Understanding how galaxy properties are linked to the dark matter halos they reside in, and how they co-evolve is a powerful tool to constrain the processes related to galaxy formation. The stellar-to-halo mass relation (SHMR) and its evolution over the history of the Universe provides insights on galaxy formation models and allows to assign galaxy masses to halos in N-body dark matter simulations. We use a statistical approach to link the observed galaxy stellar mass functions on the COSMOS field to dark matter halo mass functions from the DUSTGRAIN simulation and from a theoretical parametrization from z=0 to z=4. We also propose an empirical model to describe the evolution of the stellar-to-halo mass relation as a function of redshift. We calculate the star-formation efficiency (SFE) of galaxies and compare results with previous works and semi-analytical models.
The neutral hydrogen (HI) content of dark matter haloes forms an intermediate state in the baryon cycle that connects the hot shock-heated gas and cold star-forming gas in haloes. Measurement of the relationship between HI mass and halo mass therefore puts important constraints on galaxy formation models. We combine radio observations of HI in emission at low redshift ($z\sim 0$) with optical/UV observations of HI in absorption at high redshift ($1<z<4$) to derive constraints on the evolution of the HI-mass halo-mass (HIHM) relation from redshift $z=4$ to $z=0$. We find that one can model the …
NGC 5128 (Centaurus A) is, at the distance of just 3.8 Mpc, the nearest easily observable giant elliptical galaxy. Therefore it is the best target to investigate the early star formation history of an elliptical galaxy. Our aims are to establish when the oldest stars formed in NGC 5128, and whether this galaxy formed stars over a long period. We compare simulated colour-magnitude diagrams with the deep ACS/HST photometry. We find that that the observed colour-magnitude diagram can be reproduced satisfactorily only by simulations that have the bulk of the stars with ages in excess of ~10 Gyr, a…
Star streams in galactic halos are long, thin, unbound structures that will be disturbed by the thousands dark matter sub-halos that are predicted to be orbiting within the main halo. A sub-halo generally induces a localized wave in the stream which often evolves into a "z-fold" as an initially trailing innermost part rotates faster than an initially leading outermost part. The folding, which becomes increasingly complex with time, leads to an apparent velocity dispersion increase and thickening of the stream. We measure the equivalent velocity dispersion around the local mean in the simulatio…
We present constraints on the timescale of star formation variability and the correlation between star formation and host halo accretion histories of star-forming (SF) central galaxies from the scatter of the stellar-to-halo mass relation (SHMR). SF galaxies are found to have a tight relationship between their star formation rates and stellar masses on the so-called "star-forming sequence" (SFS), which characterizes their SF histories and $M_*$ growths. Meanwhile, observed SHMR constraints connect $M_*$ growth to halo accretion history. Combining these observed trends with a cosmological $N$-b…
We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Ly-alpha absorbers (DLAs) at low redshift (z < 1.6). Our statistical sample includes 463 quasars with spectral coverage spanning a total redshift path, dz = 123.3 or an absorption path, dX = 229.7. Within this survey path, we identify 4 DLAs, defined as absorbers with HI column density N(HI) >= 10^20.3cm-2, which implies an incidence per absorption length, l(X)= 0.017(+0.014-0.008) at a median survey path redshift of z=0.623. While our estimate of l(X) is lower t…
Dark matter sub-halos create gaps in the stellar streams orbiting in the halos of galaxies. We evaluate the sub-halo stream crossing integral with the guidance of simulations to find that the linear rate of gap creation, R_gap, in a typical Cold Dark Matter (CDM) galactic halo at 100 kpc is R_gap = 0.0066 M_8^-0.35 kpc^-1 Gyr^-1$, where M_8 = M/10^8 M_sun, is the minimum mass halo that creates a visible gap. The relation can be recast entirely in terms of observables, as R_gap= 0.059 w^-0.85 kpc^-1 Gyr^-1, for w in kpc, normalized at 100 kpc. Using published data, the density of gaps is estima…
