An enormous skinny stellar stream within the Coma Galaxy Cluster

1. Introduction

Extraordinarily low-surface-brightness options within the type of stellar streams and haloes present essential info for understanding the hierarchical mannequin of galaxy evolution in a Λ-CDM framework (Bullock & Johnston 2005; Johnston et al. 2008; Cooper et al. 2010; Pillepich et al. 2014; Monachesi et al. 2019; Rey & Starkenburg 2022; Genina et al. 2023). These buildings are created from the continual accretion of satellites, and consultant examples are discovered within the environments of the Native Group (e.g., Belokurov et al. 2006; McConnachie et al. 2018; Ibata et al. 2021; Dodd et al. 2023) and of close by galaxies (e.g., Mouhcine et al. 2010; Crnojević et al. 2016) by counting particular person stars.

The provision of high-precision stellar positions and velocities – primarily within the Milky Manner setting – has promoted intense analysis on this discipline (see a evaluation by Helmi 2020). One of many functions of the examine of stellar streams, given their extraordinarily low stellar density, is their capability to disclose the gravitational potential during which they reside (e.g., Johnston et al. 1999; Dubinski et al. 1999; Sanders & Binney 2013; Reino et al. 2021; Pearson et al. 2022), particularly for the case of chilly stellar streams (Bonaca & Hogg 2018). Due to their coherent stellar movement, any close by perturbation by a conspicuous low-mass potential will be recognized in parameter area (e.g., Ibata et al. 2002; Carlberg 2012; Erkal & Belokurov 2015). That is significantly fascinating for the case of a possible perturbation by darkish matter subhaloes, which might present related details about the properties of darkish matter in already identified streams within the Milky Manner comparable to Pal 5 or GD-1 (Erkal et al. 2016; Banik & Bovy 2019; Ibata et al. 2020; Banik et al. 2021).

Due to the massive quantity of data contained in stellar streams, there have been sustained efforts to discover these buildings in exterior galaxies with the intention to get hold of a bigger environmental and statistical context (Tal et al. 2009; Martínez-Delgado et al. 2010; Rich et al. 2012; Duc et al. 2015; Trujillo et al. 2021; Martínez-Delgado et al. 2023a). Nonetheless, resolving particular person stars is simply possible out to some megaparsecs, and the numerous observational challenges of large-area, low-surface-brightness photometry (Knapen & Trujillo 2017; Mihos 2019) imply that the very low-surface-brightness regimes at which chilly stellar streams have been recognized within the Milky Manner are principally unexplored at larger distances, and many of the anticipated faint stellar streams stay undetected (Martin et al. 2022).

With the upcoming arrival of the brand new technology of instrumentation and deep optical surveys comparable to Euclid (Euclid Collaboration 2022a), the Rubin Observatory (Ivezić et al. 2019), and the Nancy Grace Roman House Telescope (Akeson et al. 2019), together with vital technical efforts (Euclid Collaboration 2022b; Smirnov et al. 2023; Kelvin et al. 2023), it’s anticipated that the attainable surface-brightness limits will enhance the variety of stellar streams detected in exterior galaxies by orders of magnitude (Pearson et al. 2019). This may present a broader environmental context and a larger understanding of the processes concerned, yielding invaluable info in each galactic evolution fashions and near-field cosmology.

We current the primary outcomes of an intensive observational marketing campaign to discover the Coma cluster on the ultralow-surface-brightness regime: the HERON Coma Cluster Venture. The Coma cluster is likely one of the most-studied extragalactic objects, and is of specific historic significance (see a historic evaluation by Biviano 1998), for instance being the location of the invention of first proof of darkish matter (Zwicky 1933) or intracluster-light (Zwicky 1951). The existence of galactic particles in Coma (Trentham & Mobasher 1998; Gregg & West 1998) and different clusters (Conselice & Gallagher 1999; Calcáneo-Roldán et al. 2000; Mihos et al. 2017) is direct proof of the processes of galactic cannibalism and accretion giving rise to the constructing of the intragroup and intracluster mild haloes (Rudick et al. 2009; DeMaio et al. 2015; Montes 2022). As Coma is likely one of the most huge native clusters with intense merger exercise (e.g., Jiménez-Teja et al. 2019; Gu et al. 2020), it is a perfect setting for finishing up an exploration of this kind of construction, offering essential info on the environmental and interplay processes happening in clusters.

Right here, we report the invention of the Large Coma Stream, an especially faint, skinny, and free-floating stellar stream within the outskirts of the Coma galaxy cluster. At 510 kpc in size, it’s a number of instances longer than the 2 beforehand recognized stellar streams within the Coma cluster (Trentham & Mobasher 1998; Gregg & West 1998) or different clusters (Conselice & Gallagher 1999; Calcáneo-Roldán et al. 2000; Mihos et al. 2017), whereas exhibiting orders-of-magnitude decrease floor brightness and whole mass. We present that this new stream is in step with options present in numerical simulations of hierarchical cluster formation (Illustris TNG). We assume a distance of 100 Mpc for Coma (Liu & Graham 2001), similar to a distance modulus of m − M = 35.0 magazine and a spatial scale of 0.462 kpc arcsec⁻¹ utilizing cosmological parameters from Planck Collaboration VI (2020). We use the AB photometric system all through this work.

2. Observations and detection

2.1. HERON knowledge

We carried out an intensive observational marketing campaign of deep observations within the Coma Cluster in g and r bands with the 0.7 m Jeanne Wealthy Telescope. This telescope is especially devoted to the Halos and Environments of Close by Galaxies (HERON) Survey (Rich et al. 2019), and is designed to be significantly environment friendly within the low-surface-brightness regime. It has a single Finger Lakes Devices ML09000 detector with 3048² 12 μm pixels with a scale of 1.114 arcsec pix⁻¹, permitting a 57 × 57 arcmin discipline of view. An intensive technical description of the instrumentation is offered by Rich et al. (2017). Observations on this work are a part of the HERON Coma Cluster Venture (Román et al., in prep.), the aim of which is to hold out a examine of the diffuse mild of the Coma cluster to unprecedented limits in floor brightness.

