Nuage moléculaire

Résumé

En astronomie, les nuages moléculaires sont des nébuleuses interstellaires qui ont une densité et une taille suffisante pour permettre la formation d'hydrogène moléculaire, H2. Cependant, il est difficile de le détecter et le moyen le plus employée pour tracer les molécules de H2 est l'utilisation du monoxyde de carbone CO. En effet, le rapport entre la luminosité du CO et la masse de H2 est presque constant. Cependant, l'utilisation du CO comme traceur de H2 par ailleurs invisible, pose encore de nombreuses questions fondamentales, notamment, comment lier l'évolution d'un nuage moléculaire à l'évolution d'une galaxie dans son ensemble. Voie lactée Dans la Voie lactée, les nuages moléculaires représentent approximativement la moitié de toute la masse de gaz dans la région dans l'orbite du Soleil, faisant d'eux un composant significatif du disque galactique. Les catalogues des nuages montrent que la majeure partie de la masse moléculaire est concentrée dans l'objet le plus

Source officielle

https://fr.wikipedia.org/wiki/Nuage_mol%C3%A9culaire

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Molecular gas in distant brightest cluster galaxies

Gianluca Castignani

The mechanisms governing the stellar mass assembly and star formation history of brightest cluster galaxies (BCGs) are still being debated. By means of new and archival molecular gas observations we investigate the role of dense megaparsec-scale environments in regulating the fueling of star formation in distant BCGs, through cosmic time. We observed in CO with the IRAM 30 m telescope two star-forming BCGs belonging to SpARCS clusters, namely, 3C 244.1 (z=0.4) and SDSS J161112.65+550823.5 (z=0.9), and compared their molecular gas and star formation properties with those of a compilation of similar to 100 distant cluster galaxies from the literature, including nine additional distant BCGs at z similar to 0.4-3.5. We set robust upper limits of M-H2< 1.0x10(10) M-circle dot and < 2.8x10(10) M-circle dot to their molecular gas content, respectively, and to the ratio of molecular gas to stellar mass M(H-2)/M-star less than or similar to 0.2 and depletion time tau(dep)less than or similar to 40 Myr of the two targeted BCGs. They are thus among the distant cluster galaxies with the lowest gas fractions and shortest depletion times. The majority (64%+/- 15% and 73%+/- 18%) of the 11 BCGs with observations in CO have lower M(H-2)/M-star values and tau(dep), respectively, than those estimated for main sequence galaxies. Statistical analysis also tentatively suggests that the values of M(H-2)/M-star and tau(dep) for the 11 BCGs deviates, with a significance of similar to 2 sigma, from those of the comparison sample of cluster galaxies. A morphological analysis for a subsample of seven BCGs with archival HST observations reveals that 71%+/- 17% of the BCGs are compact or show star-forming components or substructures. Our results suggest a scenario where distant star-forming BCGs assemble a significant fraction similar to 16% of their stellar mass on the relatively short timescale similar to tau(dep), while environmental mechanisms might prevent the replenishment of gas feeding the star formation. We speculate that compact components also favor the rapid exhaustion of molecular gas and ultimately help to quench the BCGs. Distant star-forming BCGs are excellent targets for ALMA and for next-generation telescopes such as the James Webb Space Telescope.

2020

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Molecular gas in radio galaxies in dense megaparsec-scale environments at z=0.4-2.6

