Optical Major Axis Research Articles

Neutral hydrogen and optical properties of three amorphous galaxies

We present new interferometric H I and optical observations of three amorphous galaxies, systems with a smooth, high surface brightness but an asymmetrical distribution of light. All three galaxies are forming stars and have LMC-like emission-line ratios, low dust content, and high H I velocity dispersions. NGC 1140 has a boxy inner morphology with a hook off one corner. At low light levels unusual extensions of starlight are seen curving to the northwest and southeast. The galaxy contains a very luminous central star-forming region and a small chain of H II regions that coincide with the hook. The central H II region has broad H(alpha) velocity profiles full width at half maximum (FWHM) less than or equal to 140 km/s, and it is a radio continuum source. There is a rotating H I gas disk, 40 kpc in radius, at a position angle 51 deg from the optical major axis. The central gas ridge follows the chain of H II regions, and the H I peak is on the hook. The outer gas on the southeast side curves away from the H I major axis. The central gas density is high, and the surface density declines very slowly with radius. The rotation velocity yields a mass of 1 x 10(exp 11) solar mass at 3.3 Holmberg radii (R(sub H)). NGC 1800 has a hook that coincides with a large H II region, and an r(exp 1/4) luminosity distribution. There are numerous H II regions along the major axis and extraordinary filaments of ionized gas. Emanating from the major axis on either side of the galaxy are H(alpha) fingers approximately 750 pc long. About 2.3 kpc to the north is a web of filaments approximately 3 kpc in extent. H(alpha) profiles of H II regions and filaments are narrow. The H I gas disk has a position angle that is approximately 13 deg different from that of the optical axis. There are two peaks near the center, one of which is near the largest H II region. Beyond the Holmberg radius to the west is a 6 x 10(exp 6) solar mass H I cloud. Its velocity indicates a mass of approximately 6 x 10(exp 9) solar mass for NGC 1800 at 1.5 R(sub H). At approximately R(sub 25) to the east there is a large H I shell. Also at approximately R(sub 25) on both sides the velocity gradient switches by 90 deg, and in the interior the rotation is about the major axis. The central gas density is low and falls off slowly. In the inner regions NGC 4670 resembles an S0/a galaxy seen rather edge-on. It contains a central supergiant H II region with very high velocity widths (FWHM less than or equal to 180 km/s) and complex velocity structures. It is a radio continuum source as well. The H I gas is a single spherical cloud or a disk at low inclination centered on the galaxy with a slight elongation along the optical major axis and rotation about the minor axis. The central gas density is high, and there is a high degree of concentration. The rotation speed indicates a total mass of 5 x 10(exp 10) solar mass at 1.1 R(sub H). We compare these characteristics with properties of gas in the presence of stellar bar potentials, gas warps, and interacting and merging galaxy models. Although there are inconsistencies and uncertainties, we conclude that NGC 1140 is a spiral of low surface brightness that has undergone a merger, while NGC 1800 and NGC 4670 are, respectively, probably an Im system and a spiral that had an encounter of the Noguchi (1988a) kind.

Ram-pressure stripping of the multiphase interstellar medium of the Virgo cluster elliptical galaxy M86 (NGC 4406)

The available infrared, optical, and X-ray data on the elliptical galaxy M86, which is experiencing strong ram-pressure stripping in the intracluster medium of the Virgo Cluster, are analyzed. A significant component of infrared 60 micron emission displaced from the center of the galaxy is found. The displaced 60 micron emission lies on the optical major axis of the galaxy in the direction of perturbations to the optical isophotes and is coincident with a small feature in X-ray emission southwest of the X-ray plume. The displaced infrared emission is interpreted in terms of collisionally heated dust exposed to hot gas where ram pressure and turbulence are disrupting the stripped interstellar medium of the galaxy. The displacement of the outer optical isophotes in the direction of the stripped gas in suggested to be due to reflection of star-light on the dust grains. Ram pressure has separated and exposed the various components of the multiphase interstellar medium of M86, enabling these constituents to be identified and analyzed separately for the first time in an elliptical galaxy.

