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A JWST Study of the Starburst-AGN Connection in Merging Luminous Infrared Galaxies

Director's Discretionary Early Release Science Program #1328


***Our first set of 8 papers have been accepted for publication in the Astrophysical Journal Letters!  See the News and Publications pages for the full list.***


Background: Galaxies evolve through a combination of secular processes, such as cold gas accretion, and nonsecular processes, such as galactic mergers, which can trigger massive starbursts and powerful AGN. JWST will transform our understanding of galactic evolution, providing a detailed look at the physics of star formation and black hole growth in nearby and distant galaxies. In this ERS program, we will observe four nearby, Luminous Infrared Galaxies (LIRGs) selected from the GOALS sample to have a range of properties, such as relative starburst and AGN power, merger stage, luminosity, infrared spectral slope, and optical depth. With NIRSPEC, NIRCAM and MIRI, we will create a rich dataset for understanding the dynamics and energetics of the ISM on scales of 50-100pc in the nuclei of local LIRGs. The four GOALS ERS targets are: NGC 7469 (IRAS 23007+0836, UGC 12332), NGC 3256 (IRAS 10257-4338), VV114 (IRAS 01053-1746, Arp 236) and II Zw 096.


NGC 7469 contains a bright, Seyfert 1 nucleus surrounded by a 1.8” (580 pc) radius circumnuclear ring of star formation. It is a face-on spiral, ~79” (26 kpc) away from an inclined companion galaxy (IC 4283) with a highly disturbed morphology. NGC 7469 has one of the best-studied AGN in the sky, including optical monitoring campaigns to measure the BH mass (107 M -Peterson et al. 2014) and the role of reprocessing in producing the optical/UV non-stellar emission. The starburst ring is visible at multiple wavelengths, with strong PAH emission and a bi-modal age population (Diaz-Santos et al. 2007). The nucleus is compact, with extended diffuse emission in the K-band continuum, and offset (~0.2”, 65pc) Br-γ emission, which might trace shocked gas from an outflow (U et al. 2019). It is the nearest example of a galactic center hosting both a rapidly accreting BH and a powerful circumnuclear starburst, and an ideal candidate to explore the SB-AGN connection at high resolution with JWST.

NGC 3256 is a cluster-rich, late-stage merger with log LIR = 11.64 L⊙and an ideal candidate for studying nuclear outflows powered by young stars and a buried AGN. Only the northern nucleus is visible at optical wavelengths, as the southern nucleus is hidden behind dust and gas in the disk, becoming visible only in the infrared. Both nuclei show evidence of outflows as traced by molecular gas, and it has been suggested that the southern outflow is powered by an AGN (Sakamoto et al. 2014). Outflows have also been seen in ionized atomic (Rich et al. 2011) and neutral gas (Cazzoli et al. 2016). The galaxy is among the most star cluster-rich systems in the GOALS sample, with a significant number of star clusters concentrated along the inner spiral structure within ~20” (3.8 kpc) of the nucleus. In NGC 3256, we will target both nuclei with the NIRSpec and MIRI IFUs, which will allow us to study the resolved energetics and source of the outflows, and the properties of the circumnuclear star clusters and ISM.

II Zw 096 is a merging system studied extensively across the electromagnetic spectrum, yet the nature of the dominant infrared emitting source remains elusive. At UV and visual wavelengths there are two interacting galaxies separated by 11.6” (8.4 kpc). However, at near-IR and mid-IR wavelengths, the system is dominated by a third bright component located ~5 kpc from one of the merging galaxies, which produces over 80% of the total luminosity of the entire system (log LIR = 11.9 L - see Inami et al. 2010). In the NIR with HST, two major sub-components are revealed along with numerous star clusters. The Spitzer/IRS spectra have relatively weak PAH EQW but no strong, high-ionization lines, suggesting that it may be a composite source, with a powerful starburst and a weak AGN, consistent with the presence of a compact, hard (2-7 keV) X-ray source. JVLA radio observations suggest an extremely compact starburst emitting close to the star-forming Eddington limit (Barcos-Munoz et al. 2017), with a luminosity density of ~1014 L⊙ kpc-2 - more than an order of magnitude more than the most well studied off nuclear starburst in the local Universe - the Antennae. The presence of both OH and H2O mega-masers and an implied mass of 109 M (Migenes et al. 2011, Wiggins et al. 2016) may suggest this is a third nucleus in the system. JWST will provide the crucial spectroscopic information needed to determine the true nature and properties of the dominant energy source in II Zw 096.

