arXiv:1605.03938v1 [astro-ph.CO] 12 May 2016 cetd21 a 2 eevd21 pi 8 noiia for original in 18; April 2016 Received 12. May 2016 Accepted h rjce isenrdu Θ within radius mass Einstein enclosed projected the the accuracy perm these great rare; with are isolated complete constraining galaxy almost lensing is central (ER) the ring Einstein and dynam- the the which on in assumption Cases any ics. mass without total object, the lensing as the such of parameters deriva- physical of permit important study they of the tion because evolution in and important formation very galaxy are galaxies lensed Strongly INTRODUCTION 1 MNRAS aino h ig oteoew ics ntepeetwork. present the ( in MG1131+0456 discuss elon- we and one morphology the objects, to in similarity, ring, these the close among of a and gation show far, few so a only identified been have ERs Leh´arMiralda-Escud´e & of iesres(e o example for (see surveys sive .R Walker R. A. 2013 ⋆ magni- a to down sky, of whole limit the over tude detectable be to ER cal

h aaisEnti ig el icvrdOptical Discovered Newly Ring a : Einstein Canarias The c 1 3 2 7 6 5 4 .Bettinelli M. nttt eAto`sc eCnra,Vı `ce /,E- V`ıa L`actea S/N, Canarias, Astrof`ısica de de Instituto iatmnod iiaeAtooi GlloGlli,Uni Galilei”, “Galileo Astronomia E-382 e Laguna, Fisica La di of Dipartimento University Astrophysics, of Department ainlOtclAtooyOsraoy ..Bx272 Tu 26732, Box P.O. Observatory, Astronomy dell’Oss Optical Vicolo National Padova, di Optica Astronomico National INAF-Osservatorio I Observatory, Maggini, Inter-American M. Tololo Via Cerro Teramo, di Astronomico INAF-Osservatorio -al btieice,[email protected] [email protected], E-mail: M 06TeAuthors The 2016 h rtE ob icvrdi h ai source radio the is discovered be to ER first The nyafwtn fcmlt rnal opeeoptical complete nearly or complete of tens few a only ) ∼ 000 5 · 10 , B 1 11 – 6adalwrlmtfrteecoe mass enclosed the for limit lower a and 26 = 5 M . eite l 1988 al. et Hewitt 21)Pern 3My21 oplduigMRSL MNRAS using Compiled 2016 May 13 Preprint (2016) ⊙ 5 1 hsntihtnig ept exten- despite notwithstanding, This . .Piotto G. , , 2 , 3 ( ⋆ 1992 .Simioni M. , otne l 2008 al. et Bolton rdce eea 10 several predicted ) erpr h icvr fa pia isenRn nteSupo co Sculptor Spheroid the Dwarf in Sculptor Ring ( the ring Einstein of complete vicinity optical almost the an an in of J010127-334319, discovery IAC the report We ABSTRACT n etclr D–glxe:sabrt–gaiainllnig str lensing: gravitational – starburst galaxies: – cD lenticular, and esit o ohcmoet,ln n ore rmobservat der from by source, obtained and been lens has components, nature both for object the (DECam) of Camera Confirmation Energy Dark data. inspecting from serendipitously made al-yeglx,hsardhf fz=0 = z len of The OSIRIS. a spectrograph has the galaxy, with early-type (GTC) CANARIAS Telescopio e words: Key a enetmtdt eM be to estimated been has ihrdhf fz=1 = z of redshift with E ). ( arne al. et Warren ohnke l 2001 al. et Kochanek 3 , 6 .Valdes F. , 1 ; , aais vlto aais itne n esit aais ellip galaxies: – redshifts and distances galaxies: – evolution galaxies: 2 tr tal. et Stark , ( 3 1996 .Aparicio A. , 6 opti- 80 aLgn,Tnrf,Spain Tenerife, Laguna, La 38200 re- ) srnm bevtr,Csla63 aSrn,Chile Serena, La 603, Casilla Observatory, Astronomy l estadgiSuid aoa ioodl’sevtro3 dell’Osservatorio Vicolo Padova, di Studi versit`a degli . raoi ,I312Pdv,Italy Padova, I-35122 5, ervatorio 06Fbur 18. February 2016 m 6.Tettlecoe asta rdcstelnigeffect lensing the produces that mass enclosed total The 165. 7 ). it 0L aua eeie aayIlns Spain Islands, Canary Tenerife, Laguna, La 00 sn Z879 USA 85719, AZ cson, ∼ 610Trm,Italy Teramo, -64100 tot 300 h rtkoncs nteltrtr faE icvrdat discovered ER a of literature the wavelengths. in optical case known first the slne ya litclmsieglx tz=0 = z at galaxy massive elliptical an by lensed is 1 h hsc ftesuc aay Xglx,i h ocalled so the is galaxy, in BX ( not a Horseshoe” galaxy, but ”Cosmic morphology, source in the Letter, of this physics in the report we one the to oreglx sasabrta 3 = z at starburst a is galaxy source yamsieadioae litclglx tz=0 = z at galaxy elliptical isolated and massive a by Rdsoee eetyae h Csi y”( Eye” ”Cosmic the are: recently discovered ER ( 2007 ( here, report we one the to similar is sion otcmlt R( ER complete most a uems of mass huge a has ottedsoeyo ata R( ER partial a of discovery the port on nteltrtr.Sbeunl eosre twith it nature. observed its of been we confirmation has spectroscopic Subsequently a object for literature. DE- OSIRIS@GTC the the in to in object reference found peculiar previous No ”Ca- a the images. as as Cam noticed to Ring”, refer we Einstein that narias ER, complete almost optical, an isenrdu sdul,Θ double, is radius Einstein (1 = i ta.2009 al. et Lin . ◦ 5ace;tebcgon I mtigglx tz=3 = z at galaxy emitting OII background the arcsec; 35 ihadaee of diameter a with ) eew eottedsoeyo A J010127-334319, IAC of discovery the report we Here ,te” ’lc arc”( o’clock ”8 the ), . 2 86 , 1 .L Hidalgo L. S. , ± 0 . . 8 hl h orei trus galaxy starburst a is source the while 581 23) ). · 10 ∼ aaa tal. et Cabanac eouo ta.2007 al. et Belokurov ∼ 260 12 M 5 = M ◦ ∼ la ta.2007 al. et Allam ihΘ with ) ⊙ E 4 . . rsc h icvr was discovery The arcsec. 5 ∼ . 1 4 rsc h esn galaxy lensing the arcsec; 5 , 2 × osa h 10 the at ions .Cassisi S. , E . 10 ( 7.Te,asmlrER similar a Then, 773. 2005 ∼ 12 ∼ ong vn spectroscopic iving 1 . M 8ace produced arcsec 48 170 icvrda al- an discovered ) A ⊙ ;tern exten- ring the ); rhv imaging archive n h ”Clone” the and ) ∼ T lGlx.I is It Galaxy. al -52 aoa Italy Padova, I-35122 , E te partial Other . ◦ tl l v3.0 file style X 300 ihΘ with ) ,amassive a s, . nstellation, mi tal. et Smail 8.Ti is This 485. . ◦ Gran m 4 ,btthe but ), . 8.The 986. 4 , 1 , tical E . 595 ∼ 2 M. Bettinelli et al.

