Publications (23)30.4 Total impact
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Article: The Redshift and Mass Dependence on the Formation of The Hubble Sequence at z>1 from CANDELS/UDS
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ABSTRACT: In this paper we present a detailed study of the structures and morphologies of a sample of 1188 massive galaxies with Mstar>10^10Msun between redshifts z=1-3 within the Ultra Deep Survey (UDS) region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this sample we determine how galaxy structure and morphology evolve with time. We visually classify our sample into disks, ellipticals and peculiar systems and correct for redshift effects on our classifications through simulations. We find evolution in the fractions of galaxies at a given visual classification as a function of redshift. The peculiar population is dominant at z>2 with a substantial spheroid population, and a negligible disk population. We compute the transition redshift, ztrans, where the combined fraction of spheroids and disks is equal to that of peculiar galaxies, as ztrans=1.86+/-0.62 for galaxies in our stellar mass range. We find that this changes as a function of stellar mass, with Hubble-type systems becoming dominant at higher redshifts for higher mass galaxies (ztrans=2.22+/-0.82), than for the lower mass galaxies (ztrans=1.73+/-0.57). Higher mass galaxies become morphologically settled before their lower mass counterparts, a form of morphological downsizing. We furthermore compare our visual classifications with Sersic index, the concentration, asymmetry and clumpiness (CAS) parameters, star formation rate and rest frame U-B colour. We find links between the colour of a galaxy, its star formation rate and how extended or peculiar it appears. Finally, we discuss the negligible z>2 disk fraction based on visual morphologies and speculate that this is an effect of forming disks appearing peculiar through processes such as violent disk instabilities or mergers. We conclude that to properly define high redshift morphology a new and more exact classification scheme is needed.05/2013; -
Article: CANDELS Multiwavelength catalogs: Source Identification and Photometry in the CANDELS UKIDSS Ultra-Deep Survey Field
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ABSTRACT: We present the multiwavelength - ultraviolet to mid-infrared - catalog of the UKIDSS Ultra-Deep Survey (UDS) field observed as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). Based on publicly available data, the catalog includes: the CANDELS data from the Hubble Space Telescope (near-infrared WFC3 F125W and F160W data and visible ACS F606W and F814W data), u-band data from CFHT/Megacam, B, V, Rc, i' and z' band data from Subaru/Suprime-Cam, Y and Ks band data from VLT/HAWK-I, J, H and K bands data from UKIDSS (Data Release 8), and Spitzer/IRAC data (3.6, 4.5 from SEDS, 5.8 and 8.0um from SpUDS). The present catalog is F160W-selected and contains 35932 sources over an area of 201.7 square arcmin and includes radio and X-ray detected sources and spectroscopic redshifts available for 210 sources.05/2013; -
Article: CANDELS Observations of the Environmental Dependence of the Color-Mass-Morphology Relation at z = 1.6
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ABSTRACT: We study the environmental dependence of color, stellar mass, and morphology by comparing galaxies in a forming cluster to those in the field at z = 1:6 with Hubble Space Telescope near-infrared imaging in the CANDELS/UDS field. We quantify the morphology of the galaxies using the effective radius, reff, and S\'ersic index, n. In both the cluster and field, approximately half of the bulge-dominated galaxies (n > 2) reside on the red sequence of the color-magnitude diagram, and most disk-dominated galaxies (n < 2) have colors expected for star-forming galaxies. There is weak evidence that cluster galaxies have redder rest-frame U - B colors and higher stellar masses compared to the field. Star-forming galaxies in both the cluster and field show no significant differences in their morphologies. In contrast, there is evidence that quiescent galaxies in the cluster have larger median effective radii and smaller S\'ersic indices compared to the field with a significance of 2?. These differences are most pronounced for galaxies at clustercentric distances 1 Mpc < Rproj < 1.5 Mpc, which have low S\'ersic indices and possibly larger effective radii, more consistent with star-forming galaxies at this epoch and in contrast to other quiescent galaxies. We argue that star-forming galaxies are processed under the influence of the cluster environment at distances greater than the cluster-halo virial radius. Our results are consistent with models where gas accretion onto these galaxies is suppressed from processes associated with the cluster environment.05/2013; -
