Professor Andrew Bunker

Abstract:

The distribution of molecular gas on small scales regulates star formation and the growth of supermassive black holes in galaxy centers. Yet, the role of active galactic nuclei (AGN) feedback in shaping this distribution remains poorly constrained. We investigate how AGNs influence the small-scale structure of molecular gas in galaxy centers by measuring the clumpiness of CO($3-2$) emission observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in the nuclear regions ($50-200$ pc from the AGNs) of 16 nearby Seyfert galaxies from the Galaxy Activity, Torus, and Outflow Survey (GATOS). To quantify clumpiness we applied three different methods: (1) the median of the pixel-by-pixel contrast between the original and smoothed maps; (2) the ratio of the total excess flux to the total flux, after subtracting the background smoothed emission; and (3) the fraction of total flux coming from clumpy regions, interpreted as the mass fraction in clumps. We find a negative correlation between molecular gas clumpiness and AGN X-ray luminosity (L_ X ), suggesting that higher AGN activity is associated with smoother gas distributions. All methods reveal a turnover in this relation around L_ X erg s^-1, possibly indicating a threshold above which AGN feedback becomes efficient at dispersing dense molecular structures and suppressing future star formation. Our findings provide new observational evidence that AGN feedback can smooth out dense gas structures in galaxy centers.

Abstract:

We present combined James Webb Space Telescope (JWST) NIRSpec and MIRI/MRS integral field spectroscopy data of the nuclear and circumnuclear regions of the highly dust obscured Seyfert 2 galaxy NGC 7582, which is part of the sample of active galactic nucleaus (AGN) in the Galaxy Activity, Torus and Outflow Survey (GATOS). Spatially resolved analysis of the pure rotational H lines (S(1)–S(7)) reveals a characteristic power-law temperature distribution in different apertures, with the two prominent southern star-forming regions exhibiting unexpectedly high molecular gas temperatures, comparable to those in the AGN powered nuclear region. We investigate potential heating mechanisms including direct AGN photoionization, UV fluorescent excitation from young star clusters, and shock excitation. We find that shock heating gives the most plausible explanation, consistent with multiple near- and mid-IR tracers and diagnostics. Using photoionization models from the PhotoDissociation Region Toolbox, we quantify the ISM conditions in the different regions, determining that the southern star-forming regions have a high density ( cm) and are irradiated by a moderate UV radiation field ( Habing). Fitting a suite of Paris-Durham shock models to the rotational H lines, as well as rovibrational 1-0 S(1), 1-0 S(2), and 2-1 S(1) H emission lines, we find that a slow ( km s−1) C-type shock is likely responsible for the elevated temperatures. Our analysis loosely favours local starburst activity as the driver of the shocks and circumnuclear gas dynamics in NGC 7582, though the possibility of an AGN jet contribution cannot be excluded.

Abstract:

Recent observations from James Webb Space Telescope (JWST) have revealed an abundant population of active galactic nuclei (AGNs) and the so-called ‘Little Red Dots’ (LRDs) at , many of which are characterized by V-shaped UV-to-optical continua with turnovers around the Balmer limit. The physical nature of these LRDs is unclear, and it remains debated whether the peculiar spectral shape originates from AGN, compact galaxies, or both. We present the analysis of new NIRSpec-IFU data from the BlackTHUNDER JWST Large Programme and archival NIRSpec-MSA data of a lensed LRD at . The spectra confirm the presence of a smooth Balmer break and a broad H tracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the H narrow component indicates a small dynamical mass of the host galaxy of , which implies that the stellar population cannot contribute more than 10 per cent to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense () and nearly dust-free gas along our line of sight (possibly gas in the BLR or its surrounding). The same gas is expected to produce H absorption, at a level consistent with a tentative detection () in the high-resolution spectrum. Such a non-stellar origin of the Balmer break may apply to other LRDs, and would alleviate the issue of extremely high stellar mass surface densities inferred in the case of a stellar interpretation of the Balmer break. We note that this is a rare case of a black hole that is overmassive relative to both the host galaxy stellar and dynamical masses. We finally report indications of variability and the first attempt of AGN reverberation mapping at such an early epoch.

Abstract:

During the second half of Cycle 1 of the James Webb Space Telescope (JWST), we conducted the Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE) program. PASSAGE received the largest allocation of JWST observing time in Cycle 1, 591 hr of NIRISS observations to obtain direct near-IR imaging and slitless spectroscopy. About two-thirds of this was ultimately executed, to observe 63 high-latitude fields in pure-parallel mode. These have provided more than 10,000 near-infrared grism spectrograms of faint galaxies. PASSAGE brings unique advantages in studying galaxy evolution: (a) Unbiased spectroscopic search, without prior photometric preselection. By including the typical galaxies which have low masses and strong emission lines, slitless spectroscopy is the indispensable complement to any pretargeted spectroscopy. (b) The combination of several dozen independent fields to overcome cosmic variance. (c) Near-infrared spectral coverage, spanning a wide wavelength range of up to 1.0 to 2.3 μm, with minimal wavelength gaps, to measure multiple diagnostic rest-frame optical lines, minimizing sensitivity to dust reddening. (d) JWST’s unprecedented spatial resolution, in some cases using two orthogonal grism orientations, to overcome contamination due to blending of overlapping spectra. (e) Discovery of rare bright objects especially for detailed JWST follow-up. PASSAGE data are public immediately, and our team plans to deliver fully processed high-level data products. In this PASSAGE overview, we describe the survey and data quality, and present examples of these accomplishments in several areas of current interest in the evolution of emission-line galaxy properties, particularly at low masses.