NRIAG Journal of Astronomy and Geophysics (2016) xxx, xxx–xxx
National Research Institute of Astronomy and Geophysics NRIAG Journal of Astronomy and Geophysics
www.elsevier.com/locate/nrjag
The fundamental plane of early-type galaxies in different environments
R.M. Samir a,*, F.M. Reda a, A.A. Shaker a, A.M.I. Osman a, M.Y. Amin b,c a National Research Institute of Astronomy and Geophysics (NRIAG), 11421 Helwan, Cairo, Egypt b Physics Dept., College of Sci. Humanities-Hawtat Sudair, Majmaah Univ., Saudi Arabia c Astronomy, Space Science and Meteorology Dept., Cairo University, Egypt
Received 19 May 2015; revised 19 May 2016; accepted 23 June 2016
KEYWORDS Abstract The study of Early-Type Galaxies (ETGs) in different environments is a strong tool to Early-type galaxies; understand their star formation history and their evolution. The Fundamental Plane (FP) of ETGs The fundamental plane; has been studied in different environments in the nearby universe such as in groups, clusters and the The Kormendy relation; field. We found that our sample of ETGs in different environments shows a good agreement with The Faber-Jackson relation; the FP of Coma cluster, except for a scatter of some galaxies. A major part of the scatter in the FP is Shells; due to variations in mass to light ratio as a result of metallicity or age trends in the stellar popula- Tidal tails tions and structural or dynamical properties of galaxies. We noticed that the most deviant galaxies from the FP show many fine structures as tidal tails, shells, dust and a kinematically distinct core which indicates a past merger involving at least one gas-rich progenitor. Ó 2016 Production and hosting by Elsevier B.V. on behalf of National Research Institute of Astronomy and Geophysics. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).
1. Introduction of the visible mass in the universe (for a detailed review, see Renzini, 2006, and references therein). Therefore, by under- Early-Type galaxies (ETGs) represent a group which includes standing their evolution, we can understand the evolution of both elliptical (E0–E7) and lenticular (S0) galaxies. They rep- galaxies in general, and the evolution of the universe as a resent a class of well studied objects both because of their whole. homogeneous properties and their high luminosities Although ETGs seem to be a nearly homogeneous class, the data collected in the last 30 years showed that there are signif- ( 24 6 MB 6 20) which allows to detect them at large dis- tances. They are specifically important as they contain most icant departures from the general properties found in the form of large quantities of gas and dust (Capaccioli and Longo, 1994; Goudfrooij et al., 1994a,1994b), counter rotating nuclei * Corresponding author. and polar rings (Bender, 1988; Whitmore et al., 1987), shells, Peer review under responsibility of National Research Institute of ripples, and disky or boxy components (e.g. Malin and Astronomy and Geophysics. Carter, 1980; Schweizer, 1980; Schweizer et al., 1990) and dis- tinctive tidal tails (Fort et al., 1986; Schweizer and Seitzer, 1992; Michard and Prugniel, 2004; Bennert et al., 2008; Tal Production and hosting by Elsevier et al., 2009; Janowiecki et al., 2010). These morphological http://dx.doi.org/10.1016/j.nrjag.2016.06.004 2090-9977 Ó 2016 Production and hosting by Elsevier B.V. on behalf of National Research Institute of Astronomy and Geophysics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: Samir, R.M. et al., The fundamental plane of early-type galaxies in different environments. NRIAG Journal of Astronomy and Geophysics (2016), http://dx.doi.org/10.1016/j.nrjag.2016.06.004 2 R.M. Samir et al. structures are explained in most of the theoretical models as a an important tool to study the properties of early type and result of past merging in early stages of galaxy formation or of dwarf galaxies and compute cosmological parameters. It is also tidal interactions with close neighbors (e.g., de Zeeuw and an important diagnostic tool for galaxy evolution and mass-to- Franx, 1989; Franx et al., 1989). light (M/L) variations with redshift. The role that environment plays in shaping the properties Although the FP relation is quite tight, there is a significant of ETGs is still an open issue in our understanding of galaxy