We present the results of a study of weak gravitational lensing by galaxies using imaging data that were obtained as part of the second Red Sequence Cluster Survey (RCS2). In order to compare to the ...baryonic properties of the lenses we focus here on the ~300 square degrees that overlap with the data release 7 (DR7) of the Sloan Digital Sky Survey (SDSS). The depth and image quality of the RCS2 enables us to significantly improve upon earlier work for luminous galaxies at z ≥ 0.3. To model the lensing signal we employ a halo model which accounts for the clustering of the lenses and distinguishes between satellite and central galaxies. Comparison with dynamical masses from the SDSS shows a good correlation with the lensing mass for early-type galaxies. The correlation is less clear for late-type galaxies, possibly due to rotation. For low luminosity (stellar mass) early-type galaxies we find a satellite fraction of ~40% which rapidly decreases to <10% with increasing luminosity (stellar mass). The satellite fraction of the late-types has a value in the range 0–15%, independent of luminosity or stellar mass. At high masses the satellite fraction is not well constrained, which we partly attribute to the modelling assumptions. To infer virial masses we apply simple models based on an independent satellite kinematics analysis to account for intrinsic scatter in the scaling relations. We find that early-types in the range 1010 < Lr < 1011.5 L⊙ have virial masses that are about five times higher than those of late-type galaxies and that the mass scales as M200 ∝ L2.34-0.16+0.09. For an early-type galaxy with a fiducal luminosity of 1011 Lr, ⊙ , we obtain a mass M200 = (1.93-0.14+0.13)×1013 h-1 M⊙. We also measure the virial mass-to-light ratio, and find for L200 < 1011 L⊙ a value of M200/L200 = 42 ± 10 for early-types, which increases for higher luminosities to values that are consistent with those observed for groups and clusters of galaxies. For late-type galaxies we find a lower value of M200/L200 = 17 ± 9. Our measurements also show that early- and late-type galaxies have comparable halo masses for stellar masses M∗ < 1011 M⊙, whereas the virial masses of early-type galaxies are higher for higher stellar masses. To compare the efficiency with which baryons have been converted into stars, we determine the total stellar mass within r200. Our results for early-type galaxies suggest a variation in efficiency with a minimum of ~10% for a stellar mass M∗,200 = 1012 M⊙. The results for the late-type galaxies are not well constrained, but do suggest a larger value.
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We study the shapes of galaxy dark matter haloes by measuring the anisotropy of the weak gravitational lensing signal around galaxies in the second Red-sequence Cluster Survey (RCS2). We determine ...the average shear anisotropy within the virial radius for three lens samples: the “all” sample, which contains all galaxies with 19 < mr′ < 21.5, and the “red” and “blue” samples, whose lensing signals are dominated by massive low-redshift early-type and late-type galaxies, respectively. To study the environmental dependence of the lensing signal, we separate each lens sample into an isolated and clustered part and analyse them separately. We address the impact of several complications on the halo ellipticity measurement, including PSF residual systematics in the shape catalogues, multiple deflections, and the clustering of lenses. We estimate that the impact of these is small for our lens selections. Furthermore, we measure the azimuthal dependence of the distribution of physically associated galaxies around the lens samples. We find that these satellites preferentially reside near the major axis of the lenses, and constrain the angle between the major axis of the lens and the average location of the satellites to ⟨θ⟩ = 43.7° ± 0.3° for the “all” lenses, ⟨θ⟩ = 41.7° ± 0.5° for the “red” lenses and ⟨θ⟩ = 42.0° ± 1.4° for the “blue” lenses. We do not detect a significant shear anisotropy for the average “red” and “blue” lenses, although for the most elliptical “red” and “blue” galaxies it is marginally positive and negative, respectively. For the “all” sample, we find that the anisotropy of the galaxy-mass cross-correlation function ⟨f − f45⟩ = 0.23 ± 0.12, providing weak support for the view that the average galaxy is embedded in, and preferentially aligned with, a triaxial dark matter halo. Assuming an elliptical Navarro-Frenk-White profile, we find that the ratio of the dark matter halo ellipticity and the galaxy ellipticity fh = eh/eg = 1.50-1.01+1.03, which for a mean lens ellipticity of 0.25 corresponds to a projected halo ellipticity of eh = 0.38-0.25+0.26 if the halo and the lens are perfectly aligned. For isolated galaxies of the “all” sample, the average shear anisotropy increases to ⟨f-f45⟩ = 0.51-0.25+0.26 and fh = 4.73-2.05+2.17, whilst for clustered galaxies the signal is consistent with zero. These constraints provide lower limits on the average dark matter halo ellipticity, as scatter in the relative position angle between the galaxies and the dark matter haloes is expected to reduce the shear anisotropy by a factor ~2.
