Photometric Redshift Analysis Research Articles

The bright end of the galaxy luminosity function at z ≃ 7 from the VISTA VIDEO survey

ABSTRACT We have conducted a search for z ≃ 7 Lyman-break galaxies over 8.2 deg2 of near-infrared imaging from the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey in the XMM–Newton-Large Scale Structure (XMM-LSS) and the Extended Chandra Deep Field-South (ECDF-S) fields. Candidate galaxies were selected from a full photometric redshift analysis down to a Y + J depth of 25.3 (5σ), utilizing deep auxiliary optical and Spitzer/Infrared Array Camera (IRAC) data to remove brown dwarf and red interloper galaxy contaminants. Our final sample consists of 28 candidate galaxies at 6.5 ≤ z ≤ 7.5 with −23.5 ≤ MUV ≤ −21.6. We derive stellar masses of 9.1 ≤ log10(M⋆/M⊙) ≤ 10.9 for the sample, suggesting that these candidates represent some of the most massive galaxies known at this epoch. We measure the rest-frame ultraviolet (UV) luminosity function (LF) at z ≃ 7, confirming previous findings of a gradual decline in number density at the bright end (MUV < −22) that is well described by a double power law (DPL). We show that quasar contamination in this magnitude range is expected to be minimal, in contrast to conclusions from recent pure-parallel Hubble studies. Our results are up to a factor of 10 lower than previous determinations from optical-only ground-based studies at MUV ≲ −23. We find that the inclusion of YJHKs photometry is vital for removing brown dwarf contaminants, and z ≃ 7 samples based on red optical data alone could be highly contaminated (≳50 per cent). In comparison with other robust z > 5 samples, our results further support little evolution in the very bright end of the rest-frame UV LF from z = 5–10, potentially signalling a lack of mass quenching and/or dust obscuration in the most massive galaxies in the first Gyr.

Physical Characterization of Early Galaxies in the Webb’s First Deep Field SMACS J0723.3-7327

This paper highlights initial photometric analyses of JWST NIRCam imaging data in the sightline of SMACS0723, aiming to identify galaxies at redshift z > 7. By applying a conservative Lyman-break selection followed by photometric-redshift analysis and visual inspection, we identify four F090W-dropout and two F150W-dropout sources, three of which were recently confirmed in an independent spectroscopic analysis to z = 7.663, 7.665, and 8.499. We then supplement our sample with a photometric-redshift selection, and identify five additional candidates at 7 < z phot < 13. The NIRCam images clearly resolve all sources and reveal their subgalactic components that were not resolved/detected in the previous imaging by Hubble Space Telescope. Our spectral energy distribution analysis reveals that the selected galaxies are characterized by young stellar populations (median age of ∼50 Myr) of subsolar metallicity (∼0.2 Z ⊙) and little dust attenuation (A V ∼ 0.5). In several cases, we observe extreme Hβ+[O iii] lines being captured in the F444W band and seen as color excess, which is consistent with their observed high star formation rate surface density. Eight of the 11 sources identified in this study appear in at least one of the recent studies (Adams et al.; Atek et al.; Donnan et al.; Harikane et al.; Yan et al.) of the same fields, implying the high fidelity of our selection. We crossmatch all high-z galaxy candidates presented in the five studies with our catalog and discuss the possible causes of discrepancy in the final lists.

Unresolved z ∼ 8 Point Sources and Their Impact on the Bright End of the Galaxy Luminosity Function

The distribution and properties of the first galaxies and quasars are critical pieces of the puzzle in understanding galaxy evolution and cosmic reionization. Previous studies have often excluded unresolved sources as potential low-redshift interlopers. We combine broadband color and photometric redshift analysis with morphological selections to identify a robust sample of candidates consistent with unresolved point sources at redshifts z ∼ 8 using deep Hubble Space Telescope images. We also examine G141 grism spectroscopic data to identify and eliminate dwarf star contaminants. From these analyses, we identify three bright (M UV ≲ −22 AB mag) dropout point sources at 7.5 < z < 8.1. Spectral energy distribution analyses suggest that these sources are either quasars or compact star-forming galaxies. The flux captured by the IRAC 4.5 μm channel suggests that they have moderate Hβ + [O III] equivalent widths. We calculate the number density of point sources at z ∼ 7–8, and find that a double-power-law model well describes the point-source distribution. We then extend our analysis to estimate the combined point-source + galaxy luminosity function and find that the point sources have a nonnegligible contribution to the bright-end excess. The fact that the point sources dominate only at M UV ≲ −22 suggests that their contribution to cosmic reionization is likely limited. While spectroscopic follow-up is needed to confirm the nature of these point sources, this work demonstrates that the inclusion of Lyman-dropout point sources is necessary for a complete census of early galaxies at the epoch of cosmic reionization.

