Μm Luminosity Function Research Articles

Gauging the mass of metals in the gas phase of galaxies from the Local Universe to the Epoch of Reionization

The chemical enrichment of dust and metals are vital processes in constraining the star formation history of the universe. These are important ingredients in the formation and evolution of galaxies overall. Previously, the dust masses of high-redshift star-forming galaxies have been determined through their far-infrared continuum, however, equivalent, and potentially simpler, approaches to determining the metal masses have yet to be explored at z ≳ 2. Here, we present a new method of inferring the metal mass in the interstellar medium (ISM) of galaxies out to z ≈ 8, using the far-infrared [C II]−158 μm emission line as a proxy. We calibrated the [C II]-to-MZ, ISM conversion factor based on a benchmark observational sample at z ≈ 0, in addition to gamma-ray burst sightlines at z > 2 and cosmological hydrodynamical simulations of galaxies at z ≈ 0 and z ≈ 6. We found a universal scaling across redshifts of log(MZ, ISM/M⊙) = log(L[CII]/L⊙)−0.45, with a 0.4 dex scatter, which is constant over more than two orders of magnitude in metallicity. We applied this scaling to recent surveys for [C II] in galaxies at z ≳ 2 and compared their inferred MZ, ISM to their stellar mass (M⋆). In particular, we determined the fraction of metals retained in the gas-phase ISM, MZ, ISM/M⋆, as a function of redshift and we showed that an increasing fraction of metals reside in the ISM of galaxies at higher redshifts. We place further constraints on the cosmic metal mass density in the ISM (ΩZ, ISM) at z ≈ 5 and ≈7 based on recent estimates of the [C II]−158 μm luminosity functions at these epochs, yielding ΩZ,ISM = 6.6−4.3+13 × 10−7 M⊙ Mpc−3 (z ≈ 5) and ΩZ,ISM = 2.0−1.3+3.5 × 10−7 M⊙ Mpc−3 (z ≈ 7), respectively. These results are consistent with the expected metal yields from the integrated star formation history at the respective redshifts. This suggests that the majority of metals produced at z ≳ 5 are confined to the ISM, with strong implications that disfavor efficient outflow processes at these redshifts. Instead, these results suggest that the extended [C II] halos predominantly trace the extended neutral gas reservoirs of high-z galaxies.

The Massive and Distant Clusters of WISE Survey. XI. Stellar Mass Fractions and Luminosity Functions of MaDCoWS Clusters at z ∼ 1

We present stellar mass fractions and composite luminosity functions (LFs) for a sample of 12 clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) in the redshift range 0.951 ≤ z ≤ 1.43. Using spectral energy distribution fitting of optical and deep mid-infrared photometry, we establish the membership of objects along the lines of sight to these clusters and calculate the stellar masses of member galaxies. This allows us to calculate the stellar mass of the clusters much more precisely than in previous works. We find stellar mass fractions for these clusters largely consistent with previous works, and an apparent negative correlation with total cluster mass. We measure a composite 3.6 μm LF down to m* + 2.5 for all 12 clusters. Fitting a Schechter function to the LF, we find a characteristic 3.6 μm magnitude of m* = 19.83 ± 0.12 and faint-end slope of α = −0.81 ± 0.10 for the full sample at a mean redshift of . We also divide the clusters into high- and low-redshift bins at and , respectively, and measure a composite LF for each bin. We see a small, but statistically significant, evolution in m* and α—consistent with passive evolution—when we study the joint fit to the two parameters, which is probing the evolution of faint cluster galaxies at z ∼ 1. This highlights the importance of deep IR data in studying the evolution of cluster galaxy populations at high redshift.

