arXiv subjects

W. van Driel

Publications and source records attributed to W. van Driel.

At least 55 records · Page 3Linked to original sources

arXiv2007

NIBLES: an HI census of local SDSS galaxies

NIBLES is a Key Project proposed for the 100m-class Nancay Radio Telescope (NRT) in France. Its aim is a census of the HI gas content and dynamics of 4,000 Sloan Digital Sky Survey galaxies in the Local Volume (900<cz<12,000 km/s). The galaxies were selected based on their total stellar mass (absolute z-band magnitude Mz), and are distributed evenly over the entire range of Mz covered by local SDSS galaxies (-10 to -24 mag, for H0=70 km/s/Mpc). A pilot survey is being made of over 600 galaxies. NIBLES will be complementary to the ALFALFA and EBHIS blind HI surveys, which will detect a different ensemble of local galaxies, and which our pilot survey results indicate will detect about 40-45% of the NIBLES sample. NIBLES is an open collaboration and anyone interested in the science and willing to contribute to the project is welcome to join the score of NIBLErS.

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arXiv2007

The Arecibo Galaxy Environment Survey: II. A HI view of the Abell cluster 1367 and its outskirts

We present 21 cm HI line observations of 5x1 square degrees centered on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new HI measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the HI data with SDSS optical imaging we show that our HI selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between HI and optically selected samples resides in their large scale distribution: whereas optical and X-ray observations trace the cluster core very well, in HI there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and HI distribution for samples selected at different wavelength are also discussed.

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arXiv2006

NGC5719/13: interacting spirals forming a counter-rotating stellar disc

(Context) When a galaxy acquires material from the outside, it is likely that the resulting angular momentum of the accreted material is decoupled from that of the pre-existing galaxy. The presence of stars counter-rotating with respect to other stars and/or gas represents an extreme case of decoupling. (Aims) NGC5719, an almost edge-on Sab galaxy with a prominent skewed dust lane, shows a spectacular on-going interaction with its face-on Sbc companion NGC5713. Observations of such interacting systems provide insight into the processes at work in assembling and reshaping galaxies. (Methods) Studies were made of the distribution and kinematics of neutral hydrogen in the NGC5719/13 galaxy pair and the ionised gas and stellar kinematics along the major axis of NGC5719. (Results) Two HI tidal bridges that loop around NGC5719 and connect to NGC5713, and two HI tidal tails departing westward from NGC5713 were detected. There is a correspondence between the HI condensations and the location of clumps of young stars within and outside the disc of NGC5719. The low-mass satellite PGC135857 at the tip of the northern tail was detected in HI, and is likely a by-product of the interaction. The neutral and ionised hydrogen in the disc of NGC5719 are counter-rotating with respect to the main stellar disc. The counter-rotating stellar disc contains about 20% of the stars in the system, and has the same radial extension as the main stellar disc. This is the first interacting system in which a counter-rotating stellar disc has been detected. (Conclusions) The data support a scenario where HI from the large reservoir available in the galaxy's surroundings was accreted by NGC5719 onto a retrograde orbit and subsequently fuelled the in-situ formation of the counter-rotating stellar disc.

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arXiv2006

The Arecibo Galaxy Environments Survey - Description and Early Results

The Arecibo Galaxy Environments Survey (AGES) is a 2000-hour neutral hydrogen (HI) survey using the new Arecibo L-band Feed Array (ALFA) multibeam instrument at Arecibo Observatory. It will cover 200 square degrees of sky, sampling a range of environments from the Local Void through to the Virgo Cluster with higher sensitivity, spatial resolution and velocity resolution than previous neutral hydrogen surveys.

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arXiv2005

Completing HI observations of galaxies II. The Coma Supercluster

High sensitivity 21-cm HI line observations, with an rms noise level of \sim 0.5 mJy, were made of 35 spiral galaxies in the Coma Supercluster, using the refurbished Arecibo telescope, which resulted in the detection of 25 objects. These data, combined with the measurements available from the literature, provide the set of HI data for 94% of all late-type galaxies in the Coma Supercluster with an apparent photographic magnitude m_p <15.7 mag. We confirm that the typical scale of HI deficiency around the Coma cluster is 2 Mpc, i.e. one virial radius. Comparing the HI mass function (HIMF) of cluster with non-cluster members of the Coma Supercluster we detect a shortage of high HI mass galaxies among cluster members that can be ascribed to the pattern of HI deficiency found in rich clusters.

