arXiv subjects

P. Kampczyk

Publications and source records attributed to P. Kampczyk.

64 records · Page 4Linked to original sources

arXiv2008

Ongoing and co-evolving star formation in zCOSMOS galaxies hosting Active Galactic Nuclei

We present a study of the host galaxies of AGN selected from the zCOSMOS survey to establish if accretion onto supermassive black holes and star formation are explicitly linked up to z~1. We identify 152 galaxies that harbor AGN, based on XMM observations of 7543 galaxies (i<22.5). Star formation rates (SFRs), including those weighted by stellar mass, are determined using the [OII]3727 emission-line, corrected for an AGN contribution. We find that the majority of AGN hosts have significant levels of star formation with a distribution spanning ~1-100 Msun yr^-1. The close association between AGN activity and star formation is further substantiated by an increase in the AGN fraction with the youthfulness of their stars as indicated by the rest-frame color (U-V) and spectral index Dn(4000); we demonstrate that mass-selection alleviates an artifical peak falling in the transition region when using luminosity-limited samples. We also find that the SFRs of AGN hosts evolve with cosmic time in a manner that closely mirrors the overall galaxy population and explains the low SFRs in AGNs (z<0.3) from the SDSS. We conclude that the conditions most conducive for AGN activity are a massive host galaxy and a large reservoir of gas. Furthermore, a direct correlation between mass accretion rate onto SMBHs and SFR is shown to be weak although the average ratio is constant with redshift, effectively shifting the evidence for a co-evolution scenario in a statistical manner to smaller physical scales. Our findings illustrate an intermittent scenario with an AGN lifetime substantially shorter than that of star formation and underlying complexities regarding fueling over vastly different physical scales yet to be determined [Abridged].

astro-ph↗

arXiv2008

The zCOSMOS redshift survey: the three-dimensional classification cube and bimodality in galaxy physical properties

Aims. We investigate the relationships between three main optical galaxy observables (spectral properties, colours, and morphology), exploiting the data set provided by the COSMOS/zCOSMOS survey. The purpose of this paper is to define a simple galaxy classification cube, using a carefully selected sample of around 1000 galaxies. Methods. Using medium resolution spectra of the first 1k zCOSMOS-bright sample, optical photometry from the Subaru/COSMOS observations, and morphological measurements derived from ACS imaging, we analyze the properties of the galaxy population out to z~1. Applying three straightforward classification schemes (spectral, photometric, and morphological), we identify two main galaxy types, which appear to be linked to the bimodality of galaxy population. The three parametric classifications constitute the axes of a "classification cube". Results. A very good agreement exists between the classification from spectral data (quiescent/star-forming galaxies) and that based on colours (red/blue galaxies). The third parameter (morphology) is less well correlated with the first two: in fact a good correlation between the spectral classification and that based on morphological analysis (early-/late-type galaxies) is achieved only after partially complementing the morphological classification with additional colour information. Finally, analyzing the 3D-distribution of all galaxies in the sample, we find that about 85% of the galaxies show a fully concordant classification, being either quiescent, red, bulge-dominated galaxies (~20%) or star-forming, blue, disk-dominated galaxies (~65%). These results imply that the galaxy bimodality is a consistent behaviour both in morphology, colour and dominant stellar population, at least out to z~1.

astro-ph↗

arXiv2008

The close environment of 24 micron galaxies at 0.6<z<1.0 in the COSMOS field

We investigate the close environment of 203 Spitzer 24 micron-selected sources at 0.6 1.4. We find that LIRGs at 0.6 1.4 within 1 Mpc and +/- 500 km/s). The contrast between the activities of the close environments of LIRGs and ULIRGs appears especially enhanced in the COSMOS field density peak at z~0.67, because LIRGs on this peak have a larger fraction of passive neighbours, while ULIRGs have as active close environments as those outside the large-scale structure. The differential environmental activity is related to the differences in the distributions of stellar mass ratios between LIRGs/ULIRGs and their close neighbours, as well as in the general local density fields. At 0.8<z<1.0, instead, we find no differences in the environment densities of ULIRGs and other similarly massive galaxies, in spite of the differential activities. We discuss a possible scenario to explain these findings.

astro-ph↗

arXiv2008

COSMOS Photometric Redshifts with 30-bands for 2-deg2

We present accurate photometric redshifts in the 2-deg2 COSMOS field. The redshifts are computed with 30 broad, intermediate, and narrow bands covering the UV (GALEX), Visible-NIR (Subaru, CFHT, UKIRT and NOAO) and mid-IR (Spitzer/IRAC). A chi2 template-fitting method (Le Phare) was used and calibrated with large spectroscopic samples from VLT-VIMOS and Keck-DEIMOS. We develop and implement a new method which accounts for the contributions from emission lines (OII, Hbeta, Halpha and Ly) to the spectral energy distributions (SEDs). The treatment of emission lines improves the photo-z accuracy by a factor of 2.5. Comparison of the derived photo-z with 4148 spectroscopic redshifts (i.e. Delta z = zs - zp) indicates a dispersion of sigma_{Delta z/(1+zs)}=0.007 at i<22.5, a factor of 2-6 times more accurate than earlier photo-z in the COSMOS, CFHTLS and COMBO-17 survey fields. At fainter magnitudes i<24 and z<1.25, the accuracy is sigma_{Delta z/(1+zs)}=0.012. The deep NIR and IRAC coverage enables the photo-z to be extended to z~2 albeit with a lower accuracy (sigma_{Delta z/(1+zs)}=0.06 at i~24). The redshift distribution of large magnitude-selected samples is derived and the median redshift is found to range from z=0.66 at 22<i<22.5 to z=1.06 at 24.5<i<25. At i<26.0, the multi-wavelength COSMOS catalog includes approximately 607,617 objects. The COSMOS-30 photo-z enable the full exploitation of this survey for studies of galaxy and large scale structure evolution at high redshift.

