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ABSTRACT: We present a study on the clustering of a stellar mass selected sample of
18,482 galaxies with stellar masses M*>10^10M(sun) at redshifts 0.4<z<2.0,
taken from the Palomar Observatory Wide-field Infrared Survey. We examine the
clustering properties of these stellar mass selected samples as a function of
redshift and stellar mass, and discuss the implications of measured clustering
strengths in terms of their likely halo masses. We find that galaxies with high
stellar masses have a progressively higher clustering strength, and amplitude,
than galaxies with lower stellar masses. We also find that galaxies within a
fixed stellar mass range have a higher clustering strength at higher redshifts.
We furthermore use our measured clustering strengths, combined with models from
Mo & White (2002), to determine the average total masses of the dark matter
haloes hosting these galaxies. We conclude that for all galaxies in our sample
the stellar-mass-to-total-mass ratio is always lower than the universal
baryonic mass fraction. Using our results, and a compilation from the
literature, we furthermore show that there is a strong correlation between
stellar-mass-to-total-mass ratio and derived halo masses for central galaxies,
such that more massive haloes contain a lower fraction of their mass in the
form of stars over our entire redshift range. For central galaxies in haloes
with masses M(halo)>10^13M(sun) we find that this ratio is <0.02, much lower
than the universal baryonic mass fraction. We show that the remaining baryonic
mass is included partially in stars within satellite galaxies in these haloes,
and as diffuse hot and warm gas. We also find that, at a fixed stellar mass,
the stellar-to-total-mass ratio increases at lower redshifts. This suggests
that galaxies at a fixed stellar mass form later in lower mass dark matter
haloes, and earlier in massive haloes. We interpret this as a "halo downsizing"
effect, however some of this evolution could be attributed to halo assembly
bias.
03/2010;
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W. G. Hartley, K. P. Lane,
O. Almaini,
M. Cirasuolo,
S. Foucaud,
C. Simpson,
S. Maddox,
I. Smail,
C. J. Conselice,
R. J. McLure,
J. S. Dunlop
[show abstract]
[hide abstract]
ABSTRACT: We use the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Ultra-deep survey (UDS), currently the deepest panoramic near-infrared survey, together with deep Subaru optical imaging to measure the clustering, number counts and luminosity function of galaxies at z∼ 2 selected using the BzK selection technique. We find that both star-forming (sBzK) and passive (pBzK) galaxies, to a magnitude limit of KAB < 23, are strongly clustered. The passive galaxies are the most strongly clustered population, with scalelengths of r0= 15.0+1.9−2.2 h−1 Mpc compared with r0= 6.75+0.34−0.37 h−1 Mpc for star-forming galaxies. The direct implication is that passive galaxies inhabit the most massive dark matter haloes, and are thus identified as the progenitors of the most massive galaxies at the present day. In addition, the pBzKs exhibit a sharp flattening and potential turnover in their number counts, in agreement with other recent studies. This plateau cannot be explained by the effects of incompleteness. We conclude that only very massive galaxies are undergoing passive evolution at this early epoch, consistent with the downsizing scenario for galaxy evolution. Assuming a purely passive evolution for the pBzKs from their median redshift to the present day, their luminosity function suggests that only ∼2.5 per cent of present-day massive ellipticals had a pBzK as a main progenitor.
Monthly Notices of the Royal Astronomical Society 11/2008; 391(3):1301 - 1307. · 4.90 Impact Factor
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W. G. Hartley, K. P. Lane,
O. Almaini,
M. Cirasuolo,
S. Foucaud,
C. Simpson,
S. Maddox,
I. Smail,
C. Conselice,
R. J. McLure,
J. S. Dunlop
[show abstract]
[hide abstract]
ABSTRACT: We use the UKIDSS Ultra-deep survey (UDS), currently the deepest panoramic near infra-red survey, together with deep Subaru optical imaging to measure the clustering, number counts and luminosity function of galaxies at $z\sim 2$ selected using the BzK selection technique. We find that both star-forming (sBzK) and passive (pBzK) galaxies, to a magnitude limit of $K_{AB} < 23$, are strongly clustered. The passive galaxies are the most strongly clustered population, with scale lengths of $r_0 = 15.0^{+1.9}_{-2.2}$h$^{-1}$Mpc compared with $r_0 = 6.75^{+0.34}_{-0.37}$h$^{-1}$Mpc for star-forming galaxies. The direct implication is that passive galaxies inhabit the most massive dark-matter halos, and are thus identified as the progenitors of the most massive galaxies at the present day. In addition, the pBzKs exhibit a sharp flattening and potential turn-over in their number counts, in agreement with other recent studies. This plateau cannot be explained by the effects of incompleteness. We conclude that only very massive galaxies are undergoing passive evolution at this early epoch, consistent with the downsizing scenario for galaxy evolution. Assuming a purely passive evolution for the pBzKs from their median redshift to the present day, their luminosity function suggests that only $\sim 2.5 %$ of present day massive ellipticals had a pBzK as a main progenitor. Comment: 8 pages, 7 figures, accepted for publication in MNRAS
09/2008;
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K. P. Lane,
O. Almaini,
S. Foucaud,
C. Simpson,
Ian Smail,
R. J. McLure,
C. J. Conselice,
M. Cirasuolo,
M. J. Page,
J. S. Dunlop,
P. Hirst,
M. G. Watson,
K Sekiguchi
[show abstract]
[hide abstract]
