A ghostly damped Ly α system revealed by metal absorption lines

Fathivavsari, H.; Petitjean, P.; Zou, Siwei; Noterdaeme, P.; Ledoux, C.; Krühler, T.; Srianand, R.

doi:10.1093/mnrasl/slw233

Cited by 25 publications

(32 citation statements)

References 25 publications

(27 reference statements)

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“…Therefore, the grain size distribution is important for CO at both young and old ages (both low and high metallicities). The importance of small grains on the enhancement of CO abundance has already been suggested for damped Lyman α systems (Shaw et al 2016;Fathivavsari et al 2017;Noterdaeme et al 2017).…”

Section: Co Abundancementioning

confidence: 86%

Populating H2 and CO in galaxy simulation with dust evolution

Chen

Hirashita

Hou

et al. 2017

Monthly Notices of the Royal Astronomical Society

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There are two major theoretical issues for the star formation law (the relation between the surface densities of molecular gas and star formation rate on a galaxy scale): (i) At low metallicity, it is not obvious that star-forming regions are rich in H 2 because the H 2 formation rate depends on the dust abundance; and (ii) whether or not CO really traces H 2 is uncertain, especially at low metallicity. To clarify these issues, we use a hydrodynamic simulation of an isolated disc galaxy with a spatial resolution of a few tens parsecs. The evolution of dust abundance and grain size distribution is treated consistently with the metal enrichment and the physical state of the interstellar medium. We compute the H 2 and CO abundances using a subgrid post-processing model based on the dust abundance and the dissociating radiation field calculated in the simulation. We find that when the metallicity is 0.4 Z ⊙ (t < 1 Gyr), H 2 is not a good tracer of star formation rate because H 2 -rich regions are limited to dense compact regions. At Z 0.8 Z ⊙ , a tight star formation law is established for both H 2 and CO. At old (t ∼ 10 Gyr) ages, we also find that adopting the so-called MRN grain size distribution with an appropriate dust-to-metal ratio over the entire disc gives reasonable estimates for the H 2 and CO abundances. For CO, improving the spatial resolution of the simulation is important while the H 2 abundance is not sensitive to sub-resolution structures at Z 0.4 Z ⊙ .

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Section: Co Abundancementioning

confidence: 86%

Populating H2 and CO in galaxy simulation with dust evolution

Chen

Hirashita

Hou

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…When the redshift of the system is high enough, the absorptions from the other Lyman series lines are seen in the quasar spectrum (Fathivavsari et al 2016) and the neutral column density can be derived directly from these absorptions. We have therefore fixed the column density to the correct value and reproduce the exercise.…”

Section: Spherical Modelmentioning

confidence: 99%

“…In addition, the correlation between the distance to the centre and the radius of the cloud is tight which means that the cloud cannot be much larger than its distance to the centre. This is a very interesting constraint as, one could estimate independently the radius of the cloud by deriving the particle density in case C absorption lines are detected (Fathivavsari et al 2016).…”

Section: Size and Position Of The Absorbing Cloudmentioning

confidence: 99%

“…In extreme cases where the hydrogen density is very high (i.e. HI > 1000 cm −3 ) and the cloud size is smaller than the size of the quasar BLR, the leaked broad Lyman-emission from the BLR can fill the DLA trough completely and the DLA absorption profile is therefore not seen in the spectrum (Fathivavsari et al 2016). This is why these DLAs are called ghostly-DLAs.…”

Section: Introductionmentioning

confidence: 99%

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Towards modelling ghostly damped Ly αs

Laloux

Petitjean

2021

Monthly Notices of the Royal Astronomical Society

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We use simple models of the spatial structure of the quasar broad line region (BLR) to investigate the properties of so-called ghostly damped Lyman-α (DLA) systems detected in SDSS data. These absorbers are characterized by the presence of strong metal lines but no H i Lyman-α trough is seen in the quasar spectrum indicating that, although the region emitting the quasar continuum is covered by an absorbing cloud, the BLR is only partially covered. One of the models has a spherical geometry, another one is the combination of two wind flows whereas the third model is a Keplerian disk. The models can reproduce the typical shape of the quasar Lyman-α emission and different ghostly configurations. We show that the DLA H i column density can be recovered precisely independently of the BLR model used. The size of the absorbing cloud and its distance to the centre of the AGN are correlated. However it may be possible to disentangle the two using an independent estimate of the radius from the determination of the particle density. Comparison of the model outputs with SDSS data shows that the wind and disk models are more versatile than the spherical one and can be more easily adapted to the observations. For all the systems we derive log N(H i)(cm−2) > 20.5. With higher quality data it may be possible to distinguish between the models.

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“…In extreme cases where the hydrogen density is very high (i.e. 𝑛 HI > 1000 cm −3 ) and the cloud size is smaller than the size of the quasar BLR, the leaked broad Lyman-𝛼 emission from the BLR can fill the DLA trough completely and the DLA absorption profile is therefore not seen in the spectrum (Fathivavsari et al 2016). This is why these DLAs are called ghostly-DLAs.…”

Section: Introductionmentioning

confidence: 99%

Towards modelling Ghostly DLAs

Laloux,

Petitjean,

Noûs

2021

Preprint

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We use simple models of the spatial structure of the quasar broad line region (BLR) to investigate the properties of so-called ghostly damped Lyman-𝛼 (DLA) systems detected in SDSS data. These absorbers are characterized by the presence of strong metal lines but no H Lyman-𝛼 trough is seen in the quasar spectrum indicating that, although the region emitting the quasar continuum is covered by an absorbing cloud, the BLR is only partially covered. One of the models has a spherical geometry, another one is the combination of two wind flows whereas the third model is a Keplerian disk. The models can reproduce the typical shape of the quasar Lyman-𝛼 emission and different ghostly configurations. We show that the DLA H column density can be recovered precisely independently of the BLR model used. The size of the absorbing cloud and its distance to the centre of the AGN are correlated. However it may be possible to disentangle the two using an independent estimate of the radius from the determination of the particle density. Comparison of the model outputs with SDSS data shows that the wind and disk models are more versatile than the spherical one and can be more easily adapted to the observations. For all the systems we derive log 𝑁(H )(cm −2 ) > 20.5. With higher quality data it may be possible to distinguish between the models.

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A ghostly damped Ly α system revealed by metal absorption lines

Cited by 25 publications

References 25 publications

Populating H2 and CO in galaxy simulation with dust evolution

Populating H2 and CO in galaxy simulation with dust evolution

Towards modelling ghostly damped Ly αs

Towards modelling Ghostly DLAs

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