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[Abridged] We present a detailed study of the physical properties of the molecular gas in a sample of 18 molecular gas-rich early-type galaxies (ETGs) from the ATLAS$ 3D sample. Our goal is to better understand the star formation processes occurring in those galaxies, starting here with the dense star-forming gas. We use existing integrated $^{12}$CO(1-0, 2-1), $^{13}$CO(1-0, 2-1), HCN(1-0) and HCO$^{+}$(1-0) observations and present new $^{12}$CO(3-2) single-dish data. From these, we derive for the first time the average kinetic temperature, H$_{2}$ volume density and column density of the emitting gas, this using a non-LTE theoretical model. Since the CO lines trace different physical conditions than of those the HCN and HCO$^{+}$ lines, the two sets of lines are treated separately. We also compare for the first time the predicted CO spectral line energy distributions (SLEDs) and gas properties of our molecular gas-rich ETGs with those of a sample of nearby well-studied disc galaxies. The gas excitation conditions in 13 of our 18 ETGs appear analogous to those in the centre of the Milky Way. Such results have never been obtained before for ETGs and open a new window to explore further star-formation processes in the Universe. The conclusions drawn should nevertheless be considered carefully, as they are based on a limited number of observations and on a simple model. In the near future, with higher CO transition observations, it should be possible to better identify the various gas components present in ETGs, as well as more precisely determine their associated physical conditions. To achieve these goals, we show here from our theoretical study, that mid-J CO lines (such as the $^{12}$CO(6-5) line) are particularly useful., 28 pages, Accepted in MNRAS, 7 figures, 6 tables

We have carried out a survey for CO J = 1-0 and J = 2-1 emission in the 260 early-type galaxies of the volume-limited ATLAS(3D) sample, with the goal of connecting their star formation and assembly histories to their cold gas content. This is the largest volume-limited CO survey of its kind and is the first to include many Virgo cluster members. Sample members are dynamically hot galaxies with a median stellar mass similar to 3 x 10(10) M-circle dot; they are selected by their morphology rather than colour, and the bulk of them lie on the red sequence. The overall CO detection rate is 56/259 = 0.22 +/- 0.03, with no dependence on the K luminosity and only a modest dependence on the dynamical mass. There are a dozen CO detections among the Virgo cluster members; statistical analysis of their H-2 mass distributions and their dynamical status within the cluster shows that the cluster's influence on their molecular masses is subtle at best, even though (unlike spirals) they seem to be virialized within the cluster. We suggest that the cluster members have retained their molecular gas through several Gyr residences in the cluster. There are also a few extremely CO-rich early-type galaxies with H2 masses greater than or similar to 10(9) M-circle dot and these are in low-density environments. We do find a significant trend between the molecular content and stellar specific angular momentum. The galaxies of low angular momentum also have low CO detection rates, suggesting that their formation processes were more effective at destroying the molecular gas or preventing its re-accretion. We speculate on the implications of these data for the formation of various subclasses of early-type galaxies.

We have carried out a survey for CO J = 1-0 and J = 2-1 emission in the 260 early-type galaxies of the volume-limited ATLAS(3D) sample, with the goal of connecting their star formation and assembly histories to their cold gas content. This is the largest volume-limited CO survey of its kind and is the first to include many Virgo cluster members. Sample members are dynamically hot galaxies with a median stellar mass similar to 3 x 10(10) M-circle dot; they are selected by their morphology rather than colour, and the bulk of them lie on the red sequence. The overall CO detection rate is 56/259 = 0.22 +/- 0.03, with no dependence on the K luminosity and only a modest dependence on the dynamical mass. There are a dozen CO detections among the Virgo cluster members; statistical analysis of their H-2 mass distributions and their dynamical status within the cluster shows that the cluster's influence on their molecular masses is subtle at best, even though (unlike spirals) they seem to be virialized within the cluster. We suggest that the cluster members have retained their molecular gas through several Gyr residences in the cluster. There are also a few extremely CO-rich early-type galaxies with H2 masses greater than or similar to 10(9) M-circle dot and these are in low-density environments. We do find a significant trend between the molecular content and stellar specific angular momentum. The galaxies of low angular momentum also have low CO detection rates, suggesting that their formation processes were more effective at destroying the molecular gas or preventing its re-accretion. We speculate on the implications of these data for the formation of various subclasses of early-type galaxies.

An important aspect of solving the long-standing question as to what triggers various types of active galactic nuclei (AGN) involves a thorough understanding of the overall properties and formation history of their host galaxies. This is the second in a series of papers that systematically study the large-scale properties of cold neutral hydrogen (H 0 gas in nearby radio galaxies. The main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. In this paper, we present results of a complete sample of classical low-power radio galaxies. We find that extended Fanaroff & Riley type-I radio sources are generally not associated with gas-rich galaxy mergers or ongoing violent interactions, but occur in early-type galaxies without large (greater than or similar to 10(8) M(circle dot)) amounts of extended neutral hydrogen gas. In contrast, enormous discs/rings of H I gas (with sizes up to 190 kpc and masses up to 2 x 10(10) M(circle dot)) are detected around the host galaxies of a significant fraction of the compact radio sources in our sample. This segregation in H I mass with radio-source size likely indicates that either these compact radio sources are confined by large amounts of gas in the central region or that their fuelling is inefficient and different from the fuelling process of classical FR I radio sources. To first order, the overall Hi properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short and recurrent phase that occurs at some point during the lifetime of many early-type galaxies.

