250 research outputs found
Truncation of stellar disks in galaxies at z~1
We report here the first evidence for stellar disk truncation at high
redshift, based on surface photometry of a sample of 16 high redshift (0.6 < z
< 1.0) disk galaxies from the GOODS HST/ACS data. The radial profiles are best
fit by a double exponential profile. This result agrees with the profile of
disks in local galaxies. The cosmological surface brightness dimming at this
redshift range only allows us to detect galaxies with spatially ``early''
truncation, R_br/h_in <= 3.5. Six galaxies show the radial double exponential
structure, with an average value of R_br/h_in ~ 1.8. Such ``early'' truncated
galaxies are missing in local samples so far. This result opens the ground for
observing directly disk evolution through the study of the truncation radius as
a function of redshift.Comment: 4 pages, 1 figure, accepted for publication in the A&A Letter
Gas flow and dark matter in the inner parts of early-type barred galaxies
This paper presents the dynamical simulations run in the potential derived
from the light distribution of 5 late-type barred spiral galaxies. The aim is
to determine whether the mass distribution together with the hydrodynamical
simulations can reproduce the observed line-of-sight velocity curves and the
gas morphology in the inner regions of the sample barred galaxies. The light
distribution is obtained from the -band and the -band combined together.
The M/L is determined using population synthesis models. The observations and
the methodology of the mass distribution modelling are presented in a companion
paper. The SPH models using the stellar mass models obtained directly from the
-band light distributions give a good representation of the gas distribution
and dynamics of the modelled galaxies, supporting the maximum disk assumption.
This result indicates that the gravitational field in the inner region is
mostly provided by the stellar luminous component. When 40% of the total mass
is transferred to an axisymmetric dark halo, the modelled kinematics clearly
depart from the observed kinematics, whereas the departures are negligible for
dark mass halos of 5% and 20% of the total mass. This result sets a lower limit
for the contribution of the luminous component of about 80%, which is in
agreement with the maximum disk definition of the stellar mass contribution to
the rotation curve (about 85%10).Comment: 28 pages, 30 figures. Accepted for publication in A&A on 17/05/2004.
High resolution figures on publicatio
Very Luminous Carbon Stars in the Outer Disk of the Triangulum Spiral Galaxy
Stars with masses in the range from about 1.3 to 3.5 Mo pass through an
evolutionary stage where they become carbon stars. In this stage, which lasts a
few Myr, these stars are extremely luminous pulsating giants. They are so
luminous in the near-infrared that just a few of them can double the integrated
luminosity of intermediate-age (0.6 to 2 Gyr) Magellanic Cloud clusters at 2.2
microns. Astronomers routinely use such near-infrared observations to minimize
the effects of dust extinction, but it is precisely in this band that carbon
stars can contribute hugely. The actual contribution of carbon stars to the
outer disk light of evolving spiral galaxies has not previously been
morphologically investigated. Here we report new and very deep near-IR images
of the Triangulum spiral galaxy M33=NGC 598, delineating spectacular arcs of
carbon stars in its outer regions. It is these arcs which dominate the
near-infrared m=2 Fourier spectra of M33. We present near-infrared photometry
with the Hale 5-m reflector, and propose that the arcs are the signature of
accretion of low metallicity gas in the outer disk of M33.Comment: 4 pages, 4 figures. Revised version submitted to A&A Letter
Structure, mass and stability of galactic disks
In this review I concentrate on three areas related to structure of disks in
spiral galaxies. First I will review the work on structure, kinematics and
dynamics of stellar disks. Next I will review the progress in the area of
flaring of HI layers. These subjects are relevant for the presence of dark
matter and lead to the conclusion that disk are in general not `maximal', have
lower M/L ratios than previously suspected and are locally stable w.r.t.
Toomre's Q criterion for local stability. I will end with a few words on
`truncations' in stellar disks.Comment: Invited review at "Galaxies and their Masks" for Ken Freeman's 70-th
birthday, Sossusvlei, Namibia, April 2010. A version with high-res. figures
is available at
http://www.astro.rug.nl/~vdkruit/jea3/homepage/Namibiachapter.pd
The structure of galactic disks: Studying late-type spiral galaxies using SDSS
Using imaging data from the SDSS survey, we present the g' and r' radial
stellar light distribution of a complete sample of ~90 face-on to intermediate
inclined, nearby, late-type (Sb-Sdm) spiral galaxies. The surface brightness
profiles are reliable (1sigma uncertainty less than 0.2 mag) down to
mu=~27magsqarcsec. Only ~10% of all galaxies have a normal/standard purely
exponential disk down to our noise limit.
The surface brightness distribution of the rest of the galaxies is better
described as a broken exponential. About 60% of the galaxies have a break in
the exponential profile between ~1.5-4.5 times the scalelength followed by a
downbending, steeper outer region. Another ~30% shows also a clear break
between ~4.0-6.0 times the scalelength but followed by an upbending, shallower
outer region. A few galaxies have even a more complex surface brightness
distribution.
The shape of the profiles correlates with Hubble type. Downbending breaks are
more frequent in later Hubble types while the fraction of upbending breaks
rises towards earlier types. No clear relation is found between the
environment, as characterised by the number of neighbours, and the shape of the
profiles of the galaxies.Comment: LaTeX, 69 pages, 213 (very low resolution) figures, A&A accepted.