scatter around the plane and there is some contradiction in the formation and evolution (see Conselice et al., 2013 as a recent literature regarding the source of this scatter. Some studies review). It is accepted that galaxy encounters, merging and found that the scatter could be due to some reasons, such as interaction with inter cluster medium (ICM) are all processes variations in the formation times of galaxies, differences in that affect on the properties of galaxies to some extent. The the dark matter content of galaxies or metallicity trends in stel- influence of environment on the evolution of galaxies is testi- lar populations. According to observations, the scatter around fied by the presence of the well-known morphology-density the FP is very low, and the position of a galaxy above or below relation (Dressler, 1980), according to which ETGs are pre- the plane is independent of galaxy flattening, velocity aniso- ferred to be found in high density environments (Postman tropy and isophotal twisting. and Geller, 1984; Dressler et al., 1997; Postman et al., 2005; Faber et al. (1987) found that deviations from the FP can Bamford et al., 2009), while late-type galaxies are more found be formed by M/L variation due to e.g. metallicity or age in low density environments. This distribution was proved in trends in stellar populations, dynamical or structural proper- many studies: for example, Calvi et al. (2012) showed that ties, and relative distribution of dark matter. In fact, each of there is a smooth increase in the fraction of ETGs when going these effects may also introduce a tilt into the FP if they rep- from single galaxies, to pairs, to groups. Another relation that resent a function of elliptical galaxy mass. shows the influence of environment is the star formation- The origin of the scatter around the FP has been investi- density relation (Lewis et al., 2002; Go´ mez et al., 2003; gated by many authors. Jørgensen et al. (1996) could not Haines et al., 2007). reduce the scatter around the FP by introducing additional The study of galaxies in different environments is a robust parameters, such as isophotal shape of the galaxies or elliptic- tool to understand their evolution and star formation history ity. Other studies found that variations in stellar populations (e.g., Kuntschner et al., 2002; Sa´ nchez-Bla´ zquez et al., 2003, in ETGs are partially responsible for the intrinsic scatter 2006; Thomas et al., 2005; Collobert et al., 2006). ETGs dis- (e.g. Gregg, 1992; Guzma´ n and Lucey, 1993; Guzma´ n et al., play a relation in the 3-dimensional parameter space among 1993). Forbes et al. (1998) found that the scatter of the FP their effective radius re, the central velocity dispersion ro and for a sample of non cluster galaxies is partly due to variation the luminosity L (or equivalently the effective surface bright- in galaxy age at a given mass, and to variations in the time 2 ness expressed as Ie in linear flux units, where Ie = L/(2pre), of the last starburst. Also Reda et al. (2005) found the same or le in magnitudes). They are concentrated on a plane called results by studying a sample of isolated galaxies. They found the fundamental plane (FP, Dressler et al., 1987; Djorgovski that some galaxies deviate from the FP having lower M/L ratio and Davis, 1987) with, and they explained this as due to younger stellar populations of those galaxies, probably induced by recent gaseous merger. r / ra hI ib ð1Þ e o e Other studies showed that a major part of the scatter in the FP Which can be written as, is due to variations in M/L ratio (e.g., Cappellari et al., 2006; Bolton et al., 2008; Auger et al., 2010; Cappellari et al., 2013). log r ¼ a log r þ bhl iþc ð2Þ e o e On the other hand, some studies (e.g., Magoulas et al., where a and b are the slopes and c is the offset (intercept) of the 2012) found that the age of galaxies is the most important FP. hlei is the mean effective surface brightness enclosed by re source of offset from the FP and may drive other trends (simply referred to as the mean surface brightness). The expo- through its correlation with environment, morphology and nents a and b depend on the specific band used for measuring metallicity. the luminosity. This indicates that, besides being in virial equi- The FP appears to be