52 research outputs found
The dark matter halo density profile, spiral arm morphology and black hole mass of M33
In this paper, we investigate the dark matter halo density profile of M33. We
find that the HI rotation curve of M33 is best described by a NFW dark matter
halo density profile model, with a halo concentration of cvir = 4.0\pm1.0 and a
virial mass of Mvir = (2.2\pm0.1)\times10^11 Msun. We go on to use the NFW
concentration (cvir)of M33, along with the values derived for other galaxies
(as found in the literature), to show that cvir correlates with both spiral arm
pitch angle and supermassive black hole mass.Comment: 18 pages, accepted for publicatio
The connection between shear and star formation in spiral galaxies
We present a sample of 33 galaxies for which we have calculated (i) the
average rate of shear from publish rotation curves, (ii) the far-infrared
luminosity from IRAS fluxes and (iii) The K-band luminosity from 2MASS. We show
that a correlation exists between the shear rate and the ratio of the
far-infrared to K-band luminosity. This ratio is essentially a measure of the
star formation rate per unit mass, or the specific star formation rate. From
this correlation we show that a critical shear rate exists, above which star
formation would turn off in the disks of spiral galaxies. Using the correlation
between shear rate and spiral arm pitch angle, this shear rate corresponds to
the lowest pitch angles typically measured in near-infrared images of spiral
galaxies.Comment: Accepted for publication in MNRAS letters. 5 figures, 1 tabl
A test of arm-induced star formation in spiral galaxies from near-IR and H imaging
We have imaged a sample of 20 spiral galaxies in H and in the
near-infrared K band (2.2 um), in order to determine the location and strength
of star formation in these objects with respect to perturbations in the old
stellar population. We have found that star formation rates are significantly
enhanced in the vicinity of K band arms. We have also found that this
enhancement in star formation rate in arm regions correlates well with a
quantity that measures the relative strengths of shocks in arms. Assuming that
the K band light is dominated by emission from the old stellar population, this
shows that density waves trigger star formation in the vicinity of spiral arms.Comment: 6 pages, 1 figure, accpeted for publication in MNRA
Is Messier 74 a barred spiral galaxy?
We have obtained ground-based I, J and K band images of the spiral galaxy,
Messier 74 (NGC 628). This galaxy has been shown to possess a circumnuclear
ring of star formation from both near-infrared spectroscopy of CO absorption
and sub-millimetre imaging of CO emission. Circumnuclear rings of star
formation are believed to exist only as a result of a bar potential. In this
paper we show evidence for a weak oval distortion in the centre of M74. We use
the results of Combes & Gerin (1985) to suggest that this weak oval potential
is responsible for the circumnuclear ring of star formation observed in M74.Comment: 4 pages, 3 figures, accepted for publication in A&
Constraining dark matter halo profiles and galaxy formation models using spiral arm morphology. II. Dark and stellar mass concentrations for 13 nearby face-on galaxies
We investigate the use of spiral arm pitch angles as a probe of disk galaxy
mass profiles. We confirm our previous result that spiral arm pitch angles (P)
are well correlated with the rate of shear (S) in disk galaxy rotation curves.
We use this correlation to argue that imaging data alone can provide a powerful
probe of galactic mass distributions out to large look-back times. We then use
a sample of 13 galaxies, with Spitzer 3.6-m imaging data and observed
H rotation curves, to demonstrate how an inferred shear rate coupled
with a bulge-disk decomposition model and a Tully-Fisher-derived velocity
normalization can be used to place constraints on a galaxy's baryon fraction
and dark matter halo profile. Finally we show that there appears to be a trend
(albeit a weak correlation) between spiral arm pitch angle and halo
concentration. We discuss implications for the suggested link between
supermassive black hole (SMBH) mass and dark halo concentration, using pitch
angle as a proxy for SMBH mass.Comment: 14 pages, 6 figures. Accepted for publication in the Astrophysical
Journa
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