Showing papers by "Carlton M. Baugh published in 2014"

How sensitive are predicted galaxy luminosities to the choice of stellar population synthesis model

Abstract: We present a new release of the GALFORM semi-analytical model of galaxy formation and evolution, which exploits a Millennium Simulation-class N-body run performed with the Wilkinson Microwave Anisotropy Probe 7 cosmology. We use this new model to study the impact of the choice of stellar population synthesis (SPS) model on the predicted evolution of the galaxy luminosity function. The semi-analytical model is run using seven different SPS models. In each case, we obtain the rest-frame luminosity function in the far-ultraviolet, optical and near-infrared (NIR) wavelength ranges. We find that both the predicted rest-frame ultraviolet and optical luminosity function are insensitive to the choice of SPS model. However, we find that the predicted evolution of the rest-frame NIR luminosity function depends strongly on the treatment of the thermally pulsating asymptotic giant branch (TP-AGB) stellar phase in the SPS models, with differences larger than a factor of 2 for model galaxies brighter than MAB(K) − 5 log h < −22 (∼L* for 0 ≤ z ≤ 1.5). We have also explored the predicted number counts of galaxies, finding remarkable agreement between the results with different choices of SPS model, except when selecting galaxies with very red optical–NIR colours. The predicted number counts of these extremely red galaxies appear to be more affected by the treatment of star formation in discs than by the treatment of TP-AGB stars in the SPS models.

Using the Milky Way satellites to study interactions between cold dark matter and radiation

Abstract: The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, the model significantly overestimates the number of satellite galaxies around the Milky Way. Attempts to solve this problem remain controversial and have even led some to abandon CDM altogether. However, current simulations are limited by the assumption that dark matter feels only gravity. Here we show that including interactions between CDM and radiation (photons or neutrinos) leads to a dramatic reduction in the number of satellite galaxies, providing a potential solution to the Milky Way satellite problem and indicating that physics beyond gravity may be essential to make accurate predictions of structure formation on small scales. The methodology introduced here gives constraints on dark matter interactions that are significantly improved over those from the cosmic microwave background.

The observational status of Galileon gravity after Planck

Abstract: We use the latest CMB data from Planck, together with BAO measurements, to constrain the full parameter space of Galileon gravity. We constrain separately the three main branches of the theory known as the Cubic, Quartic and Quintic models, and find that all yield a very good fit to these data. Unlike in $\Lambda{\rm CDM}$, the Galileon model constraints are compatible with local determinations of the Hubble parameter and predict nonzero neutrino masses at over $5\sigma$ significance. We also identify that the low-$l$ part of the CMB lensing spectrum may be able to distinguish between $\Lambda{\rm CDM}$ and Galileon models. In the Cubic model, the lensing potential deepens at late times on sub-horizon scales, which is at odds with the current observational suggestion of a positive ISW effect. Compared to $\Lambda$CDM, the Quartic and Quintic models predict less ISW power in the low-$l$ region of the CMB temperature spectrum, and as such are slightly preferred by the Planck data. We illustrate that residual local modifications to gravity in the Quartic and Quintic models may render the Cubic model as the only branch of Galileon gravity that passes Solar System tests.

The 0.1<z<1.65 evolution of the bright end of the [OII] luminosity function

Abstract: We present the [OII] luminosity function measured in the redshift range 0.1

Which galaxies dominate the neutral gas content of the Universe

Abstract: We study the contribution of galaxies with different properties to the global densities of star formation rate (SFR), atomic (H I) and molecular hydrogen (H2) as a function of redshift. We use the GALFORM model of galaxy formation, which is set in the Λ cold dark matter (ΛCDM) framework. This model includes a self-consistent calculation of the SFR, which depends on the H2 content of galaxies. The predicted SFR density and how much of this is contributed by galaxies with different stellar masses and infrared luminosities are in agreement with observations. The model predicts a modest evolution of the H I density at z 10 M⊙ yr−1 at z > 1. Current high-redshift galaxy surveys are limited to detect carbon monoxide in galaxies with SFR ≳ 30 M⊙ yr−1, which in our model make up, at most, 20 per cent of the H2 in the universe. In terms of stellar mass, the predicted H2 density is dominated by massive galaxies, Mstellar > 1010 M⊙, while the H I density is dominated by low-mass galaxies, Mstellar < 109 M⊙. In the context of upcoming neutral gas surveys, we suggest that the faint nature of the galaxies dominating the H I content of the Universe will hamper the identification of optical counterparts, while for H2, we expect follow-up observations of molecular emission lines of already existing galaxy catalogues to be able to uncover the H2 density of the Universe.

