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The circumgalactic medium (CGM) contains information on the cumulative effect of galactic outflows over time, generally thought to be caused by feedback from star formation and active galactic nuclei. Observations of such outflows via absorption in CGM gas of quasar sightlines show a significant amount of cold ($\lesssim 10^4 \; \rm{K}$) gas which cosmological simulations struggle to reproduce. Here, we use the adaptive mesh refinement hydrodynamical code RAMSES to investigate the effect of cosmic rays (CR) on the cold gas content of the CGM using three zoom realizations of a $z=1$ star-forming galaxy with supernova mechanical feedback: one with no CR feedback (referred to as no-CR), one with a medium CR diffusion coefficient $\kappa = 10^{28} \; \rm{cm^{2}\; s^{-1}}$ (CR$-\kappa_{\rm med}$), and one with a high rate of diffusion of $\kappa = 3\times10^{29} \; \rm{cm^{2}\; s^{-1}}$ (CR$-\kappa_{\rm high}$). We find that, for CR$-\kappa_{\rm med}$, the effects of CRs are largely confined to the galaxy itself as CRs do not extend far into the CGM. However, for CR$-\kappa_{\rm high}$, the CGM temperature is lowered and the amount of outflowing gas is boosted. Our CR simulations fall short of the observed Mg II covering fraction, a tracer of gas at temperatures $\lesssim 10^4 \; \rm{K}$, but the CR$-\kappa_{\rm high}$ simulation is more in agreement with covering fractions of C IV and O VI, which trace higher temperature gas., Comment: Accepted to MNRAS. 14 pages, 10 figures

We have analysed two cosmological zoom simulations with $M_{\rm vir}\sim 10^{12}{\rm\,M}_\odot$ from the NIHAO series, both with and without feedback. We show that an entropy criterion based on the equation of state of the intergalactic medium can successfully separate cold- and hot-mode accretion. The shock-heated gas has non-negligible turbulent support and cools inefficiently. In the simulations without feedback, only a small fraction ($\sim 20$ per cent) of the stellar mass comes from baryons that have been in the hot circumgalactic medium, although quantitative conclusions should be taken with caution due to our small-number statistics. With feedback, the fraction is larger because of the reaccretion of gas heated by supernovae, which has lower entropies and shorter cooling times than the gas heated by accretion shocks. We have compared the results of NIHAO to predictions of the GalICS 2.1 semianalytic model of galaxy formation. The shock-stability criterion implemented in GalICS 2.1 successfully reproduces the transition from cold- to hot-mode accretion., Comment: 23 pages, 16 figures, Accepted for publication in MNRAS

The unprecedented amount and the excellent quality of lensing data that the upcoming ground- and space-based surveys will produce represent a great opportunity to shed light on the questions that still remain unanswered concerning our universe and the validity of the standard $\Lambda$CDM cosmological model. Therefore, it is important to develop new techniques that can exploit the huge quantity of data that future observations will give us access to in the most effective way possible. For this reason, we decided to investigate the development of a new method to treat weak lensing higher order statistics, which are known to break degeneracy among cosmological parameters thanks to their capability of probing the non-Gaussian properties of the shear field. In particular, the proposed method directly applies to the observed quantity, i.e., the noisy galaxy ellipticity. We produced simulated lensing maps with different sets of cosmological parameters and used them to measure higher order moments, Minkowski functionals, Betti numbers, and other statistics related to graph theory. This allowed us to construct datasets with different size, precision, and smoothing. We then applied several machine learning algorithms to determine which method best predicts the actual cosmological parameters associated with each simulation. The best model resulted to be simple multidimensional linear regression. We used this model to compare the results coming from the different datasets and found out that we can measure with good accuracy the majority of the parameters that we considered. We also investigated the relation between each higher order estimator and the different cosmological parameters for several signal-to-noise thresholds and redshifts bins. Given the promising results, we consider this approach as a valuable resource, worth of further development.

Dekel & Birnboim06 proposed that the mass-scale that separates late-type and early-type galaxies is linked to the critical halo mass for the propagation of a stable shock and showed that they could reproduce the observed bimodality scale for plausible values of the metallicity of the accreted gas and the shock radius. Here, we take their analysis one step further and present a new semianalytic model that computes the shock radius from first principles. This advancement allows us to compute the critical mass individually for each halo. Separating cold-mode and hot-mode accretion has little effect on the final galaxy masses if feedback does not preferentially couple to the hot gas. We also present an improved model for stellar feedback where 70% of the wind mass is in a cold galactic fountain with a shorter reaccretion timescale at high masses. The latter is the key mechanism that allows us to reproduce the low-mass end of the mass function of galaxies over the entire redshift range 0

We have used the NIHAO simulations to explore how supernovae (SNe) affect star formation in galaxies. We find that SN feedback operates on all scales from the interstellar medium (ISM) to several virial radii. SNe regulate star formation by preventing condensation of HI into H$_2$ and by moving cold neutral gas to the hot HII phase. The first effect explains why the cold neutral gas in dwarf galaxies forms stars inefficiently. The second maintains the hot ISM of massive galaxies (HII vents out at lower masses). At $v_{\rm vir}\simeq 67{\rm\,km\,s}^{-1}$, the outflow rate follows the relation: $\dot{M}_{\rm out}=23\,(v_{\rm vir}/67{\rm\,km\,s}^{-1})^{-4.6}\,{\rm SFR}$. $20\%$ to $70\%$ of the gas expelled from galaxies escapes from the halo (ejective feedback) but outflows are dominated by cold swept-up gas, most of which falls back onto the galaxy on a $\sim 1\,$Gyr timescale. This `fountain feedback' reduces the masses of galaxies by a factor of two to four, since gas spends half to three quarter of its time in the fountain. Less than $10\%$ of the ejected gas mixes with the hot circumgalactic medium and this gas is usually not reaccreted. On scales as large as $6r_{\rm vir}$, galactic winds divert the incoming gas from cosmic filaments and prevent if from accreting onto galaxies (pre-emptive feedback). This process is the main reason for the low baryon content of ultradwarves., Comment: Submitted for publication in MNRAS

