1,103 research outputs found
SDSS J092712.64+294344.0: recoiling black hole or merging galaxies?
We report long-slit spectroscopic observations of SDSS J092712+294344
carried-out at the recently commissioned 2m telescope in IUCAA Girawali
Observatory, India. This AGN-like source is known to feature three sets of
emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as
a recoiling black hole after asymmetric emission of gravitational waves, binary
black holes and possible merging systems are proposed for this object. We test
these scenarios by comparing our spectra with that from the Sloan Digital Sky
Survey (SDSS), obtained 4 years prior to our observations. Comparing the
redshifts of [OIII]4960,5008 we put a 3 sigma limit on the relative
acceleration to be less than 32 km s^-1 yr^-1 between different emitting
regions. Using the 2D spectra obtained at different position angles we show
that the [OIII]5008 line from the zem = 0.7128 component is extended beyond the
spectral point spread function. We infer the linear extent of this line
emitting region is ~8 kpc. We also find a tentative evidence for an offset
between the centroid of the [OIII]5008 line at zem = 0.7128 and the QSO trace
when the slit is aligned at a position angle of 299 degrees. This corresponds
to the zem = 0.7128 system being at an impact parameter of ~1 kpc with respect
to the zem = 0.6972 in the north west direction. Based on our observations we
conclude that the binary black hole model is most unlikely. The spatial extent
and the sizes are consistent with both black hole recoil and merging scenarios.Comment: accepted for publication in MNRAS Letter
Microstructural modifications in tungsten induced by high flux plasma exposure : TEM examination
We have performed microstructural characterization using transmission electron microscopy (TEM) techniques to reveal nanometric features in the sub-surface region of tungsten samples exposed to high flux, low energy deuterium plasma. TEM examination revealed formation of a dense dislocation network and dislocation tangles, overall resulting in a strong increase in the dislocation density by at least one order of magnitude as compared to the initial one. Plasma-induced dislocation microstructure vanishes beyond a depth of about 10 mu m from the top of the exposed surface where the dislocation density and its morphology becomes comparable to the reference microstructure. Interstitial edge dislocation loops with Burgers vector a(0)/2 and a(0) were regularly observed within 6 mu m of the sub-surface region of the exposed samples, but absent in the reference material. The presence of these loops points to a co-existence of nanometric D bubbles, growing by loop punching mechanism, and sub-micron deuterium flakes, resulting in the formation of surface blisters, also observed here by scanning electron microscopy
Probing the time variability of five Fe low broad absorption line quasars
We study the time variability of five Fe Low ionization Broad Absorption Line
(FeLoBAL) QSOs using repeated spectroscopic observations with the 2m telescope
at IUCAA Girawali observatory (IGO) spanning an interval of upto 10 years. We
report a dramatic variation in Al III and Fe III fine-structure lines in the
spectra of SDSS J221511.93-004549.9 (z_em ~ 1.478). However, there is no such
strong variability shown by the C IV absorption. This source is known to be
unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe
III absorption being stronger than Fe II and (iii) the apparent ratio of Fe III
UV 48 to Fe III UV 34 absorption suggesting an inverted population ratio. This
is the first reported detection of time variability in the Fe III
fine-structure lines in QSO spectra. There is a strong reduction in the
absorption strength of these lines between year 2000 and 2008. Using the
template fitting techniques, we show that the apparent inversion of strength of
UV lines could be related to the complex spectral energy distribution of this
QSO. The observed variability can be related to change in the ionization state
of the gas or due to transverse motion of this absorbing gas. The shortest
variability timescale of Al III line gives a lower limit on the electron
density of the absorbing gas as n_e >= 1.1 x 10^4 cm^-3. The remaining 4
FeLoBALs do not show any changes beyond the measurement uncertainties either in
optical depth or in the velocity structure. We present the long-term
photometric light curve for all of our sources. Among them only SDSS
J221511.93-004549.9 shows significant (>= 0.2 mag) variability.Comment: 15 pages, 9 figures, 3 tables, Accepted for publication in MNRA
A new B-dot probe-based diagnostic for amplitude, polarization, and wavenumber measurements of ion cyclotron range-of frequency fields on ASDEX Upgrade
A new B-dot probe-based diagnostic has been installed on an ASDEX Upgrade tokamak to characterize ion cyclotron range-of frequency (ICRF) wave generation and interaction with magnetized plasma. The diagnostic consists of a field-aligned array of B-dot probes, oriented to measure fast and slow ICRF wave fields and their field-aligned wavenumber (k(//)) spectrum on the low field side of ASDEX Upgrade. A thorough description of the diagnostic and the supporting electronics is provided. In order to compare the measured dominant wavenumber of the local ICRF fields with the expected spectrum of the launched ICRF waves, in-air near-field measurements were performed on the newly installed 3-strap ICRF antenna to reconstruct the dominant launched toroidal wavenumbers (k(tor)). Measurements during a strap current phasing scan in tokamak discharges reveal an upshift in k(//) as strap phasing is moved away from the dipole configuration. This result is the opposite of the k(tor) trend expected from in-air near-field measurements; however, the near-field based reconstruction routine does not account for the effect of induced radiofrequency (RF) currents in the passive antenna structures. The measured exponential increase in the local ICRF wave field amplitude is in agreement with the upshifted k(//), as strap phasing moves away from the dipole configuration. An examination of discharges heated with two ICRF antennas simultaneously reveals the existence of beat waves at 1 kHz, as expected from the difference of the two antennas' operating frequencies. Beats are observed on both the fast and the slow wave probes suggesting that the two waves are coupled outside the active antennas. Although the new diagnostic shows consistent trends between the amplitude and the phase measurements in response to changes applied by the ICRF antennas, the disagreement with the in-air near-field measurements remains. An electromagnetic model is currently under development to address this issue. (C) 2015 AIP Publishing LLC
Optical/near-infrared selection of red QSOs: Evidence for steep extinction curves towards galactic centers?
