# Tag Info

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There are other shapes of galaxies. In particular, look at ellipticals.

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galaxy come in many different sizes: some of the small-er ones do rotate ["orbit"] around the edge of a large galaxy ... one can also visualize galaxy-clusters, in which the entire cluster rotates .....

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The progenitor bias arises in attempts to study early-type (elliptical) galaxies at higher redshift. The desire is to choose a sample of galaxies at high $z$ that are the analogs of the galaxies that evolved to form the low $z$ sample. The bias arises if one chooses a sample of only early-types at high $z$. Because some late-types eventually evolve into ...

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Not directly, because these two quantities are not known to correlate as strongly as other "intermediate" relations. But they do correlate, with bigger disks in bigger haloes; it's fairly intuitive. You could construct a relation from e.g. The Luminosity-Size and Mass-Size Relations of Galaxies out to z ~ 3 (or more specific to B-band, but more simulation ...

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Well, first of all, that's not the NFW profile, instead you should have: $$\rho(r) = \frac{\rho_0}{\frac{r}{r_s}(1+\frac{r}{r_s})^2}$$ The radius $r_s$ is usually called the scale radius, and is the place where the logarithmic derivative of the density is $-2$. This isn't especially physically meaningful, but is mathematically convenient. The integral is ...

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The raisin bread analogy can be used to help in understanding this too: Dough is much more expandable than the raisin material. Raisins will expand a bit due to the heat and the pull from the dough stuck on their surface, but it is the dough that is moving. The forces that are holding the raisin together are much stronger than the force expanding the ...

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You are correct, the recession velocity predicted by the hubble law is negligible at the local group, even if gravity among them could be absent. Their gravitational attraction though, is hard enough to keep them bound together.

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The relationship they're claiming is a little more subtle than what comes across in the press article: The black hole masses are not directly measured. They are inferred from the $M-\sigma$ relation for black holes, which says that the larger the central velocity dispersion of stars in a galaxy, the larger the black hole. The velocity dispersion is the (...

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Good numbers for this have only been coming out for a decade or so, so its a relatively new topic. There does seem to be a strong tendency for dwarf and satellite galaxies to have much lower mass-to-light ratios, and correspondingly smaller baryon-to-DM ratios. See, for example, Stringer+2009, Strigari+2008. These observations are backed up by simulations ...

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You need to look in to the GZK cutoff. In 1966, Greisen, Kuzmin and Zatsepin calculated that above a threshold of $5\times10^{19} eV$ cosmic ray protons would lose energy to photo-pion production on the cosmic microwave background fairly rapidly. The consequence of this is that cosmic rays above that energy can't travel more than about $50 Mpc$ without ...

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