arXiv subjects

A. Aragon-Salamanca

Publications and source records attributed to A. Aragon-Salamanca.

At least 19 recordsLinked to original sources

arXiv2016

The fundamental plane of EDisCS galaxies - The effect of size evolution

We study the evolution of spectral early-type galaxies in clusters, groups and the field up to redshift 0.9 using the EDisCS dataset. We measure Re, Ie, and sigma for 154 cluster and 68 field galaxies. We study the evolution of the zero point of the fundamental plane (FP) and confirm results in the literature, but now also for the low cluster velocity dispersion regime. The mass-to-light ratio varies as Delta log M/L_B=(-0.54+-0.01)z=(-1.61+-0.01)log(1+z) in clusters, independent of their velocity dispersion. The evolution is stronger (Delta log M/L_B=(-0.76+-0.01)z=(-2.27+-0.03)log(1+z)) for field galaxies. The FP residuals correlate with galaxy mass and become progressively negative at low masses. The effect is visible at z>=0.7 for cluster galaxies and at z>=0.5 for field galaxies. We investigate the size evolution of our galaxy sample. We find that the half-luminosity radius for a galaxy with a dynamical or stellar mass of 2x10^11 Msol varies as (1+z)^{-1.0+-0.3} for both cluster and field galaxies. At the same time, stellar velocity dispersions grow with redshift, as (1+z)^{0.59+-0.10} at constant dynamical mass, and as (1+z)^{0.34+- 0.14} at constant stellar mass. The measured size evolution reduces to Re (1+z)^{-0.5+- 0.2} and sigma (1+z)^{0.41+-0.08}, at fixed dynamical masses, and Re (1+z)^{-0.68+-0.4} and sigma (1+z)^{0.19+-0.10}, at fixed stellar masses, when the progenitor bias (galaxies that locally are of spectroscopic early-type, but not very old, disappear from the EDisCS high-redshift sample; these galaxies tend to be large in size) is taken into account. Taken together, the variations in size and velocity dispersion imply that the luminosity evolution with redshift derived from the zero point of the FP is somewhat milder than that derived without taking these variations into account.

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arXiv2010

Superdense massive galaxies in the ESO Distant Cluster Survey (EDisCS)

We find a significant number of massive and compact galaxies in clusters from the ESO Distant Clusters Survey (EDisCS) at 0.4 4x10^11 Msun have significantly increased by a factor of 2 and 4, respectively, confirming the results of a number of recent works on the subject. Our findings show that progenitor bias effects play an important role in the size-growth paradigm of massive and passive galaxies.

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arXiv2009

Photometric redshifts and cluster tomography in the ESO Distant Cluster Survey

This paper reports the results obtained on the photometric redshifts measurement and accuracy, and cluster tomography in the ESO Distant Cluster Survey (EDisCS) fields. Photometric redshifts were computed using two independent codes (Hyperz and G. Rudnick's code). The accuracy of photometric redshifts was assessed by comparing our estimates with the spectroscopic redshifts of ~1400 galaxies in the 0.3<z<1.0 domain. The accuracy for galaxies fainter than the spectroscopic control sample was estimated using a degraded version of the photometric catalog for the spectroscopic sample. The accuracy of photometric redshifts is typically sigma(Delta z/(1+z)) ~ 0.05+/-0.01, depending on the field, the filter set, and the spectral type of the galaxies. The quality of the photometric redshifts degrades by a factor of two in sigma(Delta z/(1+z)) between the brightest (I~22) and the faintest (I~24-24.5) galaxies in the EDisCS sample. The photometric determination of cluster redshifts in the EDisCS fields using a simple algorithm based on photoz is in excellent agreement with the spectroscopic values (delta(z) ~0.03-0.04 in the high-z sample and ~0.05 in the low-z sample). We also developed a method that uses both photz codes jointly to reject interlopers at magnitudes fainter than the spectroscopic limit. When applied to the spectroscopic sample, this method rejects ~50-90% of all spectroscopically confirmed non-members, while retaining at least 90% of all confirmed members. Photometric redshifts are found to be particularly useful for the identification and study of clusters of galaxies in large surveys. They enable efficient and complete pre-selection of cluster members for spectroscopy, allow accurate determinations of the cluster redshifts, and provide a means of determining cluster membership. (Abridged)

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arXiv2009

Evolution of Cluster Red-Sequence Galaxies from redshift 0.8 to 0.4: ages, metallicities and morphologies

