This is the second in a series of papers in which we assemble and analyze a homogeneous catalog o... more This is the second in a series of papers in which we assemble and analyze a homogeneous catalog of peculiar velocity data. In Paper I, we treated two Tully-Fisher (TF) cluster samples. Here, we study four TF field samples: the I-band sample of Mathewson, Ford, & Buchhorn, the r-band samples of Willick and Courteau Faber, and the H-band sample of
Background: The distribution of the blood vessel network at any point in time in any body tissue,... more Background: The distribution of the blood vessel network at any point in time in any body tissue, may provide valuable information with regards to the tissue condition and its angiogenesis functionality. The blood vessel three-dimensional network of the endometrium goes through a process of change over a relatively short period of 4 weeks on average. It is well accepted that this angiogenesis is closely related to the success or failure of the implantation of the embryo Objective and rationale: Our study aims to present a method to follow the three-dimensional evolution of the superficial blood vessel distribution in the endometrium throughout the uterine cycle. Method: This method utilizes differences in the observed broadband colors of the blood vessels in order to assess their depth coordinate below the endometrial tissue surface. We implemented the method using microscopic images of fresh, ex-vivo, endometrial samples of different cycle days to obtain the statistical evolution t...
The interaction rates of dark-matter halos and subhalos, including collisions and mergers, are co... more The interaction rates of dark-matter halos and subhalos, including collisions and mergers, are computed using high-resolution cosmological N-body simulations of the ΛCDM model. Although the number fraction of subhalos of mass > 2 × 10 11 h −1 M ⊙ is only ∼ 10%, we find that the interaction rate of such subhalos is relatively high because they reside in high density environments. At low redshift, the subhalo collisions dominate the total collision rate, and even at z = 3 they are involved in more than 30% of all collisions. About 40% of the "major" mergers (those of mass ratio > 0.3) are between subhalos. Therefore subhalo interactions must be incorporated in models of structure formation. We find that the collision rate between halos in physical density units, is ∝ (1+z) δ , with δ = 3 − 4, in agreement with earlier simulations and most observational data. We test previous analytic estimates of the interaction rates of subhalos based on statistical models, which could be very inaccurate because of the small number of subhalos and the variation of conditions within small host halos. We find that, while such statistical estimates may severely overestimate the rate within hosts < 10 13 h −1 M ⊙ , typical of high redshifts, they are valid for larger hosts regardless of the number of subhalos in them. We find the Makino & Hut (1997) estimate of the subhalo merger rate to be valid for hosts > ∼ 6 × 10 11 h −1 M ⊙ at all redshifts. The collision rate between subhalos and the central object of their host halo is approximated relatively well using the timescale for dynamical friction in circular orbits. This approximation fails in ∼ 40% of the cases, partly because of deviations from the assumption of circular orbits (especially at low redshift) and partly because of the invalidity of the assumption that the subhalo mass is negligible (especially at high redshift).
We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-... more We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-resolution cosmological N-body simulation of a ΛCDM cosmology. At each analyzed redshift z we divide the dark matter particles into 4 components: (i) isolated galactic halos, (ii) subhalos, (iii) the diffuse medium of group and cluster halos, and (iv) the background outside of virialized halos. We follow the time evolution of the mass distribution and flows between these components and provide fitting functions for the exchange rates. The exchange rates show gradual evolution as z decreases to 2, and become more steady thereafter. For z < ∼ 2 about 15% of the isolated galactic halos cluster per Gyr to become subhalos and a similar fraction of their mass returns to the unvirialized background. Mass accumulation onto subhalos is equally shared between previously isolated halos and unvirialized matter, and is dominated by accretion from the host's diffuse matter beyond z ≃ 1. This accumulation is balanced for z ≃ 0.5 by subhalo disruption at a rate of about half of their mass per Gyr. The diffuse component in host halos is built by accreting isolated halos and un-virialized material in mass shares of 40% and 60%, respectively, and at z < 0.5 also by disruption of subhalos. The unvirialized IGM is enriched mostly by stripping of isolated halos, and at z < 1 also by mass loss from groups and clusters. We go on to use our derived exchange rates together with a simple recipe for metal production to gauge the importance of metal redistribution in the universe due solely to gravity-induced interactions. This crude model predicts some trends regarding metallicity ratios. The diffuse metallicity in clusters is predicted to be ∼ 40% that in isolated galaxies (∼ 55% of groups) at z = 0, and should be lower only slightly by z = 1, consistent with observations. The metallicity of the diffuse media in large galaxy halos and poor groups is expected to be lower by about a factor of 5 by z ∼ 2, in agreement with the observed metallicity of damped Lyα systems. The metallicity of the background IGM is predicted to be (1 − 3) × 10 −4 that of z = 0 clusters, also consistent with observations. The agreement of predicted and observed trends indicates that gravitational interaction alone may play an important role in metal enrichment of the intra-cluster and intergalactic media.
