| 1. |
- Combes, Françoise, et al.
(författare)
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PKS 1413+135: OH and H i at z = 0.247 with MeerKAT
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 671
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Tidskriftsartikel (refereegranskat)abstract
- The BL Lac object PKS 1413+135 was observed by the Large Survey Project MeerKAT Absorption Line Survey (MALS) in the L-band, at 1139 MHz and 12931379 MHz, targeting the HI and OH lines in absorption at z=0.24671. The radio continuum might come from the nucleus of the absorbing galaxy or from a background object at redshift lower than 0.5, as suggested by the absence of gravitational images. The HI absorption line is detected at a high signal-To-noise ratio, with a narrow central component, and with a red wing, confirming previous results. The OH 1720 MHz line is clearly detected in (maser) emission, peaking at a velocity shifted by-10 to-15 km s-1 with respect to the HI peak. The 1612 MHz line is lost due to radio frequency interference. The OH 1667 MHz main line is tentatively detected in absorption, but not the 1665 MHz line. Over 30 years a high variability is observed in optical depths, due to the rapid changes of the line of sight caused by the superluminal motions of the radio knots. The HI line has varied by 20% in depth, while the OH-1720 MHz depth has varied by a factor of ∼3. The position of the central velocity and the widths also varied. The absorbing galaxy is an early-Type spiral (maybe S0) seen edge-on, with a prominent dust lane, covering the whole disk. Given the measured mass concentration and the radio continuum size at centimeter wavelengths (100 mas corresponding to 400 pc at z=0.25), the width of the absorption lines from the nuclear regions are expected up to 250 km s-1. The narrowness of the observed lines (< 15 km s-1) suggests that the absorption comes from an outer gas ring, as frequently observed in S0 galaxies. The millimetric lines are even narrower (< 1 km s-1), which corresponds to the continuum size restricted to the core. The radio core is covered by individual 1 pc molecular clouds, whose column density is a few 1022 cm-2, which is compatible with the gas screen detected in X-rays.
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| 2. |
- Combes, F., et al.
(författare)
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PKS 1830-211: OH and HI at z = 0.89 and the first MeerKAT UHF spectrum
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 648
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Tidskriftsartikel (refereegranskat)abstract
- The Large Survey Project (LSP) "MeerKAT Absorption Line Survey"(MALS) is a blind H I 21 cm and OH 18 cm absorption line survey in the L- and UHF-bands, primarily designed to better determine the occurrence of atomic and molecular gas in the circumgalactic and intergalactic medium, and its redshift evolution. Here we present the first results using the UHF band obtained towards the strongly lensed radio source PKS 1830-211, revealing the detection of absorption produced by the lensing galaxy. With merely 90 min of data acquired on-source for science verification and processed using the Automated Radio Telescope Imaging Pipeline (ARTIP), we detect in absorption the known H I 21 cm and OH 18 cm main lines at z = 0.89 at an unprecedented signal-to-noise ratio (4000 in the continuum, in each 6 km s-1 wide channel). For the first time we report the detection of OH satellite lines at z = 0.89, which until now have not been detected at z > 0.25. We decompose the OH lines into a thermal and a stimulated contribution, where the 1612 and 1720 MHz lines are conjugate. The total OH 1720 MHz emission line luminosity is 6100 L⊙. This is the most luminous known 1720 MHz maser line and is also among the most luminous of the OH main line megamasers. The absorption components of the different images of the background source sample different light paths in the lensing galaxy, and their weights in the total absorption spectrum are expected to vary in time on daily and monthly time scales. We compare our normalized spectra with those obtained more than 20 years ago, and find no variation. We interpret the absorption spectra with the help of a lens galaxy model derived from an N-body hydrodynamical simulation, with a morphology similar to its optical HST image. The resulting absorption lines depend mainly on the background continuum and the radial distribution of the gas surface density for each atomic and molecular species. We show that it is possible to reproduce the observations assuming a realistic spiral galaxy disk without invoking any central gas outflows. However, there are distinct and faint high-velocity features in the ALMA millimeter absorption spectra that most likely originate from high-velocity clouds or tidal features. These clouds may contribute to broaden the H I and OH spectra.
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| 3. |
- Emig, K.L., et al.
