Cold molecular gas and PAH emission in the nuclear and circumnuclear regions of Seyfert galaxies
Cold molecular gas and PAH emission in the nuclear and circumnuclear regions of Seyfert galaxies
We investigate the relation between the detection of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature in the nuclear (∼24-230 pc) regions of 22 nearby Seyfert galaxies and the properties of the cold molecular gas. For the former we use ground-based (0.3-0.6″ resolution) mid-infrared (mid-IR) spectroscopy. The cold molecular gas is traced by ALMA and NOEMA high (0.2-1.1″) angular resolution observations of the CO(2-1) transition. Galaxies with a nuclear detection of the 11.3 μm PAH feature contain more cold molecular gas (median 1.6 × 107 MO ) and have higher column densities (N(H2) = 2 × 1023 cm-2) over the regions sampled by the mid-IR slits than those without a detection. This suggests that molecular gas plays a role in shielding the PAH molecules in the harsh environments of Seyfert nuclei. Choosing the PAH molecule naphthalene as an illustration, we compute its half-life in the nuclear regions of our sample when exposed to 2.5 keV hard X-ray photons. We estimate shorter half-lives for naphthalene in nuclei without a 11.3 μm PAH detection than in those with a detection. The Spitzer/IRS PAH ratios on circumnuclear scales (∼4″ ∼ 0.25-1.3 kpc) are in between model predictions for neutral and partly ionized PAHs. However, Seyfert galaxies in our sample with the highest nuclear H2 column densities are not generally closer to the neutral PAH tracks. This is because in the majority of our sample galaxies, the CO(2-1) emission in the inner ∼4″ is not centrally peaked and in some galaxies traces circumnuclear sites of strong star formation activity. Spatially resolved observations with the MIRI medium-resolution spectrograph on the James Webb Space Telescope will be able to distinguish the effects of an active galactic nucleus (AGN) and star formation on the PAH emission in nearby AGN.
Galaxies: ISM, Galaxies: Seyfert, Galaxies: nuclei, Radio lines: galaxies
Alonso-Herrero, A.
ae11bfb3-7ba7-43a3-a071-8fac055b6f62
Pereira-Santaella, M.
273d2fb4-ea55-4bd1-9031-37bf7a2cda75
Rigopoulou, D.
0abdde70-e513-47fa-8bf3-595203aa6a6a
Garcia-Bernete, I.
8ec1dc74-5706-41fe-bb4e-06638981842d
Dominguez-Fernandez, A.J.
372f7bd2-25a0-4f43-a463-9d6efccf7080
Combes, F.
f579a8bb-a74b-41fd-b046-d6084e59ee4a
Davies, R.I.
36b948e2-f8af-4a85-868a-c61e68c91c7d
Diaz-Santos, T.
3bba8f94-f3b2-494f-acd1-3f16ca1e7f14
Esparza-Arrendondo, D.
f9459089-a253-4442-b28b-3f94b0694f10
Gonzalez-Martin, O.
dc84a0b8-4350-4053-b1d5-5d2d75142b61
Hernan-Caballero, A.
1a5c091c-a1a7-4d93-abc1-491a5fde08a1
Hicks, E.K.S.
fd8dcd79-878b-45f9-bc29-ba28dc1ad846
Hoenig, S.F.
be0bb8bc-bdac-4442-8edc-f735834f3917
Levenson, N.A.
918ae4cf-bab1-4658-aef3-3d9587ee5bba
Ramos Almeida, C.
5de8e01a-be52-4502-864b-f47ea0d6473c
Roche, P.F.
5958aab9-9a2e-4fe3-a5b6-1769f32260a6
Rosario, D.
3e714b97-1e01-4691-813a-e0f7e510d9de
7 July 2020
Alonso-Herrero, A.
ae11bfb3-7ba7-43a3-a071-8fac055b6f62
Pereira-Santaella, M.
273d2fb4-ea55-4bd1-9031-37bf7a2cda75
Rigopoulou, D.
0abdde70-e513-47fa-8bf3-595203aa6a6a
Garcia-Bernete, I.
8ec1dc74-5706-41fe-bb4e-06638981842d
Dominguez-Fernandez, A.J.
372f7bd2-25a0-4f43-a463-9d6efccf7080
Combes, F.
f579a8bb-a74b-41fd-b046-d6084e59ee4a
Davies, R.I.
36b948e2-f8af-4a85-868a-c61e68c91c7d
Diaz-Santos, T.
