55 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
Galaxy Zoo: Dust in Spirals
We investigate the effect of dust on spiral galaxies by measuring the
inclination-dependence of optical colours for 24,276 well-resolved SDSS
galaxies visually classified in Galaxy Zoo. We find clear trends of reddening
with inclination which imply a total extinction from face-on to edge-on of 0.7,
0.6, 0.5 and 0.4 magnitudes for the ugri passbands. We split the sample into
"bulgy" (early-type) and "disky" (late-type) spirals using the SDSS fracdeV (or
f_DeV) parameter and show that the average face-on colour of "bulgy" spirals is
redder than the average edge-on colour of "disky" spirals. This shows that the
observed optical colour of a spiral galaxy is determined almost equally by the
spiral type (via the bulge-disk ratio and stellar populations), and reddening
due to dust. We find that both luminosity and spiral type affect the total
amount of extinction, with "disky" spirals at M_r ~ -21.5 mags having the most
reddening. This decrease of reddening for the most luminous spirals has not
been observed before and may be related to their lower levels of recent star
formation. We compare our results with the latest dust attenuation models of
Tuffs et al. We find that the model reproduces the observed trends reasonably
well but overpredicts the amount of u-band attenuation in edge-on galaxies. We
end by discussing the effects of dust on large galaxy surveys and emphasize
that these effects will become important as we push to higher precision
measurements of galaxy properties and their clustering.Comment: MNRAS in press. 25 pages, 22 figures (including an abstract comparing
GZ classifications with common automated methods for selecting disk/early
type galaxies in SDSS data). v2 corrects typos found in proof
Growth of galactic bulges by mergers. II. Low-density satellites
Satellite accretion events have been invoked for mimicking the internal
secular evolutionary processes of bulge growth. However, N-body simulations of
satellite accretions have paid little attention to the evolution of bulge
photometric parameters, to the processes driving this evolution, and to the
consistency of this evolution with observations. We want to investigate whether
satellite accretions indeed drive the growth of bulges, and whether they are
consistent with global scaling relations of bulges and discs. We perform N-body
models of the accretion of satellites onto disc galaxies. A Tully-Fisher (M
\propto V_{rot}^ {alpha_TF}) scaling between primary and satellite ensures that
density ratios, critical to the outcome of the accretion, are realistic. We
carry out a full structural, kinematic and dynamical analysis of the evolution
of the bulge mass, bulge central concentration, and bulge-to-disc scaling
relations. The remnants of the accretion have bulge-disc structure. Both the
bulge-to-disc ratio (B/D) and the Sersic index (n) of the remnant bulge
increase as a result of the accretion, with moderate final bulge Sersic
indices: n = 1.0 to 1.9. Bulge growth occurs no matter the fate of the
secondary, which fully disrupts for alpha_TF=3 and partially survives to the
remnant center for alpha_TF = 3.5 or 4. Global structural parameters evolve
following trends similar to observations. We show that the dominant mechanism
for bulge growth is the inward flow of material from the disc to the bulge
region during the satellite decay. The models confirm that the growth of the
bulge out of disc material, a central ingredient of secular evolution models,
may be triggered externally through satellite accretion.Comment: Accepted for publication in A&A, 20 pages, 11 figures. Figs. 1 and 2
are low resolution ones: high-resolution versions available under request to
the author
- …