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Context. Observations of the Sunyaev-Zel'dovich effect (SZE) from galaxy clusters are emerging as a powerful tool in cosmology. Besides large cluster surveys, resolved SZE images of individual clusters can shed light on the physics of the intra-cluster medium (ICM) and allow accurate measurements of the cluster gas and total masses.

The Medusa (NGC 4194) is a well-studied nearby galaxy with the disturbed appearance of a merger and evidence for ongoing star formation. In order to test whether it could be the result of an interaction between a gas-rich disk-like galaxy and a larger elliptical, we have carried out optical and radio observations of the stars and the gas in the Medusa, and performed N-body numerical simulations of the evolution of such a system. We used the Nordic Optical Telescope to obtain a deep V-band image and the Westerbork Radio Synthesis Telescope to map the large-scale distribution and kinematics of atomic hydrogen. A single Hitail was found to the South of the Medusa with a projected length of ~56 kpc (~$5'$) and a gas mass of 7 $\times$$10^8~M_{\odot}$, thus harbouring about one third of the total Himass of the system. Hiwas also detected in absorption toward the continuum in the center. Hiwas detected in a small nearby galaxy to the North-West of the Medusa at a projected distance of 91 kpc. It is, however, unlikely that this galaxy has had a significant influence on the evolution of the Medusa. The simulations of the slightly prograde infall of a gas-rich disk galaxy on an larger, four time more massive elliptical (spherical) galaxy reproduce most of the observed features of the Medusa. Thus, the Medusa is an ideal object to study the merger-induced star formation contribution from the small galaxy of a minor merger.

The dynamical evolution of the large (>100 kpc), barred spiral galaxy NGC 6872 and its small companion IC 4970 in the southern group Pavo is investigated. We present N-body simulations with stars and gas and 21 cm Hi observations carried out with the Australia Telescope Compact Array of the large-scale distribution and kinematics of atomic gas. Hi is detected toward the companion, corresponding to a gas mass of ~$ 1.3\times 10^9~ M_\odot$. NGC 6872 contains ∼$1.4\times 10^{10}~ M_\odot$of Hi gas, distributed in an extended rotating disk. Massive concentrations of gas (∼$10^9~ M_\odot$) are found at the tip of both tidal tails and towards the break seen in the optical northern arm near the companion. We detect no Hi counterpart to the X-ray trail between NGC 6872 and NGC 6876, the dominant elliptical galaxy in the Pavo group located ∼$8'$to the southeast. At the sensitivity and the resolution of the observations, there is no sign in the overall Hi distribution that NGC 6876 has affected the evolution of NGC 6872. There is no evidence of ram pressure stripping either. The X-ray trail could be due to gravitational focusing of the hot gas in the Pavo group behind NGC 6872 as the galaxy moves supersonically through the hot medium. The simulations of a gravitational interaction with a small nearby companion on a low-inclination prograde passage are able to reproduce most of the observed features of NGC 6872, including the general morphology of the galaxy, the inner bar, the extent of the tidal tails and the thinness of the southern tail.

Context.The origin of the spiral pattern of magnetic fields in disc galaxies is an open question.

In this work we use the Hubble Deep Field South (HDF-S) version 2 images to assess the galaxy population out to $z \sim 2$. We have used two methods of templates fitting of the spectral energy distributions to obtain photometric redshifts and classify the objects. The Bayesian photometric redshifts gave better results when compared with 54 spectroscopic redshifts available in the literature. Analysis of the rest-frame colour distribution shows a bimodality out to $ z \sim 1.4$. We separated our sample in a blue and a red population at $B-V=0.29$. At low redshifts ($0.2< z <0.6$), ~60% of the galaxies have $B-V>0.29$whereas at higher redshifts ~60% of the galaxies are bluer than $B-V<0.29$. Although in low numbers, a population of early-type galaxies (or heavily obscured low redshift galaxies) is seen out to $z\sim2$.

Key Odin operational and instrumental features and highlights from our sub-millimetre and millimetre wave observations of H2O, H$_2^{18}$O, NH3, 15NH3and O2are presented, with some insights into accompanying Odin Letters in this A&A issue. We focus on new results where Odin's high angular resolution, high frequency resolution, large spectrometer bandwidths, high sensitivity or/and frequency tuning capability are crucial: H2O mapping of the Orion KL, W 3, DR 21, S 140 regions, and four comets; H2O observations of Galactic Centre sources, of shock enhanced H2O towards the SNR IC 443, and of the candidate infall source IRAS 16293-2422; H$_2^{18}$O detections in Orion KL and in comet Ikeya-Zhang; sub-mm detections of NH3in Orion KL (outflow, ambient cloud and bar) and ρ Oph, and very recently, of 15NH3in Orion KL. Simultaneous sensitive searches for the 119 GHz line of O2have resulted in very low abundance limits, which are difficult to accomodate in chemical models. We also demonstrate, by means of a quantitative comparison of Orion KL H2O results, that the Odin and SWAS observational data sets are very consistently calibrated.