(författare)
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Discovery of Hydrogen Radio Recombination Lines at z = 0.89 toward PKS 1830-211
- 2023
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 944:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a z = 0.89 galaxy using 580-1670 MHz observations from the MeerKAT Absorption Line Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (z = 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144α (and H163α) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21σ (14σ) significance. The RRL emission contains two main velocity components and is coincident in velocity with H i 21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (n e ) and the volume-averaged path length (ℓ) of the ionized gas. We determine log ( n e ) = 2.0 − 0.7 + 1.0 cm−3 and log ( ℓ ) = − 0.7 − 1.1 + 1.1 pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine log ( n e ) = 3.2 − 1.0 + 0.4 cm−3 and log ( ℓ ) = − 2.7 − 0.2 + 1.8 pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of ΣSFR ∼ 0.6 M ⊙ yr−1 kpc−2 or SFR ∼ 50 M ⊙ yr−1, consistent with a star-forming main-sequence galaxy of M ⋆ ∼ 1011 M ⊙. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities.
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| 4. |
- Wagenveld, Jonah D., et al.
(författare)
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The MeerKAT Absorption Line Survey: Homogeneous continuum catalogues towards a measurement of the cosmic radio dipole
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 673
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Tidskriftsartikel (refereegranskat)abstract
- The number counts of homogeneous samples of radio sources are a tried and true method of probing the large-scale structure of the Universe, as most radio sources outside the Galactic plane are at cosmological distances. As such, they are expected to trace the cosmic radio dipole, an anisotropy analogous to the dipole seen in the cosmic microwave background (CMB). Results have shown that although the cosmic radio dipole matches the direction of the CMB dipole, it has a significantly larger amplitude. This unexplained result challenges our assumption of the Universe being isotropic, which can have large repercussions for the current cosmological paradigm. Though significant measurements have been made, sensitivity to the radio dipole is generally hampered by systematic effects that can cause large biases in the measurement. Here we assess these systematics with data from the MeerKAT Absorption Line Survey (MALS), a blind search for absorption lines with pointings centred on bright radio sources. With the sensitivity and field of view of MeerKAT, thousands of sources are observed in each pointing, allowing for the possibility of measuring the cosmic radio dipole given enough pointings. We present the analysis of ten MALS pointings, focusing on systematic effects that could lead to an inhomogeneous catalogue. We describe the calibration and creation of full band continuum images and catalogues, producing a combined catalogue containing 16 307 sources and covering 37.5 square degrees of sky down to a sensitivity of 10 μJy beam-1. We measure the completeness, purity, and flux recovery statistics for these catalogues using simulated data. We investigate different source populations in the catalogues by looking at flux densities and spectral indices and how they might influence source counts. Using the noise characteristics of the pointings, we find global measures that can be used to correct for the incompleteness of the catalogue, producing corrected number counts down to 100-200 μJy. We show that we can homogenise the catalogues and properly account for systematic effects. We determine that we can measure the dipole to 3significance with 100 MALS pointings.
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| 5. |
- De Cia, A., et al.
(författare)
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Dust-depletion sequences in damped Lyman-alpha absorbers A unified picture from low-metallicity systems to the Galaxy
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 596
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Tidskriftsartikel (refereegranskat)abstract
- We study metal depletion due to dust in the interstellar medium (ISM) to infer the properties of dust grains and characterize the metal and dust content of galaxies down to low metallicity and intermediate redshift z. We provide metal column densities and abundances of a sample of 70 damped Lyman-alpha absorbers (DLAs) towards quasars, observed at high spectral resolution with the Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). This is the largest sample of phosphorus abundances measured in DLAs so far. We use literature measurements for Galactic clouds to cover the high-metallicity end. We discover tight (scatter less than or similar to 0.2 dex) correlations between [Zn/Fe] and the observed relative abundances from dust depletion. This implies that grain growth in the ISM is an important process of dust production. These sequences are continuous in [Zn/Fe] from dust-free to dusty DLAs, and to Galactic clouds, suggesting that the availability of refractory metals in the ISM is crucial for dust production, regardless of the star formation history. We observe [S/Zn] up to similar to 0.25 dex in DLAs, which is broadly consistent with Galactic stellar abundances. Furthermore, we find a good agreement between the nucleosynthetic pattern of Galactic halo stars and our observations of the least dusty DLAs. This supports recent star formation in low-metallicity DLAs. The derived depletions of Zn, O, P, S, Si, Mg, Mn, Cr, and Fe correlate with [Zn/Fe], with steeper slopes for more refractory elements. P is mostly not affected by dust depletion. We present canonical depletion patterns to be used as reference in future studies of relative abundances and depletion. We derive the total (dust-corrected) metallicity, typically -2 8 [M/H](tot) less than or similar to 0 for DLAs, and scattered around solar metallicity for the Galactic ISM. The dust-to-metal ratio (DTM) increases with metallicity, again supporting the importance of grain growth for dust production. The dust extinction AV derived from the depletion is typically <0.2 mag in DLAs. Finally, we derive elemental abundances in dust, which is key to understanding the dust composition and its evolution. We observe similar abundances of Mg, Si, and Fe in dust; this suggests that grain species such as pyroxenes and iron oxides are more important than olivine, but this needs to be confirmed by more detailed analysis. Overall, we characterize dust depletion, nucleosynthesis, and dust-corrected metallicity in DLAs, providing a unified picture from low-metallicity systems to the Galactic ISM.
