Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies (original) (raw)
Related papers
The Central Mass Distribution in Dwarf and Low Surface Brightness Galaxies
Astrophysical Journal, 2002
From these, we derive limits on the slopes of the central mass distributions. Assuming the density distributions of dark matter halos follow a power-law at small radii, rho(r)~r^(-alpha), we find inner slopes in the range 0<alpha<1 for most galaxies. In general, halos with constant density cores (\alpha=0) provide somewhat better fits, but the majority of our galaxies (~75%) are also consistent with alpha=1, provided that the R-band mass-to-light ratios are smaller than about 2. Halos with alpha=1.5, however, are ruled out in virtually every case. To investigate the robustness of these results we discuss and model several possible causes of systematic errors including non-circular motions, slit width, seeing, and slit alignment errors. Taking the associated uncertainties into account, we conclude that even for the 25% of the cases where alpha=1 seems inconsistent with the rotation curves, we cannot rule out cusp slopes this steep. Inclusion of literature samples similar to the one presented here leads to the same conclusion when possible systematic errors are taken into account. In the ongoing debate on whether the rotation curves of dwarf and LSB galaxies are consistent with predictions for a CDM universe, we argue that our sample and the literature samples discussed in this paper provide insufficient evidence to rule out halos with alpha=1. At the same time, we note that none of the galaxies in these samples require halos with steep cusps, as most are equally well or better explained by constant density cores. (abridged)
Monthly Notices of The Royal Astronomical Society, 2010
We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of <ρDM> ~ R-2eff provides the first clear indication of cuspy DM haloes in these galaxies - akin to standard Λ cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo profile for dwarf and late-type galaxies. We introduce a new fundamental constraint on galaxy formation by finding that the central DM fraction decreases with stellar age. This result is only partially explained by the size-age dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore, we suggest that there may be a connection between age and halo contraction and that galaxies forming earlier had stronger baryonic feedback, which expanded their haloes, or lumpier baryonic accretion, which avoided halo contraction. An alternative explanation is a lighter initial mass function for older stellar populations.
Density profile slopes of dwarf galaxies and their environment
Mon Notic Roy Astron Soc, 2012
In this paper, we study how the dark matter density profiles of dwarf galaxies in the mass range 108-1010 M⊙ are modified by the interaction of the dwarf galaxy with neighbouring structures, and by the changing baryon fraction in dwarf galaxies. With this aim, and referring to an earlier paper by Del Popolo, we determine the density profiles of the dwarf galaxies, taking into account the effect of tidal interaction with neighbouring structures, the effects of ordered and random angular momentum, dynamical friction, the response of dark matter haloes to the condensation of baryons and the effects produced by the presence of baryons. As already shown in the earlier paper, the slope of the density profile of inner haloes flattens with decreasing halo mass, and the profile is well approximated by a Burkert profile. We thus treat the angular momentum generated by tidal torques and the baryon fraction as a parameter in order to understand how the latter influences the density profiles. The analysis shows that dwarf galaxies that have suffered a smaller tidal torque (and consequently have smaller angular momentum) are characterized by steeper profiles with respect to dwarf galaxies subject to higher torque. Similarly, dwarf galaxies that have a smaller baryon fraction also have steeper profiles than those that have a larger baryon fraction. When tidal torquing is shut down and baryons are not present, the density profile is very well approximated by an Einasto profile, similarly to dwarf galaxies obtained in dissipationless N-body simulations. Then, we apply the result of the previous analysis to the dark matter halo rotation curves of three different dwarfs: NGC 2976, which is known to have a flat inner core; NGC 5949, which has a profile intermediate between a cored and a cuspy one; and NGC 5963, which has a cuspy profile. After calculating the baryon fraction, which is ≃0.1 for the three galaxies, we fitted the rotation curves, changing the value of the angular momentum. NGC 2976 has a higher value of ordered angular momentum (λ≃ 0.04) than NGC 5949 (λ≃ 0.025). For NGC 5963, a very steep profile can be obtained with a low value of λ (λ≃ 0.02) and also by decreasing the value of the random angular momentum. For NGC 2976, the tidal interaction with M81 could also have influenced the inner part of the density profile. Finally, we show how the inner density profile correlates with the tidal index for dwarf and low surface brightness galaxies given by Karachentsev et al.
Monthly Notices of The Royal Astronomical Society, 2010
We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of 〈ρDM〉∝R−2eff provides the first clear indication of cuspy DM haloes in these galaxies – akin to standard Λ cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo profile for dwarf and late-type galaxies.We introduce a new fundamental constraint on galaxy formation by finding that the central DM fraction decreases with stellar age. This result is only partially explained by the size–age dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore, we suggest that there may be a connection between age and halo contraction and that galaxies forming earlier had stronger baryonic feedback, which expanded their haloes, or lumpier baryonic accretion, which avoided halo contraction. An alternative explanation is a lighter initial mass function for older stellar populations.
According to the now strongly supported concordance cold dark matter model, galaxies may be grossly described as a luminous component embedded in a dark matter halo. The density profile of these mass-dominating haloes may be determined by N-body simulations which mimic the evolution of the tiny initial density perturbations during the process leading to the structures we observe today. Unfortunately, when the effect of baryons is taken into account, the situation gets much more complicated due to the difficulties in simulating their physics. As a consequence, a definitive prediction of how dark matter haloes should presently look is still missing. We revisit here this issue from an observational point of view devoting our attention to dwarf galaxies. Being likely dark matter dominated, these systems are ideal candidates to investigate the present-day halo density profiles and check whether dark matter related quantities correlate with stellar ones or the environment. By fitting a large sample of well-measured rotation curves, we infer constraints on both halo structural parameters (such as the logarithmic slope of the density profile and its concentration) and derived quantities (e.g. the mass fraction and the Newtonian acceleration) which could then be used to constrain galaxy formation scenarios. Moreover, we investigate whether the halo properties correlate with the environment the galaxy lives in, thus offering a new tool to deepen our understanding of galaxy formation.
Astronomy & Astrophysics, 2021
We derive the stellar-to-halo mass relation (SHMR), namely f⋆ ∝ M⋆/Mh versus M⋆ and Mh, for early-type galaxies from their near-infrared luminosities (for M⋆) and the position-velocity distributions of their globular cluster systems (for Mh). Our individual estimates of Mh are based on fitting a flexible dynamical model with a distribution function expressed in terms of action-angle variables and imposing a prior on Mh from the correlation between halo concentration and mass in the standard Λ cold dark matter (ΛCDM) cosmology. We find that the SHMR for early-type galaxies declines with mass beyond a peak at M⋆ ∼ 5 × 1010 M⊙ and Mh ∼ 1 × 1012 M⊙ (near the mass of the Milky Way). This result is consistent with the standard SHMR derived by abundance matching for the general population of galaxies, and also with previous, less robust derivations of the SHMR for early-type galaxies. However, it contrasts sharply with the monotonically rising SHMR for late-type galaxies derived from exten...