The ALMA REBELS Survey: The Cosmic H i Gas Mass Density in Galaxies at z ≈ 7

The neutral atomic gas content of individual galaxies at large cosmological distances has until recently been difficult to measure due to the weakness of the hyperfine H i 21 cm transition. Here we estimate the H i gas mass of a sample of main-sequence star-forming galaxies at z ∼ 6.5–7.8 surveyed for [C ii] 158 μm emission as part of the Reionization Era Bright Emission Line Survey (REBELS), using a recent calibration of the [C ii]-to-H i conversion factor. We find that the H i gas mass excess in galaxies increases as a function of redshift, with an average of M Hi /M ⋆ ≈ 10, corresponding to H i gas mass fractions of f Hi = M Hi /(M ⋆ + M Hi ) = 90%, at z ≈ 7. Based on the [C ii] 158 μm luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H i gas mass density in galaxies (ρ Hi ) at this redshift, which we measure to be . This estimate is substantially lower by a factor of ≈10 than that inferred from an extrapolation of damped Lyα absorber (DLA) measurements and largely depends on the exact [C ii] LF adopted. However, we find this decrease in ρ Hi to be consistent with recent simulations and argue that this apparent discrepancy is likely a consequence of the DLA sight lines predominantly probing the substantial fraction of H i gas in high-z galactic halos, whereas [C ii] traces the H i in the ISM associated with star formation. We make predictions for this buildup of neutral gas in galaxies as a function of redshift, showing that at z ≳ 5, only ≈10% of the cosmic H i gas content is confined in galaxies and associated with the star-forming ISM.

The ALPINE–ALMA [C II] survey

We present the first [C II] 158 μm luminosity function (LF) at z ∼ 5 from a sample of serendipitous lines detected in the ALMA Large Program to INvestigate [C II] at Early times (ALPINE). A study of the 118 ALPINE pointings revealed several serendipitous lines. Based on their fidelity, we selected 14 lines for the final catalog. According to the redshift of their counterparts, we identified eight out of 14 detections as [C II] lines at z ∼ 5, along with two as CO transitions at lower redshifts. The remaining four lines have an elusive identification in the available catalogs and we considered them as [C II] candidates. We used the eight confirmed [C II] and the four [C II] candidates to build one of the first [C II] LFs at z ∼ 5. We found that 11 out of these 12 sources have a redshift very similar to that of the ALPINE target in the same pointing, suggesting the presence of overdensities around the targets. Therefore, we split the sample in two (a “clustered” and “field” subsample) according to their redshift separation and built two separate LFs. Our estimates suggest that there could be an evolution of the [C II] LF between z ∼ 5 and z ∼ 0. By converting the [C II] luminosity to the star-formation rate, we evaluated the cosmic star-formation rate density (SFRD) at z ∼ 5. The clustered sample results in a SFRD ∼10 times higher than previous measurements from UV–selected galaxies. On the other hand, from the field sample (likely representing the average galaxy population), we derived a SFRD ∼1.6 higher compared to current estimates from UV surveys but compatible within the errors. Because of the large uncertainties, observations of larger samples will be necessary to better constrain the SFRD at z ∼ 5. This study represents one of the first efforts aimed at characterizing the demography of [C II] emitters at z ∼ 5 using a mm selection of galaxies.

Reproducing submillimetre galaxy number counts with cosmological hydrodynamic simulations

ABSTRACT Matching the number counts of high-z submillimetre-selected galaxies (SMGs) has been a long-standing problem for galaxy formation models. In this paper, we use 3D dust radiative transfer to model the submm emission from galaxies in the simba cosmological hydrodynamic simulations, and compare predictions to the latest single-dish observational constraints on the abundance of 850 μm-selected sources. We find good agreement with the shape of the integrated 850 μm luminosity function, and the normalization is within 0.25 dex at >3 mJy, unprecedented for a fully cosmological hydrodynamic simulation, along with good agreement in the redshift distribution of bright SMGs. The agreement is driven primarily by simba’s good match to infrared measures of the star formation rate (SFR) function between z = 2 and 4 at high SFRs. Also important is the self-consistent on-the-fly dust model in simba, which predicts, on average, higher dust masses (by up to a factor of 2.5) compared to using a fixed dust-to-metals ratio of 0.3. We construct a light-cone to investigate the effect of far-field blending, and find that 52 per cent of sources are blends of multiple components, which makes a small contribution to the normalization of the bright end of the number counts. We provide new fits to the 850 μm luminosity as a function of SFR and dust mass. Our results demonstrate that solutions to the discrepancy between submm counts in simulations and observations, such as a top-heavy initial mass function, are unnecessary, and that submillimetre-bright phases are a natural consequence of massive galaxy evolution.

