B. A. Williams

VLA neutral hydrogen imaging of compact groups of galaxies. II - HCG 31, 44, and 79

Neutral hydrogen images of three compact groups of galaxies are presented: HCG 31, 44, and 79. The images were obtained with the very large array (VLA), an on-line Hanning smoothing was applied to the data, and the H I spectral channel was isolated. The images were made on the Pipeline, and were produced by means of a method described by Gorkon and Ekers (1988). The images of HCG 44 are compared with earlier Arecibo observations. The H I emission in HCG 44 is discovered within the galaxies, whereas the emission in 31 and 79 can be found throughout the group in clouds that are larger than the galaxies. Evidence of a relationship between the compact groups is found in the H I data, and the groups are considered to be merging into a single object. Some of the groups are theorized to be young amorphous galaxies where the H I is still bound to individual galaxies, and which have just begun to condense from the intergalactic medium. The kinematics of the gas are shown to vary, and a common gaseous envelope contains the dwarf galaxies. 42 refs.

Neutral hydrogen in compact groups of galaxies

Integrated H I profiles were detected for 34 of 51 Hickson compact groups (HCGs) of galaxies, and sensitive upper limits to the H I flux density were measured for the other 17. About 60 percent of the galaxies within compact groups are spirals, and a significant tendency exists for the fraction of elliptical galaxies to increase with group surface brightness. The amount of dark matter within the compact group region is negligibly small. An HCG on average contains half as much neutral hydrogen as a loose group with a similar spectrum of galaxy luminosities and morphological types, implying that compact groups are independent dynamical entities and not transient or projected configurations of loose groups. The observed fraction of galaxies which are luminous enough to be possible merger products of compact groups is small compared with the fraction required by the theory of dynamical friction. A clear discrepancy thus exists between solid empirical evidence and a straightforward prediction of Newtonian dynamical theory in a setting which does not permit a dark matter explanation. 44 references.

VLA observations of hydrogen in HCG 18

Images are presented of the neutral hydrogen (H I) in the direction of the compact group of galaxies HCG 18. This H I emission is identified with a single cloud, centered on the galaxies b, c, and d and smoothly distributed over a region twice the size of the compact group. The cloud appears to be in regular rotation with a period no longer than 8 x 10 to the 8th yr. The systematic velocity of the gas lies within 1 sigma of the mean velocity of the group; however, the cloud is not clearly associated with any particular galaxy, but surrounds all three, which may be one irregular galaxy. 17 references.

The distance to the Coma cluster using the B-band Tully-Fisher relation

The present estimate of the distance to the Coma cluster on the basis of the B-band Tully-Fisher (T-F) relation has conducted photographic surface photometry on all galaxies for which H I line width data in a circle of 4-deg radius centered on the Coma cluster. A detailed estimate is made of the cluster population incompleteness bias for the distance estimation. While the correction for sample incompleteness, in conjunction with the T-F relation, increases the distance modulus, the result cannot be as large as the value indicated by Kraan-Kortweg et al. (1988). 65 refs.

Community-based multi-disease prevention campaigns for controlling human immunodeficiency virus-associated tuberculosis

Human immunodeficiency virus (HIV) infection increases the risk of tuberculosis (TB) 21-34 fold, and has fuelled the resurgence of TB in sub-Saharan Africa. The World Health Organization (WHO) recommends the Three Is for HIV/TB (infection control, intensified case finding [ICF] and isoniazid preventive therapy) and earlier initiation of antiretroviral therapy for preventing TB in persons with HIV. Current service delivery frameworks do not identify people early enough to maximally harness the preventive benefits of these interventions. Community-based campaigns were essential components of global efforts to control major public health threats such as polio, measles, guinea worm disease and smallpox. They were also successful in helping to control TB in resource-rich settings. There have been recent community-based efforts to identify persons who have TB and/or HIV. Multi-disease community-based frameworks have been rare. Based on findings from a WHO meta-analysis and a Cochrane review, integrating ICF into the recent multi-disease prevention campaign in Kenya may have had implications in controlling TB. Community-based multi-disease prevention campaigns represent a potentially powerful strategy to deliver prevention interventions, identify people with HIV and/or TB, and link those eligible to care and treatment.Human immunodeficiency virus (HIV) infection increases the risk of tuberculosis (TB) 21-34 fold, and has fuelled the resurgence of TB in sub-Saharan Africa. The World Health Organization (WHO) recommends the Three Is for HIV/TB (infection control, intensified case finding [ICF] and isoniazid preventive therapy) and earlier initiation of antiretroviral therapy for preventing TB in persons with HIV. Current service delivery frameworks do not identify people early enough to maximally harness the preventive benefits of these interventions. Community-based campaigns were essential components of global efforts to control major public health threats such as polio, measles, guinea worm disease and smallpox. They were also successful in helping to control TB in resource-rich settings. There have been recent community-based efforts to identify persons who have TB and/or HIV. Multi-disease community-based frameworks have been rare. Based on findings from a WHO meta-analysis and a Cochrane review, integrating ICF into the recent multi-disease prevention campaign in Kenya may have had implications in controlling TB. Community-based multi-disease prevention campaigns represent a potentially powerful strategy to deliver prevention interventions, identify people with HIV and/or TB, and link those eligible to care and treatment.

