arXiv subjects

Carmelle Robert

Publications and source records attributed to Carmelle Robert.

33 records · Page 2Linked to original sources

arXiv2022

WISDOM project -- XI. Star Formation Efficiency in the Bulge of the AGN-host Galaxy NGC 3169 with SITELLE and ALMA

The star formation efficiency (SFE) has been shown to vary across different environments, particularly within galactic starbursts and deep within the bulges of galaxies. Various quenching mechanisms may be responsible, ranging from galactic dynamics to feedback from active galactic nuclei (AGN). Here, we use spatially-resolved observations of warm ionised gas emission lines from the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope (CFHT) and cold molecular gas (CO(2-1)) from the Atacama Large Millimeter/sub-millimeter Array (ALMA) to study the SFE in the bulge of the AGN-host galaxy NGC 3169. After distinguishing star-forming regions from AGN-ionised regions using emission-line ratio diagnostics, we measure spatially-resolved molecular gas depletion times (τ_dep = 1/SFE) with a spatial resolution of \approx 100 pc within a galactocentric radius of 1.8 kpc. We identify a star-forming ring located at radii 1.25 \pm 0.6 kpc with an average τ_dep of 0.3 Gyr. At radii < 0.9 kpc, however, the molecular gas surface densities and depletion times increase with decreasing radius, the latter reaching approximately 2.3 Gyr at a radius \approx 500 pc. Based on analyses of the gas kinematics and comparisons with simulations, we identify AGN feedback, bulge morphology and dynamics as the possible causes of the radial profile of SFE observed in the central region of NGC 3169.

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arXiv2022

Stellar feedback in M83 as observed with MUSE -- I. Overview, an unprecedented view of the stellar and gas kinematics and evidence of outflowing gas

We present a large VLT/MUSE mosaic (3.8 x 3.8 kpc) of the nearby spiral galaxy M83, with a spatial resolution ~20 pc. We obtained the kinematics of the stars and ionised gas, and compared them with molecular gas kinematics from ALMA CO(2-1). We separated the ionised gas into HII regions and diffuse ionised gas (DIG) and determined the fraction of Ha luminosity originating from the DIG (f_DIG). We observe that both stars and gas trace the galactic disk rotation, as well as a fast-rotating nuclear component, likely connected to secular processes driven by the galactic bar. In the gas kinematics, we observe a stream east of the nucleus, redshifted with respect to the disk. The stream is surrounded by an extended ionised gas region with enhanced velocity dispersion and a high ionisation state, which is largely consistent with being ionised by slow shocks. We interpret this feature as either the superposition of the disk and an extraplanar layer of DIG, or as a bar-driven inflow of shocked gas. A double Gaussian component fit to the Ha line also reveals the presence of a nuclear biconic structure whose axis of symmetry is perpendicular to the bar. The two cones appear blue- and redshifted along the line of sight and stand out for having an Ha emission separated by up to 200 km s-1 from that of the disk, and a high velocity dispersion ~80-200 km s-1. At the far end of the cones, we observe that the gas is consistent with being ionised by shocks. These features had never been observed before in M83; we postulate that they are tracing a starburst-driven outflow shocking into the surrounding ISM. Finally, we obtain f_DIG ~ 13% in our field of view. We inspect the emission of the HII regions and DIG in `BPT' diagrams, finding that in HII regions photoionisation accounts for 99.8% of the Ha flux, whereas the DIG has a mixed contribution from photoionisation (94.9%) and shocks (5.1%). [abridged]

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arXiv2019

NGC628 with SITELLE : I. Imaging Spectroscopy of 4285 HII region candidates

This is the first paper of a series dedicated to nebular physics and the chemical evolution of nearby galaxies by investigating large samples of HII regions with the CFHT imaging spectrograph SITELLE. We present a technique adapted to imaging spectroscopy to identify and extract parameters from 4285 HII region candidates found in the disc of NGC628. Using both the spatial and spectral capabilities of SITELLE, our technique enables the extraction of the position, dust extinction, velocity, Halpha profile, diffuse ionised gas (DIG) background, luminosity, size, morphological type, and the emission line fluxes for individual spaxels and the integrated spectrum for each region. We have produced a well-sampled HII region luminosity function and studied its variation with galactocentric radius and level of the DIG background. We found a slope of 1.12+/-0.03 with no evidence of a break at high luminosity. Based on the width of the region profile, bright regions are rather compact, while faint regions are seen over a wide range of sizes. The radius function reveals a slope of 1.81+/-0.02. BPT diagrams of the individual spaxels and integrated line ratios confirm that most detections are HII regions. Also, maps of the line ratios show complex variations of the ionisation conditions within HII regions. All this information is compiled in a new catalogue for HII regions. The objective of this database is to provide a complete sample which will be used to study the whole parameter space covered by the physical conditions in active star-forming regions.

