84 research outputs found
The Luminosity Function Of Field Galaxies And Its Evolution Since z=1
We present the B-band luminosity function and comoving space and luminosity
densities for a sample of 2779 I-band selected field galaxies based on
multi-color data from the CADIS survey. The sample is complete down to I_815 =
22 without correction and with completeness correction extends to I_815=23.0.
By means of a new multi-color analysis the objects are classified according to
their spectral energy distributions (SEDs) and their redshifts are determined
with typical errors of delta z <= 0.03. We have split our sample into four
redshift bins between z=0.1 and z=1.04 and into three SED bins E-Sa,Sa-Sc and
starbursting (emission line) galaxies. The evolution of the luminosity function
is clearly differential with SED. The normalization phi* of luminosity function
for the E-Sa galaxies decreases towards higher redshift, and we find evidence
that the comoving galaxy space density decreases with redshift as well. In
contrast, we find phi* and the comoving space density increasing with redshift
for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the
luminosity function at the faint end and their comoving space density increases
with redshift.Comment: 15 pages, 14 figures, accepted by Astronomy&Astrophysic
The Gemini Deep Deep Survey: II. Metals in Star-Forming Galaxies at Redshift 1.3<z<2
The goal of the Gemini Deep Deep Survey (GDDS) is to study an unbiased sample
of K<20.6 galaxies in the redshift range 0.8<z<2.0. Here we determine the
statistical properties of the heavy element enrichment in the interstellar
medium (ISM) of a subsample of 13 galaxies with 1.34<z<1.97 and UV absolute
magnitude M_2000 < -19.65. The sample contains 38% of the total number of
identified galaxies in the first two fields of the survey with z>1.3. The
selected objects have colors typical of irregular and Sbc galaxies. Strong
[OII] emission indicates high star formation activity in the HII regions
(SFR~13-106 M_sun/yr). The high S/N composite spectrum shows strong ISM MgII
and FeII absorption, together with weak MnII and MgI lines. The FeII column
density, derived using the curve of growth analysis, is logN_FeII =
15.54^{+0.23}_{-0.13}. This is considerably larger than typical values found in
damped Ly-alpha systems (DLAs) along QSO sight lines, where only 10 out of 87
(~11%) have logN_FeII > 15.2. High FeII column densities are observed in the
z=2.72 Lyman break galaxy cB58 (logN_FeII ~ 15.25) and in gamma-ray burst host
galaxies (logN_FeII ~ 14.8-15.9). Given our measured FeII column density and
assuming a moderate iron dust depletion (delta_Fe ~ 1 dex), we derive an
optical dust extinction A_V ~ 0.6. If the HI column density is log N(HI)<21.7
(as in 98% of DLAs), then the mean metallicity is Z/Z_sun > 0.2. The high
completeness of the GDDS sample implies that these results are typical of
star-forming galaxies in the 1<z<2 redshift range, an epoch which has
heretofore been particularly challenging for observational programs.Comment: ApJ in press, corrected HI column density estimat
Gemini Deep Deep Survey VI: Massive Hdelta-strong galaxies at z=1
We show that there has been a dramatic decline in the abundance of massive
galaxies with strong Hdelta stellar absorption lines from z=1.2 to the present.
