Rm Halo Research Articles

Be it therefore resolved: cosmological simulations of dwarf galaxies with 30 solar mass resolution

ABSTRACT We study a suite of extremely high-resolution cosmological Feedback in Realistic Environments simulations of dwarf galaxies ($M_{\rm halo} \lesssim 10^{10}\rm \, M_{\odot }$), run to z = 0 with $30\, \mathrm{M}_{\odot }$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $M_{\rm halo} \gtrsim 10^{8.6}\, \mathrm{M}_{\odot }$ is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $M_{\ast }\lt 10^{5}\, \mathrm{M}_{\odot }$) have their star formation (SF) truncated early (z ≳ 2), likely by reionization, while classical dwarfs ($M_{\ast }\gt 10^{5}\, \mathrm{M}_{\odot }$) continue forming stars to z < 0.5. The systems have bursty star formation histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows our dwarf with M*/Mhalo > 10−4 to form a dark matter core ${\gt}200\rm \, pc$, while lower mass UFDs exhibit cusps down to ${\lesssim}100\rm \, pc$, as expected from energetic arguments. Our dwarfs with $M_{\ast }\gt 10^{4}\, \mathrm{M}_{\odot }$ have half-mass radii (R1/2) in agreement with Local Group (LG) dwarfs (dynamical mass versus R1/2 and stellar rotation also resemble observations). The lowest mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (e.g. LSST). The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars. Consistency with lower resolution studies implies that our simulations are numerically robust (for a given physical model).

The total stellar halo mass of the Milky Way

ABSTRACT We measure the total stellar halo luminosity using red giant branch (RGB) stars selected from Gaia data release 2. Using slices in magnitude, colour, and location on the sky, we decompose RGB stars belonging to the disc and halo by fitting two-dimensional Gaussians to the Galactic proper motion distributions. The number counts of RGB stars are converted to total stellar halo luminosity using a suite of isochrones weighted by age and metallicity, and by applying a volume correction based on the stellar halo density profile. Our method is tested and calibrated using Galaxia and N-body models. We find a total luminosity (out to 100 kpc) of $L_{\rm halo} = 7.9 \pm 2.0 \times 10^8\, \mathrm{L}_\odot$ excluding Sgr, and $L_{\rm halo} = 9.4 \pm 2.4 \times 10^8\, \mathrm{L}_\odot$ including Sgr. These values are appropriate for our adopted stellar halo density profile and metallicity distribution, but additional systematics related to these assumptions are quantified and discussed. Assuming a stellar mass-to-light ratio appropriate for a Kroupa initial mass function (M⋆/L = 1.5), we estimate a stellar halo mass of $M^\star _{\rm halo} = 1.4 \pm 0.4\times 10^9 \, \mathrm{M}_\odot$. This mass is larger than previous estimates in the literature, but is in good agreement with the emerging picture that the (inner) stellar halo is dominated by one massive dwarf progenitor. Finally, we argue that the combination of a ${\sim}10^9\, \mathrm{M}_\odot$ mass and an average metallicity of 〈[Fe/H]〉 ∼ −1.5 for the Galactic halo points to an ancient (∼10 Gyr) merger event.

Dwarf galaxies in CDM, WDM, and SIDM: disentangling baryons and dark matter physics

ABSTRACT We present a suite of FIRE-2 cosmological zoom-in simulations of isolated field dwarf galaxies, all with masses of $M_{\rm halo} \approx 10^{10}\, {\rm M}_{\odot }$ at z = 0, across a range of dark matter models. For the first time, we compare how both self-interacting dark matter (SIDM) and/or warm dark matter (WDM) models affect the assembly histories as well as the central density structure in fully hydrodynamical simulations of dwarfs. Dwarfs with smaller stellar half-mass radii (r1/2 < 500 pc) have lower σ⋆/Vmax ratios, reinforcing the idea that smaller dwarfs may reside in haloes that are more massive than is naively expected. The majority of dwarfs simulated with self-interactions actually experience contraction of their inner density profiles with the addition of baryons relative to the cores produced in dark-matter-only runs, though the simulated dwarfs are always less centrally dense than in ΛCDM. The V1/2–r1/2 relation across all simulations is generally consistent with observations of Local Field dwarfs, though compact objects such as Tucana provide a unique challenge. Overall, the inclusion of baryons substantially reduces any distinct signatures of dark matter physics in the observable properties of dwarf galaxies. Spatially resolved rotation curves in the central regions (<400 pc) of small dwarfs could provide a way to distinguish between CDM, WDM, and SIDM, however: at the masses probed in this simulation suite, cored density profiles in dwarfs with small r1/2 values can only originate from dark matter self-interactions.

