A co-rotating gas and satellite structure around the interacting galaxy pair NGC 4490/85

The interacting binary system NGC 4490/85 = Arp 269 is intermediate in mass between the Milky Way/Large Magellanic Cloud and the Large/Small Magellanic Cloud binary systems. It is a system of 14 known galaxies. We estimate the total Newtonian gravitating mass of the NGC\,4490/85 group to be M_T = (1.37 +- 0.43) times 10^{12} M_Sun using radial velocities and projected separations of its 13~candidate members. The system of dwarf satellites in the group demonstrates signs of coherent rotation in the same direction as that of the extended HI-shell surrounding the central interacting galaxy pair. The origin of this phase-space correlated population of star-forming late-type satellite galaxies raises questions in view of the planes-of-satellites observed around more massive galaxy pairs that are, however, made up of old early-type dwarf galaxies. We also report the detection of a candidate stellar Plume near the binary. This elongated structure of low surface brightness is a likely optical counterpart to the HI-tail north of NGC 4490/85, recently discovered by the FAST radio telescope.


INTRODUCTION
The discovery of planes of satellites around nearby luminous galaxies has become one of the most important developments in 100 kpcscale cosmology.A significant portion of Milky Way's (MW's) dwarf satellites are concentrated in a thin disk of satellites (DoS), the members of which show signs of co-rotation (Lynden-Bell 1976; Kroupa et al. 2005;Metz, Kroupa, & Libeskind 2008;Pawlowski & Kroupa 2020).A similar planes-of-satellites structure has been found around the nearest spiral galaxy M31 (Koch & Grebel 2006;Metz, Kroupa, & Jerjen 2007;Ibata et al. 2013).The rotating planar satellite structures of the Milky Way and of M31 appear to be correlated with each other (Pawlowski, Kroupa, & Jerjen 2013).This has been interpreted to be evidence for an encounter between the two galaxies about 8 to 10 Gyr ago (Bílek et al. 2018;Banik et al. 2022).Moreover, the evidence for planar structures composed of dwarf satellites has been noted to also exist around neighbouring galaxies: Centaurus-A (Tully et al. 2015;Müller et al. 2021), M81 (Chiboucas et al. 2013) andNGC 253 (Martínez-Delgado et al. 2021).All these 5 galaxies have a high K-band luminosity in the range of (0.5 − 1.0) × 10 11  K⊙ and are located in a sphere with a radius of 4 Mpc around us.In fact, every single galaxy brighter than   = 5 × 10 10  K⊙ in the nearest volume has been found to have a ★ idkarach@gmail.comflattened satellite-galaxy system.The MW, M31 and NGC 253 systems have a ratio of thickness to diameter of about 0.1, being seen nearly edge-on, while the Cen A and M81 systems are observed at an inclination.In addition to the satellite-systems within a few Mpc distance of us, a survey of regions spanning 150 kpc around galaxies within a redshift  < 0.05 shows host galaxies to prefer, with 99.994 per cent confidence, to have phase-space correlated satellite systems (Ibata et al. 2014(Ibata et al. , 2015)).Additional flattened and disk-like satellite systems have been reported (Heesters et al. 2021;Crosby et al. 2023).
Here we present evidence for the presence of co-moving satellites around the spiral galaxy NGC 4490 with a K-band luminosity of 1.9 × 10 10  K⊙ .
The paper is organised as follows: Section 2 presents the basic properties of the 14 dwarf galaxies forming a group together with NGC 4490.Section 3 presents some peculiar features of the group.Section 4 reports the discovery of a new candidate stellar structure in the vicinity of the NGC 4490/85, which we call the "Plume".Section 5 contains a discussion and the conclusions.

PROPERTIES OF THE NGC 4490/85 GALAXY GROUP
The spiral galaxy NGC 4490 together with its neighbour, NGC 4485, form the known pair Holm 414 = Arp 269 = VV 30 = KPG 341.The galaxies NGC 4490 and NGC 4485 have, respectively, radial velocities of 623 km s −1 and 517 km s −1 in the Local Group rest frame.According to the Extragalactic Distance Database (=EDD, Anand et al. 2021), the pair is located at a distance of 8.91 Mpc, which we use in our calculations.Thus 1 ′ = 2.59 kpc at that distance.NGC 4490 and its in-contact-neighbour, NGC 4485, have K-band luminosities of, respectively, log 10 ( K / K⊙ ) = 10.28 and 8.99 (Table 1 below).For comparison, the corresponding log-luminosities of M31, the MW, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are, respectively, 10.73, 10.78, 9.42 and 8.85 (Karachentsev et al. 2013a) 1 .Thus, given their luminosities, the NGC 4490/85 pair is intermediate between the MW/LMC and the LMC/SMC interacting binaries.The projected on-sky distance between NGC 4490 and NGC 4485 is 8.8 kpc.
