This Letter reports the discovery of five new globular clusters (GCs) in the Galactic bulge (Camargo 1102, 1103, 1104, 1105, and 1106) using Wide-field Infrared Survey Explorer (WISE) images. Their natures are established by using 2MASS and Gaia second data release (DR2) photometry. The new findings are old and metal-poor GCs located less than 4 kpc from the Galactic center. Camargo 1102 seems to be located over the Galactic bar on the far side of the Milky Way and at a vertical distance lower than 1 kpc. The other four clusters lie even closer to the Milky Way mid-plane. The old ages and low metallicities suggest that the newly discovered GCs may have the potential of providing important clues on the early inner Galaxy formation and its subsequent evolution, as well as the current bulge structure and kinematics.

1. Five New Globular Clusters Discovered in the Galactic Bulge
Denilso Camargo
Colégio Militar de Porto Alegre, Ministério da Defesa—Exército Brasileiro Av. José Bonifácio 363,
Porto Alegre, 90040-130, RS, Brazil; denilso.camargo@gmail.com
Received 2018 May 14; revised 2018 June 5; accepted 2018 June 12; published 2018 June 25
Abstract
This Letter reports the discovery of five new globular clusters (GCs) in the Galactic bulge (Camargo 1102, 1103,
1104, 1105, and 1106) using Wide-field Infrared Survey Explorer (WISE) images. Their natures are established by
using 2MASS and Gaia second data release (DR2) photometry. The new findings are old and metal-poor GCs
located less than 4 kpc from the Galactic center. Camargo 1102 seems to be located over the Galactic bar on the far
side of the Milky Way and at a vertical distance lower than 1 kpc. The other four clusters lie even closer to the
Milky Way mid-plane. The old ages and low metallicities suggest that the newly discovered GCs may have the
potential of providing important clues on the early inner Galaxy formation and its subsequent evolution, as well as
the current bulge structure and kinematics.
Key words: catalogs – Galaxy: bulge – globular clusters: general – surveys
1. Introduction
Globular clusters (GCs) were the first stellar systems formed
in the early universe and are often considered to be living
fossils of galaxy formation. Thus, they have become a powerful
tool for improving our understanding of the Milky Way
formation and early evolution. GCs also provide a means for
tracing the Galaxy’s properties at the present time, for example,
the bulge structure and kinematics.
The Galactic bulge formation and evolution is one of the
most important unsolved problems in the present epoch and,
thus, remains the subject of intense debate (Di Matteo
et al. 2015). Therefore, the discovery of new GCs in the
bulge, as well as deriving accurate parameters for known ones,
are essential for improving our knowledge of the inner Milky
Way history as well as characterizing its current evolutionary
stage. As the infrared wavelengths are less affected by dust
than the visible ones, advances in the near- and mid-IR
instrumentation in recent decades has made it possible to
conduct wide-field sky surveys such as 2MASS, Wide-field
Infrared Survey Explorer (WISE), and the European Southern
Observatory-VISTA Variables in the Via Lactea (ESO-VVV),
which have boosted the number of known star clusters
contributing significantly to improve our knowledge about
our Galaxy. In addition, the most recent surveys, including
Gaia’s second data release (DR2) and the VVV EXtended
Survey (VVVX), may provide answers for many of the still-
unanswered questions. In this respect, the Harris (1996) GC
catalog1
provides 157 objects. Additionally, advances in GC
research, such as large sky surveys, have updated the list of
Galactic GCs (Minniti et al. 2010, 2011; Fadely et al. 2011;
Moni-Bidin et al. 2011; Kim et al. 2015, 2016). Recently, the
ESO-VVV survey provided a list of 84 GC candidates toward
the bulge (Minniti et al. 2017a, 2017b, 2017c), and Minniti
et al. (2017c) suggested an amount of 50 unknown GCs in the
Galactic bulge. Piatti (2018) established the nature of 22 GCs
from Minniti et al. (2017c). Bica et al. (2016) provided a list of
bulge clusters containing 43 entries. Valenti et al. (2007)
derived parameters for a sample of 24 bulge GCs, and Cohen
et al. (2017) analyzed another 16.
This study presents five new GCs in the bulge. Following the
recent star cluster catalog (Camargo et al. 2015a, 2016a) the
new findings are named Camargo 1102, 1103, 1104, 1105, and
1106. The discovery were made by eye on WISE images.
2. Methods
The cluster analysis is based on the 2MASS and Gaia-DR2
photometry. The 2MASS color–magnitude diagrams (CMDs),
built with photometry extracted in circular concentric regions
centered in the coordinates of each cluster, provide the basic
parameters. However, in addition to the high extinction the
newly discovered GCs suffer from crowding (strong disk and
bulge contamination) toward the Galactic center. Thus, to
uncover the cluster-intrinsic CMDs a field decontamination
procedure is employed that has been successfully applied in the
analysis of star clusters in previous works (Camargo
et al. 2015a, 2015c, 2016a). The current algorithm is based
on Bonatto & Bica (2007).
