Galaxy clusters and groups are thought to accrete material along the preferred direction of cosmic filaments. Yet these structures have proven difficult to detect due to their low contrast with few ...studies focusing on cluster infall regions. In this work, we detected cosmic filaments around galaxy clusters using photometric redshifts in the range 0.15<z<0.7. We characterised galaxy populations in these structures to study the influence of "pre-processing" by cosmic filaments and galaxy groups on star-formation quenching. The cosmic filament detection was performed using the AMASCFI Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) T0007 cluster sample (Sarron et al. 2018). The filament reconstruction was done with the DISPERSE algorithm in photometric redshift slices. We showed that this reconstruction is reliable for a CFHTLS-like survey at 0.15<z<0.7 using a mock galaxy catalogue. We split our galaxy catalogue in two populations (passive and star-forming) using the LePhare SED fitting algorithm and worked with two redshift bins (0.15<z<=0.4 and 0.4<z<0.7). We showed that the AMASCFI cluster connectivity (i.e. the number of filaments connecting to a cluster) increases with cluster mass M200. Filament galaxies outside R200 are found to be closer to clusters at low redshift, whatever the galaxy type. Passive galaxies in filaments are closer to clusters than star-forming galaxies in the low redshift bin only. The passive fraction of galaxies decreases with increasing clustercentric distance up to d~5 cMpc. Galaxy groups/clusters that are not located at nodes of our reconstruction are mainly found inside cosmic filaments. These results give clues for "pre-processing" in cosmic filaments, that could be due to smaller galaxy groups. This trend could be further explored by applying this method to larger photometric surveys such as HSC-SPP or Euclid.
We examine how the mass assembly of central galaxies depends on their location in the cosmic web. The HORIZON-AGN simulation is analysed at z~2 using the DISPERSE code to extract multi-scale cosmic ...filaments. We find that the dependency of galaxy properties on large-scale environment is mostly inherited from the (large-scale) environmental dependency of their host halo mass. When adopting a residual analysis that removes the host halo mass effect, we detect a direct and non-negligible influence of cosmic filaments. Proximity to filaments enhances the build-up of stellar mass, a result in agreement with previous studies. However, our multi-scale analysis also reveals that, at the edge of filaments, star formation is suppressed. In addition, we find clues for compaction of the stellar distribution at close proximity to filaments. We suggest that gas transfer from the outside to the inside of the haloes (where galaxies reside) becomes less efficient closer to filaments, due to high angular momentum supply at the vorticity-rich edge of filaments. This quenching mechanism may partly explain the larger fraction of passive galaxies in filaments, as inferred from observations at lower redshifts.
Galaxy merger histories correlate strongly with stellar mass, largely regardless of morphology. Thus, at fixed stellar mass, spheroids and discs share similar assembly histories, both in terms of the ...frequency of mergers and the distribution of their mass ratios. Since mergers are the principal drivers of disc-to-spheroid morphological transformation, and the most massive galaxies typically have the richest merger histories, it is surprising that discs exist at all at the highest stellar masses (e.g. beyond the knee of the mass function). Using Horizon-AGN, a cosmological hydro-dynamical simulation, we show that extremely massive (M*> 10^11.4 MSun) discs are created via two channels. In the primary channel (accounting for ~70% of these systems and ~8% of massive galaxies) the most recent, significant merger (stellar mass ratio > 1:10) between a massive spheroid and a gas-rich satellite `spins up' the spheroid by creating a new rotational stellar component, leaving a massive disc as the remnant. In the secondary channel (accounting for ~30% of these systems and ~3% of massive galaxies), a system maintains a disc throughout its lifetime, due to an anomalously quiet merger history. Not unexpectedly, the fraction of massive discs is larger at higher redshift, due to the Universe being more gas-rich. The morphological mix of galaxies at the highest stellar masses is, therefore, a strong function of the gas fraction of the Universe. Finally, these massive discs have similar black-hole masses and accretion rates to massive spheroids, providing a natural explanation for why a minority of powerful AGN are surprisingly found in disc galaxies.
