Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 415, Issue 4, Pages 3473-3484Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2011.18959.x
Keywords
galaxies: evolution; galaxies: individual: SDP.81: H-ATLAS J090311.6+003906; galaxies: individual: SDP.130: H-ATLAS J091305.0-005343; infrared: galaxies; radio continuum: galaxies; submillimetre: ISM
Categories
Funding
- BMVIT (Austria)
- ESA-PRODEX (Belgium)
- CEA/CNES (France)
- DLR (Germany)
- ASI/INAF (Italy)
- CICYT/MCYT (Spain)
- CSA (Canada)
- NAOC (China)
- CEA, CNES, CNRS (France)
- ASI (Italy)
- MCINN (Spain)
- SNSB (Sweden)
- STFC (UK)
- NASA (USA)
- Science and Technology Facilities Council [ST/G002533/1, ST/I001212/1, ST/I001573/1, ST/G002630/1, PP/E001637/1, ST/I005765/1, ST/G002622/1, PP/D000963/1, ST/H002456/1] Funding Source: researchfish
- UK Space Agency [ST/G003874/1] Funding Source: researchfish
- STFC [ST/G002622/1, ST/I005765/1, PP/D000963/1, ST/G002533/1, ST/I001573/1, PP/E001637/1, ST/H001530/1, ST/I001212/1, ST/H002456/1, ST/G002630/1] Funding Source: UKRI
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We present Herschel-Spectral and Photometric Imaging Receiver (SPIRE) Fourier transform spectrometer (FTS) and radio follow-up observations of two Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS)-detected strongly lensed distant galaxies. In one of the targeted galaxies H-ATLAS J090311.6+003906 (SDP. 81), we detect [O III] 88 mu m and [C II] 158 mu m lines at a signal-to-noise ratio of similar to 5. We do not have any positive line identification in the other fainter target H-ATLAS J091305.0-005343 (SDP. 130). Currently, SDP. 81 is the faintest submillimetre galaxy with positive line detections with the FTS, with continuum flux just below 200 mJy in the 200-600 mu m wavelength range. The derived redshift of SDP. 81 from the two detections is z = 3.043 +/- 0.012, in agreement with ground-based CO measurements. This is the first detection by Herschel of the [O III] 88 mu m line in a galaxy at redshift higher than 0.05. Comparing the observed lines and line ratios with a grid of photodissociation region (PDR) models with different physical conditions, we derive the PDR cloud density n approximate to 2000 cm(-3) and the far-ultraviolet ionizing radiation field G(0) approximate to 200 (in units of the Habing field - the local Galactic interstellar radiation field of 1.6 x 10(-6) W m(-2)). Using the CO-derived molecular mass and the PDR properties, we estimate the effective radius of the emitting region to be 500-700 pc. These characteristics are typical for star-forming, high-redshift galaxies. The radio observations indicate that SDP. 81 deviates significantly from the local far-infrared/radio (FIR/radio) correlation, which hints that some fraction of the radio emission is coming from an active galactic nucleus (AGN). The constraints on the source size from millimetre-wave observations put a very conservative upper limit of the possible AGN contribution to less than 33 per cent. These indications, together with the high [OIII]/FIR ratio and the upper limit of [O I] 63 mu m/[C II] 158 mu m, suggest that some fraction of the ionizing radiation is likely to originate from the AGN.
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