Article

# The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies

[more]
(Impact Factor: 4.38). 06/2011; 535(0004-6361). DOI: 10.1051/0004-6361/201116872
Source: arXiv

ABSTRACT

Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster
Survey (HeViCS), we investigated the relationship between the metallicity
gradients expressed by metal abundances in the gas phase as traced by the
chemical composition of HII regions, and in the solid phase, as traced by the
dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass
ratio for all galaxies observed by HeViCS whose metallicity gradients are
available in the literature. They are all late type Sbc galaxies, namely
NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on
metallicity of the CO-to-H$_2$ conversion factor (\xco), used to transform the
$^{12}$CO observations into the amount of molecular hydrogen. We found that in
these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive
to choice of the \xco\ value, since the molecular gas is the dominant component
in the inner parts. We found that for three galaxies of our sample, namely
NGC4254, NGC4321, and NGC4501, the slopes of the oxygen and of the dust-to-gas
radial gradients agree up to $\sim$0.6-0.7R$_{25}$ using \xco\ values in the
range 1/3-1/2 Galactic \xco. For NGC4303 a lower value of \xco$\sim0.1\times$
10$^{20}$ is necessary. We suggest that such low \xco\ values might be due to a
metallicity dependence of \xco (from close to linear for NGC4254, NGC4321, and
NGC4501 to superlinear for NGC4303), especially in the radial regions
R$_G<$0.6-0.7R$_{25}$ where the molecular gas dominates. On the other hand, the
outer regions, where the atomic gas component is dominant, are less affected by
the choice of \xco, and thus we cannot put constraints on its value.

### Full-text

Available from: Laura Magrini,
0 Followers
·
• Source
##### Article: Atomic and Molecular Gas Components in Spiral Galaxies of the Virgo Cluster
[Hide abstract]
ABSTRACT: Based on two models, we investigate the molecular-to-atomic gas ratio in Virgo cluster galaxies in comparison with field galaxies. We show that the enhanced metallicity for cluster members and the ram pressure stripping of atomic gas from the disk periphery cannot fully explain the observed gas component ratios. The additional environmental factors affecting the interstellar medium and leading to an increase in the molecular gas fraction should be taken into account for cluster galaxies.
Astronomy Letters 01/2012; 38(2). DOI:10.1134/S1063773712020041 · 1.43 Impact Factor
• Source
##### Article: The Dust & Gas Properties of M83
[Hide abstract]
ABSTRACT: We examine the dust and gas properties of the nearby, barred galaxy M83, which is part of the Very Nearby Galaxy Survey. Using images from the PACS and SPIRE instruments of Herschel, we examine the dust temperature and dust mass surface density distribution. We find that the nuclear, bar and spiral arm regions exhibit higher dust temperatures and masses compared to interarm regions. However, the distribution of dust temperature and mass are not spatially coincident. Assuming a trailing spiral structure, the dust temperature peaks in the spiral arms lie ahead of the dust surface density peaks. The dust mass surface density correlates well with the distribution of molecular gas as traced by CO (J=3-2) images (JCMT) and the star formation rate as traced by H?2 with a correction for obscured star formation using 24 micron emission. Using HI images from THINGS to trace the atomic gas component, we make total gas mass surface density maps and calculate the gas-to-dust ratio. We find a mean gas-to-dust ratio of 84 \pm 4 with higher values in the inner region assuming a constant CO-to-H2 conversion factor. We also examine the gas-to-dust ratio using CO-to-H2 conversion factor that varies with metallicity.
Monthly Notices of the Royal Astronomical Society 01/2012; 421(4). DOI:10.1111/j.1365-2966.2012.20520.x · 5.11 Impact Factor
• Source
##### Article: FIR colours of nearby late-type galaxies in the Herschel Reference Survey
[Hide abstract]
ABSTRACT: We study the far infrared (60-500 $\mu$m) colours of late-type galaxies in the $Herschel$ Reference Survey, a K-band selected, volume limited sample of nearby galaxies. The far infrared colours are correlated with each other, with tighter correlations for the indices that are closer in wavelength. We also compare the different colour indices to various tracers of the physical properties of the target galaxies, such as the surface brightness of the ionising and non-ionising stellar radiation, the dust attenuation and the metallicity. The emission properties of the cold dust dominating the far infrared spectral domain are regulated by the properties of the interstellar radiation field. Consistent with that observed in nearby, resolved galaxies, our analysis shows that the ionising and the non-ionising stellar radiation, including that emitted by the most evolved, cold stars, both contribute to the heating of the cold dust component. This work also shows that metallicity is another key parameter characterising the cold dust emission of normal, late-type galaxies. A single modified black body with a grain emissivity index $\beta$=1.5 better fits the observed SPIRE flux density ratios $S250/S350$ vs. $S350/S500$ than $\beta$=2, although values of $\beta$ $\simeq$ 2 are possible in metal rich, high surface brightness galaxies. Values of $\beta$ $\lesssim$ 1.5 better represent metal poor, low surface brightness objects. This observational evidence provides strong constraints for dust emission models of normal, late type galaxies.
Astronomy and Astrophysics 01/2012; 540. DOI:10.1051/0004-6361/201118602 · 4.38 Impact Factor