123 research outputs found
NICMOS Observations of Interaction Triggered Star Formation in the Luminous Infrared Galaxy NGC 6090
High resolution, 1.1, 1.6, and 2.2 micron imaging of the luminous infrared
galaxy NGC 6090 obtained with NICMOS of the Hubble Space Telescope are
presented. These new observations are centered on the two nuclei of the merger,
and reveal the spiral structure of the eastern galaxy and the amorphous nature
of the western galaxy. The nuclear separation of 3.2 kpc (H_0 = 75 km/s/Mpc)
indicates that NGC 6090 is at an intermediate stage of merging. Bright
knots/clusters are also visible in the region overlapping the merging galaxies;
four of these knots appear bluer than the underlying galaxies and have colors
consistent with young (<~ 10^7 yr) star clusters. The spatial coincidence of
the knots with the molecular gas in NGC 6090 indicates that much of the present
star formation is occuring outside of the nuclear region of merging galaxies,
consistent with recent studies of other double nuclei luminous infrared
galaxies.Comment: LaTex, 18 pages with 4 jpg figures, ApJ, in pres
NICMOS Imaging of the Nuclei of Arp 220
We report high resolution imaging of the ultraluminous infrared galaxy Arp
220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The
diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve
both nuclei of the merging galaxy system and reveal for the first time a number
of luminous star clusters in the circumnuclear envelope. The morphologies of
both nuclei are strongly affected by dust obscuration, even at 2.2 microns :
the primary nucleus (west) presents a crescent shape, concave to the south and
the secondary (eastern) nucleus is bifurcated by a dust lane with the southern
component being very reddened. In the western nucleus, the morphology of the
2.2 micron emission is most likely the result of obscuration by an opaque disk
embedded within the nuclear star cluster. The morphology of the central
starburst-cluster in the western nucleus is consistent with either a
circumnuclear ring of star formation or a spherical cluster with the bottom
half obscured by the embedded dust disk. Comparison of cm-wave radio continuum
maps with the near-infrared images suggests that the radio nuclei lie in the
dust disk on the west and near the highly reddened southern component of the
eastern complex. The radio nuclei are separated by 0.98 arcseconds
(corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei
are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources
-- probably globular clusters -- are also seen in the circumnuclear envelope at
radii 2-7 arcseconds . Their near-infrared colors do not significantly
constrain their ages.Comment: LaTex, 15 pages with 1 gif figure and 5 postscript figures. ApJL
accepte
Hubble Space Telescope NICMOS Observations of Rest‐Frame Optical Continuum and Hɑ + [N I] Emission in FSC 10214 + 4724
High-resolution 1.10, 2.05, 2.12, and 2.15 μm imaging of the gravitationally lensed system FSC 10214+4724 are presented. These data extend Hubble Space Telescope (HST) observations of the lens system to redder wavelengths, thus providing the highest resolution images to date of the rest-frame optical and narrow-line (i.e., Hα+[N II]) regions of the background quasar. The length of the arc in the wide-band continuum images increases with increasing wavelength, and the Hα+[N II] emission has a length in between that of the 1.10 and 2.05 μm emission. The structure of the arc changes from having an eastern and western peak at 1.10 μm to having a single peak in the center at 2.05 μm. The changing structure and length of the arc can be understood in terms of a model in which the background quasar consists of a region of scattered active galactic nucleus (AGN) light that dominates at 1.10 μm (rest frame 3300 Å), surrounded by a more extended narrow-line region. An even more extended red stellar population would thus contribute light at 2.05 μm (rest frame 6200 Å). In addition, the Hα+[N II] emission has structural features similar to the 1.10 μm emission normalized by the (predominantly stellar) 2.05 μm emission, possibly confirming that the 1.10 μm emission is a superposition of the sources associated with the line emission (AGNs/massive stars) and the red stellar component that dominates the 2.05 μm emission. The counterimage of the lensed quasar is detected in the 1.10 and 2.05 μm images, and the rest frame 3300 and 6200 Å magnifications of the lensed quasar are calculated to be 50 ± 11 and 25 ± 6, respectively, which translates into a rest-frame optical luminosity for the quasar of ~6 × 10^9 L_☉. These magnification values are lower than the previously measured magnification of ~100 at rest frame 2400 Å. If the dust in the primary lensing galaxy is not affecting the measurement of the counterimage flux at 2400 and 3300 Å, the magnification of the quasar appears to decrease with increasing wavelength. Flux measurements of the primary lensing galaxy fit the spectral energy distribution of an unevolving elliptical galaxy at a redshift of 0.9, consistent with previous determinations of the redshift
How Filaments are Woven into the Cosmic Web
Observations indicate galaxies are distributed in a filament-dominated
web-like structure. Numerical experiments at high and low redshift of viable
structure formation theories also show filament-dominance. We present a simple
quantitative explanation of why this is so, showing that the final-state web is
actually present in embryonic form in the overdensity pattern of the initial
fluctuations, with nonlinear dynamics just sharpening the image. The web is
largely defined by the position and primordial tidal fields of rare events in
the medium, with the strongest filaments between nearby clusters whose tidal
tensors are nearly aligned. Applications of the cosmic web theory to
observations include probing cluster-cluster bridges by weak gravitational
lensing, X-rays, and the Sunyaev-Zeldovich effect and probing high redshift
