How Stochastic is the Relative Bias Between Galaxy Types?

Examining the nature of the relative clustering of different galaxy types can help tell us how galaxies formed. To measure this relative clustering, I perform a joint counts-in-cells analysis of galaxies of different spectral types in the Las Campanas Redshift Survey (LCRS). I develop a maximum-likelihood technique to fit for the relationship between the density fields of early- and late-type galaxies. This technique can directly measure nonlinearity and stochasticity in the biasing relation. At high significance, a small amount of stochasticity is measured, corresponding to a correlation coefficient of about 0.87 on scales corresponding to 15 Mpc/h spheres. A large proportion of this signal appears to derive from errors in the selection function, and a more realistic estimate finds a correlation coefficient of about 0.95. These selection function errors probably account for the large stochasticity measured by Tegmark & Bromley (1999), and may have affected measurements of very large-scale structure in the LCRS. Analysis of the data and of mock catalogs shows that the peculiar geometry, variable flux limits, and central surface-brightness selection effects of the LCRS do not seem to cause the effect.Comment: 38 pages, 14 figures. Submitted to Apj. Modified from a chapter of my Ph.D. Thesis at Princeton University, available at http://www-astro-theory.fnal.gov/Personal/blanton/thesis/index.htm

The scale-dependence of relative galaxy bias: encouragement for the halo model description

We investigate the relationship between the colors, luminosities, and environments of galaxies in the Sloan Digital Sky Survey spectroscopic sample, using environmental measurements on scales ranging from 0.2 to 6 Mpc/h. We find: (1) that the relationship between color and environment persists even to the lowest luminosities we probe (absolute magnitude in the r band of about -14 for h=1); (2) at luminosities and colors for which the galaxy correlation function has a large amplitude, it also has a steep slope; and (3) in regions of a given overdensity on small scales (1 Mpc/h), the overdensity on large scales (6 Mpc/h) does not appear to relate to the recent star formation history of the galaxies. Of these results, the last has the most immediate application to galaxy formation theory. In particular, it lends support to the notion that a galaxy's properties are related only to the mass of its host dark matter halo, and not to the larger scale environment.Comment: submitted to ApJ; full resolution figures and slide material available at http://cosmo.nyu.edu/blanton/scale_density.htm

KEWENANGAN ANKUM TERHADAP WARGA NEGARA YANG DIMOBILISASI DALAM HUKUM DISIPLIN MILITER

The guidance and development of military law are needed and intended to guarantee the respect for human rights, rule of law and justice in the military environment, which among others are manifested through a system of law and order in the law number 25 of 2014 on the law of military discipline. Under the provisions of article 6 paragraph (1) of law number 25 0f 2014, then the law of military discipline should be imposed on any person  who under the law equated with the military, including the citizens who are mobilized for their expertise in time of war. The enforcement is considered to be too early, given the sentencing of military discipline for offenders who have violated the law of military discipline must be performed by the Authorized adjudge (Ankum), but on the other hand, the law of number 25 of 2014 on the law military discipline does not provide any explicit and complete arrangements or provisions about the Ankum’s authority in enforcing discipline  against citizen who are mobilized in time of war. Through the method of the normative legal research with an approach to the concept and approach to legislation, it can be concluded that assesment  of vagueness  of these arrangements is quite essential, considering that the vaqueness of these arrangements may result in legal uncertainty, therefore, it is needed more complete arrangement in order to implement the provisions of the law of military discipline against citizens who mobilized in time of war. Keywords : Authority, The Authorized adjudge, Citizens who are mobilized. Pembinaan dan pengembangan hukum militer diperlukan dan ditujukan untuk menjamin terciptanya penghormatan terhadap hak asasi manusia, kepastian hukum dan keadilan di lingkungan militer, yang diantaranya diwujudkan melalui suatu sistem dan tatanan hukum dalam Undang-Undang Nomor 25 Tahun 2014 tentang Hukum Disiplin Militer. Berdasarkan ketentuan Pasal 6 ayat (1) Undang-Undang Nomor 25 Tahun 2014, maka Hukum Disiplin Militer juga diberlakukan kepada setiap orang yang berdasarkan undang-undang dipersamakan dengan militer, diantaranya adalah warga negara yang dimobilisasi karena keahliannya pada waktu perang. Pemberlakuan ini dianggap terlampau dini, mengingat penjatuhan hukuman disiplin militer bagi pelaku yang melakukan pelanggaran hukum disiplin militer harus dilakukan oleh seorang Atasan Yang Berhak Menghukum (Ankum), namun di sisi lain, Undang-Undang Nomor 25 Tahun 2014 tentang Hukum Disiplin Militer tidak memberikan pengaturan secara tegas dan lengkap tentang kewenangan Ankum dalam menegakkan hukum disiplin terhadap warga negara yang dimobilisasi pada waktu perang. Melalui penelitian hukum normatif dengan pendekatan konsep hukum dan pendekatan perundangan-undangan, maka dapat disimpulkan bahwa pembahasan tentang kekaburan pengaturan ini merupakan hal yang cukup penting, mengingat kekaburan tersebut dapat menimbulkan ketidakpastian hukum, dan oleh karenanya diperlukan pengaturan lanjutan yang lebih lengkap dalam upaya menerapkan ketentuan hukum disiplin militer terhadap warga negara yang dimobilisasi pada waktu perang

