共查询到20条相似文献,搜索用时 15 毫秒
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Adrian Collister Ofer Lahav Chris Blake Russell Cannon Scott Croom Michael Drinkwater Alastair Edge Daniel Eisenstein Jon Loveday Robert Nichol Kevin Pimbblet Roberto De Propris Isaac Roseboom Nic Ross Donald P. Schneider Tom Shanks David Wake 《Monthly notices of the Royal Astronomical Society》2007,375(1):68-76
We describe the construction of MegaZ-LRG, a photometric redshift catalogue of over one million luminous red galaxies (LRGs) in the redshift range 0.4 < z < 0.7 with limiting magnitude i < 20 . The catalogue is selected from the imaging data of the Sloan Digital Sky Survey (SDSS) Data Release 4. The 2dF-SDSS LRG and Quasar (2SLAQ) spectroscopic redshift catalogue of 13 000 intermediate-redshift LRGs provides a photometric redshift training set, allowing use of ann z, a neural network-based photometric-redshift estimator. The rms photometric redshift accuracy obtained for an evaluation set selected from the 2SLAQ sample is σ z = 0.049 averaged over all galaxies, and σ z = 0.040 for a brighter subsample ( i < 19.0) . The catalogue is expected to contain ∼5 per cent stellar contamination. The ann z code is used to compute a refined star/galaxy probability based on a range of photometric parameters; this allows the contamination fraction to be reduced to 2 per cent with negligible loss of genuine galaxies. The MegaZ-LRG catalogue is publicly available on the World Wide Web from http://www.2slaq.info . 相似文献
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Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we explore the environmental dependence of five photometric band concentration indexes of LRGs. It turns out that the trends for all the five band concentration indexes to change with the local density are the same: galaxies with higher concentration reside preferentially in overdense environments, while galaxies with lower concentration are located preferentially in underdense environments (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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In this paper we describe a set of models to predict the colours of galaxies over a wide range of redshifts. We present examples of output from the simulations, and discuss their application to the selection of galaxies at high redshifts, particularly through identification of the Lyman break. Additionally we consider the optimal choices of filters for selection at a range of redshifts.
An interface to a subset of the simulations has been made available on the World Wide Web for the benefit of the community at the location http://www-astro.physics.ox.ac.uk/~rejs/research/galcols.html/ 相似文献
An interface to a subset of the simulations has been made available on the World Wide Web for the benefit of the community at the location http://www-astro.physics.ox.ac.uk/~rejs/research/galcols.html/ 相似文献
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Isaac G. Roseboom Kevin A. Pimbblet Michael J. Drinkwater Russell D. Cannon Roberto De Propris Alastair C. Edge Daniel J. Eisenstein Robert C. Nichol Ian Smail David A. Wake Joss Bland-Hawthorn Terry J. Bridges Daniel Carson Matthew Colless Warrick J. Couch Scott M. Croom Simon P. Driver Paul C. Hewett Jon Loveday Nic Ross Donald P. Schneider Tom Shanks Robert G. Sharp Peter Weilbacher 《Monthly notices of the Royal Astronomical Society》2006,373(1):349-360
We present a detailed investigation into the recent star formation histories of 5697 luminous red galaxies (LRGs) based on the Hδ (4101 Å), and [O ii ] (3727 Å) lines and the D4000 index. LRGs are luminous ( L > 3 L *) galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study, we utilize LRGs from the recently completed 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of the Hδ and [O ii ] lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong [O ii ] in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (∼80 per cent); however, significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low-redshift comparison. While the em and em+a fractions are consistent with the low-redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected lifetime of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activities is not sufficient to reconcile the predicted mass growth for massive early types in a hierarchical merging scenario. 相似文献
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A.I. Terlevich N. Caldwell R.G. Bower 《Monthly notices of the Royal Astronomical Society》2001,326(4):1547-1562
We present a new photometric catalogue of the Coma galaxy cluster in the Johnson U and V bands. We cover an area of 3360 arcmin2 of sky, to a depth of in a 13-arcsec diameter aperture, and produce magnitudes for ∼1400 extended objects in metric apertures from 8.8- to 26-arcsec diameters. The mean internal rms scatter in the photometry is 0.014 mag in V , and 0.026 mag in U , for .