Hydrodynamical cosmological simulations have recently made great advances in reproducing galaxy mass assembly over cosmic time - as often quantified from the comparison of their predicted stellar ...mass functions to observed stellar mass functions from data. In this paper we compare the clustering of galaxies from the hydrodynamical cosmological simulated lightcone Horizon-AGN, to clustering measurements from the VIDEO survey observations. Using mocks built from a VIDEO-like photometry, we first explore the bias introduced into clustering measurements by using stellar masses and redshifts derived from SED-fitting, rather than the intrinsic values. The propagation of redshift and mass statistical and systematic uncertainties in the clustering measurements causes us to underestimate the clustering amplitude. We find then that clustering and halo occupation distribution (HOD) modelling results are qualitatively similar in Horizon-AGN and VIDEO. However at low stellar masses Horizon-AGN underestimates the observed clustering by up to a factor of ~3, reflecting the known excess stellar mass to halo mass ratio for Horizon-AGN low mass haloes, already discussed in previous works. This reinforces the need for stronger regulation of star formation in low mass haloes in the simulation. Finally, the comparison of the stellar mass to halo mass ratio in the simulated catalogue, inferred from angular clustering, to that directly measured from the simulation, validates HOD modelling of clustering as a probe of the galaxy-halo connection.
The upcoming WEAVE-QSO survey will target a high density of quasars over a
large area, enabling the reconstruction of the 3D density field through
Lyman-$\alpha$ tomography over unprecedented volumes ...smoothed on intermediate
scales ($\approx$ 16 Mpc/$h$). We produce mocks of the Lyman-$\alpha$ forest
using LyMAS, and reconstruct the 3D density field between sightlines through
Wiener filtering in a configuration compatible with the future WEAVE-QSO
observations. The fidelity of the reconstruction is assessed by measuring one-
and two-point statistics from the distribution of critical points in the cosmic
web. In addition, initial Lagrangian statistics are predicted from first
principles, and measurements of the connectivity of the cosmic web are
performed. The reconstruction captures well the expected features in the auto-
and cross-correlations of the critical points. This remains true after a
realistic noise is added to the synthetic spectra, even though sparsity of
sightlines introduces systematics, especially in the cross-correlations of
points with mixed signature. Specifically, for walls and filaments, the most
striking clustering features could be measured with up to 4 sigma of
significance with a WEAVE-QSO-like survey. Moreover, the connectivity of each
peak identified in the reconstructed field is globally consistent with its
counterpart in the original field, indicating that the reconstruction preserves
the geometry of the density field not only statistically, but also locally.
Hence the critical points relative positions within the tomographic
reconstruction could be used as standard rulers for dark energy by WEAVE-QSO
and similar surveys.
ALMA observations of the long wavelength dust continuum are used to estimate the gas masses in a sample of 708 star-forming (SF) galaxies at z = 0.3 to 4.5. We determine the dependence of gas masses ...and star formation efficiencies (SFE=SFR per unit gass mass). We find that 70 percent of the increase in SFRs of the MS is due to the increased gas masses at earlier epochs while 30 percent is due to increased efficiency of SF. For galaxies above the MS this is reversed with 70 percent of the increased SFR relative to the MS being due to elevated SFEs. Thus, the major evolution of star formation activity at early epochs is driven by increased gas masses, while the starburst activity taking galaxies above the MS is due to enhanced triggering of star formation (likely due to galactic merging). The interstellar gas peaks at z = 2 and dominates the stellar mass down to z = 1.2. Accretion rates needed to maintain continuity of the MS evolution exceed 100 Msun per yr at z > 2. The galactic gas contents are likely the driving determinant for both the rise in SF and AGN activity from z = 5 to their peak at z = 2 and subsequent fall to lower z. We suggest that for self-gravitating clouds with supersonic turbulence, cloud collisions and the filamentary structure of the clouds regulate the star formation activity.
