UR: Effects of AGN activity on neutral gas outflows

UR: Effects of AGN activity on neutral gas outflows

In the Undergraduate Research series, we present the research that you are do. If you are a student who has participated in an REU or similar astro research project and would like to share this on Astrobites, please visit our submission page for more details. We’d also like to hear about your more general research experience!


The University of Sheffield

Hello, my name is Matthew. I just finished my Masters in Astrophysics and I wanted to share my research project with interested people. This research was for my fourth year undergraduate dissertation project completed under the supervision of Clive Tadhunter at the University of Sheffield. While university has been great, there’s almost nothing you can’t learn online at an undergraduate level! So if you are interested in physics and space, keep researching and keep asking questions!

Over the past 20 years, AGN feedback has become a rapidly evolving area of ​​astrophysical research. It is currently believed that there is a fundamental connection between the growth of a supermassive black hole and the evolution of the entire host galaxy in which it resides. The most well-known theory is that when a black hole is very active, it somehow expels much of the surrounding gas that would otherwise be flung at the black hole. This research examines the extent to which the environment neutral Gas is affected by AGN activity in infrared ultraluminous galaxies (ULIRGs).

All massive galaxies host supermassive black holes (SMBH) at their centers. The rapid accretion of material onto a supermassive black hole releases so much energy that it often outshines the galaxy’s entire stellar population, illuminating the galaxy’s center as an active galactic nucleus (AGN). This stage of black hole growth results in both relativistic particle jets and radiative winds that heat, shake, and redistribute the interstellar medium within the host galaxy, quenching star formation (aka feedback). While simulations suggest that AGN feedback is inextricably linked to the evolution of the entire galaxy, the observational evidence of radiative feedback on galaxy-wide scales in the neutral gas phase is less clear.

Therefore, this research uses spectroscopic observations made with the Very Large Telescope (fantastic name!) and the William Herschel Telescope to measure the gas kinematics of neutral sodium in the most luminous and fastest evolving galaxies in the local universe, where radiative winds in The SMBH’s accretion disk is believed to have accelerated the surrounding gas to high speeds, allowing us to test how capable they are. Since the gas flows along the line of sight (ie directly towards the viewer), one cannot directly measure the radial extent of the flow, so other methods must be used.

Figure 1: The Na-ID absorption profile for F19254 is shown, with a prominent blue-shifted feature from the blue of the main absorption doublet. This indicates outflowing gas, likely driven by radiative winds.

The graph above shows the Na I feature for the case of the galaxy F19254-7245S, also known as the superantennas. The main feature of the doublet absorption is visible, as is a third “dip” to the left of the two main absorption profiles. This third sink is indicative of outflowing gas likely driven by AGN-driven winds, allowing us to measure its strength and make assumptions about its radial extent. This type of analysis was performed for 17 different galaxies in our sample.

Of the 17 ULIRGs examined in this report, 15 have clear NaI absorption profiles and kinematics have been calculated for 13 of these objects. There is strong evidence that galaxy-wide, neutral outflows are present in F19254 and possibly in galaxy F12072. In addition, small (< kpc) neutral outflows are likely present near the accretion disk in radio-loud quasar PKS1549. This is interesting because previous HI observations of the neutral phase did not reveal the presence of outflowing gas.

Nonetheless, looking at the study as a whole, it appears that AGN-driven neutral outflows are not galaxy-wide and are incapable of affecting the galaxy-wide star formation history. Instead, they are likely to have a significant impact on sub-kpc scale nuclear starbursts, with the potential to eject surrounding gas and quench star formation at the galaxy’s core.

If you are interested in this field of research, I recommend the following links for a barrier-free scientific introduction:
– The many ways to AGN feedback
– Observational evidence from AGN feedback

Astrobit edited by: Mitchell Cavanagh

#Effects #AGN #activity #neutral #gas #outflows

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