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| 6. |
- Noterdaeme, P., et al.
(författare)
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Discovery of a compact gas-rich damped Lyman-alpha galaxy at z = 2.2 : evidence of a starburst driven outflow
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 540, s. A63-
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Tidskriftsartikel (refereegranskat)abstract
- We present the detection of Ly alpha, [OIII], and H alpha emission associated with an extremely strong damped Lyman-alpha (DLA) system (N(HI) = 10(22.10) cm(-2)) at z = 2.207 towards the quasar SDSS J113520.39-001053.56. This is the largest Hi column density ever measured along a quasi-stellar object (QSO) line of sight, though typical of those often found in DLAs associated to gamma-ray bursts (GRBs). This absorption system can also be classified as an ultra-strong Mg II system with W-r(lambda 2796) similar or equal to 3.6 angstrom. 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]-H alpha emitting region has a very small impact parameter with respect to the QSO line of sight, b approximate to 0.1 '' (0.9 kpc proper distance), and is unresolved. From the H alpha line, we measure a significant star formation rate (SFR) approximate to 25 M-circle dot yr(-1) (uncorrected for dust). The shape of the Ly alpha line is double-peaked, which is the signature of a resonant scattering of Ly alpha photons, and the Ly alpha emission is spatially extended. More strikingly, the blue and red Ly alpha 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 a Ly alpha transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the high SFR together with the small size and low mass of the galaxy (M-vir similar to 10(10) M-circle dot). By placing constraints on 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 these 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 alpha 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 (spectral shape and width of the Lyman-alpha emission, spatial configuration, escape fraction as well as absorption kinematics, HI column density, and dust reddening). Finally, we propose that selecting DLAs with very high Hi column densities may be an efficient way of detecting star-forming galaxies at small impact parameters from the background QSO lines of sight.
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| 7. |
- Ranjan, A., et al.
(författare)
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Molecular gas and star formation in an absorption-selected galaxy : Hitting the bull's eye at z similar or equal to 2.46
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 618
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Tidskriftsartikel (refereegranskat)abstract
- We present the detection and detailed analysis of a diffuse molecular cloud at z(abs) = 2.4636 towards the quasar SDSS J 1513+0352 (z(em) similar or equal to 2.68) observed with the X-shooter spectrograph at the Very Large Telescope. We measured very high column densities of atomic and molecular hydrogen with log N(H-I; H-2) similar or equal to 21.8; 21.3. This is the highest H-2 column density ever measured in an intervening damped Lyman-alpha system but we did not detect CO, implying log N(CO)/N(H-2) < -7.8, which could be due to a low metallicity of the cloud. From the metal absorption lines, we derived the metallicity to be Z similar or equal to 0.15 Z(circle dot) and determined the amount of dust by measuring the induced extinction of the background quasar light, A(V) similar or equal to 0.4. We simultaneously detected Lyman-alpha emission at the same redshift with a centroid located at a most probable impact parameter of only rho similar or equal to 1.4 kpc. We argue that the line of sight is therefore likely passing through the interstellar medium (ISM), as opposed to the circumgalactic medium (CGM), of a galaxy. The relation between the surface density of gas and that of star formation seems to follow the global empirical relation derived in the nearby Universe although our constraints on the star formation rate (SFR) and the galaxy extent remain too loose to be conclusive. We study the transition from atomic to molecular hydrogen using a theoretical description based on the microphysics of molecular hydrogen. We use the derived chemical properties of the cloud and physical conditions (T-k similar or equal to 90K and n similar or equal to 250 cm(3)) derived through the excitation of H-2 rotational levels and neutral carbon fine structure transitions to constrain the fundamental parameters that govern this transition. By comparing the theoretical and observed HI column densities, we are able to bring an independent constraint on the incident ultra-violet (UV) flux, which we find to be in agreement with that estimated from the observed SFR.
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