54 research outputs found
The dragonfly nearby galaxies survey. Iv. A giant stellar disk in ngc 2841
Neutral gas is commonly believed to dominate over stars in the outskirts of
galaxies, and investigations of the disk-halo interface are generally
considered to be in the domain of radio astronomy. This may simply be a
consequence of the fact that deep HI observations typically probe to a lower
mass surface density than visible wavelength data. This paper presents low
surface brightness optimized visible wavelength observations of the extreme
outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an
enormous low-surface brightness stellar disk in this object. When azimuthally
averaged, the stellar disk can be traced out to a radius of 70 kpc (5
or 23 inner disk scale lengths). The structure in the stellar disk
traces the morphology of HI emission and extended UV emission. Contrary to
expectations, the stellar mass surface density does not fall below that of the
gas mass surface density at any radius. In fact, at all radii greater than
20 kpc, the ratio of the stellar to gas mass surface density is a
constant 3:1. Beyond 30 kpc, the low surface brightness stellar disk
begins to warp, which may be an indication of a physical connection between the
outskirts of the galaxy and infall from the circumgalactic medium. A
combination of stellar migration, accretion and in-situ star formation might be
responsible for building up the outer stellar disk, but whatever mechanisms
formed the outer disk must also explain the constant ratio between stellar and
gas mass in the outskirts of this galaxy.Comment: 11 pages, 5 figures, accepted for publication in Ap
The Outer Stellar Halos of Galaxies: how Radial Merger Mass Deposition, Shells and Streams depend on Infall-Orbit Configurations
Galaxy mergers are a fundamental part of galaxy evolution. To study the
resulting mass distributions of different kinds of galaxy mergers, we present a
simulation suite of 36 high-resolution isolated merger simulations, exploring a
wide range of parameter space in terms of mass ratios (mu = 1:5, 1:10, 1:50,
1:100) and orbital parameters. We find that mini mergers deposit a higher
fraction of their mass in the outer halo compared to minor mergers, while their
contribution to the central mass distribution is highly dependent on the
orbital impact parameter: for larger pericentric distances we find that the
centre of the host galaxy is almost not contaminated by merger particles. We
also find that the median of the resulting radial mass distribution for mini
mergers differs significantly from the predictions of simple theoretical
tidal-force models. Furthermore, we find that mini mergers can increase the
size of the host disc significantly without changing the global shape of the
galaxy, if the impact occurs in the disc plane, thus providing a possible
explanation for extended low-surface brightness disks reported in observations.
Finally, we find clear evidence that streams are a strong indication of nearly
circular infall of a satellite (with large angular momentum), whereas the
appearance of shells clearly points to (nearly) radial satellite infall.Comment: 17 pages, 15 figures, published by MNRAS doi: 10.1093/mnras/stz125
The FRB20190520B Sightline Intersects Foreground Galaxy Clusters
The repeating fast radio burst FRB20190520B is an anomaly of the FRB
population thanks to its high dispersion measure (DM)
despite its low redshift of . This excess has been
attributed to a host contribution of , far larger than any other known FRB. In this paper,
we describe spectroscopic observations of the FRB20190520B field obtained as
part of the FLIMFLAM survey on the 2dF/AAOmega facility, which yielded 701
galaxies redshifts in a field of . Applying a
friends-of-friends group finder reveals multiple galaxy groups and clusters,
for which we then estimated halo masses by comparing their richness with
forward-modeled mocks from numerical simulations. We discover two separate
galaxy clusters, at and
, respectively, that are directly intersected by the FRB sightline
within their characteristic radius . Subtracting off their estimated
DM contributions as well that of the diffuse intergalactic medium, we estimate
a host contribution of or
(observed frame)
depending on whether we assume the halo gas extends to or . This significantly smaller -- no longer the largest known
value -- is now consistent with H emission measure estimates of the
host galaxy without having to invoke unusually high gas temperatures. We also
re-estimate the turbulent fluctuation and geometric amplification factor of the
scattering layer to be . This
result illustrates the importance of incorporating foreground data for FRB
analyses, both for understanding the nature of FRBs and to realize their
potential as a cosmological probe.Comment: 14 pages, 5 figures, 2 tables. Interactive figure (link in text).
Submitted to ApJ
A galaxy lacking dark matter
Studies of galaxy surveys in the context of the cold dark matter paradigm
have shown that the mass of the dark matter halo and the total stellar mass are
coupled through a function that varies smoothly with mass. Their average ratio
M_{halo}/M_{stars} has a minimum of about 30 for galaxies with stellar masses
near that of the Milky Way (approximately 5x10^{10} solar masses) and increases
both towards lower masses and towards higher masses. The scatter in this
relation is not well known; it is generally thought to be less than a factor of
two for massive galaxies but much larger for dwarf galaxies. Here we report the
radial velocities of ten luminous globular-cluster-like objects in the
ultra-diffuse galaxy NGC1052-DF2, which has a stellar mass of approximately
2x10^8 solar masses. We infer that its velocity dispersion is less than 10.5
kilometers per second with 90 per cent confidence, and we determine from this
that its total mass within a radius of 7.6 kiloparsecs is less than 3.4x10^8
solar masses. This implies that the ratio M_{halo}/M_{stars} is of order unity
(and consistent with zero), a factor of at least 400 lower than expected.
NGC1052-DF2 demonstrates that dark matter is not always coupled with baryonic
matter on galactic scales.Comment: To appear in the 29 March issue of Natur
A Revised Velocity for the Globular Cluster GC-98 in the Ultra Diffuse Galaxy NGC1052-DF2
We recently published velocity measurements of luminous globular clusters in
the galaxy NGC1052-DF2, concluding that it lies far off the canonical stellar
mass - halo mass relation. Here we present a revised velocity for one of the
globular clusters, GC-98, and a revised velocity dispersion measurement for the
galaxy. We find that the intrinsic dispersion km/s
using Approximate Bayesian Computation, or km/s
using the likelihood. The expected dispersion from the stars alone is ~7 km/s.
Responding to a request from the Editors of ApJ Letters and RNAAS, we also
briefly comment on the recent analysis of our measurements by Martin et al.
(2018).Comment: Published in the Research Notes of the AAS. 2 pages, 1 figur
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