14 research outputs found
The galaxy "missing dark matter" NGC1052-DF4 is undergoing tidal disruption
The existence of long-lived galaxies lacking dark matter represents a
challenge to our understanding of how galaxies form. Here, we present evidence
that explains the lack of dark matter in one of such galaxies: NGC1052-DF4.
Deep optical imaging of the system has detected tidal tails in this object
caused by its interaction with its neighbouring galaxy NGC1035. As stars are
more centrally concentrated than the dark matter, the tidal stripping will
remove a significant percentage of the dark matter before affecting the stars
of the galaxy. Only ~7% of the stellar mass of the galaxy is in the tidal
tails, suggesting that the stars of NGC1052-DF4 are starting only now to be
affected by the interaction, while the percentage of remaining dark matter is
<1%. This naturally explains the low content of dark matter inferred for this
galaxy and reconciles these type of galaxies with our current models of galaxy
formation.Comment: 18 pages, 9 figures, accepted for publication in ApJ; The main
results of the paper are shown in figures 5 and
The truncation of the disk of NGC 4565: Detected up to z=4 kpc, with star formation, and affected by the warp
Context: The hierarchical model of galaxy formation suggests that galaxies
are continuously growing. However, our position inside the Milky Way prevents
us from studying the disk edge. Truncations are low surface brightness features
located in the disk outskirts of external galaxies. They indicate where the
disk brightness abruptly drops and their location is thought to change
dynamically. In previous analyses of Milky Way-like galaxies, truncations were
detected up to 3 kpc above the mid-plane but whether they remain present beyond
that height remains unclear.
Aims: Our goal is to determine whether truncations can be detected above 3
kpc height in the Milky Way-like galaxy NGC 4565, thus establishing the actual
disk thickness. We also aim to study how the truncation relates to disk
properties such as star formation activity or the warp.
Methods: We perform a vertical study of the disk of NGC 4565 edge in
unprecedented detail. We explore the truncation radius at different heights
above/below the disk mid-plane (0<z<8 kpc) and at different wavelengths. We use
new ultra-deep optical data ( mag arcsec; within arcsec boxes) in the , and broad
bands, along with near- and far-ultraviolet, H, and \ion{H}{i}
observations.
Results: We detect the truncation up to 4 kpc in the , and
ultra-deep bands which is 1 kpc higher than in any previous study for any
galaxy. The radial position of the truncation remains constant up to 3 kpc
while higher up it is located at a smaller radius. This result is independent
of the wavelength but is affected by the presence of the warp.
Conclusions: We propose an inside-out growth scenario for the formation of
the disk of NGC 4565. Our results point towards the truncation feature being
linked to a star-forming threshold and to the onset of the disk warp.Comment: 27 pages, 18 figures (incl. 2 appendix); accepted for publication in
A&A; Fixed labels in Fig.
Extragalactic magnetism with SOFIA (SALSA Legacy Program). VI. The magnetic fields in the multi-phase interstellar medium of the Antennae galaxies
Mergers are thought to be a fundamental channel for galaxy growth, perturbing
the gas dynamics and the magnetic fields (B-fields) in the interstellar medium
(ISM). However, the mechanisms that amplify and dissipate B-fields during a
merger remain unclear. We characterize the morphology of the ordered B-fields
in the multi-phase ISM of the closest merger of two spiral galaxies, the
Antennae galaxies. We compare the inferred B-fields using m thermal
dust and cm radio synchrotron emission polarimetric observations. We find
that the m B-fields are more ordered across the Antennae galaxies than
the cm B-fields. The turbulent-to-ordered m B-field increases at
the galaxy cores and star-forming regions. The relic spiral arm has an ordered
spiral m B-field, while the cm B-field is radial. The m
B-field may be dominated by turbulent dynamos with high CO(1-0) velocity
dispersion driven by star-forming regions, while the cm B-field is
cospatial with high HI velocity dispersion driven by galaxy interaction. This
result shows the dissociation between the warm gas mainly disturbed by the
merger, and the dense gas still following the dynamics of the relic spiral arm.
