Far-infrared Herschel SPIRE spectroscopy of lensed starbursts reveals physical conditions of ionized gas

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Zhang, Zhi-Yu, Ivison, R. J., George, R. D., Zhao YH(赵应和), Dunne, L., Herrera-Camus, R., Lewis, A. J. R., Liu, Daizhong, Naylor, D., Oteo, Ivan, Riechers, D. A., Smail, Ian, Yang, Chentao, Eales, Stephen, Hopwood, Ros, Maddox, Steve, Omont, Alain, van der Werf, Paul
• Format: Article in Journal/Newspaper
• Language: English
• Published: OXFORD UNIV PRESS 2018
• Subjects: galaxies: active; galaxies: high-redshift; galaxies: starburst; infrared: galaxies; submillimetre: galaxies; 天文学; 天文学::天体物理学; 理学; 理学::天文学; Astronomy & Astrophysics; FOURIER-TRANSFORM SPECTROMETER; H-II REGIONS; ACTIVE GALACTIC NUCLEI; HUBBLE-SPACE-TELESCOPE; STAR-FORMATION HISTORY; SOUTH-POLE TELESCOPE; NARROW-LINE REGIONS; EARLY-TYPE GALAXIES; DEEP-FIELD-SOUTH; SUBMILLIMETER GALAXIES; Ionization of gases; 657.2 Extraterrestrial Physics and Stellar Phenomena - 703.2 Electric Filters - 723.1.1 Computer Programming Languages - 802.2 Chemical Reactions - 941.4 Optical Variables Measurements; Hubble; South Pole; South pole
• Online Access: http://ir.ynao.ac.cn/handle/114a53/18399; http://ir.ynao.ac.cn/handle/114a53/18400; https://academic.oup.com/mnras/article/481/1/59/5067311; https://doi.org/10.1093/mnras/sty2082

The most intensively star-forming galaxies are extremely luminous at far-infrared ( FIR) wavelengths, highly obscured at optical and ultraviolet wavelengths, and lie at z >= 1-3. We present a programme of FIR spectroscopic observations with the SPIRE FTS, as well as photometric observations with PACS, both on board Herschel, towards a sample of 45 gravitationally lensed, dusty starbursts across z similar to 1-3.6. In total, we detected 27 individual lines down to 3 sigma, including nine [C II] 158 mu m lines with confirmed spectroscopic redshifts, five possible [C II] lines consistent with their FIR photometric redshifts, and in some individual sources a few [OIII] 88 mu m, [O III] 52 mu m, [O I] 145 mu m, [O I] 63 mu m, [N II] 122 mu m and OH 119 mu m ( in absorption) lines. To derive the typical physical properties of the gas in the sample, we stack all spectra weighted by their intrinsic luminosity and by their 500 mu m flux densities, with the spectra scaled to a common redshift. In the stacked spectra, we detect emission lines of [CII] 158 mu m, [N II] 122 mu m, [O III] 88 mu m, [O III] 52 mu m, [O I] 63 mu m and the absorption doublet of OH at 119 mu m, at high fidelity. We find that the average electron densities traced by the [NII] and [O III] lines are higher than the average values in local star-forming galaxies and ULIRGs, using the same tracers. From the [NII]/[C II] and [O I]/[C II] ratios, we find that the [CII] emission is likely dominated by the photodominated regions (PDR), instead of by ionized gas or large-scale shocks.