HI observations of nearby galaxies I. The first list of the Karachentsev catalog

We present HI observations of the galaxies in the first list of the Karachentsev catalog of previously unknown nearby dwarf galaxies (Karachentseva & Karachentsev 1998). This survey covers all known nearby galaxy groups within the Local Volume (i.e. within 10 Mpc) and their environment, that is about 25% of the total sky. A total of 257 galaxies have been observed with a detection rate of 60%. We searched a frequency band corresponding to heliocentric radial velocities from -470 km/s to about +4000 km/s. Non-detections are either due to limited coverage in radial velocity, confusion with Local HI (mainly in the velocity range -140 km/s to +20 km/s, or lack of sensitivity for very weak emission. 25% of the detected galaxies are located within the Local Volume. Those galaxies are dwarf galaxies judged by their optical linear diameter (1.4 +/- 0.2 kpc on the average), their mean total HI mass (4.6 E7 solar masses), and their observed linewidths (39 km/s).Comment: 22 pages, 9 ps figures, A&AS, in pres

Neutral Hydrogen and Star Formation in the Irregular Galaxy NGC 2366

We present UBVJHKHalpha and HI data of the irregular galaxy NGC 2366. It is a normal boxy-shaped disk seen at high inclination angle. We do not see any unambiguous observational signature of a bar. There is an asymmetrical extension of stars along one end of the major axis of the galaxy, and this is where the furthest star-forming regions are found, at 1.3R_Holmberg. The HI is normal in many respects but shows some anomalies: 1) The integrated HI shows two ridges running parallel to the major axis that deproject to a large ring. 2) The velocity field exhibits several large-scale anomalies superposed on a rotating disk. 3) The inclination and position angles derived from the kinematics differ from those dervied from the optical and HI mor- phology. 4) There are regions in the HI of unusually high velocity dispersion that correlate with deficits of HI emission in a manner suggestive of long-range, turbulent pressure equilibrium. Star-forming regions are found where the gas densities locally exceed 6 Msolar/pc^2. NGC 2366, like other irregulars, has low gas densities relative to the critical gas densities of gravitational instability models. Because of the lack of shear in the optical galaxy, there is little competition to the slow gravitational contraction that follows energy dissipation. However, the peak gas densities in the star-forming regions are equal to the local tidal densities for gravitational self-binding of a rotating cloud. Evidently the large scale gas concentrations are marginally bound against background galactic tidal forces. This condition for self-binding may be more fundamental than the instability condition because it is local, three-dimensional, and does not involve spiral arm generation as an intermediate step toward star formation.Comment: To be published in ApJ; better figures available ftp.lowell.edu, cd pub/dah/n2366pape

Kinematic Evidence of Minor Mergers in Normal Sa Galaxies: NGC3626, NGC3900, NGC4772 and NGC5854

BVRI and H-alpha imaging and long-slit optical spectroscopic data are presented for four morphologically normal and relatively isolated Sa galaxies, NGC3626, NGC3900, NGC4772 and NGC5854. VLA HI synthesis imaging is presented for the first 3 objects. In all 4 galaxies, evidence of kinematic decoupling of ionized gas components is found; the degree and circumstances of the distinct kinematics vary from complete counterrotation of all of the gas from all of the stars (NGC3626) to nuclear gas disks decoupled from the stars (NGC5854) to anomalous velocity central gas components (NGC3900 and NGC4772). In the 3 objects mapped in HI, the neutral gas extends far beyond the optical radius, R_HI/R_25 > 2. In general, the HI surface density is very low and the outer HI is patchy and asymmetric or found in a distinct ring, exterior to the optical edge. While the overall HI velocity fields are dominated by circular motions, strong warps are suggested in the outer regions. Optical imaging is also presented for NGC 4138 previously reported by Jore et al. (1996) to show counterrotating stellar components. The multiwavelength evidence is interpreted in terms of the kinematic "memory" of past minor mergers in objects that otherwise exhibit no morphological signs of interaction.Comment: 26 pages, 15 figures, accepted for publication in Astron. J., postscript figures available at ftp://culebra.tn.cornell.edu/pub/haynes/figures.tar.g