We use N-body simulations combined with semi-analytic models to compute the clustering properties... more We use N-body simulations combined with semi-analytic models to compute the clustering properties of modeled galaxies at z ∼ 3, and confront these predictions with the clustering properties of the observed population of Lyman-break galaxies (LBGs). Several scenarios for the nature of LBGs are explored, which may be broadly categorized into models in which high-redshift star formation is driven by collisional starbursts and those in which quiescent star formation dominates. For each model, we make predictions for the LBG overdensity distribution, the variance of counts-in-cells, the correlation length, and close pair statistics. Models which assume a one-to-one relationship between massive darkmatter halos and galaxies are disfavored by close pair statistics, as are models in which colliding halos are associated with galaxies in a simplified way. However, when modeling of gas consumption and star formation is included using a semi-analytic treatment, the quiescent and collisional sta...
We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functi... more We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functions and luminosity-velocity relations. Such a velocity function is desirable for several reasons. First, it enables an objective comparison of luminosity functions obtained in different bands and for different galaxy morphologies, with a statistical correction for dust extinction. In addition, the velocity function simplifies comparison of observations with predictions from high-resolution cosmological N-body simulations. We derive velocity functions from five different data sets and find rough agreement among them, but about a factor of 2 variation in amplitude. These velocity functions are then compared with N-body simulations of a ΛCDM model (corrected for baryonic infall) in order to demonstrate both the utility and current limitations of this approach. The number density of dark matter halos and the slope of the velocity function near v∗, the circular velocity corresponding to an ∼ ...
Spatiotemporal variations in attributes of particulate matter (PM) in ambient air are important e... more Spatiotemporal variations in attributes of particulate matter (PM) in ambient air are important estimates of environmental pollution and public health risks. In particularly, the exposure to fine PM, with count mean diameters of less than 4µm, has been associated with undesirable health effects. Therefore, methodologies that analyze the size profiles of fine PM in ambient air segments at ground-level are entailed. Indeed, remote sensing in the visible-NIR range has already been engaged in measuring the multi-spectral signatures of PM, providing estimated size distributions of fine PM in atmospheric columns. However, the solar-based measurements require daylight and provide PM profiles in vertical atmospheric columns that do not correlate well with the ground-level PM attributes in an urban-scale resolution, which is the most relevant to public health. A ground hyperspectral camera was used for imaging illuminating targets through horizontal, urban-scale, open paths in order to detec...
Lyman break galaxies (LBGs) at z ∼ 3 exhibit number densities and clustering similar to local L *... more Lyman break galaxies (LBGs) at z ∼ 3 exhibit number densities and clustering similar to local L * galaxies; however, their star formation rates (SFRs) are much higher. We explore the scenario in which LBGs are starburst galaxies triggered by collisions, and thus provide an explanation for these key properties. The relative paucity of starburst galaxies at low redshift can be attributed to a much higher collision rate in the past. We use high-resolution cosmological Nbody simulations and a hierarchical halo finder to estimate the galaxy collision rate as a function of time in the popular ΛCDM cosmological model. We find that bright collisional starbursts are frequent enough to account for most of the high-z (2.5 − 4.5) LBGs. Moreover, many of the objects are of relatively small mass, but they cluster about large-mass halos. They therefore exhibit strong clustering, similar to that observed and stronger than that of the relevant massive halos.
