| 1. |
- Aalto, Susanne, 1964, et al.
(författare)
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13CO 1-0 imaging of the Medusa merger, NGC 4194. Large scale variations in molecular cloud properties
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 522:5
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Studying molecular gas properties in merging galaxies gives important clues to the onset and evolution of interaction-triggered starbursts. The (CO)-C-12/(CO)-C-13 line intensity ratio can be used as a tracer of how dynamics and star formation processes impact the gas properties. The Medusa merger (NGC 4194) is particularly interesting to study since its L-FIR/L-CO ratio rivals that of ultraluminous galaxies (ULIRGs), despite the comparatively modest luminosity, indicating an exceptionally high star formation efficiency (SFE) in the Medusa merger. Methods. High resolution OVRO (Owens Valley Radio Observatory) observations of the (CO)-C-13 1-0 have been obtained and compared with matched resolution OVRO (CO)-C-12 1-0 data to investigate the molecular gas cloud properties in the Medusa merger. Results. Interferometric observations of (CO)-C-12 and (CO)-C-13 1-0 in the Medusa (NGC 4194) merger show the (CO)-C-12 (CO)-C-13 1-0 intensity ratio (R) increases from normal, quiescent values (7-10) in the outer parts (r > 2 kpc) of the galaxy to high (16 to > 40) values in the central (r
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| 2. |
- Aalto, Susanne, 1964, et al.
(författare)
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A precessing molecular jet signaling an obscured, growing supermassive black hole in NGC 1377?
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590, s. Art. no. A73-
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Tidskriftsartikel (refereegranskat)abstract
- With high resolution (0."25 × 0."18) ALMA CO 3-2 (345 GHz) observations of the nearby (D = 21 Mpc, 1" = 102 pc), extremely radio-quiet galaxy NGC 1377, we have discovered a high-velocity, very collimated nuclear outflow which we interpret as a molecular jet with a projected length of ± 150 pc. The launch region is unresolved and lies inside a radius r 40% of the flux in NGC 1377 and may be a slower, wide-angle molecular outflow which is partially entrained by the molecular jet. We discuss the driving mechanism of the molecular jet and suggest that it is either powered by a (faint) radio jet or by an accretion disk-wind similar to those found towards protostars. It seems unlikely that a massive jet could have been driven out by the current level of nuclear activity which should then have undergone rapid quenching. The light jet would only have expelled 10% of the inner gas and may facilitate nuclear activity instead of suppressing it. The nucleus of NGC 1377 harbours intense embedded activity and we detect emission from vibrationally excited HCN J = 4-3?2 = 1f which is consistent with hot gas and dust. We find large columns of H2 in the centre of NGC 1377 which may be a sign of a high rate of recent gas infall. The dynamical age ofthe molecular jet is short (
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| 3. |
- Aalto, Susanne, 1964, et al.
(författare)
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ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
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Tidskriftsartikel (refereegranskat)abstract
- Submillimetre and millimetre line and continuum observations are important in probing the morphology, column density, and dynamics of the molecular gas and dust around obscured active galactic nuclei (AGNs) and their mechanical feedback. With very high-resolution (0.'' 02x0.'' 03 (2x3 pc)) ALMA 345 GHz observations of CO 3-2, HCO+ 4-3, vibrationally excited HCN 4-3 nu (2)=1f, and continuum we have studied the remarkable, extremely radio-quiet, molecular jet and wind of the lenticular galaxy NGC 1377. The outflow structure is resolved, revealing a 150 pc long, clumpy, high-velocity (similar to 600 km s(-1)), collimated molecular jet where the molecular emission is emerging from the spine of the jet with an average diameter of 3-7 pc. The jet widens to 10-15 pc about 25 pc from the centre, which is possibly due to jet-wind interactions. A narrow-angle (50 degrees -70 degrees), misaligned and rotating molecular wind surrounds the jet, and both are enveloped by a larger-scale CO-emitting structure at near-systemic velocity. The jet and narrow wind have steep radial gas excitation gradients and appear turbulent with high gas dispersion (sigma> 40 km s(-1)). The jet shows velocity reversals that we propose are caused by precession, or more episodic directional changes. We discuss the mechanisms powering the outflow, and we find that an important process for the molecular jet and narrow wind is likely magneto-centrifugal driving. In contrast, the large-scale CO-envelope may be a slow wind, or cocoon that stems from jet-wind interactions. An asymmetric, nuclear r similar to 2 pc dust structure with a high inferred molecular column density N(H-2) similar or equal to 1.8x10(24) cm(-2) is detected in continuum and also shows compact emission from vibrationally excited HCN. The nuclear dust emission is hot (T-d> 180 K) and its luminosity is likely powered by a buried AGN. The lopsided structure appears to be a warped disk, which is responsible for a significant part of the nuclear obscuration and possibly formed as a result of uneven gas inflows. The dynamical mass inside r=1.4 pc is estimated to 9(-3)(+2) x 10(6)M(circle dot) 9 - 3 + 2 x 10 6 M circle dot , implying that the supermassive black hole (SMBH) has a high mass with respect to the stellar velocity dispersion of NGC 1377. We suggest that the SMBH of NGC 1377 is currently in a state of moderate growth, at the end of a more intense phase of accretion and also evolving from a state of more extreme nuclear obscuration. The nuclear growth may be fuelled by low-angular momentum gas inflowing from the gas ejected in the molecular jet and wind. Such a feedback-loop of cyclic outflows and central accretion could explain why there is still a significant reservoir of molecular gas in this ageing, lenticular galaxy. A feedback-loop would be an effective process in growing the nuclear SMBH and thus would constitute an important phase in the evolution of NGC 1377. This also invites new questions as to SMBH growth processes in obscured, dusty galaxies.
