145 research outputs found
Clustering of star-forming galaxies detected in mid-infrared with the Spitzer wide-area survey
We discuss the clustering properties of galaxies with signs of ongoing star
formation detected by the Spitzer Space Telescope at 24mum band in the SWIRE
Lockman Hole field. The sample of mid-IR-selected galaxies includes ~20,000
objects detected above a flux threshold of S24mum=310muJy. We adopt
optical/near-IR color selection criteria to split the sample into the
lower-redshift and higher-redshift galaxy populations. We measure the angular
correlation function on scales of theta=0.01-3.5 deg, from which, using the
Limber inversion along with the redshift distribution established for similarly
selected source populations in the GOODS fields (Rodighiero et al. 2010), we
obtain comoving correlation lengths of r0=4.98+-0.28 h^-1 Mpc and r0
=8.04+-0.69 h^-1 Mpc for the low-z (=0.7) and high-z (=1.7) subsamples,
respectively. Comparing these measurements with the correlation functions of
dark matter halos identified in the Bolshoi cosmological simulation (Klypin et
al. 2011}, we find that the high-redshift objects reside in progressively more
massive halos reaching Mtot>3e12 h^-1 Msun, compared to Mtot>7e11 h^-1 Msun for
the low-redshift population. Approximate estimates of the IR luminosities based
on the catalogs of 24mum sources in the GOODS fields show that our high-z
subsample represents a population of "distant ULIRGs" with LIR>10^12Lsun, while
the low-z subsample mainly consists of "LIRGs", LIR~10^11Lsun. The comparison
of number density of the 24mum selected galaxies and of dark matter halos with
derived minimum mass Mtot shows that only 20% of such halos may host
star-forming galaxies.Comment: 15 pages, 12 figure
Learning Behavioral Representations of Human Mobility
In this paper, we investigate the suitability of state-of-the-art
representation learning methods to the analysis of behavioral similarity of
moving individuals, based on CDR trajectories. The core of the contribution is
a novel methodological framework, mob2vec, centered on the combined use of a
recent symbolic trajectory segmentation method for the removal of noise, a
novel trajectory generalization method incorporating behavioral information,
and an unsupervised technique for the learning of vector representations from
sequential data. Mob2vec is the result of an empirical study conducted on real
CDR data through an extensive experimentation. As a result, it is shown that
mob2vec generates vector representations of CDR trajectories in low dimensional
spaces which preserve the similarity of the mobility behavior of individuals.Comment: ACM SIGSPATIAL 2020: 28th ACM SIGSPATIAL International Conference on
Advances in Geographic Information Systems.November 2020 Seattle, Washington,
US
Using the 1.6um Bump to Study Rest-frame NIR Selected Galaxies at Redshift 2
We explore the feasibility and limitations of using the 1.6um bump as a
photometric redshift indicator and selection technique and use it to study the
rest-frame H-band galaxy luminosity and stellar mass functions at redshift z~2.
We use publicly available Spitzer/IRAC images in the GOODS fields and find that
color selection in the IRAC bandpasses alone is comparable in completeness and
contamination to BzK selection. We find that the shape of the 1.6um bump is
robust, and photometric redshifts are not greatly affected by choice of model
parameters. Comparison with spectroscopic redshifts shows photometric redshifts
to be reliable. We create a rest-frame NIR selected catalog of galaxies at z~2
and construct a galaxy stellar mass function (SMF). Comparisons with other SMFs
at approximately the same redshift but determined using shorter wavelengths
show good agreement. This agreement suggests that selection at bluer
wavelengths does not miss a significant amount of stellar mass in passive
galaxies. Comparison with SMFs at other redshifts shows evidence for the
downsizing scenario of galaxy evolution. We conclude by pointing out the
potential for using the 1.6um technique to select high-redshift galaxies with
the JWST, whose lambda > 0.6 um coverage will not be well suited to selecting
galaxies using techniques that require imaging at shorter wavelengths.Comment: Accepted for publication in Ap
The Mass-Dependent Clustering History of K-selected Galaxies at z < 4 in the SXDS/UDS Field
We investigate mass-dependent galaxy evolution based on a large sample of
(more than 50,000) K-band selected galaxies in a multi-wavelength catalog of
the Subaru/XMM-Newton Deep Survey (SXDS) and the UKIRT Infrared Deep Sky Survey
(UKIDSS)/Ultra Deep Survey (UDS). We employ the optical to near-infrared
photometry to determine photometric redshifts of these galaxies. Then, we
estimate the stellar mass of our sample galaxies using a standard fitting
procedure. From the sample galaxies, we obtain the stellar mass function of
galaxies and the cosmic stellar mass density up to z<4. Our results are
consistent with previous studies and we find a considerable number of low-mass