We investigate the population of dwarf galaxies with stellar masses similar to the Large Magellanic Cloud (LMC) and M33 in the EAGLE galaxy formation simulation. In the field, galaxies reside in haloes with stellar-to-halo mass ratios of $1.03^{+0.50}_{-0.31}\times10^{-2}$ (68% confidence level); systems like the LMC, which have an SMC-mass satellite, reside in haloes about 1.3 times more massive, which suggests an LMC halo mass at infall, $M_{200}=3.4^{+1.8}_{-1.2}\times10^{11}M_\odot$ (68% confidence level). The colour distribution of dwarfs is bimodal, with the red galaxies ($g-r>0.6$) bein…
Scaling relations are salient ingredients of galaxy evolution and formation models. I summarize results from the IMAGES survey, which combines spatially-resolved kinematics from FLAMES/GIRAFFE with imaging from HST/ACS and other facilities. Specifically, I will focus on the evolution of the stellar mass and baryonic Tully-Fisher Relations (TFR) from z=0.6 down to z=0. We found a significant evolution in zero point and scatter of the stellar mass TFR compared to the local Universe. Combined with gas fractions derived by inverting the Schmidt-Kennicutt relation, we derived for the first time a b…
We present direct observational evidence for star formation quenching in galaxy groups in the redshift range 0<z<2.5. We utilize a large sample of nearly 6000 groups, selected by fixed cumulative number density from three photometric catalogs, to follow the evolving quiescent fractions of central and satellite galaxies over roughly 11 Gyr. At z~0, central galaxies in our sample range in stellar mass from Milky Way/M31 analogs (M=6.5x10^10 M\solar) to nearby massive ellipticals (M=1.5x10^11 M\solar). Satellite galaxies in the same groups reach masses as low as twice that of the Large Magellanic…
The dark matter halos that surround Milky Way-like galaxies in cosmological simulations are, to first order, triaxial. Nearly 30 years ago it was predicted that such triaxial dark matter halos should exhibit steady figure rotation or tumbling motions for durations of several gigayears. The angular frequency of figure rotation predicted by cosmological simulations is described by a log-normal distribution of pattern speed with a median value 0.15hkm/s/kpc (~ 0.15h rad/Gyr ~ 9h deg/Gyr) and a width of 0.83km/s/kpc. These pattern speeds are so small that they have generally been considered both u…
Simulations of ultralight, $\sim 10^{-22}\,\rm eV$, bosonic dark matter exhibit rich wave-like structure, including a soliton core within a surrounding halo that continuously self-interferes on the de Broglie scale. We show here that as an inherent consequence, the soliton undergoes a confined random walk at the base of the halo potential. This is significant for the fate of the ancient central star cluster in Eridanus II, as the agitated soliton gravitationally shakes the star cluster in and out of the soliton on a time scale of $\sim 100\,\rm Myr$, so complete tidal disruption of the star cl…
Context: Clumpy disk galaxies in the distant universe, at redshift of z>1, have been observed to host several giant clumps in their disks. They are thought to correspond to early formative stages of disk galaxies. On the other hand, halo objects, such as old globular clusters and halo stars, are likely to consist of the oldest stars in a galaxy (age>10 Gyr), therefore the clumpy disk formation can be presumed to take place in a pre-existing halo system. Aims: Giant clumps are orbiting in the same direction in a premature disk and so massive that they may be expected to interact gravitationally…
Clusters of galaxies, being dark matter dominated, have long been and still are the ideal cosmological targets to study the nature of dark matter. Constraints on the nature of dark matter comes in particular from the observational determination of the distribution of total and baryonic mass in clusters, by comparison with results from cosmological numerical simulations. I present here past and recent results on this research topic.
