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Register a new userThe ISM scaling relations in DustPedia late-type galaxies: A benchmark study for the Local Universe
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The purpose of this work is the characterization of the main scaling relations between all the ISM components (dust, atomic/molecular/total gas), gas-phase metallicity, and other galaxy properties, such as Mstar and galaxy morphology, for late-type galaxies in the Local Universe. This study is performed by extracting late-type galaxies from the entire DustPedia sample and by exploiting the large and homogeneous dataset available thanks to the DustPedia project. The sample consists of 436 galaxies with morphological stage from T = 1 to 10, Mstar from 6 x 10^7 to 3 x 10^11 Msun, SFR from 6 x 10^(-4) to 60 Msun/yr, and 12 + log(O/H) from 8 to 9.5. The scaling relations involving the molecular gas are studied by assuming both a constant and a metallicity-dependent XCO. The analysis has been performed by means of the survival analysis technique. We confirm that the dust mass correlates very well with the total gas mass, and find -- for the first time -- that the dust mass correlates better with the atomic gas mass than the molecular one. We characterize important mass ratios such as gas fraction, molecular-to-atomic gas mass ratio, dust-to-total gas mass ratio (DGR), and dust-to-stellar mass ratio. Only the assumption of a metallicity-dependent XCO reproduces the expected decrease of the DGR with increasing morphological stage and decreasing gas-phase metallicity, with a slope of about 1. DGR, gas-phase metallicity, and the dust-to-stellar mass ratio are, for our galaxy sample, directly linked to the galaxy morphology. The molecular-to-atomic gas mass ratio and the DGR show a positive correlation for low molecular gas fractions, but for molecular gas rich galaxies this trend breaks down. This trend has never been found previously, to our knowledge. It provides new constraints for theoretical models of galaxy evolution and a reference for high-redshift studies.
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We build templates of rotation curves as a function of the $I-$band luminosity via the mass modeling (by the sum of a thin exponential disk and a cored halo profile) of suitably normalized, stacked data from wide samples of local spiral galaxies. We then exploit such templates to determine fundamental stellar and halo properties for a sample of about $550$ local disk-dominated galaxies with high-quality measurements of the optical radius $R_{rm opt}$ and of the corresponding rotation velocity $V_{rm opt}$. Specifically, we determine the stellar $M_star$ and halo $M_{rm H}$ masses, the halo size $R_{rm H}$ and velocity scale ${V_{rm H}}$, and the specific angular momenta of the stellar $j_star$ and dark matter $j_{rm H}$ components. We derive global scaling relationships involving such stellar and halo properties both for the individual galaxies in our sample and for their mean within bins; the latter are found to be in pleasing agreement with previous determinations by independent methods (e.g., abundance matching techniques, weak lensing observations, and individual rotation curve modeling). Remarkably, the size of our sample and the robustness of our statistical approach allow us to attain an unprecedented level of precision over an extended range of mass and velocity scales, with $1sigma$ dispersion around the mean relationships of less than $0.1$ dex. We thus set new standard local relationships that must be reproduced by detailed physical models, that offer a basis for improving the sub-grid recipes in numerical simulations, that provide a benchmark to gauge independent observations and check for systematics, and that constitute a basic step toward the future exploitation of the spiral galaxy population as a cosmological probe.
Several dedicated surveys focusing on early-type galaxies (ETGs) reveal that significant fractions of them are detectable in all interstellar medium phases studied to date. We select ETGs from the Herschel Reference Survey that have both far-infrared Herschel and either HI or CO detection (or both). We derive their star formation rates (SFR), stellar masses and dust masses via modelling their spectral energy distributions. We combine these with literature information on their atomic and molecular gas properties, in order to relate their star formation, total gas mass and dust mass on global scales. The ETGs deviate from the dust mass-SFR relation and the Schmidt-Kennicutt relation that SDSS star forming galaxies define: compared to SDSS galaxies, ETGs have more dust at the same SFR, or less SFR at the same dust mass. When placing them in the M*-SFR plane, ETGs show a much lower specific SFR as compared to normal star-forming galaxies. ETGs show a large scatter compared to the Schmidt-Kennicutt relation found locally within our Galaxy, extending to lower SFRs and gas mass surface densities. Using an ETGs SFR and the Schmidt-Kennicutt law to predict its gas mass leads to an underestimate. ETGs have similar observed-gas-to-modelled-dust mass ratios to star forming-galaxies of the same stellar mass, as well as they exhibit a similar scatter.
