Cluster Luminosity Function Research Articles

The population structure of the Large Magellanic Cloud disk. I - Photographic and photoelectric observations of the underlying stellar component of the central regions

view Abstract Citations (11) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The population structure of the Large Magellanic Cloud disk. I. Photographic and photoelectric observations of the underlying stellar component of the central regions. Hardy, E. Abstract Three homogeneous regions in the vicinities of the Large Magellanic Cloud bar that are 3'.4 in diameter and that represent the underlying background sheet of old stars have been observed photographically in the B, V system. Color-magnitude (C-M) diagrams have been constructed to V = 19.3 l 0.3 (Mv = 0.7 I 0.3). In addition, surface photometry in the UBV and DDO systems have been obtained for each area. The C-M diagrams show a weak young component superposed on what may be a strong old metal-poor population as typified by a sequence of red giant branches of intermediate to high metallicity in the globular cluster sense. The residual surface colors after subtraction of the contribution from the young population are compatible with this interpretation. However, the uncertainties in the identification of the horizontal branch of Population II together with the lack of integrated color observations and luminosity functions of intermediate-age clusters of the galactic NGC 2158 type or the Magellanic NGC 2209 type, prevent us from excluding an intermediate-age population as the main contributor to the light of the bar. Fitting of the young population to the Salpeter luminosity function shows that only 20% of the total light is contributed by this population. It is shown in a unique way that a large fraction of the light of the central region of the LMC disk is contributed by evolved giants, a result of importance for the problem of luminosity evolution of galaxies. Subject headings: galaxies: Magellanic Clouds - galaxies: stellar content Publication: The Astrophysical Journal Pub Date: February 1977 DOI: 10.1086/154982 Bibcode: 1977ApJ...211..718H Keywords: Astronomical Photometry; Early Stars; Magellanic Clouds; Star Clusters; Giant Stars; Interstellar Extinction; Stellar Luminosity; Stellar Magnitude; Ubv Spectra; Astronomy full text sources ADS |

The structure and contents of NGC 6822.

view Abstract Citations (113) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The structure and content of NGC 6822. Hodge, P. W. Abstract Photoelectric and photographic studies of surface brightness and color, and of individual stars and nonstellar objects, in NOC 6822 are used to establish the galaxy's structure and content. Its bar has a position angle of 100 + 30 and a mean ellipticity of 0.47 + 0.18. Its peak surface brightness is V = 21.4 mag arcsec -2, and isophotes are given out to V = 24.0. Star counts on five plates are used to compare the star density distribution with the surface brightness; the stellar luminosity function is found to vary across the galaxy, in relation to the bar. Luminosity proffles and stellar density profiles show an overall exponential decrease outward, with a slope of 0.37 1 0.05 mag arcmin . The minor axis of the bar, on the other hand, has a slope that depends on the objects sampled, being much steeper for the supergiant (resolved) stars than for the luminosity in general. The mean color of the galaxy is B - V = 0.79 1 0.06, U - = 0.04 + 020 and the reddening is E(B - V) = 0.28 + 0.03. Sixteen OB associations are cataloged and compared with those in other galaxies. Their spatial distribution is similar to that of the LMC, as are the size distribution and the relationship between size and stellar density. Their mean diameter is 163 pc. A study of 30 star clusters shows that NGC 6822 is normal in its population of these objects. Photoelectric integrated data for the brightest show normal UBV colors. The cluster luminosity function and age function are similar to those of the Magellanic Clouds, after allowance is made for the different galaxy luminosities. The H ii regions are rediscussed, and their size distribution is compared with those for other galaxies. Agreement with Sandage and Tammann's (1974) halo diameters for the three largest is good. Eleven discrete dust clouds are identified and compared with those of other galaxies. They average 39 pc in diameter, about the same as those of the SMC, but are of somewhat smaller opacity. Subject headings: galaxies: individual - galaxies: photometry - galaxies: stellar content - galaxies: structure Publication: The Astrophysical Journal Supplement Series Pub Date: January 1977 DOI: 10.1086/190419 Bibcode: 1977ApJS...33...69H full text sources ADS | data products SIMBAD (52) NED (42) GCPD (1)

A Radio Study of Abell Clusters

A search for radio sources close to 247 clusters of galaxies in the Abell catalogue has been carried out at the Molonglo Radio Observatory at a frequency of 408 MHz. A list of 116 sources near 89 clusters is given, identifications have been made and criteria for cluster membership have been established. A cluster luminosity function is derived in the range 1()23_1025 WHz-l SCi, and spectra have been obtained for sources in 25 clusters utilizing published surveys made at other frequencies. It is found that there is no correlation between the richness of a cluster and its inclusion of at least one radio source, but those clusters containing multiple sources are significantly richer than average.

