Alberto Molino | USP - Academia.edu (original) (raw)
Papers by Alberto Molino
The Astrophysical Journal, 2014
We utilize 16-band Hubble Space Telescope (HST ) observations of 18 lensing clusters obtained as ... more We utilize 16-band Hubble Space Telescope (HST ) observations of 18 lensing clusters obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program to search for z ∼ 6 − 8 galaxies. We report the discovery of 206, 45, and 13 Lyman-break galaxy (LBG) candidates at z ∼ 6, z ∼ 7, and z ∼ 8, respectively, identified from purely photometric redshift selections. This large sample, representing nearly an order of magnitude increase in the number of magnified star-forming galaxies at z ∼ 6 − 8 presented to date, is unique in that we have observations in four WFC3/UVIS UV, seven ACS/WFC optical and all five WFC3/IR broad-band filters, which enable very accurate photometric redshift selections. We construct detailed lensing models for all 18 clusters (although some are preliminary) to estimate object magnifications and to identify two new multiply-lensed z 6 candidates. The median magnifications for these 18 clusters are 4, 4, and 5 for the z ∼ 6, z ∼ 7, and z ∼ 8 samples, respectively, over an average area of 4.5 arcmin 2 per cluster. We compare our observed number counts with expectations based on convolving "blank" field UV luminosity functions through our cluster lens models and find agreement down to ∼ 27 mag, where we begin to suffer significant incompleteness. In all three redshift bins we find a higher number density at brighter observed magnitudes than the field predictions, in excellent agreement with the lensed expectations and clearly demonstrating the enhanced efficiency of lensing clusters over field surveys. Once again, lensing clusters appear to be a powerful tool in the discovery and study of high-redshift galaxies and allow for the first glimpse of faint galaxies beyond the reach of the deepest HST legacy field surveys, a technique that will continue be exploited with the upcoming ultradeep Hubble Frontier Fields campaign.
The Astrophysical Journal, 2015
We present a new determination of the concentration-mass relation for galaxy clusters based on ou... more We present a new determination of the concentration-mass relation for galaxy clusters based on our comprehensive lensing analysis of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble (CLASH). Our sample spans a redshift range between 0.19 and 0.89. We combine weak-lensing constraints from the Hubble Space Telescope (HST) and from groundbased wide-field data with strong lensing constraints from HST. The result are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids. Our derivation of NFW parameters yields virial masses between 0.53 × 10 15 M /h and 1.76 × 10 15 M /h and the halo concentrations are distributed around c 200c ∼ 3.7 with a 1σ significant negative trend with cluster mass. We find an excellent 4% agreement between our measured concentrations and the expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology. The simulations are analyzed in 2D to account for possible biases in the lensing reconstructions due to projection effects. The theoretical concentration-mass (c-M) relation from our X-ray selected set of simulated clusters and the c-M relation derived directly from the CLASH data agree at the 90% confidence level.
The Astrophysical Journal, 2014
We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodyna... more We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodynamical simulations, aimed at estimating the expected concentration-mass relation for the CLASH cluster sample. We study nearly 1400 halos simulated at high spatial and mass resolution, which were projected along many linesof-sight each. We study the shape of both their density and surface-density profiles and fit them with a variety of radial functions, including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the Einasto density profiles. We derive concentrations and masses from these fits and investigate their distributions as a function of redshift and halo relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra observations of the halos and we use them to identify objects resembling the X-ray morphologies and masses of the clusters in the CLASH X-ray selected sample. We also derive a concentration-mass relation for strong-lensing clusters. We find that the sample of simulated halos which resemble the X-ray morphology of the CLASH clusters is composed mainly by relaxed halos, but it also contains a significant fraction of unrelaxed systems. For such a heterogeneous sample we measure an average 2D concentration which is ∼ 11% higher than found for the full sample of simulated halos. After accounting for projection and selection effects, the average NFW concentrations of CLASH clusters are expected to be intermediate between those predicted in 3D for relaxed and super-relaxed halos. Matching the simulations to the individual CLASH clusters on the basis of the X-ray morphology, we expect that the NFW concentrations recovered from the lensing analysis of the CLASH clusters are in the range [3 − 6], with an average value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray morphologies similar to those of the CLASH clusters are affected by a modest orientation bias.
