Cosmic Collisions I: Optical Morphologies for MIRI-selected galaxies from the PRIMER survey

abstract · abstract

We present the first results of visual morphology classifications from the Cosmic Collisions project, comprising 14,657 galaxies from the JWST Public Release IMaging for Extragalactic Research (PRIMER) survey. The sample consists of galaxies detected with MIRI F770W and spans the epoch of peak cosmic star formation (1<z<3). We produce rest-frame optical and observed-frame mid-IR images and enlisted citizen science volunteers through the Zooniverse platform to classify galaxy morphology, surface features, and interactions. The project accumulated 304,524 classifications from more than 4,700 volunteers. We find that mid-IR selected galaxies have significantly different morphologies relative to optical and near-IR selected galaxies, favoring dust-rich disk galaxies at z<2 and compact systems at z>2. This inverts findings from optical selection, which shows galaxies becoming more bulge-dominated and elliptical over cosmic time. In addition, we identify a population of galaxies with disk-like optical morphologies and luminous mid-IR point-source cores that may represent obscured AGN candidates, offering a promising path to identify AGNs based on imaging alone. Comparison with visual classifications from HST imaging demonstrates the impact of JWST's improved sensitivity and resolution on the identification of galaxy structure and interactions, with systems previously identified by HST as compact, smooth, or featureless showing significant extended and internal structure in JWST. These results provide a foundation for future investigations into the connection between morphology, dust structure, star formation, and AGN activity.

article / block 1 · html

We present the first results of visual morphology classifications from the Cosmic Collisions project, comprising 14,657 galaxies from the JWST Public Release IMaging for Extragalactic Research (PRIMER) survey. The sample consists of galaxies detected with MIRI F770W and spans the epoch of peak cosmic star formation ( z ∼ 1 − 3 z\sim 1-3 ). We produce rest-frame optical and observed-frame mid-IR images and enlisted citizen science volunteers through the Zooniverse platform to classify galaxy morphology, surface features, and interactions. The project accumulated 304,524 classifications from more than 4,700 volunteers. We find that mid-IR selected galaxies have significantly different morphologies relative to optical and near-IR selected galaxies, favoring dust-rich disk galaxies at z < 2 z<2 and compact systems at z > 2 z>2 . This inverts findings from optical/near-IR selection, which shows galaxies becoming more bulge-dominated and elliptical over cosmic time. In addition, we identify a population of galaxies with disk-like optical morphologies and luminous mid-IR point-source cores that may represent obscured AGN candidates, offering a promising path to identify AGNs based on imaging alone. Comparison with visual classifications from HST imaging demonstrates the impact of JWST’s improved sensitivity and resolution on the identification of galaxy structure and interactions, with systems previously identified by HST as compact, smooth, or featureless showing significant extended and internal structure in JWST. These results provide a foundation for future investigations into the connection between morphology, dust structure, star formation, and AGN activity.

S2.SS2: II.2 PRIMER and Sample Selection / block 1 · html

For the visual classification dataset, we made further cuts to ensure that a reasonable image could be produced. First, we require acceptable redshifts based on the reduced χ 2 \chi^{2} of the EAZY fits. We also require SNR > > 10 in F770W and at least two NIRCam bands. This resulted in the final classification set of 14,657 objects, with 7485 in the COSMOS field and 7172 in the UDS field. The redshift and luminosity distribution of these objects are shown in Figure 1 .

S1: I Introduction / block 1 · html

There are observational limits to our ability to distinguish the shape and structure of distant objects. For example, cosmological redshift means optical surveys no longer probe the broad stellar population at z > 1 z>1 , resulting in peculiar or clumpy measurements of the restframe UV [ 1 , e.g.] which are incomparable to local optical measurements. In addition, the substructure of distant galaxies is difficult to resolve, with angular size scales reaching a minimum at z ∼ 1.0 − 1.5 z\sim 1.0-1.5 and staying relatively small as redshift increases [ 93 , 92 , 67 ] , while empirical studies [ 55 , 72 , e.g.] show galaxies tend to decrease in angular size with redshift. Likewise, surface brightness fades rapidly with redshift, dropping the faint features associated with galaxy disturbances [ 40 , 24 ] below the level of detectability [ 57 ] .

S3.SS2: III.2 Zooniverse Project / block 1 · html

Figure 3: A flowchart showing the questions asked of visual classifiers. Blue rectangles denote Tasks within the workflow. Purple and gray ovals denote responses within our workflow and the Zooniverse user interface, respectively, which result in traversing different branches of the decision tree. Green rounded rectangles denote start/end points.

