577 research outputs found
The dwarf low surface brightness population in different environments of the Local Universe
The nature of the dwarf galaxy population as a function of location in the
cluster and within different environments is investigated. We have previously
described the results of a search for low surface brightness objects in data
drawn from an East-West strip of the Virgo cluster (Sabatini et al., 2003) and
have compared this to a large area strip outside of the cluster (Roberts et
al., 2004). In this talk I compare the East-West data (sampling sub-cluster A
and outward) to new data along a North-South cluster strip that samples a
different region (part of sub-cluster A, and the N,M clouds) and with data
obtained for the Ursa Major cluster and fields around the spiral galaxy M101.
The sample of dwarf galaxies in different environments is obtained from uniform
datasets that reach central surface brightness values of ~26 B mag/arcsec^2 and
an apparent B magnitude of 21 (M_B=-10 for a Virgo Cluster distance of 16 Mpc).
We discuss and interpret our results on the properties and distribution of
dwarf low surface brightness galaxies in the context of variuos physical
processes that are thought to act on galaxies as they form and evolve.Comment: 10 pages, 3 figures, to appear in "Dark Galaxies and Lost Baryons",
IAU244 conference proceeding
The Shape and Orientation of NGC 3379: Implications for Nuclear Decoupling
The intrinsic shape and orientation of the elliptical galaxy NGC 3379 are
estimated by dynamical modeling. The maximal ignorance shape estimate, an
average over the parameter space, is axisymmetric and oblate in the inner
parts, with an outward triaxiality gradient. The 1 sigma limits on total-mass
triaxiality T are T < 0.13 at 0.33 kpc and T = 0.08 +/- 0.07 at 3.5 kpc from
the center. The luminous short-to-long axis ratio c_L = 0.79 +0.05-0.1 inside
0.82 kpc, flattening to c_L = 0.66 +0.07-0.08 at 1.9 kpc. The results are
similar if the galaxy is assumed to rotate about its short axis. Estimates for
c_L are robust, but those for T are dependent on whether the internal rotation
field is disklike or spheroid-like. Short-axis inclinations between 30 and 50
degrees are preferred for nearly axisymmetric models; but triaxial models in
high inclination are also allowed, which can affect central black hole mass
estimates. The available constraints on orientation rule out the possibility
that the nuclear dust ring at R = 1.5" is in a stable equilibrium in one of the
galaxy's principal planes. The ring is thus a decoupled nuclear component not
linked to the main body of the galaxy. It may be connected with ionized gas
that extends to larger radii, since the projected gas rotation axis is near the
minor axis of the ring. The gas and dust may both be part of a strongly warped
disk; however, if caused by differential precession, the warp will wind up on
itself in a few 10^7 years. The decoupling with the stellar component suggests
that the gas has an external origin, but no obvious source is present.Comment: Astronomical Journal, accepted. 15 pages, incl. 5 figs, 1 table.
AASTeX 4.0. Paper with better quality figures in PDF format at
http://www.phy.ohiou.edu/~tss/Shape3379.pd
New UBVRI colour distributions in E-type galaxies I.The data
New colour distributions have been derived from wide field UBVRI frames for
36 northern bright elliptical galaxies and a few lenticulars. The classical
linear representations of colours against log r were derived, with some
improvements in the accuracy of the zero point colours and of the gradients.
The radial range of signicant measurements was enlarged both towards the
galaxian center and towards the outskirts of each object. Thus, the "central
colours", integrated within a radius of 3", and the "outermost colours"
averaged near the mu_V = 24 surface brightness, could also be obtained. Some
typical deviations of colour profiles from linearity are described.
Colour-colour relations of interest are presented. Very tight correlations are
found between the U-V colour and the Mg2 line-index, measured either at the
galaxian center or at the effective radius.Comment: 34 pages, 10 figures, to appear in A&A journa
A Correlation between Galaxy Light Concentration and Supermassive Black Hole Mass
We present evidence for a strong correlation between the concentration of
bulges and the mass of their central supermassive black hole (M_bh) -- more
concentrated bulges have more massive black holes. Using C_{r_e}(1/3) from
Trujillo, Graham & Caon (2001b) as a measure of bulge concentration, we find
that log (M_bh/M_sun) = 6.81(+/-0.95)C_{r_e}(1/3) + 5.03(+/-0.41). This
correlation is shown to be marginally stronger (Spearman's r_s=0.91) than the
relationship between the logarithm of the stellar velocity dispersion and log
M_bh (Spearman's r_s=0.86), and has comparable, or less, scatter (0.31 dex in
log M_bh), which decreases to 0.19 dex when we use only those galaxies whose
supermassive black hole's radius of influence is resolved and remove one well
understood outlying data point).Comment: 7 pages, 1 table, 2 figures. ApJ Letters, accepte
Correlations among global photometric properties of disk galaxies
Using a two-dimensional galaxy image decomposition technique, we extract
global bulge and disk parameters for a complete sample of early type disk
galaxies in the near infrared K band. We find significant correlation of the
bulge parameter n with the central bulge surface brightness and with
effective radius r_e. Using bivar iate analysis techniques, we find that , and are distributed in a plane with small scatter. We
do not find a strong correlation of n with bulge-to-disk luminosity ratio,
contrary to earlier reports. r_e and the disk scale length r_d are well
correlated for these early type disk galaxies, but with large scatter. We
examine the implications of our results to various bulge formation scenarios in
disk galaxies.Comment: 14 pages, LaTeX including 14 figures. To appear in the Astrophysical
Journa
The Stellar Kinematic Fields of NGC 3379
We have measured the stellar kinematic profiles of NGC 3379 along four
position angles using the MMT. The data extend 90" from the center, at
essentially seeing-limited resolution out to 17". The mean velocities and
dispersions have total errors better than 10 km/s (frequently better than 5
km/s) out to 55". We find very weak (3 km/s) rotation on the minor axis
interior to 12", and no detectable rotation above 6 km/s from 12" to 50" or
above 16 km/s out to 90" (95% confidence). However, a Fourier reconstruction of
the mean velocity field from all 4 sampled PAs does indicate a 5 degree twist
of the kinematic major axis, opposite to the known isophotal twist. The h_3 and
h_4 parameters are small over the entire observed region. The
azimuthally-averaged dispersion profile joins smoothly at large radii with the
dispersions of planetary nebulae. Unexpectedly, we find sharp bends in the
major-axis rotation curve, also visible (though less pronounced) on the
diagonal position angles. The outermost bend coincides in position with other
sharp kinematic features: an abrupt flattening of the dispersion profile, and
local peaks in h_3 and h_4. All of these features are in a region where the
surface brightness profile departs significantly from a de Vaucouleurs law.
