We use velocity dispersion measurements of 21 individual cluster members in the core of Abell 383, obtained with Multiple Mirror Telescope Hectospec, to separate the galaxy and the smooth dark halo ...(DH) lensing contributions. While lensing usually constrains the overall, projected mass density, the innovative use of velocity dispersion measurements as a proxy for masses of individual cluster members breaks inherent degeneracies and allows us to (a) refine the constraints on single galaxy masses and on the galaxy mass-to-light scaling relation and, as a result, (b) refine the constraints on the DM-only map, a high-end goal of lens modelling. The knowledge of cluster member velocity dispersions improves the fit by 17 per cent in terms of the image reproduction χ2, or 20 per cent in terms of the rms. The constraints on the mass parameters improve by ∼10 per cent for the DH, while for the galaxy component, they are refined correspondingly by ∼50 per cent, including the galaxy halo truncation radius. For an L* galaxy with
$M^{*}_{B}=-20.96$
, for example, we obtain best-fitting truncation radius
$r_{\rm tr}^{*}=20.5^{+9.6}_{-6.7}$
kpc and velocity dispersion σ* = 324 ± 17 km s−1. Moreover, by performing the surface brightness reconstruction of the southern giant arc, we improve the constraints on r
tr of two nearby cluster members, which have measured velocity dispersions, by more than ∼30 per cent. We estimate the stripped mass for these two galaxies, getting results that are consistent with numerical simulations. In the future, we plan to apply this analysis to other galaxy clusters for which velocity dispersions of member galaxies are available.
We construct a set of model spectra specifically designed to match the colours of the Baryon Oscillation Spectroscopic Survey CMASS galaxies and to be used with photometric redshift template fitting ...techniques. As a basis, we use a set of spectral energy distributions(SEDs) of single and composite stellar population models. These models cannot describe well the whole colour range populated by the CMASS galaxies at all redshifts, wherefore we modify them by multiplying the SEDs with λ−β for λ > λ
i
for different values of λ
i
and β. When fitting these SEDs to the colours of the CMASS sample, with a burst and dust components in superposition, we can recreate the location in colour spaces inhabited by the CMASS galaxies. From the best-fitting models, we select a small subset in a two-dimensional plane, whereto the galaxies were mapped by a self-organizing map. These models are used for the estimation of photometric redshifts with a Bayesian template fitting code. The photometric redshifts with the novel templates have a very small outlier rate of 0.22 per cent, a low bias 〈Δz/(1 + z)〉 = 2.0 × 10−3, and scatter of σ68 = 0.026 in the rest frame. Using our models, the galaxy colours are reproduced to a better extent with the photometric redshifts of this work than with photometric redshifts of Sloan Digital Sky Survey.
We present a quintuply lensed z ∼ 6 candidate discovered in the field of the galaxy cluster RXC J2248.7−4431 (z ∼ 0.348) targeted within the Cluster Lensing and Supernova survey with Hubble (CLASH) ...and selected in the deep Hubble Space Telescope (HST) frontier fields survey. Thanks to the CLASH 16-band HST imaging, we identify the quintuply lensed z ∼ 6 candidate as an optical dropout in the inner region of the cluster, the brightest image having magAB = 24.8 ± 0.1 in the f105w filter. We perform a detailed photometric analysis to verify its high-z and lensed nature. We get as photometric redshift z
ph ∼ 5.9, and given the extended nature and NIR colours of the lensed images, we rule out low-z early-type and galactic star contaminants. We perform a strong lensing analysis of the cluster, using 13 families of multiple lensed images identified in the HST images. Our final best model predicts the high-z quintuply lensed system with a position accuracy of 0.8 arcsec. The magnifications of the five images are between 2.2 and 8.3, which leads to a delensed UV luminosity of
$L_{1600}\sim 0.5L_{1600}^*$
at z = 6. We also estimate the UV slope from the observed NIR colours, finding a steep β = −2.89 ± 0.38. We use singular and composite stellar population SEDs to fit the photometry of the high-z candidate, and we conclude that it is a young (age <300 Myr) galaxy with mass of M ∼ 108 M⊙, subsolar metallicity (Z < 0.2 Z⊙) and low dust content (A
V
∼ 0.2–0.4).
We describe the construction of a template set of spectral energy distributions (SEDs) for the estimation of photometric redshifts of luminous red galaxies (LRGs) with a Bayesian template fitting ...method. By examining the color properties of several publicly available SED sets within a redshift range of 0 < z < or ~ 0.5 and comparing them to Sloan Digital Sky Survey (SDSS) Data Release 7 data, we show that only some of the investigated SEDs approximately match the colors of the LRG data throughout the redshift range, however not at the quantitative level required for precise photometric redshifts. Our findings based on the photometry of the SDSS LRGs and our SED template fitting are supported by comparison to the average SDSS LRG spectra in different luminosity and redshift bins.
