We present details of the Automated Radio Telescope Imaging Pipeline (ARTIP) and the results of a sensitive blind search for H i and OH absorbers at z < 0.4 and z < 0.7, respectively. ARTIP is ...written in Python 3.6, extensively uses the Common Astronomy Software Application tools and tasks, and is designed to enable the geographically distributed MeerKAT Absorption Line Survey (MALS) team to collaboratively process large volumes of radio interferometric data. We apply it to the first MALS data set obtained using the 64-dish MeerKAT radio telescope and 32 K channel mode of the correlator. With merely 40 minutes on target, we present the most sensitive spectrum of PKS 1830-211 ever obtained and characterize the known H i (z = 0.19) and OH (z = 0.89) absorbers. We further demonstrate ARTIP's capabilities to handle realistic observing scenarios by applying it to a sample of 72 bright radio sources observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) to blindly search for H i and OH absorbers. We estimate the numbers of H i and OH absorbers per unit redshift to be n21(z ∼ 0.18) < 0.14 and nOH(z ∼ 0.40) < 0.12, respectively, and constrain the cold gas covering factor of galaxies at large impact parameters (50 kpc < < 150 kpc) to be less than 0.022. Due to the small redshift path, Δz ∼ 13 for H i with column density >5.4 × 1019 cm−2, the survey has probed only the outskirts of star-forming galaxies at > 30 kpc. MALS with the expected Δz ∼ 103-4 will overcome this limitation and provide stringent constraints on the cold gas fraction of galaxies in diverse environments over 0 < z < 1.5.
ABSTRACT
We present a pilot search of CO emission in three H2-absorbing, long-duration gamma-ray burst (GRB) host galaxies at z ∼ 2–3. We used the Atacama Large Millimeter/submillimeter Array (ALMA) ...to target the CO(3 − 2) emission line and report non-detections for all three hosts. These are used to place limits on the host molecular gas masses, assuming a metallicity-dependent CO-to-H2 conversion factor (αCO). We find, $M_{\rm mol} \lt 3.5\times 10^{10}\, M_{\odot }$ (GRB 080607), $M_{\rm mol} \lt 4.7\times 10^{11}\, M_{\odot }$ (GRB 120815A), and $M_{\rm mol} \lt 8.9\times 10^{11}\, M_{\odot }$ (GRB 181020A). The high limits on the molecular gas mass for the latter two cases are a consequence of their low stellar masses M⋆ ($M_\star \lesssim 10^{8}\, M_{\odot }$) and low gas-phase metallicities ($Z\sim 0.03\, Z_{\odot }$). The limit on the Mmol/M⋆ ratio derived for GRB 080607, however, is consistent with the average population of star-forming galaxies at similar redshifts and stellar masses. We discuss the broader implications for a metallicity-dependent CO-to-H2 conversion factor and demonstrate that the canonical Galactic αCO will severely underestimate the actual molecular gas mass for all galaxies at z > 1 with $M_\star \lt 10^{10}\, M_\odot$. To better quantify this we develop a simple approach to estimate the relevant αCO factor based only on the redshift and stellar mass of individual galaxies. The elevated conversion factors will make these galaxies appear CO-‘dark’ and difficult to detect in emission, as is the case for the majority of GRB hosts. GRB spectroscopy thus offers a complementary approach to identify low-metallicity, star-forming galaxies with abundant molecular gas reservoirs at high redshifts that are otherwise missed by current ALMA surveys.
We report the detections of molecular hydrogen (H2), vibrationally-excited H2 (H 2∗ 2 ∗ $ _{2}^{*} $ ), and neutral atomic carbon (C I), an efficient tracer of molecular gas, in two new afterglow ...spectra of GRBs 181020A (z = 2.938) and 190114A (z = 3.376), observed with X-shooter at the Very Large Telescope (VLT). Both host-galaxy absorption systems are characterized by strong damped Lyman-α absorbers (DLAs) and substantial amounts of molecular hydrogen with logN(H I, H2) = 22.20 ± 0.05, 20.40 ± 0.04 (GRB 181020A) and logN(H I, H2) = 22.15 ± 0.05, 19.44 ± 0.04 (GRB 190114A). The DLA metallicites, depletion levels, and dust extinctions are within the typical regimes probed by GRBs with Zn/H = −1.57 ± 0.06, Zn/Fe = 0.67 ± 0.03, and AV = 0.27 ± 0.02 mag (GRB 181020A) and Zn/H = −1.23 ± 0.07, Zn/Fe = 1.06 ± 0.08, and AV = 0.36 ± 0.02 mag (GRB 190114A). In addition, we examine the molecular gas content of all known H2-bearing GRB-DLAs and explore the physical conditions and characteristics required to simultaneously probe C I and H 2∗ 2 ∗ $ _{2}^{*} $ . We confirm that H2 is detected in all C I- and H 2∗ 2 ∗ $ _{2}^{*} $ -bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H2 absorbers. We find that a large molecular fraction of fH2 ≳ 10−3 is required for C I to be detected. The defining characteristic for H 2∗ 2 ∗ $ _{2}^{*} $ to be present is less clear, though a large H2 column density is an essential factor. We also find that the observed line profiles of the molecular-gas tracers are kinematically “cold”, with small velocity offsets of δv < 20 km s−1 from the bulk of the neutral absorbing gas. We then derive the H2 excitation temperatures of the molecular gas and find that they are relatively low with Tex ≈ 100−300 K, however, there could be evidence of warmer components populating the high-J H2 levels in GRBs 181020A and 190114A. Finally, we demonstrate that even though the X-shooter GRB afterglow campaign has been successful in recovering several H2-bearing GRB-host absorbers, this sample is still hampered by a significant dust bias excluding the most dust-obscured H2 absorbers from identification. C I and H 2∗ 2 ∗ $ _{2}^{*} $ could open a potential route to identify molecular gas even in low-metallicity or highly dust-obscured bursts, though they are only efficient tracers for the most H2-rich GRB-host absorption systems.
