We study the time variability of five Fe low-ionization broad absorption line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2-m telescope at IUCAA Girawali Observatory (IGO) ...spanning an interval of up to 10 years. We report a dramatic variation in the 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 2000 and 2008. Using the template-fitting techniques, we show that the apparent inversion of the strength of ultraviolet lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to a change in the ionization state of the gas or due to the transverse motion of this absorbing gas. The shortest variability time-scale of Al iii line gives a lower limit on the electron density of the absorbing gas as
cm−3. The remaining four 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.
We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyα absorbers (DLAs). Our rationale is that high-metallicity DLAs due ...to the luminosity–metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Lyα emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines (O ii, O iii, Hβ and Hα) fall in the near-infrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the zabs= 2.354 DLA towards the z= 2.926 quasar Q 2222−0946. This DLA is amongst the most metal-rich z > 2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn ii, Si ii, Ni ii, Mn ii and Fe ii of −0.46 ± 0.07, − 0.51 ± 0.06, − 0.85 ± 0.06, − 1.23 ± 0.06 and −0.99 ± 0.06, respectively. The galaxy is detected in the Lyα, O iiiλλ4959, 5007 and Hα emission lines at an impact parameter of about 0.8 arcsec (6 kpc at zabs= 2.354). Based on the Hα line, we infer a star formation rate of 10 M⊙ yr−1, which is a lower limit due to the possibility of slit loss. Compared to the recently determined Hα luminosity function for z= 2.2 galaxies, the DLA-galaxy counterpart has a luminosity of L∼ 0.1L*Hα. The emission-line ratios are 4.0 (Lyα/Hα) and 1.2 (O iii/Hα). In particular, the Lyα line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA are consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.
We present a systematic search for molecular hydrogen absorption systems at high redshift in quasar spectra from the Sloan Digital Sky Survey (SDSS)-II Data Release 7 and SDSS-III Data Release 9. We ...have selected candidates using a modified profile fitting technique taking into account that the Lyα forest can effectively mimic H2 absorption systems at the resolution of SDSS data. To estimate the confidence level of the detections, we use two methods: a Monte Carlo sampling and an analysis of control samples. The analysis of control samples allows us to define regions of the spectral quality parameter space where H2 absorption systems can be confidently identified. We find that H2 absorption systems with column densities log NH2
> 19 can be detected in only less than 3 per cent of SDSS quasar spectra. We estimate the upper limit on the detection rate of saturated H2 absorption systems (NH2
> 19) in damped Lyα (DLA) systems to be about 7 per cent. We provide a sample of 23 confident H2 absorption system candidates that would be interesting to follow up with high-resolution spectrographs. There is a 1σ r − i colour excess and non-significant A
V
extinction excess in quasar spectra with an H2 candidate compared to standard DLA-bearing quasar spectra. The equivalent widths of C ii, Si ii and Al iii (but not Fe ii) absorptions associated with H2 candidate DLAs are larger compared to standard DLAs. This is probably related to a larger spread in velocity of the absorption lines in the H2-bearing sample.
ABSTRACT
This is the second paper of a series reporting on the results from a survey conducted with the ESO VLT/X‐shooter spectrograph. We target high‐metallicity damped Lyman α absorbers (DLAs) with ...the aim of investigating the relation between galaxies detected in emission and those detected in absorption. Here, we report on the discovery of the galaxy counterpart of the zabs= 2.58 DLA on the line‐of‐sight to the z= 3.07 quasar SDSS J 091826.16+163609.0 (hereafter Q 0918+1636). The galaxy counterpart of the DLA is detected in the O iiiλ5007 and O iiλλ3726, 3729 emission lines redshifted into the NIR at an impact parameter of 2.0 arcsec (16 kpc at z= 2.58). Lyα emission is not detected down to a 3σ detection limit of 5 × 10−18 erg s−1 cm−2, which, compared to the strength of the oxygen lines, implies that Lyα emission from this galaxy is suppressed by more than an order of magnitude. The DLA has one of the highest metallicities measured so far at comparable redshifts. We find evidence for substantial depletion of refractory elements on to dust grains. Fitting the main metal line component of the DLA, which is located at zabs= 2.5832, we measure the metal abundances from Zn ii, S ii, Si ii, Cr ii, Mn ii, Fe ii and Ni ii to be −0.12 ± 0.05, −0.26 ± 0.05, −0.46 ± 0.05, −0.88 ± 0.05, −0.92 ± 0.05, −1.03 ± 0.05 and −0.78 ± 0.05, respectively. In addition, we detect absorption in the Lyman and Werner bands of molecular hydrogen (H2), which represents the first detection of H2 molecules with X‐shooter. The background quasar Q 0918+1636 is amongst the reddest QSOs at redshifts 3.02 < z < 3.12 from the SDSS catalogue. Its UV to NIR spectrum is well fitted by a composite QSO spectrum reddened by SMC‐/LMC‐like extinction curves at zabs= 2.58 with a significant amount of extinction given by AV≈ 0.2 mag. This supports previous claims that there may be more metal‐rich DLAs missing from current samples due to dust reddening of the background QSOs. The fact that there is evidence for dust both in the central emitting regions of the galaxy (as evidenced by the lack of Lyα emission) and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust is widespread in this system.
