599 research outputs found
IAU Symposium 241 - Stellar Populations as Building Blocks of Galaxies
Stellar populations, building blocks of galaxies, are direct tracers of the
star formation history, the chemical enrichment and the assembly of galaxies in
the Universe. They therfore allow us to understand how galaxies formed and
evolved. This last decade has witnessed a revolution in our observations of
galaxies; with larger telescopes and new instruments we are not only able to
look deeper in the Universe, we can also study nearby galaxies with greater
detail. The fact that now is becoming possible to resolve stars up to the
distance of Virgo Cluster allows us to rigorously compare and calibrate the
analysis of the integrated light with resolved stellar populations. These
Proceedings report the considerable progress made in recent years in this
topic. Theorists and observers, researchers of resolved and unresolved stellar
populations, discussed the ingredients of stellar population models, and
rigorously compared them to new data, forcing theorists to develop more refined
models and methods to derive the physical parameters of the stellar
populations. New results from the Milky Way, the Local Group, and nearby and
distant galaxies were presented.Comment: This is the table of contents of the upcoming proceedings of IAU
Symposium 241. The book will appear in September, from Cambridge University
Press, and will also be available electronically at
http://www.journals.cambridge.org/action/displayJournal?jid=IA
Near-Infrared Surface Photometry of Bulges and Disks of Spiral Galaxies. The Data
We present optical and near-infrared (NIR) surface brightness and colour
profiles,in bands ranging from U to K, for the disk and bulge components of a
complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than
50 degrees. We describe in detail the observations and the determination of
colour parameters. Calibrated monochromatic and real-colour images are
presented, as well as colour index maps. This data set, tailored for the study
of the population characteristics of galaxy bulges, provides useful information
on the colours of inner disks as well. In related papers, we have used them to
quantify colour gradients in bulges, and age differentials between bulge and
inner disk.Comment: 18 pages Latex with 2 postscript figures. Accepted for New Astronomy.
This is an electronic paper; a complete preprint, including all of the tables
and figures can be found at
ftp://www.astro.rug.nl/peletier/newast/newast.htm
Stellar Distributions and NIR Colours of Normal Galaxies
We discuss some results of a morphological study of edge-on galaxies, based
on optical and especially near-infrared surface photometry. We find that the
vertical surface brightness distributions of galaxies are fitted very well by
exponential profiles, much better than by isothermal distributions. We find
that in general the vertical scale height increases when going outward. This
increase is strong for early-type spiral galaxies and very small for late
types. We argue that it can be due to the presence of thick discs with scale
lengths larger than the galaxy's main disc. Finally we discuss the
colour-magnitude relation in I-K for spiral galaxies. We find that it is a
tight relation, for which the scatter is similar to the observational
uncertainties, with a steeper slope than for elliptical galaxies.Comment: Invited review, to appear in "Extragalactic Astronomy in the
Infrared", eds. G.A. Mamon, Trinh Xuan Thuan, and J. Tran Thanh Van, Editions
Frontieres, Gif-sur-Yvette. LaTeX2e, 10 pages, 6 postscript figures and
moriond.sty included. See also
ftp://kapteyn.astro.rug.nl/peletier/lesarcs.ps.g
Spiral galaxy distance indicators based on near-infrared photometry
We compare two methods of distance determination to spiral galaxies using
optical/near-infrared (NIR) observations, the (I-K) versus M_K colour -
absolute magnitude (CM) relation and the I and K-band Tully-Fisher relation
(TFR). Dust-free colours and NIR absolute magnitudes greatly enhance the
usefulness of the NIR CM relation as a distance indicator for moderately to
highly inclined_spiral_ galaxies_in the field_ (inclinations between ~ 80 and
90 deg); by avoiding contamination by dust the scatter in the CM relation is
significantly reduced, compared to similar galaxy samples published previously.
