M. Fernández Lorenzo

Study of star-forming galaxies in SDSS up to redshift 0.4 - II. Evolution from the fundamental parameters: mass, metallicity and star formation rate

To understand the formation and evolution of galaxies, it is important to have a full comprehension of the role played by the metallicity, star formation rate (SFR), morphology, and color. The interplay of these parameters at different redshifts will substantially affect the evolution of galaxies and, as a consequence, the evolution of them will provide important clues and constraints on the galaxy evolution models. In this work we focus on the evolution of the SFR, metallicity of the gas, and morphology of galaxies at low redshift in search of signs of evolution. We use the S2N2 diagnostic diagram as a tool to classify star--forming, composite, and AGN galaxies. We analyzed the evolution of the three principal BPT diagrams, estimating the SFR and specific SFR (SSFR) for our samples of galaxies, studying the luminosity and mass-metallicity relations, and analyzing the morphology of our sample of galaxies through the g-r color, concentration index, and SSFR. We found that the S2N2 is a reliable diagram to classify star--forming, composite, and AGNs galaxies. We demonstrate that the three principal BPT diagrams show an evolution toward higher values of [OIII]5007/Hb due to a metallicity decrement. We found an evolution in the mass-metallicity relation of ~ 0.2 dex for the redshift range 0.3 < z < 0.4 compared to our local one. From the analysis of the evolution of the SFR and SSFR as a function of the stellar mass and metallicity, we discovered a group of galaxies with higher SFR and SSFR at all redshift samples, whose morphology is consistent with those of late-type galaxies. Finally, the comparison of our local (0.04<z<0.1) with our higher redshift sample (0.3<z<0.4), show that the metallicity, the SFR and morphology, evolve toward lower values of metallicity, higher SFRs, and late--type morphologies for the redshift range 0.3<z<0.4

The AMIGA sample of isolated galaxies - X. A first look at isolated galaxy colors

Context. The basic properties of galaxies can be affected by both nature (internal processes) or nurture (interactions and effects of environment). Deconvolving the two effects is an important current effort in astrophysics. Observed properties of a sample of isolated galaxies should be mainly the result of internal (natural) evolution. It follows that nurture–induced galaxy evolution can only be understood through a comparative study of galaxies in different environments. Aims. We take a first look at SDSS (g − r) colors of galaxies in the AMIGA sample, which consists of many of the most isolated galaxies in the local Universe. This alerted us at the same time to the pitfalls of using automated SDSS colors. Methods. We focused on median values for the principal morphological subtypes found in the AMIGA sample (E/S0 and Sb-Sc) and compared them with equivalent measures obtained for galaxies in denser environments. Results. We find a weak tendency for AMIGA spiral galaxies to be redder than objects in close pairs. We find no clear difference when we compared this with galaxies in other (e.g. group) environments. However, the (g − r) color of isolated galaxies shows a Gaussian distribution, as might be expected assuming nurture-free evolution. We find a smaller median absolute deviation in colors for isolated galaxies compared to both wide and close pairs. The majority of the deviation on median colors for spiral subtypes is caused by a color-luminosity correlation. Surprisingly, isolated and non-isolated early-type galaxies show similar (g −r). We see little evidence for a green valley in our sample because most spirals redder than (g − r) = 0.7 have spurious colors. Conclusions. The redder colors of AMIGA spirals and lower color dispersions for AMIGA subtypes – compared with close pairs – are likely caused by a more passive star formation in very isolated galaxies.

The stellar mass–size relation for the most isolated galaxies in the local Universe

Disentangling processes governing the formation and evolution of galaxies is a fundamental challenge in extragalactic research. In this sense t he current belief that galaxies grow by the action of minor mergers makes the study of the stellar mass‐size relation in different environments an important tool for distinguishing effects of internal and external processes. The aim of this work is to study the effects of environment on the growth in size of galaxies. As part of AMIGA project (Analysis of the Interstellar Medium of Isolated GAlaxies), we examine the stellar mass‐size relation for a sample of the most isolated galaxies in the local Universe interpreted as stellar systems where evolution has been mainly governed by internal processes. Effects of environment on the stellar mass‐size relation are evaluated by comparing our results with samples of less isolated early‐ and late‐type galaxies, as well as, for the first time, di fferent spiral subtypes. Stellar masses in our sample were derived by fitting the SED of each galaxy with kcorrect. We used two different size estimators, the half‐light radius obtained with .. .. .. .. .. .. .. .. .. .. .. ! ,

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.

