Oral Presentation
Spatially resolved ISM properties and AGN-galaxy decomposition of HyLIRG at redshift 4.4
Presenter: Takafumi Tsukui (Australian National University)
Star formation rate is usually estimated by assuming that the far infrared (FIR) part of the spectral energy distribution (SED) is dominated by the cold dust heated by the UV photon. However, the contribution of the AGN heated dust to the FIR part of the spectrum is an open question, requiring a thorough investigation with spatially resolved data. We report the spatially resolved dust properties of the quasar host galaxy BRI 1335-0417 at redshift z = 4.4, constrained by the observations of the Atacama Large Millimeter/submillimeter Array. The dust temperature map, derived by fitting two continuum images at rest-frame 90μm and 161μm at each pixel with a single greybody, shows a steep increase towards the centre, reaching 57.1 ± 0.3 K. The image decomposition analysis reveals a point source in both dust continuum images at the same position as the highest temperature peak. We assume that the point source flux is attributed to the warm dust heated by an active galactic nucleus (AGN) and the rest of the extended flux to the cold dust component. Based on this interpretation, we find that these two components better describe the global SED (including other ancillary photometric data points) over a single component resulting in dust temperatures of ~96 K (warm component) and ~29 K (cold component). The star formation rate estimated from the cold dust component is 1500±300 Msun/yr — a factor of three less than the previously estimated value of 5040 ± 1300 Msun/yr due to the high AGN fraction in the FIR luminosity(~63%). The unresolved warm dust component can explain the steep temperature gradient, as the temperature profile derived after the point source subtraction from the images becomes flat. The estimated central SFR surface density ΣSFR is also lowered by over a factor of three after the subtraction, placing the spatially resolved measurements of ΣSFR and the surface molecular gas mass density Σgas in a roughly linear sequence in the Kennicutt-Schmidt diagram (Σgas-ΣSFR) with a gas depletion time of 50-200Myr.
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