1、Active GalaxiesA Short SurveyAll 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 a

2、lone produceQuasar 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 disti

3、nguished for galactic stellar absorption spectra Now all are seen to be embedded in a galaxyZ TimeAnother DepictionGeneral 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 pe

4、aking A coincidence? Yes, star formation is now decreasing! About 112 light months in size but with the energy of 100s of galaxiesEnd 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 sm

5、all fraction to the interstellar medium, star formation will pretty much be over Unless Smiths cloud replenishes our galaxy A huge cloud of hydrogen gas, is heading toward our Milky Way Galaxy at 250 kilometers per second This shows the rate of star formation as a function of time Mass of stars per

6、Earth Volume is a proxy for rateDavid Sobral (Leiden Observatory) NGC4261Formation 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 Msu

7、n M15 may have a wussy MBH of 1700 MsunDriving 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 massesConsistent Mass As can be seen from the graph, there is a relationship between t

8、he mass of the SMBH and the rotation speed of the galaxys stars Always 0.2% of nuclear bulgeAccretion 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 energyAccretion disk Ac

9、cretion disk for NGC4261 21cm line from VLBA (right) HI absorptionRadiant EnergyDropping matter into a SMBH turns out to be ten times more efficient than fusionActive galaxies can emit as much light a 1014 suns!They do this in a region too small to be seen by most telescopes, 1 parsecA jet along gal

10、actic north and southTpEddcGMmL4TpEddcGMmL41030kg X 1017 (mc2) X 10% = 1046 J = 1053 ergs (a Type II SN every year (or more!)Galaxy Cygnus AJet v = 95%c for hundreds of KpcDriving Star FormationArtists RenderingArtists RenderingHE0450-2958HE0450-2958The quasars intense wind blew proto-stellar materi

11、al out into the disk regions and provided the shock wave for star formationEvidence of “Inside-Out” Dark galaxies detected by VLT Small, gas-rich galaxies in the early Universe Inefficient star formation by themselvesDark galaxy illuminated by quasarHypervelocity Stars Stars that have been so accele

12、rated 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, implyi

13、ng it has a SMBH Motion Around a SMBHAt our galactic centerA 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 Qu

14、asar 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 skipSeyferts Unusually bright nucleus Unusual spectrum indicated high speed gas emissionNGC4151Blazar Highest energy Like a Seyfert with one

15、 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 rayWhy 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 Likely all galaxies had a quasar phase Over time they settle downFor Us Active galaxies give a good, if skewed view of t