While molecular quasar absorption systems provide unique probes of the physical and chemical properties of the gas as well as original constraints on fundamental physics and cosmology, their ...detection remains challenging. Here we present the results from a complete survey for molecular gas in thirty-nine absorption systems selected solely upon the detection of neutral carbon lines in Sloan Digital Sky Survey (SDSS) spectra, without any prior knowledge of the atomic or molecular gas content. H2 is found in all twelve systems (including seven new detections) where the corresponding lines are covered by the instrument setups and measured to have logN(H2) ≳ 18, indicating a self-shielded regime. We also report seven CO detections (7/39) down to logN(CO) ~ 13.5, including a new one, and put stringent constraints on N(CO) for the remaining 32 systems. N(CO) and N(C I) are found to be strongly correlated with N(CO)/N(C I) ~ 1/10. This suggests that the C I-selected absorber population is probing gas deeper than the H I–H2 transition in which a substantial fraction of the total hydrogen in the cloud is in the form of H2. We conclude that targeting C I-bearing absorbers is a very efficient way to find high-metallicity molecular absorbers. However, probing the molecular content in lower-metallicity regimes as well as high-column-density neutral gas remains to be undertaken to unravel the processes of gas conversion in normal high-z galaxies.
We present the results of a systematic Giant Metrewave Radio Telescope (GMRT) survey of 21-cm absorption in a representative and unbiased sample of 35 strong Mg ii systems in the redshift range: ...zabs∼ 1.10–1.45, 33 of which have Wr≥ 1 Å. The survey using ∼400 h of telescope time has resulted in nine new 21-cm detections and stringent 21-cm optical depth upper limits (median 3σ optical depth per 10 km s−1 of 0.017) for the remaining 26 systems. This is by far the largest number of 21-cm detections from any single survey of intervening absorbers. Prior to our survey, no intervening 21-cm system was known in the above redshift range, and only one system was known in the redshift range 0.7 ≤z≤ 1.5. We discuss the relation between the detectability of 21-cm absorption and various properties of UV absorption lines. We show that if Mg ii systems are selected with the following criteria, Mg ii doublet ratio ≤1.3 and Wr(Mg i)/Wr(Mg ii) ≥ 0.3, then a detection rate of 21-cm absorption up to 90 per cent can be achieved. We estimate n21, the number per unit redshift of 21-cm absorbers with Wr(Mg ii) >Wo and integrated optical depth , and show that n21 decreases with increasing redshift. In particular, for Wo= 1.0 Å and falls by a factor of 4 from 〈z〉= 0.5 to 〈z〉= 1.3. The evolution seems to be stronger for stronger Mg ii systems. Using a subsample of systems for which high-frequency Very Long Baseline Array (VLBA) images are available, we show that the effect is not related to the structure of the background radio sources and is most probably due to the evolution of the cold neutral medium filling factor in Mg ii systems. We find no correlation between the velocity spread of the 21-cm absorption feature and Wr(Mg ii) at z∼ 1.3.
The Lyman α emission of high-z damped Lyman α systems Rahmani, H.; Srianand, R.; Noterdaeme, P. ...