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arXiv2019

3D Optical Spectroscopic Study of NGC3344 with SITELLE: I. Identification and Confirmation of Supernova Remnants

We present the first optical identification and confirmation of a sample of supernova remnants (SNRs) in the nearby galaxy NGC3344. Using high spectral and spatial resolution data, obtained with the CFHT imaging Fourier transform spectrograph SITELLE, we identified about 2200 emission line regions, many of which are HII regions, diffuse ionized gas regions, and also SNRs. Considering the stellar population and diffuse ionized gas background, that are quite important in NGC3344, we have selected 129 SNR candidates based on four criteria for regions where the emission lines flux ratio [S II]/H$α$$\ge$0.4. Emission lines of [O II]$λ$3727, H$α$, [O III]$λλ$4959,5007, H$α$, [N II]$λλ$6548,6583, and [S II]$λλ$6716,6731 have been measured to study the ionized gas properties of the SNR candidates. We adopted a self-consistent spectroscopic analysis, based on Sabbadin plots and BPT diagrams, to confirm the shock-heated nature of the ionization mechanism in the candidates sample. With this analysis, we end up with 42 Confirmed SNRs, 45 Probable SNRs, and 42 Less likely SNRs. Using shock models, the Confirmed SNRs seems to have a metallicity ranging between LMC and 2$\times$solar. We looked for correlations between the size of the Confirmed SNRs and their emission lines ratios, their galaxy environment, and their galactocentric distance: we see a trend for a metallicity gradient among the SNR population, along with some evolutionary effects.

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arXiv2018

SITELLE: An Imaging Fourier Transform Spectrometer for the Canada-France-Hawaii Telescope

We present an overview of SITELLE, an Imaging Fourier Transform Spectrometer (iFTS) available at the 3.6-meter Canada-France-Hawaii Telescope. SITELLE is a Michelson-type interferometer able to reconstruct the spectrum of every light source within its 11' field of view in filter-selected bands of the visible (350 to 900 nm). The spectral resolution can be adjusted up to R = 10 000 and the spatial resolution is seeing-limited and sampled at 0.32 arcsec per pixel. We describe the design of the instrument as well as the data reduction and analysis process. To illustrate SITELLE's capabilities, we present some of the data obtained during and since the August 2015 commissioning run. In particular, we demonstrate its ability to separate the components of the [OII] $λλ$ 3726,29 doublet in Orion and to reach R = 9500 around H-alpha; to detect diffuse emission at a level of 4 x 10e-17 erg/cm2/s/arcsec2; to obtain integrated spectra of stellar absorption lines in galaxies despite the well-known multiplex disadvantage of the iFTS; and to detect emission-line galaxies at different redshifts.

astro-ph.IM↗

arXiv2011

Galactic Outflows and Evolution of the Interstellar Medium

We present a model to self-consistently describe the joint evolution of starburst galaxies and the galactic wind resulting from this evolution. We combine the population synthesis code Starburst99 with a semi-analytical model of galactic outflows and a model for the distribution and abundances of chemical elements inside the outflows. Starting with a galaxy mass, formation redshift, and adopting a particular form for the star formation rate, we describe the evolution of the stellar populations in the galaxy, the evolution of the metallicity and chemical composition of the interstellar medium (ISM), the propagation of the galactic wind, and the metal-enrichment of the intergalactic medium (IGM). In this paper, we study the properties of the model, by varying the mass of the galaxy, the star formation rate, and the efficiency of star formation. Our main results are the following: (1) For a given star formation efficiency f*, a more extended period of active star formation tends to produce a galactic wind that reaches a larger extent. If f* is sufficiently large, the energy deposited by the stars completely expels the ISM. Eventually, the ISM is being replenished by mass loss from supernovae and stellar winds. (2) For galaxies with masses above 10^11 Msun, the material ejected in the IGM always falls back onto the galaxy. Hence lower-mass galaxies are the ones responsible for enriching the IGM. (3) Stellar winds play a minor role in the dynamical evolution of the galactic wind, because their energy input is small compared to supernovae. However, they contribute significantly to the chemical composition of the galactic wind. We conclude that the history of the ISM enrichment plays a determinant role in the chemical composition and extent of the galactic wind, and therefore its ability to enrich the IGM.

