Spinning Dust and the 3mm Excess

Transcription

1 Spinning Dust and the 3mm Excess 8th October 2010

2 Spinning dust 1996: COBE DMR-DIRBE (Kogut et al.) observe correlated microwave and 100 µm emission. 1997: Saskatoon 30 & 40 GHz observations; OVRO 14.5 & 32 GHz observations (Leitch et al.) I Hα (R) = 0.36EM(cm 6 pc)t(10 4 K) 0.9

3 Spinning dust 1996: COBE DMR-DIRBE (Kogut et al.) observe correlated microwave and 100 µm emission. 1997: Saskatoon 30 & 40 GHz observations; OVRO 14.5 & 32 GHz observations (Leitch et al.) I Hα (R) = 0.36EM(cm 6 pc)t(10 4 K) 0.9

4 Spinning dust 1996: COBE DMR-DIRBE (Kogut et al.) observe correlated microwave and 100 µm emission. 1997: Saskatoon 30 & 40 GHz observations; OVRO 14.5 & 32 GHz observations (Leitch et al.) I Hα (R) T 1.2

5 Spinning dust 1996: COBE DMR-DIRBE (Kogut et al.) observe correlated microwave and 100 µm emission. 1997: Saskatoon 30 & 40 GHz observations; OVRO 14.5 & 32 GHz observations (Leitch et al.) I Hα (R) T 1.2 T 10 6 K

6 Spinning dust 1998: Drain & Lazarian spinning dust model 1994: Ferrara & Dettmar - didn t consider damping 1957: Erickson - dust grains in radio sources P = 2 ω 4 µ 2 sin(θ) 2 3 c 3

7 Open diamonds: COBE (Kogut et al. 1996) Filled diamonds: Saskatoon (de Oliveira-Costa et al. 1997) Filled Squares: OVRO (Leitch et al. 1997) DL98

8 Size distribution: MRN Distribution dn da = n HA MRN [ a 3.5 +Ba 1 exp 1 2 [ ln(a/a0 ) sigma ] 2 ] DL98 MRN distribution is known to underestimate the population of small grains 12 µm and 25 µm IRAS emission as well as MIR emission features suggest a substantial population of small grains

9 Size distribution: MRN Distribution dn da = n HA MRN [ a 3.5 +Ba 1 exp 1 2 [ ln(a/a0 ) sigma ] 2 ] DL98 MRN distribution is known to underestimate the population of small grains 12 µm and 25 µm IRAS emission as well as MIR emission features suggest a substantial population of small grains

10 HII regions, dark clouds and PDRs... Green Bank (Finkbeiner et al. 2002) looked at 10 dust clouds and found two positive results: LPH96 and L1622 Scaife et al. 2007; Dickinson et al Casassus et al. 2006

11 NGC 6946

12 NGC 6946

13 NGC 6946

14 LDN 1111 Ultra-compact HII? EM > pc cm 6 M 100 M M = 0.3 M (Visser et al. 2001)

15 LDN 1111 Ultra-compact HII? EM > pc cm 6 M 100 M M = 0.3 M (Visser et al. 2001)

16 LDN 1111 Ultra-compact HII? EM > pc cm 6 M 100 M M = 0.3 M (Visser et al. 2001)

17 LDN 1111 Ultra-compact HII? EM > pc cm 6 M 100 M v = 21.4 km s 1 (Heiles et al. 1996)

18 Lynds Clouds No correlation with: Mass Protostellar activity Position And not a sample bias.

19 LDN 675 No correlation with: Mass Protostellar activity Position And not a sample bias.

20 L1221-IRS and the AMI-LA P* sample VeLLO: L int 0.1 L Is thermal emission from protostars contributing significantly?

21 LDN 1246 No correlation with: Mass Protostellar activity Position And not a sample bias.

22 LDN 1246 No correlation with: Mass Protostellar activity Position And not a sample bias.

23 The HII region contradiction RCW175: 8.6σ excess at 31 GHz. (Dickinson et al. 2008) Southern hemisphere: 6 HII regions Frequency coverage: GHz Slight excess observed in all regions Most significant excess 3.3 σ. Dickinson et al. 2007

24 The HII region contradiction Northern hemisphere: 16 HII regions Frequency coverage: GHz Correlation with IRAS 100 µm (r=0.88) but stronger correlation with NVSS 1.4 GHz (r=0.99) No excess above 1 σ Opposite effect - steepening of the spectrum Scaife et al. 2008

25 HCHII contamination Galactic observations with CMB instruments have large PSFs Objects which appear to be approx. point-like can contain contributions from a number of different sources Contamination by dense plasma is difficult to identify without priors (Todorovíc et al. 2010)

26 Contamination The optically thick spectra of HCHII regions can be confused with the low frequency side of a spinning dust spectrum. Excesses at cm-wave frequencies can be caused by a variety of protostellar emission mechanisms.

27 The 3mm excess Is the 3 mm excess seen in the spectra of UC/HCHII regions dues to spinning dust...? We need to rule out the thermal dust tail - Herschel? Could it be similar to the emission postulated in the SMC?

28 The Small Magellanic Cloud (Bot et al. 2010)

29 The Small Magellanic Cloud (Bot et al. 2010)

30 The Small Magellanic Cloud Model=Diffuse + dense PDR + moderately dense PDR PAH mass fraction consistent with MIR spectra Peak at ν 160 GHz 1 grain size : smaller grains higher emission frequencies 2 density : denser medium higher frequencies 3 ISRF : at G 0 > 10 higher ISRF higher frequencies

31 m dishes

32 m dishes

33 Conclusions Spinning dust emission has been detected in a number of distinct astronomical objects At present it is unclear what differentiates those objects which do exhibit the emission and those which do not The 3 mm excess seen in UC/HCHII regions could be due to spinning dust emission Correctly identifying the excess, given alternatives, requires well matched data at many frequencies