Table 1. List of parameters Imaging and low-Intermediate-Resolution Integrated Spec- troscopy (OSIRIS) spectrograph (Cepa 1998). OSIRIS has a × Lens mosaic of two E2V CCD42-82 (2048 4096 px). All the ob- tained spectra were registered on the second detector, which Right ascension(J2000): 01h01m27.83s is the default for long-slit spectroscopy. We used a binning of ′ 1 Declination(J2000): −33◦43 19.68′′ 2×2 providing a pixel size of 0.254 arcsec px− , and the grism Redshift: 0.581 ± 0.001 R300B, which provides a spectral coverage of 4000 − 9000 ˚A −2 Surface brightness Lens (g,r) [mag arcsec ]: 25.2, 22.2 and a nominal dispersion of 4.96 ˚A px−1. The slit width was (g,r) 23.61, 21.48 0.6 arcsec. Long-slit spectral observations were performed on g r − . , − . Absolute magnitude ( , ) 21 05 23 18 2015 December 2 in good seeing conditions of ∼ 0.8 arcsec. The slit was placed along the N-S direction, in order to min- Ring imize the effects of atmospheric differential refraction at cul- mination. The total exposure time was 3600 s divided into 6 Redshift: 1.165 ± 0.001 exposures of 600 s each. In each of the 6 exposures the two Einstein radius: 2.16′′ ± 0.13 12 components, ring and lensing galaxy, have been detected and Enclosed mass [10 M⊙]: 1.86 ± 0.23 Surface brightness A (g,r) [mag arcsec−2]: 23.7, 22.9 in particular their spectra were not overlapping. The posi- Surface brightness B (g,r) [mag arcsec−2]: 23.9, 23.2 tion of the slit was such that the spectra obtained for the Surface brightness C (g,r) [mag arcsec−2]: 23.7, 23.0 ring refers to peak B. Apparent magnitude (g,r) 20.94, 20.12 For the pre-reduction we have used the OSIRIS Offline Pipeline Software (OOPS); sky subtraction and flux cali- bration were performed using IRAF1. We performed wave- length calibration using standard HgAr+Ne+Xe arc lamps; In this Letter we provide the first physical parameters of this the resulting error on wavelength determination has been system. In the following discussion we assume a flat cosmol- measured to be consistent with the above spectral resolu- −1 −1 ogy with Ωm = 0.3, ΩΛ = 0.7 and H0 = 70 km s Mpc . tion. We corrected the extracted spectra for instrumental response using observations of the spectrophotometric stan- dard star GD140, a white dwarf, obtained the same night. 2 DISCOVERY The fluxes of this standard star are available in Massey et al. (1988). The serendipitous discovery of IAC J010127-334319 was made while performing photometry on stacked images, in g and r filters, taken with DECam (Flaugher et al. 2015) at the Blanco 4m telescope at the Cerro Tololo Inter-American 4 ANALYSIS AND DISCUSSION Observatory (CTIO), reduced with the NOAO Community Pipeline (Valdes et al. 2014) and obtained from the NOAO In order to derive the redshifts for the two components we Science Archive (Seaman et al. 2002). The total exposure noted the strong emission line in the source spectrum and time is 7680 s in the g filter and 5700 s in the r filter. Figure 1 the 4000 A˚ Balmer discontinuity in the lens spectrum. This shows the resulting color composite image: it is evident that led us to choose template models for a starburst galaxy and a two components with different colors are present. In par- early-type galaxy respectively, as specified below. Following ticular the central one (the lens) appears redder than the line identification, we determined redshifts. second component (the lensed image of the source), which in turn appears as elongated all around the first. The ring is almost perfectly circular with an apparent radius of 8 px 4.1 Lens which translates to 2.16 arcsec. Three peaks, A, B and C, are clearly visible (bottom right panel of Figure 1); they Using the template spectra by Kinney et al. (1996) results − are located respectively at 150 deg, 14 deg and 83 deg from that the spectrum of the lens galaxy fits well the spectrum North counterclockwise. In Table 1 all the derived parame- of a S0 galaxy (see Figure 2), a typical early-type galaxy ters for the object are listed. From the DECam photometry characterized by a large increase in flux from the UV part we estimated an apparent magnitude for the lens in both g of the spectrum to the optical. The 4000 A˚ Balmer discon- − and r bands of g = 23.61, r = 21.40. The color (g r) > 2 tinuity at ∼ 6330 A˚ is noticeable. The redshift of the lens indicates that this galaxy is probably a luminous red galaxy galaxy is z = 0.581 ± 0.001 and it has been determined (Eisenstein et al. 2001). All the details about the photomet- from the measurements of: Hη λ3835.4, Ca K λ3933.7, Ca ric calibration will be given in a forthcoming paper (Bet- H λ3968.5, Hδ λ4141.8, G-band λ4307.7, Mg-b2 λ5172.7, tinelli et al. in prep.). Mg-b1 λ5183.6 (marked red features from left to right in Figure 2 middle panel).