SuperBoRG: Exploration of Point Sources at z ∼ 8 in HST Parallel Fields*

Abstract To extend the search for quasars in the epoch of reionization beyond the tip of the luminosity function, we explore point-source candidates at redshift z ∼ 8 in SuperBoRG, a compilation of ∼0.4 deg2 archival medium-deep (m F160W ∼ 26.5 ABmag, 5σ) parallel infrared (IR) images taken with the Hubble Space Telescope (HST). Initial candidates are selected by using the Lyman-break technique. We then carefully analyze source morphology, and robustly identify three point sources at z ∼ 8. Photometric redshift analysis reveals that they are preferentially fit by extragalactic templates, and we conclude that they are unlikely to be low-z interlopers, including brown dwarfs. A clear IRAC ch2 flux excess is seen in one of the point sources, which is expected if the source has strong Hβ+[O iii] emission with a rest-frame equivalent width of ∼3000 Å. Deep spectroscopic data taken with Keck/MOSFIRE, however, do not reveal Lyα emission from the object. In combination with the estimated Hβ+[O iii] equivalent width, we place an upper limit on its Lyα escape fraction of . We estimate the number density of these point sources as ∼1 × 10−6 Mpc−3 mag−1 at M UV ∼ −23 mag. The final interpretation of our results remains inconclusive: extrapolation from low-z studies of faint quasars suggests that ≳100× survey volume may be required to find one of this luminosity. The James Webb Space Telescope will be able to conclusively determine the nature of our luminous point-source candidates, while the Roman Space Telescope will probe ∼200 times the area of the sky with the same observing time considered in this HST study.

Photometric redshifts for the Kilo-Degree Survey

We present a machine-learning photometric redshift (ML photo-z) analysis of the Kilo-Degree Survey Data Release 3 (KiDS DR3), using two neural-network based techniques: ANNz2 and MLPQNA. Despite limited coverage of spectroscopic training sets, these ML codes provide photo-zs of quality comparable to, if not better than, those from the Bayesian Photometric Redshift (BPZ) code, at least up to zphot ≲ 0.9 and r ≲ 23.5. At the bright end of r ≲ 20, where very complete spectroscopic data overlapping with KiDS are available, the performance of the ML photo-zs clearly surpasses that of BPZ, currently the primary photo-z method for KiDS. Using the Galaxy And Mass Assembly (GAMA) spectroscopic survey as calibration, we furthermore study how photo-zs improve for bright sources when photometric parameters additional to magnitudes are included in the photo-z derivation, as well as when VIKING and WISE infrared (IR) bands are added. While the fiducial four-band ugri setup gives a photo-z bias 〈δz/(1 + z)〉 = −2 × 10−4 and scatter σδz/(1+z) &lt; 0.022 at mean 〈z〉 = 0.23, combining magnitudes, colours, and galaxy sizes reduces the scatter by ~7% and the bias by an order of magnitude. Once the ugri and IR magnitudes are joined into 12-band photometry spanning up to 12 μm, the scatter decreases by more than 10% over the fiducial case. Finally, using the 12 bands together with optical colours and linear sizes gives 〈δz/(1 + z)〉 &lt; 4 × 10−5 and σδz/(1+z) &lt; 0.019. This paper also serves as a reference for two public photo-z catalogues accompanying KiDS DR3, both obtained using the ANNz2 code. The first one, of general purpose, includes all the 39 million KiDS sources with four-band ugri measurements in DR3. The second dataset, optimised for low-redshift studies such as galaxy-galaxy lensing, is limited to r ≲ 20, and provides photo-zs of much better quality than in the full-depth case thanks to incorporating optical magnitudes, colours, and sizes in the GAMA-calibrated photo-z derivation.

