Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters

0.76 MB·

by  E. Toloba

Draftversion June23,2014
PreprinttypesetusingLATEXstyleemulateapjv.5/2/11
STELLAR KINEMATICS AND STRUCTURAL PROPERTIESOF VIRGO CLUSTER DWARF EARLY-TYPE
GALAXIES FROM THE SMAKCED PROJECT.I. KINEMATICALLY DECOUPLED CORES AND
IMPLICATIONS FOR INFALLEN GROUPS IN CLUSTERS
E. Toloba1,2, P. Guhathakurta1, G. van de Ven3, S. Boissier4, A. Boselli4, M. den Brok5, J. Falco´n-Barroso6,7,
G. Hensler8, J. Janz9,10, E. Laurikainen10,11, T. Lisker9, S. Paudel12, R. F. Peletier13, A. Ry´s6,7, and H. Salo10
1UCO/LickObservatory,UniversityofCalifornia,SantaCruz,1156HighStreet, SantaCruz,CA95064, USA
2ObservatoriesoftheCarnegieInstitution forScience,813SantaBarbaraStreet, Pasadena,CA91101,USA
4 3 MaxPlanckInstitute forAstronomy,K¨onigstuhl17,69117Heidelberg,Germany
1 4 Laboratoired’AstrophysiquedeMarseille-LAM,Universit´ed’Aix-Marseille&CNRS,UMR7326, 38rueF.Joliot-Curie,13388
0 5 DepartmentofPhysicsandAstMroanrosemilyl,eUCnediveexrs1it3y,FofraUntcaeh,SaltLakeCity,UT84112, USA
2 6 Instituto deAstrof´ısicadeCanarias,V´ıaL´acteas/n,LaLaguna,Tenerife,Spain
n 7 DepartamentodeAstrof´ısica,UniversidaddeLaLaguna,E-38205, LaLaguna, Tenerife,Spain
8 UniversityofVienna,Department ofAstrophysics,Tu¨rkenschanzstraße 17,1180Vienna,Austria
a 9 AstronomischesRechen-Institut, Zentrum fu¨rAstronomiederUniversit¨atHeidelberg,M¨onchhofstraße12-14,D-69120Heidelberg,
J
Germany
8 10 DivisionofAstronomy,DepartmentofPhysics,P.O.Box3000, FI-90014UniversityofOulu,Finland
2 11 FinnishCenterforAstronomywithESO(FINCA), UniversityofTurku,Finland
12 LaboratoireAIMParis-Saclay,CNRS/INSU,Universit´eParisDiderot,CEA/IRFU/SAp,91191Gif-sur-YvetteCedex,Franceand
] 13 KapteynAstronomicalInstitute, Postbus 800,9700AVGroningen,TheNetherlands
A Draft version June 23, 2014
G
ABSTRACT
.
h Wepresentevidenceforkinematicallydecoupledcores(KDCs)intwodwarfearly-type(dE)galaxies
p in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-
- line spectroscopyand imaging survey. These KDCs have radii of 1.8′′ (0.14 kpc) and 4.2′′ (0.33 kpc),
o
respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1)
r
t inverted sense of rotation; and (2) younger (and possibly more metal-rich) stellar population. The
s observedstellarpopulationdifferencesareprobablyassociatedwiththeKDC,althoughwecannotrule
a
out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis
[
methodtodetect,quantifythesignificanceof,andcharacterizeKDCsinlong-slitrotationcurvedata.

1 We apply this method to the two dE galaxies presented in this paper and to five other dEs for which
v KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC
6 detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly
3 that may be an asymmetric KDC.The frequency of occurence of KDCs and their properties provide
3
important constraints on the formation history of their host galaxies. We discuss different formation
7
scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas
.
1 accretion can explain the properties of these KDCs. Both of these mechanisms require that the
0 progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed
4 in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the
1 cluster quenched star formation.
v: Subject headings: galaxies: dwarf–galaxies: elliptical–galaxies: clusters: individual(Virgo)– galax-
i ies: kinematics and dynamics – galaxies: stellar content – galaxies: photometry
X
r
a 1. INTRODUCTION ness (µB &22 mag arcsec−2) section of the ETG class.
Detailed photometric and spectroscopic studies of
Early-type galaxies (ETGs) are characterized by a
dEs suggest that they are a heterogeneous popula-
smooth surface brightness distribution, minimal inter-
tion. Beneath their mostly smooth light distribu-
stellar gas and dust, and a red color indicating an old
tion and apparent morphological simplicity, some dEs
stellar population. These galaxies are sometimes re-
display subtle signs of structural complexity in the
ferred to as quiescent or quenched, in contrast to star-
form of disks, spiral arms, and/or irregular features
forminggalaxies. TheETGclassiscomposedoftwomor-
(e.g., Jerjen et al. 2000; Barazza et al. 2002; Geha et al.
phological classes, ellipticals (Es) and lenticulars (S0s),
2003; Graham & Guzma´n 2003; De Rijcke et al. 2003;
distinguished by the absence/presence of a stellar disk.
Lisker et al. 2006; Ferrarese et al. 2006; Janz et al.
Dwarf early-type galaxies (dEs for simplicity)1 occupy
2012). Kinematically too, dEs display a range of di-
the low luminosity (M &−18) and low surface bright-
B versityin thatgalaxieswith similar photometric proper-
tiescanhaveverydifferentrotationspeeds(Pedraz et al.
[email protected] 2002; Simien & Prugniel 2002; Geha et al. 2002, 2003;
1 The term dE has traditionally been used to refer to dwarf van Zee et al. 2004; Chilingarian 2009; Toloba et al.
ellipticalgalaxies,whereaswelooselyusethetermheretoinclude 2009, 2011; Ry´s et al. 2013).
dwarf elliptical, dwarf lenticular (dS0), dwarf spheroidal (dSph),
The dE galaxy class is dominant by number
andeventheoccasional low-luminosityelliptical(E)galaxies.
