We construct rest-frame luminosity functions (LFs) at 3.6, 4.5, 5.8, 8 and 24 μm over the redshift range 0 < z < 2 for galaxies and 0 < z < 4 for optical quasi-stellar objects (QSOs), using optical ...and infrared (IR) data from the Spitzer Wide-area Infrared Extragalactic (SWIRE) Survey. The 3.6- and 4.5-μm galaxy LFs show evidence for moderate positive luminosity evolution up to z∼ 1.5, consistent with the passive ageing of evolved stellar populations. Their comoving luminosity density was found to evolve passively, gradually increasing out to z∼ 0.5-1 but flattening, or even declining, at higher redshift. Conversely, the 24-μm galaxy LF, which is more sensitive to obscured star formation and/or active galactic nuclei (AGN) activity, undergoes strong positive evolution, with the derived IR energy density and star formation rate (SFR) density ∝ (1 +z)γ with γ= 4.5+0.7
−0.6 and the majority of this evolution occurring since z∼ 1. Optical QSOs, however, show positive luminosity evolution in all bands, out to the highest redshifts (3 < z < 4). Modelling as L*∝ (1 +z)γ gave γ= 1.3+0.1
−0.1 at 3.6 μm, γ= 1.0+0.1
−0.1 at 4.5 μm and stronger evolution at the longer wavelengths (5.8, 8 and 24 μm), of γ∼ 3. Comparison of the galaxy LFs to predictions from a semi-analytic model based on cold dark matter (CDM) indicates that an initial mass function (IMF) skewed towards higher mass star formation in bursts compared to locally be preferred. As a result, the currently inferred massive SFRs in distant submm sources may require substantial downwards revision.
We use the unparalleled statistics of the VIPERS survey to investigate the relation between the surface mean stellar mass density Σ = ℳ/ (2 πRe2) ( 2 π R e 2 ) $ (2\,\pi{R}_{\mathrm{e}}^{2}) $ of ...massive passive galaxies (MPGs, ℳ ≥ 1011 M⊙) and their local environment in the redshift range 0.5 ≤ z ≤ 0.8. Passive galaxies were selected on the basis of their NUVrK colors (∼900 objects), and the environment was defined as the galaxy density contrast, δ, using the fifth nearest-neighbor approach. The analysis of Σ versus δ was carried out in two stellar mass bins. In galaxies with ℳ ≤ 2 × 1011 M⊙, no correlation between Σ and δ is observed. This implies that the accretion of satellite galaxies, which is more frequent in denser environments (groups or cluster outskirts) and efficient in reducing the galaxy Σ, is not relevant in the formation and evolution of these systems. Conversely, in galaxies with ℳ > 2 × 1011 M⊙, we find an excess of MPGs with low Σ and a deficit of high-Σ MPGs in the densest regions with respect to other environments. We interpret this result as due to the migration of some high-Σ MPGs (< 1% of the total population of MPGs) into low-Σ MPGs, probably through mergers or cannibalism of small satellites. In summary, our results imply that the accretion of satellite galaxies has a marginal role in the mass-assembly history of most MPGs. We have previously found that the number density of VIPERS massive star-forming galaxies (MSFGs) declines rapidily from z = 0.8 to z = 0.5, which mirrors the rapid increase in the number density of MPGs. This indicates that the MSFGs at z ≥ 0.8 migrate to the MPG population. Here, we investigate the Σ–δ relation of MSFGs at z ≥ 0.8 and find that it is consistent within 1σ with that of low-Σ MPGs at z ≤ 0.8. Thus, the results of this and our previous paper show that MSFGs at z ≥ 0.8 are consistent in terms of number and environment with being the progenitors of low-Σ MPGs at z < 0.8.
We present SHARC-2 350 μm data on 20 luminous z ~ 2 starbursts with S 1.2 mm > 2 mJy from the Spitzer-selected samples of Lonsdale et al. and Fiolet et al. All the sources were detected, with S 350 ...μm > 25 mJy for 18 of them. With the data, we determine precise dust temperatures and luminosities for these galaxies using both single-temperature fits and models with power-law mass-temperature distributions. We derive appropriate formulae to use when optical depths are non-negligible. Our models provide an excellent fit to the 6 μm-2 mm measurements of local starbursts. We find characteristic single-component temperatures T 1 ~= 35.5 ± 2.2 K and integrated infrared (IR) luminosities around 1012.9 ± 0.1 L sun for the SWIRE-selected sources. Molecular gas masses are estimated at sime4 × 1010 M sun, assuming κ850 μm = 0.15 m2 kg-1 and a submillimeter-selected galaxy (SMG)-like gas-to-dust mass ratio. The best-fit models imply gsim2 kpc emission scales. We also note a tight correlation between rest-frame 1.4 GHz radio and IR luminosities confirming star formation as the predominant power source. The far-IR properties of our sample are indistinguishable from the purely submillimeter-selected populations from current surveys. We therefore conclude that our original selection criteria, based on mid-IR colors and 24 μm flux densities, provides an effective means for the study of SMGs at z ~ 1.5-2.5.