The 1400-MHz luminosity function for Abell clusters of galaxies

view Abstract Citations (35) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The 1400-MHz luminosity function for Abell clusters of galaxies. Owen, F. N. Abstract New observations have been used to derive the radio luminosity function of Abell clusters of galaxies at 1400 MHz. A relatively narrow, approximately Gaussian luminosity function is found. Correlations of detection probability with optical properties are examined. No strong correlation with cluster richness is found; however, a correlation of detection above a constant absolute luminosity with distance is detected. A correlation with Rood and Sastry cluster type is also found. The mutual relation of these correlations is discussed. The relation of the cluster luminosity function to field galaxies detections and previously derived radio luminosity functions is examined. The observations are found to agree well with the predicted shape and peak luminosity of a multiple source emission model of the cluster luminosity function; however, the amplitude of the model function is higher than the observed function by a factor of 3. The possible significance of the multiple source emission model is briefly discussed. Publication: The Astrophysical Journal Pub Date: February 1975 DOI: 10.1086/153360 Bibcode: 1975ApJ...195..593O Keywords: Galactic Clusters; Luminous Intensity; Microwave Emission; Radiant Flux Density; Radio Astronomy; Astronomical Models; Luminosity; Normal Density Functions; Optical Properties; Statistical Correlation; Tables (Data); Astrophysics full text sources ADS | data products NED (127)

The Extragalactic Relative Distance Scale

Arguments are given to support the hypothesis that a characteristic point on a cluster luminosity function, m*, corresponds to the same absolute magnitude in all clusters, and thus is an appropriate standard candle for determination of relative cluster distances. It is shown, however, that if m*is a good standard candle, then the first and tenth brightest cluster galaxies, m(1) and m(10), respectively, are not, for m* – m(1) and m* – m(10) both differ significantly from cluster to cluster. Moreover, m(1) and especially m(10) depend on cluster richness. Distances derived from them for remote clusters chosen for analysis are thus subject to selection effects that depend on cluster richness and on Bautz-Morgan type. Finally, a procedure suggested by Bautz and Abell is described whereby m* can be estimated from observed properties of distant clusters.

Concerning the Forms of the Velocity-Distance Relation Clusters

view Abstract Citations (36) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Concerning the Forms of the Velocity-Distance Relation Clusters Bautz, Laura P. ; Abell, G. O. Abstract "Brightest galaxy" form types are given for 14 Humason-Mayall-Sandage clusters, for five other clusters with z < 0.2, and for the three known clusters beyond z = 0.2. A preliminary calibration of the difference in apparent magnitude between the brightest galaxy and the break in the cluster luminosity function is proposed for clusters of various richnesses and form types. This relation is used to determine a revised velocity-apparent-magnitude diagram based on matching the cluster luminosity functions. The determination of the value of q0 is shown to be very sensitive to the adopted relation. Subject headings: cosmology - galaxies, clusters of Publication: The Astrophysical Journal Pub Date: September 1973 DOI: 10.1086/152363 Bibcode: 1973ApJ...184..709B full text sources ADS |

Brightest Members of Clusters of Galaxies

THE work of Humason, Mayall and Sandage1 and the more recent work of Sandage2–5 and Peterson6 show that the dispersion in the absolute magnitude of the first brightest galaxies in rich clusters of galaxies is only 0.3 magnitude. Peebles7 suggested that this small dispersion is simply the consequence of the cluster luminosity function and compared the distribution predicted by the statistical theory with the observations of Humason, Mayall and Sandage1. I have shown8 how the distributions predicted by the statistical theory vary with the richness of the cluster of galaxies and has compared the predicted distributions with the observations of Humason, Mayall and Sandage1, and with his own observations6. But Peach9 considered that the statistical theory is inadequate when he compared the distributions calculated from the statistical theory with new data of Sandage.

