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Register a new userPredictions for deep galaxy surveys with JWST from $Lambda$CDM
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William Cowley
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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 $M_{rm halo}>2times10^{9}$ $h^{-1}$ 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 $zlesssim6$, and we show here that it can also predict evolution of the rest-frame far-UV luminosity function for $7lesssim zlesssim10$ 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 $zsim11$ 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 $sim5times$ greater at this redshift. Similar observations with MIRI are predicted not to detect any galaxies at $zgtrsim6$. 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.
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Telescopes to be launched over the next decade-and-a-half, such as JWST, EUCLID, ATHENA and Lynx, promise to revolutionise the study of the high redshift Universe and greatly advance our understanding of the early stages of galaxy formation. We use a model that follows the evolution of the masses and spins of supermassive black holes (SMBHs) within a semi-analytic model of galaxy formation to make predictions for the Active Galactic Nucleus (AGN) luminosity function at $zgeq7$ in the broadband filters of JWST and EUCLID at near-infrared wavelengths, and ATHENA and Lynx at X-ray energies. The predictions of our model are relatively insensitive to the choice of seed black hole mass, except at the lowest luminosities ($L_{mathrm{bol}}<10^{43}mathrm{ergs^{-1}}$) and the highest redshifts ($z>10$). We predict that surveys with these different telescopes will select somewhat different samples of SMBHs, with EUCLID unveiling the most massive, highest accretion rate SMBHs, Lynx the least massive, lowest accretion rate SMBHs, and JWST and ATHENA covering objects inbetween. At $z=7$, we predict that typical detectable SMBHs will have masses, $M_{mathrm{BH}}sim10^{5-8}M_{odot}$, and Eddington normalised mass accretion rates, $dot{M}/dot{M}_{mathrm{Edd}}sim0.6-2$. The SMBHs will be hosted by galaxies of stellar mass $M_{star}sim10^{8-10}M_{odot}$, and dark matter haloes of mass $M_{mathrm{halo}}sim10^{11-12}M_{odot}$. We predict that the detectable SMBHs at $z=10$ will have slightly smaller black holes, accreting at slightly higher Eddington normalised mass accretion rates, in slightly lower mass host galaxies compared to those at $z=7$, and reside in haloes of mass $M_{mathrm{halo}}sim10^{10-11}M_{odot}$.
The leading tensions to the collisionless cold dark matter (CDM) paradigm are the small-scale controversies, discrepancies between observations at the dwarf-galactic scale and their simulational counterparts. In this work we consider methods to infer 3D morphological information on Local Group dwarf spheroidals, and test the fitness of CDM+hydrodynamics simulations to the observed galaxy shapes. We find that the subpopulation of dwarf galaxies with mass-to-light ratio $gtrsim 100 M_odot/L_odot$ reflects an oblate morphology. This is discrepant with the dwarf galaxies with mass-to-light ratio $lesssim 100 M_odot/L_odot$, which reflect prolate morphologies, and more importantly with simulations of CDM-sourced galaxies which are explicitly prolate. Although more simulations and data are called for, if evidence of oblate pressure-supported stellar distributions persists, we argue that an underlying oblate non-CDM dark matter halo may be required, and present this as motivation for future studies.
The James Webb Space Telescop (JWST) promises to revolutionise our understanding of the early Universe, and contrasting its upcoming observations with predictions of the $Lambda$CDM model requires detailed theoretical forecasts. Here, we exploit the large dynamic range of the IllustrisTNG simulation suite, TNG50, TNG100, and TNG300, to derive multi-band galaxy luminosity functions from $z=2$ to $z=10$. We put particular emphasis on the exploration of different dust attenuation models to determine galaxy luminosity functions for the rest-frame ultraviolet (UV), and apparent wide NIRCam bands. Our most detailed dust model is based on continuum Monte Carlo radiative transfer calculations employing observationally calibrated dust properties. This calibration results in constraints on the redshift evolution of the dust attenuation normalisation and dust-to-metal ratios yielding a stronger redshift evolution of the attenuation normalisation compared to most previous theoretical studies. Overall we find good agreement between the rest-frame UV luminosity functions and observational data for all redshifts, also beyond the regimes used for the dust-model calibrations. Furthermore, we also recover the observed high redshift ($z=4-6$) UV luminosity versus stellar mass relation, the H$alpha$ versus star formation rate relation, and the H$alpha$ luminosity function at $z=2$. The bright end ($M_{rm UV}>-19.5$) cumulative galaxy number densities are consistent with observational data. For the F200W NIRCam band, we predict that JWST will detect $sim 80$ ($sim 200$) galaxies with a signal-to-noise ratio of $10$ ($sim 5$) within the NIRCam field of view, $2.2times2.2 ,{rm arcmin}^{2}$, for a total exposure time of $10^5{rm s}$ in the redshift range $z=8 pm 0.5$. These numbers drop to $sim 10$ ($sim 40$) for an exposure time of $10^4{rm s}$.
We derive lens distortion and magnification profiles of four well known clusters observed with Subaru. Each cluster is very well fitted by the general form predicted for Cold Dark Matter (CDM) dominated halos, with good consistency found between the independent distortion and magnification measurements. The inferred level of mass concentration is surprisingly high, 8<c_{vir}<15 (<c_{vir}> = 10.4 pm 0.9), compared to the relatively shallow profiles predicted by the Lambda CDM model, c_{vir}=5.1 pm 1.1 (for <M_{vir}> =1.25times 10^{15}M_{odot}/h). This represents a 4sigma discrepancy, and includes the relatively modest effects of projection bias and profile evolution derived from N-body simulations, which oppose each other with little residual effect. In the context of CDM based cosmologies, this discrepancy implies clusters collapse earlier (zgeq 1) than predicted (z<0.5), when the Universe was correspondingly denser.
We present a new prospective analysis of deep multi-band imaging with the James Webb Space Telescope (JWST). In this work, we investigate the recovery of high-redshift $5<z<12$ galaxies through extensive image simulations of accepted JWST programs such as CEERS in the EGS field and HUDF GTO. We introduce complete samples of $sim300,000$ galaxies with stellar masses $log(M_*/M_odot)>6$ and redshifts $0<z<15$, as well as galactic stars, into realistic mock NIRCam, MIRI and HST images to properly describe the impact of source blending. We extract the photometry of the detected sources as in real images and estimate the physical properties of galaxies through spectral energy distribution fitting. We find that the photometric redshifts are primarily limited by the availability of blue-band and near-infrared medium-band imaging. The stellar masses and star-formation rates are recovered within $0.25$ and $0.3$ dex respectively, for galaxies with accurate photometric redshifts. Brown dwarfs contaminating the $z>5$ galaxy samples can be reduced to $<0.01$ arcmin$^{-2}$ with a limited impact on galaxy completeness. We investigate multiple high-redshift galaxy selection techniques and find the best compromise between completeness and purity at $5<z<10$ using the full redshift posterior probability distributions. In the EGS field, the galaxy completeness remains higher than $50%$ for $m_text{UV}<27.5$ sources at all redshifts, and the purity is maintained above $80$ and $60%$ at $zleq7$ and $10$ respectively. The faint-end slope of the galaxy UV luminosity function is recovered with a precision of $0.1-0.25$, and the cosmic star-formation rate density within $0.1$ dex. We argue in favor of additional observing programs covering larger areas to better constrain the bright end.
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