J/A+A/611/A21 Globular cluster candidates in NGC253 (Cantiello+, 2018)
A VST and VISTA study of globular clusters in NGC253.
Cantiello M., Grado A., Rejkuba M., Arnaboldi M., Capaccioli M.,
Greggio L., Iodice E., Limatola L.
<Astron. Astrophys. 611, A21 (2018)>
=2018A&A...611A..21C 2018A&A...611A..21C (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Photometry, ugriz ; Photometry, infrared
Keywords: galaxies: star clusters: general - galaxies: individual: NGC253 -
galaxies: stellar content - galaxies: evolution - catalogs -
galaxies: photometry
Abstract:
Globular clusters (GCs) are key to our understanding of the Universe,
as laboratories of stellar evolution, fossil tracers of the past
formation epoch of the host galaxy, and effective distance indicators
from local to cosmological scales.
We analyze the properties of the sources in the NGC 253 with the aim
of defining an up to date catalog of GC candidates in the galaxy.
Given the distance of the galaxy, GCs in NGC 253 are ideal targets for
resolved color-magnitude diagram studies of extragalactic GCs with
next-generation diffraction limited ground-based telescopes.
Our analysis is based on the science verification data of two ESO
survey telescopes, VST and VISTA. Using ugri photometry from VST and
JKs from VISTA, GC candidates were selected using as reference the
morpho-photometric and color properties of spectroscopically confirmed
GCs available in the literature. The strength of the results was
verified against available archival HST/ACS data from the GHOSTS
survey: all but two of the selected GC candidates appear as star
clusters in HST footprints.
The adopted GC selection leads to the definition of a sample of ∼350
GC candidates. At visual inspection, we find that 82 objects match all
the requirements for selecting GC candidates and 155 are flagged as
uncertain GC candidate; however, 110 are unlikely GCs, which are most
likely background galaxies. Furthermore, our analysis shows that four
of the previously spectroscopically confirmed GCs, i.e., ∼20% of the
total spectroscopic sample, are more likely either background galaxies
or high-velocity Milky Way stars. The radial density profile of the
selected best candidates shows the typically observed r1/4-law
radial profile. The analysis of the color distributions reveals only
marginal evidence of the presence of color bimodality, which is
normally observed in galaxies of similar luminosity. The GC luminosity
function does not show the typical symmetry, mainly because of the
lack of bright GCs. Part of the bright GCs missing might be at very
large galactocentric distances or along the line of sight of the
galaxy dusty disk. As an alternative possibility, we speculate that a
fraction of low luminosity GC candidates might instead be metal-rich,
intermediate age clusters, but fall in a similar color interval of
old, metal-poor GCs.
Defining a contaminant-free sample of GCs in extragalactic systems is
not a straight forward exercise. Using optical and near-IR photometry
we purged the list of GCs with spectroscopic membership and
photometric GC candidates in NGC 253. Our results show that the use of
either spectroscopic or photometric data only does not generally
ensure a contaminant-free sample and a combination of both
spectroscopy and photometry is preferred.
Description:
Photometric catalogs for globular cluster (GC) candidates over the
1 sq. degree area around NGC253. The catalogues are based on ugri-band
photometry from the VST data, and JKs photometry from VISTA. Aperture
magnitudes, corrected for aperture correction are reported.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 234 347 Globular cluster candidates in NGC253
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See also:
J/ApJ/602/231 : Chandra X-ray point sources in nearby galaxies (Colbert+, 2004)
J/AJ/127/2674 : Globular clusters in Sculptor group (Olsen+, 2004)
J/A+A/611/A93 : NGC3115 & NGC1399 VEGAS-SSS globular clusters (Cantiello+ 2018)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/347] Internal designation
5- 13 F9.6 deg RAdeg Right ascension (J2000.0)
15- 24 F10.6 deg DEdeg Declination (J2000.0)
26- 31 F6.3 mag umag VST u-band aperture magnitude (1)
33- 37 F5.3 mag e_umag VST u-band magnitude error
39- 44 F6.3 mag gmag ?=99.000 VST g-band aperture magnitude (1)
46- 50 F5.3 mag e_gmag ?=9.000 VST g-band magnitude error
52- 57 F6.3 mag rmag VST r-band aperture magnitude (1)
59- 63 F5.3 mag e_rmag VST r-band magnitude error
65- 70 F6.3 mag imag VST i-band aperture magnitude (1)
72- 76 F5.3 mag e_imag VST i-band magnitude error
78- 83 F6.3 mag Jmag ?=99.999 VISTA J-band aperture magnitude (1)
85- 89 F5.3 mag e_Jmag ?=9.000 VISTA J-band magnitude error
91- 96 F6.3 mag Ksmag ?=99.999 VISTA Ks-band aperture magnitude (1)
98-102 F5.3 mag e_Ksmag ?=9.000 VISTA Ks-band magnitude error
104 A1 --- l_Rh Limit flag on Rh
105-110 F6.3 pc Rh Half-light radius (2)
112-117 F6.4 pc e_Rh Error on Half-light radius
119-125 F7.4 --- b/a Axis ratio
127-168 A42 --- OtherID Other identification from the literature (3)
170-189 A20 --- Spectra Presence in GHOSTS footprints, spectroscopic
or HST samples, or previous identifications
in the photometric sample by Liller et al.
