123 research outputs found
3D spectroscopy of dwarf elliptical galaxies
I present some results of 3D spectroscopy for a small sample of dwarf
elliptical galaxies, mostly members of small groups. The galaxies under
consideration have a typical absolute magnitude of -18 (B-band), and at the
Kormendy's relation they settle within a transition zone between the main cloud
of giant ellipticals and the sequence of diffuse ellipticals. By measuring Lick
indices and investigating radial profiles of the SSP-equivalent ages and
metallicities of the stellar populations in their central parts, I have found
evolutionary distinct cores in all of them. Typically, the ages of these cores
are 2-4 Gyr, and the metallicities are higher than the solar one. Outside the
cores, the stellar populations are always old, T>12 Gyr, and the metallicities
are subsolar. This finding implies that the well-known correlation between the
stellar age and the total mass (luminosity) of field ellipticals (Trager et al.
2000, Caldwell et al. 2003, Howell 2005) may be in fact a direct consequence of
a larger contribution of nuclear starbursts into the integrated stellar
population in dwarfs with respect to giants, and does not relate to
`downsizing'.Comment: 2 pages, 1 figure. Poster contribution to the proceedings of the
conference "A Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010
Synchronous Evolution of Galaxies in Groups: NGC 524 Group
By means of panoramic spectroscopy at the SAO RAS BTA telescope, we
investigated the properties of stellar populations in the central regions of
five early-type galaxies -- the NGC 524 group members. The evolution of the
central regions of galaxies looks synchronized: the average age of stars in the
bulges of all the five galaxies lies in the range of 3--6 Gyr. Four of the five
galaxies revealed synchronized bursts of star formation in the nuclei 1--2 Gyr
ago. The only galaxy, in which the ages of stellar population in the nucleus
and in the bulge coincide (i.e. the nuclear burst of star formation did not
take place) is NGC 502, the farthest from the center of the group of all the
galaxies studied.Comment: Slightly edited version of the paper to appear in the Astrophysical
Bulletin, 67(3); 24 pages including 8 figure
Star Formation History at the Centers of Lenticular Galaxies with Bars and Purely Exponential Outer Disks from SAURON Data
We have investigated the stellar population properties in the central regions
of a sample of lenticular galaxies with bars and single-exponential outer
stellar disks using the data from the SAURON integral-field spectrograph
retrieved from the open Isaac Newton Group Archive. We have detected chemically
decoupled compact stellar nuclei with a metallicity twice that of the stellar
population in the bulges in seven of the eight galaxies. A starburst is
currently going on at the center of the eighth galaxy and we have failed to
determine the stellar population properties from its spectrum. The mean stellar
ages in the chemically decoupled nuclei found range from 1 to 11 Gyr. The
scenarios for the origin of both decoupled nuclei and lenticular galaxies as a
whole are discussed.Comment: 10 pages, 4 figures, a slightly edited version of the paper published
by Astronomy Letters, v. 37, no.1, 201
A new method for reconstructing the density distribution of matter in the disks of spiral galaxies from the rotation velocity curve in it
In this paper we propose a new method for reconstructing the surface density
of matter in flat disks of spiral galaxies. The surface density is expressed
through observational rotation velocity curves of visible matter in the disks
of spiral galaxies. The new method is not based on quadrature of special
functions. The found solution is used for processing and analysis of
observational data from several spiral galaxies. The new method can be used to
more accurately estimate the amount of dark matter in spiral galaxies.Comment: 18 pages, 6 figure
Face-on galaxies NGC 524 and NGC 6340: chemically decoupled nuclei and inclined circumnuclear disks
Central regions of the early-type disk galaxies NGC 524 and NGC 6340 have
been investigated with the Multi-Pupil Field Spectrograph at the 6m telescope
of the Special Astrophysical Observatory of the Russian Academy of Sciences. I
confirm the existence of chemically distinct stellar nuclei in these galaxies
which have been claimed earlier. The metallicity differences which are found
between the nuclei and the bulges, 0.5 - 1.0 kpc from the centers, reach 0.5 -
0.6 dex. Both nuclei are magnesium overabundant, but the bulges have different
magnesium-to-iron ratios: it is solar in NGC 6340 and the same as the nuclear
one in NGC 524. The kinematical and morphological analyses reveal the existence
of inclined central disks in these galaxies. In NGC 524 the central disk
consists of stars, dust, and ionized gas; its extension may be as large as up
to R=3 kpc, and it is inclined by more than 20 deg to the global galactic
plane. In NGC 6340 only a gaseous polar disk with the radius less than 500 pc
is detected.Comment: 25 pages, 15 figures, to appear in Astronomical Journal, August2000
issu
Nature of nuclear rings in unbarred galaxies: NGC 7742 and NGC 7217
We have studied the unbarred Sb galaxy with a nuclear star-forming ring, NGC
7742, by means of 2D spectroscopy, long-slit spectroscopy, and imaging, and
have compared the results with the properties of another galaxy of this type,
NGC 7217, which is studied by us earlier. Both galaxies have many peculiar
features in common: each has two global exponential stellar disks with
different scalelengths, each possesses a circumnuclear inclined gaseous disk
with a radius of 300 pc, and each has a global counterrotating subsystem,
gaseous one in NGC 7742 and stellar one in NGC 7217. We suggest that past minor
merger is the probable cause of all these peculiarities, including appearance
of the nuclear star-forming rings without global bars; the rings might be
produced as resonance features by tidally induced oval distortions of the
global stellar disks.Comment: Accepted to AJ, 11 PS/EPS figures (5 figures were added in color
Inner Polar Rings and Disks: Observed Properties
A list of galaxies with inner regions revealing polar (or strongly inclined
to the main galactic plane) disks and rings is compiled from the literature
data. The list contains 47 galaxies of all morphological types, from E to Irr.