The group of galaxies around NGC 4490 has in total currentlyknown 15 proposed members as listed in Table 1.The columns of Table 1 contain: (1) -the name of the galaxy: (2) -equatorial coordinates in degrees; (3) -super-galactic coordinates; (4)morphological type in de Vaucouleurs digital scale; (5) -distance to the galaxy; (6) -the method by which the distance is estimated: via the tip of the red giant branch (trgb), by the Tully-Fisher relation (TF), by radial velocity of the galaxy in the Numerical Action Method (NAM) (Shaya et al. 2017), by probable membership in the group (mem); (7) -radial velocity of the galaxy relative to the Local Group centroid; (8) -luminosity of the galaxy in the -band; (9) -projected separation of the galaxy from NGC 4490; (10)radial velocity of the galaxy relative to NGC 4490; (11) -orbital estimate of the total Newtonian gravitating mass of the group via each satellite, where  is the gravitational constant.The estimate of   assumes an isotropic distribution of orbits of satellites with an average eccentricity ⟨ 2 ⟩ = 0.5 (Karachentsev & Kashibadze 2021).The values given in Table 1 are taken from the latest version of the Updated Nearby Galaxy Catalog (=UNGC) (Karachentsev et al. 2013a) available at www.sao.ru/lv/lvgdb.Links to individual distance estimates are provided in the last column of the table and notes to it.It should be noted here that for the dominant member of the group, NGC 4490, the EDD database (Anand et al. 2021) gives a trgb-distance of 7.07 Mpc (rather than 8.91 Mpc which is the distance of NGC 4485 adopted here).In this case, the components of the interacting pair NGC 4490/85 would be separated by a 3D distance of 1.84 Mpc, which would question them being a physical pair and would disfavour a relatively recent intense interaction of the galaxies.Analysis of the color-magnitude diagram presented in EDD shows that the position of the trgb on it is determined unreliably.Therefore, we adopted a single value of 8.91 Mpc for both components of the pair.
Relative to NGC 4490, the 12 companions (Table 1) with measured radial velocities have an average velocity of ⟨Δ⟩ = −27 ± 26 km s −1 .The average distance of 5 companions with accurately measured trgb-distances is 8.80 ± 0.27 Mpc, in agreement with the adopted distance of 8.91 Mpc for the central galaxy pair.This can be regarded as evidence that the galaxies in Table 1 (except Dw 1224+39) are real members of a single group.Elmegreen et al. (1998) took deep images of the NGC4490/85 pair with the 0.6-m Burrell telescope and noted several tidal features around the object and star-forming regions.Huchtmeier et al. (1980) 1 For the up-to-date Local Volume database see www.sao.ru/lv/lvgdb/ .and Clemens et al. (1998) investigated this interacting pair in the HI 21-cm line using the 100-m Effelsberg radio telescope and the Very Large Array (VLA).They found that the pair is immersed in a common prolate HI-shell, the size of which reaches 60 kpc.The last authors suggested that the distribution of neutral hydrogen can best be explained by a galactic-scale bipolar outflow of HI driven by supernovae in NGC 4490.The recent deeper HI observations with the Five-Hundred-meter Aperture Spherical radio Telescope (FAST) demonstrate that the HI-envelope has an extension of more than 100 kpc (Liu et al. 2023).At the northern end of the HI-shell, the authors found an HI-tail that stretches in the direction of the nearby dwarf galaxy KK 149.
The distribution of the 15 candidate members of the NGC 4490/85 group is presented in Fig. 1 with circles, the sizes of which correspond to the luminosity of the galaxy with color indicating the galaxy radial velocity according to the scale in the left upper corner.The numbers near the galaxies correspond to radial velocity differences in km s −1 relative to the central galaxy NGC 4490.The new dwarf system, Plume (see Sec. 4), is shown by the asterisk.Two dwarf galaxies without measured velocities are marked by grey circles.The small ellipse in the center of Fig. 1 reproduces the size and orientation of the HI-shell around the interacting pair NGC 4490/85 according to the data by Liu et al. (2023).The large ellipse encloses the main body of the group.
