Multiwavelength radio observations of the compact starburst in Arp - - PowerPoint PPT Presentation

Multiwavelength radio observations

• f the compact starburst in Arp 220

Rodrigo Parra & John Conway

Onsala Space Observatory

O N S A L A R Y M D O B S E R V A T O R I U M

T E K N I S K A H Ö G S K O L A CHALMERS

8th EVN symposium Toru´ n, Poland, 26–29 September 2006

1

Colaborators

The Arp 220 team

Philip J. Diamond

Jodrell Bank

Hannah Thrall

Jodrell Bank

Colin J. Lonsdale

Haystack, MIT

Carol J. Lonsdale

IPAC, CALTECH

Harding E. Smith

CASS, UCSD

2

Outline

• 18 cm Global VLBI continuum observations of Arp 220

Previous results on the compact sources in Arp 220

• 6 cm Eb–Wb–Ar @ 1 Gbit s−1 (Delay–Rate map)
• Simultaneous 13, 6 and 3.6 cm VLBA
• Spectra – Model fits – Speculation

3

Arp 220 in context

ULIRG and OHMM

5"

HST HCS/HRT Wilson et al. (2006)

1 kpc

HST NICMOS Scoville et al. (1998)

• D = 77 Mpc (1 asec = 373 pc =

⇒ 10000 km s−1 = 28 µasec year−1)

• L8−1000µm = 1.3×1012 L⊙ ⇒ SFR= 50 − 100 M⊙ year−1
• ∼1010 M⊙ in the central kiloparsec ⇒ nH2 ≈ 2×104 cm−3

4

18 cm Global VLBI

“A starburst revealed” Smith et al. (1998), Rovilos et al. (2003), Lonsdale et al. (2006)

18 cm continuum image of the nuclear region of Arp 220 observed in November

• 2002. The resolution is ∼4 mas and the map noise is ∼8 µJy beam−1. (Taken

from EVN newsletter number 5, May 2003). See also Lonsdale et al. 2006 for a more recent and deeper image. 5

18 cm Global VLBI

Main conclusions

• From rate of appearence of new sources, the estimated

supernova rate is νSN = 4 ± 2 year−1

• The SFR derived from νSN is consistent with the SFR

derived from the FIR luminosity if all detected sources are as luminous as SN1986J

• 18 cm lightcurves too stable to be SNe.
• Not detected at shorter wavelengths

6

6 cm Eb–Wb–Ar @ 1 Gbit s−1

COLA Sample

57.22 57.24 57.26 57.28 57.30 11.0 11.2 11.4 11.6 11.8 seconds of RA seconds of DEC 100 pc

Overall view of the Arp 220 nuclear region. Contours are 6 cm “single baseline snapshot image” made using the Eb–Ar data. The map noise is 40 µJy and the contours are separated by 500 µJy. The resolution is ∼100 mas but sensitive

• nly to features of <1 mas (Parra et al. In prep.). Circles indicate the positions
• f the 49 compact sources catalogued by Lonsdale et al. (2006).

7

13, 6 and 3.6 cm VLBA

Color radio image

RA offset [mas] DEC offset [mas] −500 −450 −400 −350 −300 140 160 180 200 220 240

RGB (SCX bands respectively) composite image of the central region of the western nucleus (Parra et al. Submitted). The axes are in mas from the refer- ence position indicated in the previous figure. 18 sources detected. One source possibly resolved at 3.6 cm. 8

18 cm variability classification

We classified the detections in 2 categories according to their 18 cm flux variation between 2003 November 9 (Lonsdale et al. 2006) and 2005 March 6 (Thrall et al. In prep.)

Variable          Single epoch (S) Rising (R) Ambiguous (A) Non variable (L) (10/18) (8/18)

First seen after ∼2002 Known since ∼1994 Stable 18 cm light curves

9

Source model

Core collapse supernova

Before SN phase SNR phase

˙ m vwind m∗ PISM ρ(r) ∝ r−2 τForeground τCSM τForeground να ≈ 1051 erg τForeground

t < 0 0 < t < 5 − 10 years t > 5 − 10 years rb ∝ ( ˙ m×vwind/PISM)0.5 Lsynch ∝ ( ˙ m/vwind)1−4 rs ∝ (mejecta/nISM)1/3 10

Expected radio spectrum

An expanding SN/SNR shell can be modelled as a free–free

• bscured synchrotron source. The expected radio flux at a

fixed time is given by Sν ∝ να exp

• −τ18ν−2.1

(1) where τ18 = τCSM(t) + τForeground is the total free–free opacity at 18 cm along the line of sight and α is the synchrotron spectral index.

