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In this paper we describe a focal plane array (FPA) prototype, based on Vivaldi elements, developed for the Westerbork Synthesis Radio Telescope (WSRT) to increase its instantaneous field of view by a factor 25 and double its current bandwidth. This prototype is the first step in a project that has the ambition to equip most of the WSRT antennas with FPAs to improve the survey speed of the telescope. Examples of scientific applications are surveys of the northern sky in polarised continuum and HI emission, and efficient searches for pulsars and transients., Comment: 7 pages, 6 figures. Presented at "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3, 2008, Arecibo Observatory, Puerto Rico. High resolution versions of figures available in jpg-format

We study the location of massive disk galaxies on the Tully-Fisher relation. Using a combination of K-band photometry and high-quality rotation curves, we show that in traditional formulations of the TF relation (using the width of the global HI profile or the maximum rotation velocity), galaxies with rotation velocities larger than 200 km/s lie systematically to the right of the relation defined by less massive systems, causing a characteristic `kink' in the relations. Massive, early-type disk galaxies in particular have a large offset, up to 1.5 magnitudes, from the main relation defined by less massive and later-type spirals. The presence of a change in slope at the high-mass end of the Tully-Fisher relation has important consequences for the use of the Tully-Fisher relation as a tool for estimating distances to galaxies or for probing galaxy evolution. In particular, the luminosity evolution of massive galaxies since z = 1 may have been significantly larger than estimated in several recent studies. We also show that many of the galaxies with the largest offsets have declining rotation curves and that the change in slope largely disappears when we use the asymptotic rotation velocity as kinematic parameter. The remaining deviations from linearity can be removed when we simultaneously use the total baryonic mass (stars + gas) instead of the optical or near-infrared luminosity. Our results strengthen the view that the Tully-Fisher relation fundamentally links the mass of dark matter haloes with the total baryonic mass embedded in them., Comment: 12 pages, 7 figures. Accepted for publication in MNRAS

We have carried out the harmonic analysis of the atomic hydrogen (HI) surface density maps and the velocity fields for 11 galaxies belonging to the Ursa Major group, over a radial range of 4-6 disc scalelengths in each galaxy. This analysis gives the radial variation of spatial lopsidedness, quantified by the Fourier amplitude A$_1$ of the m=1 component normalised to the average value. The kinematical analysis gives a value for the elongation of the potential to be $\sim 10 % $. The mean amplitude of spatial lopsidedness is found to be $\sim 0.14$ in the inner disc, similar to the field galaxies, and is smaller by a factor of $\sim 2$ compared to the Eridanus group galaxies. It is also shown that the the average value of A$_1$ does not increase with the Hubble type, contrary to what is seen in field galaxies. We argue that the physical origin of lopsidedness in the Ursa Major group of galaxies is tidal interactions, albeit weaker and less frequent than in Eridanus. Thus systematic studies of lopsidedness in groups of galaxies can provide dynamical clues regarding the interactions and evolution of galaxies in a group environment., Comment: 12 pages, 7 figures, 3 tables. Accepted for publication by MNRAS

SUMMARIZED ABSTRACT: We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy was obtained using PMAS/PPAK@3.5m CAHA to obtain a complete flux limited sample of cluster members within its field-of-view (~74"X64"). In addition of 31 galaxies with known redshifts in the outer regions, we built up a final sample of 59 spectroscopically confirmed cluster members. Multiban photometry and detailed morphologies were obtained using deep images taken with the HST/ACS camera in the BVRI and z-bands. The CM diagram shows that the E-type galaxies cover the range of brighter and redder colors. A large fraction of spiral galaxies ($\sim$50%) is found. They cover a wide range in colors. This result, together with the distributions of ages, metallicities and masses, indicates that E-type galaxies are more massive and have older stellar populations, while L-type galaxies are less massive and have a wider range of stellar Our results agree with a proposed two-step scenario for the evolution of galaxies in clusters. In addition, an extremely blue merging galaxy system is found at the core, with the nominal redshift of the cluster., Comment: 29 pages, 17 figures, accepted for publishing in MNRAS. (HST/ACS composite image: http://www.caha.es/sanchez/abell2218/BRI_big.jpg)