These ``Hdelta-strong'', or HDS, galaxies have undergone a recent and rapid
break in their star-formation activity. Combining data from the Gemini Deep
Deep and the Sloan Digital Sky Surveys to make mass-matched samples
(M*>=10^10.2 Msun), with 25 and 50,255 galaxies, respectively), we find that
the fraction of galaxies in an HDS phase has decreased from about 50% at z=1.2
to a few percent today. This decrease in fraction is due to an actual decrease
in the number density of massive HDS systems by a factor of 2-4, coupled with
an increase in the number density of massive galaxies by about 30 percent. We
show that this result depends only weakly on the threshold chosen for the
Hdelta equivalent width to define HDS systems (if greater than 4 A) and
corresponds to a (1+z)^{2.5\pm 0.7} evolution. Spectral synthesis studies of
the high-redshift population using the PEGASE code, treating Hdelta_A, EW[OII],
Dn4000, and rest-frame colors, favor models in which the Balmer absorption
features in massive Hdelta-strong systems are the echoes of intense episodes of
star-formation that faded about 1 Gyr prior to the epoch of observation. The
z=1.4-2 epoch appears to correspond to a time at which massive galaxies are in
transition from a mode of sustained star formation to a relatively quiescent
mode with weak and rare star-formation episodes. We argue that the most likely
local descendants of the distant massive HDS galaxies are passively evolving
massive galaxies in the field and small groups.Comment: 16 pages, 12 figures, 3 tables, uses emulateapj.sty; updated to match
the version accepted by ApJ. One figure added, conclusions unchange
Biometric variables predict stone tool functional performance more effectively than toolâform attributes: a case study in handaxe loading capabilities
Both the form of a stone tool and the anatomy of the individual using it have potential to influence its cutting performance. To date, however, the selective pressures acting on stoneâtool form and hominin biometric/biomechanical attributes have been investigated in isolation and their relative influence on performance have never been compared directly. This paper examines the influence of both toolâform attributes and biometric variation on the functional performance of Acheulean handaxes. Specifically, it investigates the impact of 13 tool attributes and eight biometric traits on the working forces applied through the edge of 457 replica tools. The relative contribution of toolâform and biometric attributes to handaxe loading levels were examined statistically. Results identify that both toolâform attributes and biometric traits are significantly related to loading; however, toolâuser biometric variation has a substantially greater impact relative to toolâform attributes. This difference was demonstrated by up to a factor of 10. These results bear directly on the coâevolutionary relationships of stone tools and hominin anatomy, and the comparative strength of selective pressure acting on each. They also underline why handaxe forms may have been free to vary in form across time and space without necessarily incurring critical impacts on their functional capabilities
The Las Campanas IR Survey: Early Type Galaxy Progenitors Beyond Redshift One
(Abridged) We have identified a population of faint red galaxies from a 0.62
square degree region of the Las Campanas Infrared Survey whose properties are
consistent with their being the progenitors of early-type galaxies. The optical
and IR colors, number-magnitude relation and angular clustering together
indicate modest evolution and increased star formation rates among the
early-type field population at redshifts between one and two. The counts of red
galaxies with magnitudes between 17 and 20 rise with a slope that is much
steeper than that of the total H sample. The surface density of red galaxies
drops from roughly 3000 per square degree at H = 20.5, I-H > 3 to ~ 20 per
square degree at H = 20, I-H > 5. The V-I colors are approximately 1.5
magnitudes bluer on average than a pure old population and span a range of more
than three magnitudes. The colors, and photometric redshifts derived from them,
indicate that the red galaxies have redshift distributions adequately described
by Gaussians with sigma_z ~ 0.2V-I3$ are primarily in the 1.5 < z < 2
range. We find co-moving correlation lengths of 9-10 Mpc at z ~ 1, comparable
to, or larger than, those found for early-type galaxies at lower redshifts. A
simple photometric evolution model reproduces the counts of the red galaxies,
with only a ~ 30% decline in the underlying space density of early-type
galaxies at z ~ 1.2. We suggest on the basis of the colors, counts, and
clustering that these red galaxies are the bulk of the progenitors of present
day early-type galaxies.Comment: 5 pages, 3 figures, accepted for publication in the ApJ Letter
Dynamically Close Galaxy Pairs and Merger Rate Evolution in the CNOC2 Redshift Survey
We investigate redshift evolution in the galaxy merger and accretion rates,
using a well-defined sample of 4184 galaxies with 0.12 < z < 0.55 and R_C <
21.5. We identify 88 galaxies in close (5 < r_p < 20 h^{-1} kpc) dynamical
(delta v < 500 km/s) pairs. These galaxies are used to compute global pair
statistics, after accounting for selection effects resulting from the flux
limit, k-corrections, luminosity evolution, and spectroscopic incompleteness.
We find that the number of companions per galaxy (for -21 < M_B^{k,e} < -18) is
Nc = 0.0321 +/- 0.0077 at z=0.3. The luminosity in companions, per galaxy, is
Lc = 0.0294 +/- 0.0084 x 10^10 h^2 L_sun. We assume that Nc is proportional to
the galaxy merger rate, while Lc is directly related to the mass accretion
rate. After increasing the maximum pair separation to 50 h^{-1} kpc, and
comparing with the low redshift SSRS2 pairs sample, we infer evolution in the
galaxy merger and accretion rates of (1+z)^{2.3 +/- 0.7} and (1+z)^{2.3 +/-
0.9} respectively. These are the first such estimates to be made using only
confirmed dynamical pairs. When combined with several additional assumptions,
this implies that approximately 15% of present epoch galaxies with -21 < M_B <
-18 have undergone a major merger since z=1.Comment: 40 pages, 8 figures. Accepted for publication in the Astrophysical
Journa
Cosmological constraints from lensing statistics and supernovae on the cosmic equation of state
We investigate observational constraints from lensing statistics and high-z
type Ia supernovae on flat cosmological models with nonrelativistic matter and
an exotic fluid with equation of state, . We show that
agreement with both tests at the 68% confidence level is possible if the
parameter is low () and with lower values of corresponding to higher .
