Evolutionary properties of galaxies and mass assembly up to z ~ 2 from VVDS+SWIRE data - PowerPoint PPT Presentation

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Evolutionary properties of galaxies and mass assembly up to z ~ 2 from VVDS+SWIRE data

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  1. Evolutionary properties of galaxies and mass assembly up to z ~ 2 from VVDS+SWIRE data PI O. Le Fèvre Co-PI G. Vettolani PI : Carole Lonsdale G. Zamorani On behalf of the VVDS-SWIRE collaboration

  2. Outline of the talk The VVDS 02hr field (The “deep” part of the VVDS) : A) Environmental effects up to z ~ 1.2 luminosity functions (Ilbert et al. 2006) and colors (Cucciati et al. 2006) as a function of the local environment B) K band luminosity function and stellar mass density up to z ~ 2 from VVDS + SWIRE data (Arnouts et al. and Pozzetti et al.)

  3. The 02hr VVDS field The 02hr VVDS field is an extragalactic field with extensive multi-wavelength observations (radio(VLA), UV (GALEX), far infrared (SPITZER), X-ray (XMM)) and deep optical photometry (VVDS + CFHTLS) and spectroscopy (more than 6000 galaxy redshifts from the VVDS over about 0.5 sq.deg. (IAB < 24.0 purely magnitude selected) Very well adapted for investigations on galaxy evolution and LSS(see Le Fevre talk on Monday)

  4. A) Luminosity functions, colors and environment At z ~ 0.1 and over a wide range of local galaxy densities, a strong dependency of galaxy properties with environment is observed. In addition to the well defined spectral type-density relation, Croton et al. 2005; 2dF there are also significant differences in the LFs in over- and under-dense regions

  5. 2dF Luminosity functions (Croton et al. 2005) N ~ 50,000 Clusters Voids -17 -19 -21 MbJ A larger fraction of bright (red) galaxies in over-dense regions(see also Balogh et al. 2004) Similar slopes in different environments, but brighter M* in over-dense regions

  6. Naïve question: Why is the slope of the global LF essentially independent from the environment, even if the fraction of different spectral types is a strong function of the environment and the slopes of the LFs of different types are so different from each other? Possible explanation : If the conditional luminosity function (CLF) of galaxies is only a function of the halo masses ( (L,Mh); halo-occupation models(Mo et al. 2004; Cooray 2005)) the -dependence of the galaxy LF enters only through the conditional halo mass function n(M | ) and therefore the slope of the LF is approximately constant in different environments, while M* is brighter in over-dense environments. If this is the correct explanation, it has to be checked if these environmental effects remain the same at high redshift

  7. Estimate of local density in the VVDS 02hr field 02hr field: More than 6,500 highly reliable galaxies’ redshifts, in about 0.5 sq.deg, with average spectroscopic sampling rate of ~ 20% (and as high as ~ 35% in the central region), allow good 3D density field reconstruction over scales of the order of 5 h-1 Mpc Sampling rate : For each ith galaxy the local density contrast i with respect to the average density <(zi)> is measured:  i (RS) = ( i(RS) - < (zi)> ) / < (zi)> , where i(RS) is computed with a gaussian filter with smoothing length RS Simulations show a good correspondence between input and reconstructed density fields for scales RS > 5 h-1 Mpc

  8. (r, R) - (r,R)= (r) (r) F(R)  gaussian filter S(r,MC)  radial selection function (m)  target sampling rate (z,m)  spectroscopic success rate (,)  angular sampling rate (r, R, <MC)= D(r-ri) F(|r-ri|/R) S(r,MC) (m) (z,m) (,) 3D galaxy density contrast: A critical factor for the reliability of the density contrast estimator is a high spatial sampling rate. At z ~ 0.75 the VVDS mean inter-particle separation is ~ 4.4h-1 Mpc, similar to that of the 2dFGRS at its median depth.

