64 research outputs found
Does the stellar disc flattening depend on the galaxy type?
We analyze the dependence of the stellar disc flatness on the galaxy
morphological type using 2D decomposition of galaxies from the reliable
subsample of the Edge-on Galaxies in SDSS (EGIS) catalogue. Combining these
data with the retrieved models of the edge-on galaxies from the Two Micron All
Sky Survey (2MASS) and the Spitzer Survey of Stellar Structure in Galaxies
(SG) catalogue, we make the following conclusions:
(1) The disc relative thickness in the near- and mid-infrared
passbands correlates weakly with morphological type and does not correlate with
the bulge-to-total luminosity ratio in all studied bands.
(2) Applying an 1D photometric profile analysis overestimates the disc
thickness in galaxies with large bulges making an illusion of the relationship
between the disc flattening and the ratio .
(3) In our sample the early-type disc galaxies (S0/a) have both flat and
"puffed" discs. The early spirals and intermediate-type galaxies have a large
scatter of the disc flatness, which can be caused by the presence of a bar:
barred galaxies have thicker stellar discs, on average. On the other hand, the
late-type spirals are mostly thin galaxies, whereas irregular galaxies have
puffed stellar discs.Comment: 17 pages, 17 figures, accepted for publication in MNRA
Polar-bulge galaxies
Based on SDSS data, we have selected a sample of nine edge-on spiral galaxies
with bulges whose major axes show a high inclination to the disk plane. Such
objects are called polar-bulge galaxies. They are similar in their morphology
to polar-ring galaxies, but the central objects in them have small size and low
luminosity. We have performed a photometric analysis of the galaxies in the g
and r bands and determined the main characteristics of their bulges and disks.
We show that the disks of such galaxies are typical for the disks of spiral
galaxies of late morphological types. The integrated characteristics of their
bulges are similar to the parameters of normal bulges. The stellar disks of
polar-bulge galaxies often show large-scale warps, which can be explained by
their interaction with neighboring galaxies or external accretion from outside.Comment: 8 pages, 3 figure
The possible evolution of pitch angles of spiral galaxies
The origin and maintenance of spiral structure in galaxies, the correlation
between different types of spiral structure and several proposed mechanisms for
their generation, and the evolution of spiral arms of galaxies with time are
questions that are still controversial. In this note we study the spiral
structure in a sample of distant galaxies in order to infer the evolution of
spiral arm characteristics with redshift. We considered a sample of 171 face-on
spiral galaxies in the Hubble Space Telescope COSMOS (The Cosmic Evolution
Survey) field. The galaxies are distributed up to with a mean
value of 0.44. For all galaxies, we determined the pitch angles of the spiral
arms and analysed their dependence on redshift; a total of 359 arms were
measured. Analyses of our measurements combined with the literature data
suggest a possible evolution of the pitch angles of spiral galaxies: by the
modern epoch the spiral pattern, on average, becomes more tightly wound. This
may be a consequence of the general evolution of the structure of galaxies as
galaxies become more massive over time and their bulges grow. In addition, the
distribution of the cotangent of pitch angle of galaxies indicates the
possibility that the dominant mechanism of spiral pattern generation changes
over time.Comment: 5 pages, accepted for publication on Astronomy & Astrophysics Letter
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