Spectroscopic Galaxy Redshift Surveys Research Articles

Testing general relativity with the Doppler magnification effect

ABSTRACT The apparent sizes and brightnesses of galaxies are correlated in a dipolar pattern around matter overdensities in redshift space, appearing larger on their near side and smaller on their far side. The opposite effect occurs for galaxies around an underdense region. These patterns of apparent magnification induce dipole and higher multipole terms in the cross-correlation of galaxy number density fluctuations with galaxy size/brightness (which is sensitive to the convergence field). This provides a means of directly measuring peculiar velocity statistics at low and intermediate redshift, with several advantages for performing cosmological tests of general relativity (GR). In particular, it does not depend on empirically calibrated scaling relations like the Tully–Fisher and Fundamental Plane methods. We show that the next generation of spectroscopic galaxy redshift surveys will be able to measure the Doppler magnification effect with sufficient signal-to-noise ratio to test GR on large scales. We illustrate this with forecasts for the constraints that can be achieved on parametrized deviations from GR for forthcoming low-redshift galaxy surveys with DESI and SKA2. Although the cross-correlation statistic considered has a lower signal-to-noise ratio than RSD, it will be a useful probe of GR since it is sensitive to different systematics.

Forward modeling of spectroscopic galaxy surveys: application to SDSS

Galaxy spectra are essential to probe the spatial distribution of galaxies in our Universe. To better interpret current and future spectroscopic galaxy redshift surveys, it is important to be able to simulate these data sets. We describe USPEC, a forward modeling tool to generate galaxy spectra taking into account some intrinsic galaxy properties as well as instrumental responses of a given telescope. The model for the intrinsic properties of the galaxy population, i.e., the luminosity functions, and size and spectral coefficients distributions, was developed in an earlier work for broad-band imaging surveys [1], and we now aim to test the model further using spectroscopic data. We apply USPEC to the SDSS/CMASS sample of Luminous Red Galaxies (LRGs). We construct selection cuts that match those used to build this LRG sample, which we then apply to data and simulations in the same way. The resulting real and simulated average spectra show a good statistical agreement overall, with residual differences likely coming from a bluer galaxy population of the simulated sample. We also do not explore the impact of non-solar element ratios in our simulations. For a quantitative comparison, we perform Principal Component Analysis (PCA) of the sets of spectra. By comparing the PCs constructed from simulations and data, we find good agreement for all components. The distributions of the eigencoefficients also show an appreciable overlap. We are therefore able to properly simulate the LRG sample taking into account the SDSS/BOSS instrumental responses. The differences between the two samples can be ascribed to the intrinsic properties of the simulated galaxy population, which can be reduced by further improvements of our modeling method in the future. We discuss how these results can be useful for the forward modeling of upcoming large spectroscopic surveys.

Unbiased clustering estimation in the presence of missing observations

In order to be efficient, spectroscopic galaxy redshift surveys do not obtain redshifts for all galaxies in the population targeted. The missing galaxies are often clustered, commonly leading to a lower proportion of successful observations in dense regions. One example is the close-pair issue for SDSS spectroscopic galaxy surveys, which have a deficit of pairs of observed galaxies with angular separation closer than the hardware limit on placing neighbouring fibers. Spatially clustered missing observations will exist in the next generations of surveys. Various schemes have previously been suggested to mitigate these effects, but none works for all situations. We argue that the solution is to link the missing galaxies to those observed with statistically equivalent clustering properties, and that the best way to do this is to rerun the targeting algorithm, varying the angular position of the observations. Provided that every pair has a non-zero probability of being observed in one realisation of the algorithm, then a pair-upweighting scheme linking targets to successful observations, can correct these issues. We present such a scheme, and demonstrate its validity using realisations of an idealised simple survey strategy.

The 2.4 μm Galaxy Luminosity Function As Measured Using WISE. I. Measurement Techniques

Abstract The astronomy community has at its disposal a large back catalog of public spectroscopic galaxy redshift surveys that can be used for the measurement of luminosity functions (LFs). Utilizing the back catalog with new photometric surveys to maximum efficiency requires modeling the color selection bias imposed on the selection of target galaxies by flux limits at multiple wavelengths. The likelihood derived herein can address, in principle, all possible color selection biases through the use of a generalization of the LF, , over the space of all spectra: the spectro-luminosity functional, . It is, therefore, the first estimator capable of simultaneously analyzing multiple redshift surveys in a consistent way. We also propose a new way of parametrizing the evolution of the classic Schechter function parameters, L ⋆ and ϕ ⋆, that improves both the physical realism and statistical performance of the model. The techniques derived in this paper are used in a companion paper by Lake et al. to measure the LF of galaxies at the rest-frame wavelength of using the Widefield Infrared Survey Explorer (WISE).

