Large Velocity Widths Research Articles

A High‐Velocity Molecular Cloud near the Center of the Galaxy

We report the detection of a peculiar molecular cloud, CO 0.02-0.02, lying about 5' Galactic east from the center of the Galaxy. 12CO images taken with Nobeyama Radio Observatory (NRO) 45 m telescope showed that it is relatively compact (~3×4 pc2) as well as having a very large velocity width (ΔV≥100 km s-1). The cloud has a virial mass about 1 order of magnitude larger than the LTE mass, 9×104 M☉, indicating the cloud is apparently gravitationally unbound. New observations with the James Clerk Maxwell Telescope 15 m and the NRO 45 m telescopes show that CO 0.02-0.02 is very bright in the CO (J=3-2) and in the HCN and HCO+ (J=1-0) lines. It appears that the environment may have an unusually high density and temperature, which may be related to the very broad CO line width. We propose that CO 0.02-0.02 may have been accelerated, heated, and compressed in a series of supernovae shocks that have occurred within the last (3-5)×104 yr.

A Large‐Scale CO Survey of the Galactic Center

We present high-resolution CO images of the Galactic center region taken with the 2 × 2 focal-plane array receiver mounted on the 45 m telescope of Nobeyama Radio Observatory. We have collected about 44,00012C16O (J = 1-0) spectra and over 13,00013C16O (J = 1-0) spectra with a 34'' (1.4 pc) grid spacing. The 12CO mapping area is roughly -15 ≤ l ≤ +34 and -06 ≤ b ≤ +06, which covers almost the full extent of the molecular gas concentration in the Galactic center. These CO images demonstrate extremely complex distribution and kinematics of molecular gas in the Galactic center. While its large-scale behavior can be attributed to the well-known coherent features, bright CO emission arises from a number of compact (d ≤ 10 pc) clouds with large velocity widths (ΔV ≥ 30 km s-1). The small-scale structure of molecular gas is characterized by filaments, arcs, and shells. The boisterous molecular gas kinematics there may be a result of violent release of kinetic energy by a number of supernova explosions and/or Wolf-Rayet stellar winds.

4.13. A high velocity molecular cloud near the center of the Galaxy

Molecular clouds in the Galactic center region are characterised by their large velocity widths and physical conditions which differ from clouds in the Galactic disk (e.g., Morris 1996). These clouds may not be gravitationally bound, but in equilibrium with the high external pressure in the Galactic bulge (Spergel & Blitz 1992, Oka et al. 1997a).

Unusual Emission-Line Regions in the Tidal Arm of NGC 7318B in Stephan's Quintet

We report the optical spectroscopic discovery of two unusual emission-line regions in the tidal arm of a galaxy, NGC 7318B, that belongs to Stephan's Quintet. They are associated spatially with the unusual radio continuum emission discovered between the two galaxies NGC 7318B and NGC 7319. Taking account of both the large velocity widths of the emission lines, ~900 km s−1, and the strong [S II] λλ6717, 6731 emission with respect to Hα emission, we identify them as optical emission-line filaments of supernova remnants (SNRs) traced by the radio continuum and soft X-ray emission. Our narrowband Hα imaging shows that the unusual emission-line regions are indeed parts of the ionized bubble associated with one radio continuum peak. The required number of SNRs is estimated to be ~105-106 on the basis of the Hα, radio, and soft X-ray luminosities. Since there is no optical counterpart like a star cluster, it is suggested that ~105-106 supernova events occurred nearly simultaneously in this region several times 106 yr ago.

Measuring the Hubble constant and our Virgo-infall velocity independently

A sample of spiral galaxies with B(sub T) less than 14.5 located in two local volumes, one in the direction of, but behind, the Virgo Cluster (behind-Virgo volume (BV)) and the other in the opposite direction (anti-Virgo volume (AV)), were used via a Tully-Fisher (TF) relation to derive the following two parameters: H(sub AB), the mean Hubble ratio between AV and BV, and delta v(sub parallel), the peculiar velocity of the Local Group in the direction of the Virgo Cluster (VC) with respect to a uniformly expanding reference system defined by our AV and BV sub-samples. The two sampled volumes, separated by a velocity interval of 5600 km/s, form an antipodal pair. This particular geometry not only allows us to derive the two parameters independently but also reduces the dynamical effect of the Local Supercluster on H(sub AB) without increasing the Malmquist bias. By limiting our sample to spiral galaxies having large velocity widths W(sub R), we effectively reduce the TF scatter and Malmquist bias in our sample. The TF zero point and dispersion were then determined by further correcting for the small residual Malmquist bias. An additional sample of fainter galaxies was used to test for a non-Gaussian tail to the TF disperison. We found no evidence for such a tail and formally give an upper limit of about 18% for the fractional contribution of an unseen tail. The average intrinsic TF dispersion for the dominant Gaussian component is sigma(sub TF)(sup 0) approximately 0.33 mag for W(sub R) approximately equal to or greater than 180 km/s. Our numerical results are delta v(sub parallel) approximately equals 414 +/- 82 km/s and H(sub AB) approximately equals (84.0 +/- 2.4)(1 + epsilon) km/s Mpc, where (1 + epsilon) accounts for any systematic error between the calibrators and the sample galaxies. Various dynamical models were tested to explore the effect on H(sub AB) of the uncertainties in the local velocity field. Constrained by our observed delta v(sub parallel) as well as other observational quantities, we found that the rms deviation from unity of H(sub AB)/H(sub 0) (where H(sub 0) is the Hubble constant for each model) is 5%, making H(sub AB) a good indicator for H(sub 0). Taking this variation as an additional error, our formal estimate for the Hubble constant is H(sub 0) approximately equals (84 +/- 5)(1 + epsilon) km/s Mpc.

