Physical conditions of the interstellar medium of high-redshift, strongly lensed submillimetre galaxies from the Herschel-ATLAS
Creators: name: Valtchanov, Ivan
name: Virdee, J.
name: Ivison, R. J.
name: Swinyard, B.
name: van der Werf, P.
name: Rigopoulou, D.
name: da Cunha, E.
name: Lupu, R.
name: Benford, D. J.
name: Riechers, D.
name: Smail, Ian
name: Jarvis, M.
name: Pearson, C.
name: Gomez, H.
name: Hopwood, R.
name: Altieri, B.
name: Birkinshaw, M.
name: Coia, D.
name: Conversi, L.
name: Cooray, A.
name: De Zotti, G.
name: Dunne, L.
name: Frayer, D.
name: Leeuw, L.
name: Marston, A.
name: Negrello, M.
name: Portal, M. Sanchez
name: Scott, D.
name: Thompson, M. A.
name: Vaccari, M.
name: Baes, M.
name: Clements, D.
name: Michalowski, M. J.
name: Dannerbauer, H.
name: Serjeant, S.
name: Auld, R.
name: Buttiglione, S.
name: Cava, A.
name: Dariush, A.
name: Dye, S.
name: Eales, S.
name: Fritz, J.
name: Ibar, E.
name: Maddox, S.
name: Pascale, E.
name: Pohlen, M.
name: Rigby, E.
name: Rodighiero, G.
name: Smith, D. J. B.
name: Temi, P.
name: Carpenter, J.
name: Bolatto, A.
name: Gurwell, M.
name: Vieira, J. D.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present Herschel-SPIRE Fourier Transform Spectrometer (FTS) and radio follow-up observations of two Herschel-ATLAS (H-ATLAS) detected strongly lensed distant galaxies. In one of the targeted galaxies H-ATLAS J090311.6+003906 (SDP.81) we detect [OIII] 88\mum and [CII] 158\mum 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 sub-mm galaxy with positive line detections with the FTS, with continuum flux just below 200 mJy in the 200-600 \mum 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 [OIII] 88\mum line in a galaxy at redshift higher than 0.05. Comparing the observed lines and line ratios with a grid of photo-dissociation region (PDR) models with different physical conditions, we derive the PDR cloud density n ~ 2000 cm^{-3} and the far-UV ionizing radiation field G_0 ~ 200 (in units of the Habing field -- the local Galactic interstellar radiation field of 1.6x10^{-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 FIR/radio correlation, which hints that some fraction of the radio emission is coming from an AGN. The constraints on the source size from millimiter-wave observations put a very conservative upper limit of the possible AGN contribution to less than 33%. These indications, together with the high [OIII]/FIR ratio and the upper limit of [OI] 63\mum/[CII] 158\mum suggest that some fraction of the ionizing radiation is likely to originate from an AGN.
description: 13 pages, 6 figures, published in MNRAS