Infrared luminosity functions based on 18 mid-infrared bands: revealing cosmic star formation history with AKARI and Hyper Suprime-Cam

AbstractMuch of star formation is obscured by dust. For a complete understanding of the cosmic star formation history (CSFH), infrared (IR) census is indispensable. AKARI carried out deep mid-infrared observations using its continuous nine-band filters in the North Ecliptic Pole (NEP) field (5.4 deg2). This took a significant amount of the satellite’s lifetime, ∼10% of the entire pointed observations. By combining archival Spitzer (five bands) and WISE (four bands) mid-IR photometry, we have, in total, 18-band mid-IR photometry, which is the most comprehensive photometric coverage in the mid-IR for thousands of galaxies. However, we only had shallow optical imaging (∼25.9 AB magnitude) in a small area, 1.0 deg2. As a result, thousands of AKARI’s infrared sources remained undetected in the optical. Using the new Hyper Suprime-Cam on the Subaru telescope, we obtained deep enough optical images of the entire AKARI NEP field in five broad bands (g ∼ 27.5 mag). These provided photometric redshift, and thereby IR luminosity, for the previously undetected faint AKARI IR sources. Combined with the accurate mid-IR luminosity measurement, we constructed mid-IR luminosity functions (LFs), and thereby performed a census of dust-obscured CSFH in the entire AKARI NEP field. We have measured rest-frame 8 μm and 12 μm LFs, and estimated total infrared LFs at 0.35 < $z$ < 2.2. Our results are consistent with our previous work, but with much reduced statistical errors thanks to the large-area coverage of the new data. We have possibly witnessed the turnover of CSFH at $z$ ∼ 2.

The 2.4 μm Galaxy Luminosity Function as Measured Using WISE. III. Measurement Results

Abstract The Widefield Infrared Survey Explorer (WISE) satellite surveyed the entire sky multiple times in four infrared wavelengths (3.4, 4.6, 12, and 22 μm). The unprecedented combination of coverage area and depth gives us the opportunity to measure the luminosity function (LF) of galaxies, one of the fundamental quantities in the study of them, at 2.4 μm to an unparalleled level of formal statistical accuracy in the near-infrared. The big advantage of measuring LFs at wavelengths in the window of ≈2–3.5 μm is that it correlates more closely to the total stellar mass in galaxies than others. In this paper we report on the parameters of the 2.4 μm LF of galaxies obtained from applying the spectro-luminosity-functional-based methods to datasets from the previous papers in this series using the mean and covariance of 2.4 μm normalized spectral energy distributions (SEDs) from our previous work. In terms of the single Schechter function parameters evaluated at the present epoch, the combined result is: , (M ⋆ = −21.67 ± [0.02stat, 0.05sys] AB mag), and α = −1.050 ± [0.004stat, 0.04sys]. The high statistical accuracy comes from combining public redshift surveys with the wide coverage from WISE, and the unevenness in statistical accuracy is a result of our efforts to work around biases of uncertain origin that affect resolved and marginally resolved galaxies. With further refinements, the techniques applied in this work promise to advance the study of the SED of the universe.

THE MID-INFRARED LUMINOSITY EVOLUTION AND LUMINOSITY FUNCTION OF QUASARS WITH WISE AND SDSS

ABSTRACT We determine the 22 μm 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 ∼ 10 31 erg s−1 Hz−1, which has been reported previously at 15 μm for AGN classified as both type 1 and type 2. We calculate the integrated total emission from quasars at 22 μm 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.

