Cold molecular gas and PAH emission in the nuclear and circumnuclear regions of Seyfert galaxies

Alonso‐Herrero, A.; Pereira-Santaella, M.; Rigopoulou, D.; García-Bernete, I.; García‐Burillo, S.; Domínguez-Fernández, A. J.; Combes, F.; Davies, R. I.; Díaz-Santos, T.; Esparza-Arredondo, Donají; González‐Martín, O.; Hernán-Caballero, A.; Hicks, E. K. S.; Hönig, S. F.; Levenson, N. A.; Almeida, C. Ramos; Roche, P. F.; Rosario, D. J.

doi:10.1051/0004-6361/202037642

Cited by 30 publications

(17 citation statements)

References 110 publications

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“…The nuclear molecular gas surface density is very high: Σ H 2 = 10 4.4 M pc −2 . It is comparable to the Σ H 2 observed in more extreme ULIRGs (e.g., Wilson et al 2019), about 200 times higher than the values observed in nearby disk galaxies (e.g., Bigiel et al 2011), and ∼10 times higher than in local Seyfert galaxies (e.g., Alonso-Herrero et al 2020). Therefore, this object allows us to carry out a detailed study of the properties of outflows produced in compact and obscured nuclear regions similar to those of more distant starburst-dominated ULIRGs.…”

Section: Introductionsupporting

confidence: 66%

Excitation and acceleration of molecular outflows in LIRGs: The extended ESO 320-G030 outflow on 200-pc scales

Pereira-Santaella

Colina

García‐Burillo

et al. 2020

A&A

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We used high-spatial resolution (70 pc; 0$ {{\overset{\prime\prime}{.}}} $3) 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.

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Section: Introductionsupporting

confidence: 66%

Excitation and acceleration of molecular outflows in LIRGs: The extended ESO 320-G030 outflow on 200-pc scales

Pereira-Santaella

Colina

García‐Burillo

et al. 2020

A&A

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“…This is in agreement with experimental (Monfredini et al 2019; Quitián‐Lara et al 2018) and observational works (Lambrides et al 2019; Minsley et al 2020). This is also consistent with Alonso‐Herrero et al (2020), who points out that PAH molecules are being shielded from AGN radiation by the large content of molecular cold gas.…”

Section: Resultssupporting

confidence: 91%

Starbursts versus active galactic nuclei: Studying astrochemistry of dusty galaxies

Martins-Franco

Menéndez‐Delmestre

2021

Astron Nachr

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Infrared luminous galaxies are rare locally but dominate the star formation activity at z ≥ 1. The study of these objects is difficult at optical wavelengths especially on account of the abundant dust. At the smallest scales, dust becomes micron-sized molecules known as PAHs that are excited by UV photons and whose emission can be used to reveal physical properties of obscured regions that otherwise remain invisible to our instruments. We can thus use infrared spectroscopy to classify the emission in these systems as arising from star formation activity or active galactic nuclei (AGN). In this work, we go further than this and undertake an astrochemical analysis of the ISM by probing the PAH population. Based on Spitzer/IRS mid-infrared spectra of ∼700 dusty galaxies from the GOALS and ATLAS surveys, we analyze the PAH population in terms of size, charge, and composition using the NASA Ames PAH Database, a large theoretical spectroscopic library of PAH molecules. We find that the PAH population in these galaxies is dominated by small and neutral molecules, with very little diversity in composition, beyond Carbon and Hydrogen. These results are consistent with theoretical models of PAH emission for star-forming galaxies. We also see a weak trend of an increased proportion of charged PAHs in galaxies with a more pronounced AGN contribution, suggesting that the radiation field of the power source may ultimately affect the ISM astrochemistry. Although our results point to AGN being capable of altering PAHs molecules, PAH features are still significant in AGN regions, suggesting that the AGN does not destroy them. This is in agreement with recent laboratory works pointing and motivating further use of PAH molecules to probe for the radiation field in these dusty, extreme environments.

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“…Concerning the strength of the AGN, we find that AGNdominated systems are generally located in the leftmost corner of the grid or even outside of the range of the grid (with measured 6.2/7.7 PAH ratios smaller than 0.25; see Fig. 11 and also Alonso-Herrero et al 2020). The fact that a fraction of AGN-dominated systems lies beyond the values predicted by the current grid suggests that perhaps larger PAH molecules (N c >400), are required to reproduce their PAH ratio values.…”

Section: Pah Diagnostic Diagramsmentioning

confidence: 79%

“…We note that the Spitzer/IRS spectra of the majority of the galaxies in this sample have been previously studied (e.g. Baum et al 2010;Gallimore et al 2010;LaMassa et al 2010;Lyu & Rieke 2018;Alonso-Herrero et al 2020) by using the same method to extract the PAH feature strengths.…”

Section: Mir Modellingmentioning

confidence: 99%

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Polycyclic aromatic hydrocarbons in Seyfert and star-forming galaxies

García-Bernete

Rigopoulou

Alonso‐Herrero

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules resulting from the union of aromatic rings and related species, which are likely responsible for strong infrared emission features. In this work, using a sample of 50 Seyfert galaxies (DL < 100 Mpc) we compare the circumnuclear (inner kpc) PAH emission of AGN to that of a control sample of star-forming galaxies (22 luminous infrared galaxies and 30 H ii galaxies), and investigate the differences between central and extended PAH emission. Using Spitzer/InfraRed Spectrograph spectral data of Seyfert and star-forming galaxies and newly developed PAH diagnostic model grids, derived from theoretical spectra, we compare the predicted and observed PAH ratios. We find that star-forming galaxies and AGN-dominated systems are located in different regions of the PAH diagnostic diagrams. This suggests that not only are the size and charge of the PAH molecules different, but also the nature and hardness of the radiation field that excite them. We find tentative evidence that PAH ratios in AGN-dominated systems are consistent with emission from larger PAH molecules (Nc > 300–400) as well as neutral species. By subtracting the spectrum of the central source from the total, we compare the PAH emission in the central versus extended region of a small sample of AGN. In contrast to the findings for the central regions of AGN-dominated systems, the PAH ratios measured in the extended regions of both type 1 and type 2 Seyfert galaxies can be explained assuming similar PAH molecular size distribution and ionized fractions of molecules to those seen in central regions of star-forming galaxies (100 < Nc < 300).

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Cold molecular gas and PAH emission in the nuclear and circumnuclear regions of Seyfert galaxies

Cited by 30 publications

References 110 publications

Excitation and acceleration of molecular outflows in LIRGs: The extended ESO 320-G030 outflow on 200-pc scales

Excitation and acceleration of molecular outflows in LIRGs: The extended ESO 320-G030 outflow on 200-pc scales

Starbursts versus active galactic nuclei: Studying astrochemistry of dusty galaxies

Polycyclic aromatic hydrocarbons in Seyfert and star-forming galaxies

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