Transcript Comments

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 URL
We 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 formation
Authors: 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 Gyr
Authors: 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 galaxies
Authors: 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 lightaveraged 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
IJMPD
We 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 URL
We 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
Evolution
Authors: A. Kashlinsky
•
Comments: Invited review, Physics Reports, in press. 97 pages, 24 figures
The 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 Surveys
Authors: Mike Jarvis, Bhuvnesh Jain (U. Penn)
•
We introduce a new algorithm for interpolating measurements of the pointspread 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 fields
Authors: Hideki Maeda, Tomohiro Harada
Comments
•
Comments: 8 pages, 2 tables, submitted to Physics Letters B
Report-no: WU-AP/182/04
The 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 experiment
Authors: 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 &
Astrophysics
We 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 Feedback
Authors: 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 oldstar 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 bimodality features and solve other open
astro-ph/0412343 Properties of Ly-alpha and Gamma
Ray Burst selected starbursts at high redshifts
Authors: 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&A
In 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 selflensing .
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 proceedings
We 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 linearnegative 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 URL
Evolving 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 Galli
Comments: 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. 18
Blue 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 substructures
Authors: 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'kin
Comments: 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 URL
This 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 AstroE2 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
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Authors: Tobias Kaufmann, Lucio Mayer, Ben Moore, Joachim Stadel, James Wadsley
Comments: 4 pages, to appear in the Proceedings of Science (published by
SISSA),Conference "Baryons in Dark Matter Haloes", Novigrad, Croatia, 5-9 October
2004
We 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.