Evolution of the fundamental plane of 0.2 < z < 1.2 early-type galaxies in the EGS

Context. The fundamental plane links the structural properties of early-type galaxies such as its surface brightness and effective radius with its dynamics. The study of the fundamental plane evolution therefore has important implications for models of galaxy formation and evolution. Aims. This work aims to identify signs of evolution of early-type galaxies through the study of parameter correlations such as the fundamental plane, the Kormendy, and the Faber-Jackson relations, using a sample of 135 field galaxies extracted from the Extended Groth Strip in the redshift range 0.2 < z < 1.2. Methods. We calculate the internal velocity dispersions with DEEP2 data by extracting the stellar kinematics from absorption line spectra, using a maximum penalized-likelihood approach. Morphology was determined through visual classification of the V + I images of ACS. The structural parameters of these galaxies were obtained by fitting de Vaucouleurs stellar profiles to the ACS I-band images with the GALFIT code. To check the effect on the fundamental plane of the structural parameters, Sersic and bulge-to-disc decomposition models were fitted to our sample of galaxies. A good agreement was found in the fundamental plane derived from the three models. Results. Assuming that effective radii and velocity dispersions do not evolve with redshift, we found a brightening of 0.68 mag in the

Evolution of the infrared Tully-Fisher relation up to z = 1.4

Context. The Tully-Fisher relation represents a connection between fundamental galaxy parameters, such as its total mass and the mass locked in stars. Therefore, the study of the evolution of this relation in the optical and infrared bands can provide valuable information about the evolution of the individual galaxies through the changes found in each band. Aims. This work aims to study the Tully-Fisher relation at high redshift in the B,V,R,I ,a ndKS-bands by comparison with the local relations derived from a large sample of galaxies in the redshift range 0.1 < z < 0.3, processed in the same way, and with the same instrumental constraints that the high-redshift sample. Methods. Using the large amount of photometric information available in the AEGIS database, we determined the optimal procedure for obtaining reliable k-corrections. Instrumental magnitudes were then k- and extinction corrected and the absolute magnitudes derived, using the concordance cosmological model. The rotational velocities were inferred from the widths of optical lines in DEEP2 spectra. At high redshift, this method is found to provide more accurate results than using the rotation curve, because of spatial resolution limitations. Morphology was determined by visual classification of the HST images. From the above information, the Tully-Fisher relations in B,V,R,I ,a ndKS-bands are derived for the local and high-redshift sample. Results. We detect evolution in the B,V ,a ndR-bands in the sense that galaxies were brighter in the past at the same rotation velocity. The change in luminosity is more noticeable in the bluer bands. This colour evolution, unnoticed in our previous work, is detected thanks to the more reliable k-corrections carried out in this paper, which included photometry from B to IRAC bands. The change in the (V − KS )a nd (R − I) colours (for a fixed velocity) could be interpreted as an ageing of the stellar populations as consequence of the star formation decrease since z = 1.25. In addition, we conclude that spiral galaxies may have doubled their stellar masses in the past 8.6 Gyr.