galaxies (M<10^{10.5}) at the redshift range 3<z<4. The stellar-mass dependent
correlation functions of our sample galaxies show clear evolution and they
connect to that in the local universe consistently. Also, the massive galaxies
show strong clustering throughout our studied redshift range. The correlation
length of massive galaxies rapidly decreases from z=4 to 2. We also find some
high mass density regions of massive galaxies at 1.4<z<2.5 in our sample, which
may be candidate progenitors of the present-day clusters of galaxies. At this
redshift range, massive star-forming galaxies are the dominant population
making up the structures and the passively evolving galaxies show stronger
clustering and they may have formed earlier than those star-forming galaxies.Comment: 13 pages, 13 figures, 2 table
Genetic and biochemical analyses of chromosome and plasmid gene homologues encoding ICL and ArCP domains in Vibrioanguillarum strain 775
Anguibactin, the siderophore produced by Vibrio anguillarum 775 is synthesized from 2,3-dihydroxybenzoic acid (DHBA), cysteine and hydroxyhistamine via a nonribosomal peptide synthetase (NRPS) mechanism. Most of the genes encoding anguibactin biosynthetic proteins are harbored by the pJM1 plasmid. In this work we report the identification of a homologue of the plasmid-encoded angB on the chromosome of strain 775. The product of both genes harbor an isochorismate lyase (ICL) domain that converts isochorismic acid to 2,3-dihydro-2,3-dihydroxybenzoic acid, one of the steps of DHBA synthesis. We show in this work that both ICL domains are functional in the production of DHBA in V. anguillarum as well as in E. coli. Substitution by alanine of the aspartic acid residue in the active site of both ICL domains completely abolishes their isochorismate lyase activity in vivo. The two proteins also carry an aryl carrier protein (ArCP) domain. In contrast with the ICL domains only the plasmid encoded ArCP can participate in anguibactin production as determined by complementation analyses and site-directed mutagenesis in the active site of the plasmid encoded protein, S248A. The site-directed mutants, D37A in the ICL domain and S248A in the ArCP domain of the plasmid encoded AngB were also tested in vitro and clearly show the importance of each residue for the domain function and that each domain operates independently.
Clustering and descendants of MUSYC galaxies at z<1.5
We measure the evolution of galaxy clustering out to a redshift of z~1.5
using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S)
and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift
information to calculate the projected-angular correlation function,
omega(sigma), from which we infer the projected correlation function Xi(sigma).
We demonstrate that this technique delivers accurate measurements of clustering
even when large redshift measurement errors affect the data. To this aim we use
two mock MUSYC fields extracted from a LambdaCDM simulation populated with
GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy
of our estimates of Xi(sigma) and to identify and correct for systematic
effects in our measurements. We study the evolution of clustering for volume
limited subsamples of galaxies selected using their photometric redshifts and
rest-frame r-band absolute magnitudes. We find that the real-space correlation
length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered
out to z~1.5, particularly for ECDF-S given its near-infrared photometric
coverage. There is mild evidence for a luminosity dependent clustering in both
fields at the low redshift samples (up to =0.57), where the correlation
length is higher for brighter galaxies by up to 1Mpc/h between median
rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the
photometric redshift measurement, each galaxy is assigned a best-fit template;
we restrict to E and E+20%Sbc types to construct subsamples of early type
galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift
increases, making it unlikely (95% level) that ETGs at median redshift
z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent
passively evolved luminosities. (ABRIDGED)Comment: 16 pages, 12 figures, 2 tables, accepted for publication in MNRA
A Steep Faint-End Slope of the UV Luminosity Function at z~2-3: Implications for the Global Stellar Mass Density and Star Formation in Low Mass Halos
We use the deep ground-based optical photometry of the Lyman Break Galaxy
(LBG) Survey to derive robust measurements of the faint-end slope (alpha) of
the UV LF at redshifts 1.92000 spectroscopic
redshifts and ~31000 LBGs in 31 spatially-independent fields over a total area
of 3261 arcmin^2. These data allow us to select galaxies to 0.07L* and 0.10L*
at z~2 and z~3, respectively. A maximum likelihood analysis indicates steep
values of alpha(z=2)=-1.73+/-0.07 and alpha(z=3)=-1.73+/-0.13. This result is
robust to luminosity dependent systematics in the Ly-alpha equivalent width and
reddening distributions, is similar to the steep values advocated at z>4, and
