arXiv subjects

Andrew R. Zentner

Publications and source records attributed to Andrew R. Zentner.

At least 37 records · Page 2Linked to original sources

arXiv2018

Updated Results on the Galaxy-Halo Connection from Satellite Kinematics in SDSS

We present new results on the relationship between central galaxies and dark matter haloes inferred from observations of satellite kinematics in the Sloan Digital Sky Survey (SDSS) DR7. We employ an updated analysis framework that includes detailed mock catalogues to model observational effects in SDSS. Our results constrain the colour-dependent conditional luminosity function (CLF) of dark matter haloes, as well as the radial profile of satellite galaxies. Confirming previous results, we find that red central galaxies live in more massive haloes than blue galaxies at fixed luminosity. Additionally, our results suggest that satellite galaxies have a radial profile less centrally concentrated than dark matter but not as cored as resolved subhaloes in dark matter-only simulations. Compared to previous works using satellite kinematics by More et al., we find much more competitive constraints on the galaxy-halo connection, on par with those derived from a combination of galaxy clustering and galaxy-galaxy lensing. We compare our results on the galaxy-halo connection to other studies using galaxy clustering and group catalogues, showing very good agreement between these different techniques. We discuss future applications of satellite kinematics in the context of constraining cosmology and the relationship between galaxies and dark matter haloes.

astro-ph.CO↗

arXiv2018

Maturing Satellite Kinematics into a Competitive Probe of the Galaxy-Halo Connection

The kinematics of satellite galaxies moving in a dark matter halo are a direct probe of the underlying gravitational potential. Thus, the phase-space distributions of satellites represent a powerful tool to determine the galaxy-halo connection from observations. By stacking the signal of a large number of satellite galaxies this potential can be unlocked even for haloes hosting a few satellites on average. In this work, we test the impact of various modelling assumptions on constraints derived from analysing satellite phase-space distributions in the non-linear, 1-halo regime. We discuss their potential to explain the discrepancy between average halo masses derived from satellite kinematics and gravitational lensing previously reported. Furthermore, we develop an updated, more robust analysis to extract constraints on the galaxy-halo relation from satellite properties in spectroscopic galaxy surveys such as the SDSS. We test the accuracy of this approach using a large number of realistic mock catalogues. Furthermore, we find that constraints derived from such an analysis are complementary and competitive with respect to the commonly used galaxy clustering and galaxy-galaxy lensing observables.

astro-ph.CO↗

arXiv2018

Particle decay in post inflationary cosmology

We study scalar particle decay during the radiation and matter dominated epochs of a standard cosmological model. An adiabatic approximation is introduced that is valid for degrees of freedom with typical wavelengths much smaller than the particle horizon ($\propto$~Hubble radius) at a given time. We implement a non-perturbative method that includes the cosmological expansion and obtain a cosmological Fermi's Golden Rule that enables one to compute the decay law of a parent particle of mass $m_1$, along with the build up of the population of daughter particles of mass $m_2$. The survival probability of the decaying particle is $P(t)=e^{-\widetildeΓ_k(t)\,t}$ with $\widetildeΓ_k(t)$ being an \emph{effective momentum and time dependent decay rate}. It features a transition time scale $t_{nr}$ between the relativistic and non-relativistic regimes and for $k \neq 0$ is always smaller than the analogous rate in Minkowski spacetime, as a consequence of (local) time dilation and the cosmological redshift. For $t \ll t_{nr}$ the decay law is a "stretched exponential" $P(t) = e^{-(t/t^*)^{3/2}}$, whereas for the non-relativistic stage with $t \gg t_{nr}$, we find $P(t) = e^{-Γ_0 t}\,(t/t_{nr})^{Γ_0\,t_{nr}/2}$. The Hubble time scale $\propto 1/H(t)$ introduces an energy uncertainty $ΔE \sim H(t)$ which relaxes the constraints of kinematic thresholds. This opens new decay channels into heavier particles for $2πE_k(t) H(t) \gg 4m^2_2-m^2_1$, with $E_k(t)$ the (local) comoving energy of the decaying particle. As the expansion proceeds this channel closes and the usual two particle thresholds restrict the decay kinematics.

