The instantaneous radial growth rate of stellar discs

We present a new and simple method to measure the instantaneous mass and radial growth rates of the stellar discs of spiral galaxies, based on their star formation rate surface density (SFRD) profiles. Under the hypothesis that discs are exponential with time-varying scalelengths, we derive a universal theoretical profile for the SFRD, with a linear dependence on two parameters: the specific mass growth rate $\nu_\textrm{M} \equiv \dot{M_\star}/M_\star$ and the specific radial growth rate $\nu_\textrm{R} \equiv \dot{R}_\star/R_\star$ of the disc. We test our theory on a sample of 35 nearby spiral galaxies, for which we derive a measurement of $\nu_\textrm{M}$ and $\nu_\textrm{R}$. 32/35 galaxies show the signature of ongoing inside-out growth ($\nu_\textrm{R} > 0$). The typical derived e-folding timescales for mass and radial growth in our sample are ~ 10 Gyr and ~ 30 Gyr, respectively, with some systematic uncertainties. More massive discs have a larger scatter in $\nu_\textrm{M}$ and $\nu_\textrm{R}$, biased towards a slower growth, both in mass and size. We find a linear relation between the two growth rates, indicating that our galaxy discs grow in size at ~ 0.35 times the rate at which they grow in mass; this ratio is largely unaffected by systematics. Our results are in very good agreement with theoretical expectations if known scaling relations of disc galaxies are not evolving with time.Comment: MNRAS, accepted. 14 pages, 4 figures, 3 tables. Additional material (Atlas.pdf) available at http://www.filippofraternali.com/downloads/index.htm

The Holographic Life of the eta'

In the string holographic dual of large-N_c QCD with N_f flavours of Kruczenski et al, the eta' meson is massless at infinite N_c and dual to a collective fluctuation of N_f D6-brane probes in a supergravity background. Here we identify the string diagrams responsible for the generation of a mass of order N_f/N_c, consistent with the Witten-Veneziano formula, and show that the supregravity limit of these diagrams corresponds to mixings with pseudoscalar glueballs. We argue that the dependence on the theta-angle in the supergravity description occurs only through the combination theta + 2 \sqrt{N_f} eta' / f_pi, as dictated by the U(1) anomaly. We provide a quantitative test by computing the linear term in the eta' potential in two independent ways, with perfect agreement.Comment: 1+26 pages, 8 figures; V4: Appendix added, version published in JHE

Cuestión de honor. Los periodistas se baten en duelo.

Sin resume

The Spitzer Survey of Stellar Structure in Galaxies (S^4G): Stellar Masses, Sizes, and Radial Profiles for 2352 nearby Galaxies

The Spitzer Survey of Stellar Structure in Galaxies is a volume, magnitude, and size-limited survey of 2352 nearby galaxies with deep imaging at 3.6 and 4.5 μm. In this paper, we describe our surface photometry pipeline and showcase the associated data products that we have released to the community. We also identify the physical mechanisms leading to different levels of central stellar mass concentration for galaxies with the same total stellar mass. Finally, we derive the local stellar mass–size relation at 3.6 μm for galaxies of different morphologies. Our radial profiles reach stellar mass surface densities below ~1 M⊙ pc^(-2). Given the negligible impact of dust and the almost constant mass-to-light ratio at these wavelengths, these profiles constitute an accurate inventory of the radial distribution of stellar mass in nearby galaxies. From these profiles we have also derived global properties such as asymptotic magnitudes (and the corresponding stellar masses), isophotal sizes and shapes, and concentration indices. These and other data products from our various pipelines (science-ready mosaics, object masks, 2D image decompositions, and stellar mass maps) can be publicly accessed at IRSA (http://irsa.ipac.caltech.edu/data/SPITZER/S4G/)

Holographic Complex Conformal Field Theories

The loss of criticality in the form of weak first-order transitions or the end of the conformal window in gauge theories can be described as the merging of two fixed points that move to complex values of the couplings. When the complex fixed points are close to the real axis, the system typically exhibits walking behavior with Miransky (or Berezinsky-Kosterlitz-Thouless) scaling. We present a novel realization of these phenomena at strong coupling by means of the gauge/gravity duality, and give evidence for the conjectured existence of complex conformal field theories at the fixed points

Optimization of CRISPR-Cas systems in ectothermal organisms

CRISPR-Cas systems have been traditionally optimized for gene editing in different types of models, such as in mammalian cell lines. However, their implementation in animal models requires additional work. In addition, another impediment is the number of genomic targets of CRISPR-Cas systems since it is limited due to PAM (Protospacer adjacent motif) sequence restriction. PAM sequence is a short DNA sequence, characteristic of each CRISPR-Cas system, near to the target DNA region and required for each Cas nuclease to recognize the target and cut it. Therefore, the possibility of having different CRISPR-Cas systems with different PAM sequences allows us to have a greater number of targets in the genome, which would simplify and increase our possibilities of carrying out a gene editing anywhere in the genome and in a more precise manner.In the laboratory we are interested in implementing new CRISPR-Cas systems in vivo such as CRISPR-Cas12b and a Type I CRISPR-Cas, using zebrafish embryos as a model in animals. First, we are optimizing CRISPR-Cas12b system that has been recently characterized in cell culture (1,2) and allows gene editing in genome locations rich in AT regions where other endonucleases already characterized such as Cas12a or Cas9 cannot target. Optimizing this system in zebrafish embryos will increase the number of genomic targets that can be used in vivo. Second, type I CRISPR-Cas system is formed by Cas3 and a ribonucleoprotein complex (RNP) called Cascade. This system has been able to trigger long-range deletions (3) but its activity in vivo has not been shown yet. Therefore in this project we are implementing type I CRISPR-Cas tool in vivo to facilitate the elimination of large regions in the genome with potential role during embryogenesis.To evaluate the activity of both CRISPR-Cas systems, we are generating different expression vectors by cloning, to subsequently obtain the mRNA of the protein. On the other hand, we are designing specific guide RNAs (gRNAs) for these systems whose targets are genes involved in the pigmentation of zebrafish that facilitates the analysis of these CRISPR-Cas systems. We are currently co-injecting mRNAs and gRNAs of each system in the zebrafish embryos and evaluating the in vivo activity of each system. All together, we will optimize novel CRISPR-Cas systems that will be used for precise gene editing in vivo