Browsing by Author "Gupta, Neeraj"

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Detecting cold gas at intermediate redshifts: GMRT survey using MgII systems
(2006-11-28) Gupta, Neeraj; Srianand, R.; Petitjean, Patrick; et al.
Intervening H i 21-cm absorption systems at z ≥ 1.0 are very rare and only 4 conﬁrmed detections have been reported in the literature. Despite their scarcity, they provide interesting and unique insights into the physical conditions in the interstellar medium of high-z galaxies. Moreover, they can provide independent constraints on the variation of fundamental constants. We report 3 new detections based on our ongoing Giant Metrewave Radio Telescope (GMRT) survey for 21-cm absorbers at 1.10 ≤ zabs ≤ 1.45 from candidate damped Lyman-α systems. The 21-cm lines are narrow for the zabs= 1.3710 system towards SDSS J0108−0037 and zabs= 1.1726 system toward SDSS J2358−1020. Based on line full-width at half maximum, the kinetic temperatures are ≤ 5200 K and ≤ 800 K, respectively. The 21-cm absorption proﬁle of the third system, zabs=1.1908 system towards SDSS J0804+3012, is shallow, broad and complex, extending up to 100 km s−ᶥ . The centroids of the 21-cm lines are found to be shifted with respect to the corresponding centroids of the metal lines derived from SDSS spectra. This may mean that the 21-cm absorption is not associated with the strongest metal line component.
Detection of 21-cm, H2 and Deuterium absorption at z>3 along the line-of-sight to J1337+3152
(2010-02-24) Srianand, R.; Gupta, Neeraj; Petitjean, Patrick; et al.
We report the detection of 21-cm and molecular hydrogen absorption lines in the same damped Lyman-α system (with log N(H i)=21.36±0.10) at zabs=3.17447 towards SDSS J133724.69+315254.55 (zem ∼3.174). We estimate the spin temperature of the gas to be, TS = 600+222−159 K, intermediate between the expected values for cold and warm neutral media. This suggests that the H i absorption originates from a mixture of diﬀerent phases. The total molecular fraction is low, fH2=10−7, and H2 rotational level populations are not in equilibrium. The average abundance of the α- elements is, [S/H]=−1.45 ± 0.22. Nitrogen and iron are found underabundant with respect to α-elements by ∼1.0 dex and ∼0.5 dex respectively. Using photoionization models we conclude that the gas, of mean density, nH ∼2 cm−3, is located more than 270 kpc away from the QSO. While the position of 21-cm absorption line coincides with the H2 velocity proﬁle, its centroid is shifted by ∼2.7±1.0 km s−1 with respect to the redshift measured from the H2 lines. However, the position of the strongest metal absorption component matches the position of the 21-cm absorption line within 0.5 km s−1. From this, we constrain the variation of the combination of fundamental constants x = α2Gp/µ, ∆x/x = −(1.7±1.7)×10−6. This system is unique as we can at the same time have an independent constrain on µ using H2 lines. However, as the H2 column density is low, only Werner band absorption lines are seen and, unfortunately, the range of sensitivity coeﬃcients is too narrow to provide a stringent constraint: ∆µ/µ ≤ 4.0 × 10−4. The Ultraviolet and Visual Echelle Spectrograph (UVES) spectrum reveals another DLA at zabs= 3.16768 with log N(H i) = 20.41±0.15 and low metallicity, [Si/H] = −2.68 ± 0.11, in which [O/C] ∼ 0.18 ± 0.18 and [O/Si] ∼ 0. This shows that even in the very early stages of chemical evolution, the carbon or silicon to oxygen ratios can be close to solar. Using Voigt proﬁle ﬁtting we derive log(N(D i)/N(H i)) = −(4.93 ± 0.15) in this system. This is a factor of two smaller than the value expected from the best ﬁtted value of Ωb from theWilkinson Microwave Anisotropy Probe (WMAP) 5 year data. This conﬁrms the presence of astration of deuterium even at very low metallicity.
