Tracing the general structure of Galactic molecular clouds using Planck data: I. The Perseus region as a test case

We present an analysis of probability distribution functions (pdfs) of column density in different zones of the star-forming region Perseus and its diffuse environment based on the map of dust opacity at 353 GHz available from the Planck archive. The pdf shape can be fitted by a combination of a lognormal function and an extended power-law tail at high densities, in zones centred at the molecular cloud Perseus. A linear combination of several lognormals fits very well the pdf in rings surrounding the cloud or in zones of its diffuse neighbourhood. The slope of the mean density scaling law $\langle\rho\rangle_L \propto L^\alpha$ is steep ($\alpha=-1.93$) in the former case and rather shallow ($\alpha=-0.77\pm0.11$) in the rings delineated around the cloud. We interpret these findings as signatures of two distinct physical regimes: i) a gravoturbulent one which is characterized by nearly linear scaling of mass and practical lack of velocity scaling; and ii) a predominantly turbulent one which is best described by steep velocity scaling and by invariant for compressible turbulence $\langle\rho\rangle_L u_L^3/L$, describing a scale-independent flux of the kinetic energy per unit volume through turbulent cascade. The gravoturbulent spatial domain can be identified with the molecular cloud Perseus while a relatively sharp transition to predominantly turbulent regime occurs in its vicinity.Comment: Accepted for publication in MNRAS; 16 pages with Appendix, 15 figure

Distribution of Damped Lyman-alpha Absorbers in a Lambda Cold Dark Matter Universe

We present the results of a numerical study of a galactic wind model and its implications on the properties of damped Lyman-alpha absorbers (DLAs) using cosmological hydrodynamic simulations. We vary both the wind strength and the internal parameters of the the wind model in a series of cosmological SPH simulations that include radiative cooling and heating by a UV background, star formation, and feedback from supernovae and galactic winds. To test our simulations, we examine the DLA `rate-of-incidence' as a function of halo mass, galaxy apparent magnitude, and impact parameter. We find that the statistical distribution of DLAs does not depend on the exact values of internal numerical parameters that control the decoupling of hydrodynamic forces when the gas is ejected from starforming regions. The DLA rate-of-incidence in our simulations at z=3 is dominated by the faint galaxies with apparent magnitude R_AB < 25.5. However, interestingly in a `strong wind' run, the differential distribution of DLA sight-lines is peaked at Mhalo = 10^{12} Msun/h (R_AB~27), and the mean DLA halo mass is Mmean=10^{12.4} Msun/h (R_AB ~ 26). These mass-scales are much larger than those if we ignore winds, because galactic wind feedback suppresses the DLA cross section in low-mass halos and increases the relative contribution to the DLA incidence from more massive halos. The DLAs in our simulations are more compact than the present-day disk galaxies, and the impact parameter distribution is very narrow unless we limit the search for the host galaxy to only bright LBGs. The comoving number density of DLAs is higher than that of LBGs down to R_AB=30 mag if the physical radius of each DLA is smaller than 5 kpc/h_70. We discuss conflicts between current simulations and observations, and potential problems with simulations based on the CDM model.Comment: 37 pages, 11 figures. Accepted to ApJ. Additional numerical tests of the internal parameters of the galactic wind model are presente

Strong Evolution in the Luminosity-Velocity Relation at z>1?

We present a method for constraining the evolution of the galaxy luminosity-velocity (LV) relation in hierarchical scenarios of structure formation. The comoving number density of dark-matter halos with circular velocity of 200 km/s is predicted in favored CDM cosmologies to be nearly constant over the redshift range 0<z<5. Any observed evolution in the density of bright galaxies implies in turn a corresponding evolution in the LV relation. We consider several possible forms of evolution for the zero-point of the LV relation and predict the corresponding evolution in galaxy number density. The Hubble Deep Field suggests a large deficit of bright (M_V < -19) galaxies at 1.4 < z < 2. If taken at face value, this implies a dimming of the LV zero-point by roughly 2 magnitudes. Deep, wide-field, near-IR selected surveys will provide more secure measurements to compare with our predictions.Comment: 4 pages, 2 figures. Submitted to ApJ Letter

