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Register a new userGHASP: an H$alpha$ kinematical survey of spiral galaxies -- XIII. Distribution of luminous and dark matter in spiral and irregular nearby galaxies using H$alpha$ and HI rotation curves and WISE photometry
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We present the mass models of 31 spiral and irregular nearby galaxies obtained using hybrid rotation curves (RCs) combining high resolution GHASP Fabry-Perot H$alpha$ RCs and extended WHISP HI ones together with 3.4 $mu$m WISE photometry. The aim is to compare the dark matter (DM) halo properties within the optical radius using only H$alpha$ RCs with the effect of including and excluding the mass contribution of the neutral gas component, and when using HI or hybrid RCs. Pseudo-isothermal (ISO) core and Navarro-Frenk-White (NFW) cuspy DM halo profiles are used with various fiducial fitting procedures. Mass models using H$alpha$ RCs including or excluding the HI gas component provide compatible disc M/L. The correlations between DM halo and baryon parameters do not strongly depend on the RC. Clearly, the differences between the fitting procedures are larger than between the different datasets. Hybrid and HI RCs lead to higher M/L values for both ISO and NFW best fit models but lower central densities for ISO halos and higher concentration for NFW halos than when using H$alpha$ RCs only. The agreement with the mass model parameters deduced using hybrid RCs, considered as a reference, is better for HI than for H$alpha$ RCs. ISO density profiles better fit the RCs than the NFW ones, especially when using H$alpha$ or hybrid RCs. Halo masses at the optical radius determined using the various datasets are compatible even if they tend to be overestimated with H$alpha$ RCs. Hybrid RCs are thus ideal to study the mass distribution within the optical radius.
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We present Rc-band surface photometry for 170 of the 203 galaxies in GHASP, Gassendi H-Alpha survey of SPirals, a sample of late-type galaxies for which high-resolution Fabry-Perot H{alpha} maps have previously been obtained. Our data set is constructed by new Rc-band observations taken at the Observatoire de Haute-Provence (OHP), supplemented with Sloan Digital Sky Survey (SDSS) archival data, obtained with the purpose of deriving homogeneous photometric profiles and parameters. Our results include Rc-band surface brightness profiles for 170 galaxies and $ugriz$ profiles for 108 of these objects. We catalogue several parameters of general interest for further reference, such as total magnitude, effective radius and isophotal parameters -- magnitude, position angle, ellipticity and inclination. We also perform a structural decomposition of the surface brightness profiles using a multi-component method in order to separate disks from bulges and bars, and to observe the main scaling relations involving luminosities, sizes and maximum velocities. We determine the Rc-band Tully Fisher relation using maximum velocities derived solely from H$alpha$ rotation curves for a sample of 80 galaxies, resulting in a slope of $-8.1 pm 0.5$, zero point of $-3.0 pm 1.0$ and an estimated intrinsic scatter of $0.28 pm 0.07$. We note that, different from the TF-relation in the near-infrared derived for the same sample, no change in the slope of the relation is seen at the low-mass end (for galaxies with $V_{max} < 125$ km/s). We suggest that this different behaviour of the Tully Fisher relation (with the optical relation being described by a single power-law while the near-infrared by two) may be caused by differences in the stellar mass to light ratio for galaxies with $V_{max} < 125$ km/s.
We perform a deep wide-field imaging survey of nearby galaxies using H$alpha$ and broadband filters to investigate the characteristics of star formation in galaxies. Motivated by the finding that star formation rates (SFRs) derived from H$alpha$ fluxes in dwarf galaxies are systematically lower than those inferred from far-ultraviolet (FUV) fluxes, we attempt to determine whether the same trend exists in the extended disks of two star-forming galaxies. We perform spatially resolved photometry using grid-shaped apertures to measure the FUV and H$alpha$ fluxes of star-forming regions. We also perform spectral energy distribution (SED) fittings using 11 photometric data (FUV-to-MIR) including data from the literature to estimate the local properties such as internal attenuation of individual star-forming clumps. Comparing SFR$_mathrm{FUV}$ and SFR$_mathrm{Halpha}$, which are converted from the H$alpha$ and FUV fluxes corrected for the local properties, we find that SFR$_mathrm{Halpha}$/SFR$_mathrm{FUV}$ tends to decrease as the SFR decreases. We evaluate possible causes of this discrepancy between the two SFRs by restricting parameters in the SED fitting and conclude that deficient H$alpha$ fluxes in the extended disks of galaxies are tightly correlated with recent starbursts. The strong and short starburst which is being rapidly suppressed over the last 10 Myr seems to induce a significant discrepancy between the SFR$_mathrm{Halpha}$ and SFR$_mathrm{FUV}$. In addition, the recent bursts in the extended disks of galaxies appear to have occurred azimuth-symmetrically, implying that these were likely triggered by gas accretion or internal processes rather than external perturbation.
We compare vertical profiles of the extraplanar H$alpha$ emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the diffuse extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar H$alpha$ emission. A strong correlation between the scale heights of the extraplanar H$alpha$ and UV emissions is also found; the scale height at H$alpha$ is found to be $sim0.74$ of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in the galactic halos. The existence of eDust in galaxies where the extraplanar H$alpha$ emission is detected suggests that a larger portion of the extraplanar H$alpha$ emission than that predicted in previous studies may be caused by H$alpha$ photons that originate from H II regions in the galactic plane and are subsequently scattered by the eDust. This possibility raise a in studying the eDIG. We also find that the scale heights of the extraplanar emissions normalized to the galaxy size correlate well with the star formation rate surface density of the galaxies. The properties of eDust in our galaxies is on a continuation line of that found through previous observations of the extraplanar polycyclic aromatic hydrocarbons emission in more active galaxies known to have galactic winds.
Using a sample of dwarf irregular galaxies selected from the ALFALFA blind HI-survey and observed using the VIMOS IFU, we investigate the relationship between H$alpha$ emission and Balmer optical depth ($tau_{text{b}}$). We find a positive correlation between H$alpha$ luminosity surface density and Balmer optical depth in 8 of 11 at $geq$ 0.8$sigma$ significance (6 of 11 at $geq$ 1.0$sigma$) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearmans rank correlation coefficient to test for correlation between $Sigma_{text{H}alpha}$ and $tau_{text{b}}$ in all the galaxies combined, we find $rho = 0.39$, indicating a positive correlation at 4$sigma$ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between H$alpha$ luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.
We present high-resolution rotation curves of a sample of 26 low surface brightness galaxies. From these curves we derive mass distributions using a variety of assumptions for the stellar mass-to-light ratio. We show that the predictions of current Cold Dark Matter models for the density profiles of dark matter halos are inconsistent with the observed curves. The latter indicate a core-dominated structure, rather than the theoretically preferred cuspy structure.
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