Nonlinear Structure Formation in Nonlocal Gravity

Abstract: We now turn our attention to large scale structure formation in nonlocal gravity models. In these models, the modifications to gravity arise via the addition of nonlocal terms (i.e. which depend on more than one point in spacetime) to the Einstein field equations. These terms typically involve the inverse of the d’Alembertian operator, \(\Box ^{-1}\), acting on curvature tensors.

The origin of the atomic and molecular gas contents of early-type galaxies – I. A new test of galaxy formation physics.

Abstract: We study the atomic (H I) and molecular hydrogen (H2) contents of early-type galaxies (ETGs) and their gas sources using the GALFORM model of galaxy formation. This model uses a self-consistent calculation of the star formation rate, which depends on the H2 content of galaxies. We first present a new analysis of H I Parkes All-Sky Survey and ATLAS3D surveys, with special emphasis on ETGs. The model predicts H I and H2 contents of ETGs in agreement with the observations from these surveys only if partial ram pressure stripping of the hot gas is included, showing that observations of neutral gas in ‘quenched’ galaxies place stringent constraints on the treatment of the hot gas in satellites. We find that ≈90 per cent of ETGs at z = 0 have neutral gas contents supplied by radiative cooling from their hot haloes, 8 per cent were supplied by gas accretion from minor mergers that took place in the last 1 Gyr, while 2 per cent were supplied by mass-loss from old stars. The model predicts neutral gas fractions strongly decreasing with increasing bulge fraction. This is due to the impeded disc regeneration in ETGs, resulting from both active galactic nuclei feedback and environmental quenching by partial ram pressure stripping of the hot gas.

Halo model and halo properties in Galileon gravity cosmologies

Abstract: We investigate the performance of semi-analytical modelling of large-scale structure in Galileon gravity cosmologies using results from N-body simulations We focus on the Cubic and Quartic Galileon models that provide a reasonable fit to CMB, SNIa and BAO data We demonstrate that the Sheth-Tormen mass function and linear halo bias can be calibrated to provide a very good fit to our simulation results We also find that the halo concentration-mass relation is well fitted by a power law The nonlinear matter power spectrum computed in the halo model approach is found to be inaccurate in the mildly nonlinear regime, but captures reasonably well the effects of the Vainshtein screening mechanism on small scales In the Cubic model, the screening mechanism hides essentially all of the effects of the fifth force inside haloes In the case of the Quartic model, the screening mechanism leaves behind residual modifications to gravity, which make the effective gravitational strength time-varying and smaller than the standard value Compared to normal gravity, this causes a deficiency of massive haloes and leads to a weaker matter clustering on small scales For both models, we show that there are realistic halo occupation distributions of Luminous Red Galaxies that can match both the observed large-scale clustering amplitude and the number density of these galaxies

The evolution of the star-forming sequence in hierarchical galaxy formation models.

Abstract: It has been argued that the specific star formation rates of star forming galaxies inferred from observational data decline more rapidly below z = 2 than is predicted by hierarchical galaxy formation models. We present a detailed analysis of this problem by comparing predictions from the GALFORM semi-analytic model with an extensive compilation of data on the average star formation rates of star-forming galaxies. We also use this data to infer the form of the stellar mass assembly histories of star forming galaxies. Our analysis reveals that the currently available data favours a scenario where the stellar mass assembly histories of star forming galaxies rise at early times and then fall towards the present day. In contrast, our model predicts stellar mass assembly histories that are almost flat below z = 2 for star forming galaxies, such that the predicted star formation rates can be offset with respect to the observational data by factors of up to 2 3. This disagreement can be explained by the level of coevolution between stellar and halo mass assembly that exists in contemporary galaxy formation models. In turn, this arises because the standard implementations of star formation and supernova feedback used in the models result in the efficiencies of these process remaining approximately constant over the lifetime of a given star forming galaxy. We demonstrate how a modification to the timescale for gas ejected by feedback to be reincorporated into galaxy haloes can help to reconcile the model predictions with the data.

Galaxy And Mass Assembly (GAMA): the dependence of the galaxy luminosity function on environment, redshift and colour

Abstract: We use 80 922 galaxies in the Galaxy And Mass Assembly (GAMA) survey to measure the galaxy luminosity function (LF) in different environments over the redshift range 0.04 < z < 0.26. The depth and size of GAMA allows us to define samples split by colour and redshift to measure the dependence of the LF on environment, redshift and colour. We find that the LF varies smoothly with overdensity, consistent with previous results, with little environmental dependent evolution over the last 3 Gyr. The modified GALFORM model predictions agree remarkably well with our LFs split by environment, particularly in the most overdense environments. The LFs predicted by the model for both blue and red galaxies are consistent with GAMA for the environments and luminosities at which such galaxies dominate. Discrepancies between the model and the data seen in the faint end of the LF suggest too many faint red galaxies are predicted, which is likely to be due to the over-quenching of satellite galaxies. The excess of bright blue galaxies predicted in underdense regions could be due to the implementation of AGN feedback not being sufficiently effective in the lower mass haloes.

