Characterizing Star Forming Clumps in the Galaxy: A Comparison of JCMT and Herschel Observations
Date
2018-08-23
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Abstract
We present the first comparison between the Herschel Infrared Galactic plane survey (Hi-GAL) at 500 µm and the James Clerk Maxwell Telescope (JCMT) Plane Survey (JPS) using SCUBA-2 at 450 µm. The JCMT data were taken as a part of a follow up project for the JPS - circular regions with a radius of ∼ 0.8◦ at ` = 10◦ & ` = 30◦ . Given the higher resolution of the JPS 450 µm observations we were able to determine the number of clumps identified in the Hi-GAL 500 µm data (PLW), that are actually composed of multiple, smaller clumps (i.e. the fragmentation). At ` = 10◦ , we find that 35% of the PLW clumps fragment into smaller pieces and at ` = 30◦ this multiplicity number is 23%. While there is no apparent correlation with the radius or mass of the PLW clumps, there are weak trends with flux and density. PLW clumps with densities greater than 104 cm−3 seem to always fragment into smaller clumps, and PLW clumps with integrated flux greater than 50 Jy, have a 50% chance of fragmenting (and all PLW clumps with an integrated flux of > 200 Jy fragment). Pixel-by-pixel and clump-by-clump comparisons between the PLW 500 µm and JPS 450 µm datasets reveal good agreement in the flux levels for compact bright regions suggesting that the JPS calibration at 450 µm is good. The amount of missing flux in the JPS 450 µm data at different spatial scales is investigated quantitatively via a power spectrum analysis and suggests that observations with SCUBA-2 are, in general, able to fully recover the flux for structures with sizes smaller than ∼ 1 arcmin. Moreover, we present the results of our SED fitting to the combined datasets by extracting the clumps from five Hi-GAL bands, two JPS bands, and counterpart data at ∼20 µm. We determine the current physical conditions (i.e. temperature, luminosity, mass, density, etc.) of the star forming clumps in these Galactic coordinates. Our work identifies that 30 of these clumps had a Class 0 characteristics and 52 of them are compatible with Class I or II stars. We investigate how SFE calculated for the monolithic Hi-GAL clumps changes when the multiplicity fraction is incorporated. The average SFE is observed to increase from 8% to 13% once the clump multiplicity was taken into account. Our simulations suggest that the low SFE in the most massive clumps is most likely due to the formation of massive stars. We then determine the SFE and investigate differences/similarities in these two galactic longitudes. The average SFE at ` = 10◦ is 16% while at ` = 30◦ the average SFE is 9%. We propose that the turbulence at ` = 30◦ is supporting this region against gravitational collapse, which potentially results in formation of more massive cores/stars and therefore lower SFE.
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Keywords
Physics & Astronomy, Star Formation, ISM, SFE, Physics & Astronomy, Star Formation, ISM, SFE
Citation
Tahani, K. (2018). Characterizing Star Forming Clumps in the Galaxy: A Comparison of JCMT and Herschel Observations (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/32875