  9. Luminosity functions in under- and over-dense regions Red : galaxies in over-dense regions Blue: galaxies in under-dense regions N = 924 N = 623 N = 1440 N = 641 Up to z ~ 1.2, we find: Brigther galaxies preferentially seen in denser regions (same as locally) N = 820 N = 471 Significant differences in the LFs : flatter slopes in over-dense regions( ~ 0.2 – 0.3), while the M* values are consistent with each other in the two environments (differently from local samples) N = 194 N = 193

  10. Is the difference in slope, mainly due to different fractions of early and late type galaxies in different environments? This can be tested in the redshift range 0.6 – 0.9, where we have the highest statistics, deriving separately the LFs of red (left; MU – MV > 1.5) and blue (right; MU – MV < 1.5) galaxies Blue curve : LF in under-dense regions Red curve : LF in over-dense regions Not only the global LFs, but also the type-specific LFs significantly depend on environment The LFs are steeper in under-dense regions both for red and blue galaxies

  11. Comparison with local results While the higher fraction of bright galaxies in over-dense regions seen locally is already present at z ~ 1.2, the environmental dependency of the LF shape at high redshift appears to be different from what is seen at low redshift. Is this difference due to an increase with cosmic time of the number of faint red galaxies, developing a steep slope of LF of early type galaxies in over-dense regions as in 2dF ? But : a) We do not see any change on the environmental effect from z ~ 0.3 up to z ~ 1.2… b) is it reasonable that the environmental effect on the LF changes so quickly from our first redshift bin (z ~ 0.3) to z ~ 0? To be better understood which physical mechanism can produce this change with redshift of environmental effects on the LF

  12. Evolution with z and luminosity of the color-density Select Blue (U-V < 0.65) and red (U-V > 1.40) galaxies and compute their fraction as a function of  for different absolute magnitudes and redshifts A well defined color–density relation is seen up to different z for different MB : for MB <-19.0 up to z~0.6 for MB <-20.0 up to z~0.9 for MB <-21.0 up to z~1.2 The color - density relation is building up, differentially with luminosity, as cosmic time goes by, earlier for brighter galaxies and later for fainter galaxies …

  13. What does it mean? Assuming that the adopted colors correspond to different star formation histories, these data suggest that: a) Star formation is differentially suppressed in high and low density regions : the drop in star formation occurred earlier in higher density environment b) The drop in star formation is also a function of luminosity (and mass?) Both these findings are consistent with a downsizing scenario in which star-formation activity is progressively shifted with cosmic time toward lower luminosity systems and out of high density peaks

  14. B) The K band LF’s and the mass density up to z ~2 We use the photometric data collected by SWIRE (red),VVDS in BVRI and JK (magenta) and by CFHTLSsurvey in ugriz (white). The VVDS-spectroscopic survey has collected >6500 spectra up to I=24 (blue). In the following, we restrict the analysis to the area in common between SWIREand CFHTLS ( ~ 0.85 sq. deg.; ~ half of which with spectroscopic redshifts) SWIRE+VVDS in the 02hr field

  15. IRAC Number counts The IRAC 3.6 (red) and 4.5m(green) (shifted by 2.5 magnitudes) differential galaxy (circles) and star (triangles) number counts. Adopted flux limits are 9Jy and 15Jy or 21.5 and 21.0 (in AB mag), respectively (70% completeness at these limits). A small completeness correction at the faint end is applied for the luminosity function analysis to match the Fazio et al. (2004) number counts (red and green lines). 4.5m countsare shifted by 2.5 mag for clarity

