1,969 research outputs found
What are S0 (0) Galaxies?
Among early-type galaxies with almost circular isophotes E0 and E1 galaxies
are, at 99.3% significance, more luminous than face-on objects classified as S0
(0) and S(0) (1). This result supports the view that rotation and "diskiness"
are more important in the outer regions of faint-early type galaxies than they
are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres
Caltech Faint Galaxy Redshift Survey XV: Classification of Galaxies with 0.2 < z < 1.1 in the Hubble Deep Field (North) and its Flanking Fields
To circumvent the spatial effects of resolution on galaxy classification, the
images of 233 objects of known redshift in the Hubble Deep Field (HDF) and its
Flanking Fields (FF) that have redshifts in the range 0.20 < z < 1.10 were
degraded to the resolution that they would have had if they were all located at
a redshift z= 1.00. As in paper XIV of the present series, the effects of
shifts in rest wavelength were mitigated by using R-band images for the
classification of galaxies with 0.2 < z < 0.6 and I-band images for objects
with redshifts 0.6 < z < 1.1. A special effort was made to search for bars in
distant galaxies. The present data strongly confirm the previous conclusion
that the Hubble tuning fork diagram only provides a satisfactory framework for
the classification of galaxies with z ~< 0.3. More distant disk galaxies are
often difficult to shoehorn into the Hubble classification scheme. The paucity
of barred spirals and of grand-design spirals at large redshifts is confirmed.
It is concluded that the morphology of disk galaxies observed at look-back
times smaller than 3--4 Gyr differs systematically from that of more distant
galaxies viewed at look-back times of 4--8 Gyr. The disks of late-type spirals
at z >0.5 are seen to be more chaotic than those of their nearer counterparts.
Furthermore the spiral structure in distant early-type spirals appears to be
less well-developed than it is in nearby early-galaxies.Comment: Accepted for publication in the A
Caltech Faint Galaxy Redshift Survey XIV: Galaxy Morphology in the HDF (North) and its Flanking Fields to z=1.2
Morphological classifications are reported for Hubble Space Telescope (HST)
images of 241 galaxies in the Hubble Deep Field (HDF) and its Flanking Fields
(FF) with measured redshifts in the interval 0.25 < z < 1.2, drawn from a
magnitude-limited redshift survey to R = 24.0. The galaxies are divided into
three groups with redshifts in the intervals [0.25,0.6], [0.6,0.8], [0.8,1.2].
R606 images from the first group and I814 images from the second and third
groups are compared with B-band images of nearby galaxies. All classifications
were therefore made at approximately the same rest wavelength. Selection biases
are discussed. We corroborate and extend the results of earlier investigations
by observing that: Most intermediate and late-type galaxies with
have morphologies that are dramatically different from those of local galaxies
and cannot be shoehorned into the Hubble ``tuning fork'' classification scheme.
Grand-design spirals appear to be rare or absent for . Many Sa and
Sb spirals with do not exhibit well-defined spiral arms. The arms
of distant Sc galaxies appear more chaotic than those of their nearby
counterparts. (abridged) On the basis of these and similar observations, it is
inferred that the development of pronounced spiral structure was delayed until
\~5 Gyr and that most bulges are probably not formed by disintegrating bars.
Major morphological changes were still taking place only ~5 Gyr ago even though
changes in the integrated light of most galaxies were then much slower than
they were ~10 Gyr ago.Comment: Accepted by the Astronomical Journa
Some Musings on Galaxy Morphology
Careful inspection of large-scale photographs of Shapley-Ames galaxies seems
to show a smooth transition between the morphological characteristics of
galaxies located on the narrow red, and on the broad blue, sequences in the
galaxian color-magnitude diagram. In other words there does not appear to be a
dichotomy between blue and red galaxies. Both the colors and the morphologies
of galaxies are found to correlate strongly with their environments. Red and
early-type Shapley-Ames galaxies are dominant in clusters, whereas blue
late-type star forming objects dominate the general field. Interestingly the
colors and morphologies of galaxies in small groups resemble the field and
differ from those in clusters. As noted by Baade the presence of dust and star
formation are very closely correlated, except in a few galaxies that probably
had unusual evolutionary histories. Over the entire range from S0 to Sc there
is no significant difference between the integrated colors of normal and barred
objects suggesting that the formation of a bar does not significantly affect
the stellar evolutionary history of a galaxy.Comment: 13 figures; Astronomical Journal in pres
Globular Clusters and Dwarf Spheroidal Galaxies
Traditionally globular clusters and dwarf spheroidal galaxies have been
distinguished by using one or more of the following criteria: (1) mass, (2)
luminosity, (3) size, (4) mass-to-light ratio and (5) spread in metallicity.
However, a few recently discovered objects show some overlap between the
domains in parameter space that are occupied by galaxies and clusters. In the
present note it is shown that ellipticity can, in some cases, be used to help
distinguish between globular clusters and dwarf spheroidal galaxies.Comment: MNRAS (Letters), in pres
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