4,244 research outputs found
The Nature of the Compact/Symmetric Near-IR Continuum Source in 4C 40.36
Using NICMOS on HST, we have imaged the emission-line nebulae and the
line-free continuum in 4C 40.36, a ultra-steep spectrum FR II radio galaxy at
z=2.269. The line-free continuum was found to be extremely compact and
symmetric while the emission-line nebulae seen in H-alpha+[N II] show very
clumpy structures spreading almost linearly over 16 kpc. However, this linear
structure is clearly misaligned from the radio axis. The SED of the line-free
continuum is very flat, suggesting that if the continuum emission is produced
by a single source, it is likely to be a young bursting stellar population or
scattered AGN light. However, because of the lack of a line-free optical image
with a comparable spatial resolution, we cannot exclude the possibility that
the observed SED is a composite of a young blue population and an old red
population.Comment: 4 pages, 2 figures; to appear in the proceedings of "The Hy-Redshift
Universe: Galaxy Formation and Evolution at High Redshift", eds. A.J.Bunker
and W. J. M. van Breuge
Age-Dating Ultraluminous Infrared Galaxies Along the Merger Sequence
Imaging spectroscopy using the new Palomar Integral Field Spectrograph is
presented for the Pa-alpha line in four ultraluminous infrared galaxies. In
most cases, we are able to establish the geometry of the merger, and thus
estimate the time in the merger process at which we are viewing the system. The
resulting range in estimated ages, some of which are very young encounters
(~5x10^7 yr), is not predicted by merger models, which produce high rates of
star formation either 1-2x10^8 years after the first encounter or very late
(~10^9 yr) in the merger process. Even in the very young mergers, the
ultraluminous activity appears to be centrally concentrated on the nucleus of
one of the progenitor galaxies---namely the galaxy with a prograde orbital
geometry. Very high star formation rates (2-5 M_sun/yr) are also observed in
structures believed to be newly formed tidal tails.
The presence of a significant population of very young ultraluminous mergers,
together with the majority of ultraluminous infrared galaxies existing in the
final stages of merger activity, indicates that the ultraluminous galaxy phase
is at least bimodal in time. An evolutionary scenario is proposed for
ultraluminous infrared galaxies, wherein the far-infrared luminosity may
undergo multiple ultraluminous bursts during the course of the encounter. A
substantial fraction of the merger lifetime may be spent in a phase identified
with the less powerful luminous infrared galaxy class.Comment: 27 pages, 21 figures, 5 in color, uses AASTeX 5.02 & emulateapj5.sty;
To appear in the Astrophysical Journa
APM 08279+5255: Keck Near- and Mid-IR High-Resolution Imaging
We present Keck high-resolution near-IR (2.2 microns; FWHM~0.15") and mid-IR
(12.5 microns; FWHM~0.4") images of APM08279+5255, a z=3.91 IR-luminous BALQSO
with a prodigious apparent bolometric luminosity of 5x10^{15} Lsun, the largest
known in the universe. The K-band image shows that this system consists of
three components, all of which are likely to be the gravitationally lensed
images of the same background object, and the 12.5 micron image shows a
morphology consistent with such an image configuration. Our lens model suggests
that the magnification factor is ~100 from the restframe UV to mid-IR, where
most of the luminosity is released. The intrinsic bolometric luminosity and IR
luminosity of APM08279+5255 are estimated to be 5x10^{13} Lsun and 1x10^{13}
Lsun, respectively. This indicates that APM 08279+5255 is intriniscally
luminous, but it is not the most luminous object known. As for its dust
contents, little can be determined with the currently available data due to the
uncertainties associated with the dust emissivity and the possible effects of
differential magnification. We also suggest that the lensing galaxy is likely
to be a massive galaxy at z~3.Comment: 32 pages, 4 tables, 11 figures; Accepted for publication in Ap
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