3 FOLLOW-UP SPECTROSCOPY

In order to confirm the lensing nature of this system we per- 1 IRAF is distributed by the National Optical Astronomy Obser- formed a spectroscopic follow-up at the 10.4 m Gran Tele- vatory, which is operated by the Association of Universities for scopio CANARIAS (GTC) on Roque de los Muchachos Ob- Research in Astronomy, Inc., under cooperative agreement with servatory (La Palma, Spain) using the Optical System for the National Science Foundation

MNRAS 000, 1–5 (2016) The Canarias Einstein Ring 3

Figure 1. Composite g, r field of view of 2.5 arcmin × 2.5 arcmin centered on the object (on the left), North is up, while East points left; a zoom of the object with overplotted the best fitting circle, the slit position and width are also plotted as green lines (right upper panel); counts from photometry along the best fit circle of the ring (lower right panel): the measured sky value is indicated by the red solid line, the 1σ value is indicated by the red dashed one.

4.2 Source of sight. Under these assumptions, for an arbitrary mass profile M(Θ), (i.e. without assuming any particular model For the source galaxy we used the template spectra by for the potential), we can apply the following relation Calzetti et al. (1994) and we found that the spectrum best (Narayan & Bartelmann 1996) and solve it for the mass. fitting our observed spectrum corresponds to a starburst galaxy in the case of clumpy scattering slab, where it is assumed that clumped dust is located close to the source 2 4G dLS ΘE = 2 M(Θ) (1) of radiation. In such circumstances, Calzetti et al. (1994) c dLdS show that scattering into the line of sight dominates over Here ΘE is the Einstein radius in radians; M(Θ) is the absorption by the dust, providing a significant positive con- mass enclosed within the Einstein radius; dLS, dL, dS are the tribution to the emerging radiation. This template spectrum angular diameter distances respectively of source-lens, lens- ii fits well the strong O λ3727 emission line. We also iden- observer and source-observer. These last quantities are re- ii ii i tified the following lines: Fe λ2344.0, Fe λ2600.0, H 11 lated to the relative comoving distances and, in general, this ii i λ3770.6, O λ3727.3,H 10 λ3797.9 (marked blue features relation depends on the assumed curvature of the Universe from left to right in Figure 2 upper panel). According to (Hogg 1999). In our case ΩK = 0 has been assumed and the −1 these features, we derived for the source galaxy a redshift resulting angular diameter distances are dL = 951 h Mpc, ± −1 −1 of z = 1.165 0.001. We note that the selected slit position dS = 1192 h Mpc and dLS = 498 h Mpc. We calculated enable us to extract only the portion of the spectrum cor- 12 a total mass Mtot = (1.86 ± 0.23) · 10 M⊙ where the er- responding to peak B (see Figure 1); this notwithstanding, ror on the mass (12%) is overwhelmingly due to the mea- ii the O emission coming from the opposite side of the ring surement error in the determination of the Einstein radius, can be easily noted in our spectra. that we have estimated to be 0.5 px which corresponds to 0.135 arcsec. The error on the redshift derives from the er- ∼ ˚ 4.3 Enclosed Mass Derivation ror estimated on the wavelength calibration which is 5 A. This value is consistent with the spectral resolution (4.96 ˚A The strong circular symmetry of our object (see Figure 1) px−1) of the grating R300B that we used. suggests that it can be approximated to the case of a cir- Under the assumption of a singular isothermal sphere cularly symmetric lens, with source and lens in the line (SIS) it is possible to give an estimate of the magnifica-

MNRAS 000, 1–5 (2016) 4 M. Bettinelli et al.

Figure 2. Top panel: source galaxy spectrum (in blue) with overplotted a starburst template spectrum by Calzetti et al. (1994). Middle panel: lens galaxy spectrum (in red) with overplotted an early-type galaxy template by Kinney et al. (1996). Bottom panel: measured wavelength displacement between observed and laboratory line position for the selected features (see text for details).

ing the gravlens/lensmodel software (Keeton 2001). This software allows to fit a SIE model using only the image po- sitions and fluxes. The obtained best-fit model is plotted in Figure 3. The solutions have been derived for pointlike sources; the ring shape is due to the fact that the source should actually be more extended with respect to the caus- tics than is shown here. The best fit ellipticity is 0.2 calcu- lated as 1 − q where q is the axis ratio; the associated po- sition angle is -57 deg, angle measured from North to East. The best fit χ2 value is 6.12, calculated setting to 0 the weights relative to image fluxes. The derived Einstein ra- dius is ΘE = 2.38 arcsec, which translates in an enclosed ∼ · 12 Figure 3. Best fitting SIE model obtained with the mass of 2.26 10 M⊙, hence in excellent agreement with gravlens/lensmodel software. On the left (image plane): the our previous estimate. source images positions are plotted as blue triangles, the fitted position recovered by the software as blue squares, the red cen- tral dot represents the position of the lensing galaxy and the red curve is the critical curve. On the right (source plane): the blue 5 CONCLUSIONS square represent the calculated position of the source; the caustics are shown in red. We report the discovery of an almost complete (∼ 300◦) circular optical Einstein ring in the of Sculp- tor. The is a massive luminous red tion of the ring: µ = 4ΘE /δΘs, where δΘs is the source galaxy at z = 0.581. The source galaxy is a starburst size. From Nagy et al. (2011) the average size of a starburst at redshift z = 1.165; its spectrum is dominated by a galaxy in our redshift range is ∼ 2 Kpc which corresponds strong O ii emission line. Using these redshift determina- to 0.24 arcsec. The derived magnification is ∼ 36. tions and the Einstein radius ΘE = 2.16 arcsec we calcu- We determined also the mass-to-light ratio of the lens lated the total enclosed mass that produced the lensing ef- in the g band; a K-correction of 2.1 has been derived for the 12 fect: Mtot = (1.86 ± 0.23) · 10 M⊙. lens using the NED calculator (Chilingarian & Zolotukhin All the parameters we determined for IAC J010127- 2012). The resulting ratio is Mtot/L ∼ 58 M⊙/L⊙. 334319 are listed in Table 1. The former mass estimate can be improved by applying to the system a singular isothermal ellipsoid (SIE) model us-