2 Toloba et al.
in high density environments (Sandage et al. 1985;
TABLE 1
Binggeli et al. 1988) and these galaxies are rarely seen GalaxyProperties
in isolation (Gavazzi et al. 2010). In a recent study,
Geha et al. (2012) found that quenched galaxies with Galaxy RA(J2000) Dec(J2000) mr mH Re (′′) n
(1) (2) (3) (4) (5) (6) (7)
stellarmassesof∼109M⊙ andmagnitudesofMr >−18 VCC1183 12:29:22.5 +11:26:02 13.27 11.12 19.1 1.72
(properties that include those of dEs) are invariably
VCC1453 12:32:44.2 +14:11:44 13.25 11.00 16.9 2.22
located within 1.5 Mpc (∼ 4 virial radii) of a rela-
tively massive host, while star-forming galaxies of simi- NOTES:(1)galaxyname;(2)rightascensioninhh:mm:ss;(3)dec-
lar masses are found beyond that distance. It should be linationindd:mm:ss;(4)magnitudeinther-bandbyJanz&Lisker
notedthoughthatanexceptiontotheGehaetal.finding (2008);(5)magnitudeintheH-band;(6)half-lightradiusintheH-
band;(7)S´ersicindexofasinglemodelfittothesurfacebrightness
is the discovery by Pasquali et al. (2005) of a quiescent
profileintheH-band. Columns(5),(6),and(7)aremeasurements
dwarfatadistanceof1.9Mpcfromitsnearestneighbor. byJanzetal.(2013).
Thisstrongmorphologicalsegregationandtheirstruc-
encountersbetweenclustermembersaresorapidthatthe
tural complexity suggest that dEs are late-type galax-
energy available is too small to produce such perturba-
ies transformed by the environment. A few different
tions in the core of a dwarf galaxy (Binney & Tremaine
transformationmechanismshavebeenproposedoverthe
1987; Boselli & Gavazzi 2006).
years, but none of these mechanisms appear to explain
This paper is organized as follows. In Section 2, we
all of the observed properties of dEs. The most promis-
describe the spectroscopicandphotometric data used to
ing ofthese mechanismsinvolvegravitationaltidal heat-
find the KDCs in VCC 1183 and VCC 1453. In Sec-
ing (i.e., harassment, as described in Moore et al. 1998;
tion3, we presentthe measurementof stellarkinematics
Mastropietro et al.2005)orhydrodynamicalinteractions
and stellar population parameters. In Section 4, we use
with the intracluster medium (i.e., ram-pressure strip-
these measurements to infer the properties of the KDCs
ping, as discussed in Lin & Faber 1983; Boselli et al.
and their host galaxies. In Section 5, we introduce a
2008a,b).
statistical metric to quantify the significance of the de-
With the goal of understanding the physical processes
tection of the two new KDCs as well as other candidate
that form dEs, we have begun the SMAKCED2 (Stel-
KDCs from the literature. In Section 6, we discuss the
lar content, MAss and Kinematics of Cluster Early-type
most likely formation scenarios for KDCs. Finally, in
Dwarf galaxies) project, a new spectroscopic and pho-
Section 7, we summarize our findings and conclusions.
tometric survey of dEs in the Virgo cluster, the near-
est dense galaxy cluster. This paper is part of a series 2. THEDATA
in which we present analysis of the structural and kine-
This paper uses H-bandphotometry andopticalspec-
matical properties of Virgo cluster dEs. Details of the
troscopycollectedaspartoftheSMAKCEDproject. We
photometricandspectroscopicdatasetsaredescribedin
presentabriefsummaryhereofthesampleselection,ob-
Toloba et al. (2014, in preparation — hereafter referred
servations,and data reduction. The readeris referredto
to as Paper II). This paper, the first in the series, is fo-
Paper II for more details.
cused on the analysis of newly discovered kinematically
decoupledcores(KDCs)intwoofthedEsinoursample,
2.1. The Sample
VCC 1183 and VCC 1453.
A KDC refers to a region in the center of a galaxy Thephotometric SMAKCEDsurvey,conductedin the
whose kinematical properties are distinct from those H-band, consists of a nearly complete sample of 121
of the main body of the galaxy. While KDCs have early-type galaxies in the Virgo cluster in the absolute
long been known in luminous ETGs (e.g., Rix et al. r-band magnitude range −19.0 < M < −16.0, in-
r
1992; Surma & Bender 1995; Mehlert et al. 1998; cluding a complete magnitude-limited subsample with
Wernli et al. 2002; Emsellem et al. 2004; Geha et al. M <−16.8. We assume a distance to the Virgo cluster
r
2005; Emsellem et al. 2011; Krajnovi´c et al. 2011), they of 16.5 Mpc (Mei et al. 2007). The galaxies are selected
are harder to detect in dEs due to their lower surface from the Virgo Cluster Catalog (VCC, Binggeli et al.
brightness. Nevertheless, it is important to study and 1985) based on their early-type morphology and low lu-
characterize KDCs in dEs in order to understand the minosity, see details in Janz et al. (2013). While this
physical processes that produce them, including how sample consists mostly of galaxies with dwarf elliptical
these processes may be distinct from those that produce ordwarflenticular (dS0) morphologicalclassificationsin
KDCs in luminous ETGs. the literature, it also contains a small fraction (9.9%,
The formation of KDCs in luminous ETGs is thought 12/121)ofgalaxieswithelliptical(E)morphologicalclas-
to be associated with gas accretion, merging sce- sification. For the purpose of this series of papers, we
narios, or flyby encounters (e.g., Balcells & Quinn looselyrefertoalloftheseETGsinthismagnituderange
1990; Hernquist & Barnes 1991; Weil & Hernquist 1993; as dEs.
Gonz´alez-Garc´ıaet al. 2005). Whether these scenarios Thespectroscopicsurveyconsistsofasubsampleof39
apply to dEs is far from obvious given that dEs are dwarf early-type galaxies in the absolute r-band magni-
mainly found in galaxy clusters where there is a dearth tuderange−18.6<M <−16.4classifiedasdwarfellip-
r
ofcoldgastoaccrete,thestatisticalprobabilityofdwarf- ticalor dwarflenticular (dS0) by Binggeli et al.(1985)3.
dwarf mergers is low (e.g., as indicated by the simu- These 39 dEs are representative of the Virgo cluster
lations and observations of De Lucia et al. (2006) and ETGs in the magnitude range −19.0 < M < −16.0.
r
Mart´ınez-Delgado et al. (2012), respectively), and flyby
3 Low-luminosity ETGs with high surface brightness are not
2 http://smakced.net/index.html includedinthespectroscopicsubsample.
