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New Light and Shadows on Stephan's Quintet
We present deep broadband R and narrowband Hα images of Stephan'sQuintet. The observations in the R band show that the diffuse halo ofStephan's Quintet is larger than previously thought and extends out toNGC 7320C. However, we have not found emission connecting NGC 7331 andNGC 7320 to R~26.7 mag arcsec-2 (at more than a 3 σlevel), so there is no direct evidence up to this limiting magnitude ofa relation between the peculiar kinematical structure found in NGC 7331and an ongoing or past interaction between this galaxy and NGC 7320. TheHα emission at high velocity (6000-7000 km s-1) isdistributed in a diffuse structure running north-south between NGC 7319and NGC 7318B and in some other more concentrated features. Some ofthese are located in the tidal tails produced by the interaction betweenthe galaxies of the group. With the Hα images we have made atwo-dimensional velocity map that helps to identify the origin of eachstructure detected. This map does not show features at intermediatevelocities between the high- and low-redshift members of the group. Thisis in agreement with the standard scenario in which the apparentproximity of NGC 7320 to the rest of the galaxies of the Quintet ismerely a projection effect. The only point that is unclear in thisinterpretation is an Hα filament that is seen extending throughoutNGC 7320 with velocity at 6500 km s-1 instead of the 800 kms-1 expected for this galaxy. Accepted in final form 20002July 12.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| The Hubble Space Telescope Extragalactic Distance Scale Key Project. X. The Cepheid Distance to NGC 7331
The distance to NGC 7331 has been derived from Cepheid variablesobserved with the Hubble Space Telescope (HST) WFPC2, as part of theExtragalactic Distance Scale Key Project. Multiepoch exposures in F555W(~V) and F814W (~I), with photometry derived independently from DoPHOTand DAOPHOT/ALLFRAME programs, were used to detect a total of 13reliable Cepheids, with periods between 11 and 42 days. The relativedistance moduli between NGC 7331 and the LMC, derived from the V and Imagnitudes, imply an extinction to NGC 7331 of AV = 0.47 +/- 0.15 magand an extinction-corrected distance modulus to NGC 7331 of 30.89 +/-0.14 (random), equivalent to a distance of 15.1^{+1.0}_{-0.9} Mpc. Thereare additional systematic uncertainties in the distance modulus of+/-0.12 mag resulting from the calibration of the Cepheidperiod-luminosity relation and a systematic offset of +0.05 +/- 0.04 magif the metallicity correction inferred from the M101 results ofKennicutt et al. are applied.
| ISOCAM Mid-Infrared Imaging of the Quiescent Spiral Galaxy NGC 7331
Using the mid-infrared camera (ISOCAM) on the Infrared Space Observatory(ISO), the Sb LINER galaxy NGC 7331 has been imaged in two broadband andfour narrowband filters between 6.75 and 15 mu m. These maps show aprominent circumnuclear ring of radius 0.'25 x 0.'75 (1.1 x 3.3 kpc)encircling an extended central source. The 7.7 and 11.3 mu m dustemission features are strong in this galaxy, contributing approximatelyone-third of the total IRAS 12 mu m broadband flux. In contrast tostarburst galaxies, the 15 mu m continuum is weak in NGC 7331. Themid-infrared spectrum does not vary dramatically with position in thisquiescent galaxy, showing neither large-scale destruction of thecarriers of the emission bands nor a large increase in the 15 mu mcontinuum in the star-forming ring. In the bulge there is someenhancement of the LW2 (6.75 mu m) flux, probably because ofcontributions from photospheric light; however, the 11.3 mu m dustfeature is also seen, showing additional emission from interstellar orcircumstellar dust.
