153 research outputs found
Extented ionized gas emission and kinematics of the compact group galaxies in HCG 16: Signatures of mergers
We report on kinematic observations of Ha emission line from four late-type
galaxies of Hickson Compact Group 16 (H16a,b,c and d) obtained with a scanning
Fabry-Perot interferometer and samplings of 16 km/s and 1". The velocity fields
show kinematic peculiarities for three of the four galaxies: H16b, c and d.
Misalignments between the kinematic and photometric axes of gas and stellar
components (H16b,c,d), double gas systems (H16c) and severe warping of the
kinematic major axis (H16b and c) were some of the peculiarities detected. We
conclude that major merger events have taken place in at least two of the
galaxies group. H16c and d, based on their significant kinematic peculiarities,
their double nuclei and high infrared luminosities. Their Ha gas content is
strongly spatially concentred - H16d contains a peculiar bar-like structure
confined to the inner 1 h^-1 kpc region. These observations are in
agreement with predictions of simulations, namely that the gas flows towards
the galaxy nucleus during mergers, forms bars and fuel the central activity.
Galaxy H16b, and Sb galaxy, also presents some of the kinematic evidences for
past accretion events. Its gas content, however, is very spare, limiting our
ability to find other kinematic merging indicators, if they are present. We
find that isolated mergers, i.e., they show an anormorphous morphology and no
signs of tidal tails. Tidal arms and tails formed during the mergers may have
been stripped by the group potential (Barnes & Hernquist 1992) ar alternatively
they may have never been formed. Our observations suggest that HCG 16 may be a
young compact group in formation throught the merging of close-by objects in a
dense environment.Comment: Accepted for publication in ApJ. 35 pages, 13 figures. tar file
gzipped and uuencode
Calibrating Type Ia Supernovae using the Planetary Nebula Luminosity Function I. Initial Results
We report the results of an [O III] lambda 5007 survey for planetary nebulae
(PN) in five galaxies that were hosts of well-observed Type Ia supernovae: NGC
524, NGC 1316, NGC 1380, NGC 1448 and NGC 4526. The goals of this survey are to
better quantify the zero-point of the maximum magnitude versus decline rate
relation for supernovae Type Ia and to validate the insensitivity of Type Ia
luminosity to parent stellar population using the host galaxy Hubble type as a
surrogate. We detected a total of 45 planetary nebulae candidates in NGC 1316,
44 candidates in NGC 1380, and 94 candidates in NGC 4526. From these data, and
the empirical planetary nebula luminosity function (PNLF), we derive distances
of 17.9 +0.8/-0.9 Mpc, 16.1 +0.8/-1.1 Mpc, and 13.6 +1.3/-1.2 Mpc respectively.
Our derived distance to NGC 4526 has a lower precision due to the likely
presence of Virgo intracluster planetary nebulae in the foreground of this
galaxy. In NGC 524 and NGC 1448 we detected no planetary nebulae candidates
down to the limiting magnitudes of our observations. We present a formalism for
setting realistic distance limits in these two cases, and derive robust lower
limits of 20.9 Mpc and 15.8 Mpc, respectively.
After combining these results with other distances from the PNLF, Cepheid,
and Surface Brightness Fluctuations distance indicators, we calibrate the
optical and near-infrared relations for supernovae Type Ia and we find that the
Hubble constants derived from each of the three methods are broadly consistent,
implying that the properties of supernovae Type Ia do not vary drastically as a
function of stellar population. We determine a preliminary Hubble constant of
H_0 = 77 +/- 3 (random) +/- 5 (systematic) km/s/Mpc for the PNLF, though more
nearby galaxies with high-quality observations are clearly needed.Comment: 25 pages, 12 figures. Accepted for publication by the Astrophysical
Journal. Figures degraded to comply with limit. Full paper is available at:
http://www.as.ysu.edu/~jjfeldme/pnlf_Ia.pd
Fabrication of corrugated Ge-doped silica fibers
We present a method of fabricating Ge-doped SiO2 fibers with corrugations around their full circumference for a desired length in the longitudinal direction. The procedure comprises three steps: hydrogenation of Ge-doped SiO2 fibers to increase photosensitivity, recording of Bragg gratings with ultraviolet light to achieve modulation of refractive index, and chemical etching. Finite-length, radially corrugated fibers may be used as couplers. Corrugated tapered fibers are used as high energy throughput probes in scanning near-field optical microscopy
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
Magellanic Cloud Structure from Near-IR Surveys II: Star Count Maps and the Intrinsic Elongation of the LMC
I construct a near-IR star count map of the LMC and demonstrate, using the
viewing angles derived in Paper I, that the LMC is intrinsically elongated. I
argue that this is due to the tidal force from the Milky Way. The near-IR data
from the 2MASS and DENIS surveys are used to create a star count map of RGB and
AGB stars, which is interpreted through ellipse fitting. The radial number
density profile is approximately exponential with a scale-length 1.3-1.5 kpc.
