arXiv subjects

L. Infante

Publications and source records attributed to L. Infante.

At least 91 records · Page 5Linked to original sources

arXiv2008

The clustering of Ly-alpha emitters in a LambdaCDM Universe

We combine a semi-analytical model of galaxy formation with a very large simulation which follows the growth of large scale structure in a LambdaCDM universe to predict the clustering of Ly-alpha emitters. We find that the clustering strength of Ly-alpha emitters has only a weak dependence on Ly-alpha luminosity but a strong dependence on redshift. With increasing redshift, Ly-alpha emitters trace progressively rarer, higher density regions of the universe. Due to the large volume of the simulation, over 100 times bigger than any previously used for this application, we can construct mock catalogues of Ly-alpha emitters and study the sample variance of current and forthcoming surveys. We find that the number and clustering of Ly-alpha emitters in our mock catalogues are in agreement with measurements from current surveys, but that there is a considerable scatter in these quantities. We argue that a proposed survey of emitters at z=8.8 should be extended significantly in solid angle to allow a robust measurement of Ly-alpha emitter clustering.

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arXiv2008

The ALHAMBRA Project: A large area multi medium-band optical and NIR photometric survey

(ABRIDGED) We describe the first results of the ALHAMBRA survey which provides cosmic tomography of the evolution of the contents of the Universe over most of Cosmic history. Our approach employs 20 contiguous, equal-width, medium-band filters covering from 3500 to 9700 A, plus the JHKs bands, to observe an area of 4 sqdeg on the sky. The optical photometric system has been designed to maximize the number of objects with accurate classification by SED and redshift, and to be sensitive to relatively faint emission lines. The observations are being carried out with the Calar Alto 3.5m telescope using the cameras LAICA and O-2000. The first data confirm that we are reaching the expected magnitude limits of AB<~25 mag in the optical filters from the blue to 8300 A, and from AB=24.7 to 23.4 for the redder ones. The limit in the NIR is (Vega) K_s~20, H~21, J~22. We expect to obtain accurate redshift values, Delta z/(1+z) <~ 0.03 for about 5x10^5 galaxies with I<~25 (60% complete), and z_med=0.74. This accuracy, together with the homogeneity of the selection function, will allow for the study of the redshift evolution of the large scale structure, the galaxy population and its evolution with redshift, the identification of clusters of galaxies, and many other studies, without the need for any further follow-up. It will also provide targets for detailed studies with 10m-class telescopes. Given its area, spectral coverage and its depth, apart from those main goals, the ALHAMBRA-Survey will also produce valuable data for galactic studies.

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arXiv2008

First results from the ALHAMBRA-Survey

We present the first results from the ALHAMBRA survey. ALHAMBRA will cover a relatively wide area (4 square degrees) using a purposely-designed set of 20 medium-band filters, down to an homogeneous magnitude limit AB~25 in most of them, adding also deep near-infrared imaging in JHK. To this aim we are using the Calar Alto 3.5m telescope. A small area of the ALHAMBRA survey has already been observed through our complete filter set, and this allows for the first time to check all the steps of the survey, including the pipelines that have been designed for the project, the fulfilment of the data quality expectations, the calibration procedures, and the photometric redshift machinery for which ALHAMBRA has been optimised. We present here the basic results regarding the properties of the galaxy sample selected in a 15x15 square arcmin area of the ALHAMBRA-8 field, which includes approximately 10000 galaxies with precise photometric redshift measurements. In a first estimate, approximately 500 of them must be galaxies with z>2.