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| 4. |
- Aalto, Susanne, 1964
(författare)
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Chemistry in luminous AGN and starburst galaxies
- 2008
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Ingår i: Astrophysics and Space Science. - : Springer Science and Business Media LLC. - 1572-946X .- 0004-640X. ; 313:1-3, s. 273-278
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Tidskriftsartikel (refereegranskat)abstract
- Molecular line emission is a useful tool for probing the highly obscured inner kpc of starburst galaxies and buried AGNs. Molecular line ratios serve as diagnostic tools of the physical conditions of the gas-but also of its chemical properties. Both provide important clues to the type and evolutionary stage of the nuclear activity. While CO emission remains the main tracer for molecular distribution and dynamics, molecules such as HCN, HNC, HCO+, CN and HC3N are useful for probing the properties of the denser (n greater than or similar to 10(4) cm(-3)), star-forming gas. Here I discuss current views on how line emission from these species can be interpreted in luminous galaxies. HNC, HCO+ and CN are all species that can be associated both with photon dominated regions (PDRs) in starbursts-as well as X-ray dominated regions (XDRs) associated with AGN activity. HC3N line emission may identify galaxies where the starburst is in the early stage of its evolution.
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| 5. |
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| 6. |
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| 7. |
- Aalto, Susanne, 1964, et al.
(författare)
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Detection of HCN, HCO+, and HNC in the Mrk 231 molecular outflow. Dense molecular gas in the AGN wind
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 537, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- We obtained high-resolution (1.''55 × 1.''28) observations of HCN, HCO+, HNC 1-0 and HC3N 10-9 of the ultraluminous galaxy (ULIRG) Mrk 231 with the IRAM Plateau de Bure Interferometer.Results: We detect luminous emission from HCN, HCO+ and HNC 1-0 in the QSO ULIRG Mrk 231. All three lines show broad line wings - which are particularly prominent for HCN. Velocities are found to be similar ( ≈ ± 750 km s-1) to those found for CO 1-0. This is the first time bright HCN, HCO+ and HNC emission has been detected in a large-scale galactic outflow. We find that both the blue- and red-shifted line wings are spatially extended by at least 0.''75 (>700 pc) in a north-south direction. The line wings are brighter (relative to the line center intensity) in HCN than in CO 1-0 and line ratios suggest that the molecular outflow consists of dense (n > 104 cm-3) and clumpy gas with a high HCN abundance X(HCN) > 10-8. These properties are consistent with the molecular gas being compressed and fragmented by shocks in the outflow. Alternatively, HCN is instead pumped by mid-IR continuum, but we propose that this effect is not strong for the spatially extended outflowing gas. In addition, we find that the rotation of the main disk, in east-west direction, is also evident in the HCN, HCO+ and HNC line emission. An unexpectedly bright HC3N 10-9 line is detected inside the central 400 pc of Mrk 231. This HC3N emission may emerge from a shielded, dust-enshrouded region within the inner 40-50 pc where the gas is heated to high temperatures (200-300 K) by the AGN.
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| 8. |
- Aalto, Susanne, 1964, et al.
(författare)
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H3O+ line emission from starbursts and AGNs
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 527:8
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Tidskriftsartikel (refereegranskat)abstract
- Context. The H3O+ molecule probes the chemistry and the ionization rate of dense circumnuclear gas in galaxies. Aims. We use the H3O+ molecule to investigate the impact of starburst and AGN activity on the chemistry of the molecular interstellar medium. Methods. Using the JCMT, we have observed the 3(2)(+)-2(2)(-) 364 GHz line of p-H3O+ towards the centres of seven active galaxies. Results. We have detected p-H3O+ towards IC 342, NGC 253, NGC 1068, NGC 4418, and NGC 6240. Upper limits were obtained for IRAS 15250 and Arp 299. We find large H3O+ abundances (N(H3O+)/N(H-2) greater than or similar to 10(-8)) in all detected galaxies apart from in IC 342 where it is about one order of magnitude lower. We note, however, that uncertainties in N(H3O+) may be significant due to lack of definite information on source size and excitation. We furthermore compare the derived N(H3O+) with N(HCO+) and find that the H3O+ to HCO+ column density ratio is large in NGC 1068 ( 24), moderate in NGC 4418 and NGC 253 ( 4-5), slightly less than unity in NGC 6240 ( 0.7) and lowest in IC 342 ( 0.2-0.6). We compare our results with models of X-ray and photon dominated regions ( XDRs and PDRs). Conclusions. For IC 342 we find that a starburst PDR chemistry can explain the observed H3O+ abundance. For the other galaxies, the large H3O+ columns are generally consistent with XDR models. In particular for NGC 1068 the elevated N(H3O+)/N(HCO+) ratio suggests a low column density XDR. For NGC 4418 however, large HC3N abundances are inconsistent with the XDR interpretation. An alternative possibility is that H3O+ forms through H2O evaporating off dust grains and reacting with HCO+ in warm, dense gas. This scenario could also potentially fit the results for NGC 253. Further studies of the excitation and distribution of H3O+-aswell as Herschel observations of water abundances - will help to further constrain the models.