We place new limits on the levels of scatter in the colour–magnitude relation (CMR) in the Coma cluster, and investigate how the slope and scatter of the CMR depend on galaxy morphology, luminosity and position within the cluster. As expected, the lowest levels of scatter are found in the elliptical galaxies, while the late-type galaxies have the highest numbers of galaxies bluewards of the CMR. We investigate whether the slope of the CMR is an artefact of colour gradients within galaxies, and show that it persists when the colours are measured within a diameter that scales with galaxy size. Looking at the environmental dependence of the CMR, we find a trend of systematically bluer galaxy colours with increasing projected radius from the centre of the cluster. Surprisingly, this is accompanied by a decreased scatter of the CMR. We investigate whether this gradient could be caused by dust in the cluster potential, however the reddening required would produce too large a scatter in the colours of the central galaxies. The gradient appears to be better reproduced by a gradient in the mean galactic ages with projected radius. 相似文献
We place new limits on the levels of scatter in the colour–magnitude relation (CMR) in the Coma cluster, and investigate how the slope and scatter of the CMR depend on galaxy morphology, luminosity and position within the cluster. As expected, the lowest levels of scatter are found in the elliptical galaxies, while the late-type galaxies have the highest numbers of galaxies bluewards of the CMR. We investigate whether the slope of the CMR is an artefact of colour gradients within galaxies, and show that it persists when the colours are measured within a diameter that scales with galaxy size. Looking at the environmental dependence of the CMR, we find a trend of systematically bluer galaxy colours with increasing projected radius from the centre of the cluster. Surprisingly, this is accompanied by a decreased scatter of the CMR. We investigate whether this gradient could be caused by dust in the cluster potential, however the reddening required would produce too large a scatter in the colours of the central galaxies. The gradient appears to be better reproduced by a gradient in the mean galactic ages with projected radius. 相似文献
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Using two volume‐limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) with the luminosity –20.0 ≤ Mr ≤ –18.5 and –22.40 ≤ Mr ≤–20.16, we have explored the environmental dependence of the fractions of red star‐forming and blue passive galaxies. It is found that the fractions of red star‐forming and blue passive galax‐ies decline mildly with increasing local density in the luminous volume‐limited sample, but in the faint volume‐limited sample these fractions rise slightly with increasing local density except that the fraction of red star‐forming decreases with density in the densest regime. Only according to statistical results of this study, it is difficult to reach the conclusion: there is an environmental dependence for color beyond that for star formation activities or for star formation activities beyond that for color. In this condition, we preferentially believe that star formation activities and color possiblely have equally strong environmental dependence. In the faint volume‐limited sample, we observe that the fraction of star‐forming galaxies‐the density relation has a “critical density” at the projected local density PLD ≈ 1 h–2 Mpc–2: below this density the fraction of star‐forming galaxies is high and nearly constant, while above this density this fraction drops rapidly. Thus, it is possible that in the densest regime of the faint volume‐limited sample, there is an environmental dependence for star formation activities beyond that for color, which leads to the fraction of red star‐forming decreasing with density in the densest regime of the faint volume‐limited sample (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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David A. Wake Robert C. Nichol Daniel J. Eisenstein Jon Loveday Alastair C. Edge Russell Cannon Ian Smail Donald P. Schneider Ryan Scranton Daniel Carson Nicholas P. Ross Robert J. Brunner Matthew Colless Warrwick J. Couch Scott M. Croom Simon P. Driver José da Ângela Sebastian Jester Roberto de Propris Michael J. Drinkwater Joss Bland-Hawthorn Kevin A. Pimbblet Isaac G. Roseboom Tom Shanks Robert G. Sharp Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,372(2):537-550
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D. Wang Y. X. Zhang C. Liu Y. H. Zhao 《Monthly notices of the Royal Astronomical Society》2007,382(4):1601-1606
We present a new approach, namely kernel regression, to determine photometric redshifts for 399 929 galaxies in the Fifth Data Release of the Sloan Digital Sky Survey (SDSS). Kernel regression is a weighted average of spectral redshifts of the neighbours for a query point, and higher weights are associated with points that are closer to the query point. One important design decision when using kernel regression is the choice of bandwidth. We apply 10-fold cross-validation to choose the optimal bandwidth, which is obtained as the cross-validation error approaches its minimum. The results show that the optimal bandwidth is different for different input patterns: the lowest rms error of photometric redshift estimation arrives at 0.019 using colour+eClass as the inputs, the lowest rms errors comes to 0.020 using ugriz +eClass as the inputs. Where eClass is a galaxy spectral type, and 0.021 using colour+ r as the inputs. Thus, in addition to parameters such as magnitude and colour, eClass is a valid parameter with which to predict photometric redshifts. Moreover, the results suggest that the accuracy of estimating photometric redshifts is improved when the sample is divided into early-type and late-type galaxies; in particular, for early-type galaxies, the rms scatter is 0.016 with colour+eClass as the inputs. In addition, kernel regression achieves high accuracy when predicting the photometric eClass (σrms = 0.034) using colour+ r as the input pattern. For kernel regression, the accuracy of the photometric redshifts does not always increase with the number of parameters considered, but is satisfactory only when appropriate parameters are chosen. Kernel regression is a comprehensible and accurate regression method. Experiments reveal the superiority of kernel regression over other empirical training approaches. 相似文献