Article: Studying the emergence of the red sequence through galaxy clustering: host halo masses at z > 2
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ABSTRACT: We use the UKIDSS Ultra-Deep Survey, the deepest degree-scale near-infrared survey to date, to investigate the clustering of star-forming and passive galaxies to z ~ 3.5. Our new measurements include the first determination of the clustering for passive galaxies at z > 2, which we achieve using a cross-correlation technique. We find that passive galaxies are the most strongly clustered, typically hosted by massive dark matter halos with M_halo > 5 x 10^12 M_sun irrespective of redshift or stellar mass. Our findings are consistent with models in which a critical halo mass determines the transition from star-forming to passive galaxies. Star-forming galaxies show no strong correlation between stellar mass and halo mass, but passive galaxies show evidence for an anti-correlation; low-mass passive galaxies appear, on average, to be located in the most massive halos. These results can be understood if the termination of star formation is most efficient for galaxies of low stellar mass in very dense environments.03/2013; -
Article: The Nature of Extremely Red H-[4.5]>4 Galaxies revealed with SEDS and CANDELS
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ABSTRACT: We have analysed a sample of 25 extremely red H-[4.5]>4 galaxies, selected using 4.5 micron data from the Spitzer SEDS survey and deep H-band data from the Hubble Space Telescope (HST) CANDELS survey, over ~180 square arcmin of the UKIDSS Ultra Deep Survey (UDS) field. Our aim is to investigate the nature of this rare population of mid-infrared (mid-IR) sources that display such extreme near-to-mid-IR colours. Using up to 17-band photometry (U through 8.0 microns), we have studied in detail their spectral energy distributions, including possible degeneracies in the photometric redshift/internal extinction (zphot-Av) plane. Our sample appears to include sources of very different nature. Between 45% and 75% of them are dust-obscured, massive galaxies at 3<zphot<5. All of the 24 micron-detected sources in our sample are in this category. Two of these have S(24 micron)>300 microJy, which at 3<zphot<5 suggests that they probably host a dust-obscured active galactic nucleus (AGN). Our sample also contains four highly obscured (Av>5) sources at zphot<1. Finally, we analyse in detail two zphot~6 galaxy candidates, and discuss their plausibility and implications. Overall, our red galaxy sample contains the tip of the iceberg of a larger population of z>3 galaxies to be discovered with the future James Webb Space Telescope.02/2012; -
Article: Radio imaging of the Subaru/XMM-Newton Deep Field - III. Evolution of the radio luminosity function beyond z=1
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ABSTRACT: We present spectroscopic and eleven-band photometric redshifts for galaxies in the 100-uJy Subaru/XMM-Newton Deep Field radio source sample. We find good agreement between our redshift distribution and that predicted by the SKA Simulated Skies project. We find no correlation between K-band magnitude and radio flux, but show that sources with 1.4-GHz flux densities below ~1mJy are fainter in the near-infrared than brighter radio sources at the same redshift, and we discuss the implications of this result for spectroscopically-incomplete samples where the K-z relation has been used to estimate redshifts. We use the infrared--radio correlation to separate our sample into radio-loud and radio-quiet objects and show that only radio-loud hosts have spectral energy distributions consistent with predominantly old stellar populations, although the fraction of objects displaying such properties is a decreasing function of radio luminosity. We calculate the 1.4-GHz radio luminosity function (RLF) in redshift bins to z=4 and find that the space density of radio sources increases with lookback time to z~2, with a more rapid increase for more powerful sources. We demonstrate that radio-loud and radio-quiet sources of the same radio luminosity evolve very differently. Radio-quiet sources display strong evolution to z~2 while radio-loud AGNs below the break in the radio luminosity function evolve more modestly and show hints of a decline in their space density at z>1, with this decline occurring later for lower-luminosity objects. If the radio luminosities of these sources are a function of their black hole spins then slowly-rotating black holes must have a plentiful fuel supply for longer, perhaps because they have yet to encounter the major merger that will spin them up and use the remaining gas in a major burst of star formation.01/2012; -