Degradation analysis in the estimation of photometric redshifts from non-representative training sets

We perform an analysis of photometric redshifts estimated by using a non-representative training sets in magnitude space. We use the ANNz2 and GPz algorithms to estimate the photometric redshift both in simulations as well as in real data from the Sloan Digital Sky Survey (DR12). We show that for the representative case, the results obtained by using both algorithms have the same quality, either using magnitudes or colours as input. In order to reduce the errors when estimating the redshifts with a non-representative training set, we perform the training in colour space. We estimate the quality of our results by using a mock catalogue which is split samples cuts in the $r$-band between $19.4< r< 20.8$. We obtain slightly better results with GPz on single point z-phot estimates in the complete training set case, however the photometric redshifts estimated with ANNz2 algorithm allows us to obtain mildly better results in deeper $r$-band cuts when estimating the full redshift distribution of the sample in the incomplete training set case. By using a cumulative distribution function and a Monte-Carlo process, we manage to define a photometric estimator which fits well the spectroscopic distribution of galaxies in the mock testing set, but with a larger scatter. To complete this work, we perform an analysis of the impact on the detection of clusters via density of galaxies in a field by using the photometric redshifts obtained with a non-representative training set.

Multi-wavelength characterisation ofz~ 2 clustered, dusty star-forming galaxies discovered byPlanck

(abridged) We report the discovery of PHz G95.5-61.6, a complex structure detected in emission in the Planck all-sky survey that corresponds to two over-densities of high-redshift galaxies. This is the first source from the Planck catalogue of high-z candidates that has been completely characterised with follow-up observations from the optical to the sub-millimetre domain. Herschel/SPIRE observations at 250, 350 and 500 microns reveal the existence of five sources producing a 500 microns emission excess that spatially corresponds to the candidate proto-clusters discovered by Planck. Further observations at CFHT in the optical bands (g and i) and in the near infrared (J, H and K_s), plus mid infrared observations with IRAC/Spitzer (at 3.6 and 4.5 microns) confirm that the sub-mm red excess is associated with an over-density of colour-selected galaxies. Follow-up spectroscopy of 13 galaxies with VLT/X-Shooter establishes the existence of two high-z structures: one at z~1.7 (three confirmed member galaxies), the other at z~2.0 (six confirmed members). This double structure is also seen in the photometric redshift analysis of a sample of 127 galaxies located inside a circular region of 1'-radius containing the five Herschel/SPIRE sources, where we found a double-peaked excess of galaxies at z~1.7 and z~2.0 with respect to the surrounding region. These results suggest that PHz G95.5-61.6 corresponds to two accreting nodes, not physically linked to one another, embedded in the large scale structure of the Universe at z~2 and along the same line-of-sight. In conclusion, the data, methods and results illustrated in this pilot project confirm that Planck data can be used to detect the emission from clustered, dusty star forming galaxies at high-z, and, thus, to pierce through the early growth of cluster-scale structures.

PHOTOMETRIC REDSHIFT WITH BAYESIAN PRIORS ON PHYSICAL PROPERTIES OF GALAXIES

We present a proof-of-concept analysis of photometric redshifts with Bayesian priors on physical properties of galaxies. This concept is particularly suited for upcoming/on-going large imaging surveys, in which only several broad-band filters are available and it is hard to break some of the degeneracies in the multi-color space. We construct model templates of galaxies using a stellar population synthesis code and apply Bayesian priors on physical properties such as stellar mass and star formation rate. These priors are a function of redshift and they effectively evolve the templates with time in an observationally motivated way. We demonstrate that the priors help reduce the degeneracy and deliver significantly improved photometric redshifts. Furthermore, we show that a template error function, which corrects for systematic flux errors in the model templates as a function of rest-frame wavelength, delivers further improvements. One great advantage of our technique is that we simultaneously measure redshifts and physical properties of galaxies in a fully self-consistent manner, unlike the two-step measurements with different templates often performed in the literature. One may rightly worry that the physical priors bias the inferred galaxy properties, but we show that the bias is smaller than systematic uncertainties inherent in physical properties inferred from the SED fitting and hence is not a major issue. We will extensively test and tune the priors in the on-going Hyper Suprime-Cam survey and will make the code publicly available in the future.

The bright end of the galaxy luminosity function at z≃7: before the onset of mass quenching?

