A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies
Date
2023/09/15
Journal Title
Journal ISSN
Volume Title
Publisher
EDP SCIENCES S A
Abstract
Green Pea galaxies (GPs) present among the most intense starbursts known in the nearby Universe. These galaxies are regarded as local analogs of high-redshift galaxies, making them a benchmark in the understanding of the star formation processes and the galactic evolution in the early Universe. In this work, we performed an integral field spectroscopic (IFS) study for a set of 24 GPs to investigate the interplay between its ionized interstellar medium (ISM) and the massive star formation that these galaxies present. Observations were taken in the optical spectral range (lambda 4750 angstrom-lambda 9350 angstrom) with the MUSE spectrograph attached to the 8.2m telescope VLT. Spatial extension criteria were employed to verify which GPs are spatially resolved in the MUSE data cubes. We created and analyzed maps of spatially distributed emission lines (at di fferent stages of excitation), continuum emission, and properties of the ionized ISM (e.g., ionization structure indicators, physical-chemical conditions, dust extinction). We also took advantage of our IFS data to produce integrated spectra of selected galactic regions in order to study their physical-chemical conditions. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located in the center of the galaxy, where the starburst is present. The continuum maps, with an average angular extent of 4 '', exhibit more complex structures than the emission line maps. However, the [OIII]lambda 5007 angstrom emission line maps tend to extend beyond the continuum images (the average angular extent is 5.5 ''), indicating the presence of low surface brightness ionized gas in the outer parts of the galaxies. H alpha/H beta, [SII]/H alpha, and [OI]/H alpha maps trace low-extinction, optically thin regions. The line ratios [OIII]/H beta and [NII]/H alpha span extensive ranges, with values varying from 0.5 dex to 0.9 dex and from 1.7 dex to 0.8 dex, respectively. Regarding the integrated spectra, the line ratios were fit to derive physical properties including the electron densities n(e) = 30-530 cm(-3), and, in six GPs with a measurable [OIII]lambda 4363 angstrom line, electron temperatures of T-e = 11 500 K-15 500 K, so the direct method was applied in these objects to retrieve metallicities 12 + log(O/H) similar or equal to 8. We found the presence of the high-ionizing nebular HeII lambda 4686 angstrom line in three GPs, where two of them present among the highest sSFR values ( >8 x 10(8) yr(-1)) in this sample. Non-Wolf-Rayet (WR) features are detected in these galaxy spectra.
Description
Keywords
LY-ALPHA ESCAPE, INTEGRAL FIELD SPECTROSCOPY, STAR-FORMATION, CHEMICAL ABUNDANCES, OPTICAL DEPTH, IONIZING-RADIATION, HOST GALAXIES, LINE GALAXIES, MASSIVE STARS, GAS