The Astrophysical Journal, 2014
We utilise a two-color Lyman-Break selection criterion to search for z ∼ 9-10 galaxies over the f... more We utilise a two-color Lyman-Break selection criterion to search for z ∼ 9-10 galaxies over the first 19 clusters in the CLASH program. Key to this search are deep observations over our clusters in five near-IR passbands to 1.6µm, allowing us good constraints on the position of the Lyman break to z ∼ 10. A systematic search yields three z ∼ 9-10 candidates in total above a 6σ detection limit. While we have already reported the most robust of these candidates, MACS1149-JD, in a previous publication, two additional z ∼ 9 candidates are also revealed in our expanded search. The new candidates have H 160 -band AB magnitudes of ∼26.2-26.9 and are located behind MACSJ1115.9+0129 and MACSJ1720.3+3536. The observed H 160 − Spitzer/IRAC colors for the sources are sufficiently blue to strongly favor redshifts of z ≥ 9 for these sources. A careful assessment of various sources of contamination suggests 1 contaminants for our z ∼ 9-10 selection. To determine the implications of these search results for the LF and SFR density at z ∼ 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z ∼ 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower redshift sample (after correcting for the differences in selection volumes), here taken to be z ∼ 8. This procedure takes advantage of the fact that the relative selection volumes available for the z ∼ 8 and z ∼ 9-10 selections behind lensing clusters are not greatly dependent on the details of the gravitational lensing models. We find that the normalization of the UV LF at z ∼ 9 is just 0.22 +0.30 −0.15 × that at z ∼ 8, ∼2 +3 −1 × lower than what we would infer extrapolating z ∼ 4-8 LF results. These results therefore suggest a more rapid evolution in the U V LF at z > 8 than seen at lower redshifts (although the current evidence here is weak). Compared to similar evolutionary findings from the HUDF, our result is much more insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe.
Proceedings of the International Astronomical Union, 2012
Astronomy & Astrophysics, 2015
Aims. Our goal is to develop and test a novel methodology to compute accurate close pair fraction... more Aims. Our goal is to develop and test a novel methodology to compute accurate close pair fractions with photometric redshifts. Methods. 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. Results. 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 red m = 0.57 ± 0.05 for red galaxies and N blue m = 0.26 ± 0.02 for blue galaxies. Conclusions. 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.
... The two-point correlation function ξ(r) is a simple tool ⋆ E-mail: pablo.arnalte@uv. es (PAM)... more ... The two-point correlation function ξ(r) is a simple tool ⋆ E-mail: pablo.arnalte@uv. es (PAM) † This version is submitted to the ALHAMBRA Core Team for analysis and discussion, the author list may be incomplete and outdated ...
The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey has observ... more The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey has observed 8 different regions of the sky, including sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 contiguous ∼300Å filters covering the optical range, combining them with deep JHKs imaging. The observations, carried out with the Calar Alto 3.5m telescope using the wide field (0.25 deg 2 FOV) optical camera LAICA and the NIR instrument Omega-2000, correspond to ∼700hrs of on-target science images. The photometric system was specifically designed to maximize the effective depth of the survey in terms of accurate spectral-type and photometric redshift estimation along with the capability of identification of relatively faint emission lines. Here we present multicolor photometry and photometric redshifts for ∼438,000 galaxies, detected in synthetic F 814W images, complete down to a magnitude I∼24.5AB, carefully taking into account realistic noise estimates, and correcting by PSF and aperture effects with the ColorP ro software. The photometric zeropoints have been calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission line galaxies. We calculate photometric redshifts with the BPZ2.0 code, which includes new empirically calibrated galaxy templates and priors. Our photometric redshifts have a precision of δ z /(1+z s )=1% for I<22.5 and δ z /(1+z s )=1.4% for 22.5<I<24.5. Precisions of δ z /(1+z s )< 0.5 % are reached for the brighter spectroscopic sample, showing the potential of medium-band photometric surveys. The global photometric redshift distribution shows a mean redshift =0.56 for I<22.5 AB and =0.86 for I<24.5 AB. The data presented here covers an effective area of 2.79 deg 2 , split into 14 strips of 58.5'x15.5' and represents ∼32 hrs of on-target. Given its depth, multiband coverage and a much smaller cosmic variance than other similar projects, ALHAMBRA is a unique dataset for galaxy evolution studies. Several of the techniques presented here will have a wide applicability to future large scale photometric redshift surveys like JPAS.
