SMILES Data Release II: Probing Galaxy Evolution during Cosmic Noon and Beyond with NIRSpec Medium-Resolution Spectra

TL;DR

The paper presents SMILES NIRSpec MOS Data Release II, delivering medium-resolution rest-optical spectroscopy for $0 < z < 7.5$ galaxies to illuminate galaxy evolution during cosmic noon and beyond. It combines three customized MSA masks with G140M/F100LP and G235M/F170LP observations to produce calibrated 2D/1D spectra, redshift and emission-line catalogs, and extensive SED fits, enabling robust diagnostics of star formation, metallicity, AGN activity, and outflows. Key contributions include a diverse, well-characterized sample (SF, quiescent, AGN), a rigorous data reduction pipeline with 1/$f$ noise correction and extended-source handling, and science demonstrations of obscured AGN demographics, multi-phase outflows, and environment-driven ionizing properties. The dataset offers critical insights into feedback, quenching, and chemical enrichment processes and provides a valuable resource for cross-comparison with ALMA, HST/JWST ancillary data, and theoretical models. $R \sim 1000$ spectra over $0.97$–$3.17\ \mu$m, combined with $MIRI$-selected targets and deep photometric coverage, make this release a pivotal step in characterizing galaxy evolution during cosmic noon with JWST. $\ldots$

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.

Figures (10)

• Figure 1: Footprint of the SMILES survey over the GOODS-S field, overlaid with key observational programs. The SMILES coverage is shown in orange, while the footprints of FRESCO (blue) and JADES (deep and medium tiers in green) are also indicated. The black markers represent the locations of MSA slitlets that yield spectra from all three masks (size not to scale). The background shading provides a reference to the larger HST ACS footprint. This region is also covered by Chandra X-ray observations, as well as JVLA radio observations at 3 GHz and 6 GHz, making it a prime multi-wavelength field for deep extragalactic studies.
• Figure 2: Example SMILES spectra from the G140M and G235M gratings. From top to bottom: a star-forming galaxy at $z = 1.57$ showing strong Balmer and forbidden emission lines; an AGN at $z = 2.23$ with prominent broad H$\alpha$ emission; and a quiescent galaxy at $z = 2.35$ dominated by absorption features. Key emission/absorption lines are labeled. The small vertical dashed line near 1.8 $\mu$m marks the approximate boundary between the G140M and G235M grating coverage.
• Figure 3: Correction of 1/$f$ noise in NIRSpec 2D spectra. Left: Original uncorrected image showing prominent low-frequency vertical banding due to correlated readout noise. Right: Same exposure after applying the 1/$f$ correction using a Chebyshev polynomial fit along detector columns. The correction significantly reduces the striping pattern and improves the background uniformity across the detector.
• Figure 4: Comparison between standard 3-nod (top) and modified 2-nod (middle) extractions for a spatially extended source in the SMILES dataset (ID: 199580, $z=1.8501$). The top panel includes background subtraction using all three nod positions, which can partially suppress extended emission due to self-subtraction. In contrast, the middle panel excludes the central nod during background subtraction and stacking, preserving more of the extended flux. The 2D and 1D spectra (bottom) show a stronger H$\alpha$ peak under the 2-nod scheme. The NIRCam RGB image (F200W/F150W/F115W), with the slit position overplotted, is shown at upper left.
• Figure 5: Summary of redshift measurements in the SMILES NIRSpec sample. (a) Histogram of confirmed spectroscopic redshifts ($z_{\rm spec}$), showing broad coverage from $z < 1$ to $z > 6$, with a peak near $z\sim2$. (b) Comparison between spectroscopic redshifts and photometric redshifts ($z_{\rm phot}$) derived from multi-band imaging. The dashed line shows the one-to-one relation. Most sources lie close to the line, demonstrating good agreement, with a small number of outliers primarily at high redshift.