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Measuring the [C II]-to-H I connection in high-redshift absorption-selected galaxies

Senthil Kumar, Gaurav LU (2022) ASTK02 20221
Lund Observatory - Undergoing reorganization
Abstract
HI neutral gas is the basic building block of galaxies. It dictates the star formation rate and hence the metal enrichment rates within high redshift galaxies. HI neutral gas cannot be directly observed beyond z ≈ 0.38 due to the weakness of the 21 cm transition, therefore alternate methods need to be developed for studying high redshift galaxies. The emission luminosity of [C II]-157.741 μm transition as a potential tracer for neutral HI gas mass is explored. The [C II] line emission from galaxies in the range z ≈ (1.6, 3.7) is studied using absorption-selected QSO whose sightline passes through DLAs. 83 QSO-DLA spectroscopic data was obtained from X-shooter and HIRES spectrograph and some were fitted with Voigt profile using VoigtFit.... (More)
HI neutral gas is the basic building block of galaxies. It dictates the star formation rate and hence the metal enrichment rates within high redshift galaxies. HI neutral gas cannot be directly observed beyond z ≈ 0.38 due to the weakness of the 21 cm transition, therefore alternate methods need to be developed for studying high redshift galaxies. The emission luminosity of [C II]-157.741 μm transition as a potential tracer for neutral HI gas mass is explored. The [C II] line emission from galaxies in the range z ≈ (1.6, 3.7) is studied using absorption-selected QSO whose sightline passes through DLAs. 83 QSO-DLA spectroscopic data was obtained from X-shooter and HIRES spectrograph and some were fitted with Voigt profile using VoigtFit. The results were used to find a relationship between the luminosity L[C II] and the gas mass MHI. Using the [C II]-to-H I relation, log β[C II], it is found that log β[C II] is decreasing as a function of impact parameter. Further analysis on the metallicity dependence of log β[C II] shows a decreasing trend as metallicity increases. The metallicity-log β[C II] relation was compared to Gamma Ray Burst data from Heintz et al. (2021). The linear regression of the log β[C II] as function of metallicity for QSO is shown to be decreasing linearly with a similar slope but a factor of 10 higher than GRB relation for all N(H I). It was then concluded that the usage of QSO sightlines to probe HI using [C II] emission as a tracer is not feasible. (Less)
Popular Abstract
75 % of the Universe’s baryonic content consists of hydrogen (H) and is the main
component of galaxy composition making it an important gas in galactic processes. In high-red shifted galaxies, the concentration of neutral hydrogen as a function of galactic radius is still an open research question. Detection of elements in galactic gas clouds is done by performing spectroscopy. The current method of measuring hydrogen is done using the 21 cm hyperfine transition of HI, however it can only be directly observed inside galaxies at moderate distances. Hence other efficient methods to trace HI needs to be developed. One suggested method is to use the emission of the fine structure transition of singly ionised carbon [C II]. The emission of... (More)
75 % of the Universe’s baryonic content consists of hydrogen (H) and is the main
component of galaxy composition making it an important gas in galactic processes. In high-red shifted galaxies, the concentration of neutral hydrogen as a function of galactic radius is still an open research question. Detection of elements in galactic gas clouds is done by performing spectroscopy. The current method of measuring hydrogen is done using the 21 cm hyperfine transition of HI, however it can only be directly observed inside galaxies at moderate distances. Hence other efficient methods to trace HI needs to be developed. One suggested method is to use the emission of the fine structure transition of singly ionised carbon [C II]. The emission of this line can be measured using the absorption spectrum of quasar sightlines passing through the outer edges of large elliptical Damped Lyman Alphas (DLA) galaxy counterparts.
Quasars are active galactic nuclei that emit broad-spectral profile due to morphology of the object. Quasars are brightest object in the universe and the most powerful of them can easily outshine their host galaxies some even being bright enough to be measured easily across most of the observable universe. Their emitting region being no bigger than our own solar system. The broad-spectral profile of a quasar covers gamma rays to radio waves, hence covering vast regions of the electromagnetic spectrum. This is advantageous because anything in the line of sight of a quasar will be visible through the absorption in the quasar’s emission spectrum. Hence performing spectroscopy on the quasar is advantages due to its brightness and the breadth of the emission spectrum.
Using spectroscopy, ratio of [C II]-to-H I using line profile can be derived. A conversion factor can be then identified between Hydrogen and single ionised Carbon. This would provide a direct calibration of [C II]to HI in high-redshift galaxies, opening the possibility to determine the HI gas mass with [C II] of the most distant galaxies that are otherwise too faint to be detected with 21 cm hyperfine transition observations.
This project uses imaging data from the Hubble Space Telescope and spectroscopic
data from the X-shooter spectrograph mounted on the ESO Very Large Telescope in Chile. Python libraries such as Astropy, PetroFit are used for photometric analysis to determine the galactic properties of DLA. Using a program, developed in Copenhagen University’s Niels Bohr Institute, called VoigtFit, spectral analysis of line profiles can be performed to determine the [C II]-to-H I ratio. This research is to compliment HI density developed using Gamma Ray Burst sightlines that penetrate the inner region with quasar sightlines that penetrate the outer regions of the DLAs. If the proposed theory proves correct with factual evidence, this will open new doors to understanding baryonic density in early galaxies alongside the star formation rate as a function of galactic radius. (Less)
Please use this url to cite or link to this publication:
author
Senthil Kumar, Gaurav LU
supervisor
organization
course
ASTK02 20221
year
type
M2 - Bachelor Degree
subject
keywords
QSO, Quasar, Black Hole, AGN, Active Galactic Nuclei, DLA, Damped Lyman Alpha, C II, [C II], H I, Sightline, HST, X-shooter, Spectroscopy, Echelle Spectroscope, Hyperfine transition, Hyperfine
report number
2022-EXA-199
language
English
id
9096403
date added to LUP
2022-08-11 11:51:01
date last changed
2022-08-11 11:51:23
@misc{9096403,
  abstract     = {{HI neutral gas is the basic building block of galaxies. It dictates the star formation rate and hence the metal enrichment rates within high redshift galaxies. HI neutral gas cannot be directly observed beyond z ≈ 0.38 due to the weakness of the 21 cm transition, therefore alternate methods need to be developed for studying high redshift galaxies. The emission luminosity of [C II]-157.741 μm transition as a potential tracer for neutral HI gas mass is explored. The [C II] line emission from galaxies in the range z ≈ (1.6, 3.7) is studied using absorption-selected QSO whose sightline passes through DLAs. 83 QSO-DLA spectroscopic data was obtained from X-shooter and HIRES spectrograph and some were fitted with Voigt profile using VoigtFit. The results were used to find a relationship between the luminosity L[C II] and the gas mass MHI. Using the [C II]-to-H I relation, log β[C II], it is found that log β[C II] is decreasing as a function of impact parameter. Further analysis on the metallicity dependence of log β[C II] shows a decreasing trend as metallicity increases. The metallicity-log β[C II] relation was compared to Gamma Ray Burst data from Heintz et al. (2021). The linear regression of the log β[C II] as function of metallicity for QSO is shown to be decreasing linearly with a similar slope but a factor of 10 higher than GRB relation for all N(H I). It was then concluded that the usage of QSO sightlines to probe HI using [C II] emission as a tracer is not feasible.}},
  author       = {{Senthil Kumar, Gaurav}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Measuring the [C II]-to-H I connection in high-redshift absorption-selected galaxies}},
  year         = {{2022}},
}