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arXiv2005

A Dark Galaxy in the Virgo Cluster Imaged at 21-cm

Dark Matter supposedly dominates the extragalactic, yet no totally dark structure of galactic proportions has ever been convincingly identified. Earlier (Minchin et al. 2005) we suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster at Jodrell Bank using single-dish observations (Davies et al. 2004), was probably such a dark galaxy because of its broad line-width (~ 200 km/s) unaccompanied by any visible gravitational source to account for it. Now we have managed to image VIRGOHI 21 in the neutral-hydrogen line, and indeed we find what appears to be a dark, edge-on, spinning disc with the mass and diameter of a typical spiral galaxy. Moreover the disc has unquestionably interacted with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor invariably responsible for such a feature. Published numerical models (Vollmer, Huchtmeier & van Driel 2005) of NGC 4254 call for a close interaction ~ 10^8 years ago with a perturber of 10^11 solar masses. This we take as completely independent evidence for the massive nature of VIRGOHI 21.

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arXiv2005

NGC 4254: a spiral galaxy entering the Virgo cluster

Deep Effelsberg HI spectra of the one-armed, bright Virgo cluster spiral galaxy NGC 4254 are presented.Five different positions were observed in the 21 cm HI line with the Effelsberg 100-m telescope: one in the center and 4 located one HPBW to the NE, NW, SW, and SE, respectively, from the galaxy center. The spectra are compared to existing deep VLA observations, and the single dish and interferometric HI data are used to constrain a dynamical model which includes the effects of ram pressure. The peculiar, one-armed spiral pattern of NGC 4254 and its distorted and kinematically perturbed atomic gas distribution can be explained by a close and rapid encounter ~280 Myr ago with another massive Virgo galaxy, followed by ram pressure stripping that is still ongoing. The stripping occurs almost face-on, since the angle between the disk and the orbital plane is 70 degrees. The galaxy with which NGC 4254 had its encounter is tentatively identified as the lenticular NGC 4262.

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arXiv2005

The precision of large radio continuum source catalogues- An application of the SPECFIND tool

The accuracy in position and flux density of 19 large radio continuum source catalogues has been determined using SPECFIND, a new tool recently made available through the CDS. The ~67000 radio continuum spectra with three or more frequencies produced by SPECFIND were used to cross-correlate sources from different catalogues and to calculate offsets in right ascension and declination in the various catalogues with respect to the positions given in the NRAO VLA Sky Survey (NVSS) catalogue, which was adopted as a reference. The flux densities reported in the catalogues were compared to those predicted by the composite spectra, enabling us to assess the quality of the flux density calibration of the different catalogues.

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arXiv2004

Galaxy transmutations: The double ringed galaxy ESO 474-G26

Surface photometry and a 21cm HI line spectrum of the giant double-ringed galaxy ESO 474-G26 are presented. The morphology of this system is unique among the 30,000 galaxies with >B15. Two almost orthogonal optical rings with diameters of 60 and 40 kpc surround the central body (assuming H0=70 km/s/Mpc). The outer one is an equatorial ring, while the inner ring lies in a nearly polar plane. The rings have blue optical colors typical of late-type spirals. Both appear to be rotating around the central galaxy, so that this system can be considered as a kinematically confirmed polar ring galaxy. Its observational characteristics are typical of galaxy merger remnants. Although the central object has a surface brightness distribution typical of elliptical galaxies, it has a higher surface brightness for its effective radius than ordinary ellipticals. Possible origins of this galaxy are discussed and numerical simulations are presented that illustrate the formation of the two rings in the merging process of two spiral galaxies, in which the observed appearance of ESO 474-G26 appears to be a transient stage.

