10 research outputs found
PAHs in the Halo of NGC 5529
We present sensitive ISO m observations of the edge-on
galaxy, NGC 5529, finding an extensive MIR halo around NGC 5529. The emission
is dominated by PAHs in this band. The PAH halo has an exponential scale height
of 3.7 kpc but can still be detected as far as kpc from the plane
to the limits of the high dynamic range (1770/1) data. This is the most
extensive PAH halo yet detected in a normal galaxy. This halo shows
substructure and the PAHs likely originate from some type of disk outflow. PAHs
are long-lived in a halo environment and therefore continuous replenishment
from the disk is not required (unless halo PAHs are also being destroyed or
removed), consistent with the current low SFR of the galaxy. The PAHs correlate
spatially with halo H emission, previously observed by Miller &
Veilleux (2003); both components are likely excited/ionized by in-disk photons
that are leaking into the halo. The presence of halo gas may be related to the
environment of NGC 5529 which contains at least 17 galaxies in a small group of
which NGC 5529 is the dominant member. Of these, we have identified two new
companions from the SDSS.Comment: 16 pages, 5 gif figures, accepted for publication in A&A, For pdf
with higher quality figures, see http://www.astro.queensu.ca/~irwi
ISOCAM Mid-infrared spectroscopy and NIR photometry of the HII complex N4 in LMC
[Abridged] We present the analysis of ISOCAM-CVF and NIR photometry data of
the HII region complex N4 in LMC. The aim is twofold: 1) to study the
connection between the ISM and the star content of this region; 2)to
investigate the effects of the lower than galactic metallicity on dust
properties. A dust features -- gas lines -- continuum fitting technique on the
data, allows the production of images in each single emission and the detailed
analysis of dust, and ionized gas. The NIR photometry provides, for the first
time, information on the stellar content of N4. The images in single dust
feature bands and gas lines clearly show that the HII region core is completely
devoid of the carriers responsible for the Aromatic Features (AFs). On the
other hand, the ionized gas arises almost completely in this dust cavity, where
also the two main exciting stars of N4 are located. We find evidences that the
effect of lower than Galactic metallicity on the carriers responsible for the
AFs, is not to prevent their formation or to modify their chemical properties,
but to enhance their destruction by the high and hard ISRF. We show that this
mechanism is more efficient on smaller dust particles/molecules thus affecting
the dust-size distribution. We argue that effects on dust--size distribution,
rather than thedifferent dust properties due to a lower metallicity, should be
taken into account when analyzing more distant relatively low metallicity
galaxies. Finally, the analysis of the stellar content of N4 reveals 7 stars: 4
reddened O MS stars and 3 stars with envelopes. In particular, one of these,
seems to be an Ultra Compact HII region containing an embedded YSO.Comment: 14 pages including 16 figures, Accepted for publication in A&
Local Luminous Infrared Galaxies: Spatially resolved mid-infrared observations with Spitzer/IRS
Luminous Infrared (IR) Galaxies (LIRGs) are an important cosmological class
of galaxies as they are the main contributors to the co-moving star formation
rate density of the universe at z=1. In this paper we present a GTO Spitzer IRS
program aimed to obtain spectral mapping of a sample of 14 local (d<76Mpc)
LIRGs. The data cubes map, at least, the central 20arcsec x 20arcsec to
30arcsec x 30arcsec regions of the galaxies, and use all four IRS modules
covering the full 5-38micron spectral range. The final goal of this project is
to characterize fully the mid-IR properties of local LIRGs as a first step to
understanding their more distant counterparts. In this paper we present the
first results of this GTO program. The IRS spectral mapping data allow us to
build spectral maps of the bright mid-IR emission lines (e.g., [NeII], [NeIII],
[SIII], H_2), continuum, the 6.2 and 11.3micron PAH features, and the 9.7micron
silicate feature, as well as to extract 1D spectra for regions of interest in
each galaxy. The IRS data are used to obtain spatially resolved measurements of
the extinction using the 9.7micron silicate feature, and to trace star forming
