The Radio-IR Correlation: Coupling of Thermal and Non-Thermal Processes Amy Kimball General Exam...

The Radio-IR Correlation:

Coupling of Thermal and Non-Thermal

Processes

The Radio-IR Correlation:

Coupling of Thermal and Non-Thermal

Processes

Amy KimballGeneral Exam

February 28, 2007

Radio

Radio

Gamma

X-ray

Optical

Near-IR

Mid-IR

Infrared

H2

H

www.astro.cornell.edu/research/projects/us-kaz/

OutlineOutline

• Radio and Infrared emission processes

• Discovery of the IR-radio correlation

• The connection between thermal and non-thermal emission in galaxies

• Dispersion in the IR-radio correlation

• Conclusion

Typical spectrum (M82)Typical spectrum (M82)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Black-body (dust)

Synchrotron

(SNe, AGN)

ThermalBremsstrahlung(HII regions)

(Radio regime) (Far-infrared regime)Condon 1992

Radio emissionRadio emission

• Accelerating charged particles emit radiation– In astrophysics: e-

– Electric field: Bremsstrahlung

– Magnetic field: synchrotron

Radiation from Accelerating, Charged

Particles

Radiation from Accelerating, Charged

Particles

change in electric field due to motion of particle; integrate power radiated in all directions

Larmor’s Radiation Formula:

QuickTime™ and aTIFF (Uncompressed) decompressor


Thermal Bremsstrahlung:

accelerating e- in E-field


accelerating e- in E-field



e-e-

h

b

Ze+


are needed to see this picture.Single electron:



Electron velocity distribution:


Spectrum


Spectrum



Log (frequency)

Log (intensity)

Thermal cutoffIe(-h/

kT)

Bremsstrahlung self-absorption

I 2

Thermal radio: HII regions

Thermal radio: HII regions

• O and B stars ionize their surrounding hydrogen

Synchrotron spectrum:

accelerating e- in B-field

Synchrotron spectrum:

accelerating e- in B-field



Frequency (/c)

Relative intensity

Spectrum from a single

electron

Synchrotron emission: Ensemble of electrons

Synchrotron emission: Ensemble of electrons

• Spectrum depends on energy distribution of the ensemble

• Cosmic ray electrons (non-thermal)Accelerated in shocks• Supernovae• AGN jets

Cosmic ray energy spectrum

Cosmic ray energy spectrum

• Empirically known to have a power-law energy distribution

Where x ~ 2.2-3

• Fermi acceleration at shock front:– Most particles scattered few times– Few particles scattered many times– Predicts x~2

Synchrotron spectrum: power-law e- ensemble

(non-thermal)

Synchrotron spectrum: power-law e- ensemble

(non-thermal)

Summary: Radio emission in galaxies

Summary: Radio emission in galaxies

• Thermal Bremsstrahlung– Free electrons interacting with nuclei

– HII regions around O and B stars

• (Non-thermal) Synchrotron– Free electrons interacting with magnetic field

– Accelerated by supernovae or AGN jets

Blackbody (Thermal) Radiation

Blackbody (Thermal) Radiation

Thermal equilibrium:

Stars heat dust in galaxies

Stars heat dust in galaxies

http://www.arcetri.astro.it/~irasita/cosmodust/DUST.html

Dust particularly opaque to UV;Transparent to IR

FIR: Dust ReprocessingFIR: Dust

Reprocessing

Summary: Infrared emission in galaxiesSummary: Infrared

emission in galaxies

• Thermal emission from dust heated by:– Massive O and B stars– Red giants– “cirrus” radiation (all stars)– AGN (dominates!)

• (can also see infrared synchrotron in some AGN)

Infrared DataInfrared Data

• Infrared Astronomical Satellite (IRAS)

• First major infrared space telescope

• Covered 96% of sky• 20,000 galaxies

– Late-type (spirals)– ULIRGs– AGNs

http://irsa.ipac.caltech.edu/Missions/iras.html

IRASIRAS

LFIR (infrared)LFIR (infrared)

• LFIR: Estimate of 40-120m emission

Wavelength (m)

Filter response

function

12 m 24 m 60 m

100 m

http://irsa.ipac.caltech.edu/

• Radio emission at a single frequency: usually 1.4 GHz (20cm)– Westerbork or NVSS


are needed to see this picture.Synchrotron

ThermalBremss.

Condon 1992

S (radio)

S (radio)

Subtract thermal radio to obtain pure non-thermal radio

First strong detection:

Disk galaxies; no AGN

First strong detection:

Disk galaxies; no AGN

– Virgo cluster spirals

– “field” spirals– “starburst nuclei” (HII region-like spectra)

Helou, Soifer, & Rowan-Robinson 1985



Far-infrared: Log LFIR (W/m2)

Radio: Log S6.3GHz (mJy)

Spirals, Irregulars, Blue compact dwarfsSpirals, Irregulars, Blue compact dwarfs

Wunderlich, Klein, & Wielebinski 1987

24

23

22

21

20

19



34 35 36 37 38

Radio: Log S6.3cm [W/Hz]

Infrared: Log LFIR [W]

IRAS + NVSS (more radio matches)

IRAS + NVSS (more radio matches)



Log

Log

All IRAS galaxies with NVSS match (many more radio matches!)

Yun, Reddy, & Condon 2001

Q: ratio LFIR/SQ: ratio LFIR/S




Log Q

Log L60m (L)

AGN do not share relation

AGN do not share relation

Sopp & Alexander 1991



Ellipticals

SO

Radio galaxies

Late-typespirals

Log (LFIR/L)

Log (Lradio/L

)

What is the connection?What is the connection?