The 9th astrophysics conference: After the dark ages, when galaxies were young (the Universe at 2<Z<5), 1999
Explaining the nature of the Lyman Break Galaxies (LBGs) recently discovered [1,2] at redshift z ... more Explaining the nature of the Lyman Break Galaxies (LBGs) recently discovered [1,2] at redshift z ~ 3, is an exciting challenge for the paradigm of hierarchical structure formation. These galaxies are forming stars at a rate comparable to locally rare "starburst" galaxies [3], but are as luminous and numerous as local bright galaxies. In addition, the brightest LBGs have small emission line-widths [4], indicating virial masses of ,~ 1-5 x 101°M®, however LBGs exhibit strong clustering, similar to the properties expected of the most massive (,.~ 1012Mo) dark matter halos [5-8] at this redshift. We explore a possible solution to these apparent paradoxes: that LBGs are a population of collision-driven starburst galaxies which are abundant due to an increased collision rate at high redshift [2,9]. We use high-resolution cosmological Nbody simulations and a hierarchical halo finder to estimate the galaxy collision rate as a function of time in a popular cosmological model (ACDM). We find that appropriate collisions are frequent enough, and the ensuing bursts are plausibly bright enough, to account for most of the LBGs. Although many of the simulated collisions have relatively small masses (~ 101°Mo), they tend to cluster about large-mass halos. They therefore exhibit strong clustering, similar to that observed [1,11,8] and stronger than that of halos. The collision-induced starburst scenario [2,9] thus appears to explain the key observed properties of the high-z galaxies. This picture can be further tested observationally, and distinguished from other scenarios, by more detailed studies of the evolution of the number density of LBGs with redshift and the dependence of their clustering on scale and environment.
Second international workshop on particle physics and the early universe (COSMO-98), 1999
The nature of the galaxies recently discovered at redshift [1,2] z&amp;amp;amp;gt;~3, when th... more The nature of the galaxies recently discovered at redshift [1,2] z&amp;amp;amp;gt;~3, when the Universe was only about two billion years old, is an intriguing puzzle. They are forming stars at a high rate, comparable to local ``starburst&amp;amp;#39;&amp;amp;#39; galaxies [3], but while the latter are relatively rare, the high-z galaxies are as numerous as local normal galaxies. Since many local starbursts
We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functi... more We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functions and luminosity-velocity relations. Such a velocity function is desirable for several reasons. First, it enables an objective comparison of luminosity functions obtained in different bands and for different galaxy morphologies, with a statistical correction for dust extinction. In addition, the velocity function simplifies comparison of observations with predictions from high-resolution cosmological N-body simulations. We derive velocity functions from five different data sets and find rough agreement among them, but about a factor of 2 variation in amplitude. These velocity functions are then compared with N-body simulations of a ΛCDM model (corrected for baryonic infall) in order to demonstrate both the utility and current limitations of this approach. The number density of dark matter halos and the slope of the velocity function near v * , the circular velocity corresponding to an ∼ L * spiral galaxy, are found to be comparable to that of observed galaxies. The primary sources of uncertainty in construction of Ψ(log v) from observations and N-body simulations are discussed and explanations are suggected to account for these discrepancies.