S3.SS3.SSS5: III.3.5 Stage 5: Consensus and Subsets / block 1 · html

For Task 4, the ‘Merger’ or ‘Interacting Companion(s)’ choices both indicate that the object is undergoing or has recently undergone some form of disturbance. We find that these two options often dilute one another, leading to difficulty drawing a conclusion. We therefore reduce this Task to two possible results, ‘Interacting’ or ‘Non-interacting’. We conclude the former if the sum of ‘Merger’ and ‘Interacting Companion(s)’ votes is greater than 0.667 and the latter if the sum of ‘Non-interacting Companion(s)’ and ‘None’ votes is greater than 0.667. If neither threshold is cleared, the object is marked as inconclusive.

S5: V Summary and Future Work / block 1 · html

We collected and processed morphology classifications by citizen science volunteers for 14,657 mid-IR selected galaxies at cosmic noon. We present weighted and unweighted classification fractions for morphology, interactions, and surface features, as well as a number of useful descriptors to aid usage of our value-added catalog. We find that

S5: V Summary and Future Work / block 1 · html

Evolution of irregular and interacting populations is largely in line with previous works in terms of evolution with redshift. However, we find a lower interaction rate.

S5: V Summary and Future Work / block 1 · html

Galaxies detected in the mid-IR show differences in their morphologies as a function of redshift when compared with optically or near-IR selected samples. In the local universe, they are more disk-like, because we are generally selecting for more dust-rich galaxies; in the distant universe, they are more compact, possibly due to over-representation of AGNs.

S5: V Summary and Future Work / block 1 · html

The resolution, sensitivity, and wavelength range of JWST can drastically alter the way a galaxy is classified in comparison to HST. Because the disparity is often due to improved imaging, in cases of extreme difference, JWST morphologies are likely more reliable.

S6: VI Conclusions / block 1 · html

This 77.2 hour program generated imaging data with NIRCam and MIRI, and spectroscopic data with NIRSpec (MSA) and NIRCam (slitless). The NIRCam imaging data reaches point-source limiting magnitudes of ∼ \sim 29–29.5 across 1–5 μ \mu m. The MIRI imaging reaches a depth of ∼ \sim 26th mag at λ < \lambda< 10 μ \mu m, and ∼ \sim 22-23rd mag at λ ∼ \lambda\sim 20 μ \mu m. The NIRSpec spectroscopic data reach limiting emission line fluxes of ∼ \sim 1–2 × \times 10 -18 erg s -1 cm -2 with the medium-resolution gratings, while the prism detects continuum emission to m ∼ \sim 26 (as well as brighter emission lines). The NIRCam WFSS data detect emission lines to ∼ \sim 5–8 × \times 10 -18 erg s -1 cm -2 . These sensitivities are modestly deeper than pre-launch expectations, consistent with JWST post-launch documentation [ 160 ] .

S5.SS2: V.2 Active Galactic Nuclei / block 1 · html

One of the more surprising results to come from the CEERS observations is the detection of numerous faint, broad-line AGN at z > 5 z>5 . The first of these objects was identified photometrically as a candidate low-luminosity quasar by [ 142 ] and spectroscopically confirmed by [ 98 ] . Using the CEERS NIRSpec G395M/F290LP spectroscopy, [ 98 ] found broad H α \alpha emission in two sources at z ∼ 5 z\sim 5 and measured their BH masses to be 10 6 − 7 10^{6-7} M ⊙ , making these sources the least massive BHs known in the early universe. Soon thereafter, [ 112 ] reported broad H β \beta emission in a galaxy at z = 8.679 z=8.679 , making it, at the time, the most distant AGN ever identified. A subsequent survey of broad-line AGN in CEERS by [ 76 ] reported the number density of these sources to be 1–2 dex higher than that of bright quasars identified by ground-based surveys at similar redshifts (see also Matthee et al. 127 , Maiolino et al. 122 ).

S7: VII Summary / block 1 · html

To test the quality of our source detection, we test for false positives two ways. We rereduce the CEERS obervations and use our detection method and fount a false positive rate of 3.5%. However, we note our super background method makes use of a large set of observations and due to CEERS being split over two period the super backgrounds are created based on 8 _cal.fits files which is 11 times smaller than our MEGA observations. Additionally, we rereduce our observations to match the CEERS reductions and detection method found a false positive rate of 2.1%. Our photometic reductions also found 140 new source increasing the catalog by 4.6%.

