216 research outputs found
The Public Pays, the Corporation Profits: The Emasculation of the Public Purpose Doctrine and a Not-for-Profit Solution
Massive subsidies by state and local governments to private corporations for the purpose of inducing such corporations to retain or locate facilities in their respective locales are attracting greater public scrutiny. Commentators are beginning to question whether the public entity receives benefits anywhere near the value of the subsidy. In Virginia, where Governor George Allen proposed giving the Walt Disney Corporation $163 million in subsidies to establish a theme park, the public responded with bumper stickers that read Virginia Pays-Disney Profits
Discrete dynamical classes for galaxy discs and the implication of a second generation of Tully-Fisher methods
We consider the four large optical rotation curve samples of Mathewson, Ford
& Buchhorn (900 ORCs), Mathewson & Ford (1200 ORCs), Dale, Giovanelli, Haynes
et al (494 ORCs) and Courteau (300 ORCs).
We show how it is possible to partition any given ORC into two distinct
dynamical regions - an interior region and an exterior region. Each of the
samples considered is partitioned in this way, so that we are able to consider
the dynamics on the exterior parts of the ORCs for each of the samples. This
technique was originaly introduced by Roscoe astro-ph/0107305.
We then find that the dynamics in the exterior part of spiral discs fall into
one of four sharply defined classes. Taking account of the various correlations
which exist between luminosity properties and dynamical properties of discs,
our final phenomonological conclusion is that spiral discs in the samples
considered appear constrained to occupy one of four distinct planes, F(M,S,a) =
k0, k1, k2, k3, where M = absolute magnitude, S = surface brightness, "a" is a
parameter computed directly from each ORC and k0, k1, k2, k3 are well defined
numerical constants.
These results are statistically supported at the level of virtual certainty.
We suggest three possible mechanisms for this phenomonology. The overall
analysis implies the existence of a second generation of Tully-Fisher methods
in which the standard TF relation is augmented with a second relation defining
where on an ORC the linewidth should be measured.Comment: 22 pages, 17 figures, to appear in A&A 2002. Expanded with an
additional large sample analysed, and implications for extended Tully-Fisher
methods include
Towards an Understanding of the Mid-Infrared Surface Brightness of Normal Galaxies
We report a mid-infrared color and surface brightness analysis of IC 10, NGC
1313, and NGC 6946, three of the nearby galaxies studied under the Infrared
Space Observatory Key Project on Normal Galaxies. Images with < 9 arcsecond
(170 pc) resolution of these nearly face-on, late-type galaxies were obtained
using the LW2 (6.75 mu) and LW3 (15 mu) ISOCAM filters. Though their global
I_nu(6.75 mu)/I_nu(15 mu) flux ratios are similar and typical of normal
galaxies, they show distinct trends of this color ratio with mid-infrared
surface brightness. We find that I_nu(6.75 mu)/I_nu(15 mu) ~< 1 only occurs for
regions of intense heating activity where the continuum rises at 15 micron and
where PAH destruction can play an important role. The shape of the
color-surface brightness trend also appears to depend, to the second-order, on
the hardness of the ionizing radiation. We discuss these findings in the
context of a two-component model for the phases of the interstellar medium and
suggest that star formation intensity is largely responsible for the
mid-infrared surface brightness and colors within normal galaxies, whereas
differences in dust column density are the primary drivers of variations in the
mid-infrared surface brightness between the disks of normal galaxies.Comment: 19 pages, 6 figures, uses AAS LaTeX; to appear in the November
Astronomical Journa
ISO--LWS observations of the two nearby spiral galaxies: NGC6946 and NGC1313
(Abridged) We present the analysis of the main FIR fine structure lines
emission in NGC1313 and NGC6946. We calculate that a component probably
associated with the diffuse disks contributes <~40% in N6946 and ~30 % in N1313
to the total [CII] emission. The main PDR physical parameters responsible for
the neutral atomic gas emission in N1313 and N6946 do not significantly differ