Article: Average Metallicity and Star Formation Rate of Lyα Emitters Probed by a Triple Narrowband Survey
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ABSTRACT: We present the average metallicity and star formation rate (SFR) of Lyα emitters (LAEs) measured from our large-area survey with three narrowband (NB) filters covering the Lyα, [O II]λ3727, and Hα+[N II] lines of LAEs at z = 2.2. We select 919 z = 2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted [O II] and Hα nebular lines, respectively. By stacking the near-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by NB imaging or deep spectroscopy. The stacked object has an Hα luminosity of 1.7 × 1042 erg s–1 corresponding to an SFR of 14 M ☉ yr–1. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z 0.09 Z ☉ (2σ) based on the [O II]/(Hα+[N II]) index together with photoionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at z ~ 2, are extremely metal-poor (Z < 2 × 10–2 Z ☉) galaxies at the 4σ level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of z ~ 2 UV-selected galaxies toward lower masses (5 × 108 M ☉), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The Hα and Lyα luminosities of our NB-selected LAEs indicate that the escape fraction of Lyα photons is ~12%-30%, much higher than the values derived for other galaxy populations at z ~ 2.The Astrophysical Journal 12/2011; 745(1):12. · 6.02 Impact Factor -
Article: CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey—The Hubble Space Telescope Observations, Imaging Data Products, and Mosaics
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ABSTRACT: This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at z 1.5-8, and to study Type Ia supernovae at z > 1.5. Five premier multi-wavelength sky regions are selected, each with extensive multi-wavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 infrared channel (WFC3/IR) and the WFC3 ultraviolet/optical channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers ~125 arcmin2 within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of ~800 arcmin2 across GOODS and three additional fields (Extended Groth Strip, COSMOS, and Ultra-Deep Survey). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up-to-date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including charge transfer efficiency degradation for ACS, removal of electronic bias-striping present in ACS data after Servicing Mission 4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.The Astrophysical Journal Supplement Series 12/2011; 197(2):36. · 13.46 Impact Factor -
Article: CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
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ABSTRACT: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over the approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies using three separate cameras on the Hubble Space Telescope, from the mid-ultraviolet to the near-infrared, and will find and measure Type Ia supernovae at z>1.5 to test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8. The survey covers approximately 800 arcmin^2 and is divided into two parts. The CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125 arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (EGS, COSMOS, and UDS) and covers the full area to a 5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach that has proven efficient for extragalactic surveys. Data from the survey are nonproprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design. The Hubble data processing and products are described in a companion paper.05/2011; -
Article: Average Metallicity and Star Formation Rate of Lya Emitters Probed by a Triple Narrow-Band Survey
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ABSTRACT: We present the average metallicity and star-formation rate of Lya emitters (LAEs) measured from our large-area survey with three narrow-band (NB) filters covering the Lya, [OII]3727, and Ha+[NII] lines of LAEs at z=2.2. We select 919 z=2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted [OII] and Ha nebular lines, respectively. By stacking the near-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by narrow-band imaging or deep spectroscopy. The stacked object has an Ha luminosity of 1.7x10^{42} erg s^{-1} corresponding to a star formation rate (SFR) of 14 M_{sun} yr^{-1}. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z>~0.09 Z_{sun} (2sigma) based on the [OII]/(Ha+[NII]) index together with photo-ionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at z~2, are extremely metal poor (Z<2x10^{-2} Z_{sun}) young galaxies at the 4sigma level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of z~2 UV-selected galaxies toward lower masses (5x10^{8} M_{sun}), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The Ha and Lya luminosities of our NB-selected LAEs indicate that the escape fraction of Lya photons is ~12-30 %, much higher than the values derived for other galaxy populations at z~2.05/2011; -