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The classification and identification of quasars is fundamental to many astronomical research areas. Given the large volume of photometric survey data available in the near future, automated methods ...for doing so are required. In this article, we present 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. 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 colors. 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. 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: 6529 quasar candidates are identified from 16 898 sources, with a precision and recall of 97.0% and 97.5%, respectively. 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 compiled 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. 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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We present the results of Chandra and Suzaku X-ray observations of nine moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence Cluster Survey (RCS). Surface brightness profiles ...are fitted to β-models, gas masses are determined, integrated spectra are extracted within R
2500, and X-ray temperatures and luminosities are inferred. The L
X-T
X relationship expected from self-similar evolution is tested by comparing this sample to our previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically selected clusters. We find that optically selected clusters are systematically less luminous than X-ray selected clusters of similar X-ray temperature at both moderate and high z. We are unable to constrain evolution in the L
X-T
X relation with these data, but find it consistent with no evolution, within relatively large uncertainties. To investigate selection effects, we compare the X-ray properties of our sample to those of clusters in the representative X-ray selected sample, also determined within R
2500. We find that while RCS cluster X-ray properties span the entire range of those of massive clusters selected by other methods, their average X-ray properties are most similar to those of dynamically disturbed X-ray selected clusters. This similarity suggests that the true cluster distribution might contain a higher fraction of disturbed objects than are typically detected in X-ray selected surveys.
We present weak gravitational lensing analysis of 22 high-redshift (z 1) clusters based on Hubble Space Telescope images. Most clusters in our sample provide significant lensing signals and are well ...detected in their reconstructed two-dimensional mass maps. Combining the current results and our previous weak-lensing studies of five other high-z clusters, we compare gravitational lensing masses of these clusters with other observables. We revisit the question whether the presence of the most massive clusters in our sample is in tension with the current Delta *LCDM structure formation paradigm. We find that the lensing masses are tightly correlated with the gas temperatures and establish, for the first time, the lensing mass-temperature relation at z 1. For the power-law slope of the M-TX relation (MT Delta *a), we obtain Delta *a = 1.54 ? 0.23. This is consistent with the theoretical self-similar prediction Delta *a = 3/2 and with the results previously reported in the literature for much lower redshift samples. However, our normalization is lower than the previous results by 20%-30%, indicating that the normalization in the M-TX relation might evolve. After correcting for Eddington bias and updating the discovery area with a more conservative choice, we find that the existence of the most massive clusters in our sample still provides a tension with the current Delta *LCDM model. The combined probability of finding the four most massive clusters in this sample after the marginalization over cosmological parameters is less than 1%.
