68 research outputs found
Quantitative interpretation of the rotation curves of spiral galaxies at redshifts z~0.7 and z~1
We present decompositions of the rotation curves of three spiral galaxies at
redshifts z~0.7 and 1 into contributions by their bulges, disks, and dark
halos, respectively. In order to set constraints on the degeneracy of the
decompositions we interpret the morphology of the spiral structures
quantitatively in the framework of density wave theory. Galaxy models
constrained in such a way show that the distant galaxies, which are much
younger than nearby galaxies, have very likely 'maximum disks', i.e. are
dominated in their inner parts by baryonic matter. We argue that current
theories of the cosmogony of galaxies must allow for these types of galaxies.Comment: 6 pages, accepted for publication in A&
Modelling the spectral energy distribution of galaxies. IV Correcting apparent disk scalelengths and central surface brightnesses for the effect of dust at optical and near-infrared wavelengths
We present corrections for the change in the apparent scalelengths, central
surface brightnesses and axis ratios due to the presence of dust in pure disk
galaxies, as a function of inclination, central face-on opacity in the B-band
(tau^f_B) and wavelength. The correction factors were derived from simulated
images of disk galaxies created using geometries for stars and dust which can
reproduce the entire spectral energy distribution from the ultraviolet (UV) to
the Far-infrared (FIR)/submillimeter (submm) and can also account for the
observed surface-brightness distributions in both the optical/Near-infrared and
FIR/submm. We found that dust can significantly affect both the scalelength and
central surface brightness, inducing variations in the apparent to intrinsic
quantities of up to 50 percent in scalelength and up to 1.5 magnitudes in
central surface brightness. We also identified some astrophysical effects for
which, although the absolute effect of dust is non-negligible, the predicted
variation over a likely range in opacity is relatively small, such that an
exact knowledge of opacity is not needed. Thus, for a galaxy at a typical
inclination of 37 degrees and having any tau^f_B>2, the effect of dust is to
increase the scalelength in B relative to that in I by a factor of 1.12 +- 0.02
and to change the B-I central colour by 0.36 +- 0.05 magnitudes. Finally we use
the model to analyse the observed scalelength ratios between B and I for a
sample of disk-dominated spiral galaxies, finding that the tendency for
apparent scalelength to increase with decreasing wavelength is primarily due to
the effects of dust.Comment: 16 pages, 13 figures and 5 tables; accepted for publication in
Astronomy & Astrophysic
Internal kinematics of spiral galaxies in distant clusters. Part II. Observations and data analysis
We have conducted an observing campaign with FORS at the ESO-VLT to explore
the kinematical properties of spiral galaxies in distant galaxy clusters. Our
main goal is to analyse transformation- and interaction processes of disk
galaxies within the special environment of clusters as compared to the
hierarchical evolution of galaxies in the field. Spatially resolved MOS-spectra
have been obtained for seven galaxy clusters at 0.3<z<0.6 to measure rotation
velocities of cluster members. For three of the clusters, Cl0303+17, Cl0413-65,
and MS1008-12, for which we presented results including a TF-diagram in Ziegler
et al. 2003, we describe here in detail the observations and data analysis.