We consider the statistics of the parameters of polar structures known from
observations. The radii of the majority of them do not exceed 1.5 kpc. The
polar structures are equally common in barred and unbarred galaxies. At the
same time, if a galaxy has a bar (or a triaxial bulge), this leads to the polar
disk stabilization - its axis of rotation usually coincides with the major axis
of the bar. More than two thirds of all considered galaxies reveal one or
another sign of recent interaction or merging. This fact indicates a direct
relation between the external environment and the presence of an inner polar
structure.Comment: 12 pages, 3 figures, accepted to Astrophysical Bulletin. Minor
changes and corrections are still possibl
Assessing the Formation Scenarios for the Double Nucleus of M31 Using Two-Dimensional Image Decomposition
The double nucleus geometry of M31 is currently best explained by the
eccentric disk hypothesis of Tremaine, but whether the eccentric disk resulted
from the tidal disruption of an inbounding star cluster by a nuclear black
hole, or by an m=1 perturbation of a native nuclear disk, remains debatable. I
perform detailed 2-D decomposition of the M31 double nucleus in the Hubble
Space Telescope V-band to study the bulge structure and to address competing
formation scenarios of the eccentric disk. I deblend the double nucleus (P1 and
P2) and the bulge simultaneously using five Sersic and one Nuker components. P1
and P2 appear to be embedded inside an intermediate component (r_e=3.2") that
is nearly spherical (q=0.97+/-m0.02), while the main galaxy bulge is more
elliptical (q=0.81+/-0.01). The spherical bulge mass of 2.8x10^7 M_sol is
comparable to the supermassive black hole mass (3x10^7 M_sol). In the 2-D
decomposition, the bulge is consistent with being centered near the UV peak of
P2, but the exact position is difficult to pinpoint because of dust in the
bulge. P1 and P2 are comparable in mass. Within a radius r=1\arcsec of P2, the
relative mass fraction of the nuclear components is M_BH:M_bulge:P1: P2 =
4.3:1.2:1:0.7, assuming the luminous components have a common mass-to-light
ratio of 5.7. The eccentric disk as a whole (P1+P2) is massive, M ~ 2.1x10^7
M_sol, comparable to the black hole and the local bulge mass. As such, the
eccentric disk could not have been formed entirely out of stars that were
stripped from an inbounding star cluster. Hence, the more favored scenario is
that of a disk formed in situ by an m=1 perturbation, caused possibly by the
passing of a giant molecular cloud, or the passing/accretion of a small
globular cluster.Comment: 19 pages, 8 figures. AJ accepted. For the version of this paper with
high resolution figures, go to:
http://zwicky.as.arizona.edu/~cyp/work/m31.ps.g
The Leo I Cloud: Secular nuclear evolution of NGC 3379, NGC 3384, and NGC 3368?
The central regions of the three brightest members of the Leo I galaxy group
-- NGC 3368, NGC 3379, and NGC 3384 -- are investigated by means of 2D
spectroscopy. In all three galaxies we have found separate circumnuclear
stellar and gaseous subsystems -- more probably, disks -- whose spatial
orientations and spins are connected to the spatial orientation of the
supergiant intergalactic HI ring reported previously by Schneider et al. (1983)
and Schneider (1985, 1989). In NGC 3368 the global gaseous disk seems also to
be inclined to the symmetry plane of the stellar body, being probably of
external origin. Although the rather young mean stellar age and spatial
orientations of the circumnuclear disks in NGC 3379, NGC 3384, and NGC 3368
could imply their recent formation from material of the intergalactic HI cloud,
the time scale of these secondary formation events, of order 3 Gyr, does not
support the collision scenario of Rood & Williams (1985), but is rather in line
with the ideas of Schneider (1985, 1989) regarding tidal interactions of the
galaxies with the HI cloud on timescales of the intergroup orbital motions.Comment: Accepted to ApJ, 46 pages (figs 18 and 22 are low resolution
Structure of the Galaxies in the NGC 80 Group
BV-bands photometric data obtained at the 6-m telescope of the Special
Astrophysical Observatory are used to analyze the structure of 13 large disk
galaxies in the NGC 80 group. Nine of the 13 galaxies under consideration are
classified by us as lenticular galaxies. The stellar populations in the
galaxies are very different, from old ones with ages of T>10 Gyrs (IC 1541) to
relatively young, with the ages of T<2-3 Gyr (IC 1548, NGC 85). In one case,
current star formation is known (UCM 0018+2216). In most of the galaxies, more
precisely in all of them more luminous than M(B) -18, two-tiered
(`antitruncated') stellar disks are detected, whose radial surface brightness
profiles can be fitted by two exponential segments with different scalelengths
-- shorter near the center and longer at the periphery. All dwarf S0 galaxies
with single-scalelength exponential disks are close companions to giant
galaxies. Except for this fact, no dependence of the properties of S0 galaxies
on distance from the center of the group is found. Morphological traces of
minor merger are found in the lenticular galaxy NGC 85. Basing on the last two
points, we conclude that the most probable mechanisms for the transformation of
spirals into lenticular galaxies in groups are gravitational ones, namely,
minor mergers and tidal interactions.Comment: 24 pages, 9 figures, slightly improved version of the paper published
in the December, 2009, issue of the Astronomy Report
- …