Bright End of the Galaxy Luminosity Function in Clusters

PEACH1 has presented an important new set of values of M1, the absolute magnitude of the first brightest member of a rich cluster of galaxies, derived from unpublished data of Sandage. The results show again the small spread found by Humason, Mayall and Sandage2, but Peach finds that the standard deviation of the new M1 values is smaller by a factor of 2.7 than the standard deviation computed from a statistical model3 based in part on the older data of ref. 2. Peach concludes that the statistical model is inadequate, that perhaps the magnitude of the brightest cluster member is fixed and given (within standard deviation 0.27 mag.) “independent of cluster richness or the luminosity function governing the fainter members”1.

Brightest Members of Clusters of Galaxies

THERE are two opposing interpretations of the small dispersion σ1∼0.35 mag in the absolute magnitudes M1 of the brightest members of rich clusters of galaxies measured by Sandage1. In one view, advanced, among others, by Peebles2,3, it is assumed that there is a universal cluster luminosity function, and that the value of σ1 and of the variation of M1 with cluster richness can be explained as the statistical result of drawing the brightest member from a set of clusters obeying this function. There is therefore nothing physically remarkable about the brightest member, and its luminosity is determined by the same mechanism as that which determines the luminosity of the fainter members. The opposing view, which has been advanced by Peach4, Sandage1, and Tremaine and Richstone5, claims that the small dispersion is due to special conditions governing the formation or evolution of the brightest member, and is therefore entirely or in part independent of the luminosity function of the other cluster members. On this view one evokes either special conditions at the epoch of galaxy formation1, or a mechanism, such as galactic accretion6, which governs the size and luminosity of the most massive galaxy in such a way as to give a small dispersion in the metric magnitude. The weakness of the statistical model, according to its opponents, is its inability to account for σ1 without postulating a luminosity function steeper than those directly observed. The opposing view is open to the criticism that it is either ad hoc or that the mechanisms of galaxy evolution are too uncertain to lead to reliable conclusions. Here, we discuss the two interpretations in the light of new results and suggest that the case against the statistical model may not be as strong as sometimes suggested.

On the Luminosity Function of Cluster 194.

On the Luminosity Function of Cluster 194.

Evolutional changes in galactic cluster luminosity functions

view Abstract Citations (8) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolutional changes in galactic cluster luminosity functions Gray, David F. Abstract The bright end of 52 galactic cluster luminosity functions is investigated statistically, and the slope of the functions is found to change slowly and smoothly with log time. A fairly adequate explanation is given by taking into account the brightening of the stars as they leave the main sequence. Alternative theories are suggested briefly. Publication: The Astronomical Journal Pub Date: October 1963 DOI: 10.1086/109184 Bibcode: 1963AJ.....68..572G full text sources ADS |

Photometric Investigation of the Galactic Clusters NGC 6087 and M25.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Investigation of the Galactic Clusters NGC 6087 and M25. Landolt, Arlo U. Abstract V system are given for 547 and 1401 stars, respectively, in the galactic clusters NGC 6087 and M25. The photographic measures were calibrated by a photoelectric sequence obtained independently by Irwin and Fernie in NGC 6087; independent observations by Johnson, by Sandage, by Irwin, and by Wampler, Pesch, Hiltuer, and Kraft were combined to define a photoelectric sequence in M25. The reddening across NGC 6087 appears constant at 0.20 mag.; differential reddening exists across M25 and ranges from EB v=O 29 to 0.60 mag. The evolutionary deviation curve method of Johnson indicates a distance modulus of 9.8+0.1 mag. for NGC 6087 and 9.0+0.2 mag. for M25. Each cluster apparently contains two red giant stars in addition to the classical Cepheids S Normae in NGC 6087 and U Sagittarii in M25. The cluster luminosity functions were investigated to Mv = t4.0 in NGC 6087 and to Mv=Y5.0 in M25; both agree with the Sal peter ii~itial lumii~osit~ fui~ction. The differential reddening across M25 permitted a discussion of the ratio of total to selective absorption; a value of 2.9+0.3 was adopted. Publication: The Astronomical Journal Pub Date: 1963 DOI: 10.1086/109042 Bibcode: 1963AJ.....68Q.283L full text sources ADS |

