49 research outputs found
Stellar Motions in the Polar Ring Galaxy NGC 4650A
We present the first measurement of the stellar kinematics in the polar ring
of NGC 4650A. There is well defined rotation, with the stars and gas rotating
in the same direction, and with similar amplitude. The gaseous and stellar
kinematics suggest an approximately flat rotation curve, providing further
support for the hypothesis that the polar material resides in a disk rather
than in a ring. The kinematics of the emission line gas at and near the center
of the S0 suggests that the polar disk lacks a central hole. We have not
detected evidence for two, equal mass, counterrotating stellar polar streams,
as is predicted in the resonance levitation model proposed by Tremaine & Yu. A
merger seems the most likely explanation for the structure and kinematics of
NGC 4650A.Comment: 4 pages, accepted for publication in ApJ Letter
High Velocity Gas in the Halos of Spiral Galaxies
Recent, high sensitivity, HI observations of nearby spiral galaxies show that
their thin `cold' disks are surrounded by thick layers (halos) of neutral gas
with anomalous kinematics. We present results for three galaxies viewed at
different inclination angles: NGC891 (edge-on), NGC2403 (i=60 deg), and NGC6946
(almost face-on). These studies show the presence of halo gas up to distances
of 10-15 kpc from the plane. Such gas has a mean rotation 25-50 km/s lower than
that of the gas in the plane, and some complexes are detected at very high
velocities, up to 200-300 km/s. The nature and origin of this halo gas are
poorly understood. It can either be the result of a galactic fountain or of
accretion from the intergalactic medium. It is probably the analogous of some
of the High Velocity Clouds (HVCs) of the Milky Way.Comment: 6 pages, 4 figures. To appear in the ASP proceedings of IAU Symposium
217, "Recycling intergalactic and interstellar matter", eds. Pierre-Alain
Duc, Jonathan Braine, Elias Brink
The Disk Mass project; science case for a new PMAS IFU module
We present our Disk Mass project as the main science case for building a new
fiber IFU-module for the PMAS spectrograph, currently mounted at the Cassegrain
focus of the 3.5m telescope on Calar Alto. Compared to traditional long-slit
observations, the large light collecting power of 2-dimensional Integral Field
Units dramatically improves the prospects for performing spectroscopy on
extended low surface brightness objects with high spectral resolution. This
enables us to measure stellar velocity dispersions in the outer disk of normal
spiral galaxies. We describe some results from a PMAS pilot study using the
existing lenslet array, and provide a basic description of the new fiber
IFU-module for PMAS.Comment: 4 pages, 5 figures. Refereed proceeding for the `Euro3D Science
Workshop'. Contains updated layout of PPAK fibers, and improved M/L value for
N398
The Stellar and Gas Kinematics of Several Irregular Galaxies
We present long-slit spectra of three irregular galaxies from which we
determinethe stellar kinematics in two of the galaxies (NGC 1156 and NGC 4449)
and ionized-gas kinematics in all three (including NGC 2366). We compare this
to the optical morphology and to the HI kinematics of the galaxies. In the
ionized gas, we see a linear velocity gradient in all three galaxies. In NGC
1156 we also detect a weak linear velocity gradient in the stars of (5+/-1/sin
i) km/s/kpc to a radius of 1.6 kpc. The stars and gas are rotating about the
same axis, but this is different from the major axis of the stellar bar which
dominates the optical light of the galaxy. In NGC 4449 we do not detect
organized rotation of the stars and place an upper limit of (3/sin i) km/s/kpc
to a radius of 1.2 kpc. For NGC 4449, which has signs of a past interaction
with another galaxy, we develop a model to fit the observed kinematics of the
stars and gas. In this model the stellar component is in a rotating disk seen
nearly face-on while the gas is in a tilted disk with orbits whose planes
precess in the gravitational potential. This model reproduces the apparent
counter-rotation of the inner gas of the galaxy. The peculiar orbits of the gas
are presumed due to acquisition of gas in the past interaction.Comment: To be published in ApJ, November 20, 200
The DiskMass Survey. X. Radio synthesis imaging of spiral galaxies
We present results from 21 cm radio synthesis imaging of 28 spiral galaxies
from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We
detail the observations and data reduction procedures and present a brief
analysis of the radio data. We construct 21 cm continuum images, global HI
emission-line profiles, column-density maps, velocity fields, and
position-velocity diagrams. From these we determine star formation rates
(SFRs), HI line widths, total HI masses, rotation curves, and
azimuthally-averaged radial HI column-density profiles. All galaxies have an HI
disk that extends beyond the readily observable stellar disk, with an average
ratio and scatter of R_{HI}/R_{25}=1.35+/-0.22, and a majority of the galaxies
appear to have a warped HI disk. A tight correlation exists between total HI
mass and HI diameter, with the largest disks having a slightly lower average
column density. Galaxies with relatively large HI disks tend to exhibit an
enhanced stellar velocity dispersion at larger radii, suggesting the influence
of the gas disk on the stellar dynamics in the outer regions of disk galaxies.