A Neutral Hydrogen Study of Seyfert’s Very Compact Group

A cloud of neutral hydrogen with an extent greater than that of any individual galaxy is present in the direction of Seyfert’s very compact group of galaxies. At each position within this cloud, the velocity width is about 160 km s −1and the radial velocity lies in the range 4530 km s −1 to more than 4600 km s −1 he largest radial velocity of any galaxy in the group is 4503 km s −1.

The VLA H I Observations of Stephan’s Quintet (HCG 92)*

Using the Very Large Array, we have made spectral-line and continuum observations of the neutral hydrogen in the direction of the compact group of galaxies Stephans Quintet. The high-velocity clouds between 5600 and 6600 km s-1, the disk of the foreground galaxy NGC 7320 at 800 km s-1, the extended continuum ridge near the center of the group, and three faint dwarflike galaxies in the surrounding field were imaged with the C, CS, and D configurations. Four of the H I clouds previously detected are confirmed. The two largest H I features are coincident with and concentrated mainly along separate large tidal tails that extend eastward. The most diffuse of the four clouds is resolved into two clumps, one coinciding with tidal features south of NGC 7318A and the other devoid of any detectable stellar or Hα sources. The two compact clouds along the same line of sight have peak emission at luminous infrared and bright Hα sources probably indicative of star-forming activity. The total amount of H I detected at high redshifts is ~1010M⊙. As in previous H I studies of the group, no detectable emission was measured at the positions of any high-redshift galaxies, so that any H I still bound to their disks must be less than 2.4 × 107 M⊙.Using the VLA, we have made spectral-line and continuum observations of the neutral hydrogen in the direction of the compact group of galaxies Stephans Quintet. The high-velocity clouds between 5600 and 6600 km/s, the disk of the foreground galaxy, NGC 7320, at 800 km/s, the extended continuum ridge near the center of the group, and 3 faint dwarf-like galaxies in the surrounding field were imaged with C, CS, and D arrays. Four of the HI clouds previously detected are confirmed. The two largest HI features are coincident with and concentrated mainly along separate large tidal tails that extend eastward. The most diffuse of the four clouds is resolved into two clumps, one coincide with tidal features south of NGC 7318a and the other devoid of any detectable stellar or Halfa sources. The two compact clouds, along the same line of sight, have peak emission at luminous infrared and bright Halfa sources probably indicative of star-forming activity. The total amount of HI detected at high redshifts is ~ 10**10Msol. As in previous HI studies of the group, no detectable emission was measured at the positions of any high-redshift galaxies so that any HI still bound to their disks must be less than 2.4 x 10**7Msol.

VLA neutral hydrogen imaging of compact groups

Images of the neutral hydrogen (H I) in the direction of the compact groups of galaxies, HCG 31, HCG 44, and HCG 79 are presented. The authors find in HCG 31 and HCG 79, emission contained within a cloud much larger than the galaxies as well as the entire group. The H I emission associated with HCG 44 is located within the individual galaxies but shows definite signs of tidal interactions. The authors imaged the distribution and kinematics of neutral hydrogen at the two extremes of group sizes represented in Hicksons sample. HCG 44 is at the upper limit while HCG 18, HCG 31, and HCG 79 are at the lower end. Although the number of groups that have been imaged is still very small, there may be a pattern emerging which describes the H I morphology of compact groups. The true nature of compact groups has been the subject of considerable debate and controversy. The most recent observational and theoretical evidence strongly suggests that compact groups are physically dense, dynamical systems that are in the process of merging into a single object (Williams and Rood 1987, Hickson and Rood 1988, Barnes 1989). The neutral hydrogen deficiency observed by Williams and Rood (1987) is consistent with a model in which frequent galactic collisions and interactions have heated some of the gas during the short lifetime of the group. The H I disks which are normally more extended than the luminous ones are expected to be more sensitive to collisions and to trace the galaxys response to recent interactions. Very Large Array observations can provide in most cases the spatial resolution needed to confirm the dynamical interactions in these systems.

A Dynamical Study of Two Groups in the Coma/A1367 Supercluster

Located ~12° southwest of A1367, the IC 698 group and the NGC 3825 group are two systems of galaxies within the Coma/A1367 supercluster. All of the spiral galaxies in both groups were observed and detected at 21 cm with the 305-m Arecibo radio telescope• The dynamical stability of each group was analyzed by using the accurate radial velocities and the direct estimates of the masses obtained from these 21-cm line observations. Application of the virial theorem to the IC 698 group gives a mass which is comparable to the sum of the individual masses of its galaxies. When the virial theorem is applied to the NGC 3825 group, its virial mass is found to be ~6 times larger than the sum of the masses derived for the individual members.