The Atacama Large Millimeter/submillimeter Array: Overview & status

The Atacama Large Millimeter/submillimeter Array (ALMA) is an international radio telescope under construction in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components: an array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ~14 km, and a set of four 12-m and twelve 7-m antennas operating in closely-packed configurations ~50m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators

A Study of the Large-Scale Distribution of Galaxies in the South Galactic Pole Region: II. Further Evidence for a Preferential Clustering Scale?

We analyse a set of new pencil-beam galaxy redshift data in three small regions around the South Galactic Pole (SGP) area. We investigate whether we can find any evidence of the quasi-periodic peaks discovered by Broadhurst et al. (1990) in the distribution of galaxies along the NGP-SGP directions. We use both a power spectrum analysis and a cross-correlation with a sliding comb-like window (the comb-template technique). Despite the data are less deep (~600 h^{-1} Mpc) and certainly not optimal for such an investigation, there is evidence of the same preferential ~130 h^{-1} Mpc scale in two fields displaced respectively 15 and 30 degrees West of the Broadhurst et al. original probe. Taken alone, however, this peak would not be statistically distinguishable from a noise fluctuation. Nevertheless, the statistical significance of the detection raises to 99% when one considers the CONDITIONAL probability of finding a peak around THE SAME scale measured by Broadhurst et al.Comment: 5 LaTeX mn-style pages plus 3 tables and 7 PS figures, uses mn.sty, accepted for publication in MNRA

A Study of the Large--Scale Distribution of Galaxies in the South Galactic Pole Region: I. The Data

We present the data from an extensive, moderately deep (b_J = 19.5) spectroscopic survey of $\sim 600$ galaxies within four regions of sky located near the South Galactic Pole. About 75% of the measured galaxies are in a 3deg x 1.5deg region dominated by the rich cluster Klemola 44 (Abell 4038). The other three smaller areas cover about 1 square degree each. Here we discuss in detail the observing and data reduction strategies, the completeness and errors on the measured redshifts. The data collected are being used for: (1) a study of the large--scale redshift distribution of the galaxies in each field, and (2) a thorough dynamical investigation of Klemola 44. Results from these analyses will be presented in forthcoming papers.Comment: 7 MN-style text pages + 5 reduced-size tables, all in uu-compressed- tarred PS format. 16 figures available in hardcopy from the authors. MNRAS, in pres

Infrared Candidates for the Intense Galactic X-ray Source GX 17+2

We present new astrometric solutions and infrared Hubble Space Telescope observations of GX 17+2 (X1813-140), one of the brightest X-ray sources on the celestial sphere. Despite 30 years of intensive study, and the existence of a strong radio counterpart with a sub-arcsecond position, the object remains optically unidentified. The observed X-ray characteristics strongly suggest that it is a so-called "Z-source," the rare but important category that includes Sco X-1 and Cyg X-2. Use of the USNO-A2.0 catalog enables us to measure the position of optical and infrared objects near the radio source to sub-arcsecond precision within the International Celestial Reference Frame, for direct comparison with the radio position, which we also recompute using modern calibrators. With high confidence we eliminate the V~17.5 star NP Ser, often listed as the probable optical counterpart of the X-ray source, as a candidate. Our HST NICMOS observations show two faint objects within our 0.5" radius 90% confidence error circle. Even the brighter of the two, Star A, is far fainter than expected (H~19.8), given multiple estimates of the extinction in this field and our previous understanding of Z sources, but it becomes the best candidate for the counterpart of GX 17+2. The probability of a chance coincidence of an unrelated faint object on the radio position is high. However, if the true counterpart is not Star A, it is fainter still, and our conclusion that the optical counterpart is surprisingly underluminous is but strengthened.Comment: 15 pages including 3 figures and 3 tables. Accepted for publication in The Astrophysical Journa

Infrared Photometric Variability of GX13+1 and GX17+2

We present infrared photometry of the Galactic Bulge X-ray binary systems GX13+1 and GX17+2 obtained in 1997 July and August using OSIRIS on the 1.8m Perkins Telescope at Lowell Observatory. GX13+1 clearly varies over ~0.6 magnitudes in the K-band. Our light curve suggests a modulation on a timescale of ~20 days, which is in agreement with previously proposed orbital periods for the system. The IR counterpart of GX17+2 is also variable in the K-band over \~0.8 magnitudes on a timescale of days to weeks, extending the variability first seen by Naylor, Charles, & Longmore (1991). We discuss the implications our data have for Deutsch et al's (1999) identification of ``star A'' as the true IR counterpart of GX17+2. The variability observed in our photometry of the blend of star A and the foreground star NP Ser implies a ~4 magnitude intrinsic variation in the K-band for GX17+2.Comment: Accepted for publication in ApJ, 5 pages, 4 figure

