Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userUnderstanding the strong intervening OVI absorber at z$_{abs}$ ~0.93 towards PG1206+459
341
0
0.0
(
0
)
Added by
Benjamin Rosenwasser
Publication date
2018
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We have obtained new observations of the partial Lyman limit absorber at zabs$=0.93$ towards quasar PG~1206+459, and revisit its chemical and physical conditions. The absorber, with $ N(HI) sim 10^{17.0}$ ~sqcm and absorption lines spread over $gtrsim$1000~kms in velocity, is one of the strongest known OVI absorbers at $log N(OVI)=$15.54$pm$0.17. Our analysis makes use of the previously known low-(e.g. MgII), intermediate-(e.g. SiIV), and high-ionization (e.g., CIV, NV, NeVIII) metal lines along with new $HST/$COS observations that cover OVI, and an $HST/$ACS image of the quasar field. Consistent with previous studies, we find that the absorber has a multiphase structure. The low-ionization phase arises from gas with a density of $log (n_{rm H}/rm cm^{-3})sim-2.5$ and a solar to super-solar metallicity. The high-ionization phase stems from gas with a significantly lower density, i.e. $log (n_{rm H}/rm cm^{-3}) sim-3.8$, and a near-solar to solar metallicity. The high-ionization phase accounts for all of the absorption seen in CIV, NV, and OVI. We find the the detected NeVIII, reported by cite{Tripp2011}, is best explained as originating in a stand-alone collisionally ionized phase at $Tsim10^{5.85}~rm K$, except in one component in which both OVI and NeVIII can be produced via photoionization. We demonstrate that such strong OVI absorption can easily arise from photoionization at $zgtrsim1$, but that, due to the decreasing extragalactic UV background radiation, only collisional ionization can produce large OVI features at $zsim0$. The azimuthal angle of $sim88$degree of the disk of the nearest ($rm 68~kpc$) luminous ($1.3L_*$) galaxy at $z_{rm gal}=0.9289$, which shows signatures of recent merger, suggests that the bulk of the absorption arises from metal enriched outflows.
rate research
Read More
Previous studies have shown that the incidence rate of intervening strong MgII absorbers towards GRBs were a factor of 2 - 4 higher than towards quasars. Exploring the similar sized and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong MgII absorbers with rest-frame equivalent widths $W_r^{2796} >$ 1 {AA} towards GRBs and quasars in the redshift range 0.1 < z < 5. With large and similar sample sizes, and path length coverages of $Delta$z = 57.8 and 254.4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1 sigma uncertainty levels at all redshifts. For absorbers at z < 2.3 the incidence towards GRBs is a factor of 1.5$pm$0.4 higher than the expected number of strong MgII absorbers in SDSS quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4$pm$0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high spectral resolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS MgII catalogues and high spectral resolution studies. The rest-frame equivalent width distribution also agrees to within 1 sigma uncertainty levels between the GRB and quasar samples. Intervening strong MgII absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.
We present the results from VLT/X-shooter spectroscopic observations of 11 extremely strong intervening damped Lyman-alpha absorbers (ESDLAs) initially selected as high N(Hi) (i.e.>=5x10^21 cm-2) candidates from the Sloan Digital Sky Survey (SDSS). We confirm the high Hi column densities which we measure to be in the range log N(Hi) = 21.6-22.4. Molecular hydrogen is detected with high column densities (N(H_2)>=10^18 cm-2) in five out of eleven systems, three of which are reported here for the first time. We compare the chemical properties of this sample of ESDLAs, supplemented with literature measurements, to that of DLAs located at the redshift of long-duration gamma-ray bursts (GRB-DLAs). We confirm that the two populations are almost indistinguishable in terms of chemical enrichment, H_2 column density and gas kinematics. All this suggests that ESDLAs and GRB-DLAs probe similar galactic environments. We search for the galaxy counterparts of ESDLAs and find associated emission lines in three out of eleven systems, two of which are reported here for the first time (towards the quasars SDSS J002503.03+114547.80 and SDSS J114347.21+142021.60, respectively). The measured separations between the quasar sightlines and the emission associated with the ESDLA galaxy are all very small (rho < 3 kpc). While the small impact parameters are similar to what is observed for GRB-DLAs, the associated star-formation rates are on average lower than seen for GRB host galaxies. This is explained by long-duration GRBs being associated with the death of massive stars, hence pinpointing regions of active star formation in the GRB host galaxies. Our observations support the suggestion from the literature that ESDLAs could act as blind analogues of GRB-DLAs, probing high column density neutral gas in the heart of high-redshift galaxies, without any prior on the instantaneous star-formation rate.
