arXiv subjects

Jesús Varela

Publications and source records attributed to Jesús Varela.

32 records · Page 2Linked to original sources

arXiv2022

The miniJPAS survey quasar selection I: Mock catalogues for classification

In this series of papers, we employ several machine learning (ML) methods to classify the point-like sources from the miniJPAS catalogue, and identify quasar candidates. Since no representative sample of spectroscopically confirmed sources exists at present to train these ML algorithms, we rely on mock catalogues. In this first paper we develop a pipeline to compute synthetic photometry of quasars, galaxies and stars using spectra of objects targeted as quasars in the Sloan Digital Sky Survey. To match the same depths and signal-to-noise ratio distributions in all bands expected for miniJPAS point sources in the range $17.5\leq r<24$, we augment our sample of available spectra by shifting the original $r$-band magnitude distributions towards the faint end, ensure that the relative incidence rates of the different objects are distributed according to their respective luminosity functions, and perform a thorough modeling of the noise distribution in each filter, by sampling the flux variance either from Gaussian realizations with given widths, or from combinations of Gaussian functions. Finally, we also add in the mocks the patterns of non-detections which are present in all real observations. Although the mock catalogues presented in this work are a first step towards simulated data sets that match the properties of the miniJPAS observations, these mocks can be adapted to serve the purposes of other photometric surveys.

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arXiv2021

J-PLUS: Stellar Parameters, C, N, Mg, Ca and [α/Fe] Abundances for Two Million Stars from DR1

Context. The Javalambre Photometric Local Universe Survey (J-PLUS) has obtained precise photometry in twelve specially designed filters for large numbers of Galactic stars. Deriving their precise stellar atmospheric parameters and individual elemental abundances is crucial for studies of Galactic structure, and the assembly history and chemical evolution of our Galaxy. Aims. Our goal is to estimate not only stellar parameters (effective temperature, Teff, surface gravity, log g, and metallicity, [Fe/H]), but also [α/Fe] and four elemental abundances ([C/Fe], [N/Fe], [Mg/Fe], and [Ca/Fe]) using data from J-PLUS DR1. Methods. By combining recalibrated photometric data from J-PLUS DR1, Gaia DR2, and spectroscopic labels from LAMOST, we design and train a set of cost-sensitive neural networks, the CSNet, to learn the non-linear mapping from stellar colors to their labels. Results. We have achieved precisions of δTeff {\sim}55K, δlogg{\sim}0.15dex, and δ[Fe/H]{\sim}0.07dex, respectively, over a wide range of temperature, surface gravity, and metallicity. The uncertainties of the abundance estimates for [α/Fe] and the four individual elements are in the range 0.04-0.08 dex. We compare our parameter and abundance estimates with those from other spectroscopic catalogs such as APOGEE and GALAH, and find an overall good agreement. Conclusions. Our results demonstrate the potential of well-designed, high-quality photometric data for determinations of stellar parameters as well as individual elemental abundances. Applying the method to J-PLUS DR1, we have obtained the aforementioned parameters for about two million stars, providing an outstanding data set for chemo-dynamic analyses of the Milky Way. The catalog of the estimated parameters is publicly accessible.

