53 research outputs found
Evolution of field early-type galaxies: The view from GOODS CDFS
We explore the evolution of field early-type galaxies in a sample extracted from the ACS images of the southern GOODS field. The galaxies are selected by means of a nonparametric analysis, followed by visual inspection of the candidates with a concentrated surface brightness distribution. We furthermore exclude from the final sample those galaxies that are not consistent with an evolution into the Kormendy relation between surface brightness and size that is observed for z = 0 ellipticals. The final set, which comprises 249 galaxies with a median redshift z(m) = 0.71, represents a sample of early-type systems not selected with respect to color, with similar scaling relations as those of bona fide elliptical galaxies. The distribution of number counts versus apparent magnitude rejects a constant number density with cosmic time and suggests a substantial decrease with redshift: n proportional to (1 + z)(-2.5). The majority of the galaxies (78%) feature passively evolving old stellar populations. One-third of those in the upper half of the redshift distribution have blue colors, in contrast to only 10% in the lower redshift subsample. An adaptive binning of the color maps using an optimal Voronoi tessellation is performed to explore the internal color distribution. We find that the red and blue early-type galaxies in our sample have distinct behavior with respect to the color gradients, so that most blue galaxies feature blue cores whereas most of the red early-types are passively evolving stellar populations with red cores, i.e., similar systems to local early-type galaxies. Furthermore, the color gradients and scatter do not evolve with redshift and are compatible with the observations at z 0, assuming a radial dependence of the metallicity within each galaxy. Significant gradients in the stellar age are readily ruled out. This work emphasizes the need for a careful sample selection, as we found that most of those galaxies that were visually classified as candidate early types-but then rejected based on the Kormendy relation-feature blue colors characteristic of recent star formation
Late-type galaxies observed with SAURON. Two-dimensional stellar and emission-line kinematics of 18 spirals
We present the stellar and gas kinematics of a sample of 18 nearby late-type
spiral galaxies (Hubble types ranging from Sb to Sd), observed with the
integral-field spectrograph SAURON at the 4.2-m William Herschel Telescope.
SAURON covers the spectral range 4800-5380 A, allowing us to measure the Hbeta,
Fe, Mgb absorption features and the emission in the Hbeta line and the [OIII],
and [NI] doublets over a 33x41 arcsec field of view. The maps cover the nuclear
region of these late-type galaxies and in all cases include the entire bulge.
In many cases the stellar kinematics suggests the presence of a cold inner
region, as visible from a central drop in the stellar velocity dispersion. The
ionised gas is almost ubiquitous and behaves in a complicated fashion: the gas
velocity fields often display more features than the stellar ones, including
wiggles in the zero-velocity lines, irregular distributions, ring-like
structures. The line ratio [OIII]/Hbeta often takes on low values over most of
the field, probably indicating a wide-spread star formation.Comment: 34 pages, 24 figures. Accepted for publication in MNRAS. A version
with full resolution figures is available at
http://www.strw.leidenuniv.nl/sauron/papers/ganda2005_late_types.pd
Secular Evolution and the Growth of Pseudobulges in Disk Galaxies
Galaxy evolution is in transition from an early universe dominated by
hierarchical clustering to a future dominated by secular processes. These
result from interactions involving collective phenomena such as bars, oval
disks, spiral structure, and triaxial dark halos. This paper summarizes a
review by Kormendy & Kennicutt (2004) using, in part, illustrations of
different galaxies. In simulations, bars rearrange disk gas into outer rings,
inner rings, and galactic centers, where high gas densities feed starbursts.
Consistent with this picture, many barred and oval galaxies have dense central
concentrations of gas and star formation rates that can build bulge-like
stellar densities on timescales of a few billion years. We conclude that
secular evolution builds dense central components in disk galaxies that look
like classical, merger-built bulges but that were made slowly out of disk gas.
We call these pseudobulges. Many pseudobulges can be recognized because they
have characteristics of disks: (1) flatter shapes than those of classical
bulges, (2) correspondingly large ratios of ordered to random velocities, (3)
small velocity dispersions, (4) spiral structure or nuclear bars, (5) nearly
exponential brightness profiles, and (6) starbursts. These structures occur
preferentially in barred and oval galaxies in which secular evolution should be
most rapid. Thus a variety of observational and theoretical results contribute
to a new paradigm of secular evolution that complements hierarchical
clustering.Comment: 19 pages, 9 Postscript figures; requires kapproc.cls and procps.sty;
to appear in "Penetrating Bars Through Masks of Cosmic Dust: The Hubble
Tuning Fork Strikes a New Note", ed. Block, Freeman, Puerari, Groess, and
Block, Dordrecht: Kluwer, in press; for a version with full resolution
figures, see http://chandra.as.utexas.edu/~kormendy/ar3ss.htm
The Distribution of Dust and Gas in Elliptical Galaxies
Results from IRAS and recent optical CCD surveys are examined to discuss the
distribution and origin of dust and ionized gas in elliptical galaxies. In
strong contrast with the situation among spiral galaxies, masses of dust in
elliptical galaxies as derived from optical extinction are an order of
magnitude LOWER than those derived from IRAS data. I find that this dilemma can
be resolved by assuming the presence of a diffusely distributed component of
dust which is not detectable in optical data.
