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Cold Molecular Gas in Gravitationally Lensed AGN HE1104−1805

Venendaal, Sebastiaan (2019) Cold Molecular Gas in Gravitationally Lensed AGN HE1104−1805. Bachelor's Thesis, Astronomy.


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In this thesis, we first present an introduction on some fundamental concepts used, followed by an in-depth description of the calibration process. We use 34.7 GHz VLA observations of the gravitationally lensed quasar HE1104-1805 to investigate its velocity structure by using CO(1-0) emission to trace its cold molecular gas. In the created zeroth moment maps, we detect two spatially resolved gravitationally lensed images, separated by $\Delta\theta_{1-0} = 3.4 \pm 0.4$ arcsec. The CO(1-0) spectra show a highly asymmetric double horn profile, with a detection of the lower frequency peak about thrice as strong as the higher frequency peak. We argue this can be caused by differential magnification or a gas in- or outflow. We create velocity fields (first moment maps) with respect to the systemic velocity at $z=2.3221$ and they all show positively dominated gradients, due to the positive velocity peak dominating over the negative velocity peak. We find that the positive and negative component of the velocity structure are marginally spatially offset. The created dispersion fields (second moment maps) all show a peak velocity dispersion in the centre of the images, indicating a more chaotic gas motion in the AGN region. Using the measured integrated flux density of the CO(1-0) emission of $\mu S_{1-0}\Delta v = 0.49 \pm 0.05$ Jy km s\n{-1}, we obtain an apparent CO luminosity of $\mu L'_\un{CO} = (1.32 \pm 0.13)\e{11}$ K km s\n{-1} pc\n{2}. To obtain the gas mass of HE1104-1805, we use a CO-H$_2$ conversion factor of $\alpha_{\un{CO}} = 0.8$ M$_\odot$ (K km s\n{-1} pc\n{2})\n{-1}, empirically derived from local ULIRGs, and a common estimated magnification factor to find $M_\un{gas} = (1.1 \pm 0.5)\e{10}$ M$_\odot$. Using an assumed spectral index, we extrapolate our measured integrated flux density of $S_\un{34.7GHz} = 100 \pm 10$ $\mu$Jy from the continuum emission at 34.7 GHz to 1.4 GHz and relate this to the rest-frame luminosity at 1.4 GHz, to derive a radio-infrared correlation factor of $q_\un{IR} = 2.05 \pm 0.27$, consistent with the population of star-forming galaxies. We position HE1104-1805 in the $L_\un{IR}-L'_\un{CO}$ plane against the K-S relation for high redshift disk galaxies and find it close to the mean position for local ULIRGs, but with an increased SFE, which indicates HE1104-1805 might be a starburst galaxy. We find the continuum emission to be more compact than the CO(1-0) emission, indicating that its emission region must be more compact than the cold molecular gas. Together with a fit of the heated dust emission, we argue the continuum emission is not dominated by heated dust emission due to star formation. Finally, we suggest additional observations at a higher angular resolution and argue a source plane reconstruction through lens modelling might support further investigations into the velocity structure and continuum origin of HE1104-1805.

Item Type: Thesis (Bachelor's Thesis)
Supervisor nameSupervisor E mail
Degree programme: Astronomy
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 12 Jul 2019
Last Modified: 24 Jul 2019 12:40

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