Observations have been performed within the spring and summer season of 2019 for the g band and 2020 for the r band. A complete of 461 and 579 exposures of 300 s have been taken within the g and r bands, respectively. Observational circumstances have been principally darkish. Dithering steps of tens of arcminutes have been carried out with the goal of masking an space of 1.5 × 1.5° centered on Coma. The information discount was carried out by customary subtraction of mixed superbias and superdarks for every evening from the science photos. Flat fields have been constructed by combining and normalizing the closely masked bias-subtracted and dark-subtracted science photos. Astrometry was carried out on all photos individually with the Astrometry.web software program package deal (Lang et al. 2010) and SCAMP (Bertin 2006). The photographs have been then reprojected onto a typical astrometrical grid with SWARP (Bertin et al. 2002) and photometrically calibrated with the Darkish Power Digicam Legacy Survey (DECaLS; Dey et al. 2019) as a reference. The photographs have been mixed with a really conservative sky becoming primarily based on Zernike polynomials to protect the knowledge at low floor brightness. We used orders between 1 and 4 relying on the diploma of gradients within the photos, at all times utilizing the bottom attainable order capable of match the gradients of every particular person picture.

The entire publicity time was 38.4 h and 48.25 h within the g and r bands, respectively. The utmost floor brightness limits in these knowledge are 30.1 and 29.8 magazine arcsec⁻² [3σ, 10″ × 10″] in each g and r bands (see definition by Román et al. 2020). Within the area of curiosity right here, the floor brightness limits attain 29.5 magazine arcsec⁻² [3σ, 10″ × 10″] in each g and r bands. The seeing circumstances weren’t restrictive as we have been within the diffuse mild, producing a closing seeing of roughly 3 arcsec in each g and r bands. Additional particulars about this venture and knowledge shall be offered in an upcoming publication.

A preliminary visible evaluation of those knowledge allowed us to establish an especially faint characteristic with very skinny morphology (see Fig. 1a). Its detected size and width are roughly 18.5 and 1 arcmin, respectively.

Fig. 1. Common view of the Large Coma Stream and its location within the Coma Cluster. Backside: Colour composite HERON picture within the g and r bands. The darkish background is constructed with the sum picture. Uper proper: WHT picture of the Large Coma Stream in L luminance (darkish background) on a shade picture utilizing g and r bands from the DECaLS survey. Higher left: Zoom onto the central area of the WHT picture.

2.2. WHT knowledge

Because of the in depth dithering of the observations, the publicity time varies with place. In Fig. A.1 we present the publicity time and equal depth alongside the footprint of the observations. Within the most publicity area of 10 h, the limiting floor brightness reaches 31.4 magazine arcsec⁻² [3σ, 10″ × 10″] within the L luminance band. A comparatively massive portion of about 6 × 8 arcmin of the realm of the picture, together with the central area of the stream, has a floor brightness restrict of 31.0 magazine arcsec⁻² [3σ, 10″ × 10″]. The decision is 1.2 arcsec in full width at half most (FWHM).

The WHT luminance band picture confirms the existence of the slim characteristic recognized within the HERON knowledge, reaching deeper floor brightness limits and better decision (see Figs. 1b and c) over the central area (14 × 17 arcmin) of the stream. We searched visually for potential remnants or overdensity from a mum or dad galaxy. Nonetheless, the stream seems fully featureless, particularly within the larger decision and deeper WHT picture that samples the central area.

3. Affiliation with the Coma Cluster

The presence of globular clusters normally traces the trajectories of streams (Mackey et al. 2019), and also can present an estimate of their distance via measurement of the height of the globular cluster luminosity operate (Rejkuba 2012). Nonetheless, the HERON knowledge do not need sufficient point-source depth, and don’t enable shade filtering with solely the g and r bands. There aren’t any HST knowledge out there over the realm, and the one multi-band knowledge out there from DECaLS have inadequate level supply depth, making detection of globular clusters infeasible till higher knowledge are obtained. On this part, we current an evaluation carried out to make sure that the detected characteristic is certainly a stellar stream situated in Coma.

3.1. Potential resolved stars

We discover the opportunity of the existence of an overdensity of point-like sources over the stream area, which might point out an in depth distance. For this, we use SExtractor (Bertin 2006) with a detection threshold of 1σ. We don’t apply any magnitude standards apart from deciding on sources suitable with point-like sources, and for this we choose sources with a stellarity index of upper than 0.5.

The center panel of Fig. 2 reveals the density of point-like sources that we will affiliate with low-luminosity stars. Apparently, this stream isn’t resolved into stars within the WHT knowledge, showing as an especially clean and low-surface-brightness characteristic. Contemplating that this characteristic isn’t resolved into stars, we comply with the evaluation by Zackrisson et al. (2012) to impose a decrease restrict on distance. The truth that stars are unresolved in our highest-resolution knowledge with a seeing of 1.2 arcsec and a floor brightness of roughly 29 magazine arcsec⁻² (detailed in later sections) means that the characteristic should be at a distance of at the least 1 Mpc.

Fig. 2. Comparability between optical point-like supply density and far-IR emission within the central area (13.5 × 7.6 arcmin). High panel: WHT picture within the luminance L filter shade coded in floor brightness in response to the higher shade bar. Center panel: density of detected point-like sources within the area with WHT knowledge. Decrease panel: 250 μm counterpart with the Herschel area telescope. The picture is shade coded in S​ν in response to the decrease shade bar. The dashed strains mark elliptical floor brightness contours of roughly μL = 26 magazine arcsec−2 for the galaxies named within the prime panel, and μL = 29.5 magazine arcsec−2 for the placement of the Large Coma Stream.

3.2. Far-infrared counterpart

With a view to discover the likelihood that the stream could possibly be a hint of mud from the interstellar medium (ISM) or Galactic cirrus of the Milky Manner, we used knowledge out there from the Herschel area telescope at 250 μm (Pilbratt et al. 2010). On account of its low temperature, Galactic cirrus are effectively detected in far-infrared (FIR) and submillimeter bands (Low et al. 1984; Veneziani et al. 2010). The Herschel knowledge at 250 μm provide a big benefit over knowledge from different devices, comparable to IRAS (Neugebauer et al. 1984) or the Planck observatory with its 857 GHz band (Planck Collaboration XXIV 2011), each in detection energy and – importantly for our case – decision.

The decrease panel of Fig. 2 reveals a comparability between our optical knowledge and the Herschel 250 μm band of the identical discipline. The photographs have been stretched within the optical to offer most distinction for the detection of the faintest sources. The FWHM of the 250 μm Herschel knowledge is 17.6 arcsec, which is decrease than the detected stream width in optical bands of 1 arcmin. Visually, there isn’t any emission hint within the 250 μm band, both within the area the place the stream is situated or adjoining to it. The one detectable emission in 250 μm is that similar to galaxies alongside the road of sight, amongst which we will spotlight the robust emission from the late-type galaxy NGC 4848.

