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تسجيل مستخدم جديدThe PAU Survey: An improved photo-$z$ sample in the COSMOS field
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We present -- and make publicly available -- accurate and precise photometric redshifts in the ACS footprint from the COSMOS field for objects with $i_{mathrm{AB}}leq 23$. The redshifts are computed using a combination of narrow band photometry from PAUS, a survey with 40 narrow bands spaced at $100r{A}$ intervals covering the range from $4500r{A}$ to $8500r{A}$, and 26 broad, intermediate, and narrow bands covering the UV, visible and near infrared spectrum from the COSMOS2015 catalogue. We introduce a new method that models the spectral energy distributions (SEDs) as a linear combination of continuum and emission line templates and computes its Bayes evidence, integrating over the linear combinations. The correlation between the UV luminosity and the OII line is measured using the 66 available bands with the zCOSMOS spectroscopic sample, and used as a prior which constrains the relative flux between continuum and emission line templates. The flux ratios between the OII line and $mathrm{H}_{alpha}$, $mathrm{H}_{beta}$ and $mathrm{OIII}$ are similarly measured and used to generate the emission line templates. Comparing to public spectroscopic surveys via the quantity $Delta_zequiv(z_{mathrm{photo}}-z_{mathrm{spec}})/(1+z_{mathrm{spec}})$, we find the photometric redshifts to be more precise than previous estimates, with $sigma_{68}(Delta_z) approx (0.003, 0.009)$ for galaxies at magnitude $i_{mathrm{AB}}sim18$ and $i_{mathrm{AB}}sim23$, respectively, which is $3times$ and $1.66times$ tighter than COSMOS2015. Additionally, we find the redshifts to be very accurate on average, yielding a median of the $Delta_z$ distribution compatible with $|mathrm{median}(Delta_z)|leq0.001$ at all redshifts and magnitudes considered. Both the added PAUS data and new methodology contribute significantly to the improved results.
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The PAU Survey (PAUS) is an innovative photometric survey with 40 narrow bands at the William Herschel Telescope (WHT). The narrow bands are spaced at 100AA intervals covering the range 4500AA to 8500AA and, in combination with standard broad bands,
enable excellent redshift precision. This paper describes the technique, galaxy templates and additional photometric calibration used to determine early photometric redshifts from PAUS. Using BCNz2, a new photometric redshift code developed for this purpose, we characterise the photometric redshift performance using PAUS data on the COSMOS field. Comparison to secure spectra from zCOSMOS DR3 shows that PAUS achieves $sigma_{68} /(1+z) = 0.0037$ to $i_{mathrm{AB}} < 22.5$ when selecting the best 50% of the sources based on a photometric redshift quality cut. Furthermore, a higher photo-z precision ($sigma_{68}/(1+z) sim 0.001$) is obtained for a bright and high quality selection, which is driven by the identification of emission lines. We conclude that PAUS meets its design goals, opening up a hitherto uncharted regime of deep, wide, and dense galaxy survey with precise redshifts that will provide unique insights into the formation, evolution and clustering of galaxies, as well as their intrinsic alignments.
We present the largest high-redshift (3<z<6.85) sample of X-ray-selected active galactic nuclei (AGN) on a contiguous field, using sources detected in the Chandra COSMOS Legacy survey. The sample contains 174 sources, 87 with spectroscopic redshift,
the other 87 with photometric redshift (z_phot). In this work we treat z_phot as a probability weighted sum of contributions, adding to our sample the contribution of sources with z_phot<3 but z_phot probability distribution >0 at z>3. We compute the number counts in the observed 0.5-2 keV band, finding a decline in the number of sources at z>3 and constraining phenomenological models of X-ray background. We compute the AGN space density at z>3 in two different luminosity bins. At higher luminosities (logL(2-10 keV) > 44.1 erg/s) the space density declines exponentially, dropping by a factor ~20 from z~3 to z~6. The observed decline is ~80% steeper at lower luminosities (43.55 erg/s < logL(2-10 keV) < 44.1 erg/s), from z~3 to z~4.5. We study the space density evolution dividing our sample in optically classified Type 1 and Type 2 AGN. At logL(2-10 keV) > 44.1 erg/s, unobscured and obscured objects may have different evolution with redshift, the obscured component being three times higher at z~5. Finally, we compare our space density with predictions of quasar activation merger models, whose calibration is based on optically luminous AGN. These models significantly overpredict the number of expected AGN at logL(2-10 keV) > 44.1 erg/s with respect to our data.
In Sedgwick et al. (2019) we introduced and utilised a method to combat surface brightness and mass biases in galaxy sample selection, using core-collapse supernovae (CCSNe) as pointers towards their host galaxies, in order to: (i) search for low-sur
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