astro-ph/0412257

Authors: Manuel Merchan Ariel Zandivarez

• Comments: 4 pages, 3 figures, Submitted to ApJ. Files containing galaxy groups data can be fount at this http URLWe present a new sample of galaxy groups identified in the Sloan Digital Sky Survey Data Release 3. Following previous works we use the well tested friend-of-friend algorithm developed by Huchra & Geller which take into account the number density variation due to the apparent magnitude limit of the galaxy catalog. To improve the identification we implement a procedure to avoid the artificial merging of small systems in high density regions and then apply an iterative method to recompute the group centers position. As a result we obtain a new catalog with 10864 galaxy groups with at least four members. The final group sample has a mean redshift of 0.1 and a median velocity dispersion of $230 km s^{-1}$. Full-text: PostScript, PDF, or Other formats

astro-ph/0412254 Thermodynamic evolution of the cosmological baryonic gas : II. Galaxy

formationAuthors: J.-M. Alimi (1), S. Courty (1,2) ((1)

LUTh/Observatoire de Paris-Meudon, France, (2) University of Iceland)

• Comments: 17 pages, 19 figures, 6 tables. Accepted for publication in A&AThe problem of galaxy formation and its dependence on thermodynamic properties is addressed by using Eulerian hydrodynamic numerical simulations of large scale structure formation. Global galaxy properties are explored in simulations including gravitation, shock heating and cooling processes, and following self-consistently the chemical evolution of a primordial composition hydrogen-helium plasma without assuming

collisional ionization equilibrium. The galaxy formation model is mainly based on the identification of converging dense cold gas regions.

• We show that the evolution at low redshift of the observed cosmic star formation rate density is reproduced, and that the galaxy-like object mass function is dominated by low-mass objects. The galaxy mass functions are well described by a two power-law Schechter function whose parameters are in good agreement with observational fits of the galaxy luminosity function. The high-mass end of the galaxy mass function includes objects formed at early epochs and residing in high-mass dark matter halos whereas the low-mass end includes galaxies formed at later epochs and active in their ``stellar'' mass formation. Finally, the influence of two other physical processes, photoionization and non-equipartition processes between electrons, ions and neutrals of the cosmological plasma is discussed and the modifications on galaxy formation are examined.

astro-ph/0412256 The Evolution of Field Spiral Galaxies over the

Past 8 GyrAuthors: Asmus Boehm, Bodo L. Ziegler

• The Evolution of Field Spiral Galaxies over the Past 8 Gyr• Authors: Asmus Boehm, Bodo L. Ziegler

Comments: 20 pages, 9 figures. To appear in "Reviews in Modern Astronomy", Vol. 18, S. Roeser (Ed.), Astronomische Gesellschaft 2004, ("highlight talk")We have performed a large observing campaign of intermediate-redshift disk galaxies including spectroscopy with the FORS instruments of the VLT and imaging with the Advanced Camera for Surveys onboard the HST. Our data set comprises 113 late-type galaxies in the redshift range 0.1<z<1.0 and thereby probes galaxy evolution over more than half the age of the universe. Spatially resolved rotation curves have been extracted and fitted with synthetic velocity fields that account for geometric distortions and blurring effects. With these models, the intrinsic maximum rotation velocity Vmax was derived for 73 spirals. By comparing our sample to the Tully-Fisher Relation of local spiral galaxies, we find evidence for a differential luminosity evolution: the massive distant galaxies are of comparable luminosity as their present-day counterparts, while the distant low-mass spirals are brighter than locally by up to >2mag in rest-frame B. This evolution would be at variance with the predictions from numerical simulations. On the other hand, the disks of the distant galaxies are, for a given Vmax, slightly smaller than those of their local counterparts, as expected for a hierarchical structure growth. Hence, the discrepancy between the observations and theoretical predictions would be limited to the properties of the stellar populations. A possible explanation could be the suppression of star formation in low-mass disks which is not yet properly implemented in models of galaxy evolution. (abridged)

astro-ph/0412250 Kinematic and chemical evolution

of early-type galaxiesAuthors: B. L. Ziegler (1), D. Thomas (2), A. Boehm (1),

R. Bender (2 and 3), A. Fritz (1), C. Maraston (2) ((1) Goettingen, (2) MPE Munich/Garching, (3) Sternwarte Munich)

• Comments: A&A acc., 17p., 7 colour figures, comments/discussion welcome! full resolution version available from this http URL