The build-up of pseudo-bulges in a hierarchical universe

ABSTRACT We study the cosmological build-up of pseudo-bulges using the L-Galaxies semi-analytical model for galaxy formation with a new approach for following separately the assembly of classical bulges and pseudo-bulges. Classical bulges are assumed to be the result of violent processes (i.e. mergers and starbursts), while the formation of pseudo-bulges is connected to the secular growth of discs. We apply the model to both the Millennium and the Millennium II simulations, in order to study our results across a wide range of stellar masses ($\rm 10^{7}\!-\!10^{11.5}\, {\rm M}_{\odot }$). We find that z = 0 pseudo-bulges mainly reside in galaxies of $\mathit{ M}_{\rm stellar} \, {\sim }\, 10^{10}\!-\!10^{10.5}\, {\rm M}_{\odot }$ ($\mathit{ M}_{\rm halo} \, {\sim }\, 10^{11.5}\!-\!10^{12}\, {\rm M}_{\odot }$) and we recover structural properties of these objects (e.g. sizes and bulge-to-total ratios) that are in good agreement with observational results. Tracing their formation history, we find that pseudo-bulges assembled in galaxies with a very quiet merger history, as opposed to the host galaxies of classical bulges. Regarding the bulge structure, we find that $\, {\sim }\, 30{{\ \rm per\ cent}}$ of the galaxies with a predominant pseudo-bulge feature a composite structure, hosting both a pseudo- and a classical bulge component. The classical component typically constitutes ${\sim }\, 10{{\ \rm per\ cent}}$ of the total bulge galaxy mass. When looking at the properties of the host galaxies, we find that z = 0 pseudo-bulges are hosted by main-sequence galaxies, characterized by a stellar population which is generally younger compared to the one of the hosts of classical bulges.

Dust attenuation, dust emission, and dust temperature in galaxies at z ≥ 5: a view from the FIRE-2 simulations

Abstract We present a suite of 34 high-resolution cosmological zoom-in simulations consisting of thousands of haloes up to $M_{\rm halo}\sim 10^{12}\, \mathrm{M}_{\odot }$ ($M_{\ast }\sim 10^{10.5}\, \mathrm{M}_{\odot }$) at z ≥ 5 from the Feedback in Realistic Environments project. We post-process our simulations with a three-dimensional Monte Carlo dust radiative transfer code to study dust attenuation, dust emission, and dust temperature within these simulated z ≥ 5 galaxies. Our sample forms a tight correlation between infrared excess (IRX ≡ FIR/FUV) and ultraviolet (UV)-continuum slope (βUV), despite the patchy, clumpy dust geometry shown in our simulations. We find that the IRX–βUV relation is mainly determined by the shape of the attenuation law and is independent of its normalization (set by the dust-to-gas ratio). The bolometric IR luminosity (LIR) correlates with the intrinsic UV luminosity and the star formation rate (SFR) averaged over the past 10 Myr. We predict that at a given LIR, the peak wavelength of the dust spectral energy distributions for z ≥ 5 galaxies is smaller by a factor of 2 (due to higher dust temperatures on average) than at z = 0. The higher dust temperatures are driven by higher specific SFRs and SFR surface densities with increasing redshift. We derive the galaxy UV luminosity functions (UVLFs) at z = 5–10 from our simulations and confirm that a heavy attenuation is required to reproduce the observed bright-end UVLFs. We also predict the IR luminosity functions (IRLFs) and UV luminosity densities at z = 5–10. We discuss the implications of our results on current and future observations probing dust attenuation and emission in z ≥ 5 galaxies.