THE [N ii] 205 μm EMISSION IN LOCAL LUMINOUS INFRARED GALAXIES*

ABSTRACT In this paper, we present the measurements of the [N ii] 205 μm line for a flux-limited sample of 122 (ultra-)luminous infrared galaxies [(U)LIRGs] and 20 additional normal galaxies, obtained with the Herschel Space Observatory (Herschel). We explore the far-infrared (FIR) color dependence of the [N ii] 205 μm (L [N ii]205 μm) to the total infrared (L IR) luminosity ratio, and find that L [N ii]205 μm/L IR only depends modestly on the 70–160 μm flux density ratio ( f 70 / f 160 ?> ) when f 70 / f 160 ≲ 0.6 ?> , whereas such dependence becomes much steeper for f 70 / f 160 > 0.6 ?> . We also investigate the relation between L [N ii]205 μm and star formation rate (SFR), and show that L [N ii]205 μm has a nearly linear correlation with SFR, albeit the intercept of such a relation varies somewhat with f 60 / f 100 ?> , consistent with our previous conclusion that [N ii] 205 μm emission can serve as an SFR indicator with an accuracy of ∼0.4 dex, or ∼0.2 dex if f 60 / f 100 ?> is known independently. Furthermore, together with the Infrared Space Observatory measurements of [N ii], we use a total of ∼200 galaxies to derive the local [N ii] 205 μm luminosity function (LF) by tying it to the known IR LF with a bivariate method. As a practical application, we also compute the local SFR volume density ( &rgr; ˙ SFR ?> ) using the newly derived SFR calibrator and LF. The resulting log &rgr; ˙ SFR = − 1.96 ± 0.11 ?> M ⊙ ?> yr−1 Mpc−3 agrees well with previous studies. Finally, we determine the electron densities (n e ) of the ionized medium for a subsample of 12 (U)LIRGs with both [N ii] 205 μm and [N ii] 122 μm data, and find that n e is in the range of ∼1–100 cm−3, with a median value of 22 cm−3.

THE 18 ㎛ LUMINOSITY FUNCTION OF GALAXIES WITH AKARI

We present the 18 ㎛ luminosity function (LF) of galaxies at 0.006 < z < 0.8 (the average redshift is~0.04) using the AKARI mid-infrared All-Sky Survey catalogue. We have selected 243 galaxies at 18 ㎛ from the Sloan Digital Sky Survey (SDSS) spectroscopic region. These galaxies then have been classified into five types; Seyfert 1 galaxies (Sy1, including quasars), Seyfert 2 galaxies (Sy2), low ionization narrow emission line galaxies (LINER), galaxies that are likely to contain both star formation and Active Galactic Nuclei (AGN) activities (composites), and star forming galaxies (SF) using optical emission lines such as the line width of Hα or the emission line ratios of [OIII]/Hβ and [NII]/Hα. As a result of constructing the LF of Sy1 and Sy2, we found the following results; (i) the number density ratio of Sy2 to Sy1 is 1.64 ± 0.37, larger than the results obtained from optical LF and (ii) the fraction of Sy2 in the entire AGN population may decrease with 18 ㎛ luminosity. These results suggest that most of the AGNs in the local universe are obscured by dust and the torus structure probably depends on the mid-infrared luminosity.

Far Infrared Luminosity Function of Local Galaxies in the AKARI Deep Field South

AbstractWe present the first far-infrared luminosity function in the AKARI Deep Field South, a premier deep field of the AKARI Space Telescope, using spectroscopic redshifts obtained with AAOmega. To date, we have found spectroscopic redshifts for 389 galaxies in this field and have measured the local (z&lt;0.25) 90 μm luminosity function using about one-third of these redshifts. The results are in reasonable agreement with recent theoretical predictions.