We present a comprehensive analysis of the stellar population properties (age, metallicity and the alpha-element enhancement [E/Fe]) and morphologies of red-sequence galaxies in 24 clusters and groups from z~0.75 to z~0.45. The dataset, consisting of 215 spectra drawn from the ESO Distant Cluster Survey, constitutes the largest spectroscopic sample at these redshifts for which such an analysis has been conducted. Analysis reveals that the evolution of the stellar population properties of red-sequence galaxies depend on their mass: while the properties of most massive are well described by passive evolution and high-redshift formation, the less massive galaxies require a more extended star formation history. We show that these scenarios reproduce the index-sigma relations as well as the galaxy colours. The two main results of this work are (1) the evolution of the line-strength indices for the red-sequence galaxies can be reproduced if 40% of the galaxies with sigma < 175 km/s entered the red-sequence between z=0.75 to z=0.45, in agreement with the fraction derived in studies of the luminosity functions, and (2) the percentage the red-sequence galaxies exhibiting early-type morphologies (E and S0) decreases by 20% from z=0.75 to z=0.45. This can be understood if the red-sequence gets populated at later times with disc galaxies whose star formation has been quenched. We conclude that the processes quenching star formation do not necessarily produce a simultaneous morphological transformation of the galaxies entering the red-sequence.

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arXiv2008

Exploring Disk Galaxy Dynamics Using IFU Data

In order to test the basic equations believed to dictate the dynamics of disk galaxies, we present and analyze deep two-dimensional spectral data obtained using the PPAK integral field unit for the early-type spiral systems NGC 2273, NGC 2985, NGC 3898 and NGC 5533. We describe the care needed to obtain and process such data to a point where reliable kinematic measurements can be obtained from these observations, and a new more optimal method for deriving the rotational motion and velocity dispersions in such disk systems. The data from NGC 2273 and NGC 2985 show systematic variations in velocity dispersion with azimuth, as one would expect if the shapes of their velocity ellipsoids are significantly anisotropic, while the hotter disks in NGC 3898 and NGC 5533 appear to have fairly isotropic velocity dispersions. Correcting the rotational motion for asymmetric drift using the derived velocity dispersions reproduces the rotation curves inferred from emission lines reasonably well, implying that this correction is quite robust, and that the use of the asymmetric drift equation is valid. NGC 2985 is sufficiently close to face on for the data, combined with the asymmetric drift equation, to determine all three components of the velocity ellipsoid. The principal axes of this velocity ellipsoid are found to be in the ratio sigma_z:sigma_phi:sigma_R ~ 0.7:0.7:1, which shows unequivocally that this disk distribution function respects a third integral of motion. The ratio is also consistent with the predictions of epicyclic theory, giving some confidence in the application of this approximation to even fairly early-type disk galaxies.

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arXiv2008

The evolution of the brightest cluster galaxies since z~1 from the ESO Distant Cluster Survey (EDisCS)

[Abridged] We present K-band data for the brightest cluster galaxies (BCGs) from the ESO Distant Cluster Survey. These data are combined with photometry from Aragon-Salamanca et al. (1998) and a low-redshift comparison sample from von der Linden et al. (2007). The K-band Hubble diagram for BCGs exhibits very low scatter (~0.35mag) since z=1. The colour and $K$-band luminosity evolution of the BCGs are in good agreement with passively-evolving stellar populations formed at z>2. We do not detect any significant change in the stellar mass of the BCG since z~1. These results do not seem to depend on the velocity dispersion of the parent cluster. There is a correlation between the 1D velocity dispersion of the clusters and the K-band luminosity of the BCGs (after correcting for passive evolution). The clusters with large velocity dispersions tend to have brighter BCGs, i.e., BCGs with larger stellar masses. This dependency, although significant, is relatively weak: the stellar mass of the BCGs changes only by ~70% over a two-order-of-magnitude range in cluster mass. This dependency doesn't change significantly with redshift. The models of De Lucia & Blaizot (2007) predict colours which are in reasonable agreement with the observations because the growth in stellar mass is dominated by the accretion of old stars. However, the stellar mass in the model BCGs grows by a factor of 3-4 since z=1, a growth rate which seems to be ruled out by the observations. The models predict a dependency between the BCG's stellar mass and the velocity dispersion of the parent cluster in the same sense as the data, but the dependency is significantly stronger than observed. However, one major difficulty in this comparison is that we have measured fixed metric aperture magnitudes while the models compute total luminosities.