We present a method for constraining the evolution of the galaxy luminosity-velocity (LV) relatio... more We present a method for constraining the evolution of the galaxy luminosity-velocity (LV) relation in hierarchical scenarios of structure formation. The comoving number density of dark-matter halos with circular velocity of 200 km s −1 is predicted in favored CDM cosmologies to be nearly constant over the redshift range 0 < ∼ z < ∼ 5. Any observed evolution in the density of bright galaxies implies in turn a corresponding evolution in the LV relation. We consider several possible forms of evolution for the zero-point of the LV relation and predict the corresponding evolution in galaxy number density. The Hubble Deep Field suggests a large deficit of bright (M V < −19) galaxies at 1.4 < ∼ z < ∼ 2. If taken at face value, this implies a dimming of the LV zero-point by roughly 2 magnitudes. Deep, wide-field, near-IR selected surveys will provide more secure measurements to compare with our predictions.
We present a new method to determine Υ HI , the total mass-to-neutral gas ratio in Lyman-limits s... more We present a new method to determine Υ HI , the total mass-to-neutral gas ratio in Lyman-limits systems. The method exploits the relation between the neutral hydrogen column density and the magnification of background sources due to the weak gravitational lensing that these systems induce. Because weak lensing does not provide a direct measure of mass, one must use this relation in a statistical sense to solve for the average Υ HI and its distribution. We use a detailed mock catalog of quasars (sources) and Lyman-limit systems (lenses) to demonstrate the applicability of this approach through our ability to recover the parameter Υ HI. This mock catalog also allows us to check for systematics in the method and to sketch its limitations. For a universal constant Υ HI and a sample of n QSO quasars, we obtain an unbiased estimate of its value with 95% confidence limits (independent of its actual value) of Υ HI ± 140 10 5 /n QSO .
Precise determinations of the image positions in quad gravitational lenses using VLBI can be used... more Precise determinations of the image positions in quad gravitational lenses using VLBI can be used to measure the transverse velocity of the lens galaxy and the observer. The typical proper motions are as yr 1 , so the time scale to measure the motion is ten years. By measuring the dipole of the proper motions in an ensemble of lenses we can set limits on the deviation of the inertial frame de ned by the lenses from that de ned by the CMB dipole and estimate the Hubble constant. The residual proper motions after subtracting the dipole probe the evolution of peculiar velocities with redshift and can be used to estimate the density parameter 0. For N lenses, VLBI measurement accuracies of , and a baseline of T years, we estimate that the 2{ limit on the rms peculiar velocity of the lens galaxies is 3100(=10 as)(yrs=T)=N 1=2 km s 1 , and that the time required for the 2{ limit to reach the level of the local rms peculiar velocity v 0;rms is approximately 10N 1=2 (v 0;rms =600 km s 1)(=10 as) years. For a ten year baseline and N = 10 lenses we expect the 1{ limit on the misalignment with the CMB dipole to be = 20 or equivalently to obtain an upper limit of H 0 =H 0 < 0:34.
Monthly Notices of the Royal Astronomical Society, 2000
We study the merging history of dark matter haloes in N-body simulations and semianalytical`merge... more We study the merging history of dark matter haloes in N-body simulations and semianalytical`merger trees' based on the extended Press±Schechter (EPS) formalism. The main focus of our study is the joint distribution of progenitor number and mass as a function of redshift and parent halo mass. We begin by investigating the mean quantities predicted directly by the Press±Schechter (PS) and EPS formalism, such as the halo mass and conditional mass functions, and compare these predictions with the results of the simulations. The higher moments of this distribution are not predicted by the EPS formalism alone and must be obtained from the merger trees. We find that the Press± Schechter model deviates from the simulations at the level of 30±50 per cent on certain mass scales, and that the sense of the discrepancy changes as a function of redshift. We show that this discrepancy is reflected in the higher moments of the distribution of progenitor mass and number. We investigate some related statistics such as the accretion rate and the mass ratio of the largest two progenitors. For galaxy sized haloes M , 10 12 M (Y we find that the merging history of haloes, as represented by these statistics, is well reproduced in the merger trees compared with the simulations. The agreement deteriorates for larger mass haloes. We conclude that merger trees based on the extended Press±Schechter formalism provide a reasonably reliable framework for semi-analytical models of galaxy formation.