With a view to quantify the 250 μm emission over the area of the stream, we calculated the full flux within the aperture outlined by the dashed strains proven in Fig. 2 and outdoors this area. This aperture is outlined utilizing HERON optical knowledge, and is detailed in Sect. 4.1. That is carried out on the closely masked picture, avoiding the mixing of areas similar to exterior sources that seem within the picture. The common sky background worth over the area of the stream is S​_{ν, 250 μm} = −0.02 ± 0.04 MJy sr⁻¹ and that exterior this area is S​_{ν, 250 μm} = 0.02 ± 0.01 MJy sr⁻¹. Due to this fact, the stream has no emission within the 250 μm band, at the least as much as the worth outlined by the sky background noise of those knowledge.

The absence of a 250 μm counterpart to the optically detected stream means that the Galactic cirrus emission is an unlikely clarification for the origin of the characteristic. Extra causes to rule out a Galactic cirrus contamination are that this celestial area may be very near the Galactic pole (b = 88°), with a low extinction by mud (A_r = 0.02 magazine; Schlafly & Finkbeiner 2011) and that the stream is sort of one dimensional, not exhibiting the anticipated fractal morphology of cirrus in optical wavelengths (Marchuk et al. 2021).

3.3. Environmental evaluation

The extraordinarily low floor brightness of this characteristic makes it extremely difficult to acquire spectroscopic info with which to measure its redshift. We’ve got not discovered any fuel detections within the area utilizing the NASA/IPAC Extragalactic Database, nor counterparts in latest work by Bonafede et al. (2022).

Assuming that the characteristic is certainly a stellar stream, its elongated morphology means that it should be a tidal characteristic and due to this fact ought to be related to some construction that impacts it gravitationally. Contemplating its massive obvious measurement, past the plain attainable affiliation with the adjoining Coma cluster, we explored a possible affiliation with some close by buildings in shut projection.

Determine 3 reveals a celestial coordinate map with large-scale buildings within the line of sight of the stream. We make use of {the catalogue} of close by teams inside 3500 km s⁻¹ by Kourkchi & Tully (2017) to establish these buildings. Kourkchi & Tully (2017) additionally provide estimates of the virial radius of those buildings.

Fig. 3. Graphical illustration of galactic associations within the line of sight of the Large Coma Stream. Teams and clusters of native galaxies (Vrad < 3500 km s−1) and their obvious virial radii are represented with grey circles. Galaxies with redshift within the vary of 3500 km s−1 < Vrad < 10 000 km s−1 are represented with black dots. The obvious Coma virial radius is represented with a purple circle. The place and longitude of the Large Coma Stream is represented with a purple section.

We plot all teams along with their virial radii in Fig. 3. We convert from bodily to projected coordinates utilizing the identical cosmological parameters as these in Kourkchi & Tully (2017) with H₀ = 75 km s⁻¹ Mpc⁻¹. The place a distance isn’t out there for a gaggle, we use a direct conversion by Hubble’s legislation utilizing the radial velocity. We discover that solely sparse teams do not need measured distances, and in any case, they don’t seem to be shut in projection to the Coma Cluster. As a complement, and provided that the Kourkchi & Tully (2017) catalogue solely comprises teams as much as 3500 km s⁻¹, we plot galaxies with radial velocities of between 3500 and 10 000 km s⁻¹ obtained from the NASA/IPAC Extragalactic Database as black factors. This higher restrict is used as a result of it’s the most radial velocity of the galaxies contained within the central area of the Coma cluster. To characterize the virial radius of the Coma cluster, we depend on Ho et al. (2022), giving 2.4 Mpc with H₀ = 75 km s⁻¹ Mpc⁻¹. We additionally plot the size and placement of the stream as a purple section.

We will touch upon some close by buildings. First, the Virgo Galaxy Cluster, which could possibly be a possible host for the stream, is situated at roughly 13° projected separation from Coma. With a calculated virial radius of 1.3 Mpc for the Virgo Cluster, this corresponds to an obvious measurement of 4.4°. The stream would due to this fact be situated at a projected distance of three.9 instances the virial radius of the Virgo Cluster. The M 94 group is the opposite construction with a big obvious measurement, having a virial radius of 365 kpc, which is equal to 4.4°. The stream is situated at 3 times the virial radius of the M 94 Group. NGC 4725, situated at a distance of 12 Mpc, has a virial radius of 143 kpc, equal to 0.63°, with the stream at 5.1 instances its virial radius. Subsequent, the group of NGC 4565, situated at a distance of 13 Mpc, has a virial radius of 343 kpc, equal to 1.4°, leaving the stream at greater than 4.4 instances its virial radius. Lastly, the closest construction by way of virial radius is M 64, situated at a distance of 5 Mpc, with a virial radius of 224 kpc, equal to 2.34°. The stream would due to this fact be projected at a distance of two.8 instances this virial radius.

We explored the likelihood that the stream could possibly be brought on by a disturbance from a galaxy that overlaps with it within the line of sight. In Fig. 2 essentially the most outstanding candidates are recognized by identify. Particularly, the pair of overlapping galaxies UGC 08071 and LEDA 083688 could possibly be candidates to provide the stream. Nonetheless, our very deep photos don’t present any signal of asymmetry in them. Moreover, the radial velocities of UGC 08071 and LEDA 083688 are 6933 ± 2 km s⁻¹ and 8169 ± 2 km s⁻¹, respectively, and these objects are due to this fact situated greater than 1200 km s⁻¹ aside in velocity area (the radial velocity of galaxies in Coma ranges from 4000 to 10 000 km s⁻¹). This makes it extremely unlikely that they may have interacted at such a excessive velocity whereas leaving no asymmetry within the time throughout which the stream expanded. The opposite galaxies within the line of sight additionally present no considerable asymmetry that might be suitable with the incidence of the stream. We word that for a tidal-force calculation between galaxies within the line of sight, a distance worth between them is critical. Nonetheless, on this case, a relative distance worth isn’t simply obtained, contemplating that we’re in a clustered setting, and that very shut projections between galaxies would possibly solely be obvious. This is able to imply that galaxies in shut projection could possibly be separated by tens and even tons of of kiloparsecs. We due to this fact think about the potential presence of disturbance within the outer elements of galaxy haloes to kind the premise of essentially the most dependable strategy to figuring out the presence of interplay between galaxies.