Multiwavelength investigation of a near-solar metallicity sub-DLA at Zabs=1.3647 towards PKS 0237-233
(2006-11-10) Srianand, R.; Gupta, Neeraj; Petitjean, Patrick
Outflowing material in the CSS quasar 3C48: evidence of jet-cloud interaction?
(2005-05-01) Gupta, Neeraj; Srianand, R.; Saikia, D. J.
We report the detection of a zabs=0.3654 associated absorption-line system in the UV spectrum of the CSS quasar 3C48. The absorbing material is blue shifted with respect to the quasar emission-line redshift, zem =0.3700, suggesting an outﬂow velocity of ∼1000 km s−1. We detect absorption lines over a range of ionization states from Lyβ, Lyγ, C iv, N iv, S vi to O vi and possibly O iv and Ne viii. The kinematical properties of the absorption-line system are similar to the blue-shifted emission line gas seen in [Oiii] λ5007 (Chatzichristou, Vanderriest & Jaﬀe 1999), which is believed to have interacted with the radio jet. We study the properties of the absorbing material using CLOUDY and ﬁnd that photoionization models with Solar abundance ratios (with overall metallicity in the range 0.16Z/Z⊙61.3) are enough to explain the observed column densities of all the species except Ne viii , detection of which requires conﬁrmation. Since the cooling and recombination time for the gas is ∼105 yr, the consistency with the photoionization models suggests that any possible interaction of absorbing material with the jet must have taken place before ∼105 yr. The abundance ratio of nitrogen to carbon is close to Solar values, unlike in the case of most quasars, especially at high-redshifts, which have super-Solar values.We observed 3C48 with the Giant Metrewave Radio Telescope (GMRT) to search for redshifted 21cm H i absorption. However, we did not detect any signiﬁcant feature in our spectra and estimate the 3σ upper limit to the optical depth to be in the range 0.001 to 0.003. However, due to the diﬀuse nature of the radio source, optical depths as high as 0.1 towards individual knots or compact components cannot be ruled out.
Outflowing material in the Zem=4.92 BAL QSO SDSS J160501.21 - 011220.0
(2011-07-05) Gupta, Neeraj; Srianand, R.; Petitjean, Patrick; et al.
We present the analysis of broad absorption lines (BALs) seen in the spectrum of the zem ≃4.92 QSO SDSS J160501.21-011220.0. Our high spectral resolution UVES spectrum shows two well detached absorption line systems at zabs= 4.685 and 4.855. The system at zabs= 4.855 covers the background source completely suggesting that the gas is located outside the broad emission line region. On the contrary the system at zabs= 4.685, which covers only on the continuum source, has a covering factor of the order of 0.9. Physical conditions are investigated in the BAL system at zabs= 4.855 using detailed photoionization models. The observed H i absorption line together with the limits on C ii and Si ii absorptions suggest that 16 < log N(H i) (cm−2 ) < 17 in this system. Comparison with models show that the observed column densities of N v , Si iv and C iv in this system require that nitrogen is underabundant by more than a factor 3 compared to silicon if the ionizing radiation is similar to a typical QSO spectrum. This is contrary to what is usually derived for the emission line gas in QSOs. We show that the relative suppression in the N v column density can be explained for Solar abundance ratios or abundance ratios typical of Starburst abundances if an ionizing spectrum devoid of X-rays is used instead. Thus, if the composition of BAL is like that of the emission line regions it is most likely that the cloud sees a spectrum devoid of X-rays similar to what we observe from this QSO. This is consistent with the fact that none of our models have high Compton optical depth to remove X-rays from the QSO. Similar arguments lead to the conclusion that the system at zabs= 4.685 as well is not Compton thick. Using simple Eddington arguments we show that the mass of the central black hole is ∼ 8 × 108 M⊙. This suggests that the accretion onto a seed black hole must have started as early as z = 11.