Modified gravity with massive neutrinos as a testable alternative cosmological model.

Abstract: We show that, in the presence of massive neutrinos, the Galileon gravity model provides a very good fit to the current cosmic microwave background (CMB) temperature, CMB lensing and baryonic acoustic oscillation data. This model, which we dub $\ensuremath{ u}\text{Galileon}$, when assuming its stable attractor background solution, contains the same set of free parameters as lambda cold dark matter ($\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$), although it leads to different expansion dynamics and nontrivial gravitational interactions. The data provide compelling evidence ($\ensuremath{\gtrsim}6\ensuremath{\sigma}$) for nonzero neutrino masses, with $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{ u}}\ensuremath{\gtrsim}0.4\text{ }\text{ }\mathrm{eV}$ at the $2\ensuremath{\sigma}$ level. Upcoming precision terrestrial measurements of the absolute neutrino mass scale therefore have the potential to test this model. We show that CMB lensing measurements at multipoles $l\ensuremath{\lesssim}40$ will be able to discriminate between the $\ensuremath{ u}\text{Galileon}$ and $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ models. Unlike $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, the $\ensuremath{ u}\text{Galileon}$ model is consistent with local determinations of the Hubble parameter. The presence of massive neutrinos lowers the value of ${\ensuremath{\sigma}}_{8}$ substantially, despite of the enhanced gravitational strength on large scales. Unlike $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, the $\ensuremath{ u}\text{Galileon}$ model predicts a negative ISW effect, which is difficult to reconcile with current observational limits.

Velocity and mass bias in the distribution of dark matter haloes

Abstract: The non-linear, scale-dependent bias in the mass distribution of galaxies and the underlying dark matter is a key systematic affecting the extraction of cosmological parameters from galaxy clustering. Using 95 million haloes from the Millennium-XXL N-body simulation, we find that the mass bias is scale independent only for k < 0.1 h Mpc−1 today (z = 0) and for k < 0.2 h Mpc−1 at z = 0.7. We test analytic halo bias models against our simulation measurements and find that the model of Tinker et al. is accurate to better than 5 per cent at z = 0. However, the simulation results are better fitted by an ellipsoidal collapse model at z = 0.7. We highlight, for the first time, another potentially serious systematic due to a sampling bias in the halo velocity divergence power spectra which will affect the comparison between observations and any redshift-space distortion model which assumes dark matter velocity statistics with no velocity bias. By measuring the velocity divergence power spectra for different sized halo samples, we find that there is a significant bias which increases with decreasing number density. This bias is approximately 20 per cent at k = 0.1 h Mpc−1 for a halo sample of number density n¯=10−3(h/ Mpc)3 at both z = 0 and 0.7 for the velocity divergence auto power spectrum. Given the importance of redshift-space distortions as a probe of dark energy and the major ongoing effort to advance models for the clustering signal in redshift space, our results show that this velocity bias introduces another systematic, alongside scale-dependent halo mass bias, which cannot be neglected.

Clustering of extremely red objects in Elais-N1 from the UKIDSS DXS with optical photometry from Pan-STARRS 1 and Subaru

Abstract: We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg2, which cover the redshift range z = 0.8 to 2. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and PanSTARRS PS1 data sets. We confirm the existence of a clear break in the angular correlation function at ∼0.02◦ corresponding to 1 h-1 Mpc at z ∼ 1. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo occupation distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over 1013 h-1 M⊙ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at z ∼ 1.1, at z ∼ 1.5 EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host 1011.0 M⊙ < M∗ < 1011.5 M⊙ galaxies. We compare our new measurement and HOD fits with the predictions of the GALFORM semi-analytical galaxy formation model. Overall, the clustering predicted by GALFORM gives an encouraging match to our results. However, compared to our deductions from the measurements, GALFORM puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.

