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Galaxies with superthin stellar disks: A Puzzle
Our Proposed Solution to the Puzzle
Results for a Classic Superthin Galaxy: UGC 7321
Pure disk galaxies (with no bulge component) with R-band images
as sharp as razor blades : A puzzle to galaxy formation models
● Vertical-to-planar axes ratio of the stellar disk < 0.1
● Pure disk galaxies with no bulge component
● Gas Rich, Dark Matter dominated
● Metal poor, Low Star Formation Rate , Low Surface Brightness
● Ubiquitous: Common end product of disk galaxy formation
Why are some galaxy disks extremely thin?*Arunima Banerjee 1 & Chanda J. Jog 2
1National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune – 411007, India2Indian Institute of Science, Bangalore – 560012, India
* Banerjee, A. & Jog, C. J. 2013, MNRAS, 431, 582
We propose that the presence of a dense and compact dark matter halo is essential for the existence of a superthin stellar disk in a low surface brightness , pure disk (with no bulge component) galaxy.
Plot of the ratio z0/RD (where z0 is the calculated stellar exponentialverticalscale height and RD the exponential disk scale length) withgalactocentric radius R for UGC 7321 for different realizations of the two-component galaxy model of gravitationally-coupled stars and gas in the fieldof the dark matter halo. This clearly shows that it is the dense, compact darkmatter halo and not the gas-rich disk, that is responsible for the superthinstellar disk observed in UGC 7321.
Plot of the average value of the ratio z0/RD (where z0 is the stellar verticalscale height and RD the exponential scale length) as a function of the darkmatter core radius Rc, here RD = 2.1 kpc as in UGC 7321. From the plot itis clear that the stellar disk becomes superthin only for compact darkmatter halos i.e Rc ≤ 2RD
Conclusions
The presence of a dense and compact dark matter halo is essential for the existence of a superthin stellar disk in a low surfacebrightness , pure disk (with no bulge component) galaxy.
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