NIR H_2_ line em. from 5 photodissociation regions Virtual Observatory Resource

Authors
  1. Kaplan K.F.
  2. Dinerstein H.L.
  3. Kim H.
  4. Jaffe D.T.
  5. Published by
    CDS
Abstract

We present a comparative study of the near-infrared (NIR) H_2_ line emission from five regions near hot young stars: Sharpless 140, NGC2023, IC63, the Horsehead Nebula, and the Orion Bar. This emission originates in photodissociation or photon-dominated regions (PDRs), interfaces between photoionized and molecular gas near hot (O) stars or reflection nebulae illuminated by somewhat cooler (B) stars. In these environments, the dominant excitation mechanism for NIR emission lines originating from excited rotational-vibrational (rovibrational) levels of the ground electronic state is radiative or UV excitation (fluorescence), wherein absorption of far-UV photons pumps H2 molecules into excited electronic states from which they decay into the upper levels of the NIR lines. Our sources span a range of UV radiation fields (G_0_=10^2^-10^5^) and gas densities (n_H_=10^4^-10^6^cm^-3^), enabling examination of how these properties affect the emergent spectrum. We obtained high-resolution (R~45000) spectra spanning 1.45-2.45{mu}m on the 2.7m Harlan J. Smith Telescope at McDonald Observatory with the Immersion Grating INfrared Spectrometer (IGRINS), detecting up to over 170 transitions per source from excited vibrational states (v=1-14). The populations of individual rovibrational levels derived from these data clearly confirm UV excitation. Among the five PDRs in our survey, the Orion Bar shows the greatest deviation of the populations and spectrum from pure UV excitation, while Sharpless 140 shows the least deviation. However, we find that all five PDRs exhibit at least some modification of the level populations relative to their values under pure UV excitation, a result we attribute to collisional effects.

Keywords
  1. molecular-clouds
  2. h-ii-regions
  3. interstellar-medium
  4. infrared-astronomy
  5. spectroscopy
  6. molecular-physics
Bibliographic source Bibcode
2021ApJ...919...27K
See also HTML
https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/919/27
IVOA Identifier IVOID
ivo://CDS.VizieR/J/ApJ/919/27
Document Object Identifer DOI
doi:10.26093/cds/vizier.19190027

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History

2023-02-27T15:03:29Z
Resource record created
2023-02-27T15:03:29Z
Created
2023-11-21T14:41:54Z
Updated

Contact

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