Herschel-ATLAS: The angular correlation function of submillimetre galaxies at high and low redshift

Original article can be found at: http://www.aanda.org/ Copyright The European Southern ObservatoryWe present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 μm-selected sample we detect no significant clustering, consistent with the expectation that the 250 μm-selected sources are mostly normal galaxies at z 1. For our 350 μm and 500 μm-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z~2–3 we detect significant strong clustering, leading to an estimate of r0 ~ 7–11 h-1 Mpc. The slope of our clustering measurements is very steep, δ ~ 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.Peer reviewe

NuSTAR and XMM-Newton Observations of Luminous, Heavily Obscured, WISE-selected Quasars at z \~ 2

We report on a NuSTAR and XMM-Newton program that has observed a sample of three extremely luminous, heavily obscured WISE-selected active galactic nuclei (AGNs) at z ~ 2 across a broad X-ray band (0.1 – 79 keV). The parent sample, selected to be faint or undetected in the WISE 3.4 μm (W1) and 4.6 μm (W2) bands but bright at 12 μm (W3) and 22 μm (W4), are extremely rare, with only ~1000 so-called "W1W2-dropouts" across the extragalactic sky. Optical spectroscopy reveals typical redshifts of z ~ 2 for this population, implying rest-frame mid-IR luminosities of νL ν(6 μm) ~ 6 × 1046 erg s–1 and bolometric luminosities that can exceed L bol ~ 1014 L ☉. The corresponding intrinsic, unobscured hard X-ray luminosities are L(2-10 keV) ~ 4 × 1045 erg s–1 for typical quasar templates. These are among the most AGNs known, though the optical spectra rarely show evidence of a broad-line region and the selection criteria imply heavy obscuration even at rest-frame 1.5 μm. We designed our X-ray observations to obtain robust detections for gas column densities N H ≤ 1024 cm–2. In fact, the sources prove to be fainter than these predictions. Two of the sources were observed by both NuSTAR and XMM-Newton, with neither being detected by NuSTAR (f 3-24 keV lsim 10–13 erg cm–2 s–1), and one being faintly detected by XMM-Newton (f 0.5-10 keV ~ 5 × 10–15 erg cm–2 s–1). A third source was observed only with XMM-Newton, yielding a faint detection (f 0.5-10 keV ~ 7 × 10–15 erg cm–2 s–1). The X-ray data imply these sources are either X-ray weak, or are heavily obscured by column densities N H gsim 1024 cm–2. The combined X-ray and mid-IR analysis seems to favor this second possibility, implying the sources are extremely obscured, consistent with Compton-thick, luminous quasars. The discovery of a significant population of heavily obscured, extremely luminous AGNs would not conform to the standard paradigm of a receding torus, in which more luminous quasars are less likely to be obscured, and instead suggests that an additional source of obscuration is present in these extreme sources

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

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.Comment: 13 pages, 6 figures, published in MNRA