Outer and inner mass distributions of the irregular galaxies UGC 4284 and UGC 11861: constraining the baryonic content through stellar population synthesis studies

Abstract

In this article we investigate the outer and inner mass distributions of the irregular galaxies UGC 4284 and UGC 11861, taking advantage of published HI and Hα high resolution rotation curves and constraining the stellar disk of both galaxies throughout stellar population synthesis studies. In addition we take into account the gas content of both galaxies deriving the HI+He rotation curve. The deduced baryonic rotation curves (star+gas) are inadequate to account for the total mass of UGC 4284 and UGC 11861, for that reason we examine the possibility of dark matter to explain the incongruity between the observed HI and Hα rotation curves of UGC 4284 and UGC 11861 and the derived baryonic rotation curves. We consider NFW, Burkert, DiCintio, Einasto, and the Stadel dark matter halos, to analyse the dark matter content of UGC 4284 and UGC 11861. The principal results of this work are that cored dark matter models better reproduce the dark matter Hα and HI rotation curves of UGC 11861 and the dark matter HI rotation curve of UGC 4284, while, the Hα rotation curve of UGC 4284 is better reproduced by a cuspy DiCintio DM model. In general, cored exponential two-parameters models Einasto and Stadel, give better fits than Burkert. This trend, as well as to confirm past results, presents for the first time a comparison between two different exponential dark matter models, Einasto and Stadel, in an attempt to better constrain the range of possible exponential dark matter models applied to real galaxies.

Tensorial solution of the Poisson equation and the dark matter amount and distribution of UGC 8490 and UGC 9753

“…We have to clarify that the values of the EIN form parameters, determined through our fitting analysis, are in total agreement with the outcomes of the Cold DM N-body numerical simulations of Navarro et al (2004), and Dutton & Macciò (2014) (DM14), given that, the EIN density profile, that those authors employ has the reciprocal shape index with respect to our profile, as also observed by Chemin et al (2011) (CH11). The STD λ index is also concordant with the prescription of STD, given that in the velocity formula derived in Repetto et al (2015), the STD index appear as the reciprocal of the STD index λ. We found different values of the indexes parameters of EIN and STD, for the Hα and HI RCs of UGC 8490 and UGC 9753, and a possible interpretation could be that the two distinct tracers denote different parts of the same gravitational potential, as partially confirmed by the fact that the resulting Hα and HI DM masses and scale radii delineate a dissimilar DM mass density distribution among the Hα and HI gaseous tracers.…”

“…the prescription of STD, given that in the velocity formula derived in Repetto et al (2015), the STD index appear as the reciprocal of the STD index λ. We found different values of the indexes parameters of EIN and STD, for the Hα and HI RCs of UGC 8490 and UGC 9753, and a possible interpretation could be that the two distinct tracers denote different parts of the same gravitational potential, as partially confirmed by the fact that the resulting Hα and HI DM masses and scale radii delineate a dissimilar DM mass density distribution among the Hα and HI gaseous tracers.…”

Comparing rotation curve observations to hydrodynamic ΛCDM simulations of galaxies

“…This profile has already been used to model rotation curves for several galaxies (Karukes et al 2015;Repetto et al 2015) but not with a large sample. It can potentially solve the TBTF problem in the Local Group (Brook & Di Cintio 2015a) and explain the Tully-Fisher relation (Brook & Di Cintio 2015b).…”

General circular velocity relation of a test particle in a 3D gravitational potential: application to the rotation curves analysis and total mass determination of UGC 8490 and UGC 9753

“…Martínez-García et al (2017) (MG17) have recently ideated an alternative method to that of ZB09 to avoid the production of spurious filamentary mass portions in the resultant mass maps of ZB09, and also to mitigate the creation of other possible mass artefacts originated by the apparent superposition of dust lanes and spiral arms in the sample of analysed galaxies. Some authors, that determined the mass distribution of galaxies through the analysis of the observed RCs, employed the SPS strategy to derive the mass and circular velocity curve of the stellar discs considered, the results obtained are diverse and dependent on the specific assumptions of the particular approach they adopted, but in general concordant with the first prescription described above Oh et al 2008;Kuzio de Naray et al 2008;Salucci et al 2008;de Denus-Baillargeon et al 2013) and also (Repetto et al 2015(Repetto et al , 2017 (the latter paper RP17).…”

“…The DM RCs fitting procedure is similar to the one applied in Repetto et al (2015) and RP17, the principal difference in this work is represented by the introduction of the prolate and oblate circular velocity fit. We employ the minuit fitting routine through the ROOT package (Brun & Rademakers 1997) to adjust the spherical, prolate and oblate circular velocity relations to the DM RCs of UGC 8490 and UGC 9753.…”