arXiv subjects

D. N. A. Murphy

Publications and source records attributed to D. N. A. Murphy.

16 recordsLinked to original sources

arXiv2024

WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan's Quintet

We present a detailed study of the large-scale shock front in Stephan's Quintet, a byproduct of past and ongoing interactions. Using integral-field spectroscopy from the new William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE), recent 144 MHz observations from the LOFAR Two-metre Sky Survey (LoTSS), and archival data from the Very Large Array and James Webb Space Telescope (JWST), we obtain new measurements of key shock properties and determine its impact on the system. Harnessing the WEAVE large integral field unit's (LIFU) field of view (90 $\times$ 78 arcsec$^{2}$), spectral resolution ($R\sim2500$) and continuous wavelength coverage across the optical band, we perform robust emission line modeling and dynamically locate the shock within the multi-phase intergalactic medium (IGM) with higher precision than previously possible. The shocking of the cold gas phase is hypersonic, and comparisons with shock models show that it can readily account for the observed emission line ratios. In contrast, we demonstrate that the shock is relatively weak in the hot plasma visible in X-rays (with Mach number of $\mathcal{M} \sim 2 - 4$), making it inefficient at producing the relativistic particles needed to explain the observed synchrotron emission. Instead, we propose that it has led to an adiabatic compression of the medium, which has increased the radio luminosity ten-fold. Comparison of the Balmer line-derived extinction map with the molecular gas and hot dust observed with JWST suggests that pre-existing dust may have survived the collision, allowing the condensation of H$_{2}$ - a key channel for dissipating the shock energy.

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arXiv2024

The VST ATLAS Quasar Survey III: Halo mass function via quasar clustering and quasar-CMB lensing cross-clustering

We exploit the VST ATLAS quasar/QSO catalogue to perform three measurements of the quasar halo mass profile. First, we make a new estimate of the angular auto-correlation function of $\approx230,000$ ATLAS quasars with $z_{photo}\lesssim 2.5$ and $17<g<22$. By comparing with the $Λ$CDM mass clustering correlation function, we measure the quasar bias to be $b_Q\approx2.1$, implying a quasar halo mass of $M_{halo}\approx8.5\times10^{11}$h$^{-1} M_\odot$. Second, we cross-correlate these $z\approx1.7$ ATLAS quasars with the Planck Cosmic Microwave Background (CMB) lensing maps, detecting a somewhat stronger signal at $4'<θ<60'$ than previous authors. Scaling these authors' model fit to our data we estimate a quasar host halo mass of $M_{halo}\approx8.3\times10^{11}h^{-1}$M$_{\odot}$. Third, we fit Halo Occupation Distribution (HOD) model parameters to our quasar auto-correlation function and from the derived halo mass function we estimate a quasar halo mass of $M_{halo}\approx2.5\times10^{12}$h$^{-1} M_\odot$. We then compare our HOD model prediction to our quasar-CMB lensing result, confirming their consistency. We find that most ($\approx2/3$) QSOs have halo masses within a factor of $\approx3$ of this average mass. An analysis based on the probability of X-ray detections of AGN in galaxies and the galaxy stellar mass function gives a similarly small mass range. Finally, we compare the quasar halo mass and luminosity functions and suggest that gravitational growth may produce the constant space density with redshift seen in the quasar luminosity function.

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arXiv2024

Retrieval of the physical parameters of galaxies from WEAVE-StePS-like data using machine learning

The WHT Enhanced Area Velocity Explorer (WEAVE) is a new, massively multiplexing spectrograph. This new instrument will be exploited to obtain high S/N spectra of $\sim$25000 galaxies at intermediate redshifts for the WEAVE Stellar Population Survey (WEAVE-StePS). We test machine learning methods for retrieving the key physical parameters of galaxies from WEAVE-StePS-like spectra using both photometric and spectroscopic information at various S/Ns and redshifts. We simulated $\sim$105000 galaxy spectra assuming SFH with an exponentially declining star formation rate, covering a wide range of ages, stellar metallicities, sSFRs, and dust extinctions. We then evaluated the ability of the random forest and KNN algorithms to correctly predict such parameters assuming no measurement errors. We checked how much the predictive ability deteriorates for different S/Ns and redshifts, finding that both algorithms still accurately estimate the ages and metallicities with low bias. The dispersion varies from 0.08-0.16 dex for ages and 0.11-0.25 dex for metallicity, depending on the redshift and S/N. For dust attenuation, we find a similarly low bias and dispersion. For the sSFR, we find a very good constraining power for star-forming galaxies, log sSFR$\gtrsim$ -11, where the bias is $\sim$ 0.01 dex and the dispersion is $\sim$ 0.10 dex. For more quiescent galaxies, with log sSFR$\lesssim$ -11, we find a higher bias, 0.61-0.86 dex, and a higher dispersion, $\sim$ 0.4 dex, for different S/Ns and redshifts. Generally, we find that the RF outperforms the KNN. Finally, the retrieved sSFR was used to successfully classify galaxies as part of the blue cloud, green valley, or red sequence. We demonstrate that machine learning algorithms can accurately estimate the physical parameters of simulated galaxies even at relatively low S/N=10 per angstrom spectra with available ancillary photometric information.