A Second Galaxy Missing Dark Matter in the NGC 1052 Group

Abstract The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion, indicating that it has little or no dark matter. Here we report the discovery of a second galaxy in this class, residing in the same group. NGC1052-DF4 closely resembles NGC1052-DF2 in terms of its size, surface brightness, and morphology; has a similar distance of ; and also has a population of luminous globular clusters extending out to from the center of the galaxy. Accurate radial velocities of the diffuse galaxy light and seven of the globular clusters were obtained with the Low Resolution Imaging Spectrograph on the Keck I telescope. The velocity of the diffuse light is identical to the median velocity of the clusters, , and close to the central velocity of the NGC 1052 group. The rms spread of the globular cluster velocities is very small at . Taking observational uncertainties into account we determine an intrinsic velocity dispersion of , consistent with the expected value from the stars alone ( ) and lower than expected from a standard NFW halo ( ). We conclude that NGC1052-DF2 is not an isolated case but that a class of such objects exists. The origin of these large, faint galaxies with an excess of luminous globular clusters and an apparent lack of dark matter is, at present, not understood.

A comparison between semi-analytical gas cooling models and cosmological hydrodynamical simulations

We compare the mass cooling rates and cumulative cooled-down masses predicted by several semi-analytical (SA) cooling models with cosmological hydrodynamical simulations performed using the AREPO code (ignoring processes such as feedback and chemical enrichment). The SA cooling models are the new GALFORM cooling model introduced in Hou et al. (2017), along with two earlier GALFORM cooling models and the L-GALAXIES and MORGANA cooling models. We find that the predictions of the new GALFORM cooling model are generally in best agreement with the simulations. For halos with $M_{\rm halo}\lesssim 3\times 10^{11}\,{\rm M}_{\odot}$, the SA models predict that the timescale for radiative cooling is shorter than or comparable to the gravitational infall timescale. Even though SA models assume that gas falls onto galaxies from a spherical gas halo, while the simulations show that the cold gas is accreted through filaments, both methods predict similar mass cooling rates, because in both cases the gas accretion occurs on similar timescales. For halos with $M_{\rm halo}\gtrsim 10^{12}\,{\rm M}_{\odot}$, gas in the simulations typically cools from a roughly spherical hot gas halo, as assumed in the SA models, but the halo gas gradually contracts during cooling, leading to compressional heating. SA models ignore this heating, and so overestimate mass cooling rates by factors of a few. At low redshifts halo major mergers or a sequence of successive smaller mergers are seen in the simulations to strongly heat the halo gas and suppress cooling, while mergers at high redshifts do not suppress cooling, because the gas filaments are difficult to heat up. The new SA cooling model best captures these effects.

Chemical evolution of disc galaxies from cosmological simulations

We perform a suite of cosmological hydrodynamical simulations of disc galaxies, with zoomed-in initial conditions leading to the formation of a halo of mass $M_{\rm halo, \, DM} \simeq 2 \cdot 10^{12}$ M$_{\odot}$ at redshift $z=0$. These simulations aim at investigating the chemical evolution and the distribution of metals in a disc galaxy, and at quantifying the effect of $(i)$ the assumed IMF, $(ii)$ the adopted stellar yields, and $(iii)$ the impact of binary systems originating SNe Ia on the process of chemical enrichment. We consider either a Kroupa et al. (1993) or a more top-heavy Kroupa (2001) IMF, two sets of stellar yields and different values for the fraction of binary systems suitable to give rise to SNe Ia. We investigate stellar ages, SN rates, stellar and gas metallicity gradients, and stellar $\alpha$-enhancement in simulations, and compare predictions with observations. We find that a Kroupa et al. (1993) IMF has to be preferred when modelling late-type galaxies in the local universe. On the other hand, the comparison of stellar metallicity profiles and $\alpha$-enhancement trends with observations of Milky Way stars shows a better agreement when a Kroupa (2001) IMF is assumed. Comparing the predicted SN rates and stellar $\alpha$-enhancement with observations supports a value for the fraction of binary systems producing SNe Ia of $0.03$, at least for late-type galaxies and for the considered IMFs. Adopted stellar yields are crucial in regulating cooling and star formation, and in determining patterns of chemical enrichment for stars, especially for those located in the galaxy bulge.