We present the results of a new search for bright star-forming galaxies at redshift | $z$ | ≃ 7 within the UltraVISTA second data release (DR2) and UKIDSS (UKIRT Infrared Deep Sky Survey) UDS (Ultra Deep Survey) DR10 data, which together provide 1.65 deg2 of near-infrared imaging with overlapping optical and Spitzer data. Using a full photometric redshift analysis, to identify high-redshift galaxies and reject contaminants, we have selected a sample of 34 luminous (| $-22.7<M_{\text{UV}}<-21.2$ |) galaxies with 6.5 < | $z$ | < 7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al., validating our selection technique. Our new expanded galaxy sample includes the most massive galaxies known at | $z$ | ≃ 7, with M* ≃ 1010舁M⊙, and the majority are resolved, consistent with larger sizes (r1/2 ≃ 1–1.5 kpc) than displayed by less massive galaxies. From our final robust sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at | $z$ | ≃ 7, providing strong evidence that it does not decline as steeply as predicted by the Schechter-function fit to fainter data. We exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by active galactic nuclei (AGN). Rather, our results favour a double power-law form for the galaxy LF at high redshift, or, more interestingly, an LF which simply follows the form of the dark matter halo mass function at bright magnitudes. This suggests that the physical mechanism which inhibits star formation activity in massive galaxies (i.e. AGN feedback or some other form of ‘mass quenching’) has yet to impact on the observable galaxy LF at | $z$ | ≃ 7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical ‘quenching mass’ of M* ≃ 1010.2舁M⊙ derived from studies of the mass function of star-forming galaxies at lower redshift.

SERENDIPITOUS ALMA DETECTION OF A DISTANT CO-EMITTING X-RAY BRIGHT GALAXY

We report the detection of a distant star-forming galaxy, ALMA J010748.3−173028, which is identified by a 13σ emission line at 99.75 GHz (SΔv = 3.1 Jy km s−1), behind the nearby merging galaxies VV114 using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3. We also find an 880 μm counterpart with ALMA Band 7 (S880μm = 11.2 mJy). A careful comparison of the intensities of the line and the continuum suggests that the line is a redshifted 12CO transition. A photometric redshift analysis using the infrared to radio data favors a CO redshift of z = 2.467, although z = 3.622 is acceptable. We also find a hard X-ray counterpart, suggesting the presence of a luminous (LX ∼ 1044 erg s−1) active galactic nucleus obscured by a large hydrogen column (NH ∼ 2 × 1023 cm−2 if z = 2.47). A cosmological simulation shows that the chance detection rate of a CO-emitting galaxy at z > 1 with ⩾1 Jy km s−1 is ∼10−3 per single ALMA field of view and 7.5 GHz bandwidth at 99.75 GHz. This demonstrates that ALMA has sufficient sensitivity to find an emission-line galaxy such as ALMA J010748.3−173028 even by chance, although the likelihood of stumbling across such a source is not high.

Oii] emitters atz∼ 4.6 in the GOODS field: a homogeneous measure of evolving star formation

We present the results of a high-redshift, z = 4.6, survey of [O ii] λ3727 emission line galaxies in the GOODS-S field. The survey uses deep near-infrared data in the NB2090 (λc = 2.095 μm, Δ λ = 0.02 μm) and Ks (λc = 2.146 μm, Δ λ = 0.324 μm) filters taken with the European Southern Observatory instrument, HAWK-I. The images reach an emission line flux limit (5σ) of 3.16 × 10−18 erg s−1 cm −2. At z = 4.6, the survey probes a comoving volume of ∼6680 Mpc3. Three [O ii] emission line candidates at z ∼ 4.6 are selected using the Lyman-break criteria. Photometric redshift analysis supports the conclusion that these are genuine [O ii] emitters, ruling out a z < 3 solution entirely for one of the candidates. In the analysis presented in this paper, two scenarios are considered: first, all three candidates are genuine [O ii] emitters and secondly, only the most likely candidate is a genuine [O ii] emitter. We use the line fluxes of these objects to place confidence limits on the star formation rate density (SFRD) in bright (log( [O ii] emission line galaxies. Assuming an observed [O ii]/Hα line ratio of 0.45 and A(Hα) = 1.0 mag, we report an SFRD of in our objects. Using small number statistics, we then place a 50 per cent confidence interval on the global star formation rate of . By combining our results with those from low-z surveys, we compile the first homogeneous set of measurements of the SFRD in bright [O ii] emitters from z = 0 to 4.6. From this, we conclude that there was an increase in the SFRD in the brightest [O ii] emitters of at least a factor of 2 between z = 4.6 and 1.85.

