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A New Candidate for the Dark Group of Galaxies, RX J0419+0225
The bright extended X-ray source RX J0419 + 0225, first discovered inthe ROSAT All Sky Survey and identified with an S0 galaxy NGC 1550, wasobserved with ASCA for 48ks in 1999 August. The detected diffuse X-rayemission is centered at NGC 1550, whose redshift is 0.0123, extendingout to at least 15', or 210h-175 kpc, whereh75 is the Hubble constant in units of 75 km s-1Mpc-1. The X-ray surface brightness is represented by aβ model with β = 0.47 and a core radius of 15 ± 1h -175 kpc. The temperature and 1-10keV X-rayluminosity (up to 15') of this system were measured as being 1.4keV and4.7 × 1042 h-275 ergs-1, respectively. There is no strong evidence of atemperature gradient. Within a radius of 210h-175, the estimated total mass of the systembecomes 1.5 × 1013 h-175Msolar, which is typical of a galaxy group. With the opticalinformation currently available, there are only two other faintgalaxies. Including their B-band luminosity, the mass-to-light ratio ofthe system comes to 400 h75MsolarLsolar, which is comparable to those ofgalaxy clusters. Therefore, RX J0419 + 0225 can be regarded as a ``darkgroup candidate'' in that it has an unusually high mass-to-light ratiofor its optical luminosity. This object is one of the nearest amongthose ever identified as such candidates.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
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