P. Gratier

Université de Bordeaux

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Maryvonne Gérin

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

J. Pety

Centre National de la Recherche Scientifique

Viviana V. Guzmán

Pontificia Universidad Católica de Chile

J. R. Goicoechea

Consejo Superior de Investigaciones Científicas

E. Roueff

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

C. Krämer

Institut de Radioastronomie Millimétrique

J. Braine

Laboratoire d'Astrophysique de Bordeaux

Valentine Wakelam

Laboratoire d'Astrophysique de Bordeaux

P. van der Werf

Leiden University

Franck Le Petit

Sorbonne Université

Cooperative Institutions

Centre National de la Recherche Scientifique

191

Max Planck Society

Sorbonne Université

Université de Bordeaux

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

Laboratoire d'Astrophysique de Bordeaux

Observatoire de Paris

Université Paris Sciences et Lettres

Max Planck Institute for Radio Astronomy

Max Planck Institute for Astronomy

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

The molecular gas mass of M 33

Astronomy and Astrophysics (2016)

P. Gratier J. Braine Karl F. Schuster Erik Rosolowsky M. Boquien

[Abridged] Do some environments favor efficient conversion of molecular gas into stars? To answer this, we need to be able to estimate the H2 mass. Traditionally, this is done using CO and a few assumptions but the Herschel observations in the FIR make it possible to estimate the molecular gas mass independently of CO. Previous attempts to derive gas masses from dust emission suffered from biases. Generally, dust surface densities, HI column densities, and CO intensities are used to derive a gas-to-dust ratio (GDR) and the local CO intensity to H2 column density ratio (XCO), sometimes allowing for an additional CO-dark gas component (Kdark). We tested earlier methods, revealing degeneracies among the parameters, and then used a Bayesian formalism to derive the most likely values for each of the parameters mentioned above as a function of position in the nearby low metallicity spiral galaxy M33. The data are from the IRAM 30m CO(2-1) line, high-resolution HI and Herschel dust continuum observations. Solving for GDR, XCO, and Kdark in macro pixels 500 pc in size, we find that (i) allowing for CO-dark gas significantly improves fits; (ii) Kdark decreases with galactocentric distance; (iii) GDR is slightly higher than initially expected and increases with galactocentric distance; (iv) the total amount of dark gas closely follows the radially decreasing CO emission, as might be expected if the dark gas is H2 where CO is photodissociated. The total amount of H2, including dark gas, yields an average XCO of twice the galactic value of 2e20 cm^-2/(K km/s), 55% of this traced directly through CO. The rather constant fraction of dark gas suggests that there is no large population of diffuse H2 clouds (unrelated to GMCs) without CO emission. Unlike in large spirals, we detect no systematic radial trend in XCO, possibly linked to the absence of a radial decrease in CO line ratios.

10.1051/0004-6361/201629300

Cite

Citations (26)

Star Formation in M 33 (HerM33es)

EAS Publications Series (2011)

C. Krämer M. Boquien J. Braine C. Buchbender Daniela Calzetti

Within the key project "Herschel M33 extended survey" (HerM33es), we are studying the physical and chemical processes driving star formation and galactic evolution in the nearby galaxy M33, combining the study of local conditions affecting individual star formation with properties only becoming apparent on global scales. Here, we present recent results obtained by the HerM33es team. Combining Spitzer and Herschel data ranging from 3.6um to 500um, along with HI, Halpha, and GALEX UV data, we have studied the dust at high spatial resolutions of 150pc, providing estimators of the total infrared (TIR) brightness and of the star formation rate. While the temperature of the warm dust at high brightness is driven by young massive stars, evolved stellar populations appear to drive the temperature of the cold dust. Plane-parallel models of photon dominated regions (PDRs) fail to reproduce fully the [CII], [OI], and CO maps obtained in a first spectroscopic study of one 2'x2' subregion of M33, located on the inner, northern spiral arm and encompassing the HII region BCLMP302.

Galactic plane

10.1051/eas/1152016

Cite

Citations (1)

Results of the IRAM M33 Large Program

Proceedings of the International Astronomical Union (2012)

J. Braine K. Schüster P. Gratier C. Druard

Abstract A very sensitive survey of the CO(2−1) emission of the entire disk of the Local Group galaxy M 33 is virtually complete. Hundreds of clouds down to a mass of 10000M ⊙ are detected and we show that the cloud mass function (assuming a constant ratio between CO emission and H 2 mass) steepens away from the center of M 33. Through comparison with dust emission and cloud Virial masses, we estimate a N (H 2 )/ I CO factor roughly twice Galactic.

Virial mass

10.1017/s1743921313000793

Cite

Citations (0)

Star formation in M33 (HerM33es)

C. Krämer M. Boquien J. Braine C. Buchbender Daniela Calzetti

Within the key project M33 extended survey (HerM33es), we are studying the physical and chemical processes driving star formation and galactic evolution in the nearby galaxy M33, combining the study of local conditions affecting individual star formation with properties only becoming apparent on global scales. Here, we present recent results obtained by the HerM33es team. Combining Spitzer and Herschel data ranging from 3.6um to 500um, along with HI, Halpha, and GALEX UV data, we have studied the dust at high spatial resolutions of 150pc, providing estimators of the total infrared (TIR) brightness and of the star formation rate. While the temperature of the warm dust at high brightness is driven by young massive stars, evolved stellar populations appear to drive the temperature of the cold dust. Plane-parallel models of photon dominated regions (PDRs) fail to reproduce fully the [CII], [OI], and CO maps obtained in a first spectroscopic study of one 2'x2' subregion of M33, located on the inner, northern spiral arm and encompassing the HII region BCLMP302.

