A Mon. Not. R. Astron. So c. 000, 000{000 (0000) Printed 12 May1999 (MN L T Xstyle le v1.4) E The evolution of cluster E and S0 galaxies measured from ? the Fundamental Plane 1;2 yzx 3;4;5 zx 6;7;8 x 3;5 x Inger Jrgensen Marijn Franx , Jens Hjorth , Pieter G. van Dokkum 1 McDonald Observatory, The University of Texas at Austin, RLM 15.308, Austin, TX 78712, USA 2 Gemini Observatory, 670 N. A`ohoku Pl., Hilo, HI 96720, USA (Postal address for IJ) 3 Kapteyn Institute, P.O.Box 800, 9700 AVGroningen, The Netherlands 4 Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 5 Leiden Observatory, P.O.Box 9513, 2300 RA Leiden, The Netherlands (Postal address for MF and PvD) 6 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK 7 NORDITA, Blegdamsvej 17, DK-2100 Copenhagen , Denmark 8 Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen , Denmark (Postal address for JH) May 5, 1999, accepted for publication in Mon. Not. Royal Astron. Sco., Gemini Preprint #43 ABSTRACT Photometry has b een obtained for magnitude limited samples of galaxies in the two rich clusters Ab ell 665 (37 galaxies) and Ab ell 2218 (61 galaxies). Both clusters have m a redshift of 0.18. The limiting magnitude of the samples is 19 in the I-band. Sp ec- troscopy has b een obtained for seven galaxies in A665 and nine galaxies in A2218, all of whichalsohaveavailable photometry. Sp ectroscopy has b een obtained for two additional galaxies in A2218, one of whichisabackground galaxy. E ectiveradiir and mean surface brightnesses <I> were derived from the pho- e e tometry. The typical uncertainties are 0:078 in log r and 0:12 in log <I> . The e e combination log r +0:82 log <I> that enters the Fundamental Plane (FP) has an un- e e certainty of only 0:018. The sp ectroscopywas used for measurements of the velo city disp ersions, . The typical uncertaintyis 0:023 on log . The data are used to establish the FP,logr = log + log <I> + , for the e e clusters. The FP for these two clusters adds imp ortantknowledge ab out the prop erties of E and S0 galaxies in the relatively unexplored redshift interval 0.05 to 0.3. Wehave compared the FP for A665 and A2218 with the FP for the three clusters CL0024+16, CL1358+62 and MS2053-04 with redshifts between 0.33 and 0.58, and with the FP for the Coma cluster. The scatter around the FP is similar for all six clusters. We nd that the FP for the intermediate redshift clusters has a smaller co ecient than found for the Coma cluster and other nearby clusters. This mayeitherbecausedby selection e ects for the intermediate redshift clusters or by di erences in the evolution of low luminosity galaxies and high luminosity galaxies. The mass-to-light (M/L) ratios, as measured from the FP,change with redshift. At z =0.18 the M/L ratio for photometry in Gunn r in the rest frame of the clusters is (11 7)% smaller than for the Coma cluster. Using the data for A665 and A2218 together with the previously published data for CL0024+16, CL1358+62 and MS2053- 04, we nd that the M/L ratios for photometry calibrated to Gunn r change with redshift as log M=L =(0:26 0:06)z for q =0:5. This change in the M/L ratio r o is equivalent to the absolute magnitudes changing as M =(0:65 0:15)z .These r T new results are consistent with the previously published analysis for CL0024+16, CL1358+62 and MS2053-04. For q =0:5 the results are consistent with passiveevolution of a stellar p opulation o which formed at a redshift larger than ve. For q =0:15 the formation redshift must o b e larger than 1.7. Our new data for A665 and A2218 con rm the gradual and slow evolution of the bright E and S0 galaxies. However, p ossible star formation in E and S0 galaxies during the last 3-4 Gyr of the history of the Universe, as well as the selection e ects complicate the interpretation of the data. Key words: galaxies: clusters: individual: Ab ell 665, Ab ell 2218 { galaxies: elliptical and lenticular, cD { galaxies: evolution { galaxies: stellar content. c 0000 RAS 2 I. Jrgensen, M. Franx, J. Hjorth, P. G. van Dokkum plies a relation b etween the M/L ratios and the masses of 1 INTRODUCTION the galaxies. Observational studies show that the formation and evolu- The scatter of the FP is very low, equivalent to a scatter tion of galaxies is a complex pro cess, whichmayinvolve in- of 23% in the M/L ratio (e.g., JFK96). Thus, the FP o ers teractions, star bursts and infall (e.g., Dressler et al. 1994ab; the p ossibility of detecting even small di erences in the M/L Lilly et al. 1996; Mo ore et al. 1996). It has also b een found ratios by observing a handful of galaxies in a distant cluster. that some nearby E and S0 galaxies mayhave exp erienced The FP has been used to study the evolution of the star formation in the last 3-4 Gyr. Caldwell et al. (1993) M/L ratios of cluster galaxies as a function of redshift up found some E and S0 galaxies in the Coma cluster to have to a redshift of 0.83 (van Dokkum & Franx 1996; Kelson p ost-starburst sp ectra, and Fab er et al. (1995) suggest that et al. 1997; Bender et al. 1998; van Dokkum et al. 1998; nearby eld E galaxies havea substantial variation in the Pahre, Djorgovski & de Carvalho 1999). All of these studies mean age of their stellar p opulations. nd the M/L ratios of the galaxies to increase slowly with In order to study the evolution of galaxies we need to decreasing redshift. Only the study byPahre et al. contains study b oth the morphological evolution as well as the evolu- clusters with redshifts b etween 0.05 and 0.3. In this pap er tion of the luminosities and the mass-to-light (M/L) ratios of we establish the FP for the tworich clusters Ab ell 665 and the galaxies. High-resolution imaging with the Hubble Space Ab ell 2218. Both clusters have a redshift of 0.18, adding Telescop e (HST) and from the ground, combined with sp ec- data to a redshift interval not well-covered by the previous troscopy from the ground make it p ossible to carry out this studies. kind of studies. Studies of the morphological evolution show We use the data for A665 and A2218, data for the three that the fraction of spiral galaxies and irregular galaxies in clusters studied byvan Dokkum & Franx (1996) and Kelson clusters was higher at larger redshifts (e.g., Dressler et al. et al. (1997), and data for the Coma and the HydraI clusters 1994ab; Oemler et al. 1997; Dressler et al. 1997; Couchet to study how the FP and the M/L ratios of the E and S0 al. 1998). A detailed investigation of how the luminosities galaxies change with redshift. The full sample covers ab out of disk galaxies change with redshift is p ossible using the half the age of the Universe. Tully-Fisher (1977) relation. Vogt et al. (1996) established The available photometry and sp ectroscopy,aswell as the Tully-Fisher relation for a sample of eld galaxies with the derivation of the photometric and sp ectroscopic parame- redshifts b etween 0.1 and 1 and found a luminosityevolution ters is describ ed in Sections 2 and 3, resp ectively. The details m in the B-band of 0: 6between z = 1 and the present. of the data reduction are provided in App endix A and B. The Fundamental Plane (FP) (Dressler et al. 1987; App endix A also contains photometric parameters (e ective Djorgovski & Davis 1987) for elliptical galaxies makes it radii, mean surface brightnesses and colors) of magnitude p ossible to study how the luminosities and the M/L ra- limited samples of galaxies in A665 and A2218. Section 4 tios of these galaxies change with redshift. Also, S0 galaxies brie y describ es the data for the other clusters. The FP is in nearby clusters follow the FP (e.g., Jrgensen, Franx & analyzed in Section 5. In this section we also discuss the Kjrgaard 1996, hereafter JFK96). The FP relates the ef- evolution of the M/L ratios of the galaxies. The conclusions fective radius, r , the mean surface brightness within this e are summarized in Section 6. radius, <I> , and the (central) velo city disp ersion, , in e a tight relation, which is linear in log-space. For 226 E and S0 galaxies in nearby clusters JFK96 found log r = e 2 THE PHOTOMETRY 1:24 log 0:82 log <I> + cst, for photometry in Gunn r . e 0:24 0:02 This relation may be interpreted as M=L / M r e The central parts of the two rich clusters Ab ell 665 and (cf., Fab er et al. 1987). The change of the M/L ratio with Ab ell 2218 were observed with the Nordic Optical Telescop e the mass is partly caused bychanges in the stellar p opula- (NOT), La Palma, in March 1994. Observations were done in tions. Some of the apparentchange may also b e explained the I-band and the V-band.
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