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arXiv2008

Discovery of a Very Bright Strongly-Lensed Galaxy Candidate at z ~ 7.6

Using HST and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z~7.6 in the field of the massive galaxy cluster Abell 1689. The galaxy candidate, which we refer to as A1689-zD1, shows a strong z-J break of at least 2.2 mag and is completely undetected (<1 sigma) in HST/ACS g, r, i, and z-band data. These properties, combined with the very blue J-H and H-[4.5] colors, are exactly the properties of an z~7.6 LBG and can only be reasonably fit by a star-forming galaxy at z=7.6 +/- 0.4. Attempts to reproduce these properties with a model galaxy at z<4 yield particularly poor fits. A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 sigma) in the NICMOS H band and is ~1.3 mag brighter than the brightest-known z-dropout galaxy. When corrected for the cluster magnification of 9.3 at z~7.6, the candidate has an intrinsic magnitude of H=27.1 AB, or about an L* galaxy at z~7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size ~<300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9) x 10^9 M_sun, stellar ages 45-320 Myr, star-formation rates ~<7.6 M_sun/yr, and low reddening with A_V <= 0.3. These properties are generally similar to those of LBGs found at z~5-6. The inferred stellar ages suggest a formation redshift of z~8-10 (t~<0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date.

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arXiv2008

Galaxy populations in the Antlia cluster. I. Photometric properties of early-type galaxies

We present the first colour-magnitude relation (CMR) of early-type galaxies in the central region of the Antlia cluster, obtained from CCD wide-field photometry in the Washington photometric system. Integrated (C -T1) colours, T1 magnitudes, and effective radii have been measured for 93 galaxies (i.e. the largest galaxies sample in the Washington system till now) from the FS90 catalogue (Ferguson & Sandage 1990). Membership of 37 objects can be confirmed through new radial velocities and data collected from the literature. The resulting colour-magnitude diagram shows that early-type FS90 galaxies that are spectroscopically confirmed Antlia members or that were considered as definite members by FS90, follow a well defined CMR (sigma_(C -T1) ~ 0.07 mag) that spans 9 magnitudes in brightness with no apparent change of slope. This relation is very tight for the whole magnitude range but S0 galaxies show a larger dispersion, apparently due to a separation of ellipticals and S0s. Antlia displays a slope of -13.6 in a T1 vs. (C -T1) diagram, in agreement with results for clusters like Fornax, Virgo, Perseus and Coma, which are dynamically different to Antlia. This fact might indicate that the build up of the CMR in cluster of galaxies is more related to galaxies internal processes than to the influence of the environment. Interpreting the CMR as a luminosity-metallicity relation of old stellar systems, the metallicities of the Antlia galaxies define a global relation down to Mv ~ -13. We also find, for early-type dwarfs, no clear relation between luminosity and effective radius, indicating a nearly constant mean effective radius of ~ 1 kpc. This value is also found in several samples of dwarf galaxies in Virgo and Coma.

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arXiv2007

VLT and ACS observations of RDCS J1252.9-2927: dynamical structure and galaxy populations in a massive cluster at z=1.237

We present results from an extensive spectroscopic survey, carried out with VLT FORS, and from an extensive multiwavelength imaging data set from the HST Advanced Camera for Surveys and ground based facilities, of the cluster of galaxies RDCS J1252.9-2927. We have spectroscopically confirmed 38 cluster members in the redshift range 1.22 < z < 1.25. A cluster median redshift of z=1.237 and a rest-frame velocity dispersion of 747^{+74}_{-84} km/s are obtained. Using the 38 confirmed redshifts, we were able to resolve, for the first time at z > 1, kinematic structure. The velocity distribution, which is not Gaussian at the 95% confidence level, is consistent with two groups that are also responsible for the projected east-west elongation of the cluster. The groups are composed of 26 and 12 galaxies with velocity dispersions of 486^{+47}_{-85} km/s and 426^{+57}_{-105} km/s, respectively. The elongation is also seen in the intracluster gas and the dark matter distribution. This leads us to conclude that RDCS J1252.9-2927 has not yet reached a final virial state. We extend the analysis of the color-magnitude diagram of spectroscopic members to more than 1 Mpc from the cluster center. The scatter and slope of non-[OII]-emitting cluster members in the near-IR red sequence is similar to that seen in clusters at lower redshift. Furthermore, most of the galaxies with luminosities greater than ~ K_s*+1.5 do not show any [OII], indicating that these more luminous, redder galaxies have stopped forming stars earlier than the fainter, bluer galaxies. Our observations provide detailed dynamical and spectrophotometric information on galaxies in this exceptional high-redshift cluster, delivering an in-depth view of structure formation at this epoch only 5 Gyr after the Big Bang.

