Luminosity Segregation Research Articles

Mass segregation in young compact star clusters in the Large Magellanic Cloud - I. Data and luminosity functions

We have undertaken a detailed analysis of HST/WFPC2 and STIS imaging observations, and of supplementary wide-field ground-based observations obtained with the ESO New Technology Telescope (NTT) of two young (∼10–25 Myr) compact star clusters in the LMC, NGC 1805 and 1818. The ultimate goal of our work is to improve our understanding of the degree of primordial mass segregation in star clusters. This is crucial for the interpretation of observational luminosity functions (LFs) in terms of the initial mass function (IMF), and for constraining the universality of the IMF. We present evidence for strong luminosity segregation in both clusters. The LF slopes steepen with cluster radius; in both NGC 1805 and 1818 the LF slopes reach a stable level well beyond the core of the clusters or half-light radii. In addition, the brightest cluster stars are strongly concentrated within the inner ∼4Rhl. The global cluster LF, although strongly non-linear, is fairly well approximated by the core or half-light LF; the (annular) LFs at these radii are dominated by the segregated high-luminosity stars, however. We present tentative evidence for the presence of an excess number of bright stars surrounding NGC 1818, for which we argue that they are most probably massive stars that have been collisionally ejected from the cluster core. We therefore suggest that the cores of massive young stars clusters undergo significant dynamical evolution, even on time-scales as short as ∼25 Myr.

The Redshift‐Space Two‐Point Correlation Functions of Galaxies and Groups in the Nearby Optical Galaxy Sample

We use the two-point correlation function in redshift space, ξ(s), to study the clustering of the galaxies and groups of the Nearby Optical Galaxy (NOG) sample, which is a nearly all-sky (|b| > 20°), complete, magnitude-limited sample of ~7000 bright and nearby optical galaxies (cz ≤ 6000 km s-1). The correlation function of galaxies is well described by a power law, ξ(s) = (s/s0)-γ, with slope γ ~ 1.5 and s0 ~ 6.4 h-1 Mpc (on scales 2.7-12 h-1 Mpc), in substantial agreement with previous results of several redshift surveys of optical galaxies. Splitting NOG into different morphological subsamples, we confirm the existence of morphological segregation between early- and late-type galaxies (out to 20 h-1 Mpc), and, in particular, we find a gradual decreasing of the strength of clustering from the S0 galaxies to the late-type spirals on intermediate scales (around 5 h-1 Mpc). The relative bias factor between early- and late-type galaxies appears to be substantially constant with scale. Furthermore, luminous galaxies turn out to be more clustered than dim galaxies. The luminosity segregation, which is significant for both early- and late-type objects, starts to become appreciable only for galaxies brighter than MB ~ -19.5 + 5 log h (~0.6L*) and is independent of scale. The NOG groups identified with the hierarchical and percolation algorithms show similar clustering properties, with a degree of clustering that is intermediate between galaxies and clusters. The group correlation functions are characterized by s0-values ranging from ~8 h-1 Mpc (for groups with at least three members) to ~10 h-1 Mpc (for groups with at least five members). The degree of group clustering depends on the physical properties of groups. Specifically, groups with greater velocity dispersions, sizes, and masses tend to be more clustered than those with lower values of these quantities.

Scaling Laws and Luminosity Segregation

We debate how the scaling properties of the angular correlation function w(θ) depend on luminosity segregation. Under the approximation that there is no deviation from Euclidean geometry and no evolution, we find that the scaling with catalog depth (D*) is the same both for a luminosity (L) independent clustering length (r0) and for a generic dependence of r0 on L. Recent angular data, however, extend to depths where the above approximation is unsuitable and the simple scaling w ∝ D should be modified. We find that such modifications depend on the shape of the L-dependence of r0 and are indeed different depending on whether luminosity segregation is or is not considered. In particular, we find that a luminosity segregation as observed at z = 0 causes effects of the same order as varying the rate of clustering evolution. For the sake of example, we apply our expressions to available angular galaxy data in the B- and R-bands and show that significant constraints on the evolution of clustering can already be found with public data.