Aims: Our goal is to develop and test a novel methodology to compute accurate close-pair fraction... more Aims: Our goal is to develop and test a novel methodology to compute accurate close-pair fractions with photometric redshifts. Methods: We improved the currently used methodologies to estimate the merger fraction fm 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 sample selection and the luminosity ratio constrain; and (iii) splitting individual PDFs into red and blue spectral templates to reliably work with colour selections. We tested the performance of our new methodology with the PDFs provided by the ALHAMBRA photometric survey. Results: The merger fractions and rates from the ALHAMBRA survey agree excellently well with those from spectroscopic work for both the general population and red and blue galaxies. With the merger rate of bright (MB <= -20-1.1z) galaxies evolving as (1 + z)n, the power-law index n is higher 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 Nmred = 0.57 ± 0.05 for red galaxies and Nmblue = 0.26 ± 0.02 for blue galaxies. Conclusions: Our new methodology statistically exploits all the available information provided by photometric redshift codes and yields accurate measurements of the merger fraction by close pairs from using photometric redshifts alone. Current and future photometric surveys will benefit from this new methodology.
This documents describes J-PAS and outlines its main scientific goals
Astronomy & Astrophysics, 2015
Context. Most observational results on the high redshift restframe UV-bright galaxies are based o... more Context. Most observational results on the high redshift restframe UV-bright galaxies are based on samples pinpointed using the so called dropout technique or Ly-α selection. However, the availability of multifilter data allows now replacing the dropout selections by direct methods based on photometric redshifts. In this paper we present the methodology to select and study the population of high redshift galaxies in the ALHAMBRA survey data. Aims. Our aim is to develop a less biased methodology than the traditional dropout technique to study the high redshift galaxies in ALHAMBRA and other multifilter data. Thanks to the wide area ALHAMBRA covers, we especially aim at contributing in the study of the brightest, less frequent, high redshift galaxies. Methods. The methodology is based on redshift probability distribution functions (zPDFs). It is shown how a clean galaxy sample can be obtained by selecting the galaxies with high integrated probability of being within a given redshift interval. However, reaching both a complete and clean sample with this method is challenging. Hence, a method to derive statistical properties by summing the zPDFs of all the galaxies in the redshift bin of interest is introduced. Results. Using this methodology we derive the galaxy rest frame UV number counts in five redshift bins centred at z = 2.5, 3.0, 3.5, 4.0, and 4.5, being complete up to the limiting magnitude at m UV (AB)=24, where m UV refers to the first ALHAMBRA filter redwards the Ly-α line. With the wide field ALHAMBRA data we especially contribute in the study of the brightest ends of these counts, sampling well the surface densities down to m UV (AB)=21-22. Conclusions. We show that using the zPDFs it is easy to select a very clean sample of high redshift galaxies. We also show that statistical analysis of the properties of galaxies is better done using a probabilistic approach, which takes into account both the incompleteness and contamination issues in a natural way.
The Astrophysical Journal, 2014
We present profiles of temperature, gas mass, and hydrostatic mass estimated from new and archiva... more We present profiles of temperature, gas mass, and hydrostatic mass estimated from new and archival X-ray observations of CLASH clusters. We compare measurements derived from XMM and Chandra observations with one another and compare both to gravitational lensing mass profiles derived with CLASH Hubble Space Telescope and Subaru Telescope lensing data. We find that Chandra and XMM measurements of electron density and enclosed gas mass as functions of radius are highly consistent with one another, indicating that any differences in hydrostatic masses inferred from X-ray observations arise from differences in gas-temperature measurements. Encouragingly, gas temperatures measured in clusters by XMM and Chandra are consistent with one another at ∼ 100 kpc radii but XMM temperatures systematically decline relative to Chandra temperatures as the radius of the temperature measurement increases. We suggest that the most plausible reason for this apparent temperature difference is large-angle scattering of soft X-ray photons in excess of that amount expected from the standard XMM PSF correction. We present the CLASH-X mass-profile comparisons in the form of cosmology-independent and redshift-independent circular-velocity profiles. We argue that comparisons of circular-velocity profiles are the most robust way to assess mass bias. Ratios of Chandra HSE mass profiles to CLASH lensing profiles show no obvious radial dependence in the 0.3-0.8 Mpc range. However, the mean mass biases inferred from the WL and SaWLens data are different, with a weighted-mean value at 0.5 Mpc of b = 0.12 for the WL comparison and b = −0.11 for the SaWLens comparison. The ratios of XMM HSE mass profiles to CLASH lensing profiles show a pronounced radial dependence in the 0.3-1.0 Mpc range, with a weighted-mean mass bias of value rising to b 0.3 at ∼ 1 Mpc for the WL comparison and b ≈ 0.25 for the SaWLens comparison. The enclosed gas mass profiles from both Chandra and XMM rise to a value ≈ 1/8 times the total-mass profiles inferred from lensing at ≈ 0.5 Mpc and remain constant outside of that radius, suggesting that 8M gas profiles may be an excellent proxy for total-mass profiles at 0.5 Mpc in massive galaxy clusters.