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arXiv2024

The Gaia-ESO Survey: The DR5 analysis of the medium-resolution GIRAFFE and high-resolution UVES spectra of FGK-type stars

The Gaia-ESO Survey is an European Southern Observatory (ESO) public spectroscopic survey that targeted $10^5$ stars in the Milky Way covering the major populations of the disk, bulge and halo. The observations were made using FLAMES on the VLT obtaining both UVES high ($R\sim47,000$) and GIRAFFE medium ($R\sim20,000$) resolution spectra. The analysis of the Gaia-ESO spectra was the work of multiple analysis teams (nodes) within five working groups (WG). The homogenisation of the stellar parameters within WG11 (high resolution observations of FGK stars) and the homogenisation of the stellar parameters within WG10 (medium resolution observations of FGK stars) is described here. In both cases, the homogenisation was carried out using a bayesian Inference method developed specifically for the Gaia-ESO Survey by WG11. The WG10 homogenisation primarily used the cross-match of stars with WG11 as the reference set in both the stellar parameter and chemical abundance homogenisation. In this way the WG10 homogenised results have been placed directly onto the WG11 stellar parameter and chemical abundance scales. The reference set for the metal-poor end was sparse which limited the effectiveness of the homogenisation in that regime. For WG11, the total number of stars for which stellar parameters were derived was 6,231 with typical uncertainties for Teff, log g and [Fe/H] of 32~K, 0.05 and 0.05 respectively. One or more chemical abundances out of a possible 39 elements were derived for 6,188 of the stars. For WG10, the total number of stars for which stellar parameters were derived was 76,675 with typical uncertainties for Teff, log g and [Fe/H] of 64~K, 0.15 and 0.07 respectively. One or more chemical abundances out of a possible 30 elements were derived for 64,177 of the stars.

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arXiv2023

The Gaia-ESO Survey: homogenisation of stellar parameters and elemental abundances

The Gaia-ESO Survey is a public spectroscopic survey that has targeted $\gtrsim10^5$ stars covering all major components of the Milky Way from the end of 2011 to 2018, delivering its public final release in May 2022. Unlike other spectroscopic surveys, Gaia-ESO is the only survey that observed stars across all spectral types with dedicated, specialised analyses: from O ($T_\mathrm{eff} \sim 30,000-52,000$~K) all the way to K-M ($\gtrsim$3,500~K). The physics throughout these stellar regimes varies significantly, which has previously prohibited any detailed comparisons between stars of significantly different type. In the final data release (internal data release 6) of the Gaia-ESO Survey, we provide the final database containing a large number of products such as radial velocities, stellar parameters and elemental abundances, rotational velocity, and also, e.g., activity and accretion indicators in young stars and membership probability in star clusters for more than 114,000 stars. The spectral analysis is coordinated by a number of Working Groups (WGs) within the Survey, which specialise in the various stellar samples. Common targets are analysed across WGs to allow for comparisons (and calibrations) amongst instrumental setups and spectral types. Here we describe the procedures employed to ensure all Survey results are placed on a common scale to arrive at a single set of recommended results for all Survey collaborators to use. We also present some general quality and consistency checks performed over all Survey results.