Article: On the co-evolution of supermassive black holes and their host galaxies since z = 3
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ABSTRACT: [Abridged] To investigate the evolution in the relation between galaxy stellar and central black hole mass we construct a volume limited complete sample of 85 AGN with host galaxy stellar masses M_{*} > 10^{10.5} M_{sol}, and specific X-ray luminosities L_{X} > 2.35 x 10^{43} erg s^{-1} at 0.4 < z < 3. We calculate the Eddington limiting masses of the supermassive black holes residing at the centre of these galaxies, and observe an increase in the average Eddington limiting black hole mass with redshift. By assuming that there is no evolution in the Eddington ratio (\mu) and then that there is maximum possible evolution to the Eddington limit, we quantify the maximum possible evolution in the M_{*} / M_{BH} ratio as lying in the range 700 < M_{*}/M_{BH} < 10000, compared with the local value of M_{*}/M_{BH} ~ 1000. We furthermore find that the fraction of galaxies which are AGN (with L_{X} > 2.35 x 10^{43} erg s^{-1}) rises with redshift from 1.2 +/- 0.2 % at z = 0.7 to 7.4 +/- 2.0 % at z = 2.5. We use our results to calculate the maximum timescales for which our sample of AGN can continue to accrete at their observed rates before surpassing the local galaxy-black hole mass relation. We use these timescales to calculate the total fraction of massive galaxies which will be active (with L_{X} > 2.35 x 10^{43} erg s^{-1}) since z = 3, finding that at least ~ 40% of all massive galaxies will be Seyfert luminosity AGN or brighter during this epoch. Further, we calculate the energy density due to AGN activity in the Universe as 1.0 (+/- 0.3) x 10^{57} erg Mpc^{-3} Gyr^{-1}, potentially providing a significant source of energy for AGN feedback on star formation. We also use this method to compute the evolution in the X-ray luminosity density of AGN with redshift, finding that massive galaxy Seyfert luminosity AGN are the dominant source of X-ray emission in the Universe at z < 3. Comment: 25 pages, 10 figures, accepted for publication in MNRAS08/2010; -
Article: The evolution of galaxy clustering since z = 3 using the UKIDSS Ultra Deep Survey: the divergence of passive and star-forming galaxies
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ABSTRACT: We use the UKIDSS Ultra-Deep Survey to trace the evolution of galaxy clustering to z = 3. Using photometric redshifts derived from data covering the wavelength range 0.3 - 4.5 um we examine this clustering as a function of absolute K-band luminosity, colour and star-formation rate. Comparing the deprojected clustering amplitudes, we find that red galaxies are more strongly clustered than blue galaxies out to at least z = 1.5, irrespective of rest-frame K-band luminosity. We then construct passive and star-forming samples based on stellar age, colour and star-formation histories calculated from the best fitting templates. The clustering strength of star-forming galaxies declines steadily from r_0 ~ 7 h^-1 Mpc at z ~ 2 to r_0 ~ 3 h^-1 Mpc at z ~ 0, while passive galaxies have clustering strengths up to a factor of two higher. Within the passive and star-forming subsamples, however, we find very little dependence of galaxy clustering on K-band luminosity. Galaxy `passivity' appears to be the strongest indicator of clustering strength. We compare these clustering measurements with those predicted for dark matter halos and conclude that passive galaxies typically reside in halos of mass M > 10^13 M_sun while luminous star-forming galaxies occupy halos an order of magnitude less massive over the range 0.5 < z < 1.5. The decline in the clustering strength of star-forming galaxies with decreasing redshift indicates a decline in the hosting halo mass for galaxies of a given luminosity. We find evidence for convergence of clustering in star-forming and passive galaxies around z ~ 2, which is consistent with this being the epoch at which the red sequence of galaxies becomes distinct.05/2010; -
Article: Dust and Gas Obscuration in ELAIS Deep X-Ray Survey Reddened Quasars