An important aspect of solving the long-standing question as to what triggers various types of active galactic nuclei (AGN) involves a thorough understanding of the overall properties and formation history of their host galaxies. This is the second in a series of papers that systematically study the large-scale properties of cold neutral hydrogen (H 0 gas in nearby radio galaxies. The main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. In this paper, we present results of a complete sample of classical low-power radio galaxies. We find that extended Fanaroff & Riley type-I radio sources are generally not associated with gas-rich galaxy mergers or ongoing violent interactions, but occur in early-type galaxies without large (greater than or similar to 10(8) M(circle dot)) amounts of extended neutral hydrogen gas. In contrast, enormous discs/rings of H I gas (with sizes up to 190 kpc and masses up to 2 x 10(10) M(circle dot)) are detected around the host galaxies of a significant fraction of the compact radio sources in our sample. This segregation in H I mass with radio-source size likely indicates that either these compact radio sources are confined by large amounts of gas in the central region or that their fuelling is inefficient and different from the fuelling process of classical FR I radio sources. To first order, the overall Hi properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short and recurrent phase that occurs at some point during the lifetime of many early-type galaxies.

We present the results of deep Westerbork Synthesis Radio Telescope observations of the neutral hydrogen in 12 nearby elliptical and lenticular galaxies selected from a representative sample of nearby galaxies that were studied earlier at optical wavelengths with the integral-field spectrograph sauron. The observed objects are field galaxies, or (in two cases) are located in poor-group environments. We detect Hi in 70% of the galaxies. This detection rate is much higher than in previous, shallower single-dish surveys, and is similar to that for the ionised gas. The results suggest that at faint detection levels the presence of Hi is a relatively common characteristic of field early-type galaxies. The presence of regular disc-like structures is as common as Hi in offset clouds and tails. All galaxies where Hi is detected also contain ionised gas, whereas no Hi is found around galaxies without ionised gas. Galaxies with regular HI discs tend to have strong emission from ionised gas. In these cases, the similar kinematics of the neutral hydrogen and ionised gas suggest that they form one structure. We do not find a trend between the presence of Hi and the global age of the stellar population or with the global dynamical characteristics of the galaxies. If fast and slow rotators represent the relics of different formation paths, this does not appear in the presence and characteristics of the Hi. The links observed between the large-scale gas and the characteristics on the nuclear scale (e.g. the presence of kinematically decoupled cores and radio continuum emission), suggest that for the majority of the cases the gas is acquired through merging, but the lack of correlation with the stellar-population age suggests that smooth, cold accretion could be an alternative scenario, at least in some galaxies. In either case, the data suggest that early-type galaxies continue to build-up their mass to the present. (c) 2006 Elsevier B.V. All rights reserved.

We present a kinematical study of 29 spiral galaxies included in the Spitzer Survey of Stellar Structure in Galaxies, using Ha Fabry Perot (FP) data obtained with the Galaxy Ha Fabry Perot System instrument at the William Herschel Telescope in La Palma, complemented with images in the R band and in Ha. The primary goal is to study the evolution and properties of the main structural components of galaxies through the kinematical analysis of the FP data, complemented with studies of morphology, star formation and mass distribution. In this paper we describe how the FP data have been obtained, processed and analysed. We present the resulting moment maps, rotation curves, velocity model maps and residual maps. Images are available in Errs format through the NASA/IPAC Extragalactic Database and the Centre de Donnees Stellaires. With these data products we study the non-circular motions, in particular those found along the bars and spiral arms. The data indicate that the amplitude of the non-circular motions created by the bar does not correlate with the bar strength indicators. The amplitude of those non-circular motions in the spiral arms does not correlate with either arm class or star formation rate along the spiral arms. This implies that the presence and the magnitude of the streaming motions in the arms is a local phenomenon.

We investigate a sample of 3 dwarf elliptical galaxies in the Virgo Cluster which have significant reservoirs of HI. We present deep optical imaging (from CFHT and KPNO), HI spectra (Arecibo) and resolved HI imaging (VLA) of this sample. These observations confirm their HI content and optical morphologies, and indicate that the gas is unlikely to be recently accreted. The sample has more in common with dwarf transitionals, although dwarf transitionals are generally lower in stellar mass and gas fraction. VCC 190 has an HI tidal tail from a recent encounter with the massive spiral galaxy NGC 4224. In VCC 611, blue star-forming features are observed which were unseen by shallower SDSS imaging., Comment: 11 pages, 6 figures, accepted in AJ

We have carried out a survey for 12CO J=1-0 and J=2-1 emission in the 260 early-type galaxies of the volume-limited Atlas3D sample, with the goal of connecting their star formation and assembly histories to their cold gas content. This is the largest volume-limited CO survey of its kind and is the first to include many Virgo Cluster members. Sample members are dynamically hot galaxies with a median stellar mass 3\times 10^{10} Msun; they are selected by morphology rather than colour, and the bulk of them lie on the red sequence. The overall CO detection rate is 56/259 = 0.22 \error 0.03, with no dependence on K luminosity and only a modest dependence on dynamical mass. There are a dozen CO detections among the Virgo Cluster members; statistical analysis of their H_2 mass distributions and their dynamical status within the cluster shows that the cluster's influence on their molecular masses is subtle at best, even though (unlike spirals) they seem to be virialized within the cluster. We suggest that the cluster members have retained their molecular gas through several Gyr residences in the cluster. There are also a few extremely CO-rich early-type galaxies with H_2 masses >= 10^9 Msun, and these are in low density environments. We do find a significant trend between molecular content and the stellar specific angular momentum. The galaxies of low angular momentum also have low CO detection rates, suggesting that their formation processes were more effective at destroying molecular gas or preventing its re-accretion. We speculate on the implications of these data for the formation of various sub-classes of early-type galaxies., Fixed typo in author list. 33 pages. MNRAS, accepted