KDC in dEs in the Virgo cluster 3
More details on the spectroscopic sample can be found 3. MEASUREMENTOFTHEKINEMATICANDSTELLAR
in Toloba et al. (2011) and Paper II. POPULATIONPROFILES
This paper focuses on the two dEs, out of the 39 an- Fromthereducedtwodimensionalspectra,wemeasure
alyzed in Paper II, that turned out to host a KDC: the line-of-sight radial velocity (V) and velocity disper-
VCC1183andVCC1453. Someoftheirbasicproperties sion(σ)alongthegalaxy’smajoraxisusingthepenalized
can be found in Table 1. pixel-fitting software (pPXF) of Cappellari & Emsellem
(2004). The parameters V and σ are obtained by cross-
2.2. Observations and Data Reduction
correlating each science spectrum with a model cre-
The observations and data reduction for the H-band ated as a linear combination of stellar templates that
photometryaredetailedinJanz et al.(2013),theoptical best reproduces the science spectrum, allowing differ-
spectroscopy is detailed in Toloba et al. (2011) and Pa- ent weights for each template. The stellar templates
per II. Here we summarize the instrumental setups and used for this analysis are a compilation of stars selected
the main steps of the reduction procedure. from the MILES stellar library (Sa´nchez-Bl´azquez et al.
VCC 1183 was observed for 720s using the SOFI in- 2006; Cenarro et al. 2007; Falco´n-Barrosoet al. 2011)
frared camera at the 3.6-m New Technology Telescope and cover a variety of spectral types and luminosity
(NTT) at the ESO Observatory (Chile). VCC 1453 was classes (B9, A0, A5V, G2III, G2V, G8III, G9III, K0I,
observed for 2820s using the NOTCam wide-field cam- K1V,K2III,K3III,K4III,M2III). These templates were
era at the 2.5-m Nordic Optical Telescope (NOT) at El observedwith the sameinstrumentalsetup asthe galax-
Roque de los Muchachos Observatory (Spain). The ob- ies. We defocusedthe telescope to makethe starshomo-
servationsweredoneusingstandardditherpatternsthat geneously fill the slit as galaxies do.
allowed us to get the sky level simultaneously with the Each one dimension science spectrum is obtained by
target galaxy. spatially co-adding individual spectra following the size
ThedatareductionwasperformedwithIRAF4 follow- andS/NthresholdsdescribedinToloba et al.(2011)and
ing the standard steps for infrared photometry. These in Paper II. The minimum binning size is 3 pixels (com-
included illumination correction, flat fielding, sky sub- parabletothe averageseeingaffectingtheobservations),
traction, and correction for field distortions. and the minimum S/N is 10 ˚A−1 for V and 15 ˚A−1 for
The spectroscopic observations were performed at El
σ. The minimum S/N threshold for the red configura-
Roque de los Muchachos Observatory (Spain).
tion of VCC 1453 is S/N=15 and S/N=25 ˚A−1 for V
VCC 1183 was observed as part of the MAGPOP-
andσ,respectively,tocompensatefortheseveralmasked
ITP collaboration (Multiwavelength Analysis of
regions due to sky line residuals.
Galaxy POPulations-International Time Program, PI:
Theresultingkinematicalprofilesareshowninthefirst
R. Peletier) and already presented in Toloba et al.
two rows of panel a in Figures 1 and 2. The rotation
(2011). In this paper, we reanalyze the kinematics
curve shown in the first row is obtained subtracting to
changing the radial binning scheme from a minimum of
each radial velocity the systemic velocity which is the
1 pixel to 3 pixels (see Section 3). This galaxy was ob-
weightedaverageofall the velocities alongthe slit. This
servedfor 3600s with the 2.5-m IsaacNewton Telescope
technique finds the center of the amplitude of the rota-
(INT) using the IDS spectrograph with the 1200l/mm
tioncurve. Thesecondrowshowsthevelocitydispersion
grating covering the wavelength range 4600–5690˚A.
profile.
VCC 1453,shownforthe firsttime here,wasobserved
As VCC 1453 was observed with two independent in-
for 7000s with the 4.2-m William Herschel Telescope
strumental setups, the final rotation curve is a weighted
(WHT) and the double-arm spectrograph ISIS in two
average of the velocity measurements obtained from the
independent instrumental setups. The blue setup used
blue and red setups in those regions where they overlap.
the 1200l/mm grating and covered 4200–5000 ˚A. The Atlargerradii,onlytheredsetupisused. Regardingthe
red setup used the 600l/mm grating and covered 5500– σ profile, we take advantage of the higher resolution of
6700 ˚A. the blue setup and use only those values.
Both galaxies were observed using a slit width of 2′′ The stellar populations along the major axis of the
which leads to a spectral resolution of 1.6 ˚A (full width galaxies are estimated using hydrogen (H ) and iron
β
at half the maximum, FWHM) for VCC 1183, and 1.4 (Fe4668 and Fe5709) Lick spectral indices (Worthey
and 3.2 ˚A (FWHM) for VCC 1453 in the blue and red 1994). Hβ is used as an indicator of age, and Fe4668
setup, respectively. and Fe5709 are used as indicators of metallicity. We use
The data was reduced following the standard pro- Fe5709for VCC 1453to have the largestradialcoverage
cedure for long-slit spectroscopy using the package possible.
REDumcE (Cardiel 1999). The main steps consisted of These Lick indices are measured in the Line-Index-
bias and dark current subtraction, flat fielding, and cos- System LIS-5˚A, i.e., broadened to a constant FWHM of
mic ray cleaning. The spectra were spatially aligned 5˚A(Vazdekis et al.2010). Thespatialco-additionofthe
and wavelengthcalibrated leading to typical wavelength spectra to measure the spectral indices follows the same
residualsof 0.2˚A. The spectra were then sky subtracted strategyas thatfor V andσ with the exceptionthat the
and flux calibrated using the response function derived minimum binning size required is 4 pixels to have larger
from our observed flux standards. S/N per spatial bin.
The last two rows of panel a in Figures 1 and 2 show
4 IRAF is distributed by the National Optical Astronomy Ob- theresultingH andFe4668,forVCC1183,andFe5709,
β
servatory, whichisoperated bytheAssociationofUniversitiesfor for VCC 1453, profiles.
Research in Astronomy, Inc., under cooperative agreement with
theNationalScienceFoundation.