(1983ApJ...265..166L 1983ApJ...265..166L) or
Blecha (1986A&A...154..321B 1986A&A...154..321B) (4)
190-224 A35 --- Visual Comments based on visual inspection (5)
226-234 A9 --- Class Final classification
(Bona fide, Uncertain, No)
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Note (1): Correction for foreground Galactic extinction according to Schlafly &
Finkbeiner (2011ApJ...737..103S 2011ApJ...737..103S) recalibration of the Schlegel et al.
(1998ApJ...500..525S 1998ApJ...500..525S) infrared-based dust map. Magnitudes are derived within
8 pixel aperture; aperture correction is applied.
Note (2): The value of Rh is meaningless for sources classified as No in
Class column.
Note (3): Designations:
LA83#NN GC candidate number NN ([LA83] NGC 253 NN in Simbad) in
Liller et al. (1983ApJ...265..166L 1983ApJ...265..166L), cited as LANN in Beasley et al.
(2000MNRAS.311..673B 2000MNRAS.311..673B)
B86#NN GC candidate number NN ([B86c] NN in Simbad) in Blecha
(1986A&A...154..321B 1986A&A...154..321B), cited as BNN in Beasley et al., (2000MNRAS.311..673B 2000MNRAS.311..673B)
BS00#NN GC candidate number NN ([BS2000] NGC 253 NN) in Beasley et al.
(2000MNRAS.311..673B 2000MNRAS.311..673B)
OMS04#NN GC candidate number NN ([OMS2004] NGC 253 NNN in Simbad) in
Olsen et al. (2004, Cat. J/AJ/127/2674)
CHP04 source ([CHP2004] JHHMMSS.s+DDMMSS) in Simbad) in
Colbert et al. (2004, Cat. J/ApJ/602/231)
Redshift are from the Nasa Extragalactic Database.
Note (4): Codes as follows:
sgxy = spectroscopic confirmed galaxy
sGC = spectroscopic confirmed GC
GHOSTS#GC = star cluster candidate visible in GHOSTS footprints;
galaxy in GHOSTS footprints
BS00#tab.6 = photometric candidate GC from
Beasley et al. (2000MNRAS.311..673B 2000MNRAS.311..673B)
OMS04weakspectrum = source with low signal to noise spectrum in
Olsen et al. (2004, Cat. J/AJ/127/2674)
HKW09 = An extended disk galaxy in a spiral galaxy discovered in
the ACS Nearby Galaxy Survey Treasury observations of
NGC253 (Holwerda et al., 2009AJ....137.3000H 2009AJ....137.3000H)
N/A = Not analysed
Note (5): Visual Inspection flags as follows:
box10 = at least ∼10 sources equally bright or brighter observed in an
area of 2'x2'
features = faint extended structures close to or around the source
NbriM = N similar or brighter sources within M arcseconds
gxy-group? = the source is angularly close to several clearly extended or
disk-shaped sources
blend = close (<5") object, blended with the candidate
J = indicates any of the previous flags, only observed in the J-band
frame, the deepest in our dataset.
elongated = elongated
extended = extended
faint = faint
N/A = Not analysed
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History:
From Michele Cantiello, cantiello(at)oa-abruzzo.inaf.it
Acknowledgements:
INAF for financial support to the VSTceN
(End) Patricia Vannier [CDS] 06-Nov-2017