138 research outputs found
A spiral-like disk of ionized gas in IC 1459: Signature of a merging collision
The authors report the discovery of a large (15 kpc diameter) H alpha + (NII) emission-line disk in the elliptical galaxy IC 1459, showing weak spiral structure. The line flux peaks strongly at the nucleus and is more concentrated than the stellar continuum. The major axis of the disk of ionized gas coincides with that of the stellar body of the galaxy. The mass of the ionized gas is estimated to be approx. 1 times 10 (exp 5) solar mass, less than 1 percent of the total mass of gas present in IC 1459. The total gas mass of 4 times 10(exp 7) solar mass has been estimated from the dust mass derived from a broad-band color index image and the Infrared Astronomy Satellite (IRAS) data. The authors speculate that the presence of dust and gas in IC 1459 is a signature of a merger event
ISO far-infrared observations of rich galaxy clusters II. Sersic 159-03
The far-infrared emission from rich galaxy clusters is investigated. Maps
have been obtained by ISO at 60, 100, 135, and 200 microns using the PHT-C
camera. Ground based imaging and spectroscopy were also acquired. Here we
present the results for the cooling flow cluster Sersic 159-03. An infrared
source coincident with the dominant cD galaxy is found. Some off-center sources
are also present, but without any obvious counterparts.Comment: 6 pages, 4 postscript figures, accepted for publication in `Astronomy
and Astrophysics
The Spectrum of Integrated Millimeter Flux of the Magellanic Clouds and 30-Doradus from TopHat and DIRBE Data
We present measurements of the integrated flux relative to the local
background of the Large and Small Magellanic Clouds and the region 30-Doradus
(the Tarantula Nebula) in the LMC in four frequency bands centered at 245, 400,
460, and 630 GHz, based on observations made with the TopHat telescope. We
combine these observations with the corresponding measurements for the DIRBE
bands 8, 9, and 10 to cover the frequency range 245 - 3000 GHz (100 - 1220
micrometers) for these objects. We present spectra for all three objects and
fit these spectra to a single-component greybody emission model and report
best-fit dust temperatures, optical depths, and emissivity power-law indices,
and we compare these results with other measurements in these regions and
elsewhere. Using published dust grain opacities, we estimate the mass of the
measured dust component in the three regions.Comment: 41 pages, 4 figures. Accepted for publication in Astrophysical
Journa
On the Nature of the NGC 1275 System
Sub-arcsecond images, taken in B, R, and H-Alpha filters, and area
spectroscopy obtained with the WIYN 3.5-m telescope provide the basis for an
investigation of the unusual structures in the stellar body and ionized gas in
and around the Perseus cluster central galaxy, NGC 1275. Our H-Alpha filter is
tuned to gas at the velocity of NGC 1275, revealing complex, probably
unresolved, small-scale features in the extended ionized gas, located up to
50/h kpc from NGC 1275. The mean H-Alpha surface brightness varies little along
the outer filaments; this, together with the complex excitation state
demonstrated by spectra, imply that the filaments are likely to be tubes, or
ribbons, of gas. The morphology, location and inferred physical parameters of
the gas in the filaments are consistent with a model whereby the filaments form
through compression of the intracluster gas by relativistic plasma emitted from
the active nucleus of NGC 1275. Imaging spectroscopy with the Densepak fiber
array on WIYN suggests partial rotational support of the inner component of low
velocity ionized gas. We confirm and extend evidence for features in the
stellar body of NGC 1275, and identify outer stellar regions containing very
blue, probably very young, star clusters. We interpret these as evidence for
recent accretion of a gas-rich system, with subsequent star formation. We
suggest that two main processes, which may be causally connected, are
responsible for the rich phenomenology of the NGC 1275 system -- NGC 1275
experienced a recent merger/interaction with a group of gas-rich galaxies, and
recent outflows from its AGN have compressed the intracluster gas, and perhaps
the gas in the infalling galaxies, to produce a complex web of filaments.