The Mid-Infrared luminosity function of galaxies using the AKARI mid-infrared All-Sky Survey Catalogue

AbstractWe present the first determination of the 18 μm luminosity function (LF) of galaxies at 0.006 &lt; z &lt; 0.7 (the average redshift is ~ 0.04) using the AKARI mid-infrared All-Sky Survey catalogue. We have selected a 18 μm flux-limited sample of 243 galaxies from the catalogue in the SDSS spectroscopic region. We then classified the sample into four types; Seyfert 1 galaxies (including QSOs), Seyfert 2 galaxies, LINERs and Star-Forming galaxies using mainly [OIII]/Hβ vs. [NII]/Hα line ratios obtained from the SDSS.As a result of constructing Seyfert 1 and Seyfert 2 LFs, we found the following results; (i) the number density ratio of Seyfert 2s to Seyfert 1s is 3.98 ± 0.41 obtained from Sy1 and Sy2 LFs; this value is larger than the results obtained from optical LFs. (ii) the fraction of Sy2s in the entire AGNs may be anti-correlated with 18 μm luminosity. These results suggest that the torus structure probably depends on the mid-infrared luminosity of AGNs and most of the AGNs in the local Universe are obscured by dust.

THE MID-INFRARED LUMINOSITY FUNCTION ATz&lt; 0.3 FROM 5MUSES: UNDERSTANDING THE STAR FORMATION/ACTIVE GALACTIC NUCLEUS BALANCE FROM A SPECTROSCOPIC VIEW

We present rest-frame 15 and 24 μm luminosity functions (LFs) and the corresponding star-forming LFs 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 μm Infrared Spectrograph spectra allow us to estimate accurately the luminosities and build the LFs. Using a combination of starburst and quasar templates, we quantify the star formation (SF) and active galactic nucleus (AGN) contributions in the mid-IR spectral energy distribution. We then compute the SF LFs at 15 and 24 μm, and compare with the total 15 and 24 μm LFs. When we remove the contribution of AGNs, the bright end of the LF exhibits a strong decline, consistent with the exponential cutoff of a Schechter function. Integrating the differential LF, we find that the fractional contribution by SF to the energy density is 58% at 15 μm and 78% at 24 μm, while it goes up to ∼86% when we extrapolate our mid-IR results to the total IR luminosity density. We confirm that the AGNs 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.

The Local Galaxy 8 μm Luminosity Function

A Spitzer Space Telescope survey in the NOAO Deep Wide Field in Boötes provides a complete, 8 μm-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg2 field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an accurate determination of the local (z < 0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 μm luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1%. A subsample of the 8 μm-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 μm luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 μm luminosity function, the characteristic luminosity is νL(8.0 μm) = 1.8 × 1010 L☉, while for the dust emission alone it is 1.6 × 1010 L☉. The average 8 μm luminosity density at z < 0.3 is 3.1 × 107 L☉ Mpc-3, and the average luminosity density from dust alone is 2.5 × 107 L☉ Mpc-3. This luminosity arises predominantly from galaxies with 8 μm luminosities (νLν) between 2 × 109 and 2 × 1010 L☉, i.e., normal galaxies, not luminous or ultraluminous infrared galaxies (LIRGs/ULIRGs).

Infrared Luminosity Functions from the Chandra Deep Field–South: TheSpitzerView on the History of Dusty Star Formation at 0 ≲z≲ 1