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arXiv2008

Extended UV (XUV) Emission in Nearby Galaxy Disks

We summarize the main properties of the extended UV (XUV) emission found in roughly 30% of the nearby spiral galaxies observed by the GALEX satellite. Two different classes of XUV disks are identified, the Type 1 XUV disks where significant, structured UV-bright features are found beyond the "classical" azimuthally-averaged star-formation threshold, and the Type 2 XUV disks, which are characterized by very extended (seven times the area where most of the stellar mass is found), blue [(FUV-K)<5mag] outer disks. These latter disks are extreme examples of galaxies growing inside-out. The few XUV disks studied in detail to date are rich in HI but relatively poor in molecular gas, have stellar populations with luminosity-weighted ages of ~1 Gyr, and ionized-gas metal abundances of ~Zsun/10. As part of the CAHA-XUV project we are in the process of obtaining deep multi-wavelength imaging and spectroscopy of 65 XUV-disk galaxies so to determine whether or not these properties are common among XUV disks.

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arXiv2007

The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP

Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby Universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP (Peletier et al., 2007). In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo Cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal-poor than normal elliptical galaxies, and that their [alpha/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations between the luminosity-weighted mean age, the large-scale asymmetry, and the projected Virgocentric distance. We find that environment plays an important role in the termination of the star formation activity by ram pressure stripping of the gas in short timescales, and in the transformation of disky dwarfs to more spheroidal objects by harassment over longer timescales. This points towards a continuing infall scenario for the evolution of dEs.

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arXiv2007

The formation of S0 galaxies: evidence from globular clusters

We test the theory that lenticular (S0) galaxies form from spirals whose star formation has been shut down. We use the globular cluster specific frequency S_N, defined as the number of globular clusters normalised by the galaxy luminosity as a diagnostic. NTT/EMMI long-slit spectroscopic observations of 11 S0 galaxies at z < 0.006 are used to measure the absorption-line indices, Hdelta, Hgamma, Mgb, Fe5270 and Fe5335 within the central r_e/8. By inverting single-stellar population models, luminosity-weighted mean ages, metallicities and alpha-element abundance ratios are derived. We estimate the amount of fading a galaxy has undergone by comparing each galaxy's S_N with its deviation from the mean spiral S_N. Galaxies with higher S_N have older stellar populations. Moreover, we find that the zero-point and amount of fading is consistent with a scenario where lenticulars are formed by the quenching of star formation in spiral galaxies. Our data also rule out any formation method for S0s which creates a large number of new globular clusters. We confirm that previous results showing a relationship between S_N and color are driven by the S_N - Age relation. Five galaxies show detectable Hbeta, [OIII], Halpha or [NII] emission lines. However, only in the two youngest galaxies is this emission unambiguously from star formation. Our results are consistent with the theory that S0 galaxies are formed when gas in normal spirals is removed, possibly as a result of a change in environment. The on-going star formation in the youngest galaxies hints that the timescale of quenching is ~< 1 Gyr. We speculate, therefore, that the truncation of star formation is a rather gentle process unlikely to involve a rapid burst of star formation.

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arXiv2007

Galaxy morphologies and environment in the Abell 901/902 supercluster from COMBO-17

We present a morphological study of galaxies in the A901/902 supercluster from the COMBO-17 survey. A total of 570 galaxies with photometric redshifts in the range 0.155 < z_phot < 0.185 are visually classified by three independent classifiers to M_V=-18. These morphological classifications are compared to local galaxy density, distance from the nearest cluster centre, local surface mass density from weak lensing, and photometric classification. At high local galaxy densities, log(Sigma_10 /Mpc^2) > 1.5, a classical morphology-density relation is found. A correlation is also found between morphology and local projected surface mass density, but no trend is observed with distance to the nearest cluster. This supports the finding that local environment is more important to galaxy morphology than global cluster properties. The breakdown of the morphological catalogue by colour shows a dominance of blue galaxies in the galaxies displaying late-type morphologies and a corresponding dominance of red galaxies in the early-type population. Using the 17-band photometry from COMBO-17, we further split the supercluster red sequence into old passive galaxies and galaxies with young stars and dust according to the prescription of Wolf et al. (2005). We find that the dusty star-forming population describes an intermediate morphological group between late-type and early-type galaxies, supporting the hypothesis that field and group spiral galaxies are transformed into S0s and, perhaps, ellipticals during cluster infall.

