Pseudo-isothermal Profile Research Articles

Modelling dark matter halo spin using observations and simulations: application to UGC 5288

ABSTRACT Dark matter (DM) halo properties are extensively studied in cosmological simulations but are very challenging to estimate from observations. The DM halo density profile of observed galaxies is modelled using multiple probes that trace the DM potential. However, the angular momentum distribution of DM halos is still a subject of debate. In this study, we investigate a method for estimating the halo spin and halo concentration of low surface brightness (LSB), gas-rich dwarf barred galaxy UGC 5288, by forward modelling disc properties derived from observations – stellar and gas surface densities, disc scalelength, H i rotation curve, bar length, and bar ellipticity. We combine semi-analytical techniques, N-body/SPH, and cosmological simulations to model the DM halo of UGC 5288 with both a cuspy Hernquist profile and a flat-core pseudo-isothermal profile. We find that the best match with observations is a pseudo-isothermal halo model with a core radius of rc = 0.23 kpc and halo spin of λ = 0.08 at the virial radius. Although our findings are consistent with previous core radius estimates of the halo density profile of UGC 5288, as well as with the halo spin profiles of similar mass analogues of UGC 5288 in the high-resolution cosmological-magneto-hydrodynamical simulation TNG50, there still remain some uncertainties as we are limited in our knowledge of the formation history of the galaxy. Additionally, we find that the inner halo spin (r < 10 kpc) in barred galaxies is different from the unbarred ones, and the halo spin shows weak correlations with bar properties.

A comprehensive analysis using 9 dark matter halo models on the spiral galaxy NGC 4321

This paper addressed the dark matter analysis on the spiral galaxy NGC 4321 (M100) by considering the nine different dark matter profiles, so far lacking in the scientific literature, i.e., pseudoisothermal, Burkert, NFW, Moore, Einasto, core-modified, DC14, coreNFW and Lucky13 profiles. In this paper, we analyzed the rotation curve analysis on the galaxy NGC 4321 by using nonlinear fitting of star, gaseous and dark matter halo equations with selected VLA HI observation data. Among the nine dark matter profiles, four dark matter profiles (DC14, Lucky13, Burkert and Moore profiles) showed declining features and hence not suitable for this galaxy. This is concluded to be mainly due to the characteristics of those dark matter profiles and also the varying levels of problems within the inner region fittings. For the remaining five accepted dark matter profiles, we further conducted the analysis by using reduced Chi-square test. Four out of the five accepted dark matter profiles lie within the range of 0.40 < \(\chi _{\mathrm{red}}^2\) < 1.70, except for the core-modified profile. In addition, pseudoisothermal profile achieved the best fitting with \(\chi _{\mathrm{red}}^2\) nearest to 1, mainly due to its linearity in the inner region and flatness at large radii.

Effect comparison of dark matter annihilation pressure to NFW and pseudo-isothermal profiles of low surface brightness galaxies

We have studied the effect of gas pressure created by electrons and positrons produced from dark matter annihilation for low surface brightness (LSB) galaxies. We have applied 4 different gas and stellar disk models and 2 different dark matter density profiles, i.e. Navarro Frenk and White (NFW) and pseudo-isothermal, to each galaxy. We assume that electrons and positrons are produced from dark matter annihilation and they can lose their energy to photons and the interstellar medium in the galaxies by different loss processes. The pressure of electron and positron gas is a function of the electron-positron spectrum obtained from a diffusion-loss equation which included source term, diffusion coefficient and loss rate. We have added the pressure gradient to the rotation curves of LSB galaxies. We have compared the results with observations by using reduced chi-square. We have found that the pressure from dark matter annihilation provided better fits for several galaxies for NFW profiles but it doesn’t play any role for pseudo-isothermal profiles. From these results, we can use NFW profile with pressure from dark matter annihilation to improve the situation of cusp-core problems and to constrain properties of dark matter particles by rotation curves of LSB galaxies for future studies.

Baryon-Interacting Dark Matter: heating dark matter and the emergence of galaxy scaling relations

