El gas molecular en las galaxias luminosas y ultraluminosas en el infrarrojo

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 13-03-0

A Detection of Sgr A* in the far infrared

We report the first detection of the Galactic Centre massive black hole, Sgr~A*, in the far infrared. Our measurements were obtained with PACS on board the \emph{Herschel} satellite at $100~\mathrm{\mu m}$ and $160~\mathrm{\mu m}$. While the warm dust in the Galactic Centre is too bright to allow for a direct detection of Sgr~A*, we measure a significant and simultaneous variation of its flux of $\Delta F_{\nu\widehat{=}160 ~\mathrm{\mu m}} = (0.27\pm0.06)~\mathrm{Jy}$ and $\Delta F_{\nu\widehat{=}100 ~\mathrm{\mu m}}= (0.16\pm0.10)~\mathrm{Jy}$ during one observation. The significance level of the $160 ~\mathrm{\mu m}$ band variability is $4.5\sigma$ and the corresponding $100 ~\mathrm{\mu m}$ band variability is significant at $1.6\sigma$. We find no example of an equally significant false positive detection. Conservatively assuming a variability of $25\%$ in the FIR, we can provide upper limits to the flux. Comparing the latter with theoretical models we find that 1D RIAF models have difficulties explaining the observed faintness. However, the upper limits are consistent with modern ALMA and VLA observations. Our upper limits provide further evidence for a spectral peak at $\sim 10^{12} ~ \mathrm{Hz}$ and constrain the number density of $\gamma \sim 100$ electrons in the accretion disk and or outflow.Comment: accepted for publication in AP

The impact of interactions, bars, bulges, and AGN on star formation efficiency in local massive galaxies

Using observations from the GASS and COLD GASS surveys and complementary data from SDSS and GALEX, we investigate the nature of variations in gas depletion time observed across the local massive galaxy population. The large and unbiased COLD GASS sample allows us to assess the relative importance of galaxy interactions, bar instabilities, morphologies and the presence of AGN in regulating star formation efficiency. Both the H2 mass fraction and depletion time vary as a function of the distance of a galaxy from the main sequence in the SFR-M* plane. The longest gas depletion times are found in below-main sequence bulge-dominated galaxies that are either gas-poor, or else on average less efficient than disk-dominated galaxy at converting into stars any cold gas they may have. We find no link between AGN and these long depletion times. The galaxies undergoing mergers or showing signs of morphological disruptions have the shortest molecular gas depletion times, while those hosting strong stellar bars have only marginally higher global star formation efficiencies as compared to matched control samples. Our interpretation is that depletion time variations are caused by changes in the ratio between the gas mass traced by the CO(1-0) observations, and the gas mass in high density star-forming cores, with interactions, mergers and bar instabilities able to locally increase pressure and raise the ratio of efficiently star-forming gas to CO-detected gas. Building a sample representative of the local massive galaxy population, we derive a global Kennicutt-Schmidt relation of slope 1.18+/-0.24, and observe structure within the scatter around this relation, with galaxies having low (high) stellar mass surface densities lying systematically above (below) the mean relation, suggesting that gas surface density is not the only parameter driving the global star formation ability of a galaxy.Comment: 19 pages, 12 figures, accepted for publication in Ap

COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies: II. The non-universality of the Molecular Gas Depletion Timescale