A remarkably high fraction of strong Lyα emitters amongst luminous redshift 6.0 &lt; z &lt; 6.5 Lyman-break galaxies in the UKIDSS Ultra-Deep Survey

We present spectroscopic confirmation of ten highly luminous (L >= 2L*) Lyman alpha emitters in the redshift range 6.01<z<6.49 (nine galaxies and one AGN), initially drawn from a sample of fourteen z_phot >= 6 Lyman break galaxies (LBGs) selected from an area of 0.25 square degrees within the UKIDSS Ultra-deep Survey (UDS). Overall, our high rate of spectroscopic confirmation (>= 71%) and low rate of contamination provides a strong vindication of the photometric redshift analysis used to define the original sample. By considering star-formation rate estimates based on the Ly_alpha and UV continuum luminosity we conclude that our sample is consistent with a Ly_alpha escape fraction of ~25%. Moreover, after careful consideration of the potential uncertainties and biases, we find that 40%-50% of our sample of L >= 2L* galaxies at 6.0<z<6.5 display strong Ly_alpha emission (rest-frame equivalent width >= 25 Angs), a fraction which is a factor of ~2 higher than previously reported for L <= L* galaxies at z~6. Our results suggest that, as the epoch of reionization is approached, it is plausible that the Ly_alpha emitter fraction amongst luminous (L >=2 L*) LBGs shows a similarly sharp increase to that observed in their lower-luminosity (L <= L*) counterparts.

A robust sample of galaxies at redshifts 6.0&lt;z&lt;8.7: stellar populations, star formation rates and stellar masses

We present the results of a photometric redshift analysis designed to identify z>6 galaxies from the near-IR HST imaging in three deep fields (HUDF, HUDF09-2 & ERS). By adopting a rigorous set of criteria for rejecting low-z interlopers, and by employing a deconfusion technique to allow the available IRAC imaging to be included in the candidate selection process, we have derived a robust sample of 70 Lyman-break galaxies (LBGs) spanning the redshift range 6.0<z<8.7. Based on our final sample we investigate the distribution of UV spectral slopes (beta), finding a variance-weighted mean value of <beta>=-2.05 +/- 0.09 which, contrary to some previous results, is not significantly bluer than displayed by lower-redshift starburst galaxies. We confirm the correlation between UV luminosity and stellar mass reported elsewhere, but based on fitting galaxy templates featuring a range of star-formation histories, metallicities and reddening we find that, at z>=6, the range in mass-to-light ratio (M*/L_UV) at a given UV luminosity could span a factor of ~50. Focusing on a sub-sample of twenty-one candidates with IRAC detections at 3.6-microns we find that L* LBGs at z~6.5 have a median stellar mass of M* = (2.1 +/- 1.1) x 10^9 Msun and a median specific star-formation rate of 1.9 +/- 0.8 Gyr^-1. Using the same sub-sample we have investigated the influence of nebular continuum and line emission, finding that for the majority of candidates (16 out of 21) the best-fitting stellar-mass estimates are reduced by less than a factor of 2.5. Finally, a detailed comparison of our final sample with the results of previous studies suggests that, at faint magnitudes, several high-redshift galaxy samples in the literature are significantly contaminated by low-redshift interlopers (abridged).

The evolution of radio sources in the UKIDSS-DXS-XMM-LSS field

We investigate the cosmic evolution of low luminosity ($L_{\rm{1.4GHz}}<10^{25}\rm{W~Hz^{-1}sr^{-1}}$) radio sources in the XMM Large Scale Structure survey field (XMM-LSS). We match low frequency selected (610~MHz) radio sources in the XMM-LSS field with near infrared $K$-band observations over the same field from the UKIRT Infrared Deep Sky Survey. We use both the mean $V/V_{\rm{max}}$ statistic and the radio luminosity function of these matched sources to quantify the evolution of the co-moving space density of the low luminosity radio sources in our sample. Our results indicate that the low luminosity sources evolve differently to their high luminosity counterparts out to a redshift of z$\sim$0.8. The derived luminosity function is consistent with an increase in the co-moving space density of low luminosity sources by a factor of $\sim$1.5 at z=0.8. We show that the use of the $K-z$ diagram for the radio source population, although coarser than a full photometric redshift analysis, produces consistent results with previous studies using $\sim >10$ band photometry. This offers a promising method for conducting similar analyses over the whole sky with future near- and mid-infrared surveys.

