99 research outputs found
Census of Gaseous Satellites around Local Spiral Galaxies
We present a search for gas-containing dwarf galaxies as satellite systems
around nearby spiral galaxies using 21 cm neutral hydrogen (HI) data from the
Arecibo Legacy Fast ALFA (ALFALFA) Survey. We have identified 15 spiral
`primary' galaxies in a local volume of 10 Mpc with a range of total masses,
and have found 19 gas-containing dwarf satellite candidates within the
primaries' virial volumes () and 46 candidates within . Our
sensitivity using ALFALFA data converts to at 10 Mpc, which includes 13 of the 26 gaseous dwarf
galaxies in the Local Group, and the HI properties of our sample are overall
similar to these 13. We found gaseous satellites per host galaxy within
and within , which agrees with the low numbers
present for the Milky Way and M31. There is also agreement with the
star-forming satellite numbers per host in the deep optical surveys SAGA and
ELVES, and the Auriga cosmological simulations. When scaled to , the
optical surveys do not show a trend of increasing quenched fraction with host
mass; there is a slight increase in the total number of gaseous satellites with
host mass for our sample. The low numbers of gaseous/star-forming satellites
around spiral hosts are consistent with the idea that a universal and effective
satellite quenching mechanism, such as ram pressure stripping by the host halo,
is likely at play.Comment: 18 pages, 13 figures, accepted by MNRA
The Kinematic Structure of Magnetically Aligned HI Filaments
We characterize the kinematic and magnetic properties of HI filaments located
in a high Galactic latitude region ( and
). We extract three-dimensional filamentary
structures using \texttt{fil3d} from the Galactic Arecibo L-Band Feed Array HI
(GALFA-HI) survey 21-cm emission data. Our algorithm identifies coherent
emission structures in neighboring velocity channels. Based on the mean
velocity, we identify a population of local and intermediate velocity cloud
(IVC) filaments. We find the orientations of the local (but not the IVC) HI
filaments are aligned with the magnetic field orientations inferred from Planck
353 GHz polarized dust emission. We analyze position-velocity diagrams of the
velocity-coherent filaments, and find that only 15 percent of filaments
demonstrate significant major-axis velocity gradients with a median magnitude
of 0.5 km s pc, assuming a fiducial filament distance of 100 pc.
We conclude that the typical diffuse HI filament does not exhibit a simple
velocity gradient. The reported filament properties constrain future
theoretical models of filament formation.Comment: 15 pages, 16 figure
A Limit on the Metallicity of Compact High Velocity Clouds
There is a fortuitous coincidence in the positions of the quasar TonS210 and
the compact H I high velocity cloud CHVC224.0-83.4-197 on the sky. Using Far
Ultraviolet Spectroscopic Explorer observations of the metal-line absorption in
this cloud and sensitive H I 21cm emission observations obtained with the
multibeam system at Parkes Observatory, we determine a metallicity of (O/H)
<0.46 solar at a confidence of 3 sigma. The metallicity of the high velocity
gas is consistent with either an extragalactic or Magellanic Cloud origin, but
is not consistent with a location inside the Milky Way unless the chemical
history of the gas is considerably different from that of the interstellar
medium in the Galactic disk and halo. Combined with measurements of highly
ionized species (C III and O VI) at high velocities, this metallicity limit
indicates that the cloud has a substantial halo of ionized gas; there is as
much ionized gas as neutral gas directly along the Ton S210 sight line. We
suggest several observational tests that would improve the metallicity
determination substantially and help to distinguish between possible origins
for the high velocity gas. Additional observations of this sight line would be
valuable since the number of compact HVCs positioned in front of background
sources bright enough for high resolution absorption-line studies is extremely
limited.Comment: 15 pages, 3 postscript figures + 1 JPEG figure (reduced from
postscript for size considerations), accepted for publication in ApJ (June
2002
The Origin and Distribution of Cold Gas in the Halo of a Milky Way-Mass Galaxy
We analyze an adaptive mesh refinement hydrodynamic cosmological simulation
of a Milky Way-sized galaxy to study the cold gas in the halo. HI observations
of the Milky Way and other nearby spirals have revealed the presence of such
gas in the form of clouds and other extended structures, which indicates
on-going accretion. We use a high-resolution simulation (136-272 pc throughout)
to study the distribution of cold gas in the halo, compare it with
observations, and examine its origin. The amount (10^8 Msun in HI), covering
fraction, and spatial distribution of the cold halo gas around the simulated
galaxy at z=0 are consistent with existing observations. At z=0 the HI mass
accretion rate onto the disk is 0.2 Msun/yr. We track the histories of the 20
satellites that are detected in HI in the redshift interval 0.5>z>0 and find
that most of them are losing gas, with a median mass loss rate per satellite of
3.1 x 10^{-3} Msun/yr. This stripped gas is a significant component of the HI
gas seen in the simulation. In addition, we see filamentary material coming
into the halo from the IGM at all redshifts. Most of this gas does not make it
directly to the disk, but part of the gas in these structures is able to cool
and form clouds. The metallicity of the gas allows us to distinguish between
filamentary flows and satellite gas. We find that the former accounts for at
least 25-75% of the cold gas in the halo seen at any redshift analyzed here.
Placing constraints on cloud formation mechanisms allows us to better
understand how galaxies accrete gas and fuel star formation at z=0.Comment: 13 pages, 8 figures. Accepted for publication in Ap
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