arXiv subjects

R. D. Ekers

Publications and source records attributed to R. D. Ekers.

113 records · Page 7Linked to original sources

arXiv1998

New HI-detected Galaxies in the Zone of Avoidance

We present the first results of a blind HI survey for galaxies in the southern Zone of Avoidance with a multibeam receiver on the Parkes telescope. This survey is eventually expected to catalog several thousand galaxies within Galactic latitude |b|<5 degrees, mostly unrecognised before due to Galactic extinction and confusion. We present here results of the first three detections to have been imaged with the Australia Telescope Compact Array (ATCA). The galaxies all lie near Galactic longitude 325 degrees and were selected because of their large angular sizes, up to 1.3 degrees. Linear sizes range from 53 to 108 kpc. The first galaxy is a massive 5.7x10^11 solar mass disk galaxy with a faint optical counterpart, SGC 1511.1--5249. The second is probably an interacting group of galaxies straddling the Galactic equator. No optical identification is possible. The third object appears to be an interacting pair of low column density galaxies, possibly belonging to an extended Circinus or Centaurus A galaxy group. No optical counterpart has been seen despite the predicted extinction (A(B) = 2.7 - 4.4 mag) not being excessive. We discuss the implications of the results, in particular the low HI column densities (~10^19 atoms/sq.cm) found for two of the three galaxies.

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arXiv1998

The disruption of nearby galaxies by the Milky Way

Interactions between galaxies are common and are an important factor in determining their physical properties such as position along the Hubble sequence and star-formation rate. There are many possible galaxy interaction mechanisms, including merging, ram-pressure stripping, gas compression, gravitational interaction and cluster tides. The relative importance of these mechanisms is often not clear, as their strength depends on poorly known parameters such as the density, extent and nature of the massive dark halos that surround galaxies. A nearby example of a galaxy interaction where the mechanism is controversial is that between our own Galaxy and two of its neighbours -- the Large and Small Magellanic Clouds. Here we present the first results of a new HI survey which provides a spectacular view of this interaction. In addition to the previously known Magellanic Stream, which trails 100 degrees behind the Clouds, the new data reveal a counter-stream which lies in the opposite direction and leads the motion of the Clouds. This result supports the gravitational model in which leading and trailing streams are tidally torn from the body of the Magellanic Clouds.

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arXiv1998

The gamma-ray burst of 980425 and its association with the extraordinary radio emission from a most unusual supernova

Supernova SN 1998bw exploded in the same direction and at the same time as the gamma-ray burst GRB 980425. Here we report radio observations of this type Ic supernova, beginning 4 days after the gamma-ray burst. At its peak the radio source is the most luminous ever seen from a supernova, nu L_nu = 4 x 10^38 erg/s at 5 GHz. More remarkably, the traditional synchrotron interpretation of the radio emission requires that the radio source be expanding at an apparent velocity of at least twice the speed of light, indicating that this supernova was accompanied by a shock wave moving at relativistic speed. The energy U_e associated with the radio-emitting relativistic electrons must lie between 10^49 erg <U_e< 10^52 erg, and thus represents a significant fraction of the total kinetic energy ~10^51 erg associated with supernova explosions. The presence of a relativistic shock in SN 1998bw suggests a physical connection with the gamma-ray burst GRB 980425. We argue that this represents a second class of gamma-ray burst, with much lower emitted energy ~10^48 erg in gamma-rays than the two powerful ~10^53 erg high-redshift gamma-ray bursts previously identified.

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arXiv1998

Radio jet interactions in the radio galaxy PKS 2152-699

We present radio observations of the radio galaxy PKS 2152-699 obtained with the Australia Telescope Compact Array (ATCA). The much higher resolution and s/n of the new radio maps reveals the presence of a bright radio component about 10 arcsec NE of the nucleus. This lies close to the highly ionized cloud previously studied in the optical and here shown in a broadband red snapshot image with the HST PC2. It suggests that PKS 2152-699 may be a jet/cloud interaction similar to 3C277.3. This could cause the change in the position angle (of ~20 deg) of the radio emission from the inner to the outer regions. On the large scale, the source has Fanaroff & Riley type II morphology although the presence of the two hot-spots in the centres of the lobes is unusual. The northern lobe shows a particularly relaxed structure while the southern one has an edge-brightened, arc-like structure.

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arXiv1997

Observations of the 57Fe+23 Hyperfine Transition in Clusters

We present a search for the hyperfine transition of the 57Fe+23 ion at 3.071 mm in clusters of galaxies with the ATNF Mopra telescope. The results are compared with a realistic estimate of the peak brightness temperature of the line in a cooling flow cluster A85, using the available X-ray data.

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