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Register a new userThe mid-IR Luminosity Function at z<0.3 from 5MUSES: Understanding the Star-formation/AGN Balance from a Spectroscopic View
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We present rest-frame 15 and 24 um luminosity functions and the corresponding star-forming luminosity functions at z<0.3 derived from the 5MUSES sample. Spectroscopic redshifts have been obtained for ~98% of the objects and the median redshift is ~0.12. The 5-35 um IRS spectra allow us to estimate accurately the luminosities and build the luminosity functions. Using a combination of starburst and quasar templates, we quantify the star-formation and AGN contributions in the mid-IR SED. We then compute the star-formation luminosity functions at 15 um and 24 um, and compare with the total 15 um and 24 um luminosity functions. When we remove the contribution of AGN, the bright end of the luminosity function exhibits a strong decline, consistent with the exponential cutoff of a Schechter function. Integrating the differential luminosity function, we find that the fractional contribution by star formation to the energy density is 58% at 15 um and 78% at 24 um, while it goes up to ~86% when we extrapolate our mid-IR results to the total IR luminosity density. We confirm that the active galactic nuclei play more important roles energetically at high luminosities. Finally, we compare our results with work at z~0.7 and confirm that evolution on both luminosity and density is required to explain the difference in the LFs at different redshifts.
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[Abridged] We present new measurements of the H-alpha luminosity function (LF) and SFR volume density for galaxies at z~0.8. Our analysis is based on 1.18$mu$m narrowband data from the NEWFIRM H-alpha Survey, a comprehensive program designed to capture deep samples of intermediate redshift emission-line galaxies using narrowband imaging in the near-infrared. The combination of depth ($approx1.9times10^{-17}$ erg s$^{-1}$ cm$^{-2}$ in H-alpha at 3$sigma$) and areal coverage (0.82 deg$^2$) complements other recent H-alpha studies at similar redshifts, and enables us to minimize the impact of cosmic variance and place robust constraints on the shape of the LF. The present sample contains 818 NB118 excess objects, 394 of which are selected as H-alpha emitters. Optical spectroscopy has been obtained for 62% of the NB118 excess objects. Empirical optical broadband color classification is used to sort the remainder of the sample. A comparison of the LFs constructed for the four individual fields reveals significant cosmic variance, emphasizing that multiple, widely separated observations are required. The dust-corrected LF is well-described by a Schechter function with L*=10^{43.00pm0.52} ergs s^{-1}, phi*=10^{-3.20pm0.54} Mpc^{-3}, and alpha=-1.6pm0.19. We compare our H-alpha LF and SFR density to those at z<1, and find a rise in the SFR density propto(1+z)^{3.4}, which we attribute to significant L* evolution. Our H-alpha SFR density of 10^{-1.00pm0.18} M_sun yr^{-1} Mpc^{-3} is consistent with UV and [O II] measurements at z~1. We discuss how these results compare to other H-alpha surveys at z~0.8, and find that the different methods used to determine survey completeness can lead to inconsistent results. This suggests that future surveys probing fainter luminosities are needed, and more rigorous methods of estimating the completeness should be adopted as standard procedure.
We present the J-band luminosity function of 1838 mid-infrared and X-ray selected AGNs in the redshift range 0<z<5.85. These luminosity functions are constructed by combining the deep multi-wavelength broad-band observations from the UV to the mid-IR of the NDWFS Bootes field with the X-ray observations of the XBootes survey and the spectroscopic observations of the same field by AGES. Our sample is primarily composed of IRAC-selected AGNs, targeted using modifications of the Stern et al.(2005) criteria, complemented by MIPS 24 microns and X-ray selected AGNs to alleviate the biases of IRAC mid-IR selection against z~4.5 quasars and AGNs faint with respect to their hosts. This sample provides an accurate link between low and high redshift AGN luminosity functions and does not suffer from the usual incompleteness of optical samples at z~3. We find that the space density of the brightest quasars strongly decreases from z=3 to z=0, while the space density of faint quasars is at least flat, and possibly increasing, over the same redshift range. At z>3 we observe a decrease in the space density of quasars of all brightnesses. We model the luminosity function by a double power-law and find that its evolution cannot be described by either pure luminosity or pure density evolution, but must be a combination of both. Our best-fit model has bright and faint power-law indices consistent with the low redshift measurements based on the 2QZ and 2SLAQ surveys and it generally agrees with the number of bright quasars predicted by other LFs at all redshifts. If we construct the QSO luminosity function using only the IRAC-selected AGNs, we find that the biases inherent to this selection method significantly modify the behavior of phi*(z) only for z<1 and have no significant impact upon the characteristic magnitude M*_J(z).