We present and interpret observations of atomic and molecular gas toward the southern elliptical galaxy NGC 1316 (Fornax A), a strong double-lobe radio source with a disturbed optical morphology that includes numerous shells and loops. The 12CO(1-0), 12CO(2-1), and Hiobservations were made with SEST and the VLA. CO emission corresponding to a total molecular hydrogen mass of ~$5 \times 10^8$$M_\odot$was detected towards the central position as well as northwest and southeast of the nucleus in the regions of the dust patches. The origin of that gas is likely external and due to accretion of one or several small gas-rich galaxies. Hiwas not detected in the central region of NGC 1316, but ~$2 \times 10^7$$M_\odot$of atomic gas was found towards the giant Hiiregion discovered by Schweizer (1980) located $6{\farcm}7$(or 36.2 kpc) from the nucleus. Hiwas also found at three other locations in the outer part of NGC 1316. The Hidistributions and kinematics of the two nearby spiral companions of NGC 1316, NGC 1317 (a barred galaxy to the north) and NGC 1310 (to the west) could be studied. Both galaxies have unusually small Hidisks that may have been affected by ram-pressure stripping.

A new model of the Cartwheel galaxy is presented, based on the nearly central inclined collision of a rigid companion galaxy with a self-gravitating disc containing both stars and gas. We assume that the intruder is the most distant companion (G3 in J. Higdon's notation). Two rings and a transient network of gaseous spokes develop after the passage of the companion. The expansion velocity of the outer ring is in agreement with the one observed for the atomic gas. At the end of the simulation, the position and velocity of the companion agree with those of G3.

Abstract: We present the analysis of a survey of atomic and molecular gas in interacting and merging galaxies (Horellou and Booth, 1997). The sample is optically selected and contains all interacting galaxies (≈ 60 systems) in a well-defined region of the Southern sky (Bergvall, 1981). In order to take into account the upper limits due to non-detections, we have carried out a survival analysis. The results are compared with the ones obtained when ignoring the non-detections. We have found evidence for a lower atomic gas content per unit area in interacting galaxies compared to isolated ones. Except for a few systems with high far-infrared luminosity and correspondingly high CO fluxes, the interacting galaxies are not unusually CO-bright. The observed HI deficiency is therefore not due to a conversion of HI into H2.Atomic gas from the outer part of the galaxies may have been swept by tidal interaction, or the optical extent of the galaxies may have increased due to the tidal interaction. The interacting galaxies seem to be more efficient at transforming their molecular gas into stars, as indicated by their higher LFIR/M(H2) ratio. We found no correlation between molecular gas fraction and degree of morphological distortion.

Context.Submillimeter galaxies are a population of dusty star-forming galaxies at high redshift. Measuring their properties will help relate them to other types of galaxies, both at high and low redshift. This is needed in order to understand the formation and evolution of galaxies.

Aims. We aim to demonstrate the usability of mm-wavelength imaging data obtained from the APEX-SZ bolometer array to derive the radial temperature profile of the hot intra-cluster gas out to radius r500and beyond. The goal is to study the physical properties of the intra-cluster gas by using a non-parametric de-projection method that is, aside from the assumption of spherical symmetry, free from modeling bias.Methods. We use publicly available X-ray spectroscopic-imaging data in the 0.7-2 keV energy band from the XMM-Newtonobservatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data from the APEX-SZ experiment at 150 GHz to de-project the density and temperature profiles for a well-studied relaxed cluster, Abell 2204. We derive the gas density, temperature and entropy profiles assuming spherical symmetry, and obtain the total mass profile under the assumption of hydrostatic equilibrium. For comparison with X-ray spectroscopic temperature models, a re-analysis of recent Chandraobservation is done with the latest calibration updates. We compare the results with that from an unrelaxed cluster, Abell 2163, to illustrate some differences between relaxed and merging systems.Results. Using the non-parametric modeling, we demonstrate a decrease of gas temperature in the cluster outskirts, and also measure gas entropy profiles, both of which are done for the first time independently of X-ray spectroscopy using the SZE and X-ray imaging data. The gas entropy measurement in the central 100 kpc shows the usability of APEX-SZ data for inferring cluster dynamical states with this method. The contribution of the SZE systematic uncertainties in measuring Teat large radii is shown to be small compared to XMM-Newtonand Chandrasystematic spectroscopic errors. The total mass profile obtained using the hydrostatic equilibrium assumption is in agreement with the published X-ray and weak lensing results; the upper limit on M200derived from the non-parametric method is consistent with the NFW model prediction from weak lensing analysis.