Monthly Notices of the Royal Astronomical Society, 2013
Monthly Notices of the Royal Astronomical Society, 2014
Monthly Notices of the Royal Astronomical Society, 2014
We study the characteristics of a narrow band type Ia supernova survey through simulations based ... more We study the characteristics of a narrow band type Ia supernova survey through simulations based on the upcoming Javalambre Physics of the accelerating universe Astrophysical Survey (J-PAS). This unique survey has the capabilities of obtaining distances, redshifts, and the SN type from a single experiment thereby circumventing the challenges faced by the resource-intensive spectroscopic follow-up observations. We analyse the flux measurements signal-to-noise ratio and bias, the supernova typing performance, the ability to recover light curve parameters given by the SALT2 model, the photometric redshift precision from type Ia supernova light curves and the effects of systematic errors on the data. We show that such a survey is not only feasible but may yield large type Ia supernova samples (up to 300 supernovae at z < 0.5 per month of search) with low core collapse contamination (∼ 3 per cent), good precision on the SALT2 parameters (average σ mB = 0.063, σ x1 = 0.47 and σ c = 0.040) and on the distance modulus (average σ µ = 0.17, assuming an intrinsic scatter σ int = 0.14), with identified systematic uncertainties σ sys 0.10σ stat . Moreover, the filters are narrow enough to detect most spectral features and obtain excellent photometric redshift precision of σ z = 0.005, apart from ∼ 2 per cent of outliers. We also present a few strategies for optimising the survey's outcome. Together with the detailed host galaxy information, narrow band surveys can be very valuable for the study of supernova rates, spectral feature relations, intrinsic colour variations and correlations between supernova and host galaxy properties, all of which are important information for supernova cosmological applications.
The Astrophysical Journal, 2014
ABSTRACT We report the detection of 18 Lyman-break candidates at z>~7.0, in the completed ... more ABSTRACT We report the detection of 18 Lyman-break candidates at z>~7.0, in the completed WFC3/IR data Hubble Frontier Fields (HFF) observations of Abell 2744 (z=0.308), plus Spitzer/IRAC data and archival ACS data. Half of these candidates fall in the range of 8 < z < 9, but no convincing detection lies beyond, despite the extreme depth and lens magnification. The sample includes a triple image system with a photometric redshift of z~7.4. This high redshift is geometrically confirmed by our lens model corresponding to deflection angles that are 12% larger than the lower-redshift systems used to calibrate the lens model at z=2.019. The majority of our high-redshift candidates are not expected to be multiply lensed given their locations in the image plane, but are magnified by factors of ~1.3-6, so that we are seeing further down the luminosity function than comparable deep field imaging. It is apparent that the redshift distribution of these sources does not smoothly extend over the full redshift range accessible at z<12, but appears to break above z=8.5. Nine candidates are clustered within a small region of 20" across, and so it will be necessary to average over the additional HFF clusters to properly examine this potentially steep transition in galaxy density at z~8-9. The physical properties of our candidates are examined using the range of lens models developed for the HFF program by various groups including our own, for a better estimate of underlying systematics. Our spectral-energy-distribution fits for the brightest objects suggest stellar masses of ~1E9 solar masses, star-formation rates of ~5 solar masses per year, and a typical formation redshift of z<~16. The upcoming deep optical data will be helpful in extending the utility of the very deep near-infrared data and potentially enhancing the numbers of lower luminosity dropout galaxies at z>7.
