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GLOBULAR CLUSTERS AROUND GALAXIES in GROUPS Cristiano Da Rocha and Claudia Mendes De Oliveira Michael Bolte Bodo L. Ziegler

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GLOBULAR CLUSTERS AROUND GALAXIES in GROUPS Cristiano Da Rocha and Claudia Mendes De Oliveira Michael Bolte Bodo L. Ziegler The Astronomical Journal, 123:690–701, 2002 February # 2002. The American Astronomical Society. All rights reserved. Printed in U.S.A. GLOBULAR CLUSTERS AROUND GALAXIES IN GROUPS Cristiano Da Rocha and Claudia Mendes de Oliveira Instituto de Astronomia, Geofı´sica e Cieˆncias Atmosfe´ricas, Universidade de Sa˜o Paulo, Avenida Miguel Stefano 4200, 04301-904 Sa˜o Paulo, SP, Brazil; [email protected], [email protected] Michael Bolte Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, California 95064; [email protected] Bodo L. Ziegler Universita¨tssternwarte Go¨ttingen, Geismarlandstrasse 11, D-37083 Go¨ttingen, Germany; [email protected] and Thomas H. Puzia Universita¨tssternwarte Mu¨nchen, Scheinerstrasse 1, D-81679 Mu¨nchen, Germany; [email protected] Received 2001 August 27; accepted 2001 October 30 ABSTRACT We have obtained deep photometry of NGC 1199 (in the compact group HCG 22) and NGC 6868 (in the Telescopium loose group) with the Keck II and the ESO VLT-I telescopes. Each galaxy is the optically brightest galaxy of its group. NGC 1199 has two companion galaxies at a median projected distance of only 33 kpc and, based on its peculiar internal structure and large X-ray halo, NGC 6868 has been proposed to be a merger remnant. Our analysis of B and R images uncovered a population of globular clusters around both galaxies, with total (and local) specific frequency SN =3.6Æ 1.8 (3.4 Æ 1.5) for NGC 1199 and SN =1.8Æ 1.1 (0.8 Æ 0.4) for NGC 6868. The radial profile of the globular clusters of NGC 1199 follows the light distribution of the galaxy and can be fitted by a power law and a core model with a very steep slope ( =2.5Æ 0.3). In the case of NGC 6868, the profile of the globular clusters is well fitted by a power law and a core model profile of slope 1.4 Æ 0.3 and is shallower than the galaxy light distribution. Maximum likeli- hood fitting of two Gaussians to the globular cluster color distribution yields a high significance for multimo- dality, with peaks centered at (BÀR)0 = 1.13 Æ 0.04 and 1.42 Æ 0.04 (NGC 1199) and (BÀR)0 = 1.12 Æ 0.07 and 1.42 Æ 0.07 (NGC 6868). NGC 1199 and NGC 6868 are good examples of galaxies in which the group environment is likely to have affected their dynamical evolution. We find that for NGC 1199 the properties of the globular cluster system are similar to those for other systems around external elliptical galaxies located in less dense environments but with a very steep radial profile. In the case of NGC 6868, we find a regular radial profile and color distribution and a comparatively low specific frequency for the globular cluster system of the galaxy. Key words: galaxies: elliptical and lenticular, cD — galaxies: individual (NGC 1199, NGC 6868) — galaxies: star clusters 1. INTRODUCTION The main goal of this work is to characterize the GCSs of two galaxies in small groups: NGC 1199, the central ellipti- Variations in the properties of extragalactic globular clus- cal galaxy in the compact group HCG 22, and NGC 6868, a ter systems (GCSs) as a function of the environment of the suspected merger remnant in the center of the Telescopium host galaxy hold some of the keys to understanding the for- group. In particular, we are looking for suggestions that the mation and evolution of GCSs. Environment has been pro- basic properties of the globular cluster systems around these posed as one of the important factors in setting the specific galaxies have been modified by the dense environment of frequency SN (number of clusters normalized by galaxy the compact group or the merger event, respectively. luminosity). Harris, in a review paper of 1991, pointed out The compact group HCG 22 contains three bright gal- that elliptical galaxies in small groups and sparse environ- axies. This group was originally cataloged as a quintet of ments have on average half the SN of elliptical galaxies in galaxies (Hickson 1982). However, Hickson et al. (1992) the Virgo and Fornax clusters (excluding the central gal- showed this to be a triplet at a mean redshift of 0.009 with a axies, which have the well-known extremely high specific superposed discordant pair at z = 0.0296. The group has a frequencies). On the other hand Djorgovski & Santiago median velocity of 2686 km sÀ1 and a velocity dispersion of À1 (1992) found an increase of the SN with the host galaxy 54 km s . Based on the surface brightness fluctuation luminosity, which was confirmed by Zepf, Geisler, & Ash- method, Tonry et al. (2001) derive a distance modulus man (1994; see Ashman & Zepf 1998; Elmegreen 2000; Har- (mÀM)V = 32.6 Æ 0.3 to NGC 1199, the dominant galaxy ris 2001 for detailed discussion on the subject). As the of the group, corresponding to 33.1 Mpc, and a median pro- majority of the very bright galaxies are found in clusters and jected galaxy separation in the group of 33 kpc (Tonry et al. À1 À1 the faint ones are in groups and in the field, the environmen- 2001 assume H0 =74kms Mpc ). NGC 1199 (also tal effect on SN and its luminosity dependency are not easily known as HCG 22A) is classified as an E2 (Hickson 1982). disentangled. The effects of host-galaxy environment on NGC 6868 is also classified as an E2 (de Vaucouleurs et other details of the GCSs, the radial and color distributions, al. 1991). The Telescopium group contains five bright gal- are not well documented. axies with a median velocity of 2601 km sÀ1 and a velocity 690 GLOBULAR CLUSTERS AROUND GALAXIES IN GROUPS 691 dispersion of 219 km sÀ1. Tonry et al. (2001) measure TABLE 1 (mÀM)V = 32.1 Æ 0.2 based on the surface brightness fluc- General Properties of the Observed Galaxies tuation method, which corresponds to a distance of 26.8 Mpc, and a median projected separation for group galaxies Parameter NGC 1199 NGC 6868 of 209 kpc. Although NGC 6868 is located in an environ- l....................................... 199.2 350.9 ment that has a number density of bright galaxies lower b...................................... À57.3 À32.6 than that of a typical compact group, the interest in study- R.A................................. 03h03m38s620h09m5491 ing the globular cluster system of this galaxy is that it is Decl. ............................... À153605100 À482204700 almost certainly a recent merger (Hansen, Jørgensen, & Morphological type ........ E2 E2 a b Nørgaard-Nielsen 1991). NGC 6868 appears from its global BT ................................... 12.5 Æ 0.13 11.4 Æ 0.11 properties to be an ordinary elliptical galaxy, but in a MV .................................. À21.3 Æ 0.34 À21.9 Æ 0.29 detailed study Hansen et al. (1991) showed that there are a BÀV................................ 0.99b 1.00b À1 b b system of dust features close to the NGC 6868 core and a VRad (km s ) .................. 2705 2876 Distancec (Mpc) .............. 33.1 26.8 disk of ionized gas within 1 kpc of its center, indicating the d e presence of a young population of stars. The kinematics of Effective Radius.............. 33>6 38>4 Int. Vel. Disp.f (km sÀ1)... 201 277 the gas disk was studied by Plana et al. (1998), who found a flat rotation curve with velocity amplitude Æ150 km sÀ1. a Hickson et al. 1989. The presence of the dust structure and the ionized gas sug- b Faber et al. 1989. c gest that NGC 6868 may have captured one or more gas- Tonry et al. 2001. d Zepf & Whitmore 1993. rich galaxies. In addition, NGC 6868 has a halo of X-ray e Kobayashi & Arimoto 1999. gas associated with it. Its X-ray and optical luminosities are f Prugniel & Simien 1996. in good agreement with the LB À LX relation proposed by Beuing et al. (1999) for early-type galaxies. The general properties of the two galaxies can be seen in Table 1. 2.2. Data Reduction The paper is organized as follows. Section 2 describes the Image Processing and Photometry observations and data reduction. In x 3 we show the results 2.2.1. and x 4 has our discussion. Using the IRAF1 package (Image Reduction and Analy- sis Facility) we carried out the basic image reduction proce- dures (bias correction, flat-fielding and image combining). We next used the ELLIPSE and BMODEL of the STSDAS 2. OBSERVATIONS AND DATA REDUCTION package to model and subtract the light from bright gal- axies. We masked the very bright objects on the images and 2.1. Observations the central regions of the giant galaxies that could not be The images of HCG 22 were obtained with the Keck II modeled by ELLIPSE. Subtraction of the sky level of the telescope in 1997 June using the Low Resolution Imaging image was done using the SExtractor package (Source Spectrometer (LRIS; Oke et al. 1995). Images in B and R of Extractor), Version 2.1.6 (Bertin & Arnouts 1996) with a total exposure times of 720 s (4 Â 180) and 630 s (7 Â 90) background mesh size of 64 pixels. The combined images were obtained with an average seeing on the combined for NGC 1199 and NGC 6868 and the final masked and images of 0>77 and 0>74, respectively. The field size is background-subtracted images are shown in Figure 1. 5<7 Â 7<3 and the pixel size is 0>215. The NGC 6868 images The combined, masked and background-subtracted were obtained with the ESO VLT-I in 1999 October using images were then used for detection and photometry of the the Focal Reducer/Low Dispersion Spectrograph 1 faint objects by using SExtractor with a Gaussian convolu- (FORS1).
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