S7: VII Summary / block 1 · html

We have estimated the imaging depth for each pointing/band to be 0.18 μ \mu m, 0.41 μ \mu m, 1.26 μ \mu m, and 4.1 μ \mu m for the F770W, F1000W, F1500W, and F2100W filters respectively. These are comparable to 80% completeness we derive. This completeness is then used to derive number counts for the fields. Our total number counts are comparable to CEERS and SMILES, and the deviation could be explained by difference in the fields, as shown by the deviation in our individual MIRI pointings number counts. These assessments indicate that our MIRI photometry catalog is of good quality and is able to complete our science goals.

S2.SS2: 2.2 Main photometric catalogue / block 1 · html

The VIPERS spectroscopic results, such as spectroscopic redshifts, are complemented by ancillary information. We especially leverage the multiwavelength photometric catalogue, taken from the VIPERS database ( Moutard et al., 2016 ) , which contains observations from ultraviolet (UV) to mid-infrared (MIR) wavelengths. Throughout this study, we use the following bands from the catalogue: far-UV (FUV) and near-UV (NUV) from Galaxy Evolution Explorer (GALEX); u, g, r, i, z, y from CFHTLS photometric measurements; K s from the CFHT Wide-field Infrared Camera (WIRCam); K from Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey ( Jarvis et al., 2013 ) ; W1, W2, W3, and W4 passbands (3.4, 4.6, 12.1, and 22.5 μ \mu m) from NASA’s Wide-field Infrared Survey Explorer ( Wright et al., 2010 , WISE;) .

S3: 3 Sample selection / block 1 · html

Table 1: Summary of our selection.

abstract · abstract

We combine the deepest X-ray survey from the Chandra Deep Field-South (CDF-S) `7-Ms' survey with the deepest mid-infrared (5.6$ μm$) image from the JWST/MIRI Deep Imaging Survey (MIDIS) in the Hubble Ultra-Deep Field (HUDF) to study the infrared counterparts and point-source emission of 31 X-ray sources with a median, intrinsic, rest-frame X-ray luminosity of $\log_{10}(L_{\rm Xc}^{\rm 0.5-7keV})$=42.04$\pm$0.22 erg $\rm s^{-1}$. The sample includes 24 AGN with a redshift range, as set by the X-ray detectability, of $z \simeq 0.5-3$. Through a multi-wavelength morphological decomposition, employing three separate classifications (visual, parametric and non-parametric) we separate (where present) the luminosity of the point-like AGN component from the remainder of the host-galaxy emission. The unprecedented mid-infrared sensitivity and imaging resolution of MIRI allows, in many cases, the direct characterisation of point-like (i.e. unresolved) components in the galaxies' emission. We establish a broad agreement between the three morphological classifications. At least 70% of the X-ray sources, including some classified as galaxies, show unresolved emission in the MIRI images, with the unresolved-to-total flux fraction at rest-frame 2$μm$ ranging from $\sim$0.2 to $\sim$0.9. At high X-ray luminosities ($\log_{10}(L_{\rm Xc}$)>43 erg $\rm s^{-1}$) we derive a consistent rest-frame near-infrared 2$ μm$ point-source luminosity to that derived for local AGN, whilst at lower X-ray luminosity we identify an excess in the 2$ μm$ emission compared to pre-JWST studies. We speculate this offset may be driven by a combination of Compton-thick AGN components and nuclear starburst, merger driven activity. Our observations highlight the complex nature of X-ray sources in the distant Universe and demonstrate the power of JWST/MIRI in quantifying their nuclear infrared emission. (Abridged)

abstract · abstract

We investigate the role of obscured active galactic nuclei (AGN) in recently quenched post-starburst galaxies (PSBs), using a sample of 65 photometrically selected PSBs in the PRIMER-UDS field at $1 < z < 2$. Combining JWST/MIRI 7.7 $μ$m and 18 $μ$m (F770W and F1800W) imaging with eight NIRCam and three HST/ACS bands, we probe hot dust emission to test for hidden AGN or dust-enshrouded star formation. We find strong differences between the low- and high-mass PSBs. Most high-mass PSBs ($ > 10^{10}\textrm{M}_\odot$) show no excess infrared emission (consistent with the quiescent population), indicating little or no dust-obscured activity, while low-mass PSBs display enhanced emission at 18 $μ$m, which we attribute to residual star formation. AGN template modelling indicates that the absence of mid-IR excess in massive PSBs limits any dust-enshrouded AGN to Eddington ratios of $ < 1\%$. In addition, we show that the F770W--F1800W colour alone is a highly effective diagnostic for separating passive and star-forming galaxies, particularly at high stellar masses. Overall, our results provide further evidence for distinct quenching pathways within the PSB population, and confirm that massive PSBs show no evidence for excess AGN activity relative to older passive galaxies.