Each of them was observed with two setups of the standard FORS MOS-unit.With
typical exposure times of >2 hours we reach an S/N>5 in the emission lines
appropriate for the deduction of the galaxies' internal rotation velocities
from [OII], Hbeta, or [OIII] profiles. Preselection of targets was done on the
basis of available redshifts as well as from photometric and morphological
information gathered from own observations, archive data, and from the
literature. Emphasis was laid on the definition of suitable setups to avoid the
typical restrictions of the standard MOS unit for this kind of observations. In
total we assembled spectra of 116 objects of which 50 turned out to be cluster
members. Position velocity diagrams, finding charts as well as tables with
photometric, spectral, and structural parameters of individual galaxies are
presented.Comment: 18 pages, 6 figures, accepted for publication in Astronomy and
Astrophysics. A version with full resolution figures can be downloaded from
http://www.uni-sw.gwdg.de/~vwgroup/publications.htm
The FORS Deep Field: Field selection, photometric observations and photometric catalog
The FORS Deep Field project is a multi-colour, multi-object spectroscopic
investigation of an approx. 7 times 7 region near the south galactic pole based
mostly on observations carried out with the FORS instruments attached to the
VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this
study is to improve our understanding of the formation and evolution of
galaxies in the young Universe. In this paper the field selection, the
photometric observations, and the data reduction are described. The source
detection and photometry of objects in the FORS Deep Field is discussed in
detail. A combined B and I selected UBgRIJKs photometric catalog of 8753
objects in the FDF is presented and its properties are briefly discussed. The
formal 50% completeness limits for point sources, derived from the co-added
images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R,
I, J and Ks (Vega-system), respectively. A comparison of the number counts in
the FORS Deep Field to those derived in other deep field surveys shows very
good agreement.Comment: 15 pages, 11 figures (included), accepted for publication in A&
High-resolution X-ray spectroscopy of the low and high states of the Seyfert 1 galaxy NGC 4051 with Chandra LETGS
Methods. We analyse two observations taken with the Low Energy Transmission
Grating Spectrometer of Chandra. We investigated the spectral response to a
sudden flux decrease by a factor of 5, which occurred during the second
observation. Results. We detect a highly ionised absorption component with an
outflow velocity of -4670 km/s, one of the highest outflow velocity components
observed in a Seyfert 1 galaxy. The spectra contain a relativistic O VIII Ly
alpha line, and four absorption components spanning a range in ionisation
parameter xi between 0.07 and 3.19. An emission component producing radiative
recombination continua of C VI and C V appears during the low state. The black
body temperature decreases with the drop in flux observed in the second
observation. Conclusions. For all absorber components we exclude that the
ionisation parameter linearly responded to the decrease in flux by a factor of
5. The variability of the absorber suggest that at least three out of four
detected components are located in the range 0.02-1 pc. ABRIDGEDComment: Accepted by A&A, 14 pages, 9 figure
An evolutionary disc model of the edge-on galaxy NGC 5907
We present a physical model that explains the two disparate observational
facts: 1) the exponential vertical disc structure in the optical and NIR of the
non-obscured part of the stellar disc and 2) the enhanced FIR/submm luminosity
by about a factor of four near the obscured mid-plane, which requires
additional dust and also stellar light to heat the dust component. We use
multi-band photometry in U, B, V, R, and I- band combined with radiative
transfer through a dust component to fit simultaneously the vertical
surface-brightness and colour index profiles in all bands adopting a reasonable
star formation history and dynamical heating function. The final disc model
reproduces the surface-brightness profiles in all bands with a moderately
declining star formation rate and a slowly starting heating function for young
stars. The total dust mass is 57 million solar masses as required from the
FIR/submm measurements. Without a recent star burst we find in the midplane an
excess of 5.2-, 4.0-, and 3.0-times more stellar light in the U-, B-, and
V-band, respectively. The corresponding stellar mass-to-light ratios are 0.91
in V- and 1.0 in R-band. The central face-on optical depth in V-band is 0.81
and the radial scale length of the dust is 40% larger than that of the stellar
disc. Evolutionary disc models are a powerful method to understand the vertical
structure of edge-on galaxies. Insights to the star formation history and the
dynamical evolution of stellar discs can be gained. FIR/submm observations are
necessary to restrict the parameter space for the models.Comment: 17 pages, 12 figures (24 files), A&A in pres