hep-ph↗

arXiv2018

Beyond Assembly Bias: Exploring Secondary Halo Biases for Cluster-size Haloes

Secondary halo bias, commonly known as 'assembly bias,' is the dependence of halo clustering on a halo property other than mass. This prediction of the Lambda-Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalo properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. This results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.

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arXiv2017

Brightest galaxies as halo centre tracers in SDSS DR7

Determining the positions of halo centres in large-scale structure surveys is crucial for many cosmological studies. A common assumption is that halo centres correspond to the location of their brightest member galaxies. In this paper, we study the dynamics of brightest galaxies with respect to other halo members in the Sloan Digital Sky Survey DR7. Specifically, we look at the line-of-sight velocity and spatial offsets between brightest galaxies and their neighbours. We compare those to detailed mock catalogues, constructed from high-resolution, dark-matter-only $N$-body simulations, in which it is assumed that satellite galaxies trace dark matter subhaloes. This allows us to place constraints on the fraction $f_{\rm BNC}$ of haloes in which the brightest galaxy is not the central. Compared to previous studies we explicitly take into account the unrelaxed state of the host haloes, velocity offsets of halo cores and correlations between $f_{\rm BNC}$ and the satellite occupation. We find that $f_{\rm BNC}$ strongly decreases with the luminosity of the brightest galaxy and increases with the mass of the host halo. Overall, in the halo mass range $10^{13} - 10^{14.5} h^{-1} M_\odot$ we find $f_{\rm BNC} \sim 30\%$, in good agreement with a previous study by Skibba et al. We discuss the implications of these findings for studies inferring the galaxy--halo connection from satellite kinematics, models of the conditional luminosity function and galaxy formation in general.

astro-ph.GA↗

arXiv2017

The Immitigable Nature of Assembly Bias: The Impact of Halo Definition on Assembly Bias

Dark matter halo clustering depends not only on halo mass, but also on other properties such as concentration and shape. This phenomenon is known broadly as assembly bias. We explore the dependence of assembly bias on halo definition, parametrized by spherical overdensity parameter, $Δ$. We summarize the strength of concentration-, shape-, and spin-dependent halo clustering as a function of halo mass and halo definition. Concentration-dependent clustering depends strongly on mass at all $Δ$. For conventional halo definitions ($Δ\sim 200\mathrm{m}-600\mathrm{m}$), concentration-dependent clustering at low mass is driven by a population of haloes that is altered through interactions with neighbouring haloes. Concentration-dependent clustering can be greatly reduced through a mass-dependent halo definition with $Δ\sim 20\mathrm{m}-40\mathrm{m}$ for haloes with $M_{200\mathrm{m}} \lesssim 10^{12}\, h^{-1}\mathrm{M}_{\odot}$. Smaller $Δ$ implies larger radii and mitigates assembly bias at low mass by subsuming altered, so-called backsplash haloes into now larger host haloes. At higher masses ($M_{200\mathrm{m}} \gtrsim 10^{13}\, h^{-1}\mathrm{M}_{\odot}$) larger overdensities, $Δ\gtrsim 600\mathrm{m}$, are necessary. Shape- and spin-dependent clustering are significant for all halo definitions that we explore and exhibit a relatively weaker mass dependence. Generally, both the strength and the sense of assembly bias depend on halo definition, varying significantly even among common definitions. We identify no halo definition that mitigates all manifestations of assembly bias. A halo definition that mitigates assembly bias based on one halo property (e.g., concentration) must be mass dependent. The halo definitions that best mitigate concentration-dependent halo clustering do not coincide with the expected average splashback radii at fixed halo mass.