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.Comment: 43 pages, uses AASTeX 4.0 macros. Includes 8 tables and 16 Postscript figures, updated reference

Stochasticity of Bias and Nonlocality of Galaxy Formation: Linear Scales

If one wants to represent the galaxy number density at some point in terms of only the mass density at the same point, there appears the stochasticity in such a relation, which is referred to as ``stochastic bias''. The stochasticity is there because the galaxy number density is not merely a local function of a mass density field, but it is a nonlocal functional, instead. Thus, the phenomenological stochasticity of the bias should be accounted for by nonlocal features of galaxy formation processes. Based on mathematical arguments, we show that there are simple relations between biasing and nonlocality on linear scales of density fluctuations, and that the stochasticity in Fourier space does not exist on linear scales under a certain condition, even if the galaxy formation itself is a complex nonlinear and nonlocal precess. The stochasticity in real space, however, arise from the scale-dependence of bias parameter, $b$. As examples, we derive the stochastic bias parameters of simple nonlocal models of galaxy formation, i.e., the local Lagrangian bias models, the cooperative model, and the peak model. We show that the stochasticity in real space is also weak, except on the scales of nonlocality of the galaxy formation. Therefore, we do not have to worry too much about the stochasticity on linear scales, especially in Fourier space, even if we do not know the details of galaxy formation process.Comment: 24 pages, latex, including 2 figures, ApJ, in pres

Redshift-Space Distortions and the Real-Space Clustering of Different Galaxy Types

We study the distortions induced by peculiar velocities on the redshift-space correlation function of galaxies of different morphological types in the Pisces-Perseus redshift survey. Redshift-space distortions affect early- and late-type galaxies in different ways. In particular, at small separations, the dominant effect comes from virialized cluster cores, where ellipticals are the dominant population. The net result is that a meaningful comparison of the clustering strength of different morphological types can be performed only in real space, i.e., after projecting out the redshift distortions on the two-point correlation function xi(r_p,pi). A power-law fit to the projected function w_p(r_p) on scales smaller than 10/h Mpc gives r_o = 8.35_{-0.76}^{+0.75} /h Mpc, \gamma = 2.05_{-0.08}^{+0.10} for the early-type population, and r_o = 5.55_{-0.45}^{+0.40} /h Mpc, \gamma = 1.73_{-0.08}^{+0.07} for spirals and irregulars. These values are derived for a sample luminosity brighter than M_{Zw} = -19.5. We detect a 25% increase of r_o with luminosity for all types combined, from M_{Zw} = -19 to -20. In the framework of a simple stable-clustering model for the mean streaming of pairs, we estimate sigma_12(1), the one-dimensional pairwise velocity dispersion between 0 and 1 /h Mpc, to be 865^{+250}_{-165} km/s for early-type galaxies and 345^{+95}_{-65} km/s for late types. This latter value should be a fair estimate of the pairwise dispersion for ``field'' galaxies; it is stable with respect to the presence or absence of clusters in the sample, and is consistent with the values found for non-cluster galaxies and IRAS galaxies at similar separations.Comment: 17 LaTeX pages including 3 tables, plus 11 PS figures. Uses AASTeX macro package (aaspp4.sty) and epsf.sty. To appear on ApJ, 489, Nov 199

