518 research outputs found
Star formation in outer rings of S0 galaxies. I. NGC 6534 and MCG 11-22-015
Though S0 galaxies are usually thought to be `red and dead', they often
demonstrate star formation organized in ring structures. We try to clarify the
nature of this phenomenon and its difference from star formation in spiral
galaxies. Two early-type galaxies with outer rings, NGC 6534 and MCG 11-22-015,
are selected to be studied. The ionized gas is excited by young stars in the
ring of NGC 6534 and partly by shocks -- in MCG 11-22-015. The oxygen
abundances in the HII regions of the rings are close to solar. We estimate the
star formation rates (SFR) in the two outer rings of the galaxies by using
several SFR indicators derived from narrow-band photometry in the H-alpha
emission line and archival GALEX ultraviolet images of the galaxies. The
derived SFRs allow to qualitatively restore star formation histories (SFH) in
the rings: in NGC 6534 the SFH is flat during the last 100-200 Myr, and in MCG
11-22-015 the star formation has started only a few Myr ago. We suggest that
the rings in NGC 6534 and MCG 11-22-015 have different natures: the former is a
resonant one supplied with gas perhaps through tidal effects, and the latter
has been produced by a satellite accretion. Recent outer gas accretion is
implied in both cases.Comment: 5 pages, 6 figures, accepted into the Astronomy and Astrophysic
Possibly interacting Vorontsov-Velyaminov galaxies. I. Observations of VV432, VV543 and VV747
Among the galaxies which were included in the Atlas and Catalogue of
Interacting galaxies by Vorontsov-Velyaminov (hereafter VV) as multiple systems
("nests", "chains" and similarly looking systems), there are many objects,
where the interaction is not evident. Some of them are single objects,
including low-mass galaxies with active star formation (SF). In this work we
present the description of observations and results of the long-slit
spectrophotometry with the Russian 6-m telescope of three VV-galaxies looking
like double or multiple systems, and HI-observations of one of them in order to
elucidate their nature, determine their metallicity, kinematic properties and
the evolution status. Galaxies VV432 and VV747 are found to be dwarf systems
with low oxygen abundance (O/H = 1/22 and 1/12 of the solar value,
respectively). Their velocity curves indicate quite slow rotation with
respective maximum velocities of about 60 and 80 km/s, in agreement with their
low luminosities. The distance to VV432 is rather uncertain. If it is a member
of Virgo Cluster, this is the most metal-deficient known galaxy of this
aggregate. For galaxy VV543 the measured emission-line redshift 0.047 appeared
ten times larger than it was given in the original paper and is cited in
databases. This "system" evidently represents an optical pair of two galaxies
with large velocity difference. The fainter western component is an HII-galaxy,
while the brighter one is an absorption-line early-type galaxy with the radial
velocity being 1600 km/s lower.Comment: 11 pages, A&AS in press. Version of the paper with Figures 1-3 of the
higher quality is available via
http://precise.sao.ru/Laboratory/Publications/2000_pub.htm
Spectral monitoring of AGNs: Preliminary results for Ark 564 and Arp 102B
We present preliminary results of the long term spectral monitoring of two
active galactic nuclei with different broad line shapes: Ark 564 and Arp 102B.
Ark 564 is a bright nearby narrow line Syfert 1 (NLS1) galaxy with relatively
narrow permitted optical emission lines and a high FeII/H ratio, while
Arp 102B is a nearby broad-line radio galaxy with broad double-peaked Balmer
emission lines. The spectra of Ark 564 were observed during 11-year period
(1999-2009) and the spectra of Arp 102B in the 12-year period (1998-2009), with
SAO 6-m and 1-m telescopes (Russia) and the GHAO 2.1-m telescope (Cananea,
Mexico).Comment: Presented on "8th Serbian Conference on Spectral Line Shapes in
Astrophysics". In revised version minor changes in the tex
Two epoch spectro-imagery of FS Tau B outflow system
Herbig-Haro (HH) flows exhibit a large variety of morphological and
kinematical structures such as bow shocks, Mach disks, and deflection shocks.
Both proper motion (PM) and radial velocity investigations are essential to
understand the physical nature of such structures. We investigate the
kinematics and PM of spectrally separated structures in the FS~Tau~B HH flow.
Collating these data makes it possible to understand the origin of these
structures and to explain the unusual behavior of the jet. On the other hand,
the study of emission profiles in the associated reflection nebulae allows us
to consider the source of the outflow both from edge-on and pole-on points of
view. We present the observational results obtained with the 6 m telescope at
the Special Astrophysical Observatory of the Russian Academy of Sciences using
the SCORPIO multimode focal reducer with a scanning Fabry-Perot interferometer.
Two epochs of the observations of the FS~Tau~B region in H emission
(2001 and 2012) allowed us to measure the PM of the spectrally separated inner
structures of the jet. In addition to already known emission structures in the
FS~Tau~B system, we discover new features in the extended part of the jet and
in the counter-jet. Moreover, we reveal a new HH knot in the HH~276 independent
outflow system and point out its presumable source. In the terminal working
surface of the jet, structures with different radial velocities have PMs of the
same value. This result can be interpreted as the direct observation of
bow-shock and Mach disk regions. A bar-like structure, located southwest from
the source demonstrates zero PM and can be considered as one more example of
deflection shock. An analysis of H profiles in the reflection nebulae
R1 and R3 indicates the uniqueness of this object, which can be studied in
pole-on and edge-on directions simultaneously.Comment: 8 pages, 11 figure
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