Distance and mass of the NGC 253 galaxy group
Igor D. Karachentsev, R. Brent Tully, Gagandeep S. Anand, Luca Rizzi, Edward J. Shaya
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Distance and mass of the NGC 253 galaxy group
Igor D. Karachentsev, R. Brent Tully, Gagandeep S. Anand, Luca Rizzi, and Edward J. Shaya Special Astrophysical Observatory, The Russian Academy of Sciences, Nizhnij Arkhyz, Karachai-Cherkessian Republic 369167, Russia Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA W. M. Keck Observatory, 65-1120 Mamalahoa Hwy, Kamuela, HI 96743, USA Astronomy Department, University of Maryland, College Park, MD 20743, USA (Received December 1, 2020; Revised; Accepted February 24, 2021)
Submitted to ApJABSTRACTTwo dwarf galaxies: WOC2017-07 and PGC 704814 located in the vicinity of the nearby luminousspiral galaxy NGC 253 were observed with the Advanced Camera for Surveys on the Hubble SpaceTelescope. Their distances of 3.62 ± ± . ± . M (cid:12) , giving a total-mass-to- K -luminosity ratio M orb /L K = (8 . ± . M (cid:12) /L (cid:12) . A notable property of NGC 253 is itsdeclined rotation curve. NGC 253 joins four other luminous spiral galaxies in the Local Volume withdeclined rotation curves (NGC 2683, NGC 2903, NGC 3521 and NGC 5055) that together have thelow average total-mass-to-luminosity ratio, M orb /L K = (5 . ± . M (cid:12) /L (cid:12) . This value is only ∼ Keywords: galaxies: dwarf — galaxies: distances and redshifts — galaxies: haloes — galaxies: indi-vidual (NGC 253) INTRODUCTIONBright spiral galaxies in Sculptor constellation form a diffuse association marked by de Vaucouleurs (1959) and Arp(1985). According to Jerjen et al. (1998) and Karachentsev et al. (2003), these galaxies: NGC 24, NGC 45, NGC 55,NGC 247, NGC 253, NGC 300, NGC 7793 and their dwarf companions are located in a filamentary structure, whichextends along the line of sight from the Local Group to a distance D ∼ K s = 3 . m (Jarrett etal. 2003) and the distance of 3.70 Mpc (Anand et al. 2021), the luminosity of NGC 253 corrected for Galactic andinternal extinction is L K /L (cid:12) = 10 .
98 dex, that exceeds the luminosity of the Milky Way or M 31.In the vicinity of NGC 253 within a radius of 15 ◦ ( ∼ V LG = 276 ± − (Koribalski et al. 2004). Accurate distances formost of them have been measured via the luminosity of the tip of red giant branch (TRGB) (Karachentsev et al.2003; Cannon et al. 2003; Sand et al. 2014; Toloba et al. 2016). Only two assumed dwarf satellites of NGC 253:WOC2017-07 (Westmeier et al. 2017) and 2DFGRS-S431Z = PGC 704814 (Colless et al. 2003) have not had reliabledistance estimates. In § Hubble Space Telescope (HST) . The distances
Corresponding author: Igor [email protected] a r X i v : . [ a s t r o - ph . GA ] F e b Karachentsev, Tully, Anand et al. measured by us confirm the association of both galaxies with the NGC 253 group. In §
3, updated information on thegroup membership is used to evaluate the mass of the NGC 253 group. TRGB DISTANCES TO WOC2017-07 AND PGC 704814We obtained
HST
ACS imaging of WOC2017-07 and PGC 704814 in both F606W and F814W bands (760s each)as part of the Every Known Nearby Galaxy survey (SNAP-15922, PI R. Tully). Color cutouts of these two galaxiesproduced with this data are shown in Figure 1. Both galaxies contain visible young and older stellar populations.WOC2017-07 is irregular and lacks clear definition, whereas PGC 704814 is roughly spherical in shape with at leastone very prominent young star cluster. The image for PGC 704814 contains numerous artifacts (“figure-eight ghosts”),that are caused by an extremely bright foreground star located in the ACS field of view (but not shown in the cutoutsin Figure 1). For each galaxy, we used DOLPHOT (Dolphin 2000, 2016) to produce PSF photometry with the .flc images, using the drizzled F814W image as the alignment reference frame. We cull these photometric catalogs toensure only resolved sources of the highest quality remain. For this work, we use the quality cuts modified fromMcQuinn et al. (2017), selecting stars with a signal-to-noise ratio ≥ ≤ F606W + Crowd
F814W ) ≤ .