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arXiv2021

J-PLUS: Searching for very metal-poor star candidates using the SPEEM pipeline

We explore the stellar content of the Javalambre Photometric Local Universe Survey (J-PLUS) Data Release 2 and show its potential to identify low-metallicity stars using the Stellar Parameters Estimation based on Ensemble Methods (SPEEM) pipeline. SPEEM is a tool to provide determinations of atmospheric parameters for stars and separate stellar sources from quasars, using the unique J-PLUS photometric system. The adoption of adequate selection criteria allows the identification of metal-poor star candidates suitable for spectroscopic follow-up. SPEEM consists of a series of machine learning models which uses a training sample observed by both J-PLUS and the SEGUE spectroscopic survey. The training sample has temperatures Teff between 4\,800 K and 9\,000 K; $\log g$ between 1.0 and 4.5, and $-3.1<[Fe/H]<+0.5$. The performance of the pipeline has been tested with a sample of stars observed by the LAMOST survey within the same parameter range. The average differences between the parameters of a sample of stars observed with SEGUE and J-PLUS, which were obtained with the SEGUE Stellar Parameter Pipeline and SPEEM, respectively, are $ΔTeff\sim 41$ K, $Δ\log g\sim 0.11$ dex, and $Δ[Fe/H]\sim 0.09$ dex. A sample of 177 stars have been identified as new candidates with $[Fe/H]<-2.5$ and 11 of them have been observed with the ISIS spectrograph at the William Herschel Telescope. The spectroscopic analysis confirms that $64\%$ of stars have $[Fe/H]<-2.5$, including one new star with $[Fe/H]<-3.0$. SPEEM in combination with the J-PLUS filter system has shown the potential to estimate the stellar atmospheric parameters (Teff, $\log g$, and [Fe/H]). The spectroscopic validation of the candidates shows that SPEEM yields a success rate of $64\%$ on the identification of very metal-poor star candidates with $[Fe/H]<-2.5$.

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arXiv2021

J-PAS: Forecasts for dark matter - dark energy elastic couplings

We consider a cosmological model where dark matter and dark energy feature a coupling that only affects their momentum transfer in the corresponding Euler equations. We perform a fit to cosmological observables and confirm previous findings within these scenarios that favour the presence of a coupling at more than $3σ$. This improvement is driven by the Sunyaev-Zeldovich data. We subsequently perform a forecast for future J-PAS data and find that clustering measurements will permit to clearly discern the presence of an interaction within a few percent level with the uncoupled case at more than $10σ$ when the complete survey, covering $8500$ sq. deg., is considered. We found that the inclusion of weak lensing measurements will not help to further constrain the coupling parameter. For completeness, we compare to forecasts for DESI and Euclid, which provide similar discriminating power.

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arXiv2021

J-PLUS: A first glimpse at spectrophotometry of asteroids -- The MOOJa catalog

Context: The Javalambre Photometric Local Universe Survey (J-PLUS) is an observational campaign that aims to obtain photometry in 12 ultraviolet-visible filters (0.3-1 μm) of approximately 8 500 deg{^2} of the sky observable from Javalambre (Teruel, Spain). Due to its characteristics and strategy of observation, this survey will let us analyze a great number of Solar System small bodies, with improved spectrophotometric resolution with respect to previous large-area photometric surveys in optical wavelengths. Aims: The main goal of this work is to present here the first catalog of magnitudes and colors of minor bodies of the Solar System compiled using the first data release (DR1) of the J-PLUS observational campaign: the Moving Objects Observed from Javalambre (MOOJa) catalog. Methods: Using the compiled photometric data we obtained very-low-resolution reflectance (photospectra) spectra of the asteroids. We first used a σ-clipping algorithm in order to remove outliers and clean the data. We then devised a method to select the optimal solar colors in the J-PLUS photometric system. These solar colors were computed using two different approaches: on one hand, we used different spectra of the Sun, convolved with the filter transmissions of the J-PLUS system, and on the other, we selected a group of solar-type stars in the J-PLUS DR1, according to their computed stellar parameters. Finally, we used the solar colors to obtain the reflectance spectra of the asteroids. Results: We present photometric data in the J-PLUS filters for a total of 3 122 minor bodies (3 666 before outlier removal), and we discuss the main issues of the data, as well as some guidelines to solve them

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arXiv2020

J-PLUS: Unveiling the brightest-end of the Lyα luminosity function at 2.0<z<3.3 over 1000 deg^2

We present the photometric determination of the bright-end (L_Lya>10^43.5 erg/s) of the Lya luminosity function (LF) within four redshifts windows in the interval 2.2 10^43.3 erg/s) Lya-emitting candidates. We test our selection with two spectroscopic follow-up programs at the GTC telescope, confirming ~89% of the targets as line-emitting sources, with ~64% being genuine z~2.2 QSOs. We extend the 2.2 2 AGN/QSOs (likely dominant in our samples) are described by a structurally different LF than z>2 star-forming LAEs, namely with L^*_QSOs ~ 100 L^*_LAEs and Phi^*_QSOs ~ 10^-3 Phi^*_LAEs. Finally, our method identifies very efficiently as high-z line-emitters sources without previous spectroscopic confirmation, currently classified as stars (~2000 objects in each redshift bin, on average). Assuming a large predominance of Lya-emitting AGN/QSOs in our samples, this supports the scenario by which these are the most abundant class of z>2 Lya emitters at L_Lya>10^43.3 erg/s.

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arXiv2019

J-PLUS: Synthetic galaxy catalogues with emission lines for photometric surveys

We present a synthetic galaxy lightcone specially designed for narrow-band optical photometric surveys. To reduce time-discreteness effects, unlike previous works, we directly include the lightcone construction in the \texttt{L-Galaxies} semi-analytic model applied to the subhalo merger trees of the {\tt Millennium} simulation. Additionally, we add a model for the nebular emission in star-forming regions, which is crucial for correctly predicting the narrow/medium-band photometry of galaxies. Explicitly, we consider, individually for each galaxy, the contribution of 9 different lines: $\rm Lyα$ (1216Å), \Hb (4861Å), \Ha (6563Å), {\oii} (3727Å, 3729Å), {\oiii} (4959Å, 5007Å), $\rm [\ion{Ne}{III}]$ (3870Å), {\oi} (6300Å), $\rm [\ion{N}{II}]$ (6548Å, 6583Å), and $\rm [\ion{S}{II}]$ (6717Å, 6731Å). We validate our lightcone by comparing galaxy number counts, angular clustering, and \Ha, \Hb, {\oii} and {\oiiiFd} luminosity functions to a compilation of observations. As an application of our mock lightcones, we generate catalogues tailored for J-PLUS, a large optical galaxy survey featuring 5 broad and 7 medium band filters. We study the ability of the survey to correctly identify, with a simple \textit{three filter method}, a population of emission-line galaxies at various redshifts. We show that the $4000Å$ break in the spectral energy distribution of galaxies can be misidentified as line emission. However, all significant excess (larger than 0.4 magnitudes) can be correctly and unambiguously attributed to emission line galaxies. Our catalogues are publicly released to facilitate their use in interpreting narrow-band surveys and for quantifying the impact of line emission in broad band photometry.

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arXiv2018

J-PLUS: A wide-field multi-band study of the M15 globular cluster. Evidence of multiple stellar populations in the RGB

The Javalambre Photometric Local Universe Survey (J-PLUS) provides wide field-of-view images in 12 narrow, intermediate and broad-band filters optimized for stellar photometry. Here we have applied J-PLUS data for the first time for the study of Galactic GCs using science verification data obtained for the very metal-poor GC M\,15. Our J-PLUS data provide low-resolution spectral energy distributions covering the near-UV to the near-IR, allowing us to search for MPs based on pseudo-spectral fitting diagnostics. J-PLUS CMDs are found to be particularly useful to search for splits in the sequences formed by the upper red giant branch (RGB) and asymptotic giant branch (AGB) stars. We interpret these split sequences as evidence for the presence of MPs. This demonstrates that the J-PLUS survey will have sufficient spatial coverage and spectral resolution to perform a large statistical study of GCs through multi-band photometry in the coming years.

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arXiv2016

An Accurate Cluster Selection Function for the J-PAS Narrow-Band wide-field survey

The impending Javalambre Physics of the accelerating universe Astrophysical Survey (J-PAS) will be the first wide-field survey of $\gtrsim$ 8500 deg$^2$ to reach the `stage IV' category. Because of the redshift resolution afforded by 54 narrow-band filters, J-PAS is particularly suitable for cluster detection in the range z$<$1. The photometric redshift dispersion is estimated to be only $\sim 0.003$ with few outliers $\lesssim$ 4\% for galaxies brighter than $i\sim23$ AB, because of the sensitivity of narrow band imaging to absorption and emission lines. Here we evaluate the cluster selection function for J-PAS using N-body+semi-analytical realistic mock catalogues. We optimally detect clusters from this simulation with the Bayesian Cluster Finder, and we assess the completeness and purity of cluster detection against the mock data. The minimum halo mass threshold we find for detections of galaxy clusters and groups with both $>$80\% completeness and purity is $M_h \sim 5 \times 10^{13}M_{\odot}$ up to $z\sim 0.7$. We also model the optical observable, $M^*_{\rm CL}$-halo mass relation, finding a non-evolution with redshift and main scatter of $σ_{M^*_{\rm CL} | M_{\rm h}}\sim 0.14 \,dex$ down to a factor two lower in mass than other planned broad-band stage IV surveys, at least. For the $M_{\rm h} \sim 1 \times 10^{14}M_{\odot}$ Planck mass limit, J-PAS will arrive up to $z\sim 0.85$ with a $σ_{M^*_{\rm CL} | M_{\rm h}}\sim 0.12 \, dex$. Therefore J-PAS will provide the largest sample of clusters and groups up to $z\sim 0.8$ with a mass calibration accuracy comparable to X-ray data.

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arXiv2015

Galaxy clusters and groups in the ALHAMBRA Survey

We present a catalogue of 348 galaxy clusters and groups with $0.2<z<1.2$ selected in the 2.78 $deg^2$ ALHAMBRA Survey. The high precision of our photometric redshifts, close to $1\%$, and the wide spread of the seven ALHAMBRA pointings ensure that this catalogue has better mass sensitivity and is less affected by cosmic variance than comparable samples. The detection has been carried out with the Bayesian Cluster Finder (BCF), whose performance has been checked in ALHAMBRA-like light-cone mock catalogues. Great care has been taken to ensure that the observable properties of the mocks photometry accurately correspond to those of real catalogues. From our simulations, we expect to detect galaxy clusters and groups with both $70\%$ completeness and purity down to dark matter halo masses of $M_h\sim3\times10^{13}\rm M_{\odot}$ for $z<0.85$. Cluster redshifts are expected to be recovered with $\sim0.6\%$ precision for $z<1$. We also expect to measure cluster masses with $σ_{M_h|M^*_{CL}}\sim0.25-0.35\, dex$ precision down to $\sim3\times10^{13}\rm M_{\odot}$, masses which are $50\%$ smaller than those reached by similar work. We have compared these detections with previous optical, spectroscopic and X-rays work, finding an excellent agreement with the rates reported from the simulations. We have also explored the overall properties of these detections such as the presence of a colour-magnitude relation, the evolution of the photometric blue fraction and the clustering of these sources in the different ALHAMBRA fields. Despite the small numbers, we observe tentative evidence that, for a fixed stellar mass, the environment is playing a crucial role at lower redshifts (z$<$0.5).

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arXiv2011

The orientation of disk galaxies around large cosmic voids

Using a large sample of galaxies from the SDSS-DR7, we have analysed the alignment of disk galaxies around cosmic voids. We have constructed a complete sample of cosmic voids (devoid of galaxies brighter than M_r-5 log(h) =-20.17) with radii larger than 10 Mpc/h up to redshift 0.12. Disk galaxies in shells around these voids have been used to look for particular alignments between the angular momentum of the galaxies and the radial direction of the voids. We find that disk galaxies around voids larger than >~ 15 Mpc/h within distances not much larger than 5 Mpc/h from the surface of the voids present a significant tendency to have their angular momenta aligned with the void's radial direction with a significance >~ 98.8% against the null hypothesis. The strength of this alignment is dependent on the void's radius and for voids with ~<15 Mpc/h the distribution of the orientation of the galaxies is compatible with a random distribution. Finally, we find that this trend observed in the alignment of galaxies is similar to the one observed for the minor axis of dark matter halos around cosmic voids found in cosmological simulations, suggesting a possible link in the evolution of both components.