However, there is an excess density at large radii that may be due to the tidal
effect of the Milky Way. The position angle and ellipticity profile converge to
PA_maj = 189.3 +/- 1.4 degrees and epsilon = 0.199 +/- 0.008 for r > 5 deg. At
large radii there is a drift of the center of the star count contours towards
the near side of the plane, which can be undrestood as due to viewing
perspective. The fact that PA_maj differes from the line of nodes position
angle Theta = 122.5 +/- 8.3 (cf. Paper I) indicates that the LMC disk is not
circular, but has an intrinsic ellipticity of 0.31. The LMC is elongated in the
general direction of the Galactic center, and is elongated perpendicular to the
Magellanic Stream and the velocity vector of the LMC center of mass. This
suggests that the elongation of the LMC has been induced by the tidal force of
the Milky Way. The position angle of the line of nodes differs from the
position angle Theta_max of the line of maximum line of sight velocity
gradient: Theta_max - Theta = 20-60 degrees. This could be due to: (a)
streaming along non-circular orbits in the elongated disk; (b) uncertainties in
the transverse motion of the LMC center of mass; (c) precession and nutation of
the LMC disk as it orbits the Milky Way (expected on theoretical grounds).
[Abridged]Comment: Astronomical Journal, in press. 34 pages, LaTeX, with 7 PostScript
figures. Contains minor revisions with respect to previously posted version.
Check out http://www.stsci.edu/~marel/lmc.html for a large scale (23x21
degree) stellar number-density image of the LMC constructed from RGB and AGB
stars in the 2MASS and DENIS surveys. The paper is available with higher
resolution color figures from
http://www.stsci.edu/~marel/abstracts/abs_R32.htm
Star formation and figure rotation in the early-type galaxy NGC2974
We present Galaxy Evolution Explorer (GALEX) far (FUV) and near (NUV)
ultraviolet imaging of the nearby early-type galaxy NGC2974, along with
complementary ground-based optical imaging. In the ultraviolet, the galaxy
reveals a central spheroid-like component and a newly discovered complete outer
ring of radius 6.2kpc, with suggestions of another partial ring at an even
larger radius. Blue FUV-NUV and UV-optical colours are observed in the centre
of the galaxy and from the outer ring outward, suggesting young stellar
populations (< 1Gyr) and recent star formation in both locations. This is
supported by a simple stellar population model which assumes two bursts of star
formation, allowing us to constrain the age, mass fraction and surface mass
density of the young component pixel by pixel. Overall, the mass fraction of
the young component appears to be just under 1per cent (lower limit,
uncorrected for dust extinction). The additional presence of a nuclear and an
inner ring (radii 1.4 and 2.9kpc, respectively), as traced by [OIII] emission,
suggests ring formation through resonances. All three rings are consistent with
a single pattern speed of km/s/kpc, typical of S0 galaxies and only
marginally slower than expected for a fast bar if traced by a small observed
surface brightness plateau. This thus suggests that star formation and
morphological evolution in NGC2974 at the present epoch are primarily driven by
a rotating asymmetry (probably a large-scale bar), despite the standard
classification of NGC2974 as an E4 elliptical.Comment: 13 pages, 10 figures, Changed content, Accepted for publication in
MNRA
Deep CCD Surface Photometry of Galaxy Clusters I: Methods and Initial Studies of Intracluster Starlight
We report the initial results of a deep imaging survey of galaxy clusters.
