Physical conditions in three high-<i>z</i>H<sub>2</sub>-bearing DLAs: implications for grain size

Shaw, Gargi; Rawlins, K.; Srianand, R.

doi:10.1093/mnras/stw788

Cited by 23 publications

(27 citation statements)

References 79 publications

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“…The chosen radiation field has three components: a meta-galactic radiation at appropriate redshift (Haardt & Madau 2012), a synchrotron radiation (power-law continuum) arising from GRB afterglow and a blackbody radiation from in situ star formation. Our GRB-DLA models are similar to our previous QSO-DLA models (Srianand et al 2005a;Shaw et al 2016;Rawlins et al 2018) except that here we have an additional synchrotron radiation arising from GRB afterglows. While the gas is exposed to UV radiation from everywhere it is exposed to GRB afterglow only from one side.…”

Section: Modellingsupporting

confidence: 84%

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

Shaw

Ferland

2020

Monthly Notices of the Royal Astronomical Society

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The gamma-ray burst (GRB) afterglows provide an unique opportunity to study the interstellar medium (ISM) of star-forming galaxies at high-redshift. The GRB-DLAs (damped Lyman-α absorbers) contain a large neutral hydrogen column density, N(H I), and are observed against the GRB afterglow. A large fraction of GRB-DLAs show presence of molecular hydrogen (H 2 ) which is an indicator of star-formation. Hence it is important to study those GRB-DLAs which have H 2 lines to decipher and understand their physical conditions. The GRB-DLAs 121024A and 120815A, situated at redshift 2.30 and 2.36 respectively, are two such important H 2 -bearing GRB-DLAs. Besides H 2 , these two GRB-DLAs also show many metal lines. In this work we have carried out a detail numerical study on the H 2 lines, as well as on those metal lines, in GRB-DLAs 121024A and 120815A self-consistently. We use the spectral synthesis code CLOUDY for this study. This modeling helps us to determine the underlying physical conditions which give rise such lines and hence to understand these two GRB-DLAs in much more detail than any other previous investigation. We find that the hydrogen densities for these two H 2 -bearing DLAs are ≥ 60 cm −3 . Moreover our study infers that the linear sizes are ≤ 17.7 pc for these two GRB-DLAs, and the mean gas temperatures averaged over the cloud thickness, are ≤ 140 K. Overall, we find that these two H 2 -bearing GRB-DLAs are denser, cooler and smaller compared to those without H 2 .

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Section: Modellingsupporting

confidence: 84%

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

Shaw

Ferland

2020

Monthly Notices of the Royal Astronomical Society

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“…The dust-to-gas ratio in this system could be higher than that observed in the SMC, i.e. κ could be greater than unity, as is possible in high-z absorbers due to different grain chemistry or size (see Shaw et al 2016;Noterdaeme et al 2017;Dutta et al 2017b;Rawlins et al 2018). This is similar to what is inferred from the lack of H i 21-cm absorption towards the red quasar J0956+4046 (see Section 2.1.1 and Gupta et al 2012).…”

Section: H I 21-cm Absorption Towards J1521+5508supporting

confidence: 75%

uGMRT search for cold gas at z ∼ 1–1.4 towards red quasars

Dutta

Raghunathan

Gupta

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present results from our search for H i 21-cm and OH 18-cm absorption at z ∼ 1 − 1.4 towards red quasars showing strong Mg ii absorption using uGMRT. The quasars J1501+1822 and J1521+5508 show multiple strong associated Mg ii absorption at z ∼ 1.1 and signature of reddening in their optical spectra. We report the detection of H i 21-cm absorption towards J1521+5508 at the systemic redshift of the quasar, with N (H i) = (1.2 ± 0.2) × 10 20 cm −2 for spin temperature of 100 K and unit covering factor. The H i 21-cm absorption is offset from the blueshifted strong Mg ii absorbers by 1500 km s −1 . We do not detect H i 21-cm absorption at the redshift of the associated Mg ii absorption and at the systemic redshift towards J1501+1822. We argue that lack of one-to-one correspondence between Mg ii and H i 21-cm absorption could be related with clumpiness of the neutral gas and the radio and optical sightlines probing different volume of the gas. We find that the presence of strong associated Mg ii absorption and reddening in the optical spectra of the quasars lead to an increased detection rate of associated H i 21-cm absorption at z 1. We also report non-detection of intervening OH absorption ([OH]/[H i] (1-4)×10 −8 ) at z = 1.3 towards two red quasars, J0850+5159 and J0852+3435, which show strong metal and H i 21-cm absorption and the 2175Å dust extinction bump.

