
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This image is distributed as CC0 but for its use please refer to what is indicated in the info here: www.flickr.com/people/133259498@N05/
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This image offers a good overview of the main structures on the disc and the external halo of Andromeda (M31).
The disc appears quite regular and there is an abundant presence of young stars, gases and dusts. The bulge is dominated by an older population. The external halo presents various irregularities and thickenings that we can consider as vestiges of dwarf galaxies progressively incorporated by the greater galaxy, as foreseen by the growth models.
M31 is thought to have assimilated a few hundred small galaxies or globular clusters.
This process is still ongoing.
According to Ferguson et al. (2002), the names attributed to various substructures, unknown to most, are reported in the negative image with disc color inset.
However, the figure shows some unpublished structures. In particular, the structures I have called "S Spur" and "S Arch" seem not reported so far. Equally interesting are the thin "shadows" that present a trend compatible with streams (Black Ribbon 1, 2 and 3, "Phantom Shade". These structures have very low contrast and can be formed both by dust and by populations of cold stars coming from destroyed dwarf galaxies. They are all to be verified.
More about: iopscience.iop.org/article/10.1086/342019/fulltext/202181...
The outskirts of galaxies contain vital clues to their formation history. It is in these regions that new material continues to arrive as part of their ongoing assembly, and it is also in these regions that material was deposited during violent interactions in the galaxy's past. Furthermore, the long dynamical timescales ensure that debris from accreted material takes a long time to be washed away by the merger process. This means that many formation legacies can be detected as coherent structures in space.
Andromeda is the nearest large spiral galaxy and the only other significant one in the Local Group. In many ways, Andromeda is the Milky Way, having very similar total masses, they share a common origin and, probably, the same ultimate fate when they merge. However, there are significant differences between them. M31 is slightly brighter than the Milky Way and has a higher rotation rate and a bulge with a higher velocity dispersion. M31 has a globular cluster system with ~500 members, about 3 times more than the Milky Way.
Andromeda's disk is also much more extended, but is now forming stars at a slower rate than the Galaxy. There are indications that the Milky Way has undergone an exceptionally low amount of mergers and has an unusually low specific angular momentum, while M31 appears to be a much more normal galaxy in these respects.
Andromeda has one compact elliptical galaxy (M32), three dwarf elliptical galaxies (NGC 205, NGC 147, NGC 185) among its entourage of 39 satellites, as well as no dwarf irregular (dIrr) star-forming galaxies within 200 kpc. The Milky Way has no ellipticals but two dIrr (Magellanic Clouds). However, it is perhaps in their supposed halo populations that the differences between the two galaxies are most curious and interesting.
This study of mine, based on ultra-deep imaging, highlights faint structures in the extended halo of M31, NGC 147 3 NGC 185. Some structures appear here for the first time and on the right I propose a possible interpretation. Note how some structures pass for some dwarf satellite galaxies suggesting a possible connection.
Andromeda Galaxy - M31 (nomenclature structures in the outer halo of the galaxy)
Andromeda Galaxy - M31 (nomenclature structures in the outer halo of the galaxy)
Credit: Giuseppe Donatiello
(revision 2023)
-----------------------
This image is distributed as CC0 but for its use please refer to what is indicated in the info here: www.flickr.com/people/133259498@N05/
-----------------------
This image offers a good overview of the main structures on the disc and the external halo of Andromeda (M31).
The disc appears quite regular and there is an abundant presence of young stars, gases and dusts. The bulge is dominated by an older population. The external halo presents various irregularities and thickenings that we can consider as vestiges of dwarf galaxies progressively incorporated by the greater galaxy, as foreseen by the growth models.
M31 is thought to have assimilated a few hundred small galaxies or globular clusters.
This process is still ongoing.
According to Ferguson et al. (2002), the names attributed to various substructures, unknown to most, are reported in the negative image with disc color inset.
However, the figure shows some unpublished structures. In particular, the structures I have called "S Spur" and "S Arch" seem not reported so far. Equally interesting are the thin "shadows" that present a trend compatible with streams (Black Ribbon 1, 2 and 3, "Phantom Shade". These structures have very low contrast and can be formed both by dust and by populations of cold stars coming from destroyed dwarf galaxies. They are all to be verified.
More about: iopscience.iop.org/article/10.1086/342019/fulltext/202181...
The outskirts of galaxies contain vital clues to their formation history. It is in these regions that new material continues to arrive as part of their ongoing assembly, and it is also in these regions that material was deposited during violent interactions in the galaxy's past. Furthermore, the long dynamical timescales ensure that debris from accreted material takes a long time to be washed away by the merger process. This means that many formation legacies can be detected as coherent structures in space.
Andromeda is the nearest large spiral galaxy and the only other significant one in the Local Group. In many ways, Andromeda is the Milky Way, having very similar total masses, they share a common origin and, probably, the same ultimate fate when they merge. However, there are significant differences between them. M31 is slightly brighter than the Milky Way and has a higher rotation rate and a bulge with a higher velocity dispersion. M31 has a globular cluster system with ~500 members, about 3 times more than the Milky Way.
Andromeda's disk is also much more extended, but is now forming stars at a slower rate than the Galaxy. There are indications that the Milky Way has undergone an exceptionally low amount of mergers and has an unusually low specific angular momentum, while M31 appears to be a much more normal galaxy in these respects.
Andromeda has one compact elliptical galaxy (M32), three dwarf elliptical galaxies (NGC 205, NGC 147, NGC 185) among its entourage of 39 satellites, as well as no dwarf irregular (dIrr) star-forming galaxies within 200 kpc. The Milky Way has no ellipticals but two dIrr (Magellanic Clouds). However, it is perhaps in their supposed halo populations that the differences between the two galaxies are most curious and interesting.
This study of mine, based on ultra-deep imaging, highlights faint structures in the extended halo of M31, NGC 147 3 NGC 185. Some structures appear here for the first time and on the right I propose a possible interpretation. Note how some structures pass for some dwarf satellite galaxies suggesting a possible connection.