We present a low-resolution spectroscopic survey of the Orion nebula which data we release for public use. In this article, we intend to show the possible applications of this dataset analyzing some of the main properties of the nebula. We perform an integral field spectroscopy mosaic of an area of ~5' X 6' centered on the Trapezium region of the nebula, including the ionization front to the south-east. The analysis of the line fluxes and line ratios of both the individual and integrated spectra allowed us to determine the main characteristics of the ionization throughtout the nebula.The final dataset comprises 8182 individual spectra, which sample each one a circular area of \~2.7" diameter. The data can be downloaded as a single row-stacked spectra fits file plus a position table or as an interpolated datacube with a final sampling of 1.5"/pixel. The integrated spectrum across the field-of-view was used to obtain the main integrated properties of the nebula, including the electron density and temperature, the dust extinction, the Halpha integrated flux (after correcting for dust reddening), and the main diagnostic line ratios. The individual spectra were used to obtain line intensity maps of the different detected lines. These maps were used to study the distribution of the ionized hydrogen, the dust extinction, the electron density and temperature, and the helium and oxygen abundance..., Comment: 13 pages, 8 figures, accepted for publishing in Astronomy & Astrophysics

We report on integral field spectrocopy observations, performed with the PPAK module of the PMAS spectrograph, covering a field-of-view of ~74''X64'' centered on the core of the galaxy cluster Abell 2218. A total of 43 objects were detected, 27 of them galaxies at the redshift of the cluster. We deblended and extracted the integrated spectra of each of the objects in the field using an adapted version of galfit for 3D spectroscopy (galfit3d). We use these spectra, in combination with morphological parameters derived from deep HST/ACS images, to study the stellar population and evolution of galaxies in the core of this cluster., Comment: 5 pages, 3 figures

A comprehensive analysis of 355 high-quality WSRT HI 21-cm line maps of nearby galaxies shows that the properties and incident rate of Damped Lyman-alpha (DLA) absorption systems observed in the spectra of high redshift QSOs are in good agreement with DLAs originating in gas disks of galaxies like those in the z~0 population. Comparison of low-z DLA statistics with the HI incidence rate and column density distribution f(N) for the local galaxy sample shows no evidence for evolution in the integral "cross section density" below z~1.5, implying that there is no need for a hidden population of galaxies or HI clouds to contribute significantly to the DLA cross section. Compared with z~4, our data indicates evolution of a factor of two in the comoving density along a line of sight. We find that dN/dz(z=0)=0.045 +/- 0.006. The idea that the local galaxy population can explain the DLAs is further strengthened by comparing the properties of DLAs and DLA galaxies with the expectations based on our analysis of local galaxies. The distribution of luminosities of DLA host galaxies, and of impact parameters between QSOs and the centres of DLA galaxies, are in good agreement with what is expected from local galaxies. Approximately 87% of low z DLA galaxies are expected to be fainter than L* and 37 per cent have impact parameters less than 1'' at z=0.5. The analysis shows that some host galaxies with very low impact parameters and low luminosities are expected to be missed in optical follow up surveys. The well-known metallicity-luminosity relation in galaxies, in combination with metallicity gradients in galaxy disks, cause the expected median metallicity of low redshift DLAs to be low (~1/7 solar), which is also in good agreement with observations of low z DLAs. (Abridged), Comment: 22 pages, 22 figures. Accepted for publication in MNRAS. Fixed typos

We calculate in detail the expected properties of low redshift DLA systems under the assumption that they arise in the gaseous disks of galaxies like those in the z=0 population. A sample of 355 nearby galaxies is analysed, for which high quality HI 21-cm emission line maps are available as part of an extensive survey with the Westerbork telescope (WHISP). We find that expected luminosities, impact parameters between quasars and DLA host galaxies, and metal abundances are in good agreement with the observed properties of DLAs and DLA galaxies. The measured redshift number density of z=0 gas above the DLA limit is dN/dz=0.045 +/- 0.006, which compared to higher redshift measurements implies that there is no evolution in the comoving density of DLAs along a line of sight between z=1.5 and z=0, and a decrease of only a factor of two from z=4 to the present time. We conclude that the local galaxy population can explain all properties of low redshift DLAs., Comment: 6 pages, 2 figures. To appear in "Island Universes - Structure and Evolution of Disk Galaxies", Terschelling (Netherlands), July 2005

