Persona: Arribas, Santiago
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Publicación Restringido Accelerated quenching and chemical enhancement of massive galaxies in a z ≈ 4 gas-rich halo(Nature Astronomy, 2025-07-21) Pérez-González, Pablo G.; D'Eugenio, Francesco; Rodriguez Del Pino, Bruno; Perna, Michele; Übler, Hannah; Maiolino, Roberto; Arribas, Santiago; Cresci, Giovanni; Lamperti, Isabella; Bunker, Andrew J.; Carniani, Stefano; Willott, Chris J.; Böker, Torsten; Parlanti, Eleonora; Scholtz, Jan; Venturi, Giacomo; Barro, Guillermo; Costantin, Luca; Martin-Navarro, Ignacio; Dunlop, James S.; Magee, Daniel; Ministerio de Ciencia e Innovación (MICINN); Agencia Estatal de Investigación (España); European Commission; Science and Technology Facilities Council (STFC); European Research Council (ERC); Istituto Nazionale di Astrofisica (INAF); Fundación La CaixaStars in galaxies form when baryons radiatively cool down and fall into gravitational wells whose mass is dominated by dark matter. Eventually, star formation quenches as gas is depleted and/or perturbed by feedback processes, no longer being able to collapse and condense. We report the first spatially resolved spectroscopic observations, using the JWST/NIRSpec IFU, of a massive, completely quiescent galaxy (Jekyll) and its neighborhood at $z=3.714$, when the Universe age was 10% of today's. Jekyll resides in a massive dark matter halo (with mass M$_\mathrm{DM}>10^{12}$ M$_\odot$) and forms a galaxy pair with Hyde, which shows very intense dust-enshrouded star formation (star formation rate $\sim300$ M$_\odot$yr$^{-1}$). We find large amounts of kinematically perturbed ionized and neutral gas in the circumgalactic medium around the pair. Despite this large gas reservoir, Jekyll, which formed $10^{11}$ M$_\odot$ in stars and chemically enriched early (first billion years of the Universe) and quickly (200-300 Myr), has remained quiescent for over 500 Myr. The properties of the gas found around the two galaxies are consistent with intense, AGN-induced photoionization, or intense shocks. However, with the current data no obscured or unobscured AGN is detected in the central galaxy (Jekyll) nor in the very active and dust rich star-forming galaxy (Hyde).Publicación Acceso Abierto A fast-rotator post-starburst galaxy quenched by supermassive black-hole feedback at z = 3(Springer Nature, 2024-09-16) D’Eugenio, Francesco; Pérez-González, Pablo G., E. M.; Maiolino, Roberto; Scholtz, Jan; Perna, Michele; Circosta, Chiara; Übler, Hannah; Arribas, Santiago; Böker, Torsten; Bunker, Andrew J.; Carniani, Stefano; Charlot, Stephane; Chevallard, Jacopo; Cresci, Giovanni; Curtis-Lake, Emma; Jones, Gareth C.; Kumari, Nimisha; Lamperti, Isabella; Looser, Tobias J.; Parlanti, Eleonora; Rix, Hans Walter; Robertson, Brant; Rodriguez Del Pino, Bruno; Tacchella, Sandro; Venturi, Giacomo; Willott, Chris J.; European Research Council (ERC); Ministerio de Ciencia e Innovación (MICINN); Comunidad De Madrid; Agencia Estatal de Investigación (España); Istituto Nazionale di Astrofisica (INAF); Arizona State University (ASU); State University of Santa Cruz (UESC); National Science Foundation (NSF)The most massive galaxies in the Universe stopped forming stars due to the time-integrated feedback from central supermassive black holes (SMBHs). However, the exact quenching mechanism is not yet understood, because local massive galaxies were quenched billions of years ago. Here we present JWST/NIRSpec integral-field spectroscopy observations of GS-10578, a massive, quiescent galaxy at redshift z = 3.064 ± 0.002. From its spectrum, we measure a stellar mass M⋆ = 1.6 ± 0.2 × 1011 M⊙ and a dynamical mass Mdyn = 2.0 ± 0.5 × 1011 M⊙. Half of its stellar mass formed at z = 3.7–4.6, and the system is now quiescent, with a current star-formation rate of less than 19 M⊙ yr−1. We detect ionized- and neutral-gas outflows traced by [O iii] emission and Na i absorption, with mass outflow rates 0.14–2.9 and 30–100 M⊙ yr−1, respectively. Outflow velocities reach vout ≈ 1,000 km s−1, comparable to the galaxy escape velocity. GS-10578 hosts an active galactic nucleus, evidence that these outflows