The morphology of dust lanes and their association with ionized gas in
elliptical galaxies argues for an external origin of BOTH components of the
ISM.Comment: Invited talk given at conference on "NEW EXTRAGALACTIC PERSPECTIVES
IN THE NEW SOUTH AFRICA: Changing Perceptions of the Morphology, Dust Content
and Dust-Gas Ratios in Galaxies", Held in Johannesburg, South Africa, during
January 22-26, 1996. Proceedings will be edited by D.L. Block and published
by Kluwer, Dordrecht, The Netherlands. uuencoded, gzipped LaTeX file of 8
pages; figures included as PostScript files (enclosed). Uses crckapb.sty
(enclosed) and psfig.st
The Interstellar Medium In Galaxies Seen A Billion Years After The Big Bang
Evolution in the measured rest frame ultraviolet spectral slope and
ultraviolet to optical flux ratios indicate a rapid evolution in the dust
obscuration of galaxies during the first 3 billion years of cosmic time (z>4).
This evolution implies a change in the average interstellar medium properties,
but the measurements are systematically uncertain due to untested assumptions,
and the inability to measure heavily obscured regions of the galaxies. Previous
attempts to directly measure the interstellar medium in normal galaxies at
these redshifts have failed for a number of reasons with one notable exception.
Here we report measurements of the [CII] gas and dust emission in 9 typical
(~1-4L*) star-forming galaxies ~1 billon years after the big bang (z~5-6). We
find these galaxies have >12x less thermal emission compared with similar
systems ~2 billion years later, and enhanced [CII] emission relative to the
far-infrared continuum, confirming a strong evolution in the interstellar
medium properties in the early universe. The gas is distributed over scales of
1-8 kpc, and shows diverse dynamics within the sample. These results are
consistent with early galaxies having significantly less dust than typical
galaxies seen at z<3 and being comparable to local low-metallicity systems.Comment: Submitted to Nature, under review after referee report. 22 pages, 4
figures, 4 Extended Data Figures, 5 Extended Data table
Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
We review internal processes of secular evolution in galaxy disks,
concentrating on the buildup of dense central features that look like
classical, merger-built bulges but that were made slowly out of disk gas. We
call these pseudobulges. As an existence proof, we review how bars rearrange
disk gas into outer rings, inner rings, and gas dumped into the center. In
simulations, this gas reaches high densities that plausibly feed star
formation. In the observations, many SB and oval galaxies show central
concentrations of gas and star formation. Star formation rates imply plausible
pseudobulge growth times of a few billion years. If secular processes built
dense central components that masquerade as bulges, can we distinguish them
from merger-built bulges? Observations show that pseudobulges retain a memory
of their disky origin. They have one or more characteristics of disks: (1)
flatter shapes than those of classical bulges, (2) large ratios of ordered to
random velocities indicative of disk dynamics, (3) small velocity dispersions,
(4) spiral structure or nuclear bars in the bulge part of the light profile,
(5) nearly exponential brightness profiles, and (6) starbursts. These
structures occur preferentially in barred and oval galaxies in which secular
evolution should be rapid. So the cleanest examples of pseudobulges are
recognizable. Thus a large variety of observational and theoretical results
contribute to a new picture of galaxy evolution that complements hierarchical
clustering and merging.Comment: 92 pages, 21 figures in 30 Postscript files; to appear in Annual
Review of Astronomy and Astrophysics, Vol. 42, 2004, in press; for a version
with full resolution figures, see
http://chandra.as.utexas.edu/~kormendy/ar3ss.htm
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
Dynamics of Disks and Warps
This chapter reviews theoretical work on the stellar dynamics of galaxy
disks. All the known collective global instabilities are identified, and their
mechanisms described in terms of local wave mechanics. A detailed discussion of
warps and other bending waves is also given. The structure of bars in galaxies,
and their effect on galaxy evolution, is now reasonably well understood, but
there is still no convincing explanation for their origin and frequency. Spiral
patterns have long presented a special challenge, and ideas and recent
developments are reviewed. Other topics include scattering of disk stars and
the survival of thin disks.Comment: Chapter accepted to appear in Planets, Stars and Stellar Systems, vol
5, ed G. Gilmore. 32 pages, 17 figures. Includes minor corrections made in
proofs. Uses emulateapj.st
M87 in the near-infrared: The jet and the counterjet regions
We have investigated the structure at near-infrared wavelengths (J and K bands) of the jet in M87, and of the expected counterjet region. We discuss the morphology of the IR emission not associated with optical sources and find that the near-IR structures of the jet and of the hotspot are morphologically intermediate between the radio and the optical, with both the hotspot and the jet more extended than in the optical. We attempt to measure the flux from the counterjet region and obtain an upper limit to its flux. Finally, we apply models of synchrotron emission to our data and discuss the implications of these fits
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