We additional examine a attainable counterpart to a radio relic. Radio relics are diffuse buildings detected in radio by synchrotron emission continuously present in interacting galaxy clusters (see a evaluation by van Weeren et al. 2019). Notably, these radio relics are sometimes discovered within the peripheral areas of galaxy clusters, with morphologies just like these of the stream (Feretti et al. 2012; Jee et al. 2015). Though no optical counterpart has been discovered for these radio relics by earlier works, as a result of excessive floor brightnesses that we discover on this work, it’s fascinating to search for a counterpart to a radio relic. Nonetheless, we don’t establish a counterpart within the deepest and most up-to-date knowledge in Coma by Bonafede et al. (2022).

From this evaluation, we conclude that the stream is embedded inside the area of affect or virial radius of the Coma Galaxy Cluster, and doesn’t overlap with the virial radius of every other construction within the line of sight. No different galactic affiliation, comparable to a gaggle or cluster, overlaps with the placement of the stream, and there’s no galaxy within the line of sight that could possibly be the origin of the stream. This means that the stream is most definitely related to Coma and that there isn’t any different specific galaxy or galactic affiliation that may clarify its clearly disturbed morphology.

4. Evaluation

4.1. Photometry

We first analyzed the photometry utilizing the HERON knowledge. Within the prime panel of Fig. 4, we present a composite shade picture with each g and r bands from HERON. This picture is beneficial for visualizing the total extent of the stream and its morphology. The obvious measurement in size and width of 18.5 × 1 arcmin by visible inspection corresponds to roughly 510 × 25 kpc on the Coma distance. The center panels of Fig. 4 present the masking and subsequent binning (5 × 5 pixels, equal to five.58 × 5.58 arcsec) of those knowledge, permitting us to isolate the stream from exterior sources. We will see that the stream has a sure curvature. We estimate a radius of curvature of about 3620 arcsec, which is about 1°, and is equal to 1.7 Mpc. The Coma virial radius is 2.4 Mpc (Ho et al. 2022). Within the center panel of Fig. 4, we point out with dashed strains the contours of an annular aperture of 45 arcsec in width with this calculated radius of curvature. This aperture is the width at which the stream is detected within the HERON knowledge, corresponding roughly to a floor brightness of 30 magazine arcsec⁻² within the r band (the shallowest of the HERON knowledge; see Sect. 2.1). This aperture is similar because the one utilized in Sect. 3.2 to discover the potential IR emission of the stream.

Fig. 4. Pictures and photometric profiles with HERON knowledge. High panel: composite shade picture with HERON in g and r bands. The high-contrast grey background is constructed with the sum g + r picture. Center panels: high-contrast photos in the identical discipline as the highest panel in g, g + r, and r. Sources exterior to the stream have been masked and the picture was then rebinned to five × 5 pixels. The area sure by inexperienced dashed strains within the g + r picture marks the place of the stream. Backside panel: floor brightness profiles of the stream alongside the aperture indicated within the g + r picture. HERON g and r bands are proven in blue and purple, respectively, with an error of 1σ. Grey areas are spatial areas alongside the stream, that are discarded as a result of absence of sign produced by the masking from exterior sources.

We use this aperture on the masked picture to derive g and r band photometric profiles alongside the stream, that are proven within the decrease panel of Fig. 4. Due to the robust fluctuations within the profiles, we clean them with a Gaussian kernel of roughly 10 binned pixel items with the intention to get hold of a enough signal-to-noise ratio (S/N) within the profile. We calibrate the zero-flux sky stage within the area adjoining to, however sufficiently removed from, the stream. We discover common floor brightnesses alongside the stream size of roughly 29.5 magazine arcsec⁻² within the g band and 29.0 magazine arcsec⁻² within the r band. The robust fluctuations of the photometric profiles of the stream are as a result of extraordinarily low floor brightness, along with the presence of masked areas, but additionally to attainable systematic results comparable to background fluctuation resulting from flat-fielding and sky subtraction.

Regardless of the plain fluctuations, we observe that the distinction between the g and r photometric profiles is comparatively fixed. Determine 5 reveals the distribution of pixel shade values for the stream. This latter faithfully follows a Gaussian operate, suitable with a relentless shade that might correspond to the colour of the stream. To acquire the typical shade and error, we calculate the imply worth and error utilizing a 3σ strong imply, yielding g − r = 0.53 ± 0.05 magazine. This shade not directly signifies {that a} potential lensing of a high-redshift background supply amplified by Coma will be dominated out, as a high-redshift supply ought to seem a lot redder in g − r shade, and moreover, Coma is just too close by to behave successfully as a lens. In complement to this, we match the distribution with a Gaussian operate that gives an equal worth (see Fig. 5). With a view to get hold of a pseudo shade g − L with which to narrate the photometric magnitudes between HERON (g and r bands) and WHT (L band), we constructed a picture with the typical of the g and r bands. Utilizing this pseudo L band, we carried out the same evaluation, which yielded g − L = 0.32 ± 0.03 magazine.

Fig. 5. Histogram of g − r shade utilizing HERON knowledge on the chosen aperture for the Large Coma Stream (see Fig. 4). The strong purple line reveals the most effective match to a Gaussian operate. The dashed purple vertical line marks the imply shade calculated with a 3σ resistant imply.

We now give attention to the evaluation of the WHT knowledge, with larger nominal depth and higher decision, albeit solely out there within the central area of the stream. Determine 6 reveals a photometric profile alongside the cross-section of the stream. The left panel reveals a high-contrast picture binned 5 × 5 from the unique pixel measurement of 0.2667 arcsec, giving at a pixel scale of 1.334 arcsec. The central panel, reveals this identical picture with masking utilized to cover exterior sources to the stream. This masking is carried out with a mix of SExtractor, which aggressively hides primarily sources of small sizes (DETECT_THRESH = 0.3), and a guide masking with vast round apertures hiding bigger galaxies and their anticipated haloes that might seem even under the floor brightness detectable visibly within the photos. After this masking, the pictures are binned at 1.334 arcsec pix⁻¹, permitting the diffuse mild to emerge effectively (see Román et al. 2021, for the same processing).

Fig. 6. Floor-brightness photos and profiles with the WHT knowledge within the luminance filter. Left panel: binned picture at a measurement of 5 × 5 pixels (equal to 1.333 × 1.333 arcsec) color-coded in floor brightness and oriented in order that the stream seems vertically. Center panel: just like left panel however with all exterior sources masked after which binned to five × 5 pixels. Proper panel: photometric profile within the luminance band L (roughly equal to g + r) within the cross part (left-right) route. The grey error areas correspond to 1σ. The widths within the transverse route of the three panels coincide in spatial scale.