ULTRA-LARGE-SCALE COSMOLOGY IN NEXT-GENERATION EXPERIMENTS WITH SINGLE TRACERS

Future surveys of large-scale structure will be able to measure perturbations on the scale of the cosmological horizon, and so could potentially probe a number of novel relativistic effects that are negligibly small on sub-horizon scales. These effects leave distinctive signatures in the power spectra of clustering observables and, if measurable, would open a new window on relativistic cosmology. We quantify the size and detectability of the effects for the most relevant future large-scale structure experiments: spectroscopic and photometric galaxy redshift surveys, intensity mapping surveys of neutral hydrogen, and radio continuum surveys. Our forecasts show that next-generation experiments, reaching out to redshifts $z\simeq 4$, will not be able to detect previously-undetected general-relativistic effects by using individual tracers of the density field, although the contribution of weak lensing magnification on large scales should be clearly detectable. We also perform a rigorous joint forecast for the detection of primordial non-Gaussianity through the excess power it produces in the clustering of biased tracers on large scales, finding that uncertainties of $\sigma(f_{\rm NL})\sim 1-2$ should be achievable. We study the level of degeneracy of these large-scale effects with several tracer-dependent nuisance parameters, quantifying the minimal priors on the latter that are needed for an optimal measurement of the former. Finally, we discuss the systematic effects that must be mitigated to achieve this level of sensitivity, and some alternative approaches that should help to improve the constraints. The computational tools developed to carry out this study, which requires the full-sky computation of the theoretical angular power spectra for $\mathcal{O}(100)$ redshift bins, as well as realistic models of the luminosity function, are publicly available.

ABSORPTION-LINE DETECTIONS OF 105-106K GAS IN SPIRAL-RICH GROUPS OF GALAXIES

Using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs. In a previous paper (Savage et al. 2014) these far-UV spectra were used to discover 14 "warm" ($T > 10^5$ K) absorbers using a combination of broad Ly\alpha\ and O VI absorptions. A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers could be present in this sample. A shallow, wide spectroscopic galaxy redshift survey has been conducted around these sight lines to investigate the warm absorber environment, which is found to be spiral-rich galaxy groups or cluster outskirts with radial velocity dispersions of \sigma\ = 250-750 km/s. While 2\sigma\ evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual, nearest galaxies, this evidence has considerable systematic uncertainties and is based on a small sample size so it is not entirely conclusive. If the associations are with galaxy groups, the observed frequency of warm absorbers (dN/dz = 3.5-5 per unit redshift) requires them to be very large (~1 Mpc in radius at high covering factor). Most likely these warm absorbers are interface gas clouds whose presence implies the existence of a hotter ($T \sim 10^{6.5}$ K), diffuse and probably very massive ($>10^{11}~M_{\odot}$) intra-group medium which has yet to be detected directly.

Probing neutrinos from Planck and forthcoming galaxy redshift surveys

We investigate how much the constraints on the neutrino properties can be improvedby combining the CMB, the photometric and spectroscopic galaxyredshift surveys which include the CMB lensing, galaxy lensingtomography, galaxy clustering and redshift space distortion observables. We pay a particular attention to the constraint onthe neutrino mass in view of the forthcoming redshift surveys such asthe Euclid satellite and the LSST survey along with the Planck CMB lensing measurements.Combining the transverse mode information from the angular powerspectrum and the longitudinal mode information from the spectroscopic survey with the redshiftspace distortion measurements can determine the total neutrino masswith the projected error of \U0001d4aa(0.02) eV.Ouranalysis fixes the mass splittings among the neutrino species to beconsistent with the neutrino oscillation data, and we accordingly study thesensitivity of our parameter estimations on the minimal neutrino mass. Thecosmological measurement of the total neutrino mass can distinguishbetween the normal and inverted mass hierarchy scenarios if the minimalneutrino mass ≲0.005 eV with the predicted 1–σuncertainties taken into account.

Principal component analysis of modified gravity using weak lensing and peculiar velocity measurements

We perform a principal component analysis to assess ability of futureobservations to measure departures from General Relativity inpredictions of the Poisson and anisotropy equations on linearscales. In particular, we focus on how the measurements ofredshift-space distortions (RSD) observed from spectroscopic galaxyredshift surveys will improve the constraints when combined withlensing tomographic surveys. Assuming a Euclid-like galaxy imaging andredshift survey, we find that adding the 3D information decreases thestatistical uncertainty by a factor between 3 and 7 compared to thecase when only observables from lensing tomographic surveys areused. We also find that the number of well-constrained modes increasesby a factor between 3 and 6. Our study indicates the importance ofjoint galaxy imaging and redshift surveys such as SuMIRe and Euclid togive more stringent tests of the ΛCDM model and to distinguishbetween various modified gravity and dark energy models.