the same in all environments (univer- librium, ETGs show striking regularity in their structures and sal), in the sense that the coefficients are similar for galaxies in stellar populations (Renzini and Ciotti, 1993; Borriello et al., environments ranging from high density clusters to the low- 2003). density field (de la Rosa et al., 2001; Reda et al., 2005; The FP can be understood as a demonstration of the virial Holden et al., 2010). On the other side, there are suggestions plane predicted for relaxed systems (Binney and Tremaine, in the literatures that there are moderate, but significant, envi- 2008), with assuming that galaxy mass-to-light ratios (Mdyn/ ronmental variations (e.g. Lucey et al., 1991; de Carvalho and L) are constant or smoothly varying for galaxies. If Mdyn/L Djorgovski, 1992; Bernardi et al., 2003; La Barbera et al., is constant and if the structures were homologous for all 2010a, 2010b; Ibarra-Medel and Lo´ pez-Cruz, 2011). On the ETGs, then the FP would be equivalent to the virial plane other side, Cappellari et al. (2013) showed that the larger scat- 2 1 which takes the form re / r hlei with coefficients of a =2 ter in the FP is due to stellar population effects. They also con- and b = 1(Faber et al., 1987). Otherwise, the FP is rotated firmed that the deviation of the FP coefficients from the virial from the virial plane and the tilt of the FP is the difference plane is due to M/L variation. between the observed coefficients of the plane, a and b, and The aim of this study was to investigate the effect of local those from the virial plane. Jørgensen et al. (1996) found that environment on the properties of early-type galaxies, in partic- 1.24 0.82 re / r Ie for the FP of local cluster ETGs. Also Pahre ular their scaling relations using a sample of ETGs in different et al. (1998) found that the slopes, a 1.53 and b 0.79 environments such as in groups, clusters and in the field. In for ellipticals observed in the near-infrared. The FP represents Section 2, we present the data used in this study that comes from photometric and spectroscopic observations of galaxies
Please cite this article in press as: Samir, R.M. et al., The fundamental plane of early-type galaxies in different environments. NRIAG Journal of Astronomy and Geophysics (2016), http://dx.doi.org/10.1016/j.nrjag.2016.06.004 Fundamental plane of early-type galaxies 3 at 0 < z < 0.08. Section 3 presents our results concerning the For example, the projection effects can be reflected on a large fundamental plane, the Kormendy relation and the Faber- spread in the measurement of ro. Also, r anomalies and the Jackson relation of ETGs. In Section 4, we discuss our results. presence of inner subcomponents such as disks or central black Section 5 summarizes our main conclusions. holes (e.g., D’Onofrio et al., 1997; Goudfrooij et al., 2004) and the effects of aperture sizes must be taken into account. 2. The data In the next subsections we will analyze the available scaling relations such as the fundamental plane in j-space, the Kor- In our study we used a sample consisting of 94 ETGs collected mendy relation and the Faber-Jackson relation to introduce from different sources from literature as follows: 64 galaxies some reasonable explanation for the observed scatter of our from Annibali et al. (2010, sample 1), 20 galaxies from sample galaxies about the FP. Koleva et al. (2011, sample 2) and 10 galaxies from Ma´ rmol- In Fig. 2, we performed fitting for our sample using the Queralto´ et al. (2009, sample 3). Their effective radii (r00) and least square method and we obtained the parameters a, b e and c of the FP as follows: a = 1.235 with error 0.608, central velocity dispersions (r ) are published by the authors. o b c Their mean surface brightnesses hl i are calculated following = 0.222 with error 0.107 and = 3.983 with error 2.145. e B a b Graham and Driver (2005). Effective radii were converted It is clear that the values of and of our fitting are close to those of the Coma cluster, while the value of parameter c from arcsecond to parsec at the distance of the galaxy assum- 1 1 is somehow different. ing that the Hubble constant H0 =75kmsec Mpc . Sample 1 consists of 64 galaxies from Annibali et al. (2010), j mostly located in low density environments (see Table 1). All 3.2. The