are due to SMBH feedback. The neutral outflow rate is higher than the star-formation rate. Hence, this is direct evidence for ejective SMBH feedback, with a mass loading capable of interrupting star formation by rapidly removing its fuel. Stellar kinematics show ordered rotation, with spin parameter λRe=0.62±0.07, meaning GS-10578 is rotation-supported. This study presents direct evidence for ejective active galactic nucleus feedback in a massive, recently quenched galaxy, thus helping to clarify how SMBHs quench their hosts. The high value of λRe implies that quenching can occur without destroying the stellar disk.Publicación Acceso Abierto Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): The Core of the Highest-redshift Galaxy Overdensity at z = 7.88 Confirmed by NIRSpec/JWST(American Astronomical Society, 2023-09-01) Hashimoto, T., T.; Álvarez-Márquez, J., J.; Fudamoto, Y.; Colina, L.; Inoue, A. K.; Nakazato, Y.; Ceverino, D.; Yoshida, N.; Costantin, Luca; Sugahara, Y.; Gómez Crespo, A.; Blanco-Prieto, C.; Mawatari, K.; Arribas, Santiago; Marques-Chaves, R.; González, E. M.; Bakx, T. J.L.C.; Hagimoto, M.; Hashigaya, T.; Matsuo, H.; Tamura, Y.; Usui, M.; Ren, Y. W.; Japan Society for the Promotion of Science (KAKENHI); Ministerio de Ciencia e Innovación (MICINN); Ministry of Education, Science, Sports and Culture (MEXT); National Astronomical Observatory of Japan (NAOJ); Comunidad de Madrid; The European Space Agency (ESA)The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O iii] 4960 and 5008 Å in a small area of ∼3″ × 3″, corresponding to ∼11 × 11 kpc, after the lensing magnification correction. Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter Array Band 6, which is consistent with their red ultraviolet continuum slopes, β ∼ −1.3. The member galaxies have stellar masses in the range of log(M */M ⊙) ∼7.6-9.2 and star formation rates of ∼3-50 M ⊙ yr−1, showing a diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member galaxies including the stellar mass, [O iii] luminosity, and dust-to-stellar mass ratio, and predict that the member galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with M * ∼ 6 × 109 M ⊙. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD indicates that environmental effects are already at work 650 Myr after the Big Bang.Publicación Acceso Abierto Extreme gas kinematics in an off-nuclear HII region of SDSS J143245.98+404300.3(EDP Sciences, 2019-10-03) Rodriguez Del Pino, Bruno; Arribas, Santiago; Piqueras López, Javier; Crespo Gómez, A.; Vílchez, J. M.; Ministerio de Economía y Competitividad (MINECO); University of Utah; Alfred P. Sloan Foundation (APSF); Agencia Estatal de Investigación (AEI); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737We present and discuss the properties of an ionized gas component with extreme kinematics in a recently reported off-nuclear HII region located at ∼0.8−1.0 kpc from the nucleus of SDSS J143245.98+404300.3. The high-velocity-gas component is identified by the detection of very broad emission wings in the Hα line, with full width at half maximum (FWHM) ≥ 850−1000 km s−1. Such gas kinematics are outstandingly high compared to other HII regions in local galaxies and are similar to those reported in some star-forming clumps of galaxies at z ∼ 2. The spatially resolved analysis indicates that the high-velocity gas extends at least ∼90 pc and it could be compatible with an ionized outflow entraining gas at a rate between approximately seven and nine times faster than the rate at which gas is being converted into stars. We do not detect broad emission wings in other emission lines such as Hβ, perhaps due to moderate dust extinction, nor in [N II]λλ6548, 6584 or [S II]λλ6717, 6731, which could be due to the presence of turbulent mixing layers originated by the impact of fast-flowing winds. The lack of spectral signatures associated to the presence of Wolf–Rayet stars points towards stellar winds from a large number of massive stars and/or supernovae as the likely mechanisms driving the high-velocity gas.Publicación Acceso Abierto MUSE view of Arp220: Kpc-scale multi-phase outflow and evidence for positive feedback(EDP