THE PRISM MULTI-OBJECT SURVEY (PRIMUS). II. DATA REDUCTION AND REDSHIFT FITTING

The PRIsm MUti-object Survey (PRIMUS) is a spectroscopic galaxy redshift survey to z~1 completed with a low-dispersion prism and slitmasks allowing for simultaneous observations of ~2,500 objects over 0.18 square degrees. The final PRIMUS catalog includes ~130,000 robust redshifts over 9.1 sq. deg. In this paper, we summarize the PRIMUS observational strategy and present the data reduction details used to measure redshifts, redshift precision, and survey completeness. The survey motivation, observational techniques, fields, target selection, slitmask design, and observations are presented in Coil et al 2010. Comparisons to existing higher-resolution spectroscopic measurements show a typical precision of sigma_z/(1+z)=0.005. PRIMUS, both in area and number of redshifts, is the largest faint galaxy redshift survey completed to date and is allowing for precise measurements of the relationship between AGNs and their hosts, the effects of environment on galaxy evolution, and the build up of galactic systems over the latter half of cosmic history.

THE WEIGHT OF EMPTINESS: THE GRAVITATIONAL LENSING SIGNAL OF STACKED VOIDS

The upcoming new generation of spectroscopic galaxy redshift surveys will provide large samples of cosmic voids, the distinct, large underdense structures in the universe. Combining these with future galaxy imaging surveys, we study the prospects of probing the underlying matter distribution in and around cosmic voids via the weak gravitational lensing effects of stacked voids, utilizing both shear and magnification information. The statistical precision is greatly improved by stacking together a large number of voids along different lines of sight, even when taking into account the impact of inherent miscentering and projection effects. We show that Dark Energy Task Force Stage IV surveys, such as the Euclid satellite and the Large Synoptic Survey Telescope, should be able to detect the void lensing signal with sufficient precision from stacking abundant medium-sized voids, thus providing direct constraints on the matter density profile of voids independent of assumptions on galaxy bias.

Evidence for spin alignment of spiral and elliptical/S0 galaxies in filaments

Galaxies are not distributed randomly in the cosmic web but are instead arranged in filaments and sheets surrounding cosmic voids. Observationally there is still no convincing evidence of a link between the properties of galaxies and their host structures. However, by the tidal torque theory (our understanding of the origin of galaxy angular momentum), such a link should exist. Using the presently largest spectroscopic galaxy redshift survey (SDSS) we study the connection between the spin axes of galaxies and the orientation of their host filaments. We use a three dimensional field of orientations to describe cosmic filaments. To restore the inclination angles of galaxies, we use a 3D photometric model of galaxies that gives these angles more accurately than traditional 2D models. We found evidence that the spin axes of bright spiral galaxies have a weak tendency to be aligned parallel to filaments. For elliptical/S0 galaxies, we have a statistically significant result that their spin axes are aligned preferentially perpendicular to the host filaments; we show that this signal practically does not depend on the accuracy of the estimated inclination angles for elliptical/S0 galaxies.

WiggleZ Dark Energy Survey: Cosmological neutrino mass constraint from blue high-redshift galaxies

The absolute neutrino mass scale is currently unknown, but can be constrained from cosmology. The WiggleZ high redshift star-forming blue galaxy sample is less sensitive to systematics from non-linear structure formation, redshift-space distortions and galaxy bias than previous surveys. We obtain a upper limit on the sum of neutrino masses of 0.60eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble Parameter and the baryon acoustic oscillation scale gives an upper limit of 0.29eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys.