fundamental plane in -space galaxies in this sample belong to the Revised Shapley Ames Catalog of Bright Galaxies (RSA) (Sandage and Tammann, By a simple orthogonal coordinate transformation (i.e., a rota- 1987) and have redshift lower than 5500 km s 1. For this tion), a different expression for the FP in terms of kappa (j) sample the effective radii in arcsec are obtained from RC3 space was introduced by Bender et al. (1992). The axes of this (de Vaucouleurs et al., 1991) and the ro is from HyperLeda coordinate system are directly proportional to the physical database (http://leda.univ-lyon1.fr/). The values of ro are parameters of galaxies and defined as obtained from apertures in re/8 region. ðrÞþ ð Þ j ¼ 2 log pffiffiffi log re ð Þ Sample 2 consists of 20 galaxies from Koleva et al. (2011). 1 3 2 Their basic properties are summarized in Table 2. Eight of these galaxies are in The Fornax cluster and 12 galaxies are ðrÞþ ð Þ ð Þ j ¼ 2 log 2 logpffiffiffi Ie log re ð Þ in the Virgo cluster. For this sample the values of r are from 2 4 o 6 HyperLeda. For galaxies in the Fornax cluster, the velocity dispersion is overestimated in the external regions and more ðrÞ ð Þ ð Þ 2 log logpffiffiffiIe log re importantly, it is underestimated in the central regions. j3 ¼ ð5Þ 3 Sample 3 consists of 10 galaxies (see Table 3). Two of them are in the Fornax cluster and 8 galaxies are in the field or low where logIe = 0.4(hlei 27), j1 is proportional to the loga- density environment. This sample is selected from Ma´ rmol- rithm of the mass, j2 is proportional to the logarithm of (M/L) 2 j Queralto´ et al. (2009). Their re values in arcsec in the B-band Ie and 3 is proportional to the logarithm of M/L. The edge-on r and their o are obtained through private communication with view of the FP is represented by j1 and j3. Ma´ rmol-Queralto´ , where they collect them from the literature. In Fig. 3 we show the distribution of our sample of ETGs in j1–j3 space. They show a similar tilt and dispersion to those of 3. Results Virgo cluster galaxies from Bender et al. (1992). The galaxies that show deviation above the FP in Fig. 1 also show a ten- j Table 4 lists the calculated logarithmic values for the photo- dency to have larger values of 3 i.e. larger M/L ratios as metric and spectroscopic parameters of our samples in addi- expected for their old ages. On the other side, the galaxies that are deviated below the FP in Fig. 1 also show a tendency to tion to the mean surface brightness hleiB. have smaller values of j3 which indicate lower M/L ratios. Pre- vious studies (e.g. Forbes et al., 1998) show that there is a cor- 3.1. The fundamental plane in log (re), hlei, and log (ro) space relation between the residuals from the FP and the age of the central stellar populations of the galaxies. Table 5 shows the Fig. 1 shows the FP of our samples of ETGs in different envi- available published ages for some of our sample galaxies. ronments. The edge-on projection of the FP of Coma cluster is These published ages are luminosity-weighted central ages represented by a solid line, while the dashed line represents the based on Lick absorption lines and single stellar population r 1 dispersion of galaxies in Coma cluster. Our samples of models to break the age-metallicity degeneracy. ETGs are illustrated using different symbols for different refer- ences as shown in Table 4. It is clear in this Figure that most of 3.3. The Kormendy relation the deviant galaxies from the FP are those of sample 2 in Virgo and Fornax clusters which are located below it. As mentioned in Section 3, the values of r for the Fornax galaxies are under- Fig. 4 shows the Kormendy relation (KR) between the mean o hl i estimated and this can be responsible for their direction of surface brightness within the effective radius e B and effec- scatter relative to the FP. For the other galaxies, many differ- tive radius in the B-band of our galaxies. The solid line repre- ent reasons can cause them to show such significant deviation. sents the Hamabe and Kormendy (1987) relation,
Please cite this article in press as: Samir, R.M. et al., The fundamental plane of early-type galaxies in different environments. NRIAG Journal of Astronomy and Geophysics (2016), http://dx.doi.org/10.1016/j.nrjag.2016.06.004 4 R.M. Samir et al.
