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تسجيل مستخدم جديدALMA resolves extended star formation in high-z AGN host galaxies
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We present high resolution (0.3) Atacama Large Millimeter Array (ALMA) 870um imaging of five z~1.5-4.5 X-ray detected AGN with luminosities of L(2-8keV)>10^42 erg/s. These data provide a >~20x improvement in spatial resolution over single-dish rest-frame FIR measurements. The sub-millimetre emission is extended on scales of FWHM~0.2-0.5, corresponding to physical sizes of 1-3 kpc (median value of 1.8 kpc). These sizes are comparable to the majority of z=1-5 sub-millimetre galaxies (SMGs) with equivalent ALMA measurements. In combination with spectral energy distribution analyses, we attribute this rest-frame far-infrared (FIR) emission to dust heated by star formation. The implied star-formation rate surface densities are ~20-200 Mo/yr/kpc^2, which are consistent with SMGs of comparable FIR luminosities (i.e., L(IR)~[1-5]x10^(12)Lo). Although limited by a small sample of AGN, which all have high FIR luminosities, our study suggests that the kpc-scale spatial distribution and surface density of star formation in high-redshift star-forming galaxies is the same irrespective of the presence of X-ray detected AGN.
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We investigate the location of an ultra-hard X-ray selected sample of AGN from the Swift Burst Alert Telescope (BAT) catalog with respect to the main sequence (MS) of star-forming galaxies using Herschel-based measurements of the star formation rate
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HSC) survey. The [CII] line and FIR continuum luminosities lie in the ranges $L_{rm [CII]} = (3.8-10.2) times 10^8~L_odot$ and $L_{rm FIR} = (1.2-2.0) times 10^{11}~L_odot$, which are at least one order of magnitude smaller than those of optically-luminous quasars at $z gtrsim 6$. We estimate the star formation rates (SFR) of our targets as $simeq 23-40~M_odot ~{rm yr}^{-1}$. Their line and continuum-emitting regions are marginally resolved, and found to be comparable in size to those of optically luminous quasars, indicating that their SFR or likely gas mass surface densities (key controlling parameter of mass accretion) are accordingly different. The $L_{rm [CII]}/L_{rm FIR}$ ratios of the hosts, $simeq (2.2-8.7) times 10^{-3}$, are fully consistent with local star-forming galaxies. Using the [CII] dynamics, we derived their dynamical masses within a radius of 1.5-2.5 kpc as $simeq (1.4-8.2) times 10^{10}~M_odot$. By interpreting these masses as stellar ones, we suggest that these faint quasar hosts are on or even below the star-forming main sequence at $z sim 6$, i.e., they appear to be transforming into quiescent galaxies. This is in contrast to the optically luminous quasars at those redshifts, which show starburst-like properties. Finally, we find that the ratios of black hole mass to host galaxy dynamical mass of the most of low-luminosity quasars including the HSC ones are consistent with the local value. The mass ratios of the HSC quasars can be reproduced by a semi-analytical model that assumes merger-induced black hole-host galaxy evolution.
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