Tests with a Carlina-type diluted telescope; Primary coherencing

Studies are under way to propose a new generation of post-VLTI interferometers. The Carlina concept studied at the Haute- Provence Observatory is one of the proposed solutions. It consists in an optical interferometer configured like a diluted version of the Arecibo radio telescope: above the diluted primary mirror made of fixed cospherical segments, a helium balloon (or cables suspended between two mountains), carries a gondola containing the focal optics. Since 2003, we have been building a technical demonstrator of this diluted telescope. First fringes were obtained in May 2004 with two closely-spaced primary segments and a CCD on the focal gondola. We have been testing the whole optical train with three primary mirrors. The main aim of this article is to describe the metrology that we have conceived, and tested under the helium balloon to align the primary mirrors separate by 5-10 m on the ground with an accuracy of a few microns. The servo loop stabilizes the mirror of metrology under the helium balloon with an accuracy better than 5 mm while it moves horizontally by 30 cm in open loop by 10-20 km/h of wind. We have obtained the white fringes of metrology; i.e., the three mirrors are aligned (cospherized) with an accuracy of {\approx} 1 micron. We show data proving the stability of fringes over 15 minutes, therefore providing evidence that the mechanical parts are stabilized within a few microns. This is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or under a balloon. Carlina, like the MMT or LBT, could be one of the first members of a new class of telescopes named diluted telescopes.Comment: 18 pages, 17 figures, A&A, accepte

The V-band luminosity function of galaxies in A2151

We present a wide field $V$-band imaging survey of approximately 1 deg$^2$ ($\sim7.2 h^{-2}_{75}$ Mpc$^{2}$) in the direction of the nearby cluster of galaxies Abell 2151 (the Hercules Cluster). The data are used to construct the luminosity function (LF) down to $M_V \approx -14.85$, thus allowing us to study the dwarf galaxy population in A2151 for the first time. The obtained global LF is well described by a Schechter function with best-fit parameters $\alpha = -1.29^{+0.09}_{-0.08}$ and $M_V^* = -21.41^{+0.44}_{-0.41}$. The radial dependence of the LF was investigated, with the faint-end slope tending to be slightly steeper in the outermost regions and farther away than the virial radius. Given the presence of significant substructure within the cluster, we also analysed the LFs in three different regions. We find that the dwarf to giant ratio increases from the northern to the southern subcluster, and from low to high local density environments, although these variations are marginally significant (less than 2$\sigma$).Comment: Accepted for publication in A&

A study of HI-selected galaxies in the Hercules cluster

The present study is aimed at a sample of 22 galaxies detected in the blind VLA HI survey of the Hercules cluster by Dickey (1997), 18 of which were selected on an HI line width smaller than 270 km/s and 4 others with only tentative optical counterparts on the Palomar Sky Survey. Sensitive single-dish HI line spectra were obtained for 20 of them, and for one (47-154) the VLA detection was not confirmed. Optical surface photometry was obtained of 10 objects, for 8 of which optical spectroscopy was obtained as well. Based on various selection criteria, two (ce-143 and ne-204) can be classified as dwarfs. The objects of which optical observations were made show star formation properties similar to those of published samples of actively star forming galaxies, and approximately half of them have properties intermediate between those of dwarf galaxies and low-luminosity disc galaxies. No optical redshifts could be obtained for two of the galaxies (sw-103 and sw-194) and their physical association with the HI clouds detected at their positions therefore remains uncertain. Unique among the objects is the Tidal Dwarf Galaxy ce-061 in a tail of the IC 1182 merger system.Comment: 20 pages, 19 figures, accepted for publication in A&

The Hierarchical Structure and Dynamics of Voids

Contrary to the common view voids have very complex internal structure and dynamics. Here we show how the hierarchy of structures in the density field inside voids is reflected by a similar hierarchy of structures in the velocity field. Voids defined by dense filaments and clusters can de described as simple expanding domains with coherent flows everywhere except at their boundaries. At scales smaller that the void radius the velocity field breaks into expanding sub-domains corresponding to sub- voids. These sub-domains break into even smaller sub-sub domains at smaller scales resulting in a nesting hierarchy of locally expanding domains. The ratio between the magnitude of the velocity field responsible for the expansion of the void and the velocity field defining the sub voids is approximately one order of magnitude. The small-scale components of the velocity field play a minor role in the shaping of the voids but they define the local dynamics directly affecting the processes of galaxy formation and evolution. The super-Hubble expansion inside voids makes them cosmic magnifiers by stretching their internal primordial density fluctuations allowing us to probe the small scales in the primordial density field. Voids also act like time machines by "freezing" the development of the medium-scale density fluctuations responsible for the formation of the tenuous web of structures seen connecting proto galaxies in computer simulations. As a result of this freezing haloes in voids can remain "connected" to this tenuous web until the present time. This may have an important effect in the formation and evolution of galaxies in voids by providing an efficient gas accretion mechanism via coherent low-velocity streams that can keep a steady inflow of matter for extended periods of time.Comment: High-res version are related media here: http://skysrv.pha.jhu.edu/~miguel/Papers/Hierarchy_voids/index.htm

High-redshift objects as probes of nearby cosmic voids

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