STRRINGS: STReams in Residual Images of Nearby GalaxieS

TL;DR

This work catalogs tidal features around 19{,}387 nearby galaxies using residual DESI-LS images to enhance faint structures, finding an overall tidal feature incidence of $11.9\pm0.2\%$ and a stream incidence of $4.4\pm0.1\%$. From this census, the authors define STRRINGS, a first release of 35 long, curved streams suitable for dynamical modelling of dark matter haloes, with detailed segmentation, track geometry, surface brightness, colours, and stellar masses. The STRRINGS streams are typically $\sim124$ kpc long with $\sim5.6$ kpc width, show a weak positive correlation between stream and host mass, and suggest minor-merger progenitors (mass ratios $\sim0.7\%$–$2\%$). They also identify six candidate satellite progenitors and discuss how environment, host morphology, and depth influence tidal feature detectability. The dataset provides a foundation for future halo-property constraints and will be extended with deeper and larger surveys, enabling population-level tests of dark matter halo shapes and mass profiles.

Abstract

Tidal features from galaxy mergers, particularly stellar streams, offer valuable insights into galaxy assembly and dark matter halo properties. This paper aims to identify a large sample of nearby stellar streams suitable for detailed modelling and comparison with simulations to enable population-level constraints on halo properties. We visually inspect and compile a tidal feature catalogue for $19,387$ galaxies with redshift $z \leq 0.02$ from the Siena Galaxy Atlas 2020 using original, model, and residual images from the DESI Legacy Imaging Surveys. Residual images, produced by subtracting models of all sources, enhance the detectability of faint asymmetries such as tidal features. We find that $11.9 \pm 0.2\%$ of galaxies host detectable tidal features, more frequently around early-type than late-type galaxies. The tidal feature fraction increases with stellar mass, from $2.4 \pm 0.4\%$ at $\sim10^8$M$_\odot$ to $36.5 \pm 1.2\%$ at $\sim 5\times10^{11}$M$_\odot$. From this, we present the first release of STRRINGS: STReams in Residual Images of Nearby GalaxieS, a subsample of 35 galaxies with long, narrow streams suitable for modelling. We segment these streams and derive their geometry, surface brightness, colours, and stellar masses. The median $g$-band surface brightness is 26.8 mag$\,$arcsec$^{-2}$, reaching 27.5 mag$\,$arcsec$^{-2}$ for the faintest stream. Mass ratios are consistent with minor mergers, and we identify five potential dwarf galaxy progenitors. Our streams are typically longer (median 124 kpc) than the literature, with comparable widths. Stream mass correlates with length and colour, and wider streams lie at larger galactocentric radii. STRRINGS will be expanded and used to constrain halo properties in future work.

Figures (22)

• Figure 1: Illustration of the legacypipe processing of one image (UGC08717). A scalebar of $1'$ is indicated at the bottom of each image. North is up, East is left. Left: original $grz$ data image. Middle:Tractor$grz$ model image of all astronomical sources. Right: residual image, obtained by subtracting the model from the original data. This black-and-white residual image is obtained by computing the median of the residual images in $g$, $r$ and $z$, then computing the 35-90% percentile range of the pixel distribution of that median image and clipping the pixel values accordingly. White regions indicate areas where the model overestimates the light, while black regions show an excess of light in the data. The images is plotted as the median of the $g,r,z$ residuals, smoothed and stretched to enhance the visibility of faint features, that appear as black regions. Note that these images were used for photometric measurements, but a different set of images were used for visual inspection (i.e. the already available PNG montage of the $grz$ colour image, model and residuals, see Section \ref{['section:data-images']}).
• Figure 2: Top: Morphology ratio per bin of host galaxy's stellar mass for ETGs (red circles), LTGs (blue crosses) and galaxies with unknown morphological information (black dots). The mass bins contains approximately the same number of galaxies (about $1,615$). LTGs dominate the sample for stellar masses below $10^{11} M_\odot$. Bottom: Tidal feature fractions as a function of the host galaxy's stellar mass (in $M_\odot$). The mass bins contains approximately the same number of galaxies (about $1,615$). The errorbars represent the $1\sigma$ standard error on proportions in each bin. Streams are plotted as blue pentagons, tails as orange squares, plumes as green triangles, shells as red rhombuses and any tidal feature as purple circles. The fraction of galaxies with tidal features increases with host stellar mass.
• Figure 3: Illustration of the original and model images, segmentation and track of a stream for one galaxy (ESO079-003_GROUP). A scalebar of $1'$ is indicated at the bottom of each panel. North is up, East is left. Left: original $grz$ data image. Middle, left: Tractor$grz$ model of all astronomical sources. Middle, right: residual image (obtained by subtracting the model from the data), plotted as the median of the $r,g,z$ residuals, smoothed and stretched to enhance faint features. White areas correspond to an excess of light in the model, black areas show an excess of light in the data. Right: residual image with the stream segmentation (red contours) from Jafar and the stream track (orange crosses) as described in Section \ref{['section:method-segmentation']}.
• Figure 4: Cartesian projection (in kpc) of the track (solid lines) and width (shaded regions) of all the individual STRRINGS streams, centred around their respective host galaxy (at X=0,Y=0). The majority of streams are located within 30 kpc of their host galaxy.
• Figure 5: Illustration of some streams from our STRRINGS sample. The residual images are displayed, and represent the median of $g,r,z$ residual images, smoothed and stretched to enhance faint features. Black regions correspond to light excess in the data, white regions to areas where the model overestimates the light. Streams clearly appear as black regions in the residuals. A scalebar of $1'$ and the corresponding physical length (in kpc) is indicated at the bottom of each panel, the galaxy names are at the top. North is up, East is left.