Tracing the Sagittarius stream with blue horizontal branch stars

The definitive version is available at www.blackwell-synergy.com--Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2006.10110.xPeer reviewe

Integral-field studies of the high-redshift Universe

We present results from a new method of exploring the distant Universe. We use 3-D spectroscopy to sample a large cosmological volume at a time when the Universe was less than 3 billion years old to investigate the evolution of star-formation activity. Within this study we also discovered a high redshift type-II quasar which would not have been identified with imaging studies alone. This highlights the crucial role that integral-field spectroscopy may play in surveying the distant Universe in the future.Comment: From proceedings of Euro3D Spectroscopy annual RTN network meeting (ed. J. Walsh). 5 pages, accepted for publication in Astron. Nach

The discovery of a type II quasar at z= 1.65 with integral-field spectroscopy

In this Letter we report the serendipitous discovery of a genuine type II quasar at z= 1.65 using integral-field data from the Visual Multi-Object Spectrograph (VIMOS) on the Very Large Telescope (VLT). This is the first discovery of a type II quasar at z > 1 from optical data alone. J094531-242831, hereafter J0945-2428, exhibits strong narrow (v < 1500 km s-1) emission lines, has a resolved host galaxy, and is undetected to a radio flux density limit of S5 GHz= 0.15 mJy (3σ) . All of these characteristics lead us to believe that J0945-2428 is a bona fide type II quasar. The luminosity of the narrow emission lines in this object suggest that the intrinsic power of the central engine is similar to that found in powerful radio galaxies, indicative of a similarly large supermassive black hole of ∼ 3 × 108 M⊙ (assuming that it is accreting at its Eddington limit). However, from near-infrared imaging observations we find that the old stellar population in the host galaxy has a luminosity of ∼ 0.2 L⋆, mildly inconsistent with the correlation between black hole mass and bulge luminosity found locally, although the uncertainty in the black hole mass estimate is large. This discovery highlights the power that integral-field units have in discovering hidden populations of objects, particularly the sought-after type II quasars, which are invoked to explain the hard X-ray background. As such, future large integral-field surveys could open up a new window on the obscured accretion activity in the Universe

The clustering of subp-mJy radio sources in the Bootes Deep Field

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HI in proto-cluster environments at z>2: absorbing haloes and the Lya forest

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A new perspective on the longitudinal variability of the semidiurnal tide

The longitudinal variability of the semidiurnal tide in the Antarctic upper mesosphere is investigated by comparison of observations from two radars at approximately opposite sides of Antarctica. Under the assumption that the tide is composed of an S = 2 (migrating) and S = 1 (westward-propagating, non-migrating) component only, the relative phases of the components are shown to vary with season such that the waves are typically in constructive interference during the winter (summer) months at longitudes around 0 degrees E (180 degrees E). We show that this has profound effects on the seasonal behaviour of the semidiurnal tide around 78 degrees S dependent on the longitude, and that no single-station observations at this latitude can be considered representative of a "zonal mean". The superposition of these two waves is used to interpret differences in previously-published ground-based climatologies of the tide. Citation: Hibbins, R. E., O. J. Marsh, A. J. McDonald, and M. J. Jarvis (2010), A new perspective on the longitudinal variability of the semidiurnal tide, Geophys. Res. Lett., 37, L14804, doi:10.1029/2010GL044015

Herschel-atlas/Gama: a difference between star formation rates in strong-line and weak-line radio galaxies

We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources (‘high-excitation radio galaxies’) have, on average, a factor of ∼4 higher 250-μm Herschel luminosity than weak-line (‘lowexcitation’) radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line active galactic nuclei (AGN) activity. The strong-line sources are estimated to have star formation rates at least a factor of 3–4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts.Web of Scienc

The cluster environments of radio-loud AGN

Copyright IAURadio-loud AGN play an important role in galaxy evolution. We need to understand their properties, and the processes that affect their behaviour in order to model galaxy formation and development. We here present preliminary results of an investigation into the cluster environments of radio galaxies. We have found evidence of a strong correlation between radio luminosity and environment richness for low excitation radio galaxies, and no evidence of evolution of the environment with redshift. Conversely, for high excitation radio galaxies, we found no correlation with environment richness, and tentative evidence of evolution of the cluster environment

A sample of 6C radio sources designed to find objects at redshift z>4: III - imaging and the radio galaxy K-z relation

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Infrared and millimetre-wavelength evidence for cold accretion within a z = 2.83 Lyman-alpha blob

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.13580.xThis paper discusses infrared and millimetre-wavelength observations of a Lyman alpha blob (LAB) discovered by Smith & Jarvis, a candidate for ionization by the cold accretion scenario discussed in Fardal et al. and Dijkstra et al. We have observed the counterpart galaxy at infrared wavelengths in deep observations with the Spitzer Space Telescope using the IRAC 3.6, 4.5, 5.8 and 8.0 mu m and MIPS 24 mu m bands, as well as using the Max-Planck Millimeter Bolometer (MAMBO-2) at a wavelength of 1.2 mm with the IRAM 30 m telescope. These observations probe the greater than or similar to 95 kpc Lyman alpha halo for the presence of obscured active galactic nucleus (AGN) components or the presence of a violent period of star formation invoked by other models of ionization for these mysterious objects. 24 mu m observations suggest that an obscured AGN would be insufficiently luminous to ionize the halo, and that the star formation rate within the halo may be as low as < 140 M-circle dot yr(-1) depending on the model spectral energy distribution (SED) used. This is reinforced by our observations at 1.2 mm using MAMBO-2, which yield an upper limit of star formation rate < 550 M-circle dot yr(-1) from our non-detection to a 3 sigma flux limit of 0.86 mJy beam(-1). Finding no evidence for either AGN or extensive star formation, we conclude that this halo is ionized by a cold accretion process. We derive model SEDs for the host galaxy, and use the Bruzual & Charlot and Maraston libraries to show that the galaxy is well described by composite stellar populations of total mass 3.42 +/- 0.13 x 10(11) or 4.35 +/- 0.16 x 10(11) M-circle dot depending on the model SEDs used.Peer reviewe