16 research outputs found
El gas molecular en las galaxias luminosas y ultraluminosas en el infrarrojo
Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de FÃsica 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 and .
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 and during one observation. The significance level of
the band variability is and the corresponding
band variability is significant at . We find
no example of an equally significant false positive detection. Conservatively
assuming a variability of 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 and
constrain the number density of 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
XCOLD GASS:The Complete IRAM 30 m Legacy Survey of Molecular Gas for Galaxy Evolution Studies
We introduce xCOLD GASS, a legacy survey providing a census of molecular gas in the local universe. Building on the original COLD GASS survey, we present here the full sample of 532 galaxies with CO (1-0) measurements from the IRAM 30 m telescope. The sample is mass-selected in the redshift interval 0.01 < z < 0.05 from the Sloan Digital Sky Survey (SDSS) and therefore representative of the local galaxy population with M∗ > 109 M⊙. The CO (1-0) flux measurements are complemented by observations of the CO (2-1) line with both the IRAM 30 m and APEX telescopes, H I observations from Arecibo, and photometry from SDSS, WISE, and GALEX. Combining the IRAM and APEX data, we find that the ratio of CO (2-1) to CO (1-0) luminosity for integrated measurements is r21 = 0.79 ± 0.03, with no systematic variations across the sample. The CO (1-0) luminosity function is constructed and best fit with a Schechter function with parameters LCO ∗ = (7.77 ± 2.11) × 109 K km s-1 pc2, φ∗ = (9.84 ± 5.41) × 10-4 Mpc-3, and α = -1.19 ± 0.05.With the sample now complete down to stellar masses of 109M⊙, we are able to extend our study of gas scaling relations and confirm that both molecular gas fractions ( fH2) and depletion timescale (tdep (H2)) vary with specific star formation rate (or offset from the star formation main sequence) much more strongly than they depend on stellar mass. Comparing the xCOLD GASS results with outputs from hydrodynamic and semianalytic models, we highlight the constraining power of cold gas scaling relations on models of galaxy formation.</p
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