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arXiv2007

The Morphological Content of Ten EDisCS Clusters at 0.5 < z < 0.8

We describe Hubble Space Telescope (HST) imaging of 10 of the 20 ESO Distant Cluster Survey (EDisCS) fields. Each ~40 square arcminute field was imaged in the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based on these data, we present visual morphological classifications for the ~920 sources per field that are brighter than I_auto=23 mag. We use these classifications to quantify the morphological content of 10 intermediate-redshift (0.5 < z < 0.8) galaxy clusters within the HST survey region. The EDisCS results, combined with previously published data from seven higher redshift clusters, show no statistically significant evidence for evolution in the mean fractions of elliptical, S0, and late-type (Sp+Irr) galaxies in clusters over the redshift range 0.5 < z < 1.2. In contrast, existing studies of lower redshift clusters have revealed a factor of ~2 increase in the typical S0 fraction between z=0.4 and z=0, accompanied by a commensurate decrease in the Sp+Irr fraction and no evolution in the elliptical fraction. The EDisCS clusters demonstrate that cluster morphological fractions plateau beyond z ~ 0.4. They also exhibit a mild correlation between morphological content and cluster velocity dispersion, highlighting the importance of careful sample selection in evaluating evolution. We discuss these findings in the context of a recently proposed scenario in which the fractions of passive (E,S0) and star-forming (Sp,Irr) galaxies are determined primarily by the growth history of clusters.

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arXiv2006

Morphology-dependent trends of galaxy age with environment in Abell 901/902 seen with COMBO-17

We investigate correlations between galaxy age and environment in the Abell 901/2 supercluster for separate morphologies. Using COMBO-17 data, we define a sample of 530 galaxies, complete at $M_V -5\log h<-18$ on an area of $3.5\times 3.5$ (Mpc/$h$)$^2$. We explore several age indicators including an extinction-corrected residual from the colour-magnitude relation (CMR). As a result, we find a clear trend of age with density for galaxies of all morphologies that include a spheroidal component, in the sense that galaxies in denser environments are older. This trend is not seen among Scd/Irr galaxies since they all have young ages. However, the trend among the other types is stronger for fainter galaxies. While we also see an expected age-morphology relation, we find no evidence for a morphology-density relation at fixed age.

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arXiv2006

The X-ray properties of optically-selected z>0.6 clusters in the ESO Distant Cluster Survey

We present XMM-Newton observations of three optically-selected z > 0.6 clusters from the ESO Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and -- unlike other high-redshift, optically-selected clusters -- are consistent with the T - sigma and L_x - sigma relations determined from X-ray selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalog may, like selection by X-ray luminosity, be well-suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ~ 0.8.

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arXiv2006

Measuring the fading of S0 galaxies using globular clusters

We test the hypothesis that S0 galaxies are the descendants of fading spirals whose star formation has been shut down, by using the properties of their globular cluster (GC) systems. We estimate the amount by which the GC specific frequency (number of GCs per unit V-band luminosity) is enhanced in S0s relative to spirals. If the transformation hypothesis is correct, and no GCs are created or destroyed in the process, then this difference provides a measure of the degree to which the S0's V-band luminosity has faded relative to that of its spiral progenitor. We also explore whether the degree to which the GC specific frequency is enhanced in S0s correlates with the colour of the stellar population, as also predicted by this hypothesis in which galaxies become redder as they fade. We find that, on average, the GC specific frequency is a factor ~3 larger for S0s than for spirals, which can be interpreted as meaning that passively-evolving S0s have faded by about a factor of 3 from their spiral progenitors. This value fits remarkably well with the predictions of stellar population synthesis calculations, and the offset between the S0 and spiral Tully-Fisher relations. We also find that the global colours of S0 galaxies are strongly correlated with their GC specific frequencies: the redder the stellar population of an S0, the larger its specific frequency, as we might expect if we are catching different S0s at different stages of passively fading and reddening. Comparison to the predictions of stellar population synthesis models show that this explanation works quantitatively as well as qualitatively. These tests strongly support the hypothesis that S0 galaxies were once normal spirals, whose star formation was cut off, presumably due to a change of environment.

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arXiv2006

An imaging survey of a uniform sample of Brightest Cluster Galaxies and Intracluster Light

We present deep, large area B and r' imaging for a sample of 49 brightest cluster galaxies (BCGs). The clusters were selected by their x-ray luminosity and redshift to form two volume limited samples, one with mean redshift ~ 0.07 and one at a mean redshift ~ 0.17. For each cluster the data cover 41' by 41'. We discuss our data reduction techniques in detail, and show that we can reliably measure the surface brightness at the levels of mu_B ~ 29 and mu_r' ~ 28. For each galaxy we present the B and r' images together with the surface brightness profile, B-r' colour, eccentricity and position angle as a function of radius. We investigate the distribution of positional offsets between the optical centroid of the BCG and the centre of the X-ray emission, and conclude that the mass profiles are cuspy, and do not have extended cores. We also introduce a method to objectively identify the transition from BCG to extended envelope of intra-cluster light, using the Petrosian index as a function of radius.