We investigate in detail 13 early-type field galaxies with 0.2<z<0.7 drawn from the FORS Deep Field. Since the majority (9 galaxies) is at z~0.4, we compare the field galaxies to 22 members of three rich clusters with z=0.37 to explore possible variations caused by environmental effects. We exploit VLT/FORS spectra (R~1200) and HST/ACS imaging to determine internal kinematics, structures and stellar population parameters. From the Faber-Jackson and Fundamental Plane scaling relations we deduce a modest luminosity evolution in the B-band of 0.3-0.5mag for both samples. We compare measured Lick absorption line strengths (Hdelta, Hgamma, Hbeta, Mg_b, & Fe5335) with evolutionary stellar population models to derive light-averaged ages, metallicities and the element abundance ratios Mg/Fe. We find that all these three stellar parameters of the distant galaxies obey a scaling with velocity dispersion (mass) which is very well consistent with the one of local nearby galaxies. In particular, the distribution of Mg/Fe ratios of local galaxies is matched by the distant ones, and their derived mean offset in age corresponds to the average lookback time. This indicates that there was little chemical enrichment and no significant star formation within the last ~5Gyr. The calculated luminosity evolution of a simple stellar population model for the derived galaxy ages and lookback times is in most cases very consistent with the mild brightening measured by the scaling relations.

astro-ph/0412241 Three Components Evolution in a Simple Big Bounce Cosmological Model

Authors: Lixin Xu, Hongya Liu

• Comments: ws-ijmpd.cls, 9 pages, 5 figures, final version accepted by IJMPDWe consider a five-dimensional Ricci flat Bouncing cosmology and assume that the four-dimensional universe is permeated smoothly by three minimally coupled matter components: CDM+baryons $\rho_{m}$, radiation $\rho_{r}$ and dark energy $\rho_{x}$. Evolutions of these three components are studied and it is found that dark energy dominates before the bounce, and pulls the universe contracting. In this process, dark energy decreases while radiation and the matter increase. After the bounce, the radiation and matter dominates alternatively and then decrease with the expansion of the universe. At present, the dark energy dominates again and pushes the universe accelerating. In this model, we also obtain that the equation of state (EOS) of dark energy at present time is $w_{x0}\approx -1.05$ and the redshift of the transition from decelerated expansion to accelerated expansion is $z_{T}\approx 0.37$, which are compatible with the current observations.

astro-ph/0412237 The 3-D clustering of radio

galaxies in the TONS survey The 3-D clustering of radio galaxies in the TONS survey

Authors: Kate Brand, Steve Rawlings, Gary J. Hill, Joseph R. Tufts

• Comments: 18 pages, MNRAS accepted. Full paper including all spectra can be found at this http URLWe present a clustering analysis of the Texas-Oxford NVSS Structure (TONS) radio galaxy redshift survey. This complete flux-limited survey consists of 268 radio galaxies with spectroscopic redshifts in three separate regions of the sky covering a total of 165 deg^2. By going to faint radio flux densities (s_1.4>3 mJy) but imposing relatively bright optical limits (E R 19.5), the TONS sample is optimised for looking at the clustering properties of low luminosity radio galaxies in a region of moderate (0 < z < 0.5) redshifts. We use the two point correlation function to determine the clustering strength of the combined TONS08 and TONS12 sub-samples and find a clustering strength of r_0(z)=8.7+/-1.6 Mpc (h=0.7). If we assume growth of structure by linear theory and that the median redshift is 0.3, this corresponds to r_0(0)=11.0+/-2.0 Mpc which is consistent with the clustering strength of the underlying host galaxies (~ 2.5 Lstar ellipticals) of the TONS radio galaxy population.