8, and (Sharp
F606W + Sharp
F814W ) ≤ . m T RGB = 23.71 ± m T RGB = 23.74 ± D = 3 . ± .
18 Mpc for WOC2017-07,and D = 3.66 ± (Jacobs et al. 2009; Anand et al.2021). THE TOTAL MASS OF THE NGC 253 GROUPA summary of data on 18 galaxies belonging to the NGC 253 group and its vicinity is presented in Table 1. Its columnscontain: (1) galaxy name; (2) supergalactic coordinates; (3) morphological type on the de Vaucouleurs scale; (4) radialvelocity in km s − relative to the Local Group centroid as given in HypeLEDA (Makarov et al. 2014, http://leda.univ-lyon1.fr) with the standard error; (5) galaxy distance in Mpc from Extragalactic Distance Database, EDD (Anand et al.2021, http://edd.ifa.hawaii.edu); distances for Scl-MM-Dw1 and Scl-MM-Dw2 were derived by Sand et al. (2014) andToloba et al. (2016), respectively; (6) method used to determine the distance; a typical error of distance measurementvia TRGB is ∼ K s = max[log( L i /D i )] + C, i = 1 , , ....N, edd.ifa.hawaii.edu istance and mass of the NGC 253 galaxy group L i is a luminosity of the neighboring galaxy in the K -band, D i is its separation from the neighbor; ranking thesurrounding galaxies by the magnitude of their tidal force, F i ∼ L i /D i . The most significant neighbor is the “MainDisturber”, MD, where the constant C is chosen so that a galaxy with Θ = 0 is located at the “zero velocity sphere”relative to its MD. Consequently, the unrelated galaxies with a negative Θ are referred to as the population of the“general field”. (11) name of the Main Disturber; (12) orbital mass estimate via the given satellite, described below.All galaxies in Table 1 are ranked according to their angular separation from NGC 253.As seen from Table 1, the luminosity of principal galaxy NGC 253 exceeds the luminosity of its neighbors by morethan one order of magnitude. In a case when a group is dominated by one massive galaxy surrounded by a set of lighttest particles, one can use the “orbital” mass estimate (Karachentsev & Kudrya 2014): M orb = (32 / π )(1 − e / − G − (cid:104) ∆ V i R pi (cid:105) . Here, G is the gravitation constant, e is the prevailing orbit eccentricity, and ∆ V is the radial velocity difference of acompanion “i” at the projected separation R pi relative to the principal galaxy. Basing on N-body simulations, Barberet al. (2014) estimated the typical eccentricity value of (cid:104) e (cid:105) (cid:39) / M orb = (16 /π ) G − (cid:104) ∆ V i R pi (cid:105) or ( M orb /M (cid:12) ) = 1 . × (cid:104) ∆ V i R pi (cid:105) , where ∆ V and R pi are expressed in km s − and kpc, respectively. Individual values of M orb derived via differentcompanions are given in the last column of Table 1 in units of 10 M (cid:12) .The distribution of galaxies in the vicinity of NGC 253 is presented in Fig.3 in supergalactic coordinates. Assumedsatellites of NGC 253 with measured radial velocities are shown with solid symbols and assumed companions withoutradial velocities are indicated with open circles. The field galaxies with Θ < L K /L (cid:12) = 10 . , the typical virial radius is R v (cid:39)
300 kpc, and the radius of zero-velocitysphere is R (cid:39) . R v (Tully 2015b). The minor and the major circles in Fig.3 corresponds to R v = 4 . ◦
65 and R = 16 . ◦ R ) there are 8 satellites with measured radialvelocities. For one of them, PGC 704814, the velocity error is too large and we ignore this galaxy. For the 7 remainingcompanions of NGC 253, the mean radial velocity difference is (cid:104) ∆ V (cid:105) = − ±
17 km s − , the radial velocity dispersionis σ v = 42 km s − , and the mean projected separation is (cid:104) R p (cid:105) = 465 kpc. The average estimate of orbital mass via 7satellites is M orb = (8 . ± . M (cid:12) , that yields the mass-to-luminosity ratio M orb /L K = (8 . ± . M (cid:12) /L (cid:12) . Thelatter value is four times less than the ratios of (27 ± M (cid:12) /L (cid:12) for the Milky Way and (33 ± M (cid:12) /L (cid:12) for M 31(Karachentsev & Kudrya 2014).With such a low halo mass for NGC 253, the expected virial radius should not be 300 kpc, but rather ∼
200 kpc(Tully 2015a). Then only 5 satellites are inside of the sphere of a radius R ∼
