The MUSTANG Galactic Plane Survey

Highlights & Outlook

Adam Ginsburg

Anderson, L. D.; Dicker, Simon; Romero, Charles; Svoboda, Brian; Devlin, Mark; Galván-Madrid, Roberto; Indebetouw, Remy; Liu, Hauyu Baobab; Mason, Brian; Mroczkowski, Tony; Armentrout, W. P.; Bally, John; Brogan, Crystal; Butterfield, Natalie; Hunter, Todd R.; Reese, Erik D.; Rosolowsky, Erik; Sarazin, Craig; Shirley, Yancy Sievers, Jonathan; Stanchfield, Sara
Slides available at
https://keflavich.github.io/talks/gbt_mgps.html.
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The MUSTANG Galactic Plane Survey (MGPS90)

90 GHz, 9" Galactic Plane Survey;
Ginsburg+ 2020 gives first results

MUSTANG data reduction

  • Charles Romero, Simon Dicker led the data processing and map making using MINKASI.
  • Maps were made with a normal boustrephedonic scan pattern.
  • The largest recovered scale is about 4.25 arcminutes.
  • The resulting beam is ~9"
  • Sensitivity is ~1-2 mJy/beam
  • Small (<5") pointing offsets corrected by x-corr with VLA data
  • Data on dataverse, reduction scripts and tables on github

Blind Surveys of the Galactic Plane

Why do them?
  • Reveal unexpected new things.
  • Enable systematic searches.
  • Enable systematic Spectral Energy Distribution analysis.
  • Provide legacy data products for future surveys.
  • Provide short spacings for interferometers (ALMA).

What's special about 90 GHz?

Global minimum of Galactic SEDs
Elisabete da Cunha

What's special about 90 GHz?

  • Dust emission, with α~3-4, is dropping fast - but not gone yet
  • Synchrotron emission, with α < 0, is dropping fast, and usually gone
  • Free-free emission, with α~0ish, is present
  • Optically thick free-free emission, with α=2, is peaking for a subset of sources: hypercompact HII regions.
  • AME, Anomalous Microwave Emission, peaks in the 10-60 GHz range; mechanism is still uncertain

MGPS-90

  • Our goal is to perform a complete Galactic plane survey from ~-5 to ~55 degrees longitude.
  • This range contains the highest density of millimeter emission sources.
  • It has been surveyed at every other wavelength - Spitzer GLIMPSE, Herschel HiGal, BGPS, ATLASGAL, SCUBA, VLA THOR and GLOSTAR
  • ... but there is no coverage between 1mm and 6cm at better than ~several arcminute resolution

MGPS-90 Pilot

For the pilot, we selected several cluster forming regions that include our Galaxy's most actively star-forming clouds.

MGPS-90 Pilot

We imaged seven of ten targets. The others were not observed because of lack of time.

MGPS-90 Pilot: Catalog

We identified 706 sources, of which 73 were compact (unresolved).

MGPS-90 Pilot: Extended and Compact Sources

MGPS-90 Pilot: Catalog Sources

MGPS-90 Pilot: Catalog Sources

MGPS-90 Pilot: Catalog Sources

MGPS-90 Pilot: PN

MGPS-90 Pilot: OH/IR star

MGPS-90 Pilot: cm-nondetected HCHII candidate

MGPS-90 Pilot: Known HCHII region

MGPS-90 Pilot: Lifetimes

  • N(HCHII)/N(UCHII)=tHCHII / tUCHII → tHCHII ~ 0.16-0.46 tUCHII
    • tUCHII~ 3x104 years (CORNISH; Kalcheva+ 2018)
    • tHCHII ~ 5-15x103 years
  • For a B0, proto-O-star to double its mass, from 20⊙ to 40⊙, an accretion rate 2-5x10-3 M⊙ yr -1 is required
    • These accretion rates are very high
    • Ionized accretion is probably not sustainable
    • Instead, maybe stars stay cool & bloated?

MGPS-90 Pilot

Goal: Find and count HCHII regions.
  • Massive stars contract onto the main sequence quickly, tkh ~ 104 years
  • An ionizing photosphere ignites at ~20 M⊙
  • Once they turn on, they either:
    1. Ionize their accretion flow and continue to accrete as HCHII regions
    2. Blow a rapidly-expanding HII region, cutting off their food source
  • An ionized accretion flow will appear as a dense HII region with R ~ 100 AU, optically thick at 3 mm
  • The relative number of HCHII regions to UCHII regions tells us how long they spend small, providing limits on their ionized accretion time
    • We found tHCHII ~ 0.16-0.46 tUCHII

MGPS-90 Pilot: Dust or Hot Gas?

Most of the extended emission in the pilot is free-free at 3mm

MGPS-90 Pilot: Dust vs Gas in the GC

MGPS-90 Pilot: Dust vs Gas in the plane

MGPS-90 Pilot: Dust vs Gas in the plane

MGPS-90 Pilot: Dust vs Gas in W49

MGPS-90 Pilot: Dust vs Gas in W51

MGPS-90 Pilot: Multiscale combination

MGPS-90 Pilot: Multiscale combination

MGPS-90 Pilot: Multiscale combination

Student Dani Diaz is working with Roberto Galvan-Madrid to combine ALMA with MGPS data

MGPS-90 Future Companions

There are several forthcoming data sets that further motivate an MGPS-90 Galactic Plane Survey
  • LMT AzTEC/TolTEC ~10" maps at 1mm, 15" at 2mm
  • IRAM NIKA, same resolution
  • ALMA mosaics, everywhere! (ALMA-IMF plus many others)

Summary

  • The MGPS Pilot detected ~10-100 new HCHII candidates; the full program can be complete to all isolated HCHII regions
    • The lifetime of HCHII regions is ~1/6th to ~1/2 that of HCHII regions, hinting that the HCHII region phase is not a major accretion phase for HMYSOs
  • The 3mm maps are dominated by free-free emission in high-mass star-forming regions
  • GBT 3mm maps bridge between ALMA and Planck
    • We need these to understand dust at multiple physical scales
Slides available at
https://keflavich.github.io/talks/gbt_mgps.html