11

Variable at 18 cm

Young SNe?

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

E24 (S)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W56 (S)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W55 (S)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W34 (R)

20 50 100 200 500 1000 µJy

W12 (R)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W11 (R)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W25 (R)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

E14 (A)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

E10 (A)

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W15 (A)

Radio spectra for the 10 detections classified as variable at 18 cm. Filled circles are from

• ur

multiwavelength obser- vations from Jan 2006. Open circles are 18 cm from Mar 2006 and Di- amonds are from Nov

• 2003. Errorbars are ±σ

and upper limits are 5σ 12

Non variable 18 cm

SNRs?

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W42

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W17

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W10

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W39

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W18

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W8

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W33

1 2 4 6 8 10 20 50 100 200 500 1000 GHz µJy

W30 Radio spectra for the 8 detections classified as non variable at 18 cm. These sources present stable 18 cm light curves since Smith et al.(1998). 13

3.6 cm flux vs τ18

Decouple intrinsic synchrotron strength from foreground absorption.

0.1 1 10 500 1000 1500

3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 1 1 2 3 4 5 6 7 8

1986J 1978K 10 × 1980K 1979C

τ18 S3.6 [ µJy ] 3.6 cm flux versus 18 cm opac-

• ity. Stars indicate the long lived

stable sources (class L). Red lines indicate the loci traced by well studied Type II RSNe from Weiler et al. (2002) with their fluxes scaled to the distance of Arp 220. This is evidence that younger sources have higher τ18 which is consistent with RSN models. 14

Σ − D relation for SNRs

Huang et al. (1994)

0.1 1 10 0.1 1.0 10 100 1000

W42

86J 80K 79C

41.95+575 44.01+596 43.31+592

D [ pc ] S3.6 [ µJy ] Flux–D relation for SNRs. The stars indicate sources of class

• L. Arrows indicate upper limits

in size (unresolved). From the correlation we estimate diame- ters between 0.2 and 0.4 pc. Crosses are SNRs in M82. Red lines are the tracks traced by well studied Type II SNe from Weiler et al. (2002). These tracks are expected to join the correlation at a diameter set by the equilibrium between the stellar wind pressure and the ISM pressure. 15

Σ − D relation for SNRs

Derived ISM properties

Using typical values of ˙ m = 10−4 M⊙ year−1, vwind = 10 km s−1 and mejecta = 5 M⊙, combined with the typical radius of ∼0.1 pc for the remnant size predicted by the Σ − D we obtain PISM > 4×107 K cm−3 (Dopita et al. 2005, estimate PISM ≈ 107 by modelling the pan-spectral energy distribution) and nISM > 3×104 cm−3 (Scoville et al. 1997, estimate nISM = 1.4×104 cm−3 using CO(1-0) observations.)

16

Resolved source W42

Hypernova remnant?

4 2 −2 −4 −4 −2 2 4 mas mas

W42

3.6 cm uniformly weighted map of source W42. Contours are −25, 25, 50, 75 and 95% of the peak flux. The deconvolved diameter is 2.3 mas (0.86 pc).

= ⇒ vexp < 40000 km s−1

The integrated flux at 3.6 cm is 574 µJy and the fitted spectral index is α = −0.24

= ⇒ Wtotal(min) = 2×1050 ergs

As usual, we need more data to confirm this result. We have new data from May 2006 plus new high frequency Global VLBI scheduled for November. 17

Main Conclusions

For more, see Parra et al. submitted

• First detection of compact radio sources in Arp 220 at λ <18 cm.

Previous non-detections at 6 cm due to large angular distance to calibrator used.

• We find evidence that younger sources have higher foreground

absorption consistent with SN models.

• The bright 18 cm sources from Smith et al. (1998) in addition to show

little time variability at 18 cm have significantly lower foreground absorption consistent with SNR models.

• The previous two points imply that the compact sources in Arp 220 are

a mixed population of supernovae and supernova remnants.

• One source possibly resolved at 3.6 cm (D = 0.86 pc). Minimum

energy calculations suggest initial kinetic energy in the order of 1051 ergs.

18

THE END

M82

1 kpc HST ACS/WFC 100 pc 18 cm EVN Pedlar et al. (1999)

• D = 3.7 Mpc (1 asec = 18 pc)

20