Second version to match the accepted one including all referee's comments.
Version with full resolution figures (highly recommended, but with 7.6MB)
available at http://www.astro.rug.nl/~pohlen/pohlenSDSS.pd
Gravitational stability and dynamical overheating of stellar disks of galaxies
We use the marginal stability condition for galactic disks and the stellar
velocity dispersion data published by different authors to place upper limits
on the disk local surface density at two radial scalelengths .
Extrapolating these estimates, we constrain the total mass of the disks and
compare these estimates to those based on the photometry and color of stellar
populations. The comparison reveals that the stellar disks of most of spiral
galaxies in our sample cannot be substantially overheated and are therefore
unlikely to have experienced a significant merging event in their history. The
same conclusion applies to some, but not all of the S0 galaxies we consider.
However, a substantial part of the early type galaxies do show the stellar
velocity dispersion well in excess of the gravitational stability threshold
suggesting a major merger event in the past. We find dynamically overheated
disks among both seemingly isolated galaxies and those forming pairs. The ratio
of the marginal stability disk mass estimate to the total galaxy mass within
four radial scalelengths remains within a range of 0.4---0.8. We see no
evidence for a noticeable running of this ratio with either the morphological
type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter
The Gas Content in Galactic Disks: Correlation with Kinematics
We consider the relationship between the total HI mass in late-type galaxies
and the kinematic properties of their disks. The mass for galaxies with
a wide variety of properties, from dwarf dIrr galaxies with active star
formation to giant low-brightness galaxies, is shown to correlate with the
product ( is the rotational velocity, and is the radial
photometric disks scale length), which characterizes the specific angular
momentum of the disk. This relationship, along with the anticorrelation between
the relative mass of HI in a galaxy and , can be explained in terms of the
previously made assumption that the gas density in the disks of most galaxies
is maintained at a level close to the threshold (marginal) stability of a
gaseous layer to local gravitational perturbations. In this case, the
regulation mechanism of the star formation rate associated with the growth of
local gravitational instability in the gaseous layer must play a crucial role
in the evolution of the gas content in the galactic disk.Comment: revised version to appear in Astronomy Letters, 8 pages, 5 EPS
figure
PINGS: the PPAK IFS Nearby Galaxies Survey
We present the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey:
PINGS, a 2-dimensional spectroscopic mosaicking of 17 nearby disk galaxies in
the optical wavelength range. This project represents the first attempt to
obtain continuous coverage spectra of the whole surface of a galaxy in the
nearby universe. The final data set comprises more than 50000 individual
spectra, covering in total an observed area of nearly 80 arcmin^2. In this
paper we describe the main astrophysical issues to be addressed by the PINGS
project, we present the galaxy sample and explain the observing strategy, the
data reduction process and all uncertainties involved. Additionally, we give
some scientific highlights extracted from the first analysis of the PINGS
sample.Comment: Accepted for publication in MNRAS, 26 pages, 14 figures (some in low
resolution), 3 table
The outer disks of galaxies: "To be or not to be truncated?"
We have in recent years come to view the outer parts of galaxies as having
vital clues about their formation and evolution. Here, we would like to briefly
present our results from a complete sample of nearby, late-type, spiral
galaxies, using data from the SDSS survey, especially focused on the stellar
light distribution in the outer disk. Our study shows that only the minority of
late-type galaxies show a classical, exponential Freeman Type I profile down to
the noise limit, whereas the majority exhibit either downbending (stellar
truncation as introduced 1979 by Piet van der Kruit) or upbending profiles.Comment: LaTeX, 6 pages. To appear in the proceedings of the "Island
Universes: Structure and Evolution of Disk Galaxies" conference held in
Terschelling, Netherlands, July 2005, ed. R. de Jong (Springer: Dordrecht
The circumnuclear environment of the peculiar galaxy NGC 3310
Gas and star velocity dispersions have been derived for eight circumnuclear
star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC3310
using high resolution spectroscopy in the blue and far red. Stellar velocity
dispersions have been obtained from the CaII triplet in the near-IR, using
cross-correlation techniques, while gas velocity dispersions have been measured
by Gaussian fits to the Hb 4861A and [OIII]5007A emission lines.
The CNSFRs stellar velocity dispersions range from 31 to 73 km/s. These
values, together with the sizes measured on archival HST images, yield upper
limits to the dynamical masses for the individual star clusters between 1.8 and
7.1 x 10 M, for the whole CNSFR between 2 x 10 and 1.4 x 10
M, and 5.3 x 10 M for the nucleus inside the inner 14.2 pc.
The masses of the ionizing stellar population responsible for the HII region
gaseous emission have been derived from their published Ha luminosities and are
found to be between 8.7 x 10 and 2.1 x 10 M for the
star-forming regions, and 2.1 x 10 M for the galaxy nucleus; they
therefore constitute between 1 and 7 per cent of the total dynamical mass.
The ionized gas kinematics is complex; two different kinematical components
seem to be present as evidenced by different line widths and Doppler shifts.Comment: 24 pages, accepted by MNRA
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