How Large Are the Bars in Barred Galaxies?

I present a study of the sizes (semimajor axes) of bars in disc galaxies, combining a detailed study of 65 S0-Sb galaxies with measurements of 70 Sb-Sd galaxies from Martin (1995). As has been noted before with smaller samples, bars in early-type (S0-Sb) galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies; this is true both for relative sizes (bar length as fraction of isophotal radius R_25 or exponential disc scale length h) and absolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~3.3 kpc), ~0.2-0.8 R_25 (mean \~0.38 R_25) and ~0.5-2.5 h (mean ~1.4 h). Late-type bars extend to only \~0.5-3.5 kpc, 0.05-0.35 R_25 and 0.2-1.5 h; mean sizes are ~1.5 kpc, 0.14 R_25 and 0.6 h. Sb galaxies resemble earlier-type galaxies in terms of bar size relative to h; their smaller R_25-relative sizes may be a side effect of higher star formation, which increases R_25 but not h. For S0-Sbc galaxies, bar size correlates well with disc size (both R_25 and h); these correlations are stronger than the known correlation with M_B. All correlations appear to be weaker or absent for late-type galaxies; in particular, there seems to be no correlation between bar size and either h or M_B for Sc-Sd galaxies. I show that the bars detected in HST near-IR images at z ~ 1 by Sheth et al. (2003) have absolute sizes consistent with those in bright, nearby S0-Sb galaxies. I also compare the sizes of real bars with those produced in simulations, and discuss some possible implications for scenarios of secular evolution along the Hubble sequence. Simulations often produce bars as large as -- or larger than -- those seen in S0-Sb galaxies, but rarely any as small as those in Sc-Sd galaxies. (Abridged.)Comment: LaTeX, 22 pages, 15 EPS figures. To appear in Monthly Notices of the Royal Astronomical Societ

Saving the Higgs Portal for Singlet Scalar Dark Matter

The Higgs-portal model with a singlet scalar Dark Matter particle is one of the simplest extensions to the Standard Model that can reproduce the relic density. Unfortunately this model is strongly constrained by direct and indirect DM detection, as well as by collider physics. Most of the parameter space is already ruled-out and the rest will be explored in the next future. We show that a simple extension of the DM sector with a second scalar singlet enables a substantial opening of the allowed window in the parameter space.Comment: 5 pages, 4 figures, proceedings of the EPS-HEP 2017, EPS-HEP, 5-12 July 2017, Venice, Italy. Based on arXiv:1701.0813

Galaxy clusters and microwave background anisotropy

Previous estimates of the microwave background anisotropies produced by freely falling spherical clusters are discussed. These estimates are based on the Swiss-Cheese and Tolman-Bondi models. It is proved that these models give only upper limits to the anisotropies produced by the observed galaxy clusters. By using spherically symmetric codes including pressureless matter and a hot baryonic gas, new upper limits are obtained. The contributions of the hot gas and the pressureless component to the total anisotropy are compared. The effects produced by the pressure are proved to be negligible; hence, estimations of the cluster anisotropies based on N-body simulations are hereafter justified. After the phenomenon of violent relaxation, any realistic rich cluster can only produce small anisotropies with amplitudes of order $10^{-7}$. During the rapid process of violent relaxation, the anisotropies produced by nonlinear clusters are expected to range in the interval $(10^{-6},10^{-5})$. The angular scales of these anisotropies are discussed.Comment: 31 pages, 3 postscript figures, accepted MNRA

Cosmological shock waves: clues to the formation history of haloes

Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $\Lambda$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes harbouring them. The shocks in the simulation can be split into two broad classes: internal weak shocks related with evolutionary events within haloes, and external strong shocks associated with large-scale events. The shock distribution function contains information on the abundances and strength of the different shocks, and it can be fitted by a double power law with a break in the slope around a Mach number of 20. We introduce a generalised scaling relation that correlates the average Mach numbers within the virial radius of haloes and their virial masses. In this plane, haloes occupy different areas according to their early evolutionary histories: those with a quiet evolution have an almost constant Mach number independently of their masses, whereas haloes undergoing significant merger events very early in their evolution show a linear dependence with their masses. At high redshift, the halo distribution in this scaling relation forms a L-like pattern that changes due to the evolution of the haloes. The analysis of the propagation speed and size of the shock waves around haloes could give some hints on the formation time and main features of the haloes. (Abridged)Comment: 14 pages, 9 figures, accepted for publication in MNRA

Combining benchmarking and chain-linking for short-term regional forecasting

In this paper we propose a methodology to estimate and forecast the GDP of the different regions of a country, providing quarterly profiles paper offers a new instrument for short degree of synchronicity among regional business cycles. Technically, we combine time series models with benchma quarterly indicators and to estimate quarterly regional GDPs ensuring their temporal and transversal consistency with the National Accounts data. The methodology addresses the issue of non-additivity taking into account linked volume indexes used by the National Accounts and provides an efficient combination of structural as well as short-term information. The methodology is illustrated by an application to the quarterly GDP estimates and forecasts at the regional level (i.e., with a minimum compilation delay with respect to the national quarterly GDP)Forecasting, Spanish economy, Regional analysis, Benchmarking, Chain-linking

Gas stripping in galaxy groups - the case of the starburst spiral NGC 2276

Ram pressure stripping of galactic gas is generally assumed to be inefficient in galaxy groups due to the relatively low density of the intragroup medium and the small velocity dispersions of groups. To test this assumption, we obtained Chandra X-ray data of the starbursting spiral NGC 2276 in the NGC 2300 group of galaxies, a candidate for a strong galaxy interaction with hot intragroup gas. The data reveal a shock-like feature along the western edge of the galaxy and a low-surface-brightness tail extending to the east, similar to the morphology seen in other wavebands. Spatially resolved spectroscopy shows that the data are consistent with intragroup gas being pressurized at the leading western edge of NGC 2276 due to the galaxy moving supersonically through the intragroup medium at a velocity ~850 km/s. Detailed modelling of the gravitational potential of NGC 2276 shows that the resulting ram-pressure could significantly affect the morphology of the outer gas disc but is probably insufficient to strip large amounts of cold gas from the disc. We estimate the mass loss rates due to turbulent viscous stripping and starburst outflows being swept back by ram pressure, showing that both mechanisms could plausibly explain the presence of the X-ray tail. Comparison to existing HI measurements shows that most of the gas escaping the galaxy is in a hot phase. With a total mass loss rate of roughly 5 M_Sun/yr, the galaxy could be losing its entire present HI supply within a Gyr. This demonstrates that the removal of galactic gas through interactions with a hot intragroup medium can occur rapidly enough to transform the morphology of galaxies in groups. Implications of this for galaxy evolution in groups and clusters are briefly discussed.Comment: 16 pages, 8 figures, accepted for publication in MNRA