ALMA-IMF Core Working Group, September 10 2020

Connection:
https://ufl.zoom.us/j/96368629056?pwd=c1JmbWN6Rll0ZkNjYzJZamtXZFdmUT09

Attendees: Fred, Sasha, Yohan, Timea, Alex, Sylvain, Nichol, Adam, Leo, Jeff, Tapas, Hongli, Quang, Nathalie, Fabrice, Mélisse, 
Not attending: Fabien, Roberto

For memory:
Minutes from our last telecon
Members and their main interests


Agenda:

1. News on the core extraction strategy of detailed CMF papers

• Tests using MnGseg to remove the Gaussian noise: 
  

by Sasha: spurious sources and reliability of flux measurements
On sky250: No major trend/bias but sizes of small sources can have overestimated and those of large sources could be underestimated. 
On SimAlma240: 20% overestimation of the sizes and below S/N=10, measurements are more spread using the MnGSeg/denoised image.
The measurement step done on the original image removes most of the spurious sources (because artefacts are badly measured) and allows a better flux estimate for most sources.
→ detection on the MnGSeg-BSENS image, measurements on the original BSENS image

Ideas for improvement and cautions:

• Question from Jeff: what is the level of noise that we need to keep? Sasha’s proposition: Regular noise should cover the artefacts observed as circular waves. It seems OK.
  
• Caution by Sylvain: Distortions of the position should not bias too much the position of sources. It generally seems OK.
  

by Jeff: difference maps and wavelet reconstruction residuals

• artefacts: circular waves + negative/positives jet-like feature
  

peak of residuals are weak, 0.3%-0.6% of the peak fluxes of compact sources

    → We can be confident in extractions done on MnGSeg images.

• Tests using BSENS and PURECONT instead of CLEANEST:
  

by Yohan: difference maps

• BSENS-CLEANEST difference map: 50% more flux at the position of the hot core. Compact emission of hot cores + extended emission arising from CO. No surprise.
  

→ 3 hot cores? [TBC]

• CLEANEST-PURECONT difference map: very similar (only 10% variations) in positive (extended emission) and negative (hot core). Since PURECONT is underestimating the continuum flux of the central hot core, CLEANEST seems good enough, even possibly better, to estimate the real continuum flux of hot cores.
  

• Tests using 12M-only B6_BSENS instead of 7M+12M B6_BSENS:
  

• There is no more extended flux in the currently-reduced 7M+12M image!
  

• Remaining tests on core extraction: 
  
  • For evolved regions with extended free-free emission @ 3mm and, to a smaller extent, at 1mm (News from Gemma?): 
    

Is using **only** 1.3mm for detection and filtering out cores with small 1.3mm/3mm fluxes enough to remove spurious cores/free-free blobs?

• Flux and CMF comparisons using different extraction tools (getsf, GExt2D and dendrogram). 
  

1. Mass estimates (WG led by Alex & Fred)

• News from Alex
  

Improvements: Change of the re-sampling method for observations
  Adjustment of the noise level   
TBD: Apply filtering scales to all observed images

• Pending questions and issues:
  
  • Are 12M+7M and/or 7M-only data data useful? 
    

No, see above.

• Evaluation of the filtering scale of each image using MnGSeg 
  

→ started by Jeff, will communicate values in the coming week.

* Max recov. scale = ~0.6 x \lambda/Lmin         See equation nº6.1 (p53) in https://www.iram.fr/IRAMFR/ARC/documents/cycle1/alma-technical-handbook.pdf

• Free-free contamination level from H41a images.
  

    Not discussed.

1. First CMF results

by Yohan: CMFs with PPMAP temperature estimations, for BSENS and CLEANEST measurements
    BSENS and CLEANEST are consistent, flat CMF
    → The temperatures of the 3? hot cores have to be estimated through line emission...