We present high-resolution observations of the atomic hydrogen (H I) and Hbeta emission lines in the southern grand-design spiral galaxy M 83. Contrary to the case of M51, we have not detected streaming motions of a magnitude of 60-90 km s-1 (in the plane of the disk) across the spiral arms of M 83 either in H I or in Hbeta. The Hbeta observations hint at streaming motions at a level of 35 km s-1, comparable to the motions seen in M81. Significant deviations from circular rotation are observed in the regions where the bar connects with the spiral arms, both in H I and Hbeta. The gas is moving tangentially faster in these regions compared to a simple model for the rotation in the disk of M 83. These motions are similar to the streaming motions observed in CO (Kenney & Lord 1991). The H I observations have revealed a large-scale displacement (700 pc) of the atomic gas from the dust lane along a 7 kpc stretch of the inner eastern spiral arm of M 83. This separation can not be explained by beam smoothing. The atomic gas in that part of the arm is coincident with the ridge of H II complexes along the outer edge of the spiral arm. The observations, as well as recent CO observations of the eastern arm of M 83, are discussed in the context of two scenarios that attempt to explain the observed morphology of the interstellar medium (ISM) in the eastern spiral arm. The dissociation scenario assumes the ISM to be predominantly molecular at the position of the dust lanes and to (partly) dissociate into the observed H I ridge downstream. The diffuse-shock scenario assumes that the massive clouds shock at the observed location of the CO, H I, and H II regions, whereas a shock in a more diffuse medium results in the dust lane upstream. We argue in this paper that the effect of heating of the CO in the spiral arm may have been underestimated in the interpretation of the CO observations. Heating may have increased the CO brightness downstream from the shock substantially in which case the observed CO distribution across the spiral arm does not accurately reflect the underlying distribution of the molecular gas. The dissociation scenario appears to apply in M51, and the diffuse-shock scenario in M81; these are two galaxies which may be at opposite extremes with regard to the strength of the density-wave shock and the fraction of ISM in molecular hydrogen. M 83 may be an intermediate case lacking the strong density-wave shock, a suggestion which is observationally supported by our failure to detect streaming motions like those in M51.

We present high-resolution observations of the atomic hydrogen (H I) and Hbeta emission lines in the southern grand-design spiral galaxy M 83. Contrary to the case of M51, we have not detected streaming motions of a magnitude of 60-90 km s-1 (in the plane of the disk) across the spiral arms of M 83 either in H I or in Hbeta. The Hbeta observations hint at streaming motions at a level of 35 km s-1, comparable to the motions seen in M81. Significant deviations from circular rotation are observed in the regions where the bar connects with the spiral arms, both in H I and Hbeta. The gas is moving tangentially faster in these regions compared to a simple model for the rotation in the disk of M 83. These motions are similar to the streaming motions observed in CO (Kenney & Lord 1991).The H I observations have revealed a large-scale displacement (700 pc) of the atomic gas from the dust lane along a 7 kpc stretch of the inner eastern spiral arm of M 83. This separation can not be explained by beam smoothing. The atomic gas in that part of the arm is coincident with the ridge of H II complexes along the outer edge of the spiral arm.The observations, as well as recent CO observations of the eastern arm of M 83, are discussed in the context of two scenarios that attempt to explain the observed morphology of the interstellar medium (ISM) in the eastern spiral arm. The dissociation scenario assumes the ISM to be predominantly molecular at the position of the dust lanes and to (partly) dissociate into the observed H I ridge downstream. The diffuse-shock scenario assumes that the massive clouds shock at the observed location of the CO, H I, and H II regions, whereas a shock in a more diffuse medium results in the dust lane upstream.We argue in this paper that the effect of heating of the CO in the spiral arm may have been underestimated in the interpretation of the CO observations. Heating may have increased the CO brightness downstream from the shock substantially in which case the observed CO distribution across the spiral arm does not accurately reflect the underlying distribution of the molecular gas.The dissociation scenario appears to apply in M51, and the diffuse-shock scenario in M81; these are two galaxies which may be at opposite extremes with regard to the strength of the density-wave shock and the fraction of ISM in molecular hydrogen. M 83 may be an intermediate case lacking the strong density-wave shock, a suggestion which is observationally supported by our failure to detect streaming motions like those in M51.

The velocity field of the exceptionally large Sc galaxy UGC 2885 (Holmberg radius 84 h-1 kpc, where h = H-0/100 km s-1 Mpc-1) has been mapped in Halpha emission with the TAURUS I imaging Fabry-Perot spectrometer using the 2.5 m telescope at La Palma. The rotation curve extracted from the velocity field agrees with published data. Ripples in the velocity field around the minor axis indicate radial flows across the spiral arms. The radial flow speeds in the plane of the disk show 50-70 km s-1 peak-to-peak variation, suggesting that a strong density wave is present in the underlying stellar disk. Such high speeds may alternatively be a natural consequence of the open arm spiral pattern. In addition, strong density waves may naturally occur in large spiral galaxies or in spiral galaxies as massive as UGC 2885. (Its mass is over 10(12) h-1 M. within the radius to which spiral arms reach, 52 h-1 kpc.) A strong density wave may also be necessary for the effective maintenance of the orderly, two-armed spiral pattern that is visible in the outer disk of UGC 2885, where the gas has made only about a dozen revolutions in a Hubble time.