A kinematic search for supernova remnants in giant extragalactic H II regions

We have obtained velocity fields of the Giant H II complexes NGC 5471 in M101, NGC 2363 in NGC 2366, and the largest H II region in NGC 2403 from H-alpha observations using the TAURUS imaging Fabry-Perot interferometer. We have detected five H-alpha sources with velocity profiles which are broad when compared with the surrounding H II region. Region B in NGC 5471 has been previously determined to contain a supernova remnant by the presence of nonthermal radio continuum radiation and enhanced (O I) and (S II) emission (Skillman 1985) and broad H-alpha emission (Chu & Kennicutt 1986). Two broad H-alpha sources in NGC 2363 coincide with regions where strong splitting has been found in the (O III) line (Roy et al. 1991). Two more broad H-alpha sources have been identified in the largest H II region in NGC 2403. Very Large Array (VLA) radio continuum observations with a resolution of 2 sec at lambda(6) and lambda(20) cm of all 3 H II complexes are presented. In addition, high resolution (subarcsecond) VLA images of NGC 5471 were made at lambda(2) and lambda(6) cm. The presence of a nonthermal source in region NGC 5471 B was confirmed while region NGC 5471 A appears to be dominated by thermal emission. The nonthermal spectral index in NGC 2363 A indicates the existence of none or more supernova remnants at the position of a large velocity width source detected in H-alpha emission. No similar nonthermal sources were detected in NGC 2403 #1. Supernovae explosions and stellar winds are considered as causes for these large velocity width sources (LVWS). If the emission from the LVWSs is attributed to single supernova remnants, they are unusually luminous in both nonthermal radio continuum and H-alpha emision. The very large H-alpha luminosities could be a result of high velocity gas being ionized by the neighboring stellar cluster.

UGC 7636 and NGC 4472 - Tidal interaction between a stripped dwarf irregular and a giant elliptical galaxy

view Abstract Citations (26) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS UGC 7636 and NGC 4472: Tidal Interaction between a Stripped Dwarf Irregular and a Giant Elliptical Galaxy Patterson, Richard J. ; Thuan, Trinh X. Abstract We present new B and I CCD and H I observations of the system in the Virgo Cluster composed of the dwarf irregular galaxy UGC 7636 and the giant elliptical galaxy NGC 4472. These observations strongly suggest that both ram-pressure and tidal stripping have occurred in this system. The H I gas between the two galaxies has been stripped from UGC 7636. Its M(H I)/L_B_ ratio is 0.26 M_sun_/L_B_sun_, in the range observed for dwarf irregulars. Ram-pressure stripping of the H I gas from the dwarf is suggested by the large velocity width ({DELTA}v_50_~110 km s^-1^) of the spatially extended H I envelope. The presence of a red optical tidal tail and countertail in the dwarf, with the same colors as the stars in the dwarf's outer regions, as well as a disturbed morphology in the dwarf's inner parts, are evidence for tidal interaction between the two galaxies. Publication: The Astrophysical Journal Pub Date: December 1992 DOI: 10.1086/186648 Bibcode: 1992ApJ...400L..55P Keywords: Dwarf Galaxies; Elliptical Galaxies; Interacting Galaxies; Irregular Galaxies; Virgo Galactic Cluster; Astronomical Photometry; Cosmology; Galactic Structure; H I Regions; Intergalactic Media; Interstellar Gas; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4472; GALAXIES: INDIVIDUAL ALPHANUMERIC: UGC 7636; GALAXIES: INTERACTIONS; GALAXIES: INTERSTELLAR MATTER; GALAXIES: PHOTOMETRY full text sources ADS | data products SIMBAD (2) NED (2)

Properties of ionized interstellar froth in irregular galaxies

Results are reported from new observations of large-scale H-alpha filamentary structures lying outside of classical H II regions in Magellanic irregular galaxies. These structures (froth) are seen as arcs, loops, and filaments, some of which are centered on OB associations and some of which extend away from giant H II regions into regions of lower H I column density. The data show the following: (1) the level of ionization of the froth is lower than in H II regions in the same galaxies; (2) frothy features have large line velocity widths that often exceed those found in classical giant H II regions in the same galaxies; (3) the froth has H-alpha surface brightnesses of about 100 Rayleighs, 10-100 times brighter than typical diffuse Galactic emission; and (4) dimensions are large, a typical filament is 700 x 50 pc. 94 refs.