Dichotomy in host environments and signs of recycled AGN

We analyse the relation between AGN host properties and large scale environment for a representative red and blue AGN host galaxy sample selected from the DR4 SDSS. A comparison is made with two carefully constructed control samples of non-active galaxies, covering the same redshift range and color baseline. The cross-correlation functions show that the density distribution of neighbours is almost identical for blue galaxies, either active, or non-active. Although active red galaxies inhabit environments less dense compared to non-active red galaxies, both reside in environments considerably denser than those of blue hosts. Moreover, the radial density profile of AGN, relative to galaxy group centres is less concentrated than galaxies. This is particularly evident when comparing red AGN and non-active galaxies. The properties of the neighbouring galaxies of blue and red AGN and non active galaxies reflect this effect. While the neighbourhood of the blue samples is indistinguishable, the red AGN environs show an excess of blue-star forming galaxies with respect to their non-active counterpart. On the other hand, the active and non-active blue systems have similar environments but markedly different morphological distributions, showing an excess of blue early-type AGN, which are argued to be late stage mergers. This comparison reveals that the observable differences between active red and blue host galaxy properties including star formation history and AGN activity depends on the environment within which the galaxies form and evolve.Comment: 11 pages, 10 figures. Accepted for publication in MNRA

Modeling Luminosity-Dependent Galaxy Clustering Through Cosmic Time

We employ high-resolution dissipationless simulations of the concordance LCDM cosmology to model the observed luminosity dependence and evolution of galaxy clustering through most of the age of the universe, from z~5 to z~0. We use a simple, non-parametric model which monotonically relates galaxy luminosities to the maximum circular velocity of dark matter halos (V_max) by preserving the observed galaxy luminosity function in order to match the halos in simulations with observed galaxies. The novel feature of the model is the use of the maximum circular velocity at the time of accretion, V_max,acc, for subhalos, the halos located within virial regions of larger halos. We argue that for subhalos in dissipationless simulations, V_max,acc reflects the luminosity and stellar mass of the associated galaxies better than the circular velocity at the epoch of observation, V_max,now. The simulations and our model L-V_max relation predict the shape, amplitude, and luminosity dependence of the two-point correlation function in excellent agreement with the observed galaxy clustering in the SDSS data at z~0 and in the DEEP2 samples at z~1 over the entire probed range of projected separations, 0.1<r_p/(Mpc/h)<10.0. In particular, the small-scale upturn of the correlation function from the power-law form in the SDSS and DEEP2 luminosity-selected samples is reproduced very well. At z~3-5, our predictions also match the observed shape and amplitude of the angular two-point correlation function of Lyman-break galaxies (LBGs) on both large and small scales, including the small-scale upturn.Comment: 16 pages 11 figures, ApJ in pres

An Isocurvature CDM Cosmogony. II. Observational Tests

A companion paper presents a worked model for evolution through inflation to initial conditions for an isocurvature model for structure formation. It is shown here that the model is consistent with the available observational constraints that can be applied without the help of numerical simulations. The model gives an acceptable fit to the second moments of the angular fluctuations in the thermal background radiation and the second through fourth moments of the measured large-scale fluctuations in galaxy counts, within the possibly significant uncertainties in these measurements. The cluster mass function requires a rather low but observationally acceptable mass density, 0.1\lsim\Omega\lsim 0.2 in a cosmologically flat universe. Galaxies would be assembled earlier in this model than in the adiabatic version, an arguably good thing. Aspects of the predicted non-Gaussian character of the anisotropy of the thermal background radiation in this model are discussed.Comment: 14 pages, 3 postscript figures, uses aas2pp4.st

Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution

The determination of the dynamical causes of the morphological Butcher-Oemler (BO) effect, or the rapid transformation of a large population of late-type galaxies to earlier Hubble types in the rich cluster environment between intermediate redshifts and the local universe, has been an important unsolved problem which is central to our understanding of the general problems of galaxy formation and evolution. In this article, we survey the existing proposed mechanisms for cluster galaxy transformation, and discuss their relevance and limitations to the explanation of the morphological BO effect. A new infrared diagnostic approach is devised to disentangle the relative importance of several major physical mechanisms to account for the BO effect, and an example of the first application of this procedure to a single rich, intermediate redshift galaxy cluster is given to demonstrate the viability of this approach. The preliminary result of this analysis favors the interaction-enhanced secular evolution process as the major cause of the cluster-galaxy morphological transformation. This conclusion is also supported by a wide range of other published results which are assembled here to highlight their implications on a coherent physical origin for the morphological BO effect.Comment: Accepted for publication in the PAS

