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Active Galaxies

Active Galaxies. A Short Survey. All Galaxies are active to some extent:. For "normal" galaxies, we can think of the total energy output as the sum of stellar emissions

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Active Galaxies

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  1. Active Galaxies A Short Survey

  2. All Galaxies are active to some extent: • For "normal" galaxies, we can think of the total energy output as the sum of stellar emissions • However, Astronomers label a galaxy as active when it emits high energy radiation (infrared, radio, UV, and X-ray) beyond what the stars alone produce

  3. Quasar Discovery • Maarten Schimdt examined 3S 273 • Exceedingly bright and small • Small as in quasi-stellar size • Outshined its galaxy therefore it seemed alone • Z = 0.16 (see next slide) • 2 Gyr away • Sloan DSS and 2o Field Galaxy Survey have found over 1 million • Their emission spectra was distinguished for galactic stellar absorption spectra • Now all are seen to be embedded in a galaxy

  4. Z Time

  5. Another Depiction

  6. General Properties • Active galaxies are seen throughout time, but the peak period for quasars is at redshift z=2, about 9 Gyr ago, corresponding to a time when star formation was also peaking • A coincidence? Yes, star formation is now decreasing! • About 1–12 light months in size but with the energy of 100s of galaxies

  7. End of an era… • The Milky Way is about 3% gas and 97% stars, not including dark matter • When this 3% is used up, even though supernovae and planetary nebula will return a small fraction to the interstellar medium, star formation will pretty much be over  • Unless Smith’s cloud replenishes our galaxy • A huge cloud of hydrogen gas, is heading toward our Milky Way Galaxy at 250 kilometers per second

  8. This shows the rate of star formation as a function of time • Mass of stars per Earth Volume is a proxy for rate David Sobral (Leiden Observatory)

  9. NGC4261

  10. Formation • The early Universe was smaller; dark matter caused greater clumping of stellar material • Likely low-mass (not so super) MBHs (1000Msun) merged into SMBH • Perhaps like in globular cluster W Centauri with a MBH of 40k Msun • M15 may have a wussy MBH of 1700 Msun

  11. Driving Force • The powerplant for all the activity is the supermassive black hole in the nucleus of each galaxy • This mass of the SMBH can be from a million to 10 billion solar masses

  12. Consistent Mass • As can be seen from the graph, there is a relationship between the mass of the SMBH and the rotation speed of the galaxy’s stars • Always ~ 0.2% of nuclear bulge

  13. Accretion • Gas and occasionally entire stars form a disk around the SMBH, swirling around, waiting to fall in. • The gravitational energy given up by infalling matter produces the radiant energy

  14. Accretion disk

  15. Accretion disk for NGC4261 • 21cm line from VLBA (right) • HI absorption

  16. Radiant Energy • Dropping matter into a SMBH turns out to be ten times more efficient than fusion • Active galaxies can emit as much light a 1014 suns! • They do this in a region too small to be seen by most telescopes, ~ 1 parsec • A jet along galactic north and south 1030kg X 1017 (mc2) X 10% = 1046 J = 1053 ergs (a Type II SN every year (or more!))

  17. Galaxy Cygnus A Jet v = 95%c for hundreds of Kpc

  18. Driving Star Formation The quasar’s intense wind blew proto-stellar material out into the disk regions and provided the shock wave for star formation Artist’s Rendering HE0450-2958

  19. Evidence of “Inside-Out” • Dark galaxies detected by VLT • Small, gas-rich galaxies in the early Universe • Inefficient star formation by themselves Dark galaxy illuminated by quasar

  20. Hypervelocity Stars • Stars that have been so accelerated by the SMBH that they are shot out of the galaxy • Usually 1 of a binary pair • 1 falls into a tighter orbit, the other gains enough momentum and energy to escape • Speed: 1.6 million miles per hour • Here to Mars in 2 days! • An HV star has been observed escaping from the Large Magellanic Cloud, implying it has a SMBH

  21. Motion Around a SMBH

  22. At our galactic center…

  23. A Variety • All AGN are fundamentally the same, just seen from different angles and at different stages of its life • Quasar: Quasi-stellar Radio Source • Blazer • Quasar seen from the “top” • Massive synchrotron radio emissions (radio loud) • Like a Quasar but much more variable • Seyfert Galaxy • First identified 1943 (Carl Seyfert) • Radio quiet, strong IR, UV, and X-ray • Many other kinds that we must regretfully skip

  24. Seyferts • Unusually bright nucleus • Unusual spectrum indicated high speed gas emission NGC4151

  25. Blazar • Highest energy • Like a Seyfert with one jet pointed towards Earth • Variable output • +/- 10X a Quasar • Probably due to an uneven flow of material into the SMBH • Widest range of frequencies, radio to Gamma ray

  26. Why so few nearby (now)? • As low-mass ‘seed’ SMBH coalesced in high-mass ones, they blew material (numnum) away, starving themselves • Also blew enough proto-stellar material away so that new stars in the core are rare, only Type II are found in abundance

  27. Likely all galaxies had a quasar phase • Over time they settle down

  28. For Us… • Active galaxies give a good, if skewed view of the early Universe • A clue, perhaps, that SMBH formed early on • Bottom up vs top down • That stars formed before galaxies • That early galaxies has an abundance of cold gas • That the SMBH was instrumental in widespread star formation

  29. So there’s more to learn!

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