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Register a new userThe K20 survey. V The evolution of the near-IR Luminosity Function
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L. Pozzetti
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We present the galaxy rest-frame near-IR Luminosity Function (LF) and its cosmic evolution to z=1.5 based on a spectroscopic survey of a magnitude limited sample of galaxies with Ks<20 (the K20 survey, Cimatti et al. 2002b). The LFs have been derived in the rest-frame J and Ks bands using 3 z bins (z_mean= 0.5, 1, 1.5) and compared to the local near-IR LF. The faint-end of the LFs is consistent with the local estimates, with no evidence for a change either in the slope or normalization up to z<1.3. Viceversa, the density of luminous galaxies (M_Ks-5logh_70<-25.5) is higher than locally at all z and relatively constant or mildly increasing with z within our sample. The data are consistent with a mild luminosity evolution both in the J and Ks-band up to z=1.5 (DeltaM_J=-0.69+-0.12 and DeltaM_K=-0.54+-0.12 at z=1). Moreover, we find that red and early-type galaxies dominate the bright-end of the LF, and that their number density shows at most a small decrease (<30%) up to z=1, thus suggesting that massive elliptical galaxies were already in place at z=1 and they should have formed their stars and assembled their mass at higher z. There appears to be a correlation of the optical/near-IR colors with near-IR luminosities, the most luminous/massive galaxies being red/old. We find a slow evolution with z of the near-IR comoving luminosity density to z=1.5. Finally, we show that hierarchical models overpredict significantly the density of low luminosity galaxies at z<=1 and underpredict the density of luminous galaxies at z>=1, whereas PLE models are more consistent with the data up to z=1.5. The GIF model (Kaufmann et al. 1999) shows a clear deficiency of red luminous galaxies at z=1 compared to our observations and predicts a decrease of luminous galaxies with z not observed in our sample.
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We present new results on the cosmological evolution of the near-infrared galaxy luminosity function, derived from the analysis of a new sample of ~22,000 K(AB) < 22.5 galaxies selected over an area of 0.6 square degrees from the Early Data Release of the UKIDSS Ultra Deep Survey (UDS). Our study has exploited the multi-wavelength coverage of the UDS field provided by the new UKIDSS WFCAM K and J-band imaging, the Subaru/XMM-Newton Deep Survey and the Spitzer-SWIRE Survey. The unique combination of large area and depth provided by this new survey minimises the complicating effect of cosmic variance and has allowed us, for the first time, to trace the evolution of the brightest sources out to z~2 with good statistical accuracy. In agreement with previous studies we find that the characteristic luminosity of the near-infrared luminosity function brightens by 1 magnitude between z=0 and z~2, while the total density decreases by a factor ~2. Using the rest-frame (U-B) colour to split the sample into red and blue galaxies, we confirm the classic luminosity-dependent colour bimodality at z<1. However, the strength of the colour bimodality is found to be a decreasing function of redshift, and seems to disappear by z>1.5. Due to the large size of our sample we are able to investigate the differing cosmological evolution of the red and blue galaxy populations. It is found that the space density of the brightest red galaxies (M_K < -23) stays approximately constant with redshift, and that these sources dominate the bright-end of the luminosity function at redshifts z<1. In contrast, the brightening of the characteristic luminosity and mild decrease in space density displayed by the blue galaxy population leads them to dominate the bright-end of the luminosity function at redshifts z>1.
The Smithsonian Hectospec Lensing Survey (SHELS) is a window on the star formation history over the last 4 Gyr. SHELS is a spectroscopically complete survey for Rtot < 20.3 over 4 square degrees. We use the 10k spectra to select a sample of pure star forming galaxies based on their Halpha emission line. We use the spectroscopy to determine extinction corrections for individual galaxies and to remove active galaxies in order to reduce systematic uncertainties. We use the large volume of SHELS with the depth of a narrowband survey for Halpha galaxies at z ~ 0.24 to make a combined determination of the Halpha luminosity function at z ~ 0.24. The large area covered by SHELS yields a survey volume big enough to determine the bright end of the Halpha luminosity function from redshift 0.100 to 0.377 for an assumed fixed faint-end slope alpha = -1.20. The bright end evolves: the characteristic luminosity L* increases by 0.84 dex over this redshift range. Similarly, the star formation density increases by 0.11 dex. The fraction of galaxies with a close neighbor increases by a factor of 2-5 for L(Halpha) >~ L* in each of the redshift bins. We conclude that triggered star formation is an important influence for star forming galaxies with Halpha emission.