Given the practically straight morphology of the stream on this partial area, we venture the mixed flux on this route, acquiring a photometric profile alongside the cross-section. That is carried out within the area of the picture with a nominal depth of fainter than 31.0 magazine arcsec⁻² within the L band (see Fig. A.1), avoiding the outermost areas, which as a result of dithering of the observations have a decrease S/N. The entire area proven within the central panel is the one used for the photometric profile. For averaging, we use the median worth alongside the stream route, with errors calculated as 1σ. We introduce a tilt airplane that matches the sky background with the intention to get rid of a small gradient current within the profile. The obtained profile is smoothed with a three-pixel Gaussian kernel to get rid of small fluctuations from the results of masking.

The utmost floor brightness of the stream is roughly 29.2 magazine arcsec⁻² within the L band. Utilizing the beforehand calculated g − L shade of 0.32 magazine, this may translate right into a most floor brightness of roughly 29.5 magazine arcsec⁻² within the g band, agreeing with the values obtained from the HERON knowledge, and giving confidence to the outcomes. The WHT profile reaches reliably right down to a floor brightness of about 32 magazine arcsec⁻², past which spurious fluctuations start to indicate up, in all probability resulting from sky fluctuations and masking residuals. The form of the profile is roughly straight in its slope, and is due to this fact suitable with an exponential decay. By analyzing this profile in flux items, we will establish an roughly Gaussian form (see Fig. 7). By modeling this flux profile with a Gaussian operate, the 1σ fitted width has a price of 20.1 arcsec or 9.3 kpc. The FWHM is 42.3 arcsec or 19.5 kpc. We discover a small asymmetry within the profile, the place on the left facet (towards the route the place Coma is situated) the profile reveals a slight extra. Nonetheless, this asymmetry isn’t robust, and is doubtlessly brought on by the masking residuals of close by galaxies situated in that area.

Fig. 7. Photometric profile equal to that in the best panel of Fig. 6 however in arbitrary flux items. The dashed purple line signifies the most effective match to a Gaussian operate (see textual content). The grey error areas correspond to 1σ.

Because of the quite a few sources overlapping the stream, a direct flux measurement isn’t attainable. With a view to get hold of an built-in magnitude, we use the great match to a Gaussian profile to mannequin the full flux. To this finish, we assume the typical profile to be that obtained within the evaluation of Fig. 7 with the intention to combine it alongside the estimated size of 510 kpc (see Fig. 4). We think about this a comparatively good approximation due to the roughly fixed floor brightness alongside your entire size of the stream. The worth produced is L = 20.90 ± 0.12 magazine, which corresponds to g = 21.22 ± 0.15 magazine in response to the colour g − L = 0.32 ± 0.03 magazine calculated above. Absolutely the magnitude of the stream in response to this mannequin on the distance of Coma would due to this fact be L_g = −13.78 ± 0.15 magazine. Following mass to mild ratio predictions by Roediger & Courteau (2015), this interprets to a stellar mass of M_⋆ = 6.8 ± 0.8 × 10⁷ M_⊙. We word the potential presence of uncertainties on the built-in photometric portions, each due to systematic errors resulting from modeling and attainable nondetection of additional construction in our knowledge. Due to this fact, built-in magnitudes are to be thought of as order-of-magnitude estimates, and as decrease limits on the mass of each the stream and its potential progenitor.

Based on the expected mass–metallicity relations for a galaxy of this vary of stellar mass (Panter et al. 2008; Simon 2019), a metallicity of roughly Z/H = −1 is anticipated. The colour g − r = 0.53 ± 0.05 magazine would due to this fact point out that that is an outdated, passive dwarf galaxy in response to single stellar inhabitants fashions by Vazdekis et al. (2015; see additionally Román & Trujillo 2017).

4.2. Comparable buildings in simulations

To acquire an concept of how such buildings might come up in ΛCDM, we use the Illustris-TNG50 (TNG50 for brief) simulations to perception the existence of comparable streams in clusters. The TNG50 simulation has a field measurement ∼50 Mpc on a facet and a baryonic mass-per-particle of ∼8.5 × 10⁴ M_⊙. TNG50 is a part of the Illustris-TNG suite of galaxy simulations in several volumes, which all embrace gravity, magnetohydrodynamics, and a therapy for essentially the most related bodily processes concerned in galaxy formation, comparable to star formation, steel enrichment, and stellar and black gap suggestions (Pillepich et al. 2018; Nelson et al. 2019).

It’s tough to estimate the frequency with which one ought to anticipate to look at the sort of skinny construction seen for the Large Coma Stream inside the ΛCDM mannequin. The formation of those skinny buildings will rely totally on two circumstances: timing of the merger or infall, and the intrinsic properties of the progenitors. Tidal disruption that units in too early with respect to the current time at z = 0 – at which we analyze the cluster – or progenitors which have overly prolonged intrinsic sizes will result in stellar streams which might be too vast to be akin to the Large Coma Stream. However, satellite tv for pc infall that’s too late or intrinsic sizes which might be too compact will result in inadequate disruption to generate stellar streams which might be so long as this stream.

Whereas the comparatively small field measurement in TNG50 doesn’t enable for clusters as huge as Coma to exist within the simulated quantity, the excessive numerical decision wanted to resolve the inside properties of the progenitors with an estimated mass of M_⋆ ∼ 10^8 − 9 M_⊙ makes the 50 Mpc field essentially the most sufficient to conduct our evaluation. From the TNG database, we use their friend-of-friends group info to establish spatially coherent teams (Davis et al. 1985), the details about haloes and subhaloes as offered by Subfind catalogs (Springel 2005; Dolag et al. 2009), and the SubLink merger bushes (Rodriguez-Gomez et al. 2015).

Probably the most huge cluster in TNG50 (group 0) has a virial mass of M₂₀₀ ∼ 2 × 10¹⁴ M_⊙ and a virial radius of r₂₀₀ ∼ 1200 kpc (virial portions are outlined on the radius the place the typical enclosed density is 200 instances the important density of the Universe). We word that the mass of Coma is roughly bigger by an element of ten, M₂₀₀ ∼ 2 × 10¹⁵ M_⊙ (Ho et al. 2022), which implies that that even analyzing the highest-mass cluster in TNG50 falls wanting an acceptable comparability. Nonetheless, our use of the TNG50 simulation is justified given the mass and spatial decision wanted to discover the presence of such slim streams with dwarf-mass progenitors as these inferred in our calculations.