Sciences, 2020-11-17) Perna, Michele; Arribas, Santiago; Catalán Torrecilla, Cristina; Colina, L. ; Bellocchi, Enrica; Fluetsch, A.; Maiolino, R.; Cazzoli, Sara; Hernán Caballero, A.; Pereira Santaella, Miguel; Piqueras López, Javier; Rodriguez Del Pino, Bruno; Ministerio de Economía y Competitividad (MINECO); ESO Multi Unit Spectroscopic Explorer (MUSE); Comunidad de Madrid; European Research Council (ERC); Agencia Estatal de Investigación (AEI); Perna, M. [0000-0002-0362-5941]; Arribas, S. [0000-0001-7997-1640]; Colina, L. [0000-0002-9090-4227]; Bellocchi, E. [0000-0001-9791-4228]; Cazzoli, S. [0000-0002-7705-2525]; Pereira Santaella, M. [0000-0002-4005-9619]; Piqueras López, J. [0000-0003-1580-1188]; Rodríguez del Pino, B. [0000-0001-5171-3930]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709Context. Arp220 is the nearest and prototypical ultra-luminous infrared galaxy; it shows evidence of pc-scale molecular outflows in its nuclear regions and strongly perturbed ionised gas kinematics on kpc scales. It is therefore an ideal system for investigating outflow mechanisms and feedback phenomena in detail. Aims. We investigate the feedback effects on the Arp220 interstellar medium (ISM), deriving a detailed picture of the atomic gas in terms of physical and kinematic properties, with a spatial resolution that had never before been obtained (0.56″, i.e. ∼210 pc). Methods. We use optical integral-field spectroscopic observations from VLT/MUSE-AO to obtain spatially resolved stellar and gas kinematics, for both ionised ([N II]λ6583) and neutral (Na IDλλ5891, 96) components; we also derive dust attenuation, electron density, ionisation conditions, and hydrogen column density maps to characterise the ISM properties. Results. Arp220 kinematics reveal the presence of a disturbed kpc-scale disc in the innermost nuclear regions as well as highly perturbed multi-phase (neutral and ionised) gas along the minor axis of the disc, which we interpret as a galactic-scale outflow emerging from the Arp220 eastern nucleus. This outflow involves velocities up to ∼1000 km s−1 at galactocentric distances of ≈5 kpc; it has a mass rate of ∼50 M⊙ yr−1 and kinetic and momentum power of ∼1043 erg s−1 and ∼1035 dyne, respectively. The inferred energetics do not allow us to distinguish the origin of the outflows, namely whether they are active galactic nucleus- or starburst-driven. We also present evidence for enhanced star formation at the edges of – and within – the outflow, with a star-formation rate SFR ∼ 5 M⊙ yr−1 (i.e. ∼2% of the total SFR). Conclusions. Our findings suggest the presence of powerful winds in Arp220: They might be capable of heating or removing large amounts of gas from the host (“negative feedback”) but could also be responsible for triggering star formation (“positive feedback”).Publicación Acceso Abierto Physics of ULIRGs with MUSE and ALMA: The PUMA project III. Incidence and properties of ionised gas disks in ULIRGs, associated velocity dispersion, and its dependence on starburstiness(EDP Sciences, 2022-06-23) Perna, Michele; Arribas, Santiago; Colina, L. ; Pereira Santaella, Miguel; Lamperti, Isabella; Di Teodoro, Enrico M.; Übler, Hannah; Costantin, Luca; Maiolino, R.; Cresci, Giovanni; Bellocchi, Enrica ; Catalán Torrecilla, Cristina; Cazzoli, Sara; Piqueras López, Javier; European Research Council (ERC); European Commission; Ministerio de Ciencia e Innovación (MICINN); Comunidad de Madrid; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709Context. A classical scenario suggests that ultra-luminous infrared galaxies (ULIRGs) transform colliding spiral galaxies into a spheroid-dominated early-type galaxy. Recent high-resolution simulations have instead shown that, under some circumstances, rotation disks can be preserved during the merging process or rapidly regrown after coalescence. Our goal is to analyse in detail the ionised gas kinematics in a sample of ULIRGs to infer the incidence of gas rotational dynamics in late-stage interacting galaxies and merger remnants. Aims. We analysed integral field spectrograph MUSE data of a sample of 20 nearby (z < 0.165) ULIRGs (with 29 individual