A giant green pea identified in the spectroscopy of spatially extended [O III] sources

Suraphong Yuma, Masami Ouchi, Seiji Fujimoto, Takashi Kojima, Yuma Sugahara

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We present the results of the deep Subaru/FOCAS and Keck/MOSFIRE spectroscopy for four spatially extended [O III]λλ4959,5007 sources, dubbed [O III] blobs, at z = 0.6 − 0.8 that are originally pinpointed by large-area Subaru imaging surveys. The line diagnostics of the rest-frame optical lines suggests that only one [O III] blob, OIIIB-3, presents an AGN signature, indicating that hot gas of the rest of the [O III] blobs is heated by star formation. One of such star-forming [O III] blobs, OIIIB-4, at z = 0.838 has an [O III] equivalent width of 845 ±27 Å and an [O III] to [O II]λλ3726,3729 ratio of [O III]/[O II]= 6.5 ±2.7 that are as high as those of typical green peas (Cardamone et al. 2009). The spatially resolved spectrum of OIIIB-4 shows [O III]/[O II]= 5−10 over 14 kpc in the entire large [O III] extended regions of OIIIB-4, unlike the known green peas whose strong [O III] emission region is compact. Moreover, OIIIB-4 presents no high-ionization emission lines unlike green beans that have extended [O III] emission with a type-2 AGN. OIIIB-4 is thus a giant green pea, which is a low stellar mass (7×107M ) galaxy with a very high specific star-formation rate (sSFR = 2×102 Gyr−1), a high ionization parameter (qion ∼ 3×108cm s−1), and a low metallicity similar to those of green peas. Neither an AGN-light echo nor a fast radiative shock likely takes place due to the line diagnostics for spatially-resolved components of OIIIB-4 and no detections of He IIλ4686 or [Ne V]λ3346,3426 lines that are fast-radiative shock signatures. There is a possibility that the spatially-extended [O III] emission of OIIIB-4 is originated from outflowing gas produced by the intense star formation in a density-bounded ionization state. Keywords: galaxies: high redshift — galaxies: evolution — galaxies: formation —ISM: jets and outflows

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2019 Apr 25
Externally publishedYes

ASJC Scopus subject areas

  • General

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