The velocity field of the exceptionally large Sc galaxy UGC 2885 (Holmberg radius 84 h-1 kpc, where h = H-0/100 km s-1 Mpc-1) has been mapped in Halpha emission with the TAURUS I imaging Fabry-Perot spectrometer using the 2.5 m telescope at La Palma. The rotation curve extracted from the velocity field agrees with published data. Ripples in the velocity field around the minor axis indicate radial flows across the spiral arms. The radial flow speeds in the plane of the disk show 50-70 km s-1 peak-to-peak variation, suggesting that a strong density wave is present in the underlying stellar disk. Such high speeds may alternatively be a natural consequence of the open arm spiral pattern. In addition, strong density waves may naturally occur in large spiral galaxies or in spiral galaxies as massive as UGC 2885. (Its mass is over 10(12) h-1 M. within the radius to which spiral arms reach, 52 h-1 kpc.) A strong density wave may also be necessary for the effective maintenance of the orderly, two-armed spiral pattern that is visible in the outer disk of UGC 2885, where the gas has made only about a dozen revolutions in a Hubble time.

We have mapped the blue gas-rich S0 galaxy NGC 5102 in the 21-cm HI line with a spatial resolution of 34'' x 37'' (DELTAalpha x DELTAdelta) and a velocity resolution of 12 km s-1. Optically NGC 5102 is a peculiar S0 galaxy, in the sense that it has unusually blue colours, and shows evidence for a burst of star formation a few times 10(8) years ago in its nucleus. Also the inner bulge and parts of its disk show signs of low-level star formation activity. It further has a 'supershell' of 1.7 kpc diameter seen in Halpha around its central regions, a unique feature for a lenticular galaxy.The HI distribution has a pronounced central depression of 1.9 kpc radius, and most of the HI is concentrated in a 3.6 kpc wide ring with an average radius of 3.7 kpc (= 0.7 R25), assuming a distance of 4 Mpc for NGC 5102. The maximum azimuthally averaged HI surface density in the ring is 1.4 M. pc-2, comparable to that found in other SO galaxies. The extent of the HI gas is not much larger than the optical de Vaucouleurs' radius (R25) of die galaxy, contrary to what is found in other gas-rich S0's, which often have large outer HI rings at R approximately 2 R25. The HI velocity field is quite regular, showing no evidence for large-scale deviations from circular rotation, and the HI is found to rotate in the plane of the stellar disk. The rotation curve is essentially flat at V(rot) approximately 95 km s-1 out to R = 6 kpc (1.1 R25). Assuming a simple spherical mass model, we find a total mass-to-light ratio M(T)/L(B)0 = 4.3 M./L. within R = 6 kpc.In contrast to other SO galaxies studied in this series of papers, both the HI mass/blue luminosity ratio and the radial HI distribution are similar to those in early-type spirals. The HI may be an old, ''smouldering'', disk or it may have been acquired through capture of a gas-rich smaller galaxy. The recent starburst in the nuclear region, which gave the galaxy its blue colour, may have been caused by partial radial collapse of the gas disk, or by infall of a gas-rich dwarf galaxy.

We have mapped the blue gas-rich S0 galaxy NGC 5102 in the 21-cm HI line with a spatial resolution of 34'' x 37'' (DELTAalpha x DELTAdelta) and a velocity resolution of 12 km s-1. Optically NGC 5102 is a peculiar S0 galaxy, in the sense that it has unusually blue colours, and shows evidence for a burst of star formation a few times 10(8) years ago in its nucleus. Also the inner bulge and parts of its disk show signs of low-level star formation activity. It further has a 'supershell' of 1.7 kpc diameter seen in Halpha around its central regions, a unique feature for a lenticular galaxy. The HI distribution has a pronounced central depression of 1.9 kpc radius, and most of the HI is concentrated in a 3.6 kpc wide ring with an average radius of 3.7 kpc (= 0.7 R25), assuming a distance of 4 Mpc for NGC 5102. The maximum azimuthally averaged HI surface density in the ring is 1.4 M. pc-2, comparable to that found in other SO galaxies. The extent of the HI gas is not much larger than the optical de Vaucouleurs' radius (R25) of die galaxy, contrary to what is found in other gas-rich S0's, which often have large outer HI rings at R approximately 2 R25. The HI velocity field is quite regular, showing no evidence for large-scale deviations from circular rotation, and the HI is found to rotate in the plane of the stellar disk. The rotation curve is essentially flat at V(rot) approximately 95 km s-1 out to R = 6 kpc (1.1 R25). Assuming a simple spherical mass model, we find a total mass-to-light ratio M(T)/L(B)0 = 4.3 M./L. within R = 6 kpc. In contrast to other SO galaxies studied in this series of papers, both the HI mass/blue luminosity ratio and the radial HI distribution are similar to those in early-type spirals. The HI may be an old, ''smouldering'', disk or it may have been acquired through capture of a gas-rich smaller galaxy. The recent starburst in the nuclear region, which gave the galaxy its blue colour, may have been caused by partial radial collapse of the gas disk, or by infall of a gas-rich dwarf galaxy.

An important aspect of solving the long-standing question as to what triggers various types of active galactic nuclei (AGN) involves a thorough understanding of the overall properties and formation history of their host galaxies. This is the second in a series of papers that systematically study the large-scale properties of cold neutral hydrogen (H 0 gas in nearby radio galaxies. The main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. In this paper, we present results of a complete sample of classical low-power radio galaxies. We find that extended Fanaroff & Riley type-I radio sources are generally not associated with gas-rich galaxy mergers or ongoing violent interactions, but occur in early-type galaxies without large (greater than or similar to 10(8) M(circle dot)) amounts of extended neutral hydrogen gas. In contrast, enormous discs/rings of H I gas (with sizes up to 190 kpc and masses up to 2 x 10(10) M(circle dot)) are detected around the host galaxies of a significant fraction of the compact radio sources in our sample. This segregation in H I mass with radio-source size likely indicates that either these compact radio sources are confined by large amounts of gas in the central region or that their fuelling is inefficient and different from the fuelling process of classical FR I radio sources. To first order, the overall Hi properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short and recurrent phase that occurs at some point during the lifetime of many early-type galaxies.