We analyze a sample of ~2600 Spitzer MIPS 24 μm sources brighter than ~80 μJy and located in the Chandra Deep Field-South to characterize the evolution of the comoving infrared (IR) energy density of the universe up to z ~ 1. Using published ancillary optical data, we first obtain a nearly complete redshift determination for the 24 μm objects associated with R 24 mag counterparts at z 1. These sources represent ~55%-60% of the total MIPS 24 μm population with f24 μm 80 μJy, the rest of the sample likely lying at higher redshifts. We then determine an estimate of their total IR luminosities using various libraries of IR spectral energy distributions. We find that the 24 μm population at 0.5 z 1 is dominated by infrared (i.e., 1011 L☉ ≤ LIR ≤ 1012 L☉), the counterparts of which appear to be also luminous at optical wavelengths and tend to be more massive than the majority of optically selected galaxies. A significant number of fainter sources (5 × 1010 L☉ LIR ≤ 1011 L☉) are also detected at similar distances. We finally derive 15 μm and total IR luminosity functions (LFs) up to z ~ 1. In agreement with the previous results from the Infrared Space Observatory (ISO) and SCUBA and as expected from the MIPS source number counts, we find very strong evolution of the contribution of the IR-selected population with look-back time. Pure evolution in density is firmly excluded by the data, but we find considerable degeneracy between strict evolution in luminosity and a combination of increases in both density and luminosity [L ∝ (1 + z), ∝ (1 + z)]. A significant steepening of the faint-end slope of the IR luminosity function is also unlikely, as it would overproduce the faint 24 μm source number counts. Our results imply that the comoving IR energy density of the universe evolves as (1 + z)3.9±0.4 up to z ~ 1 and that galaxies luminous in the infrared (i.e., LIR ≥ 1011 L☉) are responsible for 70% ± 15% of this energy density at z ~ 1. Taking into account the contribution of the UV luminosity evolving as (1 + z)~2.5, we infer that these IR-luminous sources dominate the star-forming activity beyond z ~ 0.7. The uncertainties affecting these conclusions are largely dominated by the errors in the k-corrections used to convert 24 μm fluxes into luminosities.

The Mid‐Infrared Luminosity Function of Galaxies in the European Large AreaInfrared Space ObservatorySurvey Southern Fields

We present the first determination of the 15 μm luminosity function of galaxies from the European Large Area ISO Survey (ELAIS) southern fields. We have adopted a new criterion to separate the quiescent, nonevolving and the starburst, evolving populations based on the ratio of mid-infrared to optical luminosity. Strong evolution is suggested by our data for the starburst galaxy population, while normal spiral galaxies are consistent with no evolution. The starburst population must evolve both in luminosity and in density with rates of the order L(z) ∝ (1 + z)3.5 and ρ(z) ∝ (1 + z)3.8, respectively, up to z ~ 1. The evolutionary parameters of our model have been tested by comparing the model predictions with other observables, like source counts at all flux density levels (from 0.1 to 300 mJy) and redshift distributions and luminosity functions at high z (0.7 < z < 1.0 from Hubble Deep Field North [HDF-N] data). The agreement between our model predictions and the observed data is remarkably good. We use our data to estimate the star formation density of the universe up to z = 0.4, and we use the luminosity function model to predict the trend of the star formation history up to z = 1.

CO Luminosity Functions for Far‐Infrared– andB‐Band–selected Galaxies and the First Estimate for \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\Omega _{\mathrm{H}\,\, {}^{\textsc{i}}+\mathrm{H}\,_{2}}$ \end{document}

We derive a nonparametric CO luminosity function using an FIR- and an optical B-band-selected sample of the galaxies included in the FCRAO Extragalactic CO Survey. The FIR-selected sample is defined using the IRAS bright galaxy samples (BGS; IRAS 60 μm flux density ≥5.24 Jy). Although our CO sample is not complete, the normalization using the BGS reproduces the IRAS 60 μm luminosity function in excellent agreement with those found in the literature. Similarly, a B-band-selected sample defined using the Revised Shapley-Ames catalog is used to derive a CO luminosity function for a comparison. A Schechter function describes both the derived CO luminosity functions reasonably well. Adopting the standard CO-to-H2 conversion factor, we derive a molecular gas density of ρ = (3.1 ± 1.2) × 107 h M☉ Mpc-3 for the local volume. Combining with the measurements of the local H I mass density and the helium contribution, we estimate that the total mass density of cold neutral gas in the local universe is Ωgas = (4.3 ± 1.1) × 10-4 h-1, which is about 20% of the total stellar mass density Ω*.