We find a kpc scale ordered B-field connecting the two galaxies. The
base of the tidal tail is cospatial with the HI and CO(1-0) emission and
has compressed and/or sheared m and cm B-fields driven by the
merger. We suggest that amplify B-fields, with respect to the rest of the
system and other spiral galaxies, may be supporting the gas flow between both
galaxies and the tidal tail.Comment: 11 pages, 5 figures, Accepted for publication in ApJ Letter
Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- V: First results on the magnetic field orientation of galaxies
We present the analysis of the magnetic field (-field) structure of
galaxies measured with far-infrared (FIR) and radio (3 and 6 cm) polarimetric
observations. We use the first data release of the Survey on extragALactic
magnetiSm with SOFIA (SALSA) of 14 nearby ( Mpc) galaxies with resolved (5
arcsec-18 arcsec; pc-- kpc) imaging polarimetric observations using
HAWC+/SOFIA from to \um. We compute the magnetic pitch angle
() profiles as a function of the galactrocentric radius. We introduce
a new magnetic alignment parameter () to estimate the
disordered-to-ordered -field ratio in spiral -fields. We find FIR and
radio wavelengths to not generally trace the same -field morphology in
galaxies. The profiles tend to be more ordered with galactocentric
radius in radio () than in FIR
(). For spiral galaxies, FIR -fields
are \% more turbulent than the radio -fields. For starburst galaxies,
we find that FIR polarization is a better tracer of the -fields along the
galactic outflows than radio polarization. Our results suggest that the
-fields associated with dense, dusty, turbulent star-forming regions, those
traced at FIR, are less ordered than warmer, less-dense regions, those traced
at radio, of the interstellar medium. The FIR -fields seem to be more
sensitive to the activity of the star-forming regions and the morphology of the
molecular clouds within a vertical height of few hundred pc in the disk of
spiral galaxies than the radio -fields.Comment: 26 pages, 13 figure
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A tomographic view of far infrared and radio polarimetric observations through MHD simulations of galaxies
The structure of magnetic fields in galaxies remains poorly constrained,
despite the importance of magnetism in the evolution of galaxies. Radio
synchrotron and far-infrared dust polarization (FIR) polarimetric observations
are the best methods to measure galactic scale properties of magnetic fields in
galaxies beyond the Milky Way. We use synthetic polarimetric observations of a
simulated galaxy to identify and quantify the regions, scales, and interstellar
medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of
magnetohydrodynamical cosmological zoom-in simulations features
high-resolutions (10 pc full-cell size) and multiple magnetization models. Our
synthetic observations have a striking resemblance to those of observed
galaxies. We find that the total and polarized radio emission extends to
approximately double the altitude above the galactic disk (half-intensity disk
thickness of kpc)
relative to the FIR total and polarized emission that are concentrated in the
disk midplane ( kpc).
Radio emission traces magnetic fields at scales of pc, whereas
FIR emission probes magnetic fields at the smallest scales of our simulations.
These scales are comparable to our spatial resolution and well below the
spatial resolution ( pc) of existing FIR polarimetric measurements.