We present the first attempt to measure CO distributions in a number of southern S0 galaxies. In all but two of the 11 galaxies in our sample, we searched for CO emission in several offset positions as well as in the central beam. CO was detected at the greater-than-or-equal-to 3-sigma level in at least one position in six of the galaxies. In NGC 1326 the CO emission is found to be extended beyond the central regions, and has been detected in several positions in the disk. In all of the other galaxies, our data are consistent with the CO emission being partially resolved. However, more recent observations of a second sample of galaxies show extended, resolved CO emission in a few more S0's. To investigate the gas distributions in these systems we have developed a modeling routine which generates and fits synthetic spectra to the data. In NGC 1326 the best fit indicates that the molecular gas is mainly distributed in a ring which is located approximately 1 kiloparsec from the nucleus of the galaxy. The simple ringed distribution cannot explain all of profile features which are seen along the major axis, however. A zeroth order attempt to include a CO bar in the model did not improve the model fits to the data.

We present the first attempt to measure CO distributions in a number of southern S0 galaxies. In all but two of the 11 galaxies in our sample, we searched for CO emission in several offset positions as well as in the central beam. CO was detected at the greater-than-or-equal-to 3-sigma level in at least one position in six of the galaxies. In NGC 1326 the CO emission is found to be extended beyond the central regions, and has been detected in several positions in the disk. In all of the other galaxies, our data are consistent with the CO emission being partially resolved. However, more recent observations of a second sample of galaxies show extended, resolved CO emission in a few more S0's.To investigate the gas distributions in these systems we have developed a modeling routine which generates and fits synthetic spectra to the data. In NGC 1326 the best fit indicates that the molecular gas is mainly distributed in a ring which is located approximately 1 kiloparsec from the nucleus of the galaxy. The simple ringed distribution cannot explain all of profile features which are seen along the major axis, however. A zeroth order attempt to include a CO bar in the model did not improve the model fits to the data.

The atomic hydrogen (H I) and the H-alpha emission lines in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the TAURUS Fabry-Perot imaging spectrometer, respectively. Across the inner spiral arms significant tangential and radial velocity gradients are detected in the H-alpha emission after subtraction of an axi-symmetric component of the velocity field. These gradients are similar to the ones observed recently in CO across the inner northern spiral arm, and resemble streaming motions expected from a density-wave shock: the gas is moving inward and faster compared to pure circular rotation after passing through the spiral arm. The amplitudes of the velocity shifts are very large, reaching 60-90 km s-1 in the plane of the galaxy. We discuss more extensively a scenario which we have previously proposed to account for the approximately 500 pc displacements observed between the spiral arms in H I and the nonthermal radio continuum and/or the dust lanes in M51 and M83. The scenario describes the observations in the framework of density-wave streaming of the interstellar gas. Presuming the nonthermal continuum ridge and/or dust lane trace the locus of maximum density of the interstellar gas, the observations are consistent with the view that most of the H I in the inner spiral arms of M51 and M83 is a product of the dissociation of predominantly molecular gas by the star-formation process. This explains the coincidence observed between the H I arms and the ionized arms. A simple quantitative model of the dissociation process yields the observed H I column densities. We also investigate several alternative explanations involving peculiar geometry and radiative transfer effects, but find them inadequate or unlikely to explain the observed displacement of the H I from the spiral shock.

The atomic hydrogen (H I) and the H-alpha emission lines in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the TAURUS Fabry-Perot imaging spectrometer, respectively.Across the inner spiral arms significant tangential and radial velocity gradients are detected in the H-alpha emission after subtraction of an axi-symmetric component of the velocity field. These gradients are similar to the ones observed recently in CO across the inner northern spiral arm, and resemble streaming motions expected from a density-wave shock: the gas is moving inward and faster compared to pure circular rotation after passing through the spiral arm. The amplitudes of the velocity shifts are very large, reaching 60-90 km s-1 in the plane of the galaxy.We discuss more extensively a scenario which we have previously proposed to account for the approximately 500 pc displacements observed between the spiral arms in H I and the nonthermal radio continuum and/or the dust lanes in M51 and M83. The scenario describes the observations in the framework of density-wave streaming of the interstellar gas. Presuming the nonthermal continuum ridge and/or dust lane trace the locus of maximum density of the interstellar gas, the observations are consistent with the view that most of the H I in the inner spiral arms of M51 and M83 is a product of the dissociation of predominantly molecular gas by the star-formation process. This explains the coincidence observed between the H I arms and the ionized arms. A simple quantitative model of the dissociation process yields the observed H I column densities.We also investigate several alternative explanations involving peculiar geometry and radiative transfer effects, but find them inadequate or unlikely to explain the observed displacement of the H I from the spiral shock.