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arXiv2017

Updated Constraints on Self-Interacting Dark Matter from Supernova 1987A

We revisit SN1987A constraints on light, hidden sector gauge bosons ("dark photons") that are coupled to the standard model through kinetic mixing with the photon. These constraints are realized because excessive bremsstrahlung radiation of the dark photon can lead to rapid cooling of the SN1987A progenitor core, in contradiction to the observed neutrinos from that event. The models we consider are of interest as phenomenological models of strongly self-interacting dark matter. We clarify several possible ambiguities in the literature and identify errors in prior analyses. We find constraints on the dark photon mixing parameter that are in rough agreement with the early estimates of Dent et al., but only because significant errors in their analyses fortuitously canceled. Our constraints are in good agreement with subsequent analyses by Rrapaj & Reddy and Hardy & Lasenby. We estimate the dark photon bremsstrahlung rate using one-pion exchange (OPE), while Rrapaj & Reddy use a soft radiation approximation (SRA) to exploit measured nuclear scattering cross sections. We find that the differences between mixing parameter constraints obtained through the OPE approximation or the SRA approximation are roughly a factor of $\sim 2-3$. Hardy & Laseby include plasma effects in their calculations finding significantly weaker constraints on dark photon mixing for dark photon masses below $\sim 10\, \mathrm{MeV}$. We do not consider plasma effects. Lastly, we point out that the properties of the SN1987A progenitor core remain somewhat uncertain and that this uncertainty alone causes uncertainty of at least a factor of $\sim 2-3$ in the excluded values of the dark photon mixing parameter. Further refinement of these estimates is unwarranted until either the interior of the SN1987A progenitor is more well understood or additional, large, and heretofore neglected effects, are identified.

hep-ph↗

arXiv2017

General Relativistic Corrections to the Weak Lensing Convergence Power Spectrum

We compute the weak lensing convergence power spectrum, $C^{κκ}(θ)$, in a dust-filled universe using fully non-linear general relativistic simulations. The spectrum is then compared to more standard, approximate calculations by computing the Bardeen (Newtonian) potentials in linearized gravity and utilizing the Born approximation. We find corrections to the angular power spectrum amplitude of order ten percent at very large angular scales, $\ell ~ 2-3$, and percent-level corrections at intermediate angular scales of $\ell ~ 20-30$.

astro-ph.CO↗

arXiv2017

The Galaxy Clustering Crisis in Abundance Matching

Galaxy clustering on small scales is significantly under-predicted by sub-halo abundance matching (SHAM) models that populate (sub-)haloes with galaxies based on peak halo mass, $M_{\rm peak}$. SHAM models based on the peak maximum circular velocity, $V_{\rm peak}$, have had much better success. The primary reason $M_{\rm peak}$ based models fail is the relatively low abundance of satellite galaxies produced in these models compared to those based on $V_{\rm peak}$. Despite success in predicting clustering, a simple $V_{\rm peak}$ based SHAM model results in predictions for galaxy growth that are at odds with observations. We evaluate three possible remedies that could "save" mass-based SHAM: (1) SHAM models require a significant population of "orphan" galaxies as a result of artificial disruption/merging of sub-haloes in modern high resolution dark matter simulations; (2) satellites must grow significantly after their accretion; and (3) stellar mass is significantly affected by halo assembly history. No solution is entirely satisfactory. However, regardless of the particulars, we show that popular SHAM models based on $M_{\rm peak}$ cannot be complete physical models as presented. Either $V_{\rm peak}$ truly is a better predictor of stellar mass at $z\sim 0$ and it remains to be seen how the correlation between stellar mass and $V_{\rm peak}$ comes about, or SHAM models are missing vital component(s) that significantly affect galaxy clustering.

astro-ph.GA↗

arXiv2017

The Radial Acceleration Relation in Disk Galaxies in the MassiveBlack-II Simulation