(Abridged)Comment: AJ, accepted; a recommended full resolution version is available at
http://www.astro.wisc.edu/~chris/pera.p
Ultraviolet Imaging Observations of the cD Galaxy in Abell 1795: Further Evidence for Massive Star Formation in a Cooling Flow
We present images from the Ultraviolet Imaging Telescope of the Abell 1795
cluster of galaxies. We compare the cD galaxy morphology and photometry of
these data with those from existing archival and published data. The addition
of a far--UV color helps us to construct and test star formation model
scenarios for the sources of UV emission. Models of star formation with rates
in the range \sim5-20M_{\sun}yr indicate that the best fitting models
are those with continuous star formation or a recent ( Myr old) burst
superimposed on an old population. The presence of dust in the galaxy,
dramatically revealed by HST images complicates the interpretation of UV data.
However, we find that the broad--band UV/optical colors of this cD galaxy can
be reasonably matched by models using a Galactic form for the extinction law
with . We also briefly discuss other objects in the large UIT
field of view.Comment: To appear in the Astrophysical Journal. 14 AAS preprint style pages
plus 7 figure
Keck Spectroscopy of Candidate Proto-globular Clusters in NGC 1275
Keck spectroscopy of 5 proto-globular cluster candidates in NGC 1275 has been
combined with HST WFPC2 photometry to explore the nature and origin of these
objects and discriminate between merger and cooling flow scenarios for globular
cluster formation. The objects we have studied are not HII regions, but rather
star clusters, yet their integrated spectral properties do not resemble young
or intermediate age Magellanic Cloud clusters or Milky Way open clusters. The
clusters' Balmer absorption appears to be too strong to be consistent with any
of the standard Bruzual & Charlot evolutionary models at any metallicity. If
these models are adopted, an IMF which is skewed to high masses provides a
better fit to the data. A truncated IMF with a mass range of 2-3 Mo reproduces
the observed Balmer equivalent widths and colors at about 450 Myr. Formation in
a continuous cooling flow appears to be ruled out since the age of the clusters
is much larger than the cooling time, the spatial scale of the clusters is much
smaller than the cooling flow radius, and the deduced star formation rate in
the cooling flow favors a steep rather than a flat IMF. A merger would have to
produce clusters only in the central few kpc, presumably from gas in the
merging galaxies which was channeled rapidly to the center. Widespread shocks
in merging galaxies cannot have produced these clusters. If these objects are
confirmed to have a relatively flat, or truncated, IMF it is unclear whether or
not they will evolve into objects we would regard as bona fide globular
clusters.Comment: 30 pages (AAS two column style, including 9 tables and 7 figures) to
appear in the AJ (August issue), also available at
http://www.ucolick.org/~mkissler/Sages/sages.html (with a full resolution
Fig.1) Revised Version: previous posted version was an uncorrect ealier
iteration, parts of the text, tables and figures changed. The overall
conclusions remain unchange
Thermonuclear Burning Regimes and the Use of SNe Ia in Cosmology
The calculations of the light curves of thermonuclear supernovae are carried
out by a method of multi-group radiation hydrodynamics. The effects of spectral
lines and expansion opacity are taken into account. The predictions for UBVI
fluxes are given. The values of rise time for B and V bands found in our
calculations are in good agreement with the observed values. We explain why our
results for the rise time have more solid physical justification than those
obtained by other authors. It is shown that small variations in the chemical
composition of the ejecta, produced in the explosions with different regimes of
nuclear burning, can influence drastically the light curve decline in the B
band and, to a lesser extent, in the V band. We argue that recent results on
positive cosmological constant Lambda, found from the high redshift supernova
observations, could be wrong in the case of possible variations of the
preferred mode of nuclear burning in the earlier Universe.Comment: 20 pages, 5 figures, presented at the conference "Astronomy at the
Eve of the New Century", Puschino, May 17-22, 1999. A few references and a
table added, typos correcte
Observations of the Hubble Deep Field with the Infrared Space Observatory. IV. Association of sources with Hubble Deep Field Galaxies
We discuss the identification of sources detected by ISO at 6.7 and 15 micron
in the Hubble Deep Field (HDF) region. We conservatively associate ISO sources
