Near infrared view on the photodissociation regions S255, S257, NGC7538 and S140

• Main Authors: Kirsanova, M. S, Tatarnikov, A. M, Boley, P. A, Wiebe, D. S, Maslennikova, N. A, Tatarnikov, A. A
• Format: Journal Article
• Language: English
• Published: 21-06-2023
• Subjects: Physics - Astrophysics of Galaxies; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2306.12264

We performed photometric observations of the S255, S257, S140, NGC7358 and
the Orion~Bar photo-dissociation regions (PDRs) at 2 micron using narrow-band
filters centered on the Br-gamma, H2 and [FeII] lines, as well as the
narrow-band Kcont and the broad-band H filters for continuum subtraction. The
observations were done with the 2.5-m telescope of the SAI Caucasian Mountain
Observatory and the near-infrared camera and spectrograph ASTRONIRCAM. We find
several high-density arc-like structures in the Br-gamma and [FeII] images of
the ionized gas in NGC7538 and extended shells and arcs visible through the H2
emission. The H ionization front and H2 dissociation front are merged in
NGC7538. In S255 and S257 we detected only Br-gamma emission from the HII
regions and bright H2 emission from the PDRs. The projected distance between
the H ionization and H2 dissociation fronts are approx. 0.3-0.4 pc, which
cannot be explained using models of a uniform medium. Most probably, the
ionized and neutral gas in these PDRs is clumpy. The H-to-H2 transitions in the
NGC7538, S255, S257 and S140 PDRs are gradual with no sharp borders. This
conclusion also confirms the suggestion of a clumpy medium.