Abstract Substantial populations of massive quiescent galaxies at z ≥ 3 challenge our understanding of rapid galaxy growth and quenching over short timescales. In order to piece together this ...evolutionary puzzle, more statistical samples of these objects are required. Established techniques for identifying massive quiescent galaxies are increasingly inefficient and unconstrained at z > 3. As a result, studies report that as much as 70% of quiescent galaxies at z > 3 may be missed from existing surveys. In this work, we propose a new empirical color selection technique designed to select massive quiescent galaxies at 3 ≲ z ≲ 6 using JWST NIRCam imaging data. We use empirically constrained galaxy spectral energy distribution (SED) templates to define a region in the F277W − F444W versus F150W − F277W color plane that captures quiescent galaxies at z > 3. We apply these color selection criteria to the Cosmic Evolution Early Release Science (CEERS) Survey and use SED fitting on sources in the region to identify 44 candidate z ≳ 3 quiescent galaxies. Over half of these sources are newly discovered and, on average, exhibit specific star formation rates of poststarburst galaxies. Most of these sources would not be discovered using canonical UVJ diagrams. We derive volume density estimates of n ∼ 1–4 × 10 −5 Mpc −3 at 3 < z < 5, finding excellent agreement with existing reports on similar populations in the CEERS field. Thanks to NIRCam’s wavelength coverage and sensitivity, this technique provides an efficient tool to search for large samples of these rare galaxies.
The first stars formed in the early universe and shortly after assembled into the first galaxies. Since then, galaxies have been subject to a variety of processes, both internal and external, that ...affect their ability to form stars. At low redshift, environment plays a large role in inhibiting star formation, however it is less clear what effect it has at high redshift. This is predominantly due to the difficulty of determining the nature of the high redshift environment from uncertain redshift measurements, and the small coverage of high redshift surveys leading to poor sampling of the cosmic variance. In this thesis I use a variety of numerical approaches to various aspects of this problem. In the first section I use a semi-analytic model to study the relationship between observed galaxy surface overdensity and the probability of coinciding with a protocluster, the pre-collapse progenitors of galaxy clusters, and make recommendations for optimum measurement apertures for their identification. In the second section I use a suite of hydrodynamic simulations of galaxy clusters, across a range of descendant halo masses, to study the galaxy evolution in their protocluster progenitors in detail. I characterise the star-forming sequence, studying it's difference in protocluster and field environments, as well as within dense groups in the collapsing protocluster. In the final section I use a novel approach to estimate the star formation history of galaxies. Rather than studying the high redshift environment directly, I estimate when the stars in a low redshift galaxy were formed using population synthesis techniques. In this work I couple this with hydrodynamical simulations in order to provide more informative priors on the shape of the star formation history, which typically imposes strong biases on inferred properties, such as the total stellar mass, in more traditional approaches.
During the most active period of star formation in galaxies, which occurs in the redshift range 1 < z < 3, strong bursts of star formation result in significant quantities of dust, which obscures new ...stars being formed as their UV/optical light is absorbed and then re-emitted in the infrared, which redshifts into the mm/sub-mm bands for these early times. To get a complete picture of the high- z galaxy population, we need to survey a large patch of the sky in the sub-mm with sufficient angular resolution to resolve all galaxies, but we also need the depth to fully sample their cosmic evolution, and therefore obtain their redshifts using direct mm spectroscopy with a very wide frequency coverage. This requires a large single-dish sub-mm telescope with fast mapping speeds at high sensitivity and angular resolution, a large bandwidth with good spectral resolution and multiplex spectroscopic capabilities. The proposed 50-m Atacama Large Aperture Submillimeter Telescope (AtLAST) will deliver these specifications. We discuss how AtLAST allows us to study the whole population of high-z galaxies, including the dusty star-forming ones which can only be detected and studied in the sub-mm, and obtain a wealth of information for each of these up to z ∼ 7: gas content, cooling budget, star formation rate, dust mass, and dust temperature. We present worked examples of surveys that AtLAST can perform, both deep and wide, and also focused on galaxies in proto-clusters. In addition we show how such surveys with AtLAST can measure the growth rate f σ 8 and the Hubble constant with high accuracy, and demonstrate the power of the line-intensity mapping method in the mm/sub-mm wavebands to constrain the cosmic expansion history at high redshifts, as good examples of what can uniquely be done by AtLAST in this research field.