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arXiv2023

WEAVE-StePS. A stellar population survey using WEAVE at WHT

The upcoming new generation of optical spectrographs on four-meter-class telescopes will provide valuable opportunities for forthcoming galaxy surveys through their huge multiplexing capabilities, excellent spectral resolution, and unprecedented wavelength coverage. WEAVE is a new wide-field spectroscopic facility mounted on the 4.2 m William Herschel Telescope in La Palma. WEAVE-StePS is one of the five extragalactic surveys that will use WEAVE during its first five years of operations. It will observe galaxies using WEAVE MOS (~950 fibres across a field of view of ~3 deg2 on the sky) in low-resolution mode (R~5000, spanning the wavelength range 3660-9590 AA). WEAVE-StePS will obtain high-quality spectra (S/N ~ 10 per AA at R~5000) for a magnitude-limited (I_AB = 20.5) sample of ~25,000 galaxies, the majority selected at z>=0.3. The survey goal is to provide precise spectral measurements in the crucial interval that bridges the gap between LEGA-C and SDSS data. The wide area coverage of ~25 deg2 will enable us to observe galaxies in a variety of environments. The ancillary data available in each observed field (including X-ray coverage, multi-narrow-band photometry and spectroscopic redshift information) will provide an environmental characterisation for each observed galaxy. This paper presents the science case of WEAVE-StePS, the fields to be observed, the parent catalogues used to define the target sample, and the observing strategy chosen after a forecast of the expected performance of the instrument for our typical targets. WEAVE-StePS will go back further in cosmic time than SDSS, extending its reach to encompass more than ~6 Gyr, nearly half of the age of the Universe. The spectral and redshift range covered by WEAVE-StePS will open a new observational window by continuously tracing the evolutionary path of galaxies in the largely unexplored intermediate-redshift range.

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arXiv2022

VST ATLAS Galaxy Cluster Catalogue I: cluster detection and mass calibration

Taking advantage of $\sim4700$ deg$^2$ optical coverage of the Southern sky offered by the VST ATLAS survey, we construct a new catalogue of photometrically selected galaxy groups and clusters using the {\sc orca} cluster detection algorithm. The catalogue contains $\sim 22,000$ detections with $N_{200}>10$ and $\sim9,000$ with $N_{200}>20$. We estimate the photometric redshifts of the clusters using machine learning and find the redshift distribution of the sample to extend to $z\sim0.7$, peaking at $z\sim0.25$. We calibrate the ATLAS cluster mass-richness scaling relation using masses from the MCXC, Planck, ACT DR5 and SDSS redMaPPer cluster samples. We estimate the ATLAS sample to be $>95\%$ complete and $>85\%$ pure at $z<0.35$ and in the $M_{\rm 200m}$>$1\times10^{14}h^{-1}{\rm M}_\odot$ mass range. At $z<0.35$, we also find the ATLAS sample to be more complete than redMaPPer, recovering a $\sim40\%$ higher fraction of Abell clusters. This higher sample completeness places the amplitude of the $z<0.35$ ATLAS cluster mass function closer to the predictions of a $Λ$CDM model with parameters based on the Planck CMB analyses, compared to the mass functions of the other cluster samples. However, strong tensions between the observed ATLAS mass functions and models remain. We shall present a detailed cosmological analysis of the ATLAS cluster mass functions in paper II. In the future, optical counterparts to X-ray-detected eROSITA clusters can be identified using the ATLAS sample. The catalogue is also well suited for auxiliary spectroscopic target selection in 4MOST. The ATLAS cluster catalogue is publicly available at http://astro.dur.ac.uk/cosmology/vstatlas/cluster_catalogue/.

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arXiv2022

The VST ATLAS Quasar Survey I: Catalogue

We present the VST ATLAS Quasar Survey, consisting of $\sim1,229,000$ quasar (QSO) candidates with $16 2.2$. One of the aims of this catalogue is to select QSO targets for the 4MOST Cosmology Redshift Survey. To guide our selection, we use X-ray/UV/optical/MIR data in the extended William Herschel Deep Field (WHDF) where we find a $g<22.5$ broad-line QSO density of $269\pm67$ deg$^{-2}$, roughly consistent with the expected $\sim196$ deg$^{-2}$. We also find that $\sim25$% of our QSOs are morphologically classed as optically extended. Overall, we find that in these deep data, MIR, UV and X-ray selections are all $\sim70-90$% complete while X-ray suffers less contamination than MIR and UV. MIR is however more sensitive than X-ray or UV to $z>2.2$ QSOs at $g<22.5$ and the eROSITA limit. We then adjust the selection criteria from our previous 2QDES pilot survey and prioritise VST ATLAS candidates that show both UV and MIR excess, while also selecting candidates initially classified as extended. We test our selections using data from DESI (which will be released in DR1) and 2dF to estimate the efficiency and completeness of our selections, and finally we use ANNz2 to determine photometric redshifts for the QSO candidate catalogue. Applying over the $\sim4700$ deg$^2$ ATLAS area gives us $\sim917,000$ $z<2.2$ QSO candidates of which 472,000 are likely to be $z<2.2$ QSOs, implying a sky density of $\sim$100 deg$^{-2}$, which our WHDF analysis suggests will rise to at least 130 deg$^{-2}$ when eROSITA X-ray candidates are included. At $z>2.2$, we find $\sim310,000$ candidates, of which 169,000 are likely to be QSOs for a sky density of $\sim36$ deg$^{-2}$.