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ABSTRACT: Hard X-ray surveys have uncovered a large population of heavily obscured AGNs. They also reveal a population of quasars with moderate obscuration at both visible and X-ray wavelengths. We use Chandra-selected samples of quasars from the ELAIS Deep X-ray Survey (EDXS) and the Chandra Deep Field-North to investigate the obscuration toward the nuclei of moderately obscured AGNs. We find an inverse correlation between the optical-to-X-ray flux ratio and the X-ray hardness ratio that can be interpreted as being due to obscuration at visible and X-ray wavelengths. We present detailed optical and near-infrared data for a sample of optically faint (R > 23) quasars from the EDXS. These are used to constrain the amount of rest-frame UV/optical reddening toward these quasars. It is found that optically faint quasars are mostly faint because of obscuration, not because they are intrinsically weak. After correcting for reddening, the optical magnitudes of most of these quasars are similar to the brighter quasars at these X-ray fluxes. Combining with gas column densities inferred from the X-ray observations, we consider the gas-to-dust ratios of the obscuring matter. We find that the quasars generally have higher gas-to-dust absorption than that seen in the Milky Way, similar to what has been found for nearby Seyfert galaxies. We consider the possible existence of a large population of X-ray sources that have optical properties of type 1 (unobscured) quasars but X-ray properties of type 2 (obscured) quasars. However, we find that such sources only contribute about 6% of the 0.5-8 keV X-ray background. Finally, we show that the observed distribution of optical-to-X-ray flux ratios of quasars at z > 1 is skewed to low values compared to the intrinsic distribution as a result of the fact that the observed-frame R-band light is emitted in the UV and is more easily obscured than hard X-rays.The Astrophysical Journal 12/2008; 610(1):140. · 6.02 Impact Factor -
Article: Exploring the infrared/radio correlation at high redshift
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ABSTRACT: We have analysed the 24um properties of a radio-selected sample in the Subaru-XMM/Newton Deep Field in order to explore the behaviour of the FIR/radio relation at high redshifts. Statistically, the correlation is described by q24, the ratio between the observed flux densities at 24um and 1.4GHz, respectively. Using 24um data results in considerably more scatter in the correlation than previous work using data at 60-70um. Nevertheless, we do observe a steady correlation as a function of redshift, up to z~3.5, suggesting its validity back to primeval times. We find q24 = 0.30 +/- 0.56 for the observed and q24 = 0.71 +/- 0.47 for the k-corrected radio sample, based on sources with 300uJy < S(1.4GHz) < 3.2mJy and 24um detections. A suitable k-correction given by a M82-like mid-IR template suggests no extreme silicate absorption in the bulk of our radio sample. Using thresholds in q24 to identify radio-excess sources, we have been able to characterise the transition from radio-loud AGN to star-forming galaxies and radio-quiet AGN at faint (<1mJy) radio flux densities. Our results are in broad agreement with previous studies which show a dominant radio-loud AGN population at >1mJy. The rest-frame U-B colours of the expected radio-excess population have redder distribution than those that follow the correlation. This is therefore a promising way to select obscured Type-2 AGN, with a radio loud nature, missed by deep X-ray observations. Spectroscopic follow-up of these sources is required to fully test this method. Comment: The paper contains 7 figures and 1 table. In press at MNRAS02/2008; -
Article: Extremely red objects in the UKIDSS Ultra Deep Survey Early Data Release
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ABSTRACT: We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/XMM-Newton Deep Field. We find a total of 3715 objects over 2013 sq. arcmin with R-K>5.3 and K<=20.3, which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively-evolving and dusty star-forming galaxies using their RJK colours and investigate their radio properties using a deep radio map. The dusty population has a higher fraction of individually-detected radio sources and a higher mean radio flux density among the undetected objects, but the passive population has a higher fraction of bright radio sources, suggesting that AGNs are more prevalent among the passive ERO population. Comment: Accepted for publication in MNRAS Letters08/2006; -
Article: The nature, evolution, clustering and X‐ray properties of extremely red galaxies in the Chandra Deep Field South/Great Observatories Origins Deep Survey field
