NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2018-07-21 T06:30:35 PDT
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For refcode 2015A&A...577A.135C:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2015A&A...577A.135C The resolved star-formation relation in nearby active galactic nuclei Casasola, Viviana; Hunt, Leslie; Combes, Francoise; Garcia-Burillo, Santiago Abstract. Aims: We present an analysis of the relation between the star formation rate (SFR) surface density (Sigma_SFR_) and mass surface density of molecular gas (Sigma_H_2_), 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 ^12^CO emission lines used to trace Sigma_H_2_, and tests its validity in the high-density central regions of spiral galaxies. Methods: We used interferometric IRAM ^12^CO(1-0) and ^12^CO(2-1) and SMA ^12^CO(3-2) emission line maps to derive Sigma_H_2_ and HST-Halpha images to estimate Sigma_SFR_. 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 - ^12^CO(1-0),^12^CO(2-1), or ^12^CO(3-2) - is used to derive Sigma_H_2_. 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 Sigma_H_2_ and Sigma_SFR_ found between 10 and 100 M_sun_ pc^-2^ is valid even at high densities, ~10^3^ M_sun_ pc^-2^. However, by adopting a common CO-to-H_2_ conversion factor ({alpha}_CO_), the central regions of the NUGA galaxies have higher Sigma_SFR_ 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 {alpha}_CO_. The maps are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A135 Key words: galaxies: ISM, galaxies: spiral, galaxies: active, ISM: molecules, stars: formation
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