The extension of the Hubble diagram. II - New redshifts and photometry of very distant galaxy clusters - First indication of a deviation of the Hubble diagram from a straight line

Redshifts are given for 50 brightest cluster galaxies, extending as far as z = 0.75; BVR photometry is given for 33 clusters. These data are combined with earlier data of a similar kind in order to investigate several effects. The measured B - V and V - R colors as a function of redshift are well represented by Whitford's standard-galaxy K corrections, as far as these are defined (to z = 0.28 in B - V and z = 0.48 in V - R). This suggests both that the K corrections are valid over these ranges of z and that no major color change of the galaxies has occurred over the last 4-5 x 10^9 years. At larger redshifts, the colors, which start out being monotonically redder with z, turn over and become bluer with z. The data at large z seem to follow the prediction based upon ultraviolet photometry of NGC 4486 (M87), which is one extreme of a range of galaxies measured by Code and Welch. Other standard corrections to the measurements are discussed, and formal least-squares values of q_0 are computed. To explore the possibility that one might be stalemated by the fact that the value of q_0 must, in principle, be known a priori to compute the aperture correction, the data are corrected separately for assumed q_0 values of 0 and + 1. The subsequently computed values of q_0 differ by only 0.2 between the two cases, which indicates that a simple iterative procedure will converge to produce a self-consistent value of q_0. The new data do not significantly change earlier discussions of the corrections for cluster richness and Bautz-Morgan contrast type. If these two corrections are not made, the effect on the present data is to significantly increase the positive curvature of the Hubble diagram, as well as the dispersion in apparent magnitude. To within the limits of the present data, the absolute magnitude of the brightest cluster galaxy does not, in general, depend on whether it is also a bright radio source. The present sample, cut off at z = 0.4 to avoid selection effects and uncertainties in the data, shows the first significant evidence for curvature of the Hubble diagram, with V and R magnitudes giving similar results. The formal value of q_0 (with galaxy evolution ignored) is + 1.6 ± 0.4. The dispersion in absolute magnitude is less than 0.3 mag, with M_v = -23.28 ± 0.03 and M_R= -24.09 ± 0.03. The use of the Hubble diagram in cosmology now depends on a knowledge of brightness changes in galaxies, on the one hand, or of q_0 from other evidence, on the other. For example, if it were known with certainty that there has been no significant change in elliptical galaxy luminosities during the last 4 x 10^9 years, then the present data are nearly good enough for one to say definitively that the universe is closed and finite, with a finite lifetime. At the other extreme, if it were known with certainty from other evidence that the universe was nearly empty (q_0 ≈ 0), then the present data set the constraint that net galaxy luminosities have decreased by ~ 0.5 mag during the last 5 x 10^9 years, with a net color change Δ(B - V) ≤ 0.1 mag. It seems possible at present to construct a self-consistent model with q_0 ≈ 0 that satisfies the known data, but the case is not yet settled

Rapid Changes in the Optical Intensity and Radial Velocities of the X-Ray Source SCO X-1