The observed distribution and kinematics (as derived from 21-cm radio synthesis observations) of the H I gas in a sample of 24 gas-rich early-type (S0 to Sa) disk galaxies are summarized and compared to those of later type (Sb to Sm) spiral galaxies. Lenticular galaxies more frequently have inner or outer H I rings (4 and 6 out of 9, respectively) than spirals. The inner rings have a typical radius of 0.7 times the de Vaucouleurs radius, R25, and half of them appear to be slightly tilted out of the stellar disk. The outer rings have a typical radius of 1.8 R25, and half of them are tilted some 25-degrees to 55-degrees out of the plane of the stellar disk. Barred SB0 galaxies have a pronounced central hole in their H I distribution, about 3 or 4 times as large as the bar, and similar holes are found in non-barred S0 galaxies; in SBa galaxies the central holes are about twice as large as the bar. The maximum azimuthally averaged H I surface density in S0 galaxies is only approximately 1 M. pc-2 too low to sustain large-scale star formation; in S0/a galaxies we find a value of approximately 3 M . pc-2.The H I velocity fields in most early-type galaxies can be well described by circular rotation, sometimes in a considerably warped H I distribution. The derived rotation curves are essentially flat, sometimes out to 10 optical disk scalelengths, indicating the presence of massive dark haloes, which is substantiated by detailed disk/bulge/halo mass model fits to the surface photometry and rotation curves of 3 galaxies. Simple spherical mass models show that within R = R25 the total mass-to-blue luminosity ratio M(T)/L(B) of the early-type disk galaxies is similar to that of the later-type spirals, but that at R = R25 about half (3 out of 5) of the lenticulars have exceptionally large M(T)/L(B) ratios, approximately 30 M./L.. These objects seem to be "supermassive", rather than "underluminous". In the Tully-Fisher relation between rotation velocity and blue luminosity we do not find the reported separation between early and later-type spirals, but rather a similar relation for lenticular and spiral galaxies.A comparison of the observed properties of the H I in early-type disk galaxies to predictions made by various scenarios for the origin and evolution of the gaseous component in lenticular galaxies shows that none of the processes considered can readily explain all the observed properties. The most likely origins of the H I gas in S0 galaxies appear to be either (1) accretion from another galaxy (or galaxies), though in the not too recent past, say more than (a few times) 10(9)yr ago, or (2) a burnt-out disk scenario, for the lenticulars with an outer H I ring, in which the denser inner H I disk has been consumed in star formation. Also, in barred galaxies redistribution of gas by the bar potential may have been important.

The observed distribution and kinematics (as derived from 21-cm radio synthesis observations) of the H I gas in a sample of 24 gas-rich early-type (S0 to Sa) disk galaxies are summarized and compared to those of later type (Sb to Sm) spiral galaxies. Lenticular galaxies more frequently have inner or outer H I rings (4 and 6 out of 9, respectively) than spirals. The inner rings have a typical radius of 0.7 times the de Vaucouleurs radius, R25, and half of them appear to be slightly tilted out of the stellar disk. The outer rings have a typical radius of 1.8 R25, and half of them are tilted some 25-degrees to 55-degrees out of the plane of the stellar disk. Barred SB0 galaxies have a pronounced central hole in their H I distribution, about 3 or 4 times as large as the bar, and similar holes are found in non-barred S0 galaxies; in SBa galaxies the central holes are about twice as large as the bar. The maximum azimuthally averaged H I surface density in S0 galaxies is only approximately 1 M. pc-2 too low to sustain large-scale star formation; in S0/a galaxies we find a value of approximately 3 M . pc-2. The H I velocity fields in most early-type galaxies can be well described by circular rotation, sometimes in a considerably warped H I distribution. The derived rotation curves are essentially flat, sometimes out to 10 optical disk scalelengths, indicating the presence of massive dark haloes, which is substantiated by detailed disk/bulge/halo mass model fits to the surface photometry and rotation curves of 3 galaxies. Simple spherical mass models show that within R = R25 the total mass-to-blue luminosity ratio M(T)/L(B) of the early-type disk galaxies is similar to that of the later-type spirals, but that at R = R25 about half (3 out of 5) of the lenticulars have exceptionally large M(T)/L(B) ratios, approximately 30 M./L.. These objects seem to be "supermassive", rather than "underluminous". In the Tully-Fisher relation between rotation velocity and blue luminosity we do not find the reported separation between early and later-type spirals, but rather a similar relation for lenticular and spiral galaxies. A comparison of the observed properties of the H I in early-type disk galaxies to predictions made by various scenarios for the origin and evolution of the gaseous component in lenticular galaxies shows that none of the processes considered can readily explain all the observed properties. The most likely origins of the H I gas in S0 galaxies appear to be either (1) accretion from another galaxy (or galaxies), though in the not too recent past, say more than (a few times) 10(9)yr ago, or (2) a burnt-out disk scenario, for the lenticulars with an outer H I ring, in which the denser inner H I disk has been consumed in star formation. Also, in barred galaxies redistribution of gas by the bar potential may have been important.

We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131-36). Using the Australia Telescope Compact Array, we detect M_HI = 1.8 x 10^9 M_sun of HI emission-line gas that is distributed in a 140 kpc wide disc-like structure along the optical disc and dust-lane of NGC 612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850 km/s, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The HI disc in NGC 612 suggests that the total mass enclosed by the system is M_enc ~ 2.9 x 10^12 sin^-2(i) M_sun, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC 612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint HI bridge along a distance of 400 kpc in between NGC 612 and the gas-rich (M_HI = 8.9 x 10^9 M_sun) barred galaxy NGC 619, indicating that likely an interaction between both systems occurred. From the unusual amounts of HI gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infra-red luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC 612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies. --abridged, 13 pages, 9 figures. MNRAS in press. See http://www.blackwell-synergy.com/doi/full/10.1111/j.1365-2966.2008.13142.x for a full resolution version