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arXiv2007

A search for ultra-compact dwarf galaxies in the Centaurus galaxy cluster

Aim: To extend the investigations of ultra-compact dwarf galaxies (UCDs) beyond the well studied Fornax and Virgo clusters. Methods: We measured spectroscopic redshifts of about 400 compact object candidates with 19.2 < V < 22.4 mag in the central region of the Centaurus galaxy cluster (d=43Mpc), using VIMOS@VLT. The luminosity range of the candidates covers that of bright globular clusters (GCs) and of UCDs in Fornax and Virgo. Results: We confirm the cluster membership of 27 compact objects, covering an absolute magnitude range -12.2 < M_V < -10.9 mag. We do not find counterparts to the two very large and bright UCDs in Fornax and Virgo with M_V=-13.5 mag, possibly due to survey incompleteness. The compact objects' distribution in magnitude and space is consistent with that of the GC population. Their kinematics and spatial distribution associate them to the central galaxies rather than to the overall cluster potential. The compact objects have a mean metallicity consistent with that of the metal-rich globular cluster sub-population. Compact objects with high S/N spectra exhibit solar [alpha/Fe] abundances, consistent with typical dwarf elliptical galaxy values and unlike galactic bulge globular clusters. HST based size estimates for a sub-sample of eight compact objects reveal the existence of one very large object with half-light radius r_h around 30 pc, having M_V=-11.6 mag (~10^7 M_sun). This source shows super-solar [alpha/Fe] abundances. Seven further sources are only marginally larger than typical GCs with r_h in the range 4 to 10 pc. Conclusions: We consider the largest compact object found to be the only bona-fide UCD detected in our study. In order to improve our understanding of UCDs in Centaurus, a significant increase of our survey completeness is necessary.

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arXiv2007

Ly-alpha Emission-Line Galaxies at z = 3.1 in the Extended Chandra Deep Field South

We describe the results of an extremely deep, 0.28 deg^2 survey for z = 3.1 Ly-alpha emission-line galaxies in the Extended Chandra Deep Field South. By using a narrow-band 5000 Anstrom filter and complementary broadband photometry from the MUSYC survey, we identify a statistically complete sample of 162 galaxies with monochromatic fluxes brighter than 1.5 x 10^-17 ergs cm^-2 s^-1 and observers frame equivalent widths greater than 80 Angstroms. We show that the equivalent width distribution of these objects follows an exponential with a rest-frame scale length of w_0 = 76 +/- 10 Angstroms. In addition, we show that in the emission line, the luminosity function of Ly-alpha galaxies has a faint-end power-law slope of alpha = -1.49 +/- 0.4, a bright-end cutoff of log L^* = 42.64 +/- 0.2, and a space density above our detection thresholds of 1.46 +/- 0.12 x 10^-3 h70^3 galaxies Mpc^-3. Finally, by comparing the emission-line and continuum properties of the LAEs, we show that the star-formation rates derived from Ly-alpha are ~3 times lower than those inferred from the rest-frame UV continuum. We use this offset to deduce the existence of a small amount of internal extinction within the host galaxies. This extinction, coupled with the lack of extremely-high equivalent width emitters, argues that these galaxies are not primordial Pop III objects, though they are young and relatively chemically unevolved.

