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Register a new userDiscovery of 21cm absorption in a $z_{rm abs} =2.289$ DLA towards TXS 0311+430: The first low spin temperature absorber at z > 1
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Brian A. York
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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.
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We report results from a deep search for redshifted HI 21cm absorption from eight damped Lyman-$alpha$ absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. HI 21cm absorption was detected from the $z = 2.192$ DLA towards TXS2039+187, only the sixth case of such a detection at $z > 2$, while upper limits on the HI 21cm optical depth were obtained in six other DLAs at $z > 2$. Our detection of HI 21cm absorption in the eighth system, at $z = 2.289$ towards TXS0311+430, has been reported earlier. We also present high spatial resolution images of the background quasars at frequencies close to the redshifted HI 21cm line frequency, allowing us to estimate the covering factor of each DLA, and then determine its spin temperature $T_s$. For three non-detections of HI 21cm absorption, we obtain strong lower limits on the spin temperature, $T_s gtrsim 790$ K, similar to the bulk of the high-$z$ DLA population; three other DLAs yield weak lower limits, $T_s > 140-400$ K. However, for the two DLAs with detections of HI 21cm absorption, the derived spin temperatures are both low $T_s = (160 pm 35) times (f/0.35)$ K for the $z = 2.192$ DLA towards TXS2039+187 and $T_s = (72 pm 18) times (f/0.52)$ K for the $z = 2.289$ DLA towards TXS0311+430. These are the first two DLAs at $z > 1$ with $T_s$ values comparable to those obtained in local spiral galaxies. Based on the observed correlations between spin temperature and metallicity and velocity spread and metallicity in DLAs, we suggest that the hosts of the two absorbers are likely to be massive, high-metallicity galaxies.
Absorption lines in front of distant quasars are quite rare in the millimeter domain. They can however bring a very useful and complementary information to emission lines. We report here the detection with NOEMA of CO(1-0) and CN(1-0) lines in absorption, and confirmation of CO emission in the quasar/galaxy pair Q0248+430/G0248+430. The system G0248+430 corresponds to two merging galaxies (a Seyfert and a LINER) at z=0.0519 with a tidal tail just on the line of sight to the background quasar Q0248+430 at z = 1.313. Optical (CaII, NaI), HI-21cm and OH-1667 MHz absorption lines associated with the tidal tail of the foreground system have previously been detected toward the quasar, while four CO lines at different rotation J levels have been detected in emission from the foreground galaxies. New HI 21-cm line observations with the upgraded GMRT array are presented. We discuss the molecular content of the merging galaxies, and the physical conditions in the absorbing interstellar medium of the tidal tail.
Models of chemical enrichment and inhomogeneity in high-redshift galaxies are challenging to constrain observationally. In this work, we discuss a novel approach to probe chemical inhomogeneities within long Gamma-Ray Burst (GRB) host galaxies, by comparing the absorption metallicity, Z_abs, from the GRB afterglow (which probes the environment along the line of sight) with the emission-line metallicity, Z_emiss, measured via slit spectroscopy. Using the IllustrisTNG simulation, the theoretical relationship between these metallicity metrics is explored for a range of GRB formation models, varying the GRB progenitor metallicity threshold. For galaxies with fixed Z_emiss, the median value of Z_abs depends strongly on the GRB progenitor threshold metallicity, with Z_abs significantly lower than Z_emiss for high metallicity hosts. Conversely, at fixed Z_abs, the median value of Z_emiss depends primarily on the metallicity distribution of galaxies in IllustrisTNG and their chemical inhomogeneities, offering a GRB-model-independent way to constrain these processes observationally. Currently, only one host galaxy has data for both absorption and emission metallicities (GRB121014A). We re-analyse the emission spectrum and compare the inferred metallicity Z_emiss to a recent Bayesian determination of Z_abs, finding $log(Z_{rm emiss}/Z_{odot}) = log(Z_{rm abs}/Z_{odot}) +0.35^{+ 0.14}_{- 0.25}$, within ~2 standard deviations of predictions from the IllustrisTNG simulation. Future observations with the James Webb Space Telescope will be able to measure Z_emiss for 4 other GRB hosts with known Z_abs values, using ~2 hour observations. While small, the sample will provide preliminary constraints on the Z_abs-Z_emiss relation to test chemical enrichment schemes in cosmological simulations.
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.
We report the GMRT detection of HI 21cm absorption from the $z sim 3.39$ damped Lyman-$alpha$ absorber (DLA) towards PKS 0201+113, the highest redshift at which 21cm absorption has been detected in a DLA. The absorption is spread over $sim 115$ km s$^{-1}$ and has two components, at $z = 3.387144 (17)$ and $z = 3.386141 (45)$. The stronger component has a redshift and velocity width in agreement with the tentative detection of Briggs et al. (1997), but a significantly lower optical depth. The core size and DLA covering factor are estimated to be $lesssim 100$ pc and $f sim 0.69$, respectively, from a VLBA 328 MHz image. If one makes the conventional assumption that the HI column densities towards the optical and radio cores are the same, this optical depth corresponds to a spin temperature of $ts sim [(955 pm 160) times (f/0.69)] $ K. However, this assumption may not be correct, given that no metal-line absorption is seen at the redshift of the stronger 21cm component, indicating that this component does not arise along the line of sight to the optical QSO, and that there is structure in the 21cm absorbing gas on scales smaller than the size of the radio core. We model the 21cm absorbing gas as having a two-phase structure with cold dense gas randomly distributed within a diffuse envelope of warm gas. For such a model, our radio data indicate that, even if the optical QSO lies along a line-of-sight with a fortuitously high ($sim 50$%) cold gas fraction, the average cold gas fraction is low, ($lesssim 17%$), when averaged over the the spatial extent of the radio core. Finally, the large mismatch between peak 21cm and optical redshifts and the complexity of both profiles makes it unlikely that the $z sim 3.39$ DLA will be useful in tests of fundamental constant evolution.
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