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Angular Momentum of Galaxies in the Densest Environments: a FLAMES/GIRAFFE IFS Study of the Massive Cluster Abell 1689 at Z = 0

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Angular Momentum of Galaxies in the Densest Environments: a FLAMES/GIRAFFE IFS Study of the Massive Cluster Abell 1689 at Z = 0 Astronomical Science Angular Momentum of Galaxies in the Densest Environments: A FLAMES/GIRAFFE IFS Study of the Massive Cluster Abell 1689 at z = 0.18 Francesco D’Eugenio1 of these empirical laws — alongside their bined with the collecting power of the Ryan C. W. Houghton1 very small scatter — imposes strong ESO Very Large Telescope (VLT), are the Roger L. Davies1 constraints on the structure and evolution ideal tools for this task. Elena Dalla Bontà2, 3 of ETGs (Bower et al., 1992). This makes them ideal testing grounds for any galaxy formation theory. Their study, important FLAMES/GIRAFFE observations of 1 Sub-department of Astrophysics, in its own right, is also fundamental Abell 1689 Department of Physics, University of for our understanding of the process of Oxford, United Kingdom structure formation in the Universe. Abell 1689, a massive galaxy cluster at 2 Dipartimento di Fisica e Astronomia redshift z = 0.183, has regular, concen- “G. Galilei”, Università degli Studi di The advent of integral field spectroscopy tric X-ray contours suggesting that it Padova, Italy (IFS) started a revolution in the study of is re laxed. Its X-ray luminosity outshines 3 INAF–Osservatorio Astronomico di ETGs. The SAURON survey discovered Coma by a factor of three, and Virgo Padova, Italy the existence of two kinematically distinct by over an order of magnitude. Its comov- classes of ETGs, slow and fast rotators ing distance is 740 Mpc, giving a scale (SRs and FRs, see Emsellem et al. [2007]) of 1 arcsecond per 3.0 kpc. Alongside its Early-type galaxies (ETGs) exhibit kine- and Cappellari et al. (2007). The former physical properties, Abell 1689 was an matically distinct slow and fast rotator have little or no rotation, exhibit kinemati- ideal target for FLAMES because the (SR, FR) morphologies. The former cally decoupled cores and misalignment spatial resolution of the GIRAFFE-deploy- are much less common (10% of ETGs), between kinematics and photo metry. The able integral field units (IFUs) samples up but their incidence is higher in the core latter are flattened systems, compatible to one effective radius (Re) for most gal- of the Virgo Cluster (25%). Here we pre- with rotational symmetry and a disc-type axies. Finally, a wealth of archival data, sent FLAMES/GIRAFFE integral field origin. The new division crucially crosses including imaging from the Hubble Space spectroscopy of 30 galaxies in the mas- the boundary between Es and S0s, in Telescope (HST) Advanced Camera for sive cluster Abell 1689 at z = 0.183. that FRs populate both morphological Surveys (ACS), is available and vital to a Abell 1689 has a density 30 times classes. ATLAS3D (the volume-limited fol- study of this nature. higher than that of Virgo, making it the low-up survey to SAURON; Cappellari ideal place to test the effects of envi- et al., 2011a; Emsellem et al., 2011), F625W-band imaging from the HST ACS, ronment, such as local density and established that 66% of morphological combined with g:- and r:-band GEMINI cluster properties. We find 4.5 ± 1.0 ellipticals are FRs, and thus share the imaging were used for the photometry SRs (or an average ETG fraction, ƒSR, of same internal structure as S0s. This is (Houghton et al., 2012). The spectroscopic 0.15 ± 0.03) in Abell 1689, identical to evidence for a new classifi cation para- data (spectral resolution, R = 11 800, the value for field/groups in ATLAS3D. digm, based on kinematics rather than spectral range 573 nm < λ < 652 nm Within Abell 1689 ƒSR increases towards morphology (Cappellari et al., 2011b). [486 nm < λ < 552 nm rest frame]) covers the centre, ex ceeding the value found in standard V-band absorption features. the core of Virgo. This work is the high- The ATLAS3D team presented the kine- GIRAFFE provides 15 independent mini est redshift study of its kind. matic morphology–density (kT–Σ) relation, IFUs, deployable anywhere on the focal analogous to the morphology–density plane; each IFU is positioned by a mag- relation (Dressler, 1980). It links the frac- netic button and contains an array of Kinematical classification of ETGs tion of SRs in the ETG population (ƒSR) 20 square microlenses. They are arranged with the local number density of galaxies: in four rows of six (with four “dead” cor- ETGs comprise morphologically distinct they found that ƒSR is independent of ners) for a total field of view of 3 by 2 arc- elliptical (E) and