Jose Maria Solanes

THE ARECIBO LEGACY FAST ALFA SURVEY. I. SCIENCE GOALS, SURVEY DESIGN, AND STRATEGY

The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims to map ~7000 deg2 of the high Galactic latitude sky visible from Arecibo, providing a H I line spectral database covering the redshift range between -1600 and 18,000 km s-1 with ~5 km s-1 resolution. Exploiting Arecibos large collecting area and small beam size, ALFALFA is specifically designed to probe the faint end of the H I mass function in the local universe and will provide a census of H I in the surveyed sky area to faint flux limits, making it especially useful in synergy with wide-area surveys conducted at other wavelengths. ALFALFA will also provide the basis for studies of the dynamics of galaxies within the Local Supercluster and nearby superclusters, allow measurement of the H I diameter function, and enable a first wide-area blind search for local H I tidal features, H I absorbers at z < 0.06, and OH megamasers in the redshift range 0.16 < z < 0.25. Although completion of the survey will require some 5 years, public access to the ALFALFA data and data products will be provided in a timely manner, thus allowing its application for studies beyond those targeted by the ALFALFA collaboration. ALFALFA adopts a two-pass, minimum intrusion, drift scan observing technique that samples the same region of sky at two separate epochs to aid in the discrimination of cosmic signals from noise and terrestrial interference. Survey simulations, which take into account large-scale structure in the mass distribution and incorporate experience with the ALFA system gained from tests conducted during its commissioning phase, suggest that ALFALFA will detect on the order of 20,000 extragalactic H I line sources out to z ~ 0.06, including several hundred with H I masses M < 107.5 M⊙.

The H I Content of Spirals. II. Gas Deficiency in Cluster Galaxies

We derive the atomic hydrogen content for a total of 1900 spirals in the fields of 18 nearby clusters. By comparing the H I-deficiency distributions of the galaxies inside and outside one Abell radius (RA) of each cluster, we find that two-thirds of the clusters in our sample show a dearth of neutral gas in their interiors. Possible connections between the gaseous deficiency and the characteristics of both the underlying galaxies and their environment are investigated in order to gain insight into the mechanisms responsible for H I depletion. While we do not find a statistically significant variation of the fraction of H I-deficient spirals in a cluster with its global properties, a number of correlations emerge that argue in favor of the interplay between spiral disks and their environment. In the clusters in which neutral gas deficiency is pronounced, we see clear indications that the degree of H I depletion is related to the morphology of the galaxies and not to their optical size; early-type and probably dwarf spirals are more easily emptied of gas than the intermediate Sbc-Sc types. Gas contents below 1/10, and even 1/100, of the expectation value have been measured, implying that gas removal is very efficient. The radial extent of the region with significant gas ablation can reach up to 2RA. Within this zone, the proportion of gas-poor spirals increases continuously toward the cluster center. The wealth of 21 cm data collected for the Virgo region has made it possible to study the two-dimensional pattern of H I deficiency in that cluster. The map of gas deficiency in the Virgo central area points to an scenario in which gas losses result from the interaction of the disks with the inner hot intracluster gas around M87. We also find evidence that gas-poor spirals in H I-deficient clusters move in orbits more radial than those of the gas-rich objects. The implications of all these results on models of how galaxies interact with their environment are reviewed. Hydrodynamic effects appear as the most plausible cause of H I removal.

The origin of H I-deficiency in galaxies on the outskirts of the Virgo cluster. I. How far can galaxies bounce out of clusters?

Spiral galaxies that are deficient in neutral hydrogen are observed on the outskirts of the Virgo cluster. If their orbits have crossed the inner parts of the cluster, their interstellar gas may have been lost through ram pressure stripping by the hot X-ray emitting gas of the cluster. We estimate the maximum radius out to which galaxies can bounce out of a virialized system using analytical arguments and cosmological N-body simulations. In particular, we derive an expression for the turnaround radius in a flat cosmology with a cosmological constant that is simpler than previously derived expressions. We find that the maximum radius reached by infalling galaxies as they bounce out of their cluster is roughly between 1 and 2.5 virial radii. Comparing to the virial radius of the Virgo cluster, which we estimate from X-ray observations, these H I-deficient galaxies appear to lie significantly further away from the cluster center. Therefore, if their distances to the cluster core are correct, the H I-deficient spiral galaxies found outside of the Virgo cluster cannot have lost their gas by ram pressure from the hot intracluster gas.

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) - I. The UV luminosity function of the central 12 sq. deg

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering similar to 40 sq. deg in the far UV (FUV, lambda(eff) = 1539 angstrom, Delta lambda = 442 angstrom) and similar to 120 sq. deg in the near UV (NUV, lambda(eff) = 2316 angstrom, Delta lambda = 1060 angstrom). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared - submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early-and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (alpha similar to -1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference.

Structure, mass and distance of the Virgo cluster from a Tolman-Bondi model

We have applied a relativistic Tolman-Bondi model of the Virgo cluster to a sample of 183 galaxies with measured distances within a radius of 8 degrees from M 87. We nd that the sample is signicantly contaminated by background galaxies which lead to too large a cluster mean distance if not excluded. The Tolman-Bondi model predictions, together with the HI deciency of spiral galaxies, allows one to identify these background galaxies. One such galaxy is clearly identied among the 6 calibrating galaxies with Cepheid distances. As the Tolman- Bondi model predicts the expected distance ratio to the Virgo distance, this galaxy can still be used to estimate the Virgo distance, and the average value over the 6 galaxies is 15:4 0:5 Mpc. Well-known background groups of galaxies are clearly recovered, together with laments of galaxies which link these groups to the main cluster, and are falling into it. No foreground galaxy is clearly detected in our sample. Applying the B-band Tully-Fisher method to a sample of 51 true members of the Virgo cluster according to our classication gives a cluster distance of 18:0 1:2 Mpc, larger than the mean Cepheid distance. Finally, the same model is used to estimate the Virgo cluster mass, which is M =1 :2 10 15 M within 8 degrees from the cluster center (2.2 Mpc radius), and amounts to 1.7 virial mass.

The H i Content of Spirals. I. Field Galaxy H i Mass Functions and H i Mass--Optical Size Regressions

A standard parametric maximum-likelihood technique is used to determine both the probability distribution over total HI mass

Merger versus Accretion and the Structure of Dark Matter Halos

M_{\rm HI}

On the Origin of the Inner Structure of Halos

and the regression of this quantity on the linear optical diameter

H I CONTENT AND OPTICAL PROPERTIES OF FIELD GALAXIES FROM THE ALFALFA SURVEY. I. SELECTION OF A CONTROL SAMPLE

D_{\rm o}

Scale radii and aggregation histories of dark haloes

for field giant spirals (Sa-Sc) from a complete HI-flux-limited data set of these objects. Gaussian and Schechter parametrizations of the HI mass function are explored. We find that the available data are equally well described by both models, and that the different morphological classes of giant spirals have HI mass functions which, in general, agree well within the errors. The largest discrepancy corresponds to the Sb-type systems which exhibit a deficit of low HI-mass objects relative to the other types. Using a straightforward generalization of the gaussian model, we have also investigated the linear dependence of