Browsing by Author "Ledoux, C. "

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    Mapping the spatial extent of H I-rich absorbers using Mg II absorption along gravitational arcs
    (2025) Berg, T. A. M.; Afruni, A.; Ledoux, C.; López, S.; Noterdaeme, P.; Tejos, N.; Hernández Guajardo, Joaquín Aléxis; Barrientos, Luis Felipe; Johnston, E. J.
    H I-rich absorbers seen within quasar spectra contain the bulk of neutral gas in the Universe. However, the spatial extent of these reservoirs are not extensively studied due to the pencil beam nature of quasar sightlines. Using two giant gravitational arc fields (at redshifts 1.17 and 2.06) as 2D background sources with known strong Mg II absorption observed with the Multi Unit Spectroscopic Explorer integral field spectrograph (IFS), we investigated whether spatially mapped Mg II absorption can predict the presence of strong H I systems, and determine both the physical extent and H I mass of the two absorbing systems. We created a simple model of an ensemble of gas clouds in order to simultaneously predict the H I column density and gas covering fraction of H I-rich absorbers based on observations of the Mg II rest-frame equivalent width in IFS spaxels. We first test the model on the lensing field with H I observations already available from the literature, finding that we can recover H I column densities consistent with the previous estimates (although with large uncertainties). We then use our framework to simultaneously predict the gas covering fraction, H I column density and total H I gas mass (MHI) for both fields. We find that both of the observed strong systems have a covering fraction of ≈ 70% and are likely damped Lyman α systems (DLAs) with MHI > 109 M⊙. Our model shows that the typical Mg II metrics used in the literature to identify the presence of DLAs are sensitive to the gas covering fraction. However, these Mg II metrics are still sensitive to strong H I, and can be still applied to absorbers towards gravitational arcs or other spatially extended background sources. Based on our results, we speculate that the two strong absorbers are likely representative of a neutral inner circumgalactic medium and are a significant reservoir of fuel for star formation within the host galaxies.
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    Molecular gas budget and characterization of intermediate-mass star-forming galaxies at z ≈ 2–3
    (2021) Solimano, M. ; González-López, J. ; Barrientos, L. F. ; Aravena, M. ; López, S. ; Tejos, N. ; Sharon, K. ; Dahle, H. ; Bayliss, M. ; Ledoux, C. ; Rigby, J. R. ; Gladders, M.
    Star-forming galaxies (SFGs) with stellar masses below 10(10) M-circle dot make up the bulk of the galaxy population at z > 2. The properties of the cold gas in these galaxies can only be probed in very deep observations or by targeting strongly lensed galaxies. Here we report the results of a pilot survey using the Atacama Compact Array of molecular gas in the most strongly magnified galaxies selected as giant arcs in optical data. The selection in rest-frame ultraviolet (UV) wavelengths ensures that sources are regular SFGs, without a priori indications of intense dusty starburst activity. We conducted Band 4 and Band 7 observations to detect mid-J CO, [C I] and thermal continuum as molecular gas tracers from four strongly lensed systems at z approximate to 2-3: our targets are SGAS J1226651.3+215220 (A and B), SGAS J003341.5+024217 and the Sunburst Arc. The measured molecular mass was then projected onto the source plane with detailed lens models developed from high resolution Hubble Space Telescope observations. Multiwavelength photometry was then used to obtain the intrinsic stellar mass and star formation rate via spectral energy distribution modeling. In only one of the sources are the three tracers robustly detected, while in the others they are either undetected or detected in continuum only. The implied molecular gass masses range from 4 x 10(9) M-circle dot in the detected source to an upper limit of less than or similar to 10(9) M-circle dot in the most magnified source. The inferred gas fraction and gas depletion timescale are found to lie approximately 0.5-1.0 dex below the established scaling relations based on previous studies of unlensed massive galaxies, but in relative agreement with existing literature about UV-bright lensed galaxies at these high redshifts. Our results indicate that the cold gas content of intermediate to low mass galaxies should not be extrapolated from the trends seen in more massive high-z galaxies. The apparent gas deficit is robust against biases in the stellar mass or star formation rate. However, we find that in this mass-metallicity range, the molecular gas mass measurements are severely limited by uncertainties in the current tracer-to-gas calibrations.