We study the relation between molecular gas and star formation in a volume-limited sample of 222 galaxies from the COLD GASS survey, with measurements of the CO(1-0) line from the IRAM 30m telescope. The galaxies are at redshifts 0.025<z<0.05 and have stellar masses in the range 10.0<log(M*/Msun)<11.5. The IRAM measurements are complemented by deep Arecibo HI observations and homogeneous SDSS and GALEX photometry. A reference sample that includes both UV and far-IR data is used to calibrate our estimates of star formation rates from the seven optical/UV bands. The mean molecular gas depletion timescale, tdep(H2), for all the galaxies in our sample is 1 Gyr, however tdep(H2) increases by a factor of 6 from a value of ~0.5 Gyr for galaxies with stellar masses of 10^10 Msun to ~3 Gyr for galaxies with masses of a few times 10^11 Msun. In contrast, the atomic gas depletion timescale remains contant at a value of around 3 Gyr. This implies that in high mass galaxies, molecular and atomic gas depletion timescales are comparable, but in low mass galaxies, molecular gas is being consumed much more quickly than atomic gas. The strongest dependences of tdep(H2) are on the stellar mass of the galaxy (parameterized as log tdep(H2)= (0.36+/-0.07)(log M* - 10.70)+(9.03+/-0.99)), and on the specific star formation rate. A single tdep(H2) versus sSFR relation is able to fit both "normal" star-forming galaxies in our COLD GASS sample, as well as more extreme starburst galaxies (LIRGs and ULIRGs), which have tdep(H2) < 10^8 yr. Normal galaxies at z=1-2 are displaced with respect to the local galaxy population in the tdep(H2) versus sSFR plane and have molecular gas depletion times that are a factor of 3-5 times longer at a given value of sSFR due to their significantly larger gas fractions.Comment: Accepted for publication in MNRAS. 19 pages, 11 figure

COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties

We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30m telescope, we measure the CO(1-0) line in a sample of ~350 nearby (D=100-200 Mpc), massive galaxies (log(M*/Msun)>10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with SDSS photometry and spectroscopy, GALEX imaging and high-quality Arecibo HI data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. The overall CO detection rate is 54%, but our survey also uncovers the existence of sharp thresholds in galaxy structural parameters such as stellar mass surface density and concentration index, below which all galaxies have a measurable cold gas component but above which the detection rate of the CO line drops suddenly. The mean molecular gas fraction MH2/M* of the CO detections is 0.066+/-0.039, and this fraction does not depend on stellar mass, but is a strong function of NUV-r colour. Through stacking, we set a firm upper limit of MH2/M*=0.0016+/-0.0005 for red galaxies with NUV-r>5.0. The average molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with significant scatter from one galaxy to the next. The existence of strong detection thresholds in both the HI and CO lines suggests that "quenching" processes have occurred in these systems. Intriguingly, atomic gas strongly dominates in the minority of galaxies with significant cold gas that lie above these thresholds. This suggests that some re-accretion of gas may still be possible following the quenching event.Comment: Accepted for publications in MNRAS. 32 pages, 25 figure

Euclid SGS MER Processing Function Requirements Specification Document

Version 0.9 reviewed by ESA at the Euclid SGS System Requirements Review (2015) Version 0.97 provided as reference document for the ESA Euclid SGS Design Review (2017) Version 1.0 provided as reference document for the ESA Euclid SGS Implementation Review (2021)The MER Processing Function realises the merging of all the level 2 information and provides source catalogues containing object information relevant in the Euclid project. It starts from level 2 data provided by related OUs (VIS/NIR/EXT stacks or single epoch images, related PSF models and ancillary information); an object detection is performed in VIS and NIR, and the detected objects are combined. A multi-wavelength flux determination is performed on detected objects with suitable photometric techniques. The final output of the MER processing function is a catalogue of sources with unique identification number and multi-wavelength photometric information; the MER PF will also provide the required input (object identification number, position, fluxes, galactic extinction, effective wavelength of EXT passbands at objects’ positions) for photometric redshifts computation and spectra extraction. The Euclid SGS requirements specification produces the Euclid SGS Requirements Specification Document and a set of Requirements Specification Documents for specific SGS products such as the Processing Functions. The present document is part of this set. To ensure completeness and consistency with applicable documents, traceability and verification matrices complement the SGS Requirements Specification Documents

Euclid SGS MER Software Design Document

Version 1.0 reviewed by ESA at the Euclid SGS Design Review (2017) Version 1.3 provided as reference document for the ESA Euclid SGS Implementation Review (2021) and Readiness Review (2022)This Software Design Document aims at the describing design methodology and architectural overview of the MER Processing Function (PF). The document presents the system overview and where MER PF is in the Euclid Science Ground Segment, the high-level architectural overview of the PF as whole and the design of each element of the PF. It also includes the traceability matrix from software component to the requirements. This document covers the functional architecture of MER PF. It addresses a general overview of scientific issues, explains what the software does and how, but it does not explain how to operate it