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ABSTRACT: We identify a very deep sample of 198 extremely red objects (EROs) in the Chandra Deep Field South, selected on the basis of I775−Ks > 3.92, to a limit Ks≃ 22 using the public European Southern Observatory (ESO)/Great Observatories Origins Deep Survey (GOODS) survey.The ERO number counts flatten from a slope of γ≃ 0.59 to 0.16 at K > 19.5, where they remain below the predictions for pure luminosity evolution, and fall below even a non-evolving model. This suggests there is a significant decrease with redshift in the comoving number density of passive/very red galaxies.We investigate the angular correlation function, ω(θ), of these EROs and detect positive clustering for Ks= 20.5–22.0 sources. The EROs show stronger clustering than other galaxies at the same magnitudes. The ω(θ) amplitudes are best-fitted by models in which the EROs have a comoving correlation radius r0≃ 12.5 ± 1.2 h−1 Mpc, or r0≃ 21.4 ± 2.0 h−1 Mpc in a stable clustering model.We find a 40-arcsec diameter overdensity of 10 EROs, centred on the Chandra X-ray source (and ERO) XID:58. On the basis of colours we estimate that about seven, including XID:58, belong to a cluster of EROs at z≃ 1.5.The 942-ks Chandra survey detected 73 X-ray sources in the area of our ERO sample, 17 of which coincide with EROs. Of these sources, 13 have X-ray properties indicative of obscured active galactic nuclei (AGN), while the faintest four may be starbursts. In addition, we find evidence that Chandra sources and EROs are positively cross-correlated at non-zero (∼2–20 arcsec) separations, implying that they tend to trace the same large-scale structures.In conclusion, these findings appear consistent with a scenario where EROs are the z > 1 progenitors of elliptical/S0 galaxies, some forming very early as massive spheroids, which are strongly clustered and may evolve via an AGN phase, others more recently from mergers of disc galaxies.Monthly Notices of the Royal Astronomical Society 11/2003; 346(3):803 - 817. · 4.90 Impact Factor -
Article: The Nature, Evolution, Clustering and X-ray Properties of Extremely Red Galaxies in the CDFS/GOODS field
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ABSTRACT: We identify a deep sample of 198 extremely red objects (EROs) in (50.4 sq. arcmin of) the Chandra Deep Field South, selected as I-K>3.92 galaxies to a limit K=22. The ERO number counts remain well below the predictions for pure luminosity evolution, and fall below even a non-evolving model, suggesting the comoving number density of passive/very red galaxies decreases with redshift. The angular correlation function of these EROs indicates stronger clustering than that of other galaxies at the same magnitudes, and is best-fitted by models in which the EROs have a comoving correlation radius 12.5/h Mpc, or 21.4/h Mpc in a stable clustering model. We find a 40-arcsec diameter grouping of 10 EROs, centered on the Chandra source (and ERO) XID:58, with colours suggesting a cluster of mostly passive EROs at approx. z=1.5. The 942 ksec Chandra survey detected 73 X-ray sources in the area of our ERO sample, of which 17 coincide with EROs. Of these sources, 13 have X-ray properties indicative of obscured AGN, while the faintest 4 may be starburst galaxies. In addition, we find evidence that Chandra sources and EROs are positively cross-correlated at non-zero (2-20 arcsec) separations, implying that they tend to trace the same large-scale structures. Comment: 17 pages, latex, 14 figures, accepted for publication in MNRAS. Major revisions from original version, with a new, reselected sample of EROs03/2003; -
Article: Deep radio imaging of the SCUBA 8-mJy survey fields: sub-mm source identifications and redshift distribution
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ABSTRACT: The SCUBA 8-mJy survey is the largest submm extragalactic mapping survey undertaken to date, centred on the Lockman Hole and ELAIS N2 regions. Here, we present new 1.4-GHz imaging of the depth and resolution necessary to reliably identify radio counterparts for 18 of 30 submm sources. Armed with this greatly improved positional information, we present and analyse new optical, near-IR and XMM-Newton X-ray imaging to identify optical/IR host galaxies to half of the submm-selected sources in those fields. As many as 15% of the submm sources detected at 1.4 GHz are resolved by the 1.4'' beam and a further 25% have more than one radio counterpart, suggesting that radio and submm emission arise from extended starbursts and that interactions are common. We note that less than a quarter of the submm-selected