Cosmological Redshift Surveys Research Articles

Photometric Objects Around Cosmic Webs (PAC) Delineated in a Spectroscopic Survey. III. Accurate Measurement of Galaxy Stellar Mass Function with the Aid of Cosmological Redshift Surveys

We present a novel method to accurately measure the galaxy stellar mass function (GSMF) based upon the Photometric objects Around Cosmic webs (PAC) method developed in our first paper (Paper I) of the series. The method allows us to measure the GSMF to a lower-mass end that is not accessible to the spectroscopic sample used in the PAC. Compared with Paper I, the current measurement of GSMF is direct and model independent. We measure the GSMFs in the redshift ranges of z s 3 3 Throughout the paper, we use z s for spectroscopic redshift, z for the z-band magnitude. < 0.2, 0.2 < z s < 0.4, and 0.5 < z s < 0.7 down to stellar masses of M * = 108.2, 1010.6, and 1010.6 M ⊙, using the data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys and the spectroscopic samples of Slogan Digital Sky Survey (i.e., Main, LOWZ, and CMASS samples). Our results show that there is no evolution of GSMF from z s = 0.6 to z s = 0.1 for M * > 1010.6 M ⊙, and that there is a clear upturn at M * ≈ 109.5 M ⊙ toward smaller galaxies in the local GMSF at z s = 0.1. We provide an accurate double Schechter fit to the local GSMF for the entire range of M * and a table of our measurements at the three redshifts, which can be used to test theories of galaxy formation. Our method can achieve an accurate measurement of GSMF to the stellar mass limit where the spectroscopic sample is already highly incomplete (e.g., ∼ 10−3) for its target selection.

The synthetic Emission Line COSMOS catalogue: Hα and [O ii] galaxy luminosity functions and counts at 0.3 &amp;lt; z &amp;lt; 2.5

ABSTRACT Star-forming galaxies with strong nebular and collisional emission lines are privileged target galaxies in forthcoming cosmological large galaxy redshift surveys. We use the COSMOS2015 photometric catalogue to model galaxy spectral energy distributions and emission-line fluxes. We adopt an empirical but physically motivated model that uses information from the best-fitting spectral energy distribution of stellar continuum to each galaxy. The emission-line flux model is calibrated and validated against direct flux measurements in subsets of galaxies that have 3D-HST or zCOSMOS-Bright spectra. We take a particular care in modelling dust attenuation such that our model can explain both Hα and [O ii] observed fluxes at different redshifts. We find that a simple solution to this is to introduce a redshift evolution in the dust attenuation fraction parameter, f = Estar(B − V)/Egas(B − V), as f(z) = 0.44 + 0.2z. From this catalogue, we derive the Hα and [O ii] luminosity functions up to redshifts of about 2.5 after carefully accounting for emission line flux and redshift errors. This allows us to make predictions for Hα and [O ii] galaxy number counts in next-generation cosmological redshift surveys. Our modelled emission lines and spectra in the COSMOS2015 catalogue shall be useful to study the target selection for planned next-generation galaxy redshift surveys and we make them publicly available as ‘EL-COSMOS’ on the ASPIC data base.

Beyond the plane-parallel approximation for redshift surveys

Redshift space distortions privilege the location of the observer in cosmological redshift surveys, breaking the translational symmetry of the underlying theory. This violation of statistical homogeneity has consequences for the modeling of clustering observables, leading to what are frequently called `wide angle effects'. We study these effects analytically, computing their signature in the clustering of the multipoles in configuration and Fourier space. We take into account both physical wide angle contributions as well as the terms generated by the galaxy selection function. Similar considerations also affect the way power spectrum estimators are constructed. We quantify, in an analytical way the biases which enter and clarify the relation between what we measure and the underlying theoretical modeling. The presence of an angular window function is also discussed. Motivated by this analysis we present new estimators for the three dimensional Cartesian power spectrum and bispectrum multipoles written in terms of spherical Fourier-Bessel coefficients. We show how the latter have several interesting properties, allowing in particular a clear separation between angular and radial modes.