from what Malhotra etal (2001) found by modelling the integrated emission of a
sample of 60 normal galaxies,although there are evidences for a beam averaged
contribution of a less active component inside NGC6946 higher than its
contribution in the integrated emission of normal galaxies. CO and [CII] in
N6946 are well correlated with a mean [CII]/CO ratio similar to that of the
normal galaxies sample. In N1313 the [CII]/CO seems to systematically increase
from the North to the south, along the S-shaped spiral arm, indicating much
more inhomogeneous conditions than in N6946. HI and [CII] in N6946 are
completely de-correlated, probably because they arise from different gas
components. In N1313 we successfully detect two distinct gas components: a
cirrus-like component where HI and [CII] are weakly correlated as observed in
our Galaxy, and a component associated with dense PDRs completely de-correlated
from HI as observed in N6946.Finally, we find that the HI residing in dense
PDRs and presumably recently photo-dissociated, constitutes a few % of the
total HI. In turn, this dense gas component produces most of the [CII] emission
emitted by the atomic neutral medium.Comment: Latex, 100 pages, 11 Figures, 11 Tables. Accepted for publication in
A
Molecular Gas in NUclei of GAlaxies (NUGA) XIV. The barred LINER/Seyfert 2 galaxy NGC 3627
We present CO(1-0) and CO(2-1) maps of the interacting barred LINER/Seyfert 2
galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1" x
1.3" and 0.9" x 0.6", respectively. The molecular gas emission shows a nuclear
peak, an elongated bar-like structure of ~18" (~900 pc) diameter in both CO
maps and, in CO(1-0), a two-arm spiral feature from r~9" (~450 pc) to r~16"
(~800 pc). The inner ~18" bar-like structure, with a north/south orientation
(PA = 14{\deg}), forms two peaks at the extremes of this elongated emission
region. The kinematics of the inner molecular gas shows signatures of
non-circular motions associated both with the 18" bar-like structure and the
spiral feature detected beyond it. The 1.6 micron H-band 2MASS image of NGC
3627 shows a stellar bar with a PA = -21{\deg}, different from the PA (=
14{\deg}) of the CO bar-like structure, indicating that the gas is leading the
stellar bar. The torques computed with the HST-NICMOS F160W image and our PdBI
maps are negative down to the resolution limit of our images, ~60 pc in
CO(2-1). If the bar ends at ~3 kpc, coincident with corotation (CR), the
torques are negative between the CR of the bar and the nucleus, down to the
resolution limit of our observations. This scenario is compatible with a
recently-formed rapidly rotating bar which has had insufficient time to slow
down because of secular evolution, and thus has not yet formed an inner
Lindblad resonance (ILR). The presence of molecular gas inside the CR of the
primary bar, where we expect that the ILR will form, makes NGC 3627 a potential
smoking gun of inner gas inflow. The gas is fueling the central region, and in
a second step could fuel directly the active nucleus.Comment: 24 pages, 28 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
Internal kinematics of spiral galaxies in distant clusters IV. Gas kinematics of spiral galaxies in intermediate redshift clusters and in the field
(Abridged) We trace the interaction processes of galaxies at intermediate
redshift by measuring the irregularity of their ionized gas kinematics, and
investigate these irregularities as a function of the environment (cluster
versus field) and of morphological type (spiral versus irregular). Our sample
consists of 92 distant galaxies. 16 cluster (z~0.3 and z~0.5) and 29 field
galaxies (mean z=0.44) of these have velocity fields with sufficient signal to
be analyzed. We find that the fraction of galaxies that have irregular gas
kinematics is remarkably similar in galaxy clusters and in the field at
intermediate redshifts. The distribution of the field and cluster galaxies in
(ir)regularity parameters space is also similar. On the other hand galaxies
with small central concentration of light, that we see in the field sample, are
absent in the cluster sample. We find that field galaxies at intermediate
redshifts have more irregular velocity fields as well as more clumpy and less
centrally concentrated light distributions than their local counterparts.