The empirical scaling relations observed in disk galaxies remain challenging for models of galaxy formation. The most striking among these is the Mass Discrepancy-Acceleration Relation (MDAR), which encodes both a tight baryonic Tully-Fisher relation (BTFR) and the observed diversity of galaxy rotation curves through the central surface density relation (CSDR) . Building on our earlier work [1], we propose here that the MDAR is the result of interactions between baryons and `Baryon-Interacting Dark Matter' (BIDM), which heat up the dark matter. Following a bottom-up, hydrodynamical approach, we find that the MDAR follows if: i) the BIDM equation of state approximates that of an ideal gas; ii) the BIDM relaxation time is order the Jeans time; iii) the heating rate is inversely proportional to the BIDM density. Remarkably, under these assumptions the set of hydrodynamical equations together with Poisson's equation enjoy an anisotropic scaling symmetry. In the BIDM-dominated regime, this gives rise to an enhanced symmetry which fully captures the low-acceleration limit of the MDAR . We then show that, assuming a cored pseudo-isothermal profile at equilibrium, this set of equations gives rise to parameters reproducing the MDAR . Specifically, in the flat part of the rotation curve the asymptotic rotational velocity matches the parametric dependence of the BTFR . Moreover, in the central region of high-surface brightness galaxies, the profile reproduces the CSDR . Finally, by studying the time-dependent approach to equilibrium, we derive a global combination of the BTFR and CSDR, which matches the expectations in low surface-brightness galaxies. The form of the heating rate also makes model-independent predictions for various cosmological observables. We argue that our scenario satisfies existing observational constraints, and, intriguingly, offers a possible explanation to the EDGES anomaly.

The dark matter profiles in the Milky Way

Abstract We investigate the dark matter profile of the Milky Way using the observed rotation curve data out to 100 kpc. The baryonic matter of the Milky Way is divided into bulge, disc, and gas components, and each component is modelled using various possible mass profiles available in literature. The arbitrary combination of seven bulge profiles, four disc profiles, and two gas profiles results in 56 baryon models. These baryon models are combined with one of the four dark matter profiles: Burkert profile, core-modified profile, pseudo-isothermal profile, and NFW profile, to fit the observed rotation curve data. Results show that in general the NFW profile fits the data better than the Burkert profile, while the core-modified profile and the pseudo-isothermal profile are essentially ruled out. The best-fitting NFW model has the scale length r0 = 8.1 ± 0.7 kpc, and the corresponding local density of dark matter is ρdm(R = R⊙) = 0.51 ± 0.09 GeV cm−3.

NEAR-INFRARED EMISSION SPECTRUM OF WASP-103B USING HUBBLE SPACE TELESCOPE/WIDE FIELD CAMERA 3*

ABSTRACT We present here our observations and analysis of the dayside emission spectrum of the hot Jupiter WASP-103b. We observed WASP-103b during secondary eclipse using two visits of the Hubble Space Telescope with the G141 grism on Wide Field Camera 3 in spatial scan mode. We generated secondary eclipse light curves of the planet in both blended white-light and spectrally binned wavechannels from and corrected the light curves for flux contamination from a nearby companion star. We modeled the detector systematics and secondary eclipse spectrum using Gaussian process regression and found that the near-IR emission spectrum of WASP-103b is featureless across the observed near-IR region to down to a sensitivity of 175 ppm, and shows a shallow slope toward the red. The atmosphere has a single brightness temperature of K across this wavelength range. This region of the spectrum is indistinguishable from isothermal, but may not manifest from a physically isothermal system, i.e., pseudo-isothermal. A solar-metallicity profile with a thermal inversion layer at 10−2 bar fits the spectrum of WASP-103b with high confidence, as do an isothermal profile with solar metallicity and a monotonically decreasing atmosphere with C/O &gt; 1. The data rule out a monotonically decreasing atmospheric profile with solar composition, and we rule out a low-metallicity decreasing profile as unphysical for this system. The pseudo-isothermal profile could be explained by a thermal inversion layer just above the layer probed by our observations, or by clouds or haze in the upper atmosphere. Transmission spectra at optical wavelengths would allow us to better distinguish between potential atmospheric models.

Cusp-core transformations in dwarf galaxies: observational predictions

The presence of a dark matter core in the central kiloparsec of many dwarf galaxies has been a long standing problem in galaxy formation theories based on the standard cold dark matter paradigm. Recent cosmological simulations, based on Smooth Particle Hydrodynamics and rather strong feedback recipes have shown that it was indeed possible to form extended dark matter cores using baryonic processes related to a more realistic treatment of the interstellar medium. Using adaptive mesh refinement, together with a new, stronger supernovae feedback scheme that we have recently implemented in the RAMSES code, we show that it is also possible to form a prominent dark matter core within the well-controlled framework of an isolated, initially cuspy, 10 billion solar masses dark matter halo. Although our numerical experiment is idealized, it allows a clean and unambiguous identification of the dark matter core formation process. Our dark matter inner profile is well fitted by a pseudo-isothermal profile with a core radius of 800 pc. The core formation mechanism is consistent with the one proposed recently by Pontzen & Governato. We highlight two key observational predictions of all simulations that find cusp-core transformations: (i) a bursty star formation history with peak to trough ratio of 5 to 10 and a duty cycle comparable to the local dynamical time; and (ii) a stellar distribution that is hot with v/sigma=1. We compare the observational properties of our model galaxy with recent measurements of the isolated dwarf WLM. We show that the spatial and kinematical distribution of stars and HI gas are in striking agreement with observations, supporting the fundamental role played by stellar feedback in shaping both the stellar and dark matter distribution.

