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  • Adamo, A., et al. (författare)
  • Star cluster formation in the most extreme environments: Insights from the HiPEEC survey
  • 2020
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 499:3, s. 3267-3294
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey. We fit HST NUV to NIR broad-band and H α fluxes to derive star cluster ages, masses, and extinctions and determine the star formation rate (SFR) of six merging galaxies. These systems are excellent laboratories to trace cluster formation under extreme gas physical conditions, rare in the local Universe, but typical for star-forming galaxies at cosmic noon. We detect clusters with ages of 1-500 Myr and masses that exceed 107 M☉. The recent cluster formation history and their distribution within the host galaxies suggest that systems such as NGC 34, NGC 1614, and NGC 4194 are close to their final coalescing phase, while NGC 3256, NGC 3690, and NGC 6052 are at an earlier/intermediate stage. A Bayesian analysis of the cluster mass function in the age interval 1-100 Myr provides strong evidence in four of the six galaxies that an exponentially truncated power law better describes the observed mass distributions. For two galaxies, the fits are inconclusive due to low number statistics. We determine power-law slopes β ∼ −1.5 to −2.0 and truncation masses, Mc, between 106 and a few times 107 M☉, among the highest values reported in the literature. Advanced mergers have higher Mc than early/intermediate merger stage galaxies, suggesting rapid changes in the dense gas conditions during the merger. We compare the total stellar mass in clusters to the SFR of the galaxy, finding that these systems are among the most efficient environments to form star clusters in the local Universe.
  • König, Sabine, 1983, et al. (författare)
  • Major impact from a minor merger The extraordinary hot molecular gas flow in the Eye of the NGC 4194 Medusa galaxy
  • 2018
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 615
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on the growth of supermassive black holes and star formation is profound - about half of the star formation activity in the local Universe is the result of minor mergers. Aims. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales - from whole galaxies to giant molecular clouds in their molecular gas-rich centers. Methods. We use observations of HCN and HCO+ 1-0 with NOEMA and of CO 3-2 with the SMA to study the properties of the dense molecular gas in the Medusa merger (NGC 4194) at 1" resolution. In particular, we compare the distribution of these dense gas tracers with CO 2-1 high-resolution maps in the Medusa merger. To characterize gas properties, we calculate the brightness temperature ratios between the three tracers and use them in conjunction with a non-local thermodynamic equilibrium (non-LTE) radiative line transfer model. Results. The gas represented by HCN and HCO+ 1-0, and CO 3-2 does not occupy the same structures as the less dense gas associated with the lower-J CO emission. Interestingly, the only emission from dense gas is detected in a 200 pc region within the "Eye of the Medusa", an asymmetric 500 pc off-nuclear concentration of molecular gas. Surprisingly, no HCN or HCO(+ )is detected for the extended starburst of the Medusa merger. Additionally, there are only small amounts of HCN or HCO+ associated with the active galactic nucleus. The CO 3-2/2-1 brightness temperature ratio inside "the Eye" is similar to 2.5 - the highest ratio found so far - implying optically thin CO emission. The CO 2-1/HCN 1-0 (similar to 9.8) and CO 2-1/HCO+ 1-0 (similar to 7.9) ratios show that the dense gas filling factor must be relatively high in the central region, consistent with the elevated CO 3-1/2-1 ratio. Conclusions. The line ratios reveal an extreme, fragmented molecular cloud population inside the Eye with large bulk temperatures (T > 300 K) and high gas densities (n(H-2) >10(4) cm(-3) ). This is very different from the cool, self-gravitating structures of giant molecular clouds normally found in the disks of galaxies. The Eye of the Medusa is found at an interface between a large-scale minor axis inflow and the central region of the Medusa. Hence, the extreme conditions inside the Eye may be the result of the radiative and mechanical feedback from a deeply embedded, young and massive super star cluster formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas entering the central region of the Medusa may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form new stars. Thus, caution is advised in taking the detection of emission from dense gas tracers as evidence of ongoing or imminent star formation.
  • Aalto, Susanne, 1964, et al. (författare)
  • 13CO 1-0 imaging of the Medusa merger, NGC 4194. Large scale variations in molecular cloud properties
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 522:5
  • 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
  • Aalto, Susanne, 1964, et al. (författare)
  • A precessing molecular jet signaling an obscured, growing supermassive black hole in NGC 1377?
  • 2016
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 590, s. Art. no. A73-
  • 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 (
  • Aalto, Susanne, 1964, et al. (författare)
  • ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377
  • 2020
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 640
  • 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.
  • Aalto, Susanne, 1964 (författare)
  • Astrochemistry and star formation in nearby galaxies: From galaxy disks to hot nuclei
  • 2016
  • Ingår i: EAS Publications Series. - 1633-4760 .- 1638-1963. ; 75-76, s. 73-80
  • Konferensbidrag (refereegranskat)abstract
    • Studying the molecular phase of the interstellar medium in galaxies is fundamental for the understanding of the onset and evolution of compact and extended star formation, and of the growth of supermassive black holes. Molecular line emission is an excellent tracer of chemical, physical and dynamical conditions in the cold neutral gas. Key molecules in extragalactic studies are e.g. HCN, HCO+, HC3N, SiO, CH3OH, H2O. Furthermore, we can use IR excited molecular emission to probe the very inner regions of luminous infrared galaxies allowing us to get past the optically thick dust barrier of the compact obscured nuclei where lines of CO, HCN and HCO+ in their vibrational ground state (?=0) may be self-absorbed. Finally, molecular outflows and their chemistry are briefly discussed-including new ALMA results on for example the outflow of the lenticular galaxy NGC1377 and a study of the chemistry of the outflow of the quasar Mrk231.
  • Aalto, Susanne, 1964 (författare)
  • Chemistry in luminous AGN and starburst galaxies
  • 2008
  • Ingår i: Proceedings of "Science with the Atacama Large Millimeter Array", eds. R. Bachiller and J. Cernicharo, Madrid, 13-17 Nov 2006, Springer. ; , s. 273-278
  • Konferensbidrag (refereegranskat)
  • Aalto, Susanne, 1964 (författare)
  • Chemistry in luminous AGN and starburst galaxies
  • 2008
  • Ingår i: Astrophysics and Space Science. - 1572-946X .- 0004-640X. ; 313:1-3, s. 273-278
  • 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.
  • Aalto, Susanne, 1964 (författare)
  • Chemistry in the Dense Molecular Gas of Starburst Galaxies and AGNs
  • 2006
  • Ingår i: In "Astrochemistry: Throughout the Universe: Recent Successes and current Challenges". Proc. of 31st Symp. of the IAU, Pacific Grove, California, Sept. 2005, eds. D.C. Lis, G.A. Blake, E. Herbst, Cambridge University Press. ; , s. 261-270
  • Konferensbidrag (refereegranskat)
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