4 Toloba et al.
4. ANALYSISOFTHEPROPERTIESOFTHEKDCS than in the main body of the galaxy. In general, having
younger and more metal-rich central regions is not un-
In this Section we explore whether the KDCs, identi-
usual for nucleated dEs (Paudel et al. 2011). However,
fied in velocity space, have properties that are different
only in extreme cases does this trend go beyond the nu-
fromthoseofthe mainbody ofthe hostgalaxy. In addi-
clear region (R∼1′′).
tion to the rotation velocity, we investigate the velocity
The last two rows of panel a in Figures 1 and 2 show
dispersionprofile, the stellar populations, andthe struc-
the radialprofiles ofthe spectralindices usedas ageand
ture of these galaxies.
metallicityindicatorsforVCC1183andVCC1453. Fig-
4.1. Kinematics ure 3 shows the spectral index-index diagrams used to
determine the stellar populations. The open dark blue
The rotationcurvesof VCC 1183andVCC 1453show
squares and light blue circles correspond to the H and
cores with inverted sense in velocity with respect to the β
iron measurements in Figures 1 and 2. For VCC 1453,
main body of the galaxy. These KDCs have radial sizes
the radial coverage of H and Fe5709 is different, thus,
of 1.8′′ (0.14 kpc) and 4.2′′ (0.33 kpc), respectively. β
for each H value we plot the nearest value of Fe5709 in
The velocity dispersion profile of VCC 1183 is rather β
radius. The solid dark blue square and light blue circle
flat, thus the KDC does not show a different velocity
are the H and iron indices of the KDC and the main
β
dispersionfromthatofthemainbodyofthegalaxy. The
body of the galaxy, respectively. These indices are mea-
velocity dispersion profile of VCC 1453 has a dip in the
sured by co-adding the spectra inside and outside of the
center of the galaxy with respect to the values at larger
KDC region.
radii. Wedonotknowhowthevelocitydispersionofthe
mainbodyofthegalaxycompareswiththatoftheKDC 4.3. Photometry
because the data do not go beyond the radial extent of
VCC 1183 and VCC 1453 are structurally complex.
the KDC.
The H-band surface brightness profiles of these two
ThefirstandsecondrowsofpanelainFigures1and2
galaxies are fitted by several components for the main
showtherotationcurveandvelocitydispersionprofilefor
body of the galaxies and a central nucleus (Janz et al.
VCC 1183 and VCC 1453, respectively. The dark blue
2012, 2013).
squares highlight the KDCs. The yellow vertical lines
We use the IRAF task ellipse to fit isophotes to the
indicate the radius at which the velocity of the KDC
H-bandimages. Eachisophoteisanellipsewhosemajor
reachesits maximum (RKDC). That radius is calculated
vmax axis is 5% larger than the previous one. The center,
averaging the position of the peak velocity for the ap-
the position angle (PA), and the ellipticity (ǫ) of the
proaching and receding radii. Janz et al. (2013) make
isophotes are left as free parameters.
a two dimensional fit to the H-band surface brightness
The analysis of the images and the resulting profiles
distributionofthese dEs. Thedashedgreylinesindicate
from ellipse-fitting do not show any significant struc-
the radius at which the inner S´ersic and outer exponen-
ture that can be associated with the KDC. However,
tial profiles have the same surface brightnesses.
VCC 1183 shows a particularly complex structure that
4.2. Stellar Populations includes the KDC and the remaining region with kine-
matical data. At R ∼ 6′′ the isophotes twist ∼ 77◦ and
Assuming the single stellar population models (SSPs) theellipticitydropswithrespecttotheouterpartsofthe
of Vazdekis et al. (2010) based on the MILES stellar li- galaxy. The surface brightness distribution at R.6′′ is
brary(Sa´nchez-Bl´azquez et al.2006;Cenarro et al.2007; best fitted by a lens (Janz et al. 2013).
Falco´n-Barrosoet al. 2011) with a Kroupa initial mass Panel b of Figures 1 and 2 shows the H-band image
function(Kroupa2001),weestimatetheagesandmetal- of the galaxy (upper panel) and the residuals after sub-
licities ([M/H]) of the KDC and the main body of the tracting a smooth model based on the ellipse-fitting of
galaxyusingthesoftwarermodel5(Cardiel et al.2003). the isophotes (lower panel). Panel c shows the profiles
This software interpolates the age and metallicity inside for surface brightness, position angle, ellipticity, and C
4
anindex-indexgrid. Theerrorsintheageand[M/H]are parameter (C <0 indicates boxy isophotes and C >0
4 4
calculated running 1000 Monte Carlo simulations vary- diskyisophotes)obtainedbytheellipse-fittingprocedure
ing the values of the spectral indices within a Gaussian described above.
distribution with width equal to their uncertainties.
The KDC of VCC 1183 is 2.0±0.5 Gyr old and has a 5. DETECTIONOFKDCSANDTHEIRRATEOF
OCCURRENCE
metallicityof[M/H]=−0.3±0.3,whilethemainbodyis
&10Gyrold(thisvalueisoutsidethegridsoweassume In this section, we develop a method to objectively
the age in the models that is consistent with the 2σ 6 define a KDC and assess its statistical significance. We
G
uncertainty of the measurement) with [M/H] = −1.1± apply this technique to the two new KDCs presented in
0.3. thispaperandalsotofiveotherdEsforwhichKDCshave
The KDC of VCC 1453 is 4.5±1.1 Gyr old, and has been reported in the literature. Appendix A contains
a metallicity of [M/H] = −0.2±0.1. The main body of relevant plots for each of the seven dE galaxies.
the galaxyhasanageof10.3±5.7Gyrandametallicity In addition, we use the results from our statistical
of [M/H]=−0.6±0.3. method to calculate the rate of occurrence of KDCs in
The stellar populations for VCC 1183 and VCC 1453 dEsandcompareit withthe rateofoccurrenceofKDCs
are younger and possibly more metal-rich in the KDC in more luminous early-type galaxies.
5http://www.ucm.es/info/Astrof/software/rmodel/rmodel.html 5.1. Development and Application of a Statistical
6 Gaussianwidth,σG Metric to Detect KDCs
KDC in dEs in the Virgo cluster 5
Fig.1.—Spectroscopic andphotometricmeasurementsofVCC1183. Panel a: Stellarkinematics andpopulationindicesasafunction
of distance from the galaxy’s center along the slit (in units of Re and arcseconds on the upper and lower horizontal axes, respectively).