Combining weak-lensing tomography and spectroscopic redshift surveys

Redshift space distortion (RSD) is a powerful way of measuring the growth of structure and testing General Relativity, but it is limited by cosmic variance and the degeneracy between galaxy bias b and the growth rate factor f. The cross-correlation of lensing shear with the galaxy density field can in principle measure b in a manner free from cosmic variance limits, breaking the f-b degeneracy and allowing inference of the matter power spectrum from the galaxy survey. We analyze the growth constraints from a realistic tomographic weak lensing photo-z survey combined with a spectroscopic galaxy redshift survey over the same sky area. For sky coverage f_sky=0.5, analysis of the transverse modes measures b to 2-3% accuracy per \Delta z=0.1 bin at z<1 when \sim10 galaxies per square arcmin are measured in the lensing survey and all halos with M>M_min=10^13 h^{-1}M_solar have spectra. For the gravitational growth parameter parameter \gamma (f=\Omega_m^{\gamma}), combining the lensing information with RSD analysis of non-transverse modes yields accuracy \sigma(\gamma)\sim 0.01. Adding lensing information to the RSD survey improves \sigma(\gamma) by an amount equivalent to a 3 times (10 times) increase in RSD survey area when the spectroscopic survey extends down to halo mass 10^13.5 (10^14) h^{-1} M_solar. We also find that the \sigma(\gamma) of overlapping surveys is equivalent to that of surveys 1.5-2 times larger if they are separated on the sky. This gain is greatest when the spectroscopic mass threshold is 10^13 - 10^14 h^{-1} M_solar, similar to LRG surveys. The gain of overlapping surveys is reduced for very deep or very shallow spectroscopic surveys, but any practical surveys are more powerful when overlapped than when separated. The gain of overlapped surveys is larger in the case when the primordial power spectrum normalization is uncertain by >0.5%.

THE PRISM MULTI-OBJECT SURVEY (PRIMUS). I. SURVEY OVERVIEW AND CHARACTERISTICS

We present the PRIsm MUlti-object Survey (PRIMUS), a spectroscopic faint galaxy redshift survey to z~1. PRIMUS uses a low-dispersion prism and slitmasks to observe ~2,500 objects at once in a 0.18 deg^2 field of view, using the IMACS camera on the Magellan I Baade 6.5m telescope at Las Campanas Observatory. PRIMUS covers a total of 9.1 deg^2 of sky to a depth of i_AB~23.5 in seven different deep, multi-wavelength fields that have coverage from GALEX, Spitzer and either XMM or Chandra, as well as multiple-band optical and near-IR coverage. PRIMUS includes ~130,000 robust redshifts of unique objects with a redshift precision of dz/(1+z)~0.005. The redshift distribution peaks at z=0.6 and extends to z=1.2 for galaxies and z=5 for broad-line AGN. The motivation, observational techniques, fields, target selection, slitmask design, and observations are presented here, with a brief summary of the redshift precision; a companion paper presents the data reduction, redshift fitting, redshift confidence, and survey completeness. PRIMUS is the largest faint galaxy survey undertaken to date. The high targeting fraction (~80%) and large survey size will allow for precise measures of galaxy properties and large-scale structure to z~1.

PRECISION SPECTROPHOTOMETRY AT THE LEVEL OF 0.1%

Accurate relative spectrophotometry is critical for many science applications. Small wavelength scale residuals in the flux calibration can significantly impact the measurements of weak emission and absorption features in the spectra. Using Sloan Digital Sky Survey data, we demonstrate that the average spectra of carefully selected red-sequence galaxies can be used as a spectroscopic standard to improve the relative spectrophotometry precision to 0.1% on small wavelength scales (from a few to hundreds of Angstroms). We achieve this precision by comparing stacked spectra across tiny redshift intervals. The redshift intervals must be small enough that any systematic stellar population evolution is minimized and less than the spectrophotometric uncertainty. This purely empirical technique does not require any theoretical knowledge of true galaxy spectra. It can be applied to all large spectroscopic galaxy redshift surveys that sample a large number of galaxies in a uniform population.

Detecting neutral hydrogen in emission at redshift z ≃ 1

We use a large N-body simulation to examine the detectability of HI in emission at redshift z ~ 1, and the constraints imposed by current observations on the neutral hydrogen mass function of galaxies at this epoch. We consider three different models for populating dark matter halos with HI, designed to encompass uncertainties at this redshift. These models are consistent with recent observations of the detection of HI in emission at z ~ 0.8. Whilst detection of 21 cm emission from individual halos requires extremely long integrations with existing radio interferometers, such as the Giant Meter Radio Telescope (GMRT), we show that the stacked 21 cm signal from a large number of halos can be easily detected. However, the stacking procedure requires accurate redshifts of galaxies. We show that radio observations of the field of the DEEP2 spectroscopic galaxy redshift survey should allow detection of the HI mass function at the 5-12 sigma level in the mass range 10^(11.4) M_sun/h < M_halo < 10^(12.5)M_sun/h, with a moderate amount of observation time. Assuming a larger noise level that corresponds to an upper bound for the expected noise for the GMRT, the detection significance for the HI mass function is still at the 1.7-3 sigma level. We find that optically undetected satellite galaxies enhance the HI emission profile of the parent halo, leading to broader wings as well as a higher peak signal in the stacked profile of a large number of halos. We show that it is in principle possible to discern the contribution of undetected satellites to the total HI signal, even though cosmic variance limitation make this challenging for some of our models.

