The infrared luminosity function of galaxies at redshifts z=1 and z~2 in the GOODS fields

We present the rest-frame 8 micron luminosity function (LF) at redshifts z=1 and ~2, computed from Spitzer 24 micron-selected galaxies in the GOODS fields over an area of 291 sq. arcmin. Using classification criteria based on X-ray data and IRAC colours, we identify the AGN in our sample. The rest-frame 8 micron LF for star-forming galaxies at redshifts z=1 and ~2 have the same shape as at z~0, but with a strong positive luminosity evolution. The number density of star-forming galaxies with log_{10}(nu L_nu(8 micron))>11 increases by a factor >250 from redshift z~0 to 1, and is basically the same at z=1 and ~2. The resulting rest-frame 8 micron luminosity densities associated with star formation at z=1 and ~2 are more than four and two times larger than at z~0, respectively. We also compute the total rest-frame 8 micron LF for star-forming galaxies and AGN at z~2 and show that AGN dominate its bright end, which is well-described by a power-law. Using a new calibration based on Spitzer star-forming galaxies at 0<z<0.6 and validated at higher redshifts through stacking analysis, we compute the bolometric infrared (IR) LF for star-forming galaxies at z=1 and ~2. We find that the respective bolometric IR luminosity densities are (1.2+/-0.2) x 10^9 and (6.6^{+1.2}_{-1.0}) x 10^8 L_sun Mpc^{-3}, in agreement with previous studies within the error bars. At z~2, around 90% of the IR luminosity density associated with star formation is produced by luminous and ultraluminous IR galaxies (LIRG and ULIRG), with the two populations contributing in roughly similar amounts. Finally, we discuss the consistency of our findings with other existing observational results on galaxy evolution.Comment: Accepted for publication in the ApJ. 33 pages, 15 figures. Uses emulateap

The Cosmic Far-Infrared Background Buildup Since Redshift 2 at 70 and 160 microns in the COSMOS and GOODS fields

The Cosmic Far-Infrared Background (CIB) at wavelengths around 160 {\mu}m corresponds to the peak intensity of the whole Extragalactic Background Light, which is being measured with increasing accuracy. However, the build up of the CIB emission as a function of redshift, is still not well known. Our goal is to measure the CIB history at 70 {\mu}m and 160 {\mu}m at different redshifts, and provide constraints for infrared galaxy evolution models. We use complete deep Spitzer 24 {\mu}m catalogs down to about 80 {\mu}Jy, with spectroscopic and photometric redshifts identifications, from the GOODS and COSMOS deep infrared surveys covering 2 square degrees total. After cleaning the Spitzer/MIPS 70 {\mu}m and 160 {\mu}m maps from detected sources, we stacked the far-IR images at the positions of the 24 {\mu}m sources in different redshift bins. We measured the contribution of each stacked source to the total 70 and 160 {\mu}m light, and compare with model predictions and recent far-IR measurements made with Herschel/PACS on smaller fields. We have detected components of the 70 and 160 {\mu}m backgrounds in different redshift bins up to z ~ 2. The contribution to the CIB is maximum at 0.3 <= z <= 0.9 at 160{\mu}m (and z <= 0.5 at 70 {\mu}m). A total of 81% (74%) of the 70 (160) {\mu}m background was emitted at z < 1. We estimate that the AGN relative contribution to the far-IR CIB is less than about 10% at z < 1.5. We provide a comprehensive view of the CIB buildup at 24, 70, 100, 160 {\mu}m. IR galaxy models predicting a major contribution to the CIB at z < 1 are in agreement with our measurements, while our results discard other models that predict a peak of the background at higher redshifts. Our results are available online http://www.ias.u-psud.fr/irgalaxies/ .Comment: Accepted in Astronomy & Astrophysic

Direct Measurement of the Photon Statistics of a Triggered Single Photon Source

We studied intensity fluctuations of a single photon source relying on the pulsed excitation of the fluorescence of a single molecule at room temperature. We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of observation timescale T, by recording every photocount. On timescale of a few excitation periods, subpoissonian statistics is clearly observed and the probablility of two-photons events is 10 times smaller than Poissonian pulses. On longer times, blinking in the fluorescence, due to the molecular triplet state, produces an excess of noise.Comment: 4 pages, 3 figures, 1 table submitted to Physical Review Letter

