6. Cosmic Probes Flashcards
What are quasars?
Accreting SMBHs which lie at the centre of galaxies
- Part of the AGN family
When can quasars be observed?
When we view towards the polar axis of an accreting BH
How luminous are quasars, and what are they described by?
Extremely, and can be seen brighly beyond z ~ 6
- Described by the Schechter function and double power laws
Briefly describe the quasar mass problem
We assume a quasar radiates at the Eddington limit
- Suggests masses on the order of 10^9 solar masses, and assume SMBHs grow by accretion
- Seed BHs are created in CCSNe, so mass accretion is prop. to mass and growth is exponential
When calculating the age of the SMBH which created the ULAS J1120+0641 quasar, what problem do we see?
- Age of the SMBH was 0.76Gyr and the Universe was 0.77Gyr old
- Implies non-stop max accretion since U began
- First stars formed at z=20-25 (0.2Gyr)
- No quasar has 100% duty cycle (don’t constantly accrete)
Name the three possible solutions to solve the quasar mass problem
- Primordial BH seeds
- Pop III seeds
- Super Eddington accretion
Describe primordial BHs
Generated from a pure DM collapse before the first stars
- Should be rare so cannot explain the observed popualtion of SMBHs
Describe Pop III seeds
Pop III stars were massive so could they have a massive remnant?
- Most likely to go through the PISNe process leaving no remnant
- Also have a high radiation pressure
- Removal of gass is necessary for BH growth
Describe super Eddington accretion
Accretion faster than the Eddington rate
- Edd. assumed spherical infall and emission in equilibrium
- Rapid infall along a preferred axis is permitted as it is too fast to equilibrise
What are cosmic lighthouses?
If we have a distant source, we can extract information about gas, dust and galaxies along the l.o.s
- Ly alpha forest tells us about the density of neutral H
- Metal lines tell us about galaxies
What must be true about the sources for cosmic lighthouses?
Must be very bright and have a well understood spectrum
State and explain the two candidates for a cosmic lighthouse
GRBs - bright, short lived (hrs-days) but have a simple power law spectrum
Quasars/AGN - SMBH accreting from a host galaxy. Very bright, blue and stable source. All look roughly the same
What is the Bondi Hoyle rate?
When a BH will accrete from the interstellar medium as it moves through a dense cloud. Can create 10^4 seeds and then Edd takes over
- dM/dt is proportional to M^2 so it can overcome the Edd limit as the radiation doesn’t impact the same gas that falls in
