A lensing view on the Fundamental Plane

For lensing galaxies, we introduce a formal velocity dispersion σlens, based on enclosed mass and the virial theorem. This is calculated from an ensemble of pixelated lens models, and found to be fairly model-independent. A sample of 18 well-known early-type lensing galaxies and two clusters is found to be consistent with σlens=σobs. Both the early-type lensing galaxies and the clusters can thus be determined as being virialized. In a second step, we calculate the I-band luminosity and the total mass content for the sample of lensing galaxies, which enables us to analyse the mass-to-light relation L∝Mα. We determine α= 0.70 ± 0.08, excluding constant M/L and consistent with previous studies of the Fundamental Plane. Additionally, we verify that this relation does not extrapolate to clusters, which have a much higher M/L. The sample used for this analysis comprises nine lensing galaxies from the Sloan Lens ACS (Advanced Camera for Surveys) Survey and another nine from the CfA-Arizona Space Telescope LEns Survey as well as the lensing clusters ACO 1689 and ACO 266

Diagnostics of baryonic cooling in lensing galaxies

Theoretical studies of structure formation find an inverse proportionality between the concentration of dark matter haloes and virial mass. This trend has been recently confirmed for Mvir≳ 6 × 1012 M⊙ by the observation of the X-ray emission from the hot halo gas. We present an alternative approach to this problem, exploring the concentration of dark matter haloes over galaxy scales on a sample of 18 early-type systems. Our c -Mvir relation is consistent with the X-ray analysis, extending towards lower virial masses, covering the range from 4 × 1011 up to 5 × 1012 M⊙. A combination of the lensing analysis along with photometric data allows us to constrain the baryon fraction within a few effective radii, which is compared with prescriptions for adiabatic contraction (AC) of the dark matter haloes. We find that the standard methods for AC are strongly disfavoured, requiring additional mechanisms - such as mass loss during the contraction process - to play a role during the phases following the collapse of the haloe

Oscillatory regulation of Hes1: discrete stochastic delay modelling and simulation

Discrete stochastic simulations are a powerful tool for understanding the dynamics of chemical kinetics when there are small-to-moderate numbers of certain molecular species. In this paper we introduce delays into the stochastic simulation algorithm, thus mimicking delays associated with transcription and translation. We then show that this process may well explain more faithfully than continuous deterministic models the observed sustained oscillations in expression levels of hes1 mRNA and Hes1 protein

Strong Gravitational Lensing and the Stellar IMF of Early-type Galaxies

Systematic variations of the IMF in early-type galaxies, and their connection with possible drivers such as velocity dispersion or metallicity, have been much debated in recent years. Strong lensing over galaxy scales combined with photometric and spectroscopic data provides a powerful method to constrain the stellar mass-to-light ratio and hence the functional form of the IMF. We combine photometric and spectroscopic constraints from the latest set of population synthesis models of Charlot & Bruzual, including a varying IMF, with a non-parametric analysis of the lens masses of 18 ETGs from the SLACS survey, with velocity dispersions in the range 200-300 km/s. We find that very bottom-heavy IMFs are excluded. However, the upper limit to the bimodal IMF slope ($\mu \lesssim 2.2$, accounting for a dark matter fraction of 20-30%, where $\mu=1.3$ corresponds to a Kroupa-like IMF) is compatible at the $1\sigma$ level with constraints imposed by gravity-sensitive line strengths. A two-segment power law parameterisation of the IMF (Salpeter-like for high masses) is more constrained ($\Gamma \lesssim 1.5$, where $\Gamma$ is the power index at low masses) but requires a dark matter contribution of $\gtrsim 25\%$ to reconcile the results with a Salpeter IMF. For a standard Milky Way-like IMF to be applicable, a significant dark matter contribution is required within $1R_e$. Our results reveal a large range of allowed IMF slopes, which, when interpreted as intrinsic scatter in the IMF properties of ETGs, could explain the recent results of Smith et al., who find Milky Way-like IMF normalisations in a few massive lensing ETGs.Comment: Accepted for publication in MNRAS, 18 pages, 12 figures, 4 table

Constraining the low-mass end of the Initial Mass Function with Gravitational Lensing

The low-mass end of the stellar Initial Mass Function (IMF) is constrained by focusing on the baryon-dominated central regions of strong lensing galaxies. We study in this letter the Einstein Cross (Q2237+0305), a z=0.04 barred galaxy whose bulge acts as lens on a background quasar. The positions of the four quasar images constrain the surface mass density on the lens plane, whereas the surface brightness (H-band NICMOS/HST imaging) along with deep spectroscopy of the lens (VLT/FORS1) allow us to constrain the stellar mass content, for a range of IMFs. We find that a classical single power law (Salpeter IMF) predicts more stellar mass than the observed lensing estimates. This result is confirmed at the 99% confidence level, and is robust to systematic effects due to the choice of population synthesis models, the presence of dust, or the complex disk/bulge population mix. Our non-parametric methodology is more robust than kinematic estimates, as we do not need to make any assumptions about the dynamical state of the galaxy or its decomposition into bulge and disk. Over a range of low-mass power law slopes (with Salpeter being Gamma=+1.35) we find that at a 90% confidence level, slopes with Gamma>0 are ruled out.Comment: 5 pages, 6 figures. Accepted for publication in MNRAS Letter