Kinematic detection of supernova remnants in giant H II regions

view Abstract Citations (41) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematic detection of supernova remnants in giant HII regions. Chu, You-Hua ; Kennicutt, Robert C., Jr. Abstract In a kinematic survey of giant H II regions in M 101, four sources that have large velocity widths at low intensity levels are detected. Two of these large-velocity-width sources (LVWSs) are, within the limit of resolution, coincident with nonthermal radio sources several times as luminous as Cas A. The LVWS in NGC 5471 B is so bright that it is possible to separate its broad profile from the narrower profile of the background H II region. H-alpha CCD photometry, optical spectroscopy, and high-resolution radio data are combined to derive its physical properties, which support Skillman's (1985) identification of the object as a supernova remnant. The other LVWSs might be supernova remnants embedded in giant H II regions, unusually massive wind-driven shells, or the combination of both. Publication: The Astrophysical Journal Pub Date: December 1986 DOI: 10.1086/164755 Bibcode: 1986ApJ...311...85C Keywords: H Ii Regions; Spiral Galaxies; Supernova Remnants; H Alpha Line; Kinematics; Kinetic Energy; Nonthermal Radiation; Optical Emission Spectroscopy; Radio Spectra; Spectral Line Width; Astrophysics; ASTEROIDS; COLOR; COMETARY ATMOSPHERES; COMETS; HALLEY'S COMET; ASTRONOMICAL PHOTOMETRY; ATMOSPHERIC REFRACTION; CONTINUUMS; SPACE OBSERVATIONS (FROM EARTH) full text sources ADS | data products SIMBAD (8) NED (5)

FST Observations of NGC 4945 and the Circinus Galaxy

AbstractThe Fleurs synthesis telescope, which provides 20 arcsec resolution at 1.4 GHz, was used to map the continuum emission in NGC 4945 and the Circinus galaxy. Both objects have prominent small-diameter radio nuclei, containing 50% to 75% of the total intensity, superimposed on extended emission associated with the outer regions of the galaxies. The scale of the nuclei, together with the large velocity widths of the associated spectral-line profiles, are not unlike those encountered in the central region of the Galaxy.

H I observations of high-luminosity elliptical galaxies

Sensitive 21-cm line observations were made with large velocity coverage towards eight luminous early-type galaxies in a search for possible H I emission with a large velocity width. Only one object, the tidally interacting pair of S0's NGC 4105/4106, was detected, with M(H I)/L/sub B/ = 0.05 M/sub sun//L/sub sun/. Previously published detections of H I in three ellipticals (NGC 2974, 3904, and 3962) were not confirmed. Low limits on the H I content of the luminous ellipticals NGC 4472 and NGC 5322 were set; with assumed linewidths of 1100 km/s, we find M(H I)/L/sub B/ < or approx. =0.005 and < or approx. =0.04 M/sub sun//L/sub sun/, respectively.

Formaldehyde in the Galactic Centre - I. The observations

Formaldehyde 6-cm absorption in the direction of the Galactic Centre has been surveyed using the Jodrell Bank MK II radio telescope (beam-width 10 × 9 arcmin). The observations sample the region |$-2^\circ \leqslant l \leqslant 5^\circ$| and |$-0^\circ.5 \leqslant b \leqslant 0^\circ.5$|⁠, with a velocity range of 620 km s−1 a velocity resolution of 2.1 km s−1 and an rms noise level of ∼ 0.03 K. The data are presented as contour maps showing line temperature as a function of latitude and velocity (b–V maps) and as a function of longitude and velocity (l–V maps). Similar maps of the line-to-continuum ratio are also presented. The radial distribution of formaldehyde (H2CO) in the Galactic Centre region is derived using two different kinematic models which give similar results. Formaldehyde is strongly concentrated in the Galactic Centre in a layer of latitude extent ∼ 0°.5 and longitude extent ∼ 4° which contains one quarter of all the H2CO in the Galaxy. The distribution is centred on l ∼ 1°. The individual H2CO features are described in detail. Several have not previously been detected in H2CO, although they were known from H I and OH studies. The Galactic Centre features all have unusually large velocity widths. Some of the strongest features appear to be associated with H II regions.