The Pan-STARRS1 survey is obtaining multi-epoch imaging in five bands (g sub(P1)r sub(P1)i sub(P1)z sub(P1)y sub(P 1)) over the entire sky north of declination -30 deg. We describe here the ...implementation of the Photometric Classification Server (PCS) for Pan-STARRS1. PCS will allow the automatic classification of objects into star/galaxy/quasar classes based on colors and the measurement of photometric redshifts for extragalactic objects, and will constrain stellar parameters for stellar objects, working at the catalog level. We present tests of the system based on high signal-to-noise photometry derived from the Medium-Deep Fields of Pan-STARRS1, using available spectroscopic surveys as training and/or verification sets. We show that the Pan-STARRS1 photometry delivers classifications and photometric redshifts as good as the Sloan Digital Sky Survey (SDSS) photometry to the same magnitude limits. In particular, our preliminary results, based on this relatively limited data set down to the SDSS spectroscopic limits, and therefore potentially improvable, show that stars are correctly classified as such in 85% of cases, galaxies in 97%, and QSOs in 84%. False positives are less than 1% for galaxies, approx =19% for stars, and approx =28% for QSOs. Moreover, photometric redshifts for 1000 luminous red galaxies up to redshift 0.5 are determined to 2.4% precision (defined as 1.48 x Median |z sub(phot) - z sub(spec)|/(1 + z)) with just 0.4% catastrophic outliers and small (-0.5%) residual bias. For bluer galaxies up to the same redshift, the residual bias (on average -0.5%) trend, percentage of catastrophic failures (1.2%), and precision (4.2%) are higher, but still interestingly small for many science applications. Good photometric redshifts (to 5%) can be obtained for at most 60% of the QSOs of the sample. PCS will create a value-added catalog with classifications and photometric redshifts for eventually many millions of sources.
We present results from a study of the photometric redshift performance of the Dark Energy Survey (DES), using the early data from a Science Verification period of observations in late 2012 and early ...2013 that provided science-quality images for almost 200 sq. deg. at the nominal depth of the survey. We assess the photometric redshift (photo-z) performance using about 15 000 galaxies with spectroscopic redshifts available from other surveys. These galaxies are used, in different configurations, as a calibration sample, and photo-z's are obtained and studied using most of the existing photo-z codes. A weighting method in a multidimensional colour-magnitude space is applied to the spectroscopic sample in order to evaluate the photo-z performance with sets that mimic the full DES photometric sample, which is on average significantly deeper than the calibration sample due to the limited depth of spectroscopic surveys. Empirical photo-z methods using, for instance, artificial neural networks or random forests, yield the best performance in the tests, achieving core photo-z resolutions ... ~ 0.08. Moreover, the results from most of the codes, including template-fitting methods, comfortably meet the DES requirements on photo-z performance, therefore, providing an excellent precedent for future DES data sets. (ProQuest: ... denotes formulae/symbols omitted.)
MiniJPAS is a ∼1 deg
2
imaging survey of the AEGIS field in 60 bands, performed to demonstrate the scientific potential of the upcoming Javalambre-Physics of the Accelerating Universe Astrophysical ...Survey (J-PAS). Full coverage of the 3800–9100 Å range with 54 narrow-band filters, in combination with 6 optical broad-band filters, allows for extremely accurate photometric redshifts (photo-
z
), which, applied over areas of thousands of square degrees, will enable new applications of the photo-
z
technique, such as measurement of baryonic acoustic oscillations. In this paper we describe the method we used to obtain the photo-
z
that is included in the publicly available miniJPAS catalogue, and characterise the photo-
z
performance. We built photo-spectra with 100 Å resolution based on forced-aperture photometry corrected for point spread function. Systematic offsets in the photometry were corrected by applying magnitude shifts obtained through iterative fitting with stellar population synthesis models. We computed photo-
z
with a customised version of L
E
P
HARE
, using a set of templates that is optimised for the J-PAS filter-set. We analysed the accuracy of miniJPAS photo-
z
and their dependence on multiple quantities using a subsample of 5266 galaxies with spectroscopic redshifts from SDSS and DEEP, which we find to be representative of the whole
r
< 23 miniJPAS sample. Formal 1
σ
uncertainties for the photo-
z
that are calculated with the Δ
χ
2
method underestimate the actual redshift errors. The
o
d
d
s
parameter has a stronger correlation with |Δ
z
| and accurately reproduces the probability of a redshift outlier (|Δ
z
| > 0.03), regardless of the magnitude, redshift, or spectral type of the sources. We show that the two main summary statistics characterising the photo-
z
accuracy for a population of galaxies (
σ
NMAD
and
η
) can be predicted by the distribution of
o
d
d
s
in this population, and we use this to estimate the statistics for the whole miniJPAS sample. At
r
< 23, there are ∼17 500 galaxies per deg
2
with valid photo-
z
estimates, ∼4200 of which are expected to have |Δ
z
| < 0.003. The typical error is
σ
NMAD
= 0.013 with an outlier rate
η
= 0.39. The target photo-
z
accuracy
σ
NMAD
= 0.003 is achieved for
o
d
d
s
> 0.82 with
η
= 0.05, at the cost of decreasing the density of selected galaxies to
n
∼ 5200 deg
−2
(∼2600 of which have |Δ
z
| < 0.003).
In this study, we present results from a study of the photometric redshift performance of the Dark Energy Survey (DES), using the early data from a Science Verification period of observations in late ...2012 and early 2013 that provided science-quality images for almost 200 sq. deg. at the nominal depth of the survey. We assess the photometric redshift (photo-z) performance using about 15 000 galaxies with spectroscopic redshifts available from other surveys. These galaxies are used, in different configurations, as a calibration sample, and photo-z's are obtained and studied using most of the existing photo-z codes. A weighting method in a multidimensional colour–magnitude space is applied to the spectroscopic sample in order to evaluate the photo-z performance with sets that mimic the full DES photometric sample, which is on average significantly deeper than the calibration sample due to the limited depth of spectroscopic surveys. In addition, empirical photo-z methods using, for instance, artificial neural networks or random forests, yield the best performance in the tests, achieving core photo-z resolutions σ68 ~ 0.08. Moreover, the results from most of the codes, including template-fitting methods, comfortably meet the DES requirements on photo-z performance, therefore, providing an excellent precedent for future DES data sets.
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