Empirical Hα emitter count predictions for dark energy surveys

Future galaxy redshift surveys aim to measure cosmological quantities from the galaxy power spectrum. A prime example is the detection of baryonic acoustic oscillations, providing a standard ruler to measure the dark energy equation of state, w(z), to high precision. The strongest practical limitation for these experiments is how quickly accurate redshifts can be measured for sufficient galaxies to map the large-scale structure. A promising strategy is to target emission-line (i.e. star-forming) galaxies at high redshift (z∼ 0.5–2); not only is the space density of this population increasing out to z∼ 2, but also emission lines provide an efficient method of redshift determination. Motivated by the prospect of future dark energy surveys targeting Hα emitters at near-infrared wavelengths (i.e. z > 0.5), we use the latest empirical data to model the evolution of the Hα luminosity function out to z∼ 2 and thus provide predictions for the abundance of Hα emitters for practical limiting fluxes. We caution that the estimates presented in this work must be tempered by an efficiency factor, ε, giving the redshift success rate from these potential targets. For a range of practical efficiencies and limiting fluxes, we provide an estimate of ⁠, where is the 3D galaxy number density and P0.2 is the galaxy power spectrum evaluated at k= 0.2 h Mpc−1. Ideal surveys must provide in order to balance shot-noise and cosmic variance errors. We show that a realistic emission-line survey (ε= 0.5) could achieve out to z∼ 1.5 with a limiting flux of 10−16 erg s−1 cm−2. If the limiting flux is a factor of 5 brighter, then this goal can only be achieved out to z∼ 0.5, highlighting the importance of survey depth and efficiency in cosmological redshift surveys.

STATISTICAL TOOLS FOR CLASSIFYING GALAXY GROUP DYNAMICS

The dynamical state of galaxy groups at intermediate redshifts can provide information about the growth of structure in the universe. We examine three goodness-of-fit tests, the Anderson--Darling (A-D), Kolmogorov and chi-squared tests, in order to determine which statistical tool is best able to distinguish between groups that are relaxed and those that are dynamically complex. We perform Monte Carlo simulations of these three tests and show that the chi-squared test is profoundly unreliable for groups with fewer than 30 members. Power studies of the Kolmogorov and A-D tests are conducted to test their robustness for various sample sizes. We then apply these tests to a sample of the second Canadian Network for Observational Cosmology Redshift Survey (CNOC2) galaxy groups and find that the A-D test is far more reliable and powerful at detecting real departures from an underlying Gaussian distribution than the more commonly used chi-squared and Kolmogorov tests. We use this statistic to classify a sample of the CNOC2 groups and find that 34 of 106 groups are inconsistent with an underlying Gaussian velocity distribution, and thus do not appear relaxed. In addition, we compute velocity dispersion profiles (VDPs) for all groups with more than 20 members and compare the overall features of the Gaussian and non-Gaussian groups, finding that the VDPs of the non-Gaussian groups are distinct from those classified as Gaussian.

The Growth of Galaxies in Cosmological Simulations of Structure Formation

We use hydrodynamic simulations to examine how the baryonic components of galaxies are assembled, focusing on the relative importance of mergers and smooth accretion in the formation of ~L* systems. In our primary simulation, which models a (50 h-1 Mpc)3 comoving volume of a Λ-dominated cold dark matter universe, the space density of objects at our (64 particle) baryon mass resolution threshold Mc = 5.4 × 1010 M☉ corresponds to that of observed galaxies with L ~ L*/4. Galaxies above this threshold gain most of their mass by accretion rather than by mergers. At the redshift of peak mass growth, z ≈ 2, accretion dominates over merging by about 4 : 1. The mean accretion rate per galaxy declines from ~40 M☉ yr-1 at z = 2 to ~10 M☉ yr-1 at z = 0, while the merging rate peaks later (z ≈ 1) and declines more slowly, so by z = 0 the ratio is about 2 : 1. We cannot distinguish truly smooth accretion from merging with objects below our mass resolution threshold, but extrapolating our measured mass spectrum of merging objects, dP/dM ∝ M-α with α ~ 1, implies that subresolution mergers would add relatively little mass. The global star formation history in these simulations tracks the mass accretion rate rather than the merger rate. At low redshift, destruction of galaxies by mergers is approximately balanced by the growth of new systems, so the comoving space density of resolved galaxies stays nearly constant despite significant mass evolution at the galaxy-by-galaxy level. The predicted merger rate at z 1 agrees with recent estimates from close pairs in the Canada-France Redshift Survey and Canadian Network for Observational Cosmology Redshift Survey.

