J/MNRAS/488/1535 Detection of a tidal stream associated with M68 (Palau+, 2019)
Statistical detection of a tidal stream associated with the globular cluster
M68 using Gaia data.
Palau C.G., Miralda-Escude J.
<Mon. Not. R. Astron. Soc., 488, 1535-1557 (2019)>
=2019MNRAS.488.1535P 2019MNRAS.488.1535P (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, halo ; Parallaxes, trigonometric ;
Positional data ; Proper motions ; Colors ; Optical
Keywords: globular clusters: individual: M68 - Galaxy: halo -
Galaxy: kinematics and dynamics - Galaxy: structure
Abstract:
A method to search for tidal streams and to fit their orbits based on
maximum likelihood is presented and applied to the Gaia data. Tests of
the method are performed showing how a simulated stream produced by
tidal stripping of a star cluster is recovered when added to a
simulation of the Gaia catalogue. The method can be applied to search
for streams associated with known progenitors or to do blind searches
in a general catalogue. As the first example, we apply the method to
the globular cluster M68 and detect its clear tidal stream stretching
over the whole North Galactic hemisphere, and passing within 5kpc of
the Sun. This is one of the closest tidal streams to us detected so
far, and is highly promising to provide new constraints on the Milky
Way gravitational potential, for which we present preliminary fits
finding a slightly oblate dark halo consistent with other
observations. We identify the M68 tidal stream with the previously
discovered Fjorm stream by Ibata et al (2019ApJ...872..152I 2019ApJ...872..152I). The
tidal stream is confirmed to contain stars that are consistent with
the HR-diagram of M68. We provide a list of 115 stars that are most
likely to be stream members, and should be prime targets for follow-up
spectroscopic studies.
Description:
Among several globular clusters we have considered as targets for a
search for associated tidal tails, M68 (NGC4590) stands out because of
its proper motions and distance are measured with good precision, it
is projected on to the halo, its relative proximity to us, and a
predicted orbit that brings it close to us and keeps it far from the
inner region of the Galaxy.
The full sky Gaia DR2 star catalogue (Gaia Collaboration
2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345), published on 2018 April 25 based on
data collected during the first 2 yr of the Gaia Mission, includes
five-parameter astrometric solutions (parallaxes, sky coordinates, and
proper motions) and multiband photometry (G, GBP, and GRP
magnitudes) of ∼1.7 billion sources. In addition, it includes radial
velocities for ∼7.2 million sources.
We apply a set of pre-selection cuts to the star catalogue. The stars
that fulfil the following conditions are pre-selected: G=<21mag to
eliminate faint stars with large astrometric errors; plx<1/0.3mas e.g.
large distance, to eliminate foreground disc stars and |b|>15deg to
avoid the regions of high stellar density close to the disc.
We finally have 151 stars that are compatible with the phase-space
model of the stellar stream, out of which 115 are also compatible with
the HR-diagram of M68 (see Table E1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablee1.dat 90 115 Selected stars from GDR2 catalogue
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: tablee1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/115] Internal identifier
5- 23 I19 --- GaiaDR2 Gaia DR2 source identifier
25- 31 F7.4 mas plx Parallax
33- 40 F8.4 deg DEdeg Declination (ICRS) at Ep=2015.5
42- 49 F8.4 deg RAdeg Right ascension (ICRS) at Ep=2015.5
51- 56 F6.4 mas/yr pmDE Proper motion in declination
58- 64 F7.4 mas/yr pmRA Proper motion in right ascension
66- 71 F6.4 mag BP-RP Gaia DR2 BP-RP colour
73- 79 F7.4 mag Gmag Gaia DR2 G-band magnitude
81- 90 E10.4 yr3/deg2/pc/mas3 Xsel Selection threshold for the probability
density
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 05-Dec-2022