700 kpc. For them, the dispersion ofradial velocities, σ v = 44 km/,s − , and the orbital mass estimate, M orb = (6 . ± . M (cid:12) is little changed, althoughthe average projected separation of 5 satellites drops to (cid:104) R p (cid:105) = 313 kpc. It should be noted that the location of thesesatellites appears to be very asymmetric with respect to the principal galaxy.Interestingly, the field galaxies with Θ < H = 75 km s − Mpc − and σ v = 40 km s − . According to Karachentsev et al. (2003), the Hubbleflow around NGC 253 is characterized by the zero-velocity radius R = 0 . M T ( R ) (cid:39) . × M (cid:12) in agreement with the mass estimate via internal (orbital) motions.Lucero et al. (2015) performed HI observations of NGC 253 with the Karoo Array Telescope and determined itsrotation curve V ( R ) out to the projected separation of ∼
20 kpc from the galaxy center. These observations showthat the rotation velocity reaches a maximum of V m = 214 km s − at R ∼
12 kpc, and than decreases systematicallydown to ∼
185 km s − . A similar result was obtained earlier by Hlavacek-Larrondo et al. (2011) from observations inthe H α and [NII] lines using Fabry-Perot interferometry. The declining rotation curve of NGC 253 can serve as anindependent indication of a small size for the halo of this galaxy.NGC 253 is not the only case of a luminous spiral galaxy with a falling rotation curve at the periphery. Casertano &van Gorkom (1991) and Zobnina & Zasov (2020) identified four more such galaxies in the Local Volume: NGC 2683,NGC 2903, NGC 3521 and NGC 5055. All of these are located in areas of low cosmic density and have a small number Karachentsev, Tully, Anand et al. of dwarf satellites. Karachentsev et al. (2020) estimated orbital masses of these galaxies, using radial velocities andseparations of their companions. Data on 5 galaxies in the Local Volume with declined rotation curves are presentedin Table 2. As one can see, all these spirals are characterized by high luminosities and low relative masses of their darkhalos. The average dispersion of radial velocities of their satellites is 46 km s − at the average projected separation of225 kpc. The low average value of (cid:104) M orb /L K (cid:105) = (5 . ± . M (cid:12) /L (cid:12) is comparable to the cosmic baryon abundance, M DM /M bar (cid:39) K - luminosity ratio of M ∗ /L K (cid:39) M (cid:12) /L (cid:12) (Bell et al. 2003).It is implied that the galaxies with a declined rotation curve form a special category among the spiral galaxies ofhigh luminosity. In the Local Volume with the distance D <
11 Mpc there are 19 spiral galaxies with the luminositylog( L K /L (cid:12) ) > .
5. If we exclude five galaxies seen nearly face-on with indefinite rotation curves: NGC 628, IC 342,NGC 3184, M 101 and NGC 6946, then the relative number of cases with quasi- Keplerian V ( R ) is ∼ L K ) vs. log( V m ), if V m used as an argument, and not V ( R max ). Cosequently, the identi-fication of galaxies with relatively low mass dark halos is a nontrivial observational problem, requiring data on thekinematics of their distant periphery. CONCLUDING REMARKSWe measured accurate TRGB-distances of 3.62 Mpc and 3.66 Mpc for WOC2017-07 and PGC 704814, respectively,two dwarf galaxies in the vicinity of the bright spiral galaxy NGC 253, confirming their physical association withNGC 253 at 3.70 Mpc. Basing on the data on radial velocities and separations of 7 salellites of NGC 253, wedetermined its ratio of the total (orbital) mass to K- band luminosity, M orb /L K = 8 . ± . M (cid:12) /L (cid:12) , which is 3 − σ v = (42 −
54) km s − , and a low mass of dark halo, log( M orb /M (cid:12) ) = 11 . − .
91. The mean total mass-to- K -luminosity ratio for them is (5 . ± . M (cid:12) /L (cid:12) on the scale of ∼
225 kpc.It is suggested that there is a special population of galaxies with quasi-Keplerian rotation curves, which are foundmainly in regions of low cosmic density. In the Local Volume, their relative number is ∼ M DM /M ∗ , dependingon the morphology of galaxies from Sloan Digital Sky Survey. Both teams reported systematically lower values of M DM /M ∗ for disc-dominated (blue) galaxies than bulge- dominated (red) ones. A similar effect was found for 2MASSisolated galaxies by Karachentseva et al. (2011). Correa & Schaye (2020) explain this difference by the assumption thatthe stellar discs are more massive because they had more time for gas accretion and star formation. Also, accordingto Seo et al. (2020), “the system velocity dispersion of satellite galaxies show a remarkably tight correlation with thecentral velocity dispersion of their primary galaxies for both red and blue samples.” The study of the relationshipbetween the kinematics of satellites and inner kinematics of isolated luminous galaxies seems to be an importantobservational problem. Acknowledgements.