We present Sengi, https://christopherlovell.github.io/sengi , an online tool for viewing the spectral outputs of stellar population synthesis (SPS) codes. Typical SPS codes require significant disk ...space or computing resources to produce spectra for simple stellar populations with arbitrary parameters. This makes it difficult to present their results in an interactive, web-friendly format. Sengi uses Non-negative Matrix Factorisation (NMF) and bilinear interpolation to estimate output spectra for arbitrary values of stellar age and metallicity. The reduced disk requirements and computational expense allows the result to be served as a client-based Javascript application. In this paper we present the method for generating grids of spectra, fitting those grids with NMF, bilinear interpolation across the fitted coefficients, and finally provide estimates of the prediction and interpolation errors.
The SPT0311-58 system at z=6.900 is an extremely massive structure within the reionization epoch, and offers a chance to understand the formation of galaxies in an extreme peak in the primordial ...density field. We present 70mas Atacama Large Millimeter/submillimeter Array observations of the dust continuum and CII 158um emission in the central pair of galaxies and reach physical resolution ~100-350pc, among the most detailed views of any reionization-era system to date. The observations resolve the source into at least a dozen kiloparsec-size clumps. The global kinematics and high turbulent velocity dispersion within the galaxies present a striking contrast to recent claims of dynamically cold thin-disk kinematics in some dusty galaxies just 800Myr later at z~4. We speculate that both gravitational interactions and fragmentation from massive parent disks have likely played a role in the overall dynamics and formation of clumps in the system. Each clump individually is comparable in mass to other 6<z<8 galaxies identified in rest-UV/optical deep field surveys, but with star formation rates elevated by ~3-5x. Internally, the clumps themselves bear close resemblance to greatly scaled-up versions of virialized cloud-scale structures identified in low-redshift galaxies. Our observations are qualitatively similar to the chaotic and clumpy assembly within massive halos seen in simulations of high-redshift galaxies.
We report the identification of 15 galaxy candidates at $z\ge9$ using the
initial COSMOS-Web JWST observations over 77 arcmin$^2$ through four NIRCam
filters (F115W, F150W, F277W, F444W) with an ...overlap with MIRI (F770W) of 8.7
arcmin$^2$. We fit the sample using several publicly-available SED fitting and
photometric redshift codes and determine their redshifts between $z=9.3$ and
$z=10.9$ ($\langle z\rangle=10.0$), UV-magnitudes between M$_{\rm UV}$ =
$-$21.2 and $-$19.5 (with $\langle $M$_{\rm UV}\rangle=-20.2$) and rest-frame
UV slopes ($\langle \beta\rangle=-2.4$). These galaxies are, on average, more
luminous than most $z\ge9$ candidates discovered by JWST so far in the
literature, while exhibiting similar blue colors in their rest-frame UV. The
rest-frame UV slopes derived from SED-fitting are blue ($\beta\sim$$-$2.0,
$-$2.7) without reaching extremely blue values as reported in other recent
studies at these redshifts. The blue color is consistent with models that
suggest the underlying stellar population is not yet fully enriched in metals
like similarly luminous galaxies in the lower redshift Universe. The derived
stellar masses with $\langle \log_{\rm 10}
($M$_\star/$M$_\odot)\rangle\approx8-9$ are not in tension with the standard
$\Lambda$CDM model and our measurement of the volume density of such UV
luminous galaxies aligns well with previously measured values presented in the
literature at $z\sim9-10$. Our sample of galaxies, although compact, are
significantly resolved.
This paper describes the current update on macromolecular model validation services that are provided at the MolProbity website, emphasizing changes and additions since the previous review in 2010. ...There have been many infrastructure improvements, including rewrite of previous Java utilities to now use existing or newly written Python utilities in the open‐source CCTBX portion of the Phenix software system. This improves long‐term maintainability and enhances the thorough integration of MolProbity‐style validation within Phenix. There is now a complete MolProbity mirror site at http://molprobity.manchester.ac.uk. GitHub serves our open‐source code, reference datasets, and the resulting multi‐dimensional distributions that define most validation criteria. Coordinate output after Asn/Gln/His “flip” correction is now more idealized, since the post‐refinement step has apparently often been skipped in the past. Two distinct sets of heavy‐atom‐to‐hydrogen distances and accompanying van der Waals radii have been researched and improved in accuracy, one for the electron‐cloud‐center positions suitable for X‐ray crystallography and one for nuclear positions. New validations include messages at input about problem‐causing format irregularities, updates of Ramachandran and rotamer criteria from the million quality‐filtered residues in a new reference dataset, the CaBLAM Cα‐CO virtual‐angle analysis of backbone and secondary structure for cryoEM or low‐resolution X‐ray, and flagging of the very rare cis‐nonProline and twisted peptides which have recently been greatly overused. Due to wide application of MolProbity validation and corrections by the research community, in Phenix, and at the worldwide Protein Data Bank, newly deposited structures have continued to improve greatly as measured by MolProbity's unique all‐atom clashscore.
