2,559 research outputs found
A Survey of Analogs to Weak MgII Absorbers in the Present
We present the results of a survey of the analogs of weak MgII absorbers
(rest frame equivalent width W(2796) < 0.3 A) at 0 < z < 0.3. Our sample
consisted of 25 HST/STIS echelle quasar spectra (R = 45,000) which covered SiII
1260 and CII 1335 over this redshift range. Using those similar transitions as
tracers of MgII facilitates a much larger survey, covering a redshift
pathlength of g(z) = 5.3 for an equivalent width limit of MgII corresponding to
W(2796) > 0.02 A, with 30% completeness for the weakest lines. We find the
number of weak MgII absorber analogs with 0.02 < W(2796) < 0.3 to be dN/dz =
1.00 +/- 0.20 for 0 < z < 0.3. This value is consistent with cosmological
evolution of the population. We consider the expected effect on observability
of weak MgII absorbers of the decreasing intensity of the extragalactic
background radiation eld from z~1 to z~0. Assuming that all the objects that
produce absorption at z~1 are stable on a cosmological timescale, and that no
new objects are created, we would expect dN/dz of 2-3 at z~0. About 30-50% of
this z~0 population would be decendants of the parsec-scale structures that
produce single-cloud, weak MgII absorbers at z~1. The other 50-70% would be
lower density, kiloparsec-scale structures that produce CIV absorption, but not
detectable low ionization absorption, at z~1. We conclude that at least one,
and perhaps some fraction of both, of these populations has evolved away since
z~1, in order to match the z~0 dN/dz measured in our survey. This would follow
naturally for a population of transient structures whose generation is related
to star-forming processes, whose rate has decreased since z~1.Comment: 45 pages, 12 figures, 7 tables ApJ accepte
The Kinematic Evolution of Strong MgII Absorbers
We consider the evolution of strong (W_r(2796) > 0.3A) MgII absorbers, most
of which are closely related to luminous galaxies. Using 20 high resolution
quasar spectra from the VLT/UVES public archive, we examine 33 strong MgII
absorbers in the redshift range 0.3 < z < 2.5. We compare and supplement this
sample with 23 strong MgII absorbers at 0.4 < z < 1.4 observed previously with
HIRES/Keck. We find that neither equivalent width nor kinematic spread (the
optical depth weighted second moment of velocity) of MgII2796 evolve. However,
the kinematic spread is sensitive to the highest velocity component, and
therefore not as sensitive to additional weak components at intermediate
velocities relative to the profile center. The fraction of absorbing pixels
within the full velocity range of the system does show a trend of decreasing
with decreasing redshift. Most high redshift systems (14/20) exhibit absorption
over the entire system velocity range, which differs from the result for low
redshift systems (18/36) at the 95% level. This leads to a smaller number of
separate subsystems for high redshift systems because weak absorping components
tend to connect the stronger regions of absorption. We hypothesize that low
redshift MgII profiles are more likely to represent well formed galaxies, many
of which have kinematics consistent with a disk/halo structure. High redshift
MgII profiles are more likely to show evidence of complex protogalactic
structures, with multiple accretion or outflow events. Although these results
are derived from measurements of gas kinematics, they are consistent with
hierarchical galaxy formation evidenced by deep galaxy surveys.Comment: Accepted to the Astrophysical Journa
CV20017
This report provides the results of the eighth underwater television on the âPorcupine Bank Nephrops groundsâ ICES assessment area; Functional Unit 16. The survey was multi-disciplinary in nature collecting UWTV and other ecosystem data. In total 65 UWTV stations were successfully completed in a randomised 6 nautical mile isometric grid covering the full spatial extent of the stock. The mean burrow density observed in 2020, adjusted for edge effect, was 0.17 burrows/mÂČ. The final krigged abundance estimate was 1264 million burrows with a CV of 4% and an estimated stock area of 7,130 km2. The 2020 abundance estimate was 25% higher than in 2019. Using the 2020 estimate of abundance and updated stock data implies catches between 2653 and 3290 tonnes in 2021 that correspond to the F ranges in the EU multiannual plan for Western Waters (assuming that all catch is landed). Four species of sea-pen; Virgularia mirabilis, Funiculina quadrangularis, Pennatula phosphorea and the deepwater sea-pen Kophobelemnon stelliferum were observed during the survey. Trawl marks were also observed on 22% of the stations surveyed
A survey of weak MgII absorbers at redshift <z>=1.78
The exact nature of weak MgII absorbers (those with W_r(2796) < 0.3 A) is a
matter of debate, but most are likely related to areas of local star formation
or supernovae activity outside of giant galaxies. Using 18 QSO spectra obtained
with the Ultra-Violet Echelle Spectrograph (UVES) on the Very Large Telescope
(VLT), we have conducted a survey for weak MgII absorbers at 1.4 < z < 2.4. We
searched a redshift path length of 8.51, eliminating regions badly contaminated
by atmospheric absorption so that the survey is close to 100% complete to
W_r(2796) = 0.02 A. We found a total of 9 weak absorbers, yielding a number
density of absorbers of dN/dz = 1.06 +/- 0.12 for 0.02 <= W_r(2796) < 0.3 A.