This is the second in a series of papers in which we assemble and analyze a homogeneous catalog o... more This is the second in a series of papers in which we assemble and analyze a homogeneous catalog of peculiar velocity data. In Paper I, we treated two Tully-Fisher (TF) cluster samples. Here, we study four TF field samples: the I-band sample of Mathewson, Ford, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp; Buchhorn, the r-band samples of Willick and Courteau Faber, and the H-band sample of
Background: The distribution of the blood vessel network at any point in time in any body tissue,... more Background: The distribution of the blood vessel network at any point in time in any body tissue, may provide valuable information with regards to the tissue condition and its angiogenesis functionality. The blood vessel three-dimensional network of the endometrium goes through a process of change over a relatively short period of 4 weeks on average. It is well accepted that this angiogenesis is closely related to the success or failure of the implantation of the embryo Objective and rationale: Our study aims to present a method to follow the three-dimensional evolution of the superficial blood vessel distribution in the endometrium throughout the uterine cycle. Method: This method utilizes differences in the observed broadband colors of the blood vessels in order to assess their depth coordinate below the endometrial tissue surface. We implemented the method using microscopic images of fresh, ex-vivo, endometrial samples of different cycle days to obtain the statistical evolution t...
The interaction rates of dark-matter halos and subhalos, including collisions and mergers, are co... more The interaction rates of dark-matter halos and subhalos, including collisions and mergers, are computed using high-resolution cosmological N-body simulations of the ΛCDM model. Although the number fraction of subhalos of mass > 2 × 10 11 h −1 M ⊙ is only ∼ 10%, we find that the interaction rate of such subhalos is relatively high because they reside in high density environments. At low redshift, the subhalo collisions dominate the total collision rate, and even at z = 3 they are involved in more than 30% of all collisions. About 40% of the "major" mergers (those of mass ratio > 0.3) are between subhalos. Therefore subhalo interactions must be incorporated in models of structure formation. We find that the collision rate between halos in physical density units, is ∝ (1+z) δ , with δ = 3 − 4, in agreement with earlier simulations and most observational data. We test previous analytic estimates of the interaction rates of subhalos based on statistical models, which could be very inaccurate because of the small number of subhalos and the variation of conditions within small host halos. We find that, while such statistical estimates may severely overestimate the rate within hosts < 10 13 h −1 M ⊙ , typical of high redshifts, they are valid for larger hosts regardless of the number of subhalos in them. We find the Makino & Hut (1997) estimate of the subhalo merger rate to be valid for hosts > ∼ 6 × 10 11 h −1 M ⊙ at all redshifts. The collision rate between subhalos and the central object of their host halo is approximated relatively well using the timescale for dynamical friction in circular orbits. This approximation fails in ∼ 40% of the cases, partly because of deviations from the assumption of circular orbits (especially at low redshift) and partly because of the invalidity of the assumption that the subhalo mass is negligible (especially at high redshift).
We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-... more We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-resolution cosmological N-body simulation of a ΛCDM cosmology. At each analyzed redshift z we divide the dark matter particles into 4 components: (i) isolated galactic halos, (ii) subhalos, (iii) the diffuse medium of group and cluster halos, and (iv) the background outside of virialized halos. We follow the time evolution of the mass distribution and flows between these components and provide fitting functions for the exchange rates. The exchange rates show gradual evolution as z decreases to 2, and become more steady thereafter. For z < ∼ 2 about 15% of the isolated galactic halos cluster per Gyr to become subhalos and a similar fraction of their mass returns to the unvirialized background. Mass accumulation onto subhalos is equally shared between previously isolated halos and unvirialized matter, and is dominated by accretion from the host's diffuse matter beyond z ≃ 1. This accumulation is balanced for z ≃ 0.5 by subhalo disruption at a rate of about half of their mass per Gyr. The diffuse component in host halos is built by accreting isolated halos and un-virialized material in mass shares of 40% and 60%, respectively, and at z < 0.5 also by disruption of subhalos. The unvirialized IGM is enriched mostly by stripping of isolated halos, and at z < 1 also by mass loss from groups and clusters. We go on to use our derived exchange rates together with a simple recipe for metal production to gauge the importance of metal redistribution in the universe due solely to gravity-induced interactions. This crude model predicts some trends regarding metallicity ratios. The diffuse metallicity in clusters is predicted to be ∼ 40% that in isolated galaxies (∼ 55% of groups) at z = 0, and should be lower only slightly by z = 1, consistent with observations. The metallicity of the diffuse media in large galaxy halos and poor groups is expected to be lower by about a factor of 5 by z ∼ 2, in agreement with the observed metallicity of damped Lyα systems. The metallicity of the background IGM is predicted to be (1 − 3) × 10 −4 that of z = 0 clusters, also consistent with observations. The agreement of predicted and observed trends indicates that gravitational interaction alone may play an important role in metal enrichment of the intra-cluster and intergalactic media.