Monthly notices of the Royal Astronomical Society. Letters,
November 2010, Letnik:
409, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Using a spectral stacking technique we searched for the average Lyman α (Lyα) emission from high-z damped Lyα (DLA) galaxies detected in the Sloan Digital Sky Survey quasi-stellar object (QSO) ...spectra. We used a sample of 341 DLA galaxies of mean redshift 〈z〉= 2.86 and log N(H i) ≥ 20.62 to place a 3σ upper limit of 3.0 × 10−18 erg s−1 cm−2 on the Lyα flux emitted within ∼1.5 arcsec (or 12 kpc) from the QSO line of sight. This corresponds to an average Lyα luminosity of ≤2 × 1041 erg s−1 or 0.03L★(Lyα). This limit is deeper than the limit of most surveys for faint Lyα emitters. The lack of Lyα emission in DLA galaxies is consistent with the in situ star formation, for a given N(H i), being less efficient than what is seen in local galaxies. Thus, the overall DLA population seems to originate from the low-luminosity end of the high-redshift Lyα-emitting galaxies and/or to be located far away from the star-forming regions. The latter may well be true since we detect strong O vi absorption in the stacked spectrum, indicating that DLA galaxies are associated with a highly ionized phase, possibly the relics of galactic winds and/or originating from cold accretion flows. We find the contribution of DLA galaxies to the global star formation rate density to be comparatively lower than that of Lyman break galaxies.
We present a spectroscopic analysis of seven Extremely Strong Damped Lyα systems at redshifts z = 2-3, obtained with the intermediate-resolution spectrograph X-shooter on the Very Large Telescope. ...For all systems we estimated column densities of the neutral atomic hydrogen HI, metal abundances and dust depletion. We firmly detected molecular hydrogen H2 in two systems in our sample; for the remaining systems we set a conservative upper limits on the H2 column densities. The properties of the obtained systems are in consistency with the sample of the Extremely Strong Damped Lyα systems available in the literature.
We present the elemental abundance and H2 content measurements of a damped Ly alpha (DLA) system with an extremely large Hi column density, logN(H i) (cm-2) = 22.0 + or - 0.10, at zabs = 3.287 toward ...the QSO SDSS J081634+144612. We measure column densities of Hsub 2, CI, CI*, ZnII, FeII, CrII, Ni II, and Si II from a high signal-to-noise and high spectral resolution VLT-UVES spectrum. We explore the relationship between GRB-DLAs and the high column density end of QSO-DLAs finding that the properties (metallicity and depletion) of DLAs with logN(H i) < 21.5 in the two populations do not appear to be significantly different.
We present a detailed analysis of the partial coverage of the Q1232+082 (z
em= 2.57) broad-line region (BLR) by an intervening H2-bearing cloud at z
abs= 2.3377. Using curve of growth analysis and ...line profile fitting, we demonstrate that the H2-bearing component of the cloud covers the quasi-stellar object (QSO) intrinsic continuum source completely but only part of the BLR. We find that only 48 ± 6 per cent of the C iv BLR emission is covered by the C i absorbing gas. We observe residual light (∼6 per cent) as well in the bottom of the O i λ1302 absorption from the cloud, redshifted on top of the QSO Lyman α emission line. Therefore, the extent of the neutral phase of the absorbing cloud is not large enough to cover all of the background source. The most likely explanation for this partial coverage is the small size of the intervening cloud, which is comparable to the BLR size. We estimate the number densities in the cloud:
∼ 110 cm−3 for the H2-bearing core and n
H∼ 30 cm−3 for the neutral envelope. Given the column densities, N(H2) = 3.71 ± 0.97 × 1019 cm−2 and N(H i) = 7.94 ± 1.6 × 1020 cm−2, we derive the linear size of the H2-bearing core and the neutral envelope along the line of sight to be
∼ 0.15+0.05
−0.05 pc and
∼ 8.2+6.5
−4.1 pc, respectively. We estimate the size of the C iv BLR by two ways: (i) extrapolating size-luminosity relations derived from reverberation observations and (ii) assuming that the H2-bearing core and the BLR are spherical in shape and the results are ∼0.26 and ∼0.18 pc, respectively. The large size we derive for the extent of the neutral phase of the absorbing cloud together with a covering factor of ∼0.94 of the Lyman α emission means that the Lyman α BLR is probably fully covered but that the Lyman α emission extends well beyond the limits of the BLR.
At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer of star formation and ...star-forming galaxies over the whole of cosmic history. Their bright power-law afterglows provide ideal backlights for absorption studies of the interstellar and intergalactic medium back to the reionization era. The proposed THESEUS mission is designed to detect large samples of GRBs at
z
> 6 in the 2030s, at a time when supporting observations with major next generation facilities will be possible, thus enabling a range of transformative science. THESEUS will allow us to explore the faint end of the luminosity function of galaxies and the star formation rate density to high redshifts; constrain the progress of re-ionisation beyond
z
≳
6
; study in detail early chemical enrichment from stellar explosions, including signatures of Population III stars; and potentially characterize the dark energy equation of state at the highest redshifts.
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