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arXiv2006

Dynamical masses of ultra-compact dwarf galaxies in Fornax

Aims. We determine masses and mass-to-light ratios of five ultra-compact dwarf galaxies and one dwarf elliptical nucleus in the Fornax cluster from high resolution spectroscopy. Methods. Velocity dispersions were derived from selected wavelength regions using a direct-fitting method. To estimate the masses of the UCDs a new modelling program has been developed that allows a choice of different representations of the surface brightness profile (i.e. Nuker, Sersic or King laws) and corrects the observed velocity dispersions for observational parameters (i.e. seeing, slit size). Results. The observed velocity dispersions range between 22 and 30 km/s. The resulting masses are between 1.8 and 9.5x10^7M_sun. These, as well as the central and global projected velocity dispersions, were derived from the generalized King model which turned out to give the most stable results. The masses of two UCDs, that are best fitted by a two-component profile, were derived from a combined King+Sersic model. The mass-to-light ratios of the Fornax UCDs range between 3 and 5 (M/L_V)_sun. Within 1-2 half-mass radii dark matter is not dominating UCDs. Conclusions. We show that the mass-to-light ratios of UCDs in Fornax are consistent with those expected for pure stellar populations. Thus UCDs seem to be the result of cluster formation processes within galaxies rather than being compact dark matter dominated substructures themselves. Whether UCDs gained their mass in super-star cluster complexes of mergers or in nuclear star cluster formation processes remains an open question. It appears, however, clear that star clusters more massive than about 5\times10^6M_sun exhibit a more complex formation history than the less massive `ordinary' globular clusters.

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arXiv2006

The early-type dwarf galaxy population of the Fornax cluster

AIMS: We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population, based on a wide field imaging study of the central cluster area in V and I. We used the instrument/telescope combination IMACS/Magellan at Las Campanas Observatory, providing much larger light collecting area and better image resolution than previous surveys. METHODS: We create a fiducial sample of Fornax cluster dwarf ellipticals (dEs) in the following three steps: (1) To verify cluster membership, we measured I-band surface brightness fluctuation (SBF) distances to candidate dEs; (2) We re-assessed morphological classifications for candidate dEs too faint for SBF detection; and (3) We searched for new candidate dEs in the size-luminosity regime close to the resolution limit of previous surveys. RESULTS: (1) We confirm cluster membership for 28 candidate dEs in the range -16.6<M_V<-10.1 mag by means of SBF distances. We find no SBF background galaxy. (2) Of 51 further candidate dEs in the range -13.2<M_V<-8.6 mag, 2/3 are confirmed as probable cluster members by morphological re-assessment, while 1/3 are re-classified as probable background objects. (3) We find 12 new dE candidates in the range -12.3<M_V<-8.8 mag. The surface brightness-magnitude relation defined by the resulting fiducial dE sample shows that Fornax dEs are about 40% larger than Local Group dEs. The Fornax dE sample furthermore defines a colour-magnitude relation that appears slightly shallower than that of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax has a faint end slope alpha = -1.1 +/- 0.1. We discuss these findings in the context of structure formation theories. (ABRIDGED)

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arXiv2006

An I-band calibration of the SBF method at blue colours

The surface brightness fluctuation (SBF) method is a powerful tool to derive distances to galaxies for which single stars cannot be resolved. Up to now, the method has been calibrated mainly at red colours due to the intrinsic faintness of blue early-type galaxies. In this paper we address the I-band calibration of the SBF method at blue colours, the regime of dwarf elliptical galaxies (dEs). We present deep and wide-field VI photometry of the central Fornax cluster obtained at Las Campanas Observatory. With these data we perform an SBF analysis of 25 dEs in the range -16.5<M_V<-11.2 mag, 0.8<(V-I)_0<1.10 mag. For the calibration analysis we exclude eight dEs whose SBF measurement was affected by poor seeing (FWHM ~ 1"). Our SBF data are inconsistent at the 3 sigma level with a colour independent absolute SBF magnitude Mbar_I, presenting a problem for SBF models that predict such a flat relation. There is a weak indication in our data (1.8 sigma) to favour a two-branch calibration over a one-branch calibration with broad scatter in the Mbar_I - (V-I) plane. We obtain the following one-branch empirical SBF calibration: Mbar_I=-2.13 (+/- 0.17) + 2.44 (+/- 1.94) * [(V-I)_0 - 1.00] mag. We deduce a 0.34 +/- 0.14 mag cosmic scatter of Mbar_I, which is significantly larger than found at redder colours. This is in agreement with those theoretical SBF models that predict Mbar_I to be more sensitive to age-metallicity variations in the blue than in the red. We find evidence that the fainter galaxies in our samples contain younger and more metal-rich stellar populations than the brighter ones. The application of our empirical calibration to published SBF measurements of Hydra and Centaurus cluster dEs leaves the distances to both clusters unchanged.

