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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 emissionsHowever,Astronomers label a galaxy as active when it emits high energy radiation(infrared,radio,UV,and X-ray)beyond what the stars alone p
2、roduce,Quasar Discovery,Maarten Schimdt examined 3S 273Exceedingly bright and smallSmall as in quasi-stellar sizeOutshined its galaxy therefore it seemed aloneZ=0.16(see next slide)2 Gyr awaySloan DSS and 2o Field Galaxy Survey have found over 1 millionTheir emission spectra was distinguished for ga
3、lactic stellar absorption spectraNow 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 also peakingA coinciden
4、ce?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 matterWhen this 3%is used up,even though supernovae and planetary nebula will return a small fraction to the inter
5、stellar medium,star formation will pretty much be over Unless Smiths cloud replenishes our galaxyA 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 timeMass of stars per Earth Volume is a proxy for r
6、ate,David Sobral(Leiden Observatory),NGC4261,Formation,The early Universe was smaller;dark matter caused greater clumping of stellar materialLikely low-mass(not so super)MBHs(1000Msun)merged into SMBHPerhaps like in globular cluster W Centauri with a MBH of 40k MsunM15 may have a wussy MBH of 1700 M
7、sun,Driving Force,The powerplant for all the activity is the supermassive black hole in the nucleus of each galaxyThis 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 relationship between the mass of the SMBH and the rotation
8、 speed of the galaxys starsAlways 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,Accretion disk,Accretion disk for NGC426121cm line from
9、VLBA(right)HI absorption,Radiant Energy,Dropping 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 galactic north and south,1030kg X 1017(mc2)X
10、 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 regions and provided the shock wave for star formation,Evidence of“Inside
11、-Out”,Dark galaxies detected by VLTSmall,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 that they are shot out of the galaxyUsually 1 of a binary pair1 falls into a
12、 tighter orbit,the other gains enough momentum and energy to escapeSpeed:1.6 million miles per hourHere to Mars in 2 days!An HV star has been observed escaping from the Large Magellanic Cloud,implying it has a SMBH,Motion Around a SMBH,At our galactic center,A Variety,All AGN are fundamentally the s
13、ame,just seen from different angles and at different stages of its lifeQuasar:Quasi-stellar Radio SourceBlazerQuasar seen from the“top”Massive synchrotron radio emissions(radio loud)Like a Quasar but much more variableSeyfert GalaxyFirst identified 1943(Carl Seyfert)Radio quiet,strong IR,UV,and X-ra
14、yMany other kinds that we must regretfully skip,Seyferts,Unusually bright nucleusUnusual spectrum indicated high speed gas emission,NGC4151,Blazar,Highest energyLike a Seyfert with one jet pointed towards EarthVariable output+/-10X a QuasarProbably due to an uneven flow of material into the SMBHWide
15、st 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 themselvesAlso blew enough proto-stellar material away so that new stars in the core are rare,only Type II are found in abundance,Likely all ga
16、laxies had a quasar phaseOver time they settle down,For Us,Active galaxies give a good,if skewed view of the early UniverseA clue,perhaps,that SMBH formed early onBottom up vs top downThat stars formed before galaxiesThat early galaxies has an abundance of cold gasThat the SMBH was instrumental in widespread star formation,So theres more to learn!,