The primary goals of this survey are to quantify the amount of intracluster
light as a function of cluster properties, and to quantify the frequency of
tidal debris. We outline the techniques needed to perform such a survey, and we
report findings for the first two galaxy clusters in the survey: Abell 1413,
and MKW 7 . These clusters vary greatly in richness and structure. We show that
our surface photometry reliably reaches to a surface brightness of \mu_v = 26.5
mags per arcsec. We find that both clusters show clear excesses over a
best-fitting r^{1/4} profile: this was expected for Abell 1413, but not for MKW
7. Both clusters also show evidence of tidal debris in the form of plumes and
arc-like structures, but no long tidal arcs were detected. We also find that
the central cD galaxy in Abell 1413 is flattened at large radii, with an
ellipticity of , the largest measured ellipticity of any cD galaxy
to date.Comment: 58 pages, 24 figures, accepted for publication in the Astrophysical
Journal. Version has extremely low resolution figures to comply with 650k
limit. High resolution version is available at
http://burro.astr.cwru.edu/johnf/icl1.ps.gz Obtaining high resolution version
is strongly reccomende
Shall We (Math and) Dance?
Can we use mathematics, and in particular the abstract branch of category
theory, to describe some basics of dance, and to highlight structural
similarities between music and dance? We first summarize recent studies between
mathematics and dance, and between music and categories. Then, we extend this
formalism and diagrammatic thinking style to dance.Comment: preprin
VLT photometry in the Antlia Cluster: the giant ellipticals NGC 3258 and NGC 3268 and their globular cluster systems
We present a deep VLT photometry in the regions surrounding the two dominant
galaxies of the Antlia cluster, the giant ellipticals NGC 3258 and NGC 3268. We
construct the luminosity functions of their globular cluster systems (GCSs) and
determine their distances through the turn-over magnitudes. These distances are
in good agreement with those obtained by the SBF method. There is some, but not
conclusive, evidence that the distance to NGC 3268 is larger by several Mpc.
The GCSs colour distributions are bimodal but the brightest globular clusters
(GCs) show a unimodal distribution with an intermediate colour peak. The radial
distributions of both GCSs are well fitted by de Vaucouleurs laws up to 5
arcmin. Red GCs present a steeper radial density profile than the blue GCs, and
follow closely the galaxies' brightness profiles. Total GC populations are
estimated to be about 6000+/-150 GCs in NGC 3258 and 4750+/-150 GCs in NGC
3268. We discuss the possible existence of GCs in a field located between the
two giant galaxies (intracluster GCs). Their luminosity functions and number
densities are consistent with the two GCSs overlapping in projection.Comment: 13 pages, 16 figures. Accepted for publication in MNRA
Small-scale systems of galaxies. II. Properties of the NGC 4756 group of galaxies
We present results from a study of the NGC 4756 group which is dominated by
the elliptical galaxy NGC 5746. The characteristics of the group are
investigated through (a) the detailed investigation of the morphological,
photometric and spectroscopic properties of nine galaxies among the dominant
members of the group (b) the determination of the photometric parameters of the
faint galaxy population in an area of 34'x34' centered on NGC 4756 and (c) an
analysis of the X-ray emission in the area based upon archival data. The 9
member galaxies are located in the core part of the NGC 4756 group (a strip
diameter about 300 kpc in diameter which has a very loose configuration. The
central part of the NGC 4756 group contains a significant fraction of
early-type galaxies. Three new group members with previously unknown systemic
velocities are identified, one of which is a dE. At about 7.5' SW of NGC 4756 a
sub-structure of the group is detected, including IC 829, MCG -2-33-35, MCG
-2-33-36 and MCG -2-33-38, which meets the Hickson criteria for being a compact
group. Most of the galaxies in this sub-structure show interaction signatures.
We do not detect apparent fine structure and signatures of recent interaction
events in the early-type galaxy population, with the exception of a strong dust
lane in the elliptical MCG -2-33-38. This galaxy displays however signatures of
nuclear activity. Strong [O III], [N II] and [S II] line emission, combined
with comparatively weak, but broad H alpha emission suggest an intermediate
Seyfert type classification. Although the area is heavily contaminated by the
background cluster Abell 1631, X-ray data suggest the presence of a hot
intergalactic medium related to the group to the X-ray emission detected. The
present results are discussed in the context of group evolution.Comment: 45 pages including 10 figures and 8 tables accepted for publication
in A
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