Possible Detection of Baryonic Fluctuations in the Large‐Scale Structure Power Spectrum

We present a joint analysis of the power spectra of density fluctuations from three independent cosmological redshift surveys; the PSCz galaxy catalog, the APM galaxy cluster catalog and the Abell/ACO cluster catalog. Over the range 0.03 <= k <= 0.15 h/Mpc,the amplitudes of these three power spectra are related through a simple linear biasing model with b = 1.5 and b = 3.6 for Abell/ACO versus APM and Abell/ACO versus the PSCz respectively. Furthermore, the shape of these power spectra are remarkably similar despite the fact that they are comprised of significantly different objects (individual galaxies through to rich clusters). Individually, each of these surveys show visible evidence for ``valleys'' in their power spectra. We use a newly developed statistical technique called the False Discovery Rate, to show that these ``valleys'' are statistically significant. One favored cosmological explanation for such features in the power spectrum is the presence of a non-negligible baryon fraction (Omega_b/Omega_m) in the Universe which causes acoustic oscillations in the transfer function of adiabatic inflationary models. We have performed a maximum-likelihood marginalization over four important cosmological parameters of this model (Omega_m, Omega_b, n_s, H_o). We use a prior on H_0 = 69(+/-15), and find Omega_mh^2 = 0.12(+0.03/-0.02), Omega_bh^2 =0.029(+0.011/-0.015), n_s = 1.08^(+0.17/-0.20) (2 sigma confidence limits) which are fully consistent with the favored values of these cosmological parameters from the recent Cosmic Microwave Background (CMB) experiments. This agreement strongly suggests that we have detected baryonic oscillations in the power spectrum of matter at a level expected from a Cold Dark Matter model normalized to fit these CMB measurements.

Detailed Star-Formation Histories of Nearby Dwarf Irregular Galaxies using HST

Unless the nearby universe is subtly anomalous, it should contain a relatively normal selection of galaxies whose histories are representative of field galaxies in general throughout the Universe. We can therefore take advantage of our ability to resolve the nearby galaxies into individual stars to directly, and accurately, measure star formation histories. The star formation histories are determined from model-fitting analysis, based on stellar evolution tracks, of colour-magnitude diagrams. The most accurate information on star formation rates extending back to the earliest epochs can be obtained from the structure of the main sequence. However, the oldest main sequence turnoffs are very faint, and it is often necessary to use the more evolved stars to infer the star formation history. These can then be compared with the properties of galaxies seen over a large range of lookback times at moderate to high redshifts. There is considerable evidence that the faint blue galaxies seen in large numbers in cosmological redshift surveys are the progenitors of the small late-type irregular galaxies seen in copious numbers in the Local Group, and we concentrate on these here.

Star Formation in Cluster Galaxies at 0.2 &lt; [CLC][ITAL]z[/ITAL][/CLC] &lt; 0.55

The rest-frame equivalent width of the [OII] λ3727 emission line, W0(O II), has been measured for cluster and field galaxies in the Canadian Network for Observational Cosmology redshift survey of rich clusters at 0.2 10 A, as expected in a model of cluster formation in which star formation is truncated on infall. Evidence of suppressed star formation relative to the field is present in the whole cluster sample, out to 2R200, so the mechanism responsible for the differential evolution must be acting at a large distance from the cluster center and not just in the core. The mean star formation rate in the cluster galaxies with the strongest emission corresponds to an increase in the total stellar mass of less than about 4% if the star formation is due to a secondary burst lasting 0.1 Gyr.