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arXiv2004

The Dwarf LSB Galaxy Population of the Virgo Cluster II. Colours and HI line observations

In order to investigate the nature of dwarf Low Surface Brightness (LSB) galaxies we have undertaken a deep B and I band CCD survey of a 14 sq degree strip in the Virgo Cluster and applied a Fourier convolution technique to explore its dwarf galaxy population down to a central surface brightness of 26 B mag/sq arcsec and a total absolute B mag of ~ -10. In this paper we carry out an analysis of their morphology, (B-I) colours and atomic hydrogen content. We compare these properties with those of dwarf galaxies in other environments to try and assess how the cluster environment has influenced their evolution. Field dwarfs are generally of a more irregular morphology, are bluer and contain relatively more gas. We assess the importance that various physical processes have on the evolution of cluster dwarf galaxies (ram pressure stripping, tidal interactions, supernova driven gas loss). We suggest that enhanced star formation triggered by tidal interactions is the major reason for the very different general properties of cluster dwarfs: they have undergone accelerated evolution.

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arXiv2004

A method for determining radio continuum spectra, and its application to large surveys

A new tool to extract cross-identifications and radio continuum spectra from radio catalogues contained in the VIZIER database of the CDS is presented. The code can handle radio surveys at different frequencies with different resolutions. It has been applied to 22 survey catalogues at 11 different frequencies containing a total of 3.5 million sources, which resulted in over 700000 independent radio cross-identifications and ~67000 independent radio spectra with more than two frequency points. A validation of the code has been performed using independent radio cross-correlations from the literature. The mean error of the determined spectral index is +-0.3. The code produces an output of variable format that can easily be adapted to the purpose of the user.

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arXiv2004

Completing HI observations of galaxies in the Virgo cluster

High sensitivity (rms noise $\sim 0.5$ mJy) 21-cm HI line observations were made of 33 galaxies in the Virgo cluster, using the refurbished Arecibo telescope, which resulted in the detection of 12 objects. These data, combined with the measurements available from the literature, provide the first set of HI data that is complete for all 355 late-type (Sa-Im-BCD) galaxies in the Virgo cluster with $m_p \leq 18.0$ mag. The Virgo cluster HI mass function (HIMF) that was derived for this optically selected galaxy sample is in agreement with the HIMF derived for the Virgo cluster from the blind HIJASS HI survey and is inconsistent with the Field HIMF. This indicates that both in this rich cluster and in the general field, neutral hydrogen is primarily associated with late-type galaxies, with marginal contributions from early-type galaxies and isolated HI clouds. The inconsistency between the cluster and the field HIMF derives primarily from the difference in the optical luminosity function of late-type galaxies in the two environments, combined with the HI deficiency that is known to occur in galaxies in rich clusters.

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arXiv2004

A new HI catalog of Low Surface Brightness galaxies out to z=0.1 - Tripling the number of massive LSB galaxies Known

Using both the Arecibo 305m and the Nancay decimetric 100-m class radio telescopes, we have observed the HI line of 116 Low Surface Brightness (LSB) galaxies from the Bothun et al. 1985 subset of LSB galaxies in the Uppsala General Catalog. The observations had a detection rate of 70%, resulting in the new determination of HI properties for 81 galaxies. Surprisingly, roughly half of the detected objects (38) have M_HI >= 10^10 M_sol, placing them into the category of massive LSB galaxies. As previously only ~18 of these `Malin 1 cousins' were known, our results have more than tripled the number of these fascinating and enigmatic systems known. Combining our results with previous studies done on the Bothun et al. catalog results in a well-defined catalog of HI properties of 526 LSB galaxies ranging in redshift space from 0 <= z <= 0.1. With this catalog in hand, we have been able to explore the parameter space occupied by LSB galaxies more completely than has been previously possible. In agreement with previous studies, our results show LSB galaxies with some of the most extreme properties of disk galaxies, including M_HI/L_B ratios often exceeding 10 M_sol/L_sol,B.