The Descendants of Lyman Break Galaxies in Galaxy Clusters: Spatial Distribution and Orbital Properties

We combine semi-analytical methods with a ultra-high resolution simulation of a galaxy cluster (of mass 2.3 10^14h-1Msolar, and 4 10^6 particles within its virial radius) formed in a standard CDM universe to study the spatial distribution and orbital properties of the present-day descendents of Lyman Break Galaxies (LBGs). At the present time only five (out of 12) of halos containing LBGs survive as separate entities inside the cluster virial radius. Their circular velocities are in the range 200 - 550 km/sec. Seven halos merged together to form the central object at the very center of the cluster. Using semi-analytical modeling of galaxy evolution we show that descendents of halos containing LBGs now host giant elliptical galaxies. Galaxy orbits are radial, with a pericenter to apocenter ratio of about 1:5. The orbital eccentricities of LBGs descendents are statistically indistinguishable from those of the average galaxy population inside the cluster, suggesting that the orbits of these galaxies are not significantly affected by dynamical friction decay after the formation of the cluster's main body. In this cluster, possibly due to its early formation time, the descendents of LBGs are contained within the central 60% of the cluster virial radius and have an orbital velocity dispersion lower than the global galaxy population, originating a mild luminosity segregation for the brightest cluster members. Mass estimates based only on LBGs descendents (especially including the central cD) reflect this bias in space and velocity and underestimate the total mass of this well virialized cluster by up to a factor of two compared to estimates using at least 20 cluster members.

Luminosity‐ and Morphology‐dependent Clustering of Galaxies

How does the clustering of galaxies depend on their inner properties like morphological type and luminosity? We address this question in the mathematical framework of marked point processes and clarify the notion of luminosity and morphological segregation. A number of test quantities such as conditional mark-weighted two-point correlation functions are introduced. These descriptors allow for a scale-dependent analysis of luminosity and morphology segregation. Moreover, they break the degeneracy between an inhomogeneous fractal point set and actual present luminosity segregation. Using the Southern Sky Redshift Survey 2, we find both luminosity and morphological segregation at a high level of significance, confirming claims by Benoist and colleagues in 1996 and Willmer and colleagues in 1998 using these data. Specifically, the average luminosity and the fluctuations in the luminosity of pairs of galaxies are enhanced out to separations of 15 h-1 Mpc. On scales smaller than 3 h-1 Mpc the luminosities on galaxy pairs show a tight correlation. A comparison with the random field model indicates that galaxy luminosities depend on the spatial distribution and galaxy-galaxy interactions. Early-type galaxies are also more strongly correlated, indicating morphological segregation. The galaxies in the PSCz catalog do not show significant luminosity segregation. This again illustrates that mainly early-type galaxies contribute to luminosity segregation. However, based on several independent investigations we show that the observed luminosity segregation cannot be explained by the morphology-density relation alone.

Subaru Observations for the K-Band Luminosity Distribution of Galaxies in Clusters near to 3C 324 at z ∼ 1.2

We investigate the K-band luminosity distribution of galaxies in the region of clusters at z ∼ 1.2 near to the radio galaxy 3C 324. The imaging data were obtained during the commissioning period of the Subaru telescope. There is a significant excess of the surface number density of the galaxies with K = 17–20 mag in the region within ∼ 40″ from 3C 324. At this bright end, the measured luminosity distribution shows a drop, which can be represented by the exponential cut off of the Schechter-function formula; the best-fitted value of the characteristic magnitude, K*, is ∼ 18.4±0.8. This measurement follows the evolutionary trend of the K* of the rich clusters observed at an intermediate redshift, which is consistent with passive evolution models with a formation redshift zf ≳ 2. At K ≳ 20 mag, however, the excess of the galaxy surface density in the region of the clusters decreases abruptly, which may imply that the luminosity function of the cluster galaxies has a negative slope at the faint end. This may imply strong luminosity segregation between the inner and outer parts of the clusters, or some deficit of faint galaxies in the cluster central region of the cluster.

The Morphology Dependence of Luminosity Segregation in the Coma Cluster

We carry out CCD photometry of galaxies in the 5.25 square region centered on Coma cluster down to $M_R=-16.0$, beyond the limit of conventional morphological classification. We use the angular two-point correlation function as well as radial profiles in order to characterize the luminosity segregation. We find strong luminosity segregation for our total sample over the magnitude range of $-20 \leq M_R \leq -16$, which is not entirely accounted for in terms of the morphology-density relation that is known to exist only for bright galaxies. We use a single consistent parameter, the degree of luminosity concentration, to parameterize the morphology of galaxies over the wide magnitude range, where both giant and dwarf galaxies are included. Galaxies with high central concentration (HCC) show strong luminosity segregation, i.e. their clustering strength depends strongly on luminosity while those with low central concentration (LCC) show almost no luminosity segregation. Radial density profile shows that brighter HCC-type galaxies tend to more strongly concentrate near the cluster center while LCC-type galaxies do not show such a dependence on luminosity. We show that these results are tenable against the contamination by field galaxies and uncertainties in our method of classification.