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arXiv2022

The nature of sub-millimetre galaxies II: an ALMA comparison of SMG dust heating mechanisms

We compare the contribution of Active Galactic Nuclei (AGN) and star-formation towards dust heating in sub-mm galaxies (SMGs). We have used ALMA at $0."1$ resolution to image a complete flux-limited sample of seven sub-mm sources previously shown to have spectral energy distributions (SEDs) that were as well-fitted by obscured AGN as star-forming galaxy templates. Indeed, two sub-mm sources were known to be quasars from their absorbed X-ray emission. We find the sub-mm sizes of all SMGs to be small ($\approx1-2$kpc) and generally $\sim3$ times smaller than any host detected in the Near-Infra-Red (NIR). In all cases, the five SMGs are comparable in sub-mm size to the two known quasars and four $z\approx6$ quasars, also observed with ALMA. We detect no evidence of diffuse spiral arms in this complete sample. We then convert the Far-Infra-Red (FIR) luminosities to star-formation rate (SFR) surface densities and find that the SMGs occupy the same range as the known quasars in our sample. We conclude that in terms of sub-mm size, extent relative to host and SFR density as well as luminosity and Mid-IR (MIR) colour, there is little distinction between the SMGs and sub-mm bright quasars. Finally, we present preliminary evidence that SMGs with higher MIR luminosities and sub-mm loud quasars tend to have dust components that range to hotter temperatures than their less luminous SMG counterparts. In light of these results, we continue to suggest that luminous SMGs may host dust-absorbed quasars that may simultaneously dominate the FIR and hard X-ray backgrounds.

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arXiv2020

IGAPS: the merged IPHAS and UVEX optical surveys of theNorthern Galactic Plane

The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Halpha, g and U_RGO. The IGAPS footprint fills the Galactic coordinate range, |b| < 5deg and 30deg < l < 215deg. A uniform calibration, referred to the Pan-STARRS system, is applied to g, r and i, while the Halpha calibration is linked to r and then is reconciled via field overlaps. The astrometry in all 5 bands has been recalculated on the Gaia DR2 frame. Down to i ~ 20 mag (Vega system), most stars are also detected in g, r and Halpha. As exposures in the r band were obtained within the IPHAS and UVEX surveys a few years apart, typically, the catalogue includes two distinct r measures, r_I and r_U. The r 10sigma limiting magnitude is ~21, with median seeing 1.1 arcsec. Between ~13th and ~19th magnitudes in all bands, the photometry is internally reproducible to within 0.02 magnitudes. Stars brighter than r=19.5 have been tested for narrow-band Halpha excess signalling line emission, and for variation exceeding |r_I-r_U| = 0.2 mag. We find and flag 8292 candidate emission line stars and over 53000 variables (both at >5sigma confidence). The 174-column catalogue will be available via CDS Strasbourg.

