5.2-5.4 SMBH, Luminosity Function Flashcards
What is the main piece of evidence that SMBH are common at the centre of galaxies?
They produce anomalies in the rotation curve and velocity disperson near the nucleus
What is the explanation as to why the majority of SMBH don’t power an AGN (bright nucleus)
The majority of normal galaxies hosted an AGN in the past, but accretion has essentially stopped
- Accretion disk is still there
Describe the M-Sigma relation
The mass of the SMBH at the centre of the galaxy and the velocity dispersion of the bulge are related
M_BH is proportional to σ^4 of bulge
What is the unexpected behaviour about the mass of the black hole, and the dynamics of a galaxy?
Mass of the BH is much less than the bulge at the lower end, so it should not affect dynamics
- Must be momentum transfer between the energy released by the AGN and the surrounding gas
What is the momentum transfer in relation to a BH, and how does it influence SFR?
It can blow away gas preventing a collapse, and inject angular momentum influencing the velocity dispersion of the stars
Describe the method we can use to check the distance to a SN from the expanding shell
d = v_r t / theta where theta is the angle of extension
Independent check for geometric parallaxes as radial and tangential velocities are the same
Are core collapse SNe good standard candles, and why?
No because the time and evolution of the explosion varies too much
Are Type I a good standard candles, and why?
Yes as it happens once the mass of the white dwarf exceeds 1.4 solar masses
- Process is somewhat controlled and we get predictable behaviour
- Luminosity is a well known function for the shape
What is Hubble’s law, and what value do we use?
72 km/s Mpc and related to v = H(0) d
What is the evidence for mass distribution in our neighbourhood?
We have two giant galaxies, a few medium size and many dwarf galaxies
- Property of fragmentation
Why is the luminosity function useful when studying mass distribution?
Mass is proportional to light
Describe how we visualise the Schechter luminosity function on a density magntidue graph
Have a power law on the faint end (shallow)
Have the knee which is the faint and bright end transition (large downward slope)
Have the bright end which is exponential behaviour
- Reflects evolutionary properties of galaxies
What does the faint end represent in the Schechter function?
The properties of fragmentation during formation of galaxies
What does the bright end represent in the Schechter function?
A physical limit to the growth of galaxies
- e.g. If luminosity grows too much, radiation pressure halts collapse and limits size
How can we obtain the total number density of galaxies and the total luminosity density?
Number density of galaxies: Integrate n(L) dL
Total Luminosity density: Integrate L n(L) dL
