Questions and challenges of what powers galactic outflows in active galactic nuclei

Different mechanisms can drive outflows in active galactic nuclei (AGN), but it is often unclear which mechanism dominates, if any. To quantify the impact of AGN feedback on galaxy evolution, the driving mechanism of outflows must be better understood.Comment: Authors' version of Nature Astronomy Comment. View-only version of full text publicly available at this link: http://rdcu.be/HUU

The large-scale environments of radio-loud active galactic nuclei and their evolution across cosmic time

Emerging from the cosmic web, galaxy clusters are the most massive gravitationally bound structures in the universe. Thought to have begun their assembly at 2 1.5 where major assembly is in progress. The search for galaxy clusters at high redshift, so far, has been mildly successful and only a handful of clusters at z > 1.5 have been confirmed. Because this redshift range was essentially unreachable with previous instrumentation, it was dubbed a ‘redshift desert’. The work presented in this thesis has made a major contribution to this field. The Clusters Around Radio- Loud AGN (CARLA) survey, a 400 hr targeted Warm Spitzer program, observed 420 radio-loud AGN (active galactic nuclei) at 1.3 1.5. We also showed that radio-loud AGN reside in denser environments than similarly massive galaxies. This makes high-redshift clusters around radio-loud AGN particularly interesting as they can reveal how galaxies in the most massive dark matter halos assembled. A complementary project, HERGE (Herschel Radio Galaxy Evolution Project) observed a sample of 71 radio galaxies at 1 < z < 5 at far-IR wavelengths with the Herschel Space Observatory. Supporting data in the mid-IR, partially in the near-IR and at sub-mm wave- lengths allow to study cluster fields in more detail. A pilot project on a single field showed that we can identify cluster members and constrain their star-formation properties. These projects laid the foundation for future work, which will make a significant impact on understanding the formation of the most massive structures over several billion years

The large-scale environments of radio-loud active galactic nuclei and their evolution across cosmic time

Emerging from the cosmic web, galaxy clusters are the most massive gravitationally bound structures in the universe. Thought to have begun their assembly at 2 1.5 where major assembly is in progress. The search for galaxy clusters at high redshift, so far, has been mildly successful and only a handful of clusters at z > 1.5 have been confirmed. Because this redshift range was essentially unreachable with previous instrumentation, it was dubbed a ‘redshift desert’. The work presented in this thesis has made a major contribution to this field. The Clusters Around Radio- Loud AGN (CARLA) survey, a 400 hr targeted Warm Spitzer program, observed 420 radio-loud AGN (active galactic nuclei) at 1.3 1.5. We also showed that radio-loud AGN reside in denser environments than similarly massive galaxies. This makes high-redshift clusters around radio-loud AGN particularly interesting as they can reveal how galaxies in the most massive dark matter halos assembled. A complementary project, HERGE (Herschel Radio Galaxy Evolution Project) observed a sample of 71 radio galaxies at 1 < z < 5 at far-IR wavelengths with the Herschel Space Observatory. Supporting data in the mid-IR, partially in the near-IR and at sub-mm wave- lengths allow to study cluster fields in more detail. A pilot project on a single field showed that we can identify cluster members and constrain their star-formation properties. These projects laid the foundation for future work, which will make a significant impact on understanding the formation of the most massive structures over several billion years

SDSS-IV MaNGA: Identification of active galactic nuclei in optical integral field unit surveys

In this paper, we investigate 2727 galaxies observed by MaNGA as of June 2016 to develop spatially resolved techniques for identifying signatures of active galactic nuclei (AGN). We identify 303 AGN candidates. The additional spatial dimension imposes challenges in identifying AGN due to contamination from diffuse ionized gas, extra-planar gas and photoionization by hot stars. We show that the combination of spatially-resolved line diagnostic diagrams and additional cuts on H$\alpha$ surface brighness and H$\alpha$ equivalent width can distinguish between AGN-like signatures and high-metallicity galaxies with LINER-like spectra. Low mass galaxies with high specific star formation rates are particularly difficult to diagnose and routinely show diagnostic line ratios outside of the standard star-formation locus. We develop a new diagnostic -- the distance from the standard diagnostic line in the line-ratios space -- to evaluate the significance of the deviation from the star-formation locus. We find 173 galaxies that would not have been selected as AGN candidates based on single-fibre spectral measurements but exhibit photoionization signatures suggestive of AGN activity in the MaNGA resolved observations, underscoring the power of large integral field unit (IFU) surveys. A complete census of these new AGN candidates is necessary to understand their nature and probe the complex co-evolution of supermassive black holes and their hosts.Comment: 18 pages, 11 figures, accepted to MNRA

Mildly Suppressed Star Formation in Central Regions of MaNGA Seyfert Galaxies

Negative feedback from accretion onto super-massive black holes (SMBHs), that is to remove gas and suppress star formation in galaxies, has been widely suggested. However, for Seyfert galaxies which harbor less active, moderately accreting SMBHs in the local universe, the feedback capability of their black hole activity is elusive. We present spatially-resolved H$\alpha$ measurements to trace ongoing star formation in Seyfert galaxies and compare their specific star formation rate with a sample of star-forming galaxies whose global galaxy properties are controlled to be the same as the Seyferts. From the comparison we find that the star formation rates within central kpc of Seyfert galaxies are mildly suppressed as compared to the matched normal star forming galaxies. This suggests that the feedback of moderate SMBH accretion could, to some extent, regulate the ongoing star formation in these intermediate to late type galaxies under secular evolution.Comment: 12 pages, 7 figures, accepted by MNRA