Environmental effects on the evolution of galaxies have been one of the leading questions in galaxy studies for decades. In this work, we investigate the relationship between the star formation ...activity of galaxies and their environmental matter density using the cosmological hydrodynamic simulation Simba. The star formation activity indicators we explore include the star formation efficiency (SFE), specific star formation rate (sSFR) and molecular hydrogen mass fraction (\(f^*_{H_2}\)) and the environment is considered as the large-scale environmental matter density, calculated based on the stellar mass of nearby galaxies on a 1 Mpc/h grid using the cloud in cell (CIC) method. Our sample includes galaxies with \(9<\log(M_*/M_{\odot})\) at \(0<z<4\), divided into three mass bins to disentangle the effects of mass and environment on the galactic star formation activity. For low- to intermediate-mass galaxies at low-redshifts (\(z<1.5\)), we find that the star formation efficiency of those in high-density regions are \(\sim 0.3\) dex lower than those in low-density regions. However, there is no significant environmental dependence of the star formation efficiency for massive galaxies over all our redshift range, and low- to intermediate-mass galaxies at high redshifts (\(z > 1.5\)). We present a scaling relation for the depletion time of molecular hydrogen (\({t_{depl}}=1/SFE\)) as a function of galaxy parameters including environmental density. Our findings provide a framework for quantifying the environmental effects on the star formation activities of galaxies as a function of stellar mass and redshift. The most significant environmental dependence is seen at later cosmic times (\(z<1.5\)) and towards lower stellar masses (\(9<\log(M_*/M_{\odot})<10\)). Future large galaxy surveys can use this framework to look for the environmental dependence of the star formation activity and examine our predictions.
The discovery of extremely luminous galaxies at ultra-high redshifts (\(z\gtrsim 8\)) has posed a challenge for galaxy formation models. Most statistical analyses of this tension to date have not ...properly accounted for the variance due to field-to-field clustering, which causes the number counts of galaxies to vary from field to field, greatly in excess of Poisson noise. This super-Poissonian variance is often referred to as cosmic variance. Since cosmic variance increases rapidly as a function of mass, redshift, and for small observing areas, the most massive objects in deep \textit{JWST} surveys are severely impacted by cosmic variance. In this paper, we introduce a simple model to predict the distribution of the mass of the most massive galaxy found for different survey designs, which includes cosmic variance. The distributions differ significantly from previous predictions using the Extreme Value Statistics formalism, changing both the position and shape of the distribution of most massive galaxies in a counter-intuitive way. We test our model using the \texttt{UniverseMachine} simulations, where the predicted effects of including cosmic variance are clearly identifiable. Moreover, we find that the highly significant skew in the distributions of galaxy number counts for typical deep \textit{JWST} surveys lead to a high "variance on the variance", which greatly impacts the calculation of the cosmic variance itself. We conclude that it is crucial to accurately account for the impact of cosmic variance in any future analysis of tension between extreme galaxies in the early universe and galaxy formation models.
The iMaNGA project uses a forward-modelling approach to compare the predictions of cosmological simulations with observations from SDSS-IV/MaNGA. We investigate the dependency of age and metallicity ...radial gradients on galaxy morphology, stellar mass, stellar surface mass density (\(\Sigma_*\)), and environment. The key of our analysis is that observational biases affecting the interpretation of MaNGA data are emulated in the theoretical iMaNGA sample. The simulations reproduce the observed global stellar population scaling relations with positive correlations between galaxy mass and age/metallicity quite well and also produce younger stellar populations in late-type in agreement with observations. We do find interesting discrepancies, though, that can inform the physics and further development of the simulations. Ages of spiral galaxies and low-mass ellipticals are overestimated by about 2-4 Gyr. Radial metallicity gradients are steeper in iMaNGA than in MaNGA, a discrepancy most prominent in spiral and lenticular galaxies. Also, the observed steepening of metallicity gradients with increasing galaxy mass is not well matched by the simulations. We find that the theoretical radial profiles of surface mass density \(\Sigma_*\) are steeper than in observations except for the most massive galaxies. In both MaNGA and iMaNGA Z/H correlates with \(\Sigma_*\), however, the simulations systematically predict lower Z/H by almost a factor of 2 at any \(\Sigma_*\). Most interestingly, for galaxies with stellar mass \(\log M_*\leq 10.80 M_\odot\) the MaNGA data reveal a positive correlation between galaxy radius and Z/H at fixed \(\Sigma_*\), which is not recovered in iMaNGA. Finally, the dependence on environmental density is negligible in both the theoretical iMaNGA and the observed MaNGA data.
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