astro-ph/0412235 Cosmic Infrared Background and Early Galaxy

EvolutionAuthors: A. Kashlinsky

• Comments: Invited review, Physics Reports, in press. 97 pages, 24 figuresThe Cosmic Infrared Background (CIB) reflects the sum total of galactic luminosities integrated over the entire age of the universe. From its measurements one can deduce information about objects at epochs currently inaccessible to telescopic studies. This review discusses the state of the current CIB measurements and the (mostly space-based) instruments with which these measurements have been made, the obstacles (the various foreground emissions)and the physics behind the CIB and its structure. Theoretical discussion of the CIB levels can now be normalized to the standard cosmological model narrowing down theoretical uncertainties. We review the information behind and theoretical modeling of both the mean (isotropic) levels of the CIB and their fluctuations. The CIB is divided into three broad bands: near-IR, mid-IR and far-IR. For each of the bands we review the main contributors to the CIB flux and the epochs at which the bulk of the flux originates. We also discuss the data on the various quantities relevant for correct interpretation of the CIB levels: the star-formation history, the present-day luminosity function measurements, resolving the various galaxy contributors to the CIB, etc. The integrated light of all galaxies in the deepest near-IR galaxy counts to date fails to match the observed mean level of the CIB, probably indicating a significant high-redshift contribution to the CIB. Additionally, Population III stars should have left a strong and measurable signature via their contribution to the cosmic infrared background (CIB) anisotropies for a wide range of their formation scenarios, and measuring the excess CIB anisotropies coming from high z would provide direct information on that epoch.

astro-ph/0412234 Principal Component Analysis of PSF

Variation in Weak Lensing SurveysAuthors: Mike Jarvis, Bhuvnesh Jain (U. Penn)

• We introduce a new algorithm for interpolating measurements of the point-spread function (PSF) using stars from many exposures. The principal components of the variation in the PSF pattern from multiple exposures are used to solve for better fits for each individual exposure. These improved fits are then used to correct the weak lensing shapes. Since we expect some degree of correlation in the PSF anisotropy across exposures, using information from stars in all exposures leads to a significant gain in the accuracy of the estimated PSF. It means that in general, the accuracy of PSF reconstruction is limited not by the number density of stars per exposure, but by the stacked number density across all exposures in a given survey. This technique is applied to the 75 square degree CTIO lensing survey, and we find that the PSF variation is well described by a small number of components. There is a significant improvement in the lensing measurements: the residual stellar PSF correlations are reduced by several orders of magnitude, and the measured B-mode in the two-point correlation of galaxy shears is consistent with zero down to 1 arcminute. We discuss the applications of the PCA technique to future surveys.

gr-qc/0412040 Kink instability and stabilization of the Friedmann universe with scalar

fieldsAuthors: Hideki Maeda, Tomohiro Harada

Comments• Comments: 8 pages, 2 tables, submitted to Physics Letters B

Report-no: WU-AP/182/04The evolution of weak discontinuity is investigated in the flat FRW universe with a single scalar field and with multiple scalar fields. We consider both massless scalar fields and scalar fields with exponential potentials. Then we find that a new type of instability, i.e. kink instability develops in the flat FRW universe with massless scalar fields. The kink instability develops with scalar fields with considerably steep exponential potentials, while less steep exponential potentials do not suffer from kink instability. In particular, assisted inflation with multiple scalar fields does not suffer from kink instability. The stability of general spherically symmetric self-similar solutions is also discussed.

astro-ph/0412304 Flux of the cosmic X-ray backgound from

HEAO1/A2 experimentAuthors: M. Revnivtsev (1,2), M. Gilfanov (1,2), K.Jahoda (3), R. Sunyaev (1,2) (1 - MPA, Garching,

Germany, 2 - IKI, Moscow, Russia, 3 - GSFC, Greenbelt, USA)

• Comments: 5 pages, submitted to Astronomy & AstrophysicsWe reanalyze data of HEAO1/A2 -- Cosmic X-ray Experiment -- in order to repeat the measurements of cosmic X-ray background (CXB) flux and accurately compare this value with other measurements of the CXB. We used the data of MED, HED1 and HED3 detectors in scan mode, that allowed us to measure effective solid angles and effective areas of detectors self consistently, in the same mode as the CXB flux was measured. We obtained the average value of the CXB flux is 1.96+/0.10 erg/s/cm2/deg2 in the energy band 2-10 keV. We compare the obtained measurements with those obtained by different instruments over last decades

astro-ph/0412303 Dark Energy and Large-Scale Structure of the Universe

Authors: Yu. Kulinich, B. Novosyadlyj

• Comments: 4 pages, 1 figure, submitted to the proceedings of international conference "Astronomy in Ukraine - Past, Present, Future", July 15-17, Kiev, Ukraine