MNRAS 000, 1–5 (2016) The Canarias Einstein Ring 5

ACKNOWLEDGEMENTS Kinney, A. L., Calzetti, D., Bohlin, R. C., et al. 1996, ApJ, 467, 38 The authors thank the anonymous referee for the construc- Kochanek, C. S., Keeton, C. R., & McLeod, B. A. 2001, ApJ, 547, tive comments that significantly improved the manuscript. 50 The authors are grateful to all the GTC staff and in par- Lin, H., Buckley-Geer, E., Allam, S. S., et al. 2009, ApJ, 699, ticular to Dr. A. Cabrera-Lavers for his support in refining 1242 the spectroscopical observations during the Phase-2. The au- Massey, P., Strobel, K., Barnes, J. V., & Anderson, E. 1988, ApJ, thors also thank Dr. J. Falc´on-Barroso for the helpful dis- 328, 315 cussion. Miralda-Escude, J., & Lehar, J. 1992, MNRAS, 259, 31P This Letter is based on observations made with the Nagy, S. R., Law, D. R., Shapley, A. E., & Steidel, C. C. 2011, ApJ, 735, L19 GTC telescope, in the Spanish Observatorio del Roque de Narayan, R., & Bartelmann, M. 1996, arXiv:astro-ph/9606001 los Muchachos of the Instituto de Astrof´ısica de Canarias, Seaman, R. L., De La Pena, M., Zarate, N., & Lauer, T. R. 2002, under Director’s Discretionary Time. Proc. SPIE, 4846, 182 This project used data obtained with the Dark En- Smail, I., Swinbank, A. M., Richard, J., et al. 2007, ApJ, 654, L33 ergy Camera (DECam), which was constructed by the Stark, D. P., Auger, M., Belokurov, V., et al. 2013, MNRAS, 436, Dark Energy Survey (DES) collaboration. Funding for the 1040 DES Projects has been provided by the DOE and NSF Valdes, F., Gruendl, R., & DES Project 2014, Astronomical Data (USA), MISE (Spain), STFC (UK), HEFCE (UK), NCSA Analysis Software and Systems XXIII, 485, 379 (UIUC), KICP (U. Chicago), CCAPP (Ohio State), MIFPA Warren, S. J., Hewett, P. C., Lewis, G. F., et al. 1996, MNRAS, (Texas A&M), CNPQ, FAPERJ, FINEP (Brazil), MINECO 278, 139 (Spain), DFG (Germany) and the collaborating institutions in the Dark Energy Survey, which are Argonne Lab, UC This paper has been typeset from a TEX/LATEX file prepared by Santa Cruz, University of Cambridge, CIEMAT-Madrid, the author. University of Chicago, University College London, DES- Brazil Consortium, University of Edinburgh, ETH Zurich,¨ Fermilab, University of Illinois, ICE (IEEC-CSIC), IFAE Barcelona, Lawrence Berkeley Lab, LMU Munchen¨ and the associated Excellence Cluster Universe, University of Michi- gan, NOAO, University of Nottingham, Ohio State Univer- sity, University of Pennsylvania, University of Portsmouth, SLAC National Lab, Stanford University, University of Sus- sex, and Texas A&M University. M.B., M.S., A.A., S.L.H., S.C. and G.P. acknowledge support from the Spanish Ministry of Economy and Com- petitiveness (MINECO) under grant AYA2013-42781. This research has made use of the NASA/IPAC Ex- tragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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