A strong correlation has been measured between the observed centripetal accelerations in galaxies and the accelerations implied by the baryonic components of galaxies. This empirical radial acceleration relation must be accounted for in any viable model of galaxy formation. We measure and compare the radial accelerations contributed by baryons and by dark matter in disk galaxies in the MassiveBlack-II hydrodynamic galaxy formation simulation. The sample of 1594 galaxies spans three orders of magnitude in luminosity and four in surface brightness, comparable to the observed sample from the Spitzer Photometry & Accurate Rotation Curves (SPARC) dataset used by McGaugh et al. (2016). We find that radial accelerations contributed by baryonic matter only and by total matter are highly correlated, with only small scatter around their mean or median relation, despite the wide ranges of galaxy luminosity and surface brightness. We further find that the radial acceleration relation in this simulation differs from that of the SPARC sample, and can be described by a simple power law in the acceleration range we are probing.

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arXiv2016

Incorporating Astrophysical Systematics into a Generalized Likelihood for Cosmology with Type Ia Supernovae

Traditional cosmological inference using Type Ia supernovae (SNeIa) have used stretch- and color-corrected fits of SN Ia light curves and assumed a resulting fiducial mean and symmetric intrinsic dispersion for the resulting relative luminosity. As systematics become the main contributors to the error budget, it has become imperative to expand supernova cosmology analyses to include a more general likelihood to model systematics to remove biases with losses in precision. To illustrate an example likelihood analysis, we use a simple model of two populations with a relative luminosity shift, independent intrinsic dispersions, and linear redshift evolution of the relative fraction of each population. Treating observationally viable two-population mock data using a one-population model results in an inferred dark energy equation of state parameter $w$ that is biased by roughly 2 times its statistical error for a sample of N $ \gtrsim$ 2500 SNeIa. Modeling the two-population data with a two-population model removes this bias at a cost of an approximately $\sim20\%$ increase in the statistical constraint on $w$. These significant biases can be realized even if the support for two underlying SNeIa populations, in the form of model selection criteria, is inconclusive. With the current observationally-estimated difference in the two proposed populations, a sample of N $ \gtrsim$ 10,000 SNeIa is necessary to yield conclusive evidence of two populations.

astro-ph.CO↗

arXiv2016

Constraints on Assembly Bias from Galaxy Clustering

We constrain the newly-introduced decorated Halo Occupation Distribution (HOD) model using SDSS DR7 measurements of projected galaxy clustering or r-band luminosity threshold samples. The decorated HOD is a model for the galaxy-halo connection that augments the HOD by allowing for the possibility of galaxy assembly bias: galaxy luminosity may be correlated with dark matter halo properties besides mass, Mvir. We demonstrate that it is not possible to rule out galaxy assembly bias using DR7 measurements of galaxy clustering alone. Moreover, galaxy samples with Mr < -20 and Mr < -20.5 favor strong central galaxy assembly bias. These samples prefer scenarios in which high-concentration are more likely to host a central galaxy relative to low-concentration halos of the same mass. We exclude zero assembly bias with high significance for these samples. Satellite galaxy assembly bias is significant for the faintest sample, Mr < -19. We find no evidence for assembly bias in the Mr < -21 sample. Assembly bias should be accounted for in galaxy clustering analyses or attempts to exploit galaxy clustering to constrain cosmology. In addition to presenting the first constraints on HOD models that accommodate assembly bias, our analysis includes several improvements over previous analyses of these data. Therefore, our inferences supersede previously-published results even in the case of a standard HOD analysis.

astro-ph.GA↗

arXiv2016

Connecting massive galaxies to dark matter halos in BOSS - I. Is galaxy color a stochastic process in high-mass halos?