Aims. We aim to demonstrate the usability of mm-wavelength imaging data obtained from the APEX-SZ bolometer array to derive the radial temperature profile of the hot intra-cluster gas out to radius r500and beyond. The goal is to study the physical properties of the intra-cluster gas by using a non-parametric de-projection method that is, aside from the assumption of spherical symmetry, free from modeling bias.

The HerschelLensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100–500 μm bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 μm and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 μm-selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities. This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales.

We present preliminary results about the detection of high redshift (U)LIRGs in the Bullet cluster field by the PACS and SPIRE instruments within the HerschelLensing Survey (HLS) Program. We describe in detail a photometric procedure designed to recover robust fluxes and deblend faint Herschelsources near the confusion noise. The method is based on the use of the positions of Spitzer/MIPS 24 μm sources as priors. Our catalogs are able to reliably (5σ) recover galaxies with fluxes above 6 and 10 mJy in the PACS 100 and 160 μm channels, respectively, and 12 to 18 mJy in the SPIRE bands. We also obtain spectral energy distributions covering the optical through the far-infrared/millimeter spectral ranges of all the Herscheldetected sources, and analyze them to obtain independent estimations of the photometric redshift based on either stellar population or dust emission models. We exemplify the potential of the combined use of Spitzerposition priors plus independent optical and IR photometric redshifts to robustly assign optical/NIR counterparts to the sources detected by Herscheland other (sub-)mm instruments.

The HerschelLensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100–500 μm bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 μm and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 μm-selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities. This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales.

We present preliminary results about the detection of high redshift (U)LIRGs in the Bullet cluster field by the PACS and SPIRE instruments within the HerschelLensing Survey (HLS) Program. We describe in detail a photometric procedure designed to recover robust fluxes and deblend faint Herschelsources near the confusion noise. The method is based on the use of the positions of Spitzer/MIPS 24 μm sources as priors. Our catalogs are able to reliably (5σ) recover galaxies with fluxes above 6 and 10 mJy in the PACS 100 and 160 μm channels, respectively, and 12 to 18 mJy in the SPIRE bands. We also obtain spectral energy distributions covering the optical through the far-infrared/millimeter spectral ranges of all the Herscheldetected sources, and analyze them to obtain independent estimations of the photometric redshift based on either stellar population or dust emission models. We exemplify the potential of the combined use of Spitzerposition priors plus independent optical and IR photometric redshifts to robustly assign optical/NIR counterparts to the sources detected by Herscheland other (sub-)mm instruments.

Context. Clusters of galaxies are effective gravitational lenses able to magnify background galaxies and making it possible to probe the fainter part of the galaxy population. Submillimeter galaxies, which are believed to be star-forming galaxies at typical redshifts of 2 to 3, are a major contaminant to the extended Sunyaev-Zeldovich (SZ) signal of galaxy clusters. For a proper quantification of the SZ signal the contribution of submillimeter galaxies needs to be quantified.Aims. The aims of this study are to identify submillimeter sources in the field of the Bullet cluster (1E 0657-56), a massive cluster of galaxies at z$\simeq$0.3, measure their flux densities at 870 μm, and search for counterparts at other wavelengths to constrain their properties.Methods. We carried out deep observations of the submillimeter continuum emission at 870 μm using the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX) telescope. Several numerical techniques were used to quantify the noise properties of the data and extract sources.Results. In total, seventeen sources were found. Thirteen of them lie in the central 10 arcmin of the map, which has a pixel sensitivity of 1.2 mJy per 22''beam. After correction for flux boosting and gravitational lensing, the number counts are consistent with published submm measurements. Nine of the sources have infrared counterparts in Spitzer maps. The strongest submm detection coincides with a source previously reported at other wavelengths, at an estimated redshift z$\simeq$2.7. If the submm flux arises from two images of a galaxy magnified by a total factor of 75, as models have suggested, its intrinsic flux would be around 0.6 mJy, consistent with an intrinsic luminosity below 1012$L_\odot$.

Context. Clusters of galaxies are effective gravitational lenses able to magnify background galaxies and making it possible to probe the fainter part of the galaxy population. Submillimeter galaxies, which are believed to be star-forming galaxies at typical redshifts of 2 to 3, are a major contaminant to the extended Sunyaev-Zeldovich (SZ) signal of galaxy clusters. For a proper quantification of the SZ signal the contribution of submillimeter galaxies needs to be quantified.