astro-ph↗

arXiv2007

Precision photometric redshift calibration for galaxy-galaxy weak lensing

Accurate photometric redshifts are among the key requirements for precision weak lensing measurements. Both the large size of the Sloan Digital Sky Survey (SDSS) and the existence of large spectroscopic redshift samples that are flux-limited beyond its depth have made it the optimal data source for developing methods to properly calibrate photometric redshifts for lensing. Here, we focus on galaxy-galaxy lensing in a survey with spectroscopic lens redshifts, as in the SDSS. We develop statistics that quantify the effect of source redshift errors on the lensing calibration and on the weighting scheme, and show how they can be used in the presence of redshift failure and sampling variance. We then demonstrate their use with 2838 source galaxies with spectroscopy from DEEP2 and zCOSMOS, evaluating several public photometric redshift algorithms, in two cases including a full p(z) for each object, and find lensing calibration biases as low as 1% (due to fortuitous cancellation of two types of bias) or as high as 20% for methods in active use (despite the small mean photoz bias of these algorithms). Our work demonstrates that lensing-specific statistics must be used to reliably calibrate the lensing signal, due to asymmetric effects of (frequently non-Gaussian) photoz errors. We also demonstrate that large-scale structure (LSS) can strongly impact the photoz calibration and its error estimation, due to a correlation between the LSS and the photoz errors, and argue that at least two independent degree-scale spectroscopic samples are needed to suppress its effects. Given the size of our spectroscopic sample, we can reduce the galaxy-galaxy lensing calibration error well below current SDSS statistical errors.

astro-ph↗

arXiv2007

The redshift evolution of early-type galaxies in COSMOS: Do massive early-type galaxies form by dry mergers?

ABRIDGED: We study the evolution since z~1 of the rest-frame B luminosity function of the early-type galaxies (ETGs) in ~0.7 deg^2 in the COSMOS field. In order to identify ALL progenitors of local ETGs we construct the sample of high-z galaxies using two complementary criteria: (i) A morphological selection based on the Zurich Estimator of Structural Types, and (ii) A photometric selection based on the galaxy properties in the (U-V)-M_V color-magnitude diagram. We furthermore constrain both samples so as to ensure that the selected progenitors of ETGs are compatible with evolving into systems which obey the mu_B-r_{hl} Kormendy relation. Assuming the luminosity evolution derived from studies of the fundamental plane for high-z ETGs, our analysis shows no evidence for a decrease in the number density of the most massive ETGs out to z~ 0.7: Both the morphologically- and the photometrically-selected sub-samples show no evolution in the number density of bright (~L>2.5L*) ETGs. Allowing for different star formation histories, and cosmic variance, we estimate a maximum decrease in the number density of massive galaxies at that redshift of ~30%. We observe, however, in both the photometrical and morphological samples, a deficit of up to ~2-3 of fainter ETGs over the same cosmic period. Our results argue against a significant contribution of recent dissipationless ``dry'' mergers to the formation of the most massive ETGs. We suggest that the mass growth in low luminosity ETGs can be explained with a conversion from z~0.7 to z=0 of blue, irregular and disk galaxies into low- and intermediate-mass ``red'' ETGs, possibly also through gas rich mergers.

astro-ph↗

arXiv2006

zCOSMOS: A Large VLT/VIMOS redshift survey covering 0 < z < 3 in the COSMOS field

zCOSMOS is a large redshift survey that is being undertaken in the COSMOS field using 600 hours of observation with the VIMOS spectrograph on the 8-m VLT. The survey is designed to characterise the environments of COSMOS galaxies from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic web and to produce diagnostic information on galaxies and active galactic nuclei. The zCOSMOS survey consists of two parts: (a) zCOSMOS-bright, a magnitude-limited I-band IAB < 22.5 sample of about 20,000 galaxies with 0.1 < z < 1.2 covering the whole 1.7 deg2 COSMOS ACS field and designed to mimic the parameters of the 2dfGRS; and (b) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through colour-selection criteria to have 1.4 < z < 3.0, within the central 1 deg2. This paper describes the survey design and the construction of the target catalogues, and briefly outlines the observational program and the data pipeline. In the first observing season, spectra of 1303 zCOSMOS-bright targets and of 977 zCOSMOS-deep targets have been obtained. These are briefly analysed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly zCOSMOS-bright, when it is finally completed between 2008-2009. The power of combining spectroscopic and photometric redshifts is demonstrated, especially in correctly identifying the emission line in single-line spectra and in determining which of the less reliable spectroscopic redshifts are correct and which are incorrect. Our zCOSMOS-deep spectra demonstrate the effectiveness of our selection techniques to isolate high redshift galaxies at 1.4 < z < 3.0 and of VIMOS to measure their redshifts using ultraviolet absorption lines.