implies that ~93% of the unobscured UV luminosity density at z~2-3 arises from
sub-L* galaxies. With a realistic luminosity dependent reddening distribution,
faint to moderately luminous galaxies account for >70% and >25% of the
bolometric luminosity density and present-day stellar mass density,
respectively, when integrated over 1.9<z<3.4. We find a factor of 8-9 increase
in the star formation rate density between z~6 and z~2, due to both a
brightening of L* and an increasing dust correction proceeding to lower
redshifts. The previously observed discrepancy between the integral of the star
formation history and stellar mass density measurements at z~2 may be
reconciled by invoking a luminosity dependent reddening correction to the star
formation history combined with an accounting for the stellar mass contributed
by UV-faint galaxies. The steep and relatively constant alpha of the UV LF at
z>2 contrasts with the shallower value inferred locally, suggesting that the
evolution in the faint-end slope may be dictated simply by the availability of
low mass halos capable of supporting star formation at z<2. [Abridged]Comment: 29 pages, 15 figures, 7 tables; accepted for publication in Ap
Clustering properties of galaxies selected in stellar mass: Breaking down the link between luminous and dark matter in massive galaxies from z=0 to z=2
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.Comment: Accepted for publication in MNRAS. 19 pages, 8 figures and 3 tables
A galaxy populations study of a radio-selected protocluster at z~3.1
We present a population study of several types of galaxies within the
protocluster surrounding the radio galaxy MRC0316-257 at z~3.1. In addition to
the known population of Ly_alpha emitters (LAEs) and [OIII] emitters, we use
colour selection techniques to identify protocluster candidates that are Lyman
break galaxies (LBG) and Balmer break galaxies (BBGs). The radio galaxy field
contains an excess of LBG candidates, with a surface density 1.6\pm0.3 times
larger than found for comparable blank fields. This surface overdensity
corresponds to an LBG volume overdensity of ~8\pm4. The BBG photometric
redshift distribution peaks at the protocluster's redshift, but we detect no
significant surface overdensity of BBG. This is not surprising because a volume
overdensity similar to the LBGs would have resulted in a surface density of
~1.2 that found in the blank field. This could not have been detected in our
sample. Masses and star formation rates of the candidate protocluster galaxies
are determined using SED fitting. These properties are not significantly
different from those of field galaxies. The galaxies with the highest masses
and star formation rates are located near the radio galaxy, indicating that the
protocluster environment influences galaxy evolution at z~3. We conclude that
the protocluster around MRC0316-257 is still in the early stages of formation.Comment: 19 pages, 20 figures, accepted for publication in MNRA
BLAST: Correlations in the Cosmic Far-Infrared Background at 250, 350, and 500 microns Reveal Clustering of Star-Forming Galaxies
We detect correlations in the cosmic far-infrared background due to the
clustering of star-forming galaxies in observations made with the Balloon-borne
Large Aperture Submillimeter Telescope, BLAST, at 250, 350, and 500 microns. We
perform jackknife and other tests to confirm the reality of the signal. The
measured correlations are well fit by a power law over scales of 5-25
arcminutes, with Delta I/I = 15.1 +/- 1.7%. We adopt a specific model for
submillimeter sources in which the contribution to clustering comes from
sources in the redshift ranges 1.3 <= z <= 2.2, 1.5 <= z <= 2.7, and 1.7 <= z
<= 3.2, at 250, 350, and 500 microns, respectively. With these distributions,
our measurement of the power spectrum, P(k_theta), corresponds to linear bias
parameters, b = 3.8 +/- 0.6, 3.9 +/- 0.6 and 4.4 +/- 0.7, respectively. We
further interpret the results in terms of the halo model, and find that at the
smaller scales, the simplest halo model fails to fit our results. One way to
improve the fit is to increase the radius at which dark matter halos are
artificially truncated in the model, which is equivalent to having some
star-forming galaxies at z >= 1 located in the outskirts of groups and
clusters. In the context of this model we find a minimum halo mass required to
host a galaxy is log (M_min / M_sun) = 11.5 (+0.4/-0.1), and we derive
effective biases $b_eff = 2.2 +/- 0.2, 2.4 +/- 0.2, and 2.6 +/- 0.2, and
effective masses log (M_eff / M_sun) = 12.9 +/- 0.3, 12.8 +/- 0.2, and 12.7 +/-
0.2, at 250, 350, and 500 microns, corresponding to spatial correlation lengths
of r_0 = 4.9, 5.0, and 5.2 +/- 0.7 h^-1 Mpc, respectively. Finally, we discuss
implications for clustering measurement strategies with Herschel and Planck.Comment: Accepted for publication in the Astrophysical Journal. Maps and other
results available at http://blastexperiment.info
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