sample would have been recovered by targeting optically faint radio sources, underlining the selective nature of such surveys. At least 60% of the radio-confirmed optical/IR host galaxies appear to be morphologically distorted; many are composite systems - red galaxies with relatively blue companions; just over half are found to be very red or extremely red; contrary to popular belief, most are sufficiently bright to be tackled with spectrographs on 8-m telescopes. We estimate the median redshift of the S(850um) ~ 8 mJy submm galaxy population: if the radio/far-IR correlation holds at high redshift, and our sample is unbiased, we derive a conservative median z >= 2.0, or >= 2.4 using spectral templates more representative of known submm galaxies [abridged]. Comment: In press at MNRAS. Extra IR imaging now included. 27 pages; 14 figures, mostly colour. The resolution of Figs 1 and 2 has been degraded. Higher quality versions of paper available at http://www.roe.ac.uk/~rji/8mjy.ps.gz (a4) and http://www.roe.ac.uk/~rji/8mjy_letter.ps.gz (letter)06/2002; -
Article: The Clustering, Number Counts and Morphology of Extremely Red (R-K>5) Galaxies to K=21
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ABSTRACT: We investigate the number counts, clustering, morphology and radio/X-ray emission of extremely red objects (EROs), defined as galaxies with R-K>5.0. This criterion will select old, passive ellipticals at z>0.9. To K=21 we identify a total of 158 EROs in 81.5 sq. arcmin. The ERO number counts are lower than predicted by a pure luminosity evolution model, but higher than predicted by current CDM-based hierarchical models. They can be fitted by a combination of moderate merging with a decrease with redshift in the comoving number density of passive galaxies. We investigate the angular correlation function and find that the EROs have a much higher correlation amplitude than full K-limited samples of galaxies. This implies that the intrinsic clustering of EROs is stronger than that of present-day E/S0 galaxies. We estimate the comoving correlation radius as 10-13 Mpc. We estimate seeing-corrected angular sizes and morphological types for a K<19.5 subsample (31 galaxies), and find a 3:2 mixture of bulge and disk profiles. 1/4 appear to be interacting, disturbed or irregular. The angular sizes of the bulge-profile EROs are consistent with passively evolving ellipticals at 0.9<z<2. Seven of the bright EROs are detected as 1.4 GHz radio sources. The strongest, at 5 mJy, is also a Chandra X-ray detection, and lies at the centre of a possible cluster of EROs. Another source is elongated and aligned with the optical axis and may be a ULIRG-type starburst. Comment: 18 pages, latex, 18 figures, accepted for publication in MNRAS. Significant revisions and corrections following referees Comments05/2002; -
Article: Stellar contributors to the hard X-ray background?
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ABSTRACT: We use simple energetic arguments to estimate the contribution of massive X-ray binaries and supernova remnants to the cosmic X-ray background (XRB) at energies in excess of 2 keV. Recent surveys have shown that AGN probably account for most of the hard XRB (E > 2 keV), but there have been many suggestions that star-forming galaxies could emerge at fainter fluxes and perhaps account for a significant fraction of the soft and hard X-ray energy density. Assuming that the formation rate of massive X-ray binaries (MXRBs) traces the global star-formation rate, we find that their integrated contribution to the hard XRB can be estimated and is shown to be small (at less than the 1% level). Similarly, the integrated flux of SN is also shown to be insignificant, or at most comparable to MXRBs. AGN therefore remain the most viable candidates for producing the hard XRB, unless additional processes can be shown to dominate the global hard X-ray emission in distant starburst galaxies. Comment: MNRAS pink pages, accepted07/2000;
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Institutions
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2011
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University of Nottingham
- School of Physics and Astronomy
Nottingham, ENG, United Kingdom
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2002–2008
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The University of Edinburgh
- Institute for Astronomy (IfA)
Edinburgh, SCT, United Kingdom
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1996
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Durham University
- Department of Physics
Durham, ENG, United Kingdom
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