The Luminosity Function of Star Formation.

view Abstract Citations (20) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Luminosity Function of Star Formation. van den Bergh, Sidney Abstract A comparison is made between the luminosity functions of galactic clusters and the luminosity function of unevolved field stars. This comparison shows that galactic clusters contain fewer faint stars than the general stellar population in the vicinity of the sun Some possible implications of this result are briefly discussed. Publication: The Astrophysical Journal Pub Date: September 1961 DOI: 10.1086/147177 Bibcode: 1961ApJ...134..553V full text sources ADS | data products SIMBAD (7)

The luminosity function of the Coma cluster of galaxies.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The luminosity function of the Coma cluster of galaxies. Abell, George O. Abstract A program is in progress to determine the bright end of the luminosity function of each of about 30 rich clusters of galaxies with a technique of extrafocal photographic photometry with the ~8-inch Schmidt telescope of the Palomar Observatory. Magnitudes of a number of stars in each cluster field are calibrated by photographic and/or photoelectric methods. Then magnitudes of galaxies are obtained by comparing images of galaxies with the calibrated stars on each of five plates taken at various amounts out of focus. The measures are made in two colors corresponding, approximately, to international photographic and photovisual magnitudes. The integrated magnitude for each galaxy is obtained from the surface brightness of its images on two or more extrafocal plates through a method developed by Abell and Mihalas which utilizes a knowledge of the ellipticity and an assumed distribution of surface brightness of the galaxy. The luminosity function has been determined completely for the first of the clusters, the Coma cluster of galaxies. Near the limit of the observations, mpg = 19.2, the luminosity function increases rapidly. However, about two magnitudes below the bright end of the luminosity function there is a marked preliminary maximum. It is necessary to count through about the first 150 brightest galaxies to reach this maximum. About three magnitudes fainter than the brightest cluster members there is a minimum; at still fainter magnitudes the luminosity function increases rapidly. The preliminary maximum exists in the luminosity functions of galaxies of both small (~o.4) and large color indices. If further investigation shows that this maximum near the bright end is common to the luminosity functions of galaxies in the other rich clusters, it should provide a new, more reliable distance criterion for rich clusters of galaxies. Department of A stronomy, Un?versity of Calffornsa, Los A ngeles, Caiff. Publication: The Astronomical Journal Pub Date: May 1959 DOI: 10.1086/107894 Bibcode: 1959AJ.....64..125A full text sources ADS |

The Rate of Star Formation in the Galaxy.

view Abstract Citations (104) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Rate of Star Formation in the Galaxy. Salpeter, Edwin E. Abstract Consequences are derived from the following assumptions about the birth rate of stars in the entire Galaxy: (1) this rate is proportional to a time-independent function `p of magnitude AL (2) `p is given by the luminosity function for young galactic clusters; (3) the birth rate per some volume is proportional to the gas mass in this volume. It is found that an appreciable fraction of the galactic mass was converted into stars in less than a billion years and that the mass of gas at present decreases only very slowly with time. Predicted luminosity functions are derived, and comparison with observation shows that the stellar birth rate should increase slightly more strongly with gas density than in assumption 3. It is found that white dwarfs constitute about 0.17 of the total present number of stars. The total luminosity of the Galaxy is derived as a function of time. From a simple model for stellar helium production, the helium abundance in the gas is derived as a function of time. At present, this abundance for the gas is about four times the average abundance for gas plus all stars. Assuming medium-heavy nuclei to be produced by supernovae breakup of massive stars, their abundance in the gas is derived as a function of time. Publication: The Astrophysical Journal Pub Date: May 1959 DOI: 10.1086/146660 Bibcode: 1959ApJ...129..608S full text sources ADS | data products SIMBAD (1)

The Luminosity Function in Galactic Clusters

The Luminosity Function in Galactic Clusters