with objects in existing optical and near-infrared HDF catalogues using the
likelihood ratio method, confirming these results (and, in one case, clarifying
them) with independent visual searches. We find fifteen ISO sources to be
reliably associated with bright [I(AB) < 23] galaxies in the HDF, and one with
an I(AB)=19.9 star, while a further eleven are associated with objects in the
Hubble Flanking Fields (ten galaxies and one star). Amongst optically bright
HDF galaxies, ISO tends to detect luminous, star-forming galaxies at fairly
high redshift and with disturbed morphologies, in preference to nearby
ellipticals.Comment: 8 pages, LaTeX (using mn.sty, epsfig), 3 figures (2 Postscript, 1
GIF) included. Gzipped Postscipt version available from
http://artemis.ph.ic.ac.uk/hdf/papers/ps/. Further information on ISO-HDF
project can be found at http://artemis.ph.ic.ac.uk/hdf
SN 2005hj: Evidence for Two Classes of Normal-Bright SNe Ia and Implications for Cosmology
HET Optical spectra covering the evolution from about 6 days before to about
5 weeks after maximum light and the ROTSE-IIIb unfiltered light curve of the
"Branch-normal" Type Ia Supernova SN 2005hj are presented. The host galaxy
shows HII region lines at redshift of z=0.0574, which puts the peak unfiltered
absolute magnitude at a somewhat over-luminous -19.6. The spectra show weak and
narrow SiII lines, and for a period of at least 10 days beginning around
maximum light these profiles do not change in width or depth and they indicate
a constant expansion velocity of ~10,600 km/s. We analyzed the observations
based on detailed radiation dynamical models in the literature. Whereas delayed
detonation and deflagration models have been used to explain the majority of
SNe Ia, they do not predict a long velocity plateau in the SiII minimum with an
unvarying line profile. Pulsating delayed detonations and merger scenarios form
shell-like density structures with properties mostly related to the mass of the
shell, M_shell, and we discuss how these models may explain the observed SiII
line evolution; however, these models are based on spherical calculations and
other possibilities may exist. SN 2005hj is consistent with respect to the
onset, duration, and velocity of the plateau, the peak luminosity and, within
the uncertainties, with the intrinsic colors for models with M_shell=0.2 M_sun.
Our analysis suggests a distinct class of events hidden within the
Branch-normal SNe Ia. If the predicted relations between observables are
confirmed, they may provide a way to separate these two groups. We discuss the
implications of two distinct progenitor classes on cosmological studies
employing SNe Ia, including possible differences in the peak luminosity to
light curve width relation.Comment: ApJ accepted, 31 page
A Search for Very Extended Ionized Gas in Nearby Starburst and Active Galaxies
We report the results from a pilot study of 10 nearby starburst and active
galaxies conducted with the Taurus Tunable Filter (TTF) on the Anglo-Australian
and William Herschel Telescopes. The main purpose of this imaging survey is to
search for warm emission-line gas on the outskirts (galactocentric distances R
> 10 kpc) of galaxies to provide direct constraints on the size and geometry of
the ``zone of influence'' of these galaxies on their environment. Gaseous
complexes or filaments larger than ~ 20 kpc are discovered or confirmed in six
of the galaxies in the sample (NGC 1068, NGC 1482, NGC 4388, NGC 6240, NGC
7213, and MR 2251-178). Slightly smaller structures are seen for the first time
in the ionization cones and galactic winds of NGC 1365, NGC 1705, Circinus
galaxy, and ESO484-G036. The TTF data are combined with new optical long-slit
spectra as well as published and archived radio and X-ray maps to constrain the
origin and source of ionization of these filaments. A broad range of phenomena
is observed, including large-scale ionization cones and galactic winds, tidal
interaction, and ram-pressure stripping by an intracluster medium. The source
of ionization in this gas ranges from shock ionization to photoionization by
the central AGN or in-situ hot young stars. The sample is too small to draw
statistically meaningful conclusions about the extent and properties of the
warm ionized medium on large scale and its relevance to galaxy formation and
evolution. The next generation of tunable filters on large telescopes promises
to improve the sensitivity to faint emission-line fluxes at least tenfold and
allow systematic surveys of a large sample of emission-line galaxies.Comment: 17 pages + 20 gif figures (high-resolution color version of these gif
figures will be available with the electronic version of the published
paper). Accepted for publication in the Astronomical Journal, November 2003
issu
- …