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| 9. |
- Aalto, Susanne, 1964, et al.
(författare)
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High-resolution HNC 3-2 SMA observations of Arp 220
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 493:2, s. 481-487
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We study the properties of the nuclear molecular gas of the ultra luminous merger Arp 220 and effects of the nuclear source on gas excitation and chemistry. Specifically, our aim is to investigate the spatial location of the luminous HNC 3-2 line emission and address the underlying cause of its unusual brightness.Methods. We present high resolution observations of HNC J=3-2 with the submillimeter array (SMA).Results. We find luminous HNC 3-2 line emission in the western part of Arp 220, centred on the western nucleus, while the eastern side of the merger shows relatively faint emission. A bright (36 K at $0\hbox{$.\!\!^{\prime\prime}$ }4$ resolution), narrow (60 ${\rm km~s}^$) emission feature emerges from the western nucleus, superposed on a broader spectral component. A possible explanation is weak maser emission through line-of-sight amplification of the background continuum source. There is also a more extended HNC 3-2 emission feature north and south of the nucleus. This feature resembles the bipolar OH maser morphology around the western nucleus. Substantial HNC abundances are required to explain the bright line emission from this warm environment - even when the high gas column density towards the western nucleus is taken into account. We discuss this briefly in the context of an X-ray affected chemistry and radiative excitation.Conclusions. The luminous and possibly amplified HNC emission of the western nucleus of the Arp 220 merger reflects the unusual, and perhaps transient environment of the starburst/AGN activity there. The faint HNC line emission towards Arp 220-east reveals a real difference in physical conditions between the two merger nuclei.
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| 10. |
- Aalto, Susanne, 1964, et al.
(författare)
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High resolution observations of HCN and HCO+J = 3–2 in the disk and outflow of Mrk 231 -- Detection of vibrationally excited HCN in the warped nucleus
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 574, s. 85-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Our goal is to study molecular gas properties in nuclei and large scale outflows/winds from active galactic nuclei (AGNs) and starburst galaxies.Methods. We obtained high resolution (0.̋25 to 0.̋90) observations of HCN and HCO+J = 3 → 2 of the ultraluminous QSO galaxy Mrk 231 with the IRAM Plateau de Bure Interferometer (PdBI).Results. We find luminous HCN and HCO+J = 3 → 2 emission in the main disk and we detect compact (r ≲ 0''̣1 (90 pc)) vibrationally excited HCN J = 3 → 2ν2 = 1f emission centred on the nucleus. The velocity field of the vibrationally excited HCN is strongly inclined (position angle PA = 155°) compared to the east-west rotation of the main disk. The nuclear (r ≲ 0.̋1) molecular mass is estimated to 8 × 108 M⊙ with an average N(H2) of 1.2 × 1024 cm-2. Prominent, spatially extended (≳350 pc) line wings are found for HCN J = 3 → 2 with velocities up to ± 750 km s-1. Line ratios indicate that the emission is emerging in dense gas n = 104−5 × 105 cm-3 of elevated HCN abundance X(HCN) = 10-8−10-6. The highest X(HCN) also allows for the emission to originate in gas of more moderate density. We tentatively detect nuclear emission from the reactive ion HOC+ with HCO+/HOC+ = 10−20.Conclusions. The HCN ν2 = 1f line emission is consistent with the notion of a hot, dusty, warped inner disk of Mrk 231 where the ν2 = 1f line is excited by bright mid-IR 14 μm continuum. We estimate the vibrational temperature Tvib to 200−400 K. Based on relative source sizes we propose that 50% of the main HCN emission may have its excitation affected by the radiation field through IR pumping of the vibrational ground state. The HCN emission in the line wings, however, is more extended and thus likely not strongly affected by IR pumping. Our results reveal that dense clouds survive (and/or are formed) in the AGN outflow on scales of at least several hundred pc before evaporating or collapsing. The elevated HCN abundance in the outflow is consistent with warm chemistry possibly related to shocks and/or X-ray irradiated gas. An upper limit to the mass and momentum flux is 4 × 108 M⊙ and 12LAGN/c, respectively, and we discuss possible driving mechanisms for the dense outflow.
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