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Register a new userMid-Infrared Galaxy Luminosity Functions from the AGN and Galaxy Evolution Survey
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X. Dai
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We present galaxy luminosity functions at 3.6, 4.5, 5.8, and 8.0 micron measured by combining photometry from the IRAC Shallow Survey with redshifts from the AGN and Galaxy Evolution Survey of the NOAO Deep Wide-Field Survey Bootes field. The well-defined IRAC samples contain 3800-5800 galaxies for the 3.6-8.0 micron bands with spectroscopic redshifts and z < 0.6. We obtained relatively complete luminosity functions in the local redshift bin of z < 0.2 for all four IRAC channels that are well fit by Schechter functions. We found significant evolution in the luminosity functions for all four IRAC channels that can be fit as an evolution in M* with redshift, Delta M* = Qz. While we measured Q=1.2pm0.4 and 1.1pm0.4 in the 3.6 and 4.5 micron bands consistent with the predictions from a passively evolving population, we obtained Q=1.8pm1.1 in the 8.0 micron band consistent with other evolving star formation rate estimates. We compared our LFs with the predictions of semi-analytical galaxy formation and found the best agreement at 3.6 and 4.5 micron, rough agreement at 8.0 micron, and a large mismatch at 5.8 micron. These models also predicted a comparable Q value to our luminosity functions at 8.0 micron, but predicted smaller values at 3.6 and 4.5 micron. We also measured the luminosity functions separately for early and late-type galaxies. While the luminosity functions of late-type galaxies resemble those for the total population, the luminosity functions of early-type galaxies in the 3.6 and 4.5 micron bands indicate deviations from the passive evolution model, especially from the measured flat luminosity density evolution. Combining our estimates with other measurements in the literature, we found (53pm18)% of the present stellar mass of early-type galaxies has been assembled at z=0.7.
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We present infrared galaxy luminosity functions (LFs) in the AKARI North Ecliptic Pole (NEP) deep field using recently-obtained, wider CFHT optical/near-IR images. AKARI has obtained deep images in the mid-infrared (IR), covering 0.6 deg$^2$ of the NEP deep field. However, our previous work was limited to the central area of 0.25 deg$^2$ due to the lack of optical coverage of the full AKARI NEP survey. To rectify the situation, we recently obtained CFHT optical and near-IR images over the entire AKARI NEP deep field. These new CFHT images are used to derive accurate photometric redshifts, allowing us to fully exploit the whole AKARI NEP deep field. AKARIs deep, continuous filter coverage in the mid-IR wavelengths (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$mu$m) exists nowhere else, due to filter gaps of other space telescopes. It allows us to estimate restframe 8$mu$m and 12$mu$m luminosities without using a large extrapolation based on spectral energy distribution (SED) fitting, which was the largest uncertainty in previous studies. Total infrared luminosity (TIR) is also obtained more reliably due to the superior filter coverage. The resulting restframe 8$mu$m, 12$mu$m, and TIR LFs at $0.15<z<2.2$ are consistent with previous works, but with reduced uncertainties, especially at the high luminosity-end, thanks to the wide field coverage. In terms of cosmic infrared luminosity density ($Omega_{mathrm{IR}}$), we found that the $Omega_{mathrm{IR}}$ evolves as $propto (1+z)^{4.2pm 0.4}$.
We explore the connections between the evolving galaxy and AGN populations. We present a simple phenomenological model that links the evolving galaxy mass function and the evolving quasar luminosity function, which makes specific and testable predictions for the distribution of host galaxy masses for AGN of different luminosities. We show that the $phi^{*}$ normalisations of the galaxy mass function and of the AGN luminosity function closely track each other over a wide range of redshifts, implying a constant duty cycle of AGN activity. The strong redshift evolution in the AGN $L^*$ can be produced by either an evolution in the distribution of Eddington ratios, or in the $m_{bh}/m_{*}$ mass ratio, or both. To try to break this degeneracy we look at the distribution of AGN in the SDSS ($m_{bh},L$) plane, showing that an evolving ratio $m_{bh}/m_{*} propto (1+z)^2$ reproduces the observed data and also reproduces the local relations which connect the black hole population with the host galaxies for both quenched and star-forming populations. We stress that observational studies that compare the masses of black holes in active galaxies at high redshift with those in quiescent galaxies locally will always see much weaker evolution. Evolution of this form would produce, or could be produced by, a redshift-independent $m_{bh} - sigma$ relation and could explain why the local $m_{bh} - sigma$ relation is tighter than $m_{bh} - m_{*}$ even if $sigma$ is not directly linked to black hole growth. Irrespective of the evolution of $m_{bh}/m_{*}$, the model reproduces both the appearance of downsizing and the so-called sub-Eddington boundary without any mass-dependence in the evolution of black hole growth rates.