This work is based on observations made with the NASA/ESA Hubble Space Telescope.STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555. IDK is suported by RNF grant 19-12-00145.
References
Anand, G.S., Rizzi, L., Tully, R.B., et al., 2021, in preparationArp H., 1985, Astron. J. 90, 1012Barber C., Starkenburg E., Navarro J.F., et al, 2014, MNRAS, 437, 959Bell E.F., McIntosh D.H., Katz N., Weinberg M.D., 2003, ApJ Suppl., 149, 289Cannon J.M., Dohm-Palmer R.C., Skillman E.D., et al, 2003, AJ, 126, 2806Casertano S., van Gorkom J.H., 1991, AJ, 101, 1231Colless, M., Peterson, B.A., Jackson, C.A. et al. 2003, arXiv:2003.6581Correa C.A., Schaye J., 2020, MNRAS, 499, 3578de Vaucouleurs G., 1959, Astrophys. J. 130, 718Dolphin, A.E. 2000, PASP, 112, 1383Dolphin, A.E. 2016, DOLPHOT: Stellar photometry, ascl:1608.013 istance and mass of the NGC 253 galaxy group
Karachentsev, Tully, Anand et al.
WOC2017-07 PGC 704814
Figure 1.
HST/ACS combined images of WOC2017-07 and PGC 704814. Each image size is ∼ ×
52 arcseconds. North isup and east is left. The color images are composites of images with the F606W and F814W filters. The artifacts in the imageof PGC 704814 are ghosts from a bright star in the field.
F606W - F814W F W m TRGB = 23.71 ± 0.03
WOC2017-07
F606W - F814W m TRGB = 23.74 ± 0.02
PGC 704814
Figure 2.
Colour-magnitude diagrams of WOC2017-07 and PGC 704814. The TRGB position is indicated by the horizontalline. istance and mass of the NGC 253 galaxy group Figure 3.
Distribution of assumed NGC 253 satellites (squares, circles) and background galaxies (crosses) in supergalacticcoordinates. Assumed satellites without radial velocities are indicated with open circles. The virial radius of 300 kpc (4 . ◦ . ◦ ) are shown with minor and major circles. Karachentsev, Tully, Anand et al.
Table 1.
Galaxies in and around the NGC 253 group.Name SGL SGB T V LG ± e D meth log L K r p R p Θ MD M orb (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)NGC 253 271.57 − ± − Scl-MM-Dw2 272.25 − − − − Scl-MM-Dw1 270.50 − − − − WOC2017-07 274.06 − ± − ± − − SculptorSR 268.28 − − − DDO 6 275.84 − ± − ± − − − ESO 540-032 276.95 − ± − ± − ± − − PGC 704814 262.42+03.35 10 299 ±
89 3.66 trgb 6.90 12.39 800 2.1 N7793 (4.2)ESO 349-031 260.18+00.40 10 234 ± ± ± − − NGC 625 257.27 − ± − − ESO 245-005 255.13 − ± − − Note : (1) galaxy name; (2) supergalactic coordinates; (3) morphological type on the de Vaucouleurs scale; (4) radial velocityin km s − relative to the Local Group centroid; (5) galaxy distance in Mpc; (6) method used to determine the distance; (7) K s -band luminosity of galaxy in the units of solar luminosity; (8) projected separation from NGC 253 in degrees; (9) projectedseparation in kpc; (10) the “tidal index” Θ ; (11) name of the Main Disturber; (12) orbital mass estimate via the given satellite. Table 2.
Luminous galaxies in the Local Volume with declined rotation curves.Name Type D log L K n v σ v (cid:104) R p (cid:105) log M orb M orb /L K NGC 253 5 3.70 10.98 7 42 465 11.91 8.5 ± ± ± ± ± ± Note : (1) galaxy name; (2) morphological type on the de Vaucouleurs scale; (3) galaxy distance in Mpc; (4) K s - bandluminosity of galaxy in the units of solar luminosity; (5) number of companions with measured velocities; (6) velocity dispersionof companions in km s −1