A method for quantifying the gamma-ray burst bias. Application in the redshift range of 0–1.1

International audienceContext. Long gamma-ray bursts (LGRBs) are related to the final stages of evolution of very massive stars. As such, they should follow the star formation rate (SFR) of galaxies. We can use them to probe for star-forming galaxies in the distant universe following this assumption. The relation between the rate of LGRBs in a given galaxy and its SFR (which we call the LGRB bias) may however be complex, as we have good indications that the LGRB hosts are not perfect analogues to the general population of star-forming galaxies. Aims. In this work, we try to quantify how the LGRB bias depends on physical parameters of their host galaxy, such as SFR or stellar mass. These trends may reveal more fundamental properties such as the role of the metallicity of LGRBs and of their progenitors .Methods. We propose an empirical method based on the comparison of stellar mass functions (and SFR distributions) of LGRB hosts and of star-forming galaxies to find how the bias depends on the stellar mass or the SFR.Results. By applying this method to a sample of LGRB hosts at redshifts lower than 1.1, where the properties of star-forming galaxies are fairly well established and where the properties of LGRB host galaxies can be deduced from observations (limiting ourselves to stellar masses higher than 109.25M⊙ and SFR higher than ~1.8 M⊙ yr-1), we find that the LGRB bias depends on both the stellar mass and SFR. We find that the bias decreases with the SFR; that is, we see no preference for highly star-forming galaxies, once we account for the higher number of massive stars in galaxies with larger SFR. We do not find any trend with the specific star formation rate (SSFR), but the dynamical range in SSFR in our study is narrow. Through an indirect method, we relate these trends to a possible decrease in the LGRBs rate / SFR ratio with the metallicity.Conclusions. The method we propose suggests trends that may be useful to constrain models of LGRB progenitors, showing a clear decrease in the LGRB bias with the metallicity. This is promising for the future as the number of LGRB hosts studied will increase

Dust Properties and Star-Formation Rates in Star-Forming Dwarf Galaxies

We have used the Spitzer Space Telescope to study the dust properties of a sample of star-forming dwarf galaxies. The differences in the mid-infrared spectral energy distributions for these galaxies which, in general, are low metallicity systems, indicate differences in the physical properties, heating, and/or distribution of the dust. Specifically, these galaxies have more hot dust and/or very small grains and less PAH emission than either spiral or higher luminosity starburst galaxies. As has been shown in previous studies, there is a gradual decrease in PAH emission as a function of metallicity. Because much of the energy from star formation in galaxies is re-radiated in the mid-infrared, star-formation rate indicators based on both line and continuum measurements in this wavelength range are coming into more common usage. We show that the variations in the interstellar medium properties of galaxies in our sample, as measured in the mid-infrared, result in over an order of magnitude spread in the computed star-formation rates.Comment: 25 pages, 11 figures, 4 tables, ApJ accepte

Planck's dusty GEMS. V. Molecular wind and clump stability in a strongly lensed star-forming galaxy at z=2.2

We report the discovery of a molecular wind signature from a massive intensely star-forming clump of a few $10^9$ Msun, in the strongly gravitationally lensed submillimeter galaxy "the Emerald" (PLCK_G165.7+49.0) at z=2.236. The Emerald is amongst the brightest high-redshift galaxies on the submillimeter sky, and was initially discovered with the Planck satellite. The system contains two magnificient structures with projected lengths of 28.5" and 21" formed by multiple, near-infrared arcs, falling behind a massive galaxy cluster at z=0.35, as well as an adjacent filament that has so far escaped discovery in other wavebands. We used HST/WFC3 and CFHT optical and near-infrared imaging together with IRAM and SMA interferometry of the CO(4-3) line and 850 $\mu$m dust emission to characterize the foreground lensing mass distribution, construct a lens model with Lenstool, and calculate gravitational magnification factors between 20 and 50 in most of the source. The majority of the star formation takes place within two massive star-forming clumps which are marginally gravitationally bound and embedded in a $9 \times 10^{10}$ Msun, fragmented disk with 20% gas fraction. One of the clumps shows a pronounced blue wing in the CO(4-3) line profile, which we interpret as a wind signature. The mass outflow rates are high enough for us to suspect that the clump might become unbound within a few tens of Myr, unless the outflowing gas can be replenished by gas accretion from the surrounding disk. The velocity offset of -200 km s$^{-1}$ is above the escape velocity of the clump, but not that of the galaxy overall, suggesting that much of this material might ultimately rain back onto the galaxy and contribute to fueling subsequent star formation.Comment: 24 pages, 13 Figures, accepted for publication in A&