A Massive Disk Galaxy at z$&amp;gt;$ 3 along the Line of Sight of QSO 1508$+$5714

Abstract We have obtained deep images in the BVRIJHKs bands of the field centered on QSO 1508$+$5714 ($z_{\rm em}$$=$ 4.28) with the Suprime-Cam, FOCAS, and MOIRCS cameras on Subaru telescope. We report here on the detection of a $B$-dropout galaxy, which is 3${\rlap{\hskip.75pt{^{\prime\prime}}}\hskip.75pt.\hskip1.75pt}$5 north-west of the QSO sightline. A photometric redshift analysis is presented to complement the color selection. Given the photometric properties of this object ($M$$=$$-$22.2, making $L$$\approx$ 3$ L^{\ast}$, if placed at its photometric redshift, $z$$\sim$ 3.5), as well as the Sérsic index ($n$$\sim$ 1) derived from a 2-D imaging decomposition of the HST WFPC2 image taken with the $I_{\mathit{F814}}$ filter, the identified system is consistent with a massive disk galaxy at $z &amp;gt; $ 3. If confirmed, it would be one of the most distant massive disk galaxies known so far.

A CO EMISSION LINE FROM THE OPTICAL AND NEAR-IR UNDETECTED SUBMILLIMETER GALAXY GN10

We report the detection of a CO emission line from the submillimiter galaxy (SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep optical and near-IR imaging obtained with the Hubble Space Telescope and ground-based facilities. This is a prototypical case of a source that is extremely obscured by dust, for which it is practically impossible to derive a spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10 is part of a proto-cluster structure previously identified at z~4.05 in the same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure Interferometer, and successfully detected a line. We find that the most likely redshift identification is z=4.0424+-0.0013, based on: 1) the very low chance that the CO line is actually serendipitous from a different redshift; 2) a radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a scaling factor, of two other SMGs at the same redshift. The faintness at optical/near-IR wavelengths requires an attenuation of A_V~5-7.5 mag. This result supports the case that a substantial population of very high-z SMGs exists that had been missed by previous spectroscopic surveys. This is the first time that a CO emission line has been detected for a galaxy that is invisible in the optical and near-IR. Our work demonstrates the power of existing and planned facilities for completing the census of star formation and stellar mass in the distant Universe by measuring redshifts of the most obscured galaxies through millimeter spectroscopy.

A multi-wavelength survey of AGN in the XMM-LSS field

<i>Aims. <i/>We present a sample of candidate quasars selected using the <i>KX<i/>-technique. The data cover 0.68 deg<sup>2<sup/> of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources.<i>Methods. <i/>The <i>KX<i/> method identifies quasars on the basis of their optical (<i>R<i/> and <i>z'<i/>) to near-infrared photometry and point-like morphology. We combine these data with optical (<i>u<sup>*<sup/><i/>,<i>g'<i/>, <i>r'<i/>,<i>i'<i/>,<i>z'<i/>) and mid-infrared (3.6-24 <i>μ<i/>m) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars.<i>Results. <i/>Of 93 sources selected as candidate quasars by the <i>KX<i/> method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 <i>≤<i/> <i>z<i/> <i>≤<i/> 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies.

Galaxy clusters at 0.6 &amp;lt; z &amp;lt; 1.4 in the UKIDSS Ultra Deep Survey Early Data Release