The slit position angle is indicated in the upper right and corresponds to the part of the slit with positive radial distances. The rows,
fromtop to bottom, show the stellar rotation curve (with respect to the systemic velocity), the stellar velocity dispersionprofile, the Hβ
indexasatracerofage,andtheFe4668indexasatracerofmetallicity. Thefilleddarkbluesquaresindicatethekinematicallydecoupled
core based on the rotation curve and the light blue circles show the mainbody of the galaxy. The yellow vertical lines indicate the radii
forthemaximumrotationoftheKDC(RKvmDaCx). Panel b: ZoomonthecentralregionsoftheH-bandimage(upperpanel)andresiduals
(lowerpanel)aftersubtractingasmoothmodelbasedonellipse-fitting. Thegreyscalesshowbrightregionsinblack. Thebluelinesarethe
footprintofthelong-slitusedinthespectroscopicobservations. The+Rand−Rcorrespondtothepositiveandnegativeradialdistances
measuredinthespectroscopywithrespecttothecenterofthegalaxy. Theyellowandredellipsesarethecorrespondingellipticalisophotes
withsemi-majoraxesofRKvmDaCx andRe,respectively. Panel c: Profilesoftheellipse-fitting. Fromtoptobottom: surfacebrightness,PA,
ellipticity, andC4 profiles. The greydotted lineindicates aradius of 2pixels(1pixel=0.288′′). The ellipse-fittingresultsareunreliable
interiortothisradiusandarethereforeexcludedfromtheplots. Theyellowverticallines,enclosingthetriangles,arethesameasinpanel
a. Theredvertical lines,enclosingcircles,indicate the Re. Thedashed greylineindicates theradius atwhichtheinner S´ersicand outer
exponential profilesfittedtotheH-bandimagesreachthesamesurfacebrightness(Janzetal.2013).
6 Toloba et al.
Fig.2.—SameasFigure1forVCC1453,exceptthemetallicitytracerusedforthisgalaxyisFe5709andthepixelscaleis0.234′′.
KDC in dEs in the Virgo cluster 7
Fig.3.—Spectral index-indexdiagramsusedtoestimatethestellarpopulations ofgalaxies. Thegreydashedlinesrepresentthegridof
models by Vazdekisetal. (2010) in the system LIS-5˚A based on the MILES stellar library(S´anchez-Bl´azquez etal. 2006; Cenarroetal.
2007;Falco´n-Barrosoetal.2011)withaKroupainitialmassfunction(Kroupa2001). Nearlyhorizontallinesindicateconstantages,values
in Gyr printed at the right end of those lines, and nearly vertical lines show constant metallicity, labeled in the lower part of the grid.
Followingthe color code from Figures1 and 2, the open darkblue squares correspond to the KDC,and the lightblue dots represent the
main body of the galaxy. The solid dark blue square and light blue circle are the resulting spectral indices after the co-addition of the
spectrainsideandoutsideoftheKDCregion.
We propose a method to quantify whether the detec- Theinconvenienceofusinglong-slitspectraisthatthe
tion of a KDC in long-slit spectroscopic data is statisti- KDC can be missed if it is misaligned with respect to
cally significant. It is based on a statistical parameter the rotation field of the main body of the galaxy. Thus,
S(R) defined as not meeting the significance threshold described above
does not rule out the presence of a KDC in that dE.
This caveat is better addressed with integral-field spec-
|hV (<R)i−hV (>R)i|
inner outer
S(R)= (1) troscopy, but large samples of dEs observed with this
pδhVinner(<R)i2+δhVouter(<R)i2 technique are still lacking.
For eachradius R, hV (<R)i is the weightedmean
inner 5.2. The Fraction of dEs that Contain KDCs
velocity interior to that radius and hV (> R)i is the
outer
weighted mean velocity exterior to that radius. The pa- There is a total of 101 available rotation curves
rameters δhV (< R)i and δhV (< R)i are the un- for dEs in different environments combining Paper II
inner outer
certainties in the weighted mean velocities, respectively. and the literature with similar or higher spectral
We define the significance of the detection of a KDC resolution than ours (Pedraz et al. 2002; Geha et al.
(hS i) as the average of the three maximum values 2002, 2003; van Zee et al. 2004; de Rijcke et al. 2005;
max
of S(R). The average of their radii is the parameter Thomas et al. 2006; Chilingarian 2009; Toloba et al.
hR i. Itisimportanttodistinguishbetweenamono- 2011; Spolaor et al. 2010; Koleva et al. 2011; Ry´s et al.
Smax
tonically increasingrotation curve from a rotationcurve 2013, SAURON IFU spectra are considered here be-
withaKDCinthecenter. IfaKDCispresent,themean cause, despite their lower spectral resolution, their two
velocityoftheKDChastheoppositesignwithrespectto dimensionalspatialcoveragefavorsfinding KDCs). This
the meanvelocityofthe mainbody ofthe galaxy. Thus, number is large enough to statistically quantify how fre-
we calculate hS i in the region where hV (< R)i quently KDCs are detected within this galaxy class.
max inner
and hV (> R)i have opposite signs. A KDC is con- The resulting statistics presented here must be used
outer
sidered significant when hS i≫3 and marginal when cautiouslyfor four main reasons: (1)the velocityresolu-
max
hS i∼3. tionplaysagainstfinding featureswithverylowvelocity
max
Table 2showsthe resultsofthe applicationof oursta- amplitudes;(2)the majorityofthe rotationcurvescome
tistical analysis to the folded rotation curves of the two from long-slit data and thus are limited to those KDCs
KDC candidates found in our sample of dEs and the that are nearly aligned with the PA of the slit; (3) the
five other candidates reported in the literature. Four absenceofsignificantevidenceforthepresenceofaKDC
out of the seven KDC candidates meet our thresholds doesnotruleoutitsexistence;and(4)thesampleofdEs
for statistically significant detections and two more are observed spectroscopically is not complete.
marginal detections. The remaining galaxy, VCC 1036, Besides these technical problems for detecting KDCs,
is different from the other galaxies (see Figure 7). The thereis anobservationalbiasthatnotevenintegral-field
rotation curve of VCC 1036 is asymmetric in two ways: spectroscopy or larger surveys can overcome: the fading
(1)one side is rotating morerapidly than the other;and of the stellar populations over time. McDermid et al.
(2) one side is kinematically regular in the center while (2006) simulate this effect and find that in 2 − 5 Gyr
the other side is not. The statistical parameter S(R) a KDC is no longer bright enough with respect to the
forthisgalaxyhasonlythreevalueswherehV (<R)i underlying main body of the galaxy to be detectable.
inner
and hV (> R)i have opposite signs. There is not a These technical and observational biases indicate that
outer
clear peak among these three values. Thus, while there the number of galaxies hosting a KDC could be larger
is a statistically significant anomaly in the center of this than the number we currently know, although the rate
galaxy, it does not resemble a symmetric KDC. at which KDCs are being formed is yet unknown.
