145 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
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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
Are Compton-Thick AGN the Missing Link Between Mergers and Black Hole Growth?
We examine the host morphologies of heavily obscured active galactic nuclei (AGNs) at z ~ 1 to test whether obscured super-massive black hole growth at this epoch is preferentially linked to galaxy mergers. Our sample consists of 154 obscured AGNs with N_H > 10^(23.5) cm^(-2) and z 1.5. Using visual classifications, we compare the morphologies of these AGNs to control samples of moderately obscured 10^(22) cm^(-2) < N_H < 10^(23.5)cm^(-2) and unobscured (N_H < 10^(22) cm^(-2)) AGN. These control AGNs have similar redshifts and intrinsic X-ray luminosities to our heavily obscured AGN. We find that heavily obscured AGNs are twice as likely to be hosted by late-type galaxies relative to unobscured AGNs (65.3_(-4.6)^(+4.1)%) versus 34.5_(-2.7)^(+2.9)%) and three times as likely to exhibit merger or interaction signatures (21.5_(-3.3)^(+4.2)%) versus 7.8_(-1.3)^(+1.9)%). The increased merger fraction is significant at the 3.8σ level. If we exclude all point sources and consider only extended hosts, we find that the correlation between the merger fraction and obscuration is still evident, although at a reduced statistical significance (2.5σ). The fact that we observe a different disk/spheroid fraction versus obscuration indicates that the viewing angle cannot be the only thing differentiating our three AGN samples, as a simple unification model would suggest. The increased fraction of disturbed morphologies with obscuration supports an evolutionary scenario, in which Compton-thick AGNs are a distinct phase of obscured super-massive black hole (SMBH) growth following a merger/interaction event. Our findings also suggest that some of the merger-triggered SMBH growth predicted by recent AGN fueling models may be hidden among the heavily obscured, Compton-thick population
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