The unsurpassed sensitivity and resolution of the Square Kilometer Array (SKA) will make it possible for the first time to probe the continuum emission of normal star forming galaxies out to the edges of the universe. This opens the possibility for routinely using the radio continuum emission from galaxies for cosmological research as it offers an independent probe of the evolution of the star formation density in the universe. In addition it offers the possibility to detect the first star forming objects and massive black holes. In deep surveys SKA will be able to detect HI in emission out to redshifts of $z \approx 2.5$ and hence be able to trace the conversion of gas into stars over an era where considerable evolution is taking place. Such surveys will be able to uniquely determine the respective importance of merging and accreting gas flows for galaxy formation over this redshift range (i.e. out to when the universe was only one third its present age). It is obvious that only SKA will able to see literally where and how gas is turned into stars. These and other aspects of SKA imaging of galaxies will be discussed., Comment: To be published in New Astronomy Reviews, Elsevier, Amsterdam as part of "Science with the Square Kilometre Array", eds. C. Carilli and S. Rawlings. 18 pages + 13 figures; high resolution version and other chapters of "Science with the Square Kilometre Array" available at http://www.skatelescope.org/pages/science_gen.htm

Systematic effects on HI and Halpha long-slit observations make a measurement of the inner slope of the dark matter density distribution difficult to determine. Halos with constant density cores and ones with r^-1 profiles both appear consistent with the data, although constant density cores generally provide better fits. High-resolution, two-dimensional velocity fields remove most of the systematic effects, yet as a result of noncircular and random motions the inner slopes still cannot be accurately measured. Halo concentration parameters provide a more useful test of cosmological models because they are more tightly constrained by observations. The concentration parameters for LSB galaxies appear consistent with, but on the low end of the distribution predicted by CDM., Comment: Proceedings IAU 220 "Dark Matter in Galaxies", Eds. S. Ryder et al

We present a high resolution, SparsePak two-dimensional velocity field for the center of the low surface brightness (LSB) galaxy DDO 39. These data are a significant improvement on previous HI or Halpha long slit data, yet the inner rotation curve is still uncertain due to significant noncircular and random motions. These intrinsic uncertainties, probably present in other LSB galaxies too, result in a wide range of inner slopes being consistent with the data, including those expected in cold dark matter (CDM) simulations. The halo concentration parameter provides a more useful test of cosmological models than the inner slope as it is more tightly constrained by observations. DDO 39's concentration parameter is consistent with, but on the low end of the distribution predicted by CDM., Comment: 4 pages, accepted for publication in ApJ Letters

The Tully-Fisher relations for a complete sample of spirals in the Ursa Major cluster is investigated. The merits of combining B, R, I and K' photometry with HI rotation curves (RCs) have been exploited. In addition to the corrected HI global profile widths W_{R,I}^i, the HI RCs allow direct measurements of the maximum rotation Vmax and the amplitudes Vflat of the outer flat parts. The dynamical state of the gas disks could also be determined in detail. For large galaxy samples, the M^{b,i}_R - Log(W_{R,I}^i) correlation in conjunction with strict selection criteria is preferred for distance determinations with a 7% accuracy. Galaxies with rising RCs at the last measured point lie systematically on the low velocity side of the TF-relation. Galaxies with partly declining RCs (Vmax>Vflat) tend to lie on the high velocity side when using W_{R,I}^i or Vmax. These trends are eliminated when Vflat is used. The M^{b,i}_B - Log(2Vflat) residuals correlate consistently with morphology, color, surface brightness and gas mass fraction. These correlations are absent for the near-IR M^{b,i}_K' - Log(2Vflat) residuals. The tightest correlation (Xred=1.1) is found for the M^{b,i}_K' - Log(2Vflat) relation with a slope of -11.3 +/- 0.5 and a total scatter of 0.26^m with a most likely intrinsic scatter of zero. The tightness of the near-IR correlation is preserved when converting it into a baryonic TF-relation which has a slope of -10.0 for (Mgas/L_K')=1.6 while a zero intrinsic scatter remains most likely. The tightness of the near-IR and baryonic correlations suggests that the TF-relation reflects a correlation between the dark matter halo mass, indicated by Vflat, and the total baryonic mass Mbar where Mbar~Vflat^4. The distribution of the baryons inside halos of similar mass is irrelevant for this relation., Comment: 24 pages, 9 tables, 9 figures. Accepted for publication in the Astrophysical Journal