H I observations of three IRAS detected elliptical galaxies

view Abstract Citations (21) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H i Observations of Three IRAS Detected Elliptical Galaxies Walsh, D. E. P. ; van Gorkom, J. H. ; Bies, W. E. ; Katz, N. ; Knapp, G. R. ; Wallington, S. Abstract Three elliptical galaxies with strong far-infrared emission (IRAS flux density greater than 1 Jy at 100 microns) were observed in the H I 21 cm line with the VLA. Only one of these, the dwarf NGC 855, was detected. This galaxy has an extended H I distribution which is highly inclined to the optical major axis and a weak radio continuum source. Deep optical images show complex structure in the inner regions and emission lines suggestive of star formation. It is likely that this star formation and the cool interstellar medium (ISM) are sources for the far-IR luminosity. IC 1459 is in a group containing several spirals and shows signs of recent interaction. Neutral hydrogen was not detected, but there is a powerful central radio continuum source, and the 100 micron emission is plausibly explained as arising from this source. NGC 6958 has only weak radio continuum emission, and the lower limit on L_IR_/M_HI_ is at the high end of the range for this quantity among ellipticals. It is likely that a small amount of dust heated by a strong radiation field is providing the far- infrared luminosity. The infrared properties of these galaxies are similar, but the IR emission seems to have three different origins, complicating the interpretation of IRAS data for ellipticals. Publication: The Astrophysical Journal Pub Date: April 1990 DOI: 10.1086/168556 Bibcode: 1990ApJ...352..532W Keywords: Elliptical Galaxies; Infrared Astronomy Satellite; Infrared Sources (Astronomy); Neutral Gases; Radio Sources (Astronomy); Very Large Array (Vla); Data Reduction; Flux Density; H Lines; Hydrogen; Interstellar Matter; Spiral Galaxies; Astrophysics; GALAXIES: INTERACTIONS; INFRARED: SOURCES; RADIO SOURCES: GALAXIES; RADIO SOURCES: 21 CM RADIATION full text sources ADS | data products NED (8) SIMBAD (7)

Neutral hydrogen in isolated galaxies. II - The large angular diameter galaxies

Fifty-two of the large angular diameter (a> or =2.'5) galaxies included in the 21-cm survey of isolated galaxies being undertaken at Arecibo by Haynes and Giovanelli have been mapped along their optical major axes using the 305-m telescope and the low sidelobe flat feed system. The observed fluxes have then been compared with a numerical convolution of an assumed H I distribution sigma/sub H/(r) and the beam pattern G(theta) to produce an estimate of the characteristic size. The derived H I scale length R/sub 70/ is that radius interior to which 70% of the model's H I mass is contained. With still a significant scatter, the H I diameter D/sub 70/ = 2R/sub 70/ is on the average about 1.2 times the UGC blue diameter a, and shows no dependence on morphological type for types later than Sa. Application of the observed relationship between H I size and optical diameter and of an assumed double Gaussian (centrally depressed) H I surface density distribution produces proper corrections for source to beam size. Corrected fluxes derived from Arecibo data do not differ systematically from those measured at the 91-m telescope, proving the applicability of the calibration and correction procedure. The H Imore » mass M/sub H/ is shown to be nearly proportional to the square of the linear H I diameter, implying that the H I surface density averaged over the disk is almost constant.« less

The H I distribution in an extremely faint dwarf irregular galaxy M81 dwA

view Abstract Citations (62) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The HI distribution in an extremely faint dwarf irregular galaxy M 81dwA. Sargent, W. L. W. ; Sancisi, R. ; Lo, K. Y. Abstract The distribution of neutral hydrogen in the extremely faint, dwarf, irregular galaxy M81 dwA is investigated by means of synthesis radio telescopy. H I is found to be distributed around the optical object in a lumpy, flattened ring, and the H I distribution major axis of 2 kpc diameter has essentially the same orientation as the optical major axis. The H I observations studied suggest that M81 dwA consists of a lumpy H I annulus which may be supported by turbulent motions in the gas rather than by rotation. The B-V color and a negative optical search for H-beta emission from the optical object imply that there has been no recent overall star formation in the galaxy. Publication: The Astrophysical Journal Pub Date: February 1983 DOI: 10.1086/160715 Bibcode: 1983ApJ...265..711S Keywords: Dwarf Galaxies; Hydrogen Clouds; Interstellar Gas; Radio Sources (Astronomy); Brightness Temperature; Galactic Structure; Radial Velocity; Red Shift; Astrophysics full text sources ADS | data products SIMBAD (1) NED (1)

Uncertainties in the Tully-Fisher Method, and a Philosophical Remark

Studies are now in progress on the nature of various possible systematic and random errors which may be influencing the values of the Hubble parameter Ho derived from application of the Tully-Fisher method to samples of cluster spirals outside of the Local Supercluster. Three effects seem to be of most importance. (1) Clusters yield slopes in the infrared Tully-Fisher diagram varying from 8 to 12, making it problematic as to how to derive a relative distance modulus from comparison with the local calibrators, (2) errors in measured 21-cm line widths (often measured at low signal-to-noise ratios) are the dominant source of error in derived relative distances, (3) errors in measured optical major and minor axes of a galaxy influence both its derived inclination and the H-magnitude as corrected to a standard isophote. Monte Carlo simulations of cluster samples, however, have shown that the tendency not to detect H I from edge-on and/or low-luminosity galaxies introduces no important biases. Overall, the relative distance of any of these clusters to the local calibrators appears to be good to ±20%.