ABSTRACT: We investigate colour selection techniques for high redshift galaxies in the UKIDSS Ultra Deep Survey Early Data Release (UDS EDR). Combined with very deep Subaru optical photometry, the depth (K_AB = 22.5) and area (0.62 deg^2) of the UDS EDR allows us to investigate optical/near-IR selection using a large sample of over 30,000 objects. By using the B-z, z-K colour-colour diagram (the BzK technique) we identify over 7500 candidate galaxies at z > 1.4, which can be further separated into passive and starforming systems (pBzK and sBzK respectively). Our unique sample allows us to identify a new feature not previously seen in BzK diagrams, consistent with the passively evolving track of early type galaxies at z < 1.4. We also compare the BzK technique with the R-K colour selection of Extremely Red Objects (EROs) and the J-K selection of Distant Red Galaxies (DRGs), and quantify the overlap between these populations. We find that the majority of DRGs, at these relatively bright magnitudes are also EROs. Since previous studies have found that DRGs at these magnitudes have redshifts of z ~ 1 we determine that these DRG/ERO galaxies have SEDs consistent with being dusty star-forming galaxies or AGN at z < 2. Finally we observe a flattening in the number counts of pBzK galaxies, similar to other studies, which may indicate that we are sampling the luminosity function of passive z > 1 galaxies over a narrow redshift range. Comment: Accepted for publication in MNRAS Letters. 5 pages, 5 figures, 1 table. Higher-resolution figures available from the authors on request
04/2007;
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ABSTRACT: We investigate correlations between galaxy age and environment in the Abell 901/2 supercluster for separate morphologies. Using COMBO-17 data, we define a sample of 530 galaxies, complete at $M_V -5\log h<-18$ on an area of $3.5\times 3.5$ (Mpc/$h$)$^2$. We explore several age indicators including an extinction-corrected residual from the colour-magnitude relation (CMR). As a result, we find a clear trend of age with density for galaxies of all morphologies that include a spheroidal component, in the sense that galaxies in denser environments are older. This trend is not seen among Scd/Irr galaxies since they all have young ages. However, the trend among the other types is stronger for fainter galaxies. While we also see an expected age-morphology relation, we find no evidence for a morphology-density relation at fixed age.
12/2006;
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S. Foucaud,
O. Almaini,
I. Smail,
C. J. Conselice, K. P. Lane,
A. C. Edge,
C. Simpson,
J. S. Dunlop,
R. J. McLure,
M. Cirasuolo,
P. Hirst,
M. G. Watson,
M. J. Page
[show abstract]
[hide abstract]
ABSTRACT: We describe the number counts and spatial distribution of 239 Distant Red Galaxies (DRGs), selected from the Early Data Release of the UKIDSS Ultra Deep Survey. The DRGs are identified by their very red infrared colours with (J-K)AB>1.3, selected over 0.62 sq degree to a 90% completeness limit of KAB~20.7. This is the first time a large sample of bright DRGs has been studied within a contiguous area, and we provide the first measurements of their number counts and clustering. The population shows strong angular clustering, intermediate between those of K-selected field galaxies and optical/infrared-selected Extremely Red Galaxies. Adopting the redshift distributions determined from other recent studies, we infer a high correlation length of r0~11 h-1 Mpc. Such strong clustering could imply that our galaxies are hosted by very massive dark matter halos, consistent with the progenitors of present-day L>L* elliptical galaxies.
07/2006;
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ABSTRACT: We present a morphological study of galaxies in the A901/902 supercluster from the COMBO-17 survey. A total of 570 galaxies with photometric redshifts in the range 0.155 < zphot < 0.185 are visually classified by three independent classifiers to MV = -18. These morphological classifications are compared to local galaxy density, distance from the nearest cluster centre, local surface mass density from weak lensing and photometric classification. At high local galaxy densities logSigma10Mpc-2 > 1.5 a classical morphology-density relation is found. A correlation is also found between morphology and local projected surface mass density, but no trend is observed with distance to the nearest cluster. This supports the finding that local environment is more important to galaxy morphology than global cluster properties. The breakdown of the morphological catalogue by colour shows a dominance of blue galaxies in the galaxies displaying late-type morphologies and a corresponding dominance of red galaxies in the early-type population. Using the 17-band photometry from COMBO-17, we further split the supercluster red sequence into old passive galaxies and galaxies with young stars and dust. We find that the dusty star-forming population describes an intermediate morphological group between late- and early-type galaxies, supporting the hypothesis that field and group spiral galaxies are transformed into S0s and, perhaps, ellipticals during cluster infall.
Monthly Notices of the Royal Astronomical Society, v.378, 716-722 (2007).
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[show abstract]
[hide abstract]
ABSTRACT: We investigate correlations between galaxy age and environment in the A 901/2 supercluster for separate morphologies. Using COMBO-17 data, we define a sample of 530 galaxies, complete at MV - 5 logh < -18 on an area of 3.5 × 3.5 (Mpc h-1)2. We explore several age indicators including an extinction-corrected residual from the colour-magnitude relation. As a result, we find a clear trend of age with density for galaxies of all morphologies that include a spheroidal component, in the sense that galaxies in denser environments are older. This trend is not seen among Scd/Irr galaxies since they all have young ages. However, the trend among the other types is stronger for fainter galaxies. While we also see an expected age-morphology relation, we find no evidence for a morphology-density relation at fixed age.
Monthly Notices of the Royal Astronomical Society, v.376, L1-L5 (2007).
