Ministerio de Ciencia, Innovación y Universidades Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

Astrophysics Research Projects

The Local Universe

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Kinematic, Structural and Composition Studies of the Interstellar and Intergalactic Media (P/308603)

JOHN E BECKMAN

Alejandro Serrano Borlaff, Joan Font Serra, Fatemeh Tabatabaei
IAC Collaborators: Emilio Casuso Romate
, Johan H. Knapen, Begoña García Lorenzo, Martín López Corredoira

L. Gutiérrez Albores, M. Rosado, A. Rodriguez, P. Velazquez, A. Camps, (UNAM, México); J. Zaragoza (INAOE, México) P. Erwin, D. Willman (MPIE, Alemania); M. Querejeta, G. van de Ven (MPIA, Heidelberg, Alemania); P. Amram, B. Epinat (Obs. Marsella, Francia); S. Comerón, S. Díaz (Univ. Oulu, Finlandia)

Introduction

The basic objective of the project is to investigate the evolution of galaxies by deepening our understanding of the interaction between the interstellar medium and the stars. The main technique which we use is the two-dimensional kinematic study of whole galaxies observed using our instrument: GHaFaS, a Fabry-Perot interferometer on the William Herschel Telescope of the ORM.

We combine the data from GHaFaS with our own photometric imaging using ACAM on the same telescope, with a variety of sources of images in the infrared and ultraviolet, and with emission line maps in the radio and millimetre range to explore the effects, and the physical parameters which the determine the star formation rate and the mass function of the stars depending on the sites of their formation in galaxies.

In the present phase of the project the dynamical aspects which we are exploring are basically two: the resonant structure of discs and bars, and the effects of the zones of massive star formation on their surroundings via stellar winds and supernovae. In addition, in preparation for the exploration of galaxy formation in earlier epochs, we are studying how the interactions between galaxies stimulate and condition star formation within them before they merge. In the future these studies will be extended, methodically, in two directions: outwards to galaxies at increasing redshift, and inwards by applying our methods to the study of interstellar processes in the zones of massive star formation in the Local Group galaxy M33.

We combine our research into galaxy kinematics with evolutionary aspects of galaxy discs based on precise observations of their surface brightness profiles, both in local galaxies and in galaxies at intermediate redshift. In order to make progress in this direction we are collaborating with colleagues at the Instituto de Astronomía de la UNAM (México) and the Laboratoire d'Astrophysique de Marseille (France) in the implementation of a new instrument, NEFER, which will be a high resolution Fabry-Perot module incorporated into OSIRIS on the GTC. We had successful initial trials in December 2017, and will "commission" NEFER during 2018 for use as a visitor instrument permanently on the GTC.

Milestones

1. The proof that the bars in galaxies are braked during their evolution (Font et al. ApJ 835, 279, 2017). The importance of this is that in a series of previous papers their authors had reached the opposite conclusion: that bars rotate too quickly to have been braked. The implication had been that the predicted braking effect of dark matter halos had not taken place. This threw doubt on the standard model of galaxy formation with the framework of the cosmological model in which "cold dark matter" is the major constituent (apart from dark energy). Our new measurements of the angular velocity of the bars and the coronation radius of the system of density waves in which the bar is situated, taken together with the results of simulations, all of this presented in the article, show that bars have indeed been slowed down, and are a firm support of the standard model.

2. Using HST images and those from the SHARDS project on the GTC we have shown that the discs of lenticular (S0) galaxies with antitruncations (where the exponential fall-off in the surface brightness of the outer disc is more gradual than that of the inner disc) show scaling relations which have remained unchanged between z ~0.6 and z = 0. This result shows that the evolution of this type of galaxies has been passive (without significant star formation) during the past 4 Gyr. (Borlaff et al. A&A, 604, 119).

3. Using the two dimensional spectrograph with high spatial and spectral resolution GHaFaS on the 4.2m WHT profiles of Halpha emission were analysed from across the face of Tycho's supernova remnant (SN 1572), finding emission lines with multiple components in all parts of the nebula. The narrow line component is at least twice as broad as the width expected from matter in equilibrium and there is also an extensive component of intermediate width. Taken together they are evidence for non-collisional shocks, which offer a viable acceleration mechanism for cosmic ray protons observed in the TeV energy range (Knezevic et al. ApJ 846, 167, 2017).

4. Evidence that the magnetic field can limit the star formation rate around the nuclei of galaxies (Tabatabaei et al. Nature Astronomy, accepted for publication, astro-ph 1710.05696). It was shown that in the circumnuclear zone of the galaxy NGC 1097 the star formation efficiency of the giant molecular clouds falls with increasing magnetic field. It was possible to rule out the effects of turbulence and thermal pressure, leaving the magnetic field as the key parameter in the process. The result points to a feedback mechanism which moderates star formation rates in general around galactic nuclei.

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