Star Formation and AGN Feedback in the Local Universe: Combining the Radio Continuum and Integral Field Spectroscopy
Date
2021-05-25
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Abstract
The effect of active galactic nuclei (AGN) on their host galaxies-in particular their star formation rates (SFRs)-remains one of the key outstanding questions of galaxy evolution. Although successful cosmological models of galaxy evolution require a fraction of an AGN's released energy to be redistributed into the interstellar medium to reproduce massive galaxies, direct evidence of AGN winds, jets, or radiation enhancing or quenching star formation through heating, cooling, or redistributing gas is rare. Typically, AGN jets can only be identified at radio frequencies. Therefore, we take advantage of the unique capabilities of the LOw Frequency ARray (LOFAR), which can detect synchrotron emission from such jets in fainter AGN than possible in previous wide-field surveys. The radio-continuum coupled with integral field spectroscopy (IFS), which allows for the spatially resolved study of the properties of stellar populations and nebular gas, is a potent combination for studying the effect of AGNs on their host galaxies. By combining data from the LOFAR Two-meter Sky Survey (LoTSS) with data from one of the largest optical IFS surveys, Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), we probe 338 local (z < 0.15) galaxies that host radio-loud AGN (RLAGN). We compare our results to a robust control sample of non-active galaxies that match the stellar mass, redshift, visual morphology, and inclination of the RLAGN host. To identify the effect of AGN feedback on the star-forming (SF) properties of their host galaxies, we focus on several principal questions:
1. How does the distribution of SFRs in regions ionized by hot stars for RLAGN and control galaxies compare?
2. Where in relation to the SF main-sequence (SFMS) do RLAGN and control galaxies lie?
3. How does the age of stellar populations in RLAGN and control galaxies change with increasing galactocentric distance?
To investigate the first question, we use MaNGA data to spatially resolve the ionizing mechanisms of gas across the surface of each RLAGN and control galaxy. In regions excited primarily by SF activity, we use the extinction corrected luminosity of Hα as a tracer of SFR. We then rely on integrated and gradient properties from the MaNGA Pipe3D value added catalog to address our final two questions. On the whole we find no significant difference between RLAGN and control galaxies, which could indicate that AGN have no overall effect on their host galaxies, or that any effect that the jets have cannot be seen yet. Larger sample sizes observed at multiple frequencies and high resolution images are needed in order to overcome the uncertainties in the visibility of AGN feedback and the spatial scale at which these interactions occur, respectively. Further work will be needed to decompose the radio emission into that coming from SF and that from AGN jets, which is important for reliable estimates of jet power and comparison to theoretical models.
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Galaxy Formation and Evolution