With a view to establish related stream buildings, we chosen all dwarf galaxies within the stellar mass vary of M_⋆, max = 10^8 − 9 M_⊙ that interacted with our group in response to the SubLink merger bushes; we refer to those as progenitors. The choice is completed on the time of most stellar mass, M_⋆, max. This provides us a complete of 342 progenitors for group 0. We then targeted our search on progenitors which have misplaced a big fraction of their most stellar content material, f_⋆, sure < 45%, the place the sure fraction refers back to the fraction of stellar mass at z = 0 in comparison with the utmost stellar mass, as a result of we’re keen on progenitors of a large stellar stream. This lower is used as it’s near however smaller than half the utmost stellar mass of all satellites. In any case, the precise worth of the lower has little impression on our outcomes. For instance, selecting all progenitors retaining 50% of their mass would solely add two objects to the pattern, which have been recognized to be accreted very late and to go away remnants at a lot bigger distances than the noticed construction. We due to this fact determined to maintain our 45% mass lower as a very good proxy for our progenitors.

As well as, to establish progenitors that created buildings additional out within the halo of the cluster, we require that the median radius (r₅₀) of the stellar particles, right here merely outlined as the fabric that has been tidally eliminated in response to our substructure finder Subfind, be bigger than 800 kpc. Our closing pattern contains 19 progenitors. The primary panel in Fig. 8 reveals a picture created from the stellar particles of this pattern.

Fig. 8. Projected map of stellar remnants from the recognized dwarf progenitors with M⋆, max = 108 − 9 M⊙ that fell into essentially the most huge group simulated by the TNG50 simulation in response to our choice standards (see textual content). The map is color-coded by arbitrary floor brightness items, with a decision of 30 arcsec. Probably the most outstanding candidate for a Coma stream analog is highlighted, and the best panels present 2D projected maps of solely this remnant with a decision of 1 arcsec (akin to observational decision).

Encouragingly, inside this pattern, we discover one specific stream with traits which might be harking back to these of the Large Coma Stream. The analogous construction is highlighted in cyan in the primary panel of Fig. 8 after which proven in three perpendicular projections within the smaller panels on the best. Not solely is that this stream slim and really prolonged as within the case of the Large Coma Stream, but additionally beneath the best projection it seems as an virtually straight line (when the projection is near the orbital airplane). We word that the middle of curvature of the stream factors towards the middle of the cluster, as is the case for the Large Coma Stream. This could possibly be thought of as additional proof that certainly the Large Coma Stream belongs to Coma, as a result of the approximate middle of curvature coincides with the middle of the gravitational potential about which they orbit (Nibauer et al. 2023).

Our simulated analog has a progenitor stellar mass of M_⋆, max = 1.1 × 10⁸ and has misplaced ∼75% of its authentic mass at present day, which is outlined at snapshot 98 within the simulation, or redshift z = 0.009. Apparently, the formation historical past of this stream is considerably noncanonical, because the gravitational potential of the clusters isn’t the one setting answerable for the stellar stream formation. The tidal disruption resulting in the formation of this skinny stream appears to start out as a part of preprocessing in a smaller group setting. Our analog is first accreted into one other group with a virial mass of M₂₀₀ = 5.48 × 10¹¹ M_⊙ at infall time t_inf = 2.98 Gyr (z_inf = 2.2, outlined because the final time this dwarf galaxy was centered in its personal darkish matter halo). Solely at later instances, by t = 6.5 Gyr, does the analog be a part of the friends-of-friends group of the primary cluster, solely crossing its virial radius by t ∼ 12.7 Gyr, making it a comparatively latest accretion. On the closing time, the analog has gone via just one pericenter round the primary cluster, from which it just lately emerged and is on its option to the primary apocenter. The middle of the group the place the preprocessing occurred is at present greater than 1000 kpc away from our analog.

The numerical decision of TNG50 is inadequate to review the morphology of the stream intimately, for instance, by way of width or the sunshine profile throughout the stream, for which tons of of 1000’s of stellar particles can be wanted to faithfully hint the construction (in comparison with the ∼10 000 out there in TNG50 for this progenitor). As a substitute, this simulation gives a concept of a attainable formation situation for very slim and lengthy stellar streams in huge galaxy clusters, demonstrating that they do happen inside the present cosmological situation. Tailor-made idealized simulations can be the plain subsequent step to review and perceive the detailed properties of the stream by way of width, mild profile, and shade gradients.

5. Dialogue

The properties of the Large Coma Stream are exceptional. Its skinny and coherent morphology is harking back to chilly stellar streams noticed within the Milky Manner (e.g., Odenkirchen et al. 2003; Grillmair & Dionatos 2006; Balbinot et al. 2016) or streams within the Andromeda Galaxy (see a evaluation by Ferguson & Mackey 2016). Its floor brightness peaks at a really faint stage of 29.5 magazine arcsec⁻² within the g band (see Fig. 6), which is akin to the floor brightness of the Large Stream within the Andromeda Galaxy (Ibata et al. 2001). Nonetheless, the scale of the Large Coma Stream, with a detected size of roughly 510 kpc, is longer than any identified “big” stream within the literature (Ibata et al. 2001; Martínez-Delgado et al. 2009, 2021, 2023b). To the most effective of our data, no stellar stream of such measurement has ever been detected, nor has a stream of such low floor brightness been seen in floor photometry observations.

Earlier work in Coma and different galaxy clusters revealed the presence of tidally disrupted objects (Trentham & Mobasher 1998; Gregg & West 1998; Conselice & Gallagher 1999; Calcáneo-Roldán et al. 2000) exhibiting proof for the construct up of the intracluster mild by accretion of substructures. We now talk about some specific circumstances. First, the plume-like object found by Gregg & West (1998) within the coronary heart of Coma is 130 kpc lengthy and about 15−30 kpc vast. Its floor brightness is far brighter (μ_R = 25.7 magazine arcsec⁻²) than that of the Large Coma Stream, as is its built-in luminosity (R = 15.6 ± 0.1 magazine), and it’s of a a lot redder shade, specifically g − r ≈ 0.75 magazine (Gregg & West 1998). A easy calculation reveals that the stellar mass of this plume-like object is roughly 10¹⁰ photo voltaic lots, indicating that the remnant is a way more huge galaxy than a dwarf, and might be an elliptical galaxy, discarding a typical origin. Whereas the properties and areas of this plume-like object and the Large Coma Stream differ, it’s fascinating that each share the identical orientation, and that this orientation coincides of their alignment with the primary filament that feeds Coma (see Malavasi et al. 2020). Moreover, correlated accretion as a result of orientation of filaments and large-scale construction is anticipated to happen inside ΛCDM (e.g., Libeskind et al. 2014). One other fascinating object is the arc situated within the Centaurus cluster found by Calcáneo-Roldán et al. (2000). Its morphology is remarkably just like that of the Large Coma Stream, with a linear and featureless look, and a size of ∼170 kpc (Calcáneo-Roldán et al. 2000). Nonetheless, the floor brightness is significantly larger than that of the Large Coma Stream with μ_R = 26.1 magazine arcsec⁻². Calcáneo-Roldán et al. (2000) argue that this object could possibly be a tidally disrupted luminous spiral galaxy.

