Caroline van Breukelen

The luminosity function of Lyα emitters at 2.3 < z < 4.6 from integral-field spectroscopy ⋆

We have used VIsible MultiObject Spectrograph Integral-Field Unit (VIMOS-IFU) obser- vations centred on a radio galaxy at z = 2.9 to search for Lyemitters within a comov- ing volume of � 10 4 Mpc 3 . We find 14 Lyemitters with flux > 1.4 × 10 −20 W m −2 , yielding a comoving space density of 0.0018 +0.0006 −0.0005 Mpc −3 . We fit a Schechter luminos- ity function which agrees well with previous studies both at similar redshift (z � 3.4) and higher redshift (z � 5.7). We therefore find no evidence for evolution in the properti es of Lyemitters between 3 < z < 6, although our sample is small. By summing the star- formation rates of the individual Lyemitters we find a total cosmic star-formation rate den- sity ofSF R = 6.7 ± 0.5 × 10 −3 M⊙yr −1 Mpc −3 . Integrating over the luminosity function for the combined Lysurveys at z � 3.4 and accounting for the difference in obscuration between the Lyline and the UV-continuum yields an estimate ofSF R � 2.2 × 10 −2 M⊙yr −1 Mpc −3 , in line with previous multi-colour and narrow-band surveys of high-redshift

A reliable cluster detection technique using photometric redshifts: introducing the 2TecX algorithm

We present a new cluster detection algorithm designed for finding high-redshift clusters using optical/infrared imaging data. The algorithm has two main characteristics. First, it utilizes each galaxys full redshift probability function, instead of an estimate of the photometric redshift based on the peak of the probability function and an associated Gaussian error. Second, it identifies cluster candidates through cross-checking the results of two substantially different selection techniques (the name 2TecX representing the cross-check of the two techniques). These are adaptations of the Voronoi Tesselations and Friends-Of-Friends methods. Monte Carlo simulations of mock catalogues show that cross-checking the cluster candidates found by the two techniques significantly reduces the detection of spurious sources. Furthermore, we examine the selection effects and relative strengths and weaknesses of either method. The simulations also allow us to fine-tune the algorithms parameters, and define completeness and mass limit as a function of redshift. We demonstrate that the algorithm isolates high-redshift clusters at a high level of efficiency and low contamination.

Spectroscopic follow-up of a cluster candidate at z= 1.45

We have obtained deep optical spectroscopic data of the highest-redshift cluster candidate (z ∼ 1.4, CVB13) selected by Van Breukelen et al. in a photometric optical/infrared catalogue of the Subaru XMM‐Newton Deep Field. The data, which comprise 104 targeted galaxies, were taken with the DEep Imaging Multi-Object Spectrograph on the Keck 2 telescope and yielded 31 secure redshifts in the range 1.25 < z < 1.54 within a 7 × 4-arcmin 2 field centred on CVB13. Instead of one massive cluster at z = 1.4, we find evidence for three projected structures at z = 1.40, 1.45 and 1.48. The most statistically robust of these structures, at z = 1.454, has

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 VIMOS on the VLT. This is the first discovery of a type-II quasar at z > 1 from optical data alone. J094531-242831, hereafter J09452428, 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 S5GHz = 0.15 mJy (3�). All of these 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 similarly large supermassive black hole of � 3×10 8 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 integralfield surveys could open up a new window on the obscured accretion activity in the Universe.

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.