2020ApJ...903...29M


Query : 2020ApJ...903...29M

2020ApJ...903...29M - Astrophys. J., 903, 29-29 (2020/November-1)

Reconstructing the EUV spectrum of star-forming regions from millimeter recombination lines of H I, He I, and He II.

MURCHIKOVA L., MURPHY E.J., LIS D.C., ARMUS L., DE MINK S., SHETH K., ZAKAMSKA N., TRAMPER F., BONGIORNO A., ELVIS M., KEWLEY L. and SANA H.

Abstract (from CDS):

The extreme ultraviolet (EUV) spectra of distant star-forming regions cannot be probed directly using either ground- or space-based telescopes due to the high cross section for interaction of EUV photons with the interstellar medium. This makes EUV spectra poorly constrained. The millimeter/submillimeter recombination lines of H and He, which can be observed from the ground, can serve as a reliable probe of the EUV. Here we present a study based on ALMA observations of three Galactic ultracompact H II regions and the starburst region Sgr B2(M), in which we reconstruct the key parameters of the EUV spectra using millimeter recombination lines of H I, He I, and He II. We find that in all cases the EUV spectra between 13.6 and 54.4 eV have similar frequency dependence: Lν∝ν^-4.5±0.4^. We compare the inferred values of the EUV spectral slopes with the values expected for a purely single stellar evolution model (Starburst99) and the Binary Population and Spectral Synthesis code (BPASS). We find that the observed spectral slope differs from the model predictions. This may imply that the fraction of interacting binaries in H II regions is substantially lower than assumed in BPASS. The technique demonstrated here allows one to deduce the EUV spectra of star-forming regions, providing critical insight into photon production rates at λ≤ 912Å, and can serve as calibration to starburst synthesis models, improving our understanding of star formation in the distant universe and the properties of ionizing flux during reionization.

Abstract Copyright: © 2020. The American Astronomical Society. All rights reserved.

Journal keyword(s): Astrophysicists - Interstellar medium - Star-forming regions - Star formation - Radiative recombination - Compact H II region

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 [RLK73] IRc 2 IR 05 35 14.51548 -05 22 30.5943           ~ 633 1
2 IRAS 15520-5234 HII 15 55 48.336 -52 43 10.20           ~ 45 1
3 IRAS 16060-5146 HII 16 09 52.776 -51 54 52.20           ~ 32 0
4 GAL 332.8-00.6 HII 16 20 12.8 -50 54 28           ~ 13 0
5 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 399 1

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