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arXiv2004

A search for low surface brightness dwarf galaxies in different environments

According to the Cold Dark Matter (CDM) hierarchical clustering theory of galaxy and large scale structure formation, there should be numerous low mass dark matter haloes present in the Universe today. If these haloes contain sufficient stars they should be detectable as low luminosity stellar systems or dwarf galaxies. We have previously described a new detection method for faint low surface brightness objects and shown that there are relatively large numbers of very faint dwarf galaxies in the nearby Virgo cluster. In this paper we present results from a similar survey carried out on the Millennium Galaxy strip which runs along the celestial equator and samples a very different galaxy environment. We show that the dwarf-to-giant galaxy number ratio along this strip ranges from 0.7:1 to, at most, 6:1, corresponding to a flat luminosity function (alpha approx -0.8 to -1.0). This is very different to our value of 20:1 for the Virgo cluster. There is no population of low surface brightness dwarf galaxies in the field that have gone undetected by the redshift surveys. This result is exactly opposite to what CDM models predict for the environmental dependence of the dark matter mass function which is that there are proportionally more small dark matter haloes in lower density environments.

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arXiv2004

NGC 4569: recent evidence for a past ram pressure stripping event

Deep 21-cm HI line observations of the Virgo cluster spiral galaxy NGC 4569 have been obtained with the VLA in its D configuration and with the Effelsberg 100-m telescope. A low surface density arm was discovered in the west of the galaxy, whose velocity field is distinct from that of the overall disk rotation. The observed gas distribution, velocity field, and velocity dispersion are compared to snapshots of dynamical simulations that include the effects of ram pressure. Two different scenarios were explored: (i) ongoing stripping and (ii) a major stripping event that took place about 300 Myr ago. It is concluded that only the post-stripping scenario can reproduce the main observed characteristics of NGC 4569. It is not possible to determine if the gas disk of NGC 4569 had already been truncated before it underwent the ram pressure event that lead to its observed HI deficiency.

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arXiv2003

A multi-beam HI survey of the Virgo Cluster - two isolated HI clouds ?

We have carried out a fully sampled large area ($4^{\circ} \times 8^{\circ}$) 21cm \HI line survey of part of the Virgo cluster using the Jodrell Bank multi-beam instrument. The survey has a sensitivity some 3 times better than the standard HIJASS and HIPASS surveys. We detect 31 galaxies, 27 of which are well known cluster members. The four new detections have been confirmed in the HIPASS data and by follow up Jodrell Bank pointed observations. One object lies behind M86, but the other 3 have no obvious optical counter parts upon inspection of the digital sky survey fields. These 3 objects were mapped at Arecibo with a smaller \am{3}{6} HPBW and a 4 times better sensitivity than the Jodrell Bank data, which allow an improved determination of the dimensions and location of two of the objects, but surprisingly failed to detect the third. The two objects are resolved by the Arecibo beam giving them a size far larger than any optical images in the nearby field. To our mass limit of $5 \times 10^{7}$ $\frac{Δv}{50 km s^{-1}}$ $M_{\odot}$ and column density limit of $3 \times 10^{18}$ $\frac{Δv}{50 km s^{-1}}$ atoms cm$^{-2}$ these new detections represent only about 2% of the cluster atomic hydrogen mass. Our observations indicate that the \HI mass function of the cluster turns down at the low mass end making it very different to the field galaxy \HI mass function. This is quite different to the Virgo cluster optical luminosity function which is much steeper than that in the general field. Many of the sample galaxies are relatively gas poor compared to \HI selected samples of field galaxies, confirming the 'anaemic spirals' view of Virgo cluster late type galaxies.

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arXiv2003

ce-61: a Tidal Dwarf Galaxy in the Hercules cluster?

A candidate Tidal Dwarf Galaxy, ce-61, was identified in the merger system IC 1182 in the Hercules supercluster. The multi-wavelength data we obtained so far do not prove, however, that it is kinematically detached from the IC 1182 system and gravitationally bound.

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arXiv2003

A 3D Optical Spectroscopy Study of Low Surface Brightness Galaxies

We present Halpha emission line velocity fields of two Low Surface Brightness galaxies - UGC 628 and UGC 5005 - obtained using Fabry-Perot interferometry observations at the Canada-France-Hawaii telescope. Our goal is to study the dynamics of Low Surface Brightness galaxies.

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