16 research outputs found
NGC 7679: an anomalous, composite Seyfert 1 galaxy whose, X-ray luminous AGN vanishes at optical wavelengths
Morphological disturbances and gas kinematics of the SB0 galaxy NGC 7679=Arp
216 are investigated to get clues to the history of this highly composite
object, where AGN and starburst signatures dominate each other in the X-ray and
optical/IR regime, respectively. Perturbations of the ionized gas velocity
field appear quite mild within 15'' (~5 kpc) from the center, so as it can be
straightforwardly modeled as a circularly rotating disk. On the contrary,
outside that radius, significant disturbances show up. In particular, the
eastern distorted arm as well as the huge neutral hydrogen bridge connecting
NGC 7679 with the nearby Seyfert spiral NGC 7682 unambiguously represent the
vestige of a close encounter of the two objects dating back ~500 Myr ago. The
relationship of such past event with the much more recent, centrally located
starburst (not older than 20 Myr) cannot be easily established. Altogether, the
classification of NGC 7679, turns out to be less extreme than that proposed in
the past, being simply a (disturbed) galaxy where starburst and AGN activity
cohexist with a starburst dominating the bolometric luminosity.Comment: 11 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
The HI content of Early-Type Galaxies from the ALFALFA survey I. Catalogued HI sources in the Virgo cluster
Aims: We are using the Arecibo Legacy Fast ALFA survey (ALFALFA), which is
covering 17% of the sky at 21 cm, to study the HI content of Early-Type
galaxies (ETG) in an unbiased way. The aim is to get an overall picture of the
hot, warm and cold ISM of ETG, as a function of galaxy mass and environment, to
understand its origin and fate, and to relate it to the formation and evolution
history of these objects. Methods: This paper deals with the first part of our
study, which is devoted to the 8-16 deg. declination strip in the Virgo
cluster. In this sky region, using the Virgo Cluster Catalogue (VCC), we have
defined an optical sample of 939 ETG, 457 of which are brighter than the VCC
completeness limit at B_T=18.0. We have correlated this optical sample with the
catalogue of detected HI sources from ALFALFA. Results: Out of the 389 ETG from
the VCC with B_T<=18.0, outside the 1 deg. region of poor HI detection around
M87, and corrected for background contamination of VCC galaxies without a known
radial velocity, only 9 galaxies (2.3%) are detected in HI with a completeness
limit of 3.5 and 7.6 x 10^7 Mo of HI for dwarf and giant ETG, respectively. In
addition 4 VCC ETG with fainter magnitudes are also detected. Our HI detection
rate is lower than previously claimed. The majority of the detected ETG appear
to have peculiar morphology and to be located near the edges of the Virgo
cluster. Conclusions: Our preliminary conclusion is that cluster ETG contain
very little neutral gas, with the exceptions of a few peculiar dwarf galaxies
at the edge of the ETG classification and of very few larger ETG, where the
cold gas could have a recent external origin.Comment: Accepted for publication in Astronomy and Astrophysics; 6 pages, 3
figure
Evolutionary paths to and from the red sequence: Star formation and HI properties of transition galaxies at z~0
(Abridged) We investigate the properties of galaxies between the blue and the
red sequence (i.e., the transition region) by combining UV and NIR imaging to
HI line observations for a volume-limited sample of nearby galaxies. We confirm
the existence of a tight relation between colour and HI-fraction across all the
range of colours, although outside the blue cloud this trend becomes gradually
weaker. Transition galaxies are divided into two different families, according
to their atomic hydrogen content. HI-deficient galaxies are the majority of
transition galaxies in our sample. They are found in high density environments
and all their properties are consistent with a quenching of the star formation
via gas stripping. However, while the migration from the blue cloud is
relatively quick (i.e., <=1 Gyr), a longer amount of time (a few Gyr at least)
seems required to completely suppress the star formation and reach the red
sequence. At all masses, migrating HI-deficient galaxies are mainly disks,
implying that the mechanism responsible for today's migration in clusters
cannot have played a significant role in the creation of the red sequence at
high-redshift. Conversely, HI-normal transition galaxies are a more
heterogeneous population. A fraction of these objects show evidence for
accretion/minor-merging events suggesting that at least part of the HI
reservoir has an external origin. The detailed evolution of such systems is
still unclear, but our analysis suggests that some galaxies might have migrated
back from the red sequence after accretion events. Our study clearly shows the
variety of evolutionary paths leading to the transition region and suggests
that the transition galaxies may not be always associated with systems quickly
migrating from the blue to the red sequence.Comment: 19 pages, 11 Figures, 1 Table. MNRAS in press. High resolution
version available at
http://www.astro.cardiff.ac.uk/pub/Luca.Cortese/papers/mnras09_1159_hires.p
The HI content of early-type galaxies from the ALFALFA survey. II. The case of low density environments
We present the analysis of the HI content of a sample of early-type galaxies
(ETGs) in low-density environments (LDEs) using the data set provided by the
Arecibo Legacy Fast ALFA (ALFALFA) survey. We compare their properties to the
sample in the Virgo cluster that we studied in a previous paper (di Serego
Alighieri et al. 2007, Paper I). We have selected a sample of 62 nearby ETGs
(V< 3000 km/s) in an area of the sky where the ALFALFA data are already
available (8h<RA<16h, 4 deg<DEC<16deg), avoiding the region of the Virgo
cluster. Among these, 39 have absolute B magnitudes fainter than M_B = -17.
Fifteen out of 62 galaxies have been firmly detected with ALFALFA (\sim 25%).
Five additional galaxies show a weaker HI emission (S/N \sim 4) and they will
need deeper observations to be confirmed. All together, our analysis doubles
the number of known gas-rich ETGs in this area. The HI detection rate is 44% in
luminous ETGs (M_B -17). In both cases it
is 10 times higher than that of the Virgo cluster. The presence of gas can be
related to a recent star formation activity: 60% of all ETGs with HI have
optical emission line ratios typical of star-forming galaxies and blue colours
suggesting the presence of young stellar populations, especially in the dwarf
subsample. We show that the HI detection rate of ETGs depends both on the
environment and mass. The fraction of early-type systems with neutral hydrogen
is higher in more massive objects when compared to early-type dwarfs. The ETGs
in LDEs seem to have more heterogeneous properties than their Virgo cluster
counterparts, since they are able to retain a cold interstellar gas component
and to support star formation activity even at recent epochs.Comment: 11 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29