The influence of streaming velocities on the formation of the first stars

How, when and where the first stars formed are fundamental questions regarding the epoch of Cosmic Dawn. A second order effect in the fluid equations was recently found to make a significant contribution: an offset velocity between gas and dark matter, the so-called streaming velocity. Previous simulations of a limited number of low-mass dark matter haloes suggest that this streaming velocity can delay the formation of the first stars and decrease halo gas fractions and the halo mass function in the low mass regime. However, a systematic exploration of its effects in a large sample of haloes has been lacking until now. In this paper, we present results from a set of cosmological simulations of regions of the Universe with different streaming velocities performed with the moving mesh code AREPO. Our simulations have very high mass resolution, enabling us to accurately resolve minihaloes as small as $10^5 \: {\rm M_{\odot}}$. We show that in the absence of streaming, the least massive halo that contains cold gas has a mass $M_{\rm halo, min} = 5 \times 10^{5} \: {\rm M_{\odot}}$, but that cooling only becomes efficient in a majority of haloes for halo masses greater than $M_{\rm halo,50\%} = 1.6 \times 10^6 \: {\rm M_{\odot}}$. In regions with non-zero streaming velocities, $M_{\rm halo, min}$ and $M_{\rm halo,50\%}$ both increase significantly, by around a factor of a few for each one sigma increase in the value of the local streaming velocity. As a result, in regions with streaming velocities $v_\mathrm{stream} \ge 3\,\sigma_\mathrm{rms}$, cooling of gas in minihaloes is completely suppressed, implying that the first stars in these regions form within atomic cooling haloes.

Warm FIRE: simulating galaxy formation with resonant sterile neutrino dark matter

We study the impact of a warm dark matter (WDM) cosmology on dwarf galaxy formation through a suite of cosmological hydrodynamical zoom-in simulations of $M_{\rm halo} \approx10^{10}\,M_{\odot}$ dark matter halos as part of the Feedback in Realistic Environments (FIRE) project. A main focus of this paper is to evaluate the combined effects of dark matter physics and stellar feedback on the well-known small-scale issues found in cold dark matter (CDM) models. We find that the $z=0$ stellar mass of a galaxy is strongly correlated with the central density of its host dark matter halo at the time of formation, $z_{\rm f}$, in both CDM and WDM models. WDM halos follow the same $M_{\star}(z=0)-V_{\rm max}(z_{\rm f})$ relation as in CDM, but they form later, are less centrally dense, and therefore contain galaxies that are less massive than their CDM counterparts. As a result, the impact of baryonic effects on the central gravitational potential is typically diminished relative to CDM. However, the combination of delayed formation in WDM and energy input from stellar feedback results in dark matter profiles with lower overall densities. The WDM galaxies studied here have a wider diversity of star formation histories (SFHs) than the same systems simulated in CDM, and the two lowest $M_{\star}$ WDM galaxies form all of their stars at late times. The discovery of young ultra-faint dwarf galaxies with no ancient star formation -- which do not exist in our CDM simulations -- would therefore provide evidence in support of WDM.

The Three Hundred Project: The evolution of galaxy cluster density profiles

Recent numerical studies of the dark matter density profiles of massive galaxy clusters ($M_{\rm halo} > 10^{15}$M$_{\odot}$) show that their median radial mass density profile remains unchanged up to $z > 1$, displaying a highly self-similar evolution. We verify this by using the data set of the THE THREE HUNDRED project, i.e. 324 cluster-sized haloes as found in full physics hydrodynamical simulations. We track the progenitors of the mass-complete sample of clusters at $z=0$, and find that their median shape is already in place by $z=2.5$. However, selecting a dynamically relaxed subsample ($\sim16$ per cent of the clusters), we observe a shift of the scale radius $r_s$ towards larger values at earlier times. Classifying the whole sample by formation time, this evolution is understood as a result of a two-phase halo mass accretion process. Early-forming clusters -- identified as relaxed today -- have already entered their slow accretion phase, hence their mass growth occurs mostly at the outskirts. Late-forming clusters -- which are still unrelaxed today -- are in their fast accretion phase, thus the central region of the clusters is still growing. We conclude that the density profile of galaxy clusters shows a profound self-similarity out to redshifts $z\sim2.5$. This result holds for both gas and total density profiles when including baryonic physics, as reported here for two rather distinct sub-grid models.