• The evolution of matter density perturbations in two-component model of the Universe consisting of dark energy (DE) and dust-like matter (M) is considered. We have analyzed it for two kinds of DE with $\omega\ne -1$: a) unperturbed energy density and b) perturbed one (uncoupled with matter). For these cases the linear equations for evolution of the gauge-invariant amplitudes of matter density perturbations are presented. It is shown that in the case of unperturbed energy density of DE the amplitude of matter density perturbations grow slightly faster than in the second case.

astro-ph/0412300 On the Origin of Bimodality in Galaxy Properties: Cold Flows vs. Shock

Heating, Clustering and FeedbackAuthors: Avishai Dekel, Yuval Birnboim (The

Hebrew University of Jerusalem)• Comments: 26 pages, 11 figures, mn2e.cls

• We address the origin of the robust bi-modality in galaxies about a critical stellar mass ~3x10^10 Msol. Less massive galaxies tend to be ungrouped blue star-forming discs correlated along a fundamental line. More massive galaxies are typically grouped red old-star spheroids on a fundamental plane hosting AGNs. M/L is at a minimum near the critical mass. Color-magnitude data show a gap between the red and blue sequences, extremely red luminous galaxies already at z~1, a truncation of today's blue sequence above L*, and massive starbursts at z~2-4. We propose that these features are driven by the thermal properties of the inflowing gas and their interplay with the clustering and feedback processes, all functions of the dark-matter halo mass associated with a similar scale. In haloes below a critical shock-heating mass Ms~6x10^11 Msol, discs are built by cold streams, not heated by a virial shock, yielding efficient early star formation (SFR). It is regulated by supernova and radiative feedbacks into a long sequence of bursts in blue galaxies along the fundamental line. Cold streams penetrating through hot media in >Ms haloes at z>2 lead to massive starbursts in >L* galaxies. At z<2, in >Ms haloes hosting groups, the gas is heated by a virial shock, and being dilute it becomes vulnerable to AGN feedback. This shuts off gas supply and further star formation, preferentially in spheroids formed by mergers in groups. Subsequent passive evolution leads to red & dead massive spheroids starting at z~1. The SFR is high just below Ms, where the feedbacks are weak, leading to a minimum in M/L. Convolved with the clustering scale growth, this explains the observed SFR history. When these processes are incorporated in the modeling of galaxy formation, they should recover the bi-modality features and solve other open

astro-ph/0412343 Properties of Ly-alpha and Gamma Ray Burst selected starbursts at high

redshiftsAuthors: J. P. U. Fynbo, B. Krog, K. Nilsson,

G. Bjornsson, J. Hjorth, P. Jakobsson, C. Ledoux, P. Moller, B. Thomsen

• Comments: invited talk, 6 pages, 3 figures, to appear in ``Starbursts from 30 Doradus to Lyman Break Galaxies'', eds. R. de Grijs, R. M. Gonzalez Delgado, Astrophysics & Space Science Library Series, Kluwer (in press)

• Selection of starbursts through either deep narrow band imaging of redshifted Ly-alpha emitters, or localisation of host galaxies of gamma-ray bursts both give access to starburst galaxies that are significantly fainter than what is currently available from selection techniques based on the continuum (such as Lyman-break selection). We here present results from a survey for Ly-alpha emitters at z=3, conducted at the European Southern Observatory's Very Large Telescope. Furthermore, we briefly describe the properties of host galaxies of gamma-ray bursts at z>2. The majority of both Ly-alpha and gamma-ray burst selected starbursts are fainter than the flux limit of the Lyman-break galaxy sample, suggesting that a significant fraction of the integrated star formation at z~3 is located in galaxies at the faint end of the luminosity function.

astro-ph/0412340 Observational tests of the evolution of spheroidal galaxies

Authors: Laura Silva (1), Gianfranco De Zotti (2), Gian Luigi Granato (2), Roberto Maiolino (3),

Luigi Danese (4) ((1) INAF-Trieste, (2) INAF-Padova, (3) INAF-Arcetri, (4) SISSA-Trieste)