We present the results of a search for red QSOs using a selection based on
optical imaging from SDSS and near-infrared imaging from UKIDSS. For a sample
of 58 candidates 46 (79%) are confirmed to be QSOs. The QSOs are predominantly
dust-reddened except a handul at redshifts z>3.5. The dust is most likely
located in the QSO host galaxies. 4 (7%) of the candidates turned out to be
late-type stars, and another 4 (7%) are compact galaxies. The remaining 4
objects we could not identify. In terms of their optical spectra the QSOs are
similar to the QSOs selected in the FIRST-2MASS red Quasar survey except they
are on average fainter, more distant and only two are detected in the FIRST
survey. We estimate the amount of extinction using the SDSS QSO template
reddened by SMC-like dust. It is possible to get a good match to the observed
(restframe ultraviolet) spectra, but for nearly all the reddened QSOs it is not
possible to match the near-IR photometry from UKIDSS. The likely reasons are
that the SDSS QSO template is too red at optical wavelengths due to
contaminating host galaxy light and that the assumed SMC extinction curve is
too shallow. Our survey has demonstrated that selection of QSOs based on
near-IR photometry is an efficent way to select QSOs, including reddened QSOs,
with only small contamination from late-type stars and compact galaxies. This
will be useful with ongoing and future wide-field near-IR surveys such as the
VISTA and EUCLID surveys. [Abridged]Comment: 74 pages, 6 figures. Accepted for for publication in ApJ
Improved measurements of ICRF antenna input impedance at ASDEX upgrade during ICRF coupling studies
A new set of diagnostics has been implemented on ASDEX Upgrade to measure the input impedance of the ICRF antennas, in the form of a voltage and current probe pair installed on each feeding line of every antenna. Besides allowing the measurement of the reflection coefficient Gamma of each antenna port, the probes have two advantages: first, they are located close to the antenna ports (similar to 3 m) and thus the measurements are not affected by the uncertainties due to the transmission and matching network; second, they are independent of matching conditions.
These diagnostics have been used to study the behavior of the ASDEX Upgrade antennas while changing the plasma shape (low to high triangularity) and applying magnetic perturbations (MPs) via saddle coils. Scans in the separatrix position R-sep were also performed. Upper triangularity delta(o) was increased from 0.1 to 0.3 (with the lower triangularity delta(o) kept roughly constant at 0.45) and significant decreases in vertical bar Gamma vertical bar (up to similar to 30%, markedly improving antenna coupling) and moderate changes in phase (up to similar to 5 degrees) off on each feeding line were observed approximately at delta(o) >= 0.29. During MPs (in similar to 0.5 s pulses with a coil current of 1 kA), a smaller response was observed: 6% - 7% in vertical bar Gamma vertical bar, with changes in phase of 5 apparently due to R p scans only. As 1 is usually in the range 0.8 - 0.9, this still leads to a significant increase in possible coupled power. Numerical simulations of the antenna behavior were carried out using the FELICE code; the simulation results are in qualitative agreement with experimental measurements. The results presented here complement the studies on the influence of gas injection and MPs on the ICRF antenna performance presented in [4]
Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow
We present the detection of Ly-alpha, [OIII] and H-alpha emission associated
with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards
the quasar SDSS J113520-001053. This is the largest HI column density ever
measured along a QSO line of sight, though typical of what is seen in GRB-DLAs.
This absorption system also classifies as ultrastrong MgII system with
W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion
factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally
larger than) the mean values found in the general QSO-DLA population. The
[OIII]-Ha emitting region has a very small impact parameter with respect to the
QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure
SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More
strikingly, the blue and red Ly-a peaks arise from distinct regions extended
over a few kpc on either side of the star-forming region. We propose that this
is the consequence of Ly-a transfer in outflowing gas. The presence of
starburst-driven outflows is also in agreement with the large SFR together with
a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV
continuum luminosity of the galaxy, we estimate an age of at most a few 10^7
yr, again consistent with a recent starburst scenario. We interpret the data as
the observation of a young, gas rich, compact starburst galaxy, from which
material is expelled through collimated winds powered by the vigorous star
formation activity. We substantiate this picture by modelling the radiative
transfer of Ly-a photons in the galactic counterpart. Though our model (a
spherical galaxy with bipolar outflowing jets) is a simplistic representation
of the true gas distribution and velocity field, the agreement between the
observed and simulated properties is particularly good. [abridged]Comment: 15 pages, 18 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
Serendipitous discovery of a projected pair of QSOs separated by 4.5 arcsec on the sky
We present the serendipitous discovery of a projected pair of quasi-stellar
objects (QSOs) with an angular separation of arcsec. The
redshifts of the two QSOs are widely different: one, our programme target, is a
QSO with a spectrum consistent with being a narrow line Seyfert 1 AGN at
. For this target we detect Lyman-, \ion{C}{4}, and
\ion{C}{3]}. The other QSO, which by chance was included on the spectroscopic
slit, is a Type 1 QSO at a redshift of , for which we detect
\ion{C}{4}, \ion{C}{3]} and \ion{Mg}{2}. We compare this system to previously
detected projected QSO pairs and find that only about a dozen previously known
pairs have smaller angular separation.Comment: 4 pages, 3 figures. Accepted for publication in A
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