Despite decades of study, it remains unclear whether there are distinct radio-loud and radio-quiet populations of quasi-stellar objects (QSOs). Early studies were limited by inhomogeneous QSO samples, inadequate sensitivity to probe the radio-quiet population, and degeneracy between redshift and luminosity for flux-density-limited samples. Our new 6 GHz EVLA observations allow us for the first time to obtain nearly complete (97%) radio detections in a volume-limited color-selected sample of 179 QSOs more luminous than M_i = -23 from the Sloan Digital Sky Survey (SDSS) Data Release Seven in the narrow redshift range 0.2 < z < 0.3. The dramatic improvement in radio continuum sensitivity made possible with the new EVLA allows us, in 35 minutes of integration, to detect sources as faint as 20 microJy, or log[L_6 (W/Hz)] ~ 21.5 at z = 0.25, well below the radio luminosity, log[L_6 (W/Hz)] ~ 22.5, that separates star-forming galaxies from radio-loud active galactic nuclei (AGNs) driven by accretion onto a super-massive black hole. We calculate the radio luminosity function (RLF) for these QSOs using three constraints: (a) EVLA 6 GHz observations for log[L_6 (W/Hz)] < 23.5, (b) NRAO-VLA Sky Survey (NVSS) observations for log[L_6 (W/Hz)] > 23.5, and (c) the total number of SDSS QSOs in our volume-limited sample. We show that the RLF can be explained as a superposition of two populations, dominated by AGNs at the bright end and star formation in the QSO host galaxies at the faint end.
We use the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) project as a template to demonstrate how deep spectrophotometric surveys covering large cosmological volumes over extended fields (1-15 square degrees) with a mid-IR imaging spectrometer (17-36 micron) in conjunction with deep 70 micron photometry with a far-IR camera, at wavelengths which are not affected by dust extinction can answer the most crucial questions in current galaxy evolution studies. A SPICA-like mission will be able for the first time to provide an unobscured three dimensional (3-D, i.e. x, y and redshift z) view of galaxy evolution back to an age of the Universe of less than ~2 Gyrs, in the mid-IR rest-frame. This survey strategy will produce a full census of the Star formation Rate (SFR) in the Universe, using Polycyclic Aromatic Hydrocarbons (PAH) bands and fine-structure ionic lines, reaching the characteristic knee of the galaxy luminosity function, where the bulk of the population is distributed, at any redshift up to z ~3.5. Deep follow-up pointed spectroscopic observations with grating spectrometers { onboard the satellite}, across the full IR spectral range (17-210 micron), would simultaneously measure Black Hole Accretion Rate (BHAR), from high-ionization fine-structure lines, and SFR, from PAH and low- to mid-ionization lines in thousands of galaxies from solar to low metallicities, down to the knee of their luminosity functions. The analysis of the resulting atlas of IR spectra will reveal the physical processes at play in evolving galaxies across cosmic time, especially its heavily dust-embedded phase during the activity peak at the cosmic noon (z ~1-3), through IR emission lines and features that are insensitive to the dust obscuration.
We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M$_{ast}$ $sim$ 10$^{10}$ M$_odot$) IRAC- and MIPS 24$mu$m-detected Lyman Break Galaxies (LBGs) with spectroscopic redshifts z$sim$3 in the GOODS-North field (L$_{rm UV}$$>1.8times$L$^{ast}_{z=3}$). For LBGs without individual 24$mu$m detections, we employ stacking techniques at 24$mu$m, 1.1mm and 1.4GHz, to construct the average UV-to-radio spectral energy distribution and find it to be consistent with that of a Luminous Infrared Galaxy (LIRG) with L$rm_{IR}$=4.5$^{+1.1}_{-2.3}$$times 10^{11}$ L$_{odot}$ and a specific star formation rate (SSFR) of 4.3 Gyr$^{-1}$ that corresponds to a mass doubling time $sim$230 Myrs. On the other hand, when considering the 24$mu$m-detected LBGs we find among them galaxies with L$rm_{IR}> 10^{12}$ L$_{odot}$, indicating that the space density of $zsim$3 UV-selected Ultra-luminous Infrared Galaxies (ULIRGs) is $sim$(1.5$pm$0.5)$times 10^{-5}$ Mpc$^{-3}$. We compare measurements of star formation rates (SFRs) from data at different wavelengths and find that there is tight correlation (Kendalls $tau >$ 99.7%) and excellent agreement between the values derived from dust-corrected UV, mid-IR, mm and radio data for the whole range of L$rm_{IR}$ up to L$rm_{IR}$ $sim$ 10$^{13}$ L$_{odot}$. This range is greater than that for which the correlation is known to hold at z$sim$2, possibly due to the lack of significant contribution from PAHs to the 24$mu$m flux at $zsim$3. The fact that this agreement is observed for galaxies with L$rm_{IR}$ $>$ 10$^{12}$ L$_{odot}$ suggests that star-formation in UV-selected ULIRGs, as well as the bulk of star-formation activity at this redshift, is not embedded in optically thick regions as seen in local ULIRGs and submillimeter-selected galaxies at $z=2$.
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