We measure the real-space galaxy power spectrum on large scales at redshifts 0.5-1.2 using optical colour selected samples from the Canada-France-Hawaii Telescope Legacy Survey. With the redshift ...distributions measured with a preliminary ∼14 000 spectroscopic redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS), we deproject the angular distribution and directly estimate the three-dimensional power spectrum. We use a maximum likelihood estimator that is optimal for a Gaussian random field giving well-defined window functions and error estimates. This measurement presents an initial look at the large-scale structure field probed by the VIPERS. We measure the galaxy bias of the VIPERS-like sample to be b
g= 1.38 ± 0.05 (σ8= 0.8) on scales k < 0.2 h Mpc−1 averaged over 0.5 < z < 1.2. We further investigate three photometric redshift slices, and marginalizing over the bias factors while keeping other Λ cold dark matter parameters fixed, we find the matter density Ωm= 0.30 ± 0.06.
Aims. We analyse the properties of the host galaxies of a NeV-selected sample to investigate whether and how they are affected by the AGN. Methods. We have selected a sample of galaxies at 0.62 < z ...< 1.2 from the VIMOS Public Extragalactic Redshift Survey (VIPERS) and divided it in blue cloud galaxies, red passive galaxies and green valley galaxies using the NUVrK diagram. Within each category, galaxies with AGN activity were identified based on the detection of the high-ionisation NeVλ3426 emission line. For each galaxy we derived several properties (stellar age and mass, the (r−K) colour, the OII luminosity) and compared them between active and inactive galaxies matched in stellar mass and redshift. Results. We find statistically significant differences in the properties between active and inactive galaxies. These differences imply that the AGN is more often found in galaxies with younger stellar populations and more recent star-forming activity than their parent samples. Interestingly, the AGN identified through the NeVλ3426 emission line is not commonly found by traditional AGN-selection techniques based on shallow X-ray data, mid-IR colours, and classical line diagnostic diagrams, and might thus reveal a specific evolutionary phase. The spectral analysis reveals a sub-set of AGN within the blue cloud that has spectral signatures implying a sudden suppression of star formation activity similar to post-starburst galaxies. Conclusion. Using the rich dataset of the large VIPERS sample we identify a novel class of active post-starburst galaxies that would be missed by traditional selection techniques. These galaxies belong to the blue cloud, but their star-formation activity has been recently suppressed, possibly by the AGN identified through the presence of the NeVλ3426 emission line in their spectra. Our results support the idea that AGN feedback may be responsible for halting star-formation in active blue galaxies and for their transition into the red sequence, at least in the 0.6–1.2 redshift range and for stellar masses greater than 5 × 1010 ℳ⊙. Our results are based on a complete spectroscopic sample and limited by the NeV observability, and the AGN can be variable and with a relatively short duty cycle. Considering this, AGN feedback that makes blue galaxies quickly transition to the red sequence may be even more common than previously believed.
The VIPERS galaxy survey has measured the clustering of 0.5 < z < 1.2 galaxies, enabling a number of measurements of galaxy properties and cosmological redshift-space distortions (RSD). Because the ...measurements were made using one-pass of the VIMOS instrument on the Very Large Telescope (VLT), the galaxies observed only represent approximately 47% of the parent target sample, with a distribution imprinted with the pattern of the VIMOS slitmask. Correcting for the effect on clustering has previously been achieved using an approximate approach developed using mock catalogues. Pairwise inverse probability (PIP) weighting has recently been proposed to correct for missing galaxies, and we apply it to mock VIPERS catalogues to show that it accurately corrects the clustering for the VIMOS effects, matching the clustering measured from the observed sample to that of the parent. We then apply PIP-weighting to the VIPERS data, and fit the resulting monopole and quadrupole moments of the galaxy two-point correlation function with respect to the line-of-sight, making measurements of RSD. The results are close to previous measurements, showing that the previous approximate methods used by the VIPERS team are sufficient given the errors obtained on the RSD parameter.
