We present an all-sky catalog of 451 nearby galaxies, each having an individual distance estimate D P 10 Mpc or a radial velocity V LG < 550 km s À1 . The catalog contains data on basic optical and H i properties of the galaxies, in particular, their diameters, absolute magnitudes, morphological types, circumnuclear region types, optical and H i surface brightnesses, rotational velocities, and indicative mass-to-luminosity and H i massto-luminosity ratios, as well as a so-called tidal index, which quantifies the galaxy environment. We expect the catalog completeness to be roughly 70%-80% within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr, dIm, and dSph) galaxies with M B > À17:0, which contribute about 4% to the local luminosity density, and roughly 10%-15% to the local H i mass density. The H i mass-to-luminosity and the H i mass-tototal (indicative) mass ratios increase systematically from giant galaxies toward dwarfs, reaching maximum values about 5 in solar units for the most tiny objects. For the Local Volume disklike galaxies, their H i masses and angular momentum follow Zasov's linear relation, expected for rotating gaseous disks being near the threshold of gravitational instability, favorable for active star formation. We found that the mean local luminosity density exceeds 1.7-2.0 times the global density, in spite of the presence of the Tully void and the absence of rich clusters in the Local Volume. The mean local H i density is 1.4 times its ''global'' value derived from the H i Parkes Sky Survey. However, the mean local baryon density b (<8 Mpc) ¼ 2:3% consists of only a half of the global baryon density, b ¼ (4:7 AE 0:6)% (Spergel et al., published in 2003). The mean-square pairwise difference of radial velocities is about 100 km s À1 for spatial separations within 1 Mpc, increasing to $300 km s À1 on a scale of $3 Mpc. We also calculated the integral area of the sky occupied by the neighboring galaxies. Assuming the H i size of spiral and irregular galaxies to be 2.5 times their standard optical diameter and ignoring any evolution effect, we obtain the expected number of the line-of-sight intersections with the H i galaxy images to be dn=dz $ 0:4, which does not contradict the observed number of absorptions in QSO spectra.
Abstract. We have analyzed the total HI contents of 72 Hickson compact groups of galaxies (HCGs) and the detailed spatial distributions and kinematics of HI within a subset of 16 groups using the high angular resolution observations obtained with the VLA in order to investigate a possible evolutionary scenario for these densest systems in the present day galaxy hierarchy. For the more homogeneous subsample of 48 groups, we found a mean HI deficiency of DefHI = 0.40 ± 0.07, which corresponds to 40% of the expected HI for the optical luminosities and morphological types of the member galaxies. The individual galaxies show larger degrees of deficiency than the groups globally, DefHI = 0.62 ± 0.09 (24% of the expected HI), due in most cases to efficient gas stripping from individual galaxies into the group environment visible in the VLA maps. The degree of deficiency is found to be similar to the central galaxies of Virgo and Coma cluster, and Coma I group, in spite of the significantly different characteristics (number of galaxies, velocity dispersion) of these environments. It does not seem plausible that a significant amount of extended HI has been missed by the observations. Hence phase transformation of the atomic gas should explain the HI deficiency. The groups richer in early type galaxies or more compact with larger velocity dispersions show a weak tendency to be more HI deficient. The detection rate of HCGs at X-ray wavelengths is larger for HI deficient groups, although the hot gas distribution and hence its origin is only known for a few cases. In the evolutionary scenario we propose, the amount of detected HI would decrease further with evolution, by continuous tidal stripping and/or heating. The H2 content also tends to be lower than expected for the galaxies in HI deficient groups, this may suggest that the HI stripping by frequent tidal interaction breaks the balance between the disruption of molecular clouds by star formation and the replenishment from the ambient HI.
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New HI observations of Messier 31 (M31) obtained with the Effelsberg and Green Bank 100-m telescopes make it possible to measure the rotation curve of that galaxy out to ∼ 35 kpc. Between 20 and 35 kpc, the rotation curve is nearly flat at a velocity of ∼ 226 km s −1 . A model of the mass distribution shows that at the last observed velocity point, the minimum dark-to-luminous mass ratio is ∼ 0.5 for a total mass of 3.4 × 10 11 M ⊙ at R < 35 kpc. This can be compared to the estimated MW mass of 4.9 × 10 11 M ⊙ for R < 50 kpc.
Context.Measures of the H i properties of a galaxy are among the most sensitive interaction diagnostic at our disposal. We report here on a study of H i profile asymmetries (e.g., lopsidedness) in a sample of some of the most isolated galaxies in the local Universe. This presents us with an excellent opportunity to quantify the range of intrinsic H i asymmetries in galaxies (i.e., those not induced by the environment) and provides us with a zero-point calibration for evaluating these measurements in less isolated samples. Aims. We aim to characterize the H i profile asymmetries in a sample of isolated galaxies and search for correlations between H i asymmetry and their environments, as well as their optical and far infrared (FIR) properties. Methods. We use high signal-to-noise global H i profiles for galaxies in the AMIGA project (Analysis of the Interstellar Medium of Isolated GAlaxies, http://amiga.iaa.es). We restrict our study to N = 166 galaxies (out of 312) with accurate measures of the H i shape properties. We quantify asymmetries using a flux ratio parameter. Results. The asymmetry parameter distribution of our isolated sample is well described by a Gaussian model. The width of the distribution is σ = 0.13, and could be even smaller (σ = 0.11) if instrumental errors are reduced. Only 2% of our carefully vetted isolated galaxies sample show an asymmetry in excess of 3σ. By using this sample we minimize environmental effects as confirmed by the lack of correlation between H i asymmetry and tidal force (one-on-one interactions) and neighbor galaxy number density. On the other hand, field galaxy samples show wider distributions and deviate from a Gaussian curve. As a result we find higher asymmetry rates (∼10-20%) in such samples. We find evidence that the spiral arm strength is inversely correlated with the HI asymmetry. We also find an excess of FIR luminous galaxies with larger HI asymmetries that may be spirals associated with hidden accretion events. Conclusions. Our sample presents the smallest fraction of asymmetric H i profiles compared with any other yet studied. The width of the associated asymmetry parameter distribution can help to distinguish the frequency and processes of self-induced HI asymmetries, and serve as a baseline for studying asymmetry rates in other environments.
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