A number of newer research have been carried out in numerous galaxy clusters (Giallongo et al. 2014; Montes & Trujillo 2018, 2022; DeMaio et al. 2018; Montes et al. 2021; Jiménez-Teja et al. 2021). The floor brightness and backbone (as a result of shut proximity of the Coma cluster) achieved in our work are unprecedented, with one exception. The Burrell Schmidt Deep Virgo Survey (Mihos et al. 2017) is comparable by way of depth to our observations with the addition of a greater decision as a result of proximity of the Virgo Cluster. Certainly, numerous skinny stellar streams seem within the central area of Virgo; for instance, a pair of streams to the NW of M87 with lengths of round 150 kpc and equally skinny morphologies and widths of on the order of tens of kiloparsecs (streams A and B by Mihos et al. 2005; Rudick et al. 2010), in addition to a myriad of a lot smaller streams or tidal options related to totally different galaxies within the discipline of Virgo (Mihos et al. 2017).

A basic attribute that differentiates the Large Coma Stream from the streams detected in Virgo is that it’s not related to any specific galaxy however is a free-floating construction within the exterior areas of Coma. Dynamically chilly and intensely faint stellar streams are thought to kind via robust tidal fields in low-mass accretion occasions (Bullock & Johnston 2005), and within the case of galaxy clusters via interactions of low-mass galaxies passing via the inside area of the clusters (Romanowsky et al. 2012; Cooper et al. 2015). These streams are fragile, and dynamical instances of 1 or two instances the crossing time are sufficient to destroy them (Rudick et al. 2009). It’s due to this fact putting that the Large Coma Stream is a free-floating stream removed from the middle of the cluster, with such a coherent and fragile morphology.

We argue that the shortage of detected free-floating streams in Virgo could possibly be resulting from two components. First, Coma is rather more huge than Virgo, which means a a lot larger velocity dispersion, σ_v = 1008 km s⁻¹ for Coma (Struble & Rood 1999) versus σ_v = 638 km s⁻¹ for Virgo (Kashibadze et al. 2020), and so high-velocity galaxies are extra widespread in Coma. Second, a free-floating stream in Virgo can be anticipated to lie within the periphery of the cluster, however as a result of proximity of Virgo, the deep knowledge offered by Mihos et al. (2017) are restricted to its central area. If the same characteristic exists at a projected distance of the Large Coma Stream, specifically 0.8 Mpc, in Virgo, that stream can be exterior the footprint of those observations and due to this fact undetected. This makes it doubtlessly fascinating to discover the outermost areas of the Virgo cluster or different close by clusters in a seek for related free-floating streams analogous to the Large Coma Stream.

The presence of an analog stream within the TNG-50 simulation might point out that such free-floating streams with chilly or skinny morphology could also be widespread in galaxy clusters. There isn’t any assure that the Large Coma Stream was fashioned by a fancy interplay just like the one depicted by our analog. Nonetheless, it’s encouraging that we discover at the least one analog within the formation historical past of a galaxy cluster. Our evaluation signifies that whereas typical particles from this kind of progenitor tends to be wider and fewer coherent than the Large Coma Stream, at the least there may be one case the place the narrowness and size of the stellar stream are akin to it, suggesting that such buildings might happen in ΛCDM. The latest accretion of this analog is suitable with the fragility of this kind of construction, which, as talked about above, is usually capable of survive just one or two instances the crossing time in its orbit by the cluster, making it very seemingly that the Large Coma Stream is a latest accretion.

The potential presence of such skinny stellar streams of chilly morphology in galaxy clusters might lengthen the environmental vary of their examine from galactic to cluster scales. If chilly stellar streams of significantly bigger sizes than these discovered within the Native Group have been discovered to be widespread, this may make present projections of their detectability rather more optimistic (Pearson et al. 2019), and future observational work, together with by Euclid, the Rubin Observatory, the Nancy Grace Roman House Telescope or ARRAKIHS, shall be crucial with the intention to unveil related buildings in galaxy clusters and the properties of each the Large Coma Stream and potential new discoveries.

One of many imminent and most impactfull functions of the examine of chilly stellar streams is expounded to the opportunity of testing the shapes of the darkish matter haloes and the subhalo distribution of their hosts, because the presence and variety of subhaloes is finally outlined by the properties of darkish matter particles (Ibata et al. 2002; Carlberg 2012; Erkal & Belokurov 2015). Ongoing work consists of the evaluation of the morphology and kinematics of chilly stellar streams within the Milky Manner, with the target of tracing the worldwide gravitational potential and in addition analyzing the attainable impression of a low-mass darkish matter subhalo that might perturb these streams each morphologically and kinematically (Erkal et al. 2016; Banik & Bovy 2019; Ibata et al. 2020; Banik et al. 2021).

The out there observational knowledge for the Large Coma Stream are inadequate in each decision and depth and due to this fact don’t enable an in depth evaluation of this stream. We recall that the utmost decision of our knowledge is roughly 1.2 arcsec FWHM, which is equal to 550 laptop on the Coma distance. Moreover, radial velocity measurements of particular person stars are basic to those analyses (Pearson et al. 2022). Whereas present instrumental capabilities don’t enable for such analyses, the brand new technology of extraordinarily large-aperture telescopes might have enough observational capabilities for these research.

6. Abstract

• The properties of the Large Coma Stream are putting: a most floor brightness of μ_g = 29.5 magazine arcsec⁻² and a size of 510 kpc. This makes it the faintest stream ever detected by floor photometry. The stellar mass is estimated to be M_⋆ = 6.8 ± 0.8 × 10⁷ M_⊙ with a shade of g − r = 0.53 ± 0.05 magazine, which is in step with a passive dwarf galaxy being the potential progenitor for the Large Coma Stream. We don’t establish any potential galaxy remnant or core, and the stream construction seems featureless in our knowledge.