nuclei) as part of the Physics of ULIRGs with MUSE and ALMA (PUMA) project. We used multi-Gaussian fitting techniques to identify gaseous disk motions and the 3D-Barolo tool to model them. Methods. We found that 27% (8 out of 29) individual nuclei are associated with kiloparsec-scale disk-like gas motions. The rest of the sample displays a plethora of gas kinematics, dominated by winds and merger-induced flows, which makes the detection of rotation signatures difficult. On the other hand, the incidence of stellar disk-like motions is ∼2 times larger than gaseous disks, as the former are probably less affected by winds and streams. The eight galaxies with a gaseous disk present relatively high intrinsic gas velocity dispersion (σ0 ∈ [30 − 85] km s−1), rotationally supported motions (with gas rotation velocity over velocity dispersion vrot/σ0 ∼ 1 − 8), and dynamical masses in the range (2 − 7)×1010 M⊙. By combining our results with those of local and high-z disk galaxies (up to z ∼ 2) from the literature, we found a significant correlation between σ0 and the offset from the main sequence (δMS), after correcting for their evolutionary trends. Results. Our results confirm the presence of kiloparsec-scale rotating disks in interacting galaxies and merger remnants in the PUMA sample, with an incidence going from 27% (gas) to ≲50% (stars). Their gas σ0 is up to a factor of ∼4 higher than in local normal main sequence galaxies, similar to high-z starbursts as presented in the literature; this suggests that interactions and mergers enhance the star formation rate while simultaneously increasing the velocity dispersion in the interstellar medium. © ESO 2022.Publicación Acceso Abierto Physics of ULIRGs with MUSE and ALMA: The PUMA project I. Properties of the survey and first MUSE data results(EDP Sciences, 2021-02-16) Perna, Michele; Arribas, Santiago; Pereira Santaella, Miguel; Colina, L. ; Bellocchi, Enrica; Catalán Torrecilla, Cristina; Cazzoli, Sara; Crespo Gómez, A.; Maiolino, R.; Piqueras López, Javier; Rodriguez Del Pino, Bruno; Comunidad de Madrid; Agencia Estatal de Investigación (AEI); European Research Council (ERC); Science and Technology Facilities Council (STFC); Perna, M. [0000-0002-0362-5941]; Arribas, S. [0000-0001-7997-1640]; Colina, L. [0000-0002-9090-4227]; Bellocchi, E. [0000-0001-9791-4228]; Catalán Torrecilla, C. [0000-0002-8067-0164]; Cazzoli, S. [0000-0002-7705-2525]; Maiolino, R. [0000-0002-4985-3819]; Piqueras López, J. [0000-0003-1580-1188]; Rodríguez del Pino, B. [0000-0001-5171-3930]; Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709Context. Ultraluminous infrared galaxies (ULIRGs) are characterised by extreme starburst (SB) and active galactic nucleus (AGN) activity, and are therefore ideal laboratories for studying the outflow phenomena and their feedback effects. We have recently started a project called Physics of ULIRGs with MUSE and ALMA (PUMA), which is a survey of 25 nearby (z < 0.165) ULIRGs observed with the integral field spectrograph MUSE and the interferometer ALMA. This sample includes systems with both AGN and SB nuclear activity in the pre- and post-coalescence phases of major mergers. Aims. The main goals of the project are (i) to study the prevalence of (ionised, neutral, and molecular) outflows as a function of the galaxy properties, (ii) to constrain the driving mechanisms of the outflows (e.g. distinguish between SB and AGN winds), and (iii) to identify and characterise feedback effects on the host galaxy. In this first paper, we present details on the sample selection, MUSE observations, and data reduction, and derive first high-level data products. Methods. MUSE data cubes were analysed to study the dynamical status of each of the 21 ULIRGs observed so far, taking the stellar kinematics and the morphological properties inferred from MUSE narrow-band images into account. We also located the ULIRG nuclei, taking advantage of near-infrared (HST) and millimeter (ALMA) data, and studied their optical spectra to infer (i) the ionisation state through standard optical line ratio diagnostics, and (ii) outflows in both atomic ionised ([O III], Hα) and neutral (Na