Hydrodynamical cosmological simulations are increasing their level of realism by considering more physical processes and having greater resolution or larger statistics. However, usually either the ...statistical power of such simulations or the resolution reached within galaxies are sacrificed. Here, we introduce the NewHorizon project in which we simulate at high resolution a zoom-in region of \(\sim(16\,\rm Mpc)^3\) that is larger than a standard zoom-in region around a single halo and is embedded in a larger box. A resolution of up to 34 pc is reached within galaxies; this allows the simulation to capture the multi-phase nature of the interstellar medium and the clumpy nature of the star formation process in galaxies. In this introductory paper, we present several key fundamental properties of galaxies and their black holes, including the galaxy mass function, cosmic star formation rate, galactic metallicities, the Kennicutt-Schmidt relation, the stellar-to-halo mass relation, galaxy sizes, stellar kinematics and morphology, gas content within galaxies and its kinematics, and the black hole mass and spin properties over time. The various scaling relations are broadly reproduced by NewHorizon with some differences with the standard observables. Owing to its exquisite spatial resolution, NewHorizon captures the inefficient process of star formation in galaxies, which evolve over time from being more turbulent, gas rich, and star bursting at high redshift. These high-redshift galaxies are also more compact, and they are more elliptical and clumpier until the level of internal gas turbulence decays enough to allow for the formation of discs. The NewHorizon simulation gives access to a broad range of galaxy formation and evolution physics at low-to-intermediate stellar masses, which is a regime that will become accessible in the near future through surveys such as the LSST.
The high abundance of disc galaxies without a large central bulge challenges predictions of current hydrodynamic simulations of galaxy formation. We aim to shed light on the formation of these ...objects by studying the redshift and mass dependence of their intrinsic 3D shape distributions in the COSMOS galaxy survey below redshift \(z=1.0\). This distribution is inferred from the observed distribution of 2D shapes, using a reconstruction method which we test using hydrodynamic simulations. Our tests reveal a moderate bias for the inferred average disc circularity and relative thickness, but a large bias on the dispersion of these quantities. Applying the reconstruction method on COSMOS data, we find variations of the average disc circularity and relative thickness with redshift of around \(\sim1\%\) and \(\sim10\%\) respectively, which is comparable to the error estimates on these quantities. The average relative disc thickness shows a significant mass dependence which can be accounted for by the scaling of disc radius with galaxy mass. We conclude that our data provides no evidence for a strong dependence of the average circularity and absolute thickness of disc-dominated galaxies on redshift and mass that is significant with respect to the statistical uncertainties in our analysis. These findings are expected in the absence of disruptive merging or feedback events that would affect galaxy shapes. They hence support a scenario where present-day discs form early (\(z>1.0\)) and subsequently undergo a tranquil evolution in isolation. However, more data and a better understanding of systematics are needed to reaffirm our results.
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.
We use the SPHINX suite of high-resolution cosmological radiation hydrodynamics simulations to study how spatially and temporally inhomogeneous reionization impacts the baryonic content of dwarf ...galaxies and cosmic filaments. The SPHINX simulations simultaneously model an inhomogeneous reionization, follow the escape of ionising radiation from thousands of galaxies, and resolve haloes well below the atomic cooling threshold. This makes them an ideal tool for examining how reionization impacts star formation and the gas content of dwarf galaxies. We compare simulations with and without stellar radiation to isolate the effects of radiation feedback from that of supernova, cosmic expansion, and numerical resolution. We find that the gas content of cosmic filaments can be reduced by more than 80% following reionization. The gas inflow rates into haloes with \(M_{vir}<10^8M_{\odot}\) are strongly affected and are reduced by more than an order of magnitude compared to the simulation without reionization. A significant increase in gas outflow rates is found for halo masses \(M_{vir}<7\times10^7M_{\odot}\). Our simulations show that inflow suppression, rather than photoevaporation, is the dominant mechanism by which the baryonic content of high-redshift dwarf galaxies is regulated. At fixed redshift and halo mass, there is a large scatter in the halo baryon fractions that is entirely dictated by the timing of reionization in the local region surrounding a halo which can change by \(\Delta z>3\) at fixed mass. Finally, although the gas content of high-redshift dwarf galaxies is significantly impacted by reionization, we find that most haloes with \(M_{vir}<10^8M_{\odot}\) can remain self-shielded and form stars long after reionization, until their local gas reservoir is depleted, suggesting that local group dwarf galaxies do not necessarily exhibit star formation histories that peak prior to \(z=6\)...