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    Molecular gas budget of strongly magnified low-mass star-forming galaxies at cosmic noon
    (2024) Catán Valenzuela, Victoria Sofia; González López, Jorge; Solimano Gambardella, Manuel Antonio; Barrientos, Luis Felipe; Afruni, A.; Aravena, M.; Bayliss, M.; Hernández, J. A.; Ledoux, C.; Mahler, G.; Sharon, K.; Tejos, N.
    Aims. The aim of this study is to investigate the molecular gas content of strongly magnified low-mass star-forming galaxies (SFGs) around the cosmic noon period (z ∼ 2) through observations of carbon monoxide (CO) emission lines and dust continuum emission, both of which serve as tracers of molecular gas (H2). Methods. We observed 12 strongly lensed arcs with the Atacama Compact Array (ACA) to detect CO mid-J rotational transitions and dust continuum. Thanks to the strong lensing, we were able to probe the previously understudied low-mass regime. With a compiled set of observations, we recalibrated empirical relations between star formation rate density (ΣSFR) and the CO line ratios. We derived galaxy properties using spectral energy distribution fitting (SED). We also performed galaxy stacking to combine faint signals. In all cases, molecular gas masses were estimated using both tracers. Results. We detected CO emission in 3 of the 12 arcs and dust continuum emission in another 3. The obtained H2 masses indicate that most of these galaxies (M* < 1010.7 M⊙) have lower molecular gas fractions and shorter depletion times compared to expectations from established scaling relations at these redshifts. We explored several possible explanations for this gas deficit, including uncertainties in mass estimates, effects of low-metallicity environments, larger atomic gas reservoirs in low-mass systems, and the possibility that these represent low-mass analogs of main sequence starburst (MS SBs) galaxies that are undergoing sustained star formation due to gas compaction despite low overall gas fractions. Conclusions. We conclude that these mass and metallicity regimes present a molecular gas deficit. Our results suggest that this deficit is likely due to a significant amount of atomic gas, which our stacking indicates is about 91% of the total gas. However, this estimation might be an upper limit, as the possibility remains that our galaxies contain CO-dark gas.
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    The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
    (OXFORD UNIV PRESS, 2015) Friis, M.; De Cia, A.; Kruehler, T.; Fynbo, J. P. U.; Ledoux, C.; Vreeswijk, P. M.; Watson, D. J.; Malesani, D.; Gorosabel, J.; Starling, R. L. C.; Jakobsson, P.; Varela, K.; Wiersema, K.; Drachmann, A. P.; Trotter, A.; Thoene, C. C.; de Ugarte Postigo, A.; D'Elia, V.; Elliott, J.; Maturi, M.; Goldoni, P.; Greiner, J.; Haislip, J.; Kaper, L.; Knust, F.; LaCluyze, A.; Milvang Jensen, B.; Reichart, D.; Schulze, S.; Sudilovsky, V.; Tanvir, N.; Vergani, S. D.
    We present the first reported case of the simultaneous metallicity determination of a gamma- ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission- line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long- duration Swift GRB 121024A at z = 2.30, we give one of the most complete views of a GRB host/ environment to date. We observe a strong damped Lya absorber (DLA) with a hydrogen column density of log N(H i) = 21.88 +/- 0.10, H-2 absorption in the Lyman- Werner bands (molecular fraction of log(f) approximate to- 1.4; fourth solid detection of molecular hydrogen in a GRB- DLA), the nebular emission lines H alpha, H beta, [OII], [O III] and [N II], as well as metal absorption lines. We find aGRB host galaxy that is highly star forming (SFR similar to 40M circle dot yr(-1)), with a dust- corrected metallicity along the line of sight of [Zn/ H](corr) =- 0.6 +/- 0.2 ([O/H]similar to- 0.3 from emission lines), and a depletion factor [Zn/ Fe] = 0.85 +/- 0.04. The molecular gas is separated by 400 km s(-1) (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log(M*/M-circle dot) = 9.9(-0.3)(+0.2). We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line- emitting star- forming regions. The extinction curve for the line of sight is found to be unusually flat (R-V similar to 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.