We find that a conventional cosmological constant model with is the best fit model of the combined likelihood.Comment: 7 pages, 4 postscript figures, revtex, submitted to Phys. Rev.
Evidence for Evolving Spheroidals in the Hubble Deep Fields North and South
We investigate the dispersion in the internal colours of faint spheroidals in
the HDFs North and South. We find that a remarkably large fraction ~30% of the
morphologically classified spheroidals with I<24 mag show strong variations in
internal colour, which we take as evidence for recent episodes of
star-formation. In most cases these colour variations manifest themselves via
the presence of blue cores, an effect of opposite sign to that expected from
metallicity gradients. Examining similarly-selected ellipticals in five rich
clusters with 0.37<z<0.83 we find a significant lower dispersion in their
internal colours. This suggests that the colour inhomogeneities have a strong
environmental dependence being weakest in dense environments where spheroidal
formation was presumably accelerated at early times. We use the trends defined
by the cluster sample to define an empirical model based on a high-redshift of
formation and estimate that at z~1 about half the field spheroidals must be
undergoing recent episodes of star-formation. Using spectral synthesis models,
we construct the time dependence of the density of star-formation. Although the
samples are currently small, we find evidence for an increase in
between z=0 to z=1. We discuss the implications of this rise in the context of
that observed in the similar rise in the abundance of galaxies with irregular
morphology. Regardless of whether there is a connection our results provide
strong evidence for the continued formation of field spheroidals over 0<z<1.Comment: 13 pages, 11 figures. To appear in MNRAS in response to referee's
Report. Figures and paper also available at
http://www.ast.cam.ac.uk/~fmenante/HDFs
Galaxy and Cluster Biasing from Local Group Dynamics
Comparing the gravitational acceleration induced on the Local Group of
galaxies by different tracers of the underline density field we estimate,
within the linear gravitational instability theory and the linear biasing
ansatz, their relative bias factors. Using optical SSRS2 galaxies, IRAS (PSCz)
galaxies and Abell/ACO clusters, we find b_{O,I} ~ 1.21 +- 0.06 and b_{C,I} ~
4.3 +- 0.8, in agreement with other recent studies. Finally, there is an
excellent one-to-one correspondence of the PSCz and Abell/ACO cluster dipole
profiles, once the latter is rescaled by b_{C,I}, out to at least ~150 h^{-1}
Mpc.Comment: 7 pages, 5 figures, accepted for publication in MNRA
RASS-SDSS galaxy cluster survey. II. A unified picture of the Cluster Luminosity Function
We constructed the composite luminosity function (LF) of clusters of galaxies
in the five SDSS photometric bands u,g,r,i and z from the RASS-SDSS galaxy
cluster catalog. Background and foreground galaxies are subtracted using both a
local and a global background correction to take in account the presence of
large scale structures and variations from field to field, respectively. The
composite LF clearly shows two components: a bright-end LF with a classical
slope of -1.25 in each photometric band, and a faint-end LF much steeper (-2.1
<= \alpha <= -1.6) in the dwarf galaxy region. The observed upturn of the faint
galaxies has a location ranging from -16 +5log(h) in the g band to -18.5
+5log(h) in the z band. To study the universality of the cluster LF we compare
the individual cluster LFs with the composite luminosity function. We notice
that, in agreement with the composite LF, a single Schechter component is not a
good fit for the majority of the clusters. We fit a Schechter function to the
bright-end of the individual clusters LFs in the magnitude region brighter than
the observed upturn of the dwarf galaxies. We observe that the distributions of
the derived parameters is close to a Gaussian around the value of the composite
bright-end LF parameters with a dispersion compatible with the statistical
errors. We conclude that the bright-end of the galaxy clusters is universal. To
study the behavior of the individual faint-end LF we define the Dwarf to Giant
galaxy Ratio (DGR) of the single clusters. We notice that the distribution of
DGR has a spread much larger than the statistical errors. Our conclusion is
that the cluster luminosity function is not universal since the cluster
faint-end, differently from the bright-end, varies from cluster to cluster.Comment: 17 pages, 13 figures, A&A in pres
- âŠ