718 research outputs found
Extended Photometry for the DEEP2 Galaxy Redshift Survey: A Testbed for Photometric Redshift Experiments
This paper describes a new catalog that supplements the existing DEEP2 Galaxy
Redshift Survey photometric and spectroscopic catalogs with ugriz photometry
from two other surveys; the Canada-France-Hawaii Legacy Survey (CFHTLS) and the
Sloan Digital Sky Survey (SDSS). Each catalog is cross-matched by position on
the sky in order to assign ugriz photometry to objects in the DEEP2 catalogs.
We have recalibrated the CFHTLS photometry where it overlaps DEEP2 in order to
provide a more uniform dataset. We have also used this improved photometry to
predict DEEP2 BRI photometry in regions where only poorer measurements were
available previously. In addition, we have included improved astrometry tied to
SDSS rather than USNO-A2.0 for all DEEP2 objects. In total this catalog
contains ~27,000 objects with full ugriz photometry as well as robust
spectroscopic redshift measurements, 64% of which have r > 23. By combining the
secure and accurate redshifts of the DEEP2 Galaxy Redshift Survey with ugriz
photometry, we have created a catalog that can be used as an excellent testbed
for future photo-z studies, including tests of algorithms for surveys such as
LSST and DES.Comment: 12 pages, 6 figures and 5 tables. Accepted to The Astrophysical
Journal Supplement. Catalogs are publicly available at
http://deep.ps.uci.edu/DR4/photo.extended.htm
The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method Catalog of Galaxy Groups
We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above ~300 km s^(â1) to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests
X-rays across the galaxy population â I. Tracing the main sequence of star formation
We use deep imaging to measure the distribution of X-ray luminosities (LX) for samples of star-forming galaxies as a function of stellar mass and redshift, using a Bayesian method to push below the nominal X-ray detection limits. Our luminosity distributions all show narrow peaks at LX âČ 10 erg s that we associate with star formation, as opposed to AGN that are traced by a broad tail to higher LX. Tracking the luminosity of these peaks as a function of stellar mass reveals an âX-ray main sequenceâ with a constant slope â0.63 ± 0.03 over 8.5âČlogMâ/MââČ11.5 and 0.1 âČ z âČ 4, with a normalization that increases with redshift as (1 + z). We also compare the peak X-ray luminosities with UV-to-IR tracers of star formation rates (SFRs) to calibrate the scaling between LX and SFR. We find that LX â SFR Ă (1 + z), where the redshift evolution and non-linearity likely reflect changes in high-mass X-ray binary populations of star-forming galaxies. Using galaxies with a broader range of SFR, we also constrain a stellar-mass-dependent contribution to LX, likely related to low-mass X-ray binaries. Using this calibration, we convert our X-ray main sequence to SFRs and measure a star-forming main sequence with a constant slope â0.76 ± 0.06 and a normalization that evolves with redshift as (1 + z). Based on the X-ray emission, there is no evidence for a break in the main sequence at high stellar masses, although we cannot rule out a turnover given the uncertainties in the scaling of LX to SFR.JA acknowledges support from ERC Advanced Grant FEEDBACK 340442. ALC acknowledges support from NSF CAREER award AST-1055081. AG acknowledges the THALES project 383549 that is jointly funded by the European Union and the Greek Government in the framework of the programme âEducation and lifelong learningâ. This work is based in part on observations taken by the 3D-HST Treasury Program (GO 12177 and 12328) with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile , under Large Program 185.A-0791, and made available by the VUDS team at the CESAM data center, Laboratoire dâAstrophysique de Marseille, France. The scientific results reported in this article are based to a significant degree on observations made by the Chandra X-ray Observatory
Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
We present a study of the prevalence, strength, and kinematics of ultraviolet
FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected
from the DEEP2 survey. We find FeII* emission in composite spectra assembled on
the basis of different galaxy properties, indicating that FeII* emission is
prevalent at z = 1. In these composites, FeII* emission is observed at roughly
the systemic velocity. At z = 1, we find that the strength of FeII* emission is
most strongly modulated by dust attenuation, and is additionally correlated
with redshift, star-formation rate, and [OII] equivalent width, such that
