45 research outputs found
Dark matter halos and scaling relations of extremely massive spiral galaxies from extended H I rotation curves
We present new and archival atomic hydrogen (H I ) observations of 15 of the most massive spiral galaxies in the local Universe ( M (* )> 10 (11) M-?). From 3D kinematic modeling of the datacubes, we derive extended HI rotation curves, and from these, we estimate masses of the dark matter halos and specific angular momenta of the discs. We confirm that massive spiral galaxies lie at the upper ends of the Tully-Fisher relation (mass vs velocity, M infinity V (4) ) and Fall relation (specific angular momentum vs mass, j infinity M (0.6) ), in both stellar and baryonic forms, with no significant deviations from single power laws. We study the connections between baryons and dark matter through the stellar (and baryon)-to-halo ratios of mass f(M) equivalent to M (*) /M-h and specific angular momentum f (j, *) equivalent to j( *) /j(h) and f( j, bar) equivalent to j(bar) /j(h). Combining our sample with others from the literature for less massive disc-dominated galaxies, we find that f(M) rises monotonically with M (*) and M-h (instead of the inverted-U shaped f(M) for spheroid-dominated galaxies), while f (j, *) and f( j, bar) are essentially constant near unity o v er four decades in mass. Our results indicate that disc galaxies constitute a self-similar population of objects closely linked to the self-similarity of their dark halos. This picture is reminiscent of early analytical models of galaxy formation wherein discs grow by relatively smooth and gradual inflow, isolated from disruptive events such as major mergers and strong active galactic nuclei feedback, in contrast to the more chaotic growth of spheroids.National Science Foundation (NSF) 1616177European Research Council (ERC)
European Commission 101040751
ERC under the European Union Horizon 2020 research and innovation program 834148Brinson FoundationMCIN/AEI PID2020-114414GB-100Junta de Andalucia P20_00334
FEDER/Junta de Andalucia-Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades A-FQM-510-UGR20
NSF/AST-171482
Galaxy spin as a formation probe:the stellar-to-halo specific angular momentum relation
We derive the stellar-to-halo specific angular momentum relation (SHSAMR) of
galaxies at by combining i) the standard CDM tidal torque theory
ii) the observed relation between stellar mass and specific angular momentum
(Fall relation) and iii) various determinations of the stellar-to-halo mass
relation (SHMR). We find that the ratio of the
specific angular momentum of stars to that of the dark matter i) varies with
mass as a double power-law, ii) it always has a peak in the mass range explored
and iii) it is times larger for spirals than for ellipticals. The results
have some dependence on the adopted SHMR and we provide fitting formulae in
each case. For any choice of the SHMR, the peak of occurs at the same
mass where the stellar-to-halo mass ratio has a
maximum. This is mostly driven by the straightness and tightness of the Fall
relation, which requires and to be correlated with each other
roughly as , as expected if the outer and more angular
momentum rich parts of a halo failed to accrete onto the central galaxy and
form stars (biased collapse). We also confirm that the difference in the
angular momentum of spirals and ellipticals at a given mass is too large to be
ascribed only to different spins of the parent dark-matter haloes (spin bias).Comment: matches MNRAS published versio
Cold gas in the Milky Way's nuclear wind
The centre of the Milky Way is the site of several high-energy processes that
have strongly impacted the inner regions of our Galaxy. Activity from the
super-massive black hole, Sgr A*, and/or stellar feedback from the inner
molecular ring expel matter and energy from the disc in the form of a galactic
wind. Multiphase gas has been observed within this outflow, from hot
highly-ionized, to warm ionized and cool atomic gas. To date, however, there
has been no evidence of the cold and dense molecular phase. Here we report the
first detection of molecular gas outflowing from the centre of our Galaxy. This
cold material is associated with atomic hydrogen clouds travelling in the
nuclear wind. The morphology and the kinematics of the molecular gas, resolved
on ~1 pc scale, indicate that these clouds are mixing with the warmer medium
and are possibly being disrupted. The data also suggest that the mass of
molecular gas driven out is not negligible and could impact the rate of star
formation in the central regions. The presence of this cold, dense,
high-velocity gas is puzzling, as neither Sgr A* at its current level of
activity, nor star formation in the inner Galaxy seem viable sources for this
material.Comment: Published in the August 19 issue of Nature. This is the authors'
version before final edits. Published version is available at
http://www.nature.com/articles/s41586-020-2595-
The Life Cycle of the Central Molecular Zone. II: Distribution of atomic and molecular gas tracers
We use the hydrodynamical simulation of our inner Galaxy presented in
Armillotta et al. (2019) to study the gas distribution and kinematics within
the CMZ. We use a resolution high enough to capture the gas emitting in dense
molecular tracers such as NH3 and HCN, and simulate a time window of 50 Myr,
long enough to capture phases during which the CMZ experiences both quiescent
and intense star formation. We then post-process the simulated CMZ to calculate
its spatially-dependent chemical and thermal state, producing synthetic
emission data cubes and maps of both HI and the molecular gas tracers CO, NH3
and HCN. We show that, as viewed from Earth, gas in the CMZ is distributed
mainly in two parallel and elongated features extending from positive
longitudes and velocities to negative longitudes and velocities. The molecular
gas emission within these two streams is not uniform, and it is mostly
associated to the region where gas flowing towards the Galactic Center through
