The Duration of Star Formation in Galactic Giant Molecular Clouds: Brief Lifetimes for Dusty, Giant H II regions
Abstract
We present a comparative study of 20 Galactic giant molecular clouds (GMCs) hosting giant H II regions in various stages of evolution. Within 18 of the sampled regions we use multiwavelength point-source photometry data from the Chandra X-ray Observatory, Spitzer Space Telescope, ground-based near-IR point-source photometry, and Gaia DR2 to identify >10,000 X-ray selected, IR-bright ([4.5] < 13 to 14 mag, depending on the GMC) young stellar members, predominantly intermediate-mass (~2-5 MSun) pre-main sequence stars (IMPS). We use (1-8 µm) spectral energy distribution (SED) fitting to classify stars as either young stellar objects with IR excess emission due to dusty circumstellar disks/envelopes or "diskless" (no detectable 4.5 µm excess). X-ray-selected, diskless IMPS are placed on the HR diagram according to their likelihood-weighted model parameter distributions, accounting for X-ray emission decay timescales, inner dust disk lifetimes, and the intermediate-mass stellar birthline. The isochronal age distributions give the duration of star formation in each GMC, which ranges from <1 Myr to ~9 Myr among our sample. We find that the nebular IR luminosity surface density decays sharply with time after the onset of star formation. Dust has been evacuated from giant H II regions produced by massive stellar clusters older than ~3 Myr, rendering them IR-faint. This short timescale indicates that radiation pressure and winds from massive, OB stars generally disperse GMCs before the onset of supernovae. Spatially-resolved 24 and 70 µm indicators of obscured star formation rates, commonly used for nearby external galaxies, may need to be recalibrated to account for the brief lifetimes of IR-bright, dusty H II regions. This work has been supported by the NSF via award CAREER-1454224 and by NASA through Chandra Awards G07-18003B, AR7-18004X and the Pennsylvania State University ACIS Instrument Team contract, SV4-74018
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23536804P