1,791 research outputs found
HI in four star-forming low-luminosity E/S0 and S0 galaxies
We present HI data cubes of four low-luminosity early-type galaxies which are
currently forming stars. These galaxies have absolute magnitudes in the range
M_B=-17.9 to -19.9 (H_o=50 km/s/Mpc). Their HI masses range between a few times
10^8 and a few times 10^9 M_sun and the corresponding values for M_HI/L_B are
between 0.07 and 0.42, so these systems are HI rich for their morphological
type. In all four galaxies, the HI is strongly centrally concentrated with high
central HI surface densities, in contrast to what is typically observed in more
luminous early-type galaxies. In two galaxies (NGC 802 and ESO 118-G34), the
kinematics of the HI suggests that the gas is in a strongly warped disk, which
we take as evidence for recent accretion of HI. In the other two galaxies (NGC
2328 and ESO 027-G21) the HI must have been part of the systems for a
considerable time. The HI properties of low-luminosity early-type galaxies
appear to be systematically different from those of many more luminous
early-type galaxies, and we suggest that these differences are due to a
different evolution of the two classes. The star formation history of these
galaxies remains unclear. Their UBV colours and Halpha emission-line strengths
are consistent with having formed stars at a slowly-declining rate for most of
the past 10^10 years. However, the current data do not rule out a small burst
of recent star formation overlaid on an older stellar population.Comment: To appear in AJ, LateX, figures in gif format, paper also available
at http://www.nfra.nl/~morganti/LowLu
The Evolution of Radio Galaxies at Intermediate Redshift
We describe a new estimate of the radio galaxy 1.4 GHz luminosity function
and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and
color selection have been used to select Bj<23.5 early-type galaxies from the
Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields.
Approximately 230 radio galaxies have then been selected by matching early-type
galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz
luminosity function of radio galaxies measure significant evolution over the
observed redshift range. For an Omega_M=1 cosmology the evolution of the radio
power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and
3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray
selected AGN and is consistent with the same physical process being responsible
for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A
The Fornax Spectroscopic Survey I. Survey Strategy and Preliminary Results on the Redshift Distribution of a Complete Sample of Stars and Galaxies
The Fornax Spectroscopic Survey will use the Two degree Field spectrograph
(2dF) of the Anglo-Australian Telescope to obtain spectra for a complete sample
of all 14000 objects with 16.5<=Bj<=19.7 in a 12 square degree area centred on
the Fornax Cluster. By selecting all objects---both stars and
galaxies---independent of morphology, we cover a much larger range of surface
brightness and scale size than previous surveys. In this paper we present
results from the first 2dF field. Redshift distributions and velocity
structures are shown for all observed objects in the direction of Fornax,
including Galactic stars, galaxies in and around the Fornax Cluster, and for
the background galaxy population. The velocity data for the stars show the
contributions from the different Galactic components, plus a small tail to high
velocities. We find no galaxies in the foreground to the cluster in our 2dF
field. The Fornax Cluster is clearly defined kinematically. The mean velocity
from the 26 cluster members having reliable redshifts is 1560+/-80 km/s. They
show a velocity dispersion of 380+/-50 km/s. Large-scale structure can be
traced behind the cluster to a redshift beyond z=0.3. Background compact
galaxies and low surface brightness galaxies are found to follow the general
galaxy distribution.Comment: LaTeX format; uses aa.cls (included). Accepted for publication in
Astronomy and Astrophysic
A Close Look at Star Formation around Active Galactic Nuclei
We analyse star formation in the nuclei of 9 Seyfert galaxies at spatial
resolutions down to 0.085arcsec, corresponding to length scales of less than
10pc in some objects. Our data were taken mostly with the near infrared
adaptive optics integral field spectrograph SINFONI. The stellar light profiles
typically have size scales of a few tens of parsecs. In two cases there is
unambiguous kinematic evidence for stellar disks on these scales. In the
nuclear regions there appear to have been recent - but no longer active -
starbursts in the last 10-300Myr. The stellar luminosity is less than a few
percent of the AGN in the central 10pc, whereas on kiloparsec scales the
luminosities are comparable. The surface stellar luminosity density follows a
similar trend in all the objects, increasing steadily at smaller radii up to
10^{13}L_sun/kpc^2 in the central few parsecs, where the mass surface density
exceeds 10^4M_sun/pc^2. The intense starbursts were probably Eddington limited
and hence inevitably short-lived, implying that the starbursts occur in
multiple short bursts. The data hint at a delay of 50--100Myr between the onset
of star formation and subsequent fuelling of the black hole. We discuss whether
this may be a consequence of the role that stellar ejecta could play in
fuelling the black hole. While a significant mass is ejected by OB winds and
supernovae, their high velocity means that very little of it can be accreted.