We present the Synthetic UniveRses For Surveys ({\sc surfs}) simulations, a set of N-body/Hydro simulations of the concordance $Λ$ Cold Dark Matter (\LCDM) cosmology. These simulations use Planck cosmology, contain up to 10 billion particles and sample scales & halo masses down to $1~$kpc & $10^8{\rm M}_\odot$. We identify and track haloes from $z=24$ to today using a state-of-the-art 6D halo finder and merger tree builder. We demonstrate that certain properties of halo merger trees are numerically converged for haloes composed of $\gtrsim100$ particles. Haloes smoothly grow in mass, $V_{\rm m…
From various cosmological, astrophysical and terrestrial requirements, we derive conservative upper bounds on the present-day fraction of the mass of the Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark matter particles are neutral but decay lately into CHAMPs, the lack of detection of heavy hydrogen in sea water and the vertical pressure equilibrium in the Galactic disc turn out to put the most stringent bounds. Adopting very conservative assumptions about the recoiling velocity of CHAMPs in the decay and on the decay energy deposited in baryonic gas, we find that…
Present-day clusters are massive halos containing mostly quiescent galaxies, while distant protoclusters are extended structures containing numerous star-forming galaxies. We investigate the implications of this fundamental change in a cosmological context using a set of N-body simulations and semi-analytic models. We find that the fraction of the cosmic volume occupied by all (proto)clusters increases by nearly three orders of magnitude from z=0 to z=7. We show that (proto)cluster galaxies are an important, and even dominant population at high redshift, as their expected contribution to the c…
We study the properties of the stellar populations in M81's outermost part, which hereafter we will term the stellar halo, using HST ACS/WFC observations of 19 fields from the GHOSTS survey. The observed fields probe the stellar halo out to a projected distance of ~ 50 kpc from the galactic center. Each field was observed in both F606W and F814W filters. The 50% completeness levels of the color magnitude diagrams (CMDs) are typically at 2 mag below the tip of the red giant branch (TRGB). Fields at distances closer than 15 kpc show evidence of disk-dominated populations whereas fields at larger…
The most massive protoclusters virialize to become clusters at $z\sim 2$, which is also a critical epoch for the evolution of their member galaxies. XLSSC 122 is a $z=1.98$ galaxy cluster with 37 spectroscopically confirmed members. We aim to characterize their star formation histories and to put them in the context of the cluster accretion history. We measure their photometry in 12 bands and create a PSF-matched catalogue of the cluster members. We employ BAGPIPES to fit star formation histories characterized by exponentially decreasing star-forming rates. Stellar masses, metal and dust conte…
We present the Fundamental Plane (FP) of early-type galaxies in the clusters of galaxies RXJ1415.1+3612 at z=1.013. This is the first detailed FP investigation of cluster early-type galaxies at redshift z=1. The distant cluster galaxies follow a steeper FP relation compared to the local FP. The change in the slope of the FP can be interpreted as a mass-dependent evolution. To analyse in more detail the galaxy population in high redshift galaxy clusters at 0.8<z<1, we combine our sample with a previous detailed spectroscopic study of 38 early-type galaxies in two distant galaxy clusters, RXJ015…
Outskirts of large galaxies contain important information about the galaxy formation and assembly process, and resolved star count studies can probe the extremely low surface brightness of the outer halos. We use images obtained with the VISTA telescope to construct spatially resolved J vs Z-J colour-magnitude diagrams (CMDs) of NGC 253, a nearly edge-on disk galaxy in the Sculptor group. The very deep photometry, down to J ~ 23.5, and the wide area covered allows us to trace the red giant branch (RGB) and asymptotic giant branch (AGB) stars that belong to the outer disk and the halo of NGC 25…
Through numerical simulations, we study the dissolution timescale of the Ursa Minor cold stellar clump, due to the combination of phase-mixing and gravitational encounters with compact dark substructures in the halo of Ursa Minor. We compare two scenarios; one where the dark halo is made up by a smooth mass distribution of light particles and one where the halo contains 10% of its mass in the form of substructures (subhalos). In a smooth halo, the stellar clump survives for a Hubble time provided that the dark matter halo has a big core. In contrast, when the point-mass dark substructures are …
We use the galaxy stellar mass and halo merger tree information from the semi-analytic model galaxy catalogue of Font et al. (2009) to examine the accretion of galaxies into a large sample of groups and clusters, covering a wide range in halo mass (10E12.9 to 10E15.3 Msun/h), and selected from each of four redshift epochs (z=0, 0.5, 1.0 and 1.5). We find that clusters at all examined redshifts have accreted a significant fraction of their final galaxy populations through galaxy groups. A 10E14.5 Msun/h mass cluster at z=0 has, on average, accreted ~ 40% of its galaxies (Mstellar > 10E9 Msun/h)…