The CM relation can be used to determine distances to field spiral galaxies
with M_K > -25.5, to at least M_K ~ -20. Our results, supplemented with
previously published observations for which we can - to some degree - control
the effects of extinction, are consistent with a universal nature of the CM
relation for field spiral galaxies. High-resolution observations done with the
Hubble Space Telescope can provide a powerful tool to calibrate the relation
and extend the useful distance range by more than a factor of 2 compared to
ground-based observations. The intrinsic scatter in the NIR CM relation in the
absolute K-band magnitudes is ~0.5 mag, yielding a lower limit to the accuracy
of distance determinations on the order of 25%. Although we find an unusually
low scatter in the TFR (probably a statistical accident), a typical scatter in
the TFR would yield distances to our sample galaxies with uncertainties of only
about 15%. However, one of the main advantages of the use of the NIR CM
relation is that_we only need photometric data_ to obtain distance estimates;
use of the TFR requires additional kinematic data, although it can be used to
significantly greater distances.Comment: 12 pages, incl. 5 postscript files, LaTeX, accepted for publication
in MNRA
A monolithic collapse origin for the thin/thick disc structure of ESO 243-49
ESO 243-49 is a high-mass (circular velocity ) edge-on S0 galaxy in the Abell 2877 cluster at a distance of
. To elucidate the origin of its thick disc, we use MUSE
science verification data to study its kinematics and stellar populations. The
thick disc emits of the light at heights in excess of
(). The rotation velocities of its stars
lag by compared to those in the thin disc, which is
compatible with the asymmetric drift. The thick disc is found to be more
metal-poor than the thin disc, but both discs have old ages. We suggest an
internal origin for the thick disc stars in high-mass galaxies. We propose that
the thick disc formed either first in a turbulent phase with a high
star formation rate and that a thin disc formed shortly afterwards, or because of the dynamical heating of a thin pre-existing component. Either
way, the star formation in ESO 243-49 was quenched just a few Gyrs after the
galaxy was born and the formation of a thin and a thick disc must have occurred
before the galaxy stopped forming stars. The formation of the discs was so fast
that it could be described as a monolithic collapse where several generations
of stars formed in a rapid succession.Comment: Accepted for publication in A&A. The reduced data-cube as well as the
data necessary to build the kinematic and stellar population maps are
available at
https://etsin.avointiede.fi/dataset/urn-nbn-fi-csc-kata2016092414291163237
The z-structure of disk galaxies towards the galaxy planes
We present a detailed study of a statistically complete sample of highly
inclined disk galaxies in the near-infrared K' band. Since the K'-band light is
relatively insensitive to contamination by galactic dust, we have been able to
follow the vertical light distributions all the way down to the galaxy planes.
The mean levels for the sharpness of the K'-band luminosity peaks indicate that
the vertical luminosity distributions are more peaked than expected for the
intermediate sech(z) distribution, but rounder than exponential. Since
projection of not completely edge-on galaxies onto the plane of the sky causes
vertical luminosity profiles to become rounder, we have performed simulations
that show that it is possible that all our galaxies can have intrinsically
exponential vertical surface brightness distributions. We find that the profile
shape is independent of galaxy type, and varies little with position along the
major axis. The fact that we observe this in all our sample galaxies indicates
that the formation process of the galaxy disks perpendicular to the galaxy
planes is a process intrinsic to the disks themselves.Comment: 23 pages, LaTeX, includes 12 figures, accepted for publication in
Astronomy and Astrophysics. Fig. 1 will be sent on reques
The Stellar Populations of Pixels and Frames
Derived from first physical principles, a few simple rules are presented that
can help in both the planning and interpretation of CCD and IR-array camera
observations of resolvable stellar populations. These rules concern the overall
size of the population sampled by a frame as measured by its total luminosity,
and allow to estimate the number of stars (in all evolutionary stages) that are
included in the frame. The total luminosity sampled by each pixel (or
resolution element) allows instead to estimate to which depth meaningful
stellar photometry can be safely attempted, and below which crowding makes it
impossible. Simple relations give also the number of pixels (resolution
elements) in the frame that will contain an unresolved blend of two stars of
any kind. It is shown that the number of such blends increases quadratically
with both the surface brightness of the target, as well as with the angular
size of the pixel (or resolution element). A series of examples are presented
illustrating how the rules are practically used in concrete observational
situations. Application of these tools to existing photometric data for the
inner parts of the bulge of M31, M32 and NGC 147 indicates that no solid
evidence has yet emerged for the presence of a significant intermediate age
population in these objects.Comment: 28 pages, LaTeX file using aasms4.sty, 2 postscript figures To appear
on: The Astronomical Journa
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