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arXiv2006

Dwarf galaxies in the Antlia Cluster: First results

We present the first results of a project aimed to study the galaxy population of the Antlia cluster, the third nearest galaxy cluster after Virgo and Fornax. The observations for the Antlia project consist of Washington wide-field images taken with the MOSAIC camera mounted at the prime focus of the CTIO 4-m Blanco telescope. Our preliminary results correspond to the identification and classification of dwarf galaxies in the central cluster region, extending the list of Ferguson & Sandage (1990). The final aim of our project is to study the luminosity function, morphology and structural parameters of dwarf galaxies in the Antlia cluster with a more complete sample.

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arXiv2006

HST/ACS Multiband Coronagraphic Imaging of the Debris Disk around Beta Pictoris

(Abridged.) We present F435W (B), F606W (Broad V), and F814W (Broad I) coronagraphic images of the debris disk around Beta Pictoris obtained with HST's Advanced Camera for Surveys. We confirm that the previously reported warp in the inner disk is a distinct secondary disk inclined by ~5 deg from the main disk. The main disk's northeast extension is linear from 80 to 250 AU, but the southwest extension is distinctly bowed with an amplitude of ~1 AU over the same region. Both extensions of the secondary disk appear linear, but not collinear, from 80 to 150 AU. Within ~120 AU of the star, the main disk is ~50% thinner than previously reported. The surface-brightness profiles along the spine of the main disk are fitted with four distinct radial power laws between 40 and 250 AU, while those of the secondary disk between 80 and 150 AU are fitted with single power laws. These discrepancies suggest that the two disks have different grain compositions or size distributions. The F606W/F435W and F814W/F435W flux ratios of the composite disk are nonuniform and asymmetric about both projected axes of the disk. Within ~120 AU, the m_F435W-m_F606W and m_F435W-m_F814W colors along the spine of the main disk are ~10% and ~20% redder, respectively, than those of Beta Pic. These colors increasingly redden beyond ~120 AU, becoming 25% and 40% redder, respectively, than the star at 250 AU. We compare the observed red colors within ~120 AU with the simulated colors of non-icy grains having a radial number density ~r^-3 and different compositions, porosities, and minimum grain sizes. The observed colors are consistent with those of compact or moderately porous grains of astronomical silicate and/or graphite with sizes >0.15-0.20 um, but the colors are inconsistent with the blue colors expected from grains with porosities >90%.

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arXiv2006

Photometric observations of Southern Abell Cluster Redshifts Survey Clusters: Structure of galaxies in the inner region of clusters of galaxies

We analyze photometric properties of 1384 cluster galaxies as a function of the normalized distance to cluster center. These galaxies were selected in the central region ($r/r_{200} \leq$ 0.8) of 14 southern Abell clusters chosen from the Southern Abell Cluster Redshifts Survey (SARS). For 507 of these galaxies we also obtained their luminosity profiles. We have studied the morphology-clustercentric distance relation on the basis of the shape parameter $n$ of the Sérsic's law. We also have analyzed the presence of a possible segregation in magnitude for both, the galaxy total luminosity and that of their components (i.e. the bulge and the disk). Results show a marginal ($2σ$ level) decrease of the total luminosity as a function of normalized radius. However, when bulges are analyzed separately, a significant luminosity segregation is found ($3σ$ and $2σ$ for galaxies in projection and member galaxies respectively). The fraction of bulges brighter than $M_B \leq -22$ is three times larger in the core of clusters than in the outer region. Our analysis of the disk component suggests that disks are, on average, less luminous in the cluster core than at $r/r_{200} \sim 0.8$. In addition, we found that the magnitude-size relation as a function of $r/r_{200}$ indicates (at $2σ$ level) that disks are smaller and centrally brighter in the core of clusters. However, the Kormendy relation (the bulge magnitude-size relation) appears to be independent of environment.