Aims: We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies. Methods: We used Herschel observations and atomic and molecular gas masses to estimate the disc-averaged dust emissivity at 250 micrometres, and from this, the absorption cross section per H atom and per dust mass. The emissivity requires one assumption, which is the CO-to-H_2 conversion factor, and the dust temperature is additionally required for the absorption cross section per H atom; yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required for the absorption cross section dust mass. Results: We find epsilon(250) = 0.82 +/- 0.07 MJy sr^-1 (1E20 H cm^-2)^-1 for galaxies with 4 < F(250)/F(500) < 5. This depends only weakly on the adopted CO-to-H_2 conversion factor. The value is almost the same as that for the Milky Way at the same colour ratio. Instead, for F(250)/F(500) > 6, epsilon(250) is lower than predicted by its dependence on the heating conditions. The reduction suggests a variation in dust emission properties for spirals of earlier type, higher metallicity, and with a higher fraction of molecular gas. When the standard emission properties of Galactic cirrus are used for these galaxies, their dust masses might be underestimated by up to a factor of two. Values for the absorption cross sections at the Milky Way metallicity are also close to those of the cirrus. Mild trends of the absorption cross sections with metallicity are found, although the results depend on the assumptions made.
We present the extended GALEX Arecibo SDSS Survey (xGASS), a gas fraction-limited census of the atomic (HI) gas content of 1179 galaxies selected only by stellar mass ($M_star =10^{9}-10^{11.5} M_odot$) and redshift ($0.01<z<0.05$). This includes new Arecibo observations of 208 galaxies, for which we release catalogs and HI spectra. In addition to extending the GASS HI scaling relations by one decade in stellar mass, we quantify total (atomic+molecular) cold gas fractions and molecular-to-atomic gas mass ratios, $R_{mol}$, for the subset of 477 galaxies observed with the IRAM 30 m telescope. We find that atomic gas fractions keep increasing with decreasing stellar mass, with no sign of a plateau down to $log M_star/M_odot = 9$. Total gas reservoirs remain HI-dominated across our full stellar mass range, hence total gas fraction scaling relations closely resemble atomic ones, but with a scatter that strongly correlates with $R_{mol}$, especially at fixed specific star formation rate. On average, $R_{mol}$ weakly increases with stellar mass and stellar surface density $mu_star$, but individual values vary by almost two orders of magnitude at fixed $M_star$ or $mu_star$. We show that, for galaxies on the star-forming sequence, variations of $R_{mol}$ are mostly driven by changes of the HI reservoirs, with a clear dependence on $mu_star$. Establishing if galaxy mass or structure plays the most important role in regulating the cold gas content of galaxies requires an accurate separation of bulge and disk components for the study of gas scaling relations.
Observations of interstellar dust are often used as a proxy for total gas column density $N_mathrm{H}$. By comparing $textit{Planck}$ thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS (Green et al. 2018), with accurate (opacity-corrected) HI column densities and newly-published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth $tau_{353}$, reddening $E(B{-}V)$ and the total proton column density $N_mathrm{H}$ in the range (1$-$30)$times$10$^{20}$cm$^{-2}$, along sightlines with no molecular gas detections in emission. We derive an $N_mathrm{H}$/$E(B{-}V)$ ratio of (9.4$pm$1.6)$times$10$^{21}$cm$^{-2}$mag$^{-1}$ for purely atomic sightlines at $|b|$$>$5$^{circ}$, which is 60$%$ higher than the canonical value of Bohlin et al. (1978). We report a $sim$40$%$ increase in opacity $sigma_{353}$=$tau_{353}$/$N_mathrm{H}$, when moving from the low column density ($N_mathrm{H}$$<$5$times$10$^{20}$cm$^{-2}$) to moderate column density ($N_mathrm{H}$$>$5$times$10$^{20}$cm$^{-2}$) regime, and suggest that this rise is due to the evolution of dust grains in the atomic ISM. Failure to account for HI opacity can cause an additional apparent rise in $sigma_{353}$, of the order of a further $sim$20$%$. We estimate molecular hydrogen column densities $N_{mathrm{H}_{2}}$ from our derived linear relations, and hence derive the OH/H$_2$ abundance ratio of $X_mathrm{OH}$$sim$1$times$10$^{-7}$ for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with $N_{mathrm{H}_{2}}$ in the range $N_{mathrm{H}_{2}}$$sim$(0.1$-$10)$times$10$^{21}$cm$^{-2}$. This suggests that OH may be used as a reliable proxy for H$_2$ in this range, which includes sightlines with both CO-dark and CO-bright gas.
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