The group of galaxies around NGC 4490 has the following parameters: an average projected separation of satellites ⟨  ⟩ = 182 kpc, a mean-square radial velocity of satellites   = 85 km s −1 , the average estimate of the total Newtonian gravitating mass ⟨  ⟩ = (1.37±0.43)×10 12  ⊙ .According to Tully (2015), the total (virial) Newtonian mass of a group is related to the virial radius as (2) This gives for the NGC 4490 group the value   = 239 kpc, marked with a green circle in Fig. 1.With a total luminosity of the group members Σ  = 2.20 × 10 10  K⊙ , the total Newtonian mass-toluminosity ratio of the group is This value is about half the global ratio of the mean cosmic density of matter in the standard ΛCDM cosmological model, 4.38 × 10 10  ⊙ / Mpc 3 with Ω  = 0.3, to the observed mean density of -band luminosity, (4.3 ± 0.2) × 10 8  K⊙ /Mpc 3 (table 4 in Driver et al. 2012), equal to (102 ± 5)  ⊙ / K⊙ .Note that with   ≈ 1.4 × 10 12  ⊙ within  ≈ 240 kpc, the dynamical acceleration is  ≈ 0.03  0 , where  0 ≈ 3.9 pc/Myr 2 is Milgrom's critical acceleration.The Milgromian gravitating mass thus comes out to be   = (0.03 ) 2  0 / ≈ 4 × 10 10  ⊙ , i.e.   = (/0)   ≈ 0.03   , such that the K-band mass to light ratio of the system is about 2  ⊙ / K⊙ in Milgromian dynamics (Milgrom 1983).Away from the main body of the NGC 4490 group there is a dwarf galaxy Dw 1224+39.It is located 15 ′ North of the spiral galaxy NGC 4369 = Mrk 439 that has a radial velocity of   = 1038 km s −1 and a TF-distance of 29.7 Mpc, and is possibly a satellite of NGC 4369.
The group in question is located near the Local Supercluster equator, where the number density of galaxies at the line of sight is rather high.Nevertheless, the NGC 4490 group appears to be quite isolated.There are no other galaxies with radial velocities in the range (450-750) km s −1 in the indicated area of size, 7 • × 4 • .According to Karachentsev et al. (2013b), the spatially closest neighbour to the NGC 4490 group is the group of 18 galaxies around NGC 4258 (12 ℎ 19  + 47 • 18 ′ ) at a trgb-distance of 7.66 Mpc from the observer.The spatial separation between the group centers is 1.56 Mpc.

THE SYSTEM OF SATELLITES AROUND NGC 4490
The group of galaxies around the interacting pair NGC 4490/85 is characterised by the following features.i.The group can be classified as a "fossil" group because the luminosity of each satellite does not exceed 1/20th of the luminosity of the principal galaxy.This difference in luminosities will intensify if the components of the central pair were to merge.This is expected to occur on a time scale of ≈ 5 × 10 8 years, provided both are immersed in dark matter halos (but see Kroupa 2015;Roshan et al. 2021;Haslbauer et al. 2022;Kroupa et al. 2023).
ii. Almost the entire population of the group consists of latetype galaxies with ongoing star formation.Only one dwarf galaxy, Dw 1229+41, near the interacting pair, is classified by us as a quiescent dSph object.Within the Fig. 1 area, we did not find other dSph galaxies with a luminosity brighter than   = 3 × 10 6  K⊙ .
iii.The satellite system is stretched along the super-galactic plane.In the equatorial coordinates, the positional angle of its major axis (the large ellipse) is PA= 158 • ± 3 • .The positional angle of the HI-shell around the central interacting pair (small ellipse in Fig. 1) is practically oriented in the same direction, PA= 159 • ± 2 • .It is noteworthy that the major axis of the Plume (Sec.4) has also a similar direction, PA= 155 • ± 5 • .
iv.The satellite system reveals a distinct asymmetry in the distribution of radial velocities relative to the main galaxy NGC 4490.All the objects on the northern side of the group (bluish circles on the right side of Fig. 1) have negative relative velocities, whereas all the objects on the opposite side (reddish circles) have positive ones.This suggests the system of satellites to be arranged in an inclined similar rotationally supported DoS structure as observed around the MW, M31 and Cen A.
v.Moreover, as is seen on VLA-and FAST-maps, the HI-shell around NGC 4490/85 is also characterised by an increase in radial velocity from the northern side to the South, conforming with the satellite system.