3bba8f94-f3b2-494f-acd1-3f16ca1e7f14
Esparza-Arrendondo, D.
f9459089-a253-4442-b28b-3f94b0694f10
Gonzalez-Martin, O.
dc84a0b8-4350-4053-b1d5-5d2d75142b61
Hernan-Caballero, A.
1a5c091c-a1a7-4d93-abc1-491a5fde08a1
Hicks, E.K.S.
fd8dcd79-878b-45f9-bc29-ba28dc1ad846
Hoenig, S.F.
be0bb8bc-bdac-4442-8edc-f735834f3917
Levenson, N.A.
918ae4cf-bab1-4658-aef3-3d9587ee5bba
Ramos Almeida, C.
5de8e01a-be52-4502-864b-f47ea0d6473c
Roche, P.F.
5958aab9-9a2e-4fe3-a5b6-1769f32260a6
Rosario, D.
3e714b97-1e01-4691-813a-e0f7e510d9de
Alonso-Herrero, A., Pereira-Santaella, M., Rigopoulou, D., Garcia-Bernete, I., Dominguez-Fernandez, A.J., Combes, F., Davies, R.I., Diaz-Santos, T., Esparza-Arrendondo, D., Gonzalez-Martin, O., Hernan-Caballero, A., Hicks, E.K.S., Hoenig, S.F., Levenson, N.A., Ramos Almeida, C., Roche, P.F. and Rosario, D.
(2020)
Cold molecular gas and PAH emission in the nuclear and circumnuclear regions of Seyfert galaxies.
Astronomy & Astrophysics, 639, [A43].
(doi:10.1051/0004-6361/202037642).
Abstract
We investigate the relation between the detection of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature in the nuclear (∼24-230 pc) regions of 22 nearby Seyfert galaxies and the properties of the cold molecular gas. For the former we use ground-based (0.3-0.6″ resolution) mid-infrared (mid-IR) spectroscopy. The cold molecular gas is traced by ALMA and NOEMA high (0.2-1.1″) angular resolution observations of the CO(2-1) transition. Galaxies with a nuclear detection of the 11.3 μm PAH feature contain more cold molecular gas (median 1.6 × 107 MO ) and have higher column densities (N(H2) = 2 × 1023 cm-2) over the regions sampled by the mid-IR slits than those without a detection. This suggests that molecular gas plays a role in shielding the PAH molecules in the harsh environments of Seyfert nuclei. Choosing the PAH molecule naphthalene as an illustration, we compute its half-life in the nuclear regions of our sample when exposed to 2.5 keV hard X-ray photons. We estimate shorter half-lives for naphthalene in nuclei without a 11.3 μm PAH detection than in those with a detection. The Spitzer/IRS PAH ratios on circumnuclear scales (∼4″ ∼ 0.25-1.3 kpc) are in between model predictions for neutral and partly ionized PAHs. However, Seyfert galaxies in our sample with the highest nuclear H2 column densities are not generally closer to the neutral PAH tracks. This is because in the majority of our sample galaxies, the CO(2-1) emission in the inner ∼4″ is not centrally peaked and in some galaxies traces circumnuclear sites of strong star formation activity. Spatially resolved observations with the MIRI medium-resolution spectrograph on the James Webb Space Telescope will be able to distinguish the effects of an active galactic nucleus (AGN) and star formation on the PAH emission in nearby AGN.
Text
2005.11959
- Accepted Manuscript
More information
Accepted/In Press date: 5 May 2020
e-pub ahead of print date: 7 July 2020
Published date: 7 July 2020
Keywords:
Galaxies: ISM, Galaxies: Seyfert, Galaxies: nuclei, Radio lines: galaxies
Identifiers
Local EPrints ID: 442458
URI: http://eprints.soton.ac.uk/id/eprint/442458
ISSN: 0004-6361
PURE UUID: a2337839-cf90-4f86-8602-c830f554cb01
Catalogue record
Date deposited: 15 Jul 2020 16:32
Last modified: 16 Mar 2024 08:36
Export record
Altmetrics
Contributors
Author:
A. Alonso-Herrero
Author:
M. Pereira-Santaella
Author:
D. Rigopoulou
Author:
I. Garcia-Bernete
Author:
A.J. Dominguez-Fernandez
Author:
F. Combes
Author:
R.I. Davies
Author:
T. Diaz-Santos
Author:
D. Esparza-Arrendondo
Author:
O. Gonzalez-Martin
Author:
A. Hernan-Caballero
Author:
E.K.S. Hicks
Author:
N.A. Levenson
Author:
C. Ramos Almeida
Author:
P.F. Roche
Author:
D. Rosario
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics