M. A. Lara-López

Study of star-forming galaxies in SDSS up to redshift 0.4 I. Metallicity evolution

Context. The chemical composition of the gas in galaxies over cosmic time provides a very important tool for understanding galaxy evolution. Although there are many studies at high redshift, they are rather scarce at lower redshifts. However, low redshift studies can provide important clues about the evolution of galaxies, furnishing the required link between the local and high redshift universe. In this work, we focus on the metallicity of the gas of star-forming galaxies at low redshift, looking for signs of chemical evolution. Aims. We aim to analyze the metallicity contents star-forming galaxies of similar luminosities and masses at different redshifts. With this purpose, we present a study of the metallicity of relatively massive (log(Mstar/M� ) 10.5) star forming galaxies from SDSS–DR5 (Sloan Digital Sky Survey-data release 5), using different redshift intervals from 0.04 to 0.4. Methods. We used data processed with the STARLIGHT spectral synthesis code, correcting the fluxes for dust extinction, estimating metallicities using the R23 method, and segregating the samples with respect to the value of the [N ii] λ6583/[O ii] λ3727 line ratio in order to break the R23 degeneracy selecting the upper branch. We analyze the luminosity and mass-metallicity relations, and the effect of the Sloan fiber diameter looking for possible biases. Results. By dividing our redshift samples in intervals of similar magnitude and comparing them, significant signs of metallicity evolution are found. Metallicity correlates inversely with redshift: from redshift 0 to 0.4 a decrement of ∼0.1 dex in 12 + log(O/H) is found.

Star-forming galaxies in SDSS: signs of metallicity evolution

Context. Evolution of galaxies through cosmic time has been widely studied at high redshift, but there are a few studies in this field at lower redshifts. However, low-redshifts studies will provide important clues to the evolution of galaxies, furnishing the required link between local and high-redshift universe. Aims. In this work we focus on the metallicity of the gas in spiral galaxies at low redshift looking for signs of chemical evolution. We analyze the metallicity contents of star forming galaxies of similar luminosities at different redshifts, we studied the metallicity of star forming galaxies from SDSS-DR5 (Sloan Digital Sky Survey-Data Release 5), using different redshift intervals from 0.1 to 0.4. Methods. We used the public data of SDSS-DR5 processed with the STARLIGHT spectral synthesis code, correcting the fluxes for dust extinction, estimating metallicities using the R23 method, and analyzing the samples with respect to the [N ii] λ6583/[O ii] λ3727 line ratio. Results. From a final sample of 207 galaxies, we find a decrement in 12+log(O/H) corresponding to the redshift interval 0.3 < z < 0.4 of ∼0.1 dex with respect to the rest of the sample, which can be interpreted as evidence of the metallicity evolution in low-z galaxies.

OTELO SURVEY: DEEP BVRI BROADBAND PHOTOMETRY OF THE GROTH STRIP. II. OPTICAL PROPERTIES OF X-RAY EMITTERS

The Groth field is one of the sky regions that will be targeted by the OSIRIS Tunable Filter Emission Line Object survey in the optical 820 nm and 920 nm atmospheric windows. In the present paper, public Chandra X-ray data with total exposure time of 200 ks are analyzed and combined with optical broadband data of the Groth field, in order to study a set of optical structural parameters of the X-ray emitters and its relation with X-ray properties. To this aim, we processed the raw, public X-ray data using the Chandra Interactive Analysis of Observations, and determined and analyzed different structural parameters, in order to produce a morphological classification of X-ray sources. We present the morphology of 340 X-ray emitters with optical counterpart detected. Objects have been classified by X-ray type using a diagnostic diagram relating X-ray-to-optical ratio (X/O) to hardness ratio. We did not find any clear correlation between X-ray and morphological types. We analyzed the angular clustering of X-ray sources with optical counterpart using two-point correlation functions. A significant positive angular clustering was obtained from a preliminary analysis of four subsamples of the X-ray sources catalog. The clustering signal of the optically extended counterparts is similar to that of strongly clustered populations like red and very red galaxies, suggesting that the environment plays an important role in active galactic nuclei phenomena. Finally, we combined optical structural parameters with other X-ray and optical properties, and we confirmed an anticorrelation between the X/O ratio and the Abraham concentration index, which might suggest that early-type galaxies have lower Eddington rates than those of late-type galaxies.

OTELO Survey: Optimal Emission-Line Flux Determination with OSIRIS/GTC

Emission-line galaxies are important targets for understanding the chemical evolution of galaxies in the universe. Deep, narrowband imaging surveys allow detection and study of the flux and the equivalent widths (EWs) of the emission line studied. The present work has been developed within the context of the OTELO project, an emission-line survey using the tunable filters (TF) of OSIRIS, the first-generation instrument on the Gran Telescopio Canarias (GTC) 10.4 m telescope located in La Palma, Spain, that will observe through selected atmospheric windows that are relatively free of sky emission lines. With a total survey area of 0.1 deg2 distributed in different fields, reaching a 5σ depth of 10-18 ergs cm-2 s-1 and detecting objects of EW < 0.3 A, OTELO will be the deepest emission-line survey to date. As part of the OTELO preparatory activities, the objective of this study is to determine the best combination of sampling and full width at half-maximum (FWHM) for the OSIRIS tunable filters for deblending Hα from [N II] lines by analyzing the flux errors obtained. We simulated the OTELO data by convolving a complete set of synthetic H II galaxies in EWs, with different widths of the OSIRIS TFs. We estimated relative flux errors of the recovered Hα and [N II] λ6583 lines. We found that for the red TF, a FWHM of 12 A and a sampling of 5 A is an optimal combination that allows deblending Hα from the [N II] λ6583 line with a flux error lower than 20%. This combination will allow estimating SFRs and metallicities using the Hα flux and the N2 method, respectively.

ON THE ANTICORRELATION BETWEEN GALAXY LIGHT CONCENTRATION AND X-RAY-TO-OPTICAL FLUX RATIO

Active galactic nuclei (AGNs) play an important role in many aspects of modern cosmology, and of particular interest is the issue of the interplay between AGNs and their host galaxy. Using X-ray and optical data sets, we have explored the properties of a large sample of AGNs in the Subaru/XMM-Newton Deep Survey field, and studied their evolution in relation with the evolution of their host galaxy. We present here an anticorrelation between X-ray-to-optical flux (X/O) ratio and galaxy light concentration (C), which has been found for the first time and might suggest that early-type galaxies, having poor matter supply to feed the AGN activity, have lower Eddington rates than those of late-type galaxies.

X-ray luminosity functions of different morphological and X-ray type AGN populations

Luminosity functions are one of the most important observational clues when studying galaxy evolution over cosmic time. In this paper we present the X-ray luminosity functions for X-ray detected AGN in the SXDS and GWS fields. The limiting fluxes of our samples are 9.0 ×10–15 and 4.8 ×10–16 erg cm–2 s–1 in the 0.5–7.0 keV band in the two fields, respectively. We carried out analysis in three X-ray bands and in two redshift intervals up to z ≤ 1.4. Moreover, we derive the luminosity functions for different optical morphologies and X-ray types. We confirm strong luminosity evolution in all three bands, finding the most luminous objects at higher redshift. However, no signs of density evolution are found in any tested X-ray band. We obtain similar results for compact and early-type objects. Finally, we observe the “Steffen effect”, where X-ray type-1 sources are more numerous at higher luminosities in comparison with type-2 sources. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

OTELO Survey: Properties of X-ray Emitters in the Groth Field – I. Optical Counterparts and Morphological Classification

We present results from the study of optical broadband and X-ray properties of a large sample of active galactic nuclei (AGN) in the Groth–Westphal Strip (GWS) field. In order to determine the morphology of all objects, we obtained different structural parameters. Combining these parameters with other optical/X-ray properties, we were searching for possible correlations between them, which could point out some of the AGN characteristics (see the contribution OTELO Survey: X-ray Emitters in the Groth Field – II. Properties of the AGN Population by Sanchez-Portal et al., in this volume).

Metallicity Estimates with SDSS–DR6

We present a study of the metallicity of 20268 galaxies from the Sloan Digital Sky Survey—Data Release 6 (SDSS–DR6)—using the R 23 method, and derive analytical calibrations from several metallicity-sensitive line ratios: [Nii] λ6583/Hα, [Oiii] λ5007/[Nii] λ6583, [Nii] λ6583/[Oii] λ3727, [Nii] λ6583/ [Sii] λλ6717, 6731, [Sii] λλ6717, 6731/Hα, and [Oiii] λλ4959, 5007/Hβ. We have performed the study for the resdshift interval (0.04–0.1) for all the Sloan survey release. This is the first part of a more complete work which aims to study the metallicity dependences of the star-forming galaxies in the Local Universe.

Metallicity Estimation Using N2 Method with OSIRIS

The OTELO (OSIRIS Tunable Emission Line Object Survey project) is an emission line survey using the OSIRIS Tunable Filters on the GTC 10.4m telescope (Cepa et al. 2008). Observing in selected atmospheric windows relatively free of sky emission lines, and with a total survey area of 0.1square degree distributed in different fields, it is expected to reach 5 sigma depth of 10−18erg/cm2/s, detecting objects with EW<0.2. OTELO will be the deepest emission line survey to date. As part of the preparatory activities, we have selected from the simulation of OTELO spectra, including errors, the best combination of tunable filters bandwidth (FWHM) and sampling, that will allow deblending Hα from [Nii]λ6,583 lines with a flux error lower than 20%. With the selected instrumental configuration it will be possible to estimate the objects chemical abundances using the N2 method in very low metallicity systems. We estimate that OTELO will allow to estimate the metallicities of more than 3,000 Hα star forming emitters up to a redshift 0.4.