ID) gas. Results. We show that the morphological and stellar kinematic classifications are consistent: post-coalescence systems are more likely associated with ordered motions, while interacting (binary) systems are dominated by non-ordered and streaming motions. We also find broad and asymmetric [O III] and Na ID profiles in almost all nuclear spectra, with line widths in the range [300 − 2000] km s−1, possibly associated with AGN- and SB-driven winds. This result reinforces previous findings that indicated that outflows are ubiquitous during the pre- and post-coalescence phases of major mergers.Publicación Acceso Abierto Stellar kinematics in the nuclear regions of nearby LIRGs with VLT-SINFONI Comparison with gas phases and implications for dynamical mass estimations(EDP Sciences, 2021-06-22) Crespo Gómez, A.; Piqueras López, Javier; Arribas, Santiago; Pereira Santaella, Miguel; Colina, L. ; Rodriguez Del Pino, Bruno; National Aeronautics and Space Administration (NASA); Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); 0000-0003-2119-277X; 0000-0003-1580-1188; 0000-0001-7997-1640; 0000-0002-9090-4227; 0000-0001-5171-3930Context. Nearby luminous infrared galaxies (LIRGs) are often considered to be the local counterpart of the star forming galaxy (SFG) population at z > 1. Therefore, local LIRGs are ideal systems with which to perform spatially resolved studies on the physical processes that govern these objects and to validate assumptions made in high-z studies because of a lack of sensitivity and/or spatial resolution. Aims. In this work we analyse the spatially resolved kinematics of the stellar component in the inner r < 1–2 kpc of ten nearby (mean z = 0.014) LIRGs, establishing the dynamical state of the stars and estimating their dynamical masses (Mdyn). We compare the stellar kinematics with those for different gas phases, and analyse the relative effects of using different tracers when estimating dynamical masses. Methods. We use seeing-limited SINFONI H- and K-band spectroscopy in combination with ancillary infrared (IR) imaging from various instruments (NICMOS/F160W, NACO/Ks and IRAC/3.6 μm). The stellar kinematics are extracted in both near-IR bands by fitting the continuum emission using pPXF. The velocity maps are then modelled as rotating discs and used to extract the geometrical parameters (i.e. centre, PA, and inclination), which are compared with their photometric counterparts extracted from the near-IR images. We use the stellar and the previously extracted gas velocity and velocity dispersion maps to estimate the dynamical mass using the different tracers. Results. We find that the different gas phases have similar kinematics, whereas the stellar component is rotating with slightly lower velocities (i.e. V* ∼ 0.8Vg) but in significantly warmer orbits (i.e. σ* ∼ 2σg) than the gas phases, resulting in significantly lower V/σ for the stars (i.e. ∼1.5–2) than for the gas (i.e. ∼4–6). These ratios can be understood if the stars are rotating in thick discs while the gas phases are confined in dynamically cooler (i.e. thinner) rotating discs. However, these differences do not lead to significant discrepancies between the dynamical mass estimations based on the stellar and gas kinematics. This result suggests that the gas kinematics can be used to estimate Mdyn also in z ∼ 2 SFGs, a galaxy population that shares many structural and kinematic properties with local LIRGs.Publicación Acceso Abierto Excitation and acceleration of molecular outflows in LIRGs: The extended ESO 320-G030 outflow on 200-pc scales(EDP Sciences, 2020-11-06) Pereira Santaella, Miguel; Colina, L. ; García Burillo, S.; González Alfonso, E.; Alonso-Herrero, Almudena; Arribas, Santiago; Cazzoli, Sara; Piqueras López, Javier; Rigopoulou, Dimitra; Usero, A.; Comunidad de Madrid; Agencia Estatal de Investigación (AEI); Usero, A. [0000-0003-1242-505X]; Pereira Santaella, M. [0000-0002-4005-9619]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737We used high-spatial resolution (70 pc; 03) CO multi-transition (J = 1–0, 2–1, 4–3, and 6–5) ALMA data to study the physical conditions and kinematics of the cold molecular