Showing papers by "Anatoly Klypin published in 2015"

Abundance of field galaxies

Abstract: We present new measurements of the abundance of galaxies with a given circular velocity in the Local Volume: a region centered on the Milky Way Galaxy and extending to distance 10Mpc. The sample of 750 mostly dwarf galaxies provides a unique opportunity to study the abundance and properties of galaxies down to absolute magnitudes MB= -10, and virial masses Mvir= 1e9Msun. We find that the standard LCDM model gives remarkably accurate estimates for the velocity function of galaxies with circular velocities V>60kms and corresponding virial masses Mvir> 3e10Msun, but it badly fails by over-predicting 5 times the abundance of large dwarfs with velocities V= 30-50kms. The Warm Dark Matter models cannot explain the data either, regardless of mass of the WDM particle. Just as in previous observational studies, we find a shallow asymptotic slope dN/dlog V = V**alpha, alpha =-1 of the velocity function, which is inconsistent with the standard LCDM model that predicts the slope alpha =-3. Though reminiscent to the known overabundance of satellites problem, the overabundance of field galaxies is a much more difficult problem. For the LCDM model to survive, in the 10Mpc radius of the Milky Way there should be 1000 dark galaxies with virial mass Mvir= 1e10Msun, extremely low surface brightness and no detectable HI gas. So far none of this type of galaxies have been discovered.

Redshift-space clustering of SDSS galaxies – luminosity dependence, halo occupation distribution, and velocity bias

Abstract: We present the measurements and modelling of the small-to-intermediate scale (� 0.1‐ 25h 1 Mpc) projected and three-dimensional (3D) redshift-space two-point correlation functions (2PCFs) of local galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7. We find a clear dependence of galaxy clustering on luminosity in both projected and redshift spaces, generally being stronger for more luminous samples. The measurements are successfully interpreted within the halo occupation distribution (HOD) framework with central and satellite velocity bias parameters to describe galaxy kine matics inside haloes and to model redshift-space distortion (RSD) effects. In agreement wit h previous studies, we find that more luminous galaxies reside in more massive haloes. Including the redshift-space 2PCFs helps tighten the HOD constraints. Moreover, we find that luminous central galaxies are not at rest at the halo centres, with the velocity dispersion about 30% that of the dark matter. Such a relative motion may reflect the consequence of galaxy and halo me rgers, and we find that central galaxies in lower mass haloes tend to be more relaxed with respect to their host haloes. The motion of satellite galaxies in luminous samples is consist ent with their following that of the dark matter. For faint samples, satellites tends to have slo wer motion, with velocity dispersion inside haloes about 85% that of the dark matter. We discuss possible applications of the velocity bias constraints on studying galaxy evolution and cosmology. In the appendix, we characterize the distribution of galaxy redshift measurement errors, which is well described by a Gaussian-convolved double exponential distribution.

nIFTy cosmology: galaxy/halo mock catalogue comparison project on clustering statistics

Abstract: We present a comparison of major methodologies of fast generating mock halo or galaxy catalogues. The comparison is done for two-point (power spectrum and two-point correlation function in real and redshift space), and the three-point clustering statistics (bispectrum and three-point correlation function). The reference catalogues are drawn from the BigMultiDark N-body simulation. Both friend-of-friends (including distinct haloes only) and spherical overdensity (including distinct haloes and subhalos) catalogues have been used with the typical number density of a large volume galaxy surveys. We demonstrate that a proper biasing model is essential for reproducing the power spectrum at quasi-linear and even smaller scales. With respect to various clustering statistics, a methodology based on perturbation theory and a realistic biasing model leads to very good agreement with N-body simulations. However, for the quadrupole of the correlation function or the power spectrum, only the method based on semi-N-body simulation could reach high accuracy (1percent level) at small scales, i.e. r 0.15hMpc −1 . Full N-body solutions will remain indispensable to produce reference catalogues. Nevertheless, we have demonstrated that the more efficient approximate solvers can reach a fewpercent accuracy in terms of clustering statistics at the scales interesting for the large-scale structure analysis. This makes them useful for massive production aimed at covariance studies, to scan large parameter spaces, and to estimate uncertainties in data analysis techniques, such as baryon acoustic oscillation reconstruction, redshift distortion measurements, etc.

Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars

Abstract: Despite recent success in forming realistic present-day galaxies, simulations still form the bulk of their stars earlier than observations indicate We investigate the process of stellar mass assembly in low-mass field galaxies, a dwarf and a typical spiral, focusing on the effects of radiation from young stellar clusters on the star formation (SF) histories We implement a novel model of SF with a deterministic low efficiency per free-fall time, as observed in molecular clouds Stellar feedback is based on observations of star-forming regions, and includes radiation pressure from massive stars, photoheating in H II regions, supernovae and stellar winds We find that stellar radiation has a strong effect on the formation of low-mass galaxies, especially at z 〉 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component This behaviour is evident in a variety of observations but had so far eluded analytical and numerical models without radiation feedback Compared to supernovae alone, radiation feedback reduces the SF rate by a factor of 100 at z ≲ 2, yielding rising SF histories which reproduce recent observations of Local Group dwarfs Stellar radiation also produces bulgeless spiral galaxies and may be responsible for excess thickening of the stellar disc The galaxies also feature rotation curves and baryon fractions in excellent agreement with current data Lastly, the dwarf galaxy shows a very slow reduction of the central dark matter density caused by radiation feedback over the last 7 Gyr of cosmic evolution

What controls the ionized gas turbulent motions in dwarf galaxies

Abstract: Using 3D spectroscopy with a scanning Fabry-Perot interferometer, we study the ionized gas kinematics in 59 nearby dwarf galaxies. Combining our results with data from literature, we provide a global relation between the gas velocity dispersion (sigma) and the star formation rate (SFR) and H\alpha luminosity for galaxies in a very broad range of star formation rates SFR=0.001-300 Msun/yr. We find that the SFR-sigma relation for the combined sample of dwarf galaxies, star forming, local luminous, and ultra-luminous infrared galaxies can be fitted as sigma~ SFR^(5.3+-0.2). This implies that the slope of the L-sigma relation inferred from the sample of rotation supported disc galaxies (including mergers) is similar to the L-sigma relation of individual giant HII regions. We present arguments that the velocity dispersion of the ionized gas does not reflect the virial motions in the gravitational potential of dwarf galaxies, and instead is mainly determined by the energy injected into the interstellar medium by the ongoing star formation.

Direct Insights Into Observational Absorption Line Analysis Methods of the Circumgalactic Medium Using Cosmological Simulations

Abstract: We study the circumgalactic medium (CGM) of a z = 0.54 simulated dwarf galaxy using hydroART simulations. We present our analysis methods, which emulate observations, including objective absorption line detection, apparent optical depth (AOD) measurements, Voigt profile (VP) decomposition, and ionization modeling. By comparing the inferred CGM gas properties from the absorption lines directly to the gas selected by low ionization H i and Mg ii, and by higher ionization C iv and O vi absorption, we examine how well observational analysis methods recover the “true” properties of CGM gas. In this dwarf galaxy, low ionization gas arises in sub-kiloparsec “cloud” structures, but high ionization gas arises in multiple extended structures spread over 100 kpc; due to complex velocity fields, highly separated structures give rise to absorption at similar velocities. We show that AOD and VP analysis fails to accurately characterize the spatial, kinematic, and thermal conditions of high ionization gas. We find that H i absorption selected gas and O vi absorption gas arise in totally distinct physical gas structures, calling into question current observational techniques employed to infer metallicities and the total mass of “warm-hot” CGM gas. We present a method to determine whether C iv and O vi absorbing gas is photo or collisionally ionized and whether the assumption of ionization equilibrium is sound. As we discuss, these and additional findings have strong implications for how accurately currently employed observational absorption line methods recover the true gas properties, and ultimately, our ability to understand the CGM and its role in galaxy evolution.