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تسجيل مستخدم جديدThe ALHAMBRA survey: Accurate merger fractions by PDF analysis of photometric close pairs
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Our goal is to develop and test a novel methodology to compute accurate close pair fractions with photometric redshifts. We improve the current methodologies to estimate the merger fraction f_m from photometric redshifts by (i) using the full probability distribution functions (PDFs) of the sources in redshift space, (ii) including the variation in the luminosity of the sources with z in both the selection of the samples and in the luminosity ratio constrain, and (iii) splitting individual PDFs into red and blue spectral templates to deal robustly with colour selections. We test the performance of our new methodology with the PDFs provided by the ALHAMBRA photometric survey. The merger fractions and rates from the ALHAMBRA survey are in excellent agreement with those from spectroscopic work, both for the general population and for red and blue galaxies. With the merger rate of bright (M_B <= -20 - 1.1z) galaxies evolving as (1+z)^n, the power-law index n is larger for blue galaxies (n = 2.7 +- 0.5) than for red galaxies (n = 1.3 +- 0.4), confirming previous results. Integrating the merger rate over cosmic time, we find that the average number of mergers per galaxy since z = 1 is N_m = 0.57 +- 0.05 for red galaxies and N_m = 0.26 +- 0.02 for blue galaxies. Our new methodology exploits statistically all the available information provided by photometric redshift codes and provides accurate measurements of the merger fraction by close pairs only using photometric redshifts. Current and future photometric surveys will benefit of this new methodology.
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th $Ileq24$ mag to compute the posterior LF. We statistically studied quiescent and star-forming galaxies using the template information encoded in the PDFs. The LF covariance matrix in redshift-magnitude-galaxy type space was computed, including the cosmic variance. That was estimated from the intrinsic dispersion of the LF measurements in the 48 ALHAMBRA sub-fields. The uncertainty due to the photometric redshift prior is also included in our analysis. We modelled the LF with a redshift-dependent Schechter function affected by the same selection effects than the data. The measured ALHAMBRA LF at $0.2leq z<1$ and the evolving Schechter parameters both for quiescent and star-forming galaxies agree with previous results in the literature. The estimated redshift evolution of $M_B^* propto Qz$ is $Q_{rm SF}=-1.03pm0.08$ and $Q_{rm Q}=-0.80pm0.08$, and of $log phi^* propto Pz$ is $P_{rm SF}=-0.01pm0.03$ and $P_{rm Q}=-0.41pm0.05$. The measured faint-end slopes are $alpha_{rm SF}=-1.29pm0.02$ and $alpha_{rm Q}=-0.53pm0.04$. We find a significant population of faint quiescent galaxies, modelled by a second Schechter function with slope $beta=-1.31pm0.11$. We find a factor $2.55pm0.14$ decrease in the luminosity density $j_B$ of star-forming galaxies, and a factor $1.25pm0.16$ increase in the $j_B$ of quiescent ones since $z=1$, confirming the continuous build-up of the quiescent population with cosmic time. The contribution of the faint quiescent population to $j_B$ increases from 3% at $z=1$ to 6% at $z=0$. The developed methodology will be applied to future multi-filter surveys such as J-PAS.
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