Comments: 12 pages, MNRAS, accepted

• Granato et al (2004) have elaborated a physically grounded model exploiting the mutual feedback between star-forming spheroidal galaxies and the active nuclei growing in their cores to overcome, in the framework of the hierarchical clustering scenario for galaxy formation, one of the main challenges facing such scenario, the fact that massive spheroidal galaxies appear to have formed much earlier and faster than predicted by previous semi-analytical models. After having assessed the values of the two parameters that control the effect of the complex radiative transfer processes on the time-dependent SEDs we have compared the model predictions with a variety of IR to mm data. Our results support a rather strict continuity between objects where stars formed and evolved massive early-type galaxies, indicating that large spheroidal galaxies formed most of their stars when they were already assembled as single objects. The model is successful in reproducing the observed z distribution of K\le20 galaxies at z>1, in contrast with both the classical monolithic and the semi-analytic models, the ratio of star-forming to passively evolving spheroids and the counts and z distributions of EROs. The model also favourably compares with the ISOCAM 6.7 mu counts, with the corresponding z distribution, and with IRAC counts, which probe primarily the passive evolution phase, and with the submm SCUBA and MAMBO data, probing the active star-formation phase. The observed fraction of 24mu selected sources with no detectable emission in either the 8mu or R band nicely corresponds to the predicted surface density of star-forming spheroids with 8mu fluxes below the detection limit. Predictions for the z distributions of 24mu sources detected by MIPS surveys are pointed out. [Abridged]

astro-ph/0412332Galactic Model Identification Through Parallax and

Astrometry of Microlensing Events • Authors: Sohrab Rahvar, Sima Ghassemi

Comments: 10 pages, 3 figures, submitted to A&AIn recent years various models for the galactic structure and massive compact halo objects (MACHOs) for the interpretation of microlensing candidates of Large Magellanic Cloud (LMC) have been proposed. A direct way to identify the best model is measuring the lens parameters, which can be obtained by measuring the Einstein crossing time and parallax effect on the microlensing light curve and the astrometry of centroid of images. Here in this work, the theoretical distribution of these parameters for comparison with the observations is obtained for the various power-law galactic models and mass functions (MF). For the self-lensing as one of the models for the interpretation of LMC events, the maximum shift of centroid of images and the parallax parameter are one order of magnitude smaller than the halo ones. The shifting of centroid of images $0.02 mas$, for the LMC events is unlikely to be observed by the astrometric missions such as FAME, GAIA and SIM. This can be used as a test for the self-lensing .

astro-ph/0412322 Structure of visible and dark matter components of spiral galaxies

at z = 0.9 • Authors: Antti Tamm (1), Peeter Tenjes (1,2) ((1) Tartu

University, (2) Tartu Observatory)Comments: 3 pages, 3 figures. Presented at the "Baryons in Dark Matter Halos" conference in Croatia, to appear in the conference proceedingsWe construct self-consistent light and mass distribution models for 4 distant spiral galaxies. The models include a bulge, a disk and an isothermal dark matter. We find the luminosity profiles to have much steeper cut-off than that of a simple exponential disk. We apply k-corrections and derive rest-frame B-band mass-to-light ratios of the visible components and the central densities of the dark halos; we discover no significant evolution with redshift of these parameters.

astro-ph/0412308 Constraints on linear-negative potentials in quintessence and phantom models from recent supernova

data • Authors: L. Perivolaropoulos

Comments: 7 pages, 7 figures. The mathematica file with the numerical analysis of the paper can be downloaded from this http URLEvolving phantom or quintessence scalar fields in linear-negative potentials of the form $V(\phi)=s \phi$ are favored by anthropic principle considerations and produce an evolving equation of state parameter at late times. We investigate the predicted redshift dependence $w(z)$ for a wide range of slopes $s$ in both quintessence and phantom models. We show that $w(z)$ does not cross the phantom divide line $w=-1$ (hereafter PDL). This is a generic feature of all phantom and quintessence models with fixed sign of the kinetic term independent of the sign of the potential energy. We then use the gold dataset of 157 SnIa and place constraints on the allowed range of slopes $s$. We find $s=0\pm 1.6$ for quintessence and $s=\pm 0.7\pm 1$ for phantom models (the range is at the $2\sigma$ level and the units of $s$ are in $\sqrt{3}M_p H_0^2\simeq 10^{-38}eV^3$ where $M_p$ is the Planck mass). In both cases the best fit is very close to $s\simeq 0$ corresponding to a cosmological constant. We also show that specific model independent parametrizations of $w(z)$ which allow crossing of the PDL ($w=-1$) provide significantly better fits to the data. Unfortunately such crossings are not allowed in any phantom or quintessence single field model minimally coupled to gravity. Mixed models (coupled phantom-quintessence fields) can in principle lead to a $w(z)$ crossing the PDL but a preliminary investigation indicates that this does not happen for natural initial conditions.

astro-ph/0412385What do loose groups tell us about galaxy formation?