We find a striking similarity among the radial HI surface density profiles,
where the average, normalized radial profile of the late-type spirals is
described surprisingly well with a Gaussian profile. These results can be used
to estimate HI surface density profiles in galaxies that only have a total HI
flux measurement. We compare our 21 cm radio continuum luminosities with 60
micron luminosities from IRAS observations for a subsample of 15 galaxies and
find that these follow a tight radio-infrared relation, with a hint of a
deviation from this relation at low luminosities. We also find a strong
correlation between the average SFR surface density and the K-band surface
brightness of the stellar disk.Comment: 22 pages + Appendix, 16 figures + Atlas, 5 tables. Accepted for
publication in Astronomy & Astrophysic
The Luminosity Function of Lyman alpha Emitters at Redshift z=7.7
Lyman alpha (Lya) emission lines should be attenuated in a neutral
intergalactic medium (IGM). Therefore the visibility of Lya emitters at high
redshifts can serve as a valuable probe of reionization at about the 50% level.
We present an imaging search for z=7.7 Lya emitting galaxies using an
ultra-narrowband filter (filter width= 9A) on the NEWFIRM imager at the Kitt
Peak National Observatory. We found four candidate Lya emitters in a survey
volume of 1.4 x 10^4 Mpc^3, with a line flux brighter than 6x10^-18 erg/cm^2/s
(5 sigma in 2" aperture). We also performed a detailed Monte-Carlo simulation
incorporating the instrumental effects to estimate the expected number of Lya
emitters in our survey, and found that we should expect to detect one Lya
emitter, assuming a non-evolving Lya luminosity function (LF) between z=6.5 and
z=7.7. Even if one of the present candidates is spectroscopically confirmed as
a z~8 Lya emitter, it would indicate that there is no significant evolution of
the Lya LF from z=3.1 to z~8. While firm conclusions would need both
spectroscopic confirmations and larger surveys to boost the number counts of
galaxies, we successfully demonstrate the feasibility of sensitive
near-infrared (1.06 um) narrow-band searches using custom filters designed to
avoid the OH emission lines that make up most of the sky background.Comment: Published in ApJ, 3 figure
The stellar velocity dispersion in the inner 1.3 disk scale-lengths of the irregular galaxy NGC 4449
We present measurements of the stellar velocity dispersion in the inner 1
arcmin radius (1.3 disk scale-lengths) of the irregular galaxy NGC 4449
determined from long-slit absorption-line spectra. The average observed
dispersion is 29 +/-2 km/s, the same as predicted from NGC 4449's luminosity.
No significant rotation in the stars is detected. If we assume a maximum
rotation speed of the stars from the model determined from the gas kinematics
of Hunter et al. (2002), the ratio V_max/sigma_z measured globally is 3. This
ratio is comparable to values measured in spiral galaxies, and implies that the
stellar disk in NGC 4449 is kinematically relatively cold. The intrinsic
minor-to-major axis ratio (b/a)_0 is predicted to be in the range 0.3-0.6,
similar to values derived from the distribution of observed b/a of Im galaxies.
However, V/sigma_z measured locally is 0.5-1.1, and so the circular velocity of
NGC 4449 is comparable or less than the velocity of the stars within the
central 1.3 disk scale-lengths of the galaxy.Comment: To be published in ApJ, Nov 200