We present a comparison of nine galaxy formation models, eight semi-analytical and one halo occupation distribution model, run on the same underlying cold dark matter simulation (cosmological box of co-moving width 125$h^{-1}$ Mpc, with a dark-matter particle mass of $1.24\times 10^9 h^{-1}$ Msun) and the same merger trees. While their free parameters have been calibrated to the same observational data sets using two approaches, they nevertheless retain some 'memory' of any previous calibration that served as the starting point (especially for the manually-tuned models). For the first calibration, models reproduce the observed z = 0 galaxy stellar mass function (SMF) within 3-{\sigma}. The second calibration extended the observational data to include the z = 2 SMF alongside the z~0 star formation rate function, cold gas mass and the black hole-bulge mass relation. Encapsulating the observed evolution of the SMF from z = 2 to z = 0 is found to be very hard within the context of the physics currently included in the models. We finally use our calibrated models to study the evolution of the stellar-to-halo mass (SHM) ratio. For all models we find that the peak value of the SHM relation decreases with redshift. However, the trends seen for the evolution of the peak position as well as the mean scatter in the SHM relation are rather weak and strongly model dependent. Both the calibration data sets and model results are publicly available., Comment: 20 pages, 14 figures (+5 supplementary figures in the Appendix), accepted for publication in MNRAS

We estimate the stellar mass that satellite galaxies lose once they enter groups (and clusters) by identifying groups in a high-resolution cosmological N-body simulation, assigning entry masses to satellite galaxies with halo abundance matching at the entry time, and comparing the predicted conditional stellar mass function of satellite galaxies at $z\simeq0$ with observations. Our results depend on the mass of the stars that form in satellite galaxies after the entry time. A model in which star formation shuts down completely as soon a galaxy enters a group environment is ruled out because it underpredicts the stellar masses of satellite galaxies even in the absence of tidal stripping. The greater is the stellar mass that is allowed to form, the greater the fraction that needs to be tidally stripped. The stellar mass fraction lost by satellite galaxies after entering a group or cluster environment is consistent with any value in the range $0-40\%$. To place stronger constraints, we consider a more refined model of tidal stripping of galaxies on elongated orbits (where stripping occurs at orbit pericentres). Our model predicts less tidal stripping: satellite galaxies lose $\sim 20-25\%$ of their stellar mass since their entry into the group. This finding is consistent with a slow-starvation delayed-quenching picture, in which galaxies that enter a group or cluster environment keep forming stars until at least the first pericentric passage., Comment: Accepted for publication in MNRAS. 27 pages, 22 figures

We present a clustering comparison of 12 galaxy formation models (including Semi-Analytic Models (SAMs) and Halo Occupation Distribution (HOD) models) all run on halo catalogues and merger trees extracted from a single {\Lambda}CDM N-body simulation. We compare the results of the measurements of the mean halo occupation numbers, the radial distribution of galaxies in haloes and the 2-Point Correlation Functions (2PCF). We also study the implications of the different treatments of orphan (galaxies not assigned to any dark matter subhalo) and non-orphan galaxies in these measurements. Our main result is that the galaxy formation models generally agree in their clustering predictions but they disagree significantly between HOD and SAMs for the orphan satellites. Although there is a very good agreement between the models on the 2PCF of central galaxies, the scatter between the models when orphan satellites are included can be larger than a factor of 2 for scales smaller than 1 Mpc/h. We also show that galaxy formation models that do not include orphan satellite galaxies have a significantly lower 2PCF on small scales, consistent with previous studies. Finally, we show that the 2PCF of orphan satellites is remarkably different between SAMs and HOD models. Orphan satellites in SAMs present a higher clustering than in HOD models because they tend to occupy more massive haloes. We conclude that orphan satellites have an important role on galaxy clustering and they are the main cause of the differences in the clustering between HOD models and SAMs., Comment: 17 pages, 7 figures

We use the NIHAO simulations to investigate the effects of baryonic physics on the time evolution of Dark Matter central density profiles. The sample is made of $\approx 70$ independent high resolution hydrodynamical simulations of galaxy formation and covers a wide mass range: 1e10< Mhalo <1e12, i.e., from dwarfs to L* . We confirm previous results on the dependence of the inner dark matter density slope, $\alpha$, on the ratio between stellar-to-halo mass. We show that this relation holds approximately at all redshifts (with an intrinsic scatter of ~0.18 in $\alpha$). This implies that in practically all haloes the shape of their inner density profile changes quite substantially over cosmic time, as they grow in stellar and total mass. Thus, depending on their final stellar-to-halo mass ratio, haloes can either form and keep a substantial density core (size~1 kpc), or form and then destroy the core and re-contract the halo, going back to a cuspy profile, which is even steeper than CDM predictions for massive galaxies (~1e12 Msun). We show that results from the NIHAO suite are in good agreement with recent observational measurements of $\alpha$ in dwarf galaxies. Overall our results suggest that the notion of a universal density profile for dark matter haloes is no longer valid in the presence of galaxy formation., Comment: 11 pages, 13 figures. Corrected typo in table 2 (middle row) with respect to the version published in MNRAS