1	Astr 5460 Mon., Oct. 11, 2004 This week: Ex-Gal Radio Sources (Ch. 8, Combes et al.) Unless noted, all figs and eqs from Combes et al. Caroll & Ostlie isn’t bad for some of these topics. Kellerman and De Young’s books on Extragalactic Radio Sources are both recommended, too. Could do a whole course on just these. We have a week. Also now getting into active galaxies: http://nedwww.ipac.caltech.edu/level5/active_galaxies.html
2	Compilation of Galaxy Catalogs online Level 5 An important NED resource I should have pointed out already: http://nedwww.ipac.caltech.edu/level5/catalogs.html Includes interacting/peculiar galaxies, HI warps, more
3	Centaurus A
4	Many Views of Radio Galaxy Centaurus A
5	3C31
6	Radio Catalogs/Info Frequency, depth, spatial res./coverage NED – links to catalog name/info/radio fluxes Cambridge surveys and 3CR Parkes, Greenbank, other single-dish surveys FIRST – north galactic cap, 9000 sq. deg., VLA B-array (http://sundog.stsci.edu ) NVSS – “all sky” 20cm VLA D-array (Condon et al. 1998; http://heasarc.gsfc.nasa.gov/W3Browse/all/rbscnvss.html ) Many Others
7	Physical Processes Relativistic Electrons, ‘nonthermal’ synchrotron emission Energy E, Lorentz factor γ = (1-v²/c²)^-1/2 Relativistic beaming: cone angle 1/γ ν_max = 0.069 γ²(eB/mc) sinψ where the angle is between the line of sight and B. For isotropic velocity distribution, <ν>=5E²B, with frequency in MHz, E in GeV, and B in μG. One to one relationship between frequency and energy, and a power-law flux distribution means a power-law energy distribution. F_ν = k₁ν^-^α, then N(E) = k₂E^-^λ. And λ = 2α + 1 Optically thick at low frequencies (synchrotron self-absorption) and F_ν = k₁ν^2.5(see, eg. Brotherton et al. 2002)
8	Physical Processes Optically thin radio spectrum (Carrol & Ostlie:
9	Physical Processes Internal Energy: total energy of the electrons Assume equipartition: equal energy in electrons and magnetic field Minimum electron energy density U is then equal to 9.3x10^-2B² (in erg cm^-3), B in G. Estimates suggest B is usually on order of several micro-Gauss
10	Physical Processes Energy Losses Synchrotron radiation itself Inverse Compton Scattering off microwave background photons (c.f. X-rays) There seems to be a continuous stream of new particles, and in situ acceleration (shocks certainly can be present in jets)
11	Physical Processes Polarization, Faraday Rotation Synchrotron radiation is highly polarized perpendicular to the direction of B. Why? Linear polarized wave is rotated as it moves through ionized gas: Δθ = 4.64x10⁶ n_t B_p Lλ² where n is the cgs density of thermal electrons, B is the parallel magnetic field in Gauss, L is the length in kpc, and the wavelength is in cm. Measure at two wavelengths to correct for and measure the Faraday rotation. Can be helpful when looking at two radio lobes (e.g., which is foreground).
12	Radio Morphologies, Types Compact Sources (arcsecond scales and smaller) Extended Sources (Fanaroff-Riley 1974 classes) and can be very large (many arcminutes, up to Mpc) FR I, tend to be lower power, continuous, jets BL Lacs, radio galaxies FR II, higher power, edge-brightened lobes Quasars, radio galaxies Other stuff. More messes, oh yes! Messes in deep space. Optical IDs Tough game historically – point sources, (elliptical) galaxies
13	Radio Morphologies, Types
14	FR-II Morphologies
15	FR-I Morphology
16	Extended Radio Spectra, Polarizatrion Extended Light: optically thin synchrotron
17	“Radio” Jets Not just Radio, also optical, X-ray
18	“Radio” Jets Not just Radio, also optical (Caroll & Ostlie)
19	Some Jet movies http://www.astroscu.unam.mx/scu/images.html http://www.bu.edu/blazars/3c120.html
20	Some Jet movies Some embedded movies, eg.:
21	Some Jet movies Some embedded movies, eg.:
22	‘Superluminal’ Motion What are the apparent velocities of the blobs in these jet movies? Turns out to be, under the simplest of assumptions, FASTER THAN THE SPEED OF LIGHT. Oooh! Aaaah! How can this be? Put on your tin foil hats and follow along…
23	‘Superluminal’ Motion Diagram for discussion (from Caroll and Ostlie):
24	‘Superluminal’ Motion Arrival time for first photon: t1 = d/c 2^nd photon: t2 = t_e + (d-vt_e cosφ)/c Δt = t2- t1 = t_e (1 – (v/c)cos φ) Note that this time is shorter than t_e. Apparent transverse velocity is then: v_apparent =vt_esinφ/ Δt = vsin φ/(1-(v/c)cos φ) Solve for v/c = (v_app/c)/(sin φ+(v_app/c)cos φ) You can go on from here to determine things about the angle, minimum velocities, Lorentz factors, etc. (Hint good to look at for exam/qualifier questions).
25	Compact Radio Spectra So what else about these sources pointed at us? Optically Thick beamed Synchrotron Variability
26	Compact Radio Spectra Optically thick emission:
27	Compact Radio Spectra Sometimes, with careful observations, can see optically thin steep spectrum radio emission. Unified models of quasars (more next week). Relationship between morphology and radio spectrum.
28	Compact Radio Spectra Variability. Sometimes intraDAY variability. Why so very variable?
29	Jet Models People numerically model jets with MHD codes. Complicated. Instabilities. Shocks.
30	Radio Source Counts We can count radio sources in the sky as a function of flux. We can estimate how the counts should go in the absence of evolution. Can show (HINT) for a non-evolving, homogeneous universe that you expect:
31	Radio Source Counts Do need to worry about k-corrections at some level, but results are clear. Evolution has occurred. Its exact nature is more difficult to figure out. Density or luminosity? Environment also an issue.
32	Size Evolution Something that is especially of interest with radio sources is the fact that they are BIG. Ruth Daly (formerly of Princeton, American Express commericals about 10 years ago) worked on this issue. Standard Rods can be used in cosmology tests. Text describes. More next month. One complication is that there does seem to be a size-luminosity correlation.
33	For Next Week Radio Astronomy led to discovery of quasars – our next topic. Greg Shield’s “History of AGN” from astro-ph/PASP – look it up and read it, please! I used to house sit for Greg, even babysat his kids. His work was fundamental in building the accretion disk paradigm.