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Physical conditions of the interstellar medium of high-redshift, strongly lensed submillimetre galaxies from the Herschel-ATLAS

Valtchanov, I.; Virdee, J.; Ivison, R. J.; Swinyard, B.; van der Werf, P.; Rigopoulou, D.; da Cunha, E.; Lupu, R.; Benford, D. J.; Riechers, D.; Smail, Ian; Jarvis, M.; Pearson, C.; Gomez, H.; Hopwood, R.; Altieri, B.; Birkinshaw, M.; Coia, D.; Conversi, L.; Cooray, A.; De Zotti, G.; Dunne, L.; Frayer, D.; Leeuw, L.; Marston, A.; Negrello, M.; Sanchez Portal, M.; Scott, D.; Thompson, M. A.; Vaccari, M.; Baes, M.; Clements, D.; Michałowski, M. J.; Dannerbauer, H.; Serjeant, S.; Auld, R.; Buttiglione, S.; Cava, A.; Dariush, A.; Dye, S.; Eales, S.; Fritz, J.; Ibar, E.; Maddox, S.; Pascale, E.; Pohlen, M.; Rigby, E.; Rodighiero, G.; Smith, D. J. B.; Temi, P.; Carpenter, J.; Bolatto, A.; Gurwell, M. and Vieira, J. D. (2011). Physical conditions of the interstellar medium of high-redshift, strongly lensed submillimetre galaxies from the Herschel-ATLAS. Monthly Notices of the Royal Astronomical Society, 415(4) pp. 3473–3484.

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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 μm and [C ii] 158 μm lines at a signal-to-noise ratio of ∼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 μm wavelength range. The derived redshift of 200 mJy in the 200–600  SDP.81 from the two detections isz = 3.043 ± 0.012, in agreement with ground-based CO measurements. This is the first detection by Herschel of the [O  iii] 88 μm 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≈2000cm−3 and the far-ultraviolet ionizing radiation field G0≈200 (in units of the Habing field – the local Galactic interstellar radiation field of 1.6 × 10−6 Wm−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 [O iii]/FIR ratio and the upper limit of [O i] 63 μm/[C ii] 158 μm, suggest that some fraction of the ionizing radiation is likely to originate from the AGN.

Item Type: Journal Item
Copyright Holders: 2011 RAS, The Authors
ISSN: 1365-2966
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
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 31716
Depositing User: Stephen Serjeant
Date Deposited: 30 Jan 2012 16:06
Last Modified: 16 Oct 2017 14:26
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