The listed geometric and kinematic coincidences do not look accidental.The observational data show the gas component of the central part of the group and the system of satellites as a whole to have mutual coherent motions.

THE PLUME: THE DISCOVERY OF A NEW STELLAR STRUCTURE NEAR NGC 4490
About a dozen dwarf galaxies with radial velocities close to the velocity of the centroid of the NGC 4490/85 pair were known in its vicinity.Based on data from a recent DESI Legacy Imaging Surveys of the sky (Dey et al. 2019), Karachentsev & Kaisina (2022) performed a search for new dwarf satellites of NGC 4490/85 and found three objects of low surface brightness that could be companions of the pair.The recent publication (Liu et al. 2023) gave us a reason to repeat the search for faint dwarfs around NGC 4490 using the DESI Legacy Imaging Survey data.As a result, we discovered an object of extremely low surface brightness, which is located in the region of the northern HI-tail indicated by Liu et al. (2023) on their figures.The object has dimensions of ≈ 4 ′ × 1 ′ and is elongated in the direction of NGC 4485 and KK 149.It will be important to quantify this object using other deep imaging surveys (such as CFIS-r at the CFHT, Ibata et al. 2017).It is not an instrumental artefact, but could in principle be MW cirrus.However, its location in the direction of a HI tidal tail makes it a possible candidate new stellar structure, a stellar plume (hereinafter refered to as the Plume), associated with the NGC 4490/85 system.Judging by its structure, the new object may have been a past dwarf galaxy, destroyed in the pair's gravitational field and surrounded by tidal material, being similar to the time-dependent models of such systems (Kroupa 1997;Casas et al. 2012).
The DESI Legacy Imaging Survey image of the object Plume can  of 4.2 ′ ×1.2 ′ , the integral magnitude of the Plume is  ≈ 16. m 9 with a central surface brightness in the -band of ≈ 27.m 5 /⊓ ⊔ ′′ .The basic parameters of the Plume are presented in Table 2.The magnitude of the HI-flux and the radial velocity of the Plume are estimated by us using the VLA-and FAST-maps presented by Clemens et al. (1998) and Liu et al. (2023).The HI-flux is very approximate due to unknown projection factors.Assuming a distance to the Plume of 8.91 Mpc, we roughly estimate its hydrogen and stellar masses as 2.0 × 10 7  ⊙ and 8.0 × 10 7  ⊙ , respectively.The latter can be larger by an order of magnitude for a young system if the galaxywide IMF varies systematically as indicated by other observations (Jerabkova et al. 2018).
The observational parameters of the Plume, given in Table 2, are poorly determined due to its very low surface brightness.Dedicated deep follow-up observations in different (, , , ) filters will be needed to establish Plume's spectral energy distribution and to clarify whether it is young, as expected for a stellar population recently born from gaseous debris.The physical dimension of the Plume is ≈ 10 kpc×2.5 kpc if it is at the distance of the NGC 4490/85 binary (Table 2).If this were to be the physical scale of this object, then it would be larger by a factor of ten than known tidal-dwarf galaxies of similar mass (c.f.fig. 2 in Dabringhausen & Kroupa 2013;Haslbauer et al. 2019).It is thus likely unbound, consisting of an evolved version of the type of star-forming regions and stellar populations observed to be in tidal debris extended over dozens of kpc in interacting galaxies.Examples of such tidal structures, plumes and streams are the putative tidal dwarf KK 208 (PC166170) near NGC 5236 with a Holmberg diameter of 5.9 arcmin (8.8 kpc) (Karachentsev et al. 2013a), the eastern tidal structure of NGC 5907 with a diameter of 12 arcmin (Lanzetta et al. 2023) corresponding to a linear dimension of 53 kpc at a distance of 14.3 Mpc, the western stream near NGC 5907 being fainter and about twice as extended.Other examples of such structures are the dog-leg tidal stream of NGC 1097 (Galianni et al. 2010), tadpole galaxies (Elmegreen et al. 2012), the Leo Triplet (Wu et al. 2022) and other interacting galaxies (Rodruck et al. 2023) and the umbrella-like stellar stream of NGC 922 (Martínez-Delgado et al. 2023).Such tidally-produced structures of low-surface brightness constrain the galaxy encounters that produced them which test cosmological structure formation theory (e.g.Kroupa 2015) and systematic surveys for them such as through The Stellar Stream Legacy Survey are underway (Martínez-Delgado et al. 2023).On the other hand, with a central surface brightness, ≈ 27.5 mag/square arcsec and an effective linear diameter of ≈ 10 kpc, the Plume might also classify as being an ultra-diffuse galaxy (UDG, van Dokkum et al. 2015), probably having been assembled during a past encounter between NGC 4490 and NGC 4485.We emphasise that the formation of UDGs remains not understood.
