53 research outputs found
The merging/AGN connection II. Ionization of the circumnuclear regions
We report the first results of a study of a sample of 20 galaxy
mergers/interacting systems, using the VIMOS and PMAS integral field
spectrographs. For each object, we extracted the integrated spectrum of the
central regions and analyzed the ionization state using classical diagnostic
diagrams (Veilleux & Osterbrock 1987). There is evidence of AGN ionization in 4
of the objects, i.e. 20% of the sample, a considerably higher fraction than
found in previous studies ~4%Comment: 4 pages, 2 figures, accepted for publishing in A&A Letter
NICMOS Imaging of Infrared-Luminous Galaxies
We present near-infrared images obtained with the HST NICMOS camera for a
sample of 9 luminous (LIGs: L_IR (8-1000 microns) >~ 10^11 L_sun) and 15
ultra-luminous (ULIGS: L_IR >~ 10^12 L_sun) infrared galaxies. The sample
includes representative systems classified as warm (f_25/f_60 > 0.2) and cold
(f_25/f_60 <~ 0.2) based on the mid-infrared colors and systems with nuclear
emission lines classified as HII (i.e. starburst), QSO, Seyfert and LINER. The
morphologies of the sample galaxies are diverse and provide further support for
the idea that they are created by the collision or interactions of spiral
galaxies. Although no new nuclei are seen in the NICMOS images, the NICMOS
images do reveal new spiral structures, bridges, and circumnuclear star
clusters...Comment: LaTex, 27 pages with 14 gif and 4 jpg figures, AJ, in press, contour
figures of the NICMOS images can be viewed at
http://nedwww.ipac.caltech.edu/level5/Scoville/frames.htm
The NICMOS Snapshot Survey of nearby Galaxies
We present ``snapshot'' observations with the NearInfrared Camera and
MultiObject Spectrometer (NICMOS) on board the Hubble Space Telescope (HST) of
94 nearby galaxies from the Revised Shapley Ames Catalog. Images with 0.2 as
resolution were obtained in two filters, a broad-band continuum filter (F160W,
roughly equivalent to the H-band) and a narrow band filter centered on the
Paschen alpha line (F187N or F190N, depending on the galaxy redshift) with the
51x51 as field of view of the NICMOS camera 3. A first-order continuum
subtraction is performed, and the resulting line maps and integrated Paschen
alpha line fluxes are presented. A statistical analysis indicates that the
average Paschen alpha surface brightness {\bf in the central regions} is
highest in early-type (Sa-Sb) spirals.Comment: Original contained error in flux calibration. Table 1 now has correct
Paschen Alpha fluxes. 14 pages LaTeX with JPEG and PS figures. Also available
at http://icarus.stsci.edu/~boeker/publications.htm
Galaxy Collisions - Dawn of a New Era
The study of colliding galaxies has progressed rapidly in the last few years,
driven by observations with powerful new ground and space-based instruments.
These instruments have used for detailed studies of specific nearby systems,
statistical studies of large samples of relatively nearby systems, and
increasingly large samples of high redshift systems. Following a brief summary
of the historical context, this review attempts to integrate these studies to
address the following key issues. What role do collisions play in galaxy
evolution, and how can recently discovered processes like downsizing resolve
some apparently contradictory results of high redshift studies? What is the
role of environment in galaxy collisions? How is star formation and nuclear
activity orchestrated by the large scale dynamics, before and during merger?
Are novel modes of star formation involved? What are we to make of the
association of ultraluminous X-ray sources with colliding galaxies? To what do
degree do mergers and feedback trigger long-term secular effects? How far can
we push the archaeology of individual systems to determine the nature of
precursor systems and the precise effect of the interaction? Tentative answers
to many of these questions have been suggested, and the prospects for answering
most of them in the next few decades are good.Comment: 44 pages, 9 figures, review article in press for Astrophysics Update
Vol.