astro-ph↗

arXiv2006

COSMOS morphological classification with ZEST (the Zurich Estimator of Structural Types) and the evolution since z=1 of the Luminosity Function of early-, disk-, and irregular galaxies

(ABRIDGED) Motivated by the desire to reliably and automatically classify structure of thousands of COSMOS galaxies, we present ZEST, the Zurich Estimator of Structural Types. To classify galaxy structure, ZEST uses: (i) Five non-parametric diagnostics: asymmetry, concentration, Gini coefficient, 2nd-order moment of the brightest 20% of galaxy pixels, and ellipticity; and (ii) The exponent n of single--Sersic fits to the 2D surface brightness distributions. To fully exploit the wealth of information while reducing the redundancy present in these diagnostics, ZEST performs a principal component (PC) Analysis. We use a sample of ~56,000 I<24 COSMOS galaxies to show that the first three PCs fully describe the key aspects of the galaxy structure, i.e., to calibrate a three-dimensional classification grid of axis PC_1, PC_2, and PC_3. We demonstrate the robustness of the ZEST grid on the z=0 sample of Frei et al. (1996). The ZEST classification breaks most of the degeneracy between different galaxy populations that affects morphological classifications based on only some of the diagnostics included in ZEST. As a first application, we present the evolution since z~1 of the Luminosity Functions of COSMOS galaxies of early, disk and irregular galaxies and, for disk galaxies, of different bulge-to-disk ratios. Overall, we find that the LF up to a redshift z=1 is consistent with a pure-luminosity evolution (of about 0.95 magnitudes at z \~0.7). We highlight however two trends, that are in general agreement with a down-sizing scenario for galaxy formation: (1.) A deficit of a factor of about two at z~0.7 of MB>-20.5 structurally--classified early--type galaxies; and (2.) An excess of a factor of about three, at a similar redshift, of irregular galaxies.

astro-ph↗

arXiv2006

Simulating the COSMOS: The fraction of merging galaxies at high redshift

Simulations of nearby (0.015 < z < 0.025) SDSS galaxies have been used to reproduce as accurately as possible the appearance that they would have on COSMOS ACS images if they had been observed at z ~ 0.7 and z ~ 1.2. By adding the SDSS galaxies to random locations in the COSMOS images, we simulate the effects of chance superpositions of high redshift galaxies with unrelated foreground or background objects. We have used these simulated images, together with those of real COSMOS galaxies at these same redshifts, to undertake a "blind" morphological classification of galaxies to identify those that appear to be undergoing mergers and thus to estimate the change in merger fraction with redshift. We find that real mergers are harder to recognize at high redshift, and also that the chance superposition of unrelated galaxies often produces the appearance of mergers where in reality none exists. In particular, we estimate that 1.5 - 2.0% of objects randomly added to ACS images are misclassified as mergers due to projection with unrelated objects, and as a result, that 40% of the apparent mergers in COSMOS at z=0.7 are likely to be spurious. We find that the fraction of galaxies undergoing mergers increases as (1+z)^3.8+/-1.2 to z ~ 0.7 and that this trend appears to continue to z = 1.2. Merger candidates at z ~ 0.7 are bluer than the parent population, especially when the statistical effects of the chance projections are accounted for. Merger candidates are more asymmetric than the population as a whole, and are often associated with irregular morphology. Nevertheless, the majority (~60%) of the merger candidates appear to be associated with spiral galaxies although in this case we cannot correct for the effects of chance projections.

astro-ph↗

arXiv2006

The evolution of the number density of large disk galaxies in COSMOS

We study a sample of approximately 16,500 galaxies with I_AB <= 22.5 in the COSMOS field. Structural information on the galaxies is derived by fitting single Sersic models to their two-dimensional surface brightness distributions. We investigate the evolution of the number density of disk galaxies larger than 5 kpc between redshift z~1 and the present epoch. To this end, we use the measurements of the half-light radii to construct, as a function of redshift, the size function of both the total disk galaxy population and of disk galaxies split in four bins of bulge-to-disk ratio. Furthermore, we use a selected sample of roughly 1800 SDSS galaxies to calibrate our results with respect to the local universe. We find that: (i) The number density of disk galaxies with intermediate sizes (r_{1/2}~5-7 kpc) remains nearly constant from z~1 to today. (ii) The number density of the largest disks (r_{1/2}>7 kpc) decreases by a factor of about two out to z~1. (iii) There is a constancy in the number density of large bulgeless disks out to z~1; the deficit of large disks at early epochs seems to arise from a smaller number of bulged disks. Our results indicate that the bulk of the large disk galaxy population has completed its growth by z~1, and support the hypothesis that secular evolution processes produce - or at least add stellar mass to - the bulge components of disk galaxies.

astro-ph↗