Extending the halo mass resolution of N-body simulations

Abstract: We present a scheme to extend the halo mass resolution of N-body simulations of the hierarchical clustering of dark matter. The method uses the density field of the simulation to predict the number of sub-resolution dark matter haloes expected in different regions. The technique requires as input the abundance of haloes of a given mass and their average clustering, as expressed through the linear and higher order bias factors. These quantities can be computed analytically or, more accurately, derived from a higher resolution simulation as done here. Our method can recover the abundance and clustering in real- and redshift-space of haloes with mass below � 7.5×10 13 h −1 M⊙ at z = 0 to better than 10%. We demonstrate the technique by applying it to an ensemble of 50 low resolution, largevolume N-body simulations to compute the correlation function and covariance matrix of luminous red galaxies (LRGs). The limited resolution of the original simulations results in them resolving just two thirds of the LRG population. We extend the resolution of the simulations by a factor of 30 in halo mass in order to recover all LRGs. With existing simulations it is possible to generate a halo catalogue equivalent to that which would be obtained from a N-body simulation using more than 20 trillion particles; a direct simulation of this size is likely to remain unachievable for many years. Using our method it is now feasible to build the large numbers of high-resolution large volume mock galaxy catalogues required to compute the covariance matrices necessary to analyse upcoming galaxy surveys designed to probe dark energy.

Probability friends-of-friends (PFOF) group finder : performance study and observational data applications on photometric surveys.

Abstract: In tandem with observational data sets, we utilize realistic mock catalogs, based on a semi-analytic galaxy formation model, constructed specifically for Pan-STARRS1 Medium Deep Surveys to assess the performance of the Probability Friends-of-Friends (PFOF) group finder, and aim to develop a grouping optimization method applicable to surveys like Pan-STARRS1. Producing mock PFOF group catalogs under a variety of photometric redshift accuracies (), we find that catalog purities and completenesses from "good" ( 0.01) to "poor" ( 0.07) photo-zs gradually degrade from 77% and 70% to 52% and 47%, respectively. A "subset optimization" approach is developed by using spectroscopic-redshift group data from the target field to train the group finder for application to that field and demonstrated using zCOSMOS groups for PFOF searches within PS1 Medium Deep Field04 (PS1MD04) and DEEP2 EGS groups in PS1MD07. With four data sets spanning the photo-z accuracy range from 0.01 to 0.06, we find purities and completenesses agree with their mock analogs. Further tests are performed via matches to X-ray clusters. We find PFOF groups match ∼85% of X-ray clusters identified in COSMOS and PS1MD04, lending additional support to the reliability of the detection algorithm. In the end, we demonstrate, by separating red and blue group galaxies in the EGS and PS1MD07 group catalogs, that the algorithm is not biased with respect to specifically recovering galaxies by color. The analyses suggest the PFOF algorithm shows great promise as a reliable group finder for photometric galaxy surveys of varying depth and coverage. © 2014. The American Astronomical Society. All rights reserved..

Herschel-ATLAS/GAMA: How does the far-IR luminosity function depend on galaxy group properties?

Abstract: We use the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) Phase I data to study the conditional luminosity function of far-IR (250 μm) selected galaxies in optically selected galaxy groups from the Galaxy And Mass Assembly (GAMA) spectroscopic survey, as well as environmental effects on the far-IR-to-optical colour. We applied two methods, which gave consistent results for the far-IR conditional luminosity functions. The direct matching method matches H-ATLAS sources to GAMA/SDSS (Sloan Digital Sky Survey) galaxies, then links the optical counterparts to GAMA groups. The stacking method counts the number of far-IR sources within the projected radii of GAMA groups, subtracting the local background. We investigated the dependence of the far-IR (250 μm) luminosity function on group mass in the range 1012 1012 h−1 M⊙. We also find that the far-IR-to-optical colours of H-ATLAS galaxies are independent of group mass over the range 1012 < Mh < 1014 h−1 M⊙ in the local Universe. We also compare our observational results with recent semi-analytical models, and find that none of these galaxy formation models can reproduce the conditional far-IR luminosity functions of galaxy groups.

Clustering tomography: measuring cosmological distances through angular clustering in thin redshift shells

Abstract: We test the cosmological implications of studying galaxy clustering using a tomographic approach, by computing the galaxy two-point angular correlation function ω(θ) in thin redshift shells using a spectroscopic redshift galaxy survey. The advantages of this procedure are that it is not necessary to assume a fiducial cosmology in order to convert measured angular positions and redshifts into distances, and that it gives several (less accurate) measurements of the angular diameter distance DA(z) instead of only one (more precise) measurement of the effective average distance DV(z), which results in better constraints on the expansion history of the Universe. We test our model for ω(θ) and its covariance matrix against a set of mock galaxy catalogues and show that this technique is able to extract unbiased cosmological constraints. Also, assuming the best-fitting Λ cold dark matter (ΛCDM) cosmology from the cosmic microwave background measurements from the Planck satellite, we forecast the result of applying this tomographic approach to the final Baryon Oscillation Spectroscopic Survey catalogue in combination with Planck for three flat cosmological models, and compare them with the expected results of the isotropic baryon acoustic oscillation (BAO) measurements post-reconstruction on the same galaxy catalogue combined with Planck. While BAOs are more accurate for constraining cosmological parameters for the standard ΛCDM model, the tomographic technique gives better results when we allow the dark energy equation of state wDE to deviate from −1, resulting in a performance similar to BAOs in the case of a constant value of wDE, and a moderate improvement in the case of a time-dependent value of wDE, increasing the value of the figure of merit in the w0–wa plane up to 15 per cent.

