569 research outputs found
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
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
The shape of galaxy disks: how the scale height increases with galactocentric distance
We present the results of a detailed study of vertical surface brightness
profiles of edge-on disk galaxies. Although the exponential disk scale height
is constant to first order approximation, we show that for the large majority
of galaxies in our sample, the scale height increases with distance along the
major axis. The effect is strongest for early-type galaxies, where the increase
of the scale height can be as much as a factor of 1.5 per scalelength, but is
almost 0 for the latest-type galaxies. The effect can be understood if
early-type disk galaxies have thick disks with both scale lengths and scale
heights larger than those of the dominant disk component. Its origin appears to
be linked to the processes that have formed the thick disk.Comment: 4 pages, Latex, 3 figures, accepted for publication in Astronomy &
Astrophysics (Letters
The scatter in the near-infrared colour-magnitude relation in spiral galaxies
Abstract: Over the past three decades the established view of a nearly homogeneuous, featureless Universe on scales larger than a few Megaparsec has been completely overhauled. In particular through the advent of ever larger galaxy redshift surveys we were revealed a galaxy distribution displaying an intriguing cellular pattern in which filamentary and wall-like structures, as well as huge regions devoid of galaxies, are amongst the most conspicuous morphological elements. In this contribution we will provide an overview of the present observational state of affairs concerning the distribution of galaxies and the structure traced out by the matter distribution in our Universe. In conjunction with the insight on the dynamics of the structure formation process obtained through the mapping of the peculiar velocities of galaxies in our local Universe and the information on the embryonic circumstances that prevailed at the epoch of Recombination yielded by the various Cosmic Microwave Background experiments, we seek to arrive at a more or less compelling theoretical framework of structure formation.The main aspects of this framework of the rise of structure through gravitational instability can probably be most readily appreciated through illustrative examples of various scenarios, as for instance provided by some current state-of-the-art N-body simulations. We will subsequently wrap up the observational and theoretical evidence for the emergence and evolution of structure in the Universe by sketching the stage for the ultimate Holy Grail of late 20th century astrophysics, understanding the saga of the formation of what arguably are the most prominent and at the same time intoxicatingly beautiful and intriguing denizens of our Cosmos, the {it galaxies}
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