Spitzer Mid-to-Far-Infrared Flux Densities of Distant Galaxies

We study the infrared (IR) properties of high-redshift galaxies using deep Spitzer 24, 70, and 160 micron data. Our primary interest is to improve the constraints on the total IR luminosities, L(IR), of these galaxies. We combine the Spitzer data in the southern Extended Chandra Deep Field with a K-band-selected galaxy sample and photometric redshifts from the Multiwavelength Survey by Yale-Chile. We used a stacking analysis to measure the average 70 and 160 micron flux densities of 1.5 < z < 2.5 galaxies as a function of 24 micron flux density, X-ray activity, and rest-frame near-IR color. Galaxies with 1.5 < z < 2.5 and S(24)=53-250 micro-Jy have L(IR) derived from their average 24-160 micron flux densities within factors of 2-3 of those derived from the 24 micron flux densities only. However, L(IR) derived from the average 24-160 micron flux densities for galaxies with S(24) > 250 micro-Jy and 1.5 < z < 2.5 are lower than those derived using only the 24 micron flux density by factors of 2-10. Galaxies with S(24) > 250 micro-Jy have S(70)/S(24) flux ratios comparable to sources with X-ray detections or red rest-frame IR colors, suggesting that warm dust possibly heated by AGN may contribute to the high 24 micron emission. Based on the average 24-160 micron flux densities, nearly all 24 micron-selected galaxies at 1.5 < z < 2.5 have L(IR) < 6 x 10^12 solar luminosities, which if attributed to star formation corresponds to < 1000 solar masses per year. This suggests that high redshift galaxies may have similar star formation efficiencies and feedback processes as local analogs. Objects with L(IR) > 6 x 10^12 solar luminosities are quite rare, with a surface density ~ 30 +/- 10 per sq. deg, corresponding to ~ 2 +/- 1 x 10^-6 Mpc^-3 over 1.5 < z < 2.5.Comment: Accepted for Publication in ApJ. AASTeX format. 34 pages, 12 figures. Updated references and other small textual revision

Planck \u27s Dusty GEMS: VIII. Dense-gas reservoirs in the most active dusty starbursts at z ∼3

We present ALMA, NOEMA, and IRAM-30 m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at z≲ 3-3.5, part of the Planck\u27s Dusty Gravitationally Enhanced subMillimetre Sources (GEMS), with the aim of probing the gas reservoirs closely associated with their exceptional levels of star formation. We obtained robust detections of ten emission lines between Jup = 4 and 6, as well as several additional upper flux limits. In PLCK_G244.8+54.9, the brightest source at z = 3.0, the HNC(5-4) line emission at 0.1″ resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. This line is blended with CN(4-3) and in this source, we measure a HNC(5-4)/CN(4-3) flux ratio of 1.76 \ub10. 86. Dense-gas line profiles generally match those of mid-J CO lines, except in PLCK_G145.2+50.8, which also has dense-gas line fluxes that are relatively lower, perhaps due to fewer dense cores and more segregated dense and diffuse gas phases in this source. The HCO+/HCN 1 and HNC/HCN ∼ 1 line ratios in our sample are similar to those of nearby ultraluminous infrared galaxies (ULIRGs) and consistent with photon-dominated regions without any indication of important mechanical heating or active galactic nuclei feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with an H2 density of n ∼ 105-106 cm-3, although important degeneracies hinder a determination of the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z ∼ 3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional as compared to other lensed dusty star-forming galaxies at z &gt; 2, and they fall near the upper envelope of local ULIRGs. Despite the higher overall gas fractions and local gas-mass surface densities observed at high redshift, the dense-gas budget of rapidly star-forming galaxies seems to have evolved little between z ∼ 3 and z ∼ 0. Our results favor constant dense-gas depletion times in these populations, which is in agreement with theoretical models of star formation

The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip

We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. The majority of z 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.Comment: 24 pages, including 3 tables and 18 color figures; accepted to the Astrophysical Journal; high resolution version available at http://www.noao.edu/noao/staff/lotz/lotz_mergers.pd