A high-angular resolution study of spinning dust emission in NGC2023 - - PowerPoint PPT Presentation

A high-angular resolution study of spinning dust emission in NGC2023

Matias Vidal N. et al.

Universidad de Chile

TagKASI Cosmic Dust and Magnetism 2018

Credit Rolf Olsen

• Dust correlated microwave emission. First detected by the COBE mission as

a 4σ correlation between maps at 31.5GHz and 140µm (Kogut et al. 1996).

• Much stronger than expected from “normal” dust emission, and with

unexpected frequency dependence hence termed Anomalous Microwave Emission (AME). (~30 times larger at 30GHz )

• It adds to 30% of the Galactic diffuse emission at 30 GHz (Planck 2015
• results. X) → apparently more (~50%, QUIJOTE).
• Observed in different environments :
• Molecular clouds
• Transluscent clouds
• HII regions
• Protoplanetary disks
• Other galaxies (NGC 6946, NGC 4725)

Anomalous Microwave Emission

• AME can be explained by spinning dust

grains (Draine & Lazarian 1998a,b).

• Very small grains (e.g. PAHs) can get

spun up to GHz frequencies by gas collisions, radiative torques, and other processes.

• If grains have a dipole moment, this

rotation causes them to radiate.

Power radiated given by Larmor formula: And frequency:

Credit: Yacine Ali-Haïmoud

Spinning dust

• Collisions with neutrals and ions
• Interaction of charged grain with plasma (“plasma drag”)
• Interaction of grain dipole moment ~µ with plasma
• Absorption of optical photons (electronic transitions)
• Emission of IR photons (vibrational transitions)
• Emission of microwave photons (rotational transitions)
• Emission of photoelectrons
• Formation of H2

Predicted spectra for different astrophysical environments.

Rotational excitation/damping mechanisms

Spinning nanodiamonds from the circunstellar disk V892 Tau (Greaves+ 2018, Nature) Perseus and Orion molecular clouds (Planck early results XX, 2011)

Spinning dust examples

• Smaller grains are more suceptible to the spun up/damping mechanisms --> PAHs

are an attractive candidate.

• Some AME/PAHs correlation have been observed (Casassus+ 2008; Scaife+

2010 )

• As well as lack of correlation in individual clouds: Tibbs+ 11, Vidal+ 11,

Battistelli+15 and also full sky: Hensley+ 2016

• Silicates? It might well be → Hoang+ 2016, Hensley & Draine 2017.

Carriers?

See recent review !!!

NGC 2023

• Well studied reflection nebula/

edge-on PDR.

• Conspicuous PAH emission.
• Shows Extended Red Emission.
• Central B1.5 star excites the gas

and dust.

• 475 pc.

Credit: ESO, HLA, Robert Gendler

NGC 2023 mid-IR data

• Well characterized mid-IR emission

with Spitzer spectra: PAH, H2, C60

• Complememtary datasets: C-RRL,

HCO+, HCN, CN.. Peeters+ 2017

Clear differences between PAH features. → Have been modeled to trace changes in PAH size, charge and geometry. Peeters+ 2017

NGC 2023 mid-IR data

Peeters+ 2017

NGC 2023 PAH modeling

• B type star creates small HII region

and further away a CII region.

• C91α RRL and 8GHz radio

continuum

• HCO+ and H2 rovibrational lines

→ well characterized physical conditions

NGC 2023 PDR conditions

• First detection of Extended red emission

(Gorodetskii & Roshkovskii 1978).

• ERE → Excess of diffuse intensity in the
• ptical R and I bands from reflection nebulae.
• Likely due to luminiscence of carbonaceous

nanograins exposed to UV (e.g. Witt+ 2006).

• Does it relates with AME?

Unsharped-masked ERE map. Witt and Malin 1989.

NGC 2023 ERE

• Recent VLA observations at K, Ka bands (18 to 36 GHz) and also S band (2 to 4) GHz.
• ≈ 2 arcsec synthesized beam.
• Filamentary emission without counterpart at 3 GHz.

VLA observations of NGC 2023

3 GHz

18-36 GHz spectral index

VLA observations of NGC 2023

• Strong correlation with PAHs map.
• Rising GHz spectrum

• Polarization: nothing obvious: Π < 9%, 95% c.l.

Vidal+, in prep.

Q U

VLA observations of NGC 2023

Accepted ALMA Cycle 6 proposal to map thermal dust at band 4 (145 GHz). Observations have just started!! Map the cloud with a mosaic using ALMA + ACA to maps angular scales from 1.5’’ to 40’’

VLA + ALMA observations of NGC 2023

• CBI2 31 GHz observations at 4.5’

resolution

• SD emission coming from the PDR.
• One of the most conspicuous AME sources
• First Detected by CBI (Casassus+ 08)

at ~8.5 arcmin resolution

• 1 deg resolution spectrum well described by

spinning dust model (Planck early results XX, 2011)

See Carla Arce-Tord poster!!

ρ Ophiuchi

R: 250μm; G: 24μm; B: 8μm; Ctr: 31 GHz

Summary

• VLA observations of NGC 2023 show SD emission in ~arcsec scales

with rising spectra between 18-36 GHz.

• Excellent correlation with PAH emission.
• No obvious SD polarization: Π < 9%, 95% c.l.
• High angular resolution observations bring us closer to the micro

physics of the SD mechanism.