ARE (PSEUDO)BULGES IN ISOLATED GALAXIES ACTUALLY PRIMORDIAL RELICS

We present structural parameters and (g – i) bulge/disk colors for a large sample (189) of isolated AMIGA galaxies. The structural parameters of bulges were derived from the two-dimensional bulge/disk/bar decomposition of Sloan Digital Sky Survey i-band images using GALFIT. Galaxies were separated between classical bulges (nb > 2.5) and pseudobulges (nb < 2.5), resulting in a dominant pseudobulge population (94%) with only 12 classical bulges. In the μ e -R e plane, pseudobulges are distributed below the elliptical relation (smaller R e and fainter μ e ), with the closest region to the Kormendy relation populated by those pseudobulges with larger values of B/T. We derived (g – i) bulge colors using aperture photometry and find that pseudobulges show median colors (g – i) b ~ 1.06, while their associated disks are much bluer, (g – i) d ~ 0.77. Moreover, 64% (113/177) of pseudobulges follow the red sequence of early-type galaxies. Bluer pseudobulges tend to be located in galaxies with the highest likelihood of tidal perturbation. The red bulge colors and low B/T values for AMIGA isolated galaxies are consistent with an early formation epoch and not much subsequent growth. Properties of bulges in isolated galaxies contrast with a picture where pseudobulges grow continuously via star formation. They also suggest that environment could be playing a role in rejuvenating the pseudobulges.

Catalogues of isolated galaxies, isolated pairs, and isolated triplets in the local Universe

Context. The construction of catalogues of galaxies and the a posteriori study of galaxy properties in relation to their environment have been hampered by scarce redshift information. The new 3-dimensional (3D) surveys permit small, faint, physically bound satellites to be distinguished from a background-projected galaxy population, giving a more comprehensive 3D picture of the surroundings.

The ALHAMBRA survey: reliable morphological catalogue of 22 051 early- and late-type galaxies

This research was supported by the Junta de Andalucia through projects PO8-TIC-03531 and TIC114, the Spanish Ministry of Economy and Competitiveness (MINECO) through projects AYA2006-14046, AYA2010-15169, AYA2010-22111-C03-02, AYA2011-29517-C03-01, and the Generalitat Valenciana through project GV/Prometeo 2009/064. MP acknowledges financial support from JAE-Doc program of the Spanish National Research Council (CSIC), co-funded by the European Social Fund.

The AMIGA sample of isolated galaxies - XII. Revision of the isolation degree for AMIGA galaxies using the SDSS

Context. To understand the evolution of galaxies, it is necessary to have a reference sample where the e ect of the environment is minimized and quantified. In the framework of the AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies), we present a revision of the environment for galaxies in the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973, Astrof. Issledovaniia Byu. Spec. Ast. Obs., 8, 3) using the ninth data release of the Sloan Digital Sky Survey (SDSS-DR9). Aims. The aims of this study are to refine the photometric-based AMIGA sample of isolated galaxies and to provide an improvement of the quantification of the isolation degree with respect to previous works, using both photometry and spectroscopy. Methods. We developed an automatic method to search for neighbours within a projected area of 1 Mpc radius centred on each primary galaxy to revise the CIG isolation criteria introduced by Karachentseva (1973). The local number density at the fifth nearest neighbour and the tidal strength a ecting the CIG galaxy were estimated to quantify the isolation degree. Results. Of the 636 CIG galaxies considered in the photometric study, 426 galaxies fulfil the CIG isolation criteria within 1 Mpc, taking into account projected neighbours. Of the 411 CIG galaxies considered in the spectroscopic study, 347 galaxies fulfil the CIG isolation criteria when a criterion about redshift di erence is added. The available redshifts allow us to reject background neighbours and thus improve the photometric assessment. On average, galaxies in the AMIGA sample show lower values in the local number density and the tidal strength parameters than galaxies in denser environments such as pairs, triplets, compact groups, and clusters. Conclusions. For the first time, the environment and the isolation degree of AMIGA galaxies are quantified using digital data. The use of the SDSS database permits one to identify fainter and smaller-size satellites than in previous AMIGA works. The AMIGA sample is improved by this study, because we reduced the sample of isolated galaxies used in previous AMIGA works by about 20%. The availability of the spectroscopic data allows us to check the validity of the CIG isolation criteria, which is not fully e cient. About 50% of the neighbours considered as potential companions in the photometric study are in fact background objects. We also find that about 92% of the neighbour galaxies that show recession velocities similar to the corresponding CIG galaxy are not considered by the CIG isolation criteria as potential companions, which may have a considerable influence on the evolution of the central CIG galaxy.