Evolution of cold gas in active galaxies Brenda Namumba University of KwaZulu-Natal bnamumba@gmail.com September 9, 2014 Brenda Namumba (UKZN) September 9, 2014 1 / 17
Overview Introduction 1 Active galactic nuclei(AGN) Neutral hydrogen(HI) Methods of probing HI gas in AGN Previous HI studies Motivation 2 Objectives 3 Sample and Observation 4 Sample selection KAT-7 Array Results and analysis 5 PKS1814-64 PKS1717-00 Conclusion and future work 6 Brenda Namumba (UKZN) September 9, 2014 2 / 17
AGNs Compact centre of galaxy higher luminosity AGN act as most extreme laboratories of Universe Probe our physics understanding and study their unique behavior and enviroment Distance beacons.’powerful lighthouse’(excellent probe of early Universe). AGN is fueled by the supply of gas onto the supermassive black hole(Mergers and interaction) Figure : Inner structure of AGN; picture from galaxy zoo.org/ Brenda Namumba (UKZN) September 9, 2014 3 / 17
Neutral gas(HI) Most abundant element in Universe Simple physics and potential detectability over a wide range of redshift HI transition produces 21 cm line in emission and absorption at radio wavelength(1420.405752 MHz) Indicator of galaxy interaction Tracer of galaxy dynamics Figure : HI hyperfine transition: picture from Hyperphysics.phy-astr.gsu.edu Brenda Namumba (UKZN) September 9, 2014 4 / 17
Methods of probing HI gas in AGN Radio astronomy advantage the optical depth are low at radio wavelength, allowing us to bypass intervening dust and gas directly to the nuclei of distant galaxies. An important way of probing atomic components of the gas in AGN is via 21 cm HI absorption line. 21 cm HI absorption is distant independent and only depends on the brightness of the background source(advantage to probe HI at wide range of redshift) The spectra exhibit a variety of line profiles, showing complex gas motions. Brenda Namumba (UKZN) September 9, 2014 5 / 17
Previous work done Absorption line often exhibit line profiles with both narrow components and broad wings from shallow components.(miracle 1989) Evidence that in some cases broad, shallow components might be associated with circumnuclear torus (Morganti et al 2011) Detection of broad absorption line components. These have been associated with high velocity gas outflows, providing a probe of feedback between the central radio source (Morganti et al 2005b) Van Gorkom et al reported that the HI absorption feature tend to be redshifted from the systematic velocity, suggesting infall of gas. Brenda Namumba (UKZN) September 9, 2014 6 / 17
Motivation Although many HI absorption have been detected, only a few have been studied at high resolution and potential to make new detection due to high sensitivity of future telescopes Expand our knowledge of gas content in these AGNs with SKA path finders e.g MeerKAT(KAT-7), ASKAP etc and provide real data for testing line algothrithms Excellent commissioning science because most source are already known(only need to find the line) Brenda Namumba (UKZN) September 9, 2014 7 / 17
Objectives Carry out Science of HI absorption studies on already known sources using the KAT-7 Array From the results, test the system performance and stability of KAT-7 Compare the results with known literature Brenda Namumba (UKZN) September 9, 2014 8 / 17
Sample selection and observation strategy 4 radio compact sources selected from the Parkes Survey(known absorption line) Redshift range 0.0114-0.1522 Observations were done with KAT-7 during Oct 2013-May 2014 bandwidth for each observation 25 MHz Integration time for correlator 10sec Spectral channels 4096 Central frequencies ranges from 1238.8 MHz to 1404.4 MHz( ν = 1+ z ) ν 0 =1420.405752 MHz ν 0 Brenda Namumba (UKZN) September 9, 2014 9 / 17
KAT-7 Array 7 dish Array situated in the Northern part of South Africa Engineering prototype of the 64 dish MeerKAT First world radio telescope consisting of composite antenna structure and fibre glass Maximum baseline 185m Frequency range 1200 to 1950 MHz Figure : KAT-7 Array:http://namibsands.wordpress.com Brenda Namumba (UKZN) September 9, 2014 10 / 17
Results and Analysis Data calibration done using NRAO Common Astronomical Software Application(CASA) Calibration process Flagging Flux calibrator flux (setjy) Bandpass calibration(Correct for the frequency gain using bandpass calibrator) Gain calibration(Correct for the antenna gain fluctuation) Fluxscale(Correct for the phase calibrator flux using the flux calibrator) Apply calibration to target image and spectral analysis Brenda Namumba (UKZN) September 9, 2014 11 / 17
Results:PKS1814-64 Observed 19-Oct 2013 RA 18:19:34 DEC -63:45:48 Total observing hours on target ≈ 40 min Bandpass/Flux calibrator PKS1934-638 (a) spectral line profile (b) Calculated parameters of PKS1814-63 PKS1814-63 Brenda Namumba (UKZN) September 9, 2014 12 / 17
PKS1814-63: Values from line Systematic velocity is obtained at ≈ 19018 km/s The peak optical depth τ = -ln(1 - ∆S/S c ) = 0.21 Figure : PKS1814-63 Spectral profile Brenda Namumba (UKZN) September 9, 2014 13 / 17
Results:PKS1717-00 Observed from 13May 2014-21 May 2014 RA 17:20:28.1 DEC 00:58.47.0 Total time on target approx 17 hours Phase calibrator PKS1730.130 Flux/Bandpass calibrator PKS1934-638 (a) spectral line profile PKS1717-00 (b) Calculated parameters of PKS1717-00 Brenda Namumba (UKZN) September 9, 2014 14 / 17
Results:PKS1717-00 Spectral line in PKS1717-00 undetected. Fringes are observed in the data The cause of fringes is attributed to the result of solar interference and interference from stationary objects such as ground radiation etc Figure : Example of a scan being affected by fringes for PKS1717-00 Brenda Namumba (UKZN) September 9, 2014 15 / 17
Conclusion and Future Work Work is still in progress(for obtained absorption lines need to obtain optical depth, column density, etc and compare with literature) For data with undetected absorption line, we need to figure out why and tell us about the sensitivity of KAT-7 For PKS1549-79, badly affected by satellite, example below (a) (b) Figure : PKS1549-79 affected by satellite. Our final results will serve as precursor results to future absorption line studies to be carried out by KAT-7 and MeerKAT. Brenda Namumba (UKZN) September 9, 2014 16 / 17
Thanks to my supervisor Dr Caroline Zunckel and Dr Neeraj Gupta To the YERAC organizing committee for invitation and sponsorship Thank you all for listening Brenda Namumba (UKZN) September 9, 2014 17 / 17
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