Bias and Hierarchical Clustering

It is now well established that galaxies are biased tracers of the distribution of matter, although it is still not known what form this bias takes. In local bias models the propensity for a galaxy to form at a point depends only on the overall density of matter at that point. Hierarchical scaling arguments allow one to build a fully-specified model of the underlying distribution of matter and to explore the effects of local bias in the regime of strong clustering. Using a generating-function method developed by Bernardeau & Schaeffer (1992), we show that hierarchical models lead one directly to the conclusion that a local bias does not alter the shape of the galaxy correlation function relative to the matter correlation function on large scales. This provides an elegant extension of a result first obtained by Coles (1993) for Gaussian underlying fields and confirms the conclusions of Scherrer & Weinberg (1998) obtained using a different approach. We also argue that particularly dense regions in a hierarchical density field display a form of bias that is different from that obtained by selecting such peaks in Gaussian fields: they are themselves hierarchically distributed with scaling parameters $S_p=p^{(p-2)}$. This kind of bias is also factorizable, thus in principle furnishing a simple test of this class of models.Comment: Latex, accepted for publication in ApJL; moderate revision

Measuring galaxy segregation using the mark connection function

(abridged) The clustering properties of galaxies belonging to different luminosity ranges or having different morphological types are different. These characteristics or `marks' permit to understand the galaxy catalogs that carry all this information as realizations of marked point processes. Many attempts have been presented to quantify the dependence of the clustering of galaxies on their inner properties. The present paper summarizes methods on spatial marked statistics used in cosmology to disentangle luminosity, colour or morphological segregation and introduces a new one in this context, the mark connection function. The methods used here are the partial correlation functions, including the cross-correlation function, the normalised mark correlation function, the mark variogram and the mark connection function. All these methods are applied to a volume-limited sample drawn from the 2dFGRS, using the spectral type as the mark. We show the virtues of each method to provide information about the clustering properties of each population, the dependence of the clustering on the marks, the similarity of the marks as a function of the pair distances, and the way to characterise the spatial correlation between the marks. We demonstrate by means of these statistics that passive galaxies exhibit stronger spatial correlation than active galaxies at small scales (r <20 Mpc/h). The mark connection function, introduced here, is particularly useful for understanding the spatial correlation between the marks.Comment: 6 pages, 5 figures, accepted for publication in Astronomy and Astrophysic

Relationship between environment and the broad-band optical properties of galaxies in the SDSS

We examine the relationship between environment and the luminosities, surface brightnesses, colors, and profile shapes of luminous galaxies in the Sloan Digital Sky Survey (SDSS). For the SDSS sample, galaxy color is the galaxy property most predictive of the local environment. Galaxy color and luminosity jointly comprise the most predictive pair of properties. At fixed luminosity and color, density is not closely related to surface brightness or to Sersic index -- the parameter in this study that astronomers most often associate with morphology. In the text, we discuss what measureable residual relationships exist, generally finding that at red colors and fixed luminosity, the mean density decreases at the highest surface brightnesses and Sersic indices. In general, these results suggest that the morphological properties of galaxies are less closely related to galaxy environment than are their masses and star-formation histories.Comment: submitted to ApJ, pedagogy and bitmapped figures for presentations available at http://cosmo.nyu.edu/blanton/full_density.htm

Time Evolution of Galaxy Formation and Bias in Cosmological Simulations

The clustering of galaxies relative to the mass distribution declines with time because: first, nonlinear peaks become less rare events; second, the densest regions stop forming new galaxies because gas there becomes too hot to cool and collapse; third, after galaxies form, they are gravitationally ``debiased'' because their velocity field is the same as the dark matter. To show these effects, we perform a hydrodynamic cosmological simulation and examine the density field of recently formed galaxies as a function of redshift. We find the bias b_* of recently formed galaxies (the ratio of the rms fluctuations of these galaxies and mass), evolves from 4.5 at z=3 to around 1 at z=0, on 8 h^{-1} Mpc comoving scales. The correlation coefficient r_* between recently formed galaxies and mass evolves from 0.9 at z=3 to 0.25 at z=0. As gas in the universe heats up and prevents star formation, star-forming galaxies become poorer tracers of the mass density field. After galaxies form, the linear continuity equation is a good approximation to the gravitational debiasing, even on nonlinear scales. The most interesting observational consequence of the simulations is that the linear regression of the star-formation density field on the galaxy density field evolves from about 0.9 at z=1 to 0.35 at z=0. These effects also provide a possible explanation for the Butcher-Oemler effect, the excess of blue galaxies in clusters at redshift z ~ 0.5. Finally, we examine cluster mass-to-light ratio estimates of Omega, finding that while Omega(z) increases with z, one's estimate Omega_est(z) decreases. (Abridged)Comment: 31 pages of text and figures; submitted to Ap