Models for Infrared and Submillimetre Counts and Backgrounds

A simple and versatile parametrized approach to the star formation history allows a quantitative investigation of the constraints from far infrared and submillimetre counts and background intensity measurements.The models include four spectral components: infrared cirrus, an M 82-like starburst, an Arp 220-like starburst and an AGN dust torus. The 60 μm luminosity function is determined for each chosen rate of evolution using the PSCz redshift data for 15000 galaxies. The proportions of each spectral type as a function of 60 μm luminosity are chosen for consistency with IRAS and SCUBA colour-luminosity relations, and with the fraction of AGN as a function of luminosity found in 12 μm samples.A good fit to the observed counts at 0.44, 2.2, 15, 60, 90, 175 and 850 μm can be found with pure luminosity evolution in all 3 cosmological models investigated: Ω0 = 1, Ω0 = 0.3 (Λ = 0), and Ω0 = 0.3, Λ = 0.7. All 3 models also give an acceptable fit to the integrated background spectrum. The total mass-density of stars generated in all 3 cosmological models is consistent with that observed.

The Mid‐Infrared Color‐Luminosity Relation and the Local 12 Micron Luminosity Function

We have established a model to systematically estimate the contribution of the mid-IR emission features between 3 and 11.6 μm to the IRAS in-band fluxes, using the results of Infrared Space Observatory PHT Spectrophotometer observation of 16 galaxies by Lu et al. in 1997. The model is used to estimate more properly the k-corrections for calculating the rest frame 12 and 25 μm fluxes and luminosities of IRAS galaxies. We have studied the 12-25 μm color-luminosity relation for a sample of galaxies selected at 25 μm. The color is found to correlate well with the 25 μm luminosity, the mid-IR luminosity, and the ratio of far-infrared and blue luminosities. The relations with the mid-IR luminosities are more sensitive to different populations of galaxies, while a single relation of the 12-25 μm color versus the ratio of the far-infrared and blue luminosities applies equally well to these different populations. The luminous and ultraluminous infrared galaxies have redder 12-25 μm colors than those of the quasars. These relations provide powerful tools to differentiate different populations of galaxies. The local luminosity function at 12 μm provides the basis for interpreting the results of deep mid-IR surveys planned or in progress with Infrared Space Observatory, Wide-Field Infrared Explorer, and Space Infrared Telescope Facility. We have selected a sample of 668 galaxies from the IRAS Faint Source Survey flux density limited at 200 mJy at 12 μm. A 12 μm local luminosity function is derived and, for the first time in the literature, effects of density variation in the local universe are considered and corrected in the calculation of the 12 μm luminosity function. It is also found that the 12 μm selected sample is dominated by quasars and active galaxies, which therefore strongly affect the 12 μm luminosity function at high luminosities. The ultraluminous infrared galaxies are relatively rare at 12 μm compared to a 25 μm sample.

A Deep Submillimeter Survey of Lensing Clusters: A New Window on Galaxy Formation and Evolution

We present the first results of a submillimeter survey of distant clusters using the new Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. We have mapped fields in two massive, concentrated clusters, A370 at z=0.37 and Cl 2244-02 at z=0.33, at wavelengths of 450 and 850 μm. The resulting continuum maps cover a total area of about 10 arcmin2 to 1 σ noise levels less than 14 and 2 mJy beam-1 at the two wavelengths, 2-3 orders of magnitude deeper than was previously possible. We have concentrated on lensing clusters to exploit the amplification of all background sources by the cluster, improving the sensitivity by a factor of 1.3-2 as compared with a blank-field survey. A cumulative source surface density of (2.4±1.0)×103 deg-2 is found to a 50% completeness limit of ~4 mJy at 850 μm. The submillimeter spectral properties of these sources indicate that the majority lie at high redshift, z>1. Without correcting for lens amplification, our observations limit the blank-field counts at this depth. The surface density is 3 orders of magnitude greater than the expectation of a nonevolving model using the local IRAS 60 μm luminosity function. The observed source counts thus require a substantial increase in the number density of strongly star-forming galaxies in the high-redshift universe and suggest that optical surveys may have substantially underestimated the star formation density in the distant universe. Deeper submillimeter surveys with SCUBA should detect large numbers of star-forming galaxies at high redshift and so provide strong constraints on the formation of normal galaxies.