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1、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 However, Astronomers label a galaxy as active when it emits high energy radiation (infrared, radio, UV, and X-ray) beyond what the sta
2、rs alone produce,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
3、distinguished for galactic stellar absorption spectra Now all are seen to be embedded in a galaxy,Z Time,Another Depiction,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
4、 also peaking A coincidence? Yes, star formation is now decreasing! About 112 light months in size but with the energy of 100s of galaxies,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 re
5、turn a small 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 s
6、tars per Earth Volume is a proxy for rate,David Sobral (Leiden Observatory),NGC4261,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
7、 of 40k Msun M15 may have a wussy MBH of 1700 Msun,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,Consistent Mass,As can be seen from the graph, there is a relations
8、hip between the mass of the SMBH and the rotation speed of the galaxys stars Always 0.2% of nuclear bulge,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,Ac
9、cretion disk,Accretion disk for NGC4261 21cm line from VLBA (right) HI absorption,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 pa
10、rsec 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!),Galaxy Cygnus A,Jet v = 95%c for hundreds of Kpc,Driving Star Formation,Artists Rendering,HE0450-2958,The quasars intense wind blew proto-stellar material out into the disk re
11、gions and provided the shock wave for star formation,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,Hypervelocity Stars,Stars that have been so accelerated by the SMBH th
12、at 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,Mot
13、ion Around a SMBH,At our galactic center,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
14、 variable Seyfert Galaxy First identified 1943 (Carl Seyfert) Radio quiet, strong IR, UV, and X-ray Many other kinds that we must regretfully skip,Seyferts,Unusually bright nucleus Unusual spectrum indicated high speed gas emission,NGC4151,Blazar,Highest energy Like a Seyfert with one jet pointed to
15、wards 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,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 pro
16、to-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 down,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,So theres more to learn!,