  16. The combined dataset Matching : The SWIRE sources (~ 25,500 objects) have been matched with the optical catalogs. Less than 1% of the sources are not detected in the optical. The matched SWIRE catalog in the CFHTLS area consists of 22,300 galaxies with 3.6<21.5 and 19000 with 4.5<21.0 (~2300 are galaxies with a reliable spectroscopic redshift from VVDS) Color-magnitude diagram : Spectroscopic sources are shown with red (galaxies), yellow (stars) and green (QSOs) symbols. The stars classified using profile information and SED fitting from photo-z are shown in magenta. The lines show the bright (I<17.5) and faint (I<24) limits of the spectroscopic survey. Note the substantial number of red galaxies (I – 3.6 > 3.5) fainter than the VVDS spectroscopic limit

  17. Photometric redshifts and their accuracy Photo-z are derived by using the code «Le Phare» (Arnouts et al.) on the optical bands BVRI,ugriz,(+JK) and the IRAC bands 3.6 and 4.5mand exploiting the large spectroscopic redshift sample to train the photo-z estimates (see Ilbert et al. 2006). The main steps are: Iterative zero-points adjustments using spectroscopic sources+ optimization of the original templates by reconstructing the SEDs from the observed flux of the spectroscopic sample Comparison between spectroscopic and photometric redshifts for the 3.6 m sample with secure redshifts (1431 galaxies). ( a correction of 5% to the IRAC fluxes improves the comparison) The filled/open circles show photo-z with estimated errors smaller/larger than 0.3. Results: No systematic shift is observed : < z > = 0.00 for 0 < z < 1.5 Very small statistical error  (z/(1+z)) = 0.03 Very small number of catastrophic errors (~ 1.7% of the galaxies have z>0.15(1+z))

  18. Redshift distributions : The red curve shows the N(zspec) distribution, while the dashed black line shows the N(zphot) of the same objects. The solid black line shows the normalized N(z) for the total 3.6 m zphot sample. Excellent agreement between the zphot and zspec distributions (clear peaks are detected in both samples at z ~ 0.3 and z ~ 0.9, while the peak at z=0.6, although visible, is somewhat diluted in the zphot sample) Prominent high redshift tail in the total zphot 3.6 m sample (objects with red colors seen as black dots in the green ellipse in the previous slide)

  19. Redshift segregation in a color – color plot This color-color plot (r-i vs. i-3.6m), with different color contours (red for z <1 and blue for z >1) for different zphot intervals, shows how galaxies move in this plane as a function of redshift. stars (magenta) are easily separated from the galaxy population. The distribution of galaxies at z<1 is well distinguished from the highest z population (see solid lines Many of the galaxies with zphot > 1.5 have such a red i-3.6 color to be excluded in an I-selected sample, thus depleting the high z tail in the spectroscopic sample.

  20. K rest-frame Luminosity Functions from 3.6 and 4.5 m samples The IRAC 3.6 and 4.5 m data probe the 2.2m stellar light at z ≈ 0.6 and z ≈1 respectively and are therefore the best data to estimate, with minimal K-corrections, the K rest-frame LFs at these redshifts. Our LFs are very well determined up to z=2.5 and are in excellent agreement with each other at all z-bins (also with the LF derived for our spectroscopic sample) With respect to local LF (Kochanek et al.) we detect a clear evolution with z. Good agreement also with Pozzetti et al. (2003; K20), Drory et al. (2003; MUNICS) for z < 1.2, and Caputi et al. (2005,2006; GOODS/ CDFS) up to z = 2.5 from an area 20 times smaller. No evidence of the bright end to decrease up to z = 2.5 Samples: 3.6 with zphot (filled) or zspec (open) 4.5 with zphot ----- Kochanek et al. (2001) ----- Drory et al. (2003) ----- Caputi et al. 2005)

  21. Color bimodality : separation between early and late type populations See also poster by D.Vergani et al. A clear bimodality is seen in the NUV-r intrinsic color, with a red peak at NUV-r ~ 4.8. This color is a good proxy of the b parameter (SFR/<SFR>) as found by GALEX-SDSS (Salim et al. 2005). Excellent correspondence between NUV-r color and our SED 2 fitting, which we therefore used to select a population of early type galaxies With such a separation we obtain a sample of ~ 4400 Early-type and ~16800 Late-type galaxies. Red contours : elliptical templates in SED fitting Blue contours : all other templates