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arXiv2010

The evolution of early-type galaxies in clusters from z~ 0.8 to z~ 0: the ellipticity distribution and the morphological mix

We present the ellipticity distribution and its evolution for early-type galaxies in clusters from z~0.8 to z~0, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS)(0.04 M_B+1.208z>-21. Analyzing this sample, we do not recover exactly the same results of the mass-limited sample. Hence the selection criteria are crucial to characterize the galaxy properties: the choice of the magnitude-delimited sample implies the loss of many less massive galaxies and so it biases the final results. Moreover, although we are adopting the same selection criteria, our results in the magnitude-delimited sample are also not in agreement with those of Holden et al.(2009). This is due to the fact that our and their low-z samples have a different magnitude distribution because the Holden et al.(2009) sample suffers from incompleteness at faint magnitudes.

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arXiv2010

Galaxy stellar mass functions of different morphological types in clusters, and their evolution between z=0.8 and z=0

We present the galaxy stellar mass function (MF) and its evolution in clusters from z~0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04 10^11 M' does not evolve, but below M*~10^10.8 M' the MF at high redshift is flat, while in the Local Universe it flattens out at lower masses. The population of M* = 10^10.2 - 10^10.8 M' galaxies must have grown significantly between z=0.8 and z=0. We analyze the MF of different morphological types (ellipticals, S0s and late-types), and find that also each of them evolves with redshift. All types have proportionally more massive galaxies at high- than at low-z, and the strongest evolution occurs among S0 galaxies. Examining the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), we find it strongly depends on redshift. At both redshifts, ~40% of the stellar mass is in elliptical galaxies. Another ~43% of the mass is in S0 galaxies in local clusters, while it is in spirals in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the MF. We conclude that mass growth due to star formation plays a crucial role in driving the evolution. It has to be accompanied by infall of galaxies onto clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. However, comparing with high-z field samples, we do not find conclusive evidence for such an environmental mass segregation. Our results suggest that star formation and infall change directly the MF of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.

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arXiv2010

How does galaxy environment matter? The relationship between galaxy environments, colour and stellar mass at 0.4 < z < 1 in the Palomar/DEEP2 survey

We present a study characterizing the environments of galaxies in the redshift range of 0.4 < z < 1 based on data from the POWIR near infrared imaging and DEEP2 spectroscopic redshift surveys, down to a stellar mass of log M* = 10.25 M_sun. Galaxy environments are measured in terms of nearest neighbour densities as well as fixed aperture densities and kinematical and dynamical parameters of neighbour galaxies within a radius of 1 Mpc. We disentangle the correlations between galaxy stellar mass, galaxy colour and galaxy environment, using not only galaxy number densities, but also other environmental characteristics such as velocity dispersion, mean harmonic radius, and crossing time. We find that galaxy colour and the fraction of blue galaxies depends very strongly on stellar mass at 0.4 < z < 1, while a weak additional dependence on local number densities is in place at lower redshifts (0.4 < z < 0.7). This environmental influence is most visible in the colours of intermediate mass galaxies (10.5 < log M* < 11), whereas colours of lower and higher mass galaxies remain largely unchanged with redshift and environment. At a fixed stellar mass, the colour-density relation almost disappears, while the colour-stellar mass relation is present at all local densities. We find a weak correlation between stellar mass and environment at intermediate redshifts, which contributes to the overall colour-density relation. We furthermore do not find a significant correlation between galaxy colour and virial mass, i.e., parent dark matter halo mass. Galaxy stellar mass thus appears to be the crucial defining parameter for intrinsic galaxy properties such as ongoing star formation and colour.

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