Adaptive optics imaging and optical spectroscopy of a multiple merger in a luminous infrared galaxy
(abridged) We present near-infrared (NIR) adaptive optics imaging obtained
with VLT/NACO and optical spectroscopy from the Southern African Large
Telescope (SALT) of a luminous infrared galaxy (LIRG) IRAS 19115-2124. These
data are combined with archival HST imaging and Spitzer imaging and
spectroscopy, allowing us to study this disturbed interacting/merging galaxy,
dubbed the Bird, in extraordinary detail. In particular, the data reveal a
triple system where the LIRG phenomenon is dominated by the smallest of the
components.
One nucleus is a regular barred spiral with significant rotation, while
another is highly disturbed with a surface brightness distribution intermediate
to that of disk and bulge systems, and hints of remaining arm/bar structure. We
derive dynamical masses in the range 3-7x10^10 M_solar for both. The third
component appears to be a 1-2x10^10 M_solar mass irregular galaxy. The total
system exhibits HII galaxy-like optical line ratios and strengths, and no
evidence for AGN activity is found from optical or mid-infrared data. The star
formation rate is estimated to be 190 M_solar/yr. We search for SNe, super star
clusters, and detect 100-300 km/s outflowing gas from the Bird. Overall, the
Bird shows kinematic, dynamical, and emission line properties typical for cool
ultra luminous IR galaxies. However, the interesting features setting it apart
for future studies are its triple merger nature, and the location of its star
formation peak - the strongest star formation does not come from the two major
K-band nuclei, but from the third irregular component. Aided by simulations, we
discuss scenarios where the irregular component is on its first high-speed
encounter with the more massive components.Comment: 24 pages, 16 figures. Accepted MNRAS version, minor corrections only,
references added. Higher resolution version (1.3MB) is available from
http://www.saao.ac.za/~petri/bird/ulirg_bird_highres_vaisanen_v2.pd
Rings and bars: unmasking secular evolution of galaxies
Secular evolution gradually shapes galaxies by internal processes, in
contrast to early cosmological evolution which is more rapid. An important
driver of secular evolution is the flow of gas from the disk into the central
regions, often under the influence of a bar. In this paper, we review several
new observational results on bars and nuclear rings in galaxies. They show that
these components are intimately linked to each other, and to the properties of
their host galaxy. We briefly discuss how upcoming observations, e.g., imaging
from the Spitzer Survey of Stellar Structure in Galaxies (S4G), will lead to
significant further advances in this area of research.Comment: Invited review at "Galaxies and their Masks", celebrating Ken
Freeman's 70-th birthday, Sossusvlei, Namibia, April 2010. To be published by
Springer, New York, editors D.L. Block, K.C. Freeman, & I. Puerari; minor
change
The Hubble Space Telescope Wide Field Camera 3 Early Release Science data: Panchromatic Faint Object Counts for 0.2-2 microns wavelength
We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR
filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter.
Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South
mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50
square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and
0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma})
for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy
separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26
mag from the UV to the near-IR, respectively.Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.2
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
Ultraluminous Infrared Galaxies
Ever since their discovery in the 1970's, UltraLuminous InfraRed Galaxies
(ULIRGs; classically Lir>10^12Lsun) have fascinated astronomers with their
immense luminosities, and frustrated them due to their singularly opaque
nature, almost in equal measure. Over the last decade, however, comprehensive
observations from the X-ray through to the radio have produced a consensus
picture of local ULIRGs, showing that they are mergers between gas rich
galaxies, where the interaction triggers some combination of dust-enshrouded
starburst and AGN activity, with the starburst usually dominating. Very recent
results have thrown ULIRGs even further to the fore. Originally they were
thought of as little more than a local oddity, but the latest IR surveys have
shown that ULIRGs are vastly more numerous at high redshift, and tantalizing
suggestions of physical differences between high and low redshift ULIRGs hint
at differences in their formation modes and local environment. In this review
we look at recent progress on understanding the physics and evolution of local
ULIRGs, the contribution of high redshift ULIRGs to the cosmic infrared
background and the global history of star formation, and the role of ULIRGs as
diagnostics of the formation of massive galaxies and large-scale structures.Comment: Review article, published in "Astrophysics Update 2 - topical and
timely reviews on astronomy and astrophysics". Ed. John W. Mason.
Springer/Praxis books. ISBN: 3-540-30312-X. 53 pages, 5 figures. Higher
quality figures available on reques
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
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