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

Determination of resonance locations in NGC 613 from morphological arguments

In this paper, we present BVRI imaging data of NGC 613. We use these data to determine the corotation radius of the bar, using the photometric phase crossing method. This method uses the phase angle of the spiral structure in several wavebands, and looks for a crossing between the blue (B) light and the redder wavebands (e.g., R or I). For NGC 613, we find two phase crossings, an outer phase crossing at 136 +/- 8 arcsec and an inner phase crossing at 16 +/- 8 arcsec. We argue that the outer phase crossing is due to the bar corotation radius, and from the bar length of $R_{\rm bar}=90.0\pm4.0$ arcsec we go on to calculate a relative bar pattern speed of R = 1.5 +/- 0.1, which is consistent with the results of previous methods described in the literature. For a better understanding of the inner phase crossing, we have created structure maps in all four wavebands and a B-R color map. All of our structure maps and our color map highlight a nuclear ring of star formation at a radius of ~4 arcsec, which had also been observed recently using ALMA. Furthermore, the radius of our inner phase crossing appears to be consistent with the size of a nuclear disk of star formation that has been recently detected and described in the literature. We therefore suggest that the phase crossing method can be used to detect the size of nuclear star formation regions as well as the location of corotation resonances in spiral galaxies.Comment: 8 pages accepted for publication in MNRA

A test of arm-induced star formation in spiral galaxies from near-IR and Hα\alpha imaging

We have imaged a sample of 20 spiral galaxies in H$\alpha$ 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-$\mu$m imaging data and observed H$\alpha$ 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