VV114 (Arp236, IC1623) is an interacting system undergoing vigorous starburst activity. With an infrared luminosity of log LIR = 11.6 L (Soifer et al. 1987), and a distance of 80 Mpc, it is one of the brightest LIRGs in the IRAS Bright Galaxy Sample. It appears to be an early-stage merger of two galaxies that are aligned east-west with a projected nuclear separation of ∼6 kpc, designated in the literature as VV 114E and VV114W. At optical wavelengths, VV 114 shows a highly disturbed morphology with very faint tidal tails extending over 25 kpc from the center (Arp 1966). The western component, VV 114 W, is more extended than the eastern one, and dominates the emission at short wavelengths. ALMA observations (Saito et al. 2014) show abundant warm, dense gas, evidence for amolecular outflow and a possible buried AGN in VV114E.  Our JWST MIRI and NIRSPEC IFU observations will target VV114E.


Observations: We will target each galaxy nucleus with the NIRSPEC and MIRI IFUs to cover the full available spectral range and obtain deep, wide-field NIRCAM and MIRI images in the F150W, F200W, F335M, F444W, F560W, F770W and F1500W filters. The observations will be scientifically compelling and serve to demonstrate the power of JWST to unravel the complex galactic ecosystems in nearby active and starburst galaxies, setting the stage for more extensive studies of active galaxies at low and high-redshift with JWST.

HST color composite images (ACS B, I-band) of the four ERS targets with MIRI MRS long wavelength (blue) overlays drawn on each nucleus. A projected linear scale of 5 kpc is indicated in each frame. We are observing both nuclei in NGC 3256 with the MIRI MRS and NIRSpec IFUs, but only the dominant infrared sources in II Zw 096 and VV114. Note, these overlays are meant to be indicative of the planned observations and are not drawn based on the actual roll angles and IFU positioning.



HST color composite zoom-in images of the four ERS targets with MIRI MRS long wavelength (blue) overlays drawn on each nucleus. A projected linear scale of 1 kpc is indicated in each frame. Note, these overlays are meant to be indicative of the planned observations and are not drawn based on the actual roll angles and IFU positioning.

Spitzer/IRS low-resolution and AKARI spectra of the four ERS targets showing the range in mid-infrared spectral slopes, and emission and absorption feature strengths. Locations of key fine structure, PAH, H2 and silicate and ice features have been marked. Spectra have been normalized and shifted to the rest frame, and are arranged in order of increasing silicate optical depth, from top to bottom.


ERS 1328 NIRCam and MIRI filter profiles projected on the Spitzer/IRS low-resolution and AKARI spectra of the four ERS targets. Key spectral features are labeled in the NGC 7469 spectrum. Spectra have been normalized, and are arranged in order of increasing silicate optical depth, from top to bottom.


Data Products: Our science-enabling products include multi-wavelength, ancillary datasets from Spitzer, ALMA, JVLA, AKARI and HST, together with custom spectral fitting software which we will use to analyze the JWST spectral cubes.   The spectral fitting software being developed for the ERS program to analyze MIRI and NIRSpec data cubes is based on the CAFE package (Marshall et al. 2007) which has been used to fit and model Spitzer/IRS spectra and photometry for large numbers of dusty starbursts and AGN (Armus et al. 2004, 2006, 2007, etc.; Marshall et al. 2018). 


Multi-wavelength optical (HST), IR (Spitzer) and radio (VLA) images of NGC 7469.  The Southern, nearly face-on spiral is the target of the ERS program.



Multi-wavelength optical (HST), IR (Spitzer) and radio (VLA) images of NGC 3256.  Both nuclei will be targeted with the NIRSpec and MIRI IFU's.



Multi-wavelength optical (HST), IR (Spitzer) and radio (VLA) images of VV 114.  The Eastern, infrared bright nucleus is the target of the ERS program.



Multi-wavelength optical (HST) and IR (Spitzer) images of II Zw 096.  The South-eastern, IR-bright source is the target of the ERS program.