Galactic plane

Local Group

Cite

Citations (0)

The Interstellar Medium of NGC 6822

HAL (Le Centre pour la Communication Scientifique Directe) (2009)

P. Gratier

Source

Cite

Citations (0)

The Interstellar Medium of Local Group Chemically Young Galaxies

HAL (Le Centre pour la Communication Scientifique Directe) (2010)

P. Gratier

Local Group

Source

Cite

Citations (0)

The IRAM-30m line survey of the Horsehead PDR: II. First detection of the l-C3H+ hydrocarbon cation

J. Pety P. Gratier Viviana V. Guzmán E. Roueff Maryvonne Gérin

We present the first detection of the l-C3H+ hydrocarbon in the interstellar medium. The Horsehead WHISPER project, a millimeter unbiased line survey at two positions, namely the photo-dissociation region (PDR) and the nearby shielded core, revealed a consistent set of eight unidentified lines toward the PDR position. Six of them are detected with a signal-to-noise ratio from 6 to 19, while the two last ones are tentatively detected. Mostly noise appears at the same frequency toward the dense core, located less than 40 away. We simultaneously fit 1) the rotational and centrifugal distortion constants of a linear rotor, and 2) the Gaussian line shapes located at the eight predicted frequencies. The observed lines can be accurately fitted with a linear rotor model, implying a 1Sigma ground electronic state. The deduced rotational constant value is Be= 11244.9512 +/- 0.0015 MHz, close to that of l-C3H. We thus associate the lines to the l-C3H+ hydrocarbon cation, which enables us to constrain the chemistry of small hydrocarbons. A rotational diagram is then used to infer the excitation temperature and the column density. We finally compare the abundance to the results of the Meudon PDR photochemical model.

Line (geometry)

Cite

Citations (80)

Spectrally resolved C II emission in M 33 (HerM33es)

Astronomy and Astrophysics (2012)

J. Braine P. Gratier C. Krämer F. P. Israel F. van der Tak

This work presents high spectral resolution observations of the \CII\ line at 158 \micron, one of the major cooling lines of the interstellar medium, taken with the HIFI heterodyne spectrometer on the Herschel satellite. In BCLMP 691, an \HII\ region far north (3.3 kpc) in the disk of M 33, the \CII\ and CO line profiles show similar velocities within $0.5 \kms$, while the \HI\ line velocities are systematically shifted towards lower rotation velocities by $\sim 5\kms$. Observed at the same $12"$ angular resolution, the \CII\ lines are broader than those of CO by about 50% but narrower than the \HI\ lines. The \CII\ line to far-infrared continuum ratio suggests a photoelectric heating efficiency of 1.1%. The data, together with published models indicate a UV field $G_0 \sim 100$ in units of the solar neighborhood value, a gas density $n_H \sim 1000 \cc$, and a gas temperature $T\sim 200$ K. Adopting these values, we estimate the C$^+$ column density to be $N_{C^+} \approx 1.3 \times 10^{17} \cmt$. The \CII\ emission comes predominantly from the warm neutral region between the \HII\ region and the cool molecular cloud behind it. From published abundances, the inferred C$^+$ column corresponds to a hydrogen column density of $N_H \sim 2 \times 10^{21} \cmt$. The CO observations suggest that $N_H = 2 N_{H_2} \sim 3.2 \times 10^{21} \cmt$ and 21cm measurements, also at $12"$ resolution, yield $N_\HI \approx 1.2 \times 10^{21} \cmt$ within the \CII\ velocity range. Thus, some H$_2$ not detected in CO must be present, in agreement with earlier findings based on the SPIRE 250 -- 500 $\mu$m emission.

Line (geometry)

Spectral resolution

10.1051/0004-6361/201219360

Cite

Citations (24)

Astrochemical models of interstellar ices: History matters

Astronomy and Astrophysics (2023)

Aimie Clement A. Taillard Valentine Wakelam P. Gratier Jean‐Christophe Loison

Ice is ubiquitous in the interstellar medium. We model the formation of the main constituents of interstellar ices, including H2O, CO2 , CO, and CH3 OH. We strive to understand what physical or chemical parameters influence the final composition of the ice and how they benchmark to what has already been observed, with the aim of applying these models to the preparation and analysis of JWST observations. We used the Nautilus gas-grain model, which computes the gas and ice composition as a function of time for a set of physical conditions, starting from an initial gas phase composition. All important processes (gas-phase reactions, gas-grain interactions, and grain surface processes) are included and solved with the rate equation approximation. We first ran an astrochemical code for fixed conditions of temperature and density mapped in the cold core L429-C to benchmark the chemistry. One key parameter was revealed to be the dust temperature. When the dust temperature is higher than 12 K, CO2 will form efficiently at the expense of H2O, while at temperatures below 12 K, it will not form. Whatever hypothesis we assumed for the chemistry (within realistic conditions), the static simulations failed to reproduce the observed trends of interstellar ices in our target core. In a second step, we simulated the chemical evolution of parcels of gas undergoing different physical and chemical situations throughout the molecular cloud evolution and starting a few 1e7 yr prior to the core formation (dynamical simulations). Our dynamical simulations satisfactorily reproduce the main trends already observed for interstellar ices. Moreover, we predict that the apparent constant ratio of CO2/H2O observed to date is probably not true for regions of low AV , and that the history of the evolution of clouds plays an essential role, even prior to their formation.

10.1051/0004-6361/202346188

Cite

Citations (4)

Uncertainties in the diffusion rate of species on interstellar ice and its impact on the chemical abundance in the cold cores

43rd COSPAR Scientific Assembly. Held 28 January - 4 February (2021)

Wasim Iqbal Valentine Wakelam P. Gratier

Source

Cite

Citations (0)