We present the first photometric results in J, H, and K_s from 2MASS imaging of 10 classical globular clusters in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed the color-color diagram between J-K_s and V-I. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that, all of these clusters are older than $3\times 10^9$ yrs, of which 4 are older than 10 Gyrs and the other 6 are in intermediate ages between 3-8 Gyrs. The masses for these outer halo…
Deep near-infrared images recorded with NICI on Gemini South are used to investigate the evolved stellar content in the outer regions of the south east quadrant of the spiral galaxy M83. A diffuse population of asymptotic giant branch (AGB) stars is detected outside of the previously identified young and intermediate age star clusters in the outer disk. The brightest AGB stars have M_K > -8, and the AGB luminosity function (LF) is well-matched by model LFs that assume ages < 1 Gyr. The specific star formation rate (SFR) during the past few Gyr estimated from AGB star counts is consistent with …
Galaxy clusters can play a key role in modern cosmology provided their evolution is properly understood. However, observed clusters give us only a single timeframe of their dynamical state. Therefore, finding present observable data of clusters that are well correlated to their assembly history constitutes an inestimable tool for cosmology. Former studies correlating environmental descriptors of clusters to their formation history are dominated by halo mass - environment relations. This paper presents a mass-free correlation between the present neighbor distribution of cluster-size halos and t…
Stellar bars are the most common non-axisymmetric structures in galaxies and their impact on the evolution of disc galaxies at all cosmological times can be significant. Classical theory predicts that stellar discs are stabilized against bar formation if embedded in massive spheroidal dark matter halos. However, dark matter halos have been shown to facilitate the growth of bars through resonant gravitational interaction. Still, it remains unclear why some galaxies are barred and some are not. In this study, we demonstrate that co-rotating (i.e., in the same sense as the disc rotating) dark mat…
We track the histories of massive clusters of galaxies formed within a cosmological hydrodynamic simulation. Specifically, we track the time evolution of the energy in random bulk motions of the intracluster medium and X-ray measures of cluster structure and their relationship to cluster mergers. We aim to assess the viability of the turbulent re-acceleration model for the generation of giant radio halos by comparing the level of turbulent kinetic energy in simulated clusters with the observed properties of radio halo clusters, giving particular attention to the association of radio halos to c…
Using fully self-consistent N-body models for the dynamical evolution of the Large Magellanic Cloud (LMC) in the Galaxy, we show that if the LMC initially has an extended old stellar halo before its commencement of tidal interaction with the Galaxy, physical properties of the stars stripped from the LMC stellar halo can have fossil information as to when and where the LMC was accreted onto the Galaxy for the first time. If the epoch of the first LMC accretion onto the Galaxy from outside its viriral radius is more than ~4 Gyr ago (i.e., at least two pericenter passages), the stars stripped fro…
We combine the detailed Star Formation Histories of the Fornax and Sculptor dwarf Spheroidals with the Mass Assembly History of their dark matter (DM) halo progenitors to estimate if the energy deposited by Supernova type II (SNeII) is sufficient to create a substantial DM core. Assuming the efficiency of energy injection of the SNeII into DM particles is $ε_{\rm gc}=0.05$, we find that a single early episode, $z \gtrsim z_{\rm infall}$, that combines the energy of all SNeII due to explode over 0.5 Gyr, is sufficient to create a core of several hundred parsecs in both Sculptor and Fornax. Ther…
The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. We aim to determine, for the first time, the bar pattern speed evolution with redshift based on morphological measurements. We have selected a sample of 44 low inclination ringed galaxies from the SDSS and COSMOS…
The hierarchical clustering inherent in Lambda-CDM cosmology seems to produce many of the observed characteristics of large-scale structure. But some glaring problems still remain, including the over-prediction (by a factor 10) of the number of dwarf galaxies within the virialized population of the local group. Several secondary effects have already been proposed to resolve this problem. It is still not clear, however, whether the principal solution rests with astrophysical processes, such as early feedback from supernovae, or possibly with as yet undetermined properties of the dark matter its…