The Halo Masses of Galaxies to z ∼ 3: A Hybrid Observational and Theoretical Approach

We use a hybrid observational/theoretical approach to study the relation between galaxy kinematics and the derived stellar and halo masses of galaxies up to z=3 as a function of stellar mass, redshift and morphology. Our observational sample consists of a concatenation of 1125 galaxies with kinematic measurements at 0.4<z<3 from long-slit and integral-field studies. We investigate several ways to measure halo masses from observations based on results from semi-analytical models, showing that galaxy halo masses can be retrieved with a scatter of ~0.4 dex by using only stellar masses. We discover a third parameter, relating to the time of the formation of the halo, which reduces the scatter in the relation between the stellar and halo masses, such that systems forming earlier have a higher stellar mass to halo mass ratio, which we also find observationally. We find that this scatter correlates with morphology, such that early-type, or older stellar systems, have higher M_*/M_halo ratios. We furthermore show using this approach, and through weak lensing and abundance matching, that the ratio of stellar to halo mass does not significantly evolve with redshift at 1<z<3. This is evidence for the regulated hierarchical assembly of galaxies such that the ratio of stellar to dark matter mass remains approximately constant since $z = 2$. We use these results to show that the dark matter accretion rate evolves from $dM_{\rm halo}/d{\rm t} \sim 4000$ M_solar year$^{-1}$ at $z \sim 2.5$, to a few 100 M_solar year$^{-1}$ by $z \sim 0.5$.

No assembly required: mergers are mostly irrelevant for the growth of low-mass dwarf galaxies

We investigate the merger histories of isolated dwarf galaxies based on a suite of 15 high-resolution cosmological zoom-in simulations, all with masses of $M_{\rm halo} \approx 10^{10}\,{\rm M}_{\odot}$ (and M$_\star\sim10^5-10^7\,{\rm M}_{\odot}$) at $z=0$, from the Feedback in Realistic Environments (FIRE) project. The stellar populations of these dwarf galaxies at $z=0$ are formed essentially entirely "in situ": over 90$\%$ of the stellar mass is formed in the main progenitor in all but two cases, and all 15 of the galaxies have >70$\%$ of their stellar mass formed in situ. Virtually all galaxy mergers occur prior to $z\sim3$, meaning that accreted stellar populations are ancient. On average, our simulated dwarfs undergo 5 galaxy mergers in their lifetimes, with typical pre-merger galaxy mass ratios that are less than 1:10. This merger frequency is generally comparable to what has been found in dissipationless simulations when coupled with abundance matching. Two of the simulated dwarfs have a luminous satellite companion at $z=0$. These ultra-faint dwarfs lie at or below current detectability thresholds but are intriguing targets for next-generation facilities. The small contribution of accreted stars make it extremely difficult to discern the effects of mergers in the vast majority of dwarfs either photometrically or using resolved-star color-magnitude diagrams (CMDs). The important implication for near-field cosmology is that star formation histories of comparably massive galaxies derived from resolved CMDs should trace the build-up of stellar mass in one main system across cosmic time as opposed to reflecting the contributions of many individual star formation histories of merged dwarfs.

Localized massive halo properties in bahamas and MACSIS simulations: scalings, lognormality, and covariance

Using tens of thousands of halos realized in the BAHAMAS and MACSIS simulations produced with a consistent astrophysics treatment that includes AGN feedback, we validate a multi-property statistical model for the stellar and hot gas mass behavior in halos hosting groups and clusters of galaxies. The large sample size allows us to extract fine-scale mass--property relations (MPRs) by performing local linear regression (LLR) on individual halo stellar mass (${\rm M}_{\rm star}$) and hot gas mass (${\rm M}_{\rm gas}$) as a function of total halo mass (${\rm M}_{\rm halo}$). We find that: 1) both the local slope and variance of the MPRs run with mass (primarily) and redshift (secondarily); 2) the conditional likelihood, $p({\rm M}_{\rm star},\ {\rm M}_{\rm gas} | \ {\rm M}_{\rm halo}, z)$ is accurately described by a multivariate, log-normal distribution, and; 3) the covariance of ${\rm M}_{\rm star}$ and ${\rm M}_{\rm gas}$ at fixed ${\rm M}_{\rm halo}$ is generally negative, reflecting a partially closed baryon box model for high mass halos. We validate the analytical population model of Evrard et al. (2014), finding sub-percent accuracy in the log-mean halo mass selected at fixed property, $\langle \ln {\rm M}_{\rm halo} | {\rm M}_{\rm gas} \rangle$ or $\langle \ln {\rm M}_{\rm halo} | {\rm M}_{\rm star} \rangle$, when scale-dependent MPR parameters are employed. This work highlights the potential importance of allowing for running in the slope and scatter of MPRs when modeling cluster counts for cosmological studies. We tabulate LLR fit parameters as a function of halo mass at $z=0$, $0.5$ and 1 for two popular mass conventions.