lenticular (S0) galaxies. the environment density over five orders seconds. Each lenslet is then connected Despite their differences, Es and S0s of magnitude from field to group environ- to the spectrometer with a dedicated opti- have lots in common. They are both char- ments. But they noticed a sharp increase cal fibre bundle. Alongside the 15 IFUs, acterised by old stellar populations, which in ƒSR in the inner core of the Virgo Clus- the instrument also provides 15 fully de - has earned them the attribute “early- ter, the highest density probed by the ployable sky fibres. type”. The average ETG has little or no ATLAS3D survey. Virgo is an unrelaxed, cold gas, which is reflected in the star low-density cluster, but what would be Since the magnetic buttons are larger formation rate. Its light profile is smooth measured in the denser environments (10 arcseconds) than the IFU field of view, and its shape fairly regular. One of the beyond the local Universe? Addressing they cannot be deployed closer than a most puzzling facts about these galaxies this question gives further insight on minimum distance of 11 arcseconds. is how, with masses and luminosities that the kT–Σ relation, and on the processes GIRAFFE permits the observer to target span several orders of magnitude, they that drive galaxy formation and evolution. 15 objects simultaneously and we chose obey a number of tight scaling relations. to target 30 galaxies as a compromise These include the colour–magnitude Since rich, relaxed clusters are rare, they between sample statistics and integration relation, the colour–σ and Mg–σ relations can only be found at higher redshifts. time. In order to gain the maximum pos- (where σ is the velocity dispersion) and the The multiplexing capabilities of FLAMES/ sible signal-to-noise ratio, we initially fundamental plane. The mere existence GIRAFFE (Pasquini et al., 2002), com- selected the 30 ETGs with the highest The Messenger 151 – March 2013 37 Astronomical Science D’Eugenio F. et al., Angular Momentum of Galaxies in the Densest Environments 01 02 03 Figure 1. Kinematic –150/150 0/225 –100/100 0/125–150/1500/225 maps of the Abell 1689 sample. For each of the 30 galaxies in the sam- ple we present a set of four images. The first 04 05 06 –100/100 0/125 –100/100 0/300–100/1000/325 one shows FLAMES/ GIRAFFE IFU footprints superimposed on HST imaging (Gemini imaging for target 20). The sec- ond plot shows the 07 08 09 –100/100 0/150 –100/100 0/225–100/1000/150 reconstructed image from VLT integral field spectroscopy, where each square is a spaxel and corresponds to a 10 11 12 lenslet of the IFU. Also –100/100 0/225 –100/100 0/150–100/1000/350 shown is an isophote at either Re, or the closest integer fraction that fits into the IFU footprint. The four black corners 13 14 15 –100/100 0/200 –175/175 0/325–100/1000/200 correspond to unavaila- ble “dead” spaxels, while other black spax- els (seen in 11, 15 and 30) correspond to bro- ken or unused fibres. 16 17 18 –100/100 0/175 –250/250 0/325–125/1250/200 Velocity and velocity dispersion maps are depicted in the third and fourth plots. The black compass arrows show 19 20 21 north and east direc- –100/100 0/275 –100/100 0/150–100/1000/150 tions. Colour-bar limits are given in km/s. 22 23 24 –200/200 0/250 –100/100 0/200–100/1000/200 25 26 27 –200/200 0/225 –100/100 0/275–100/1000/250 28 29 30 –175/175 0/175 –150/150 0/200–100/1000/200 surface brightness within a 3-arcsecond was exposed five times for two hours, for tions of the Virgo Cluster (for which the radius. This sample was then subject a total of ten hours per galaxy. The ob - SR population is known from ATLAS3D) to two practical constraints. We needed servations were carried out in visitor using the luminosity function of our sam- all of our targets to have high-resolution mode, which proved to be both efficient ple. This showed that we could recover HST imaging, which limited our choice to and accurate in terms of object acquisi- the true value of ƒSR for Abell 1689. candidates in the innermost regions of tion. Excellent seeing of 0.60 arcseconds Although we did not do a colour selec- the cluster. The 11-arcsecond proximity reduced the correlation between neigh- tion, our sample falls entirely on the Red constraint ruled out some targets in the bouring spaxels. Sequence (RS). However, the number most crowded regions, forcing us to re- of galaxies that do not fall on the RS in select from a reserve list. This left us with Our sample is biased towards bright Abell 1689 is extremely low, and we 29 galaxies inside the HST field of view ob jects, which in turn could bias us to found the bias to be minimal. and one outside (galaxy 20). Each plate detect more SRs.
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