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Register a new userHigh redshift galaxies in the ALHAMBRA survey: II. strengthening the evidence of bright-end excess in UV luminosity functions at 2.5 <= z <= 4.5 by PDF analysis
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Context. Knowing the exact shape of the UV luminosity function of high-redshift galaxies is important in order to understand the star formation history of the early universe. However, the uncertainties, especially at the faint and bright ends of the LFs, are still significant. Aims. In this paper, we study the UV luminosity function of redshift z = 2.5 - 4.5 galaxies in 2.38 deg^2 of ALHAMBRA data with I <= 24. Thanks to the large area covered by ALHAMBRA, we particularly constrain the bright end of the luminosity function. We also calculate the cosmic variance and the corresponding bias values for our sample and derive their host dark matter halo masses. Methods. We use a novel methodology based on redshift and magnitude probability distribution functions (PDFs). This methodology robustly takes into account the uncertainties due to redshift and magnitude errors, shot noise and cosmic variance, and models the luminosity function in two dimensions (z; M_UV ). Results. We find an excess of bright ~ M*_UV galaxies as compared to the studies based on broad-band photometric data. However, our results agree well with the luminosity function of the magnitude-selected spectroscopic VVDS data. We measure high bias values, b ~ 8 - 10, that are compatible with the previous measurements considering the redshifts and magnitudes of our galaxies and further reinforce the real high-redshift nature of our bright galaxies. Conclusions. We call into question the shape of the luminosity function at its bright end; is it a double power-law as suggested by the recent broad-band photometric studies or rather a brighter Schechter function, as suggested by our multi-filter analysis and the spectroscopic VVDS data.
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Our goal is to study the evolution of the $B-$band luminosity function (LF) since $z=1$ using ALHAMBRA data. We used the photometric redshift and the $I-$band selection magnitude probability distribution functions (PDFs) of those ALHAMBRA galaxies with $Ileq24$ 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.
We report the rest-frame ultraviolet luminosity function of $g$-dropout galaxies in 177 protocluster candidates (PC UVLF) at $zsim4$ selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess towards the bright-end. This excess can not be explained by the contribution of only active galactic nuclei, and we also find that this is more significant in higher dense regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at $zsim4$. We also estimate the star formation rate density (SFRD) in protocluster regions as $simeq 6-20%$ of the cosmic SFRD, based on the measured PC UVLF after correcting for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a non-negligible contribution to the cosmic SFRD at $zsim4$, as previously suggested by simulations. Our results suggest that protoclusters are essential components for the galaxy evolution at $zsim4$.
The deep, wide-area (~800-900 arcmin**2) near-infrared/WFC3/IR + Spitzer/IRAC observations over the CANDELS fields have been a remarkable resource for constraining the bright end of high redshift UV luminosity functions (LFs). However, the lack of HST 1.05-micron observations over the CANDELS fields has made it difficult to identify z~9-10 sources robustly, since such data are needed to confirm the presence of an abrupt Lyman break at 1.2 microns. We report here on the successful identification of many such z~9-10 sources from a new HST program (z9-CANDELS) that targets the highest-probability z~9-10 galaxy candidates with observations at 1.05 microns, to search for a robust Lyman-break at 1.2 microns. The potential z~9-10 candidates are preselected from the full HST, Spitzer/IRAC S-CANDELS observations, and the deepest-available ground-based optical+near-infrared observations. We identified 15 credible z~9-10 galaxies over the CANDELS fields. Nine of these galaxies lie at z~9 and 5 are new identifications. Our targeted follow-up strategy has proven to be very efficient in making use of scarce HST time to secure a reliable sample of z~9-10 galaxies. Through extensive simulations, we replicate the selection process for our sample (both the preselection and follow-up) and use it to improve current estimates for the volume density of bright z~9 and z~10 galaxies. The volume densities we find are 5(-2)(+3)x and 8(-3)(+9)x lower, respectively, than found at z~8. When compared with the best-fit evolution (i.e., dlog_{10} rho(UV)/dz=-0.29+/-0.02) in the UV luminosities densities from z~8 to z~4 integrated to 0.3L*(z=3) (-20 mag), these luminosity densities are 2.6(-0.9)(+1.5)x and 2.2(-1.1)(+2.0)x lower, respectively, than the extrapolated trends. Our new results are broadly consistent with the accelerated evolution scenario at z>8, as seen in many theoretical models.
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.
We present a technique that permits the analysis of stellar population gradients in a relatively low cost way compared to IFU surveys analyzing a vastly larger samples as well as out to larger radii. We developed a technique to analyze unresolved stellar populations of spatially resolved galaxies based on photometric multi-filter surveys. We derived spatially resolved stellar population properties and radial gradients by applying a Centroidal Voronoi Tesselation and performing a multi-color photometry SED fitting. This technique has been applied to a sample of 29 massive (M$_{star}$ > 10$^{10.5}$ M$_{odot}$), early-type galaxies at $z$ < 0.3 from the ALHAMBRA survey. We produced detailed 2D maps of stellar population properties (age, metallicity and extinction). Radial structures have been studied and luminosity-weighted and mass-weighted gradients have been derived out to 2 - 3.5 R$_mathrm{eff}$. We find the gradients of early-type galaxies to be on average flat in age ($ abla$log Age$_mathrm{L}$ = 0.02 $pm$ 0.06 dex/R$_mathrm{eff})$ and negative in metallicity ($ abla$[Fe/H]$_mathrm{L}$ = - 0.09 $pm$ 0.06 dex/R$_mathrm{eff}$). Overall, the extinction gradients are flat ($ abla$A$_mathrm{v}$ = - 0.03 $pm$ 0.09 mag/R$_mathrm{eff}$ ) with a wide spread. These results are in agreement with previous studies that used standard long-slit spectroscopy as well as with the most recent integral field unit (IFU) studies. According to recent simulations, these results are consistent with a scenario where early-type galaxies were formed through major mergers and where their final gradients are driven by the older ages and higher metallicity of the accreted systems. We demonstrate the scientific potential of multi-filter photometry to explore the spatially resolved stellar populations of local galaxies and confirm previous spectroscopic trends from a complementary technique.
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