Radio transients in the starburst galaxy Arp 220 Lund 2015-02-09 - - PowerPoint PPT Presentation

Radio transients in the starburst galaxy Arp 220

Lund 2015-02-09 Eskil Varenius, John Conway, Ivan Martí-Vidal, Fabien Batejat, Miguel Perez-Torres et. al

Chalmers / Onsala Space Observatory

Outline

• Arp 220 and the L-D relation
• Months: Rapidly variable sources?
• Years: Supernovae
• Decades: Supernova remnants
• Summary

The starburst galaxy Arp 220

26’’ (10kpc) HST Wilson et. al (2006)

Basic facts

• Closest (77 Mpc) ULIRG (LFIR>1012L☉)
• Merger with SFR ~ 100 M☉/yr
• Expected radio supernova rate ~ 2 /yr

Big picture Study star formation (IMF, magnetic fields etc.) in extreme environments. Top transient science

• Months: Variable sources

(AGN? Microquasars?)

• Years: SNe

(interacting with CSM)

• Decades: SNR

(interacting with ISM)

Deepest image to date: Eastern nucleus

6cm global radio VLBI Resolution 0.001'', sensitivity 4 μJy beam-1 (Varenius et. al 2015, in prep.) 0.25'' 90pc

Deepest image to date: Western nucleus

0.25'' 90pc 6cm global radio VLBI Resolution 0.001'', sensitivity 4 μJy beam-1 (Varenius et. al 2015, in prep.)

20 years of monitoring!

• Dozens of submas-resolution images
• More than 50 sources detected
• Lightcurves, spectra, source sizes...

Batejat et. al (2011)

The luminosity-diameter relation

(Varenius et. al 2015, in prep.)

L-D relation compared to M82 and LMC

Green: Theoretical relation

• f S α D-9/4 for SNRs

in the Sedov phase (Berezhko&Völk 2004) Blue: Best fit of S α D-1.9

• Fig. from Batejat et. al (2011)

Months: Variable source (Batejat et. al 2012)

2008-06-10 2008-10-24 2009-02-27 2011-05-16 2014-08-01 2014-10-13

Simulation of ring, PSF, noise

2008-06-10 2008-10-24 2009-02-27 2011-05-16 2014-08-01 2014-10-13

The “variable” sources are large SNRs

Large SNRs ~ 150 yr old

Years: New radio supernovae?

New SNe? SNR at their peak, age ~10 yr

Chevalier, 2006, ApJ 641,1029

Years: New radio supernovae?

500 μJy detection limit for Arp220 (Parra et. al 2007)

Problem:

• Should see only the

brightest radio SNe

• Total SN-rate ~ 2/yr
• Observed SN-rate ~ 2/yr

Observed rate is too high!

• SNR/SNe confusion?
• New data will help!
• Big picture: variable IMF

in dense starburst (e.g. Chabrier et. al 2014)

Decades: Supernova remnants

SNR at their peak, age ~10 yr Large SNRs ~ 150 yr old

Decades: Supernova remnants

• Given density nH~104cm-3, max radius ~0.35 pc, the

largest SNR is ~ 150 years old. (Draine&Woods 1991)

• Assume all SNe produce radio SNRs.

Total SN-rate ~2/yr --> should see 300 SNRs.

• We see only 50, i.e. total SN-rate of 0.3/yr.

Why so few? Big picture:

• Large sample of SNRs for SNR physics
• SNRs probe densities and magnetic fields of ISM
• Origin of the FIR-Radio correlation

SNR at their peak, age ~10 yr New SNe? Large SNRs ~ 150 yr old

?

Decades: Supernova remnants

Summary

• Months: “Variable” sources are likely large SNRs.
• Years: We observe more SNe than expected.

Radio SNe probe stellar evolution through CSM.

• Decades: We observe fewer SNRs than expected.

SNRs probe ISM, e.g. densities and B-fields.

• Careful analysis of recent very deep images will

improve classification of weak SNe and SNRs.

• SNe/SNRs in Arp 220 can help

understanding the physics of the FIR-Radio correlation in extreme environments.