39 research outputs found
Starbursts in Barred Spiral Galaxies. III. Definition of a homogeneous sample of Starburst Nucleus Galaxies
This paper presents optical long-slit spectroscopic observations of 105
barred Markarian IRAS galaxies. These observations are used to determine the
spectral type of emission-line regions in the nucleus and along the bar of the
galaxies, in order to define a homogeneous sample of Starburst Nucleus Galaxies
(SBNGs). Our selection criteria have been very efficient for selecting
star-forming galaxies, since our sample of 221 emission-line regions includes
82% nuclear or extranuclear starbursts. The contamination by Seyferts is low
(9%). The remaining galaxies (9%) are objects with ambiguous classification
(HII or LINER). The dust content and Halpha luminosity increase towards the
nuclei of the galaxies. No significant variation of the electron density is
found between nuclear and bar HII regions. However, the mean Halpha luminosity
and electron density in the bar are higher than in typical disk HII regions. We
investigate different mechanisms for explaining the excess of nitrogen emission
observed in our starburst nuclei. There is no evidence for the presence of a
weak hidden active galactic nucleus in our starburst galaxies. The cause of
this excess is probably a selective enrichment of nitrogen in the nuclei of the
galaxies, following a succession of short and intense bursts of star formation.
Our sample of SBNGs, located at a mean redshift of 0.015, has moderate Halpha
(10^41 erg/s) and far infrared (10^10 Lsun) luminosities. The types are
distributed equally among early- and late-type giant spirals with a slight
preference for Sbc/Sc types because of their barred morphology. The majority
(62%) of SBNGs are isolated with no sign of gravitational interaction. In terms
of distance, luminosity and level of interaction, SBNGs are intermediate
between HII galaxies and luminous infrared galaxies.Comment: Accepted for publication in A&A Supplement Series. 14 pages including
12 figures and 7 table
A cosmologically motivated description of the dark matter halo profile for the Low Surface Brightness Galaxy, Malin 1
In this paper we derive a possible mass profile for the low surface
brightness galaxy, Malin 1, based upon previously published space-based and
ground-based photometric properties and kinematics. We use properties of the
bulge, normal disk, outer extended disk and \ion{H}{1} mass as inputs into mass
profile models. We find that the dark matter halo model of Malin 1 is best
described by a halo profile that has undergone adiabatic contraction,
inconsistent with the findings for most disk galaxies to date, yet consistent
with rotation curve studies of M31. More importantly, we find that Malin 1 is
baryon dominated in its central regions out to a radius of kpc (in the
bulge region). Low-surface brightness galaxies are often referred to as being
dark matter dominated at all radii. If this is the case, then Malin 1 would
seem to have characteristics similar to those of normal barred disk galaxies,
as suggested by other recent work. We also find that Malin 1 also falls on the
rotation curve shear versus spiral arm pitch angle relation for normal
galaxies, although more LSB galaxies need to be studied to determine if this is
typical.Comment: 10 pages, 3 figures (1 color), accepted for publication in PAS
Measurement of Galactic Logarithmic Spiral Arm Pitch Angle Using Two-Dimensional Fast Fourier Transform Decomposition
A logarithmic spiral is a prominent feature appearing in a majority of
observed galaxies. This feature has long been associated with the traditional
Hubble classification scheme, but historical quotes of pitch angle of spiral
galaxies have been almost exclusively qualitative. We have developed a
methodology, utilizing two-dimensional fast Fourier transformations of images
of spiral galaxies, in order to isolate and measure the pitch angles of their
spiral arms. Our technique provides a quantitative way to measure this
morphological feature. This will allow comparison of spiral galaxy pitch angle
to other galactic parameters and test spiral arm genesis theories. In this
work, we detail our image processing and analysis of spiral galaxy images and
discuss the robustness of our analysis techniques.Comment: 23 pages, 22 figures, and 3 Tables; published in ApJS 199, 33
http://iopscience.iop.org/0067-0049/199/2/33/; software available for
download at http://dafix.uark.edu/~ages/downloads.html and
http://astro.host.ualr.edu/2DFFT
Leading Wave as a Component of the Spiral Pattern of the Galaxy
The spiral pattern of the Galaxy identified by analyzing the kinematics of
young stars within 3 kpc of the Sun is Fourier decomposed into spiral
harmonics. The spiral pattern of the Galaxy is shown to be representable as a
superposition of trailing and leading waves with interarm distances of
1.8(+/-0.4) kpc and 4(+/-2) kpc, respectively. Shock waves are probably present
only in the portions of the trailing spiral pattern where it crosses the crest
of the leading wave. The small interarm distance of the trailing spiral wave
(1.8 kpc) can be explained by its evolution - by the decrease in the interarm
distance as the wave is displaced toward the inner Lindblad resonance. The
Carina arm may be part of this resonance ring.Comment: 17 pages, 4 figures, to be published in Astronomy Letters, 200