The optical flux of Seo X-1 was continuously monitored on five separate nights between April and June 1967. Pulse counting was used with sampling intervals of 5 sec on the 100- and 200-inch telescopes and 15 sec on the 60-inch reflector. The error due to photon statistics per sample interval was smaller than 0.007 mag in all cases. The data were processed entirely by computer, using a variety of special digital techniques. Rapid optical flickering with amplitudes of ~0.02 mag on a time scale of minutes was found on all five nights. These high-frequency fluctuations are superposed on slower continuous variations with amplitudes ~0.15 mag, and on occasional bursts of 0.2 mag which last about 10 min with very short rise and decay times. Radial velocities have been measured by a digital method of cross-correlation of microphotometer records of the original photographic plates (Westphal 1966). Velocity changes of about 100 km sec^(-1) were found on two different singly trailed plates, each of 3 hours' duration. The hydrogen lines and He II (⋋4686) change in opposite directions, similar to the extar Cyg X-2, suggesting, but not proving, binary motion. Systematic changes of velocity from night to night are set out in Table 2. The distance to Seo X-1 is estimated to be D ≃ 500 pc by three methods, based on the strength of interstellar Ca II K, and on the old nova hypothesis. A firm lower limit of D ≥ 300 pc seems well established. The total X-ray power is ≃2 x 10^(37) h^2 ergs sec^1, where his the distance in units of 500 pc. If the Xray energy is due to bremsstrahlung, this level requires Seo X-1 to continuously pump energy into the hot plasma, replenishing the entire energy store of gas in the cooling time of t_c = 3 X 10^(-15) h^(-1) R^(3/2) sec where R is the radius (in centimeters) of the plasma system. Reasonable values of 10^(11) cm < R < 10^(12) cm give 100 h^(-1) < t_o < 3000 h^(-1) sec, which, remarkably, is the characteristic time of the light flicker. Mechanical energy due to some type of low-Q oscillation of the system, similar in many respects to that observed in the Sun, seems capable of providing 10^(37) ergs sec^(-1) to the plasma gas. The crucial experiment remains to simultaneously monitor the optical and the X-ray flux over periods of several hours. Detailed correlation of fluctuations is not expected, but the mean X-ray flux might plausibly be expected to vary in periods of fractions of an hour as the mean amplitude of the optical fluctuations changes

Absorption-line redshifts of galaxies in remote clusters obtained with a sky-subtraction spectrograph using an SIT television detector

A prism spectrograph with an associated SIT television camera, operating as a two-dimensional detector with digital readout, has been used at the 5-m Hale telescope. The system was tested for its ability to subtract the sky spectrum, and was found to produce difference spectra that are essentially photon noise limited. Redshifts of 14 galaxies in clusters with 0.01 ≤ z ≤ 0.4 were obtained, each with exposure times of 90 minutes or less. Nine of the redshifts are new. Redshifts for the remaining five agree with previous values to within the measuring errors. The speed and sky-subtraction capabilities of the instrument are sufficient to begin routine measurement of absorption-line redshifts for remote cluster galaxies in an effort to extend the Hubble diagram

Results of Five Nights of Continuous Monitoring of the Optical Flux from SCO X-1

Data obtained during five nights of continuous monitoring of the X-ray source Seo X-1 between April and June 1967 are shown in computer-generated point plots

Rapid Photometric and Spectroscopic Variations of the X-Ray Source CYG X-2

Fluctuations of 0.04 mag on a time scale of minutes have been found in the optical flux of the candidate star for Cyg X-2. Comparison of radial velocities on a well-widened spectrogram with those of Lynds shows large changes, confirming an earlier suspicion of binary motion by E. M. Burbidge. The systemic velocity is y = -250 km/sec. A lower limit of 300 km/sec for the orbital velocity of one component relative to the other is indicated. The system parameters are m = m_1 + m_2 = 1, P < 0.4 M_☉ (days), and ɑ < 0.01 M_☉ a.u., indicative of a very close binary system (m = m_1 + m_2). Eclipses are probable and may have been observed. Spectroscopic evidence may be present for gas streams moving with speeds of greater than 700 km/sec. Three independent arguments are given why the optical flux cannot primarily be non-thermal radiation connected with the production of the X-rays

The extension of the Hubble diagram. I. New redshifts and BVR photometry of remote cluster galaxies, and an improved richness correction

Absorption-line redshifts for 37 galaxies in 31 remote clusters have been measured with the new sky-subtracting prism spectrograph, using an SIT television detector with digital readout. Twenty-five galaxies in the sample have redshifts larger than z = 0.20. New photoelectric BVR photometry has been obtained for 16 of the clusters. Magnitudes corrected for aperture effect, K-dimming, galactic absorption, cluster richness, and Bautz-Morgan contrast effect are listed. The data permit an improvement in the statistics of the Hubble diagram to z = 0.28 and a new determination of the dependence of the absolute magnitude of the brightest cluster galaxy on cluster richness. A small correlation with richness is found whose amplitude is 0.20 ± 0.18 mag over all Abell richness classes 0-4. As in previous studies, the shallowness of the correlation requires that if M(l) is governed by a general luminosity function, Φ(M), for fainter members, then the slope of Φ(M) at M(I) must be very steep. The 16 new clusters with photometry have a dispersion in M(l) of 0.26 mag. The dispersion of fully corrected magnitudes for the 65 clusters in the total sample is 0.276 mag. The new points in the Hubble diagram give no indication that the (m, z) relation deviates from the q_0(formal) = + 1 line (i.e. with no evolutionary correction applied), nor that 3C 295 is abnormally bright. The need for more data with z > 0.3 is stressed

