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http://hdl.handle.net/20.500.12386/23765
Title: | The resolved star-formation relation in nearby active galactic nuclei | Authors: | CASASOLA, VIVIANA HUNT, Leslie Kipp Combes, Françoise García-Burillo, Santiago |
Issue Date: | 2015 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 577 | First Page: | A135 | Abstract: | <BR /> Aims: We present an analysis of the relation between the star formation rate (SFR) surface density (Σ<SUB>SFR</SUB>) and mass surface density of molecular gas (Σ<SUB>H<SUB>2</SUB></SUB>), commonly referred to as the Kennicutt-Schmidt (K-S) relation, on its intrinsic spatial scale, i.e. the size of giant molecular clouds (~10-150 pc), in the central, high-density regions of four nearby low-luminosity active galactic nuclei (AGN). These are AGN extracted from the NUclei of GAlaxies (NUGA) survey. This study investigates the correlations and slopes of the K-S relation, as a function of spatial resolution and of the different <SUP>12</SUP>CO emission lines used to trace Σ<SUB>H<SUB>2</SUB></SUB>, and tests its validity in the high-density central regions of spiral galaxies. <BR /> Methods: We used interferometric IRAM <SUP>12</SUP>CO(1-0) and <SUP>12</SUP>CO(2-1) and SMA <SUP>12</SUP>CO(3-2) emission line maps to derive Σ<SUB>H<SUB>2</SUB></SUB> and HST-Hα images to estimate Σ<SUB>SFR</SUB>. <BR /> Results: Each galaxy is characterized by a distinct molecular SF relation on spatial scales between 20 to 200 pc. The K-S relations can be sublinear, but also superlinear, with slopes ranging from ~0.5 to ~1.3; slopes are generally superlinear on spatial scales >100 pc and sublinear on smaller scales. Depletion times range from ~1 and 2 Gyr, which is compatible with results for nearby normal galaxies. These findings are valid independently of which transition - <SUP>12</SUP>CO(1-0), <SUP>12</SUP>CO(2-1), or <SUP>12</SUP>CO(3-2) - is used to derive Σ<SUB>H<SUB>2</SUB></SUB>. Because of either star-formation feedback, the lifetime of clouds, turbulent cascade, or magnetic fields, the K-S relation might be expected to degrade on small spatial scales (<100 pc). However, we find no clear evidence of this, even on scales as small as ~20 pc, and this might be because of the higher density of GMCs in galaxy centers that have to resist higher shear forces. The proportionality between Σ<SUB>H<SUB>2</SUB></SUB> and Σ<SUB>SFR</SUB> found between 10 and 100 M<SUB>☉</SUB> pc<SUP>-2</SUP> is valid even at high densities, ~10<SUP>3</SUP> M<SUB>☉</SUB> pc<SUP>-2</SUP>. However, by adopting a common CO-to-H<SUB>2</SUB> conversion factor (α<SUB>CO</SUB>), the central regions of the NUGA galaxies have higher Σ<SUB>SFR</SUB> for a given gas column than those expected from the models, with a behavior that lies between the mergers or high-redshift starburst systems and the more quiescent star-forming galaxies, assuming that the first ones require a lower value of α<SUB>CO</SUB>. <P />The maps are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A135">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A135 | Acknowledgments: | We thank the anonymous referee for useful comments and suggestions that improved the quality of the manuscript. We also thank Daniela Calzetti for precious comments and suggestions. V. Casasola also wishes to thank Laura Magrini and Jacopo Fritz for helpful discussions on star-formation processes. This research made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research also made use of observations with the NASA/ESA Hubble Space Telescope and others obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA). | URI: | http://hdl.handle.net/20.500.12386/23765 | URL: | https://www.aanda.org/articles/aa/abs/2015/05/aa25313-14/aa25313-14.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201425313 | Bibcode ADS: | 2015A&A...577A.135C | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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