148 research outputs found
PRIMUS: The relationship between Star formation and AGN accretion
We study the evidence for a connection between active galactic nuclei (AGN)
fueling and star formation by investigating the relationship between the X-ray
luminosities of AGN and the star formation rates (SFRs) of their host galaxies.
We identify a sample of 309 AGN with erg
s at in the PRIMUS redshift survey. We find AGN in
galaxies with a wide range of SFR at a given . We do not find a
significant correlation between SFR and the observed instantaneous for
star forming AGN host galaxies. However, there is a weak but significant
correlation between the mean and SFR of detected AGN in star
forming galaxies, which likely reflects that varies on shorter
timescales than SFR. We find no correlation between stellar mass and
within the AGN population. Within both populations of star
forming and quiescent galaxies, we find a similar power-law distribution in the
probability of hosting an AGN as a function of specific accretion rate.
Furthermore, at a given stellar mass, we find a star forming galaxy
more likely than a quiescent galaxy to host an AGN of a given specific
accretion rate. The probability of a galaxy hosting an AGN is constant across
the main sequence of star formation. These results indicate that there is an
underlying connection between star formation and the presence of AGN, but AGN
are often hosted by quiescent galaxies
PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1
We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion
rate. Our model is based on measurements indicating that the specific accretion
rate distribution is a universal function across a wide range of host stellar
mass with slope gamma_1 = -0.65 and an overall normalization that evolves with
redshift. We test several simple assumptions to extend this model to high
specific accretion rates (beyond the measurements) and compare the predictions
for the XLF with the observed data. We find good agreement with a model that
allows for a break in the specific accretion rate distribution at a point
corresponding to the Eddington limit, a steep power-law tail to super-Eddington
ratios with slope gamma_2 = -2.1 +0.3 -0.5, and a scatter of 0.38 dex in the
scaling between black hole and host stellar mass. Our results show that samples
of low luminosity AGNs are dominated by moderately massive galaxies (M* ~
10^{10-11} M_sun) growing with a wide range of accretion rates due to the shape
of the galaxy stellar mass function rather than a preference for AGN activity
at a particular stellar mass. Luminous AGNs may be a severely skewed population
with elevated black hole masses relative to their host galaxies and in rare
phases of rapid accretion.Comment: 11 pages, 5 figures, emulateapj format, updated to match version
accepted for publication in Ap
PRIMUS + DEEP2: Clustering of X-ray, Radio and IR-AGN at z~0.7
We measure the clustering of X-ray, radio, and mid-IR-selected active
galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and
spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7
separate fields spanning ~10 square degrees. Using the cross-correlation of AGN
with dense galaxy samples, we measure the clustering scale length and slope, as
well as the bias, of AGN selected at different wavelengths. Similar to previous
studies, we find that X-ray and radio AGN are more clustered than
mid-IR-selected AGN. We further compare the clustering of each AGN sample with
matched galaxy samples designed to have the same stellar mass, star formation
rate, and redshift distributions as the AGN host galaxies and find no
significant differences between their clustering properties. The observed
differences in the clustering of AGN selected at different wavelengths can
therefore be explained by the clustering differences of their host populations,
which have different distributions in both stellar mass and star formation
rate. Selection biases inherent in AGN selection, therefore, determine the
clustering of observed AGN samples. We further find no significant difference
between the clustering of obscured and unobscured AGN, using IRAC or WISE
colors or X-ray hardness ratio.Comment: Accepted to ApJ. 23 emulateapj pages, 15 figures, 4 table
PRIMUS: Galaxy Clustering as a Function of Luminosity and Color at 0.2<z<1
We present measurements of the luminosity and color-dependence of galaxy
clustering at 0.2<z<1.0 in the PRIsm MUlti-object Survey (PRIMUS). We quantify
the clustering with the redshift-space and projected two-point correlation
functions, xi(rp,pi) and wp(rp), using volume-limited samples constructed from
a parent sample of over 130,000 galaxies with robust redshifts in seven
independent fields covering 9 sq. deg. of sky. We quantify how the
scale-dependent clustering amplitude increases with increasing luminosity and
redder color, with relatively small errors over large volumes. We find that red
galaxies have stronger small-scale (0.1<rp<1 Mpc/h) clustering and steeper
correlation functions compared to blue galaxies, as well as a strong color
dependent clustering within the red sequence alone. We interpret our measured
clustering trends in terms of galaxy bias and obtain values between
b_gal=0.9-2.5, quantifying how galaxies are biased tracers of dark matter
depending on their luminosity and color. We also interpret the color dependence
with mock catalogs, and find that the clustering of blue galaxies is nearly
constant with color, while redder galaxies have stronger clustering in the
one-halo term due to a higher satellite galaxy fraction. In addition, we
measure the evolution of the clustering strength and bias, and we do not detect
statistically significant departures from passive evolution. We argue that the
luminosity- and color-environment (or halo mass) relations of galaxies have not
significantly evolved since z=1. Finally, using jackknife subsampling methods,
we find that sampling fluctuations are important and that the COSMOS field is
generally an outlier, due to having more overdense structures than other
fields; we find that 'cosmic variance' can be a significant source of
uncertainty for high-redshift clustering measurements.Comment: 22 pages, 21 figures, matches version published in Ap
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Lentivirus Display: Stable Expression of Human Antibodies on the Surface of Human Cells and Virus Particles
Background: Isolation of human antibodies using current display technologies can be limited by constraints on protein expression, folding and post-translational modifications. Here we describe a discovery platform that utilizes self-inactivating (SIN) lentiviral vectors for the surface display of high-affinity single-chain variable region (scFv) antibody fragments on human cells and lentivirus particles. Methodology/Principal Findings: Bivalent scFvFc human antibodies were fused in frame with different transmembrane (TM) anchoring moieties to allow efficient high-level expression on human cells and the optimal TM was identified. The addition of an eight amino acid HIV-1 gp41 envelope incorporation motif further increased scFvFc expression on human cells and incorporation into lentiviral particles. Both antibody-displaying human cells and virus particles bound antigen specifically. Sulfation of CDR tyrosine residues, a property recently shown to broaden antibody binding affinity and antigen recognition was also demonstrated. High level scFvFc expression and stable integration was achieved in human cells following transduction with IRES containing bicistronic SIN lentivectors encoding ZsGreen when scFvFc fusion proteins were expressed from the first cassette. Up to 10[super]6-fold enrichment of antibody expressing cells was achieved with one round of antigen coupled magnetic bead pre-selection followed by FACS sorting. Finally, the scFvFc displaying human cells could be used directly in functional biological screens with remarkable sensitivity. Conclusions/Significance: This antibody display platform will complement existing technologies by virtue of providing properties unique to lentiviruses and antibody expression in human cells, which, in turn, may aid the discovery of novel therapeutic human mAbs
Supermassive black holes in cosmological simulations - II : the AGN population and predictions for upcoming X-ray missions
In large-scale hydrodynamical cosmological simulations, the fate of massive galaxies is mainly dictated by the modelling of feedback from active galactic nuclei (AGNs). The amount of energy released by AGN feedback is proportional to the mass that has been accreted on to the black holes (BHs), but the exact subgrid modelling of AGN feedback differs in all simulations. While modern simulations reliably produce populations of quiescent massive galaxies at z = 10(45) erg s(-1) (although this is sensitive to AGN variability), and leads to smaller fractions of AGN in massive galaxies than in the observations at zPeer reviewe
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