Prof. Dimitra Rigopoulou

Abstract:

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an Hi-selected sample of 155 galaxies spanning all morphological types with distances less than 25Mpc. We describe the scientific goals of the survey, the sample selection and the observing strategy. We also present an atlas and analysis of the CO J=3 - 2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift, which have also been observed in the CO J=3 - 2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the LFIR/LCO(3-2) ratio with the atomic-to-molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Abstract:

The Herschel Multi-tiered Extragalactic Survey (HerMES) is a legacy programme designed to map a set of nested fields totalling ~380deg2. Fields range in size from 0.01 to ~20deg2, using the Herschel-Spectral and Photometric Imaging Receiver (SPIRE) (at 250, 350 and 500μm) and the Herschel-Photodetector Array Camera and Spectrometer (PACS) (at 100 and 160μm), with an additional wider component of 270deg2 with SPIRE alone. These bands cover the peak of the redshifted thermal spectral energy distribution from interstellar dust and thus capture the reprocessed optical and ultraviolet radiation from star formation that has been absorbed by dust, and are critical for forming a complete multiwavelength understanding of galaxy formation and evolution. The survey will detect of the order of 100000 galaxies at 5σ in some of the best-studied fields in the sky. Additionally, HerMES is closely coordinated with the PACS Evolutionary Probe survey. Making maximum use of the full spectrum of ancillary data, from radio to X-ray wavelengths, it is designed to facilitate redshift determination, rapidly identify unusual objects and understand the relationships between thermal emission from dust and other processes. Scientific questions HerMES will be used to answer include the total infrared emission of galaxies, the evolution of the luminosity function, the clustering properties of dusty galaxies and the properties of populations of galaxies which lie below the confusion limit through lensing and statistical techniques. This paper defines the survey observations and data products, outlines the primary scientific goals of the HerMES team, and reviews some of the early results. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Abstract:

We use Spitzer spectroscopic and imaging observations to study the co-evolution of black hole (BH) growth and star formation (SF) activity in a complete volume-limited sample of local Luminous Infrared Galaxies (LIRGs). Using a mid-infrared (mid-IR) spectral decomposition method we identify active galactic nuclei (AGN) with Seyfert-like luminosities and relatively small bolometric contributions (median ∼ 5%) in half of the LIRG nuclei. Combining mid-IR and AGN optical detections we obtain a 62% AGN detection rate in local LIRGs. We combine gas velocity dispersions of spectrally resolved [Ne iii]15.56 µm and [O iii]λ5007Å lines and literature stellar velocity dispersions , and we obtain typical BH masses of 3 ×107 M☉ for local LIRGs. We find that the ratios of nuclear and integrated SF rates (SFR) to BH accretion rates are higher in local LIRGs than in optically selected Seyferts. We interpret our results in a scenario where local LIRGs with an AGN represent an early phase of the (possibly episodic) growth of BHs in massive spiral galaxies with high SFR, not necessarily associated with a major merger event.