• The Large Coma Stream is orders of magnitude fainter in floor brightness than earlier tidal options found in Coma and different clusters (Trentham & Mobasher 1998; Gregg & West 1998; Conselice & Gallagher 1999; Calcáneo-Roldán et al. 2000). It’s comparable in floor brightness to the skinny streams detected in Virgo (Mihos et al. 2017), nonetheless not like these, the Large Coma Stream doesn’t look like related to any specific galaxy, showing as a free-floating characteristic within the outer areas of Coma.

• By means of evaluation of the Illustris-TNG50 simulation, we discover a remarkably related analog, suggesting that such big, extraordinarily faint, and free-floating skinny stellar streams might exist in galaxy clusters in response to Λ-CDM.

This work reveals a glimpse of the sort of buildings ready to be found within the ultralow-surface-brightness Universe. These buildings, such because the Large Coma Stream, present promising properties in revealing the continued hierarchical meeting of galaxy clusters and doubtlessly unveiling the final word nature of darkish matter.

Acknowledgments

References

Appendix A: Publicity instances and depth within the WHT knowledge

The left panel of Fig. A.1 reveals the publicity time footprint for the WHT knowledge. With a view to present a map of floor brightness limits, we carried out the correlation between the usual deviation for pixels with equal publicity time and the publicity time. This correlation is proven graphically in Fig. A.2. The parameters of the most effective match are

Fig. A.1. Maps of publicity time (left panel) and equal limiting floor brightness (proper panel) for the WHT knowledge within the luminance band (equal to g + r SDSS filters). Pictures cowl a 14.15 x 17.67 arcmin rectangle. North is up, east to the left.

Fig. A.2. Linear correlation between publicity time and floor brightness limits measured as 3σ in 10×10 arcsec containers for the WHT knowledge. The blue line marks the correlation knowledge obtained. The black dashed line marks the most effective match of the correlation (see textual content).

measured as 3σ in 10×10 arcsec containers. By way of this obtained relation, we will make a floor brightness map utilizing the publicity time values for every pixel. This map is proven in the best panel of Fig. A.1.

All Figures

Fig. 1. Common view of the Large Coma Stream and its location within the Coma Cluster. Backside: Colour composite HERON picture within the g and r bands. The darkish background is constructed with the sum picture. Uper proper: WHT picture of the Large Coma Stream in L luminance (darkish background) on a shade picture utilizing g and r bands from the DECaLS survey. Higher left: Zoom onto the central area of the WHT picture.

In the text

Fig. 2. Comparability between optical point-like supply density and far-IR emission within the central area (13.5 × 7.6 arcmin). High panel: WHT picture within the luminance L filter shade coded in floor brightness in response to the higher shade bar. Center panel: density of detected point-like sources within the area with WHT knowledge. Decrease panel: 250 μm counterpart with the Herschel area telescope. The picture is shade coded in S​ν in response to the decrease shade bar. The dashed strains mark elliptical floor brightness contours of roughly μL = 26 magazine arcsec−2 for the galaxies named within the prime panel, and μL = 29.5 magazine arcsec−2 for the placement of the Large Coma Stream.

In the text

Fig. 3. Graphical illustration of galactic associations within the line of sight of the Large Coma Stream. Teams and clusters of native galaxies (Vrad < 3500 km s−1) and their obvious virial radii are represented with grey circles. Galaxies with redshift within the vary of 3500 km s−1 < Vrad < 10 000 km s−1 are represented with black dots. The obvious Coma virial radius is represented with a purple circle. The place and longitude of the Large Coma Stream is represented with a purple section.

In the text

Fig. 4. Pictures and photometric profiles with HERON knowledge. High panel: composite shade picture with HERON in g and r bands. The high-contrast grey background is constructed with the sum g + r picture. Center panels: high-contrast photos in the identical discipline as the highest panel in g, g + r, and r. Sources exterior to the stream have been masked and the picture was then rebinned to five × 5 pixels. The area sure by inexperienced dashed strains within the g + r picture marks the place of the stream. Backside panel: floor brightness profiles of the stream alongside the aperture indicated within the g + r picture. HERON g and r bands are proven in blue and purple, respectively, with an error of 1σ. Grey areas are spatial areas alongside the stream, that are discarded as a result of absence of sign produced by the masking from exterior sources.

In the text

	Fig. 5. Histogram of g − r shade utilizing HERON knowledge on the chosen aperture for the Large Coma Stream (see Fig. 4). The strong purple line reveals the most effective match to a Gaussian operate. The dashed purple vertical line marks the imply shade calculated with a 3σ resistant imply.
In the text

Fig. 6. Floor-brightness photos and profiles with the WHT knowledge within the luminance filter. Left panel: binned picture at a measurement of 5 × 5 pixels (equal to 1.333 × 1.333 arcsec) color-coded in floor brightness and oriented in order that the stream seems vertically. Center panel: just like left panel however with all exterior sources masked after which binned to five × 5 pixels. Proper panel: photometric profile within the luminance band L (roughly equal to g + r) within the cross part (left-right) route. The grey error areas correspond to 1σ. The widths within the transverse route of the three panels coincide in spatial scale.

In the text

	Fig. 7. Photometric profile equal to that in the best panel of Fig. 6 however in arbitrary flux items. The dashed purple line signifies the most effective match to a Gaussian operate (see textual content). The grey error areas correspond to 1σ.
In the text

Fig. 8. Projected map of stellar remnants from the recognized dwarf progenitors with M⋆, max = 108 − 9 M⊙ that fell into essentially the most huge group simulated by the TNG50 simulation in response to our choice standards (see textual content). The map is color-coded by arbitrary floor brightness items, with a decision of 30 arcsec. Probably the most outstanding candidate for a Coma stream analog is highlighted, and the best panels present 2D projected maps of solely this remnant with a decision of 1 arcsec (akin to observational decision).

In the text

	Fig. A.1. Maps of publicity time (left panel) and equal limiting floor brightness (proper panel) for the WHT knowledge within the luminance band (equal to g + r SDSS filters). Pictures cowl a 14.15 x 17.67 arcmin rectangle. North is up, east to the left.
In the text

	Fig. A.2. Linear correlation between publicity time and floor brightness limits measured as 3σ in 10×10 arcsec containers for the WHT knowledge. The blue line marks the correlation knowledge obtained. The black dashed line marks the most effective match of the correlation (see textual content).
In the text