We present H I 21 cm observations of the grand design spiral galaxy NGC 4321, as obtained with the VLA. From our original data, we have obtained data cubes with resolutions ranging from 13'' to 45''. The H I is observed to break up into small condensations at high resolution. These condensations, with typical masses of 3.3 +/- 0.7 x 10(7) M., are not confined to the arm regions. They may be unresolved at 15'' resolution and thus may have physical sizes smaller than 1 kpc. The total H I distribution is mostly confined to the radius of the optical disk, but a large though faint extension is seen in the H I data at 45'' resolution on the SW side of the disk. NGC 4321 is asymmetric in H I and may be called ''lopsided.'' We have derived a rotation curve which agrees fairly well with what was previously published but shows more detail due to the higher resolution of our new observations. The rotation curve does not decline within the radius of the disk, but important differences are seen between the behavior of the approaching and the receding sides. These differences are caused by deviations from circular motions in the outer disk that are probably due to a close passage of the companion galaxy NGC 4322, which may also be the cause of the observed asymmetry in the total H I distribution. Deviations from circular motion due to density wave streaming are seen in the inner disk. From skewing of the velocity contours in the central part of NGC 4321, the presence of a nonaxisymmetric potential is deduced. Near-infrared and Halpha images indicate that a bar is indeed present in this galaxy. The deviations from circular motions seen in the velocity field can be identified with gas streaming around the bar in elongated orbits, in broad agreement with theoretical predictions.

We present H I 21 cm observations of the grand design spiral galaxy NGC 4321, as obtained with the VLA. From our original data, we have obtained data cubes with resolutions ranging from 13'' to 45''. The H I is observed to break up into small condensations at high resolution. These condensations, with typical masses of 3.3 +/- 0.7 x 10(7) M., are not confined to the arm regions. They may be unresolved at 15'' resolution and thus may have physical sizes smaller than 1 kpc. The total H I distribution is mostly confined to the radius of the optical disk, but a large though faint extension is seen in the H I data at 45'' resolution on the SW side of the disk. NGC 4321 is asymmetric in H I and may be called ''lopsided.'' We have derived a rotation curve which agrees fairly well with what was previously published but shows more detail due to the higher resolution of our new observations. The rotation curve does not decline within the radius of the disk, but important differences are seen between the behavior of the approaching and the receding sides. These differences are caused by deviations from circular motions in the outer disk that are probably due to a close passage of the companion galaxy NGC 4322, which may also be the cause of the observed asymmetry in the total H I distribution. Deviations from circular motion due to density wave streaming are seen in the inner disk. From skewing of the velocity contours in the central part of NGC 4321, the presence of a nonaxisymmetric potential is deduced. Near-infrared and Halpha images indicate that a bar is indeed present in this galaxy. The deviations from circular motions seen in the velocity field can be identified with gas streaming around the bar in elongated orbits, in broad agreement with theoretical predictions.

We present high-resolution observations of the atomic hydrogen (H I) and Hbeta emission lines in the southern grand-design spiral galaxy M 83. Contrary to the case of M51, we have not detected streaming motions of a magnitude of 60-90 km s-1 (in the plane of the disk) across the spiral arms of M 83 either in H I or in Hbeta. The Hbeta observations hint at streaming motions at a level of 35 km s-1, comparable to the motions seen in M81. Significant deviations from circular rotation are observed in the regions where the bar connects with the spiral arms, both in H I and Hbeta. The gas is moving tangentially faster in these regions compared to a simple model for the rotation in the disk of M 83. These motions are similar to the streaming motions observed in CO (Kenney & Lord 1991). The H I observations have revealed a large-scale displacement (700 pc) of the atomic gas from the dust lane along a 7 kpc stretch of the inner eastern spiral arm of M 83. This separation can not be explained by beam smoothing. The atomic gas in that part of the arm is coincident with the ridge of H II complexes along the outer edge of the spiral arm. The observations, as well as recent CO observations of the eastern arm of M 83, are discussed in the context of two scenarios that attempt to explain the observed morphology of the interstellar medium (ISM) in the eastern spiral arm. The dissociation scenario assumes the ISM to be predominantly molecular at the position of the dust lanes and to (partly) dissociate into the observed H I ridge downstream. The diffuse-shock scenario assumes that the massive clouds shock at the observed location of the CO, H I, and H II regions, whereas a shock in a more diffuse medium results in the dust lane upstream. We argue in this paper that the effect of heating of the CO in the spiral arm may have been underestimated in the interpretation of the CO observations. Heating may have increased the CO brightness downstream from the shock substantially in which case the observed CO distribution across the spiral arm does not accurately reflect the underlying distribution of the molecular gas. The dissociation scenario appears to apply in M51, and the diffuse-shock scenario in M81; these are two galaxies which may be at opposite extremes with regard to the strength of the density-wave shock and the fraction of ISM in molecular hydrogen. M 83 may be an intermediate case lacking the strong density-wave shock, a suggestion which is observationally supported by our failure to detect streaming motions like those in M51.

The velocity field of the exceptionally large Sc galaxy UGC 2885 (Holmberg radius 84 h-1 kpc, where h = H-0/100 km s-1 Mpc-1) has been mapped in Halpha emission with the TAURUS I imaging Fabry-Perot spectrometer using the 2.5 m telescope at La Palma. The rotation curve extracted from the velocity field agrees with published data. Ripples in the velocity field around the minor axis indicate radial flows across the spiral arms. The radial flow speeds in the plane of the disk show 50-70 km s-1 peak-to-peak variation, suggesting that a strong density wave is present in the underlying stellar disk. Such high speeds may alternatively be a natural consequence of the open arm spiral pattern. In addition, strong density waves may naturally occur in large spiral galaxies or in spiral galaxies as massive as UGC 2885. (Its mass is over 10(12) h-1 M. within the radius to which spiral arms reach, 52 h-1 kpc.) A strong density wave may also be necessary for the effective maintenance of the orderly, two-armed spiral pattern that is visible in the outer disk of UGC 2885, where the gas has made only about a dozen revolutions in a Hubble time.