Flat central density profile and constant dark matter surface density in galaxies from scalar field dark matter

The scalar field dark matter (SFDM) model proposes that galaxies form by condensation of a scalar field (SF) very early in the universe forming Bose-Einstein Condensates (BEC) drops, i.e., in this model haloes of galaxies are gigantic drops of SF. Here big structures form like in the LCDM model, by hierarchy, thus all the predictions of the LCDM model at big scales are reproduced by SFDM. This model predicts that all galaxies must be very similar and exist for bigger redshifts than in the LCDM model. In this work we show that BEC dark matter haloes fit high-resolution rotation curves of a sample of thirteen low surface brightness galaxies. We compare our fits to those obtained using a Navarro-Frenk-White and Pseudo-Isothermal (PI) profiles and found a better agreement with the SFDM and PI profiles. The mean value of the logarithmic inner density slopes is -0.27 +/- 0.18. As a second result we find a natural way to define the core radius with the advantage of being model-independent. Using this new definition in the BEC density profile we find that the recent observation of the constant dark matter central surface density can be reproduced. We conclude that in light of the difficulties that the standard model is currently facing the SFDM model can be a worthy alternative to keep exploring further.

THE INTERACTING GALAXY PAIR KPG 390: H{alpha} KINEMATICS

In this work, we present scanning Fabry-Perot (FP) H{alpha} observations of the isolated interacting galaxy pair NGC 5278/79 obtained with the PUMA FP interferometer. We derived velocity fields and rotation curves for both galaxies. For NGC 5278 we also obtained the residual velocity map to investigate the non-circular motions, and estimated its mass by fitting the rotation curve with disk+halo components. We test three different types of halos (pseudo-isothermal, Hernquist, and Navarro-Frenk-White) and obtain satisfactory fits to the rotation curve for all profiles. The amount of dark matter required by the pseudo-isothermal profile is about 10 times smaller than that for the other two halo distributions. Finally, our kinematical results together with the analysis of dust lane distribution and of surface brightness profiles along the minor axis allowed us to determine univocally that both components of the interacting pair are trailing spirals.

THE INTERACTING GALAXY PAIR KPG 390: Hα KINEMATICS

In this work we present scanning Fabry-Perot H$\alpha$ observations of the isolated interacting galaxy pair NGC 5278/79 obtained with the PUMA Fabry-Perot interferometer. We derived velocity fields and rotation curves for both galaxies. For NGC 5278 we also obtained the residual velocity map to investigate the non-circular motions, and estimated its mass by fitting the rotation curve with a disk+halo components. We test three different types of halo (pseudo-isothermal, Hernquist and Navarro Frenk White) and obtain satisfactory fits to the rotation curve for all profiles. The amount of dark matter required by pseudo-isothermal profile is about ten times smaller than, that for the other two halo distributions. Finally, our kinematical results together with the analysis of dust lanes distribution and of surface brightness profiles along the minor axis allowed us to determine univocally that both components of the interacting pair are trailing spirals.

Dark halo properties from rotation curves

We study a large set of high spatial resolution optical rotation curves of galaxies with the goal of determining the model parameters for a disc embedded within a cold dark matter (CDM) halo, which we model with either a Navarro-Frenk-White (NFW) profile or pseudo-isothermal profile. We show that parameter degeneracies present in lower resolution data are lifted at these higher resolutions. 34 per cent of the galaxies do not have a meaningful fit when using the NFW profile and 32 per cent when using the pseudo-isothermal profile, however only 14 per cent do not have a meaningful fit in either model. In both models we find correlations between the disc baryon fraction f d and the spin parameter of the halo λ', between f d and the dark halo mass M 2 0 0 , and between M 2 0 0 and the concentration parameter c. We show that the distribution of the concentration parameter c, for a NFW halo, is in good agreement with CDM predictions; no significant galaxy population is found with very low values of c. The overall distribution of λ' is in good agreement with theoretical predictions from hierarchical tidal torque theory. The whole sample is also well fitted by a pseudo-isothermal dark halo with a core, but the size of the core is rather small (6 per cent of the virial radius or smaller; for 70 per cent of the sample the core size is less than 2 kpc). Thus we conclude that the profile of dark matter is steep (r - 1 or steeper) down to this radius; large dark matter cores (and therefore very low dark matter central densities) seem to be excluded. Low-surface-brightness galaxies tend to have higher values of λ' for a given f d and lower values of c for a given mass than high-surface-brightness galaxies. In an appendix we give some useful formulae for pseudo-isothermal profile haloes and we discuss in detail the issue of parameter degeneracies.