Systematic variation of central mass density slope in early-type galaxies

We study the total density distribution in the central regions ($<\, 1$ effective radius, $R_{\rm e}$) of early-type galaxies (ETGs), using data from the SPIDER survey. We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter (DM) halo profile, and leaving stellar mass-to-light ($M_{\rm \star}/L$) ratios as free fitting parameters to the data. For a Navarro et al. (1996) profile, the slope of the total mass profile is non-universal. For the most massive and largest ETGs, the profile is isothermal in the central regions ($\sim R_{\rm e}/2$), while for the low-mass and smallest systems, the profile is steeper than isothermal, with slopes similar to those for a constant-M/L profile. For a concentration-mass relation steeper than that expected from simulations, the correlation of density slope with mass tends to flatten. Our results clearly point to a "non-homology" in the total mass distribution of ETGs, which simulations of galaxy formation suggest may be related to a varying role of dissipation with galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on 25th-28th november 2014, to be published on Astrophysics and Space Science Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic

Light versus dark in strong-lens galaxies: Dark matter haloes that are rounder than their stars

We measure the projected density profile, shape and alignment of the stellar and dark matter mass distribution in 11 strong-lens galaxies. We find that the projected dark matter density profile - under the assumption of a Chabrier stellar initial mass function - shows significant variation from galaxy to galaxy. Those with an outermost image beyond $\sim 10$ kpc are very well fit by a projected NFW profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. We find that over several half-light radii, the dark matter haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than $e_{dm} = 0.2$, their stars can extend to $e_* > 0.2$. Galaxies with high dark matter ellipticity and weak external shear show strong alignment between light and dark; those with strong shear ($\gamma \gtrsim 0.1$) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. Our results provide a new constraint on galaxy formation models. For a given cosmology, these must explain the origin of both very round dark matter haloes and misaligned strong-lens systems.Comment: 16 pages, 7 figures, 4 tables. Accepted for publication by MNRA

Galaxy Mass, Metallicity, Radius and Star Formation Rates

Working with 108,786 Sloan Digital Sky Survey low redshift galaxies we have examined the relation between galaxy mass, metallicity, radius, and star formation rates primarily in the central portions of galaxies. We subdivided the redshift range covered in our sample, 0.07<z<0.3, into three narrower redshift bins, and three sets of radial size. We show that for 72% of the galaxies the observed gas metallicities, Zx, are consistent with (i) a quantitative physical relation for star formation through episodic infall of gas of metallicity Zi = 0.125x10^-3 +/- 1.25x10^-3; (ii) thorough mixing of infalling and native gas before onset of star formation; (iii) a star formation rate (SFR) proportional to the 3/2 power of the infalling mass rate, Mi; and (iv) intermittent quiescent phases devoid of star formation during which the native gas in a galaxy exhibits a characteristic elevated gas metallicity, Z0, dependent on galaxy mass, M*, and a characteristic ratio of stellar mass to native mass of gas, Mg. Most if not all our star-forming galaxies with M* < 2.0x10^10 Msun, and many with M* > 2.0x10^10 Msun and large radii appear fed by infall. Smaller massive galaxies with high Zx and high star formation rates show more complex behavior. A mean-field-theory toy model for the physics of infall accounts for the (SFR) \propto Mi^(3/2) relation and permits us to estimate the mean densities and velocities of clumps of baryonic matter traversing the dark matter halos in which the SDSS galaxies may be embedded.Comment: 34 pages plus bibliography and supplementary figures, 3 main figures, 131 supplementary online figures, ascii data tables availabl

Sarcopenia and Aging: Skeletal Muscle Fiber Type Composition of the Long-Lived Ames Dwarf Mouse Compared to Its Wild-Type Counterpart

Skeletal muscle fiber type composition has not been studied in the long-lived Ames dwarf mouse when compared to its wild-type counterpart. Hindlimb soleus skeletal muscle from two 3-month old dwarf and two 3-month old wild-type mice was analyzed for muscle fiber size, proportion of type I (slow-twitch) and type II (fast-twitch) muscle fibers, myonuclei content per muscle fiber, and total cross sectional area of the muscle. Results revealed a significant difference in muscle fiber size (t(58)=-9.71,