We present a study of the morphology and kinematics of the neutral hydrogen in the gas-rich (M_HI=1.5x10^{10}Msun), massive early-type galaxy NGC 1167, which was observed with the Westerbork Synthesis Radio Telescope (WSRT). The HI is located in a 160kpc disk (~3xD_25) and has low surface density (, 17 pages, 11 figures; A&A in press

We present the first attempt to measure CO distributions in a number of southern S0 galaxies. In all but two of the 11 galaxies in our sample, we searched for CO emission in several offset positions as well as in the central beam. CO was detected at the greater-than-or-equal-to 3-sigma level in at least one position in six of the galaxies. In NGC 1326 the CO emission is found to be extended beyond the central regions, and has been detected in several positions in the disk. In all of the other galaxies, our data are consistent with the CO emission being partially resolved. However, more recent observations of a second sample of galaxies show extended, resolved CO emission in a few more S0's. To investigate the gas distributions in these systems we have developed a modeling routine which generates and fits synthetic spectra to the data. In NGC 1326 the best fit indicates that the molecular gas is mainly distributed in a ring which is located approximately 1 kiloparsec from the nucleus of the galaxy. The simple ringed distribution cannot explain all of profile features which are seen along the major axis, however. A zeroth order attempt to include a CO bar in the model did not improve the model fits to the data.

The atomic hydrogen (H I) and the H-alpha emission lines in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the TAURUS Fabry-Perot imaging spectrometer, respectively. Across the inner spiral arms significant tangential and radial velocity gradients are detected in the H-alpha emission after subtraction of an axi-symmetric component of the velocity field. These gradients are similar to the ones observed recently in CO across the inner northern spiral arm, and resemble streaming motions expected from a density-wave shock: the gas is moving inward and faster compared to pure circular rotation after passing through the spiral arm. The amplitudes of the velocity shifts are very large, reaching 60-90 km s-1 in the plane of the galaxy. We discuss more extensively a scenario which we have previously proposed to account for the approximately 500 pc displacements observed between the spiral arms in H I and the nonthermal radio continuum and/or the dust lanes in M51 and M83. The scenario describes the observations in the framework of density-wave streaming of the interstellar gas. Presuming the nonthermal continuum ridge and/or dust lane trace the locus of maximum density of the interstellar gas, the observations are consistent with the view that most of the H I in the inner spiral arms of M51 and M83 is a product of the dissociation of predominantly molecular gas by the star-formation process. This explains the coincidence observed between the H I arms and the ionized arms. A simple quantitative model of the dissociation process yields the observed H I column densities. We also investigate several alternative explanations involving peculiar geometry and radiative transfer effects, but find them inadequate or unlikely to explain the observed displacement of the H I from the spiral shock.

The observed distribution and kinematics (as derived from 21-cm radio synthesis observations) of the H I gas in a sample of 24 gas-rich early-type (S0 to Sa) disk galaxies are summarized and compared to those of later type (Sb to Sm) spiral galaxies. Lenticular galaxies more frequently have inner or outer H I rings (4 and 6 out of 9, respectively) than spirals. The inner rings have a typical radius of 0.7 times the de Vaucouleurs radius, R25, and half of them appear to be slightly tilted out of the stellar disk. The outer rings have a typical radius of 1.8 R25, and half of them are tilted some 25-degrees to 55-degrees out of the plane of the stellar disk. Barred SB0 galaxies have a pronounced central hole in their H I distribution, about 3 or 4 times as large as the bar, and similar holes are found in non-barred S0 galaxies; in SBa galaxies the central holes are about twice as large as the bar. The maximum azimuthally averaged H I surface density in S0 galaxies is only approximately 1 M. pc-2 too low to sustain large-scale star formation; in S0/a galaxies we find a value of approximately 3 M . pc-2. The H I velocity fields in most early-type galaxies can be well described by circular rotation, sometimes in a considerably warped H I distribution. The derived rotation curves are essentially flat, sometimes out to 10 optical disk scalelengths, indicating the presence of massive dark haloes, which is substantiated by detailed disk/bulge/halo mass model fits to the surface photometry and rotation curves of 3 galaxies. Simple spherical mass models show that within R = R25 the total mass-to-blue luminosity ratio M(T)/L(B) of the early-type disk galaxies is similar to that of the later-type spirals, but that at R = R25 about half (3 out of 5) of the lenticulars have exceptionally large M(T)/L(B) ratios, approximately 30 M./L.. These objects seem to be "supermassive", rather than "underluminous". In the Tully-Fisher relation between rotation velocity and blue luminosity we do not find the reported separation between early and later-type spirals, but rather a similar relation for lenticular and spiral galaxies. A comparison of the observed properties of the H I in early-type disk galaxies to predictions made by various scenarios for the origin and evolution of the gaseous component in lenticular galaxies shows that none of the processes considered can readily explain all the observed properties. The most likely origins of the H I gas in S0 galaxies appear to be either (1) accretion from another galaxy (or galaxies), though in the not too recent past, say more than (a few times) 10(9)yr ago, or (2) a burnt-out disk scenario, for the lenticulars with an outer H I ring, in which the denser inner H I disk has been consumed in star formation. Also, in barred galaxies redistribution of gas by the bar potential may have been important.