Southern Sky Redshift Survey: Clustering of Local Galaxies

We use the two-point correlation function to calculate the clustering properties of the recently completed SSRS2 survey. The redshift space correlation function for the magnitude-limited SSRS2 is given by xi(s)=(s/5.85 h-1 Mpc)^{-1.60} for separations between 2 < s < 11 h-1 Mpc, while our best estimate for the real space correlation function is xi(r) = (r/5.36 h-1 Mpc)^{-1.86}. Both are comparable to previous measurements using surveys of optical galaxies over much larger and independent volumes. By comparing the correlation function calculated in redshift and real space we find that the redshift distortion on intermediate scales is small. This result implies that the observed redshift-space distribution of galaxies is close to that in real space, and that beta = Omega^{0.6}/b < 1, where Omega is the cosmological density parameter and b is the linear biasing factor for optical galaxies. We also use the SSRS2 to study the dependence of xi on the internal properties of galaxies. We confirm earlier results that luminous galaxies (L>L*) are more clustered than sub-L* galaxies and that the luminosity segregation is scale-independent. We find that early types are more clustered than late types, but that in the absence of rich clusters, the relative bias between early and late types in real space, is not as strong as previously estimated. Furthermore, both morphologies present a luminosity-dependent bias, with the early types showing a slightly stronger dependence on luminosity. We also find that red galaxies are significantly more clustered than blue ones, with a mean relative bias stronger than that seen for morphology. Finally, we find that the relative bias between optical and iras galaxies in real space is b_o/b_I $\sim$ 1.4.

Luminosity Segregation from Merging in Clusters of Galaxies

We compute the evolution of the space-dependent mass distribution of galaxies in clusters that arise from binary aggregations by solving a space-dependent Smoluchowski equation. From the solutions, we derive the distribution of intergalactic distances for different ranges of mass (and corresponding magnitudes). We compare the results with the observed distributions and find that the different degrees of luminosity segregation observed in clusters are well accounted for by our merging model. In addition, the presence of luminosity segregation is related to dynamical effects that also show up in different but connected observables, such as galaxy velocity profiles that decrease toward the center and X-ray-measured β-parameters smaller than 1. We predict that both luminosity segregation and the observables above (being a product of binary aggregations) are inversely correlated with the core radius and with the galaxy velocity dispersion; we also discuss how the whole set of predictions compares with up-to-date observations.

The Power Spectrum in a Strongly Inhomogenous Universe

The standard picture of the matter clustering, the cold dark matter model (and its variants), assumes that, on scales smaller than a certain "flattening scale" λf, the power spectrum increases with the scale, while on much larger scales it decreases so as to match the tiny fluctuations observed in the microwave background. However, there is no consensus on whether the turnaround λf has been detected or not, and on the actual importance of the luminosity segregation effect. We show that, due to the finiteness of the sample, the standard analysis applied to fractal distributions yields a turnaround for scales close to the survey scale, and a systematic amplitude shift with the survey scale. We point out that both features, bending and scaling, are in agreement with recent determinations of the power spectrum, in particular with the CfA2 spectrum in redshift space. Therefore, our conclusion is that the CfA2 sample is consistent with a fractal clustering.

Multifractality as a Link between Luminosity and Space Distribution of Visible Matter

We discuss how and space distribution of galaxies are naturally linked in view of their multifractal properties. In particular we show that the mass (luminosity) function corresponding to a multifractal distribution in a given observed volume, consists of a power law followed by an exponential cut-off. This implies that the amplitude $\phi^*$ of the Schechter function scales with the sample depth, as confirmed by various observational data. This effect is analogous to the scaling of the space density due to the fractal nature of the space distribution. This has the important consequence that the function can be properly defined only in a volume limited sample. Also the so-called luminosity segregation and the concept of bias correspond to a natural consequence of multifractality. This implies however that they should be considered from a different perspective with respect to the usual one. Such a concept allows us to unify the space and distributions as being shaped by a single cause:multifractality which should therefore claim a central stage in theoretical investigations.