The HI peaks at an RA of about 12:30:00 (Liu et al. 2023), while the optical object is at 12:30:13, which is about 3' away.In most interacting systems able to produce tidal dwarf galaxies (TDGs), the very young TDG coincides with the peak of the HI.More generally, with rare exceptions, the optical and HI tidal features overlap in space in such freshly formed dwarf satellite galaxies.This is clearly not the case here, further pointing to the Plume being a stellar stream.In this interpretation, the question arises why the southern HI tail (to the lower left but off Fig. 2) which seems to have a similar column density as the northern one does not have an optical counterpart.

DISCUSSION AND CONCLUSION
The discovery of a hitherto not know stellar structure, the Plume, in the NGC 4490/85 group of galaxies is reported (Sec.4).The Plume might be part of a stellar stream or a UDG possibly formed during a past encounter between NGC4490 and NGC 4485 (Sec.4).The Plume needs dedicated follow-up observations to improve understanding of its nature.
This work also reports the discovery that the NGC 4490/85 group has a rotating and thus highly phase-space correlated population of satellite galaxies.The kinematic pattern observed in the NGC 4490 group indicates a joint co-rotation of the system of satellites and the gas envelope surrounding the central interacting pair NGC 4490/85.Assuming regular rotation, the satellite system will have a significant angular momentum  sat = Σ  *   |Δ |.We estimated  sat , comparing it with the angular rotational momentum of the principal galaxy,  N4490 =  *    26 .Here, the amplitude of the galaxy rotation,   = 86 km s −1 , and the galaxy optical radius,  26 = 8.1 kpc, are taken from UNGC (Karachentsev et al. 2013a).Assuming the same stellar mass-to-luminosity ratio for the central galaxy and for its satellites, we obtained the value  sat / N4490 ≈ 2, which is approximate due to uncertain projection factors in the motion of the satellites.Thus, the total angular momentum of the satellites turns out to be comparable with the momentum of rotation of the dominant galaxy in the group.
The satellite galaxies not only appear to lie in a rotating plane, but also seem to be concentrated in a bar-like configuration, which is slightly offset from the line  SG = 6 o .0(see Fig. 1).Moreover, from the data in Table 1 the mass of the satellite system may be concentrated on the east (left) side of this configuration.If this is true, then it seems likely that the satellite system would exert a tidal (and  = 1) force on the outer HI distribution (which also seems aligned along about the same line).Thus, another source of tidal HI distortion could be the outer satellite system (see Criswell & Struck 2019 for a discussion of such effects).
The dwarf satellites may be in primary infall towards the massive central galaxy from both its sides along a putative diffuse cosmic filament.Such an assumption implies the possible presence of more distant companions at distances ≈ (2 − 4)  , which, in principle, is accessible to observational verification.This explanation however raises the question where all the primordial dwarf satellite galaxies are that ought to be evident in the dark matter halos of the NGC 4490/85 galaxy pair according to the ΛCDM model.