The Astrophysical Journal, 2014
We utilize 16-band Hubble Space Telescope (HST ) observations of 18 lensing clusters obtained as ... more We utilize 16-band Hubble Space Telescope (HST ) observations of 18 lensing clusters obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program to search for z ∼ 6 − 8 galaxies. We report the discovery of 206, 45, and 13 Lyman-break galaxy (LBG) candidates at z ∼ 6, z ∼ 7, and z ∼ 8, respectively, identified from purely photometric redshift selections. This large sample, representing nearly an order of magnitude increase in the number of magnified star-forming galaxies at z ∼ 6 − 8 presented to date, is unique in that we have observations in four WFC3/UVIS UV, seven ACS/WFC optical and all five WFC3/IR broad-band filters, which enable very accurate photometric redshift selections. We construct detailed lensing models for all 18 clusters (although some are preliminary) to estimate object magnifications and to identify two new multiply-lensed z 6 candidates. The median magnifications for these 18 clusters are 4, 4, and 5 for the z ∼ 6, z ∼ 7, and z ∼ 8 samples, respectively, over an average area of 4.5 arcmin 2 per cluster. We compare our observed number counts with expectations based on convolving "blank" field UV luminosity functions through our cluster lens models and find agreement down to ∼ 27 mag, where we begin to suffer significant incompleteness. In all three redshift bins we find a higher number density at brighter observed magnitudes than the field predictions, in excellent agreement with the lensed expectations and clearly demonstrating the enhanced efficiency of lensing clusters over field surveys. Once again, lensing clusters appear to be a powerful tool in the discovery and study of high-redshift galaxies and allow for the first glimpse of faint galaxies beyond the reach of the deepest HST legacy field surveys, a technique that will continue be exploited with the upcoming ultradeep Hubble Frontier Fields campaign.
The Astrophysical Journal, 2015
We present a new determination of the concentration-mass relation for galaxy clusters based on ou... more We present a new determination of the concentration-mass relation for galaxy clusters based on our comprehensive lensing analysis of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble (CLASH). Our sample spans a redshift range between 0.19 and 0.89. We combine weak-lensing constraints from the Hubble Space Telescope (HST) and from groundbased wide-field data with strong lensing constraints from HST. The result are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids. Our derivation of NFW parameters yields virial masses between 0.53 × 10 15 M /h and 1.76 × 10 15 M /h and the halo concentrations are distributed around c 200c ∼ 3.7 with a 1σ significant negative trend with cluster mass. We find an excellent 4% agreement between our measured concentrations and the expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology. The simulations are analyzed in 2D to account for possible biases in the lensing reconstructions due to projection effects. The theoretical concentration-mass (c-M) relation from our X-ray selected set of simulated clusters and the c-M relation derived directly from the CLASH data agree at the 90% confidence level.
The Astrophysical Journal, 2014
We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodyna... more We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodynamical simulations, aimed at estimating the expected concentration-mass relation for the CLASH cluster sample. We study nearly 1400 halos simulated at high spatial and mass resolution, which were projected along many linesof-sight each. We study the shape of both their density and surface-density profiles and fit them with a variety of radial functions, including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the Einasto density profiles. We derive concentrations and masses from these fits and investigate their distributions as a function of redshift and halo relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra observations of the halos and we use them to identify objects resembling the X-ray morphologies and masses of the clusters in the CLASH X-ray selected sample. We also derive a concentration-mass relation for strong-lensing clusters. We find that the sample of simulated halos which resemble the X-ray morphology of the CLASH clusters is composed mainly by relaxed halos, but it also contains a significant fraction of unrelaxed systems. For such a heterogeneous sample we measure an average 2D concentration which is ∼ 11% higher than found for the full sample of simulated halos. After accounting for projection and selection effects, the average NFW concentrations of CLASH clusters are expected to be intermediate between those predicted in 3D for relaxed and super-relaxed halos. Matching the simulations to the individual CLASH clusters on the basis of the X-ray morphology, we expect that the NFW concentrations recovered from the lensing analysis of the CLASH clusters are in the range [3 − 6], with an average value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray morphologies similar to those of the CLASH clusters are affected by a modest orientation bias.