the dust lanes collides with gas orbiting within the ring. Our simulated data
cubes reproduce a number of features found in the observed CMZ. However, some
discrepancies emerge when we use our results to interpret the position of
individual molecular clouds. Finally, we show that, when the CMZ is near a
period of intense star formation, the ring is mostly fragmented as a
consequence of supernova feedback, and the bulk of the emission comes from
star-forming molecular clouds. This correlation between morphology and star
formation rate should be detectable in observations of extragalactic CMZs.Comment: 19 pages, 11 figures, accepted for publication in MNRA
The 3D Kinematics of Gas in the Small Magellanic Cloud
We investigate the kinematics of neutral gas in the Small Magellanic Cloud
(SMC) and test the hypothesis that it is rotating in a disk. To trace the 3D
motions of the neutral gas distribution, we identify a sample of young, massive
stars embedded within it. These are stars with radial velocity measurements
from spectroscopic surveys and proper motion measurements from Gaia, whose
radial velocities match with dominant HI components. We compare the observed
radial and tangential velocities of these stars with predictions from the
state-of-the-art rotating disk model based on high-resolution 21 cm
observations of the SMC from the Australian Square Kilometer Array Pathfinder
telescope. We find that the observed kinematics of gas-tracing stars are
inconsistent with disk rotation. We conclude that the kinematics of gas in the
SMC are more complex than can be inferred from the integrated radial velocity
field. As a result of violent tidal interactions with the LMC, non-rotational
motions are prevalent throughout the SMC, and it is likely composed of distinct
sub-structures overlapping along the line of sight.Comment: 9 pages, 5 figures, 1 Appendix; ApJ accepte
Direct observations of the atomic-molecular phase transition in the Milky Way's nuclear wind
Hundreds of high-velocity atomic gas clouds exist above and below the
Galactic Centre, with some containing a molecular component. However, the
origin of these clouds in the Milky Way's wind is unclear. This paper presents
new high-resolution MeerKAT observations of three atomic gas clouds and studies
the relationship between the atomic and molecular phases at pc scales.
The clouds' atomic hydrogen column densities, , are less than
a \mbox{few}\times 10^{20} cm, but the two clouds closest to the
Galactic Centre nonetheless have detectable CO emission. This implies the
presence of H at levels of at least a factor of ten
lower than in the typical Galactic interstellar medium. For the cloud closest
to the Galactic Centre, there is little correlation between the
and the probability that it will harbour detectable CO
emissions. In contrast, for the intermediate cloud, detectable CO is heavily
biased toward the highest values of . The cloud most distant
from the Galactic Centre has no detectable CO at similar
values. Moreover, we find that the two clouds with detectable CO are too
molecule-rich to be in chemical equilibrium, given the depths of their atomic
shielding layers, which suggests a scenario whereby these clouds consist of
pre-existing molecular gas from the disc that the Galactic wind has swept up,
and that is dissociating into atomic hydrogen as it flows away from the Galaxy.
We estimate that entrained molecular material of this type has a Myr lifetime before photodissociating.Comment: 11 pages, 6 figures, 2 tables. Submitted to MNRA
A massive stellar bulge in a regularly rotating galaxy 1.2 billion years after the Big Bang.
Cosmological models predict that galaxies forming in the early Universe experience a chaotic phase of gas accretion and star formation, followed by gas ejection due to feedback processes. Galaxy bulges may assemble later via mergers or internal evolution. Here we present submillimeter observations (with spatial resolution of 700 parsecs) of ALESS 073.1, a starburst galaxy at redshift [Formula: see text] when the Universe was 1.2 billion years old. This galaxy's cold gas forms a regularly rotating disk with negligible noncircular motions. The galaxy rotation curve requires the presence of a central bulge in addition to a star-forming disk. We conclude that massive bulges and regularly rotating disks can form more rapidly in the early Universe than predicted by models of galaxy formation.ERC
STF
Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy
We study the dynamics of cold molecular gas in two main-sequence galaxies at
cosmic noon (zC-488879 at and zC-400569 at ) using
new high-resolution ALMA observations of multiple CO transitions. For
zC-400569 we also re-analyze high-quality H data from the SINS/zC-SINF
survey. We find that (1) Both galaxies have regularly rotating CO disks and
their rotation curves are flat out to 8 kpc contrary to previous results
pointing to outer declines in the rotation speed ; (2) The
intrinsic velocity dispersions are low ( km/s for CO
and km/s for H) and imply yielding no significant pressure support; (3)
Mass models using HST images display a severe disk-halo degeneracy: models with
inner baryon dominance and models with "cuspy" dark matter halos can fit the
rotation curves equally well due to the uncertainties on stellar and gas
masses; (4) Milgromian dynamics (MOND) can successfully fit the rotation curves
with the same acceleration scale measured at . The question of
the amount and distribution of dark matter in high- galaxies remains
unsettled due to the limited spatial extent of the available kinematic data; we
discuss the suitability of various emission lines to trace extended rotation
curves at high . Nevertheless, the properties of these two high- galaxies
(high ratios, inner rotation curve shapes,
bulge-to-total mass ratios) are remarkably similar to those of massive spirals
at , suggesting weak dynamical evolution over more than 10 Gyr of the
Universe's lifetime.Comment: 18 pages, 11 figures, 4 tables, 2 appendices. Accepted for
publication in Astronomy and Astrophysic