Simulating the Formation of the Local Galaxy Population

We simulate the formation and evolution of the local galaxy population starting from initial conditions with a smoothed linear density field which matches that derived from the IRAS 1.2 Jy galaxy survey. Our simulations track the formation and evolution of all dark matter haloes more massive than 10e+11 solar masses out to a distance of 8000 km/s from the Milky Way. We implement prescriptions similar to those of Kauffmann et al. (1999) to follow the assembly and evolution of the galaxies within these haloes. We focus on two variants of the CDM cosmology: an LCDM and a tCDM model. Galaxy formation in each is adjusted to reproduce the I-band Tully-Fisher relation of Giovanelli et al. (1997). We compare the present-day luminosity functions, colours, morphology and spatial distribution of our simulated galaxies with those of the real local population, in particular with the Updated Zwicky Catalog, with the IRAS PSCz redshift survey, and with individual local clusters such as Coma, Virgo and Perseus. We also use the simulations to study the clustering bias between the dark matter and galaxies of differing type. Although some significant discrepancies remain, our simulations recover the observed intrinsic properties and the observed spatial distribution of local galaxies reasonably well. They can thus be used to calibrate methods which use the observed local galaxy population to estimate the cosmic density parameter or to draw conclusions about the mechanisms of galaxy formation. To facilitate such work, we publically release our z=0 galaxy catalogues, together with the underlying mass distribution.Comment: 25 pages, 20 figures, submitted to MNRAS. High resolution copies of figures 1 and 3, halo and galaxy catalogues can be found at http://www.mpa-garching.mpg.de/NumCos/CR/index.htm

Physical Bias of Galaxies From Large-Scale Hydrodynamic Simulations

We analyze a new large-scale ($100h^{-1}$Mpc) numerical hydrodynamic simulation of the popular $\Lambda$CDM cosmological model, including in our treatment dark matter, gas and star-formation, on the basis of standard physical processes. The method, applied with a numerical resolution of $<200h^{-1}$kpc (which is still quite coarse for following individual galaxies, especially in dense regions), attempts to estimate where and when galaxies form. We then compare the smoothed galaxy distribution with the smoothed mass distribution to determine the "bias" defined as $b\equiv (\delta M/M)_{gal}/(\delta M/M)_{total}$ on scales large compared with the code numerical resolution (on the basis of resolution tests given in the appendix of this paper). We find that (holding all variables constant except the quoted one) bias increases with decreasing scale, with increasing galactic age or metallicity and with increasing redshift of observations. At the $8h^{-1}$Mpc fiducial comoving scale bias (for bright regions) is 1.35 at $z=0$ reaching to 3.6 at $z=3$, both numbers being consistent with extant observations. We also find that $(10-20)h^{-1}$Mpc voids in the distribution of luminous objects are as observed (i.e., observed voids are not an argument against CDM-like models) and finally that the younger systems should show a colder Hubble flow than do the early type galaxies (a testable proposition). Surprisingly, little evolution is found in the amplitude of the smoothed galaxy-galaxy correlation function (as a function of {\it comoving} separation). Testing this prediction vs observations will allow a comparison between this work and that of Kauffmann et al which is based on a different physical modelingmethod.Comment: in press, ApJ, 26 latex pages plus 7 fig

Quasar Evolution Driven by Galaxy Encounters in Hierarchical Structures

We link the evolution of the galaxies in the hierarchical clustering scenario with the changing accretion rates of cold gas onto the central massive black holes that power the quasars. We base on galaxy interactions as main triggers of accretion; the related scaling laws are taken up from Cavaliere & Vittorini (2000), and grafted to a semi-analytic code for galaxy formation. As a result, at high $z$ the protogalaxies grow rapidly by hierarchical merging; meanwhile, much fresh gas is imported and also destabilized, so the holes are fueled at their full Eddington rates. At lower $z$ the galactic dynamical events are mostly encounters in hierarchically growing groups; now the refueling peters out, as the residual gas is exhausted while the destabilizing encounters dwindle. So, with no parameter tuning other than needed for stellar observables, our model uniquely produces at $z>3$ a rise, and at $z\lesssim 2.5$ a decline of the bright quasar population as steep as observed. In addition, our results closely fit the observed luminosity functions of quasars, their space density at different magnitudes from $z\approx 5$ to $z\approx 0$, and the local $m_{BH}-\sigma$ relation.Comment: 5 pages. Accepted for publication in ApJ Letter