We report the detection of HI 21 cm absorption from the $z=2.289$ damped Lyman-$alpha$ system (DLA) towards TXS 0311+430, with the Green Bank Telescope. The 21 cm absorption has a velocity spread (between nulls) of $sim 110$ km s$^{-1}$ and an integrated optical depth of $int tau {rm d}V = (0.818 pm 0.085)$ km s$^{-1}$. We also present new Giant Metrewave Radio Telescope 602 MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA HI column density of hi = $(2 pm 0.5) times 10^{20}$ cm, yields a spin temperature of $T_s = (138 pm 36)$ K, assuming a covering factor of unity. This is the first case of a low spin temperature ($< 350$ K) in a $z > 1$ DLA and is among the lowest ever measured in any DLA. Indeed, the $T_s$ measured for this DLA is similar to values measured in the Milky Way and local disk galaxies. We also determine a lower limit (Si/H) $gtrsim 1/3$ solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low redshift correlations, the low $T_s$, large 21 cm absorption width and high metallicity all suggest that the $z sim 2.289$ DLA is likely to arise in a massive, luminous disk galaxy.
The metallicity in portions of high-redshift galaxies has been successfully measured thanks to the gas observed in absorption in the spectra of quasars, in the Damped Lyman-alpha systems (DLAs). Surprisingly, the global mean metallicity derived from DLAs is about 1/10th solar at 0<z<4 leading to the so-called ``missing-metals problem. In this paper, we present high-resolution observations of a sub-DLA system at z_abs=0.716 with super-solar metallicity toward SDSS J1323-0021. This is the highest metallicity intervening quasar absorber currently known, and is only the second super-solar absorber known to date. We provide a detailed study of this unique object from VLT/UVES spectroscopy. We derive [Zn/H]=+0.61, [Fe/H]=-0.51, [Cr/H]=<-0.53, [Mn/H] = -0.37, and [Ti/H] = -0.61. Observations and photoionisation models using the CLOUDY software confirm that the gas in this sub-DLA is predominantly neutral and that the abundance pattern is probably significantly different from a Solar pattern. Fe/Zn and Ti/Zn vary among the main velocity components by factors of ~ 3 and ~ 35, respectively, indicating non-uniform dust depletion. Mn/Fe is super-solar in almost all components, and varies by a factor of ~ 3 among the dominant components. It would be interesting to observe more sub-DLA systems and determine whether they might contribute significantly toward the cosmic budget of metals.
We present K-band imaging of fields around 30 strong CaII absorption line systems, at 0.7<z<1.1, three of which are confirmed Damped Lyman-alpha systems. A significant excess of galaxies is found within 60 (~50kpc) from the absorber line-of-sight. The excess galaxies are preferentially luminous compared to the population of field galaxies. A model in which field galaxies possess a luminosity-dependent cross-section for CaII absorption of the form (L/L*)^0.7 reproduces the observations well. The luminosity-dependent cross-section for the CaII absorbers appears to be significantly stronger than the established (L/L*)^0.4 dependence for MgII absorbers. The associated galaxies lie at large physical distances from the CaII-absorbing gas; we find a mean impact parameter of 24kpc (H0=70kmsMpc). Combined with the observed number density of CaII absorbers the large physical separations result in an inferred filling factor of only ~10 per cent. The physical origin of the strong CaII absorption remains unclear, possible explanations vary from very extended disks of the luminous galaxies to associated dwarf galaxy neighbours, remnants of outflows from the luminous galaxies, or tidal debris from cannibalism of smaller galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