Authors: D.J. Pisano, David Barnes, Brad Gibson,

Virginia Kilborn, Lister Staveley-Smith, Ken Freeman • Comments: 4 pages, to appear in the proceedings of "Baryons in Dark Matter

Halos" Eds R-J., Dettmar, U. Klein, P. Salucci, PoS, SISSA, this http URL

• We present the results of a Parkes Multibeam HI survey of six loose groups of galaxies analogous to the Local Group. This survey was sensitive to HI-rich objects in these groups to below 10^7 M(sun) of HI, and was designed to search for low mass, gas-rich satellite galaxies and potential analogs to the high-velocity clouds seen around the Milky Way. This survey detected a total of 79 HI-rich objects associated with the six groups, half of which were new detections. While the survey identified a small number of dwarf galaxies, no star-free HI clouds were discovered. The HI mass function of the six groups appears to be roughly flat as is that of the Local Group. The cumulative velocity distribution function (CVDF) of the HI-rich halos in the six groups is identical to that of the Local Group. Both of these facts imply that these groups are true analogs to the Local Group and that the Local Group is not unique in its lack of low-mass dwarf galaxies as compared to the predictions of cold dark matter models of galaxy formation. This survey also constrains the distance to and HI masses of the compact high-velocity clouds (CHVCs) around the Milky Way. The lack of CHVC analog detections implies that they are distributed within <160 kpc of the Milky Way and have average HI masses of <4x10^5 M(sun). The spatial distribution of CHVCs is consistent with the predictions of simulations for dark matter halos. Furthermore the CVDF of Local Group galaxies plus CHVCs matches the predicted CVDF of cold dark matter simulations of galaxy formation. This provides circumstantial evidence that CHVCs may be associated with low-mass dark matter halos.

astro-ph/0412380 The cosmic saga of 3He

• Authors: Daniele GalliComments: 6 pages, 2 figures. Invited talk presented at the ESO-ARCETRI workshop on "Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites" (September 13-17 2004), to be published in "ESO Astrophysics Symposia", Editors: L. Pasquini and S. Randich

• We recall the emergence of the ``3He problem'', its currently accepted solution, and we summarize the presently available constraints on models of stellar nucleosynthesis and studies of Galactic chemical evolution from measurements of the abundance of 3He in the Galaxy.

astro-ph/0412379 Continuous star formation in gas-rich dwarf galaxies • Authors: S. Recchi, G. Hensler (Institute of Astronomy, Vienna University)

Comments: 16 pages, 6 figures, to be published in "Reviews in Modern Astronomy" of the Astronomische Gesellschaft, Vol. 18Blue Compact Dwarf and Dwarf Irregular galaxies are generally believed to be unevolved objects, due to their blue colors, compact appearance and large gas fractions. Many of these objects show an ongoing intense burst of star formation or have experienced it in the recent past. By means of 2-D hydrodynamical simulations, coupled with detailed chemical yields originating from SNeII, SNeIa and intermediate-mass stars, we study the dynamical and chemical evolution of model galaxies with structural parameters similar to IZw18 and NGC1569. Bursts of star formation with short duration are not able to account for the chemical and morphological properties of these galaxies. The best way to reproduce the chemical composition of these objects is by assuming long-lasting episodes of star formation and a more recent burst, separated from the previous episodes by a short quiescent period. The last burst of star formation, in most of the explored cases, does not affect the chemical composition of the galaxy observable in HII regions, since the enriched gas produced by young stars is in a too hot phase to be detectable with the optical spectroscopy.

astro-ph/0412370 Effects of dynamical evolution on the distribution of substructuresAuthors: J. Penarrubia, A. J. Benson