systems at higher redshifts with lower dust levels, lower star-formation rates,
and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII
emission in at least 15% of the individual spectra and we find that objects
showing stronger MgII emission have higher specific star-formation rates,
smaller [OII] linewidths, larger [OII] equivalent widths, lower dust
attenuations, and lower stellar masses than the sample as a whole. MgII
emission strength exhibits the strongest correlation with specific
star-formation rate, although we find evidence that dust attenuation and
stellar mass also play roles in the regulation of MgII emission. Future
integral field unit observations of the spatial extent of FeII* and MgII
emission in galaxies with high specific star-formation rates, low dust
attenuations, and low stellar masses will be important for probing the
morphology of circumgalactic gas.Comment: 29 pages, 22 figures, 2 tables; accepted to Ap
The line-of-sight distribution of the gas in the inner 60 pc of the Galaxy
2MASS K_S band data of the inner 60 pc of the Galaxy are used to reconstruct
the line-of-sight distances of the giant molecular clouds located in this
region. Using the 2MASS H band image of the same region, two different
populations of point sources are identified according to their flux ratio in
the two bands. The population of blue point sources forms a homogeneous
foreground that has to be subtracted before analyzing the K_S band image. The
reconstruction is made using two basic assumptions: (i) an axis-symmetric
stellar distribution in the region of interest and
(ii) optically thick clouds with an area filling factor of ~1 that block all
light of stars located behind them. Due to the reconstruction method, the
relative distance between the different cloud complexes is a robust result,
whereas it is not excluded that the absolute distance with respect to Sgr A* of
structures located more than 10 pc in front of Sgr A* are understimated by up
to a factor of 2. It is shown that all structures observed in the 1.2 mm
continuum and in the CS(2-1) line are present in absorption. We place the 50 km
s^-1 cloud complex close to, but in front of, Sgr A*. The 20 km s^-1 cloud
complex is located in front of the 50 km s^-1 cloud complex and has a large LOS
distance gradient along the direction of the galactic longitude. The bulk of
the Circumnuclear Disk is not seen in absorption. This leads to an upper limit
of the cloud sizes within the Circumnuclear Disk of ~0.06 pc.Comment: 12 pages with 17 figures. Accepted for publication in A&
Absence of Evidence Is Not Evidence of Absence: The Color-Density Relation at Fixed Stellar Mass Persists to z ~ 1
We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the
relationship between local galaxy density, stellar mass, and rest-frame galaxy
color. At z ~ 0.9, we find that the shape of the stellar mass function at the
high-mass (log (M*/Msun) > 10.1) end depends on the local environment, with
high-density regions favoring more massive systems. Accounting for this stellar
mass-environment relation (i.e., working at fixed stellar mass), we find a
significant color-density relation for galaxies with 10.6 < log(M*/Msun) < 11.1
and 0.75 < z < 0.95. This result is shown to be robust to variations in the
sample selection and to extend to even lower masses (down to log(M*/Msun) ~
10.4). We conclude by discussing our results in comparison to recent works in
the literature, which report no significant correlation between galaxy
properties and environment at fixed stellar mass for the same redshift and
stellar mass domain. The non-detection of environmental dependence found in
other data sets is largely attributable to their smaller samples size and lower
sampling density, as well as systematic effects such as inaccurate redshifts
and biased analysis techniques. Ultimately, our results based on DEEP2 data
illustrate that the evolutionary state of a galaxy at z ~ 1 is not exclusively
determined by the stellar mass of the galaxy. Instead, we show that local
environment appears to play a distinct role in the transformation of galaxy
properties at z > 1.Comment: 10 pages, 5 Figures; Accepted for publication in MNRA
PRIMUS: The Effect of Physical Scale on the Luminosity-Dependence of Galaxy Clustering via Cross-Correlations
We report small-scale clustering measurements from the PRIMUS spectroscopic
redshift survey as a function of color and luminosity. We measure the
real-space cross-correlations between 62,106 primary galaxies with PRIMUS
redshifts and a tracer population of 545,000 photometric galaxies over
redshifts from z=0.2 to z=1. We separately fit a power-law model in redshift
and luminosity to each of three independent color-selected samples of galaxies.