We report on the discovery of a peculiar broad absorption line (BAL) quasar identified in our
Gaia
-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish ...because of the absence of conspicuous emission lines. Based on deep and broad BAL troughs of at least Si
IV
, C
IV
, and Al
III
, a redshift of
z
= 2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially extended emission line at 4450 Å that is most likely due to Lyman-
α
emission, which implies a systemic redshift of
z
= 2.66 if correctly identified. There is also evidence for the onset of Lyman-
α
forest absorption bluewards of 4450 Å and evidence for H
α
emission in the
K
band consistent with a systemic redshift of
z
= 2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BALs must originate from material moving with very large velocities ranging from 22 000 km s
−1
to 40 000 km s
−1
. To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-
α
emission for a BAL quasar. This method could also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information.
Abstract
We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased ...sample of powerful radio-bright (>200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median
z
= 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δ
i
= 0.6 mag) and redder (Δ(
g
−
i
) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar population detected in optical surveys. About 20% of the sources are narrow-line AGN (NLAGN)–65% of these, at
z
< 0.5 are galaxies without strong nuclear emission, and 10% at
z
> 1.9, have emission line ratios similar to radio galaxies. The farthest NLAGN in our sample is M1513-2524 (
z
em
= 3.132), and the largest radio source (size ∼330 kpc) is M0909-3133 (
z
em
= 0.884). We discuss in detail 110 AGN at 1.9 <
z
< 3.5. Despite representing the radio loudest quasars (median
R
= 3685), their Eddington ratios are similar to the Sloan Digital Sky Survey quasars having lower
R
. We detect four C
iv
broad-absorption line (BAL) QSOs, all among AGN with least
R
, and highest black hole masses and Eddington ratios. The BAL detection rate (
4
−
2
+
3
%) is consistent with that seen in extremely powerful (
L
1.4GHz
> 10
25
W Hz
−1
) quasars. Using optical light curves, radio polarization, and
γ
-ray detections, we identify seven high-probability BL Lacertae objects. We also summarize the full MALS footprint to search for H
i
21 cm and OH 18 cm lines at
z
< 2.
We present a study of cold gas absorption from a damped Lyman-α absorber (DLA) at redshift zabs = 1.946 toward two lensed images of the quasar J144254.78+405535.5 at redshift zQSO = 2.590. The ...physical separation of the two lines of sight at the absorber redshift is dabs = 0.7 kpc according to our lens model. We observe absorption lines from neutral carbon and H2 along both lines of sight, indicating that cold gas is present on scales larger than dabs. We measure the column densities of H I to be log N(HI) = 20.27 ± 0.02 and 20.34 ± 0.05 and those of H2 to be log N(H2) = 19.7 ± 0.1 and 19.9 ± 0.2. The metallicity inferred from sulphur is consistent with solar metallicity for both sightlines: S/HA = 0.0 ± 0.1 and S/HB = −0.1 ± 0.1. Based on the excitation of low rotational levels of H2, we constrain the temperature of the cold gas phase to be T = 109 ± 20 and T = 89 ± 25 K for the two lines of sight. From the relative excitation of fine-structure levels of C I, we constrain the hydrogen volumetric densities to lie in the range of 40 − 110 cm−3. Based on the ratio of observed column density and volumetric density, we infer the average individual “cloud” size along the line of sight to be l ≈ 0.1 pc. Using the transverse line-of-sight separation of 0.7 kpc together with the individual cloud size, we are able to place an upper limit to the volume filling factor of cold gas of fvol < 0.1%. Nonetheless, the projected covering fraction of cold gas must be large (close to unity) over scales of a few kpc in order to explain the presence of cold gas in both lines of sight. Compared to the typical extent of DLAs (∼10 − 30 kpc), this is consistent with the relative incidence rate of C I absorbers and DLAs.