The Astrophysical Journal, 2014
We utilise a two-color Lyman-Break selection criterion to search for z ∼ 9-10 galaxies over the f... more We utilise a two-color Lyman-Break selection criterion to search for z ∼ 9-10 galaxies over the first 19 clusters in the CLASH program. Key to this search are deep observations over our clusters in five near-IR passbands to 1.6µm, allowing us good constraints on the position of the Lyman break to z ∼ 10. A systematic search yields three z ∼ 9-10 candidates in total above a 6σ detection limit. While we have already reported the most robust of these candidates, MACS1149-JD, in a previous publication, two additional z ∼ 9 candidates are also revealed in our expanded search. The new candidates have H 160 -band AB magnitudes of ∼26.2-26.9 and are located behind MACSJ1115.9+0129 and MACSJ1720.3+3536. The observed H 160 − Spitzer/IRAC colors for the sources are sufficiently blue to strongly favor redshifts of z ≥ 9 for these sources. A careful assessment of various sources of contamination suggests 1 contaminants for our z ∼ 9-10 selection. To determine the implications of these search results for the LF and SFR density at z ∼ 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z ∼ 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower redshift sample (after correcting for the differences in selection volumes), here taken to be z ∼ 8. This procedure takes advantage of the fact that the relative selection volumes available for the z ∼ 8 and z ∼ 9-10 selections behind lensing clusters are not greatly dependent on the details of the gravitational lensing models. We find that the normalization of the UV LF at z ∼ 9 is just 0.22 +0.30 −0.15 × that at z ∼ 8, ∼2 +3 −1 × lower than what we would infer extrapolating z ∼ 4-8 LF results. These results therefore suggest a more rapid evolution in the U V LF at z > 8 than seen at lower redshifts (although the current evidence here is weak). Compared to similar evolutionary findings from the HUDF, our result is much more insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe.
Proceedings of the International Astronomical Union, 2012
Astronomy & Astrophysics, 2015
Aims. Our goal is to develop and test a novel methodology to compute accurate close pair fraction... more Aims. Our goal is to develop and test a novel methodology to compute accurate close pair fractions with photometric redshifts. Methods. 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. Results. 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 red m = 0.57 ± 0.05 for red galaxies and N blue m = 0.26 ± 0.02 for blue galaxies. Conclusions. 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.
... The two-point correlation function ξ(r) is a simple tool ⋆ E-mail: pablo.arnalte@uv. es (PAM)... more ... The two-point correlation function ξ(r) is a simple tool ⋆ E-mail: pablo.arnalte@uv. es (PAM) † This version is submitted to the ALHAMBRA Core Team for analysis and discussion, the author list may be incomplete and outdated ...
The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey has observ... more The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey has observed 8 different regions of the sky, including sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 contiguous ∼300Å filters covering the optical range, combining them with deep JHKs imaging. The observations, carried out with the Calar Alto 3.5m telescope using the wide field (0.25 deg 2 FOV) optical camera LAICA and the NIR instrument Omega-2000, correspond to ∼700hrs of on-target science images. The photometric system was specifically designed to maximize the effective depth of the survey in terms of accurate spectral-type and photometric redshift estimation along with the capability of identification of relatively faint emission lines. Here we present multicolor photometry and photometric redshifts for ∼438,000 galaxies, detected in synthetic F 814W images, complete down to a magnitude I∼24.5AB, carefully taking into account realistic noise estimates, and correcting by PSF and aperture effects with the ColorP ro software. The photometric zeropoints have been calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission line galaxies. We calculate photometric redshifts with the BPZ2.0 code, which includes new empirically calibrated galaxy templates and priors. Our photometric redshifts have a precision of δ z /(1+z s )=1% for I<22.5 and δ z /(1+z s )=1.4% for 22.5<I<24.5. Precisions of δ z /(1+z s )< 0.5 % are reached for the brighter spectroscopic sample, showing the potential of medium-band photometric surveys. The global photometric redshift distribution shows a mean redshift =0.56 for I<22.5 AB and =0.86 for I<24.5 AB. The data presented here covers an effective area of 2.79 deg 2 , split into 14 strips of 58.5'x15.5' and represents ∼32 hrs of on-target. Given its depth, multiband coverage and a much smaller cosmic variance than other similar projects, ALHAMBRA is a unique dataset for galaxy evolution studies. Several of the techniques presented here will have a wide applicability to future large scale photometric redshift surveys like JPAS.