We use N-body simulations combined with semi-analytic models to compute the clustering properties... more We use N-body simulations combined with semi-analytic models to compute the clustering properties of modeled galaxies at z ∼ 3, and confront these predictions with the clustering properties of the observed population of Lyman-break galaxies (LBGs). Several scenarios for the nature of LBGs are explored, which may be broadly categorized into models in which high-redshift star formation is driven by collisional starbursts and those in which quiescent star formation dominates. For each model, we make predictions for the LBG overdensity distribution, the variance of counts-in-cells, the correlation length, and close pair statistics. Models which assume a one-to-one relationship between massive darkmatter halos and galaxies are disfavored by close pair statistics, as are models in which colliding halos are associated with galaxies in a simplified way. However, when modeling of gas consumption and star formation is included using a semi-analytic treatment, the quiescent and collisional sta...
We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functi... more We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functions and luminosity-velocity relations. Such a velocity function is desirable for several reasons. First, it enables an objective comparison of luminosity functions obtained in different bands and for different galaxy morphologies, with a statistical correction for dust extinction. In addition, the velocity function simplifies comparison of observations with predictions from high-resolution cosmological N-body simulations. We derive velocity functions from five different data sets and find rough agreement among them, but about a factor of 2 variation in amplitude. These velocity functions are then compared with N-body simulations of a ΛCDM model (corrected for baryonic infall) in order to demonstrate both the utility and current limitations of this approach. The number density of dark matter halos and the slope of the velocity function near v∗, the circular velocity corresponding to an ∼ ...
Spatiotemporal variations in attributes of particulate matter (PM) in ambient air are important e... more Spatiotemporal variations in attributes of particulate matter (PM) in ambient air are important estimates of environmental pollution and public health risks. In particularly, the exposure to fine PM, with count mean diameters of less than 4µm, has been associated with undesirable health effects. Therefore, methodologies that analyze the size profiles of fine PM in ambient air segments at ground-level are entailed. Indeed, remote sensing in the visible-NIR range has already been engaged in measuring the multi-spectral signatures of PM, providing estimated size distributions of fine PM in atmospheric columns. However, the solar-based measurements require daylight and provide PM profiles in vertical atmospheric columns that do not correlate well with the ground-level PM attributes in an urban-scale resolution, which is the most relevant to public health. A ground hyperspectral camera was used for imaging illuminating targets through horizontal, urban-scale, open paths in order to detec...
Lyman break galaxies (LBGs) at z ∼ 3 exhibit number densities and clustering similar to local L *... more Lyman break galaxies (LBGs) at z ∼ 3 exhibit number densities and clustering similar to local L * galaxies; however, their star formation rates (SFRs) are much higher. We explore the scenario in which LBGs are starburst galaxies triggered by collisions, and thus provide an explanation for these key properties. The relative paucity of starburst galaxies at low redshift can be attributed to a much higher collision rate in the past. We use high-resolution cosmological Nbody simulations and a hierarchical halo finder to estimate the galaxy collision rate as a function of time in the popular ΛCDM cosmological model. We find that bright collisional starbursts are frequent enough to account for most of the high-z (2.5 − 4.5) LBGs. Moreover, many of the objects are of relatively small mass, but they cluster about large-mass halos. They therefore exhibit strong clustering, similar to that observed and stronger than that of the relevant massive halos.