The basic parameters are derived by fitting PARSEC
isochrones (Bressan et al. 2012) on the field-star decontaminated
CMDs. Such a procedure is guided by the direct comparison (red-
giant-branch (RGB)-fitting) with the CMD of a reference GC
(Bica et al. 2006; Valenti et al. 2007).
The Gaia-DR2 proper motion (PM) distribution (Gaia
Collaboration et al. 2018) is used to reinforce the cluster
nature of the new findings.
3. Present Discoveries
The present discoveries are part of a survey developed using
WISE images (Camargo et al. 2015a, 2015b, 2015c, 2016a,
2016b).
Figure 1 displays the WISE multicolor images centered on
the coordinates of the GCs discovered in this work (Table 1).
These images show only a relatively prominent central stellar
concentration, which is expected for GCs in crowded fields that
remained unknown until now.
The decontaminated CMDs are shown in the upper panels of
the Figure 2. As the photometry is limited by the crowding
The Astrophysical Journal Letters, 860:L27 (5pp), 2018 June 20 https://doi.org/10.3847/2041-8213/aacc68
© 2018. The American Astronomical Society. All rights reserved.
1
http://physwww.mcmaster.ca/~harris/mwgc.dat
1

2. toward the Galactic center, the 2MASS CMDs of bulge GCs
are typically populated by RGB+asymptotic giant branch
(AGB) stars (Anguiano et al. 2016).
Table 1 provides the coordinates and the basic parameters
derived for the new findings. Such parameters suggest that
these objects are old and metal-poor GCs.
The middle panels of Figure 2 show the Gaia-DR2 PM
distribution for stars located in the central region of the newly
identified GCs (black circles) and in a comparison field (brown
circles). The proper motion diagrams (PMDs) are built after
applying a filter that discards stars with PM uncertainties larger
than 0.5 mas yr−1
. The cluster nature of the new findings is
evident in the PMDs, which present a clear concentration in the
PM distribution of stars within the cluster central region.
The 2MASS radial density profiles (RDPs) of the new
findings (Figure 2, bottom panels) are built by using color–
magnitude filters that select the RGB stars fitted by the
isochrones, except for Camargo 1102, which has a filter that
was extended to encompass the bright stars. The RDPs of the
new findings reinforce their GC nature, but deeper photometry
is required to derive structural parameters.
Figure 2 (top-left panel) shows the 2MASS J×(J − H)
decontaminated CMD of Camargo 1102 superimposed on the
decontaminated CMD of NGC 6355 (Harris 1996), which is
located on the far side of the Milky Way’s center. To avoid noise
in the derived parameters, the CMD of Camargo 1102 is built
with stars located in the central region of the cluster, reducing the
contribution of possible non-member stars from the cluster
outskirts. The comparison between the CMDs of Camargo 1102
and NGC 6355 suggests that the new finding may also be located
on the far side of the Galactic center, but Camargo 1102 appears
to be more metal-poor than NGC 6355. The best-fitting isochrone
(Bressan et al. 2012) for Camargo 1102 suggests an age of
13.3±1.0 Gyr and a metallicity of [Fe/H]=−1.7±0.2 dex.
The CMD of the new GC also fit the RGB of M19 that is used as
reference cluster for Camargo 1103 (Figure 2). With an extinction
of AV=3.6±1 mag, Camargo 1102 seems to be located in a
region with extinction lower than the bulge average value (Dutra
et al. 2002). This cluster present an absolute magnitude of
MV=−6.3± 0.6 mag. The derived heliocentric distance
is de=8.23± 1.15 kpc and the Galactocentric distance RGC=
0.85± 0.28 kpc, adopting a distance of the Sun to the Galactic
center of Re=8.0 kpc. The rectangular coordinates are xGC=
0.19±1.15 kpc, yGC=−0.12±0.02 kpc, and a vertical dis-
tance from the Galactic plane of zGC=822.5±115 pc, which
locate Camargo 1102 over the central bar on the far side of the
Milky Way. The Gaia PM distribution (Figure 2) also suggests
its cluster nature. The brighter stars in the CMD of Camargo
1102 are located in the cluster central region and are present in
the Gaia PMD; however, most of the stars forming a possible
horizontal branch (HB) present colors and magnitudes consistent
with Galactic disk MS stars and are located on the outer parts of
the PM distribution. On the other hand, if these stars are cluster
members, the heliocentric distance may be lower than the derived
value, but the uncertainties in the basic parameters of Camargo
1102 present a solution considering such an HB.