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arXiv2006

Star formation rates and chemical abundances of emission line galaxies in intermediate-redshift clusters

We examine the evolutionary status of luminous, star-forming galaxies in intermediate-redshift clusters by considering their star formation rates and the chemical and ionsiation properties of their interstellar emitting gas. Our sample consists of 17 massive, star-forming, mostly disk galaxies with M_{B}<-20, in clusters with redshifts in the range 0.31< z <0.59, with a median of =0.42. We compare these galaxies with the identically selected and analysed intermediate-redshift field sample of Mouhcine et al. (2006), and with local galaxies from the Nearby Field Galaxy Survey of Jansen et al. (2000). From our optical spectra we measure the equivalent widths of OII, Hbeta and OIII emission lines to determine diagnostic line ratios, oxygen abundances, and extinction-corrected star formation rates. The star-forming galaxies in intermediate-redshift clusters display emission line equivalent widths which are, on average, significantly smaller than measured for field galaxies at comparable redshifts. However, a contrasting fraction of our cluster galaxies have equivalent widths similar to the highest observed in the field. This tentatively suggests a bimodality in the star-formation rates per unit luminosity for galaxies in distant clusters. We find no evidence for further bimodalities, or differences between our cluster and field samples, when examining additional diagnostics and the oxygen abundances of our galaxies. This maybe because no such differences exist, perhaps because the cluster galaxies which still display signs of star-formation have recently arrived from the field. In order to examine this topic with more certainty, and to further investigate the way in which any disparity varies as a function of cluster properties, larger spectroscopic samples are needed.

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arXiv2006

The metallicities of luminous, massive field galaxies at intermediate redshifts

We derive oxygen abundances for a sample of 40 luminous (M_{B} < -19), star-forming, mostly disk, field galaxies with redshifts in the range 0.2 < z < 0.8$, with a median of = 0.45. Oxygen abundances, relative to hydrogen, of the interstellar emitting gas are estimated by means of the empirically calibrated strong emission line ratio technique. The derived (12+log(O/H)) values range from 8.4 to 9.0, with a median of 8.7. Twenty of these galaxies have securely measured rotation velocities, in the range 50--244 km/s. The measured emission line equivalent widths and diagnostic ratios for the intermediate redshift galaxies cover similar ranges to those observed across a large sample of local galaxies. The estimated oxygen abundances for our luminous star-forming intermediate redshift galaxies cover the same range as their local counterparts. However, at a given galaxy luminosity, many of our galaxies have significantly lower oxygen abundances, i.e., $(12+log(O/H))~8.6$, than local galaxies with similar luminosities. Interestingly, these luminous, massive, intermediate redshift, star-forming galaxies with low oxygen abundances exhibit physical conditions, i.e., emission line equivalent width and ionization state, very similar to those of local faint and metal-poor star-forming galaxies. The oxygen abundance of the interstellar gas does not seem to correlate with the maximum rotation velocity or the emission scale length of the parent galaxy. This suggests that there is a diversity in the intrinsic properties of the massive field galaxy population at intermediate redshifts (ABRIDGED).

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arXiv2005

The evolution of the star formation activity in galaxies and its dependence on environment

We study how the proportion of star-forming galaxies evolves between z=0.8 and z=0 as a function of galaxy environment, using the [OII] line in emission as a signature of ongoing star formation. Our high-z dataset comprises 16 clusters, 10 groups and another 250 galaxies in poorer groups and the field at z=0.4-0.8 from the ESO Distant Cluster Survey, plus another 9 massive clusters at similar redshifts. As a local comparison, we use samples of galaxy systems selected from the Sloan Digital Sky Survey at 0.04< z < 0.08. At high-z most systems follow a broad anticorrelation between the fraction of star-forming galaxies and the system velocity dispersion. At face value, this suggests that at z=0.4-0.8 the mass of the system largely determines the proportion of galaxies with ongoing star formation. At these redshifts the strength of star formation (as measured by the [OII] equivalent width) in star-forming galaxies is also found to vary systematically with environment. Sloan clusters have much lower fractions of star-forming galaxies than clusters at z=0.4-0.8 and, in contrast with the distant clusters, show a plateau for velocity dispersions $ \ge 550 km s^-1$, where the fraction of galaxies with [OII] emission does not vary systematically with velocity dispersion. We quantify the evolution of the proportion of star-forming galaxies as a function of the system velocity dispersion and find it is strongest in intermediate-mass systems (sigma ~ 500-600 km s^-1 at z=0). To understand the origin of the observed trends, we use the Press-Schechter formalism and the Millennium Simulation and show that galaxy star formation histories may be closely related to the growth history of clusters and groups. We propose a scheme that is able to account for the observed relations between the star-forming fraction and σ[abridged].

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