Finally, we confirm that synchrotron emission traces a combination of the warm
neutral and cold neutral gas phases, whereas FIR emission follows the densest
gas in the cold neutral phase in the simulation. These results are independent
of the ISM magnetic field strength. The complementarity we measure between
radio and FIR wavelengths motivates future multiwavelength polarimetric
observations to advance our knowledge of extragalactic magnetism.Comment: Submitted to ApJ. 32 pages, 15 figure
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A Tomographic View of Far-infrared and Radio Polarimetric Observations through MHD Simulations of Galaxies
The structure of magnetic fields in galaxies remains poorly constrained, despite the importance of magnetism in the evolution of galaxies. Radio synchrotron and far-infrared (FIR) polarization and polarimetric observations are the best methods to measure galactic scale properties of magnetic fields in galaxies beyond the Milky Way. We use synthetic polarimetric observations of a simulated galaxy to identify and quantify the regions, scales, and interstellar medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of magnetohydrodynamical cosmological zoom-in simulations features high-resolutions (10 pc full-cell size) and multiple magnetization models. Our synthetic observations have a striking resemblance to those of observed galaxies. We find that the total and polarized radio emission extends to approximately double the altitude above the galactic disk (half-intensity disk thickness of h I radio ∼ h PI radio = 0.23 ± 0.03 kpc) relative to the total FIR and polarized emission that are concentrated in the disk midplane (h I FIR ∼ h PI FIR = 0.11 ± 0.01 kpc). Radio emission traces magnetic fields at scales of ≳300 pc, whereas FIR emission probes magnetic fields at the smallest scales of our simulations. These scales are comparable to our spatial resolution and well below the spatial resolution (<300 pc) of existing FIR polarimetric measurements. Finally, we confirm that synchrotron emission traces a combination of the warm neutral and cold neutral gas phases, whereas FIR emission follows the densest gas in the cold neutral phase in the simulation. These results are independent of the ISM magnetic field strength. The complementarity we measure between radio and FIR wavelengths motivates future multiwavelength polarimetric observations to advance our knowledge of extragalactic magnetism
Flares, Warps, Truncations, and Satellite: The Ultra-thin Galaxy UGC 11859
The structure of the outskirts of galaxies provides valuable information about their past and evolution. Due to their projected orientation, edge-on isolated galaxies effectively serve as test labs in which to study the three-dimensional structures of galaxies, including warps and flares, and to explore the possible sources of such distortions. We analyzed the structure of the apparently isolated edge-on ultra-thin galaxy UGC 11859 to look for the presence of distortions. The deep optical imaging observations ( and 30.0 in the g - and r -bands, respectively) we acquired with the 10.4 m Gran Telescopio Canarias are used to derive the radial and vertical surface brightness profiles and g − r color radial profile. We find that UGC 11859’s disk displays a significant gravitational distortion. A warp is clearly detected on one side of the disk, and the galactic plane on both sides of the center shows increasing scale height with an increasing galactocentric radius, indicating the presence of a flare in the stellar distribution. The surface brightness profile of the disk shows a sharp break at 24 kpc galactocentric radius, and a steep decline to larger radii, an “edge-on truncation,” which we associate with the presence of the flare. The present study is the first observational support for a connection between truncations and flares. Just beyond the warped side of the disk, a faint galaxy is observed within a small angular distance, identified as a potential interacting companion. Based on ultradeep g and r photometry we estimate that if the potential companion is at the same distance as UGC 11859, the stellar mass of the satellite galaxy is log _10 ( M _⊙ ) =
Extragalactic Magnetism with SOFIA (Legacy Program) - II: A Magnetically Driven Flow in the Starburst Ring of NGC 1097
Galactic bars are frequent in disk galaxies and they may support the transfer
of matter towards the central engine of active nuclei. The barred galaxy NGC
1097 has magnetic forces controlling the gas flow at several kpc scales, which
suggest that magnetic fields (B-fields) are dynamically important along the bar
and nuclear ring. However, the effect of the B-field on the gas flows in the
central kpc scale has not been characterized. Using thermal polarized emission
at m with HAWC+/SOFIA, here, we measure that the polarized flux is
spatially located at the contact regions of the outer-bar with the starburst
ring. The linear polarization decomposition analysis shows that the m
and radio ( and cm) polarization traces two different modes, , of
the B-field: a constant B-field orientation and dominated by at
m, and a spiral B-field dominated by at radio. We show that the
B-field at 89 m is concentrated in the warmest region of a shock driven by
the galactic-bar dynamics in the contact regions between the outer-bar with the
starburst ring. Radio polarization traces a superposition of the spiral B-field
outside and within the starburst ring. According to Faraday rotation measures
between and cm, the radial component of the B-field along the
contact regions points toward the galaxy's center on both sides. We conclude
that gas streams outside and within the starburst ring follow the B-field,
which feeds the black hole with matter from the host galaxy.Comment: 17 pages, 10 figures, Accepted for publication to Ap