Galaxies Flashcards
(25 cards)
What kind of AGNs are there?
Seyfert I & II, Quasar, Blazar
What is a Seyfert?
Seyferts are bright galaxies nucli, with distinct emission lines corresponding to hydrogen emission lines
what is the the difference between I & II seyferts?
I:
Emission lines are broad (looking into the core, the Doppler shift causes a velocity dispersion)
Type II:
Narrow emission lines as you’re seeing the outers parts of the seyfert
What is a quasar
Extreme cases of seyferts, producing distinct emission lines, however also have a extremely big luminosity values outshining the Galaxy itself
What produces the high luminosity is AGN?
Gas uses potential energy converting it into extremely high kinetic energy values. These particles collide producing friction and thus heat. Producing black body spectrums (outsider rims are cooler, so there is a consistent flat gradient opposed to a steep drop off)
What are Blazars?
Looking down a radio active quasar
What equation describes the kentic energy of a particle around a black hole at radius?
PE = -(GMm)/r
Rbh = 2GM/(c^2)
If r = Rbh
Emax = 1/2 mc^2
What are the main features of a AGN
Torus (surrounding dust)
Broadline region (inner ionised H gas)
Narrow line region (outer ionised gas)
Super massive black hole
Accretion disk
Radio jet
What kind of emission does radio galaxies produce?
Synchrotron Radiation, produced by high energy electrons accelerated in a magnetic field
What are the main regions of the Milky Way ? And what are there properties
Disk: high metallicity, younger stars (particularly in the spiral arms)
Bulge: galactic core, ancient stars, high metalicity
Halo: low metalicity, ancient stars, disordered orbits, formed prior to the collapse of dust
How does 21 cm line be produced?
Electrons transitioning from a excited state (electron spin and proton spin are the same), to a ground state (electron and proton spin are oppsite)
What are spiral arms?
Spiral arms aren’t fixed stars rotating around, instead it’s a density wave, this being an arm of mass density which causes stars to slow down, and gas to compress (producing stars) forming the arms of the Galaxy
Why do young stars form within spiral arms?
Effectively the spiral arm slows down hydrogen causing it to compress and collapse under its own weight. This causing young blue stars to form, by the time the nebula has left the arm, many of the young O type stars will have died out
What is considered a metal?
Anything that’s not H, or He
What causes the collapse from a halo to a disk?
Viscosity (drag), slows down the gas causing it to contract under its own gravity
What is the cmb red shift?
Z = 1000
What kind of objects are used as standard candles?
Type 1a supernova (more distant galaxies), & cephids for closer galaxies
What formula do you use to describe velocity in an orbit?
V = (GM(r)/r)**(1/2)
What is the main evidence for dark matter?
Visible matter implies concentrations of matter are towards the centre of the Galaxy, for this reason we expect that initially densities are high before then dropping off. This would mean according to V = (GM(r)/r)**(1/2) we would expect high velocities initially before then dropping off, however this is not the case and instead we see that velocity remains constant implying that mass increases with radius causing no change. This implies dark matter. Another evidence point is the visible mass of galaxies clusters versus the estimated mass
If the curve is steep on a radius velocity curve graph what does this mean?
That density is high so mass rapidly increases
If the curve was flat for a velocity distance curve what does this imply?
Decreasing density
V = (GM(r)/r)**(1/2)
Mass increases just enough to cancel outbreaks any increase to r, if density was constant mass would increase more rapidly than radius does so V would increase. (More matter in front of you)
If there was a constant density for a velocity radius curve what would we expect?
Linear curve, as mass increases with radius (no curve as density is constant so mass increases at a constant rate)
What are the major axis of the galaxy?
Longitude l - direction anti clockwise from the galactic centre
Latitude b - direction vertically from the plane (- below, + above)
What is the depth of the milkyway?
1,000 lyr