Are there correlations between radio and optical axes of radio galaxies?

The relative orientations of radio and optical axes of radio galaxies have been examined on the basis of combined material from several smaller samples. Rotation axes of some radio galaxies have been redetermined assuming that the published measurements refer to rotational motions only. It is found that the rotation axis is quite different from those previous determinations, where rotation-expansion models were used. In particular, the correlation between radio source axes and rotation axes disappears when the allowance for expansion is dropped. No statistically significant correlation between optical major axes of the galaxy image and radio source axes is found when all existing measurements, now exceeding 140, are combined.

First results of a sensitive search for H I envelopes in a complete sample of spiral galaxies - Extensive H I near the isolated SC I NGC 628

view Abstract Citations (85) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS First results of a sensitive search for H I envelopes in a complete sample of spiral galaxies : extensive H I near the isolated SC I NGC 628. Briggs, F. H. ; Wolfe, A. M. ; Krumm, N. ; Salpeter, E. E. Abstract Preliminary results of a search with the Arecibo 1000-foot (305-m) telescope for extended H I envelopes surrounding spiral galaxies show that column densities of H I greater than or equal to 3 x 10 to the 18th/sq cm at 2-3 Holmberg radii are not common. The sample includes all galaxies of Hubble type later than S0, with optical major-axis diameter greater than 7 arcmin, and with declination 3-35 deg, and recessional velocity greater than 200 km/s. The prevalent upper limit to H I column density suggests that these outer regions (radius greater than two Holmberg radii) cannot form QSO-like Mg II absorption lines unless the abundance of Mg is at least 10 times that observed in the interstellar medium or in Population II regions of the Galaxy. The isolated Sc I galaxy NGC 628 is an exceptional case. This large, face-on galaxy shows H I emission extending asymmetrically to the SW as far as 3 Holmberg radii. Publication: The Astrophysical Journal Pub Date: June 1980 DOI: 10.1086/158007 Bibcode: 1980ApJ...238..510B Keywords: Centimeter Waves; Hydrogen Clouds; Interstellar Gas; Radio Astronomy; Radio Sources (Astronomy); Spiral Galaxies; Abundance; Data Processing; Hydrogen Atoms; Magnesium; Astrophysics full text sources ADS | data products SIMBAD (13) NED (13)

Neutral hydrogen in the interacting pair NGC 4725/NGC 4747

view Abstract Citations (15) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Neutral hydrogen in the interacting pair NGC 4725/NGC 4747. Haynes, M. P. Abstract Neutral hydrogen observations of the galaxy pair NGC 4725/NGC 4747, a subsystem within the Coma I cloud, reveal severe distortion in the HI distribution of NGC 4747. The ridge of the HI emission within the galaxy deviates from the optical major axis by about 30 deg and appears to coincide with a faint optical appendage. The companion NGC 4725, a supergiant spiral, is the most prominent member of the Coma I cloud and is almost twenty times more massive than its neighbor. NGC 4725 itself shows small but noticeable perturbations. A tidal encounter is invoked in order to explain the catastrophic events which have led to the distortion of NGC 4747 and the formation of its HI and optical tail. Publication: The Astronomical Journal Pub Date: December 1979 DOI: 10.1086/112613 Bibcode: 1979AJ.....84.1830H Keywords: Galactic Structure; Hydrogen Clouds; Interstellar Gas; Neutral Gases; Astronomical Photography; Galactic Evolution; Photographic Plates; Spiral Galaxies; Velocity Distribution; Astrophysics full text sources ADS | data products NED (14)

Radio Map of the Andromeda Galaxy

The University of Illinois radio telescope has resolved the 610.5 Mcy/sec disk component of radio emission from the large galaxy M 31 into several discrete concentrations. In two cases, these correspond to the crossing of the optical major axis by spiral arms. A spur of emission extends southeast from the galaxy near the minor axis.