astro-ph.CO↗

arXiv2010

Stellar Populations in the Barred Spiral Galaxy NGC 4900

We present OASIS observations obtained at the Canada-France-Hawaii Telescope for the SB(rs)c galaxy NGC 4900. About 800 spectra in the wavelength range 4700-5500 AA and 6270- 7000 AA have been collected with a spatial resolution of ~50 pc. This galaxy is part of a sample to study the stellar populations and their history in the central region of galaxies. In this paper, we present our iterative technique developed to describe consistently the different stellar com- ponents seen through emission and absorption lines. In NGC 4900 we find many young bursts of star formation distributed along the galaxy large scale bar on each side of the nucleus. They represent nearly 40 per cent of the actual stellar mass in the field of view. The age for these bursts ranges from 5.5 to 8 Myr with a metallicity near and above 2 Zsun . The extinction map gives E(B-V) values from 0.19+/-0.01 near the youngest bursts to 0.62+/-0.06 in a dusty internal bar perpendicular to the large scale bar. The Mg 2 and Fe I absorption lines indicate the superposition of a background stellar population with an age between 100 Myr to 3 Gyr and a sub-solar metallicity on average. We propose that all these episodes of star formation are the consequence of a secular evolution. In this scenario, the galactic large scale bar plays an important role with respect to the recent bursts and the dusty nuclear bar observed. The iterative technique allows us to improve the determination of the stellar population parameters, mainly an older age is obtained for the old component and more reliable stellar population masses are found. A composite/transition type activity in the galaxy nucleus is also revealed with this technique.

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arXiv2009

The broad H-alpha, [O III] line wings in stellar supercluster A of NGC2363 and the turbulent mixing layer hypothesis

Context. SuperclusterA in the extragalactic HII region NGC2363 is remarkable for the hypersonic gas seen as faint extended broad emission lines with a full width zero intensity of 7000km/s. Aims. We explore the possibility that the observed broad profiles are the result of the interaction of a high velocity cluster wind with dense photoionized clumps. Methods. The geometry considered is that of near static photoionized condensations at the surface of which turbulent mixing layers arise as a result of the interaction with the hot wind. The approximative treatment of turbulence is carried out using the mixing length approach of Canto & Raga. The code mappings Ic is used to derive the mean quantities describing the flow and to compute the line emissivities within the turbulent layers. The velocity projection in three dimensions of the line sources is carried out analytically. Results. A fast entraining wind of up to ~4300km/s appears to be required to reproduce the faint wings of the broad H-alpha and [O III] profiles. A slower wind of 3500km/s, however, can still reproduce the bulk of the broad component and does provide a better fit than an ad hoc Gaussian profile. Conclusions. Radial acceleration in 3D (away from supercluster A) of the emission gas provides a reasonable first order fit to the broad line component. No broad component is predicted for the [N II] and [S II] lines, as observed. The wind velocity required is uncomfortably high and alternative processes that would provide comparable constant acceleration of the emission gas up to 4000km/s might have to be considered.

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arXiv2007

Stellar populations in the center of barred spiral galaxies

We show observations obtained with the integral field spectrometer OASIS for the central regions of a sample of barred galaxies. The high spatial resolution of the instrument allows to distinguish various structures within these regions as defined by stellar populations of different ages and metallicities. From these data we obtain important clues about the star formation history. But we advise that, in order to obtain adequately the evolutionary sequence, a combination of chemical and synthesis models may be necessary.

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arXiv2007

Physical Properties of Young Stellar Populations in 24 Starburst Galaxies Observed with FUSE

We presents the main physical properties of very young stellar populations seen with FUSE in 24 individual starbursts. These characteristics have been obtained using the evolutionary spectral synthesis technique in the far-ultraviolet range with the LavalSB code. For each starburst, quantitative values for age, metallicity, initial mass function slope, stellar mass, and internal extinction have been obtained and discussed in details. Limits of the code have been tested. One main conclusion is that most starbursts (and probably all of them) cannot be represented by any continuous star formation burst in the far-ultraviolet. Also, quantitative values of various optical diagnostics related to these stellar populations have been predicted. Underlying stellar populations, dominated by B-type stars, have been detected in NGC 1140, NGC 4449, and possibly NGC 3991. We characterized the young stellar populations of less than 5 Myr in Seyfert 2 nuclei.

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arXiv2007

Stellar Populations in the Center of the Barred Galaxy NGC 4900

We characterize the stellar populations in the nuclear region of the barred spiral galaxy NGC 4900 using the integral field spectrometer OASIS and the synthesis code LavalSB and the code from Mollá & Garc\'ıa-Vargas (2000) for the young ($< 10$ Myr) and the old stellar populations, respectively. The high spatial resolution of the instrument allows us to find an old population uniformely distributed and younger regions located at the end of the galaxy bar and on each side of a nuclear bar.