8 Toloba et al.
TABLE 2
Statisticalsignificanceof the detection of KDCs
KDC dE
Galaxy hRSmaxi hSmaxi hVinner i hVouteri KDC? Source
−1 −1
arcsec km s km s
(1) (2) (3) (4) (5) (6) (7)
VCC 1183 2.2 ± 0.4 4.6 ± 0.8 −3.5± 1.1 7.4 ± 1.7 significant This work
VCC 1453 12.4 ± 1.4 3.2 ± 0.2 −5.4± 0.6 7.4 ± 3.9 marginal This work
VCC 510 3.3 ± 1.1 4.3 ± 0.9 −3.5± 1.4 6.8 ± 1.3 significant Th06
VCC 917 3.0 ± 1.1 3.3 ± 0.2 −0.6± 0.9 5.2 ± 1.7 marginal Ch09
∗
VCC 1036 1.0 ± 0.3 12.5 ± 3.2 −0.2± 1.0 13.7 ± 0.6 ? Ch09
VCC 1261 9.4 ± 0.9 5.6 ± 0.3 −2.79± 0.6 6.4± 1.6 significant Ch09
VCC 1475 1.7 ± 0.2 56.9 ± 0.2 −1.25± 0.1 6.5 ± 0.1 significant Ko11
NOTES:Column1: Galaxyname;Column2: averageradiusofthethreemaximumvaluesofS(R)wherehVinner(<R)iandhVouter(>R)i
have opposite signs. This parameter indicates the radius where the rotation curve goes from negative velocity values to positive velocity
values;Column3: significanceoftheKDC,i.e.,averageofthethreemaximumvaluesofS(R)wherehVinner(<R)iandhVouter(>R)ihave
oppositesigns;Column4: averagevelocityintheregioninteriortohRSmaxi,i.e.,averagevelocityoftheKDC;Column5: averagevelocityin
theregionexteriortohRSmaxi,i.e.,averagevelocityofthemainbodyofthedE;Column6: istheKDCastatisticallysignificantdetection
based on the criterion described in the text?; Column 7: reference to the measurement of the rotation curve. Th06 for Thomasetal.
(2006),Ch09forChilingarian(2009),andKo11forKolevaetal.(2011). Seethetextfordetailsonthemeasurementoftheseparameters.
∗VCC1036containsasignificantkinematicanomalynearitscenter. However,thisgalaxyisdifferentfromtheothersixgalaxiesdiscussed
inthispaperinthatitskinematicanomalydoesnotresembleasymmetricKDC(seeAppendixA).
ThenumberofKDCsdetectedindEslocatedingroups to explain all the properties of dEs. The presence of
or lower density environments (dEs without neighbors KDCs in a small fractionof dEs adds a new twist to the
within a radius of ∼ 30′, as defined by Ry´s et al. story.
2013) is 14.3 ± 10.1% (2 out of 14 dEs surveyed by
de Rijcke et al. 2005; Toloba et al. 2011; Koleva et al. 6.1. Insights from KDCs
2011; Ry´s et al. 2013). In the Fornax cluster, none of
Ram-pressurestripping,hydrodynamicalinteractionof
the 16 dEs analyzed exhibit a KDC (de Rijcke et al.
thedEprogenitorwiththehotintraclustermedium,does
2005; Spolaor et al. 2010; Koleva et al. 2011). In the
not provide an obvious explanation for the formation
Virgocluster, 5.6±2.8%(8.5±3.4,including those with
of KDCs. This mechanism has no direct effect on the
marginaldetectionsinTable2)havestatisticallyreliable
stars in the progenitor galaxy. Moreover, while the in-
detections of a KDC. These are 4/71 (6/71 including
flow of cold gas could produce a KDC, the ram-pressure
marginal detections) of the dEs analyzed in this cluster
stripping mechanism is more likely to lead to the expul-
(Pedraz et al.2002;Simien & Prugniel2002;Geha et al.
sion rather than inflow of gas (e.g., Lin & Faber 1983;
2002, 2003; van Zee et al. 2004; Thomas et al. 2006;
Boselli et al. 2008a). Harassment,multiple gravitational
Chilingarian 2009; Toloba et al. 2011; Spolaor et al.
interactionsofthedEprogenitorwithotherclustermem-
2010;Koleva et al.2011;Ry´s et al.2013,PaperII).This
bers,canproduce large-scalecounter-rotatingstructures
sampleof71Virgocluster dEsspans anr-band absolute
(R > 1.5R ) but not a KDC (Gonz´alez-Garc´ıaet al.
magnitude rangeof −19.3<M <−16.1and represents e
r 2005, R ≪ R ). An example of such a large-scale
44% of the early-type galaxies in the Virgo cluster with e
(R & R ) counter-rotating feature can be found in the
updated memberships by heliocentric velocities in that e
close M31 dE satellite NGC 205 (Geha et al. 2006). De-
magnitude range (71 out of the total 161, Lisker et al.
spiteitsproximitytoM31(8kpcinprojection),thecore
2007).
of this dE shows no apparent signs of perturbation by
Combiningthe numbersforstatisticallysignificantde-
M31’s tidal forces.
tections of KDCs in dEs located in low density environ-
In luminous ETGs, a KDC can be produced in
ments, the Fornax, and the Virgo clusters, 5.9±2.4%
a dissipationless merger (i.e., dry merger). The
(7.9±2.8, including those with marginal detections) of
tightly bound core of one of the galaxies can become
the dEs host a KDC (or 5.1 ± 0.8% if we only count
the center of the final object (e.g., Kormendy 1984;
the 39 dEs homogeneously analyzed in this work). For
Holley-Bockelmann& Richstone 2000). However, the
luminous ETGs, 8.1±1.8% host a KDC (based on the
stellarpopulationsofthecentralcomponentarenotnec-
ATLAS3Dvolumecompletesurvey,Emsellem et al.2011;
essarily younger or more metal rich than the main body
Krajnovi´cet al. 2011). Besides the caveats described
of the galaxy, as it is found in the KDCs analyzed here.
above, the rate of occurrence of KDCs in dEs is very
KDCs that are younger than the main body of the
similar to the rate of occurrence of KDCs in ETGs.
galaxy and have diameter scales below ∼ 1 kpc are al-
ways found in fast rotating luminous ETGs. These are
6. DISCUSSIONOFPOSSIBLEFORMATIONSCENARIOS likely formed from gas accretionthat fall into the center
The two most discussed mechanisms by which late- of the galaxy (McDermid et al. 2006). The properties
type galaxies are transformed into dEs — ram-pressure of the KDCs found in VCC 1183 and VCC 1453 agree
strippingandharassment—havetypicallybeeninvoked well with those found in fast rotating luminous ETGs.