Probing galaxy assembly bias with LRG weak lensing observations

Abstract In Montero-Dorta et al., we show that luminous red galaxies (LRGs) from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) at z ∼ 0.55 can be divided into two groups based on their star formation histories. So-called fast-growing LRGs assemble 80 per cent of their stellar mass at z ∼ 5, whereas slow-growing LRGs reach the same evolutionary state at z ∼ 1.5. We further demonstrate that these two subpopulations present significantly different clustering properties on scales of ∼1−30 Mpc. Here, we measure the mean halo mass of each subsample using the galaxy–galaxy lensing technique, in the ${\sim }190\deg ^2$ overlap of the LRG catalogue and the CS82 and CFHTLenS shear catalogues. We show that fast- and slow-growing LRGs have similar lensing profiles, which implies that they live in haloes of similar mass: $\log (M_{\rm halo}^{\rm fast}/h^{-1}\mathrm{M}_{{\odot }}) = 12.85^{+0.16}_{-0.26}$ and $\log (M_{\rm halo}^{\rm slow}/h^{-1}\mathrm{M}_{{\odot }}) =12.92^{+0.16}_{-0.22}$. This result, combined with the clustering difference, suggests the existence of galaxy assembly bias, although the effect is too subtle to be definitively proven, given the errors on our current weak-lensing measurement. We show that this can soon be achieved with upcoming surveys like DES.

Dust extinction in the first galaxies

Using cosmological volume simulations and a custom built sub-grid model for Pop~III star formation, we examine the baseline dust extinction in the first galaxies due to Pop~III metal enrichment in the first billion years of cosmic history. We find that while the most enriched, high-density lines of sight in primordial galaxies can experience a measurable amount of extinction from Pop~III dust ($E(B-V)_{\rm max}=0.07,\ A_{\rm V,max}\approx0.28$), the average extinction is very low with $\left< E(B-V) \right> \lesssim 10^{-3}$. We derive a power-law relationship between dark matter halo mass and extinction of $E(B-V)\propto M_{\rm halo}^{0.80}$. Performing a Monte Carlo parameter study, we establish the baseline reddening of the UV spectra of dwarf galaxies at high redshift due to Pop~III enrichment only. With this method, we find $\left<\beta_{\rm UV}\right>-2.51\pm0.07$, which is both nearly halo mass and redshift independent.

Predictions for deep galaxy surveys with JWST from ΛCDM

We present predictions for the outcome of deep galaxy surveys with the $James$ $Webb$ $Space$ $Telescope$ ($JWST$) obtained from a physical model of galaxy formation in $\Lambda$CDM. We use the latest version of the GALFORM model, embedded within a new ($800$ Mpc)$^{3}$ dark matter only simulation with a halo mass resolution of $M_{\rm halo}>2\times10^{9}$ $h^{-1}$ M$_{\odot}$. For computing full UV-to-mm galaxy spectral energy distributions, including the absorption and emission of radiation by dust, we use the spectrophotometric radiative transfer code GRASIL. The model is calibrated to reproduce a broad range of observational data at $z\lesssim6$, and we show here that it can also predict evolution of the rest-frame far-UV luminosity function for $7\lesssim z\lesssim10$ which is in good agreement with observations. We make predictions for the evolution of the luminosity function from $z=16$ to $z=0$ in all broadband filters on the Near InfraRed Camera (NIRCam) and Mid InfraRed Instrument (MIRI) on $JWST$ and present the resulting galaxy number counts and redshift distributions. Our fiducial model predicts that $\sim1$ galaxy per field of view will be observable at $z\sim11$ for a $10^4$ s exposure with NIRCam. A variant model, which produces a higher redshift of reionization in better agreement with $Planck$ data, predicts number densities of observable galaxies $\sim5\times$ greater at this redshift. Similar observations with MIRI are predicted not to detect any galaxies at $z\gtrsim6$. We also make predictions for the effect of different exposure times on the redshift distributions of galaxies observable with $JWST$, and for the angular sizes of galaxies in $JWST$ bands.