Statistical analysis of the Perseus-Pisces redshift survey: spatial and luminosity properties

We analyze the spatial and the luminosity properties of the Perseus-Pisces redshift survey. We find that the two point correlation function (CF) Γ( r) is a power law up to the sample effective depth (∼ 30 h −1 Mpc), showing the fractal nature of the galaxy distribution in this catalog. The fractal dimension turns out to be D ∼ 2. We also consider the CF ξ( r) and in particular the behavior of the “ correlation length” r 0 ( ξ( r 0)1) as function of the sample size. In this respect we find, unambiguously, that the luminosity segregation effect is not supported by any experimental evidence. In addition we have studied the galaxian number-density ( n( r)) and number-counts ( N( m)) in the VL subsamples finding a good agreement with the properties of a fractal distribution. In particular our conclusion is that the n( r) relation permits to extend the analysis of the fractal nature up to a deeper depth than that reached by the CF analysis, and, we find evidence for fractal properties up to the limiting depth of 130 h −1 Mpc. We clarify the role of the small-scale fluctuations in the determination of the galaxy counts. Even in this case the results are in agreement with the previous ones. Finally we have considered the correlations between galaxy positions and luminosities by means of the multifractal analysis. We find clear evidence for self-similar behavior of the whole luminosity-space distribution. These results confirm and extend those of Coleman and Pietronero (1992).

Scaling analysis of the distribution of galaxies in the CfA catalog

view Abstract Citations (14) References (68) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Scaling Analysis of the Distribution of Galaxies in the CfA Catalog Dominguez-Tenreiro, R. ; Gomez-Flechoso, M. A. ; Martinez, V. J. Abstract A detailed analysis of the CfA1 catalog of galaxies by means of the multifractal or scaling formalism is presented in this paper. The fair sample hypothesis, the depth effect, and the problems of the luminosity and morphological segregation are extensively studied in volumes which differ by a factor of about 8 in size and of about 14 in number density. The results of our calculation suggest that the CfA1 catalog is not a fair sample drawn from a hypothetical universal galaxy distribution. Moreover, no depth effect has been found. Two kinds of (slight) luminosity segregation could have been detected: one, due to a peculiar velocity contamination of bright galaxies which trace denser regions, and other, for field galaxies, which could be a manifestation of biasing. The morphological segregation is present not only in the cores of clusters, but also at larger scales and in the moderate density regions. Both the luminosity and morphological segregations are independent effects. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173870 Bibcode: 1994ApJ...424...42D Keywords: Astronomical Catalogs; Galactic Clusters; Galactic Evolution; Luminosity; Red Shift; Galactic Structure; Many Body Problem; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: FUNDAMENTAL PARAMETERS full text sources ADS |

Luminosity Distribution in CD Clusters

The ratio of contributions from cannibalism and from cooling flows to the final cD galaxies in diverse clusters seems to be different. It should be determined by some general cluster properties as for instance the central mass concentration. Assuming that mass distribution is tantamount to luminosity distribution we have analyzed the question of possible luminosity segregation in the radial galaxy distribution of galaxy clusters (Baier &amp;amp; Schmidt 1992; Baier &amp;amp; MacGillivray 1994).

Spatial distribution of low-surface-brightness galaxies

Using redshift samples, we calculate the cross-correlation functions of LSB galaxies with normal galaxies in complete samples (i.e. CfA and IRAS), which enables us to compare directly the amplitudes and shapes of the correlation functions. For pair separations $r\gs 2\mpc$, we find that the shape is in agreement with that of the correlation functions for other galaxies. The amplitudes ($A$) of $\xiab (r)$ are lower than those of the autocorrelation functions for the CfA and IRAS samples, with $A_{\rm LSB-CfA}:A_{\rm CfA-CfA}\approx 0.4$ and $A_{\rm LSB-IRAS}:A_{\rm IRAS-IRAS}\approx 0.6$. These results suggest that LSB galaxies are imbedded in the same large scale structure as other galaxies, but are less strongly clustered. This offers the hope that LSB galaxies may be unbiased tracers of the mass density on large scales. For $r\ls 2\mpc$, the cross-correlation functions are significantly lower than that expected from the extrapolation of $\xiab$ on larger scales, showing that the formation and survival of LSB galaxies may be inhibited by interaction with neighboring galaxies. The model which matches these observations suggests that strong luminosity segregation in galaxy clustering is not a necessary consequence of biased galaxy formation, unless the effect of surface brightness is taken in to account. It is also implies a significant mass density in LSB galaxies.