| Galaxy Alignments in the Pisces-Perseus Supercluster Revisited
A search for preferential galaxy alignments in the Pisces-PerseusSupercluster (PPS) is made using the Minnesota Automated Plate ScannerPisces-Perseus Survey (MAPS-PP). The MAPS-PP is a catalog of ~1400galaxies with a (roughly) isophotal diameter greater than 30"constructed from digitized scans of the blue and red plates of thePalomar Observatory Sky Survey covering the PPS. This is the largestsample of galaxies applied to a search of galaxy alignments in thissupercluster, and it has been used in combination with previouslypublished redshifts to construct the deepest PPS galaxy luminosityfunction to date. While previous studies have relied extensively oncatalogs with visually estimated parameters for both sample selectionand determination of galaxy orientation, the MAPS-PP uses selectioncriteria and measurements that are entirely machine and computer based.Therefore, it is not susceptible to some of the biases, such as thediameter inclination effect, known to exist in some other galaxycatalogs. The presence of anisotropic galaxy distributions is determinedby use of the Kuiper statistic, a robust alternative to the chi^2statistic more traditionally used in these studies. Three statisticallysignificant anisotropic distributions are observed. The reddest galaxiesare observed to be oriented preferentially perpendicular to the locallarge-scale structure. The bluest galaxies near the supercluster planeare observed to have an anisotropic position angle distribution.Finally, a weak trend for the median position angle of color-selectedgalaxy subsamples to ``twist'' with increasing distance from the PPSplane is observed. These position angle distribution anisotropies areweak and are not consistent with any single primordial or modern-eragalaxy alignment mechanism, although a mixture of such mechanisms is notruled out.
| Kinematics of the local universe. VII. New 21-cm line measurements of 2112 galaxies
This paper presents 2112 new 21-cm neutral hydrogen line measurementscarried out with the meridian transit Nan\c cay radiotelescope. Amongthese data we give also 213 new radial velocities which complement thoselisted in three previous papers of this series. These new measurements,together with the HI data collected in LEDA, put to 6 700 the number ofgalaxies with 21-cm line width, radial velocity, and apparent diameterin the so-called KLUN sample. Figure 5 and Appendices A and B forcorresponding comments are available in electronic form at thehttp://www.edpsciences.com
| A survey of the Pisces-Perseus supercluster. V - The declination strip +33.5 deg to +39.5 deg and the main supercluster ridge
Measurements of 544 radial velocities, 229 optical and 315 in the 21 cmH I line, are presented for galaxies, mostly in the declination stripbetween +33.5 and +39.5 deg in the region of the Pisces-Perseussupercluster. These are combined with other available data toinvestigate the linear structure identified as the main superclusterridge. The main ridge of the supercluster extends at least 50/h Mpcbefore it disappears into the zone of avoidance east of Perseus.Confinement both on the plane of the sky and in the velocity dimensionimply an axial ratio of greater than 10:1 and an inclination withrespect to the plane of the sky of less than about 12 degrees. Therelative proximity, low inclination to the plane of the sky, and highcontrast relative to the foreground and background, help to make thePisces-Perseus filament one of the most prominent features in theextragalactic sky on large scales.
| Neutral hydrogen absorption by galaxies and implications for the soft X-ray background
Results are presented from a search for neutral hydrogen absorption inthe 21-cm spectra of 59 radio continuum sources in the proximity ofspiral and lenticular galaxies using the Arecibo radio telescope. Fivegalaxies showed possible but uncertain absorption. For the 54 othersources, the column density of the neutral hydrogen in the interveningmaterial is well below 2 x 10 to the 19th/cu cm or the spin temperatureis at least one order of magnitude above the microwave backgroundtemperature. For these cases, subthermal effects are not hidingappreciable amounts of neutral hydrogen.
| Low-frequency radio continuum evidence for cool ionized gas in normal spiral galaxies
A 57.5-MHz survey of a total of 133 (mostly late-type spiral) galaxieshas resulted in the detection of 68. The ratio of observed intensitiesto intensities extrapolated from higher-frequency measurements is wellcorrelated with the axial ratio of the observed galaxies, and isinterpretable due to increasing free-free absorption of nonthermalemission in galaxy disks with increasing tilt. The implied free-freeabsorption is interpreted as due to the pervasive presence of a clumpymedium of well-mixed, nonthermally emitting, thermally absorbing gaswith small filling factor.
| A Checklist of Supernovae in the NGC and IC Galaxies Through 1985
This Checklist of Supernovae in the NGC and IC Galaxies Through 1985 ispresented to assist those interested in undertaking a visual orphotographic search for extragalactic supernovae. Some galaxies appearto have had more than one or two supernovae, and these should bemonitored closely for any new outbursts.
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