Black-body (dust)

Synchrotron

(SNe, AGN)

ThermalBremsstrahlung(HII regions)

Condon 1992

(Radio regime) (Far-infrared regime)

Answer is….Answer is….

• STAR FORMATION-- MASSIVE STARS!!

• Form in dusty giant molecular clouds; nearly all their luminosity emerges in the far-infrared-- about two-thirds between 40 and 120m (M > 5M)

• Their supernova remnants accelerate free electrons which escape into the galaxy, and emit synchrotron (M > 8M)

• Not the complete answer…

LFIR SFR(star formation rate)

LFIR SFR(star formation rate)

From models:(assume starburst history, adopt IMF)

(Kennicutt 1998)

From observations: M81





Gordon et al. 2004

UV H R Infrared Radio

Non-thermal Radio SFR

Non-thermal Radio SFR

• SNRs produce Lsynch too low by factor of 10

• Cosmic ray electrons escape from SNR and emit (~107 yrs) long after SNR is gone (~105 yrs)

• Simple model: use empirical Galactic Lsync fSN to infer Lsync SFR

Dispersion in QDispersion in Q


Obric et al. 2006



2.8 2.6 2.4 2.2 2.0 1.8 1.6

Log Q (60m/20cm)

=0.11

Radio + IR

Radio + IR + optical



Log L60m (L)

Log Q60

Galaxies have different star

formation histories

Galaxies have different star

formation histories



Kennicutt 1998

Galaxies have different

metallicities

Galaxies have different

metallicities

Tremonti et al. 2004

53,000 star-forming galaxies

Galaxies have different dustGalaxies have different dust

Dumke, Krause, & Wielebinski 2004

Models fit to spectrum of NGC 4631



Relative flux

Galaxies have different magnetic

fields

Galaxies have different magnetic

fields



Hummel et al. 1988

Enter SPITZEREnter SPITZER

• New bigger and better!

• Examine IR-radio correlation on small scales--

– Does the IR-radio ratio change depending on position inside a galaxy?

Ratio of L60m to L20cm decreases with radiusRatio of L60m to L20cm decreases with radius

• Implies IR disk emission has smaller scale length than radio disk emission

Marsh & Helou 1995



Radial distance [kpc]

Even stronger relation to IR

surface brightness

Even stronger relation to IR

surface brightness

Ratio tied to star formation regions rather than radius?

Infrared: Log f70m [Jy]

Log Q70

Line of constant radio surface brightness

Murphy et al. 2006

Q maps spiral arms!Q maps spiral arms!



Gordon et al. 2004

M81

Log Q



arcsec

arcsec

log

Implications of a small global Q

dispersion

Implications of a small global Q

dispersion• UV photons and relativistic e- produced in same proportions in all star-forming regions

• Star formation controls magnetic field strength… or vice-versa

• Cosmic rays influence star formation

• Supernovae induce star formation

• Estimate SFR and LFIR (< 20%) from radio emission for a wide range of galaxies

• Constraint on galaxy properties?– Magnetic fields, dust, etc.

• (Can also seek out AGN)

Putting the correlation to use

Putting the correlation to use

What we learnedWhat we learned

• IR-Radio correlation is one of strongest in astronomy

• Holds for galaxies whose infrared and radio emission is dominated by star formation

• Is easily explained qualitatively but not quantitatively (yet)

• Can be used for good.

Cheers!Cheers!

• Committee: Željko, Eric, Scott, Marina

• Comments: Chris, Daryl, Jillian, Mirela, Lucianne, Nick, Oliver, Peter, Stephanie

• Outfit: UWAWA



• Possible trends:– Higher dispersion at higher luminosity?

– Steeper at low luminosity?



Condon, Anderson, & Helou 1991

Condon, Anderson, & Helou 1991

• Optically selected spiral and irregular galaxies

– Steepens, higher dispersion at lower LFIR



Synchrotron: Single electron


Related correlations?

Related correlations?

• What other correlations should we see– CO-FIR (ref. Devereux&Young1991)



Murgia et al. 2005

Radio-CO relation

And other galaxies?And other galaxies?

Wrobel & Heeschen 1991



AGN

E/SO

Wrobel & Heeschen 1988



Radio core or jet/lobe dominated

Radio-loud galaxiesRadio-loud galaxies

• Radio emission comes from lobes/jets: decoupled from infrared emission



Sanders & Mirabel 1996

The AGN relationThe AGN relation

• AGN have radio power coming from lobes and jets… unrelated to massive stars.

• AGN have IR emission from dusty torus… unrelated to massive stars.

• Same source directly powers radio and IR in AGN.

Individual parts of galaxies

Individual parts of galaxies

• Paladino et al.– Test of leaky box model? P. 856 fig. 10

• Murphy et al. 2006– Modeling CR diffusion w/ radio & IR maps

– Figs. 1 and 2

Bremsstrahlung:Single electron in

E-field

Bremsstrahlung:Single electron in

E-field

(Thermal radio/Thermal IR)

(Thermal radio/Thermal IR)O and B stars ionize surrounding gas and at the same time heat surrounding dust

Relation is realRelation is real

• Apparent magnitude vs. apparent magnitude: 20cm vs 60micron



Mobric et al. 2006

The Radio-IR Correlation: Coupling of Thermal and Non-Thermal Processes Amy Kimball General Exam...

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