83 research outputs found
The Ursa Major Cluster of Galaxies. IV ; HI synthesis observations
In this data paper we present the results of an extensive 21cm-line synthesis
imaging survey of 43 spiral galaxies in the nearby Ursa Major cluster using the
Westerbork Synthesis Radio Telescope. Detailed kinematic information in the
form of position-velocity diagrams and rotation curves is presented in an atlas
together with HI channel maps, 21cm continuum maps, global HI profiles, radial
HI surface density profiles, integrated HI column density maps, and HI velocity
fields. The relation between the corrected global HI linewidth and the
rotational velocities Vmax and Vflat as derived from the rotation curves is
investigated. Inclination angles obtained from the optical axis ratios are
compared to those derived from the inclined HI disks and the HI velocity
fields. The galaxies were not selected on the basis of their HI content but
solely on the basis of their cluster membership and inclination which should be
suitable for a kinematic analysis. The observed galaxies provide a
well-defined, volume limited and equidistant sample, useful to investigate in
detail the statistical properties of the Tully-Fisher relation and the dark
matter halos around them.Comment: 32 pages, including 2 sample pages of HI atlas. For full atlas (104
pages, 11 MB) see http://www.nrao.edu/library/preprints/00173.ps.gz .
Accepted for publication in Astronomy and Astrophysic
The Multi-Wavelength Tully-Fisher relation with spatially resolved HI kinematics
In this paper we investigate the statistical properties of the Tully-Fisher
relation for a sample of 32 galaxies with measured distances from the Cepheid
period-luminosity relation and/or TRGB stars.
We take advantage of panchromatic photometry in 12 bands (from FUV to 4.5
m) and of spatially resolved HI kinematics. We use these data together
with three kinematic measures (, and )
extracted from the global HI profiles or HI rotation curves, so as to construct
36 correlations allowing us to select the one with the least scatter. We
introduce a tightness parameter of the TFr, in order to obtain
a slope-independent measure of the goodness of fit. We find that the tightest
correlation occurs when we select the 3.6 m photometric band together with
the parameter extracted from the HI rotation curve.Comment: 16 pages, 16 figures, accepted for publication in MNRAS, minor
changes due to proof correction
Galaxy evolution in dense environments; a concise HI perspective
Observing the neutral Hydrogen in galaxy clusters provides crucial insights
in the physical processes that influence the evolution of gas-rich galaxies as
they migrate from the lower-density filaments through the cluster outskirts
into to the higher-density central regions. The morphology-density relation,
the Buther-Oemler effect, and the observed HI deficiencies in the central
regions of galaxy clusters suggest that infalling galaxies experience a strong
transformation of their morphologies, star formation rates, and gas content.
The physical mechanisms that trigger and govern these transformations may
depend strongly on environment. This contribution aims to illustrate that the
morphological and kinematic characteristics of the cold gas provide a sensitive
tool to determine which mechanisms dominate in which environments.Comment: 7 pages, 6 figures, To appear in `Outskirts of Galaxy Clusters;
intense life in the suburbs', IAU Colloquium No. 195, 2004, A. Diaferio e
The Ursa Major Cluster of Galaxies. III. Optical observations of dwarf galaxies and the luminosity function down to M_R=-11
Results are presented of a deep optical survey of the Ursa Major Cluster, a
spiral-rich cluster of galaxies at a distance of 18.6 Mpc which contains about
30% of the light but only 5% of the mass of the nearby Virgo Cluster. Fields
around known cluster members and a pattern of blind fields along the major and
minor axes of the cluster were studied with mosaic CCD cameras on the
Canada-France-Hawaii Telescope. The dynamical crossing time for the Ursa Major
Cluster is only slightly less than a Hubble time. Most galaxies in the local
Universe exist in similar moderate density environments. The Ursa Major Cluster
is therefore a good place to study the statistical properties of dwarf galaxies
since this structure is at an evolutionary stage representative of typical
environments yet has enough galaxies that reasonable counting statistics can be
accumulated. The main observational results of our survey are: (i) The galaxy
luminosity function is flat, with a logarithmic slope alpha = -1.1 for -17 <
M_R < -11, from a power-law fit. The error in alpha is likely to be less than
0.2 and is dominated by systematic errors, primarily associatedd with
uncertainties in assigning membership to specific galaxies. This faint end
slope is quite different to what was seen in the Virgo Cluster where
alpha=-2.26. (ii) Dwarf galaxies are as frequently found to be blue dwarf
irregulars as red dwarf spheroidals in the blind cluster fields. The density of
red dwarfs is significantly higher in the fields around luminous members than
in the blind fields. The most important result is the failure to detect many
dwarfs. If the steep luminosity function claimed for the Virgo Cluster were
valid for Ursa Major then in our blind fields we should have found about 1000
galaxies with -17 < M_R <-11 where we have found two dozen.Comment: 15 pages, 8 figs, TeX, MNRAS in press, Fig 3 at higher resolution
available from the author
The H I angular momentum-mass relation
We study the relationship between the H I specific angular momentum () and the H I mass () for a sample of galaxies with well-measured H I rotation curves. We find that the relation is well described by an unbroken power law ∝ α over the entire mass range (107-1010.5 M⊙), with α = 0.89 ± 0.05 (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H I discs in a marginally stable state. The slope we observe is also significantly different from both the j ∝ M2/3 relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disc galaxies. Our sample includes two H I-bearing ultra-diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H I discs, which are found to have significantly higher angular momentum than expected from the power-law relation. The H I discs of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar discs, consistent with the gas being recently accreted. We speculate that late-stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations
The anomalous properties of Markarian 1460
We present and discuss optical, near-infrared and HI measurements of the
galaxy Markarian 1460 at a distance of 19 Mpc in the Ursa Major Cluster. This