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arXiv2005

Spectroscopic metallicities for Fornax UCDs, GCs and dE,Ns

Various formation channels for the puzzling ultra-compact dwarf galaxies (UCDs) have been proposed in the last few years. To better judge on some of the competing scenarios, we present spectroscopic [Fe/H] estimates for a sample of 26 compact objects in the central region of the Fornax cluster, covering the magnitude range of UCDs and bright globular clusters. We find a break in the metallicity distribution of compact objects at M_V ~ -11 mag (~3*10^6 M_sun): for M_V<-11 mag the mean metallicity is [Fe/H]=-0.62 +/- 0.05 dex, 0.56 +/- 0.15 dex higher than for M_V>-11 mag. This metallicity break is accompanied by a change in the size-luminosity relation for compact objects, as deduced from HST-imaging: for M_V<-11 mag, r_h scales with luminosity, while for M_V>-11 mag, r_h is almost luminosity-independent. We therefore assume a limiting absolute magnitude of M_V=-11 mag between UCDs and globular clusters. The mean metallicity of five Fornax dE,N nuclei included in our study is about 0.8 dex lower than that of the UCDs, at 4.5 sigma significance. Because of this large metallicity discrepancy we disfavor the hypothesis that most of the Fornax UCDs are the remnant nuclei of tidally stripped dE,Ns. Our metallicity estimates for UCDs are closer to but slightly below those derived for young massive clusters (YMCs) of comparable masses. We therefore favor a scenario where most UCDs in Fornax are successors of merged YMCs produced in the course of violent galaxy-galaxy mergers. It is noted that in contrast to that, the properties of Virgo UCDs are more consistent with the stripping scenario, suggesting that different UCD formation channels may dominate in either cluster.

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arXiv2005

An Overdensity of Galaxies near the Most Distant Radio-Loud Quasar

A five square arcminute region around the luminous radio-loud quasar SDSS J0836+0054 (z=5.8) hosts a wealth of associated galaxies, characterized by very red (1.3 < i_775 - z_{850} < 2.0) color. The surface density of these z~5.8 candidates is approximately six times higher than the number expected from deep ACS fields. This is one of the highest galaxy overdensities at high redshifts, which may develop into a group or cluster. We also find evidence for a substructure associated with one of the candidates. It has two very faint companion objects within two arcseconds, which are likely to merge. The finding supports the results of a recent simulation that luminous quasars at high redshifts lie on the most prominent dark-matter filaments and are surrounded by many fainter galaxies. The quasar activity from these regions may signal the buildup of a massive system.

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arXiv2005

Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data

The Southern Abell Redshift Survey contains 39 clusters of galaxies with redshifts in the range 0.0 < z < 0.31 and a median redshift depth of z = 0.0845. SARS covers the region 0 < decl < -65 deg, R.A. < 5h, R.A. > 21h (while avoiding the LMC and SMC) with b > 40. Cluster locations were chosen from the Abell and Abell-Corwin-Olowin catalogs while galaxy positions were selected from the Automatic Plate Measuring Facility galaxy catalog with extinction-corrected magnitudes in the range 15 <= b_j < 19. SARS utilized the Las Campanas 2.5 m duPont telescope, observing either 65 or 128 objects concurrently over a 1.5 sq deg field. New redshifts for 3440 galaxies are reported in the fields of these 39 clusters of galaxies.

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arXiv2005

The Multiwavelength Survey by Yale-Chile (MUSYC): Survey Design and Deep Public UBVRIz' Images and Catalogs of the Extended Hubble Deep Field South

We present UBVRIz' optical images of the 0.32 square degree Extended Hubble Deep Field South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z=3, AGN demographics, and Galactic structure. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62968 objects is complete to a total magnitude of R_AB=25. We select z=3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4/sq. arcmin and an angular correlation function w(theta) = 2.3+-1.0 theta^{-0.8}. (Abridged)

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