On the other hand, the system of phase-space correlated satellite galaxies around the NGC 4490/85 pair plus the co-rotating gas envelope is reminiscent of the similar arrangement of MW satellite galaxies and young halo globular star clusters in a vast polar structure that co-aligns and co-orbits with the gaseous Magellanic Stream (Pawlowski, Kroupa, & Jerjen 2013;Pawlowski & Kroupa 2020).The similarity of the angular momenta of the NGC 4490/85 satellites and the dominant galaxy pair may be due to the former forming as a population of tidal dwarf galaxies from the latter.Such a process of the formation of new dwarf galaxies in gaseous tidal tails produced by an encounter of two late-type galaxies has been documented through simulations (Wetzstein, Naab, & Burkert 2007).It has also been shown that the satellite distributions around the MW and of M31, on being correlated (Pawlowski, Kroupa, & Jerjen 2013), suggest their formation through a past encounter between the MW and M31 as shown by simulations (Bílek et al. 2018;Banik et al. 2022).The NGC 4490/85 satellite system differs from the other known phase-space-correlated satellite systems that are made up of old early-type dwarf-spheroidal galaxies, by being composed of late-type star-forming dwarfs.The satellites of NGC 4490/85 would therefore be a freshly-formed system of tidal dwarf galaxies.Theoretical work via computer simulations is needed to study if the orbit of NGC4485 around NGC4490 can have expelled tidal tails that are sufficiently massive to form the observed population of satellite galaxies sufficiently recently to allow them to be still star-forming.The observational finding that even the relatively low-mass interacting binary system NGC 4490/85 can have an associated phase-space correlated satellite systems composed of star-forming dwarf galaxies thus poses an interesting problem to understand theoretically.It might be related to the distribution of (the non-satellite) star-forming dwarf galaxies in a highly-symmetrical structure around the MW/M31 pair in the Local-Group (Pawlowski, Kroupa, & Jerjen 2013), a structure that has not yet found a theoretical understanding.
While the individual plane-of-satellite system or DoS around the MW is being understood to not be a challenge by it being "common (at the 1/231 level or at the 1 per 50 Mpc cubed level)" (Xu, Kang, & Libeskind 2023, see also Sawala et al. 2023), according to Asencio et al. (2022) the MW, M31 and Cen A phase-space correlated satellite systems are, combined, in 5.27  tension with the ΛCDM model.This is confirmed by Kanehisa, Pawlowski, & Müller (2023) who show mergers cannot produce correlated systems of pre-merger satellite galaxies.Correlated satellite systems are formed from tidal-dwarf galaxies though, with Haslbauer et al. (2019) therewith confirming the dual dwarf galaxy theorem for the ΛCDM structure-formation model.The real tension would be higher if the mutual correlation of the MW and M31 systems were taken into account.The additional two systems (M81, NGC 253) together with the present discovery of another highly phase-space correlated satellite plus circum-galactic gas system (NGC 4490/85), imply the planes of satellite problem to be an until now not solved failure of the current cosmological structure formation theory (Kroupa et al. 2005;Pawlowski 2018Pawlowski , 2021a,b;,b;Kroupa et al. 2023).

Figure 1 .
Figure 1.A view of NGC 4490 galaxy group in super-galactic coordinates.Dwarf companions of NGC 4490 with positive and negative radial velocities relative to the main galaxy are marked by coloured circles according to a velocity scale in the left upper corner.The circles size corresponds to the galaxy luminosity.The asterisk shows the position of the new stellar structure, the Plume (see Sec. 4).The small central ellipse indicates the HI-shell around the interacting pair NGC 4490/85.The large ellipse encloses the main body of the group.The virial radius of the group is shown by the green circle and corresponds to 239 kpc.

Figure 2 .
Figure 2. The high-contrast image of the interacting galaxy pair NGC 4490/85 and their dwarf satellites KK 149 and MAPS1231+42 from the DESI Legacy Imaging Survey.The image size is 39 ′ × 30 ′ , corresponding to 101 × 78 kpc at the adopted distance of 8.91 Mpc.North is up, East is left, red numbers indicating the right ascension and declination.The sequence of grey squares represents the faintest (light-blue) contour of the HI-envelope around the interacting pair according to fig. 1 in Liu et al. (2023).Their size corresponds to the dimension of the HI-pixels.The elongated low-contrast Plume under consideration is located 8' to the North-North-East from the image center.The large oval structures on the upper right side of the figure are due to reflection from a bright star outside the image.

Table 1 .
Properties of the NGC 4490/85 group members.The radial velocity errors are in the range of [1 -17] km/s.The two dwarfs without velocity estimates have a low surface brightness and will need to be observed in the future.