Diffuse HI Disks in Isolated Galaxies

In order to investigate the contribution of diffuse components to their total HI emission, we have obtained high precision HI line flux densities with the 100m Green Bank Telescope for a sample of 100 isolated spiral and irregular galaxies which we have previously observed with the 43m telescope. A comparison of the observed HI line fluxes obtained with the two different telescopes, characterized by half-power beam widths of 9 arcmin and 21 arcmin respectively, exploits a ``beam matching'' technique to yield a statistical determination of the occurrence of diffuse HI components in their disks. A simple model of the HI distribution within a galaxy well describes ~75 % of the sample and accounts for all of the HI line flux density. The remaining galaxies are approximately evenly divided into two categories: ones which appear to possess a significantly more extensive HI distribution than the model predicts, and ones for which the HI distribution is more centrally concentrated than predicted. Examples of both extremes can be found in the literature but little attention has been paid to the centrally concentrated HI systems. Our sample has demonstrated that galaxies do not commonly possess extended regions of low surface brightness HI gas which is not accounted for by our current understanding of the structure of HI disks. Eight HI-rich companions to the target objects are identified, and a set of extragalactic HI line flux density calibrators is presented.Comment: 26 page

Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution

The determination of the dynamical causes of the morphological Butcher-Oemler (BO) effect, or the rapid transformation of a large population of late-type galaxies to earlier Hubble types in the rich cluster environment between intermediate redshifts and the local universe, has been an important unsolved problem which is central to our understanding of the general problems of galaxy formation and evolution. In this article, we survey the existing proposed mechanisms for cluster galaxy transformation, and discuss their relevance and limitations to the explanation of the morphological BO effect. A new infrared diagnostic approach is devised to disentangle the relative importance of several major physical mechanisms to account for the BO effect, and an example of the first application of this procedure to a single rich, intermediate redshift galaxy cluster is given to demonstrate the viability of this approach. The preliminary result of this analysis favors the interaction-enhanced secular evolution process as the major cause of the cluster-galaxy morphological transformation. This conclusion is also supported by a wide range of other published results which are assembled here to highlight their implications on a coherent physical origin for the morphological BO effect.Comment: Accepted for publication in the PAS

Neutral Gas Distribution and Kinematics of the Nearly Face-on Spiral Galaxy NGC 1232

We have analyzed high velocity resolution HI synthesis observations of the nearly face-on Sc galaxy NGC 1232. The neutral gas distribution extends well beyond the optical extent of the galaxy. As expected, local peaks in the HI column density are associated with the spiral arms. Further, the HI column density drops precipitously near the center of the galaxy. Closed contours in the velocity field suggest either that the system is warped, or that the rotation curve declines. The velocity dispersion is approximately constant throughout the system, with a median value of 9.9 +/- 1.8 km/s. When corrected for rotational broadening, there is no indication of a radial trend in the neutral gas velocity dispersion in this galaxy.Comment: 14 pages of text, 10 pages of figures. Accepted to the A

Simulations of Dust in Interacting Galaxies I: Dust Attenuation

A new Monte-Carlo radiative-transfer code, Sunrise, is used in conjunction with hydrodynamic simulations of major galaxy mergers to calculate the effects of dust in such systems. The simulations are in good agreement with observations of dust absorption in starburst galaxies, and the dust has a profound effect on their appearance. The dust attenuation increases with luminosity such that at peak luminosities ~90% of the bolometric luminosity is absorbed by dust. In general, the detailed appearance of the merging event depends on the stage of the merger and the geometry of the encounter. The fraction of bolometric energy absorbed by the dust, however, is a robust quantity that can be predicted from the intrinsic properties bolometric luminosity, baryonic mass, star-formation rate, and metallicity of the system. This paper presents fitting formulae, valid over a wide range of masses and metallicities, from which the absorbed fraction of luminosity (and consequently also the infrared dust luminosity) can be predicted. The attenuation of the luminosity at specific wavelengths can also be predicted, albeit with a larger scatter due to the variation with viewing angle. These formulae for dust attenuation appear to be valid for both isolated and interacting galaxies, are consistent with earlier studies, and would be suitable for inclusion in theoretical models, e.g. semi-analytic models of galaxy formation.Comment: 12 pages, 10 figures, submitted to Ap

