47 research outputs found
The European Large Area ISO Survey - ISOPHOT results using the MPIA-pipeline
The European Large Area ISO Survey (ELAIS) will provide Infrared observations
of 4 regions in the sky with ISO. Around 2000 Infrared sources have been
detected at 7 and 15 microns (with ISOCAM), 90 and 175 microns (with ISOPHOT))
over 13 square degrees of the sky. We present the source extraction pipeline of
the 90 microns ISOPHOT observations, describe and discuss the results obtained
and derive the limits of the ELAIS observational strategy.Comment: 4 pages, 5 figures, to appear in the ISO conference "The Universe as
seen by ISO", 1998, UNESCO, Pari
Iteration Method to Derive Exact Rotation Curves from Position-Velocity Diagrams of Spiral Galaxies
We present an iteration method to derive exact rotation curves (RC) of spiral
galaxies from observed position-velocity diagrams (PVD), which comprises the
following procedure. An initial rotation curve, RC0, is adopted from an
observed PV diagram (PV0), obtained by any simple method such as the
peak-intensity method. Using this rotation curve and an observed radial
distribution of intensity (emissivity), we construct a simulated PV diagram
(PV1). The difference between a rotation curve obtained from this PV1 and the
original RC (e.g., difference between peak-intensity velocities) is used to
correct the initial RC to obtain a corrected rotation curve, RC1. This RC1 is
used to calculated another PVD (PV2) using the observed intensity distribution,
and to obtain the second iterated RC (RC2). This iteration is repeated until
PV converges to PV0, so that the differences between PV and PV0 becomes
minimum. Finally RC is adopted as the most reliable rotation curve. We apply
this method to some observed PVDs of nearby galaxies, and show that the
iteration successfully converges to give reliable rotation curves. We show that
the method is powerful to detect central massive objects.Comment: To appear in ApJ.Letters, 5 pages Latex with 4 figure
On the nature of the ISO-selected sources in the ELAIS S2 region
We have studied the optical, near-IR and radio properties of a complete
sample of 43 sources detected at 15-micron in one of the deeper ELAIS
repeatedly observed region. The extragalactic objects in this sample have
15-micron flux densities in the range 0.4-10 mJy, where the source counts start
diverging from no evolution models. About 90% of the sources (39 out of 43)
have optical counterparts brighter than I=21 mag. Eight of these 39 sources
have been identified with stars on the basis of imaging data, while for another
22 sources we have obtained optical spectroscopy, reaching a high
identification percentage (30/43, ~70%). All but one of the 28 sources with
flux density > 0.7 mJy are identified. Most of the extragalactic objects are
normal spiral or starburst galaxies at moderate redshift (z_med~0.2); four
objects are Active Galactic Nuclei. We have used the 15-micron, H_alpha and
1.4-GHz luminosities as indicators of star-formation rate and we have compared
the results obtained in these three bands. While 1.4-GHz and 15-micron
estimates are in good agreement, showing that our galaxies are forming stars at
a median rate of ~40 Mo/yr, the raw H_alpha-based estimates are a factor ~5-10
lower and need a mean correction of ~2 mag to be brought on the same scale as
the other two indicators. A correction of ~2 mag is consistent with what
suggested by the Balmer decrements H_alpha/H_beta and by the optical colours.
Moreover, it is intermediate between the correction found locally for normal
spirals and the correction needed for high-luminosity 15-micron objects,
suggesting that the average extinction suffered by galaxies increases with
infrared luminosity.Comment: 19 pages, 11 figures (3 in JPEG format), MNRAS, accepte
The European Large Area ISO Survey: ELAIS
The European Large Area ISO Survey (ELAIS) has surveyed 12 square degrees of
the sky at 15 and 90 microns, and subsets of this area at 6.75 and 175 microns,
using the Infrared Space Observatory (ISO). This project was the largest single
open time programme executed by ISO, taking 375 hours of data. A preliminary
catalogue of more than 1000 galaxies has been produced. In this talk we
describe the goals of the project, describe the follow-up programmes that are
in progress, and present some first scientific results including a provisional
number count analysis at 15 and 90 microns.Comment: 5 pages, 3 figures, 4 tables, to appear in 'The universe as seen by
ISO', eds P.Cox and M.F.Kessler, 1998, UNESCO, Paris, ESA Special
Publications Series (SP-427
Astro-WISE: Chaining to the Universe
The recent explosion of recorded digital data and its processed derivatives
threatens to overwhelm researchers when analysing their experimental data or
when looking up data items in archives and file systems. While current hardware
developments allow to acquire, process and store 100s of terabytes of data at
the cost of a modern sports car, the software systems to handle these data are
lagging behind. This general problem is recognized and addressed by various
scientific communities, e.g., DATAGRID/EGEE federates compute and storage power
over the high-energy physical community, while the astronomical community is
building an Internet geared Virtual Observatory, connecting archival data.
These large projects either focus on a specific distribution aspect or aim to
connect many sub-communities and have a relatively long trajectory for setting
standards and a common layer. Here, we report "first light" of a very different
solution to the problem initiated by a smaller astronomical IT community. It
provides the abstract "scientific information layer" which integrates
distributed scientific analysis with distributed processing and federated
archiving and publishing. By designing new abstractions and mixing in old ones,
a Science Information System with fully scalable cornerstones has been
achieved, transforming data systems into knowledge systems. This break-through
is facilitated by the full end-to-end linking of all dependent data items,
which allows full backward chaining from the observer/researcher to the
experiment. Key is the notion that information is intrinsic in nature and thus
is the data acquired by a scientific experiment. The new abstraction is that
software systems guide the user to that intrinsic information by forcing full
backward and forward chaining in the data modelling.Comment: To be published in ADASS XVI ASP Conference Series, 2006, R. Shaw, F.