We report clustering amplitudes at fiducial values of z=0.5 and L=1.5 L*. The
clustering of the red galaxies is ~3 times as strong as that of the blue
galaxies and ~1.5 as strong as that of the green galaxies. We also find that
the luminosity dependence of the clustering is strongly dependent on physical
scale, with greater luminosity dependence being found between r=0.0625 Mpc/h
and r=0.25 Mpc/h, compared to the r=0.5 Mpc/h to r=2 Mpc/h range. Moreover,
over a range of two orders of magnitude in luminosity, a single power-law fit
to the luminosity dependence is not sufficient to explain the increase in
clustering at both the bright and faint ends at the smaller scales. We argue
that luminosity-dependent clustering at small scales is a necessary component
of galaxy-halo occupation models for blue, star-forming galaxies as well as for
red, quenched galaxies.Comment: 13 pages, 6 figures, 5 tables; published in ApJ (revised to match
published version
The dynamics of the Circumnuclear Disk and its environment in the Galactic centre
We address the question of the dynamics in the inner 50 pc of the Galactic
Centre. In a first step we investigate the cloud-cloud collision rate in the
Circumnuclear Disk (CND) with the help of a three dimensional N-body code using
gas particles that can have inelastic collisions. The CND might be a longer
lived structure than previously assumed. The whole disk-like structure of the
CND can thus survive for several million years. A realistic simulation of the
CND shows the observed disk height structure. In a second step the environment
of the CND is taken into account. Retrograde and prograde encounters of a cloud
of several 10^4 M_solar falling onto an already existing nuclear disk using
different energy loss rates per collision are simulated. The influence of the
energy loss rate per collision on the evolution of the mass accretion and cloud
collision rates is strongest for a prograde encounter. A composite data cube of
two different snapshots of a prograde encounter together with the CND shows
striking similarity with the observed Sgr A cloud complex. The current
appearance of the Galactic Centre environment can thus be explained by at least
two dynamically distinct features together with the CND. The current mass
accretion rate within the CND ranges between 10^-3 and 10^-4 M_solar yr^-1. It
can rise up to several 10^-2 M_solar yr^-1 during massive accretion events.Comment: 14 pages with 22 figures. Accepted for publication in A&
Whole genome sequence analysis reveals the broad distribution of the RtxA type 1 secretion system and four novel putative type 1 secretion systems throughout the Legionella genus.
Type 1 secretion systems (T1SSs) are broadly distributed among bacteria and translocate effectors with diverse function across the bacterial cell membrane. Legionella pneumophila, the species most commonly associated with Legionellosis, encodes a T1SS at the lssXYZABD locus which is responsible for the secretion of the virulence factor RtxA. Many investigations have failed to detect lssD, the gene encoding the membrane fusion protein of the RtxA T1SS, in non-pneumophila Legionella, which has led to the assumption that this system is a virulence factor exclusively possessed by L. pneumophila. Here we discovered RtxA and its associated T1SS in a novel Legionella taurinensis strain, leading us to question whether this system may be more widespread than previously thought. Through a bioinformatic analysis of publicly available data, we classified and determined the distribution of four T1SSs including the RtxA T1SS and four novel T1SSs among diverse Legionella spp. The ABC transporter of the novel Legionella T1SS Legionella repeat protein secretion system shares structural similarity to those of diverse T1SS families, including the alkaline protease T1SS in Pseudomonas aeruginosa. The Legionella bacteriocin (1-3) secretion systems T1SSs are novel putative bacteriocin transporting T1SSs as their ABC transporters include C-39 peptidase domains in their N-terminal regions, with LB2SS and LB3SS likely constituting a nitrile hydratase leader peptide transport T1SSs. The LB1SS is more closely related to the colicin V T1SS in Escherichia coli. Of 45 Legionella spp. whole genomes examined, 19 (42%) were determined to possess lssB and lssD homologs. Of these 19, only 7 (37%) are known pathogens. There was no difference in the proportions of disease associated and non-disease associated species that possessed the RtxA T1SS (p = 0.4), contrary to the current consensus regarding the RtxA T1SS. These results draw into question the nature of RtxA and its T1SS as a singular virulence factor. Future studies should investigate mechanistic explanations for the association of RtxA with virulence
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