galaxy-galaxy bridges by low column density Lyman alpha absorption lines.Comment: 9 pages, gzipped uuencoded postscript file, 4 figures in separate
files. The text + figures are also available from anonymous ftp site:
ftp://ftp.cita.utoronto.ca/ftp/cita/bond/bkp_natur
Small Scale Structure and High Redshift HI
Cosmological simulations with gas dynamics suggest that the Lyman-alpha
forest is produced mainly by "small scale structure" --- filaments and sheets
that are the high redshift analog of today's galaxy superclusters. There is no
sharp distinction between Lyman-alpha clouds and "Gunn-Peterson" absorption
produced by the fluctuating IGM -- the Lyman-alpha forest {\it is} the
Gunn-Peterson effect. Lyman limit and damped Lyman-alpha absorption arises in
the radiatively cooled gas of forming galaxies. At , most of the gas is
in the photoionized, diffuse medium associated with the Lyman-alpha forest, but
most of the {\it neutral} gas is in damped Lyman-alpha systems. We discuss
generic evolution of cosmic gas in a hierarchical scenario of structure
formation, with particular attention to the prospects for detecting 21cm
emission from high redshift HI. A scaling argument based on the present-day
cluster mass function suggests that objects with M_{HI} >~ 5e11 h^{-1} \msun
should be extremely rare at , so detections with existing instruments will
be difficult. An instrument like the proposed Square Kilometer Array could
detect individual damped Lyman-alpha systems at high redshift, making it
possible to map structure in the high redshift universe in much the same way
that today's galaxy redshift surveys map the local large scale structure.Comment: 15 pages, latex w/ crckapb & epsf macros, ps figures; get ps version
with all figures from ftp://bessel.mps.ohio-state.edu/pub/dhw/Preprints To
appear in Cold Gas at High Redshift, eds. M. Bremer et al. (Kluwer, 1996
Lyman alpha absorption lines from mini pancakes
[Abridged abstract:] Recent numerical simulations show that many \lyal
absorption lines of column densities \nha \la 10^{15} cm are produced
in transient, mini pancakes. Such pancakes are modeled here, approximating the
initial perturbation leading to the formation of the pancake as a single
sinusoidal wave. The density and temperature profiles of the gas in the pancake
are determined for , where is the collapse redshift. The
\lyal absorption line profiles for a line of sight through the pancake are
then calculated. The absorption lines in general have wings signifying bulk
motions in the gas. It is shown that the deviation from a single Voigt profile
is large for small H I column density lines, in which the effect of bulk
motions is large. For lines with \nha > 10^{13} cm, high temperature
tend to wash out the signatures of bulk motion. The analytical modeling of mini
pancakes associated with \lyal forest lines --- with 10^{13} \la \nha \la
10^{15} cm---gives the corresponding mass scales. It is shown here
that, for typical values of cosmological parameters, absorption lines with
\nha \sim 10^{14} cm correspond to structures with baryonic mass of
M with an overdensity of at .
The value of \nha can change by a factor in the course of evolution
of the pancake in time. It is also shown that there is an upper limit to \nha
from a pancake due to the slow recombination rate and the importance of
collisional ionization at high temperatures. Mini pancakes do not give rise to
\lyal lines with \nha \ga 10^{14.5} cm, for \j21=1 and
.Comment: Latex with aaspp4.sty (25 pages), 6 figures, Accepted for publication
in The Astrophysical Journa
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
Hubble Space Telescope NICMOS Observations of Rest‐Frame Optical Continuum and Hɑ + [N I] Emission in FSC 10214 + 4724
High-resolution 1.10, 2.05, 2.12, and 2.15 μm imaging of the gravitationally lensed system FSC 10214+4724 are presented. These data extend Hubble Space Telescope (HST) observations of the lens system to redder wavelengths, thus providing the highest resolution images to date of the rest-frame optical and narrow-line (i.e., Hα+[N II]) regions of the background quasar. The length of the arc in the wide-band continuum images increases with increasing wavelength, and the Hα+[N II] emission has a length in between that of the 1.10 and 2.05 μm emission. The structure of the arc changes from having an eastern and western peak at 1.10 μm to having a single peak in the center at 2.05 μm. The changing structure and length of the arc can be understood in terms of a model in which the background quasar consists of a region of scattered active galactic nucleus (AGN) light that dominates at 1.10 μm (rest frame 3300 Å), surrounded by a more extended narrow-line region. An even more extended red stellar population would thus contribute light at 2.05 μm (rest frame 6200 Å). In addition, the Hα+[N II] emission has structural features similar to the 1.10 μm emission normalized by the (predominantly stellar) 2.05 μm emission, possibly confirming that the 1.10 μm emission is a superposition of the sources associated with the line emission (AGNs/massive stars) and the red stellar component that dominates the 2.05 μm emission. The counterimage of the lensed quasar is detected in the 1.10 and 2.05 μm images, and the rest frame 3300 and 6200 Å magnifications of the lensed quasar are calculated to be 50 ± 11 and 25 ± 6, respectively, which translates into a rest-frame optical luminosity for the quasar of ~6 × 10^9 L_☉. These magnification values are lower than the previously measured magnification of ~100 at rest frame 2400 Å. If the dust in the primary lensing galaxy is not affecting the measurement of the counterimage flux at 2400 and 3300 Å, the magnification of the quasar appears to decrease with increasing wavelength. Flux measurements of the primary lensing galaxy fit the spectral energy distribution of an unevolving elliptical galaxy at a redshift of 0.9, consistent with previous determinations of the redshift
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