11,213 research outputs found
The potential of tracing the star formation history with HI 21-cm in intervening absorption systems
Unlike the neutral gas density, which remains largely constant over redshifts
of 0 < z < 5, the star formation density exhibits a strong redshift dependence,
increasing from the present day before peaking at a redshift of z ~ 2.5. Thus,
there is a stark contrast between the star formation rate and the abundance of
raw material available to fuel it. However, using the ratio of the strength of
the HI 21-cm absorption to the total neutral gas column density to quantify the
spin temperature of the gas, it has recently been shown that its reciprocal may
trace the star formation density. This would be expected on the grounds that
the cloud of gas must be sufficiently cool to collapse under its own gravity.
This, however, relies on very limited data and so here we explore the potential
of applying the above method to absorbers for which individual column densities
are not available (primarily MgII absorption systems). By using the mean value
as a proxy to the column density of the gas at a given redshift, we do, again,
find that 1/T (degenerate with the absorber-emitter size ratio) traces the SF
density. If confirmed by higher redshift data, this could offer a powerful tool
for future surveys for cool gas throughout the Universe with the Square
Kilometre Array.Comment: Accepted by A&
Abandonment and Reconciliation: Addressing Political and Common Law Objections to Fetal Homicide Laws
Fetal homicide laws criminalize killing a fetus largely to the same extent as killing any other human being. Historically, the common law did not generally recognize feticide as a crime, but this was because of the evidentiary born-alive rule, not because of the substantive understanding of the term human being. As medicine and science have advanced, states have become increasingly willing to abandon this evidentiary rule and to criminalize feticide as homicide. Although most states have recognized the crime of fetal homicide, fourteen have not. This is largely the result of two independent obstacles: (judicial) adherence to the born-alive rule and (legislative) concern that fetal homicide laws could erode constitutionally protected reproductive rights. This Note explores a variety of fetal homicide laws that states have adopted, demonstrating that popular opinion has shifted toward recognizing this crime. It then directly confronts the objections that have prevented other states from adopting such laws: it first reviews the literature suggesting that the born-alive rule should be abandoned, as it is an obsolete evidentiary standard; it then argues that constitutionally protected reproductive liberties can be reconciled with, and in fact augmented by, punishing the killing of a fetus as a homicide
A third HI 21-cm absorption system in the sight-line of MG J0414+0534: A redshift for Object X?
We report the detection of a third HI 21-cm absorber in the sight-line
towards the z=2.64 quasar MG J0414+0534 (4C +05.19). In addition to the
absorption at the host redshift and in the z=0.96 gravitational lens, we find,
through a decimetre-wave spectral scan towards this source, strong absorption
at z=0.38. We believe this may be associated with "Object X", an additional
feature apparent in the field of the lensing galaxy and lensed images, on the
basis of its close proximity to the quasar images and the possible detection of
the [OIII] doublet in a published optical spectrum. If real, the strength of
the [OIII] emission would suggest the presence of an active galactic nucleus,
or a gas-rich galaxy undergoing rapid star formation, either of which is
consistent with the strong outflows apparent in the 21-cm spectrum. Although
this is the strongest intervening 21-cm absorber yet found, simultaneous
observations failed to detect any of the 18-cm OH lines at the 21-cm redshift.
This suggests that, as for the lensing galaxy, this is not the primary location
of the intervening material responsible for the very red colour of MG
J0414+0534.Comment: 5 pages, accepted by MNRAS Letter
Localised HI 21-cm absorption towards a double-lobed z=0.24 radio galaxy
We present the results of a mini-survey for associated HI 21-cm absorption at
z < 0.42 with the Giant Metrewave Radio Telescope. Our targets are radio
galaxies, selected on the basis that the 1216 Angstrom luminosities are below
10^23 W/Hz, above which there has never been a detection of 21-cm absorption.
Of the three sources for which we obtained good data, two are unclassified
active galactic nuclei (AGN) and one is type-2. Being a non-detection, the
type-2 object is consistent with our previous result that 21-cm absorption in
radio sources is not dictated by unified schemes of AGN. In the case of the
detection, the absorption only occurs towards one of the two resolved radio
lobes in PKS 1649-062. If the absorption is due to an another intervening
galaxy, or cool HI gas in the intergalactic medium, covering only the
south-west lobe, then, being at the same redshift, this is likely to be
gravitationally bound to the optical object identified as PKS 1649-062. If the
absorption is due to an inclined disk centred between the lobes, intervening
the SW lobe while being located behind the NE lobe, by assuming that it covers
the emission peak at 150 kpc from the nucleus, we estimate a dynamical mass of
~3 x 10^12 solar masses for the disk.Comment: 5 pages accepted by MNRAS Letter
NIR and optical observations of the failed outbursts of black hole binary XTE J1550-564
A number of low mass X-ray binaries (LMXBs) undergo "failed outbursts" in
which, instead of evolving through the canonical states, they remain in a hard
state throughout the outburst. While the sources of X-ray and radio emission in
the hard state are relatively well understood, the origin of the near infrared
(NIR) and optical emission is more complex though it likely stems from an
amalgam of different emission processes, occurring as it does, at the
intersecting wavelengths of those processes. We aim to identify the NIR/optical
emission region(s) during a number of failed outbursts of one such low mass
X-ray binary and black hole candidate, XTE J1550-564, in order to confirm or
refute their classification as hard-state, failed outbursts. We present unique
NIR/optical images and spectra, obtained with the ESO-New Technology Telescope,
during the failed outbursts of 2001 and 2000. We compare the NIR/optical
photometric, timing, and spectral properties with those expected for the
different emission mechanisms in the various LMXB states. The NIR/optical data
are consistent with having come from reprocessing of X-rays in the accretion
disk, with no evidence of direct thermal emission from the disk itself.
However, the observed variability in high-cadence NIR light curves suggest that
the radio jet extends and contributes to the NIR wavelengths. We find that
these failed outbursts did not transition to an intermediate state but remained
in a true, hard state where there was no sign of jet quenching or deviation
from the observed hard state correlations.Comment: Accepted to Astronomy & Astrophysics (8 pages
On the detectability of HI 21-cm in MgII absorption system
We investigate the effect of two important, but oft neglected, factors which
can affect the detectability of HI 21-cm absorption in MgII absorption systems:
The effect of line-of-sight geometry of the coverage of the background radio
flux and any possible correlation between the 21-cm line strength and the rest
frame equivalent width of the MgII line. Regarding the former, while the
observed detection rate at small angular diameter distance ratios is a near
certainty, for an unbiased sample, where either a detection or a non-detection
are equally likely, at ratios > 0.8 the observed detection rate has an 8 sigma
significance, suggesting that the mix of ratios values at z < 1 is correlated
with the mix of detections and non-detections at low redshift, while the
exclusively high values of the ratio at z > 1 contribute to the low detection
rates at high redshift. In DLAs, the correlation between the 21-cm line
strength and the MgII equivalent width is dominated by the velocity spread of
the 21-cm line. This has recently been shown not to hold for MgII systems in
general. However, we do find the significance of the correlation to increase
when the MgII absorbers with MgI equivalent widths of >0.5 A are added to the
DLA sample. Large values of the angular diameter distance ratio may explain why
the absorbers which have similar equivalent widths to the detections remain
undetected. We do, however, also find the neutral hydrogen column densities of
the non-detections to be significantly lower. Applying the 21-cm line
strength/equivalent width correlation to yield column densities for the MgII
absorbers in which this is unmeasured, we find no evidence of a cosmological
evolution in the neutral hydrogen column density.Comment: 9 pages, accepted by MNRA
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