Amelie Saintonge

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 Arecibo Legacy Fast ALFA Survey. IV. Strategies for Signal Identification and Survey Catalog Reliability

We present a signal-extraction utility written for the purposes of the Arecibo Legacy Fast ALFA survey. This survey, when completed, will have covered ~7000 deg2 of the high Galactic latitude sky and should detect over 20,000 extragalactic objects. It is the most sensitive blind H I survey to date. The large size of the survey justifies in itself the need for an automated way of identifying signals in the data set. The matched-filtering signal extractor proposed is based on convolutions in the Fourier domain of templates of varying widths with each spectrum. The chosen templates are built from a simple combination of Hermite functions to mimic the shape of typical Galactic H I profiles of varying widths. The main advantages of this matched-filtering approach are a sensitivity to the total flux of the signals (and not only to peak flux), robustness against instabilities, and short computing times. The details of the algorithm are given here, as well as results of simulations that assess the reliability and completeness of the process.

THE ARECIBO LEGACY FAST ALFA SURVEY. II. RESULTS OF PRECURSOR OBSERVATIONS

In preparation for the full Arecibo Legacy Fast ALFA (ALFALFA) extragalactic H I survey, precursor observations were carried out in 2004 August–September with the seven-beam Arecibo L-band Feed Array (ALFA) receiver system and the Wideband Arecibo Pulsar Processor spectral processors. While these observations were geared mainly at testing and debugging survey strategy, hardware, and software, approximately 48 hr of telescope time yielded science-quality data. The efficiency of system usage (allowing for minor malfunctions and the impact of radio-frequency interference) during that time was 75%. From those observations, an initial list of 730 tentative detections of varying degrees of reliability was extracted. Ninety-eight high signal-to-noise ratio candidates were deemed to be bona fide H I line detections. To test our ability to discriminate cosmic signals from radio-frequency interference and noise, 165 candidates ranging in reliability likelihood were reobserved with the single-beam L-band wide system at Arecibo in 2005 January–February. Of those, 41% were confirmed as real. We present the results of both the ALFA and the single-beam observations for the sample of 166 confirmed H I sources, as well as our assessment of their optical counterparts. Of the 166 sources, 62 coincided with previously known H I sources, while optical redshifts were available for an additional 18 galaxies; thus, 52% of the redshifts reported here were previously unknown. Of the 166 H I detections, 115 are identified with previously cataloged galaxies of either known or unknown redshift, leaving 51 objects identified for the first time. Because of the higher sensitivity of the Arecibo system, fewer than 10% of the 166 H I sources would have been detected by a HIPASS-like survey of the same region. Three of the objects have H I masses less than 107 M⊙. The full ALFALFA survey, which commenced in 2005 February, should detect more than 100 times as many objects of similarly low H I mass over the next 5 years.

The Arecibo Legacy Fast Alfa Survey. V. The H I Source Catalog of the Anti-Virgo Region at δ = +27°

We present a second catalog of H I sources detected in the Arecibo Legacy Fast ALFA Survey. We report 488 detections over 135 deg2, within the region of the sky having 22 h 6.5, where the reliability of the catalog is better than 95% or (b) 5.0 < S/N < 6.5 and a previously measured redshift that corroborates our detection. Of the 488 objects presented here, 49 are high-velocity clouds or clumps thereof with negative heliocentric recession velocities. These clouds are mostly very compact and isolated, while some of them are associated with large features such as Wrights Cloud or the northern extension of the Magellanic Stream. The remaining 439 candidate detections are identified as extragalactic objects and have all been matched with optical counterparts. Five of the six galaxies detected with M ☉ are satellites of either the NGC672/IC1727 nearby galaxy pair or their neighboring dwarf irregular galaxy NGC784. The data of this catalog release include a slice through the Pisces-Perseus foreground void, a large nearby underdensity of galaxies. We report no detections within the void, where our catalog is complete for systems with masses of 108 M ☉. Gas-rich, optically-dark galaxies do not seem to constitute an important void population, and therefore do not suffice for producing a viable solution to the void phenomenon.

Geometrical tests of cosmological models - II. Calibration of rotational widths and disc scaling relations

This is the second in a series of three papers dedicated to a new technique to select galaxies that can act as standard rods and standard candles in order to perform geometrical tests on large samples of high redshift galaxies to constrain different cosmological parameters. The goals of this paper are (1) to compare different rotation indicators in order to understand the relation between rotation velocities extracted from observations of the Hα6563 A line and the [OII]λ3727 A line; and (2) to determine the scaling relations between physical size, surface brightness and magnitude of disc galaxies and their rotation velocity using the SFI++, a large catalog of nearby galaxies observed at I-band. A good correlation is observed between the rotation curve-derived velocities of the Hα- and [OII] observations, as well as between those calculated from velocity histograms, justifying the direct comparison of velocities measured from Her rotation curves in nearby galaxies and from [OII] line widths at higher redshifts. To provide calibration for the geometrical tests, we give expressions for the different scaling relations between properties of galaxies (size, surface brightness, magnitude) and their rotation speeds. We use Malmquist bias-corrected distances from the SFI++ template Tully-Fisher relation to generate a size-rotation velocity relation with unprecedentedly small scatter. We show how the best size-rotation velocity relation is derived when size is estimated not from disc scale lengths but from the isophotal diameter r 23.5 , once these have been corrected for inclination and extinction effects.

