625 research outputs found
An Objective and Automatic Cluster Finder: An Improvement of the Matched-Filter Method
We describe an objective and automated method for detecting clusters of
galaxies from optical imaging data. This method is a variant of the so-called
`matched-filter' technique pioneered by Postman et al. (1996). With
simultaneous use of positions and apparent magnitudes of galaxies, this method
can, not only find cluster candidates, but also estimate their redshifts and
richnesses as byproducts of detection. We examine errors in the estimation of
cluster's position, redshift, and richness with a number of Monte Carlo
simulations. No systematic discrepancies between the true and estimated values
are seen for either redshift or richness. Spurious detection rate of the method
is about less than 10% of those of conventional ones which use only surface
density of galaxies. A cluster survey in the North Galactic Pole is executed to
verify the performance characteristics of the method with real data. Two known
real clusters are successfully detected. We expect these methods based on
`matched-filter' technique to be essential tools for compiling large and
homogeneous optically-selected cluster catalogs.Comment: 13 pages, 12 PostScript figures, uses LaTeX L-AA, A&AS accepte
A Census of Star-Forming Galaxies at z = 1-3 in the Subaru Deep Field
Several UV and near-infrared color selection methods have identified galaxies
at z = 1-3. Since each method suffers from selection biases, we have applied
three leading techniques (Lyman break, BX/BM, and BzK selection) simultaneously
in the Subaru Deep Field. This field has reliable ({\Delta}z/(1 + z) =
0.02--0.09) photometric redshifts for ~53,000 galaxies from 20 bands
(1500{\AA}--2.2{\mu}m). The BzK, LBG, and BX/BM samples suffer contamination
from z<1 interlopers of 6%, 8%, and 20%, respectively. Around the redshifts
where it is most sensitive (z~1.9 for star-forming BzK, z~1.8 for z~2 LBGs,
z~1.6 for BM, and z~2.3 for BX), each technique finds 60-80% of the census of
the three methods. In addition, each of the color techniques shares 75-96% of
its galaxies with another method, which is consistent with previous studies
that adopt identical criteria on magnitudes and colors. Combining the three
samples gives a comprehensive census that includes ~90% of z-phot = 1-3
galaxies, using standard magnitude limits similar to previous studies. In fact,
we find that among z = 1-2.5 galaxies in the color selection census, 81-90% of
them can be selected by just combining the BzK selection with one of the UV
techniques (z~2 LBG or BX and BM). The average galaxy stellar mass, reddening
and SFRs all decrease systematically from the sBzK population to the LBGs, and
to the BX/BMs. The combined color selections yield a total cosmic SFR density
of 0.18 0.03 M_sun yr^{-1} Mpc^{-3} for K_AB <= 24. We find that 65% of
the star formation is in galaxies with E(B-V) > 0.25 mag, even though they are
only one-fourth of the census by number.Comment: 26 pages, 30 figures, 9 tables, emulateapj format. Modified to match
the final ApJ versio
Clustering of i-dropout galaxies at z=6 in GOODS and the UDF
We measured the angular clustering at z~6 from a large sample of i-dropout
galaxies (293 with z<27.5 from GOODS and 95 with z<29.0 from the UDF). Our
largest and most complete subsample (having L>0.5L*) shows the presence of
clustering at 94% significance. For this sample we derive a (co-moving)
correlation length of r_0=4.5^{+2.1}_{-3.2} h_{72}^{-1} Mpc and bias
b=4.1^{+1.5}_{-2.6}, using an accurate model for the redshift distribution. No
clustering could be detected in the much deeper but significantly smaller UDF,
yielding b<4.4 (1 sigma). We compare our findings to Lyman break galaxies at
z=3-5 at a fixed luminosity. Our best estimate of the bias parameter implies
that i-dropouts are hosted by dark matter halos having masses of ~10^11 M_sun,
similar to that of V-dropouts at z~5. We evaluate a recent claim that at z>5
star formation might have occurred more efficiently compared to that at z=3-4.
This may provide an explanation for the very mild evolution observed in the UV
luminosity density between z=6 and z=3. Although our results are consistent
with such a scenario, the errors are too large to find conclusive evidence for
this.Comment: minor changes to match published versio
Keck Deep Fields. III. Luminosity-dependent Evolution of the Ultraviolet Luminosity and Star Formation Rate Densities at z~4, 3, and 2
We use the Keck Deep Fields UGRI catalog of z~4, 3, and 2 UV-selected
galaxies to study the evolution of the rest-frame 1700A luminosity density at
high redshift. The ability to reliably constrain the contribution of faint
galaxies is critical and our data do so as they reach to M*+2 even at z~4 and
deeper still at lower redshifts. We find that the luminosity density at high
redshift is dominated by the hitherto poorly studied galaxies fainter than L*,
and, indeed, the the bulk of the UV light in the high-z Universe comes from
galaxies in the luminosity range L=0.1-1L*. It is these faint galaxies that
govern the behavior of the total UV luminosity density. Overall, there is a
gradual rise in luminosity density starting at z~4 or earlier, followed by a
shallow peak or a plateau within z~3--1, and then followed by the well-know
plunge at lower redshifts. Within this total picture, luminosity density in
sub-L* galaxies evolves more rapidly at high redshift, z>~2, than that in more
luminous objects. However, this is reversed at lower redshifts, z<~1, a
reversal that is reminiscent of galaxy downsizing. Within the context of the
models commonly used in the observational literature, there seemingly aren't
enough faint or bright LBGs to maintain ionization of intergalactic gas even as
late as z~4. This is particularly true at earlier epochs and even more so if
the faint-end evolutionary trends we observe at z~3 and 4 continue to higher
redshifts. Apparently the Universe must be easier to reionize than some recent
studies have assumed. Nevertheless, sub-L* galaxies do dominate the total UV
luminosity density at z>~2 and this dominance further highlights the need for
follow-up studies that will teach us more about these very numerous but thus
far largely unexplored systems.Comment: Accepted for publication in the Astrophysical Journal. Abstract
abridge
Dependence of the Build-up of the Colour-Magnitude Relation on Cluster Richness at z ~ 0.8
We present environmental dependence of the build-up of the colour-magnitude
relation (CMR) at z ~ 0.8. It is well established that massive early-type
galaxies exhibit a tight CMR in clusters up to at least z ~ 1. The faint end of
the relation, however, has been much less explored especially at high redshifts
primarily due to limited depths of the data. Some recent papers have reported a
deficit of the faint red galaxies on the CMR at 0.8 < z < 1, but this has not
been well confirmed yet and is still controversial. Using a deep, multi-colour,
panoramic imaging data set of the distant cluster RXJ1716.4+6708 at z=0.81,
newly taken with the Prime Focus Camera (Suprime-Cam) on the Subaru Telescope,
we carry out an analysis of faint red galaxies with a care for incompleteness.
We find that there is a sharp decline in the number of red galaxies toward the
faint end of the CMR below M*+2. We compare our result with those for other
clusters at z ~ 0.8 taken from the literature, which show or do not show the
deficit. We suggest that the "deficit" of faint red galaxies is dependent on
the richness or mass of the clusters, in the sense that poorer systems show
stronger deficits. This indicates that the evolutionary stage of less massive
galaxies depends critically on environment.Comment: 11 pages, 10 figures, accepted for publication in MNRA
- …