Properties of Active Galaxies Deduced from H I Observations

We completed a new survey for H I emission for a large, well-defined sample of 154 nearby (z < 0.1) galaxies with type 1 AGNs. We make use of the extensive database presented in a companion paper to perform a comprehensive appraisal of the cold gas content in active galaxies and to seek new strategies to investigate the global properties of the host galaxies and their relationship to their central black holes (BHs). We show that the BH mass obeys a strong, roughly linear relation with the host galaxy's dynamical mass. BH mass follows a looser, though still highly significant, correlation with the maximum rotation velocity of the galaxy, as expected from the known scaling between rotation velocity and central velocity dispersion. Neither of these H I-based correlations is as tight as the more familiar relations between BH mass and bulge luminosity or velocity dispersion, but they offer the advantage of being insensitive to the glare of the nucleus and therefore are promising new tools for probing the host galaxies of both nearby and distant AGNs. We present evidence for substantial ongoing BH growth in the most actively accreting AGNs. In these nearby systems, BH growth appears to be delayed with respect to the assembly of the host galaxy but otherwise has left no detectable perturbation to its mass-to-light ratio or its global gas content. The host galaxies of type 1 AGNs, including those luminous enough to qualify as quasars, are generally gas-rich systems, possessing a cold interstellar medium reservoir at least as abundant as that in inactive galaxies of the same morphological type. This calls into question current implementations of AGN feedback in models of galaxy formation that predict strong cold gas depletion in unobscured AGNs. (Abridged)Comment: To appear in ApJ; 14 page

Milky Way Mass Models and MOND

Using the Tuorla-Heidelberg model for the mass distribution of the Milky Way, I determine the rotation curve predicted by MOND. The result is in good agreement with the observed terminal velocities interior to the solar radius and with estimates of the Galaxy's rotation curve exterior thereto. There are no fit parameters: given the mass distribution, MOND provides a good match to the rotation curve. The Tuorla-Heidelberg model does allow for a variety of exponential scale lengths; MOND prefers short scale lengths in the range 2.0 to 2.5 kpc. The favored value of scale length depends somewhat on the choice of interpolation function. There is some preference for the `simple' interpolation function as found by Famaey & Binney. I introduce an interpolation function that shares the advantages of the simple function on galaxy scales while having a much smaller impact in the solar system. I also solve the inverse problem, inferring the surface mass density distribution of the Milky Way from the terminal velocities. The result is a Galaxy with `bumps and wiggles' in both its luminosity profile and rotation curve that are reminiscent of those frequently observed in external galaxies.Comment: Accepted for publication in the Astrophysical Journal. 31 pages including 8 figures and 3 table

A New H I Survey of Active Galaxies

We have conducted a new Arecibo survey for H I emission for 113 galaxies with broad-line (type 1) active galactic nuclei (AGNs) out to recession velocities as high as 35,000 km/s. The primary aim of the study is to obtain sensitive H I spectra for a well-defined, uniformly selected sample of active galaxies that have estimates of their black hole masses in order to investigate correlations between H I properties and the characteristics of the AGNs. H I emission was detected in 66 out of the 101 (65%) objects with spectra uncorrupted by radio frequency interference, among which 45 (68%) have line profiles with adequate signal-to-noise ratio and sufficiently reliable inclination corrections to yield robust deprojected rotational velocities. This paper presents the basic survey products, including an atlas of H I spectra, measurements of H I flux, line width, profile asymmetry, optical images, optical spectroscopic parameters, as well as a summary of a number of derived properties pertaining to the host galaxies. To enlarge our primary sample, we also assemble all previously published H I measurements of type 1 AGNs for which can can estimate black hole masses, which total an additional 53 objects. The final comprehensive compilation of 154 broad-line active galaxies, by far the largest sample ever studied, forms the basis of our companion paper, which uses the H I database to explore a number of properties of the AGN host galaxies.Comment: To appear in ApJS; 31 pages. Preprint will full-resolution figures can be downloaded from http://www.ociw.edu/~lho/preprints/ms1.pd