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arXiv2019

A few StePS forward in unveiling the complexity of galaxy evolution: light-weighted stellar ages of intermediate redshift galaxies with WEAVE

The upcoming new generation of optical spectrographs on four-meter-class telescopes will provide invaluable information for reconstructing the history of star formation in individual galaxies up to redshifts of about 0.7. We aim at defining simple but robust and meaningful physical parameters that can be used to trace the coexistence of widely diverse stellar components: younger stellar populations superimposed on the bulk of older ones. We produce spectra of galaxies closely mimicking data from the forthcoming Stellar Populations at intermediate redshifts Survey (StePS), a survey that uses the WEAVE spectrograph on the William Herschel Telescope. First, we assess our ability to reliably measure both ultraviolet and optical spectral indices in galaxies of different spectral types for typically expected signal-to-noise levels. Then, we analyze such mock spectra with a Bayesian approach, deriving the probability density function of r- and u-band light-weighted ages as well as of their difference. We find that the ultraviolet indices significantly narrow the uncertainties in estimating the r- and u-band light-weighted ages and their difference in individual galaxies. These diagnostics, robustly retrievable for large galaxy samples even when observed at moderate signal-to-noise ratios, allow us to identify secondary episodes of star formation up to an age of ~0.1 Gyr for stellar populations older than ~1.5 Gyr, pushing up to an age of ~1 Gyr for stellar populations older than ~5 Gyr. The difference between r-band and u-band light-weighted ages is shown to be a powerful diagnostic to characterize and constrain extended star-formation histories and the presence of young stellar populations on top of older ones. This parameter can be used to explore the interplay between different galaxy star-formation histories and physical parameters such as galaxy mass, size, morphology, and environment.

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arXiv2019

The Pan-STARRS1 Surveys

Pan-STARRS1 has carried out a set of distinct synoptic imaging sky surveys including the $3π$ Steradian Survey and the Medium Deep Survey in 5 bands ($grizy_{P1}$). The mean 5$σ$ point source limiting sensitivities in the stacked 3$π$ Steradian Survey in $grizy_{P1}$ are (23.3, 23.2, 23.1, 22.3, 21.4) respectively. The upper bound on the systematic uncertainty in the photometric calibration across the sky is 7-12 millimag depending on the bandpass. The systematic uncertainty of the astrometric calibration using the Gaia frame comes from a comparison of the results with Gaia: the standard deviation of the mean and median residuals ($ Δra, Δdec $) are (2.3, 1.7) milliarcsec, and (3.1, 4.8) milliarcsec respectively. The Pan-STARRS system and the design of the PS1 surveys are described and an overview of the resulting image and catalog data products and their basic characteristics are described together with a summary of important results. The images, reduced data products, and derived data products from the Pan-STARRS1 surveys are available to the community from the Mikulski Archive for Space Telescopes (MAST) at STScI.

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arXiv2018

Two more, bright, z > 6 quasars from VST ATLAS and WISE

Recently, Carnall et al. discovered two bright high redshift quasars using the combination of the VST ATLAS and WISE surveys. The technique involved using the 3-D colour plane i-z:z-W1:W1-W2 with the WISE W1 (3.4 micron) and W2 (4.5 micron) bands taking the place of the usual NIR J band to help decrease stellar dwarf contamination. Here we report on our continued search for 5.7 6 quasars, VST-ATLAS J158.6938-14.4211 at z=6.07 and J332.8017-32.1036 at z=6.32 with magnitudes of z_AB=19.4 and 19.7 mag respectively. J158.6938-14.4211 was confirmed by Keck LRIS observations and J332.8017-32.1036 was confirmed by ESO NTT EFOSC-2 observations. Here we present VLT X-shooter Visible and NIR spectra for the four ATLAS quasars. We have further independently rediscovered two z>5.7 quasars previously found by the VIKING/KiDS and PanSTARRS surveys. This means that in ATLAS we have now discovered a total of six quasars in our target 5.7<z<6.4 redshift range. Making approximate corrections for incompleteness, we find that our quasar space density agrees with the SDSS results of Jiang et al. at M_1450A~-27mag. Preliminary virial mass estimates based on the CIV and MIII emission lines give black hole masses in the range M_BH~1-6x10e9 M_solar for the four ATLAS quasars.

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arXiv2017

280 one-opposition near-Earth asteroids recovered by the EURONEAR with the Isaac Newton Telescope