Table 1 Main characteristics of Sample 1 (Annibali et al., 2010). Col. (1) gives the galaxy identification; Col. (2) provides the galaxy morphological classification according to RC3 (Third Reference Catalog of bright galaxies, de Vaucouleurs et al., 1991); Col. (3) gives 1 the effective radius re in seconds of arc from RC3; Col. (4) gives the central velocity dispersion ro in km s from HyperLeda (http:// leda.univ-lyon1.fr//); Col. (5) indicates the environment of the galaxy collected by us (when available, the name of the environment is mentioned): when the galaxy is a member of a well known cluster or group, their names are indicated; when the galaxies do not belong to a cluster or a group, it is labeled as field galaxy. The term ‘‘low density” refers to the richness parameter of galaxies as clarified by Annibali et al. (2010). 1) Galaxy Type RC3 re (arcsec) ro (km s Environment NGC 128 S0 17.3 183.0 NGC 777 E1 34.4 317.0 Group (LGG 42)a NGC 1052 E4 33.7 215.0 Group (LGG 71)a NGC 1209 E6 18.5 240.0 Groupb NGC 1297 SAB0 28.4 115.0 Low density NGC 1366 S0 10.6 120.0 Fornax and Eridanus Cloudc NGC 1380 SA0 20.3 240.0 Fornax Cluster NGC 1389 SAB(s)0 15.0 139.0 Fornax and Eridanus Cloudc NGC 1407 E0 70.3 286.0 Eridanus group (LGG 100)a NGC 1426 E4 25.0 162.0 Low density NGC 1453 E2 25.0 162.0 Group (LGG 103)a NGC 1521 E3 25.5 235.0 NGC 1533 SB0 30.0 174.0 Dorado Cloudc NGC 1553 SA(r)0 65.6 180.0 Dorado Cloudc NGC 1947 S0 32.1 142.0 Low density NGC 2749 E3 33.7 248.0 NGC 2911 SA(s)0 50.9 235.0 Group (LGG 177)a NGC 2962 RSAB(rs)0+ 23.3 180.0 NGC 2974 E4 24.4 220.0 Group (LGG 179)a NGC 3136 E: 36.9 230.0 Low density NGC 3258 E1 30.0 271.0 Antlia Hydra Cloudc NGC 3268 E2 36.1 227.0 Antlia Hydra Cloudc NGC 3489 SAB(rs) 20.3 129.0 Low density NGC 3557 E3 30.0 265.0 Antlia Hydra Cloudc NGC 3607 SA(s)0: 43.4 220.0 Fielda NGC 3818 E5 22.2 191.0 Fieldb NGC 3962 E1 35.2 225.0 Crater cloudc NGC 4374 E1 50.9 282.0 Virgo, group (LGG 292)a NGC 4552 E 29.3 264.0 Virgo clusterc NGC 4636 E0 1 88.5 209.0 Virgo clusterc NGC 4696 E+1 85.0 254.0 Centaurus Cloudc NGC 4697 E6 72.0 174.0 Cluster (Virgo)a NGC 5011 E1 2 23.8 249.0 Centaurus Cloudc NGC 5044 E0 82.3 239.0 Virgo clusterc NGC 5077 E3+ 22.8 260.0 Virgo clusterc NGC 5090 E2 62.4 269.0 Centaurus Cloudc NGC 5193 E pec 26.7 209.0 NGC 5266 SA0- 76.7 199.0 Low density NGC 5328 E1: 22.2 303.0 NGC 5328 group NGC 5363 S0-a 36.1 199.0 Group (LGG 362)a NGC 5638 E1 28.0 168.0 Group (LGG 386)a NGC 5812 E0 25.5 200.0 Fielda NGC 5813 E1 2 57.2 239.0 Group (LGG 393)a NGC 5831 E3 25.5 164.0 Group (LGG 393)a NGC 5846 E0+ 62.7 250.0 Group (LGG 393)a NGC 5898 E0 22.2 220.0 Virgo – Libra Cloudc NGC 6721 E+: 21.7 262.0 NGC 6758 E+: 20.3 242.0 NGC 6776 E+pec 17.7 242.0 Field NGC 6868 E2 33.7 277.0 Groupb NGC 6876 E3 43.0 230.0 NGC 6958 E+ 19.8 223.0 Fieldb NGC 7007 SA0-: 15.4 125.0 Low density NGC 7079 SB(s)0 19.8 155.0 Low density NGC 7097 E5 18.1 224.0 Low density NGC 7135 SA0- pec 31.4 231.0 Low density
Please cite this article in press as: Samir, R.M. et al., The fundamental plane of early-type galaxies in different environments. NRIAG Journal of Astronomy and Geophysics (2016), http://dx.doi.org/10.1016/j.nrjag.2016.06.004 Fundamental plane of early-type galaxies 5
Table 1 (continued)