Aims: Our goal is to develop and test a novel methodology to compute accurate close-pair fraction... more Aims: Our goal is to develop and test a novel methodology to compute accurate close-pair fractions with photometric redshifts. Methods: We improved the currently used methodologies to estimate the merger fraction fm 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 sample selection and the luminosity ratio constrain; and (iii) splitting individual PDFs into red and blue spectral templates to reliably work with colour selections. We tested the performance of our new methodology with the PDFs provided by the ALHAMBRA photometric survey. Results: The merger fractions and rates from the ALHAMBRA survey agree excellently well with those from spectroscopic work for both the general population and red and blue galaxies. With the merger rate of bright (MB <= -20-1.1z) galaxies evolving as (1 + z)n, the power-law index n is higher 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 Nmred = 0.57 ± 0.05 for red galaxies and Nmblue = 0.26 ± 0.02 for blue galaxies. Conclusions: Our new methodology statistically exploits all the available information provided by photometric redshift codes and yields accurate measurements of the merger fraction by close pairs from using photometric redshifts alone. Current and future photometric surveys will benefit from this new methodology.
This documents describes J-PAS and outlines its main scientific goals
Astronomy & Astrophysics, 2015
Context. Most observational results on the high redshift restframe UV-bright galaxies are based o... more Context. Most observational results on the high redshift restframe UV-bright galaxies are based on samples pinpointed using the so called dropout technique or Ly-α selection. However, the availability of multifilter data allows now replacing the dropout selections by direct methods based on photometric redshifts. In this paper we present the methodology to select and study the population of high redshift galaxies in the ALHAMBRA survey data. Aims. Our aim is to develop a less biased methodology than the traditional dropout technique to study the high redshift galaxies in ALHAMBRA and other multifilter data. Thanks to the wide area ALHAMBRA covers, we especially aim at contributing in the study of the brightest, less frequent, high redshift galaxies. Methods. The methodology is based on redshift probability distribution functions (zPDFs). It is shown how a clean galaxy sample can be obtained by selecting the galaxies with high integrated probability of being within a given redshift interval. However, reaching both a complete and clean sample with this method is challenging. Hence, a method to derive statistical properties by summing the zPDFs of all the galaxies in the redshift bin of interest is introduced. Results. Using this methodology we derive the galaxy rest frame UV number counts in five redshift bins centred at z = 2.5, 3.0, 3.5, 4.0, and 4.5, being complete up to the limiting magnitude at m UV (AB)=24, where m UV refers to the first ALHAMBRA filter redwards the Ly-α line. With the wide field ALHAMBRA data we especially contribute in the study of the brightest ends of these counts, sampling well the surface densities down to m UV (AB)=21-22. Conclusions. We show that using the zPDFs it is easy to select a very clean sample of high redshift galaxies. We also show that statistical analysis of the properties of galaxies is better done using a probabilistic approach, which takes into account both the incompleteness and contamination issues in a natural way.
The Astrophysical Journal, 2014
We present profiles of temperature, gas mass, and hydrostatic mass estimated from new and archiva... more We present profiles of temperature, gas mass, and hydrostatic mass estimated from new and archival X-ray observations of CLASH clusters. We compare measurements derived from XMM and Chandra observations with one another and compare both to gravitational lensing mass profiles derived with CLASH Hubble Space Telescope and Subaru Telescope lensing data. We find that Chandra and XMM measurements of electron density and enclosed gas mass as functions of radius are highly consistent with one another, indicating that any differences in hydrostatic masses inferred from X-ray observations arise from differences in gas-temperature measurements. Encouragingly, gas temperatures measured in clusters by XMM and Chandra are consistent with one another at ∼ 100 kpc radii but XMM temperatures systematically decline relative to Chandra temperatures as the radius of the temperature measurement increases. We suggest that the most plausible reason for this apparent temperature difference is large-angle scattering of soft X-ray photons in excess of that amount expected from the standard XMM PSF correction. We present the CLASH-X mass-profile comparisons in the form of cosmology-independent and redshift-independent circular-velocity profiles. We argue that comparisons of circular-velocity profiles are the most robust way to assess mass bias. Ratios of Chandra HSE mass profiles to CLASH lensing profiles show no obvious radial dependence in the 0.3-0.8 Mpc range. However, the mean mass biases inferred from the WL and SaWLens data are different, with a weighted-mean value at 0.5 Mpc of b = 0.12 for the WL comparison and b = −0.11 for the SaWLens comparison. The ratios of XMM HSE mass profiles to CLASH lensing profiles show a pronounced radial dependence in the 0.3-1.0 Mpc range, with a weighted-mean mass bias of value rising to b 0.3 at ∼ 1 Mpc for the WL comparison and b ≈ 0.25 for the SaWLens comparison. The enclosed gas mass profiles from both Chandra and XMM rise to a value ≈ 1/8 times the total-mass profiles inferred from lensing at ≈ 0.5 Mpc and remain constant outside of that radius, suggesting that 8M gas profiles may be an excellent proxy for total-mass profiles at 0.5 Mpc in massive galaxy clusters.