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arXiv2002

Synthetic High-Resolution Line Spectra of Star-Forming Galaxies Below 1200A

We have generated a set of far-ultraviolet stellar libraries using spectra of OB and Wolf-Rayet stars in the Galaxy and the Large and Small Magellanic Cloud. The spectra were collected with the Far Ultraviolet Spectroscopic Explorer and cover a wavelength range from 1003.1 to 1182.7A at a resolution of 0.127A. The libraries extend from the earliest O- to late-O and early-B stars for the Magellanic Cloud and Galactic libraries, respectively. Attention is paid to the complex blending of stellar and interstellar lines, which can be significant, especially in models using Galactic stars. The most severe contamination is due to molecular hydrogen. Using a simple model for the H$_2$ line strength, we were able to remove the molecular hydrogen lines in a subset of Magellanic Cloud stars. Variations of the photospheric and wind features of CIII 1176, OVI 1032, 1038, PV 1118, 1128, and SIV 1063, 1073, 1074 are discussed as a function of temperature and luminosity class. The spectral libraries were implemented into the LavalSB and Starburst99 packages and used to compute a standard set of synthetic spectra of star-forming galaxies. Representative spectra are presented for various initial mass functions and star formation histories. The valid parameter space is confined to the youngest ages of less than 10 Myr for an instantaneous burst, prior to the age when incompleteness of spectral types in the libraries sets in. For a continuous burst at solar metallicity, the parameter space is not limited. The suite of models is useful for interpreting the restframe far-ultraviolet in local and high-redshift galaxies.

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arXiv2000

Ultraviolet Line Spectra of Metal-Poor Star-Forming Galaxies

We present synthetic ultraviolet spectra of metal-poor star-forming galaxies which were calculated with the Starburst99 package. A new spectral library was generated from HST observations of O stars in the Large and Small Magellanic Clouds. The corresponding mean metallicity of the synthetic spectra is approximately 1/4\Zs. The spectra have a resolution of 1Åand cover the spectral range 1200-1600Å. A set of model spectra was calculated for a standard initial mass function and star-formation history and is compared to synthetic spectra at solar metallicity. We find that the spectral lines are generally weaker at lower metallicity, as expected from the lower elemental abundances. Stellar-wind lines, however, show a more complex behavior: the metallicity dependence of the ionization balance can be important in trace ions, like N$^{4+}$ and Si$^{3+}$. Therefore the strength of \nv and \siiv does not scale monotonically with metallicity. We compare our new models to ultraviolet spectra of NGC 5253 and \cB, two star-forming galaxies with 1/4 solar metallicity at low and high redshift, respectively. The new library provides significantly better fits to the observations than earlier models using the \Zs library. We discuss the potential of utilizing stellar photospheric and wind lines to estimate the chemical composition of star-forming galaxies. The new metal-poor synthetic spectra are available via the Starburst99 website.

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arXiv1999

Starburst99: Synthesis Models for Galaxies with Active Star Formation

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman (1995). We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. (1997). Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 10^6 to 10^9 yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at http://www.stsci.edu/science/starburst99/. This website allows users to run specific models with non-standard parameters as well. We also make the source code available to the community.

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arXiv1998

The Ultraviolet Spectroscopic Properties of Local Starbursts: Implications at High-Redshift

We report the results of a systematic study of the vacuum-ultraviolet spectra of 45 starburst and related galaxies observed with the IUE satellite. These span broad ranges in metallicity, bolometric luminosity, and galaxy properties. The projected size of the IUE spectroscopic aperture is typically one to several kpc and therefore usually encompasses the entire starburst and is similar to the aperture-sizes used for spectroscopy of high-redshift galaxies. Our principal conclusion is that local starbursts occupy a very small fractional volume in the multi-dimensional manifold defined by such fundamental parameters as the extinction, metallicity, and vacuum-UV line strengths (both stellar and interstellar) of the starburst and the rotation speed (mass) and absolute magnitude of the starburst's `host' galaxy. More metal-rich starbursts are redder and more heavily extinguished in the UV, more luminous, have stronger vacuum-UV lines, and occur in more massive and optically-brighter host galaxies. The results on local starbursts suggest that the high-redshift `Lyman Drop-Out' galaxies are typically highly reddened and extinguished by dust (average factor of 5 to 10 in the UV), may have moderately high metallicities (0.1 to 1 times solar?), are probably building galaxies with stellar surface- mass-densities similar to present-day ellipticals, and may be suffering substantial losses of metal-enriched gas that can `pollute' the IGM.

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