Comparison with a SINS sample of 11 z ~ 2 galaxies shows that these distant
galaxies have more irregular gas kinematics than our intermediate redshift
cluster and field sample. We do not find a dependence of the irregularities in
gas kinematics on morphological type. We find that two different indicators of
star formation correlate with irregularity in the gas kinematics. More
irregular gas kinematics, also more clumpy and less centrally concentrated
light distributions of spiral field galaxies at intermediate redshifts in
comparison to their local counterparts indicate that these galaxies are
probably still in the process of building their disks via mechanisms such as
accretion and mergers. On the other hand, they have less irregular gas
kinematics compared to galaxies at z ~ 2.Comment: Accepted for publication in A&A, high resolution version available at
http://www.astro.rug.nl/~kutdemir/13262/13262_hr.p
The Effect of Star Formation on the Far-Infrared--Radio Correlation within Galaxies
Using data obtained for twelve galaxies as part of the {\it Spitzer} Infrared
Nearby Galaxies Survey (SINGS) and the Westerbork Synthesis Radio Telescope
(WSRT)-SINGS radio continuum survey, we study how star formation activity
affects the far-infrared (FIR)--radio correlation {\it within} galaxies by
testing a phenomenological model, which describes the radio image as a smeared
version of the FIR image. The physical basis of this description is that
cosmic-ray (CR) electrons will diffuse measurably farther than the mean free
path of dust-heating photons before decaying by synchrotron radiation. This
description works well in general. Galaxies with higher infrared surface
brightnesses have best-fit smoothing scale-lengths of a few hundred parsecs,
substantially shorter than those for lower surface brightness galaxies. We
interpret this result to suggest that galaxies with higher disk averaged star
formation rates have had a recent episode of enhanced star formation and are
characterized by a higher fraction of young CR electrons that have traveled
only a few hundred parsecs from their acceleration sites in supernova remnants
compared to galaxies with lower star formation activity.Comment: 5 pages, 3 figures; Accepted for publication in ApJ Letter
Photon dominated regions in the spiral arms of M83 and M51
We present CI 3P1-3P0 spectra at four spiral arm positions and the nuclei of
the nearby galaxies M83 and M51 obtained at the JCMT. This data is complemented
with maps of CO 1-0, 2-1, and 3-2, and ISO/LWS far-infrared data of CII (158
micron), OI (63 micron), and NII (122 micron) allowing for the investigation of
a complete set of all major gas cooling lines. From the intensity of the NII
line, we estimate that between 15% and 30% of the observed CII emission
originate from the dense ionized phase of the ISM. The analysis indicates that
emission from the diffuse ionized medium is negligible. In combination with the
FIR dust continuum, we find gas heating efficiencies below ~0.21% in the
nuclei, and between 0.25 and 0.36% at the outer positions. Comparison with
models of photon-dominated regions (PDRs) of Kaufman et al. (1999) with the
standard ratios OI(63)/CII_PDR and (OI(63)+CII_PDR) vs. TIR, the total infrared
intensity, yields two solutions. The physically most plausible solution
exhibits slightly lower densities and higher FUV fields than found when using a
full set of line ratios, CII_PDR/CI(1-0), CI(1-0)/CO(3-2), CO(3-2)/CO(1-0),
CII/CO(3-2), and, OI(63)/CII_PDR. The best fits to the latter ratios yield
densities of 10^4 cm^-3 and FUV fields of ~G_0=20-30 times the average
interstellar field without much variation. At the outer positions, the observed
total infrared intensities are in perfect agreement with the derived best
fitting FUV intensities. The ratio of the two intensities lies at 4-5 at the
nuclei, indicating the presence of other mechanisms heating the dust
The Interstellar Medium of Star-forming Irregular Galaxies: The View with ISO
We present mid-infrared imaging and far-infrared (FIR) spectroscopy of 5 IBm
galaxies observed by ISO as part of our larger study of the inter- stellar
medium of galaxies. Most of the irregulars in our sample are very actively
forming stars. The mid-infrared imaging was in a band centered at 6.75 microns
that is dominated by polycyclic aromatic hydrocarbons (PAHs) and in a band
centered at 15 microns that is dominated by small dust grains. The spectroscopy
of 3 of the galaxies includes [CII]158 microns and [OI]63 microns, important
coolants of photodissociation regions (PDRs), and [OIII]88 microns and [NII]122
microns, which come from ionized gas. [OI]145 microns and [OIII]52 microns were
measured in one galaxy as well. These data are combined with PDR and HII region
models to deduce properties of the interstellar medium of these galaxies.Comment: To be published in ApJ, Apr 10, 2001; higher resolution figures
available from ftp.lowell.edu, cd pub/dah/isopaper
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