988 research outputs found
Molecular gas at intermediate redshifts
We present Giant Metrewave Radio Telescope (GMRT) observations of OH
absorption in B3~1504+377 () and PKS 1413+135 ().
OH has now been detected in absorption towards four intermediate redshift
systems, viz. the lensing galaxies towards B~0218+357 (; Kanekar
et al. 2001) and 1830-211 (; Chengalur et al. 1999), in addition
to the two systems listed above. All four systems also give rise to well
studied millimetre wavelength molecular line absorption from a host of
molecules, including HCO. Comparing our OH data with these millimetre line
transitions, we find that the linear correlation between and
found in molecular clouds in the Milky Way (Liszt & Lucas 1996)
persists out to . It has been suggested (Liszt & Lucas 1999) that OH
is a good tracer of , with
under a variety of physical conditions. We use this relationship to estimate
in these absorbers. The estimated is \ga 10^{22}
in all four cases and substantially different from estimates based on CO
observations.Comment: 4 pages, 3 figures. Accepted for publication in Astronomy and
Astrophysics Letter
Star formation and the interstellar medium in z>6 UV-luminous Lyman-break galaxies
We present Atacama Large Millimeter Array (ALMA) detections of atomic carbon
line and dust continuum emission in two UV-luminous galaxies at redshift 6. The
far-infrared (FIR) luminosities of these galaxies are substantially lower than
similar starbursts at later cosmic epochs, indicating an evolution in the dust
properties with redshift, in agreement with the evolution seen in ultraviolet
(UV) attenuation by dust. The [CII] to FIR ratios are found to be higher than
at low redshift showing that [CII] should be readily detectable by ALMA within
the reionization epoch. One of the two galaxies shows a complex merger nature
with the less massive component dominating the UV emission and the more massive
component dominating the FIR line and continuum. Using the interstellar atomic
carbon line to derive the systemic redshifts we investigate the velocity of
Lyman alpha emission emerging from high-z galaxies. In contrast to previous
work, we find no evidence for decreasing Lyman alpha velocity shifts at
high-redshift. We observe an increase in velocity shifts from z2 to
z6, consistent with the effects of increased IGM absorption.Comment: 10 pages, 9 figures, submitted to ApJ, revised after referees
comment
Galaxies into the Dark Ages
We consider the capabilities of current and future large facilities operating
at 2\,mm to 3\,mm wavelength to detect and image the [CII] 158\,m line
from galaxies into the cosmic "dark ages" ( to 20). The [CII] line
may prove to be a powerful tool in determining spectroscopic redshifts, and
galaxy dynamics, for the first galaxies. We emphasize that the nature, and even
existence, of such extreme redshift galaxies, remains at the frontier of open
questions in galaxy formation. In 40\,hr, ALMA has the sensitivity to detect
the integrated [CII] line emission from a moderate metallicity, active
star-forming galaxy [; star formation rate (SFR) =
5\,\,yr], at at a significance of 6. The
next-generation Very Large Array (ngVLA) will detect the integrated [CII] line
emission from a Milky-Way like star formation rate galaxy (, SFR = 1\,\,yr), at at a significance
of 6. Imaging simulations show that the ngVLA can determine rotation
dynamics for active star-forming galaxies at , if they exist. Based
on our very limited knowledge of the extreme redshift Universe, we calculate
the count rate in blind, volumetric surveys for [CII] emission at
to 20. The detection rates in blind surveys will be slow (of order unity per
40\,hr pointing). However, the observations are well suited to commensal
searches. We compare [CII] with the [OIII] 88m line, and other ancillary
information in high galaxies that would aid these studies.Comment: 11pages, 8 figures, Accepted for the Astrophysical Journa
Cosmology with Varying Constants
The idea of possible time or space variations of the `fundamental' constants
of nature, although not new, is only now beginning to be actively considered by
large numbers of researchers in the particle physics, cosmology and
astrophysics communities. This revival is mostly due to the claims of possible
detection of such variations, in various different contexts and by several
groups. Here, I present the current theoretical motivations and expectations
for such variations, review the current observational status, and discuss the
impact of a possible confirmation of these results in our views of cosmology
and physics as a whole.Comment: 14 pages, no figures. Essay to appear in Phil. Trans. Roy. Soc. Lond.
A Triennial Series (Christmas 2002 Issue
Galaxy Formation Through Filamentary Accretion at z=6.1
We present ALMA observations of the dust continuum and [C II] 158um line
emission from the z=6.0695 Lyman Break Galaxy WMH5. These observations at 0.3"
spatial resolution show a compact (~3kpc) main galaxy in dust and [C II]
emission, with a 'tail' of emission extending to the east by about 5kpc (in
projection). The [C II] tail is comprised predominantly of two distinct
sub-components in velocity, separated from the core by ~100 and 250km/s, with
narrow intrinsic widths of about 80km/s, which we call 'sub-galaxies'. The
sub-galaxies themselves are extended east-west by about 3kpc in individual
channel images. The [C II] tail joins smoothly into the main galaxy velocity
field. The [C II] line to continuum ratios are comparable for the main and
sub-galaxy positions, within a factor 2. In addition, these ratios are
comparable to z~5.5 LBGs. We conjecture that the WMH5 system represents the
early formation of a galaxy through the accretion of smaller satellite
galaxies, embedded in a smoother gas distribution, along a possibly filamentary
structure. The results are consistent with current cosmological simulations of
early galaxy formation, and support the idea of very early enrichment with dust
and heavy elements of the accreting material.Comment: 10 pages, 9 figures, Accepted for publication in Ap
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