The K20 survey is a near infrared-selected, deep (Ks < 20) redshift survey targeting galaxies in two independent regions of the sky, the CDFS and the q0055-2659 field. The total Ks-selected sample includes 545 objects. Optical spectra for 525 of them have been obtained, providing 501 spectroscopic identifications (including 12 type-1 AGN and 45 stars). This paper describes the final K20 spectroscopic catalogue, along with the technique used to determine redshifts, measure the spectral features and characterize the spectra. The classification of the galaxy spectra has been performed according to a simple parametric recipe that uses the equivalent widths of the two main emission lines (O[II] and Halpha+[N II]) and two continuum indices (the 4000A break index, and a near-UV color index, C(28-39)). We defined three main spectroscopic classes: red early-type galaxies, blue emission-line galaxies and the intermediate galaxies, which show emission lines but a red continuum. More than 95% of the examined galaxies is included in one of these spectral types and a composite spectrum is built for each of the three galaxy classes. The blue emission-line and the early-type galaxies have been divided in redshift bins, and the corresponding composite spectra have been built, in order to investigate the evolution of the spectral properties of the K20 galaxies with redshift.
We present the first results from the 2mm Mapping Obscuration to Reionization (MORA) survey, the largest ALMA contiguous blank-field survey to-date with a total area of 184 sq. arcmin and the only at 2mm to search for dusty star-forming galaxies (DSFGs). We use the 13 sources detected above 5sigma to estimate the first ALMA galaxy number counts at this wavelength. These number counts are then combined with the state-of-the-art galaxy number counts at 1.2mm and 3mm and with a backward evolution model to place constraints on the evolution of the IR luminosity function and dust-obscured star formation in the last 13 billion years. Our results suggest a steep redshift evolution on the space density of DSFGs and confirm the flattening of the IR luminosity function at faint luminosities, with a slope of $alpha_{LF} = -0.42^{+0.02}_{-0.04}$. We conclude that the dust-obscured component, which peaks at z=2-2.5, has dominated the cosmic history of star formation for the past ~12 billion years, back to z~4. At z=5, the dust-obscured star formation is estimated to be ~35% of the total star formation rate density and decreases to 25%-20% at z=6-7, implying a minor contribution of dust-enshrouded star formation in the first billion years of the Universe. With the dust-obscured star formation history constrained up to the end of the epoch of reionization, our results provide a benchmark to test galaxy formation models, to study the galaxy mass assembly history, and to understand the dust and metal enrichment of the Universe at early times.
The ALHAMBRA survey aims to cover 4 square degrees using a system of 20 contiguous, equal width, medium-band filters spanning the range 3500 A to 9700 A plus the standard JHKs filters. Here we analyze deep near-IR number counts of one of our fields (ALH08) for which we have a relatively large area (0.5 square degrees) and faint photometry (J=22.4, H=21.3 and K=20.0 at the 50% of recovery efficiency for point-like sources). We find that the logarithmic gradient of the galaxy counts undergoes a distinct change to a flatter slope in each band: from 0.44 at [17.0, 18.5] to 0.34 at [19.5, 22.0] for the J band; for the H band 0.46 at [15.5, 18.0] to 0.36 at [19.0, 21.0], and in Ks the change is from 0.53 in the range [15.0, 17.0] to 0.33 in the interval [18.0, 20.0]. These observations together with faint optical counts are used to constrain models that include density and luminosity evolution of the local type-dependent luminosity functions. Our models imply a decline in the space density of evolved early-type galaxies with increasing redshift, such that only 30% - 50% of the bulk of the present day red-ellipticals was already in place at z~1.
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