We present luminosity functions derived from a spectroscopic survey of AGN selected from Spitzer Space Telescope imaging surveys. Selection in the mid-infrared is significantly less affected by dust obscuration. We can thus compare the luminosity functions of the obscured and unobscured AGN in a more reliable fashion than by using optical or X-ray data alone. We find that the AGN luminosity function can be well described by a broken power-law model in which the break luminosity decreases with redshift. At high redshifts ($z>1.6$), we find significantly more AGN at a given bolometric luminosity than found by either optical quasar surveys or hard X-ray surveys. The fraction of obscured AGN decreases rapidly with increasing AGN luminosity, but, at least at high redshifts, appears to remain at $approx 50$% even at bolometric luminosities $sim 10^{14}L_{odot}$. The data support a picture in which the obscured and unobscured populations evolve differently, with some evidence that high luminosity obscured quasars peak in space density at a higher redshift than their unobscured counterparts. The amount of accretion energy in the Universe estimated from this work suggests that AGN contribute about 12% to the total radiation intensity of the Universe, and a high radiative accretion efficiency $approx 0.18^{+0.12}_{-0.07}$ is required to match current estimates of the local mass density in black holes.
We determine the 22$mu$m luminosity evolution and luminosity function for quasars from a data set of over 20,000 objects obtained by combining flux-limited Sloan Digital Sky Survey optical and Wide field Infrared Survey Explorer mid-infrared data. We apply methods developed in previous works to access the intrinsic population distributions non-parametrically, taking into account the truncations and correlations inherent in the data. We find that the population of quasars exhibits positive luminosity evolution with redshift in the mid-infrared, but with considerably less mid-infrared evolution than in the optical or radio bands. With the luminosity evolutions accounted for, we determine the density evolution and local mid-infrared luminosity function. The latter displays a sharp flattening at local luminosities below $sim 10^{31}$ erg sec$^{-1}$ Hz$^{-1}$, which has been reported previously at 15 $mu$m for AGN classified as both type-1 and type-2. We calculate the integrated total emission from quasars at 22 $mu$m and find it to be a small fraction of both the cosmic infrared background light and the integrated emission from all sources at this wavelength.
Because the 8 {mu}m polycyclic aromatic hydrocarbon (PAH) emission has been found to correlate with other well-known star formation tracers, it has widely been used as a star formation rate (SFR) tracer. There are, however, studies that challenge the accuracy and reliability of the 8 {mu}m emission as a SFR tracer. Our study, part of the Herschel M33 Extended Survey (HERM33ES) open time key program, aims at addressing this issue by analyzing the infrared emission from the nearby spiral galaxy M33 at the high spatial scale of 75 pc. Combining data from the Herschel Space Observatory and the Spitzer Space Telescope we find that the 8 {mu}m emission is better correlated with the 250 {mu}m emission, which traces cold interstellar gas, than with the 24 {mu}m emission. The L(8)/L(24) ratio is highly depressed in 24 {mu}m luminous regions, which correlate with known HII regions. We also compare our results with the dust emission models by Draine & Li (2007). We confirm that the depression of 8 {mu}m PAH emission near star-forming regions is higher than what is predicted by models; this is possibly an effect of increased stellar radiation from young stars destroying the dust grains responsible for the 8 {mu}m emission as already suggested by other authors. We find that the majority of the 8 {mu}m emission is fully consistent with heating by the diffuse interstellar medium, similar to what recently determined for the dust emission in M31 by Draine at al. (2013). We also find that the fraction of 8 {mu}m emission associated with the diffuse interstellar radiation field ranges between 60% and 80% and is 40% larger than the diffuse fraction at 24 {mu}m.
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