Monthly Notices of the Royal Astronomical Society, 2013
Monthly Notices of the Royal Astronomical Society, 2014
Monthly Notices of the Royal Astronomical Society, 2014
We study the characteristics of a narrow band type Ia supernova survey through simulations based ... more We study the characteristics of a narrow band type Ia supernova survey through simulations based on the upcoming Javalambre Physics of the accelerating universe Astrophysical Survey (J-PAS). This unique survey has the capabilities of obtaining distances, redshifts, and the SN type from a single experiment thereby circumventing the challenges faced by the resource-intensive spectroscopic follow-up observations. We analyse the flux measurements signal-to-noise ratio and bias, the supernova typing performance, the ability to recover light curve parameters given by the SALT2 model, the photometric redshift precision from type Ia supernova light curves and the effects of systematic errors on the data. We show that such a survey is not only feasible but may yield large type Ia supernova samples (up to 300 supernovae at z < 0.5 per month of search) with low core collapse contamination (∼ 3 per cent), good precision on the SALT2 parameters (average σ mB = 0.063, σ x1 = 0.47 and σ c = 0.040) and on the distance modulus (average σ µ = 0.17, assuming an intrinsic scatter σ int = 0.14), with identified systematic uncertainties σ sys 0.10σ stat . Moreover, the filters are narrow enough to detect most spectral features and obtain excellent photometric redshift precision of σ z = 0.005, apart from ∼ 2 per cent of outliers. We also present a few strategies for optimising the survey's outcome. Together with the detailed host galaxy information, narrow band surveys can be very valuable for the study of supernova rates, spectral feature relations, intrinsic colour variations and correlations between supernova and host galaxy properties, all of which are important information for supernova cosmological applications.
The Astrophysical Journal, 2014
ABSTRACT We report the detection of 18 Lyman-break candidates at z>~7.0, in the completed ... more ABSTRACT We report the detection of 18 Lyman-break candidates at z>~7.0, in the completed WFC3/IR data Hubble Frontier Fields (HFF) observations of Abell 2744 (z=0.308), plus Spitzer/IRAC data and archival ACS data. Half of these candidates fall in the range of 8 < z < 9, but no convincing detection lies beyond, despite the extreme depth and lens magnification. The sample includes a triple image system with a photometric redshift of z~7.4. This high redshift is geometrically confirmed by our lens model corresponding to deflection angles that are 12% larger than the lower-redshift systems used to calibrate the lens model at z=2.019. The majority of our high-redshift candidates are not expected to be multiply lensed given their locations in the image plane, but are magnified by factors of ~1.3-6, so that we are seeing further down the luminosity function than comparable deep field imaging. It is apparent that the redshift distribution of these sources does not smoothly extend over the full redshift range accessible at z<12, but appears to break above z=8.5. Nine candidates are clustered within a small region of 20" across, and so it will be necessary to average over the additional HFF clusters to properly examine this potentially steep transition in galaxy density at z~8-9. The physical properties of our candidates are examined using the range of lens models developed for the HFF program by various groups including our own, for a better estimate of underlying systematics. Our spectral-energy-distribution fits for the brightest objects suggest stellar masses of ~1E9 solar masses, star-formation rates of ~5 solar masses per year, and a typical formation redshift of z<~16. The upcoming deep optical data will be helpful in extending the utility of the very deep near-infrared data and potentially enhancing the numbers of lower luminosity dropout galaxies at z>7.