low-luminosity (M_B = -14) galaxy is unusual because (i) it is blue (B-R=0.8)
and has the spectrum of an HII galaxy, (ii) it has a light profile that is
smooth and well fit by an r^{1/4} and not an exponential function at all radii
larger than the seeing, and (iii) it has an observed central brightness of
about mu_B = 20 mag arcsec^{-2}, intermediate between those of elliptical
galaxies (on the bright mu_B side) and normal low-luminosity dwarf irregular
(on the low mu_B side) galaxies. No other known galaxy exhibits all these
properties in conjunction. On morphological grounds this galaxy looks like a
normal distant luminous elliptical galaxy, since the fundamental plane tells us
that higher luminosity normal elliptical galaxies tend to have lower
surface-brightnesses. Markarian 1460 has 2 X 10^7 M_sun of HI and a ratio
M(HI)/L_B of 0.2, which is low compared to typical values for star-forming
dwarf galaxies. From the high surface brightness and r^{1/4} profile, we infer
that the baryonic component of Markarian 1460 has become self-gravitating
through dissipative processes. From the colours, radio continuum, HI and
optical emission line properties, yet smooth texture, we infer that Markarian
1460 has had significant star formation as recently as about 1 Gyr ago but not
today.Comment: MNRAS in pres
WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192
A pilot study with the powerful new backend of the Westerbork Synthesis Radio
Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen
emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4
Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and
the large scale structure in which they are embedded. In Abell 963, a
dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction,
most of the gas-rich galaxies are located between 1 and 3 Mpc in projection,
northeast from the cluster core. Their velocities are slightly redshifted with
respect to the cluster, and this is likely a background group. None of the blue
galaxies in the core of Abell 963 are detected in HI, although they have
similar colors and luminosities as the HI detected galaxies in the cluster
outskirts and field. Abell 2192 is less massive and more diffuse. Here, the
gas-rich galaxies are more uniformly distributed. The detected HI masses range
from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing
rudimentary rotation curves useful for detailed kinematic studies of galaxies
in various environments. This is a pilot for ultra-deep integrations down to HI
masses of 8x10^8 Msun, providing a complete survey of the gas content of
galaxies at z=0.2, probing environments ranging from cluster cores to voids.Comment: 5 pages, 6 figures + 1 Plate, accepted for publication in the
Astrophysical Journal Letter
The DiskMass Survey. X. Radio synthesis imaging of spiral galaxies
We present results from 21 cm radio synthesis imaging of 28 spiral galaxies
from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We
detail the observations and data reduction procedures and present a brief
analysis of the radio data. We construct 21 cm continuum images, global HI
emission-line profiles, column-density maps, velocity fields, and
position-velocity diagrams. From these we determine star formation rates
(SFRs), HI line widths, total HI masses, rotation curves, and
azimuthally-averaged radial HI column-density profiles. All galaxies have an HI
disk that extends beyond the readily observable stellar disk, with an average
ratio and scatter of R_{HI}/R_{25}=1.35+/-0.22, and a majority of the galaxies
appear to have a warped HI disk. A tight correlation exists between total HI
mass and HI diameter, with the largest disks having a slightly lower average
column density. Galaxies with relatively large HI disks tend to exhibit an
enhanced stellar velocity dispersion at larger radii, suggesting the influence
of the gas disk on the stellar dynamics in the outer regions of disk galaxies.
We find a striking similarity among the radial HI surface density profiles,
where the average, normalized radial profile of the late-type spirals is
described surprisingly well with a Gaussian profile. These results can be used
to estimate HI surface density profiles in galaxies that only have a total HI
flux measurement. We compare our 21 cm radio continuum luminosities with 60
micron luminosities from IRAS observations for a subsample of 15 galaxies and
find that these follow a tight radio-infrared relation, with a hint of a
deviation from this relation at low luminosities. We also find a strong
correlation between the average SFR surface density and the K-band surface
brightness of the stellar disk.Comment: 22 pages + Appendix, 16 figures + Atlas, 5 tables. Accepted for
publication in Astronomy & Astrophysic
Squelched Galaxies and Dark Halos
There is accumulating evidence that the faint end of the galaxy luminosity
function might be very different in different locations. The luminosity
function might be rising in rich clusters and flat or declining in regions of
low density. If galaxies form according to the model of hierarchical clustering
then there should be many small halos compared to the number of big halos. If
this theory is valid then there must be a mechanism that eliminates at least
the visible component of galaxies in low density regions. A plausible mechanism
is photoionization of the intergalactic medium at a time before the epoch that
most dwarf galaxies form in low density regions but after the epoch of
formation for similar systems that ultimately end up in rich clusters. The
dynamical timescales are found to accommodate this hypothesis in a flat
universe with Omega_m < 0.4.
If small halos exist but simply cannot be located because they have never
become the sites of significant star formation, they still might have dynamical
manifestations. These manifestations are hard to identify in normal groups of
galaxies because small halos do not make a significant contribution to the
global mass budget. However, it could be entertained that there are clusters of
halos where there are only small systems, clusters that are at the low mass end
of the hierarchical tree. There may be places where only a few small galaxies
managed to form, enough for us to identify and use as test probes of the
potential. It turns out that such environments might be common. Four probable
groups of dwarfs are identified within 5 Mpc and the assumption they are
gravitationally bound suggests M/L_B ~ 300 - 1200 M_sun/L_sun, 6 +/- factor 2
times higher than typical values for groups with luminous galaxies.Comment: Accepted ApJ 569, (April 20), 2002, 12 pages, 6 figures, 1 tabl
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