1. Evolution of Black Hole Masses from Spectra of Quasar Gas Dynamics
Amanda Schilling, University of Arkansas Mentor: Dr. Julia Kennefick, University of Arkansas
Strategy
Spectra
Every chemical element has a unique spectrum
Because of the wave nature of light an object in motion will have a shifted spectrum - called Doppler shift
Example of Doppler shift2
SDSS has cataloged hundreds of quasar spectra
Sample quasar spectrum from SDSS3
Velocity of gas from the Broad Line Region can be determined from spectra
broad line: the slope on the left of a peak corresponds to blueshift and on the right to redshift
gas in BLR has blue and red shifts indicating its orbit around the black hole
Dynamics
Keplerian motion gives a correlation between the orbital velocity of the gas in the BLR and the black hole it is orbiting
Introduction - Quasars
Active galactic nuclei that are an intense source of radiation
First discovered as radio-wave emitting objects in the 1960s though most found since are not radio emitters
Unique because:
billions of light years away and yet luminous enough to be detected
More numerous in the distant past
powered by massive black holes
Believed to be early galaxies
Objective - Calculate masses of the black holes that power quasars
Why? To determine if the mass evolves with redshift
The sample: 47 quasars with redshifts between 1.8 and 4.3 correlating to look-back-times of billion years (most quasars have a redshift around 2)
Data: spectra of quasars from SDSS, Sloan Digital Sky Survey, database
Anatomy of a Quasar
Massive Black Hole in center powers the quasar
Accretion Disk - disk of gas and dust orbiting the black hole
Jets
perpendicular to accretion disk
can extend very far from the black hole
emit some visible but mostly radio light waves
BLR - broad line region
gas orbiting at high velocities
noticeable Doppler shifts in spectra- broad lines refers to the width of a peak on a spectrum
NLR - narrow line region, larger in volume than BLR but gas is slower and less dense
Torus of cool gas and dust
Quasar diagram1
References
1. Strobel, Nick. “Doppler Effect.” <
2. From “Introduction to Active Galactic Nuclei” NASA’s HEASARC: Education & Public Information. <
3. <