The linear increase of the cosmic microwave background (CMB) temperature with cosmological redshift,
, is a prediction of the standard cosmological
CDM model. There are currently two methods to ...measure this dependence at redshift
and, what is equally important, to estimate of the CMB temperature
at the present epoch. The first method is based on the Sunyaev–Zeldovich effect for a galaxy cluster. However, this method is limited to redshifts
and only the deviations from the standard relation can be measured with it. The second method is based on the analysis of the populations of atomic and molecular energy levels observed in the absorption spectra of quasars. This method allows
to be measured directly. We present new estimates of
in the redshift range
based on the analysis of the excitation of CO rotational levels and C I fine-structure levels in 15 absorption systems. We take into account the collisional excitation of CO and C I with hydrogen atoms and
and the radiative pumping of C I by the interstellar ultraviolet radiation. Applying this corrections leads to a systematic decrease in the previously obtained estimates of
(for some systems the magnitude of the effect is
). Combining our measurements with the measurements of
in galaxy clusters we have obtained a constraint on the parameter
, which characterizes the deviation of the CMB temperature from the standard relation,
, and an independent estimate of the CMB temperature at the present epoch,
K, which agrees well with the estimate from orbital measurements,
K.
We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 (
$z_{\rm C\, {\small {IV}}}$
∼ 3.1875), whose broad-line region (BLR) is partly eclipsed by a strong damped ...Lyman α (DLA; logN(H i) = 21.7) cloud. This allows us to study the narrow-line region (NLR) of the quasar and the Lyman α emission from the host galaxy. Using cloudy models that explain the presence of strong N v and P v absorption together with the detection of Si ii* and O i** absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 < n
H < 710 cm−3 and 580 > r
0 > 230 pc, respectively. Sizes of the neutral (∼2–9pc) and highly ionized phases (∼3–80pc) are consistent with the partial coverage of the C iv BLR by the C iv absorption from the DLA (covering factor of ∼0.85). We show that the residuals are consistent with emission from the NLR with C iv/Lyman α ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman α emission up to 25 kpc to the north and west directions and 15 kpc to the south and east. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10 kpc with emission in a wind of projected velocity ∼500 km s−1 which is seen up to 25 kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being infalling towards the active galactic nucleus and possibly being located where accretion from cold streams ends up.
We present high-resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope and 21-cm absorption spectra obtained with the Giant Metrewave ...Radio Telescope and the Green Bank Telescope of five quasars along the line of sight of which 21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsecond-scale radio images of these quasars obtained with the Very Large Baseline Array. We use the data on four of these systems to constrain the time variation of x identical with gp alpha 2/ mu , where gp is the proton gyromagnetic factor, alpha is the fine structure constant and mu is the proton-to-electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross-correlation analysis and repeated Voigt profile fitting. In both cases, we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Delta x/x to be, respectively, -(0.1 plus or minus 1.3) 10-6 and (0.0 plus or minus 1.5) 10-6 at the mean redshift of = 1.36 corresponding to a look-back time of similar to 9 Gyr. This is the most stringent constraint ever obtained on Delta x/x. If we only use the two systems towards quasars unresolved at milliarcsecond scales, we get the simple mean of Delta x/x = +(0.2 plus or minus 1.6) 10-6. Assuming the constancy of other constants, we get Delta alpha / alpha = (0.0 plus or minus 0.8) 10-6, which is a factor of 2 better than the best constraints obtained so far using the many-multiplet method. On the other hand, assuming that alpha and gp have not varied we derive Delta mu / mu = (0.0 plus or minus 1.5) 10-6 which is again the best limit ever obtained on the variation of mu over this redshift range. Using independent constraints on Delta alpha / alpha at z < 1.8 and Delta mu / mu at z similar to 0.7 available in the literature, we get Delta gp/gp less than or equal to 3.5 10-6(1 sigma ).
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