Features such as these are not generally known in ellipticals owing to a lack
of data at comparable resolution; however, very similar behavior is seen the
kinematics of the edge-on S0 NGC 3115. We discuss the suggestion that NGC 3379
could be a misclassified S0; preliminary results from dynamical modeling
indicate that it may be a flattened, weakly triaxial system seen in an
orientation that makes it appear round.Comment: 31 pages incl. 4 tables, Latex, AASTeX v4.0, with 17 eps figures. To
appear in The Astronomical Journal, February 199
M32+/-1
WFPC-2 images are used to study the central structure of M31, M32, and M33.
The dimmer peak, P2, of the M31 double nucleus is centered on the bulge to
0.1", implying that it is the dynamical center of M31. P2 contains a compact
source discovered by King et al. (1995) at 1700 A. This source is resolved,
with r_{1/2} approx0.2 pc. It dominates the nucleus at 3000 A, and is
consistent with late B-early A stars. This probable cluster may consist of
young stars and be an older version of the cluster of hot stars at the center
of the Milky Way, or it may consist of heavier stars built up from collisions
in a possible cold disk of stars orbiting P2. In M32, the central cusp rises
into the HST limit with gamma approx0.5, and the central density
rho_0>10^7M_sol pc^-3. The V-I and U-V color profiles are flat, and there is no
sign of an inner disk, dust, or any other structure. This total lack of
features seems at variance with a nominal stellar collision time of 2 X 10^10
yr, which implies that a significant fraction of the light in the central pixel
should come from blue stragglers. InM33, the nucleus has an extremely steep
gamma=1.49 power-law profile for 0.05"<r<0.2" that becomes shallower as the HST
resolution limit is approached. The profile for r<0.04" has either a gamma
approx 0.8 cusp or a small core with r_c ~<0.13 pc. The central density is
rho_0 > 2 10^6M_sol pc^-3, and the implied relaxation time is only ~3 X 10^6
yr, indicating that the nucleus is highly relaxed. The accompanying short
collision time of 7 X 10^9 yr predicts a central blue straggler component
quantitatively consistent with the strong V-I and B-R color gradients seen with
HST and from the ground.Comment: 44 pages, 22 figures (7 as separate JPEG images), submitted to The
Astronomical Journal. Full postscript image available at
http://www.noao.edu/noao/staff/lauer/lauer_paper
Morphological classification and structural parameters for early-type galaxies in the Coma cluster
We present the results of an isophotal shape analysis of three samples of
galaxies in the Coma cluster. Quantitative morphology, together with structural
and photometric parameters, is given for each galaxy. Special emphasis has been
placed on the detailed classification of early-type galaxies.
The three samples are: i) a sample of 97 early-type galaxies brighter than
m = 17.00 falling within one degree from the center of the Coma cluster;
these galaxies were observed with CCD cameras, mostly in good to excellent
resolution conditions; ii) a magnitude complete sample of 107 galaxies of all
morphological types down to m = 17.00 falling in a circular region of 50
arcmin diameter, slightly offcentered to the North-West of the cluster center;
the images for this and the next sample come from digitized photographic
plates; iii) a complete comparison sample of 26 galaxies of all morphological
types down to m = 16.05 (or m 17.5), also in a region of 50
arcmin diameter, but centered 2.6 degrees West of the cluster center.
The reliability of our morphological classifications and structural
parameters of galaxies, down to the adopted magnitude limits, is assessed by
comparing the results on those galaxies for which we had images taken with
different instrumentation and/or seeing conditions, and by comparing our
results with similar data from other observers.Comment: 22 pages, including 4 figures and 4 tables, uuencoded, gzipped
postscrip
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