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Title: Cosmic-Ray Injection from Star-Forming Regions

Authors:
; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1323575
Grant/Contract Number:
SC0010107-001; NNX13AO63H
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 117; Journal Issue: 11; Related Information: CHORUS Timestamp: 2016-09-09 18:09:52; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Carlson, Eric, Profumo, Stefano, and Linden, Tim. Cosmic-Ray Injection from Star-Forming Regions. United States: N. p., 2016. Web. doi:10.1103/PhysRevLett.117.111101.
Carlson, Eric, Profumo, Stefano, & Linden, Tim. Cosmic-Ray Injection from Star-Forming Regions. United States. doi:10.1103/PhysRevLett.117.111101.
Carlson, Eric, Profumo, Stefano, and Linden, Tim. 2016. "Cosmic-Ray Injection from Star-Forming Regions". United States. doi:10.1103/PhysRevLett.117.111101.
@article{osti_1323575,
title = {Cosmic-Ray Injection from Star-Forming Regions},
author = {Carlson, Eric and Profumo, Stefano and Linden, Tim},
abstractNote = {},
doi = {10.1103/PhysRevLett.117.111101},
journal = {Physical Review Letters},
number = 11,
volume = 117,
place = {United States},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1103/PhysRevLett.117.111101

Citation Metrics:
Cited by: 3works
Citation information provided by
Web of Science

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  • We investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using infrared, radio, and γ-ray data and a phenomenological model based on the radio-far-infrared correlation within galaxies. By employing a correlation analysis, we derive an average propagation length of ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed γ-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and γ-ray data, wemore » estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV) δ with δ ≈ 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV γ-ray data (δ ≈ 0.66 ± 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D R ≈ (0.9-1.0) × 10 27(R/GV) 0.7 cm 2 s –1. We also compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor.« less
  • Using infrared, radio, and {gamma}-ray data, we investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using a phenomenological model based on the radio-far-infrared correlation within galaxies. Employing a correlation analysis, we derive an average propagation length of {approx}100-140 pc for {approx}3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed {gamma}-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and {gamma}-ray data, we estimatemore » a {approx}20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for {approx}3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is {approx}4 times higher, scaling as (R/GV){sup {delta}} with {delta} Almost-Equal-To 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include {approx}70 GeV CR nuclei traced by the 3-10 GeV {gamma}-ray data ({delta} Almost-Equal-To 0.66 {+-} 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D{sub R} Almost-Equal-To (0.9-1.0) Multiplication-Sign 10{sup 27}(R/GV){sup 0.7} cm{sup 2} s{sup -1}. We compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor.« less
  • We investigate the properties of 'star-forming regions' in a previously published numerical simulation of molecular cloud formation out of compressive motions in the warm neutral atomic interstellar medium, neglecting magnetic fields and stellar feedback. We study the properties (density, total gas + stars mass, stellar mass, velocity dispersion, and star formation rate (SFR)) of the cloud hosting the first local, isolated 'star formation' event and compare them with those of the cloud formed by the central, global collapse event. In this simulation, the velocity dispersions at all scales are caused primarily by infall motions rather than by random turbulence. Wemore » suggest that the small-scale isolated collapses may be representative of low- to intermediate-mass star-forming regions, with gas masses (M{sub gas}) of hundreds of solar masses, velocity dispersions sigma{sub v} approx 0.7 km s{sup -1}, and SFRs approx3 x 10{sup -5} M{sub sun} yr{sup -1}, while the large-scale, massive ones may be representative of massive star-forming regions, with M{sub gas} of thousands of solar masses, sigma{sub v}approx a few km s{sup -1}, and SFRs approx3 x 10{sup -4} M{sub sun} yr{sup -1}. We also compare the statistical distributions of the physical properties of the dense cores appearing in the central region of massive collapse with those from a recent survey of the massive star-forming region in the Cygnus X molecular cloud, finding that the observed and simulated distributions are in general very similar. However, we find that the star formation efficiency per free-fall time (SFE{sub ff}) of the high mass region, similar to that of OMC-1, is low, approx0.04. In the simulated cloud, this is not a consequence of a 'slow' SFR in a nearly hydrostatic cloud supported by turbulence, but rather of the region accreting mass at a high rate. Thus, we find that measuring a low SFE{sub ff} may be incorrectly interpreted as implying a lifetime much longer than the core's local free-fall time, and an SFR much slower than that given by the free-fall rate, if the accretion is not accounted for. We suggest that rather than requiring a low value of the SFE{sub ff} everywhere in the Galaxy, attaining a globally low specific SFR requires star formation to be a spatially intermittent process, so that most of the mass in a giant molecular cloud (GMC) is not participating in the SF process at any given time. Locally, the specific SFR of a star-forming region can be much larger than the global GMC's average.« less
  • Through synthetic observations of a hydrodynamical simulation of an evolving star-forming region, we assess how the choice of observational techniques affects the measurements of properties that trace star formation. Testing and calibrating observational measurements requires synthetic observations that are as realistic as possible. In this part of the series (Paper I), we explore different techniques for mapping the distributions of densities and temperatures from the particle-based simulations onto a Voronoi mesh suitable for radiative transfer and consequently explore their accuracy. We further test different ways to set up the radiative transfer in order to produce realistic synthetic observations. We give amore » detailed description of all methods and ultimately recommend techniques. We have found that the flux around 20 μ m is strongly overestimated when blindly coupling the dust radiative transfer temperature with the hydrodynamical gas temperature. We find that when instead assuming a constant background dust temperature in addition to the radiative transfer heating, the recovered flux is consistent with actual observations. We present around 5800 realistic synthetic observations for Spitzer and Herschel bands, at different evolutionary time-steps, distances, and orientations. In the upcoming papers of this series (Papers II, III, and IV), we will test and calibrate measurements of the star formation rate, gas mass, and the star formation efficiency using our realistic synthetic observations.« less
  • Observations of the continuum emission of the Cep A and Cep B dust clouds at 1300 and 865 microns are presented. These data, together with flux densities determined from the IRAS and with additional observations made at shorter wavelengths, define the continuum spectra of the dust emission integrated over the sources. From these spectra luminosities, dust temperatures, column densities, masses, filling factors, clump sizes, and volume densities are derived. The results are compared with the observations of molecular clouds in the near vicinity of Cep A and with the characteristics of other galactic dust clouds. 48 refs.