The SCUBA 8-mJy survey is the largest submillimetre (submm) extragalactic mapping survey undertaken to date, covering 260 arcmin2 to a 4 σ detection limit of ≃8 mJy at 850 μm, centred on the Lockman ...Hole and ELAIS N2 regions. Here, we present the results of new 1.4-GHz imaging of these fields, of the depth and resolution necessary to reliably identify radio counterparts for 18 of 30 submm sources, with possible detections of a further 25 per cent. Armed with this greatly improved positional information, we present and analyse new optical, near-infrared (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 per cent of the submm sources detected at 1.4 GHz are resolved by the 1.4-arcsec beam and a further 25 per cent 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 per cent 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 one half are found to be very red (I − K > 3.3) or extremely red (I − K > 4); contrary to popular belief, most are sufficiently bright to be tackled with spectrographs on 8-m telescopes. We find one submm source which is associated with the steep-spectrum lobe of a radio galaxy, at least two more with flatter radio spectra typical of radio-loud active galactic nuclei (AGN), one of them variable. The latter is amongst four sources (≡15 per cent of the full sample) with X-ray emission consistent with obscured AGN, though the AGN would need to be Compton thick to power the observed far-IR luminosity. We exploit our well-matched radio and submm data to estimate the median redshift of the S850 μm ∼ 8 mJy submm galaxy population. If the radio/far-IR correlation holds at high redshift, and our sample is unbiased, we derive a conservative limit of 〈z〉 ⩾ 2.0, or ⩾ 2.4 using spectral templates more representative of known submm galaxies.
We present the results of Chandra observations of 13 optically selected clusters with image, discovered via the Red-Sequence Cluster Survey (RCS). All but one are detected at image, although three ...were not observed long enough to support detailed analysis. Surface brightness profiles are fitted to beta models. Integrated spectra are extracted within R sub(2500), and T sub(X) and L sub(X) information is obtained. We derive gas masses and total masses within R sub(2500) and R sub(500). Cosmologically corrected scaling relations are investigated, and we find the RCS clusters to be consistent with self-similar scaling expectations. However, discrepancies exist between the RCS sample and lower z X-ray- selected samples for relationships involving L sub(X), with the higher z RCS clusters having lower L sub(X) for a given T sub(X). In addition, we find that gas mass fractions within R sub(2500) for the high- z RCS sample are lower than expected by a factor of image2. This suggests that the central entropy of these high-z objects has been elevated by processes such as preheating, mergers, and/or AGN outbursts, that their gas is still infalling, or that they contain comparatively more baryonic matter in the form of stars. Finally, relationships between red- sequence optical richness and X-ray properties are fitted to the data. For systems with measured T sub(X), we find that optical richness correlates with both T sub(X) and mass, having a scatter of image30% with mass for both X-ray-selected and optically selected clusters. However, we also find that X-ray luminosity is not well correlated with richness and that several of our sample members appear to be significantly X-ray faint.
We report a measurement of the Type Ia supernova (SN Ia) rate in galaxy clusters at 0.9 < z < 1.46 from the Hubble Space Telescope Cluster Supernova Survey. This is the first cluster SN Ia rate ...measurement with detected z > 0.9 SNe. Finding 8 + or - 1 cluster SNe Ia, we determine an SN Ia rate of (stat) (sys) SNuB (SNuB = 10 super(-12) SNe yr super(-1)). In units of stellar mass, this translates to (stat) (sys) SNuM (SNuM = 10 super(-12) SNe yr super(-1)). This represents a factor of approximate5 + or - 2 increase over measurements of the cluster rate at z < 0.2. We parameterize the late-time SN Ia delay time distribution (DTD) with a power law: Psi(t) is proportional to t super(s). Under the approximation of a single-burst cluster formation redshift of z= 3, our rate measurement in combination with lower-redshift cluster SN Ia rates constrains s = consistent with measurements of the DTD in the field. This measurement is generally consistent with expectations for the "double degenerate" scenario and inconsistent with some models for the "single degenerate" scenario predicting a steeper DTD at large delay times. We check for environmental dependence and the influence of younger stellar populations by calculating the rate specifically in cluster red-sequence galaxies and in morphologically early-type galaxies, finding results similar to the full cluster rate. Finally, the upper limit of one hostless cluster SN Ia detected in the survey implies that the fraction of stars in the intra-cluster medium is less than 0.47 (95% confidence), consistent with measurements at lower redshifts.
We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey, a wide-field high-cadence g-band synoptic survey targeting the Galactic ...Plane. We have used fast photometry on the SAAO 1.0- and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find that many of these variables have spectra which are consistent with being d Scuti-type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the 'Bump Cepheid' phenomena in a d Scuti star, with OW J175848.21-271653.7 showing a pronounced 22 per cent amplitude dip lasting 3 min during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.
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