227 research outputs found
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
NGC 770: A Counter-Rotating Core in a Low-Luminosity Elliptical Galaxy
We present evidence for a counter-rotating core in the low-luminosity (M_B =
-18.2) elliptical galaxy NGC 770 based on internal stellar kinematic data. This
counter-rotating core is unusual as NGC 770 is not the primary galaxy in the
region and it lies in an environment with evidence of on-going tidal
interactions. We discovered the counter-rotating core via single-slit Keck/ESI
echelle spectroscopy; subsequent integral field spectroscopy was obtained with
the Gemini/GMOS IFU. The counter-rotating region has a peak rotation velocity
of 21 km/s as compared to the main galaxy's rotation speed of greater than 45
km/s in the opposite direction. The counter-rotating region extends to a radius
of 4'' (0.6 kpc), slightly smaller than the half-light radius of the galaxy
which is 5.3'' (0.8 kpc) and is confined to a disk whose scale height is less
than 0.8'' (0.1 kpc). We compute an age and metallicity of the inner
counter-rotating region of 3 +/- 0.5 Gyr and [Fe/H] = 0.2 +/- 0.2 dex, based on
Lick absorption-line indices. The lack of other large galaxies in this region
limits possible scenarios for the formation of the counter-rotating core. We
discuss several scenarios and favor one in which NGC 770 accreted a small
gas-rich dwarf galaxy during a very minor merging event. If this scenario is
correct, it represents one of the few known examples of merging between two
dwarf-sized galaxies.Comment: 26 pages, 9 figures. Accepted to AJ. See this
http://www.ociw.edu/~mgeha/geha.ps.gz for version with high resolution
figure
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: II. Rotating Versus Non-Rotating Dwarfs
We present spatially-resolved internal kinematics and stellar chemical
abundances for a sample of dwarf elliptical (dE) galaxies in the Virgo Cluster
observed with Keck/ESI. We find that 4 out of 17 dEs have major axis rotation
velocities consistent with rotational flattening, while the remaining dEs have
no detectable major axis rotation. Despite this difference in internal
kinematics, rotating and non-rotating dEs are remarkably similar in terms of
their position in the Fundamental Plane, morphological structure, stellar
populations, and local environment. We present evidence for faint underlying
disks and/or weak substructure in a fraction of both rotating and non-rotating
dEs, but a comparable number of counter-examples exist for both types which
show no evidence of such structure. Absorption-line strengths were determined
based on the Lick/IDS system (Hbeta, Mgb, Fe5270, Fe5335) for the central
region of each galaxy. We find no difference in the line-strength indices, and
hence stellar populations, between rotating and non-rotating dE galaxies. The
best-fitting mean age and metallicity for our 17 dE sample are 5 Gyr and Fe/H =
-0.3 dex, respectively, with rms spreads of 3 Gyr and 0.1 dex. The majority of
dEs are consistent with solar alpha/Fe abundance ratios. By contrast, the
stellar populations of classical elliptical galaxies are, on average, older,
more metal rich, and alpha-enhanced relative to our dE sample. The local
environments of both dEs types appear to be diverse in terms of their proximity
to larger galaxies in real or velocity space within the Virgo Cluster. Thus,
rotating and non-rotating dEs are remarkably similar in terms of their
structure, stellar content, and local environments, presenting a significant
challenge to theoretical models of their formation. (abridged)Comment: 33 pages, 12 figures. To appear in the October 2003 Astronomical
Journal. See http://www.ucolick.org/~mgeha/geha_dE.ps.gz for version with
high resolution figure
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
Dynamical Models of Elliptical Galaxies in z=0.5 Clusters: I. Data-Model Comparison and Evolution of Galaxy Rotation
We present spatially resolved stellar rotation velocity and velocity
dispersion profiles form Keck/LRIS absorption-line spectra for 25 galaxies,
mostly visually classified ellipticals, in three clusters at z=0.5. We
interpret the kinematical data and HST photometry using oblate axisymmetric
two-integral f(E,Lz) dynamical models based on the Jeans equations. This yields
good fits, provided that the seeing and observational characteristics are
carefully modeled. The fits yield for each galaxy the dynamical M/L and a
measure of the galaxy rotation rate. Paper II addresses the implied M/L
evolution. Here we study the rotation-rate evolution by comparison to a sample
of local elliptical galaxies of similar present-day luminosity. The brightest
galaxies in the sample all rotate too slowly to account for their flattening,
as is also observed at z=0. But the average rotation rate is higher at z=0.5
than locally. This may be due to a higher fraction of misclassified S0 galaxies
(although this effect is insufficient to explain the observed strong evolution
of the cluster S0 fraction with redshift). Alternatively, dry mergers between
early-type galaxies may have decreased the average rotation rate over time. It
is unclear whether such mergers are numerous enough in clusters to explain the
observed trend quantitatively. Disk-disk mergers may affect the comparison
through the so-called progenitor bias, but this cannot explain the direction of
the observed rotation-rate evolution. Additional samples are needed to
constrain possible environmental dependencies and cosmic variance in galaxy