Nonlinear structure formation in Nonlocal Gravity

Abstract: We study the nonlinear growth of structure in nonlocal gravity models with the aid of N-body simulation and the spherical collapse and halo models. We focus on a model in which the inverse-squared of the d'Alembertian operator acts on the Ricci scalar in the action. For fixed cosmological parameters, this model differs from $\Lambda{\rm CDM}$ by having a lower late-time expansion rate and an enhanced and time-dependent gravitational strength ($\sim 6\%$ larger today). Compared to $\Lambda{\rm CDM}$ today, in the nonlocal model, massive haloes are slightly more abundant (by $\sim 10\%$ at $M \sim 10^{14} M_{\odot}/h$) and concentrated ($\approx 8\%$ enhancement over a range of mass scales), but their linear bias remains almost unchanged. We find that the Sheth-Tormen formalism describes the mass function and halo bias very well, with little need for recalibration of free parameters. The fitting of the halo concentrations is however essential to ensure the good performance of the halo model on small scales. For $k \gtrsim 1 h/{\rm Mpc}$, the amplitude of the nonlinear matter and velocity divergence power spectra exhibits a modest enhancement of $\sim 12\%$ to $15\%$, compared to $\Lambda{\rm CDM}$ today. This suggests that this model might only be distinguishable from $\Lambda{\rm CDM}$ by future observational missions. We point out that the absence of a screening mechanism may lead to tensions with Solar System tests due to local time variations of the gravitational strength, although this is subject to assumptions about the local time evolution of background averaged quantities.

Halo model and halo properties in Galileon gravity cosmologies

Abstract: We investigate the performance of semi-analytical modelling of large-scale structure in Galileon gravity cosmologies using results from N-body simulations. We focus on the Cubic and Quartic Galileon models that provide a reasonable fit to CMB, SNIa and BAO data. We demonstrate that the Sheth-Tormen mass function and linear halo bias can be calibrated to provide a very good fit to our simulation results. We also find that the halo concentration-mass relation is well fitted by a power law. The nonlinear matter power spectrum computed in the halo model approach is found to be inaccurate in the mildly nonlinear regime, but captures reasonably well the effects of the Vainshtein screening mechanism on small scales. In the Cubic model, the screening mechanism hides essentially all of the effects of the fifth force inside haloes. In the case of the Quartic model, the screening mechanism leaves behind residual modifications to gravity, which make the effective gravitational strength time-varying and smaller than the standard value. Compared to normal gravity, this causes a deficiency of massive haloes and leads to a weaker matter clustering on small scales. For both models, we show that there are realistic halo occupation distributions of Luminous Red Galaxies that can match both the observed large-scale clustering amplitude and the number density of these galaxies.

Galaxy Formation & Dark Matter Modelling in the Era of the Square Kilometre Array

Abstract: Theoretical galaxy formation models are an established and powerful tool for interpreting the astrophysical significance of observational data, particularly galaxy surveys. Such models have been utilised with great success by optical surveys such as 2dFGRS and SDSS, but their application to radio surveys of cold gas in galaxies has been limited. In this chapter we describe recent developments in the modelling of the cold gas properties in the models, and how these developments are essential if they are to be applied to cold gas surveys of the kind that will be carried out with the SKA. By linking explicitly a galaxy’s star formation rate to the abundance of molecular hydrogen in the galaxy rather than cold gas abundance, as was assumed previously, the latest models reproduce naturally many of the global atomic and molecular hydrogen properties of observed galaxies. We review some of the key results of the latest models and highlight areas where further developments are necessary. We discuss also how model predictions can be most accurately compared with observational data, what challenges we expect when creating synthetic galaxy surveys in the SKA era, and how the SKA can be used to test models of dark matter.

ou rnal of Cosmology and Astroparticle Physics

Abstract: We study the nonlinear growth of structure in nonlocal gravity models with the aid of N-body simulation and the spherical collapse and halo models We focus on a model in which the inverse-squared of the d'Alembertian operator acts on the Ricci scalar in the action For xed cosmological parameters, this model diers from CDM by having a lower