The 9th astrophysics conference: After the dark ages, when galaxies were young (the Universe at 2<Z<5), 1999
Explaining the nature of the Lyman Break Galaxies (LBGs) recently discovered [1,2] at redshift z ... more Explaining the nature of the Lyman Break Galaxies (LBGs) recently discovered [1,2] at redshift z ~ 3, is an exciting challenge for the paradigm of hierarchical structure formation. These galaxies are forming stars at a rate comparable to locally rare "starburst" galaxies [3], but are as luminous and numerous as local bright galaxies. In addition, the brightest LBGs have small emission line-widths [4], indicating virial masses of ,~ 1-5 x 101°M®, however LBGs exhibit strong clustering, similar to the properties expected of the most massive (,.~ 1012Mo) dark matter halos [5-8] at this redshift. We explore a possible solution to these apparent paradoxes: that LBGs are a population of collision-driven starburst galaxies which are abundant due to an increased collision rate at high redshift [2,9]. We use high-resolution cosmological Nbody simulations and a hierarchical halo finder to estimate the galaxy collision rate as a function of time in a popular cosmological model (ACDM). We find that appropriate collisions are frequent enough, and the ensuing bursts are plausibly bright enough, to account for most of the LBGs. Although many of the simulated collisions have relatively small masses (~ 101°Mo), they tend to cluster about large-mass halos. They therefore exhibit strong clustering, similar to that observed [1,11,8] and stronger than that of halos. The collision-induced starburst scenario [2,9] thus appears to explain the key observed properties of the high-z galaxies. This picture can be further tested observationally, and distinguished from other scenarios, by more detailed studies of the evolution of the number density of LBGs with redshift and the dependence of their clustering on scale and environment.
Second international workshop on particle physics and the early universe (COSMO-98), 1999
The nature of the galaxies recently discovered at redshift [1,2] z&amp;amp;amp;gt;~3, when th... more The nature of the galaxies recently discovered at redshift [1,2] z&amp;amp;amp;gt;~3, when the Universe was only about two billion years old, is an intriguing puzzle. They are forming stars at a high rate, comparable to local ``starburst&amp;amp;#39;&amp;amp;#39; galaxies [3], but while the latter are relatively rare, the high-z galaxies are as numerous as local normal galaxies. Since many local starbursts
We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functi... more We present a galaxy circular velocity function, Ψ(log v), derived from existing luminosity functions and luminosity-velocity relations. Such a velocity function is desirable for several reasons. First, it enables an objective comparison of luminosity functions obtained in different bands and for different galaxy morphologies, with a statistical correction for dust extinction. In addition, the velocity function simplifies comparison of observations with predictions from high-resolution cosmological N-body simulations. We derive velocity functions from five different data sets and find rough agreement among them, but about a factor of 2 variation in amplitude. These velocity functions are then compared with N-body simulations of a ΛCDM model (corrected for baryonic infall) in order to demonstrate both the utility and current limitations of this approach. The number density of dark matter halos and the slope of the velocity function near v * , the circular velocity corresponding to an ∼ L * spiral galaxy, are found to be comparable to that of observed galaxies. The primary sources of uncertainty in construction of Ψ(log v) from observations and N-body simulations are discussed and explanations are suggected to account for these discrepancies.