  22. LF per typesup to z = 2.5 Very well defined LFs for both types of galaxies (early and late) up to z ~ 2.5 Significant difference in the slopes at all redshifts: -0.5 <  < 0 for early -1.4 <  < -1.1 for late The brightest objects (KAB < -24) are about 50% early and 50% late up to z ~ 1.2 At z > 1.5 there is a significant decline of the early type population

  23. Evolution of the NIR Luminosity versus z The total luminosity density (black circles) is dominated by emission from the late type galaxies (blue), which stays approximately constant up to z~2, while the NIR luminosity density of early type galaxies (red) shows a quick drop at z>1.2. Good agreement, but over a much larger area, with the results from the K20 results (Pozzetti et al. 2003) and GOODS/CDFS results for K-selected galaxies (~130 sq.arcmin) (blue dashed line;Caputi et al. 2005)

  24. Anything about downsizing? Differential evolution of number density as a function of mass (see poster by Pozzetti et al.) • Number density of most massive galaxies consistent with local density up to z = 2 • Decrease with redshift of the density of less massive galaxies

  25. Evolution of the stellar mass density versus z Slow decline of the global mass density up to z ~1.2 and faster decline for 1.2<z<2.0 : ~60% (~25%) of the stellar mass is already formed at z~1.2 (z~2.0) Mass density ~ constant up to z ~ 1.4 for the late type galaxies Slow decline up to z ~ 1.2 also for the early type population (~50% of the mass of evolved galaxies already assembled at z ~1.2), with a significant drop for 1.2<z<2. The mass assembly in our “color defined” early-type galaxies is consistent with what found by Franceschini et al. (2006) based on a morphological definition in an area ~ 20 times smaller (GOODS) (red curve) The red curve is the mass assembly in ellipticals from the Protracted Assembly model by F06 : stars in today ellipticals born at high redshift, most of which (~80%) dynamically assembled in spheroids at 0.9 < z < 1.6. The growth of the stellar mass is in excellent agreement with the integrated dust-corrected SFR from GALEX data in the same field (Schiminovich et al. 2005)

  26. Conclusions: Environmental effects up to z ~ 1.2 Luminosity function: While the higher fraction of bright galaxies in over-dense regions seen locally is already present at z ~ 1.2, the environmental dependency of the LF shape at high redshift appears to be different from what is seen at low redshift  implications on models? Color – density relation: The color – density relation changes with redshift and luminosity: Star formation is differentially suppressed in high and low density regions and for galaxies with different luminosities (masses?): the drop in star formation occurred earlier in higher density environment and in higher luminosity galaxies  consistent with a downsizing scenario in which star-formation activity is progressively shifted with cosmic time in smaller systems and out of high density peaks

  27. Conclusions : K-band LF and mass density up to z~2 A significant evolution of the bright end of the LF is detected, with no indication of a decrease up to z ~ 2.5 At all redshifts there is a significant difference in the slopes of the early (-0.5 <  < 0)and late types(-1.4 <  < -1.1) The brightest objects (KAB < -24) are about 50% early and 50% late up to z ~ 1.2 Slow decline of the global mass density up to z ~1.2 and faster decline for 1.2<z<2.0 : ~60% (~25%) of the stellar mass is already formed at z~1.2 (z~2.0) (but ~ 100% for galaxies more massive than 1011 solar masses) Slow decline up to z ~ 1.2 also for the late type population (~50% of the mass of evolved galaxies already assembled at z ~1.2), with a significant drop for 1.2<z<2. Given the same assumption on the IMF, there is an excellent agreement between the stellar mass density from LF +SED fitting ( M/LK) and that obtained with the integrated dust-corrected SFR from GALEX data in the same field (Schiminovich et al. 2005)