outflow in the local luminous infrared galaxy (LIRG) ESO 320-G030 (d = 48 Mpc, LIR/L⊙ = 1011.3). ESO 320-G030 is a double-barred isolated spiral, but its compact and obscured nuclear starburst (SFR ∼ 15 M⊙ yr−1; AV ∼ 40 mag) resembles those of ultra-luminous infrared galaxies (LIR/L⊙ > 1012). In the outflow, the CO(1–0)/CO(2–1) ratio is enhanced with respect to the rest of the galaxy and the CO(4–3) transition is undetected. This indicates that the outflowing molecular gas is less excited than the molecular gas in the nuclear starburst (i.e., outflow launching site) and in the galaxy disk. Non-local thermodynamic equilibrium radiative transfer modeling reveals that the properties of the molecular clouds in the outflow differ from those of the nuclear and disk clouds: The kinetic temperature is lower (Tkin ∼ 9 K) in the outflow, and the outflowing clouds have lower column densities. Assuming a 10−4 CO abundance, the large internal velocity gradients, 60−45+250 km s−1 pc−1, imply that the outflowing molecular clouds are not bound by self-gravity. All this suggests that the life-cycle (formation, collapse, dissipation) of the galaxy disk molecular clouds might differ from that of the outflowing molecular clouds which might not be able to form stars. The low kinetic temperature of the molecular outflow remains constant at radial distances between 0.3 and 1.7 kpc. This indicates that the heating by the hotter ionized outflow phase is not efficient and may favor the survival of the molecular gas phase in the outflow. The spatially resolved velocity structure of the outflow shows a 0.8 km s−1 pc−1 velocity gradient between 190 pc and 560 pc and then a constant maximum outflow velocity of about 700–800 km s−1 up to 1.7 kpc. This could be compatible with a pure gravitational evolution of the outflow, which would require coupled variations of the mass outflow rate and the outflow launching velocity distribution. Alternatively, a combination of ram pressure acceleration and cloud evaporation could explain the observed kinematics and the total size of the cold molecular phase of the outflow.Publicación Acceso Abierto Extinction in the 11.2 mu m PAH band and the low L-11.2/L-IR in ULIRGs(Oxford Academics: Blackwell Publishing, 2020-08-05) Hernández Caballero, A.; Spoon, H. W. W.; Alonso-Herrero, Almudena; Hatziminaoglou, Evanthia; Magdis, Georgios E.; Pérez González, Pablo G.; Pereira Santaella, Miguel; Arribas, Santiago; Cortzen, I.; Labiano, Alvaro; Piqueras López, Javier; Rigopoulou, Dimitra; National Aeronautics and Space Administration (NASA); Agencia Estatal de Investigación (AEI); Villum Fonden; Danish National Research Foundation (DNRF); Comunidad de Madrid; 0000-0002-4872-2294; 0000-0001-9197-7623; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737We present a method for recovering the intrinsic (extinction-corrected) luminosity of the 11.2 mu m PAH band in galaxy spectra. Using 105 high S/N Spitzer/IRS spectra of star-forming galaxies, we show that the equivalent width ratio of the 12.7 and 11.2 mu m PAH bands is independent on the optical depth (tau), with small dispersion (similar to 5 percent) indicative of a nearly constant intrinsic flux ratio R-int = (f(12.7)/f(11.2))(int) = 0.377 +/- 0.020. Conversely, the observed flux ratio, R-obs = (f(12.7)/f(11.2))(obs), strongly correlates with the silicate strength (S-sil) confirming that differences in R-obs reflect variation in tau. The relation between R-obs and S-sil reproduces predictions for the Galactic Centre extinction law but disagrees with other laws. We calibrate the total extinction affecting the 11.2 mu m PAH from R-obs, which we apply to another sample of 215 galaxies with accurate measurements of the total infrared luminosity (L-IR) to investigate the impact of extinction on L-11.2/L-IR. Correlation between L-11.2/L-IR and R-obs independently on L-IR suggests that increased extinction explains the well-known decrease in the average L-11.2/L-IR at high L-IR. The extinction-corrected L-11.2 is proportional to L-IR in the range L-IR = 10(9)-10(13) L-circle dot. These results consolidate L-11.2 as a robust tracer of star formation in galaxies.