We use subhalo abundance matching (SHAM) to model the stellar mass function (SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) "CMASS" sample at $z\sim0.5$. We introduce a novel method which accounts for the stellar mass incompleteness of CMASS as a function of redshift, and produce CMASS mock catalogs which include selection effects, reproduce the overall SMF, the projected two-point correlation function $w_{\rm p}$, the CMASS $dn/dz$, and are made publicly available. We study the effects of assembly bias above collapse mass in the context of "age matching" and show that these effects are markedly different compared to the ones explored by Hearin et al. (2013) at lower stellar masses. We construct two models, one in which galaxy color is stochastic ("AbM" model) as well as a model which contains assembly bias effects ("AgM" model). By confronting the redshift dependent clustering of CMASS with the predictions from our model, we argue that that galaxy colors are not a stochastic process in high-mass halos. Our results suggest that the colors of galaxies in high-mass halos are determined by other halo properties besides halo peak velocity and that assembly bias effects play an important role in determining the clustering properties of this sample.

astro-ph.CO↗

arXiv2015

Introducing Decorated HODs: modeling assembly bias in the galaxy-halo connection

The connection between galaxies and dark matter halos is often inferred from data using probabilistic models, such as the Halo Occupation Distribution (HOD). Conventional HOD formulations assume that only halo mass governs the galaxy-halo connection. Violations of this assumption, known as galaxy assembly bias, threaten the HOD program. We introduce decorated HODs, a new, flexible class of models designed to account for assembly bias. Decorated HODs minimally expand the parameter space and maximize the independence between traditional and novel HOD parameters. We use decorated HODs to quantify the influence of assembly bias on clustering and lensing statistics. For SDSS-like samples, the impact of assembly bias on galaxy clustering can be as large as a factor of two on r ~ 200 kpc scales and ~15% in the linear regime. Assembly bias can either enhance or diminish clustering on large scales, but generally increases clustering on scales r <~ 1 Mpc. We performed our calculations with Halotools, an open-source, community-driven python package for studying the galaxy-halo connection (http://halotools.readthedocs.org). We conclude by describing the use of decorated HODs to treat assembly bias in otherwise conventional likelihood analyses.

astro-ph.CO↗

arXiv2015

Mass assembly history and infall time of the Fornax dwarf spheroidal galaxy

We use cosmological simulations to identify dark matter subhalo host candidates of the Fornax dwarf spheroidal galaxy using the stellar kinematic properties of Fornax. We consider cold dark matter (CDM), warm dark matter (WDM), and decaying dark matter (DDM) simulations for our models of structure formation. The subhalo candidates in CDM typically have smaller mass and higher concentrations at z = 0 than the corresponding candidates in WDM and DDM. We examine the formation histories of the ~ 100 Fornax candidate subhalos identified in CDM simulations and, using approximate luminosity-mass relationships for subhalos, we find two of these subhalos that are consistent with both the Fornax luminosity and kinematics. These two subhalos have a peak mass over ten times larger than their z = 0 mass. We suggest that in CDM the dark matter halo hosting Fornax must have been severely stripped of mass and that it had an infall time into the Milky Way of ~ 9 Gyr ago. In WDM, we find that candidate subhalos consistent with the properties of Fornax have a similar infall time and a similar degree of mass loss, while in DDM we find a later infall time of ~ 3 - 4 Gyr ago and significantly less mass loss. We discuss these results in the context of the Fornax star formation history, and show that these predicted subhalo infall times can be linked to different star formation quenching mechanisms. This emphasizes the links between the properties of the dark matter and the mechanisms that drive galaxy evolution.

astro-ph.GA↗

arXiv2015

Indirect Probes of Dark Matter and Globular Cluster Properties From Dark Matter Annihilation within the Coolest White Dwarfs