We present VLA H I observations of the low surface brightness galaxy UGC 12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy 2333+1234. UGC 12695 shows solid body rotation but has a very lopsided morphology of the H I disk, with the majority of the H I lying in the southern arm of the galaxy. The H I column density distribution of this very blue, LSB galaxy coincides in detail with its light distribution. Comparing the H I column density of UGC 12695 with the empirical (but not well understood) value of Sigma_c = 10E21 atoms/cm^2 found in, i.e., Skillman's 1986 paper shows the star formation to be a local affair, occurring only in those regions where the column density is above this star formation threshold. The low surface brightness nature of this galaxy could thus be attributed to an insufficient gas surface density, inhibiting star formation on a more global scale. Significantly, though, the Toomre criterion places a much lower critical density on the galaxy (+/-10E20 atoms/cm^2), which is shown by the galaxy's low SFR to not be applicable. Within a projected distance of 300kpc/30kms of UGC 12695 lie two companion galaxies - UGC 12687, a high surface brightness barred spiral galaxy, and 2333+1234, a dwarf galaxy discovered during this investigation. The close proximity of the three galaxies, combined with UGC 12695's extremely blue color and regions of localized starburst and UGC 12687's UV excess bring to mind mutually induced star formation through tidal activity., Comment: 14 pages, 8 figures (2 color), To be published in A.J., May 2000?

This is the third in a series of papers in which spiral galaxy rotation curves are considered in the context of Milgrom's modified dynamics (MOND). The present sample of 30 objects is drawn from a complete sample of galaxies in the Ursa Major cluster with photometric data by Tully et al. (1996) and 21 cm line data by Verheijen (1997). The galaxies are roughly all at the same distance (15 to 16 Mpc). The radio observations are made with the Westerbork Synthesis Array which means that the linear resolution of all rotation curves is comparable. The greatest advantage of this sample is the existance of K'-band surface photometry for all galaxies; the near-infrared emission, being relatively free of the effects of dust absorption and less sensitive to recent star formation, is a more precise tracer of the mean radial distribution of the dominant stellar population. The predicted rotation curves are calculated from the K'-band surface photometry and the observed distribution of neutral hydrogen using the simple MOND prescription where the one adjustable parameter is the mass of the stellar disk or the implied mass-to-light ratio. The predicted rotation curves generally agree with the observed curves and the mean M/L in the near-infrared is about 0.9 with a small dispersion. The fitted M/L in the B-band is correlated with B-V color in the sense predicted by population synthesis models. Including earlier work, about 80 galaxy rotation curves are now well-reproduced from the observed distribution of detectable matter using the MOND formula to calculate the gravitational acceleration; this lends considerable observational support to Milgrom's unconventional hypothesis., Comment: 19 pages, 9 figures, aas style, ApJ in press. Updated and corrected references, content unchanged

Magnitude-limited samples of spiral galaxies drawn from the Ursa Major and Pisces clusters are used to determine their extinction properties as a function of inclination. Imaging photometry is available for 87 spirals in B,R,I and K' bands. Extinction causes systematic scatter in color-magnitude plots. A strong luminosity dependence is found. Relative edge-on to face-on extinction of up to 1.7 mag is found at B for the most luminous galaxies but is unmeasurably small for faint galaxies. At R the differential absorption with inclination reaches 1.3 mag, at I it reaches 1.0 mag, and at K' the differential absorption can in the extreme be as great as 0.3 mag. The luminosity dependence of reddening can be translated into a dependence on rotation rate which is a distance-independent observable. Hence, corrections can be made that are useful for distance measurements. The strong dependence of the corrections on luminosity act to steepen luminosity-linewidth correlations. The effect is greatest toward the blue, with the consequence that luminosity-linewidth slope dependencies are now only weakly a function of color., Comment: 23 pages, 5 figures

We present observations made with the Westerbork Synthesis Radio Telescope of HI emission from Dwingeloo 1, a nearby barred spiral discovered during the Dwingeloo Obscured Galaxies Survey for galaxies hidden in the Zone of Avoidance, and of Dwingeloo 2, a small galaxy discovered in the beam of these WSRT observations. The WSRT data reveal the position of the dynamical center of Dw1, its systemic LSR velocity, its total (projected) width in velocity, its inclination on the sky, and its integrated HI flux, as well as details of the velocity field and gas distribution. Dw1 is the nearest grand-design barred spiral system, and is probably amongst the ten largest galaxies closer than about 5 Mpc. We report here also the discovery of Dwingeloo 2, a small galaxy located within the WSRT primary beam as pointed to Dw1. In view of its angular and kinematic proximity to Dw1, Dw2 may well be a companion to the larger system. The two galaxies are probably both members of the group containing Maffei 1 & 2 and IC342 and may influence the peculiar motions within that group and the morphology of its individual members., Comment: A LATEX file without figures. The postscript version (1Mb in gzipped format) including all the figures can be retrieved from http://www.astro.rug.nl:80/~secr/ Accepted for publication in Astronomy & Astrophysics