Hill and D. Bell, ed
Stellar Masses of Luminous Compact Blue Galaxies at Redshifts z=0.4-1.2
We present stellar mass measurements for a sample of 36 Luminous Compact Blue
Galaxies (LCBGs) at redshifts z = 0.4-1.2 in the Flanking Fields around the
Hubble Deep Field North. The technique is based on fitting a two-component
galaxy population model to multi-broadband photometry. Best-fit models are
found to be largely independent on the assumed values for the IMF and the
metallicity of the stellar populations, but are sensitive to the amount of
extinction and the extinction law adopted. On average, the best-fit model
corresponds to a LMC extinction law with E(B-V)=0.5. Stellar mass estimates,
however, are remarkably independent on the final model choice. Using a Salpeter
IMF, the derived median stellar mass for this sample is 5 x 10^9 Mo, i.e., ~2
times smaller than previous virial mass estimates. Despite uncertainties of a
factor 2-3, our results strengthen prior claims that L* CBGs at intermediate
redshifts are, on average, about 10 times less massive than a typical L* galaxy
today.Comment: 10 pages, 2 figure
FIRBACK IV: Towards the nature of the 170microns source population
We present a detailed study of the brighter ( detections) sources
in the 170m FIRBACK northern N1 ISO survey, with the help of complementary
data in the optical, radio, and mid-IR domain. For 82% of them, an optical
galaxy counterpart is identified, either as the unique source of the IR
emission, or as part of a multiple identification. With less than 15% of AGNs,
these sources are essentially local, moderate starbursters with a dominating
cold dust component. and represent a population of cold galaxies rather
neglected up to now. Their colours do not match those of the far-IR Cosmic IR
Background (CIB), to which they contribute less than 5%. The bulk of the
sources contributing to the CIB is thus to be searched for in more distant
galaxies, possibly counterparts of the fainter FIRBACK sources still under
study. These bright, local, galaxies however play an important role in the
evolution of IR galaxies: they dominate the number counts at high 170 m
fluxes, and represent half of the contribution at 250 mJy. Although not
particularly massive (typically M*), they form more stars than a typical spiral
galaxy and many are bulge dominated, that could represent the remnant of a
former merger. The fainter part of this population may represent the missing
link with the higher-z sources found in sub-mm observations.Comment: 40 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
A study of HI-selected galaxies in the Hercules cluster
The present study is aimed at a sample of 22 galaxies detected in the blind
VLA HI survey of the Hercules cluster by Dickey (1997), 18 of which were
selected on an HI line width smaller than 270 km/s and 4 others with only
tentative optical counterparts on the Palomar Sky Survey. Sensitive single-dish
HI line spectra were obtained for 20 of them, and for one (47-154) the VLA
detection was not confirmed. Optical surface photometry was obtained of 10
objects, for 8 of which optical spectroscopy was obtained as well. Based on
various selection criteria, two (ce-143 and ne-204) can be classified as
dwarfs. The objects of which optical observations were made show star formation
properties similar to those of published samples of actively star forming
galaxies, and approximately half of them have properties intermediate between
those of dwarf galaxies and low-luminosity disc galaxies. No optical redshifts
could be obtained for two of the galaxies (sw-103 and sw-194) and their
physical association with the HI clouds detected at their positions therefore
remains uncertain. Unique among the objects is the Tidal Dwarf Galaxy ce-061 in
a tail of the IC 1182 merger system.Comment: 20 pages, 19 figures, accepted for publication in A&
Radial Distribution of the Mass-to-Luminosity Ratio in Spiral Galaxies and Massive Dark Cores
We derive radial profiles of the surface-mass-density for 19 spiral galaxies
directly from their high-resolution rotation curves. Using the corresponding
luminosity profiles, we obtain the radial distribution of the
mass-to-luminosity ratios () from the inner bulge ( a few 100 pc) to
the outer disk ( 2-10 kpc) for 11 galaxies (with inclination <
in order to reduce the influence of the interstellar extinction.
The s in the bulges of two galaxies with sufficient resolution, NGC 4527
and NGC 6946, are found to increase steeply toward the center at radii
100-500 pc at rates of 153 and 72 times per kpc, respectively. Some
other galaxies with fairly high resolution also show signs of an increase
toward the center. Such an increase may indicate the existence of a new
component, a ``massive dark core'', which may be an object linking the bulge
and a central black hole. Based on radial variations of the , we further
discuss the variation of the dark-mass fraction in spiral galaxies.Comment: Latex 19 pages, 30 ps figures. ApJ in pres
The European Large Area ISO Survey III: 90micron extragalactic source counts
We present results and source counts at 90micron extracted from the
Preliminary Analysis of the European Large Area ISO Survey (ELAIS). The survey
covered about 11.6 square degrees of the sky in four main areas and was carried
out with the PHOT instrument onboard the Infrared Space Observatory (ISO). The
survey is at least an order of magnitude deeper than the IRAS 100micron survey
and is expected to provide constraints on the formation and evolution of
galaxies. The majority of the detected sources are associated with galaxies on
optical images. In some cases the optical associations are interacting pairs or
small groups of galaxies suggesting the sample may include a significant
fraction of luminous infrared galaxies. The source counts extracted from a
reliable subset of the detected sources are in agreement with strongly evolving
models of the starburst galaxy population.Comment: 13 pages, accepted by MNRAS. For more details on the ELAIS project
see http://athena.ph.ic.ac.uk