regions using the neon lines and the PAH features. We also investigate a number
of AGN indicators, including the presence of high excitation emission lines and
a strong dust continuum emission at around 6micron. We finally use the
integrated Spitzer/IRS spectra as templates of local LIRGs. We discuss several
possible uses for these templates, including the calibration of the star
formation rate of IR-bright galaxies at high redshift. We also predict the
intensities of the brightest mid-IR emission lines for LIRGs as a function of
redshift, and compare them with the expected sensitivities of future space IR
missions.Comment: Accepted for publication in Advances in Space Researc
Pattern speed measurements in two barred galaxies
Knowledge of the pattern speed in a barred galaxy is an important prerequisite for determining the radii of its dynamical resonances. Once identified, these can in turn be used to constrain models for nuclear fueling and secular evolution. Here, we present measurements of the pattern speeds in two barred galaxies-one direct (in NGC 1068, using the Tremaine-Weinberg method in the near infrared) and one indirect (in NGC 7479, using a fit to three-dimensional molecular emission-line data). We find good evidence that a configuration of dynamically decoupled "bars within bars" is present in each system
3D: A new tool for probing the stars and ISM in AGN
3D, the new MPE NIR imaging spectrometer, provides us with a unique opportunity to probe in detail the structure of the stars, ionized gas, and hot molecular gas in the very centers of AGN. The instrument delivers data cubes with 16×160.5″ pixels which are 256 spectral channels deep. Thus, in a single observation we are able to obtain data on the entire K-Band over an 8″×8″ field of view, with a spectral resolution of R = λ/Δλ = 1000. In this paper we detail the working principles behind the instrument, and show first results from observations of the inner regions of the Seyfert 1 galaxy NGC 7469 made at the Calar Alto observatory. Copyright ©1996 Elsevier Science Ltd
PSR J1740-3052: a pulsar with a massive companion
We report on the discovery of a binary pulsar, PSR J1740-3052, during the Parkes multibeam survey. Timing observations of the 570-ms pulsar at Jodrell Bank and Parkes show that it is young, with a characteristic age of 350 kyr, and is in a 23 1-d, highly eccentric orbit with a companion whose mass exceeds 11 M.. An accurate position for the pulsar was obtained using the Australia Telescope Compact Array. Near-infrared 2.2-mum observations made with the telescopes at the Siding Spring observatory reveal a late-type star coincident with the pulsar position. However, we do not believe that this star is the companion of the pulsar, because a typical star of this spectral type and required mass would extend beyond the orbit of the pulsar. Furthermore, the measured advance of periastron of the pulsar suggests a more compact companion, for example, a main-sequence star with radius only a few times that of the Sun. Such a companion is also more consistent with the small dispersion measure variations seen near periastron. Although we cannot conclusively rule out a black hole companion, we believe that the companion is probably an early B star, making the system similar to the binary PSR J0045-7319
Chemical processing in the coma as the source of cometary HNC
The discovery of hydrogen isocyanide (HNC) in comet Hyakutake with an abundance (relative to hydrogen cyanide, HCN) similar to that seen in dense interstellar clouds raised the possibility that these molecules might be surviving interstellar material1. The preservation of material from the Sun\u27s parent molecular cloud would provide important constraints on the processes that took place in the protostellar nebula. But another possibility is that HNC is produced by photochemical processes in the coma, which means that its abundance could not be used as a direct constraint on conditions in the early Solar System. Here we show that the HNC/HCN ratio determined for comet Hale–Bopp varied with heliocentric distance in a way that matches the predictions of models of gas-phase chemical production of HNC in the coma, but cannot be explained if the HNC molecules were coming from the comet\u27s nucleus. We conclude that HNC forms mainly by chemical reactions in the coma, and that such reactions need to be considered when attempting to deduce the composition of the nucleus from observations of the coma