KDC in dEs in the Virgo cluster 9
Moreover, VCC 1183 and VCC 1453 have (λ ,ǫ ) VCC 545, is a dE at 39.3 kpc (8.3′) with a radial veloc-
Re/2 1/2
parameters of (0.14± 0.04,0.102± 0.002) and (0.15 ± ity of 1207 km s−1. VCC 559 (NGC 4312) is a spiral
0.03,0.188±0.002), respectively, inside half of the R . galaxy (Sab) at 52.9 kpc (11.12′) with a radial velocity
e
These values place these two galaxies also as fast rota- of 148 km s−1. Finally, VCC 596 (M100) is a Sc spiral
tors7. Thus, these features could be formed from gas at 86.2 kpc (18.1′) from VCC 510 with a radial velocity
accretion, but, how do two dEs in the core of the Virgo of1575kms−1. Allthese galaxies,butforVCC 559and
cluster (located at 0.3Rvirial and 0.2Rvirial, respectively, probably also VCC 596, have radial velocities that are
assumingtheprojectedvirialradiustobeRvirial =5.38◦, close enough to that of VCC 510 to suggest that they
Ferrarese et al. 2012) accrete cold gas or hot gas that are part of a group that fell into the Virgo cluster.
later cools down and forms stars?
Even though dwarf-dwarfmergers are not expected to 6.2.2. VCC 917
be very common, they can occur (e.g., De Lucia et al. VCC 917 has a radial velocity of 1258.9±0.2 km s−1
2006; Fakhouri et al. 2010). Contrary to what happens (Paper II). This dE is located at 72 kpc (15.1′) from
inmassivegalaxies,thestructuralparametersoftherem- VCC 1001, an irregular galaxy with a radial velocity of
nant dwarf are similar to those of its parents, i.e., the 340 km s−1. The large difference between these two ra-
surface brightness profile remains similar to exponential dial velocities suggests that they are not gravitationally
(Kazantzidis et al. 2011), in agreement with the struc- bound.
turalparametersofdEs(seetheS´ersicindexinTable1).
However,there are two main arguments againstmergers 6.2.3. VCC 1036
happening inside a cluster: (1) the relative velocities of The metric described in Section 5 does not find a sta-
galaxies inside a cluster are too high to merge galaxies tistically significant KDC in this galaxy. However, its
(e.g.,Binney & Tremaine1987;Boselli & Gavazzi2006); rotation curve is asymmetric which makes it interesting
and (2) the time to cool the gas down and form stars is to explore its surroundings.
significantly larger than the timescale to quench galax- VCC 1036 has a radial velocity of 1124 km s−1 and
ies via ram-pressure stripping (∼ 150 Myr, Boselli et al. has three dEs close in projection whose radial veloci-
2008a). Thus,dwarf-dwarfmergers,orjustgasaccretion, ties are similar to that of VCC 1036. This suggests
musthavehappenedinalowerdensityenvironment,such that these dEs could be part of the same gravitation-
asagrouporapair ofgalaxies,wherethe relativeveloc- allyboundstructurethatfellintotheVirgocluster. The
ityofthedwarfgalaxiesissmallerandtheenvironmental three dEsare: (1) VCC 940,∼74 kpc (15.6′) awayfrom
quenching is slower. VCC 1036 with a radial velocity of 1410.5±0.4 km s−1
In this scenario, the KDC would be formed while the (Paper II); (2) VCC 965, ∼ 83 kpc (17.4′) away from
dwarf galaxy is still in the group. Afterwards the group VCC 1036 with a radial velocity of 851 km s−1; and (3)
would enter the Virgo cluster (as shown by simulations, VCC 1010, ∼17 kpc (3.7′) away from VCC 1036 with a
e.g., Gnedin 2003) and the significantly hotter environ-
radial velocity of 915.5±0.3 km s−1 (Paper II).
ment will quench the star formation. However, there is
In addition, VCC 1036 is also in close projection to
no direct evidence that these six Virgo dEs, that host a
VCC 1035 (a luminous elliptical) and VCC 1047 (a spi-
KDC, are part of a group.
ral galaxy). The radial velocities are very different from
thatofVCC1036: −500kms−1 and724kms−1,respec-
6.2. The environment of each KDC host
tively. These two large galaxies may be responsible for
Thereisnoeasywaytoidentifycompanion(s)forthese some of the asymmetries observed in the rotation curve
galaxies that were possibly part of a group before en- of VCC 1036.
tering the cluster environment. In any case, not being
abletofindtheircompanion(s)doesnotdiscardthissce- 6.2.4. VCC 1183
nariowhereKDCsareformedwhenthegalaxiesarepart VCC 1183 is in close projection to the most dis-
of groups or pairs that subsequently fell into the Virgo turbed dwarf star-forming galaxy in Virgo, VCC 1217
cluster. The survival of such groups and pairs as grav- (Hester et al. 2010), as seen in Figure 4. This Figure
itationally bound structures of galaxies is not expected shows a deep ultraviolet (UV) color map that combines
to be long inside a cluster environment. the far UV and near UV channels of GALEX taken by
We explorethe surroundingsforeachVirgoclusterdE the GUViCS collaboration (GALEX Ultra Violet Virgo
possibly hosting a KDC. We limit our study to neigh- ClusterSurvey,Boselli et al.2011). Despite theirappar-
bors within a projected distance of 100 kpc for whom ent projected proximity (∼ 22 kpc apart), their radial
the radial velocity is known. velocities(1300.9±0.5kms−1versus176kms−1,respec-
tively—thiswork;Kenney et al.2013)suggestthatthey
6.2.1. VCC 510
are unbound. Although we do not know the total three-
VCC 510,with a radial velocity of 838 km s−1, is at a dimension distance between these two galaxies or their
closeprojecteddistancetosomegalaxiesinVirgo(radial truerelativevelocities,we carryouta simple calculation
velocitiesfromGavazzi et al.2003,unlessotherwiseindi- to constrain the age of the possible interaction between
cated). VCC490isadElocatedat33.1kpc(6.9′)inpro- them. Theminimumtime tsincetheirlastclosepassage
jectionfromVCC510andhasavelocityof1267kms−1. is given by the quotient rmin/vmax, where rmin =22 kpc
and v is their maximum relative velocity. As these
max
7 See Paper III of this series for details on the measurement of two galaxies are part of the Virgo cluster, their maxi-
λRe/2 and Emsellemetal. (2007, 2011) for the definition of λR mumrelativevelocityisvmax =3σVirgo,wheretheveloc-