CCD photometry of the nuclei of three supergiant elliptical galaxies - Evidence for a supermassive object in the center of the radio galaxy NGC 6251

We have analyzed charged coupled device (CCD) photometry in the g and r bands of three supergiant elliptical galaxies: NGC 4874 and NGC 4889 in the Coma cluster, and the radio galaxy NGC 6251. The profiles of NGC 4874 and NGC 4889 are closely fitted by King models. The profile of NGC 6251 cannot be fitted by a King model, nor by a King model plus a central point luminosity source (the presence of which is suggested by a blue trend in the colors at small radii). The previously studied profile of M87, when convolved with an appropriate Gaussian function to allow for the difference in distance, closely resembles the profile of NGC 6251 (but not those of NGC 4874 or NGC 4889). NGC 6251 was successfully fitted with a luminosity profile containing both a point luminosity source and a central point mass. The value of this point mass cannot be determined without additional dynamical data. However, if the core velocity dispersion is similar to that of other giant ellipticals of the same absolute magnitude, the point mass is likely to be about 2.4 x 10^9 M_⊙, similar to the value reported earlier for M87. The data are also used to derive upper limits for possible central point masses in NGC 4874 and NGC 4889

Evidence for a supermassive object in the nucleus of the galaxy M87 from SIT and CCD area photometry

Two-dimensional SIT and CCD detectors have been used to measure the surface brightness of the peculiar elliptical radio galaxy M87. Measurements were made in three broad-band colors (B, V, and R) to a distance of 80" from the nucleus, with 1" spatial resolution and photometric accuracy of the order of 1%. The data are given in some detail and are compared with earlier photographic results. The most obvious feature of the data is a bright, barely resolved central luminosity spike, which is not seen in similar data on other nearby normal ellipticals. Also, attempts to fit isothermal or King models away from the nuclear spike show additional excess luminosity in the central regions of the galaxy (r 60. All of the existing data is well fitted by a King model containing a central black hole of mass M = 3 x 10^9 M_⊙ and a point luminosity source. While such a model is not uniquely required by the data, it is perhaps the most plausible of several possible models considered. At present, M87 is probably the best case for a hypothetical massive black hole in a galaxy nucleus

The triple quasar Q1115+080A, B, C - A quintuple gravitational lens image

Spectroscopy and direct imaging of Qll 15+080A,B,C with a CCD camera supports the hypothesis that they are gravitational images of a single object. Spectroscopy of the C III] λ1909 emission line shows all the images to have identical spectra and redshifts (to within 100 km s^(-1)), except that Bis slightly redder. The position and brightness of the three images has been accurately measured; the images A, B, and Care magnitudes 16.30,18.64, and 18.17, respectively, in the r band, B is 1". 77 from A in position angle 266°, and C is 2".28 away at position angle 322°. A and C have the same color, but B is redder by 0.23 mag in (g-r). There is no trace of a lens galaxy, which must have a surface brightness of less than 29 mag arcsec^(-2) at a distance of 5" -8" from Q1115+080. Three bright galaxies lie near Q1115+080, apparently forming a small group. Gravitational lens imaging by a massive spiral galaxy is explored, and we find a quintuple image model resembling Q1115+080 A,B,C. In this model, Q1115+080A is a highly magnified close pair of images oriented in position angle 23°. An elongation of Q1115+080A at this angle is seen in the CCD pictures

On the Nature of Ryle and Bailey's Candidate Star for the Pulsating Radio Source CP 1919

The energy distribution and spectrum of the "blue" star near CP 1919 indicate that it is a normal early F, main-sequence star and therefore is not likely to be related to the radio source. No regular variations were found in the light from the star, to within an accuracy of a few tenths of 1 per cent