Comments: Submitted to MNRAS. 13 pages, 9 figures

• We develop a semi-analytical model that determines the evolution of the mass, position and internal structure of dark matter substructures orbiting in dark matter haloes. We apply this model to the case of the Milky Way. We focus in particular on the effects of mass loss, dynamical friction and substructure--substructure interactions, the last of which has previously been ignored in analytic models of substructure evolution. Our semi-analytical treatment reproduces both the spatial distribution of substructures and their mass function as obtained from the most recent N-body cosmological calculations of Gao et al. (2004). We find that, if mass loss is taken into account, the present distribution of substructures is practically insensitive to dynamical friction and scatterings from other substructures. Implementing these phenomena leads to a slight increase (~5%) in the number of substructures at r<0.35 r_vir, whereas their effects on the mass function are negligible. We find that mass loss processes lead to the disruption of substructures before dynamical friction and gravitational scattering can significantly alter their orbits. Our results suggest that the present substructure distribution at r>0.35 r_vir reflects the orbital properties at infall and is, therefore, purely determined by the dark matter environment around the host halo and has not been altered by dynamical evolution

astro-ph/0412369Infrared luminosities of galaxies in the Local Volume

Authors: I.D.Karachentsev, A.M.Kut'kinComments: 15 pages, 7 figures. Astronomy

Letters, submitted • Near-infrared properties of 451 galaxies with distances D \leq 10

Mpc are considered basing on the all-sky two micron survey (2MASS). A luminosity function of the galaxies in the K-band is derived within [-25,-11] mag. The local (D < 8 Mpc) luminosity density is estimated to be 6.8*10^8 L_sun/Mpc^3 that exceeds (1.5+-0.1) times the global cosmic density in the K-band. Virial mass-to-K-luminosity ratios are determined for nearby groups and clusters. In the luminosity range of (5*10^{10} - 2*10^{13})L_sun, the groups and clusters follow the relation \lg(M/L_K) propto (0.27+-0.03) lg(L_K) with a scatter of \~0.1 comparable to errors of the observables. The mean ratio <M/L_K> ~= (20-25) M_sun/L_sun for the galaxy systems turns out to be significantly lower than the global ratio, (80-90)M_sun/L_sun, expected in the standard cosmological model with the matter density of Omega_m =0.27. This discrepancy can be resolved if most of dark matter in the universe is not associated with galaxies and their systems.

astro-ph/0412353 Simulating Astro-E2 Observations of Galaxy Clusters: the Case of

Turbulent Cores Affected by Tsunamis• Authors: Yutaka Fujita (1), Tomoaki Matsumoto (2), Keiichi Wada (1),

Tae Furusho (3) ((1) NAOJ, (2) Hosei U., (3) ISAS/JAXA)Comments: 13 pages, 2 figures, ApJL in press. Movies are available at this http URLThis is the first attempt to construct detailed X-ray spectra of clusters of galaxies from the results of high-resolution hydrodynamic simulations and simulate X-ray observations in order to study velocity fields of the intracluster medium (ICM). The hydrodynamic simulations are based on the recently proposed tsunami model, in which cluster cores are affected by bulk motions of the ICM and turbulence is produced. We note that most other solutions of the cooling flow problem also involve the generation of turbulence in cluster cores. From the mock X-ray observations with Astro-E2 XRS, we find that turbulent motion of the ICM in cluster cores could be detected with the satellite. The Doppler shifts of the metal lines could be used to discriminate among turbulence models. The gas velocities measured through the mock observations are consistent with the line-emission weighted values inferred directly from hydrodynamic simulations.

astro-ph/0412348 High resolution SPH simulations of disk formation in CDM halos;

resolution tests• Authors: Tobias Kaufmann, Lucio Mayer, Ben Moore, Joachim Stadel, James

WadsleyComments: 4 pages, to appear in the Proceedings of Science (published by SISSA),Conference "Baryons in Dark Matter Haloes", Novigrad, Croatia, 5-9 October 2004We perform N-Body/SPH simulations of disk galaxy formation inside equilibrium spherical and triaxial cuspy dark matter halos. We systematically study the disk properties and morphology as we increase the numbers of dark matter and gas particles from 10^4 to 10^6 and change the force resolution. The force resolution influences the morphological evolution of the disk quite dramatically. Unless the baryon fraction is significantly lower than the universal value, with high force resolution a gaseous bar always forms within a billion years after allowing cooling to begin. The bar interacts with the disk, transferring angular momentum and increasing its scale length. In none of the simulations does the final mass distribution of the baryons obey a single exponential profile. Indeed within a few hundred parsecs to a kiloparsec from the center the density rises much more steeply than in the rest of the disk, and this is true irrespective of the presence of the bar.