The host dark matter haloes of [O II] emitters at 0.5 &lt; z &lt; 1.5

Emission line galaxies (ELGs) are used in several ongoing and upcoming surveys (SDSS-IV/eBOSS, DESI) as tracers of the dark matter distribution. Using a new galaxy formation model, we explore the characteristics of [OII] emitters, which dominate optical ELG selections at $z\simeq 1$. Model [OII] emitters at $0.5<z<1.5$ are selected to mimic the DEEP2, VVDS, eBOSS and DESI surveys. The luminosity functions of model [OII] emitters are in reasonable agreement with observations. The selected [OII] emitters are hosted by haloes with $M_{\rm halo}\geq 10^{10.3}h^{-1}{\rm M}_{\odot}$, with ~90% of them being central star-forming galaxies. The predicted mean halo occupation distributions of [OII] emitters has a shape typical of that inferred for star-forming galaxies, with the contribution from central galaxies, $\langle N \rangle_{\left[OII\right]\, cen}$, being far from the canonical step function. The $\langle N \rangle_{\left[OII\right]\, cen}$ can be described as the sum of an asymmetric Gaussian for disks and a step function for spheroids, which plateaus below unity. The model [OII] emitters have a clustering bias close to unity, which is below the expectations for eBOSS and DESI ELGs. At $z\sim 1$, a comparison with observed g-band selected galaxy, which are expected to be dominated by [OII] emitters, indicates that our model produces too few [OII] emitters that are satellite galaxies. This suggests the need to revise our modelling of hot gas stripping in satellite galaxies.

The globular cluster-dark matter halo connection.

I present a simple phenomenological model for the observed linear scaling of the stellar mass in old globular clusters (GCs) with z = 0 halo mass in which the stellar mass in GCs scales linearly with progenitor halo mass at z = 6 above a minimum halo mass for GC formation. This model reproduces the observed M GCs-M halo relation at z = 0 and results in a prediction for the minimum halo mass at z = 6 required for hosting one GC: M min(z = 6) = 1.07 × 109 M⊙. Translated to z = 0, the mean threshold mass is M halo(z = 0) ≈ 2 × 1010 M⊙. I explore the observability of GCs in the reionization era and their contribution to cosmic reionization, both of which depend sensitively on the (unknown) ratio of GC birth mass to present-day stellar mass, ξ. Based on current detections of z ≳ 6 objects with M 1500<-17, values of ξ > 10 are strongly disfavoured; this, in turn, has potentially important implications for GC formation scenarios. Even for low values of ξ, some observed high-z galaxies may actually be GCs, complicating estimates of reionization-era galaxy ultraviolet luminosity functions and constraints on dark matter models. GCs are likely important reionization sources if 5 ≲ ξ ≲ 10. I also explore predictions for the fraction of accreted versus in situ GCs in the local Universe and for descendants of systems at the halo mass threshold of GC formation (dwarf galaxies). An appealing feature of the model presented here is the ability to make predictions for GC properties based solely on dark matter halo merger trees.

Tracing the cosmic web

The cosmic web is one of the most striking features of the distribution of galaxies and dark matter on the largest scales in the Universe. It is composed of dense regions packed full of galaxies, long filamentary bridges, flattened sheets and vast low density voids. The study of the cosmic web has focused primarily on the identification of such features, and on understanding the environmental effects on galaxy formation and halo assembly. As such, a variety of different methods have been devised to classify the cosmic web -- depending on the data at hand, be it numerical simulations, large sky surveys or other. In this paper we bring twelve of these methods together and apply them to the same data set in order to understand how they compare. In general these cosmic web classifiers have been designed with different cosmological goals in mind, and to study different questions. Therefore one would not {\it a priori} expect agreement between different techniques however, many of these methods do converge on the identification of specific features. In this paper we study the agreements and disparities of the different methods. For example, each method finds that knots inhabit higher density regions than filaments, etc. and that voids have the lowest densities. For a given web environment, we find substantial overlap in the density range assigned by each web classification scheme. We also compare classifications on a halo-by-halo basis; for example, we find that 9 of 12 methods classify around a third of group-mass haloes (i.e. $M_{\rm halo}\sim10^{13.5}h^{-1}M_{\odot}$) as being in filaments. Lastly, so that any future cosmic web classification scheme can be compared to the 12 methods used here, we have made all the data used in this paper public.