On the other hand winds from AGB stars ultimately dominate the total mass loss,
and they can also be accreted very efficiently because of their slow speeds.Comment: 51 pages, including 27 figures; accepted by ApJ (paper reorganised,
but results & conclusions the same
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
The Fornax Spectroscopic Survey: The Number of Unresolved Compact Galaxies
We describe a sample of thirteen bright (18.5<Bj<20.1) compact galaxies at
low redshift (0.05<z<0.21) behind the Fornax Cluster. These galaxies are
unresolved on UK Schmidt sky survey plates, so would be missing from most
galaxy catalogs compiled from this material. The objects were found during
initial observations of The Fornax Spectroscopic Survey. This project is using
the Two-degree Field spectrograph on the Anglo-Australian Telescope to obtain
spectra for a complete sample of all 14000 objects, stellar and non-stellar,
with 16.5<Bj<19.7, in a 12 square degree area centered on the Fornax cluster of
galaxies. The surface density of compact galaxies with magnitudes 16.5<Bj<19.7
is 7+/-3 /sq.deg., representing 2.8+/-1.6% of all local (z<0.2) galaxies to
this limit. There are 12+/-3 /sq.deg. with 16.5<Bj<20.2. They are luminous
(-21.5<Mb<-18.0, for H0=50 km/s/mpc) and most have strong emission lines (H
alpha equivalent widths of 40-200 A) and small sizes typical of luminous HII
galaxies and compact narrow emission line galaxies. Four out of thirteen have
red colors and early-type spectra, so are unlikely to have been detected in any
previous surveys.Comment: LaTeX source; 5 pages including 3 figures; uses emulateapj.st
Extended Emission Line Gas in Radio Galaxies - PKS0349-27
PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a
spectacular, spiral-like structure in its extended emission line gas (EELG). We
have measured the velocity field in this gas and find that it splits into 2
cloud groups separated by radial velocities which at some points approach 400
km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta,
[SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence
for the type of HII region emission associated with starburst activity in
either velocity system. The measured emission line ratios are similar to those
found in the nuclei of narrow-line radio galaxies, but the extended
ionization/excitation cannot be produced by continuum emission from the active
nucleus alone. We present arguments which suggest that the velocity
disturbances seen in the EELG are most likely the result of a galaxy-galaxy
collision or merger but cannot completely rule out the possibility that the gas
has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.
Popular music, psychogeography, place identity and tourism: The case of Sheffield
Tourism and cultural agencies in some English provincial cities are promoting their popular music âheritageâ and, in some cases, contemporary musicians through the packaging of trails, sites, âiconicâ venues and festivals. This article focuses on Sheffield, a âpost-industrialâ northern English city which is drawing on its associations with musicians past and present in seeking to attract tourists. This article is based on interviews with, among others, recording artists, promoters, producers and venue managers, along with reflective observational and documentary data. Theoretical remarks are made on the representations of popular musicians through cultural tourism strategies, programmes and products and also on the ways in which musicians convey a âpsychogeographicalâ sense of place in the âsoundscapeâ of the city
The challenges for new academics in adopting student-centred approaches to teaching
The current article provides a perspective on the day-to-day challenges that a group of new teachers experienced as they adopted more student-centred approaches to teaching. Three semi-structured interviews were conducted over two years with 11 new teachers from a range of higher education institutions and subject disciplines. The analysis used case studies, alongside a search for common themes, to provide fine-grained insights into the teachers' development. A main finding was that in using approaches that more actively involved the students, the teachers described challenges specific to their local contexts. In particular, the idiosyncrasy of the topic being taught was a key factor. The second finding was that regardless of the conception of teaching held, all teachers described challenges in translating this way of thinking into practice. Such data provides a useful resource for academic developers to open dialogue with new academics about the challenges they face in developing as teachers
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