Voids as a precision probe of dark energy

The shapes of cosmic voids, as measured in spectroscopic galaxy redshift surveys, constitute a promising new probe of dark energy (DE). We forecast constraints on the DE equation of state and its variation from current and future surveys and find that the promise of void shape measurements compares favorably to that of standard methods such as supernovae and cluster counts even for currently available data. Owing to the complementary nature of the constraints, void shape measurements improve the Dark Energy Task Force figure of merit by 2 orders of magnitude for a future large scale experiment such as EUCLID when combined with other probes of dark energy available on a similar time scale. Modeling several observational and theoretical systematics has only moderate effects on these forecasts. We discuss additional systematics which will require further study using simulations.

Environments of nearby quasars in Sloan Digital Sky Survey

For the first time spectroscopic galaxy redshift surveys are reaching the scales where galaxies can be studied together with the nearest quasars. This gives an opportunity to study the dependence between the activity of a quasar and its environment in a more extensive way than before. We study the spatial distribution of galaxies and groups of galaxies in the environments of low redshift quasars in the Sloan Digital Sky Survey (SDSS). Our aim is to understand how the nearby quasars are embedded in the local and global density field of galaxies and how the environment affects quasar activity. We analyse the environments of nearby quasars using number counts of galaxies. We also study the dependence of group properties to their distance to the nearest quasar. The large scale environments are studied by analysing the locations of quasars in the luminosity density field. Our study of the number counts of galaxies in quasar environments shows an underdensity of bright galaxies at a few Mpc from quasars. Also, the groups of galaxies that have a quasar closer than 2Mpc are poorer and less luminous than in average. Our analysis on the luminosity density field shows that quasars clearly avoid rich superclusters. Nearby quasars seem to be located in outskirts of superclusters or in filaments connecting them. Our results suggest that quasar evolution may be affected by density variations both on supercluster scales and in the local environment.

Galaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope

We discuss the possibility of performing a substantial spectroscopic galaxy redshift survey selected via the 21-cm emission from neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope (FAST) to be built in China. We consider issues related to the estimation of the source counts and optimizations of the survey, and discuss the constraints on cosmological models that such a survey could provide. We find that a survey taking around two years could detect similar to 10(7) galaxies with an average redshift of similar to 0.15 making the survey complementary to those already carried out at optical wavelengths. These conservative estimates have used the z = 0 H I mass function and have ignored the possibility of evolution. The results could be used to constrain Gamma=Omega(m)h to 5 per cent and the spectral index, n(s), to 7 per cent independent of cosmic microwave background data. If we also use simulated power spectra from the Planck satellite, we can constrain w to be within 5 per cent of -1.

The O vi Absorbers toward PG 0953+415: High-Metallicity, Cosmic-Web Gas Far from Luminous Galaxies

The spectrum of the low-redshift QSO PG 0953+415 (zQSO = 0.234) shows two strong, intervening O VI absorption systems. To study the nature of these absorbers, we have used the Gemini Multi-Object Spectrograph to conduct a deep spectroscopic galaxy redshift survey in the 5' × 5' field centered on the QSO. This survey is fully complete for r' < 19.7 and is 73% complete for r' < 21.0. We find three galaxies at the redshift of the higher z O VI system (zabs = 0.14232), including a galaxy at projected distance ρ = 155 h kpc. We find no galaxies in the Gemini field at the redshift of the lower z O VI absorber (zabs = 0.06807), which indicates that the nearest galaxy is more than 195 h kpc away or has L < 0.04L*. Previous shallower surveys covering a larger field have shown that the zabs = 0.06807 O VI absorber is affiliated with a group or filament of galaxies, but the nearest known galaxy has ρ = 736 h kpc. The zabs = 0.06807 absorber is notable for several reasons. The absorption profiles reveal simple kinematics indicative of quiescent material. The H I line widths and good alignment of the H I and metal lines favor photoionization, and moreover, the column density ratios imply a high metallicity: [M/H] = -0.3 ± 0.12. The zabs = 0.14232 O VI system is more complex and less constrained but also indicates a relatively high metallicity. Using galaxy redshifts from the Sloan Digital Sky Survey, we show that both of the PG 0953+415 O VI absorbers are located in large-scale filaments of the cosmic web. Evidently, some regions of the web filaments are highly metal enriched. We discuss the origin of the high-metallicity gas and suggest that the enrichment might have occurred long ago (at high z).