Gianluca Castignani

Context. Low luminosity radio galaxies (LLRGs) typically reside in dense megaparsec-scale environments and are often associated with brightest cluster galaxies (BCGs). They are an excellent tool to study the evolution of molecular gas reservoirs in giant ellipticals, even close to the active galactic nucleus. Aims. We investigate the role of dense megaparsec-scale environment in processing molecular gas in LLRGs in the cores of galaxy (proto-)clusters. To this aim we selected within the COSMOS and DES surveys a sample of five LLRGs at z = 0.4-2.6 that show evidence of ongoing star formation on the basis of their far-infrared (FIR) emission. Methods. We assembled and modeled the FIR-to-UV spectral energy distributions (SEDs) of the five radio sources to characterize their host galaxies in terms of stellar mass and star formation rate. We observed the LLRGs with the IRAM-30m telescope to search for CO emission. We then searched for dense megaparsec-scale overdensities associated with the LLRGs using photometric redshifts of galaxies and the Poisson Probability Method, which we have upgraded using an approach based on the wavelet-transform (wPPM), to ultimately characterize the overdensity in the projected space and estimate the radio galaxy miscentering. Color-color and colormagnitude plots were then derived for the fiducial cluster members, selected using photometric redshifts. Results. Our IRAM-30m observations yielded upper limits to the CO emission of the LLRGs, at z = 0 : 39, 0.61, 0.91, 0.97, and 2.6. For the most distant radio source, COSMOS-FRI 70 at z = 2 : 6, a hint of CO(7 -> 6) emission is found at 2.2 sigma. The upper limits found for the molecular gas content M(H-2) = M-star< 0 : 11, 0.09, 1.8, 1.5, and 0.29, respectively, and depletion time tau(dep) less than or similar to (0.2-7) Gyr of the five LLRGs are overall consistent with the corresponding values of main sequence field galaxies. Our SED modeling implies large stellar-mass estimates in the range log(M-star/M-Theta) = 10.9-11.5, typical for giant ellipticals. Both our wPPM analysis and the cross-matching of the LLRGs with existing cluster/group catalogs suggest that the megaparsec-scale overdensities around our LLRGs are rich (less than or similar to 10(14) M-Theta) groups and show a complex morphology. The color-color and color-magnitude plots suggest that the LLRGs are consistent with being star forming and on the high-luminosity tail of the red sequence. The present study thus increases the still limited statistics of distant cluster core galaxies with CO observations. Conclusions. The radio galaxies of this work are excellent targets for ALMA as well as next-generation telescopes such as the James Webb Space Telescope.

EDP SCIENCES S A2019

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Cancer is the second leading cause of death worldwide. Cancer develops through multiple hallmark functions including apoptosis evasion, unlimited replicative potential, metastasis, and immune avoidance. Over the past few decades, researchers have reported a substantial amount of information about the role of gene expression dysregulation in cancer, whereas transposable elements (TEs) have been overlooked despite the fact they constitute nearly half of the human genome. TEs are DNA repetitive sequences that spread across the genome of living organisms throughout the evolution of species, contributing to genomic diversity and shaping the epigenomic landscape. The vast majority of TEs appear to be transcriptionally silent in adult tissues, thus avoiding deleterious mutational insertions and recombination events in somatic tissues. Due to the global epigenetic dysregulation that occurs during tumorigenesis, some TEs lose repressive marks and become transcriptionally active in cancer cells. Consequently, TE insertions into oncogenes and tumor suppressor genes may occur, thereby contributing to cancer development and disease progression. It is also widely accepted that some TEs harbor transcription factor recognition sites and have regulatory functions on gene expression. Some transcriptionally active TEs can give rise to alternative TE-derived chimeric gene products. Given these facts, integrative transcriptome analysis of TEs and genes may contribute to a better understanding of complex traits of cancer and help to better classify cancer subtypes with clinical implications for patients.To gain insights into the underlying mechanisms of cancer pathogenesis, we constructed a co-expression network based on the similarity in expression levels of TEs and genes. We focused on colorectal cancer (CRC), a heterogeneous disease with different genetic and molecular backgrounds, contributing to patient outcomes and response to therapy. We investigated the coordinated activity of TEs and genes in view of recurrent CRC chromosomal aberrations, genome organization, and functional significance. We further examined co-expression changes in network structure under the contrasting conditions of cancerous versus matched healthy colic mucosal tissues. We found that the cancer network was associated with a dramatic decrease in the number of gene interactions as opposed to an increase in TE interactions. Physical chromosomal distance affects the degree of co-expression, where the proximal distance effect of TE is contrasted with the distant effect of the gene. Our study sheds light on the complex interplay between TEs and genes and how they coordinately shape cancer and normal co-expression networks. Furthermore, we integrated gene and TE expression to develop a new consensus molecular subtype (CMS) classifier derived from multiple layers of TE and gene signatures. We demonstrated that our new approach led to better identification of CRC patients of the former CMS3 subtype, the most heterogeneous subtype with mixed biological characteristics, and a global reduction of the expected misclassification of other CMS subtypes. We further optimized our classifier for potential clinical use and obtained a set of 50 genes and 20 TE integrants with the best ability to identify CMS subtypes. Our integrative model could be a major add on for the development of future clinical trials by improving patient stratification over current gene-restricted molecular classifications.

EPFL2022

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EPFL2022

Molecular gas in radio galaxies in dense megaparsec-scale environments at z=0.4-2.6

Gianluca Castignani

EDP SCIENCES S A2019

Molecular gas in distant brightest cluster galaxies

Gianluca Castignani

2020