White Dwarfs (WD) capture Dark Matter (DM) as they orbit within their host halos. These captured particles may subsequently annihilate, heating the stellar core and preventing the WD from cooling. The potential wells of WDs are considerably deeper and core temperatures significantly cooler than those of main sequence stars. Consequently, DM evaporation is less important in WDs and DM with masses $M_χ \gtrsim 100\, \kev$ and annihilation cross-sections orders of magnitude below the canonical thermal cross-section ($\sigmav \gtrsim 10^{-46}\, \cm^3$/s) can significantly alter WD cooling in particular astrophysical environments. We consider WDs in globular clusters (GCs) and dwarf galaxies. If the parameters of the DM particle are known, then the temperature of the coolest WD in a GC can be used to constrain the DM density of the cluster's halo (potentially even ruling out the presence of a halo if the inferred density is of order the ambient Galactic density). Recently several direct detection experiments have seen signals whose origins might be due to low mass DM. In this paper, we show that if these claims from CRESST, DAMA, CDMS-Si, and CoGeNT could be interpreted as DM, then observations of NGC 6397 limit the fraction of DM in that cluster to be $f_{\mathrm{DM}} \lesssim 10^{-3}$. This would be an improvement over existing constraints of 3 orders of magnitude and clearly rule out a significant DM halo for this cluster...

astro-ph.CO↗

arXiv2015

Galaxy Assembly Bias: A Significant Source of Systematic Error in the Galaxy-Halo Relationship

It is common practice for methods that use galaxy clustering to constrain the galaxy-halo relationship, such as the halo occupation distribution (HOD) and/or conditional luminosity function (CLF), to assume that halo mass alone suffices to determine a halo's resident galaxy population. Yet, the clustering strength of cold dark matter halos depends upon halo properties in addition to mass, such as formation time, an effect referred to as assembly bias. If galaxy characteristics are correlated with any of these auxiliary halo properties, the basic assumption of HOD/CLF methods is violated. We estimate the potential for assembly bias to induce systematic errors in inferred halo occupation statistics. We use halo abundance matching and age matching to construct fiducial mock galaxy catalogs that exhibit assembly bias as well as additional mock catalogs with identical HODs, but with assembly bias removed. We fit a parameterized HOD to the projected two-point clustering of mock galaxies in each catalog to assess the systematic errors induced by reasonable levels of assembly bias. In the absence of assembly bias, the inferred HODs generally describe the true underlying HODs well, validating the basic methodology. However, in all of the cases with assembly bias, the inferred HODs have systematic errors that are statistically significant. In most cases, these systematic errors cannot be identified using void statistics as auxiliary observables. We conclude that the galaxy-halo relationship inferred from galaxy clustering should be subject to a non-negligible systematic error induced by assembly bias. Our work suggests that efforts to model and/or constrain assembly bias should be high priorities as it is a threatening source of systematic error in galaxy evolution studies as well as the precision cosmology program.

astro-ph.CO↗

arXiv2014

Predicting Galaxy Star Formation Rates via the Co-evolution of Galaxies and Halos

In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy of fixed stellar mass is determined by its dark matter halo formation history, and as such, that more quiescent galaxies reside in older halos. This simple model has been remarkably successful at predicting color-based galaxy statistics at low redshift as measured in the Sloan Digital Sky Survey (SDSS). To further test this method with observations, we present new SDSS measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star-forming galaxy samples. We find that our age matching model is in excellent agreement with these new measurements. We also employ a galaxy group finder and show that our model is able to predict: (1) the relative SFRs of central and satellite galaxies, (2) the SFR-dependence of the radial distribution of satellite galaxy populations within galaxy groups, rich groups, and clusters and their surrounding larger scale environments, and (3) the interesting feature that the satellite quenched fraction as a function of projected radial distance from the central galaxy exhibits an ~ r^-.15 slope, independent of environment. The accurate prediction for the spatial distribution of satellites is intriguing given the fact that we do not explicitly model satellite-specific processes after infall, and that in our model the virial radius does not mark a special transition region in the evolution of a satellite, contrary to most galaxy evolution models. The success of the model suggests that present-day galaxy SFR is strongly correlated with halo mass assembly history.

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