Photometric structure of the peculiar galaxy ESO 235-G58
We present the near-infrared and optical properties of the peculiar galaxy
ESO 235-G58, which resembles a late-type ringed barred spiral seen close to
face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk
galaxy of relatively low luminosity. We have analyzed the light and color
distributions of ESO 235-G58 in the NIR and optical bands and compared them
with the typical properties observed for other morphological galaxy types,
including polar ring galaxies. Similar properties are observed for ESO 235-G58,
polar ring galaxies, and spiral galaxies, which leads us to conclude that this
peculiar system is a polar-ring-related galaxy, characterized by a low inclined
ring/disk structure, as pointed out by Buta & Crocker in an earlier study,
rather than a barred galaxy.Comment: 16 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Rotation and outflow in the central kiloparsec of the water megamaser galaxies IC 2560, NGC 1386, NGC 1052, and Mrk 1210
Optical emission-line profiles were evaluated in order to explore the
structure of galactic nuclei containing H2O megamaser sources. Galactic
rotation and outflow of narrow-line gas are common features of this sample of
water megamaser galaxies. All decomposed line-systems exhibit AGN typical line
ratios. Recent detections of H2O megamasers in starburst galaxies and the
apparent asssociation of one megamaser with a Seyfert 1 AGN suggest that
megamasers can possibly be triggered by optically detectable outflows. The
frequently encountered edge-on geometry favoring large molecular column
densities appears to be verified for NGC 1386 and IC 2560. For NGC 1052 and Mrk
1210, maser emission triggered by the optically detected outflow components
cannot be ruled out.Comment: 23 pages, 26 Postscript figures, A&A Main Journa
Structure of the Galaxies in the NGC 80 Group
BV-bands photometric data obtained at the 6-m telescope of the Special
Astrophysical Observatory are used to analyze the structure of 13 large disk
galaxies in the NGC 80 group. Nine of the 13 galaxies under consideration are
classified by us as lenticular galaxies. The stellar populations in the
galaxies are very different, from old ones with ages of T>10 Gyrs (IC 1541) to
relatively young, with the ages of T<2-3 Gyr (IC 1548, NGC 85). In one case,
current star formation is known (UCM 0018+2216). In most of the galaxies, more
precisely in all of them more luminous than M(B) -18, two-tiered
(`antitruncated') stellar disks are detected, whose radial surface brightness
profiles can be fitted by two exponential segments with different scalelengths
-- shorter near the center and longer at the periphery. All dwarf S0 galaxies
with single-scalelength exponential disks are close companions to giant
galaxies. Except for this fact, no dependence of the properties of S0 galaxies
on distance from the center of the group is found. Morphological traces of
minor merger are found in the lenticular galaxy NGC 85. Basing on the last two
points, we conclude that the most probable mechanisms for the transformation of
spirals into lenticular galaxies in groups are gravitational ones, namely,
minor mergers and tidal interactions.Comment: 24 pages, 9 figures, slightly improved version of the paper published
in the December, 2009, issue of the Astronomy Report
Near-infrared observations of galaxies in Pisces-Perseus. V. On the origin of bulges
We investigate the scaling relations of bulge and disk structural parameters
for a sample of 108 disk galaxies.Structural parameters are obtained from 2D
bulge/disk decomposition of H-band images.Bulges are modelled with a
generalized exponential (Sersic) with variable shape index n. We find that
bulge effective scalelength and luminosity increase with increasing n, but disk
properties are independent of bulge shape. As Hubble type T increases, bulges
become less luminous and their mean effective surface brightness gets fainter;
disks shows a similar, but much weaker, trend. When bulge parameters are
compared with disk ones, they are tightly correlated for n=1 bulges. The
correlations gradually worsen with increasing n such that n=4 bulges appear
virtually independent of their disks. The Kormendy relation, surf. brightness
vs. effect. radius, is shown to depend on bulge shape; the two parameters are
tightly correlated in n=4 bulges, and increasingly less so as n decreases;
disks are well correlated .Bulge-to-disk size ratios are independent of Hubble
type, but smaller for exponential bulges. Strongly barred SB galaxies with
exponential bulges are more luminous than their unbarred counterparts.
Exponential bulges appear to be closely related to their underlying disks,
while bulges with higher n values are less so. We interpret our results as
being most consistent with a secular evolutionary scenario, in which
dissipative processes in the disk are responsible for building up the bulges in
most spirals.Comment: 18 pages, 12 figures, 1 table, A&A in pres
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