One-opposition near-Earth asteroids (NEAs) are growing in number, and they must be recovered to prevent loss and mismatch risk, and to improve their orbits, as they are likely to be too faint for detection in shallow surveys at future apparitions. We aimed to recover more than half of the one-opposition NEAs recommended for observations by the Minor Planet Center (MPC) using the Isaac Newton Telescope (INT) in soft-override mode and some fractions of available D-nights. During about 130 hours in total between 2013 and 2016, we targeted 368 NEAs, among which 56 potentially hazardous asteroids (PHAs), observing 437 INT Wide Field Camera (WFC) fields and recovering 280 NEAs (76% of all targets). Engaging a core team of about ten students and amateurs, we used the THELI, Astrometrica, and the Find_Orb software to identify all moving objects using the blink and track-and-stack method for the faintest targets and plotting the positional uncertainty ellipse from NEODyS. Most targets and recovered objects had apparent magnitudes centered around V~22.8 mag, with some becoming as faint as V~24 mag. One hundred and three objects (representing 28% of all targets) were recovered by EURONEAR alone by Aug 2017. Orbital arcs were prolonged typically from a few weeks to a few years; our oldest recoveries reach 16 years. The O-C residuals for our 1,854 NEA astrometric positions show that most measurements cluster closely around the origin. In addition to the recovered NEAs, 22,000 positions of about 3,500 known minor planets and another 10,000 observations of about 1,500 unknown objects (mostly main-belt objects) were promptly reported to the MPC by our team. Four new NEAs were discovered serendipitously in the analyzed fields, increasing the counting to nine NEAs discovered by the EURONEAR in 2014 and 2015.

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arXiv2015

Photometric Classification of quasars from RCS-2 using Random Forest

Aims. Construction of a new quasar candidate catalog from the Red-Sequence Cluster Survey 2 (RCS-2), identified solely from photometric information using an automated algorithm suitable for large surveys. The algorithm performance is tested using a well-defined SDSS spectroscopic sample of quasars and stars. Methods. The Random Forest algorithm constructs the catalog from RCS-2 point sources using SDSS spectroscopically-confirmed stars and quasars. The algorithm identifies putative quasars from broadband magnitudes (g, r, i, z) and colours. Exploiting NUV GALEX measurements for a subset of the objects, we refine the classifier by adding new information. An additional subset of the data with WISE W1 and W2 bands is also studied. Results. Upon analyzing 542,897 RCS-2 point sources, the algorithm identified 21,501 quasar candidates, with a training-set-derived precision (the fraction of true positives within the group assigned quasar status) of 89.5% and recall (the fraction of true positives relative to all sources that actually are quasars) of 88.4%. These performance metrics improve for the GALEX subset; 6,530 quasar candidates are identified from 16,898 sources, with a precision and recall respectively of 97.0% and 97.5%. Algorithm performance is further improved when WISE data are included, with precision and recall increasing to 99.3% and 99.1% respectively for 21,834 quasar candidates from 242,902 sources. We compile our final catalog (38,257) by merging these samples and removing duplicates. An observational follow up of 17 bright (r < 19) candidates with long-slit spectroscopy at DuPont telescope (LCO) yields 14 confirmed quasars. Conclusions. The results signal encouraging progress in the classification of point sources with Random Forest algorithms to search for quasars within current and future large-area photometric surveys.

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arXiv2011

ORCA: The Overdense Red-sequence Cluster Algorithm

We present a new cluster detection algorithm designed for the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey but with generic application to any multiband data. The method makes no prior assumptions about the properties of clusters other than (a) the similarity in colour of cluster galaxies (the "red sequence") and (b) an enhanced projected surface density. The detector has three main steps: (i) it identifies cluster members by photometrically filtering the input catalogue to isolate galaxies in colour-magnitude space, (ii) a Voronoi diagram identifies regions of high surface density, (iii) galaxies are grouped into clusters with a Friends-of-Friends technique. Where multiple colours are available, we require systems to exhibit sequences in two colours. In this paper we present the algorithm and demonstrate it on two datasets. The first is a 7 square degree sample of the deep Sloan Digital Sky Survey equatorial stripe (Stripe 82), from which we detect 97 clusters with z<=0.6. Benefiting from deeper data, we are 100% complete in the maxBCG optically-selected cluster catalogue (based on shallower single epoch SDSS data) and find an additional 78 previously unidentified clusters. The second dataset is a mock Medium Deep Survey (MDS) Pan-STARRS catalogue, based on the Lambda-CDM model and a semi-analytic galaxy formation recipe. Knowledge of galaxy-halo memberships in the mock allows a quantification of algorithm performance. We detect 305 mock clusters in haloes with mass >10^13 solar masses at z<=0.6 and determine a spurious detection rate of <1%, consistent with tests on the Stripe 82 catalogue. The detector performs well in the recovery of model Lambda-CDM clusters. (abridged)

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