Geometrical tests of cosmological models - III. The Cosmology-evolution diagram at z = 1

The rotational velocity of distant galaxies, when interpreted as a size (luminosity) indicator, may be used as a tool to select high redshift standard rods (candles) and probe world models and galaxy evolution via the classical angular diameter-redshift or Hubble diagram tests. We implement the proposed testing strategy using a sample of 30 rotators spanning the redshift range 0.2 < z < 1 with high resolution spectra and images obtained by the VIMOS/VLT Deep Redshift Survey (VVDS) and the Great Observatories Origins Deep Survey (GOODs). We show that by applying at the same time the angular diameter-redshift and Hubble diagrams to the same sample of objects (i.e. velocity selected galactic discs) one can derive a characteristic chart, the cosmology-evolution diagram, mapping the relation between global cosmological parameters and local structural parameters of discs such as size and luminosity. This chart allows to put constraints on cosmological parameters when general prior information about discs evolution is available. In particular, by assuming that equally rotating large discs cannot be less luminous at z = 1 than at present (M(z=1) ≲ M(0)), we find that a flat matter dominated cosmology (Ω_m=1) is excluded at a confidence level of 2 σ and an open cosmology with low mass density (Ωm ˜ 0.3) and no dark energy contribution (ΩΛ) is excluded at a confidence level greater than 1 σ. Inversely, by assuming prior knowledge about the cosmological model, the cosmology-evolution diagram can be used to gain useful insights about the redshift evolution of baryonic discs hosted in dark matter halos of nearly equal masses. In particular, in a Λ CDM cosmology, we find evidence for a bimodal evolution where the low-mass discs have undergone significant surface brightness evolution over the last 8.5 Gyr, while more massive systems have not. We suggest that this dichotomy can be explained by the epochs at which these two different populations last assembled.

Geometrical tests of cosmological models I. Probing dark energy using the kinematics of high redshift galaxies

We suggest to use the observationally measured and theoretically justified correlation between size and rotational velocity of galactic discs as a viable method to select a set of high redshift standard rods which may be used to explore the dark energy content of the universe via the classical angular-diameter test. Here we explore a new strategy for an optimal implementation of this test. We propose to use the rotation speed of high redshift galaxies as a standard size indicator and show how high resolution multi-object spectroscopy and ACS/HST high quality spatial images, may be combined to measure the amplitude of the dark energy density parameter, or to constrain the cosmic equation of state parameter for a smooth dark energy component. We evaluate how systematics may affect the proposed tests, and find that a linear standard rod evolution, causing galaxy dimensions to be up to 30% smaller at z=1.5, can be uniquely diagnosed, and will minimally bias the confidence level contours in the [Omega_Q, w] plane. Finally, we show how to derive, without a priori knowing the specific functional form of disc evolution, a cosmology-evolution diagram with which it is possible to establish a mapping between different cosmological models and the amount of galaxy disc/luminosity evolution expected at a given redshift.

Catalog of Galaxy Morphology in Four Rich Clusters: Luminosity Evolution of Disk Galaxies at 0.33 < z < 0.83*

Hubble Space Telescope (HST) imaging of four rich, X-ray-luminous, galaxy clusters (0.33 < z < 0.83) is used to produce quantitative morphological measurements for galaxies in their fields. Catalogs of these measurements are presented for 1642 galaxies brighter than F814W(AB) = 23.0. Galaxy luminosity profiles are fitted with three models: exponential disk, de Vaucouleurs bulge, and a disk-plus-bulge hybrid model. The best fit is selected and produces a quantitative assessment of the morphology of each galaxy: the principal parameters derived being B/T, the ratio of bulge to total luminosity, the scale lengths and half-light radii, axial ratios, position angles, and surface brightnesses of each component. Cluster membership is determined using a statistical correction for field galaxy contamination, and a mass normalization factor (mass within boundaries of the observed fields) is derived for each cluster. Morphological classes are defined using B/T: disk galaxies have 0 ≤ B/T ≤ 0.4, intermediate galaxies 0.4 < B/T < 0.8, and bulge-dominated galaxies have 0.8 ≤ B/T ≤ 1. In the present paper, this catalog of measurements is used to investigate the luminosity evolution of disk galaxies in the rich-cluster environment. Examination of the relations between disk scale length and central surface brightness suggests, under the assumption that these clusters represent a family who share a common evolutionary history and are simply observed at different ages, that there is a dramatic change in the properties of the small disks (h < 2 kpc). This change is best characterized as a change in surface brightness by ~1.5 mag between z = 0.3 and z = 0.8 with brighter disks at higher redshifts.

Galaxy Morphology in the Rich Cluster Abell 2390

We have analysed images of the field of A2390 obtained with the CFHT and HST. The analysis fits models to bulge and disk components to several hundred galaxies, with about equal samples from the cluster and field. We also have assessed and graded asymmetries in the images. The cluster galaxies are compared in different cluster locations and also compared with field galaxies. We find that the central old population galaxies are bulge-dominated, while disk systems have young populations and are found predominantly in the outer cluster. S0 and bulgy disk galaxies are found throughout, but concentrate in regions of substructure. Disks of cluster blue galaxies are generally brighter and smaller than those in the field. We find that the cluster members have a higher proportion of interacting galaxies than the field sample. Interactions in the cluster and in the field, as well as cluster infall, appear to inhibit star-formation in galaxies.We have analyzed images of the field of Abell 2390 obtained with the Canada-France-Hawaii Telescope and the Hubble Space Telescope. The analysis fits models to bulge and disk components of several hundred galaxies, with about equal samples from the cluster and field. We also have assessed and graded asymmetries in the images. The cluster galaxies are compared in different cluster locations and also compared with field galaxies. We find that the central old population galaxies are bulge-dominated, while disk systems have young populations and are found predominantly in the outer cluster. S0 and bulgy disk galaxies are found throughout but concentrate in regions of substructure. Disks of cluster blue galaxies are generally brighter and smaller than those in the field. We find that the cluster members have a higher proportion of interacting galaxies than the field sample. Interactions in the cluster and in the field, as well as cluster infall, appear to inhibit star formation in galaxies.