abstract · abstract

We present the second data release of the Systematic Mid-Infrared Instrument (MIRI) Legacy Extragalactic Survey (SMILES), focusing on JWST/NIRSpec medium-resolution spectroscopy of galaxies across cosmic time. This release includes spectroscopic observations of 166 galaxies spanning $0 < z < 7.5$, sampling star-forming galaxies, quiescent systems, and active galactic nuclei (AGN), with an emphasis on galaxies at cosmic noon ($z \sim 1$-3). We describe the target selection strategy, the observational setup with the G140M/F100LP and G235M/F170LP gratings, and the data calibration process. The final data products include the reduced spectra, redshift catalog, emission-line catalogs produced with \texttt{GELATO} for emission-line galaxies and \texttt{pPXF} fits for quiescent systems, and ancillary spectral energy distribution (SED) fit results derived from multi-band photometry. The SMILES NIRSpec dataset enables investigations of obscured AGN, multi-phase outflows, ionizing properties, and the role of environment in galaxy evolution.

abstract · abstract

Little Red Dots (LRDs) have emerged as a key population linked to early black hole growth, yet photometric selections have predominantly targeted only the most extreme red systems, thereby shaping our current understanding of this new population of objects. In this work, we deliberately explore a broad range of optical redness while enforcing stringent compactness and visual inspection to ensure robustness and minimize contamination. Leveraging the depth and multiwavelength coverage of the JWST Advanced Deep Extragalactic Survey (JADES) data in the GOODS-North and GOODS-South fields, we construct the largest photometric census of LRDs to date in these fields, comprising 412 sources over $z\approx2\text{--}11$ across $\approx349.6$ arcmin$^2$. We show that classic extreme color cuts isolate only a minor fraction of this population ($\lesssim25\%$), while the majority of LRDs span a broader, largely unexplored parameter space. We quantify how selection strategies impact UV and optical luminosity functions and number density evolution, finding that current demographic trends of LRDs are strongly driven by selection biases and further limited by incomplete identification at both high and low redshift. Spectroscopically confirmed LRDs reveal a continuous range of spectral shapes, consistent with varying Active Galactic Nucleus (AGN) and host contributions in agreement with recent findings. Our results demonstrate that commonly adopted, purity-driven selections bias current demographic constraints toward the most extreme systems, potentially misrepresenting the diversity and evolution of the LRD population. Accounting for these selection effects is essential for interpreting LRDs and their role in early black hole growth.

abstract · abstract

Active galactic nuclei (AGN) are key drivers of galaxy evolution, yet many remain undetected in ultraviolet and optical surveys due to heavy dust obscuration. In these systems, absorbed emission is re-radiated at infrared (IR) wavelengths, making IR observations essential for identifying the full AGN population. Tracking the AGN IR contribution and number fraction provides insight into both the dominance and prevalence of AGN activity across cosmic time. Using the JWST Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES) and the JWST Advanced Deep Extragalactic Survey (JADES), we leverage continuous optical-to-mid-IR coverage (0.4-25 $μ$m) in the GOODS-S field to identify obscured AGN via multi-wavelength SED fitting with CIGALE. Our sample includes 278 AGN across 0 < z < 6, representing a seven-fold increase in sample size relative to previous studies utilizing the Cosmic Evolution Early Release Science (CEERS) survey due to the larger 15-pointing SMILES MIRI footprint. We find that both AGN IR contribution and number fraction increase with redshift, with AGN fractions rising from $\lesssim$ 5% at z < 2 to ~ 30% at higher redshifts, while the median AGN contribution increases by up to ~ 0.15. In contrast, as a function of total IR luminosity over $\log(L/L_{\odot}) \approx$ 8 - 12, the AGN contribution and AGN number fraction remain fundamentally static. These trends suggest that the prevalence of obscured AGN activity is dependent on redshift while showing little to no dependence on total infrared luminosity. Our results highlight JWST's ability to uncover previously hidden AGN populations and provide new constraints on AGN-galaxy co-evolution.