We present a method for constraining the evolution of the galaxy luminosity-velocity (LV) relatio... more We present a method for constraining the evolution of the galaxy luminosity-velocity (LV) relation in hierarchical scenarios of structure formation. The comoving number density of dark-matter halos with circular velocity of 200 km s −1 is predicted in favored CDM cosmologies to be nearly constant over the redshift range 0 < ∼ z < ∼ 5. Any observed evolution in the density of bright galaxies implies in turn a corresponding evolution in the LV relation. We consider several possible forms of evolution for the zero-point of the LV relation and predict the corresponding evolution in galaxy number density. The Hubble Deep Field suggests a large deficit of bright (M V < −19) galaxies at 1.4 < ∼ z < ∼ 2. If taken at face value, this implies a dimming of the LV zero-point by roughly 2 magnitudes. Deep, wide-field, near-IR selected surveys will provide more secure measurements to compare with our predictions.
We present a new method to determine Υ HI , the total mass-to-neutral gas ratio in Lyman-limits s... more We present a new method to determine Υ HI , the total mass-to-neutral gas ratio in Lyman-limits systems. The method exploits the relation between the neutral hydrogen column density and the magnification of background sources due to the weak gravitational lensing that these systems induce. Because weak lensing does not provide a direct measure of mass, one must use this relation in a statistical sense to solve for the average Υ HI and its distribution. We use a detailed mock catalog of quasars (sources) and Lyman-limit systems (lenses) to demonstrate the applicability of this approach through our ability to recover the parameter Υ HI. This mock catalog also allows us to check for systematics in the method and to sketch its limitations. For a universal constant Υ HI and a sample of n QSO quasars, we obtain an unbiased estimate of its value with 95% confidence limits (independent of its actual value) of Υ HI ± 140 10 5 /n QSO .
Precise determinations of the image positions in quad gravitational lenses using VLBI can be used... more Precise determinations of the image positions in quad gravitational lenses using VLBI can be used to measure the transverse velocity of the lens galaxy and the observer. The typical proper motions are as yr 1 , so the time scale to measure the motion is ten years. By measuring the dipole of the proper motions in an ensemble of lenses we can set limits on the deviation of the inertial frame de ned by the lenses from that de ned by the CMB dipole and estimate the Hubble constant. The residual proper motions after subtracting the dipole probe the evolution of peculiar velocities with redshift and can be used to estimate the density parameter 0. For N lenses, VLBI measurement accuracies of , and a baseline of T years, we estimate that the 2{ limit on the rms peculiar velocity of the lens galaxies is 3100(=10 as)(yrs=T)=N 1=2 km s 1 , and that the time required for the 2{ limit to reach the level of the local rms peculiar velocity v 0;rms is approximately 10N 1=2 (v 0;rms =600 km s 1)(=10 as) years. For a ten year baseline and N = 10 lenses we expect the 1{ limit on the misalignment with the CMB dipole to be = 20 or equivalently to obtain an upper limit of H 0 =H 0 < 0:34.
Monthly Notices of the Royal Astronomical Society, 2000
We study the merging history of dark matter haloes in N-body simulations and semianalytical`merge... more We study the merging history of dark matter haloes in N-body simulations and semianalytical`merger trees' based on the extended Press±Schechter (EPS) formalism. The main focus of our study is the joint distribution of progenitor number and mass as a function of redshift and parent halo mass. We begin by investigating the mean quantities predicted directly by the Press±Schechter (PS) and EPS formalism, such as the halo mass and conditional mass functions, and compare these predictions with the results of the simulations. The higher moments of this distribution are not predicted by the EPS formalism alone and must be obtained from the merger trees. We find that the Press± Schechter model deviates from the simulations at the level of 30±50 per cent on certain mass scales, and that the sense of the discrepancy changes as a function of redshift. We show that this discrepancy is reflected in the higher moments of the distribution of progenitor mass and number. We investigate some related statistics such as the accretion rate and the mass ratio of the largest two progenitors. For galaxy sized haloes M , 10 12 M (Y we find that the merging history of haloes, as represented by these statistics, is well reproduced in the merger trees compared with the simulations. The agreement deteriorates for larger mass haloes. We conclude that merger trees based on the extended Press±Schechter formalism provide a reasonably reliable framework for semi-analytical models of galaxy formation.
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Papers by Tsafrir Kolatt