rotation rates. Either way, studies of the internal stellar dynamics of distant
galaxies provide a valuable new approach for exploring galaxy evolution.Comment: ApJ, submitted; 17 pages formatted with emulateap
The Nuclear Ionized Gas in the Radio Galaxy M84 (NGC 4374)
We present optical images of the nucleus of the nearby radio galaxy M84 (NGC
4374 = 3C272.1) obtained with the Wide Field/Planetary Camera 2 (WFPC2) aboard
the Hubble Space Telescope (HST). Our three images cover the H + [N II]
emission lines as well as the V and I continuum bands. Analysis of these images
confirms that the H + [N II] emission in the central 5'' (410 pc) is
elongated along position angle (P.A.) \approx 72\arcdeg, which is roughly
parallel to two nuclear dust lanes.Our high-resolution images reveal that the
H + [N II] emission has three components, namely a nuclear gas disk,an
`ionization cone', and outer filaments. The nuclear disk of ionized gas has
diameter pc and major axis P.A. \approx 58\arcdeg \pm
6\arcdeg. On an angular scale of 0\farcs5, the major axis of this nuclear
gas disk is consistent with that of the dust. However, the minor axis of the
gas disk (P.A. \approx 148\arcdeg) is tilted with respect to that of the
filamentary H + [N II] emission at distances > 2'' from the nucleus;
the minor axis of this larger scale gas is roughly aligned with the axis of the
kpc-scale radio jets (P.A. \approx 170\arcdeg). The ionization cone (whose
apex is offset by \approx 0\farcs3 south of the nucleus) extends 2'' from the
nucleus along the axis of the southern radio jet. This feature is similar to
the ionization cones seen in some Seyfert nuclei, which are also aligned with
the radio axes.Comment: 11 pages plus 4 figure
Detection of Radial Surface Brightness Fluctuation and Color Gradients in elliptical galaxies with ACS
We study surface brightness fluctuations (SBF) in a sample of 8 elliptical
galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data
drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the
F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when
available -- are presented. Galaxy surface brightness profiles are determined
as well. We present the first SBF--broadband color calibration for the ACS/WFC
F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies.
We detect and study in detail the SBF variations within individual galaxies
as a probe of possible changes in the underlying stellar populations.
Inspecting both the SBF and color gradients in comparison to model predictions,
we argue that SBF, and SBF-gradients, can in principle be used for unraveling
the different evolutionary paths taken by galaxies, though a more comprehensive
study of this issue would be required. We confirm that the radial variation of
galaxy stellar population properties should be mainly connected to the presence
of radial chemical abundance gradients, with the outer galaxy regions being
more metal poor than the inner ones.Comment: 47 pages, 13 figures, ApJ, accepte
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
Discovery of a Boxy Peanut Shaped Bulge in the Near Infrared
We report on the discovery of a boxy/peanut shaped bulge in the highly
inclined barred Seyfert 2 galaxy NGC~7582. The peanut shape is clearly evident
in near infrared images but obscured by extinction from dust in visible
images. This suggests that near infrared imaging surveys will discover a
larger number of boxy/peanut morphologies than visible surveys, particularly in
galaxies with heavy extinction such as NGC~7582. The bulge in NGC~7582 exhibits
strong boxiness compared to other boxy/peanut shaped bulges. If the starburst
was mediated by the bar, then it is likely that the bar formed in less than a
few bar rotation periods or a few years ago. If the bar also
caused the peanut, then the peanut would have formed quickly; on a timescale of
a few bar rotation periods.Comment: AAS Latex and Postcript Figures, accepted for publication in Ap
A Merger Scenario for the Dynamics of Abell 665
We present new redshift measurements for 55 galaxies in the vicinity of the
rich galaxy cluster Abell 665. When combined with results from the literature,
we have good velocity measurements for a sample of 77 confirmed cluster members
from which we derive the cluster's redshift z=0.1829 +/- 0.0005 and
line-of-sight velocity dispersion of 1390 +/- 120 km/s. Our analysis of the
kinematical and spatial data for the subset of galaxies located within the
central 750 kpc reveals only subtle evidence for substructure and
non-Gaussianity in the velocity distribution. We find that the brightest
cluster member is not moving significantly relative to the other galaxies near
the center of the cluster. On the other hand, our deep ROSAT high resolution
image of A665 shows strong evidence for isophotal twisting and centroid
variation, thereby confirming previous suggestions of significant substructure
in the hot X-ray--emitting intracluster gas. In light of this evident
substructure, we have compared the optical velocity data with N-body
simulations of head-on cluster mergers. We find that a merger of two similar
mass subclusters (mass ratios of 1:1 or 1:2) seen close to the time of
core-crossing produces velocity distributions that are consistent with that
observed.Comment: 30 pages and 7 figures. Accepted by the Astrophysical Journal Full
resoultion figures 1 and 3 available in postscript at
http://www.physics.rutgers.edu/~percy/A665paper.htm
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