Abstract We present the first cluster catalogue extracted from the UKIRT Infrared Deep Sky Survey (UKIDSS) Early Data Release. The catalogue is created using UKIDSS Ultra Deep Survey infrared J and K data combined with 3.6- and 4.5-μm Spitzer bands and optical BVRi′z′ imaging from the Subaru Telescope over 0.5 deg2 in the Subaru XMM–Newton Deep Field. We have created a new cluster detection algorithm, based on the friends-of-friends and Voronoi tessellation methods, which utilizes probability distribution functions derived from a photometric redshift analysis. We employ mock catalogues to understand the selection effects and contamination associated with the algorithm. The cluster catalogue contains 13 clusters at redshifts 0.61 ≤z≤ 1.39 with luminosities 10 L*≲Ltot≲ 50 L*, corresponding to masses 5 × 1013≲Mcluster≲ 3 × 1014 M⊙ for (M/M⊙)/(L/L⊙) = 75 h. The measured sky surface density of ∼10 clusters deg−2 for high-redshift (z= 0.5–1.5), massive (&amp;gt; 1014 M⊙) clusters is precisely in line with theoretical predictions presented by Kneissl et al.

Clustering of Galaxies atz ∼ 3 around the Probable Damped Lyα Absorber toward QSO APM 08279+5255

We present results on the clustering of Lyman break galaxies (LBGs) around a probable damped Ly? absorption line cloud (DLA) at zabs = 2.974 from deep UBVI images of the field containing the quasar APM 08279+5255 (zem = 3.91). The large area covered by our images, 0.31 deg2 or ~40 ? 40 Mpc comoving at redshift z = 3, and their depth, ?I,AB(sky) 27.6 mag arcsec-2, allow us to identify ~450 LBG candidates brighter than IAB = 24.80 at 2.75 < z < 3.25 both close (50 kpc) to the DLA line of sight and up to 20 Mpc (comoving) from the DLA, i.e., physically unrelated. LBG candidates were identified using photometric redshift techniques that include the I magnitude as a prior estimate in addition to the colors. The two are combined using Bayes's theorem. This helps to break the degeneracies that occur in a pure spectral template fitting scheme. The overall rms is ?z 0.15 at z ~ 3 based on our analysis of photometric redshifts in the HDF-N. From the redshift likelihood distributions, we selected LBG galaxies within a redshift slice of width Wz = 0.15( ?z) centered on the redshift of the DLA zabs. Within that redshift slice, we find an enhancement of galaxies near the DLA using both the surface density (?/?g 3) and an estimator of the three-dimensional spatial overdensity (n/g ~ 5 ? 3). The surface overdensity ?/?g is significant at the more than 95% significance level on scales 2.5 < r? < 5 Mpc comoving. The overdensity cannot be related to the QSO environment since the QSO is at zem = 3.91. These results imply that some DLA could reside in high-density regions. We search within 45'' from the line of sight for galaxies responsible for the DLA and find one candidate with zphot = 3.03 that is 26'' (145 kpc physical) away. From its magnitude I = 24.65 ? 0.2, its luminosity is MI,AB = -21.35. Due to its large impact parameter, however, this galaxy is not a likely candidate for the absorber.

The galaxy population of the z= 1 cluster of galaxies MG2016+112

A photometric redshift analysis of galaxies in the field of the wide-separation gravitational lens MG2016+112 reveals a population of 69 galaxies with photometric redshifts consistent with being in a cluster at the redshift of the giant elliptical lensing galaxy, z=1.00. The Ks-band luminosity function of the cluster galaxies is well represented by the Schechter function with a characteristic magnitude Ks*=18.90 (-0.57/+0.45) and faint-end slope alpha=-0.60 (-0.33/+0.39), consistent with what is expected for a passively evolving population of galaxies formed at high redshift, zf>2. From the total Ks-band flux of the cluster galaxies and a dynamical estimate of the total mass of the cluster, the restframe Ks-band mass-to-light ratio of the cluster is derived to be M/L=27(-17/+64)(h_50)(M/L)_{sun}, in agreement with the upper limit derived earlier from Chandra X-ray observations and the value derived locally in the Coma cluster. The cluster galaxies span a red sequence with a considerable scatter in the colour-magnitude diagrams, suggesting that they contain young stellar populations in addition to the old populations of main-sequence stars that dominate the Ks-band luminosity function. This is in agreement with spectroscopic observations which show that 5 out of the 6 galaxies in the field confirmed to be at the redshift of the lensing galaxy have emission lines. The projected spatial distribution of the cluster galaxies is filamentary-like rather than centrally concentrated around the lensing galaxy, and show no apparent luminosity segregation. A handful of the cluster galaxies show evidence of merging/interaction. The results presented in this paper suggest that a young cluster of galaxies is assembling around MG2016+112.