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“…In other words, a higher total surface of grains favours CO production without going too deep into the cloud. Shaw et al (2016) also highlight the need of increased grain surface area to reproduce the CO column density towards SDSS J1439+1117 .…”

Section: Model With Small Dust Grainsmentioning

confidence: 88%

Discovery of a Perseus-like cloud in the early Universe

Noterdaeme

Krogager

Balashev

et al. 2017

A&A

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We present the discovery of a molecular cloud at z abs ≈ 2.5255 along the line of sight to the quasar SDSS J 000015.17+004833.3. We use a high-resolution spectrum obtained with the Ultraviolet and Visual Echelle Spectrograph together with a deep multi-wavelength medium-resolution spectrum obtained with X-shooter (both on the Very Large Telescope) to perform a detailed analysis of the absorption lines from ionic, neutral atomic and molecular species in different excitation levels, as well as the broad-band dust extinction.We find that the absorber classifies as a Damped Lyman-α system (DLA) with log N(H i) (cm −2 ) = 20.8 ± 0.1. The DLA has supersolar metallicity (Z ∼ 2.5 Z , albeit to within a factor of two to three) with a depletion pattern typical of cold gas and an overall molecular fraction f = 2N(H 2 )/(2N(H 2 ) + N(H i)) ∼ 50%. This is the highest f -value observed to date in a high-z intervening system. Most of the molecular hydrogen arises from a clearly identified narrow (b ∼ 0.7 km s −1 ), cold component in which carbon monoxide molecules are also found, with log N(CO) ≈ 15. With the help of the spectral synthesis code Cloudy, we study the chemical and physical conditions in the cold gas. We find that the line of sight probes the gas deep after the H i-to-H 2 transition in a ∼4−5 pc-size cloud with volumic density n H ∼ 80 cm −3 and temperature of only 50 K. Our model suggests that the presence of small dust grains (down to about 0.001 µm) and high cosmic ray ionisation rate (ζ H ∼ a few times 10 −15 s −1 ) are needed to explain the observed atomic and molecular abundances. The presence of small grains is also in agreement with the observed steep extinction curve that also features a 2175 Å bump. Interestingly, the chemical and physical properties of this cloud are very similar to what is seen in diffuse molecular regions of the nearby Perseus complex, despite the former being observed when the Universe was only 2.5 Gyr old. The high excitation temperature of CO rotational levels towards J0000+0048 betrays however the higher temperature of the cosmic microwave background. Using the derived physical conditions, we correct for a small contribution (0.3 K) of collisional excitation and obtain T CMB (z = 2.53) ≈ 9.6 K, in perfect agreement with the predicted adiabatic cooling of the Universe.

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Physical conditions in three high-zH₂-bearing DLAs: implications for grain size

Cited by 23 publications

References 79 publications

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

uGMRT search for cold gas at z ∼ 1–1.4 towards red quasars

Discovery of a Perseus-like cloud in the early Universe

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Physical conditions in three high-zH2-bearing DLAs: implications for grain size

Cited by 23 publications

References 79 publications

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

uGMRT search for cold gas at z ∼ 1–1.4 towards red quasars

Discovery of a Perseus-like cloud in the early Universe

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Product

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Physical conditions in three high-zH₂-bearing DLAs: implications for grain size