J/ApJ/748/29 Spectroscopy of M87 globular clusters (Romanowsky+, 2012)
The ongoing assembly of a central cluster galaxy: phase-space substructures
in the halo of M87.
Romanowsky A.J., Strader J., Brodie J.P., Mihos J.C., Spitler L.R.,
Forbes D.A., Foster C., Arnold J.A.
<Astrophys. J., 748, 29 (2012)>
=2012ApJ...748...29R 2012ApJ...748...29R
ADC_Keywords: Clusters, globular ; Galaxies, nearby ; Photometry ;
Radial velocities
Keywords: galaxies: elliptical and lenticular, cD - galaxies: formation
galaxies: halos - galaxies: individual (M87) -
galaxies: kinematics and dynamics - galaxies: star clusters: general
Abstract:
The halos of galaxies preserve unique records of their formation
histories. We carry out the first combined observational and
theoretical study of phase-space halo substructure in an early-type
galaxy: M87, the central galaxy in the Virgo cluster. We analyze an
unprecedented wide-field, high-precision photometric and spectroscopic
data set for 488 globular clusters (GCs), which includes new,
large-radius Subaru/Suprime-Cam and Keck/DEIMOS observations. We find
signatures of two substructures in position-velocity phase space. One
is a small, cold stream associated with a known stellar filament in
the outer halo; the other is a large shell-like pattern in the inner
halo that implies a massive, hitherto unrecognized accretion event. We
perform extensive statistical tests and independent metallicity
analyses to verify the presence and characterize the properties of
these features, and to provide more general methodologies for future
extragalactic studies of phase-space substructure. The cold outer
stream is consistent with a dwarf galaxy accretion event, while for
the inner shell there is tension between a low progenitor mass implied
by the cold velocity dispersion, and a high mass from the large number
of GCs, which might be resolved by a ∼0.5 L* E/S0 progenitor.
Description:
We have revisited M87 in a new era high-precision wide-field survey of
GCs. The main component of our data set is presented and discussed in
detail in Strader et al. (2011, Cat. J/ApJS/197/33). In brief, it is
based on photometry from Canada-France-Hawaii Telescope (CFHT)/Megacam
and Subaru/Suprime-Cam optical images, and spectroscopy from
MMT/Hectospec, Keck/DEIMOS, and Keck/LRIS. New line-of-sight
velocities were obtained for 451 GCs over a series of campaigns from
2007 to 2010, extending over a range in galactocentric radius of
∼1-35 arcmin (∼5-170 kpc).
In a parallel campaign presented here for the first time, we observed
intensively the region around the outer stellar "stream A", at radii
of ∼35-50 arcmin (∼170-240 kpc). Our spectroscopic follow-up of the
stream GCs used Keck/DEIMOS. Four masks were observed during the
nights 2009 March 23, 2010 March 11-13, and 2010 June 12. The spectra
cover an approximate spectral range of 6500-9000Å at a moderate
resolution (1.5Å FWHM).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 57 80 Spectroscopic objects in M87 outer stream region
table2.dat 53 47 CaII Triplet measurements of M87 Globular Clusters
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See also:
J/ApJS/197/33 : The M87 globular cluster system (Strader+, 2011)
J/ApJ/743/149 : Color-metallicity relations. II. M87 GCs (Yoon+, 2011)
J/ApJ/703/42 : HST photometry of M87 globular clusters (Peng+, 2009)
J/AJ/131/866 : Hot populations in M87 globular clusters (Sohn+, 2006)
J/ApJ/613/279 : ACS Virgo Cluster Survey. III. M87 (Jordan+, 2004)
J/ApJ/559/812 : Globular cluster system in M87 (Hanes+, 2001)
J/ApJ/513/733 : Globular cluster system in M87 (Kundu+, 1999)
J/AJ/115/1801 : VRI photometry of M87 globular clusters (Harris+ 1998)
J/AJ/106/493 : Globular clusters in M87 (Lee+, 1993)
J/ApJS/73/671 : M87 globular clusters BVI photometry (Couture+, 1990)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- ID Object identification (R7403 to R22843)
9 A1 --- f_ID [a] a: probably bound to NGC 4461
11- 19 F9.5 deg RAdeg [187.213/187.464] Right Ascension (J2000)
21- 28 F8.5 deg DEdeg [12.814/13.185] Declination (J2000)
30- 34 F5.2 mag imag [15.18/22.97] Intrinsic i band magnitude (1)
36- 39 F4.2 mag g-i [0.35/2.65] Intrinsic (g-i) color index (1)
41- 44 I4 km/s RVel [-214/1876]? Radial velocity
46- 47 I2 km/s e_RVel [5/74]? Uncertainty in RVel (2)
49- 57 A9 --- Type Object type: confirmed, marginal, star,
or galaxy (3)
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Note (1): Photometry is from Subaru-Suprime/Cam imaging using 4-pixel aperture
magnitudes, bootstrapped to the Sloan Digital Sky Survey and then
corrected for Galactic extinction following Peek & Graves
(2010ApJ...719..415P 2010ApJ...719..415P).
Note (2): The uncertainties in the stellar velocities are indicative only, and
not as carefully characterized as for the GCs. The most likely
objects belonging to the cold GC stream are R16501, R16571, R17084,
R17522, R18045.
Note (3): A simple velocity boundary of 250 km/s has been used to separate
stars and GCs, but some of the higher-velocity stars might in
principle be low-velocity GCs.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ID Object identification (1)
8- 16 F9.5 deg RAdeg [187.67/188.338] Right Ascension (J2000)
18- 25 F8.5 deg DEdeg [12.153/12.481] Declination (J2000)
27- 31 F5.2 mag imag [18.63/22.44] Intrinsic i band magnitude
33- 37 F5.3 mag g-i [0.695/1.12]? Intrinsic (g-i) color index
39- 43 F5.3 mag e_g-i [0.001/0.033]? Uncertainty in g-i (2)
45- 48 F4.2 0.1nm CaT [1.95/8.25] CaII triplet line strength (Å) (3)
50- 53 F4.2 0.1nm e_CaT [0.01/0.53] Uncertainty in CaT
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Note (1): Identifications with "S" are on the extended Strom naming scheme
(see Hanes et al. 2001, Cat. J/ApJ/559/812; <[SFH81] NNNN> in Simbad).
Those starting with "T" are from Tamura et al. (2006MNRAS.373..588T 2006MNRAS.373..588T).
The two VUCD IDs are from Jones et al. (2006AJ....131..312J 2006AJ....131..312J;
<[JDJ2006] N> in Simbad). Those starting with "H" are from Strader et
al. 2011, Cat. J/ApJS/197/33, using the imaging first presented in
Harris (2009ApJ...703..939H 2009ApJ...703..939H).
Note (2): Note that the g-i color uncertainties are based on shot-noise only,
and are useful for relative comparisons of colors in this dataset.
The absolute uncertainties from calibration, reddening correction,
background estimation, etc., will be larger.
Note (3): The equivalent iron metallicities shown on the right-hand axis of
Figure 9a are derived using the expression: [Fe/H]{~=}0.438*CaT-3.641.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 09-Oct-2013