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

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

Centaurus A

Many Views of Radio Galaxy Centaurus A

3C31

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

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)

Physical Processes

Optically thin radio spectrum (Carrol & Ostlie:

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

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)

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).

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

Radio Morphologies, Types

FR-II Morphologies

FR-I Morphology

Extended Radio Spectra, Polarizatrion

Extended Light: optically thin synchrotron

“Radio” Jets

Not just Radio, also optical, X-ray

“Radio” Jets

Not just Radio, also optical (Caroll & Ostlie)

Some Jet movies

http://www.astroscu.unam.mx/scu/images.html

http://www.bu.edu/blazars/3c120.html

Some Jet movies

Some embedded movies, eg.:

‘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…

‘Superluminal’ Motion

Diagram for discussion (from Caroll and Ostlie):

‘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).

Compact Radio Spectra

So what else about these sources pointed at us?

Optically Thick beamed Synchrotron

Variability

Compact Radio Spectra

Optically thick emission:

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.

Compact Radio Spectra

Variability. Sometimes intraDAY variability. Why so very variable?

Jet Models

People numerically model jets with MHD codes. Complicated. Instabilities. Shocks.

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:

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.

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.

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.


	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


	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


	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


	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)


	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


	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)


	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).


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


	http://www.astroscu.unam.mx/scu/images.html
	http://www.bu.edu/blazars/3c120.html


	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…


	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).


	So what else about these sources pointed at us?

	Optically Thick beamed Synchrotron

	Variability


	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.


	Variability. Sometimes intraDAY variability. Why so very variable?


	People numerically model jets with MHD codes. Complicated. Instabilities. Shocks.


	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:


	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.


	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.


	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.