The decontaminated CMD of Camargo 1103 superimposed
on the M19 (Harris 1996) decontaminated photometry are
shown in Figure 2. The brighter stars in the CMD of Camargo
1103 might be foreground stars that survived a non-100%
efficient subtraction. The statistical field-star decontamination
is affected by the crowding toward the bulge. The best-fitting
isochrone and direct comparison with M19 provide the basic
parameters that are shown in Table 1.
The GC M9 is used as reference cluster to establish the
nature of Camargo 1104 (Figure 2). The decontaminated CMD
of Camargo 1104 seems to be strongly affected by differential
reddening. The isochrone fitting reveals an old and metal-poor
GC (Table 1). Most bright stars in the CMD of Camargo 1104,
and those consistent with HB stars, are present on the PMD of
stars within the cluster central region, but with a relatively
peripheral position.
The comparison with the RGB morphology of the GC
Terzan 1 (Harris 1996) plus the best-fitting isochrone (Figure 2)
provide the basic properties of Camargo 1105. Such parameters
are displayed in Table 1. Camargo 1105 is the most reddened
cluster in this sample. The bright stars in the CMD of Camargo
1105 present PMs consistent with cluster members, but the
bluer stellar sequence appears to be formed by field stars that
survived the decontamination procedure.
Figure 2 displays the field-star decontaminated CMD of
Camargo 1106 fitting the RGB of M107 (Harris 1996) and a
PARSEC isochrone of 12.5 Gyr. The faint stars in the CMD of
Camargo 1106 present magnitudes and colors consistent with
HB stars.
4. Concluding Remarks
This Letter marks the discovery of five new GCs in the
Galactic bulge: Camargo 1102, Camargo 1103, Camargo 1104,
Camargo 1105, and Camargo 1106. These low-Galactic-
latitude GCs present low contrast and are very reddened
(Table 1), which is consistent with their location in the very
high-extinction and extremely crowded central region of the
Milky Way.
The new findings are old and metal-poor GCs with ages in
the range of 12.5–13.5 Gyr and [Fe/H] ranging from −1.5 to
−1.8 dex. Camargo 1102 is located over the Galactic bar on the
far side of the Galactic center at a distance from the Sun of
8.2±1.2 kpc, at 0.85±0.28 kpc from the center of the Milky
Figure 1. WISE multicolor images (7′×4′) centered on the coordinates of the
new GCs. Top panels: Camargo 1106 (right) and Camargo 1105 (left). Middle
panels: Camargo 1104 (right) and Camargo 1103 (left). Bottom panels: WISE
(right) and 2MASS (left) images of Camargo 1102.
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3. Table 1
Coordinates and Basic Parameters for the GCs Discovered in This Study
Cluster ℓ b [Fe/H] AV MV Age de RGC xGC yGC zGC
(°) (°) (dex) (mag) (mag) (Gyr) (kpc) (kpc) (kpc) (kpc) (kpc)
Camargo 1102 359.145 5.734 −1.7±0.2 3.6±1 −6.3±0.6 13.3±1 8.2±1.2 0.85±0.28 0.19±1.15 −0.12±0.02 0.822±0.12
Camargo 1103 5.604 −2.121 −1.8±0.3 6.6±1 −6.9±1.0 13.5±1 5.0±0.8 3.03±0.77 −2.99±0.78 −0.07±0.01 −0.503±0.08
Camargo 1104 5.621 −1.778 −1.8±0.3 7.5±1 −5.7±1.7 13.5±0.5 5.4±1.0 2.68±0.98 −2.62±1.0 0.53±0.10 −0.167±0.03
Camargo 1105 359.479 2.017 −1.5±0.2 8.2±1 −6.3±1.0 13.0±1 5.8±0.9 2.18±0.90 −2.17±0.90 −0.05±0.01 0.205±0.03
Camargo 1106 357.351 1.683 −1.5±0.3 5.7±1 −5.7±1.6 12.5±1 4.5±0.4 3.54±0.41 −3.53±0.41 −0.21±0.02 0.131±0.01
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4. Way, and have a vertical distance of 0.822±0.12 kpc. The
other GCs discussed in this Letter are located in the near side of
our Galaxy, with distances from the Sun in the range of
4.5–5.8 kpc and within 2.1–3.6 kpc from the Milky Way center,
but closer to the Galactic plane.
My thanks to an anonymous referee for valuable comments,
which improved this work. This publication makes use of data
products from WISE, 2MASS, and Gaia-DR2.
ORCID iDs
Denilso Camargo https://orcid.org/0000-0001-7344-4663
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