Aims. Various galaxy classification schemes have been developed so far to constrain the main physical processes regulating evolution of different galaxy types. In the era of a deluge of astrophysical ...information and recent progress in machine learning, a new approach to galaxy classification has become imperative. Methods. In this paper, we employ a Fisher Expectation-Maximization (FEM) unsupervised algorithm working in a parameter space of 12 rest-frame magnitudes and spectroscopic redshift. The model (DBk) and the number of classes (12) were established based on the joint analysis of standard statistical criteria and confirmed by the analysis of the galaxy distribution with respect to a number of classes and their properties. This new approach allows us to classify galaxies based on only their redshifts and ultraviolet to near-infrared (UV–NIR) spectral energy distributions. Results. The FEM unsupervised algorithm has automatically distinguished 12 classes: 11 classes of VIPERS galaxies and an additional class of broad-line active galactic nuclei (AGNs). After a first broad division into blue, green, and red categories, we obtained a further sub-division into: three red, three green, and five blue galaxy classes. The FEM classes follow the galaxy sequence from the earliest to the latest types, which is reflected in their colours (which are constructed from rest-frame magnitudes used in the classification procedure) but also their morphological, physical, and spectroscopic properties (not included in the classification scheme). We demonstrate that the members of each class share similar physical and spectral properties. In particular, we are able to find three different classes of red passive galaxy populations. Thus, we demonstrate the potential of an unsupervised approach to galaxy classification and we retrieve the complexity of galaxy populations at z ∼ 0.7, a task that usual, simpler, colour-based approaches cannot fulfil.
Aims. The three-point correlation function (3PCF) is a powerful probe to investigate the clustering of matter in the Universe in a complementary way with respect to lower-order statistics, providing ...additional information with respect to the two-point correlation function and allowing us to shed light on biasing, non-linear processes, and deviations from Gaussian statistics. In this paper, we analyse the first data release of the VIMOS Public Extragalactic Redshift Survey (VIPERS), determining the dependence of the three-point correlation function on luminosity and stellar mass at z = 0.5,1.1 . Methods. We exploit the VIPERS Public Data Release 1, consisting of more than 50 000 galaxies with B-band magnitudes in the range − 21.6 ≲ MB − 5log (h) ≲ − 19.9 and stellar masses in the range 9.8 ≲ log (M⋆ h-2M⊙ ) ≲ 10.7. We measure both the connected 3PCF and the reduced 3PCF in redshift space, probing different configurations and scales, in the range 2.5 <rh-1 Mpc < 20. Results. We find a significant dependence of the reduced 3PCF on scales and triangle shapes, with stronger anisotropy at larger scales (r ~ 10h-1 Mpc ) and an almost flat trend at smaller scales, r ~ 2.5h-1 Mpc . Massive and luminous galaxies present a larger connected 3PCF, while the reduced 3PCF is remarkably insensitive to magnitude and stellar masses in the range we explored. These trends, already observed at low redshifts, are confirmed for the first time to be still valid up to z = 1.1, providing support to the hierarchical scenario for which massive and bright systems are expected to be more clustered. The possibility of using the measured 3PCF to provide independent constraints on the linear galaxy bias b has also been explored, showing promising results in agreement with other probes.
ABSTRACT
We present a combined galaxy–quasar approach to template‐fitting photometric redshift techniques and show the method to be a powerful one.
The code (ImpZ) is presented, developed and applied ...to two spectroscopic redshift catalogues, namely the Isaac Newton Telescope Wide‐Angle Survey ELAIS N1 and N2 fields and the Chandra Deep Field North. In particular, optical size information is used to improve the redshift determination. The success of the code is shown to be very good, with Δz/(1 +z) constrained to within 0.1 for 92 per cent of the galaxies in our sample.
The extension of template fitting to quasars is found to be reasonable, with Δz/(1 +z) constrained to within 0.25 for 68 per cent of the quasars in our sample. Various template extensions into the far‐ultraviolet are also tested.
We present millimetre observations of a sample of 12 high-redshift ultraluminous infrared galaxies (ULIRGs) in the extended growth strip (EGS). These objects were initially selected on the basis of ...their observed mid-IR colours (0.0 < 3.6−4.5 < 0.4 and −0.7 < 3.6−8.0 < 0.5) to lie at high redshift 1.5 ≲z≲ 3, and subsequent 20–38 μm mid-IR spectroscopy confirms that they lie in a narrow redshift window centred on z≈ 2. We detect 9/12 of the objects in our sample at high significance (>3σ) with a mean 1200 μm flux of 〈F1200 μm〉= 1.6 ± 0.1 mJy. Our millimetre photometry, combined with existing far-IR photometry from the Far-IR Deep Extragalactic Legacy Survey (FIDELS) and accurate spectroscopic redshifts, places constraints both sides of the thermal dust peak. This allows us to estimate the dust properties, including the far-IR luminosity, dust temperature and dust mass. We find that our sample is similar to other high-z and intermediate-z ULIRGs, and local systems, but has a different dust selection function than submillimeter-selected galaxies. Finally, we use existing 20-cm radio continuum imaging to test the far-IR/radio correlation at high redshift. We find that our sample is consistent with the local relation, implying little evolution. Furthermore, this suggests that our sample selection method is efficient at identifying ultraluminous, starburst-dominated systems within a very narrow redshift range centred at z∼ 2.
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