Narayanan et al. (2005) found dN/dz = 1.00 +/- 0.20 at 0 < z < 0.3 and
Churchill et al. (1999) found dN/dz = 1.74 +/- 0.10 at 0.4 < z < 1.4.
Therefore, the population of weak MgII absorbers appears to peak at z~1. We
explore the expected evolution of the absorber population subject to a changing
extragalactic background radiation (EBR) from z = 0.9 to z = 1.78 (the median
redshift of our survey), and find that the result is higher than the observed
value. We point out that the peak epoch for weak MgII absorption at z~1 may
coincide with the peak epoch of global star formation in the dwarf galaxy
environment.Comment: 25 pages, 14 figures, to be published in ApJ 01 March 2006, v639,
No bursts detected from FRB121102 in two 5-hour observing campaigns with the Robert C. Byrd Green Bank Telescope
Here, we report non-detection of radio bursts from Fast Radio Burst FRB
121102 during two 5-hour observation sessions on the Robert C. Byrd 100-m Green
Bank Telescope in West Virginia, USA, on December 11, 2017, and January 12,
2018. In addition, we report non-detection during an abutting 10-hour
observation with the Kunming 40-m telescope in China, which commenced UTC 10:00
January 12, 2018. These are among the longest published contiguous observations
of FRB 121102, and support the notion that FRB 121102 bursts are episodic.
These observations were part of a simultaneous optical and radio monitoring
campaign with the the Caltech HIgh- speed Multi-color CamERA (CHIMERA)
instrument on the Hale 5.1-m telescope.Comment: 1 table, Submitted to RN of AA
The Timing of Nine Globular Cluster Pulsars
We have used the Robert C. Byrd Green Bank Telescope to time nine previously
known pulsars without published timing solutions in the globular clusters M62,
NGC 6544, and NGC 6624. We have full timing solutions that measure the spin,
astrometric, and (where applicable) binary parameters for six of these pulsars.
The remaining three pulsars (reported here for the first time) were not
detected enough to establish solutions. We also report our timing solutions for
five pulsars with previously published solutions, and find good agreement with
past authors, except for PSR J1701-3006B in M62. Gas in this system is probably
responsible for the discrepancy in orbital parameters, and we have been able to
measure a change in the orbital period over the course of our observations.
Among the pulsars with new solutions we find several binary pulsars with very
low mass companions (members of the so-called "black widow" class) and we are
able to place constraints on the mass-to-light ratio in two clusters. We
confirm that one of the pulsars in NGC 6624 is indeed a member of the rare
class of non-recycled pulsars found in globular clusters. We also have measured
the orbital precession and Shapiro delay for a relativistic binary in NGC 6544.
If we assume that the orbital precession can be described entirely by general
relativity, which is likely, we are able to measure the total system mass
(2.57190(73) M_sun) and companion mass (1.2064(20) M_sun), from which we derive
the orbital inclination [sin(i) = 0.9956(14)] and the pulsar mass (1.3655(21)
M_sun), the most precise such measurement ever obtained for a millisecond
pulsar. The companion is the most massive known around a fully recycled pulsar.Comment: Published in ApJ; 33 pages, 5 figures, 7 table
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