Luminosity dependence of galaxy clustering in extinction-corrected CfA data

The luminosity dependence of clustering in galaxy distributions is analysed using the CfA redshift catalogue, where the magnitude correction for both Galactic and internal extinction is taken into account. It is found that, contrary to previous results, the luminosity dependence of clustering is very weak when the magnitude correction is made, showing no evidence of a positive dependence (luminosity segregation) in the magnitude ranges of interest. The results are not consistent with the luminosity segregation predicted in standard biased cold dark matter scenarios. The morphological dependence is also investigated further. The late-type galaxies cluster in the same way for most magnitude ranges after the magnitude correction. There is even some antisegregation, whereby faint galaxies cluster more strongly than luminous ones

Void probability function in the Southern Sky Redshift Survey

view Abstract Citations (18) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Void Probability Function in the Southern Sky Redshift Survey Lachieze-Rey, Marc ; da Costa, Luiz N. ; Maurogordato, Sophie Abstract We investigate the statistical properties of the distribution of galaxies in the Southern Sky Redshift Survey (SSRS) utilizing the J_3_ integral and the void probability function (VPF) to test for scaling relations, luminosity segregation, and possible variations with the depth of the sample. From the analysis of the southern sample, less sensitive to the flow model adopted to estimate galaxy distances, we confirm earlier claims for the existence of luminosity segregation. We also confirm that the VPF obeys a universal scaling relation, independent of sample depth and luminosity. However, comparison of the VPFs for volume-limited samples shows that larger voids occur more frequently in the southern hemisphere, probably indicating that the samples considered may not yet represent fair samples of the universe at large. Subject Headings: galaxies: clustering - methods: analytical Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/171897 Bibcode: 1992ApJ...399...10L Keywords: Galactic Clusters; Probability Distribution Functions; Red Shift; Sky Surveys (Astronomy); Southern Sky; Astronomical Catalogs; Luminosity; Spatial Distribution; Astrophysics; GALAXIES: CLUSTERING; METHODS: ANALYTICAL full text sources ADS |

Structure and formation of superclusters - XII. Morphological and luminosity segregation of normal and dwarf galaxies

Morphological and luminosity segregation of dwarf and normal galaxies in the Virgo Supercluster and its environs are compared using correlation functions, void probability functions and cluster analysis. Results show that dwarf galaxies follow morphological segregation similar to that for normal galaxies: dwarf early-type galaxies are concentrated in clusters with sizes about 1–2 Mpc. Morphological segregation is weak outside of clusters. Voids, determined by spiral and irregular galaxies of various luminosities, have similar sizes.

Luminosity segregation as an indication of dynamical evolution in rich clusters of galaxies

The luminosity segregation in several galaxy clusters has been analyzed by means of the intergalactic distance distribution function, corrected from the masking effects of field galaxies. It has been found that the clusters present a gradation of luminosity segregation, from highly segregated to virtually not segregated. In order to understand these results, simulations of the dynamical evolution of galaxy clusters have been carried out by means of the Fokker-Planck equation moments method. It is concluded that the observed mass segregation could be due to dynamical evolution during the two-body relaxation phase, and that their different degrees could be a reflection of either the different initial conditions present at the onset of this phase or different cluster ages. 65 refs.

Luminosity segregation as a constraint on the theory of biased galaxy formation

THE theory of biased galaxy formation with cold dark matter (CDM) is presently the most successful attempt to reproduce the distribution of galaxies in the Universe1–6, permitting a reconciliation of the observed low value of the cosmological density parameter ω0 ≤ 0.2 with the value of unity predicted by inflation. Specific tests of the bias hypothesis, namely that galaxies are more clustered than the mass1,2,4, however, have not yet led to definitive conclusions. Here we show that a systematic luminosity segregation effect in the clustering of galaxies is expected and provides an unambiguous test of the biased galaxy formation theory. We examine in detail how the clustering of galaxies correlates with their luminosity, using different biased models and numerical simulations5–7. We find that a strong effect is expected at luminosities larger than L* the characteristic luminosity of galaxies and that the amplitude of the predicted effect at these luminosities agrees with observations8. At luminosities fainter than L* however, strong limits have been put on this segregation effect9. These limits are incompatible with any biased CDM theory in which the bias parameter bb for bright galaxies is greater than 1.5 on large scales.