andslow/fastrotators. itydispersionoftheVirgoclusterisσ =753kms−1
Virgo
10 Toloba et al.
(Boselli & Gavazzi 2006). Thus, the last close passage
occurred at least t = 10 Myr ago. This timescale is
neither consistent with the luminosity-weighted age of
the stellar populations of the KDC (2 Gyr) nor with the
age of the stellar populations of the tail of star-forming
clumps(fireballs)observedinVCC1217,whichhasbeen
datedtobeyoungerthan400Myr(Fumagalli et al.2011;
Kenney et al. 2013). The energy available for an en-
counter between these two galaxies is very little because
it scales as ∆V−2, where ∆V is their radial velocity dif-
ference (Binney & Tremaine 1987). This energy is not
enough to generate a KDC in VCC 1183 or a tail of
fireballs in VCC 1217. In addition, there areseveralevi-
dence,suchasthestructuralfeaturesandlackofoldstars
in VCC 1217’s tail, that point ram-pressurestripping as
themechanismresponsibleforthefireballsonVCC1217
(Kenney et al. 2013).
6.2.5. VCC 1261
VCC 1261has a radialvelocity of 1799.4±0.3 km s−1
(Paper II) and has two close neighbors in projection.
VCC1200isanirregulargalaxylocatedat∼42kpc(9′)
fromVCC1261andhasaradialvelocityof−123kms−1.
VCC 1269 is a dE located at ∼ 71 kpc (15′) and has a Fig.4.—GALEXUVcolormapofVCC1183(dEontheright)
radial velocity of 633 km s−1. The large velocity differ- anditsclosestneighborVCC1217(thedwarfstar-forminggalaxy
with a tail of star-formingclumps on the left). Both galaxies are
ences among these three galaxies indicate that they are separated6.6′ (∼22kpc). Theidlesemicircularorangeartifactin
not gravitationally bound to one another in the present thetopedgeoftheimageiscausedbyanearbybrightstar.
time. stellar populations of the KDCs are younger and possi-
bly more metal rich than the main body of the galaxy.
6.2.6. VCC 1453 For VCC 1183, the KDC is 2.0±0.5 Gyr old and has a
VCC1453islocatedinprojecteddistanceat∼58kpc metallicity of [M/H]= −0.3±0.3, while the main body
(17′) from VCC 1401 (M88), a large spiral galaxy. of the galaxy is 9.9±4.1 Gyr old and has a metallic-
The radial velocities of these two galaxies are 1859.2± ity of [M/H] = −0.6±0.3. For VCC 1453, the KDC is
0.3 km s−1 (this work), and 2282 km s−1, respectively. 4.5±1.1Gyroldwithametallicityof[M/H]=−0.2±0.1,
These conditions suggest that these two galaxies are and the main body is &10 Gyr old with a metallicity of
gravitationally bound to each other implying that they [M/H] = −1.1±0.3. These stellar populations for the
couldhavebeenpartofthe samegroupthatfellinto the mainbodiesaresimilartothetypicalvaluesofotherdEs
Virgo cluster. intheVirgocluster(Michielsen et al.2008;Toloba et al.
2009; Paudel et al. 2011). This difference in the mea-
6.2.7. VCC 1475 sured stellar populations between the KDC and further
VCC 1475 has a radial velocity of 951 km s−1. This out the main body could also be related to an intrinsic
gradient in the host galaxy.
bright dE (M = −19.0, Janz & Lisker 2009) is close in
projection (85r.3 kpc, 17.9′) to VCC 1427, an Im/blue Photometrically, there does not appear to be a strong
compact dwarf with a radial velocity of −132 km s−1. correlationbetweenanyparticularfeatureandtheKDC.
VCC 1183 seems to be very complex structurally. At
Thelargedifferencebetweentheradialvelocitiesofthese
R∼6′′ the isophotes are twisted ∼77◦ and the elliptic-
galaxiessuggeststhattheyarenotgravitationallybound.
ity drops with respect to the outer parts of the galaxy.
7. SUMMARYANDCONCLUSIONS Thisregioncoversourfullkinematicalmeasurementsin-
cluding the KDC and the main body of the galaxy.
Inthiswork,wepresentthe discoveryofkinematically
The formation scenarios that seem more plausible to
decoupled cores in the Virgo cluster dEs VCC 1183 and
explain the properties found here, involve dwarf-dwarf
VCC1453. CombinedwiththeKDCsfoundinVCC510
wetmergersandgasaccretion. Duetothedensityofthe
by Thomas et al. (2006), VCC 917 and VCC 1261 by
Virgocluster,suchevents canonly happen inlowerden-
Chilingarian (2009), and in VCC 1475 by Koleva et al.
sity environments such as poor groups or galaxy pairs.
(2011), this makes a total of six dEs (defined as early-
type galaxies in the luminosity range −19<M <−16)
r
with a significantor marginaldetection of a KDC in the E.T. thanks Laura Ferrarese for very useful sugges-
Virgo cluster. For the two new KDCs presented in this tions on ellipse-fitting and Eric Emsellem, Jeffrey Ken-
paper,we provideradialprofiles ofthe rotation,velocity ney, and Marla Geha for very helpful discussions. The
dispersion,andstellarpopulationindices. Thesespectro- authors thank the anonymous referee for useful sugges-
scopic measurements are also compared with deep pho- tionsthathelpedimprovethemanuscript. E.T.acknowl-
tometry in the H-band. edges the financial support of the Fulbright Program
The KDCs for VCC 1183 and VCC 1453 have radii of jointly with the Spanish Ministry of Education. PG
1.8′′ (0.14 kpc), and 4.2′′ (0.33 kpc), respectively. The acknowledges the NSF grant AST-1010039. GvdV and